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Versions: 00                                                            
Media Gateway Control (Megaco)                  Madhubabu Brahmanapally
Internet Engineering Task Force                 Prerepa Viswanadham
Internet Draft                                  krishna Gundamaraju
Document: draft-madhu-megaco-callflows-00.txt   Kenetec Inc
Category: Informational
July 2001
Expires:January 2002


                   Megaco/H.248 Call flow examples


Status of this Memo

   This draft is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working drafts of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working drafts as Internet-
   Drafts. Internet-Drafts are draft drafts valid for a maximum of
   six months and may be updated, replaced, or obsoleted by other
   drafts at any time. It is inappropriate to use Internet- Drafts
   as reference material or to cite them other than as "work in
   progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

1. Abstract

        This draft illustrates the usage of Megaco (version 1)
 protocol defined between the Media Gateway Controller and Media
 Gateway. In light of the vast features presently incorporated
 and continuously evolving features of the protocol, it serves the
 purpose of representing typical use case scenarios. There are a
 lot of possible scenarios for usage of MEGACO protocol. It is not
 the intent of the draft to represent the inter-working functionality
 among various protocols, however, an attempt is made to depict
 its usage in such a case for the purpose of completeness in the
 larger perspective. An attempt has been made to show the
 supplementary call  services using MEGACO. The call flows can
 be categorized in to two sub sections,
          -     MEGACO only call scenario
          -     MEGACO and other protocols

 The draft begins with showing MEGACO only call scenarios, where
 the called and calling party lie on MEGACO domain. Various

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 permutations are possible even in this setup, viz
      RGW to RGW
      RGW to TGW
      TGW to TGW
      RGW/TGW to IVR

 In the other case, typical cases of MEGACO interaction with other
 protocols have been depicted. Here it is assumed that the MG,
 which participates in the interaction, is RGW. This can be extended
 to any type of Media GW. The scenarios include

      MEGACO user with SIP
      MEGACO user with H.323
      MEGACO user with SS7
      MEGACO user with ISDN
      MEGACO user with R1
      MEGACO user with R2

 The packages used in each of the calls flows are mentioned before each
 of the call flows. The packages that are addressed in this draft along
 with the packages defined in the base protocol also include packages
 like R2, R1, etc to illustrate the protocol usage. In case of Trunking
 gateways even though its not shown explicitly it is assumed that the
 messages from the CCS (Common Channel Signaling) switches are received
 by MGC through the Signaling Gateway. The emphasis of the draft is on
 the Megaco commands hence the messages between Signaling Gateway and
 MGC are not shown explicitly. Wherever applicable it should be assumed
 that the CCS switches/exchanges are communicating the messages to
 MGC through the Signaling Gateway.

 One of the sections illustrates the usage of SDP for ATM. For
 simplicity residential gateway with ATM connectivity is assumed.
 However the same holds true for trunking gateways also. Two methods
 of call establishment with SDP for ATM are discussed, namely the
 "Backward Bearer Connection Set-up Model" and "Forward Bearer
 Connection Set-up Model".


 This draft should be treated as only a means to illustrate the usage
 of Megaco but not as a guide for implementing Media Gateway or Media
 Gateway Controller. These calls flows are only informative. All the
 messages are encoded in the ABNF syntax for simplicity. The same calls
 flows are valid with binary messages also. Care has been taken to see
 that the messages are according to the protocol grammar, in case of
 discrepancies the protocol draft has to be considered. The Call flow
 diagrams are only a means to abstract the protocol messages exchanged
 between the MG and the MGC. These call flow diagrams are not according
 to any time scale. The IP addresses and port numbers used in the examples
 are fictitious. The statistic parameter values are also fictituous.



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1.2 References:.....................................................4
2. Internet Telephony Call Flows....................................4
2.1 Call between two residential gateways...........................4
     Case (a).......................................................7
     Case (b)......................................................18
     Case (c)......................................................18
2.2 Call between Residential Gateway and Trunking Gateway..........24
2.3 Call between Trunking gateway and Residential Gateway..........34
2.4 Call between two Trunking gateways.............................42
2.5 Call between Residential gateway and SS7 trunk in TGW..........49
2.6 Call between SS7 trunk in TGW and residential gateway..........58
2.7 Call between SS7 trunk in TGW and R2 trunk in TGW..............67
2.8 Call between R2 trunk in TGW and SS7 trunk in TGW..............76
2.9 Call between R1 trunk in TGW and SS7 trunk in TGW..............85
2.10 Call between SS7 trunk in TGW and R1 trunk in TGW.............94
2.11 Call between ISDN trunk in TGW and SS7 trunk in TGW..........103
2.12 Continuity test from TGW.....................................109
      Case (a)....................................................109
      Case (b)....................................................111
2.13 Call from residential gateway to H.323 Terminal..............112
2.14 Call from residential gateway to SIP user....................120
3 Service Change Command Usage....................................127
3.1 ROOT Termination..............................................127
3.1.1 Registration................................................127
3.1.2 Cold Start..................................................129
3.1.3 Handoff.....................................................131
3.1.4 Disconnection...............................................133
3.2 Service Change for Termination................................136
3.2.1 MG generated Service Change.................................136
3.2.2 MGC generated Service Change................................143
4.0 Audit Command Usage...........................................146
4.1 Audit Value...................................................146
4.1.1 Audit value command on ROOT Termination.....................146
4.1.2 Audit value on non-ROOT terminations........................148
4.2 Audit Capability..............................................150
4.2.1 Audit Capability on ROOT termination........................150
4.2.2 Audit Capability on non-Root Terminations...................150
5. IVR using MEGACO...............................................151
5.1 Connecting Residential gateway to IVR.........................151
5.2 Disconnecting Residential User from IVR.......................158
5.3 Connecting Trunking Gateway to IVR............................160
5.4 Disconnecting Trunking gateway from IVR.......................164
6. Wildcard ContextID usage.......................................166
7. Wildcard TerminationId Usage...................................167
8. Supplementary services support.................................168
8.1 Call Transfer.................................................168
8.2 Call waiting..................................................189
9. Conferencing...................................................211
10.0 SDP for ATM..................................................243
10.1.1 Forward Bearer Connection Set-up Method....................244
10.1.2 Backward Bearer Connection Set-up Method...................257

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1.1. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC-2119 [1].


1.2 References:

1) Cuervo, et al. "Megaco Protocol Version 1.0", RFC 3015, November2000.
2) Christian Huitema, et. Al. "Media Gateway Control Protocol (MGCP)
   Call Flows".  < <draft-huitema-megaco-mgcp-flows-01.txt>
3) Implementers' Guide for ITU Recommendation H.248. Nov 2000.
4) Megaco mail archive
   http://standards.nortelnetworks.com/archives/megaco.html
5) R2 Package for Megaco Protocol, Kushanava Laha et al,"work in
   progress"  <draft-ietf-megaco-r2package-02.txt>
6) V.Bajaj et al, Megaco/H.248 Basic CAS Packages,"Work in Progress"
   <draft-manyfolks-megaco-caspackage-00.txt>
7) Wendy et. al, draft-bothwell-megaco-mftonepkgs-01.txt, "Work in
   Progress", "MF Tone Generation and Detection Packages"
8) Rajesh Kumar et. al, Conventions for the use of the Session
   Description Protocol (SDP)for ATM Bearer Connections.
   "draft-ietf-mmusic-sdp-atm-05.txt", "Work in Progress".

2. Internet Telephony Call Flows

 This section illustrates sample Internet telephone calls. Calls between
 Trunking gateway, Residential gateway, H.323 Endpoint, etc are
 illustrated. In all these call scenarios emphasis is given on the
 Megaco protocol messages rather than the remaining entities.2.1 Call
 between two residential gateways

2.1 Call between two Residential Gateways

 The call establishment between two residential users is considered in
 this example. User A and User B are connected to two residential
 gateways RGW1 and RGW2. For simplicity we consider the case where
 the two MG's are controlled by the same MGC.  The call scenario
 assumes the implementation of analog line supervision package,
 RTP package, generic package, DTMF detection package, Call progress
 generator package, and the Network Package. Along with the successful
 call between the two users (case a), we also consider the case
 where the called party is busy (case c), and the call termination
 by both the users (case a for UserA terminated call flow and case b
 for UserB terminated call flow) is also discussed. In this example
 the registration of the MG (RGW) with the MGC is assumed to have
 happened as explained in section 3.1.1 Registration.

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 _____________________________________________________________________
             |           |           |              |
  USERA      |   RGW1    |    MGC    |   RGW2       |       USERB
_____________|___________|___________|______________|_________________
      |            |           |           |                   |
      |            |           |           |                   |
      |            |           |---------->|                   |
      |            |           |Modify to  |                   |
      |            |           |Check Offhook                  |
      |            |<----------|           |                   |
      |            |Modify to  |           |                   |
      |            |check offhook          |                   |
      |            |---------->|<----------|                   |
      |            |Modify Resp| Modify Resp                   |
      |----------->|           |           |                   |
      |UserA offhook           |           |                   |
      |            |---------->|           |                   |
      |            |Notify offhook         |                   |
      |            |<----------|           |                   |
      |            |Notify Resp|           |                   |
      |            |<----------|           |                   |
      |            |Modify SG:dialtone     |                   |
      |            |ED:al/on,dd/ce{Dmap1}  |                   |
      |            |DM:Dmap1 = 2XXX        |                   |
      |<-----------|           |           |                   |
      |Dial Tone   |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |            |           |           |                   |
      |----------->|           |           |                   |
      |User Dials Digits       |           |                   |
      |            |---------->|           |                   |
      |            |Notify digits          |                   |
      |            |<----------|           |                   |
      |            |Notify Response        |                   |
      |            |<----------|           |                   |
      |            | Add TermA SD:ringbacktone                 |
      |            | Add $, Local SDP Info -underspecified     |
      |<-----------|           |           |                   |
      |RingBack Tone           |           |                   |
      |            |---------->|           |                   |
      |            |Modify Resp TermA      |                   |
      |            |Add Resp Local SDP (Specified)             |
      |            |           |---------->|                   |
      |            |           |Add TermB SD:Ring ED:offhook   |
      |            |           |Add $ Local(Underspecified)    |
      |            |           |     Remote SDP (Specified)    |
      |            |           |           |                   |
      |            |           |           |------------------>|
      |            |           |           | UserB Phone Ringing
      |            |           |<----------|                   |
      |            |           |Add Resp TermB                 |

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      |            |           |Add Resp EphB Local Specified  |
      |            |           |           |<------------------|
      |            |           |           |UserB goes Offhook |
      |            |           |<----------|                   |
      |            |           |Notify Offhook                 |
      |            |           |---------->|                   |
      |            |           | Notify Resp                   |
      |            |<----------|           |                   |
      |            |Modify TermA SendRecv  |                   |
      |            |Modify EphA  Remote(Specified) SendRecv    |
      |            |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |            |           |---------->|                   |
      |            |           |Modify TermB SendRecv          |
      |            |           |Modify EphB SendRecv           |
      |            |           |<----------|                   |
      |            |           |Modify Resp|                   |
      |/------------------------------------------------------\|
      |                     RTP MEDIA                          |
      |\------------------------------------------------------/|
      |----------->|           |           |                   |
      |UserA goes OnHook       |           |                   |
      |            |---------->|           |                   |
      |            |Notify OnHook          |                   |
      |            |<----------|           |                   |
      |            |Notify Resp|           |                   |
      |            |           |---------->|                   |
      |            |           |Modify TermA SD:BusyTone       |
      |            |           |           |------------------>|
      |            |           |           | Busy tone to UserB|
      |            |           |<----------|                   |
      |            |           |Modify Resp|                   |
      |            |<----------|           |                   |
      |            |Subtract TermA         |                   |
      |            |Subtract EphA          |                   |
      |            |---------->|           |                   |
      |            |Subtract Resp TermA    |                   |
      |            |Subtract Resp EphA Statistics              |
      |            |           |           |<------------------|
      |            |           |           | UserB goes Onhook |
      |            |           |<----------|                   |
      |            |           |Notify Onhook                  |
      |            |           |---------->|                   |
      |            |           |Notify Resp|                   |
      |            |           |---------->|                   |
      |            |           |Subtract TermB                 |
      |            |           |Subtract EphB                  |
      |            |           |<----------|                   |
      |            |           |Subtract Resp TermB            |
      |            |           |Subtract Resp EphB Statistics  |
      |____________|___________|___________|___________________|

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Case (a)

In all the telephone scenarios explained in this draft, once the call
is terminated by either the Calling party or the called party, the
other user listens a busy tone. A dial tone can be applied for the user
to initiated another call. But for simplicity busy tone is applied so
that the user goes onhook before initiating another call. It is assumed
in the call scenarios that the registration of the MG with the MGC is
done already. In Step 1 the MGC generates the Modify message towards
both the Residential gateways to check for off hook on the
terminations. (A wildcard command may also be used in this scenario but
simplicity we consider only command to specific terminations). Modify
message generated only for Residential gateway 1 is shown, similar
message is sent to the other Residential gateway also. We are not
considering the embedded signal and event descriptors here. Another
call scenario will illustrate the use of embedded event and signal
descriptors. The MGC in NULL context generates the command to the
specific termination TermA. The off hook event of the analog supervision
package is used here. The request identifier specified here in the
example is 1111. The mode of the termination is set to receive only.
The stream parameter is used with only the Local control descriptor.

Step 1
MGC to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        },
 Events = 1111 {al/of}
           }
       }
   }

MG after receiving the command from MGC accepts it and responds with the
transaction reply.

Step 2

   MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
RGW1 and constructs and sends the Notify message towards the MGC. The
MG uses the same request id (1111) sent by the MGC in its initial

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command. The timestamp of the detected event is also passed as
parameter to the observed event.

Step 3
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
   }

MGC generates the Notify response and responds with more messages
towards the MG that generated the Notify command.

Step 4
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The MGC in the present example issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a digit
map on the termination. The digit map name used in the example is
Dmap1 and the dial pattern is 2XXX. The event descriptor lists digit
map completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the event
descriptor is 1112.

Step 5
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1 {(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after receiving the Modify command after validation responds to
the MGC and starts processing the descriptors listed.

Step 6
MG1 to MGC:

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   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the
MGC. In this example the order of descriptor is signal descriptor,
digit map descriptor followed by Events descriptor. The MG first
processes the signal descriptor. The dial tone is applied to the
Termination specified. The Digit map is updated in the Database of the
termination. The Digit map said to be ACTIVE on the termination as the
digit map completion event is listed in the events descriptor with the
digit map name. A digit map is activated whenever a new event
descriptor is applied to the termination or embedded event descriptor
is activated, and that event descriptor contains a digit map
completion event which itself contains a digit map parameter. UserA
after receiving the dial tone starts dialing digits. In this example
we will not dwell into the different possible cases of digit dialing
by the user. It's assumed that the user dials digits that match the
pattern specified in the digit map. Lets assume that the user has
dialed 2992. MG detects the digits dialed and reports the same as
parameter to the digit map completion event. A notify command is
generated from MG1 to MGC. The MG again used the same request
identifier as specified by the MGC.

Step 7
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce {ds="2992", Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 8
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example it is assumed that the called subscriber is
connected to the RGW2, which is again controlled by the same MGC. The
MGC generates a transaction with two commands clubbed into the same
Action. The first command is to create a new context and add the
physical termination TermA into it. As the MGC is aware that the

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destination user UserB is free it indicates MG1 to apply ringback
tone to the termination of UserA. The second command is generated
to create an ephemeral termination and add the created termination
in the same context that was created because of the earlier command.
Here we assumed a single set of SDP information indicating that
Reserve group is not used. The Reserve Value feature is also not used.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals {cg/rt}
                            }
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = Receiveonly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

In this example the connection fields IP address, the media field port
number are unspecified. The MG in its response indicates the IPAddress
and port number used. The contextID is also not specified indicating the
creation of a new context. In this example the MG creates a context
with contextID 1. The physical termination TermA is added to context 1.
The mode of the physical termination was earlier set to Receiveonly
and in this message the ephemeral termination is requested to create
with Receiveonly mode. The ephemeral termination created in this
example is EphA. MG responds with the allocated IP address
209.110.59.33 and port number 30000.


Step 10
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {

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                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

MGC generates a similar transaction towards the RGW2. The ContextID
specified in the action is $. The first command adds the physical
termination TermB to the newly created context. The Signal descriptor
for this termination lists the ring signal of the analog line
supervision package. This alerting signal is applied to the termination
of the TermB. The Event descriptor specifies offhook event of the
analog line supervision package. The second Add is meant to create an
ephemeral termination. MGC has the local information for the
ephemeral termination EphA in the RGW1. This information is passed
as remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
               Events =1234{al/of {events = 1235 {al/on}}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }

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             }
         }
      }
   }

MG2 after receiving the new transaction from MGC starts processing it.
It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ring" signal
to be applied on the termination. The event descriptor lists the
off hook event. The RGW2 creates an ephemeral termination with
TerminationId EphB. The local information is under-specified from
the MGC. The MG allocates the necessary resources for processing the
media descriptor for the ephemeral termination. The MG responds
to the MGC by specifying the IP address reserved for the local
connection. In this example MG2 reserves IP address 207.176.47.90
and port number 40000. The MG2 responds to MGC with the following
transaction reply.

Step 12
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC waits for the UserB to go offhook. Once the UserB goes offhook,
 MG2 reports the notification of the offhook event to the MGC.

Step 13
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}
      }
   }
The MGC responds to the MG2 with the Notify response.


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Step 14
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3000 {
       Context = 2 {Notify = TermB}
   }
The MGC generates a transaction towards MG2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook event.

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

The MG2 responds to the request from MGC.

Step 16
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC generates message to the MG1 to stop the ringback tone and to
report the remote SDP information for the ephemeral termination EphA.
The mode of the two terminations TermA and EphA is set to send receive.

Step 17
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000

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   Transaction = 1239 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, specifies to stop the ringback tone at the calling end. The
remote SDP information is updated for the ephemeral termination EphA.
The mode is changed to send receive. MG1 responds to the MGC with the
response for the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange the voice. The call can be termination
either by the calling user or the called user. In this example it is
assumed that the calling party has gone on-hook The UserA after the
conversation goes onhook indicating the tearing down of the call. The
same is reported in the Notify command from MG1 to MGC.

Step 19
RGW1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
      }
   }

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The MGC responds to the MG1s Notify message.

Step 20
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC generates a Modify command towards the RGW2 for applying busy
tone to the called subscriber. The mode of both terminations is set to
receive only.

Step 21
MGC to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
     Context = 2 {
       Modify = TermB {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphB {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The MG2 responds to this modify request.

Step 22
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1240 {
      Context = 2 {
         Modify= TermB, Modify = EphB}
   }

The MGC generates transactions with two subtracts commands one for
physical and other for ephemeral terminations. The MGC does the same
for both the Contexts one at RGW1 and the other at RGW2.


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Step 23:
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 24
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1241 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The User B after going onhook, the RGW2 generates Notify command
towards the MGC.

Step 25
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20000202T10070000:al/on}}
      }
   }
The MGC responds to the MG2 with the Notify response.

Step 26
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000

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   Reply = 3001 {
       Context = 2 {Notify = TermB}
   }

The MGC generates subtract command towards RGW2 for removing TermB
from valid context.

Step 26
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The MG2 responds to the subtract commands generated by MGC.

Step 27
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1242 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The MGC generates the message as shown in step 1 to both the RGW1 and
RGW2, to enable the users to participate/initiate in further calls.












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Case (b)

_____________________________________________________________________
             |           |           |              |
  USERA      |   RGW1    |    MGC    |   RGW2       |       USERB
_____________|___________|___________|______________|_________________
      |            |           |           |                   |
      |            |           |           |                   |
      |/------------------------------------------------------\|
      |                     RTP MEDIA                          |
      |\------------------------------------------------------/|
      |            |           |           |                   |
      |            |           |           |<------------------|
      |            |           |           |UserB goes Onhook  |
      |            |           |<----------|                   |
      |            |           |Notify Onhook                  |
      |            |           |---------->|                   |
      |            |           |Notify Resp|                   |
      |            |           |---------->|                   |
      |            |<----------|           |                   |
      |            |Modify TermA SD:BusyTone                   |
      |<-----------|           |           |                   |
      |Busy tone   |           |           |                   |
      |            |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |            |           |Subtract TermB                 |
      |            |           |Subtract EphB                  |
      |            |           |<----------|                   |
      |            |           |Subtract Resp TermB            |
      |            |           |Subtract Resp EphB Statistics  |
      |----------->|           |           |                   |
      |UserA goes Onhook       |           |                   |
      |            |---------->|           |                   |
      |            |Notify OnHook          |                   |
      |            |<----------|           |                   |
      |            |Notify Resp|           |                   |
      |            |<----------|           |                   |
      |            |Subtract TermA         |                   |
      |            |Subtract EphA          |                   |
      |            |---------->|           |                   |
      |            |Subtract Resp TermA    |                   |
      |            |Subtract Resp EphA Statistics              |
      |____________|___________|___________|___________________|


The case (a) above illustrated the call flow between two Residential

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Gateways controlled by a single MGC. In this section we will discuss
the call scenario where the called party terminates the call. The
assumptions for case (a) holds good for this call flow also. The call
flow is same till step 18. The voice path is through and both the
users are in conversation. We will consider the call flow when UserB
goes on hook. As soon as the UserB goes onhook the RGW2 generates
notify message to the MGC.

Step 19
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
             20010202T10030000:al/on}
          }
      }
   }

The MGC responds to the MG's notify message.
Step 20
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 3001 {
      Context = 2 {
          Notify = TermB
      }
   }


The MGC generates a Modify command towards the RGW1 for applying busy
tone to the called subscriber. The mode of both terminations is set
to receive only.

Step 21
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
     Context = 1 {
       Modify = TermA {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphA {
          Media {
              LocalControl {
              Mode = recvonly}
               }

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           }
       }
     }
   }

The MG1 responds to this modify request.

Step 22
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1240 {
      Context = 1 {
         Modify= TermA, Modify = EphA}
   }

The MGC generates transactions with two subtracts commands one for
physical and other for ephemeral terminations. This command is
generated towards the RGW2, since UserB has initiated the call tear
down.


Step 23
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 2 {
         Subtract = TermB {Audit {}},
         Subtract = EphB {Audit {Statistics}}
      }
   }
The MG2 responds to the subtract commands generated by MGC.

Step 24
MG2 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1242 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

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The User A after hearing the busy tone goes onhook. The same activity
is recognized as onhook event by the RGW1. The Notify command is
generated towards the MGC.

Step 25
RGW1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
      }
   }
The MGC responds to the MG1s Notify message.

Step 26
MGC to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC after receiving the Notify command with onhook event,
generates subtract commands to remove the termination from context
Identifier 1.

Step 27:
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 28
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1241 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {

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                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


The MGC generates the message as shown in step 1 to both the RGW1
and RGW2, to enable the users to participate/initiate in further
calls.

Case (c)
 _____________________________________________________________________
             |           |           |              |
  USERA      |   RGW1    |    MGC    |   RGW2       |       USERB
_____________|___________|___________|______________|_________________
      |            |           |           |                   |
      |            |           |           |                   |
      |            |           |---------->|                   |
      |            |           |Modify to  |                   |
      |            |           |Check Offhook                  |
      |            |<----------|           |                   |
      |            |Modify to  |           |                   |
      |            |check offhook          |                   |
      |            |---------->|<----------|                   |
      |            |Modify Resp| Modify Resp                   |
      |----------->|           |           |                   |
      |UserA offhook           |           |                   |
      |            |---------->|           |                   |
      |            |Notify offhook         |                   |
      |            |           |<----------|                   |
      |            |           |Notify Resp|                   |
      |            |           |<----------|                   |
      |            |           |Modify SG:dialtone             |
      |            |           |ED:al/on,dd/ce{Dmap1}          |
      |            |           |DM:Dmap1 = 2XXX                |
      |<-----------|           |           |                   |
      |Dial Tone   |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |            |           |           |                   |
      |----------->|           |           |                   |
      |User Dials Digits       |           |                   |
      |            |---------->|           |                   |
      |            |Notify digits          |                   |
      |            |<----------|           |                   |

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      |            |Notify Response        |                   |
      |            |<----------|           |                   |
      |            |Modify TermA SD:BusyTone                   |
      |<-----------|           |           |                   |
      |Busy tone   |           |           |                   |
      |            |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |----------->|           |           |                   |
      |UserA goes Onhook       |           |                   |
      |            |---------->|           |                   |
      |            |Notify OnHook          |                   |
      |            |<----------|           |                   |
      |            |Notify Resp|           |                   |
      |____________|___________|___________|___________________|


The two call flows explained in case (a) and (b) illustrate a
successful call scenario. In this subsection we will look into the
flow where UserA calls UserB and as the UserB is already in a call,
UserA receives busy tone, thus illustrating an unsuccessful call
scenario. The steps 1 through 8 remain that same.

When the MGC receives the digits dialed by UserA, it analyses the
digits and find that the digits 2992 pertain to UserB, which is again
controlled by the same MGC. In this example UserB is already in some
call. Hence the call initiation from UserA becomes unsuccessful.
MGC in this case issues a message, which instruct the MG, for busy
tone application on the Termination TermA.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
     Context = - {
       Modify = TermA {
         Signals {cg/bt}
       }
      }
     }

MG responds to the Modify message from MGC. It applies busy tone on
the termination TermA. MG also responds to the message generated from
MGC.

Step 10:
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
     Context = - {
       Modify = TermA
      }

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     }

As soon as the UserA goes onhook MG detects the same and reports that
event as parameter in the Notify command it generates towards the MGC.

Step 12:
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2002 {
     Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:al/on}
      }
     }
The MGC responds to the Notify generated by MG.

Step 11:
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
     Context = - {
          Notify = TermA
      }
     }

The MGC sends a Modify command towards that RGW1 for the Termination
TermA as shown in step 1 that takes the termination TermA to idle
state. In this state the RGW1 is again ready to detect events on the
termination TermA.


2.2 Call between Residential Gateway and Trunking Gateway

In the earlier section we illustrated the call between two users UserA
and UserB connected to residential gateways RGW1 and RGW2. In this
section we illustrate the call flow between a Residential gateway user
and a Trunking gateway. In this flow, the packages that are supported
by the RGW are analog line supervision package, RTP package, generic
package, DTMF detection package, and Call progress generator package,
Network Package. The Trunking gateway is supports RTP package, generic
package, and network package. We are not assuming any specific
signaling to the other side of the Trunking gateway. This makes call
flow simple and independent of the type of signaling towards the
other side of the Trunking gateway.








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            _________________________________________________
                         |           |           |
              USERA      |   RGW1    |    MGC    |   TGW
            _____________|___________|___________|___________
                  |            |           |           |
                  |            |           |           |
                  |            |<----------|           |
                  |            |Modify to  |           |
                  |            |check offhook          |
                  |            |---------->|           |
                  |            |Modify Resp|           |
                  |----------->|           |           |
                  |UserA offhook           |           |
                  |            |---------->|           |
                  |            |Notify offhook         |
                  |            |<----------|           |
                  |            |Notify Resp|           |
                  |            |<----------|           |
                  |            |Modify SG:dialtone     |
                  |            |ED:al/on,dd/ce{Dmap1}  |
                  |            |DM:Dmap1 = 2XXX        |
                  |<-----------|           |           |
                  |Dial Tone   |---------->|           |
                  |            |Modify Resp|           |
                  |            |           |           |
                  |----------->|           |           |
                  |User Dials Digits       |           |
                  |            |---------->|           |
                  |            |Notify digits          |
                  |            |<----------|           |
                  |            |Notify Response        |
                  |            |<----------|           |
                  |            | Add TermA SD:ringbacktone
                  |            | Add $, Local SDP Info -underspecified
                  |<-----------|           |           |
                  |RingBack Tone           |           |
                  |            |---------->|           |
                  |            |Modify Resp TermA      |
                  |            |Add Resp Local SDP (Specified)
                  |            |           |---------->|
                  |            |           |Add Phy    |
                  |            |           |Add $ Local(Underspecified)
                  |            |           |     Remote SDP (Specified)
                  |            |           |<----------|
                  |            |           |Add Resp Phy




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                  |            |           |Add Resp EphB Local Specified
                  |            |<----------|           |
                  |            |Modify TermA SendRecv  |
                  |            |Modify EphA  Remote(Specified) SendRecv
                  |            |---------->|           |
                  |            |Modify Resp|           |
                  |/----------------------------------\|
                  |             RTP MEDIA              |
                  |\----------------------------------/|
                  |----------->|           |           |
                  |UserA goes OnHook       |           |
                  |            |---------->|           |
                  |            |Notify OnHook          |
                  |            |<----------|           |
                  |            |Notify Resp|           |
                  |            |<----------|           |
                  |            |Subtract TermA         |
                  |            |Subtract EphA          |
                  |            |---------->|           |
                  |            |Subtract Resp TermA    |
                  |            |Subtract Resp EphA Statistics
                  |            |           |Subtract Phy
                  |            |           |Subtract EphB
                  |            |           |<----------|
                  |            |           |Subtract Resp Phy
                  |            |           |Subtract Resp EphB Statis
                  |____________|___________|___________|



The MGC generates modify command for to the residential gateway to
check for offhook for Termination TermA. In this message the event
offhook has an embedded signal descriptor and embedded event descriptor.
The embedded signal descriptor is sent for application of dial tone
immediately after the detection of the offhook event and the event
descriptor then will be updated with the onhook and the digit map
completion event. The Digit map is also defined in the digit map
descriptor.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        },
               DigitMap= Dmap1 {(2XXX)}
 Events = 1111 {al/of Embed {signals {cg/dt}, Events=1112 {al/on},

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                                           {dd/ce {Dmap1}}}
           }
       }
   }

The MG after receiving the MGC's message responds to it.

Step 2
   RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

When the user A goes offhook RGW detects the offhook event and as it
is listed in the event descriptor report the event detection using
Notify command.

Step 3
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }
   }
the MGC responds with the Notify response.

Step 4
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }


The user gets Dial tone as part of Embedded descriptor processing. The
digit map is active on the termination TermA. When the user dials the
digits they are reported to MGC through Notify command.

Step 5
RGW to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce {ds="2992", Meth=FM}}}
      }
   }


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MGC after receiving the Notify command responds back with the Notify
response.

Step 6
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

The MGC generates the Add command for adding the physical termination
TermA and to create an ephemeral termination EphA. The local SDP
information for the ephemeral termination EphA is under specified to
enable the RGW to allocate the necessary values by itself. The mode
of the two terminations is set to receive only.

Step 7
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = TermA {
                 Signals {cg/rt}
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

MG after creating the context adds the physical termination TermA. In
this case MG creates a context with ContextId 1. The ephemeral
termination EphA is created and added to the context 1. The MG
reserves resources for the local SDP information. In this case the
IP address allocated is 209.110.59.33 and the port number used is
30000. The MG responds to the Add command with this information in

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the response to MGC.

Step 8
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = 1 {
         Add = TermA,
         Add=EphA {
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    }; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

In this example as mentioned earlier we doesn't assume any specific
signaling in the other side of the Trunking gateway. This eliminates
the complexity of reporting the address information and alerting the
end user. The MGC then "Adds" a physical termination. The wildcard $
is used here to enable the Trunking gateway to choose one of its
trunks on the other side of the Trunking gateway. The ephemeral
termination is requested to create with the under specified SDP local
information and the remote SDP information.

Step 9
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = Trunk1/$  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0

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   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }
   }

The Trunking gateway then processes the command and does the necessary
signaling towards the other side of the Trunking gateway. The seized
trunk identifier is returned in the Add response for physical
termination. In the response for the ephemeral termination, the TGW
returns the local information of the ephemeral termination created.
In this example the TGW creates a context with ContextID 2.

Step 10
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236 {
      Context = 2 {
        Add = Trunk1/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

As mention earlier, How the MGC receives the indication about the
status of the end user is out of scope of this call flow. But once the
MGC receives the users status it forwards the remote SDP information
for the RGW and change the mode for the termination both at RGW and
TGW to SendRecv.

Step 11
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }

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         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }

The RGW after receiving the Modify command from MGC responds back with
the response.

Step 12
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1237 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }

The MGC also generates commands to the TGW to change the mode of the
Ephemeral termination to send receive. Thus enabling the virtual
voice path between the two ephemeral terminations.

Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
     Context = 2 {
       Modify = Trunk1/line1 {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
       },
       Modify = EphB {
          Media {
            LocalControl {
              Mode = sendrecv}
           }
       }
     }
   }

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The TGW after receiving the mode change information in Modify command
responds to it.

Step 14
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
      Context = 2 {Modify = Trunk1/line1, Modify = EphB}
   }
Now RTP media flow takes place. In the example the UserA goes onhook
to terminate the call. The RGW after detecting the event reports the
same to MGC in the Notify command.

Step 15:
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
          }
      }
   }
The MGC responds to the MG1s Notify message.

Step 16
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }
The MGC now generates subtract commands both to the RGW and the TGW.
The mechanism of generating call progress tone towards the called user
is not shown for simplicity. The two Subtract commands are clubbed in
a single action.

Step 17
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

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Step 18
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1239 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The MGC generates similar command towards the TGW

Step 19
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
      Context = 2 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The TGW responds to the subtract commands generated by MGC.

Step 26
TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240 {
      Context = 2 {
        Subtract = Trunk1/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }

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      }
   }



2.3 Call between Trunking gateway and Residential Gateway

The earlier section illustrated the call between a residential user and
a Trunking gateway. The call was initiated by the Residential gateway.
In this call scenario we will illustrate the case where the call
terminates on the Residential gateway when originated by the
Trunking gateway. Even in this call flow we will assume that signaling
beyond the Trunking gateway is taken care by an external entity, to
avoid CAS/CCS specific details.

