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Versions: 00                                                            
Internet Engineering Task Force
INTERNET-DRAFT                                              Authors
Transport Working Group                                 J. Matousek
Category: Informational                                      L. Ong
June 1998                                              Bay Networks
Expires: January 1999

           Bay Networks SS7-Internet Access Signaling Protocol
                    <draft-long-ss7-signal-00.txt>


Status of this Memo

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documents of the Internet Engineering Task Force (IETF), its areas,
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Distribution of this document is unlimited.




Abstract

This memo describes the Bay Networks SS7 Access Signaling Protocol
(ASP).  This protocol is used between an SS7-Internet Gateway and a
Remote Access Server/Network Access Server (NAS).  The protocol
supports call setup and termination by both Gateway and Access
Server, and includes circuit management functions such as circuit
blocking and procedures for registration of the Access Server.










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Table of Contents

1. Introduction.................................................2
2. References...................................................2
3. Basic Principles.............................................3
4. Layer 3 Protocol Messages....................................5
5. Call Establishment Messages..................................8
6. Call Clearing Messages......................................10
7. Miscellaneous Q.931 Control Messages........................12
8. Q.931 Messages with Global Call Reference...................12
9. Maintenance Messages........................................14
10.Information Elements........................................20
11.Example Message Sequences...................................36
12.Error Handling..............................................42
13.Timers......................................................42
14.State Diagrams..............................................42
15.Acknowledgements............................................42
16.Contact Information.........................................42


1. Introduction

This document specifies a protocol that is used between an SS7-
Internet Gateway device and a NAS in the Bay Networks' SS7-Internet
Gateway Architecture.  The Gateway terminates standard Signaling
System 7 (SS7) protocol from a PSTN switch or Signal Transfer Point
(STP), and uses the Access Signaling Protocol (ASP) to communicate
with the NAS.


2. References

[1] ITU-T Recommendation Q.931 (1993), ISDN user-network interface
layer 3 specification for basic control

[2] ITU-T Recommendation Q.932 (1993), Generic procedures for the
control of ISDN supplementary services.

[3] Ulysses Black: ISDN and SS7 (Architecture for Digital Signaling
Networks)

[4] ITU-T Recommendation H.225.0 Media stream packetization and
synchronization on non-guaranteed quality of service LANs.

[5] ANSI T1.609-1990: Interworking between the ISDN User-Network
Interface Protocol and the SS7 ISUP

[6] CCITT Recommendation Q.699: Interworking between Digital
Subscriber Signaling System No. 1 and Signaling System No. 7

[7] TR 41459: ATT Network ISDN Primary Rate Interface

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3. Basic Principles

The following diagram shows the use of the SS7 Gateway and the ASP
for interworking of SS7 and Internet.

         ........................      ......
         .                      .      .
         .             +------+ .      .   +-------+
         .    SS7      |    / | .  SS7 .   |  SS7  |
         .    Network  | STP  |------------|Gateway|
         .            /| /    | .      .   +-------+
         .           / +------+ .      .       |
         .........../.../........      .       |
                   /   /               .      A|           I
       __________ /   / A-link         .      S|           n
      /              /                 .      P|           t
     /              /                  .       |           e
 +------+     +------+                 .     +-----+       r
 | PSTN |     | PSTN |-----TDM---------------| NAS |-------n
 | SCP  |     |Switch|-----------------------|     |Data   e
 +------+     +------+   Circuits      .     +-----+       t
                                       .
                                       .

       Figure 2: SS7-Internet Interworking for Call Setup

The transport of ASP between the Gateway and the NAS uses IP.  The
messaging defined in this document assumes reliable message
delivery between the Gateway and the NAS.

The ASP is modeled on the Digital Subscriber Signaling system 1
(DSS1) protocol that is defined in ITU-T specification Q.931, with
extensions to support additional functions required for the Gateway
interface.

- Q.931 is well understood and widely used
- the mapping from SS7 ISUP to Q.931 is documented in standards
- this allows easier standardization for interoperability

The protocol is extended using the Protocol Discriminator function
in Q.931 to define new messages and information elements, and can
be further extended using the same mechanism.

Some functions of Q.931, such as the overlap addressing function,
are not supported.

The ASP supports several maintenance procedures defined in SS7,
including:

- busying of trunks and channels
- graceful and abrupt shutdown of trunks

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- execution of circuit continuity check requested by either the
far-end switch or the SS7 gateway, during call establishment and
due to operator request.
(NOTE: In the case where an incoming IAM indicates continuity check
required on a previous circuit, i.e., previous hop, the SS7 Gateway
will delay the SETUP message to the NAS until it receives the COT
indicating continuity check successful.)

3.1  Mapping of the Circuit Identification Code (CIC)

The Access Server will be configured to identify each interface by
a number, typically in the range 1-n where n is the number of
interfaces supported by the Access Server.  The Access Server

registers with the Gateway, specifying the number of interfaces it
supports, and the Gateway uses internal configuration tables to
allow it to translate an interface number specified within the ASP
protocol into a Circuit Identification Code (CIC) as defined in
SS7.

For calls initiated by the NAS, the Gateway is responsible for
channel selection.  If a Circuit Reservation Message (CRM) is
received from the SS7 network reserving a specific circuit, the
Gateway will generate the Circuit Reservation Acknowledgement (CRA)
and mark that circuit reserved so that it is not selected for
outgoing calls until released by the SS7 network.

3.2  Security

The SS7 gateway acts as a fire-wall between the SS7 networks and
the IP signaling network. Access Servers on the IP signaling
network do not have direct access to the SS7 network - the gateway
must proxy for all the required functionality.

Both incoming and outgoing calls (from the NAS perspective) will be
supported by the protocol. However, configuration option in the
gateway and in the NAS must be provided, which will allow the
system administrator to inhibit the placement of outgoing calls
(from the NAS into the PSTN network).

It is also assumed that the IP signaling network will be physically
separate from the NAS user traffic. The NAS needs to support two
Ethernet interfaces and must ensure that the IP traffic from the
user traffic Ethernet cannot be forwarded to the IP signaling
traffic Ethernet and vice versa.


3.3 Redundancy

The SS7 Gateway will be implemented either using high availability
fault tolerant hardware or using standby fully redundant gateways.
In the case of hot standby gateways, the gateways must continuously

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synchronize their internal states on a call by call basis.  The
NAS, during the registration process, provides information that
allows the current active gateway to consolidate its internal
states.


4. Layer 3 Protocol Messages

With reference to the Q.931 specification, the SS7 Gateway will
implement the network side and the NAS will implement the user side
of the Q.931 protocol. This document specifies when specific
messages are used in one direction only, or both directions and
when specific information elements are used. Only the Q.931
information elements which are applicable to PRI (not BRI), have
been specified. Information elements specific to ASP have also been
defined.

The following notation has been used in the tables below:
- Mandatory: the message must be supported by both the gateway and
the NAS
- Optional: the message must be supported by both gateway and NAS,
but the protocol allows that the message not be sent during
particular protocol exchange
- Not supported: neither the gateway nor the NAS will support the
message.

The following table shows the Q.931 connection control Call
Establishment messages and indicates whether ASP supports them.

+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref.   |         |
+---------------------+--------------------+---------+---------+
| ALERTING            |  Not supported (1) |  3.1.1  |   N/A   |
+---------------------+--------------------+---------+---------+
| CALL PROCEEDING     |  Not supported     |  3.1.2  |   N/A   |