            ___________________________________________________________
                         |           |              |
                 TGW     |    MGC    |   RGW1       |       USERB
            _________ ___|___________|______________|_________________
                   |           |           |                   |
                   |           |           |                   |
                   |<----------|           |                   |
                   | Add Phy   SD:ringbacktone                 |
                   | Add $, Local SDP Info -underspecified     |
                   |---------->|           |                   |
                   |Add Resp Phy           |                   |
                   |Add Resp Local SDP (Specified)             |
                   |           |---------->|                   |
                   |           |Add TermB SD:Ring ED:offhook   |
                   |           |Add $ Local(Underspecified)    |
                   |           |     Remote SDP (Specified)    |
                   |           |           |                   |
                   |           |           |------------------>|
                   |           |           | UserB Phone Ringing
                   |           |<----------|                   |
                   |           |Add Resp TermB                 |
                   |           |Add Resp EphB Local Specified  |
                   |           |           |<------------------|
                   |           |           |UserB goes Offhook |
                   |           |<----------|                   |
                   |           |Notify Offhook                 |
                   |           |---------->|                   |
                   |           | Notify Resp                   |
                   |<----------|           |                   |
                   |Modify Phy   SendRecv  |                   |
                   |Modify EphA  Remote(Specified) SendRecv    |
                   |---------->|           |                   |
                   |Modify Resp|           |                   |
                   |           |---------->|                   |
                   |           |Modify Phy   SendRecv          |
                   |           |Modify EphB SendRecv           |

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                   |           |<----------|                   |
                   |           |Modify Resp|                   |
                   |/-----------------------------------------\|
                   |                RTP MEDIA                  |
                   |\-----------------------------------------/|
                   |           |---------->|                   |
                   |           |Modify TermB SD:BusyTone       |
                   |           |           |------------------>|
                   |           |           | Busy tone to UserB|
                   |           |<----------|                   |
                   |           |Modify Resp|                   |
                   |<----------|           |                   |
                   |Subtract Phy           |                   |
                   |Subtract EphA          |                   |
                   |---------->|           |                   |
                   |Subtract Resp Phy      |                   |
                   |Subtract Resp EphA Statistics              |
                   |           |           |<------------------|
                   |           |           | UserB goes Onhook |
                   |           |<----------|                   |
                   |           |Notify Onhook                  |
                   |           |---------->|                   |
                   |           |Notify Resp|                   |
                   |           |---------->|                   |
                   |           |Subtract TermB                 |
                   |           |Subtract EphB                  |
                   |           |<----------|                   |
                   |           |Subtract Resp TermB            |
                   |           |Subtract Resp EphB Statistics  |
                   |___________|___________|___________________|

The Media Gateway controller is intimated about the call initiation
from the other side of the Trunking gateway. The MGC then indicates
the TGW to seize a trunk using the Add command with $ (choose)
wildcard. The MGC also requests for creation of an ephemeral
termination using another Add command in the same action request. The
Context Id specified by MGC is $ indicating that the TGW needs to
create a context and "Add" these terminations in the new context.

Step 1
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = $ {
          Add = Trunk1/$  {Media {
                    LocalControl {Mode = recvonly}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },

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                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
                }
             }
         }
      }
   }

The TGW after receiving the Add request from MGC creates a context. In
this example the ContextID allocated for the new context is 2. The
physical termination chosen by the TGW is Trunk1/line1. The mode of
the termination is set to Receiveonly. The TGW creates an ephemeral
termination with the SDP information specified by MGC. The response
contains all the specified values for the SDP information. To avoid
complexity in this call flow no reserve group and reserve value
properties are used. It should be assumed that they are all "OFF". In
this example the TGW reserved 207.176.47.90 as the IP address for the
RTP media stream and port number as 40000.

Step 2:

TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1234 {
      Context = 2 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC after receiving the response from TGW initiates the UserB
alerting towards the RGW. This is done by MGC in the ADD command for
the physical termination TermB. The MGC uses $ contextID. Indicating
the creation of Context at MG. The Ephemeral termination is requested
to create. The Remote SDP information is also passed as the parameters
in the media descriptor. The signal descriptor in the Add command for
physical termination enables RGW to apply the ring signal on the
termination TermB.


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Step 3
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = TermB {
                 Signals { al/ri }
                Events= 1111 { al/of Events = 1112 { al/on } }
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
          }
       }
   }

The RGW after receiving the transaction request from MGC first creates
a context. In this example the contextID allocated is 1. The RGW
"adds" the termination TermB to context 1 and as part of the signal
descriptor processing applies the "ring" signal on the termination.
The Events descriptor lists the offhook event of analog line
supervision package. The requestId specified in this example is
1111. The RGW also creates the ephemeral termination EphB. Whose
remote SDP information is specified by MGC and the local SDP
information is allocated and reserved by RGW. In this example the
RGW allocates an IP address of 209.110.59.33 and port number 30000.
The mode of the ephemeral termination is set to receive only.

Step 4

RGW to MGC:

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   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = 1 {
         Add = TermB,
         Add=EphB {
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

The UserB goes Offhook after hearing the "ring" signal. The offhook
event is reported to the MGC as observed event descriptor in Notify
command.

Step 5
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = 1 {
          Notify = TermB {ObservedEvents =1111 {
            20010202T10001000:al/of}}
      }
   }
The MGC responds with the Notify response.

Step 6
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermB}
   }

The MGC now generates commands to both RGW and TGW. These commands are
 generated to modify the mode of the physical and ephemeral
terminations towards both RGW and TGW.

Step 7:
MGC to RGW
     MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
     Context = 1 {
      Modify = TermB {
       Media {

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         LocalControl {
           Mode = sendrecv}
                  }
             }
      Modify = EphB {
        Media {
         LocalControl {
          Mode = sendrecv}
             }
         }
      }
    }

The RGW responds with the Transaction response for the commands sent
for both physical and ephemeral termination.
Step 8
RGW to MGC:
     MEGACO/1 [209.110.59.34]: 25000
   Reply= 1236 {
     Context = 1 {
      Modify = TermB {}
      Modify = EphB {
         }
      }
    }

The MGC also generates similar command towards the Trunking gateway.
The MGC in the Modify for the ephemeral termination also specifies the
remote SDP information, and this enables the TGW to change the mode of
the terminations to send and receive.

Step 9
MGC to TGW:
     MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
     Context = 2 {
      Modify = Trunk1/line1 {
       Media {
         LocalControl {
           Mode = SendRecv}
                  }
             }
      Modify = EphA {
        Media {
         LocalControl {
          Mode = SendRecv}
          Remote {
           v=0
          c=IN IP4 207.176.47.90
          m=audio 40000 RTP/AVP 4
                   }

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               } ; RTP profile for G723 is 4
             }
         }
      }
    }

The Trunking gateway responds to the MGC message and changes the mode
for both the terminations to Send and receive.

Step 10
TGW to MGC:
     MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
     Context = 2 {
      Modify = Trunk1/line1,
      Modify = EphA {
         }
      }
    }
Once both the terminations mode is change to send receive the two
users can start the conversation. The media stream is established.
The user to the other side of the Trunking gateway terminates the
Call. The MGC is updated with this information by the external
entity. The MGC generates a busy signal towards UserB connected to
the RGW.

Step 11
MGC to RGW:
     MEGACO/1 [216.33.33.61]:27000
   Transaction = 1238 {
     Context = 1 {
      Modify = TermB {
       Signals { cg/bt }
             }
         }
      }
    }
The RGW as part of signal descriptor processing plays the busy tone
towards the UserB termination TermB. The response is generated after
processing the command from MGC.

Step 12
RGW to MGC:
     MEGACO/1 [209.110.59.34]: 25000
   Reply = 1238 {
     Context = 1 {
      Modify = TermB {
             }
      }
    }


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The MGC terminates the call by generating Subtract command for both
the terminations in TGW and RGW.

Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
      Context = 2 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The TGW responds with the Statistics in the Subtract response for the
ephemeral termination. The context is created as an side effect of
deleting both the terminations in the context.

Step 14:
TGW to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1239 {
      Context = 2 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates similar command towards the RGW to delete the
physical and ephemeral terminations.

Step 15
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
      Context = 1 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW responds with the statistics for the ephemeral termination in
the Subtract response.


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Step 16
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240 {
      Context = 1 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The Call is terminated with the response received from RGW. The MGC
generates the initial Modify command to check for offhook on the
termination TermB. This takes the termination TermB to idle state and
the UserB is ready to ready to generate and receive further calls.



2.4 Call between two Trunking gateways
The earlier three sections illustrated the calls between two
residential gateways, and between residential gateway and Trunking
gateway.  This two Trunking gateway call flow scenario illustrates call
between two users connected to the other side of the Trunking gateway.
Even in this scenario to avoid unnecessary complexity we still assume
that some external entity conveys the necessary signaling information
to the MGC to enable it to control the two Trunking gateways. The
CAS/CCS signaling details towards the other side of the each Trunking
gateway is avoided for simplicity. This boils down to the message
generation from MGC for enabling media flow. No signaling is done on
either the physical or ephemeral termination.


            __________________________________________________________
                         |           |              |
                 TGW1    |    MGC    |   RGW1       |       TGW2
            _________ ___|___________|______________|_________________
                   |           |           |                   |
                   |           |           |                   |
                   |<----------|           |                   |
                   | Add Phy   SD:ringbacktone                 |
                   | Add $, Local SDP Info -underspecified     |
                   |---------->|           |                   |

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                   |Add  Resp Phy          |                   |
                   |Add Resp Local SDP (Specified)             |
                   |           |---------->|                   |
                   |           |Add Phy   SD:Ring ED:offhook   |
                   |           |Add $ Local(Underspecified)    |
                   |           |     Remote SDP (Specified)    |
                   |           |           |                   |
                   |           |<----------|                   |
                   |           |Add Resp Phy                   |
                   |           |Add Resp EphB Local Specified  |
                   |<----------|           |                   |
                   |Modify Phy   SendRecv  |                   |
                   |Modify EphA  Remote(Specified) SendRecv    |
                   |---------->|           |                   |
                   |Modify Resp|           |                   |
                   |           |---------->|                   |
                   |           |Modify Phy   SendRecv          |
                   |           |Modify EphB SendRecv           |
                   |           |<----------|                   |
                   |           |Modify Resp|                   |
                   |/-----------------------------------------\|
                   |             RTP MEDIA                     |
                   |\-----------------------------------------/|
                   |<----------|           |                   |
                   |Subtract Phy           |                   |
                   |Subtract EphA          |                   |
                   |---------->|           |                   |
                   |Subtract Resp Phy      |                   |
                   |Subtract Resp EphA Statistics              |
                   |           |---------->|                   |
                   |           |Subtract Phy                   |
                   |           |Subtract EphB                  |
                   |           |<----------|                   |
                   |           |Subtract Resp Phy              |
                   |           |Subtract Resp EphB Statistics  |
                   |___________|___________|___________________|

When the MGC receives the call establishment from one side of the
Trunking gateway it generates two ADD commands in a single action. The
action request includes creation of Context, choosing of physical
termination and adding the same to the context created and creating
of ephemeral termination and adding this to the newly created
context. The local SDP parameters are under specified. The TGW1 in
its response need to specify these under specified parameters.

Step 1
MGC to TGW1:
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = $ {
          Add = Trunk1/$  {Media {

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                    LocalControl {Mode = recvonly}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
                }
             }
         }
      }
   }
The TGW after receiving the Add request from MGC creates a context.
In this example the ContextID allocated for the new context is 1. The
physical termination chosen by the TGW is Trunk1/line1. The mode of
the termination is set to Receiveonly. The TGW creates an ephemeral
termination with the SDP information specified by MGC. The response
contains all the specified values for the SDP information. To avoid
complexity in this call flow no reserve group and reserve value
properties are used. It should be assumed that they are all "OFF".
In this example the TGW reserved 209.110.59.33 as the IP address for
the RTP media stream and port number as 40000.

Step 2:
TGW1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

In this example as mentioned earlier it doesn't assume any specific
signaling in the other side of the Trunking gateway. Thus this
eliminates the complexion of reporting the address information and
alerting the end user. The MGC hence "Adds" a physical termination.
The wildcard $ is used here to enable the Trunking gateway to choose

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one of its trunks on the other side of the Trunking gateway. The
ephemeral termination is requested to create with the under specified
SDP local information and the remote SDP information.

Step 3
MGC to TGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = Trunk2/$  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 40000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }
   }
The Trunking gateway2 then process the command and does the necessary
signaling towards the other side of the Trunking gateway. The seized
trunk identifier is returned in the Add response for physical
termination. In the response for the ephemeral termination, the TGW
returns the local information of the ephemeral termination created.
In this example the TGW creates a context with ContextID 2.

Step 4
TGW2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235 {
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4

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   }
               } ; RTP profile for G723 is 4
         }
      }
   }
Once these MGC receives the answer of the call by the end user (through
an entity outside the scope of the flow), changes the mode of the
termination towards the both Trunking gateways. The MGC also indicates
the remote SDP information for the TGW1.Thus enabling the exchange of
media parameter information to both the Trunking gateways.

Step 5
MGC to TGW1:
     MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
     Context = 1 {
      Modify = Trunk1/line1 {
       Media {
         LocalControl {
           Mode = SendRecv}
                  }
             }
      Modify = EphA {
        Media {
         LocalControl {
          Mode = SendRecv}
          Remote {
           v=0
          c=IN IP4 207.176.47.90
          m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
             }
         }
      }
    }

The TGW1 after receiving the command from MGC does the necessary
processing to update and processing the remote SDP information. The
mode of the terminations is modified to send receive. The response
of the transaction is sent back to MGC.

Step 6
TGW1 to MGC:
     MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
     Context = 1 {
      Modify = Trunk1/line1,
      Modify = EphA {
         }
      }

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    }
Similar command is generated from the MGC towards the second
Trunking gateway.

Step 7
MGC to TGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
     Context = 2 {
       Modify = Trunk2/line1 {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
       },
       Modify = EphB {
          Media {
            LocalControl {
              Mode = sendrecv}
           }
       }
     }
   }
The TGW2 after receiving the mode change information in Modify
command responds to it.

Step 8
TGW1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1237 {
      Context = 2 {Modify = Trunk1/line1, Modify = EphB}
   }
The RTP media flow takes place once the modes of the terminations are
changed to send receive. The MGC is intimated about the call clearing
from an external entity. The MGC then generates subtract commands to
both the TGWs.

Step 9
MGC to TGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The TGW responds with the Statistics in the Subtract response for the
ephemeral termination. The context is created as an side effect of
deleting both the terminations in the context.


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Step 10:
TGW2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1238 {
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
A similar command is generated from the MGC towards the second TGW.
Step 11
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The TGW responds to the subtract commands generated by MGC.

Step 12
TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1239 {
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The two Trunking gateways are now ready to receive further commands

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from MGC. The terminations are present in the idle state.



2.5 Call between Residential gateway and SS7 trunk in TGW
The calls flow scenarios from 2.2 to 2.4 illustrated the Trunking
gateway without considering the signaling performed at the other side
of the Trunking gateway. In this section we will illustrate the call
flow scenario similar to the one in section 2.2. The emphasis here will
be both on the Megaco messages exchanged between MG and MGC and also
the signaling that towards the other side of the Trunking gateway.
Here in this example the CCS SS7 is assumed. The packages that
supported are Call progress tone generation package, analog line
supervision package, generic package, RTP package and Network package
for the RGW and Network and RTP package for the TGW.


_____________________________________________________________________
             |           |           |              |
  USERA      |   RGW1    |    MGC    |   TGW        |     SS7 Switch
_____________|___________|___________|______________|________________
      |            |           |           |                 |
      |            |           |           |                 |
      |            |<----------|           |                 |
      |            |Modify to  |           |                 |
      |            |check offhook          |                 |
      |            |---------->|           |                 |
      |            |Modify Resp|           |                 |
      |----------->|           |           |                 |
      |UserA offhook           |           |                 |
      |            |---------->|           |                 |
      |            |Notify offhook         |                 |
      |            |<----------|           |                 |
      |            |Notify Resp|           |                 |
      |            |<----------|           |                 |
      |            |Modify SG:dialtone     |                 |
      |            |ED:al/on,dd/ce{Dmap1}  |                 |
      |            |DM:Dmap1 = 2XXX        |                 |
      |<-----------|           |           |                 |
      |Dial Tone   |---------->|           |                 |
      |            |Modify Resp|           |                 |
      |            |           |           |                 |
      |----------->|           |           |                 |
      |User Dials Digits       |           |                 |
      |            |---------->|           |                 |
      |            |Notify digits          |                 |
      |            |<----------| --------------------------->|
      |            |Notify Response       IAM                |




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      |            |<----------|           |                 |
      |            | Add TermA SD:ringbacktone               |
      |            | Add $, Local SDP Info -underspecified   |
      |<-----------|           |           |                 |
      |RingBack Tone           |<----------------------------|
      |            |---------->|          ACM                |
      |            |Add Resp TermA         |                 |
      |            |Add Resp Local SDP (Specified)           |
      |            |           |---------->|                 |
      |            |           |Add Phy    |                 |
      |            |           |Add $ Local(Underspecified)  |
      |            |           |     Remote SDP (Specified)  |
      |            |           |<----------------------------|
      |            |           |          ANM                |
      |            |           |<----------|                 |
      |            |           |Add Resp Phy                 |
      |            |           |Add Resp EphB Local Specified|
      |            |<----------|           |                 |
      |            |Modify TermA SendRecv  |                 |
      |            |Modify EphA  Remote(Specified) SendRecv  |
      |            |---------->|           |                 |
      |            |Modify Resp|           |                 |
      |/----------------------------------\|                 |
      |             RTP MEDIA              |                 |
      |\----------------------------------/|                 |
      |----------->|           |           |                 |
      |UserA goes OnHook       |           |                 |
      |            |---------->|           |                 |
      |            |Notify OnHook          |                 |
      |            |<----------|           |                 |
      |            |Notify Resp|           |                 |
      |            |<----------|           |                 |
      |            |Subtract TermA         |                 |
      |            |Subtract EphA          |                 |
      |            |           |---------------------------->|
      |            |           |         REL                 |
      |            |---------->|           |                 |
      |            |Subtract Resp TermA    |                 |
      |            |Subtract Resp EphA Statistics            |
      |            |           |---------->|                 |
      |            |           |Subtract Phy                 |
      |            |           |Subtract EphB                |
      |            |           |<----------------------------|
      |            |           |          RLC                |
      |            |           |<----------|                 |
      |            |           |Subtract Resp Phy            |
      |            |           |Subtract Resp EphB Statis    |
      |____________|___________|___________|_________________|




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The MGC generates modify command for to the residential gateway to
check for offhook for Termination TermA. In this message the event
offhook has an embedded signal descriptor and embedded event descriptor.
The embedded signal descriptor is sent for application of dial tone
immediately after the detection of the offhook event and the event
descriptor then will be updated with the onhook and the digit map
completion event. The Digit map is also defined in the digit map
descriptor.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        },
               DigitMap= Dmap1{(2XXX)}
 Events = 1111 {al/of Embed { signals {cg/dt}, Events=1112 { al/on},
                                      {dd/ce {Dmap1}}}
           }
       }
   }

The MG after receiving the MGC's message responds to it.

Step 2
   RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

When the user A goes offhook RGW detects the offhook event and as it
is listed in the event descriptor reports the event detection using
Notify command.

Step 3
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {Observed Events =1111 {
            20010202T10000000:al/of}}
      }
   }
the MGC responds with the Notify response.

Step 4

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MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }


The digit map is active on the termination TermA. When the user dials
the digits the they are reported to MGC through Notify command.

Step 5
RGW to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the
Notify response.

Step 6
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

The MGC generates the Add command for adding the physical termination
TermA and to create an ephemeral termination EphA. The local SDP
information for the ephemeral termination EphA is under specified to
enable the RGW to allocate the necessary values by itself. The mode of
the two terminations is set to receive only.

Step 7
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = TermA {
                 Signals {cg/rt}
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                            }
          Add = $ {
              Media {

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                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

MG after creating the context adds the physical termination TermA. In
this case MG creates a context with ContextId 1. The ephemeral
termination EphA is created and added to the context 1. The MG reserves
resources for the local SDP information. In this case the IP address
allocated is 209.110.59.33 and the port number used is 30000. The MG
responds to the Add command with this information in the response to
MGC.

Step 8
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

In this example as mentioned earlier the CCS SS7 signaling is assumed
towards  the other side of the Trunking gateway. The IAM message is
generated towards the SS7 switch, with the necessary information about
the called party and calling party. The SS7 switch responds with ACM
indicating that address complete message towards the Trunking gateway.
When the ANM "answer" message is received the MGC Adds a physical
termination. The wildcard $ is used here to enable the Trunking gateway
to choose one of its trunks on the other side of the Trunking gateway.
The ephemeral termination is requested to create with the under

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specified SDP local information and the remote SDP information.

Step 9
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = Trunk1/$  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }
   }

The Trunking gateway then processes the command and does the necessary
signaling towards the other side of the Trunking gateway. The seized
trunk identifier is returned in the Add response for physical
termination. In the response for the ephemeral termination, the TGW
returns the local information of the ephemeral termination created. In
this example the TGW creates a context with ContextID 2.

Step 10
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236 {
      Context = 2 {
        Add = Trunk1/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }

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               } ; RTP profile for G723 is 4
         }
      }
   }

As mention earlier MGC after receiving the ANM message to indicate the
status of the end user it forwards the remote SDP information for the
RGW and changes the mode for the termination both at RGW and TGW to
SendRecv.

Step 11
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }

The RGW after receiving the Modify command from MGC responds back with
the response.
Step 12
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1237 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }

The MGC also generates commands to the TGW to change the mode of the
Ephemeral termination to send receive. Thus enabling the virtual voice
path between the two ephemeral terminations.


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Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
     Context = 2 {
       Modify = Trunk1/line1 {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
       },
       Modify = EphB {
          Media {
            LocalControl {
              Mode = sendrecv}
           }
       }
     }
   }
The TGW after receiving the mode change information in Modify command
responds to it.

Step 14
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
      Context = 2 {Modify = Trunk1/line1, Modify = EphB}
   }
Now RTP media flow takes place. In the example the UserA goes onhook
to terminate the call. The RGW after detecting the event reports the
same to MGC in the Notify command.

Step 15:
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
          }
      }
   }
The MGC responds to the RGWs Notify message.

Step 16
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA

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      }
   }
The MGC now generates subtract commands both to the RGW and the TGW.
The mechanism of generating call progress tone towards the called user
is not shown for simplicity. The two Subtract commands are clubbed in
a single action.

Step 17
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
      Context = 1 {
         Subtract = TermA {Audit {}},
         Subtract = EphA {Audit {Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 18
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1239 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The MGC generates a REL "release" message towards the SS7 switch.
After receiving the RLC "release complete" message command is
generated towards the TGW to subtract the two terminations from context.

Step 19
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
      Context = 2 {
         Subtract = Trunk1/line1{Audit{ }},

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         Subtract = EphB {Audit{Statistics}}
      }
   }
The TGW responds to the subtract commands generated by MGC.

Step 26
TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240 {
      Context = 2 {
        Subtract = Trunk1/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }



2.6 Call between SS7 trunk in TGW and residential gateway

In the earlier call scenario 2.5, we illustrated the call flow between
MGC and MG considering the CCS SS7 signaling towards one side of the
Trunking gateway. The residential Gateway user in that scenario
initiated the call. In this scenario we illustrate similar situation
with call initiated by a user connected to the PSTN network that
originates SS7 signaling. The packages that are supported include
Call progress tone generation package, analog line supervision
package, generic package, RTP package and Network package for the RGW
and Network and RTP package for the TGW.

 ______________________________________________________________________
            |            |           |              |
 SS7 Switch |    TGW     |    MGC    |   RGW1       |       USERB
____________|________ ___|___________|______________|_________________
      |            |           |           |                   |
      |            |           |           |                   |
      |----------------------->|           |                   |
      |          IAM           |           |                   |
      |<-----------------------|           |                   |
      |          ACM           |           |                   |
      |            |           |           |                   |
      |            |<----------|           |                   |

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      |            | Add Phy   |           |                   |
      |            | Add $, Local SDP Info -underspecified     |
      |            |---------->|           |                   |
      |            |Add Resp Phy           |                   |
      |            |Add Resp Local SDP (Specified)             |
      |            |           |---------->|                   |
      |            |           |Add TermB SD:Ring ED:offhook   |
      |            |           |Add $ Local(Underspecified)    |
      |            |           |     Remote SDP (Specified)    |
      |            |           |           |                   |
      |            |           |           |------------------>|
      |            |           |           | UserB Phone Ringing
      |            |           |<----------|                   |
      |            |           |Add Resp TermB                 |
      |            |           |Add Resp EphB Local Specified  |
      |            |           |           |<------------------|
      |            |           |           |UserB goes Offhook |
      |<-----------------------|           |                   |
      |          ANM           |           |                   |
      |            |           |<----------|                   |
      |            |           |Notify Offhook                 |
      |            |           |---------->|                   |
      |            |           | Notify Resp                   |
      |            |<----------|           |                   |
      |            |Modify Phy   SendRecv  |                   |
      |            |Modify EphA  Remote(Specified) SendRecv    |
      |            |---------->|           |                   |
      |            |Modify Resp|           |                   |
      |            |           |---------->|                   |
      |            |           |Modify Phy   SendRecv          |
      |            |           |Modify EphB SendRecv           |
      |            |           |<----------|                   |
      |            |           |Modify Resp|                   |
      |            |/-----------------------------------------\|
      |            |                RTP MEDIA                  |
      |            |\-----------------------------------------/|
      |----------------------->|           |                   |
      |           REL          |           |                   |
      |            |           |---------->|                   |
      |            |           |Modify TermB SD:BusyTone       |
      |            |           |           |------------------>|
      |            |           |           | Busy tone to UserB|
      |            |           |<----------|                   |
      |            |           |Modify Resp|                   |
      |            |<----------|           |                   |
      |            |Subtract Phy           |                   |
      |            |Subtract EphA          |                   |
      |            |---------->|           |                   |
      |            |Subtract Resp Phy      |                   |
      |            |Subtract Resp EphA Statistics              |
      |            |           |           |<------------------|

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      |            |           |           | UserB goes Onhook |
      |<-----------------------|           |                   |
      |          RLC           |           |                   |
      |            |           |<----------|                   |
      |            |           |Notify Onhook                  |
      |            |           |---------->|                   |
      |            |           |Notify Resp|                   |
      |            |           |---------->|                   |
      |            |           |Subtract TermB                 |
      |            |           |Subtract EphB                  |
      |            |           |<----------|                   |
      |            |           |Subtract Resp TermB            |
      |            |           |Subtract Resp EphB Statistics  |
      |____________|___________|___________|___________________|



We assume that the TGW and SG are in a single box, such that both
signaling and Media adaptation is done by the same entity The Media
Gateway controller is intimated about the call initiation from the
other side of the Trunking gateway, when the SS7 message IAM is
received. The MGC after receiving the IAM messages responds with the
ACM message indicating that the called party address is sufficient to
identify the end user. The ACM message is sent to the SS7 switch
through the signaling gateway. The circuit to be used for media
information is indicated by the SS7 message received by the MGC.

The MGC generates the Modify command to the Residential gateway for
application of "ring" signal to the user. The event descriptor in the
Modify command lists the offhook event.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        },
Events = 1111 {al/of}
Signals = {al/ri} ; For application of ring signal
           }
       }
   }
The Residential gateway after receiving the Modify command responds
with the Modify response.

Step 2
   RGW to MGC:

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   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

The users after receiving the "ring" signal assume to go offhook. The
same event is reported to the MGC in the notify command.

Step 3
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {Observed Events =1111 {
            20010202T10000000:al/of}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 4
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The MGC after receiving the offhook event responds with the SS7 message
to be generated towards the SS7 switch. The ANM message generated from
MGC indicates the answering state of the user. The MGC meanwhile
generate ADD commands to both the Trunking gateway and Residential
gateway. The message towards the Trunking gateway includes the
addition of physical circuit that was seized for media transfer. The
request for creating ephemeral termination is also sent in the same
request. The Local SDP information is under specified allowing the
Trunking gateway to choose the necessary SDP parameters.

Step 5
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0

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   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }
      }
   }

The Trunking gateway after responds with a contextID in this example 1.
The ephemeral termination is created and added to the same context as
the physical termination. The ephemeral termination added in this
example is EPHA. The local parameters are specified in the response.
The IP address chosen for the media transport in this example is
209.110.59.33, and the port number specified 30000.

Step 6
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235 {
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphB {
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC after receiving the response from the Trunking gateway uses
the SDP information in the response sent from TG to the Residential
gateway. The commands for adding the physical termination TermA and
ephemeral termination to be created are sent in the same transaction.
The MGC requests creation of context and to add the two terminations
in the same.

Step 7
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
       Context = $ {
          Add = TermA  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {

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                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The Residential gateway creates a context with ContextId 2. It adds the
physical termination TermA in that context. The ephemeral termination
EPHB is created with the specified SDP information. The response from
the MG specifies the local SDP information.

Step 8
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1237 {
      Context = 2 {
        Add = TermA,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.34
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response with the local SDP information
conveys the same to the Trunking gateway as remote SDP information
in the Modify command.

Step 9
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
       Context = 1 {
          Modify = EphA

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                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 209.110.59.34
   m=audio 30000 RTP/AVP 4
                    }
               }
             }
         }
      }
   }

The Trunking gateway responds to the Modify command.

Step 10
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
      Context = 1 {
   Modify = EphA
}
}
The media properties are exchanged between the two media gateways and
the RTP media can be transferred between these two. The call be will
be disconnected with one of the two users going onhook. In this example
we consider the user connected to the SS7 domain initiates the
termination of the Call. The SS7 switch generates the REL "release"
message towards the MGC. The MGC after receiving the REL message
initiates the call teardown. The MGC generates a busy tones towards the
user connected to the Residential gateway to indicate the disconnection
of the call. The modify command is sent with event descriptor that
lists the onhook event.

Step 11
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
       Context = 2 {
          Modify = TermA  {
            Signals { cg/bt },
            Events = 1236 {   al/on },
            Media { LocalControl { recvonly } }
               }
      }
   }

The Residential gateway responds with the Modify command response.


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Step 12
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1239 {
      Context = 2 {
        Modify = TermA,
       }
   }
The media connection tears down will be complete by responding the REL
message by the RLC. The MGC subtracts the terminations added in the two
Media gateways for this call. The Subtract command is sent to the
Trunking gateway. The audit descriptor lists the statistics to enable
statistics reporting to MGC from the Trunking gateway.

Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The TGW responds to the subtract commands generated by MGC.

Step 14
TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240 {
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

Step 15
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2001 {
      Context = 2 {
          Notify = TermA {Observed Events =1236 {

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            20010202T20000000:al/on}}
      }
   }

The MGC responds the Notify command with the Notify response.

Step 16
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = 2 {Notify = TermA}
   }

The MGC after receiving the Notify for onhook from UserA generates
transaction with two Subtract command for subtracting both the physical
and ephemeral terminations from the Residential gateway.

Step 15
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
      Context = 2 {
         Subtract = TermA{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The RGW responds to the subtract commands generated by MGC.

Step 16
TGW to MGC:
   MEGACO/1 [209.110.59.34]: 26000
   Reply = 1241 {
      Context = 2 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }





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2.7 Call between SS7 trunk in TGW and R2 trunk in TGW
This section of the call flow illustrates the call between two Trunking
gateways, one that does R2 signaling towards the PSTN and the second
TGW CCS SS7 towards the PSTN. In this example the user in the CCS SS7
signaling network originates the call. The destination user is connected
to the PSTN network with R2 signaling.  The R2 package draft is taken
as the input for illustrating the events and signals used for
communication between MG and MGC. The assumption of the R2 package,
that the compelled signaling is part of the MG to generate signals or
detect events holds true for this call scenario also.


 ______________________________________________________________________
            |            |           |              |
 SS7 Switch |    TGW1    |    MGC    |   TGW2       |       R2Exch
____________|____________|___________|______________|_________________
      |            |           |            |                |
      |----------->|           |            |                |
      |    IAM     |           |            |                |
      |            |---------->|            |                |
      |            |    IAM    |            |                |
      |            |           |----------->|                |
      |            |           |Modify Phy Seize             |
      |            |           |            |--------------->|
      |            |           |            |   Seize        |
      |            |           |<-----------|                |
      |            |           |Modify Resp |                |
      |            |           |            |<---------------|
      |            |           |            | Seize Ack      |
      |            |           |<-----------|                |
      |            |           |Notify OE:sa|--------------->|
      |            |           |----------->|   Digits       |
      |            |           |Notify Resp |                |
      |            |<----------|            |                |
      |            |   ACM     |            |                |
      |<-----------|           |            |                |
      |   ACM      |           |            |                |
      |            |           |            |<---------------|
      |            |           |            |  Answer        |
      |            |           |<-----------|                |
      |            |           | Notify OE:ans               |
      |            |           |----------->|                |
      |            |           |Notify Resp |                |
      |            |<----------|            |                |
      |            |   ANM     |            |                |
      |<-----------|           |            |                |
      |    ANM     |           |            |                |




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      |            |<----------|            |                |
      |            |Add Phy    |            |                |
      |            |Add $ Local (Unspecified)                |
      |            |---------->|            |                |
      |            |Add Phy Resp            |                |
      |            |Add Eph Resp            |                |
      |            |           |----------->|                |
      |            |           |Add Phy     |                |
      |            |           |Add $ Local (Unspecified)    |
      |            |           |      Remote (Specified)     |
      |            |           |<-----------|                |
      |            |           |Add Phy Resp|                |
      |            |           |Add Eph Resp|                |
      |            |<----------|            |                |
      |            |Modify Eph |            |                |
      |            |---------->|            |                |
      |            |Modify Resp|            |                |
      |            |/----------------------\|                |
      |            |       RTP MEDIA        |                |
      |            |\----------------------/|                |
      |----------->|           |            |                |
      |   REL      |           |            |                |
      |            |---------->|            |                |
      |            |   REL     |            |                |
      |            |           |----------->|                |
      |            |           |Modify Phy ED:R2/clear       |
      |            |           |            |--------------->|
      |            |           |            |  Clear Forward |
      |            |           |<-----------|                |
      |            |           |Modify Resp |                |
      |            |           |            |<---------------|
      |            |           |            | Clear Back     |
      |            |           |<-----------|                |
      |            |           | Notify OE:clear             |
      |            |           |----------->|                |
      |            |           | Notify Resp|                |
      |            |<----------|            |                |
      |            |  RLC      |            |                |
      |<-----------|           |            |                |
      |    RLC     |           |            |                |
      |            |<----------|            |                |
      |            |Sub Phy    |            |                |
      |            |Sub Eph    |            |                |
      |            |---------->|            |                |
      |            |Sub Phy Resp            |                |
      |            |Sub Eph Resp Statistics |                |
      |            |           |----------->|                |
      |            |           |Sub Phy     |                |
      |            |           |Sub Eph     |                |
      |            |           |<-----------|                |
      |            |           |Sub Phy Resp|                |

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      |            |           |Sub Eph Resp Statistics      |
      |____________|___________|____________|________________|




When the MGC through the signaling gateway receives the IAM it generates
a Modify message towards the Trunking gateway that supports R2 package.
The signal descriptor has the seize signal and the events descriptor
has the event seizeack. The seizeack event has an embedded signal
"address". The Trunking gateway is intended to seize a circuit and
apply the address signals after the seize acknowledgement is received
from the other R2 exchange. The calling party information can also be
provided in the address signal. The embedded event of the seize
acknowledgement event is the answer. This event has to be reported
when the digits reach the other R2 exchange and there is answer from
the terminating R2 exchange. The message from MGC to R2TGW is as
follows.

Step 1
MGC to R2TGW
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
      Context = - {
        Modify = Trunk1/line1 {
Signals = {R2/sz}
 Events = 1111 {R2/sa Embed {signals {R2/address {si = 2992, di = 2989}},
                       Events=1112 {R2/clear, R2/answer}
                     }
                          }
                                     }
The R2TGW after receiving the Modify command does the command
processing and responds with Modify command response.

Step 2
R2TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {
        Modify = Trunk1/line1
                          }
                }

The R2 TGW applies seize signal on the specified circuit group and after
 receiving the acknowledgement from the other R2 exchange updates the
embedded events descriptor as the events descriptor. The R2TGW also
generates a Notify command towards the MGC to indicate that the seize
acknowledgement has been received.

Step 3
R2GW to MGC:

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   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = - {
          Notify = Trunk1/line1 {Observed Events =1111 {
            20010202T10000000:R2/sa}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 4
MGC to R2GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = Trunk1/line1}
   }

The MGC now generates the address complete message to the SS7 switch
that has generated the IAM message. The R2TGW after receiving the
answer event from the other R2 exchange generates message to notify
this event.

Step 5
R2GW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = Trunk1/line1 {Observed Events =1112 {
            20010202T10000000:R2/ans}}
      }
   }

The MGC responds the Notify command with the Notify response.

Step 6
MGC to R2GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = Trunk1/line1}
   }

MGC generates the ANM message towards the SS7 switch through the
signaling gateway. It also generates commands to add terminations into
specific contexts. It generates a single transaction with two Add
commands towards the TGW that supports R2 terminations. One command
is to add the physical circuit group Trunk1/line and the other for the
ephemeral termination. The SDP information is unspecified that enables
the TGW to choose the under specified parameters.

Step 7
MGC to R2TGW

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235{
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }
      }
   }

The R2 Trunking gateway after receiving the Add command responds with a
contextID in this example 1. The ephemeral termination is created and
added to the same context as the physical termination. The ephemeral
termination added in this example is EPHA. The local parameters are
specified in the response. The IP address chosen for the media
transport in this example is 209.110.59.33, and the port number
specified 30000.

Step 8
R2TGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235{
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA {
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates similar transaction
with two ADD commands to the other TGW. The local SDP information
specified in by the R2TGW is used to as remote SDP information for the
other TGW. The MGC conveys this information in the Add command.

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Step 9
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236{
       Context = $ {
          Add = Trunk2/$ {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The Trunking gateway creates a context with ContextId 2. It adds the
physical termination Trunk2/line1 in that context. The ephemeral
termination EPHB is created with the specified SDP information. The
response from the MG specifies the local SDP information.

Step 10
RGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236{
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }

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The MGC after receiving the response generates a modify command to the
R2TGW to inform the local SDP information of TGW as the remote SDP for
the R2TGW.

Step 11
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237{
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    }
               }
             }
         }
      }
   }

The R2 Trunking gateway responds to the Modify command.

Step 12
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237{
      Context = 1 {
   Modify = EphA
}
}
The RTP media flow is established and the two users connected to the
SS7 trunk and R2 trunk starts the conversation. After conversation any
of the user can disconnect the call, in this example the user connected
to the SS7 domain releases the call. The SS7 switch generates a REL
message towards the MGC. The Signaling gateway forwards the same
request towards the MGC. The MGC initiates the tearing down of the
call. This is done initially by generating a Modify command towards
the R2 TGW to generate clear forward signal towards the R2 exchange.
In the message the MGC sends a signal descriptor with clear signals
and events descriptor with the clear in the event. The event in the
events descriptor is for detecting the clear back signal generated
from the R2 exchange.

Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000

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   Transaction = 1238{
      Context = 1 {
         Context = Trunk1/line1{
signal { R2/clear},
 Events = 1113{ R2/clear}
     }
   }

The R2 TGW after receiving the commands does the signals and events
descriptor processing and responds to the MGC with the Modify command
response.

Step 14
R2TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1238 {
      Context = 1 {
        Modify = Trunk1/line1
                          }
                       }

Mean while the MGC generates the subtract message towards the
originating TGW to remove the terminations from the newly created
context.

Step 15
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW responds to the subtract commands generated by MGC.

Step 16
TGW to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1239
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency

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             }
          }
      }
   }
The MGC after receiving the response from the TGW generates the
Release complete message RLC towards the SS7 switch through the
Signaling Gateway.

The R2 TGW after receiving the clear back signal from the other R2
exchange detects it and generates a Notify command towards the MGC.

Step 17
R2GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = - {
          Notify = TermA {Observed Events =1113 {
            20030202T10000000:R2/clear}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 18
MGC to R2GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
       Context = - {Notify = TermA}
   }
MGC after receiving the notify command generates subtract command to
remove both the physical termination and ephemeral termination.

Step 19
MGC to R2TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240{
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The R2TGW responds to the subtract commands generated by MGC.

Step 20
R2TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240{
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {

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                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
Now the termination is free to take part in other calls.



2.8 Call between R2 trunk in TGW and SS7 trunk in TGW

This section of the call flow illustrates the call between two
Trunking gateways, one that does R2 signaling towards one end and the
second TGW CCS SS7. In this example the user in the R2 signaling
network originates the call. The destination user is connected to
the PSTN network with CCS SS7 signaling.  The R2 package draft is
considered for illustrating the events and signals used for
communication between MG and MGC. The assumption of the R2 package,
that the compelled signaling is part of the MG to generate signals
or detect events holds true for this call scenario also.


 ______________________________________________________________________
            |            |           |              |
 R2Exchange |    TGW1    |    MGC    |   TGW2       |       SS7 Switch
____________|____________|___________|______________|_________________
     |            |            |            |                |
     |            |<-----------|            |                |
     |            |Modify ED:sz{SD:sa ED:addr, cl}           |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |----------->|            |            |                |
     | Seize      |            |            |                |
     |<-----------|            |            |                |
     |SeizeAck    |----------->|            |                |
     |            |Notify OE:sa|            |                |
     |----------->|            |            |                |
     | Digit 1    |            |            |                |
     |<-----------|            |            |                |
     |Send Next Digit          |            |                |
     |     :      |            |            |                |
     |     :      |            |            |                |
     |<-----------|            |            |                |
     | End of Singaling        |            |                |
     |            |----------->|            |                |

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     |            |Notify OE:addr           |                |
     |            |            |----------->|                |
     |            |            |  IAM       |--------------->|
     |            |<-----------|            |      IAM       |
     |            |Notify Resp |            |<---------------|
     |            |            |<-----------|      ACM       |
     |            |            |    ACM     |                |
     |            |<-----------|            |                |
     |            |Modify Phy  |            |                |
     |<-----------|            |            |                |
     |  Answer    |            |            |                |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |            |<-----------|            |                |
     |            | Add Phy    |            |                |
     |            | Add Eph Local Unspecified                |
     |            |----------->|            |                |
     |            |Add Phy Resp|            |                |
     |            |Add Eph Resp Local Specified              |
     |            |            |----------->|                |
     |            |            | Add Phy    |                |
     |            |            | Add EPh Local Unspecified   |
     |            |            |         Remote Specified    |
     |            |            |<-----------|                |
     |            |            |Add Phy Resp|                |
     |            |<-----------|            |                |
     |            |Modify Eph  |            |                |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |            |/-----------------------\|                |
     |            |       RTP MEDIA         |                |
     |            |\-----------------------/|                |
     |----------->|            |            |                |
     |Clear Forward            |            |                |
     |            |----------->|            |                |
     |<-----------|Notify OE:R2/clear       |                |
     |Clear Back  |            |            |                |
     |            |<-----------|            |                |
     |            |Notify Resp |            |                |
     |            |            |----------->|                |
     |            |            |   REL      |--------------->|
     |            |            |            |     REL        |
     |            |            |            |<---------------|
     |            |            |<-----------|     RLC        |
     |            |            |   RLC      |                |
     |            |<-----------|            |                |
     |            |Sub Phy     |            |                |
     |            |Sub Eph     |            |                |
     |            |----------->|            |                |
     |            |Sub Phy Resp|            |                |
     |            |Sub Eph Resp Statistics  |                |

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     |            |            |----------->|                |
     |            |            |Sub Phy     |                |
     |            |            |Sub Eph     |                |
     |            |            |<-----------|                |
     |            |            |Sub Phy Resp|                |
     |            |            |Sub Eph Resp Statistics      |
     |____________|____________|____________|________________|





The MGC generates a Modify command towards the R2 Trunking gateway with
the seize event and an embedded seize acknowledgement signal.  The
digit map in this scenario is assumed to be provisioned in the MG
(shown to be 2XXX which may not be true for practical R2 exchanges).
The seize event has a embedded signal seizeack to be applied after
detection of seize event. The embedded signal is accompanied by
another embedded events namely the clear event to detect the clear
forwards signal if generated from the R2 domain.

Step 1
MGC to R2TGW
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
      Context = - {
        Modify = Trunk1/line1 {
 Events = 1111 {R2/sz Embed { signals {R2/sa}, Events=1112
          { R2/clear  signals { R2/clear }, R2/address}}
                                              }
                          }
                                     }
The R2TGW after receiving the Modify command does the command processing
and responds with Modify command response.

Step 2
R2TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {
        Modify = Trunk1/line1
                          }
                                     }

In this example as mentioned earlier, the call is originated from a user
connected to the R2 domain of PSTN. The R2 exchange that is connected to
the R2 Trunking gateway generates the seize signal. The seize signal is
identified by the R2TGW and seize event is detected. The seize event is
notified to the MGC. The R2TGW meanwhile does the embedded descriptor
processing for the seize event. The application of the seizeack and
detection of clear event is activated on the specific circuit group.

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The Notify command is generated towards the MGC.

Step 3
R2GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {Observed Events =1111 {
            20010202T10000000:R2/sz}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 4
MGC to R2GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }
The R2TGW collects the digits and reports the same to the MGC as
parameters of the address event. The other observed event parameters
like the source number, subscribe category, etc are also indicated to
the MGC.

Step 5
R2GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {Observed Events =1112 {
            20010302T10000000:R2/address {  di=2992, si=2804 , sc=1 } }}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 6
MGC to R2GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }
The MGC then initiates the necessary signaling towards the exchange to
which the destination user is connected. In this example the MGC has to
generates SS7 messages to the SS7 switch. The IAM message is sent with
all the necessary address signaling information. The SS7 switch
responds with the ACM message.

The MGC after receiving the ANM message generates command to apply
answer signal. The MGC sends a Modify command towards the R2 TGW to

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indicate that the answer needs to be applied

Step 7
MGC to R2TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
          Modify = Trunk1/line1
                 {signals{ R2/ans } }
      }
   }

The R2trunking gateway responds to the Modify command.

Step 8
R2TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235 {
      Context = - {
   Modify = Trunk1/line1
}
}

The MGC after receiving the ANM message generates commands to both
the Trunking gateways to add physical circuits and create ephemeral
terminations. The MGC in its message to the R2TGW in its signal
descriptor lists the answer signal to indicate that the call
establishment is successful and the end user is free to receive
the call.

Step 9
MGC to R2TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236{
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }

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      }
   }

The R2 Trunking gateway after responds with a contextID in this
example 1. The ephemeral termination is created and added to the same
 context as the physical termination. The ephemeral termination added
in this example is EPHA. The local parameters are specified in the
response. The IP address chosen for the media transport in this
example is 209.110.59.33, and the port number specified 30000.

Step 10
R2TGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236{
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates similar transaction
with two ADD commands to the other TGW. The local SDP information
specified in by the R2TGW is used to as remote SDP information for
the other TGW. The MGC conveys this information in the Add command.

Step 11
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237{
       Context = $ {
          Add = Trunk2/$ {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{

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   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The Trunking gateway creates a context with ContextId 2. It adds the
physical termination Trunk2/line1 in that context. The ephemeral
termination EPHB is created with the specified SDP information. The
response from the MG specifies the local SDP information.

Step 12
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237{
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates a modify command to the
R2TGW to inform the local SDP information of TGW as the remote SDP for
the R2TGW.

Step 13
MGC to R2TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238{
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                    }
               }

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             }
         }
      }
   }

The R2 Trunking gateway responds to the Modify command.

Step 14
R2TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238{
      Context = 1 {
   Modify = EphA
}
}
The RTP media transfer takes place. The user connected to the R2
exchange domain terminates the call. The clear forwards signal
generated by the R2 exchange connected to the R2 TGW is detected and
reported to the MGC as the clear event in the R2 package. The clear
back signal, which is part of the clear event, enables the R2TGW to
generate the clear back signal.  The clear event detection is
reported to MGC as part of the Notify command.

Step 15
R2TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2003 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010402T10030000:R2/clear}
          }
      }
   }
The MGC responds to the RGWs Notify message.

Step 16
MGC to R2TGW:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2003 {
      Context = 1 {
          Notify = TermA
      }
   }
The MGC generates necessary command to the SS7 switch like the REL
message. The SS7 switch responds with the RLC message. The MGC now
generates commands to both the TGWs for subtracting the terminations
from the contexts created.

Step 17
MGC to R2TGW:
   MEGACO/1 [216.33.33.61]: 27000

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   Transaction = 1239{
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The R2TGW responds to the subtract commands generated by MGC.

Step 18
TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1239{
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates similar transaction with two Subtract command for
subtracting both the physical and ephemeral terminations from the
second Trunking gateway.

Step 19
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW responds to the subtract commands generated by MGC.

Step 20
TGW to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1240
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent

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                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }



2.9 Call between R1 trunk in TGW and SS7 trunk in TGW

In the earlier section we illustrated the Megaco messages between MGC
and two Trunking gateway one that perform CCS SS7 and the other CAS
R2 signaling. This section illustrates another similar scenario, but
now the call is initiated by the user that originates R1 signaling to
the user connected to CCS SS7 signaling. Both the Trunking gateways
are assumed to be controlled by the same Media Gateway Controller.
The packages that are considered are R1 package, network package,
MF tone detection package and RTP package.


 ______________________________________________________________________
            |            |           |              |
 R1Exchange |    TGW1    |    MGC    |   TGW2       |       SS7 Switch
____________|____________|___________|______________|_________________
     |            |            |            |                |
     |            |<-----------|            |                |
     |            |Modify ED:sz{SD:sa ED:addr, cl}           |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |----------->|            |            |                |
     | Seize      |            |            |                |
     |<-----------|            |            |                |
     |SeizeAck    |----------->|            |                |
     |            |Notify OE:sa|            |                |
     |----------->|            |            |                |
     | KP         |            |            |                |
     |----------->|            |            |                |
     |   Digit1   |            |            |                |
     |     :      |            |            |                |
     |     :      |            |            |                |
     |----------->|            |            |                |
     |     ST     |            |            |                |
     |            |----------->|            |                |
     |            |Notify OE:addr           |                |
     |            |            |----------->|                |
     |            |            |  IAM       |--------------->|

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     |            |<-----------|            |      IAM       |
     |            |Notify Resp |            |<---------------|
     |            |            |<-----------|      ACM       |
     |            |            |    ACM     |                |
     |            |<-----------|            |                |
     |            |Modify Phy  |            |                |
     |<-----------|            |            |                |
     |  Answer    |            |            |                |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |            |<-----------|            |                |
     |            | Add Phy    |            |                |
     |            | Add Eph Local Unspecified                |
     |            |----------->|            |                |
     |            |Add Phy Resp|            |                |
     |            |Add Eph Resp Local Specified              |
     |            |            |----------->|                |
     |            |            | Add Phy    |                |
     |            |            | Add EPh Local Unspecified   |
     |            |            |         Remote Specified    |
     |            |            |<-----------|                |
     |            |            |Add Phy Resp|                |
     |            |<-----------|            |                |
     |            |Modify Eph  |            |                |
     |            |----------->|            |                |
     |            |Modify Resp |            |                |
     |            |/-----------------------\|                |
     |            |       RTP MEDIA         |                |
     |            |\-----------------------/|                |
     |----------->|            |            |                |
     |Clear Forward            |            |                |
     |            |----------->|            |                |
     |<-----------|Notify OE:R1/clear       |                |
     |Clear Back  |            |            |                |
     |            |<-----------|            |                |
     |            |Notify Resp |            |                |
     |            |            |----------->|                |
     |            |            |   REL      |--------------->|
     |            |            |            |     REL        |
     |            |            |            |<---------------|
     |            |            |<-----------|     RLC        |
     |            |            |   RLC      |                |
     |            |<-----------|            |                |
     |            |Sub Phy     |            |                |
     |            |Sub Eph     |            |                |
     |            |----------->|            |                |
     |            |Sub Phy Resp|            |                |
     |            |Sub Eph Resp Statistics  |                |
     |            |            |----------->|                |
     |            |            |Sub Phy     |                |
     |            |            |Sub Eph     |                |

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     |            |            |<-----------|                |
     |            |            |Sub Phy Resp|                |
     |            |            |Sub Eph Resp Statistics      |
     |____________|____________|____________|________________|




The MGC generates a Modify command towards the R1 Trunking gateway
with the seize event and an embedded seize acknowledgement signal.
The digit map in this scenario is assumed to be provisioned in the MG
(shown to be 2XXX which may not be true for practical R1 exchanges).
The seize event has a embedded signal seizeack to be applied after
detection of seize event. The embedded signal is accompanied by
another embedded events namely the clear event to detect the
clear forwards signal if generated from the R1 domain.

Step 1
MGC to R1TGW
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
      Context = - {
        Modify = Trunk1/line1 {
Events=1111{R1/sz Embed{ signals {R1/sd}, Events=1112 { mfd/ce{dmap},
             R1/clearforward  signals { R1/clearback }, R1/address}}
                         }
                   }
    }
The R1TGW after receiving the Modify command does the command
processing and responds with Modify command response.

Step 2
R1TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {
        Modify = Trunk1/line1
                          }
                }

In this example as mentioned earlier, the call is originated from a
user connected to the R1 domain of PSTN. The R1 exchange that is
connected to the R1 Trunking gateway generates the seize signal. The
seize signal is identified by the R1TGW and seize event is detected.
The seize event is notified to the MGC. The R1TGW meanwhile does the
embedded descriptor processing for the seize event. The application
of the seizeack and detection of clear event is activated on the
specific circuit group. The Notify command is generated
towards the MGC.

Step 3

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R1GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = Trunk1/line1 {Observed Events =1111 {
            20010202T10000000:R1/sz}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 4
MGC to R1GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = Trunk1/line1}
   }
The R1TGW collects the digits and reports the same to the MGC as
parameters of the address event The digit completion event of the MF
detection package is used here. This is extracted from the MF tone
detection package.

Step 5
R1GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2001 {
      Context = - {
          Notify = Trunk1/line1 {Observed Events =1112 {
            20010302T10000000:mfd/ce{ds=2992}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 6
MGC to R1GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = Trunk1/line1}
   }
The MGC then initiates the necessary signaling towards the exchange to
which the destination user is connected. In this example the MGC has
to generates SS7 messages to the SS7 switch. The IAM message is sent
with all the necessary address signaling information. The SS7 switch
responds with the ACM message.

The MGC sends a Modify command towards the R1 TGW to indicate that has
 gone offhook. The answer signal is sent in the Signals descriptor.

Step 7
MGC to R1TGW

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
          Modify = Trunk1/line1
                 {signals{ R1/ans } }
      }
   }

The R1 Trunking gateway responds to the Modify command.

Step 8
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235 {
      Context = - {
   Modify = Trunk1/line1
}
}

The MGC after receiving the ANM message generates commands to both the
Trunking gateways to add physical circuits and create ephemeral
terminations. The MGC in its message to the R1TGW in its signal
descriptor lists the answer signal to indicate that the call
establishment is successful and the end user is free to receive the
call.

Step 9
MGC to R1GW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }
      }
   }

The R1 Trunking gateway after responds with a contextID in this

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example 1. The ephemeral termination is created and added to the same
context as the physical termination. The ephemeral termination added
in this example is EPHA. The local parameters are specified in the
response. The IP address chosen for the media transport in this
example is 209.110.59.33, and the port number specified 30000.

Step 10
R1TGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates similar transaction
with two ADD commands to the other TGW. The local SDP information
specified in by the R1TGW is used to as remote SDP information for the
other TGW. The MGC conveys this information in the Add command.

Step 11
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
       Context = $ {
          Add = Trunk2/$ {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }

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               } ; RTP profile for G723 is 4
              }
      }
   }

The Trunking gateway creates a context with ContextId 2. It adds the
physical termination Trunk2/line1 in that context. The ephemeral
termination EPHB is created with the specified SDP information. The
response from the MG specifies the local SDP information.

Step 12
R1GW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates a modify command to the
R1TGW to inform the local SDP information of TGW as the remote SDP for
the R1TGW.

Step 13
MGC to R1TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                    }
               }
             }
         }
      }
   }

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The R1 Trunking gateway responds to the Modify command.

Step 14
R1TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
      Context = 1 {
   Modify = EphA
}
}
The RTP media transfer takes place. The user connected to the R1
exchange domain terminates the call. The clear forwards signal
generated by the R1 exchange connected to the R1 TGW is detected and
reported to the MGC as the clear event in the R1 package. The
clear back signal, which is part of the clear event, enables the R1TGW
to generate the clear back signal.  The clear event detection is
reported to MGC as part of the Notify command.

Step 15:
R1TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2003 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010402T10030000:R1/clear}
          }
      }
   }
The MGC responds to the R1GWs Notify message.

Step 16
MGC to R1TGW:
   MEGACO/1 [216.33.33.61]:27000
   Reply= 2003 {
      Context = 1 {
          Notify = TermA
      }
   }
The MGC generates necessary command to the SS7 switch like the
REL message. The SS7 switch responds with the RLC message. The MGC now
generates commands to both the TGWs for subtracting the terminations
from the contexts created.

Step 17
MGC to R1TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}

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      }
   }
The R2TGW responds to the subtract commands generated by MGC.

Step 18
R1TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1239 {
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates similar transaction with two Subtract command for
subtracting both the physical and ephemeral terminations from the
second Trunking gateway.

Step 19
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The R1GW responds to the subtract commands generated by MGC.

Step 20
TGW to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1240
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost

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                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }



2.10 Call between SS7 trunk in TGW and R1 trunk in TGW
This section of the call flow illustrates the call between two
Trunking gateways, one that does R1 signaling towards one end and the
second TGW CCS SS7. In this example the user in the CCS SS7 signaling
network originates the call. The destination user is connected to the
PSTN network with R1 signaling.

 ______________________________________________________________________
            |            |           |              |
 SS7 Switch |    TGW1    |    MGC    |   TGW2       |       R1Exch
____________|____________|___________|______________|_________________
      |            |           |            |                |
      |----------->|           |            |                |
      |    IAM     |           |            |                |
      |            |---------->|            |                |
      |            |    IAM    |            |                |
      |            |           |----------->|                |
      |            |           |Modify Phy Seize             |
      |            |           |            |--------------->|
      |            |           |            |   Seize        |
      |            |           |<-----------|                |
      |            |           |Modify Resp |                |
      |            |           |            |<---------------|
      |            |           |            |     Wink       |
      |            |           |<-----------|                |
      |            |           |Notify OE:sa|--------------->|
      |            |           |----------->|   KP,Digits,ST |
      |            |           |Notify Resp |                |
      |            |<----------|            |                |
      |            |   ACM     |            |                |
      |<-----------|           |            |                |
      |   ACM      |           |            |                |
      |            |           |            |<---------------|
      |            |           |            |  Answer        |
      |            |           |<-----------|                |
      |            |           | Notify OE:ans               |
      |            |           |----------->|                |
      |            |           |Notify Resp |                |
      |            |<----------|            |                |
      |            |   ANM     |            |                |
      |<-----------|           |            |                |
      |    ANM     |           |            |                |

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      |            |<----------|            |                |
      |            |Add Phy    |            |                |
      |            |Add $ Local (Unspecified)                |
      |            |---------->|            |                |
      |            |Add Phy Resp            |                |
      |            |Add Eph Resp            |                |
      |            |           |----------->|                |
      |            |           |Add Phy     |                |
      |            |           |Add $ Local (Unspecified)    |
      |            |           |      Remote (Specified)     |
      |            |           |<-----------|                |
      |            |           |Add Phy Resp|                |
      |            |           |Add Eph Resp|                |
      |            |<----------|            |                |
      |            |Modify Eph |            |                |
      |            |---------->|            |                |
      |            |Modify Resp|            |                |
      |            |/----------------------\|                |
      |            |       RTP MEDIA        |                |
      |            |\----------------------/|                |
      |----------->|           |            |                |
      |   REL      |           |            |                |
      |            |---------->|            |                |
      |            |   REL     |            |                |
      |            |           |----------->|                |
      |            |           |Modify Phy ED:R1/clear       |
      |            |           |            |--------------->|
      |            |           |            |  Clear Forward |
      |            |           |<-----------|                |
      |            |           |Modify Resp |                |
      |            |           |            |<---------------|
      |            |           |            | Clear Back     |
      |            |           |<-----------|                |
      |            |           | Notify OE:clear             |
      |            |           |----------->|                |
      |            |           | Notify Resp|                |
      |            |<----------|            |                |
      |            |  RLC      |            |                |
      |<-----------|           |            |                |
      |    RLC     |           |            |                |
      |            |<----------|            |                |
      |            |Sub Phy    |            |                |
      |            |Sub Eph    |            |                |
      |            |---------->|            |                |
      |            |Sub Phy Resp            |                |
      |            |Sub Eph Resp Statistics |                |
      |            |           |----------->|                |
      |            |           |Sub Phy     |                |
      |            |           |Sub Eph     |                |
      |            |           |<-----------|                |
      |            |           |Sub Phy Resp|                |

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      |            |           |Sub Eph Resp Statistics      |
      |____________|___________|____________|________________|



When the MGC through the signaling gateway receives the IAM it
generates a Modify message towards the Trunking gateway that supports
R1 package. The signal descriptor has the seize signal and the events
descriptor has the event seizeack. The seizeack event has an embedded
signal "address". The Trunking gateway is intended to seize a circuit
and apply the address signals after the seize acknowledgement is
received from the other R1 exchange. The calling party information
can also be provided in the address signal. For simplicity it is
omitted here. The embedded event of the seize acknowledgement event
is the answer. This event has to be reported when the digits reach the
other R1 exchange and there is answer from the terminating R1 exchange.
The message from MGC to R1TGW is as follows.

Step 1
MGC to R1TGW
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
      Context = - {
        Modify = Trunk1/line1 {
Signals = { R1/sz}
 Events = 1111 {R1/sd Embed { signals {R1/address { ds = 2989} },
                    Events=1112 { R1/clear, R1/ans}
                     }
                          }
                                     }
The R1TGW after receiving the Modify command does the command
processing and responds with Modify command response.

Step 2
R1TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {
        Modify = Trunk1/line1
                          }
                }

The R1 TGW applies seize signal on the specified circuit group and
after receiving the acknowledgement from the other R1 exchange
updates the embedded events descriptor as the events descriptor. The
R1TGW also generates a Notify command towards the MGC to indicate
that the seize acknowledgement has been received.

Step 3
R1GW to MGC:
   MEGACO/1 [209.110.59.34]:25000

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   Transaction = 2000 {
      Context = - {
          Notify = Trunk1/line1{Observed Events =1111 {
            20010202T10000000:R1/sd}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 4
MGC to R1GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = Trunk1/line1}
   }

The MGC now generates the address complete message to the SS7 switch
that has generated the IAM message. The R1TGW after receiving the
answer event from the other R1 exchange generates message to notify
this event.

Step 5
R1GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2001 {
      Context = - {
          Notify = Trunk1/line1{Observed Events =1112 {
            20010202T10000000:R1/ans}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 6
MGC to R1GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = Trunk1/line1}
   }

MGC generates the ANM message towards the SS7 switch through the
signaling gateway. It also generates commands to add terminations into
specific contexts. It generates a single transaction with two Add
commands towards the TGW that supports R1 terminations. One command
is to add the physical circuit group Trunk1/line and the other for
the ephemeral termination. The SDP information is unspecified that
enables the TGW to choose the underspecified parameters.

Step 7
MGC to R1TGW
   MEGACO/1 [216.33.33.61]: 27000

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   Transaction = 1235{
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }
      }
   }

The R1 Trunking gateway after receiving the Add command responds with
a contextID in this example 1. The ephemeral termination is created
and added to the same context as the physical termination. The
ephemeral termination added in this example is EPHA. The local
parameters are specified in the response. The IP address chosen for
the media transport in this example is 209.110.59.33, and the port
number specified 30000.

Step 8
R1TGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235{
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates similar transaction
with two ADD commands to the other TGW. The local SDP information
specified in by the R1TGW is used to as remote SDP information for
the other TGW. The MGC conveys this information in the Add command.


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Step 9
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236{
       Context = $ {
          Add = Trunk2/$ {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The Trunking gateway creates a context with ContextId 2. It adds the
physical termination Trunk2/line1 in that context. The ephemeral
termination EPHB is created with the specified SDP information. The
response from the MG specifies the local SDP information.

Step 10
RGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236{
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates a modify command to

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the R1TGW to inform the local SDP information of TGW as the remote SDP
for the R1TGW.

Step 11
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237{
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    }
               }
             }
         }
      }
   }

The R1 Trunking gateway responds to the Modify command.

Step 12
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237{
      Context = 1 {
   Modify = EphA
}
}
The RTP media flow is established and the two users connected to the
SS7 trunk and R1 trunk starts the conversation. After conversation any
of the user can disconnect the call in this example the user connected
to the SS7 domain releases the call. The SS7 switch generates a REL
message towards the MGC. The Signaling gateway forwards the same
request towards the MGC. The MGC initiates the tearing down of the
call. This is done initially by generating a Modify command towards
the R1 TGW to generate clear forward signal towards the R1 exchange.
In the message the MGC sends a signal descriptor with clear signals
and events descriptor with the clear in the event. The event in the
events descriptor is for detecting the clear back signal generated from
the R1 exchange.

Step 13
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238{

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      Context = 1 {
         Context = Trunk1/line1{
signal { R1/clear},
 Events = 1113{ R1/clear}
     }
   }

The R1 TGW after receiving the commands does the signals and events
descriptor processing and responds to the MGC with the Modify command
response.

Step 14
R1TGW to MGC
MEGACO/1 [209.110.59.34]: 25000
   Reply = 1238 {
      Context = 1 {
        Modify = Trunk1/line1
                          }
                       }

Mean while the MGC generates the subtract message towards the
originating TGW to remove the terminations from the newly
created context.

Step 15
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW responds to the subtract commands generated by MGC.

Step 16
TGW to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1239
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }

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          }
      }
   }
The MGC after receiving the response from the TGW generates the
Release complete message RLC towards the SS7 switch through the
Signaling Gateway.

The R1 TGW after receiving the clear back signal from the other
R1 exchange detects it and generates a Notify command towards the MGC.

Step 17
R1GW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = - {
          Notify = TermA {Observed Events =1113 {
            20030202T10000000:R1/clear}}
      }
   }

the MGC responds the Notify command with the Notify response.

Step 18
MGC to R1GW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
       Context = - {Notify = TermA}
   }
MGC after receiving the notify command generates subtract command to
remove both the physical termination and ephemeral termination.

Step 19
MGC to R1TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240{
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The R1TGW responds to the subtract commands generated by MGC.

Step 20
R1TGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1240{
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent

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                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
Now the termination is free to take part in other calls.



2.11 Call between ISDN trunk in TGW and SS7 trunk in TGW

This section illustrates the Megaco message flow between MGC and two
Trunking media gateways one that perform ISDN signaling towards the
user and the other TGW performs SS7 signaling.  In this example we
assume that an ISDN user initiates that call.

 ______________________________________________________________________
            |            |           |              |
 ISDNSwitch |  TGW1/SG   |    MGC    |   TGW2/SG    |       SS7Switch
____________|____________|___________|______________|_________________
      |            |           |            |                |
      |----------->|           |            |                |
      |    Setup   |---------->|            |                |
      |            |   Setup   |            |                |
      |            |           |----------->|                |
      |            |           |   IAM      |--------------->|
      |            |           |            |    IAM         |
      |            |           |            |<---------------|
      |            |           |<-----------|      ACM       |
      |            |           |   ACM      |                |
      |            |<----------|            |                |
      |<-----------|   Alerting|            |                |
      |   Alerting |           |            |<---------------|
      |            |           |<-----------|    ANM         |
      |            |<----------|    ANM     |                |
      |<-----------|   Connect |            |                |
      |   Connect  |<----------|            |                |
      |            |Add Phy    |            |                |
      |            |Add Eph  Local unspecfied                |
      |            |---------->|            |                |
      |            |Add Phy Resp            |                |
      |            |Add Eph Resp Local Specified             |
      |            |           |----------->|                |
      |            |           |Add Phy     |                |
      |            |           |Add Eph Local Unspecified    |
      |            |           |        Remote Specified     |

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      |            |           |<-----------|                |
      |            |           |Add Phy Resp|                |
      |            |           |Add Eph Resp Remote Specified|
      |            |<----------|            |                |
      |            |Modify EPh Remote Specified              |
      |            |---------->|            |                |
      |            |Modify Eph Resp         |                |
      |            |/----------------------\|                |
      |            |       RTP MEDIA        |                |
      |            |\----------------------/|                |
      |----------->|           |            |                |
      | Disconnect |---------->|            |                |
      |            | Disconnect|----------->|                |
      |            |           |   REL      |--------------->|
      |            |           |            |     REL        |
      |            |           |            |<---------------|
      |            |           |<-----------|      RLC       |
      |            |<----------|     RLC    |                |
      |<-----------|  Release  |            |                |
      | Release    |           |            |                |
      |----------->|           |            |                |
      | Release Complete       |            |                |
      |            |---------->|            |                |
      |            |Release Complete        |                |
      |            |<----------|            |                |
      |            |Sub Phy    |            |                |
      |            |Sub Eph    |            |                |
      |            |---------->|            |                |
      |            |Sub Phy Resp            |                |
      |            |Sub Eph Resp Statistics |                |
      |            |           |----------->|                |
      |            |           |Sub Phy     |                |
      |            |           |Sub Eph     |                |
      |            |           |<-----------|                |
      |            |           |Sub Phy Resp|                |
      |            |           |Sub Eph Resp Statistics      |
      |____________|___________|____________|________________|


The initial message sent by the ISDN switch is the Setup message. The
setup message has all the address information. The MGC after receiving
the Setup message from the Signaling gateway generates the IAM message
towards the SS7 switch through the Signaling gateway.  After receiving
the ACM address complete message from the SS7 switch the MGC
generates Alerting message towards the ISDN switch. The MGC after
receiving the ANM message generates Connect message towards the
ISDN switch. The MGC now adds terminations in both the
Trunking gateways.

Step 1
MGC to ISDNTGW

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234{
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
               }
             }
         }
      }
   }

The ISDN Trunking gateway after receiving the Add command responds
with a contextID in this example 1. The ephemeral termination is
created and added to the same context as the physical termination.
The ephemeral termination added in this example is EPHA. The local
parameters are specified in the response. The IP address chosen for
the media transport in this example is 209.110.59.33, and the
port number specified 30000.

Step 2
ISDNTGW to MGC:
   MEGACO/1 [207.176.47.89]: 25000
   Reply = 1234{
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphA{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response generates similar transaction
with two ADD commands to the other SS7TGW. The local SDP information
specified in by the ISDNTGW is used to as remote SDP information for
the other TGW. The MGC conveys this information in the Add command.

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Step 3
MGC to SS7TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235{
       Context = $ {
          Add = Trunk2/$ {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The Trunking gateway creates a context with ContextId 2. It adds the
physical termination Trunk2/line1 in that context. The ephemeral
termination EPHB is created with the specified SDP information. The
response from the MG specifies the local SDP information.

Step 4
RGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235{
      Context = 2 {
        Add = Trunk2/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }

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The MGC after receiving the response generates a modify command to the
ISDNTGW to inform the local SDP information of TGW as the remote SDP
for the ISDNTGW.

Step 5
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236{
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    }
               }
             }
         }
      }
   }

The ISDN Trunking gateway responds to the Modify command.

Step 6
ISDNTGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236{
      Context = 1 {
   Modify = EphA
}
}
The RTP flow is established. The call can be terminated either from
the ISDN user or from the user connected to SS7 domain. In this
example we assume that the ISDN user terminates the call. The ISDN
switch generates Disconnect message towards the MGC through
Signaling gateway. The MGC generates Release message towards the
SS7 switch. The MGC also generates messages to subtract termination
from contexts in both the Trunking gateways.

Step 7
MGC to ISDNTGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237{
      Context = 1 {
         Subtract = Trunk1/line1{Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }

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   }
The ISDNTGW responds to the subtract commands generated by MGC.

Step 8
ISDNTGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1237{
      Context = 1 {
        Subtract = Trunk1/line1
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The MGC generates similar transaction with two commands towards the
TGW that terminates SS7 media trunks.

Step 9
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The SS7TGW responds to the subtract commands generated by MGC.

Step 10
TGW to MGC:
   MEGACO/1 [209.110.59.34]:26000
   Reply = 1238
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,

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                rtp/delay=30 ; average latency
             }
          }
      }
   }



2.12 Continuity test from TGW
In this section we will illustrate the usage of Megaco command for
performing continuity tests. The basic continuity package as defined
in the protocol is considered. The procedures specified in the package
are illustrated. There are two cases in the continuity test. One in
which the MGC generates Megaco commands towards MG to initiate an
continuity test and the second one in which the command from MGC
enables the gateway to return any continuity test originated from
switched circuit network.

Case (a)

__________________________________________________________________
                               |
            MG                 |                MGC
_______________________________|___________________________________
             |                                   |
             |<----------------------------------|
             | Modify TermA SD:ct/ct ED:ct/cmp state=test
             |---------------------------------->|
             |     Modify TermA Resp             |
<------------|                                   |
 Continuity Signal                               |
             |                                   |
------------>|                                   |
 Continuity Signal Resp                          |
             |---------------------------------->|
             | Notify TermA OE:ct/cmp {resp=success}
             |<----------------------------------|
             | Notify TermA Resp                 |
_____________|___________________________________|__________________

The case of originating Continuity test by the Trunking gateway is
considered in this section. The MGC intends to check the continuity
of a specified circuit group line1 of the trunk Trunk1 in the Trunking
gateway.  The MGC generates a modify command with the termination
state set to "test". The event descriptor specifies the "cmp"
completion event of the continuity package. The Signal descriptor
lists the "ct" continuity test signal.

Step 1
MGC to TGW:
MEGACO/1 [216.33.33.61]: 27000

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   Transaction = 1234 {
       Context = '-' {
          Modify = Trunk1/line1  {Media {
                    TerminationState {ServiceState = test}}
            Signals = { ct/ct }
            Events = 1111 { ct/cmp }
               }
      }
   }
The TGW after receiving the Modify command for termination Trunk1/line1
in Null context, updates the termination state. The event descriptor
is updated in the Trunking gateway. The signal "ct" is applied on the
specified termination. The Trunking gateway now states for detecting
any tones/signals on the line on which the continuity test signal was
applied. The response for the message generated by MGC is sent back.

Step 2
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1234 {
      Context = '-' {
        Modify = Trunk1/line1
     }
   }

The Trunking gateway detects for any return tone/signal. The frequency
of the tone is assumed to be provisioned at the TGW. As soon as the
response is received from the other side of the trunk the Trunking
gateway reports the same to the MGC in the form of event detection.
The event "cmp" in the event descriptor is used to notify the
observed activity on the termination. The parameter value for the
response parameter indicates the result of the continuity test
performed.

Step 3
TGW to MGC:
MEGACO/1 [207.176.47.89]: 26000
   Transaction = 2000 {
      Context = '-' {
        Notify = Trunk1/line1 {ObservedEvents =1111 {
            20010202T10000000: ct/cmp { res=success}}
     }
   }
The MGC after receiving the Notify message responds to the MGC with
the response.

Step 4
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = Trunk1/line1}

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   }



Case (b)
In the earlier continuity test scenario we saw the Megaco messages
exchanged between MG and MGC when the MGC initiated the continuity
test. In some scenarios the MG should respond to the continuity test
originated from the PSTN switches. In this section we will consider
such a scenario.

__________________________________________________________________
                               |
            MG                 |                MGC
_______________________________|___________________________________
             |                                   |
             |<----------------------------------|
             | Modify TermA SD:ct/rsp            |
             |---------------------------------->|
             |     Modify TermA Resp             |
------------>|                                   |
 Continuity Signal                               |
             |                                   |
<------------|                                   |
 Continuity Signal Resp                          |
_____________|___________________________________|__________________


The continuity package signal "rsp" is used for this purpose. This
signal duration and frequency are provisioned at the TGW.  When the
MGC is intimated form the PSTN switch for responding the continuity
test, the MGC generates a Modify command with the "rsp" signal in the
signal descriptor. The termination state is set to "test".

Step 1
MGC to TGW:
MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = '-' {
          Modify = Trunk1/line1  {Media {
                    TerminationState {ServiceState = test}
                     LocalControl      { mode = loopback} }
            Signals = { ct/rsp }
           }
      }
   }
There can be two possible cases for responding the continuity test
originated from the PSTN network. One in which the Trunking gateway
generates a signal of different frequency when it receives a continuity
check specific signal. The second possibility is to respond with the
same signal looped back to the same switch that originated it. In

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this example we assume the case of Loopback. The mode of the
termination is also set to loopback to facilitate this. The
Trunking gateway after receiving the signal loops back the same
signal. The Trunking gateway also responds with the transaction
response message towards the MGC.

Step 2
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1234 {
      Context = '-' {
        Modify = Trunk1/line1
     }
   }
Once the test is complete the MGC is intimated about the success of
failure of the continuity test through the switch that originated the
continuity test.





2.13 Call from residential gateway to H.323 Terminal.


In This section we illustrate a call between a Residential gateway user
and to an endpoint in the H.323 domain. We assume that the call is
initiated from the user of the Residential gateway and after dialing
the digits the MGC does necessary mapping of the number to identify
that the called number belongs to the H.323 network.

_________________________________________________________________________
               |                 |                  |                  |
     RGW       |     MGC         |       GK         |      H.323EP     |
_______________|_________________|__________________|__________________|_
       |               |                   |                 |
       |<--------------|                   |                 |
       |     Modify    |                   |                 |
------>|               |                   |                 |
OffHook|-------------->|                   |                 |
<------|  Modify Resp  |                   |                 |
DialTone               |                   |                 |
       |-------------->|                   |                 |
       |   Notify OffHook                  |                 |
       |<--------------|                   |                 |
       |   Notify Resp |                   |                 |
------>|               |                   |                 |
Digits |-------------->|                   |                 |
       |  Notify Digits|                   |                 |
       |<--------------|                   |                 |
       |  Notify Resp  |                   |                 |

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       |               |------------------>|                 |
       |               |       ARQ         |                 |
       |               |<------------------|                 |
       |               |------------------------------------>|
       |               |                Setup                |
       |               |                   |<----------------|
       |               |                   |       ARQ       |
       |               |                   |---------------->|
       |               |                   |       ACF       |
       |               |<------------------------------------|
       |               |               Alerting              |
<------|               |                   |                 |
RingBack tone          |                   |                 |
       |<--------------|                   |                 |
       |Add Phy        |                   |                 |
       |Add Eph Local Unspecified          |                 |
       |-------------->|                   |                 |
       |Add Phy Resp   |                   |                 |
       |Add Eph Resp Local Specified       |                 |
       |               |<------------------------------------|
       |               |              Connect                |
       |               |<----------------------------------->|
       |               |                 TCS                 |
       |               |<----------------------------------->|
       |               |                  MSD                |
       |               |<----------------------------------->|
       |               | OLC (forward Logcial ch)RGW rtp/rtcp|
       |               |<----------------------------------->|
       |               | OLC (Rev Logical Ch) H.323 rtp/rtcp |
       |<--------------|                   |                 |
       | Modify Eph Remote Specified       |                 |
       |-------------->|                   |                 |
       |Modify Resp    |                   |                 |
       |/---------------------------------------------------\|
       |                   RTP Media                         |
       |\---------------------------------------------------/|
       |               |<----------------------------------->|
       |               |                CLC SessionId = 1        |
       |               |<----------------------------------->|
       |<--------------|                   |                 |
<------| Modify SD:cg/bt                   |                 |
 Ringbacktone          |<----------------------------------->|
       |               |            CLC SessionId = 2        |
       |-------------->|                   |                 |
       | Modify Resp   |                   |                 |
       |               |<------------------------------------|
       |               |            Release Complete         |
       |               |------------------>|                 |
       |               |      DRQ          |<----------------|
       |<--------------|                   |        DRQ      |
       |Sub Phy        |<------------------|---------------->|

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       |Sub Eph Stats  |      DCF          |       DCF       |
_______|_______________|___________________|_________________|_______


The MGC generates modify command for to the residential gateway to
check for offhook for Termination TermA. In this message the event
offhook has an embedded signal descriptor and embedded event
descriptor. The embedded signal descriptor is sent for application
of dial tone immediately after the detection of the offhook event
and the event descriptor then will be updated with the onhook and the
digit map completion event. The Digit map is also defined in the
digit map descriptor.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        },
               DigitMap= Dmap1 {(2XXX)}
 Events = 1111 {al/of Embed {signals {cg/dt}, Events=1112 { al/on},
                               {dd/ce {Dmap1}}}
           }
       }
   }

The MG after receiving the MGC's message responds to it.

Step 2
   RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

When the user A goes offhook RGW detects the offhook event and as it
is listed in the event descriptor report the event detection using
Notify command.

Step 3
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }

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   }
The MGC responds with the Notify response.

Step 4
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }


The digit map is active on the termination TermA. When the user dials
the digits the they are reported to MGC through Notify command.

Step 5
RGW to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {Observed Events =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify response.

Step 6
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

The MGC analyses the digits sent by the Residential Gateway. The
routing functionality in MGC enabled and it indicates that the dialed
digits belong to the user in H.323 network. The MGC acts as a H.323
Terminal towards H.323 network and generates the signaling towards
the destined Called party. The MGC initially generates an admission
request towards the Gatekeeper. The Gatekeeper acknowledges the
admission request message by generating the Admission confirmation
message ACF. Assuming that the GK used directed-routed call model,
the Gatekeeper provides the transport address information of the
destination user. The MGC then initiates the H.225 signaling by
generating the SETUP message towards the H.323 endpoint. The H.323
Endpoint after receiving the Setup message from the MGC initiates the
Admission request towards the Gatekeeper. The H.323 Endpoint after
receiving the Admission confirmation message from the Gatekeeper
generates the Alerting message towards the MGC. The MGC after
receiving the ALERT message from the H.323 Endpoint generates a
Add command to the Residential gateway to apply ring back tone to the
given termination. In the Add command the MGC requests the creation

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of ephemeral termination and under specifies the Local SDP
information. The mode of the termination is set to receive only.

Step 7
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = TermA {
              Signals { cg/ rt }
              Media {
                {
                     LocalControl {
                         Mode = sendrecv,
                    },
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = sendrecv,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

MG after creating the context adds the physical termination TermA. In
this case MG creates a context with ContextId 1. The ephemeral
termination EphA is created and added to the context 1. The MG
reserves resources for the local SDP information. In this case the
IP address allocated is 209.110.59.33 and the port number used is
30000. The MG responds to the Add command with this information in
the response to MGC.

Step 8
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33

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   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }
The H.323 Endpoint generates the CONNECT message after the called
party goes offhook. We assume that the H.245 information is passed in
Connect message. The Terminal Capability set and the Master slave
determination occurs between the MGC and the H.323 Endpoint. The
Open Logical channel messages (OLCs) indicate the session and media
related parameters. This enables the MGC to inform and receive the
SDP information of both the users. By the end of this OLCs the MGC
is aware of the SDP information of the H.323 Endpoint. The MGC now
generates Modify message towards the MG, with the Remote SDP
information for the ephemeral termination EphA.

Step 9:
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
      Context = 1 {
         Modify = TermA {
            Signals { } ; to turn off ringback tone
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphA{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
                    Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
              }
         }
      }

The RGW responds to the request from MGC.

Step 10
RGW to MGC:

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   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236 {
    Context = 1 {Modify = TermA , Modify = EphA}
   }

Now RTP media flow takes place. In the example we assume that the
H.323 goes onhook to terminate the call. The MGC initiates the tearing
down of the Call by closing the logical channels that were earlier
created for exchanging the H.245 information. The MGC after receiving
the DISCONNECT message generates a Modify message towards the
Residential gateway user for applying the busy tone and for making
the mode of the two terminations to receive only.

Step 11
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
     Context = 1 {
       Modify = TermA {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphA {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The RGW responds to this modify request.

Step 12
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1240 {
      Context = 1 {
         Modify= TermA, Modify = EphA}
   }

Step 13:
RGW1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1235{

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             20010202T10030000:al/on}
      }
   }
The MGC responds to the MG1s Notify message.

Step 14
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC after the Release Complete message waits for the Notify
command with onhook event from UserA and after receiving subtracts
the physical and ephemeral termination at the Residential gateway.
Thus enabling the user to participate in further calls.

Step 15
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with subtract of the last termination from it. The
RGW responds to this transaction from MGC with statistics on
ephemeral termination.

Step 16
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1238 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }

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   }



2.14 Call from residential gateway to SIP user.
This section illustrates a call between a user connected to Residential
gateway and another SIP user. It is assumed that the MGC acts as a SIP
server agent. The MGC generates SIP messages towards the SIP user
agent/called party. When the MGC receives the digits dialed by the
user even though not explicitly shown in the figure, it communicates
with a routing database and finds the SIP user agent's URL.

___________________________________________________________________
                  |                         |
     RGW          |         MGC             |         SIP User
__________________|_________________________|______________________
       |                     |                         |
       |<--------------------|                         |
       |Modify TermA {ED=al/of{SD:cg/dt,ED:al/on,dd/ce{dmap}}}
       |-------------------->|                         |
 ----->|                     |                         |
 OffHook                     |                         |
       |-------------------->|                         |
       |   Notify OffHook    |                         |
       |<--------------------|                         |
       |   Notify Resp       |                         |
------>|                     |                         |
 Digits|                     |                         |
       |-------------------->|                         |
       |      Notify Digits  |                         |
       |<--------------------|                         |
       |     Notify Resp     |                         |
       |                     |------------------------>|
       |                     |       INVITE            |
       |                     |<------------------------|
       |                     |        180 (RING)       |
       |<--------------------|                         |
       |Add TermA SD:cg/rt   |                         |
       |Add Eph Local Unspecified                      |
       |        Remote SPecified                       |
       |-------------------->|                         |
       |     Add Phy Resp    |                         |
       |     Add Eph Local Specified                   |
<------|                     |                         |
RingBack Tone                |                         |
       |                     |------------------------>|
       |                     |    ACK (SDP Specified)  |
       |/---------------------------------------------\|
       |               RTP Media                       |
       |\---------------------------------------------/|
------>|                     |                         |

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OnHook |-------------------->|                         |
       |     Notify OnHook   |                         |
       |<--------------------|------------------------>|
       |    Notify Resp      |      BYE                |
       |<--------------------|                         |
       |  Sub TermA          |                         |
       |  Sub EphA           |<------------------------|
       |-------------------->|         200 OK          |
       |     Sub Phy Resp    |                         |
       |     Sub Eph Resp Statistics                   |
 ______|_____________________|_________________________|________



The MGC generates modify command for to the residential gateway to
check for offhook for Termination TermA. In this message the event
offhook has an embedded signal descriptor and embedded event
descriptor. The embedded signal descriptor is sent for application of
dial tone immediately after the detection of the offhook event and the
event descriptor then will be updated with the onhook and the digit
map completion event. The Digit map is also defined in the digit map
descriptor.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        },
               DigitMap= Dmap1{(2XXX)}
 Events = 1111 {al/of Embed {signals {cg/dt}, Events=1112 { al/on},
                             {dd/ce {Dmap1}}}
           }
       }
   }

The MG after receiving the MGC's message responds to it.

Step 2
   RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

When the user A goes offhook RGW detects the offhook event and as it
is listed in the event descriptor report the event detection using

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Notify command.

Step 3
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }
   }
the MGC responds with the Notify response.

Step 4
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }


The digit map is active on the termination TermA. When the user dials
the digits the they are reported to MGC through Notify command.

Step 5
RGW to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 6
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

The MGC analyses the digits sent by the Residential Gateway. The routing
functionality in MGC enabled and it indicates that the dialed digits
belong to the SIP user. The MGC acts as a SIP User agent, and
generates a INVITE message towards the SIP user.

INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060

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   From: Bob<sip:UserA@here.com>
   To: Julien<sip:UserB@there.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: Bob<sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: 0

 The SDP information is not provided in this INVITE message. The MGC
receives the 180- OK message from the SIP user to indicate that
ringing is done towards that end.

  SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: Julien<sip:UserB@here.com>
   To: Bob<sip:UserA@there.com>;tag=8321234356
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content-Length: 0

The MGC generates a Modify message to the Residential gateway to apply
ringback tone to the given termination.

Step 7
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Modify = TermA {
                 Signals { cg/rt }
                         }
                    }
            }
The MG after receiving the Modify message applies ringback tone to the
user and generates Modify response.

Step 8
   RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = - {Modify = TermA}
   }

The MGC meanwhile receives the 200 OK message from the SIP user to
 indicate its SDP information.

SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: Julien<sip:UserA@here.com>
   To: Bob<sip:UserB@there.com>;tag=8321234356
   Call-ID: 12345601@here.com

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   CSeq: 1 INVITE
   Contact: Julien<sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: 147

   v=0
   o=UserB 2890844527 2890844527 IN IP4 there.com
   s=Session SDP
   c=IN IP4 207.176.47.90
   t=0 0
   m=audio 35000 RTP/AVP 4
   a=rtpmap:0 PCMU/8000

The MGC now generates the Add command for adding the physical
termination TermA and to create an ephemeral termination EphA. The
local SDP information for the ephemeral termination EphA is under
specified to enable the RGW to allocate the necessary values by
itself. The Remote SDP information is also sent. The mode of the two
terminations is set to send receive.

Step 9
MGC to RGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
              Media {
                {
                     LocalControl {
                         Mode = sendrecv,
                    },
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = sendrecv,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
                     Remote{
   v=0
   c=IN IP4 207.176.47.90
   m=audio 35000 RTP/AVP 4
                }
             }
          }
       }

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   }

MG after creating the context adds the physical termination TermA. In
this case MG creates a context with ContextId 1. The ephemeral
termination EphA is created and added to the context 1. The MG
reserves resources for the local SDP information. In this case the
IP address allocated is 209.110.59.33 and the port number used is
30000. The MG responds to the Add command with this information in
the response to MGC.

Step 10
RGW to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=sendrecv
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

In the ACK message of SIP, the local SDP information is indicated
 towards the remote SIP user.

ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: Bob<sip:UserA@here.com>
   To: Julien<sip:UserB@there.com>;tag=8321234356
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 147

   v=0
   o=UserA 2890844526 2890844526 IN IP4 here.com
   s=Session SDP
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=rtpmap:0 PCMU/8000


Now RTP media flow takes place. In the example we assume that the
UserA goes onhook to terminate the call. The RGW after detecting the

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event reports the same to MGC in the Notify command.

Step 11:
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
          }
      }
   }
The MGC responds to the MG1s Notify message.

Step 12
MGC to MG1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }
The MGC now generates subtract commands to the RGW. The BYE message is
generated by the MGC towards the other SIP user.

   BYE sip:UserB@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: Bob<sip:UserA@there.com>;tag=8321234356
   To: Julien<sip:UserB@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 BYE
   Content-Length: 0

The MGC after sending the BYE message recives the 200 OK message from
the remote SIP user.

  SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: Julien<sip:UserB@there.com>;tag=8321234356
   To: Bob<sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 BYE
   Content-Length: 0

The two Subtract commands are clubbed in a single action.

Step 13
MGC to RGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 1 {

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         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 14
RGW to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1238 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }



3 Service Change Command Usage

This section lists the few methods that illustrate the usage of MEGACO
protocol defined service change methods. The scenarios takes into
consideration both ROOT termination and specific terminations. The
intention of the section is to provide the usage of different methods
and the situations when each of the methods needs to be used.

3.1 ROOT Termination.
3.1.1 Registration.

The MEGACO protocol defined a special termination called the ROOT
termination to address the gateway as a whole. This enables easy
addressing from both MG and MGC to address the gateway as a single
entity. The virtual MG situations are not discussed in this version
of the call flow draft.

The Media Gateway once ready to receive messages from MGC registers
itself using the Service change command. The termination Identifier
ROOT is used for this purpose. This can be treated as the first

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messages sent from MG to MGC. The call flow assumes that the MGC is
ready to receive the messages from the MG.


_______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     | Port Num 2944
 PortNum      |------------------------------------>|
 20000        |ServiceChange ROOT Method=Restart Sca=15000
              |                                     |
 PortNum 20000|<------------------------------------| Port Num 2944
              |ServiceChange Resp ROOT sca=25000    |
              |                                     |
 PortNum 15000|<------------------------------------| PortNum 25000
              |      Modify *Event al/of            |
              |                                     |
Port Num 15000|------------------------------------>| PortNum 25000
              |       Modify       Response         |
 _____________|_____________________________________|____________________





In the following example MG generates the registration message to the
default port of MGC, it also specifies the service change address to
which the MGC has to send further messages. MGC also specifies the new
transport address so that when MG generates any messages it generates
to this address instead of the default transport address for the MGC.
In the example it is to be noted that the MGC is generating the MODIFY
command to the new transport address specified by MG in its
registration command.

The first command sent from MG (once it is ready to receive message)
is the Service Change command, with ROOT termination identifier. In
the example MG is generating the registration message to the default
port of MGC (defined by protocol 2944 for Text message)

Step 1:
MG to MGC:
   MEGACO/1 [209.110.59.34]: 20000
   Transaction = 1234 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Restart,
               ServiceChangeAddress=15000, Profile=ResGW/1,
                      12345677T87654320}
           }
       }

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   }

The MGC responds the registration request to the same transport address
used by MG to send the request. In the response MGC specifies its new
transport address, that needs to be used by MG for further messages
generated towards MGC.(In example 25000).

Step 2:
MGC to MG:
   MEGACO/1 [216.33.33.61]:2944
   Reply = 1234 {
      Context = - {ServiceChange = ROOT {
        Services {ServiceChangeAddress=25000, Profile=ResGW/1 ,
                         12345678T87654321} } }
   }

In the example it is also shown that the MGC uses the transport address
specified by MG for receiving messages. The initial MODIFY command sent
to check for offhook event on all termination is sent to the new
transport address specified by MG.

Step 3:
MGC to MG:
   MEGACO/1 [216.33.33.61]:25000
   Transaction = 9999 {
       Context = - {
           Modify = * {
                        Events = 1234 {al/of}
           }
       }
   }

The MG generates response to the new transport address specified by MGC
 in its registration response.

Step 4:
MG to MGC:
   MEGACO/1 [209.110.59.34]:15000
   Reply = 9999 {
      Context = - {Modify = A1}
        Context = - {Modify = A2}
        Context = - {Modify = A3}
   }

3.1.2 Cold Start
A MG is pre-provisioned by a management mechanism with a Primary and
(optionally) an ordered list of Secondary MGC's.  Upon a cold start of
the MG, it will issue a ServiceChange command with a "Restart" method,
 on the Root Termination to its primary MGC. If the MGC accepts the
MG, it will send a Transaction Accept, with the ServiceChangeMgcId set
to it. If the MG receives an ServiceChangeMgcId not equal to the MGC

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it contacted, it sends a ServiceChange to the MGC specified in the
ServiceChangeMgcId. In this example the MG generate a registration
command towards the secondary MGC. The secondary MGC responds with
the service change address to enable MG to send further messages to
that specified port.

____________________________________________________________________
                      |                         |
    Media Gateway     |       Primary MGC       |    Secondary MGC
______________________|_________________________|___________________
          |                        |                      |
          |----------------------->|                      |
          |  ServiceChange ROOT    |                      |
          |   Method = Restart     |                      |
          |<-----------------------|                      |
          | ServiceChange Resp ROOT|                      |
          | ServiceChangeMGCId=209.110.59.33:25000        |
          |---------------------------------------------->|
          |  ServiceChange ROOT Method=Restart            |
          |<----------------------------------------------|
          |        ServiceChange ROOT Resp                |
__________|________________________|______________________|_________




The first command sent from MG (once it is ready to receive message)
 is the Service Change command, with ROOT termination identifier. In
the example MG is generating the registration message to the Primary
MGC.

Step 1:
MG to MGC:
   MEGACO/1 [209.110.59.34]: 20000
   Transaction = 1234 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Restart,
               }
           }
       }
   }

The MGC responds the registration request by specifying a new transport
address of the secondary MGC that needs to be used by MG for generating
another registration command towards secondary MGC.

Step 2:
MGC to MG:
   MEGACO/1 [216.33.33.61]:25000
   Reply = 1234 {

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      Context = - {ServiceChange = ROOT {
        Services {mgcid=209.110.59.33:25000, Profile=ResGW/1 ,
                               12345678T87654321} } }
   }


MG generates the Service Change command to the MGC specified by the
 primary MG.

Step 3:
MG to MGC:

   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 4321 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Restart, Reason="Cold Boot",
 Profile=ResGW/1, 12345677T87654320}
           }
       }
   }

The MGC after receiving the registration request from the MG responds
with the Service Change reply.

Step 4:
MGC to MG:

   MEGACO/1 [216.33.33.62]: 27000
   Transaction = 4321 {
       Context = - {
           ServiceChange = ROOT {Services {
 Profile=ResGW/1, 12345677T87654320}
           }
       }
   }






3.1.3 Handoff

The Handoff method can be used both by MG and MGC. In the scenario
below MGC uses this method to indicate that it is going out of service
and the MGC specified in the service change need to be contacted. The
MG subsequently generates the handoff message to the MGC specified in
the Service change mgId in the message generated by the controlling MGC.



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 ____________________________________________________________________
                      |                         |
    Media Gateway     |          MGC1           |        MGC2
______________________|_________________________|___________________
          |                        |                      |
          |<-----------------------|                      |
          |  ServiceChange ROOT    |                      |
          |   Method = Handoff     |                      |
          |   mgcidtotry=199.164.0.197:45678              |
          |<-----------------------|                      |
          | ServiceChange Resp ROOT|                      |
          |                        |                      |
          |---------------------------------------------->|
          |  ServiceChange ROOT Method=Handoff            |
          |     Reason="MGC directed Change"              |
          |<----------------------------------------------|
          |        ServiceChange ROOT Resp                |
__________|________________________|______________________|_________



The MGC generates the ServiceChange command with Handoff as the method.
It also specifies the MGC that needs to be tried by the MG.

Step 1:
MGC to MG:

   MEGACO/1 [209.110.59.34]: 20000
   Transaction = 1234 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Handoff,
 MgcIdToTry=199.164.0.197:45678, Profile=ResGW/1, 12345677T87654320}
           }
       }
   }

After receiving the command from MGC, the MG tries for the MG that is
specified in the message. It first responds to the service Change
command generated by the controlling MGC.

Step 2:
MG to MGC:

   MEGACO/1 [216.33.33.61]: 25000
   Reply = 1234 {
       Context = - {
           ServiceChange = ROOT
       }
   }


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MG generates the Service Change command to the MGC specified by the
 primary MG.

Step 3:
MG to MGC:

   MEGACO/1 [209.11.59.34]: 25000
   Transaction = 4321 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Handoff, Reason="MGC Directed Change",
 Profile=ResGW/1, 12345677T87654320}
           }
       }
   }

The MGC after receiving the Handoff request from the MG responds with
the Service Change reply.

Step 4:
MGC to MG:

   MEGACO/1 [216.33.33.62]: 27000
   Reply = 4321 {
       Context = - {
           ServiceChange = ROOT {Services {
 Profile=ResGW/1, 12345677T87654320}
           }
       }
   }





3.1.4 Disconnection
The MG issues the disconnection method of Service Change when it lost
the communication with MGC and later regains it. The MGC normally
generates an Audit message to assess the state of the terminations
before and after the disconnection. The Audit command enables MGC to
synchronize its state with the MG's state.

_______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                    :                |
              |                    :                |
              |                    :                |
              |   MG lost communication with MGC    |
              |                                     |

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              |------------------------------------>|
              |ServiceChange ROOT Method=Disconnection
              | Reason="loss of lower layer Connectivity"
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp ROOT       |
              |                                     |
              |<------------------------------------|
              |      Audit * ED,SD,MD               |
              |                                     |
              |------------------------------------>|
              |       Audit EphA  Response ED,SD,MD |
_____________|_____________________________________|____________________




The MG generates ServiceChange command towards the MGC with
method = disconnection on the ROOT termination and with reason
= "Loss of lower layer connectivity".
Step 1:
MG to MGC:
   MEGACO/1 [209.110.59.34]: 20000
   Transaction = 1234 {
       Context = - {
           ServiceChange = ROOT {Services {
               Method=Disconnection,
               Reason=" Loss of lower layer connectivity"
               }
           }
       }
   }

The MGC responds the disconnection message by responding with Service
Change response.

Step 2:
MGC to MG:
   MEGACO/1 [216.33.33.61]:25000
   Reply = 1234 {
      Context = - {ServiceChange = ROOT {
         } }
   }

The MGC after receiving the disconnection message audits the
terminations that are present in the Media Gateway. The Audit response
enables MGC to assess the state of the termination before and after
disconnection.

Step 3
MGC to MG:

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   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1235 {
      Context = 2 {AuditValue = *{
         Audit{Media, DigitMap, Events, Signals, Packages, Statistics
   }}
      }
   }

The MG responds with the media descriptor, packages and statistics.
The Digit map, signal and events are not defined on this termination
hence only tokens are sent back in the response.

Step 4
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1235 {
      Context = 2 {
   AuditValue = EphA {
             Media {
                 TerminationState { ServiceState = InService,
                        Buffer = OFF },
                Stream = 1 {
                    LocalControl { Mode = SendReceive,
                       nt/jit=40 },
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP  0
   a=ptime:30
                   },
                    Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP  0
   a=ptime:30
                    } } },
            audit { Events,
             Signals,
             DigitMap},
             Packages {nt-1, rtp-1},
             Statistics { rtp/ps=1200,  ; packets sent
                          nt/os=62300, ; octets sent
                          rtp/pr=700, ; packets received
                          nt/or=45100, ; octets received
                          rtp/pl=0.2,  ; % packet loss
                          rtp/jit=20,
                          rtp/delay=40 } ; avg latency
          }
       }
   }


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3.2 Service Change for Termination

The service change command can be used on terminations to take
terminations from in-service to out-of-service and vice versa. This
section illustrates the use of service change on termination generated
both from MG and MGC. The wildcard termination identifiers scenarios
are discussed in a separate section.

3.2.1 MG generated Service Change

3.2.1.1 Graceful OOS from MG

The graceful method of service change when generated from MG is used
to intimate MGC the removal of terminations from in-service. The
Service Change delay is used to specify the period after which the
termination will be removed from service. The service change delay
can be NULL or any other 32bit-value. We will consider both the cases
here. Case a deals the simple case where the delay is 350 seconds and
in case b we will consider NULL value for the delay.

case (a)


_______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |------------------------------------>|
              |ServiceChange CtxId=2 TermA          |
              | Method=Graceful, Delay = 350        |
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp            |
              |                                     |
              |                    :                |
              |                    :                |
              |                    :                |
         After 350 Seconds TermA is taken out of service
              |                                     |
              |<------------------------------------|
              |      Subtract Ctxid=2 TermA         |
              |                                     |
              |------------------------------------>|
              |      Subtract Resp Ctxid=2 TermA    |
 _____________|_____________________________________|____________________



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Step 1
MG to MGC:
MEGACO/1 [216.33.33.61]: 25000
   Transaction = 4321 {
       Context = 123 {
           ServiceChange = TermA {Services {
               Method=Graceful, Reason="Termination taken out of
                    Service",Delay = 350 }
       }
   }

In the first step MG generates the service change command with Graceful
method. The termination "TermA" is in context 123. The delay 350
indicates MGC that the termination will be moved to out-of-service
after 350 seconds.

Step 2
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Reply = 4321 {
       Context = 123 {
           ServiceChange = TermA {
}
          }
   }

After 350 seconds the MG removes the termination "TermA" out of service.
 As the responsibility of clearing the context lies with the MGC, it
generates the Subtract command to remove the termination out of context.
  The audit descriptor in this example is shown to be present and
shown empty. This indicates that the MGC is not interested in any
statistics to be returned in the response from MG.

Step 3
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 1234 {
       Context = 123 {
           Subtract = TermA {
Audit = {}
}
          }
   }

The MG responds with the Subtract response. By the time the subtract
is received by MG, the termination is out-of-service. The Subtract
command can be received even for terminations that are out-of-service.
After subtracting the termination from the context, the dynamic
information for the context pertained to that termination is cleared.

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Step 4
MG to MGC:
MEGACO/1 [987.654,321.1]: 25000
   Reply = 1234 {
       Context = 123 {
           Subtract = TermA {
}
          }
   }


case (b)

In this subsection we consider the case where the delay specified by
MG is NULL. This indicates that the termination will be taken
out-of-service after the termination is subtracted from valid context.

_______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |------------------------------------>|
              |ServiceChange CtxId=2 TermA          |
              | Method=Graceful, Delay = NULL       |
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp            |
              |                                     |
              |                    :                |
              |                    :                |
              |                    :                |
              |                                     |
              |<------------------------------------|
              |      Subtract Ctxid=2 TermA         |
              |                                     |
              |------------------------------------>|
              |      Subtract Resp Ctxid=2 TermA    |
              |      TermA Taken Out-of-service     |
 _____________|_____________________________________|____________________




Step 1
MG to MGC:
MEGACO/1 [216.33.33.61]: 25000
   Transaction = 4321 {
       Context = 123 {

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           ServiceChange = TermA {Services {
               Method=Graceful, Reason="Termination taken out of
                     Service",Delay =0 }
       }
   }

MGC after receiving gets that information that the termination will
not be available after the call. MGC should inhibit using this
termination further in it calls. MGC responds to the MG for the
command it received.

Step 2
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Reply = 4321 {
       Context = 123 {
           ServiceChange = TermA {
}
          }
   }

The MGC after the call is complete subtracts the termination from the
 context and avoids using this termination in further calls. Even in
this example the audit descriptor is empty.

Step 3
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 1234 {
       Context = 123 {
           Subtract = TermA {
Audit = {}
}
          }
   }

MG after receiving the message from MGC, responds to the message and
immediately removes the termination to out-of-service.


Step 4
MG to MGC:
MEGACO/1 [987.654,321.1]: 25000
   Reply = 1234 {
       Context = 123 {
           Subtract = TermA {
}
          }
   }

3.2.1.2 Forced OOS from MG

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The Forced method of service change when generated from MG is used to
 intimate MGC the removal of terminations from in-service. The
termination may be in a valid Context or NULL context when MG has
generated this message. We will consider both the cases here.
Case (b) deals the simple case where the termination is in NULL context
and in case (a) the termination is in Valid Context .

case (a)



_______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |------------------------------------>|
              |ServiceChange CtxId=123 TermA        |
              |          Method = Forced            |
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp            |
              |                                     |
             Immediately TermA is taken out of service
              |                                     |
              |<------------------------------------|
              |      Subtract Ctxid=123 TermA         |
              |                                     |
              |------------------------------------>|
              |      Subtract Resp Ctxid=123 TermA    |
 _____________|_____________________________________|_________________



Step 1
MG to MGC:
MEGACO/1 [216.33.33.61]: 25000
   Transaction = 4321 {
       Context = 123 {
           ServiceChange = TermA {Services {
               Method=Forced }
}
       }
   }

In the first step MG generates the service change command with "Forced"
Service Change method. The termination "TermA" is in context 123.

Step 2
MGC to MG:

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   MEGACO/1 [207.176.47.89]: 27000
   Reply = 4321 {
       Context = 123 {
           ServiceChange = TermA {
}
          }
   }

After generating the message MG immediately removes the termination
"TermA" out of service. As the responsibility of clearing the context
lies with the MGC, it generates the Subtract command to remove the
termination out of context.  The audit descriptor in this example is
shown to be present and shown empty. This indicates that the MGC is not
interested in any statistics to be returned in the response from MG.

Step 3
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 1234 {
       Context = 123 {
           Subtract = TermA {
Audit = {}
}
          }
   }

The MG responds with the Subtract response. When the subtract message
is received by MG, the termination is out-of-service. The Subtract
command can be received even for terminations that are out-of-service.
After subtracting the termination from the context, the Call specific
information for the context pertained to that termination is cleared.

Step 4
MG to MGC:
MEGACO/1 [987.654,321.1]: 25000
   Reply = 1234 {
       Context = 123 {
           Subtract = TermA {
}
          }
   }


case (b)

In this subsection we consider the case where the termination is in NULL
context. This indicates that the termination will be immediately taken
out-of-service.




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 _______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |------------------------------------>|
              |ServiceChange CtxId=NULL TermA       |
              |          Method = Forced            |
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp            |
              |                                     |
             Immediately TermA is taken out of service
              |                                     |
 _____________|_____________________________________|_________________



Step 1
MG to MGC:
MEGACO/1 [216.33.33.61]: 25000
   Transaction = 4321 {
       Context = - {
           ServiceChange = TermA {Services {
               Method=Forced }
}
       }
   }

MGC after receiving gets that information should inhibit using this
termination further in its calls. MGC responds to the MG for the
command it received.

Step 2
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Reply = 4321 {
       Context = - {
           ServiceChange = TermA {
}
          }
   }


3.2.1.3 Restart INS from MG
In this we will consider the message generation from MG when
terminations are brought back to in-service state after they have been
removed from out-of-service. Initially when the MG comes up, it doesn't
generate any in-service message for specific terminations, as the
service change generated on ROOT terminations serves the same purpose.

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MG can generate restart for multiple terminations using the wildcard
mechanism. But for simplicity we are considering the case where the
termination "TermA" is brought back to service.

 _______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |------------------------------------>|
              |ServiceChange CtxId=NULL TermA       |
              |          Method = Restart           |
              |                                     |
              |<------------------------------------|
              |       ServiceChange Resp            |
              |                                     |
             Immediately TermA is brought back to service
              |                                     |
 _____________|_____________________________________|_________________


Step 1
MG to MGC:
MEGACO/1 [216.33.33.61]: 25000
   Transaction = 4321 {
       Context = - {
           ServiceChange = TermA {Services {
               Method=Restart}
}
       }
   }

MGC after receiving the message updates its Database for using this
Termination for future use . MGC responds to the MG for the command
it received.

Step 2
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Reply = 4321 {
       Context = - {
           ServiceChange = TermA {
}
          }
   }



3.2.2 MGC generated Service Change
In the earlier section we saw few scenarios where the MG generated

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messages to MG indicating the change of state in the termination. In
this section we will look into the cases where MGC generates the
service change message on terminations to remove the terminations from
in-service to out-of-service and vice-versa.

3.2.2.1 Forced OOS from MGC
When the MGC intends to remove the termination from in-service to
out-of-service, it generates a forced service change message towards MG.
MG immediately removes the termination from in-service to
out-of-service. If the termination is in valid context, MGC can generate
subtract command and following that another message with service change
command to remove it from service.


 _______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |<------------------------------------|
              |ServiceChange CtxId=NULL TermA       |
              |          Method = Forced            |
              |                                     |
              |------------------------------------>|
              |       ServiceChange Resp            |
             Immediately TermA is taken out of service
              |                                     |
 _____________|_____________________________________|_________________


Step 1
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 4321 {
       Context = - {
           ServiceChange = TermA {
        Method=Forced
}
          }
   }

MG after receiving the message from MG removes the termination
immediately from service. The response is generated towards for the
message received from MGC.

Step 2
MG to MGC:
   MEGACO/1 [209.11.33.62]: 25000
   Reply = 4321 {
       Context = - {

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           ServiceChange = TermA {
}
          }
   }



3.2.2.2 Restart from MGC
When the MGC intends to bring the termination from out-of-service to
in-service, it generates a restart method of service change message
towards MG. MG immediately brings the termination from out-of-service
to in-service.


 _______________________________________________________________________
                                   |
       Media Gateway               |   Media Gateway Controller
___________________________________|___________________________________
              |                                     |
              |                                     |
              |<------------------------------------|
              |ServiceChange CtxId=NULL TermA       |
              |          Method = Restart           |
              |                                     |
              |------------------------------------>|
              |       ServiceChange Resp            |
             Immediately TermA is brought back to service
              |                                     |
 _____________|_____________________________________|_________________


Step 1
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 4321 {
       Context = - {
           ServiceChange = TermA {
        Method=Restart
}
          }
   }

MG after receiving the message from MG brings the termination
immediately to service. The response is generated towards for the
message received from MGC.
Step 2
MG to MGC:
   MEGACO/1 [209.11.33.62]: 25000
   Reply = 4321 {
       Context = - {
           ServiceChange = TermA {

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}
          }
   }


4.0 Audit Command Usage
The Audit command is defined in the protocol to enable MGC to get
information from MG to MGC. The information received may contain the
values present at the MG on a given termination or possible values that
can be supported on the given termination depending upon whether the
command is Audit Value or Audit Capability. The Audit command can be
used on Root Termination also. The Audit command is used by MGC when
it needs the state of the termination and the parameter values for
that given termination. Wildcard termination identifier and wildcard
contextID can be used by MGC in these Audit command.

4.1 Audit Value
The Audit value command can be sent from MGC to know the present values
 of the descriptors requested. The Audit Value command can be sent on
either ROOT termination or any other termination in the MG.  The
section 2.1.1 illustrates the usage of Audit Value command on ROOT
termination and section 2.1.2 illustrates the usage of Audit value
command on a given termination.

4.1.1 Audit value command on ROOT Termination
The ROOT termination denotes the entire gateway as a single entity.
There are two possible cases of Audit Value command on ROOT
termination. The one in which the ContextId is NULL and the other in
which the contextID is ALL. The case (a) below illustrate when the
Audit Value command when the ContextId is * and in case (b) other in
which the ContextId is NULL. The base ROOT package is assumed to be
implemented on the ROOT termination.

Case (a)
In this section we will illustrate how MGC retrieves the lists of all
contexts in MG. The Audit Value command with ContextId '*' and
termination identifier ROOT enables MGC to get all the valid contextID
values.

Step 1
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 1234 {
       Context = * {
           AuditValue= ROOT {Audit { } }
          }
   }
The MG after receiving the command from MGC constructs the response
with all the contextID that is active in that MG.

Step 2

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MG to MGC:
   MEGACO/1 [216.33.33.61]: 25000
   Reply = 1234 {
       Context = 100 {
           AuditValue= TermA, TermB
          }
       Context = 200 {
           AuditValue= TermC, TermD
          }
       Context = 300 {
           AuditValue= TermE, TermF
          }
   }



Case (b)
This section illustrates the usage of ROOT termination identifier with
NULL ContextID. This command is supposed to return the values of
properties and statistics implemented on ROOT. The MGC generates the
AuditValue message to MGC.

Step 1
MGC to MG:
   MEGACO/1 [207.176.47.89]: 27000
   Transaction = 1234 {
       Context = - {
           AuditValue= ROOT {Audit {Media, Statistics} }
          }
   }
The MG responds with the values of properties that are defined on the
ROOT termination. These properties include the Maximum number of
contexts, Maximum number of terminations per context, normal MG
execution time, normal MGC execution time and Provisional response
timer value. There are no statistics that are defined on the ROOT
termination. Hence the MG responds with the statistics token only.

Step 2
MG to MGC:
   MEGACO/1 [216.33.33.61]: 25000
   Reply = 1234 {
       Context = - {
           AuditValue= ROOT
           Media {
             TerminationState{
              MaxNumberOfContexts = 100,
              MaxTerminationsPerContext = 2,
              NormalMGExecutionTime = 1000,
              NormalMGCExecutionTime = 1000,
              ProvisionalResponseTimerValue=1000,
               }

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              Audit {statistics}
        }
          }



4.1.2 Audit value on non-ROOT terminations
This section illustrates the usage of AuditValue command on
terminations other than ROOT. The Audit value command response
constitutes all the active value of the descriptors that are requested
by MGC. In this example we assume that the descriptors are already
updated with commands from MGC. The MGC audit is done when the
termination is in valid context. This is to include the statistics
descriptor in the response from MG. The termination is assumed to be
Ephemeral to use all the statistics defined in network package and
RTP package. The second message illustrates the use of AuditValue to
get the active descriptor values defined on physical terminations.

Step 1
MGC to MG:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
      Context = 2 {AuditValue = EphA{
         Audit{Media, DigitMap, Events, Signals, Packages, Statistics
   }}
      }
   }

The MG responds with the media descriptor, packages and statistics.
The Digit map, signal and events are not defined on this ephemeral
termination hence only tokens are sent back in the response.

Step 2
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = 2 {
   AuditValue = EphA {
             Media {
                 TerminationState { ServiceState = InService,
                        Buffer = OFF },
                Stream = 1 {
                    LocalControl { Mode = SendReceive,
                       nt/jit=40 },
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP  0
   a=ptime:30
                   },
                    Remote {

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   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP  0
   a=ptime:30
                    } } },
            audit { Events,
             Signals,
             DigitMap},
             Packages {nt-1, rtp-1},
             Statistics { rtp/ps=1200,  ; packets sent
                          nt/os=62300, ; octets sent
                          rtp/pr=700, ; packets received
                          nt/or=45100, ; octets received
                          rtp/pl=0.2,  ; % packet loss
                          rtp/jit=20,
                          rtp/delay=40 } ; avg latency
          }
       }
   }

The MGC in the following command generates audit value command for
physical termination that is in a context. Here only DigitMap, event
and signal descriptor are audited.

Step 3
MGC to MG:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1235 {
      Context = 2 {AuditValue = TermA{
         Audit{ DigitMap, Events, Signals
   }}
      }
   }
The MG after receiving the command responds with the event, signal
and digit map descriptors that are active on the termination.
Step 4
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1235 {
       Context = 2 {
           Modify = TermA{
               Events = 2223 {
                   al/on, dd/ce {DigitMap=Dialplan0}
               },
               Signals {cg/dt},
               DigitMap= Dialplan0{
   (0| 00|[1-7]xxx|8xxxxxxx|Fxxxxxxx|Exx|91xxxxxxxxxx|9011x.)}
           }
       }
   }


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4.2 Audit Capability

The Audit capability command from MGC retrieves the possible values of
the descriptors requested. The first section 5.2.1 illustrates the
Audit capability command on ROOT termination and 5.2.2 on terminations
other than ROOT termination.

4.2.1 Audit Capability on ROOT termination
The Audit Capability command on ROOT termination is used to determine
the properties that are implemented on the ROOT termination. The
response from MG includes the possible values of the properties.

Step 1:
MGC to MG:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1235 {
      Context = - {Audit Capability = ROOT{
         Audit{ Media }}
      }
   }

The properties that are defined on the ROOT in this example are the
Max number of Contexts, maximum terminations per context, normal MG
execution time, normal MGC execution time and provisional response
timer value.

Step 2
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1235 {
       Context = - {
           Modify = ROOT{
           Media { TerminationState { MaxNumberOfContexts =10,
         MaxTerminationsPerContext =2, NormalMGExecutionTime =250,
         NormalMGCExecutionTime =250,
         ProvisionalResponseTimerValue  = 200 }}
           }
       }
   }



4.2.2 Audit Capability on non-Root Terminations.
This section illustrates the usage of Audit Capability command on a
 non-ROOT termination. The MGC in this example is generating Audit
Capability for Events descriptor and signal descriptor. The MG should
respond with the possible values of these descriptors.

Step 1:

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MGC to MG:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
      Context = - {AuditCapability = TermA{
         Audit{ Events, Signals
   }}
      }
   }
The response has all the possible values. In this example for
simplicity event parameters are not included. The packages that are
realized on TermA are analog line supervision package, DTMF detection
package call progress tone generation package, tone generation package,
and generic package.

Step 2
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
       Context = - {
           Modify = TermA{
               Events = 0 {g/cause, g/signalcompletion, tonedet/std,
               tonedet/etd, tonedet/ltd, dd/ce, al/on, al/of, al/fl},
               Signals {cg/dt, cg/rt, cg/bt, cg/ct, cg/sit, cg/wt,
                            cg/pt, cg/cw, cg/cr},
           }
       }
   }




5. IVR using MEGACO

The Interactive Voice Response (IVR)  is assumed to be a gateway with
only ephemeral terminations. The IVR is capable of playing
announcements, detecting digits and reporting the same to the MGC.
In this example we assume a IVR, which is controlled by a MGC. The
IVR is assumed to play some announcement and detects the DTMF digits
and reports the same to MGC. This section presents few call scenarios
where a residential user is connected to IVR, Trunking gateway
connected to IVR, call disconnection from residential and Trunking
gateway to the IVR.

5.1 Connecting Residential gateway to IVR.


 _______________________________________________________
             |           |           |
  USERA      |   RGW1    |    MGC    |           IVR
_____________|___________|___________|__________________
      |            |           |           |

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      |            |           |           |
      |            |<----------|           |
      |            |Modify to  |           |
      |            |check offhook          |
      |            |---------->|<----------|
      |            |Modify Resp| Modify Resp
      |----------->|           |           |
      |UserA offhook           |           |
      |            |---------->|           |
      |            |Notify offhook         |
      |            |<----------|           |
      |            |Notify Resp|           |
      |            |<----------|           |
      |            |Modify SG:dialtone     |
      |            |ED:al/on,dd/ce{Dmap1}  |
      |            |DM:Dmap1 = 2XXX        |
      |<-----------|           |           |
      |Dial Tone   |---------->|           |
      |            |Modify Resp|           |
      |            |           |           |
      |----------->|           |           |
      |User Dials Digits       |           |
      |            |---------->|           |
      |            |Notify digits          |
      |            |<----------|           |
      |            |Notify Response        |
      |            |<----------|           |
      |            | Add TermA SD:ringbacktone
      |            | Add $, Local SDP Info -underspecified
      |<-----------|           |           |
      |RingBack Tone           |           |
      |            |---------->|           |
      |            |Modify Resp TermA      |
      |            |Add Resp Local SDP (Specified)
      |            |           |---------->|
      |            |           |Add $ Local(Underspecified)
      |            |           |     Remote SDP (Specified)
      |            |           |           |
      |            |           |<----------|
      |            |           |Add Resp EphB Local Specified
      |            |<----------|           |
      |            |Modify TermA SendRecv  |
      |            |Modify EphA  Remote(Specified) SendRecv
      |            |---------->|           |
      |            |Modify Resp|           |
      |/----------------------------------\|
      |              RTP MEDIA             |
      |\----------------------------------/|
      |____________|___________|___________|



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The MGC initially generates a Modify command to the Residential gateway
to which UserA is connected. The Modify command lists a offhook event
in the Events descriptor. The embedded signal descriptor lists the
dial tone and the embedded event descriptor lists the Digit completion
event of the DTMF package.

Step 1
MGC to RGW:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        } ,
 Events = 1111 {al/of { Signals {cg/dt},Embed = 1112 {al/on, dd/ce
             {DigitMap=Dmap1}} }
   DigitMap= Dmap1{(2XXX)}
           }
       }
   }

The residential gateway responds the Modify command.

Step 2:
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
RGW and constructs the Notify message to the MGC. The MG uses the same
request id (1111) sent by the MGC in its initial command. The
timestamp of the event detected is also passed as parameter to the
observed event.

Step 3
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {



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            20010202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 4
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The users dials digits and that takes the call to be terminated on the
IVR.  The digits dialed by the user are reported to the MGC in the
Notify command.

Step 6
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.
Step 7
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example the called subscriber is connected to the RGW2,
which is again controlled by the same MGC. The MGC generates a
transaction with two commands clubbed into the same Action. The first
command is to create a new context and add the physical termination
TermA into it. As the MGC is aware that the destination user UserB is
free it indicates MG1 to apply ringback tone to the termination of
UserA. The second command is generated to create an ephemeral
termination and add the created termination in the same context that
was created because of the earlier command. Here we assumed a single
set of SDP information indicating that Reserve group is not used. The
Reserve Value feature is also not used.

Step 8

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MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add = TermA {
                 Signals { cg/rt }
                            }
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

In this example the connection fields IP address, the media field port
number are unspecified. The MG in its response indicates the IPAddress
and port number used. The contextID is also not specified indicating
the creation of a new context. In this example the MG creates a context
with contextID 1. The physical termination TermA is added to context 1.
 The mode of the physical termination was earlier set to Receiveonly
and in this message the ephemeral termination is requested to create
with Receiveonly mode. The ephemeral termination created in this
example is EphA. MG responds with the allocated IP address
209.110.59.33 and port number 30000.


Step 9
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }

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         }
      }
   }
MGC generates a similar transaction towards the IVR media gateway. The
ContextID specified in the action is $. The Add command is meant for
create an ephemeral termination. MGC has the local information for the
ephemeral termination EphA in the RGW1. This information is passed as
remote information to the IVR. The new ephemeral termination that will
be created will take these parameters as the remote SDP information.

Step 10
MGC to IVR:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1236 {
       Context = $ {
       Add  = $ {
           Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
Events = 1113{ streamid = 1 dd/ce { dmap2 }}
Digits = Dmap2 {2XXX}
      }
   }

IVR after receiving the new transaction from MGC starts processing it.
It creates a new context with contextID 2. The IVR creates a ephemeral
termination with TerminationId EphB. The local information is
under-specified from the MGC. The MG allocates the necessary resources
for processing the media descriptor for the ephemeral termination. The
MG responds to the MGC by specifying the IP address reserved for the
local connection. In this example IVR reserves IP address 207.176.47.90
and port number 40000. The IVR responds to MGC with the following
transaction reply.

Step 11
MG2 to MGC:

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   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236 {
      Context = 2 {
       Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response forwards the remote SDP
information in Modify command to the Residential gateway. The MGC
generates message to the RGW to stop the ringback tone and changes
the  mode of the two terminations TermA and EphA to send receive.

Step 12
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1237 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination TermA,
stop the ringback tone at the calling end. The remote SDP information is
updated for the ephemeral termination EphA. The mode is changed to send
receive. MG1 responds to the MGC with the response for the Modify
commands.

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Step 13
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1237 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
Now the RTP flow is established. The IVR plays an announcement. The
User dials digits depending upon the announcement. The digits are
detected on the RTP stream.

5.2 Disconnecting Residential User from IVR.

This section illustrates the case of disconnecting a residential user
from IVR. The assumption is that the RTP media is already established
and now the MGC has to act upon the user actions. The MGC waits for the
user to go onhook. Once the UserB goes onhook, MG2 reports the
notification of the onhook event to the MGC.

 _______________________________________________________
              |           |           |
   USERA      |   RGW1    |    MGC    |           IVR
 _____________|___________|___________|__________________
      |            |           |           |
      |/----------------------------------\|
      |             RTP MEDIA              |
      |\----------------------------------/|
      |----------->|           |           |
      |UserA goes OnHook       |           |
      |            |---------->|           |
      |            |Notify OnHook          |
      |            |<----------|           |
      |            |Notify Resp|           |
      |            |<----------|           |
      |            |Subtract TermA         |
      |            |Subtract EphA          |
      |            |---------->|           |
      |            |Subtract Resp TermA    |
      |            |Subtract Resp EphA Statistics
      |            |           |---------->|
      |            |           |Subtract EphB
      |            |           |<----------|
      |            |           |Subtract Resp EphB Statistics
      |____________|___________|___________|




Step 1
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000

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   Transaction = 3000 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1234 {
            20000202T10020000:al/on}}
      }
   }
The MGC responds to the MG2 with the Notify response.

Step 2
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3000 {
       Context = 1 {Notify = TermA}
   }
The MGC generates transactions with two subtracts commands one for
physical and other for ephemeral terminations.

Step 3
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 4
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


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The MGC generates similar command towards the IVR to subtract the
ephemeral termination.

Step 5
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
      Context = 2 {
         Subtract = EphB {Audit{Statistics}}
      }
   }
The IVR responds to the subtract commands generated by MGC.

Step 6
MG2 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1235 {
      Context = 2 {
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

5.3 Connecting Trunking Gateway to IVR.
This section illustrates a call initiated from Trunking gateway towards
IVR. It is assumption that the same MGC controls both the IVR and the
Trunking gateway.

 ____________________________________________________
            |            |           |
 SS7 Switch |    TGW     |    MGC    |        IVR
____________|________ ___|___________|______________
      |            |           |           |
      |            |           |           |
      |----------------------->|           |
      |          IAM           |           |





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      |<-----------------------|           |
      |          ACM           |           |
      |            |           |           |
      |            |<----------|           |
      |            | Add Phy   |           |
      |            | Add $, Local SDP Info -underspecified
      |            |---------->|           |
      |            |Add Resp Phy           |
      |            |Add Resp Local SDP (Specified)
      |            |           |---------->|
      |            |           |Add $ Local(Underspecified)
      |            |           |     Remote SDP (Specified)
      |            |           |           |
      |            |           |<----------|
      |            |           |Add Resp EphB Local Specified
      |<-----------------------|           |
      |          ANM           |           |
      |            |<----------|           |
      |            |Modify Phy   SendRecv  |
      |            |Modify EphA  Remote(Specified) SendRecv
      |            |---------->|           |
      |            |Modify Resp|           |
      |            |/---------------------\|
      |            |     RTP MEDIA         |
      |            |\---------------------/|

The MGC receives IAM message from the SS7 switch. In this example we
 assume that the Signaling gateway and the Media Gateway are together
in one physical box. The MGC responds with the ACM message. The MGC
also generates add command to the Trunking gateway for addition of a
circuit group of specific trunk and also another Add for ephemeral
termination. For the ephemeral termination the MGC specifies few SDP
parameters in the Local descriptor and many of the parameters are
underspecified. This facilitates the MG to assign values by its own.

Step 1
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = $ {
          Add = Trunk1/line1  {Media {
                    LocalControl {Mode = SendRecv}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

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                    }
               }
             }
         }
      }
   }

The Trunking gateway after responds with a contextID in this example 1.
The ephemeral termination is created and added to the same context as
the physical termination. The ephemeral termination added in this
example is EPHA. The local parameters are specified in the response.
The IP address chosen for the media transport in this example is
209.110.59.33, and the port number specified 30000.

Step 2
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1234 {
      Context = 1 {
        Add = Trunk1/line1,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC after receiving the response from the Trunking gateway uses the
SDP information in the response sent from TG to the IVR. The command
is for adding the ephemeral termination. The MGC requests creation of
context and to the termination in the same.

Step 3
MGC to IVR
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = $ {
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

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                    }
Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
              }
      }
   }

The IVR creates a context with ContextId 2. The ephemeral termination
EPHB is created with the specified SDP information. The response from
the IVR specifies the local SDP information.

Step 4
RGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1235 {
      Context = 2 {
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                 }
               } ; RTP profile for G723 is 4
         }
      }
   }
The MGC after receiving the response with the local SDP information
conveys the same to the Trunking gateway as remote SDP information in
the Modify command.

Step 5
MGC to TGW
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = 1 {
          Modify = EphA
                 {Media {
                    LocalControl {
                       Mode = SendRecv,
                    },
                    Remote{
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    }

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               }
             }
         }
      }
   }

The Trunking gateway responds to the Modify command.

Step 6
TGW to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1236 {
      Context = 1 {
   Modify = EphB
}
}
5.4 Disconnecting Trunking gateway from IVR
This section illustrates the disconnection of an IVR call from
Trunking gateway. The Trunking gateway and the Signaling gateway are
assumed to be present in the same physical box. The SS7 messages are
received by the Signaling gateway and are forwarded to the MGC through
the signaling gateway.


 _____________________________________________________
            |            |           |
 SS7 Switch |    TGW     |    MGC    |        IVR
____________|________ ___|___________|______________
      |            |           |           |
      |            |/---------------------\|
      |            |      RTP MEDIA        |
      |            |\---------------------/|
      |----------------------->|           |
      |           REL          |           |
      |            |<----------|           |
      |            |Subtract Phy           |
      |            |Subtract EphA          |
      |            |---------->|           |
      |            |Subtract Resp Phy      |
      |            |Subtract Resp EphA Statistics
      |<-----------------------|           |
      |          RLC           |           |
      |            |           |---------->|
      |            |           |Subtract EphB
      |            |           |<----------|
      |            |           |Subtract Resp EphB Statistics
      |____________|___________|___________|





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It is assumed that the RTP stream is already established. The REL
message is received by the MGC through the Signaling gateway. The MGC
initiates the terminating of the IVR call. The MGC initially generates
a transaction with two subtracts towards the Trunking gateway. One
subtract for removing the physical termination and other to remove the
ephemeral termination.

Step 1
MGC to TGW:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234
      Context = 2 {
         Subtract = Trunk2/line1{Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The TGW responds to the subtract commands generated by MGC.

Step 2
TGW to MGC:
   MEGACO/1 [209.110.59.34]:26000
   Reply = 1234
      Context = 2 {
        Subtract = Trunk2/line1
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The MGC generates similar command towards the IVR.

Step 3
MGC to IVR:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235{
      Context = 1 {
        Subtract = EphA {Audit{Statistics}}
      }
   }
The IVR responds to the subtract commands generated by MGC.

Step 4

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IVR to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1235{
      Context = 1 {
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


6. Wildcard ContextID usage
The protocol defines two types of wildcards. The CHOOSE wildcard and
the ALL wildcard. The CHOOSE wildcard when used from MGC for the
ContextId enables MG to create a new context The ALL wildcard
ContextID enables MGC to multiple contexts using a single Action. If
the MGC needs to perform an operation common to all Contexts it can
use the Wildcard ContextID for this purpose. For example if MGC needs
to subtract all terminations irrespective of context they are in, it
can use ContextId '*' and termination ID '*'. This enables MG to
perform the operation on all contexts that are active in the MG. The
CHOOSE wildcard had already been in used in earlier call flows. This
section shows a scenario where MGC uses * wildcard in ContextID.

Step 1:
MGC to MG:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234{
      Context = * {
        Subtract = *{Audit{Statistics}}
      }
   }
The MG now subtracts all terminations in any of the contexts. There
will be as many actions as the number of Contexts that are active in
the MG. In this example we assume two contexts Context1 and Context2
with one two terminations in each of the context.

Step 2:
MG to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234{
      Context = 1{
              Subtract = TermA {audit = { Statistics}}

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              Subtract = EphA
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
      Context = 2 {
          Subtract = TermB { audit = {statistics }}
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


7. Wildcard TerminationId Usage
The wildcards when used for TerminationId can represent CHOOSE, ALL or
partial choose. The partial choose enables MGC to specify part of
TerminationId and leaving the remaining part of the TerminationId
either * or $. The CHOOSE wildcard usage is illustrated in earlier
examples. The Partial wildcard usage is illustrated in the Trunking
gateway examples. The * wildcard example is treated in this section.

In this example the MGC generates a command with wildcard ALL "*"
TerminationId, to enable MG to processes the command for all the
terminations in the Gateway. The Media gateway is assumed to be a
residential gateway. The events descriptor requests MG to check for
offhook and apply dial tone when the offhook event occurs.

Step 1:
MGC to RGW:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = *{
               Media {
                        LocalControl {

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                            Mode = ReceiveOnly}
                        } ,
           Events = 1111 {al/of { signals { cg / dt } ,
                    embed event { al/on , dd/ce { dmap1} } } }
           DigitMap = dmap1 { 2XXX }
           }
       }
   }

The MG responds with specifying each of the TerminationId for which
the command has been processed.

Step 2:
   MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = -
        {Modify = TermA}
        {Modify = TermB}
        {Modify = TermC}
        {Modify = TermD}
        {Modify = TermE}
        {Modify = TermF}
        {Modify = TermG}
        {Modify = TermH}
        {Modify = TermI}
        {Modify = TermJ}
   }




8. Supplementary services support

8.1 Call Transfer

 _____________________________________________________________________
                  |               |                |
      MG1       |      MGC      |      MG2       |       MG3
________________|_______________|________________|____________________
       |                 |               |                 |
       |<----------------|-------------->|                 |
       |Initial Modify   | Initial Modify|                 |
       |                 |-------------------------------->|
       |                 |        Initial Modify           |
       |---------------->|<--------------|                 |
       |Modify Response  | Modify Resp   |                 |
       |                 |<--------------------------------|
       |                 |       Modify Response           |
       |---------------->|               |                 |
       | Notify OffHook  |               |                 |

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       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|               |                 |
       |Modify ED:dd/ce{DigitMap=dmap1},al/on SD:cg/dt     |
 <-----|---------------->|               |                 |
Dial   | Modify Resp     |               |                 |
Tone   |                 |               |                 |
------>|                 |               |                 |
Digits |---------------->|               |                 |
       |Notify Digits    |               |                 |
       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|-------------->|                 |
       |Modify ringback  | Modify Ring   |                 |
<------|---------------->|<--------------|                 |
ring   | Modify Resp     |  Modify Resp  |                 |
back   |                 |<--------------|                 |
       |                 |Notify OffHook |                 |
       |<----------------|-------------->|                 |
       | Add Phy         |Notify Resp    |                 |
       |Add Eph Local Unspecified        |                 |
       |---------------->|               |                 |
       |Add Phy Resp     |               |                 |
       |Add Eph Resp Local specified     |                 |
       |                 |-------------->|                 |
       |                 |Add Phy        |                 |
       |                 |Add Eph Local unspecified        |
       |                 |        Remote Specified         |
       |                 |<--------------|                 |
       |                 | Add Phy Resp  |                 |
       |                 | Add Eph Resp Local specified    |
       |<----------------|               |                 |
       | Modify Eph Remote Specified     |                 |
       |---------------->|               |                 |
       | Modify Resp     |               |                 |
       |/-------------------------------\|                 |
       |        RTP MEDIA                |                 |
       |\-------------------------------/|                 |
       |                 |<--------------|                 |
       |                 | Notify Flash  |                 |
       |                 |-------------->|                 |
       |<----------------| Notify Resp   |                 |
       | Modify RecvOnly |           --->|                 |
       |---------------->|       DialTone|                 |
       | Modify Resp     |<--------------|                 |
       |                 | Notify Digits |                 |
       |                 |-------------->|                 |
       |                 |  Notify Resp  |                 |
       |                 |-------------------------------->|
       |                 |         Modify Ring             |
       |                 |<--------------------------------|

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       |                 |         Modify Response         |
       |                 |-------------->|                 |
       |                 | Modify Ringback tone            |
       |                 |<--------------|                 |
       |                 |  Modify Resp  |                 |
       |                 |<--------------------------------|
       |                 |      Notify OffHook             |
       |                 |-------------------------------->|
       |                 |            Notify Resp          |
       |                 |-------------------------------->|
       |                 |      Add Phy                    |
       |                 |      Add Eph Local Unspecified  |
       |                 |              Remote Specified   |
       |                 |<---------------------------------|
       |                 |      Add Phy Resp               |
       |                 |      Add Eph Resp Local Specified
       |                 |-------------->|                 |
       |                 | Modify Eph Remote               |
       |                 |<--------------|                 |
       |                 | Modify Resp   |                 |
       |                 |               |/---------------\|
       |                 |               |   RTP Media     |
       |                 |               |\---------------/|
       |                 |<--------------|                 |
       |                 | Notify OnHook |                 |
       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |                 |-------------->|                 |
       |                 | Sub Phy       |                 |
       |                 | Sub Eph       |                 |
       |                 |<--------------|                 |
       |                 | Sub Phy Resp  |                 |
       |                 | Sub Eph Resp Statistics         |
       |                 |-------------------------------->|
       |                 |      Modify Eph Remote          |
       |                 |<--------------------------------|
       |                 |       Modify Eph Resp           |
       |<----------------|               |                 |
       | Modify Eph Remote               |                 |
       |---------------->|               |                 |
       | Modify Resp     |               |                 |
       |/-------------------------------------------------\|
       |                   RTP MEDIA                       |
       |\-------------------------------------------------/|
       |---------------->|               |                 |
       | Notify OnHook   |               |                 |
       |---------------->|               |                 |
       |   Notify Resp   |               |                 |
       |                 |-------------------------------->|
       |                 |        Modify Phy busyTone      |
       |                 |<--------------------------------|
       |                 |        Modify Resp              |
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       |<----------------|               |                 |
       | Sub Phy Sub Eph |               |                 |
       |---------------->|               |                 |
       |  Sub Phy Resp   |               |                 |
       |  Sub Eph Resp Statistics        |                 |
       |                 |<--------------------------------|
       |                 |        Notify OnHook            |
       |                 |-------------------------------->|
       |                 |        Notify Resp              |
       |                 |-------------------------------->|
       |                 |        Sub Phy                  |
       |                 |        Sub Eph                  |
       |                 |<--------------------------------|
       |                 |        Sub Phy Resp             |
       |                 |        Sub Eph Resp Statistics  |
_______|_________________|_______________|_________________|____________

The call Transfer feature in PSTN allows a user to tranfer a call that he
Has received to another phone. This feature should be supported by MGC
so that it is capable of generating required messages towards MG. In this
example we assume that the MGC is capable of supporting Call Transfer.
UserB, the Called party press flash hook and initiates call towards UserC.
After UserC responds to the call, UserB goes onhook to connect UserA with
UserC.

The MGC generates the Modify message towards all the three Residential
gateways to check for off hook on the terminations. (A wildcard
command may also be used in this scenario but for simplicity we
consider only command to specific terminations). We are not
considering the embedded signal and event descriptors here.
 The MGC in NULL context generates the command to the
specific termination TermA. The off hook event of the analog
supervision package is used here. The request identifier specified
in this example is 1111. The mode of the termination is set to
receive only. The stream parameter is used with only the Local control
descriptor.

Step 1
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        } ,
 Events = 1111 {al/of}
           }
       }
   }


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MG, after receiving the command from MGC, accepts it and responds with
the transaction reply. Here for only MG1 is shown to generate the
response. In fact all the RGW generate the responses.

Step 2

   MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
 RGW1 and it constructs the Notify message to the MGC. The MG uses the
same request id (1111) sent by the MGC in its initial command. The
timestamp of the event detected is also passed as a parameter to the
observed event.

Step 3
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 4
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The MGC in the following command issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a
digit map on the termination. The digit map name used in the example
is Dmap1 and the dial patter is 2XXX. The event descriptor lists digit
map completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the
event descriptor is 1112.

Step 5
MGC to MG1:

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1{(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG validates the Modify command and responds to the MGC and then starts
processing the descriptors listed.

Step 6
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the
MGC. In this example the order of descriptor is signal descriptor,
digit map descriptor followed by Events descriptor. The MG first
processes the signal descriptor. The dial tone is applied to the
Termination specified. The Digit map is updated in the Database of the
termination. The Digit map will be ACTIVE on the termination as the
digit map completion event is listed in the events descriptor with the
digit map name. A digit map is activated whenever a new event
descriptor is applied to the termination or embedded event descriptor
is activated, and that event descriptor contains a digit map completion
event which itself contains a digit map parameter. UserA after receiving
the dial tone starts dialing digits. In this example we will not dwell
into the different possible cases of digit dialing by the user. Its
assumed that the digits dialed by the user, match with the digit map
pattern. Lets assume that the user has dialed 2992. MG detects the
digits dialed and reports the same as parameter to the digit map
completion event. A notify command is generated from MG1 to MGC. The
MG again uses the same request identifier as specified by the MGC.

Step 7
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }


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MGC after receiving the Notify command responds back with the Notify
response.

Step 8
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example the called subscriber is connected to the
RGW2, which is again controlled by the same MGC. The MGC generates a
transaction with two commands clubbed into the same Action. The first
command is to create a new context and add the physical termination
TermA into it. As the MGC is aware that the destination user UserB is
free it indicates MG1 to apply ringback tone to the termination of
UserA. The second command is generated to create an ephemeral
termination and add the created termination in the same context
that was created because of the earlier command. Here we assumed a
single set of SDP information indicating that Reserve group is not
used. The Reserve Value feature is also not used.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals { cg/rt }
                            }
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

In this example the connection fields IP address, the media field port
number are unspecified. The MG in its response indicates the IPAddress
and port number used. The contextID is also not specified indicating

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the creation of a new context. In this example the MG creates a context
with contextID 1. The physical termination TermA is added to context 1.
 The mode of the physical termination was earlier set to Receiveonly
and in this message the ephemeral termination is requested to create
with Receiveonly mode. The ephemeral termination created in this example
is EphA. MG responds with the allocated IP address 209.110.59.33 and
port number 30000.


Step 10
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

MGC generates a similar transaction towards the RGW2. The ContextID
specified in the action is $. The first command adds the physical
termination TermB to the newly created context. The Signal descriptor
for this termination lists the ring signal of the analog line
supervision package. This alerting signal is applied to the
termination of the TermB. The Event descriptor specifies offhook
event of the analog line supervision package. The second Add is meant
to create an ephemeral termination. MGC has the local information for
the ephemeral termination EphA in the RGW1. This information is passed
 as remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
                Events=1234{al/of},

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               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }
   }

MG2 after receiving the new transaction from MGC starts processing it.
 It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ring" signal to
 be applied on the termination. The event descriptor lists the off
hook event. The RGW2 creates a ephemeral termination with
TerminationId EphB. The local information is under-specified from the
MGC. The MG allocates the necessary resources for processing the media
descriptor for the ephemeral termination. The MG responds to the MGC by
specifying the IP address reserved for the local connection. In this
example MG2 reserves IP address 207.176.47.90 and port number 40000.
The MG2 responds to MGC with the following transaction reply.

Step 12
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }

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   }

The MGC waits for the UserB to go offhook. Once the UserB goes offhook,
 MG2 reports the notification of the offhook event to the MGC.

Step 13
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}
      }
   }
The MGC responds to the MG2 with the Notify response.

Step 14
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3000 {
       Context = 2 {Notify = TermB}
   }
The MGC generates a transaction towards MG2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook and flashhook events

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on, al/fl { signals cg/dt,
                                       events dd/ce{dmap1}, al/on }},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

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The MG2 responds to the request from MGC.

Step 16
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC generates message to the MG1 to stop the ringback tone and to
 report the remote SDP information for the ephemeral termination EphA.
The mode of the two terminations TermA and EphA is set to send
receive.

Step 17
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, stops the ringback tone at the calling end. The remote SDP
information is updated for the ephemeral termination EphA. The mode
is changed to send receive. MG1 responds to the MGC with the response
for the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000

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   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange media, as the RTP streams are made
bi-directional.
The UserB now press flash to dial the UserC number.
The UserB flash event is reported to MGC using the Notify message.

Step 19
MG2 to MGC:
   MEGACO/1 [209.110.59.34]:29000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20040202T10000000:al/fl}}
      }
   }

MGC generates the Notify response.


Step 20
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3001 {
       Context = 2 {Notify = TermB}
   }
The UserB gets the dial tone and starts dialing the digits. In this
example the UserB dials the number 2804 of UserC.  The dialed digits
are reported to MGC using digit map completion event. The digits are
reported using the Notify command.

Step 21
MG2 to MGC:
MEGACO/1 [209.110.59.34]: 27000
   Transaction = 3002 {
      Context = 2 {
          Notify = TermB {Observed Events =1235 {
            20040202T10010000:dd/ce{ds="2804",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
 response.

Step 22
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3002 {
       Context = 2 {Notify = TermB}
   }
The UserC is alerted with ring signal to indicate that a call is to be
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received. The Add command for the physical termination TermC with
signal descriptor allows the ring signal to be applied on the
termination. The ephemeral termination is also requested to be created
with under specified Local SDP information and fully specified Remote
SDP information.

Step 23:
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
       Context = $ {
          Add = TermC {
                 Signals { al/ri }
                Events = 1111{ al/of embedded { al/on } }
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
                  Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
             }
          }
       }
   }

In this example the SDP local information connection fields IP
address, the media field port numbers are unspecified. The MG3 in its
response indicates the IPAddress and port number used. The contextID
is also not specified indicating the creation of a new context. In
this example the MG3 creates a context with contextID 3. The physical
termination TermA is added to context 1. The mode of the physical
termination was earlier set to Receiveonly and in this message the
ephemeral termination is requested to create with Receiveonly mode.
The ephemeral termination created in this example is EphC. MG3 responds
with the allocated IP address 192.168.0.160 and port number 50000.

Step 24
MG3 to MGC:
   MEGACO/1 [209.110.59.35]: 25000

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   Reply = 1240 {
      Context = 3 {
         Add = TermC,
         Add=EphC{
            Media {
                    Local {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

The MGC generates ring back tone towards the UserB to indicate that
altering signal has been sent to the called party UserC.
Step 25
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
       Context = 2 {
          Modify = TermB {
                 Signals { cg/rt }
                            }
          }
       }
   }
The MG2 after receiving the Modify command applies the ring back tone
specified in the signals descriptor. The Modify response is sent back
to MGC.

Step 26
MG2 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1241 {
      Context = 2 {
         Modify= TermB,
      }
   }
The UserC after receiving the ring signal goes offhook. The offhook
event is reported to MGC in the Notify command.

Step 27
MG3 to MGC:
   MEGACO/1 [209.110.59.35]:25000
   Transaction = 4001 {
      Context = 3 {
          Notify = TermC {ObservedEvents =1111 {

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            20050202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 28
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4001 {
       Context = 3 {Notify = TermC}
   }
The MGC now updates the UserC connected to the Residential gateway 3
with modify command to change the mode of the terminations set to
sendrecv.

Step 29:
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 3 {
         Modify = TermC {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphC{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }
The Residential gateway responds with the Modify response command.

Step 30
MG3 to MGC:
   MEGACO/1 [209.110.59.35]: 25000
   Reply = 1242 {
    Context = 3 {Modify = TermC , Modify = EphC}
   }
The MGC now updates the UserB connected to the Residential gateway 2
with the local SDP information of UserC as remote SDP information. The
Modify command with the remote SDP information is sent to RGW2, for the
ephemeral termination.

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Step 31
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1243 {
       Context = 2 {
          Modify = TermB {
                 Media{
                  LocalControl{ mode = sendrecv },
                    Remote {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                            }
          }
       }
   }
The RGW2 responds with the Modify response.

Step 32
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1243 {
    Context = 2 {Modify = TermB }
   }

The RGW2 updates the remote SDP information and generates the Modify
response towards MGC. The Media path is established between UserB and
UserC. The two users can be in conversation. The intention of this call
scenario is to illustrate the call that is initiated from UserA to
UserC. Now the UserB is in connection with UserC and after UserB goes
onhook the MGC modifies the remote SDP information of both
UserA and UserB. This makes the remote SDP of UserA point to
UserC and remote SDP information of UserA point to UserC. When the
UserB goes onhook the event is reported to MGC in the Notify command.

Step 33
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3003 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20060202T10000000:al/on}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 34

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MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3003 {
       Context = 2 {Notify = TermB}
   }
The MGC also subtracts the terminations TermB and EphB from context2.
The context also gets destroyed after deletion of the last termination.
The Subtract commands are generated in a single transaction.

Step 35
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1244 {
      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The MG2 responds to the subtract commands generated by MGC.

Step 36
MG2 to MGC:
   MEGACO/1 [209.176.47.89]:26000
   Reply = 1244 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
UserB is not in connection with UserA and UserC. The MGC
now initiates the Modify command towards UserA and UserC.

Step 37
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1245 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}

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              }
             }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The remote SDP information is updated for the ephemeral termination
EphA. The mode is changed to send receive. MG1 responds to the MGC
with the response for the Modify commands.

Step 38
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1245 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }

Similar command is generated towards UserC connected to RGW3.
Step 39
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1246 {
     Context = 3 {
       Modify = TermC {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
       },
       Modify = EphC {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4

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           }
       }
     }
   }
The remote SDP information is updated for the ephemeral termination
EphC. The mode is changed to send receive. MG3 responds to the MGC
with the response for the Modify commands.

Step 40
MG3 to MGC:
   MEGACO/1 [209.110.59.35]: 25000
   Reply = 1246 {
      Context = 3 {Modify = TermC, Modify = EphC}
   }
The users UserA and UserC can be in conversation as the modes are
changed to sendrecv. The call is transferred completely from UserB to
UserC. The call can be terminated by any of the users. The UserA after
the conversation goes onhook indicating the tearing down of the call.
The same is reported in the Notify command from MG1 to MGC.

Step 41
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2003 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
          }
      }
   }
The MGC responds to the MG1s Notify message.

Step 42
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2003 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC generates a Modify command towards the RGW3 for applying
busy tone to the called subscriber. The mode of both terminations is
set to receive only.

Step 43
MGC to RGW3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1247 {
     Context = 3 {
       Modify = TermC {

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         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphC {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The MG3 responds to this modify request.

Step 44
MG3 to MGC:
   MEGACO/1 [209.110.59.35]: 25000
   Reply = 1247 {
      Context = 3 {
         Modify= TermC, Modify = EphC}
   }

The MGC generates a transaction with two subtracts commands one for
physical and other for ephemeral terminations


Step 45:
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1248 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 46
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1248 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {

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             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

Step 47
MG3 to MGC:
   MEGACO/1 [209.110.59.35]:25000
   Transaction = 4002 {
      Context = 3 {
          Notify = TermC {ObservedEvents =1235 {
            20050202T10000000:al/on}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 48
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4002 {
       Context = 3 {Notify = TermC}
   }

The MGC generates Subtract command towards MG3.

Step 49
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1249 {
      Context = 3 {
         Subtract = TermC {Audit{ }},
         Subtract = EphC {Audit{Statistics}}
      }
   }
The MG3 responds to the subtract commands generated by MGC.

Step 50
MG3 to MGC:
   MEGACO/1 [209.110.59.34]:28000
   Reply = 1249 {
      Context = 3 {

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        Subtract = TermC
          Subtract = EphC {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates the message as shown in step 1 to all the three gateways,
 to enable the users to participate/initiate in further calls.


8.2 Call waiting


 The call waiting feature in Telephone networks enables a user to
receive two calls simultaneously. The user can switch between the calls.
In this example UserA calls UserB and when the conversation is taking
place UserC calls UserB. The UserB hears a call waiting tone and
switches to this new call using flash hook. UserC disconnects the call
and the UserB continues his conversation with UserA. The MGC should
support such features and UserB should subscribe for this feature. The
figure above suggests that all the three MG's are controlled by the
same MGC. Even though this many not true in real world this assumption
holds good for illustration purposes.

 _____________________________________________________________________
                |               |                |
      MG1       |      MGC      |      MG2       |       MG3
________________|_______________|________________|____________________
       |                 |               |                 |
       |<----------------|-------------->|                 |
       |Initial Modify   | Initial Modify|                 |
       |                 |-------------------------------->|
       |                 |        Initial Modify           |
       |---------------->|<--------------|                 |
       |Modify Response  | Modify Resp   |                 |
       |                 |<--------------------------------|
       |                 |       Modify Response           |
       |---------------->|               |                 |
       | Notify OffHook  |               |                 |
       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|               |                 |
       |Modify ED:dd/ce{DmapName=dmap1},al/on SD:cg/dt     |

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 <-----|---------------->|               |                 |
Dial   | Modify Resp     |               |                 |
Tone   |                 |               |                 |
------>|                 |               |                 |
Digits |---------------->|               |                 |
       |Notify Digits    |               |                 |
       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|-------------->|                 |
       |Modify ringback  | Modify Ring   |                 |
<------|---------------->|<--------------|                 |
ring   | Modify Resp     |  Modify Resp  |                 |
back   |                 |<--------------|                 |
       |                 |Notify OffHook |                 |
       |<----------------|-------------->|                 |
       | Add Phy         |Notify Resp    |                 |
       |Add Eph Local Unspecified        |                 |
       |---------------->|               |                 |
       |Add Phy Resp     |               |                 |
       |Add Eph Resp Local specified     |                 |
       |                 |-------------->|                 |
       |                 |Add Phy        |                 |
       |                 |Add Eph Local unspecified        |
       |                 |        Remote Specified         |
       |                 |<--------------|                 |
       |                 | Add Phy Resp  |                 |
       |                 | Add Eph Resp Local specified    |
       |<----------------|               |                 |
       | Modify Eph Remote Specified     |                 |
       |---------------->|               |                 |
       | Modify Resp     |               |                 |
       |/-------------------------------\|                 |
       |        RTP MEDIA                |                 |
       |\-------------------------------/|                 |
       |                 |<--------------------------------|
       |                 |           Notify OffHook        |
       |                 |<--------------------------------|
       |                 |           Notify Resp           |
       |                 |<--------------------------------|
       |                 |           Notify Digits         |
       |                 |-------------------------------->|
       |                 |           Notify Response       |
       |                 |-------------------------------->|
       |                 |        Add Phy SD:cg/rt         |
       |                 |        Add Eph Local Unspecified|
       |                 |               Remote Specified  |
       |                 |<--------------------------------|
       |                 |      Add Phy Resp               |
       |                 |      Add Eph Resp Local SPecified
       |                 |-------------->|                 |
       |                 |Modify SD:callwaiting tone       |
       |                 |<--------------|                 |
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       |                 |Modify Resp    |                 |
       |                 |<--------------|                 |
       |                 | Notify Flash  |                 |
       |<----------------|               |                 |
       |Modify Eph recvonly              |                 |
       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |---------------->|               |                 |
       |  Modify Resp    |-------------->|                 |
       |                 | Modify Eph    |                 |
       |                 |<--------------|                 |
       |                 |               |/---------------\|
       |                 |               |     RTP MEDIA   |
       |                 |               |\---------------/|
       |                 |<--------------------------------|
       |                 |          Notify OnHook          |
       |                 |-------------------------------->|
       |                 |          Notify Resp            |
       |                 |-------------->|                 |
       |                 | Modify SD:cg/bt                 |
       |                 |<--------------|                 |
       |                 | Modify Resp   |                 |
       |                 |<--------------|                 |
       |                 | Notify Flash  |                 |
       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |<----------------|               |                 |
       |  Modify Eph SendRecv            |                 |
       |---------------->|               |                 |
       | Modify Resp     |-------------->|                 |
       |                 | Modify Eph    |                 |
       |                 |<--------------|                 |
       |                 | Modify Resp   |                 |
       |/-------------------------------\|                 |
       |            RTP Media            |                 |
       |\-------------------------------/|                 |
       |---------------->|               |                 |
       | Notify OnHook   |               |                 |
       |<----------------|               |                 |
       | Notify Resp     |               |                 |
       |                 |-------------->|                 |
       |                 | Modify Phy SD:cg/bt             |
       |                 |<--------------|                 |
       |                 | Modify Resp   |                 |
       |<----------------|               |                 |
       | Sub TermA       |               |                 |
       | Sub EphA        |               |                 |
       |---------------->|               |                 |
       | Sub TermA Resp  |               |                 |
       | Sub EphA Resp Statistics        |                 |
       |                 |<--------------|                 |
       |                 | Notify OnHook |                 |
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       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |                 |-------------->|                 |
       |                 | Sub TermB     |                 |
       |                 | Sub EphB      |                 |
       |                 |<--------------|                 |
       |                 | Sub TermB Resp|                 |
       |                 | Sub EphB  Resp Statistics       |
_______|_________________|_______________|_________________|




The MGC generates the Modify message towards all the three Residential
gateways to check for off hook on the terminations. (A wildcard
command may also be used in this scenario but for simplicity we consider
only command to specific terminations). The MGC
in NULL context generated the command to the specific termination
TermA. The off hook event of the analog supervision package is used
here. The request identifier specified here in the example is 1111.
The mode of the termination is set to receive only. The stream
parameter is used with only the Local control descriptor.

Step 1
MGC to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        } ,
 Events = 1111 {al/of}
           }
       }
   }

MG after receiving the command from MGC accepts it and responds with
the transaction reply. Here for only MG1 is shown to generate the
response. In fact all the three RGW generates the response.

Step 2

   MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }



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In this example User A goes off hook. This event is detected by the
RGW1 and constructs the Notify message to the MGC. The MG uses the same
request id (1111) sent by the MGC in its initial command. The
timestamp of the event detected is also passed as a parameter to the
observed event.

Step 3
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 4
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The MGC in the following command issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a
digit map on the termination. The digit map name used in the example
is Dmap1 and the dial patter is 2XXX. The event descriptor lists digit
map completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the event
descriptor is 1112.

Step 5
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1{(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after receiving validation responds the Modify command responds the

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MGC and starts processing the descriptors listed.

Step 6
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the MGC.
 In this example the order of descriptor is signal descriptor, digit
map descriptor followed by Events descriptor. The MG first processes
the signal descriptor. The dial tone is applied to the Termination
specified. The Digit map is updated in the Database of the termination.
The Digit map is ACTIVE on the termination as the digit map
completion event is listed in the events descriptor with the digit map
name. A digit map is activated whenever a new event descriptor is
applied to the termination or embedded event descriptor is activated,
and that event descriptor contains a digit map completion event which
itself contains a digit map parameter. UserA after receiving the dial
tone starts dialing digits. In this example we will not dwell into the
different possible cases of digit dialing by the user. The digits dialed
by user match with the digitmap pattern. Lets assume that the user has
dialed 2992. MG detects the digits dialed and reports the same as parameter
to the digit map completion event. A notify command is generated from MG1 to
MGC. The MG again used the same request identifier as specified by the MGC.


Step 7
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.
Step 8
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example the called subscriber is connected to the
RGW2, which is again controlled by the same MGC. The MGC generates a
transaction with two commands clubbed into the same Action. The first

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command is to create a new context and add the physical termination
TermA into it. As the MGC is aware that the destination user UserB is
free it indicates MG1 to apply ringback tone to the termination of
UserA. The second command is generated to create an ephemeral
termination and add the created termination in the same context that
was created as a result of the earlier command. Here we assumed a single
set of SDP information indicating that Reserve group is not used. The
Reserve Value feature is also not used.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals { cg/rt }
                            }
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

In this example the connection fields IP address, the media field port
number are unspecified. The MG in its response indicates the IPAddress
and port number used. The contextID is also not specified indicating
the creation of a new context. In this example the MG creates a context
with contextID 1. The physical termination TermA is added to context 1.
 The mode of the physical termination was earlier set to Receiveonly
and in this message the ephemeral termination is requested to create
with Receiveonly mode. The ephemeral termination created in this
example is EphA. MG responds with the allocated IP address
209.110.59.33 and port number 30000.


Step 10
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,

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         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

MGC generates a similar transaction towards the RGW2. The ContextID
specified in the action is $. The first command adds the physical
termination TermB to the newly created context. The Signal descriptor
for this termination lists the ring signal of the analog line
supervision package. This alerting signal is applied to the
termination of the TermB. The Event descriptor specifies offhook event
of the analog line supervision package. The second Add is meant to
create an ephemeral termination. MGC has the local information for the
ephemeral termination EphA in the RGW1. This information is passed as
remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
                Events=1234{al/of},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4

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                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }
   }

MG2, after receiving the new transaction from MGC starts processing it.
It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ring" signal to
 be applied on the termination. The event descriptor lists the off
hook event. The RGW2 creates an ephemeral termination with TerminationId
EphB. The local information is under-specified from the MGC. The MG
allocates the necessary resources for processing the media descriptor
for the ephemeral termination. The MG responds to the MGC by specifying
the IP address reserved for the local connection. In this example MG2
reserves IP address 207.176.47.90 and port number 40000. The MG2
responds to MGC with the following transaction reply.

Step 12
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC waits for the UserB to go offhook. Once the UserB goes offhook,
MG2 reports the notification of the offhook event to the MGC.

Step 13
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}
      }
   }
The MGC responds to the MG2 with the Notify response.

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Step 14
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3000 {
       Context = 2 {Notify = TermB}
   }
The MGC generates a transaction towards MG2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook event.

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

The MG2 responds to the request from MGC.

Step 16
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC generates a message to the MG1 to stop the ringback tone and to
report the remote SDP information for the ephemeral termination EphA.
The mode of the two terminations TermA and EphA is set to send receive.

Step 17
MGC to MG1:

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, stops the ringback tone at the calling end. The remote SDP
information is updated for the ephemeral termination EphA. The mode is
changed to send receive. MG1 responds to the MGC with the response for
the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange media as the RTP streams are made
bi-directional. Now UserC goes offhook to initiate a call towards
UserB. The Residential gateway reports the Offhook event to MGC through
the Notify message.

Step 19
MG3 to MGC:
   MEGACO/1 [209.110.60.35]:25000
   Transaction = 4000 {
      Context = - {
          Notify = TermC {ObservedEvents =1111 {
            20040202T10000000:al/of}}
      }
   }

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MGC generates the Notify response.


Step 20
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4000 {
       Context = - {Notify = TermC}
   }

The MGC in the following command issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a
digit map on the termination. The digit map name used in the example is
Dmap1 and the dial patter is 2XXX. The event descriptor lists digit map
completion event of the DTMF detection package and onhook of the analog
line supervision package. The request id specified in the event
descriptor is 1112.

Step 21
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
       Context = - {
           Modify = TermC {
               Signals {cg/dt},
               DigitMap= Dmap1{(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after receiving the Modify command after validation responds to the
MGC and starts processing the descriptors listed.

Step 22
MG3 to MGC:
   MEGACO/1 [209.110.60.35]: 25000
   Reply = 1240 {
       Context = - {Modify = TermC}
   }
The Media gateway applies dial tone and waits for the user to enter the
digits. The UserC dials digits 2992. The same is reported to MGC
through the Notify command.

Step 23
MG3 to MGC:
MEGACO/1 [209.110.60.35]: 25000

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   Transaction = 4001 {
      Context = - {
          Notify = TermC {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 24
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4001 {
       Context = - {Notify = TermC}
   }


The MGC after analyzing the finds that another call is waiting for
UserB. Before generating any further commands to UserB, MGC generates
ADD command for physical and to create ephemeral termination towards
UserC in RGW3. In the Remote SDP information MGC provides the Local
SDP information of UserB. The Local SDP information of UserC is left
underspecified to enable the RGW3 choose those values.

Step 25
MGC to MG3:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1241 {
       Context = $ {
          Add = TermC  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/rt}
                Events=1234{al/of},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }

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             }
         }
      }
   }

MG3 after receiving the new transaction from MGC starts processing it.
It creates a new context with contextID 3. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ringback"
signal to be applied on the termination. The event descriptor lists
the off hook event. The RGW3 creates a ephemeral termination with
TerminationId EphC. The local information is under-specified from the
MGC. The MG allocates the necessary resources for processing the media
descriptor for the ephemeral termination. The MG responds to the MGC by
specifying the IP address reserved for the local connection. In this
example MG2 reserves IP address 192.168.0.160 and port number 50000.
The MG3 responds to MGC with the following transaction reply.

Step 26
MG3 to MGC:
   MEGACO/1 [209.110.60.35]: 25000
   Reply = 1241 {
      Context = 3 {
        Add = TermC,
         Add = EphC{
            Media {
                   Local {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }



If generates a Modify command to the UserB with call waiting tone in
the Signal Descriptor.

Step 27
MGC to MG2:
   MEGACO/1 [216.33.33.61]:26000
   Transaction = 1242 {
       Context = 2 {
          Modify = TermB  { Media {
                    LocalControl {Mode = SendRecv} },
               Signals {cg/cw}
                Events=1234{al/fl, al/on},
      }

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   }
MG2 generates the response for the Modify command generated by MGC.
Step 28
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1242 {
      Context = 2 {
          Modify= TermB }
      }
   }

The UserB press flash button on the phone and the Residential gateway
generates Notify command towards the MGC.

Step 29
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20040202T10000000:al/fl}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 30
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3001 {
       Context = 2 {Notify = TermB}
   }
The MGC now is aware that the UserB should be in voice conversation
with UserC instead of UserA. The MGC now has to update the remote SDP
information of UserC. Such that any the same local SDP information is
used by UserB to continue calling UserC. The Local SDP information of
UserC is provided as the remote SDP information to UserB. Since the
Ephemeral termination is already in context, the Modify command is
used by MGC to update the remote SDP information.

Step 31
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1243 {
     Context = 2 {
       Modify = TermB {
          Media {
            LocalControl {
              Mode = sendrecv}
              }

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             }
         Signals { }
       },
       Modify = EphB {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination TermB,
 stop the Call waiting tone at the calling end. The remote SDP
information is updated for the ephemeral termination EphB. The mode is
changed to send receive. MG2 responds to the MGC with the response for
the Modify commands.

Step 32
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1243 {
      Context = 2 {Modify = TermB, Modify = EphB}
   }
The MGC now generates a Modify command to change the mode of the
termination from receive only to send receive. At the same time MGC
also sends an empty signal descriptor to stop the ring back tone that
was earlier applied on termination TermC of UserC.

Step 33
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1244 {
     Context = 3 {
       Modify = TermC {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphC {
          Media {
            LocalControl {
              Mode = sendrecv}

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           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermC, stop the ringback tone at the calling end. The mode is changed
to send receive. MG3 responds to the MGC with the response for the
Modify commands.

Step 34
MG3 to MGC:
   MEGACO/1 [209.110.60.34]: 25000
   Reply = 1244 {
      Context = 3 {Modify = TermC, Modify = EphC}
   }
Now the UserB and UserC are connected (through RTP Media). After the
conversation in the example UserC goes onhook to termination its call
with UserB. The Onhook event is reported to MGC though the Notify
command.

Step 35
MG3 to MGC:
   MEGACO/1 [209.110.60.34]:25000
   Transaction = 4002 {
      Context = 3 {
          Notify = TermC {ObservedEvents =1234 {
             20050202T10030000:al/on}
          }
      }
   }
The MGC responds to the MG3s Notify message.

Step 36
MGC to RGW3:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 4002 {
      Context = 3 {
          Notify = TermC
      }
   }

The MGC generates Subtract command towards RGW3.

Step 37
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1245 {
      Context = 3 {
         Subtract = TermC {Audit{ }},
         Subtract = EphC {Audit{Statistics}}
      }

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   }
The MG3 responds to the subtract commands generated by MGC.

Step 38
MG3 to MGC:
   MEGACO/1 [209.110.59.35]:25000
   Reply = 1245 {
      Context = 3 {
        Subtract = TermC
          Subtract = EphC {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


The MGC generates a Modify command towards the RGW2 for applying busy
tone to the called subscriber. The mode of both terminations is set
to receive only.

Step 39
MGC to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1246 {
     Context = 2 {
       Modify = TermB {
         Signals {cg/bt}
        Events = 1235 { al/fl, al/on }
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphB {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }
The MG2 responds to this modify request.

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Step 40
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1246 {
      Context = 2 {
         Modify= TermB, Modify = EphB}
   }
The User B press flash to continue its call with UserA. The flash event
is reported to MGC in the Notify command.

Step 41
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3002 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20060202T10000000:al/fl}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 42
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3002 {
       Context = 2 {Notify = TermB}
   }
The MGC now generates a Modify command towards the UserB with the
Local SDP information of UserA as Remote SDP information for the
ephemeral termination EphB. This enables UserB to continue the call
with UserA.

Step 43
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1247 {
     Context = 2 {
       Modify = TermB {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphB {
          Media {
            LocalControl {

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              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermB, stop the busy tone at the calling end. The remote SDP
information is updated for the ephemeral termination EphB. The mode is
changed to send receive. MG2 responds to the MGC with the response for
the Modify commands.

Step 44
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1247 {
      Context = 2 {Modify = TermB, Modify = EphB}
   }
The UserB and UserA can continue their conversation. The call can be
tear down either by UserA or UserB. In this example we assume that
UserA terminates the Call. The UserA goes onhook and the users action
is reported to MGC using the Notify command.

Step 45
RGW1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
          }
      }
   }
The MGC responds to the MG1s Notify message.

Step 46
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC generates a Modify command towards the RGW2 for applying busy
tone to the called subscriber. The mode of both terminations is set to

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receive only.

Step 47
MGC to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1248 {
     Context = 2 {
       Modify = TermB {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphB {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The MG2 responds to this modify request.

Step 48
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1248 {
      Context = 2 {
         Modify= TermB, Modify = EphB}
   }

The MGC generates transactions with two subtracts commands one for
physical and other for ephemeral terminations. The MGC does the same
for both the Contexts one at RGW1 and the other at RGW2.

Step 49:
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1249 {
      Context = 1 {
         Subtract = TermA {Audit {}},
         Subtract = EphA {Audit {Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

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Step 50
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1249 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The UserB after hearing the busy tone goes onhook, the same is
recognized by the Media gateway and generates Notify command towards
the MGC.

Step 51
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3003 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20060202T10000000:al/on}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 52
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3002 {
       Context = 2 {Notify = TermB}
   }

The MGC then generates subtract commands towards RGW2.

Step 53
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1250 {

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      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The MG2 responds to the subtract commands generated by MGC.

Step 54
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1250 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates the message as shown in step 1 to all the Media Gateways,
to enable the users to participate/initiate in further calls.



9. Conferencing

A Media Gateway optionally performs media conferencing. Media Gateways
that support multipoint conferences might allow three or more
terminations in a context. In this section we will illustrate
conferencing between three users. These call flows makes use of the
Topology descriptor. A topology descriptor is used to specify flow
directions between terminations in a Context.


 _____________________________________________________________________
                  |               |                |
      MG1       |      MGC      |      MG2       |       MG3
________________|_______________|________________|____________________
       |                 |               |                 |
       |<----------------|-------------->|                 |
       |Initial Modify   | Initial Modify|                 |
       |                 |-------------------------------->|
       |                 |        Initial Modify           |
       |---------------->|<--------------|                 |

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       |Modify Response  | Modify Resp   |                 |
       |                 |<--------------------------------|
       |                 |       Modify Response           |
       |---------------->|               |                 |
       | Notify OffHook  |               |                 |
       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|               |                 |
       |Modify ED:dd/cd,al/on SD:cg/dt   |                 |
 <-----|---------------->|               |                 |
Dial   | Modify Resp     |               |                 |
Tone   |                 |               |                 |
------>|                 |               |                 |
Digits |---------------->|               |                 |
       |Notify Digits    |               |                 |
       |<----------------|               |                 |
       |Notify Response  |               |                 |
       |<----------------|-------------->|                 |
       |Modify ringback  | Modify Ring   |                 |
<------|---------------->|<--------------|                 |
ring   | Modify Resp     |  Modify Resp  |                 |
back   |<----------------|<--------------|                 |
       | Add Phy         |Notify OffHook |                 |
       |Add $   Local Unspecified        |                 |
       |                 |-------------->|                 |
       |                 |Notify Resp    |                 |
       |---------------->|               |                 |
       |Add Phy Resp     |               |                 |
       |Add EphAResp Local specified     |                 |
       |                 |-------------->|                 |
       |                 |Add Phy        |                 |
       |                 |Add $   Local unspecified Remote Specified
       |                 |-------------->|                 |
       |                 | Add Phy Resp Add EphB Resp Local Specified
       |<----------------|               |                 |
       | Modify EphA Remote Specified    |                 |
       |---------------->|               |                 |
       | Modify Resp     |               |                 |
       |/-------------------------------\|                 |
       |        RTP MEDIA                |                 |
       |\-------------------------------/|                 |
       |                 |<--------------|                 |
       |                 | Notify Flash  |                 |
       |                 |-------------->|                 |
       |<----------------| Notify Resp   |                 |
       | Modify RecvOnly |    ---------->|                 |
       |---------------->|    DialTone   |                 |
       | Modify Resp     |<--------------|                 |
       |                 | Notify Digits |                 |
       |                 |-------------->|                 |
       |                 |  Notify Resp  |                 |
       |                 |-------------------------------->|
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       |                 |         Modify Ring             |
       |                 |<--------------------------------|
       |                 |         Modify Response         |
       |                 |-------------->|                 |
       |                 | Modify Ringback tone            |
       |                 |<--------------|                 |
       |                 |  Modify Resp  |                 |
       |                 |<--------------------------------|
       |                 |      Notify OffHook             |
       |                 |-------------------------------->|
       |                 |            Notify Resp          |
       |                 |-------------------------------->|
       |                 |      Add Phy                    |
       |                 | Add Eph Local Unspecified Remote Specified
       |                 |<--------------------------------|
       |                 | Add Phy Resp Add EphC Resp Local Specified
       |                 |-------------->|                 |
       |                 | Modify EphBRemote               |
       |                 |<--------------|                 |
       |                 | Modify EphB Resp                |
       |                 |/-------------------------------\|
       |                 |            RTP Media            |
       |                 |\-------------------------------/|
       |                 |<--------------|                 |
       |                 | Notify Flash  |                 |
       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |<----------------|               |                 |
       |  Add $          |               |                 |
       |---------------->|               |                 |
       |  Add EphD Resp  |               |                 |
       |                 |-------------------------------->|
       |                 |           Add $                 |
       |                 |<--------------------------------|
       |                 |           Add EphF Resp         |
       |<----------------|               |                 |
       |   Mod EphD      |               |                 |
       |---------------->|               |                 |
       |   Mod EphD Resp |               |                 |
       |                 |-------------->|                 |
       |                 | Add $         |                 |
       |                 |<--------------|                 |
       |                 | Add EphE Resp |                 |
       |<----------------|               |                 |
       |    Mod EphA     |               |                 |
       |---------------->|               |                 |
       |  Mod EphA Resp  |               |                 |
       |                 |              / \                |
       |                 |              | |                |
       |/-------------------------------   ---------------\|
       |                   RTP MEDIA                       |
       |\-------------------------------------------------/|
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       |                 |<--------------|                 |
       |                 | Notify OnHook |                 |
       |                 |-------------->|                 |
       |                 | Notify Resp   |                 |
       |<----------------|               |                 |
       | Sub EphA        |-------------->|                 |
       |---------------->| Sub EphB,EphE |                 |
       | Sub EphA Resp   |<--------------|                 |
       |   statsitics    | Sub EphB Resp Statistics        |
       |                 | Sub EphE Resp Statistics        |
       |                 |-------------------------------->|
       |                 |       Sub EphC                  |
       |                 |<--------------------------------|
       |                 |       Sub EphC Resp statistics  |
       |/-------------------------------------------------\|
       |                  RTP MEDIA                        |
       |\-------------------------------------------------/|
       |                 |<--------------------------------|
       |                 |          Notify OnHook          |
       |                 |-------------------------------->|
       |                 |           Notify Resp           |
       |<----------------|               |                 |
       | Modify Phy busyTone             |                 |
       |---------------->|               |                 |
       | Modify Resp     |               |                 |
       |                 |-------------------------------->|
       |                 |          Sub Phy, Sub EphF      |
       |                 |<--------------------------------|
       |                 |         Sub Phy Resp            |
       |                 |         Sub EphF Resp Statistics|
       |---------------->|               |                 |
       | Notify OnHook   |               |                 |
       |<----------------|               |                 |
       | Notify Resp     |               |                 |
       |<----------------|               |                 |
       | Sub Phy         |               |                 |
       | Sub EphD        |               |                 |
       |---------------->|               |                 |
       | Sub Phy Resp    |               |                 |
       | Sub EphD Resp Statistics        |                 |
_______|_________________|_______________|_________________|____________









The conferencing feature in PSTN allows a user speak with
multiple users at the same time. This feature
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should be supported by MGC so that it is capable of generating required
messages towards MG. In this example we assume that the MGC is capable
of supporting Conferencing. UserB, the called party, initially receives
a call from UserA. For adding UserC, UserB press flash hook and dials
UserC number and after UserC answers the call goes flash hook again to
connect UserA and UserC. Now UserA, User B and UserC are in the call.

The MGC generates the Modify message towards all the three Residential
gateways to check for off hook on the terminations. (A wildcard
command may also be used in this scenario but for simplicity we consider
only command to specific terminations). We are not considering the
embedded signal and event descriptors here. The MGC in
NULL context generates the command to the specific termination TermA.
The off hook event of the analog supervision package is used here. The
request identifier specified here in the example is 1111. The mode of
the termination is set to receive only. The stream parameter is used
with only the Local control descriptor.


Step 1
MGC to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = ReceiveOnly}
                        } ,
 Events = 1111 {al/of}
           }
       }
   }

MG after receiving the command from MGC accepts it and responds with
the transaction reply. Here only MG1 is shown to generate the
response. In fact all the RGW generates the response.

Step 2

   MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
RGW1 and constructs the Notify message to the MGC. The MG uses the same
request id (1111) sent by the MGC in its initial command. The timestamp
of the event detected is also passed as a parameter to the observed event.


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Step 3
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 4
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

The MGC in the following command issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a digit
map on the termination. The digit map name used in the example is Dmap1
and the dial patter is 2XXX. The event descriptor lists digit map
completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the event
descriptor is 1112.

Step 5
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1{(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after validating the Modify command responds to the MGC and starts
processing the descriptors listed.

Step 6
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {

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       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the MGC.
In this example the order of descriptor is signal descriptor, digit map
descriptor followed by Events descriptor. The MG first processes the
signal descriptor. The dial tone is applied to the Termination
specified. The Digit map is updated in the Database of the termination.
 The Digit map will be made ACTIVE on the termination as the digit map
completion event is listed in the events descriptor with the digit map
name. A digit map is activated whenever a new event descriptor is
applied to the termination or embedded event descriptor is activated,
and that event descriptor contains a digit map completion event which
itself may contain a digit map parameter. UserA after receiving the dial
tone starts dialing digits. In this example we will not dwell into the
different possible cases of digit dialing by the user.The digits dialed
by the user match with the digit map pattern.
Lets assume that the user has dialed 2992. MG detects the digits
dialed and reports the same as parameter to the digit map completion
event. A notify command is generated from MG1 to MGC. The MG again
used the same request identifier as specified by the MGC.

Step 7
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce{ds="2992",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 8
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example the called subscriber is connected to the
RGW2, which is again controlled by the same MGC. The MGC generates a
transaction with two commands clubbed into the same Action. The first
 command is to create a new context and add the physical termination
TermA into it. As the MGC is aware that the destination user
UserB is free it instructs MG1 to apply ringback tone to the
termination of UserA. The second command is generated to create an
ephemeral termination and add the created termination in the same

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context that was created as a result of the earlier command. Here we
assumed a single set of SDP information indicating that Reserve group
is not used. The Reserve Value feature is also not used.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals { cg/rt }
                            }
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

In this example the connection fields IP address, the media field port
number are unspecified. The MG in its response indicates the IPAddress
and port number used. The contextID is also not specified indicating
the creation of a new context. In this example the MG creates a context
with contextID 1. The physical termination TermA is added to context 1.
The mode of the physical termination was earlier set to Receiveonly
and in this message the ephemeral termination is requested to create
with Receiveonly mode. The ephemeral termination created in this
example is EphA. MG responds with the allocated IP address
209.110.59.33 and port number 30000.


Step 10
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   c=IN IP4 209.110.59.33

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   m=audio 30000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

MGC generates a similar transaction towards the RGW2. The ContextID
specified in the action is $. The first command adds the physical
termination TermB to the newly created context. The Signal descriptor
for this termination lists the ring signal of the analog line
supervision package. This alerting signal is applied to the
termination of the TermB. The Event descriptor specifies offhook event
of the analog line supervision package. The second Add is meant to
create an ephemeral termination. MGC has the local information for the
ephemeral termination EphA in the RGW1. This information is passed as
remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
                Events=1234{al/of},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = Receiveonly,
                    },
                    Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4

                    },
                    Remote {
   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                }
             }
         }
      }

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   }

MG2 after receiving the new transaction from MGC starts processing it.
 It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ring" signal to
be applied on the termination. The event descriptor lists the off hook
event. The RGW2 creates a ephemeral termination with TerminationId
EphB. The local information is under-specified from the MGC. The MG
allocates the necessary resources for processing the media descriptor
for the ephemeral termination. The MG responds to the MGC by
specifying the IP address reserved for the local connection. In this
example MG2 reserves IP address 207.176.47.90 and port number 40000.
The MG2 responds to MGC with the following transaction reply.

Step 12
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
         }
      }
   }

The MGC waits for the UserB to go offhook. Once the UserB goes offhook,
MG2 reports the notification of the offhook event to the MGC.

Step 13
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}
      }
   }
The MGC responds to the MG2 with the Notify response.

Step 14
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3000 {

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       Context = 2 {Notify = TermB}
   }
The MGC generates a transaction towards MG2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook event, flash hook and the dd/ce event.

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on, al/fl { signals cg/dt, events
                    dd/ce{dmap1}, al/on }},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

The MG2 responds to the request from MGC.

Step 16
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC generates message to the MG1 to stop the ringback tone and to
report the remote SDP information for the ephemeral termination EphA.
The mode of the two terminations TermA and EphA is set to send
receive.

Step 17
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
     Context = 1 {

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       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
                   }
               } ; RTP profile for G723 is 4
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, stop the ringback tone at the calling end. The remote SDP
information is updated for the ephemeral termination EphA. The mode is
changed to send receive. MG1 responds to the MGC with the response for
the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange media, as the RTP streams are made
bi-directional. The figure below shows the terminations at both in
both the Contexts.


   +------------------------------------------------------+
   |                    RGW1                              |
   |     Context1                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy A     |     +-+      |     Eph A     |    |
<---->|               |<--->|*|<---->|    LocalA     |<------>
   |  |               |     +-+      |    RemoteB    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |

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   +------------------------------------------------------+


   +------------------------------------------------------+
   |                    RGW2                              |
   |     Context2                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy B     |     +-+      |     Eph B     |    |
<---->|               |<--->|*|<---->|    LocalB     |<------>
   |  |               |     +-+      |    RemoteA    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


The UserB now presses flash to dial the UserC number. The UserB flash
event is reported to MGC using the Notify message.

Step 19
MG2 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20040202T10000000:al/fl}}
      }
   }


MGC generates the Notify response.

Step 20
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3001 {
       Context = 2 {Notify = TermB}
   }
The UserB gets the dial tone and starts dialing the digits. In this
example the UserB dials the number 2804 of UserC.  The dialed digits
are reported to MGC using digit map completion event. The digits are
reported using the Notify command.

Step 21
MG2 to MGC:
MEGACO/1 [209.110.59.34]: 27000
   Transaction = 3002 {
      Context = 2 {
          Notify = TermB {Observed Events =1235 {

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            20040202T10010000:dd/ce{ds="2804",Meth=FM}}}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 22
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3002 {
       Context = 2 {Notify = TermB}
   }
The UserC is alerted with ring signal to indicate that a call is to be
received. The Add command for the physical termination TermC with
signal descriptor allows the ring signal to be applied on the
termination. The ephemeral termination is also requested to be created
with under specified Local SDP information and fully specified Remote
SDP information.

Step 23:
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1240 {
       Context = $ {
          Add = TermC {
                 Signals { al/ri }
                Events = 1111{ al/of embedded { al/on } }
                            }
          Add = $ {
              Media {
                {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
                  Remote {
   v=0
   c=IN IP4 207.176.47.90
   m=audio 40000 RTP/AVP 4
   }
               } ; RTP profile for G723 is 4
             }
          }
       }
   }


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In this example the SDP local information connection fields IP
address, the media field port numbers are unspecified. The MG in its
response indicates the IPAddress and port number used. The contextID is
also not specified indicating the creation of a new context. In this
example the MG creates a context with contextID 3. The physical
termination TermC is added to context 3. The mode of the physical
termination was earlier set to Receiveonly and in this message the
ephemeral termination is requested to create with Receiveonly mode.
The ephemeral termination created in this example is EphC. MG responds
with the allocated IP address 192.168.0.160 and port number 50000.

Step 24
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1240 {
      Context = 3 {
         Add = TermC,
         Add=EphC{
            Media {
                    Local {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }

The MGC generates ring back tone towards the UserB to indicate that
altering signal has been sent to the called party UserC.
Step 25
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
       Context = 2 {
          Modify = TermB {
                 Signals { cg/rt }
                            }
          }
       }
   }
The MG2 after receiving the Modify command applies the ring back tone
specified in the signals descriptor. The Modify response is sent back
to MGC.

Step 26
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000

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   Reply = 1241 {
      Context = 2 {
         Modify= TermB,
      }
   }
The UserC after receiving the ring signal goes offhook. The offhook
event is reported to MGC in the Notify command.

Step 27
MG3 to MGC:
   MEGACO/1 [209.110.59.34]:28000
   Transaction = 4001 {
      Context = 3 {
          Notify = TermC {ObservedEvents =1111 {
            20050202T10000000:al/of}}
      }
   }

MGC generates the Notify response and responds with further messages
towards the MG that generated the Notify command.

Step 28
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4001 {
       Context = 3 {Notify = TermC}
   }
The MGC now updates the UserC connected to the Residential gateway 3
with modify command to change the mode of the terminations set to
sendrecv.

Step 29:
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 3 {
         Modify = TermC {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphC{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }

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         }
      }
The Residential gateway responds with the Modify response command.

Step 30
MG3 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Reply = 1242 {
    Context = 3 {Modify = TermC , Modify = EphC}
   }
The MGC now updates the UserB connected to the Residential gateway 2
with the local SDP information of UserC as remote SDP information. The
Modify command with the remote SDP information is sent to RGW2, for
the ephemeral termination.

Step 31
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1243 {
       Context = 2 {
          Modify = TermB { Event = 1234 { al/fl, al/on }}
          Modify = EphB {
                 Media{
                  LocalControl{ mode = sendrecv },
                    Remote {
   v=0
   c=IN IP4 192.168.0.160
   m=audio 50000 RTP/AVP 4
                    } ; RTP profile for G.723 is 4
                            }
          }
       }
   }
The RGW2 responds with the Modify response.

Step 32
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 28000
   Reply = 1243 {
    Context = 2 {Modify = TermB, Modify = EphB }
   }

The RGW2 updates the remote SDP information and generates the Modify
response towards MGC. The Media path is established between UserB and
UserC. The two users can be in conversation. The following figure shows
the different context created and the terminations in these Contexts.


The MGC then generates a Modify command towards MG1. The UserA mode
is set to Receive only so that UserA generate RTP is not directed
towards UserB.

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Step 33
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1244 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = recvonly}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = recvonly}
       }
     }
   }


Step 34
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1244 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }




The Ephemeral termination EphB now has the Remote SDP information of
UserC. This enables the media flow between UserB and UserC. UserA, even
though is in valid context, doesn't generate any RTP media.

The UserB after the establishment of RTP media with UserC goes flash
hook to indicate the conference creation with UserA. The Notify event
from RGW2 is reported to MGC using the Notify message. The UserB press
flash button on the phone and the Residential gateway generates Notify
command towards the MGC.

Step 35
MG2 to MGC:
   MEGACO/1 [207.176.47.89]: 26000
   Transaction = 3003 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20050202T10000000:al/fl}}
      }

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   }

MGC generates the Notify.


Step 36
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3003 {
       Context = 2 {Notify = TermB}
   }


   +------------------------------------------------------+
   |                    RGW1                              |
   |     Context1                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy A     |     +-+      |     Eph A     |    |
<---->|               |<--->|*|<---->|    LocalA     |<------
   |  |               |     +-+      |    RemoteB    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


   +------------------------------------------------------+
   |                    RGW2                              |
   |     Context2                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy B     |     +-+      |     Eph B     |    |
<---->|               |<--->|*|<---->|    LocalB     |<------>
   |  |               |     +-+      |    RemoteC    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+

   +------------------------------------------------------+
   |                    RGW3                              |
   |     Context3                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy C     |     +-+      |     Eph C     |    |
<---->|               |<--->|*|<---->|    LocalC     |<------>
   |  |               |     +-+      |    RemoteB    |    |

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   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


This call flow section illustrates the call between three users.
Already UserB and UserC are connected. The UserA remote SDP information
points to the UserB. Now the MGC has to add one more ephemeral
termination in each of the contexts created at the three different user
Gateways. In this scenario we show that EphA, EphB and EphC are
initially created. EphA of UserA points to EphB of UserB, but since the
mode of the termination is "recvonly", this can be modified as required.
The EphB or UserB is virtually connected to EphC of UserC. The MGC for
connecting UserA and UserC generates Add command towards RGW1 for
creating an Ephemeral termination. After receiving the response of the
Add command indicating the creation of EphD, the MGC passes the local
SDP information of EphD in the Add command towards UserC for creation
of another Ephemeral termination. RGW3 creates Ephemeral Termination
EphF with remote information pointing towards EphD of UserA. The MGC
now after receiving response from UserC for EphF creation "Modifies"
the EphD with the remote SDP information of EphF. Thus connecting the
UserA and UserC. The topology descriptor is used to illustrate the
control of media flows between the terminations in the context.

The MGC generates Add command towards UserB for creating an Ephemeral
termination. The Local SDP information of EphA is passed as remote SDP
information for this newly created termination. After receiving the
response from UserB indicating the successful creation of EphE, the
local SDP information of EphE is passed to UserA as remote SDP
information for EphA in the "Modify" command. UserA's EphA is modified
to point towards the EphE of UserB. Now all the Users have 3
termination in their contexts. Thus enabling them to participate in
conference. The following paragraphs illustrates the different
messages exchanged in detail, to illustrate the addition of new user
in conference. The same can be extended to any number of users but
for simplicity, only 3 users are considered.

The MGC generates an add command towards MG1 for creation of another
ephemeral termination so that the media information is directed towards
UserC. The ephemeral termination is requested to be added in context 1.
 The topology descriptor that shows the directions of media flow inside
the context is initially set to ISOLOATE so that there is no media
immediately transferred between these termination within the context.

Step 37
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1244 {
       Context = 1
Topology TermA,EphA,isolate, TermA, $, isolate, EphA,$, isolate{

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          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
             }
          }
       }
   }

The Residential gateway now generates an ephemeral termination, with
newly allocated resources for it. The IP address that is allocated is
192.168.0.155 and the port number is 35000. The response is sent back
to MGC.

Step 38
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1244 {
      Context = 1 {
         Add=EphD{
            Media {
                    Local {
   v=0
   c=IN IP4 192.168.0.155
   m=audio 35000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }
The MGC after receiving this information generates another ADD command
towards the Residential gateway 3, such that the UserA SDP information
is indicated to UserC.

Step 39
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1245 {
       Context = 3
Topology TermC,EphC,bothway, TermC, $, bothway, EphC,$, bothway {
          Add = $ {
              Media {

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                {
                     LocalControl {
                         Mode = sendrecv,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
                    Remote {
   v=0
   c=IN IP4 192.168.0.155
   m=audio 35000 RTP/AVP 4
   a=sendrecv
                    } ; RTP profile for G.723 is 4
             }
          }
       }
   }

The Residential gateway now generates an ephemeral termination, with
newly allocated resources for it. The IP address that is allocated is
192.168.0.100 and the port number is 55000. The response is sent back
to MGC.

Step 40
MG3 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1245 {
      Context = 3 {
         Add=EphF{
            Media {
                    Local {
   v=0
   c=IN IP4 192.168.0.100
   m=audio 55000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }
The MGC after receiving the response from the UserC now indicates the
same information towards the Residential gateway 1. Thus enabling media
flow between the UserA and UserC.

Step 41
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1246 {

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       Context = 1
Topology TermA,EphA,isolate, TermA, EphD, bothway, EphA,EphD, isolate{
         Modify = EphD {
              Media {
                        {
                     LocalControl {
                         Mode = ReceiveOnly,
                    },
                     Remote {
   v=0
   c=IN IP4 192.168.0.100
   m=audio 55000 RTP/AVP 4
                }
             }
          }
       }
   }

The Residential gateway now generates the Modify response to the MGC.

Step 42
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1246 {
      Context = 1 {
         Modify=EphD
   }



   +------------------------------------------------------+
   |                    RGW1         +---------------+    |
   |     Context1                    |   EPHA        |    |
   |  +---------------+              |   Local A     |    |
   |  |               |-------~------|   Remote B    |<--------
   |  |               |       +------|               |    |
   |  |     Phy A     |       |      +---------------+    |
<---->|               |       |      +---------------+    |
   |  |               |       |      |     EphD      |    |
   |  |               |       +------|    Local A    |<------>
   |  |               |<------------>|   Remote C    |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


   +------------------------------------------------------+
   |                    RGW2                              |
   |     Context2                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |

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   |  |               |              |               |    |
   |  |     Phy B     |     +-+      |     Eph B     |    |
<---->|               |<--->|*|<---->|    LocalB     |<------>
   |  |               |     +-+      |    RemoteC    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+

   +------------------------------------------------------+
   |                    RGW3         +---------------+    |
   |     Context2                    |   EPHC        |    |
   |  +---------------+              |   Local C     |    |
   |  |               |<------------>|   Remote B    |<------->
   |  |               |      +------>|               |    |
   |  |     Phy C     |      |       +---------------+    |
<---->|               |      |       +---------------+    |
   |  |               |      |       |     EphF      |    |
   |  |               |      +------>|    Local C    |<------>
   |  |               |<------------>|   Remote A    |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


The UserA and UserC are in conversation now. The UserB and UserC were
already in conversation. Now the UserA and UserB need to be connected
through RTP media.  The MGC now generates ADD command towards the
UserB of the Residential gateway 2. The Local information of UserA is
indicated as the remote information of the newly created ephemeral
termination. This ephemeral termination is requested to be
added to the earlier context 2 itself.

Step 43
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1247 {
       Context = 2
Topology TermB,EphB,bothway, TermB, $, bothway, EphB,$, bothway {
          Add = $ {
              Media {
                        {
                     LocalControl {
                         Mode = sendrecv,
                    },
                     Local {
   v=0
   c=IN IP4 $
   m=audio $ RTP/AVP 4
                }
                    Remote {

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   v=0
   c=IN IP4 209.110.59.33
   m=audio 30000 RTP/AVP 4
   a=sendrecv
                    } ; RTP profile for G.723 is 4
             }
          }
       }
   }

The Residential gateway 2 now creates an ephemeral termination, with
newly allocated resources for it. The IP address that is allocated is
192.168.0.110 and the port number is 45000. The response is sent back
to MGC.

Step 44
MG2 to MGC:
   MEGACO/1 [209.110.59.34]: 26000
   Reply = 1247 {
      Context = 2 {
         Add=EphE{
            Media {
                    Local {
   v=0
   c=IN IP4 192.168.0.110
   m=audio 45000 RTP/AVP 4
   a=recvonly
                    } ; RTP profile for G.723 is 4
                }
            }
         }
      }
   }
The MGC after receiving the local SDP information update the Ephemeral
termination EphA of the Residential Gateway 1. The Modify command is
generated towards RGW1.

Step 45
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1248 {
       Context = 1
Topology TermA, EphA,bothway, TermA, EphD, bothway, EphA,EphD, bothway{
         Modify = EphA {
              Media {
                        {
                     LocalControl {
                         Mode = sendrecv,
                    },
                     Remote {
   v=0

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   c=IN IP4 192.168.0.110
   m=audio 45000 RTP/AVP 4
                }
             }
          }
       }
   }

The Residential gateway now generates the Modify response to the MGC.

Step 46
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1248 {
      Context = 1 {
         Modify=EphA
   }
All the terminations in all the contexts are made to sendrecv, thus all
the three users are effectively in conference. The following figure
shows the direction of media transfer between terminations inside each
of the contexts.




   +------------------------------------------------------+
   |                    RGW1         +---------------+    |
   |     Context1                    |   EPHA        |    |
   |  +---------------+              |   Local A     |    |
   |  |               |<------------>|   Remote B    |<------->
   |  |               |      +------>|               |    |
   |  |     Phy A     |      |       +---------------+    |
<---->|               |      |       +---------------+    |
   |  |               |      |       |     EphD      |    |
   |  |               |      +------>|    Local A    |<------>
   |  |               |<------------>|   Remote C    |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+



   +------------------------------------------------------+
   |                    RGW2         +---------------+    |
   |     Context2                    |   EPHB        |    |
   |  +---------------+              |   Local B     |    |
   |  |               |<------------>|   Remote C    |<------->
   |  |               |       +----->|               |    |
   |  |     Phy B     |       |      +---------------+    |
<---->|               |       |      +---------------+    |
   |  |               |       |      |     EphD      |    |

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   |  |               |      +------>|    Local B    |<------>
   |  |               |<------------>|   Remote A    |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


   +------------------------------------------------------+
   |                    RGW3         +---------------+    |
   |     Context3                    |   EPHC        |    |
   |  +---------------+              |   Local C     |    |
   |  |               |<------------>|   Remote B    |<------->
   |  |               |       +----->|               |    |
   |  |     Phy C     |       |      +---------------+    |
<---->|               |       |      +---------------+    |
   |  |               |       |      |     EphF      |    |
   |  |               |       +----->|    Local C    |<------>
   |  |               |<------------>|   Remote A    |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


In this example UserB goes onhook. The onhook event is reported to MGC
using the Notify message.

Step 47
MG2 to MGC:
   MEGACO/1 [207.176.47.89]:26000
   Transaction = 3006 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
             20010202T10030000:al/on}
          }
      }
   }

The MGC responds to the MG's notify message.
Step 48
MGC to MG2:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 3006 {
      Context = 2 {
          Notify = TermB
      }
   }
The MGC generates Subtract command towards the Residential Gateway 2 to
delete all the terminations in the context 2. The statistics are
requested only for the ephemeral terminations.

Step 49

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MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1249 {
      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
         Subtract = EphE {Audit{Statistics}}
      }
   }
The MG2 responds to the subtract commands generated by MGC.

Step 50
MG2 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1249 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          Subtract = EphE {
             Statistics {
                rtp/ps=1987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }

          }
      }
   }
The MGC generates Subtract command for the ephemeral termination EphA
towards the RGW1.

Step 51
MGC to MG2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1250 {
      Context = 1 {
         Subtract = EphA {Audit{Statistics}}
      }

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   }
The MG1 responds to the subtract commands generated by MGC.

Step 52
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1250 {
      Context = 2 {
          Subtract = EphA {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }
The MGC generates similar command towards UserC at RGW2, for
subtracting the ephemeral termination EphC.

Step 53
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1251 {
      Context = 3 {
         Subtract = EphC {Audit{Statistics}}
      }
   }
The MG3 responds to the subtract commands generated by MGC.

Step 54
MG3 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1251 {
      Context = 3 {
          Subtract = EphC {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }

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   }
Media connection is present only between UserA and UserC as shown in
figure below.

   +------------------------------------------------------+
   |                    RGW1                              |
   |     Context1                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy A     |              |     Eph D     |    |
<---->|               |<------------>|    LocalA     |<------>
   |  |               |              |    RemoteC    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+


   +------------------------------------------------------+
   |                    RGW3                              |
   |     Context3                                         |
   |  +---------------+              +---------------+    |
   |  |               |              |               |    |
   |  |               |              |               |    |
   |  |     Phy C     |              |     Eph F     |    |
<---->|               |<------------>|    LocalC     |<------>
   |  |               |              |    RemoteA    |    |
   |  |               |              |               |    |
   |  +---------------+              +---------------+    |
   |                                                      |
   +------------------------------------------------------+




After completing the conversation with UserA, UserC goes onhook. The
same is indicated towards MGC in the Notify command.

Step 55
MG3 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 4004 {
      Context = 3 {
          Notify = TermC {ObservedEvents =1111 {
             20060202T10030000:al/on}
          }
      }
   }

The MGC responds to the MG's notify message.

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Step 56
MGC to MG3:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 4004 {
      Context = 3 {
          Notify = TermC
      }
   }


The MGC generates a Modify command towards the RGW1 for applying busy
tone to the called subscriber. The mode of both terminations is set to
receive only.

Step 57
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1252 {
     Context = 1 {
       Modify = TermA {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphD {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The MG1 responds to this modify request.

Step 58
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1252 {
      Context = 1 {
         Modify= TermA, Modify = EphD}
   }


The MGC generates Subtract command RGW3.

Step 59
MGC to MG3:

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   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1254 {
      Context = 3 {
         Subtract = TermC {Audit{ }},
         Subtract = EphF {Audit{Statistics}}
      }
   }
The MG3 responds to the subtract commands generated by MGC.

Step 60
MG3 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1254 {
      Context = 3 {
        Subtract = TermC
          Subtract = EphF {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


The UserA goes onhook after hearing the busy tone. The same is
indicated to MGC using the Notify command.

Step 61
MG1 to MGC:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:al/on}
      }
   }

MGC after receiving the Notify command responds back with the Notify
response.

Step 62
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2002 {
       Context = 1 {Notify = TermA}

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   }

Step 63:
MGC to MG1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1253 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphD {Audit{Statistics}}
      }
   }
The MG subtracts the two terminations from the context. The context
itself is deleted with the "subtract" of the last termination from it.
The MG1 responds to this transaction from MGC with statistics on
ephemeral termination.

Step 64
MG1 to MGC:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1253 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphD {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

 10.0 SDP for ATM

 10.1 This section illustrates the usage of SDP for ATM. The draft "ATM
 SDP" [ref] is taken as reference. The two call establishment methods
 namely "Forward  Bearer Connection Set-up model" and the "Backward
 Connection Set-up model" are considered. In the first method, the ATM
 connection establishment is initiated by the Originating Media Gateway
 whereas in the second method the Terminating Media Gateway initiates
 the ATM connection establishment.

 The SDP atrribute "eecid" is used in both the methods. The "eecid"
 is a means of correlating service-level connections with underlying
 ATM bearer connections.

 In this example we assume that the Originating Media Gateway is

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 controlled by MGC1 and terminating Gateway controlled by MGC2. The
 communication protocol between the two MGC's is out-of-scope of this
 draft.

 10.1.1 Forward Bearer Connection Set-up Method

 In this call scenario we assume that the RGW1 and RGW2 are having ATM
 connectivity towards the PDN network. RGW1 is controlled by MGC1 and
 RGW2 is controlled by MGC2. The call is initiated by user connected
 to the RGW1.

 ______________________________________________________________________
                  |                 |               |
       RGW1       |     MGC1        |      MGC2     |    RGW2
__________________|_________________|_______________|________________
         |                 |                |               |
         |<----------------|                |-------------->|
         | Initial Modify  |                | Initial Modify|
         |---------------->|                |<--------------|
         | Modify Resp     |                | Modify Resp   |
  ------>|                 |                |               |
  OffHook|---------------->|                |               |
         | Notify OffHook  |                |               |
         |<----------------|                |               |
         | Notify Resp     |                |               |
 <-------|                 |                |               |
Dial Tone|                 |                |               |
 ------->|                 |                |               |
 Digits  |---------------->|                |               |
         | Notify Digits   |                |               |
         |<----------------|                |               |
         | Notify Resp     |--------------->|               |
         |                 |MGC-MGC protocol|               |
         |                 |  Address info  |               |
         |                 |                |-------------->|
         |                 |                | Modify PhyB   |------->
         |                 |                |<--------------|Ring
         |                 |                | Modify Resp   |
         |                 |<---------------|               |
         |                 | MGC-MGC Ring indication        |
         |<----------------|                |               |
         | Add PhyA SD:cg/rt                |               |
<--------| Add $ Local Unspecified          |               |
Ringback |---------------->|                |               |
         | Add PhyA Resp   |                |               |
         | Add EphA Resp   |                |               |<--------
         |                 |                |<--------------|OffHook
         |                 |                | Notify OffHook|
         |                 |--------------->|               |
         |                 | MGC-MGC SDPexchange            |
         |                 |                |-------------->|

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         |                 |                | Add PhyB      |
         |                 |                | Add $ Local Unspecified
         |                 |                |       Remote Specified
         |                 |                |<--------------|
         |                 |                | Add PhyB Resp |
         |                 |                | Add EphB Local Specified
         |                 |<---------------|               |
         |                 | MGC-MGC SDPexchange            |
         |<----------------|                |               |
         | Modify EphA Remote Specified     |               |
         |---------------->|                |               |
         | Modify EphA Resp|                |               |
         |/------------------------------------------------\|
         |                       MEDIA                      |
         |\------------------------------------------------/|
 ------->|                 |                |               |
 OnHook  |---------------->|                |               |
         | Notify OnHook   |                |               |
         |<----------------|--------------->|               |
         | Notify Resp     | MGC-MGC teardowninfo           |
         |                 |                |-------------->|
         |                 |                | Modify PhyB cg/bt
         |                 |                |<--------------|
         |<----------------|                |               |
         | Sub PhyA        |                |               |<-------
         | Sub EphA        |                |<--------------| OnHook
         |---------------->|                | Notify OnHook |
         | Sub PhyA Resp   |                |-------------->|
         | Sub EphA Reps Statistics         |-------------->|
         |                 |                | Sub PhyB      |
         |                 |                | Sub EphB      |
         |                 |                |<--------------|
         |                 |                | Sub PhyB Resp |
         |                 |                | Sub EphB Resp Statistics
_________|_________________|________________|_______________|________

In Step 1 the MGC1 generates the Modify message towards the
RGW1 and similarly MGC2 generates Modify message towards the RGW2 to
check for off hook on the terminations. (A wildcard command may also be
used in this scenario but for simplicity we consider only command to
specific terminations). Modify message generated only for Residential
gateway 1 is shown, similar message is sent to the other Residential
gateway also. We are not considering the embedded signal and event
descriptors here. The MGC in NULL context generates the command to the
specific termination TermA. The off hook event of the analog
supervision package is used here. The request identifier specified here
in the example is 1111. The mode of the termination is set to receive
only. The stream parameter is used with only the Local control
descriptor.



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Step 1

MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        },
 Events = 1111 {al/of}
           }
       }
   }

MG after receiving the command from MGC1 accepts it and responds with
the transaction reply.

Step 2

   MG1 to MGC2:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
RGW1 and constructs and sends the Notify message towards the MGC1. The
MG uses the same request id (1111) sent by the MGC1 in its initial
command. The timestamp of the detected event is also passed as
parameter to the observed event.

Step 3
MG1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
   }

MGC1 generates the Notify response and responds with more messages
towards the MG that generated the Notify command.

Step 4
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}
   }

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The MGC1 in the present example issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a digit
map on the termination. The digit map name used in the example is
Dmap1 and the dial pattern is 2XXX. The event descriptor lists digit
map completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the event
descriptor is 1112.

Step 5
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1 {(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after receiving the Modify command after validation responds to
the MGC1 and starts processing the descriptors listed.

Step 6
MG1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the
MGC1. In this example the order of descriptor is signal descriptor,
digit map descriptor followed by Events descriptor. The MG first
processes the signal descriptor. The dial tone is applied to the
Termination specified. The Digit map is updated in the Database of the
termination. The Digit map said to be ACTIVE on the termination as the
digit map completion event is listed in the events descriptor with the
digit map name. A digit map is activated whenever a new event
descriptor is applied to the termination or embedded event descriptor
is activated, and that event descriptor contains a digit map
completion event which itself contains a digit map parameter. UserA
after receiving the dial tone starts dialing digits. In this example
we will not dwell into the different possible cases of digit dialing
by the user. It's assumed that the user dials digits that match the
pattern specified in the digit map. Lets assume that the user has
dialed 2992. MG detects the digits dialed and reports the same as
parameter to the digit map completion event. A notify command is

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generated from MG1 to MGC1. The MG again used the same request
identifier as specified by the MGC1.

Step 7
MG1 to MGC1:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce {ds="2992", Meth=FM}}}
      }
   }

MGC1 after receiving the Notify command responds back with the Notify
response.

Step 8
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example it is assumed that the called subscriber is
connected to the RGW2, which is controlled by MGC2. The MGC1 communicates
to MGC2 that there is a call initiation for UserB.


The MGC1 generates a transaction with two commands clubbed into the same
Action. The first command is to create a new context and add the
physical termination TermA into it.  The second command is generated
to create an ephemeral termination and add the created termination
in the same context that was created because of the earlier command.
Here we assumed a single set of SDP information indicating that
Reserve group is not used. The Reserve Value feature is also not used.
The MGC1 thus initiates service-level call establishment by sending the
following control message to the RGW1.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals {cg/rt}
                            }
          Add = $ {
              Media {
                {
                     LocalControl {

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                         Mode = Receiveonly,
                    },
                     Local {
   v=0
   o=- 2873397497 0 ATM - -
   s=-
   c=ATM - -
   t=0 0
   m=audio $ - -
                }
             }
          }
       }
   }

In this example the connection field specifies only the connection type
(ATM). The other fields are unspecified as they are not needed.
The RGW1 in its response indicates its NSAP address. In this example the
RGW1 creates a context with contextID 1. The physical termination TermA
is added to context 1. The mode of the physical termination was earlier
set to Receiveonly and in this message the ephemeral termination is
requested to create with Receiveonly mode. The ephemeral termination
created in this example is EphA.


Step 10
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   o=- 2873397496 0 ATM
          NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0 m=audio - AAL2/ITU 8
   a=recvonly
                    }
                }
            }
         }
      }
   }

MGC2 after receiving the message from  MGC1 generates an Add command
towards the RGW2. The ContextID specified in the action is $. The first

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command adds the physical termination TermB to the newly created context.
 The Signal descriptor for this termination lists the ring signal of
the analog line supervision package. This alerting signal is applied to
the termination of the TermB. The Event descriptor specifies offhook event
of the analog line supervision package. The second Add is meant to create
an ephemeral termination. MGC2 has the local information for the
ephemeral termination EphA in the RGW1. This information is passed
as remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC2 to RGW2:
   MEGACO/1 [216.33.33.62]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
               Events =1234{al/of {events = 1235 {al/on}}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = sendrecv,
                    },
                    Local {
   v=0
   o=- 2873397497 0 ATM - -
   s=-
   c=ATM - -
   t=0 0
   m=audio $ - -
                    },
                    Remote {
   v=0
   o=- 2873397496 0 ATM
          NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0 m=audio - AAL2/ITU 8
                    }
                }
             }
         }
      }
   }

RGW2 after receiving the new transaction from MGC2 starts processing
it. It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor

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specified in the command. The signal descriptor lists "ring" signal
to be applied on the termination. The event descriptor lists the
off hook event. The RGW2 creates an ephemeral termination with
TerminationId EphB. The local information is under-specified from
the MGC2. The RGW2 allocates the necessary resources for processing the
media descriptor for the ephemeral termination. The RGW2 responds
to the MGC2 by providing an SDP descriptor with a locally assigned
"eecid". The MG2 responds to MGC with the following transaction reply.

Step 12
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
v=0
o=- 2873397714 0 ATM
 NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
s=-
c=ATM NSAP
   47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
t=0 0
m=audio - AAL2/ITU 8
a=eecid:B3D58E32
   }
               }
         }
      }
   }

The MGC2 waits for the UserB to go offhook. Once the UserB goes offhook,
RGW2 reports the notification of the offhook event to the MGC2.

Step 13
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}
      }
   }
The MGC2 responds to the RGW2 with the Notify response.

Step 14
MGC2 to RGW2:
   MEGACO/1 [216.33.33.60]: 27000
   Reply = 3000 {

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       Context = 2 {Notify = TermB}
   }
The MGC2 generates a transaction towards RGW2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook event.

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.60]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

The MG2 responds to the request from MGC.

Step 16
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC2 generates message to the MGC1 to indicate the "eecid" generated
by the RGW2. The MGC1 generates a Modify message towards the RGW1 to
stop the ringback tone and to report the remote SDP information for
the ephemeral termination EphA. The mode of the two terminations
TermA and EphA is set to send receive.

Step 17
MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
     Context = 1 {

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       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
                   Local {
v=0
o=- 2873397874 0 ATM - -
s=-
c=ATM - -
t=0 0
m=audio $ - -
a=bearerType:SVC on

                         }
                   Remote {
v=0
o=- 2873397714 0 ATM
   NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
s=-
c=ATM NSAP
       47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
t=0 0
m=audio $ AAL2/ITU 8
a=eecid:B3D58E32
                   }
               }
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, specifies to stop the ringback tone at the calling end. The
remote SDP information specifies the "eecid" to be used for the
ephemeral termination EphA. The RGW1 using this "eecid" initiates the
connection establishment. The Local SDP information with the media
attribute "bearerType" indicates that an SVC is to be used and that the
<localInitiation> flag is on i.e. the SVC is to be set up by the
terminating Media Gateway. The mode is changed to send receive. RGW1
responds to the MGC with the response for the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000

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   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange the media. The call can be termination
either by the calling user or the called user. In this example it is
assumed that the calling party has gone on-hook The UserA after the
conversation goes onhook indicating the tearing down of the call. The
same is reported in the Notify command from RGW1 to MGC1.

Step 19
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
      }
   }
The MGC1 responds to the MG1s Notify message.

Step 20
MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC2 after receiving the information from MGC1,  generates a Modify
command towards the RGW2 for applying busy tone to the called
subscriber. The mode of both terminations is set to receive only.

Step 21
MGC2 to RGW2:
   MEGACO/1 [216.33.33.60]: 27000
   Transaction = 1240 {
     Context = 2 {
       Modify = TermB {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphB {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }

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       }
     }
   }

The RGW2 responds to this modify request.

Step 22
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1240 {
      Context = 2 {
         Modify= TermB, Modify = EphB}
   }

The MGC1 generates transactions with two subtracts commands one for
physical and other for ephemeral terminations.

Step 23:
MGC1 to RGW1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The RGW1 subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The RGW1 responds to this transaction from MGC1 with statistics on
ephemeral termination.

Step 24
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1241 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }


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The User B after going onhook, the RGW2 generates Notify command
towards the MGC2.

Step 25
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20000202T10070000:al/on}}
      }
   }
The MGC2 responds to the RGW2 with the Notify response.

Step 26
MGC2 to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 3001 {
       Context = 2 {Notify = TermB}
   }

The MGC2 generates subtract command towards RGW2 for removing TermB
from valid context.

Step 26
MGC2 to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW2 responds to the subtract commands generated by MGC2.

Step 27
RGW2 to MGC2:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1242 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }

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          }
      }
   }

The two users UserA and UserB are ready for initiating/receiving further
calls.

 10.1.2 Backward Bearer Connection Set-up Method

 In this call scenario we assume that the RGW1 and RGW2 are having ATM
 connectivity towards the PDN network. RGW1 is controlled by MGC1 and
 RGW2 is controlled by MGC2. The call is initiated by user connected
 to the RGW1.

 ______________________________________________________________________
                  |                 |               |
       RGW1       |     MGC1        |      MGC2     |    RGW2
__________________|_________________|_______________|________________
         |                 |                |               |
         |<----------------|                |-------------->|
         | Initial Modify  |                | Initial Modify|
         |---------------->|                |<--------------|
         | Modify Resp     |                | Modify Resp   |
  ------>|                 |                |               |
  OffHook|---------------->|                |               |
         | Notify OffHook  |                |               |
         |<----------------|                |               |
         | Notify Resp     |                |               |
 <-------|                 |                |               |
Dial Tone|                 |                |               |
 ------->|                 |                |               |
 Digits  |---------------->|                |               |
         | Notify Digits   |                |               |
         |<----------------|                |               |
         | Notify Resp     |--------------->|               |
         |                 |MGC-MGC protocol|               |
         |                 |  Address info  |               |
         |                 |                |-------------->|
         |                 |                | Modify PhyB   |------->
         |                 |                |<--------------|Ring
         |                 |                | Modify Resp   |
         |                 |<---------------|               |
         |                 | MGC-MGC Ring indication        |
         |<----------------|                |               |
         | Add PhyA SD:cg/rt                |               |
<--------| Add $ Local Unspecified          |               |
Ringback |---------------->|                |               |
         | Add PhyA Resp   |                |               |
         | Add EphA Resp   |                |               |<--------
         |                 |                |<--------------|OffHook
         |                 |                | Notify OffHook|

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         |                 |--------------->|               |
         |                 | MGC-MGC SDPexchange            |
         |                 |                |-------------->|
         |                 |                | Add PhyB      |
         |                 |                | Add $ Local Unspecified
         |                 |                |       Remote Specified
         |                 |                |<--------------|
         |                 |                | Add PhyB Resp |
         |                 |                | Add EphB Local Specified
         |                 |<---------------|               |
         |                 |    MGC-MGC     |               |
         |<----------------|                |               |
         | Modify EphA sendrecv             |               |
         |---------------->|                |               |
         | Modify EphA Resp|                |               |
         |/------------------------------------------------\|
         |                       MEDIA                      |
         |\------------------------------------------------/|
 ------->|                 |                |               |
 OnHook  |---------------->|                |               |
         | Notify OnHook   |                |               |
         |<----------------|--------------->|               |
         | Notify Resp     | MGC-MGC teardowninfo           |
         |                 |                |-------------->|
         |                 |                | Modify PhyB cg/bt
         |                 |                |<--------------|
         |<----------------|                |               |
         | Sub PhyA        |                |               |<-------
         | Sub EphA        |                |<--------------| OnHook
         |---------------->|                | Notify OnHook |
         | Sub PhyA Resp   |                |-------------->|
         | Sub EphA Reps Statistics         |-------------->|
         |                 |                | Sub PhyB      |
         |                 |                | Sub EphB      |
         |                 |                |<--------------|
         |                 |                | Sub PhyB Resp |
         |                 |                | Sub EphB Resp Statistics
_________|_________________|________________|_______________|________

In Step 1 the MGC1 generates the Modify message towards the
RGW1 and similarly MGC2 generates Modify message towards the RGW2 to
check for off hook on the terminations. (A wildcard command may also be
used in this scenario but for simplicity we consider only command to
specific terminations). Modify message generated only for Residential
gateway 1 is shown, similar message is sent to the other Residential
gateway also. We are not considering the embedded signal and event
descriptors here. The MGC in NULL context generates the command to the
specific termination TermA. The off hook event of the analog
supervision package is used here. The request identifier specified here
in the example is 1111. The mode of the termination is set to receive
only. The stream parameter is used with only the Local control

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descriptor.

Step 1
MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1234 {
       Context = - {
           Modify = TermA {
               Media {
                        LocalControl {
                            Mode = Receiveonly}
                        },
 Events = 1111 {al/of}
           }
       }
   }

MG after receiving the command from MGC1 accepts it and responds with
the transaction reply.

Step 2

   MG1 to MGC2:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1234 {
      Context = - {Modify = TermA}
   }

In this example User A goes off hook. This event is detected by the
RGW1 and constructs and sends the Notify message towards the MGC1. The
MG uses the same request id (1111) sent by the MGC1 in its initial
command. The timestamp of the detected event is also passed as
parameter to the observed event.

Step 3
MG1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2000 {
      Context = - {
          Notify = TermA {ObservedEvents =1111 {
            20010202T10000000:al/of}}
   }

MGC1 generates the Notify response and responds with more messages
towards the MG that generated the Notify command.

Step 4
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2000 {
       Context = - {Notify = TermA}

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   }

The MGC1 in the present example issues a MODIFY command. The Modify
command contains a signal descriptor for the application of dial tone
to the user. The digit map descriptor here is used to configure a digit
map on the termination. The digit map name used in the example is
Dmap1 and the dial pattern is 2XXX. The event descriptor lists digit
map completion event of the DTMF detection package and onhook of the
analog line supervision package. The request id specified in the event
descriptor is 1112.

Step 5
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1235 {
       Context = - {
           Modify = TermA {
               Signals {cg/dt},
               DigitMap= Dmap1 {(2XXX)}
               Events = 1112 {
                   al/on, dd/ce {DigitMap=Dmap1}
               },
           }
       }
   }

MG after receiving the Modify command after validation responds to
the MGC1 and starts processing the descriptors listed.

Step 6
MG1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1235 {
       Context = - {Modify = TermA}
   }

The descriptors are processed in the order that is specified by the
MGC1. In this example the order of descriptor is signal descriptor,
digit map descriptor followed by Events descriptor. The MG first
processes the signal descriptor. The dial tone is applied to the
Termination specified. The Digit map is updated in the Database of the
termination. The Digit map said to be ACTIVE on the termination as the
digit map completion event is listed in the events descriptor with the
digit map name. A digit map is activated whenever a new event
descriptor is applied to the termination or embedded event descriptor
is activated, and that event descriptor contains a digit map
completion event which itself contains a digit map parameter. UserA
after receiving the dial tone starts dialing digits. In this example
we will not dwell into the different possible cases of digit dialing
by the user. It's assumed that the user dials digits that match the
pattern specified in the digit map. Lets assume that the user has

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dialed 2992. MG detects the digits dialed and reports the same as
parameter to the digit map completion event. A notify command is
generated from MG1 to MGC1. The MG again used the same request
identifier as specified by the MGC1.

Step 7
MG1 to MGC1:
MEGACO/1 [209.110.59.34]: 25000
   Transaction = 2001 {
      Context = - {
          Notify = TermA {ObservedEvents =1112 {
            20010202T10010000:dd/ce {ds="2992", Meth=FM}}}
      }
   }

MGC1 after receiving the Notify command responds back with the Notify
response.

Step 8
MGC1 to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Reply = 2001 {
       Context = - {Notify = TermA}
   }

MGC after receiving the Notify command starts analyzing the dialed
digits. In this example it is assumed that the called subscriber is
connected to the RGW2, which is controlled by MGC2. The MGC1 communicates
to MGC2 that there is a call initiation for UserB.


The MGC1 generates a transaction with two commands clubbed into the same
Action. The first command is to create a new context and add the
physical termination TermA into it.  The second command is generated
to create an ephemeral termination and add the created termination
in the same context that was created because of the earlier command.
Here we assumed a single set of SDP information indicating that
Reserve group is not used. The Reserve Value feature is also not used.
The MGC1 thus initiates service-level call establishment by sending the
following control message to the RGW1.

Step 9
MGC to MG1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1236 {
       Context = $ {
          Add = TermA {
                 Signals {cg/rt}
                            }
          Add = $ {
              Media {

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                        {
                     LocalControl {
                         Mode = Receiveonly,
                    },
                     Local {
   v=0
   o=- 2873397497 0 ATM - -
   s=-
   c=ATM - -
   t=0 0
   m=audio $ - -
                }
             }
          }
       }
   }

In this example the connection field specifies only the connection type
(ATM). The other fields are unspecified as they are not needed.
The RGW1 in its response indicates its NSAP address. In this example the
RGW1 creates a context with contextID 1. The physical termination TermA
is added to context 1. The mode of the physical termination was earlier
set to Receiveonly and in this message the ephemeral termination is
requested to create with Receiveonly mode. The ephemeral termination
created in this example is EphA. The RGW1 in its Local SDP information
specifies the "eecid" that needs to be used by the other RGW for
establishing an ATM SVC between RGW1 and RGW2.


Step 10
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1236 {
      Context = 1 {
         Add = TermA,
         Add=EphA{
            Media {
                    Local {
   v=0
   o=- 2873397496 0 ATM
          NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0
   m=audio - AAL2/ITU 8
   a=eecid:b3d58e32
                    }
                }
            }
         }

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      }
   }

MGC2 after receving the SDP information from  MGC1 generates an Add
command towards the RGW2. The ContextID specified in the action is $.
The first command adds the physical termination TermB to the newly
created context. The Signal descriptor for this termination lists the
ring signal of the analog line supervision package. This alerting signal
is applied to the termination of the TermB. The Event descriptor specifies
offhook event of the analog line supervision package. The second Add is
meant to create an ephemeral termination. MGC2 has the local information
for the ephemeral termination EphA in the RGW1. This information is passed
as remote information to the RGW2. The new ephemeral termination that
will be created will take these parameters as the remote SDP
information.

Step 11
MGC2 to RGW2:
   MEGACO/1 [216.33.33.62]:27000
   Transaction = 1237 {
       Context = $ {
          Add = TermB  { Media {
                    LocalControl {Mode = Receiveonly} },
               Signals {al/ri}
               Events =1234{al/of {events = 1235 {al/on}}},
               },
          Add  = $ {Media {
                    LocalControl {
                       Mode = sendrecv,
                    },
                    Local {
   v=0
   o=- 2873397497 0 ATM - -
   s=-
   c=ATM - -
   t=0 0
   m=audio $ - -
   a= bearerType:SVC on
                    },
                    Remote {
   v=0
   o=- 2873397496 0 ATM
          NSAP 47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   s=-
   c=ATM NSAP
     47.0091.8100.0000.0060.3E64.FD01.0060.3E64.FD01.00
   t=0 0 m=audio - AAL2/ITU 8
   a=eecid:b3d58e32
                    }
                }
             }

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         }
      }
   }

RGW2 after receiving the new transaction from MGC2 starts processing
it. It creates a new context with contextID 2. It adds the physical
termination TermB to that context and start processing the descriptor
specified in the command. The signal descriptor lists "ring" signal
to be applied on the termination. The event descriptor lists the
off hook event. The RGW2 creates an ephemeral termination with
TerminationId EphB. The local information is under-specified from
the MGC2. The RGW2 allocates the necessary resources for processing the
media descriptor for the ephemeral termination. The RGW2 creates an
SVC connection using the "eecid" specified in the remote descrptor. The
RGW2 as indicated by the MGC that an SVC is to be used as the
<localInitiation> flag is on in the Local SDP information.
The RGW2 responds to MGC2 with the following transaction reply.

Step 12
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1237 {
      Context = 2 {
        Add = TermB,
         Add = EphB{
            Media {
                   Local {
v=0
o=- 2873397714 0 ATM
 NSAP 47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
s=-
c=ATM NSAP
   47.0091.8100.0000.0040.2A74.EB03.0020.4421.2A04.00
t=0 0
m=audio - AAL2/ITU 8
             }
           }
         }
      }
   }

The MGC2 waits for the UserB to go offhook. Once the UserB goes offhook,
RGW2 reports the notification of the offhook event to the MGC2.

Step 13
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Transaction = 3000 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1234 {
            20000202T10020000:al/of}}

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      }
   }
The MGC2 responds to the RGW2 with the Notify response.

Step 14
MGC2 to RGW2:
   MEGACO/1 [216.33.33.60]: 27000
   Reply = 3000 {
       Context = 2 {Notify = TermB}
   }
The MGC2 generates a transaction towards RGW2 with two commands in one
action. It changes the mode of both the terminations to sendrecv. The
Signal descriptor of the Modify command for the first termination,
stops the ring signal already applied on the termination and the event
descriptor lists the onhook event.

Step 15:
MGC to MG2:
   MEGACO/1 [216.33.33.60]: 27000
   Transaction = 1238 {
      Context = 2 {
         Modify = TermB {
            Signals { } ; to turn off ringing
            Events = 1235 {al/on},
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
          }
         Modify = EphB{
            Media {
        LocalControl {
                       Mode = SendRecv,
                    }
              }
         }
      }

The MG2 responds to the request from MGC.

Step 16
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1238 {
    Context = 2 {Modify = TermB , Modify = EphB}
   }

The MGC2 generates message to the MGC1 to indicate using the "eecid"
sent earlier the SVC is created by the RGW2. The MGC1 generates a
Modify message towards the RGW1 to stop the ringback tone and to report

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the remote SDP information for the ephemeral termination EphA. The mode
of the two terminations TermA and EphA is set to send receive.

Step 17
MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1239 {
     Context = 1 {
       Modify = TermA {
          Media {
            LocalControl {
              Mode = sendrecv}
              }
             }
         Signals { }
       },
       Modify = EphA {
          Media {
            LocalControl {
              Mode = sendrecv}
               }
           }
       }
     }
   }
The empty signal descriptor in the Modify command for termination
TermA, specifies to stop the ringback tone at the calling end.
The mode is changed to send receive. RGW1 responds to the MGC1 with
the response for the Modify commands.

Step 18
MG1 to MGC:
   MEGACO/1 [209.110.59.34]: 25000
   Reply = 1239 {
      Context = 1 {Modify = TermA, Modify = EphA}
   }
The two users can exchange the media. The call can be termination
either by the calling user or the called user. In this example it is
assumed that the calling party has gone on-hook The UserA after the
conversation goes onhook indicating the tearing down of the call. The
same is reported in the Notify command from RGW1 to MGC1.

Step 19
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]:25000
   Transaction = 2002 {
      Context = 1 {
          Notify = TermA {ObservedEvents =1112 {
             20010202T10030000:al/on}
      }
   }

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The MGC1 responds to the MG1s Notify message.

Step 20
MGC1 to RGW1:
   MEGACO/1 [216.33.33.61]:27000
   Reply = 2002 {
      Context = 1 {
          Notify = TermA
      }
   }

The MGC2 after receiving the information from MGC1,  generates a Modify
command towards the RGW2 for applying busy tone to the called
subscriber. The mode of both terminations is set to receive only.

Step 21
MGC2 to RGW2:
   MEGACO/1 [216.33.33.60]: 27000
   Transaction = 1240 {
     Context = 2 {
       Modify = TermB {
         Signals {cg/bt}
          Media {
              LocalControl {
              Mode = recvonly}
               }
       },
       Modify = EphB {
          Media {
              LocalControl {
              Mode = recvonly}
               }
           }
       }
     }
   }

The RGW2 responds to this modify request.

Step 22
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Reply = 1240 {
      Context = 2 {
         Modify= TermB, Modify = EphB}
   }

The MGC1 generates transactions with two subtracts commands one for
physical and other for ephemeral terminations.

Step 23:

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MGC1 to RGW1
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1241 {
      Context = 1 {
         Subtract = TermA {Audit{ }},
         Subtract = EphA {Audit{Statistics}}
      }
   }
The RGW1 subtracts the two terminations from the context. The context
itself is deleted with the subtract of the last termination from it.
The RGW1 responds to this transaction from MGC1 with statistics on
ephemeral termination.

Step 24
RGW1 to MGC1:
   MEGACO/1 [209.110.59.34]:25000
   Reply = 1241 {
      Context = 1 {
        Subtract = TermA
          Subtract = EphA {
             Statistics {
                rtp/ps=1234, ; packets sent
                nt/os=56789, ; octets sent
                rtp/pr=987, ; packets received
                nt/or=65432, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The User B after going onhook, the RGW2 generates Notify command
towards the MGC2.

Step 25
RGW2 to MGC2:
   MEGACO/1 [207.176.47.90]: 26000
   Transaction = 3001 {
      Context = 2 {
          Notify = TermB {ObservedEvents =1235 {
            20000202T10070000:al/on}}
      }
   }
The MGC2 responds to the RGW2 with the Notify response.

Step 26
MGC2 to RGW2:
   MEGACO/1 [216.33.33.60]: 27000
   Reply = 3001 {

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       Context = 2 {Notify = TermB}
   }

The MGC2 generates subtract command towards RGW2 for removing TermB
from valid context.

Step 26
MGC2 to RGW2:
   MEGACO/1 [216.33.33.61]: 27000
   Transaction = 1242 {
      Context = 2 {
         Subtract = TermB {Audit{ }},
         Subtract = EphB {Audit{Statistics}}
      }
   }
The RGW2 responds to the subtract commands generated by MGC2.

Step 27
RGW2 to MGC2:
   MEGACO/1 [207.176.47.89]:26000
   Reply = 1242 {
      Context = 2 {
        Subtract = TermB
          Subtract = EphB {
             Statistics {
                rtp/ps=987, ; packets sent
                nt/os=65432, ; octets sent
                rtp/pr=1234, ; packets received
                nt/or=56789, ; octets received
                rtp/pl=10, ;  % packets lost
                rtp/jit=30,
                rtp/delay=30 ; average latency
             }
          }
      }
   }

The two users UserA and UserB are ready for initiating/receiving further
calls.



 Acknowledgements:
   The authors wish to thank several colleagues at Kenetec and in the
   industry who have contributed towards the development of these call
   flow document and who have reviewed and sent valuable technical
   comments. Special thanks to Mathi Packiam for providing timely
   comments. Basic call flows have been provided by the authors of the
   MGCP call flow document. Technical ideas/comments have been provided
   by Thillaivilagam Anand, Sarika Gupta, Mehul Shah, Peter Michielsen,
   Terry L Anderson and Sasitharan R.

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  AUTHOR'S ADDRESS

  Madhubabu Brahmanapally
  Kenetec Inc
  550 Spring Street
  Naugatuck, CT 06770
  Tel 203/723-4242 Extn-378
  Fax 203/723-4187
  Email: madhubabu@kenetec.com


  Prerepa Viswanadham
  Kenetec Inc
  550 Spring Street
  Naugatuck, CT 06770
  Tel 203/723-4242 Extn-373
  Fax 203/723-4187
  Email: dham.prerepa@kenetec.com

  Krishna Gundamaraju
  Kenetec Inc
  550 Spring Street
  Naugatuck, CT 06770
  Tel 203/723-4242 Extn-407
  Fax 203/723-4187
  Email: krishna.gundamaraju@kenetec.com
























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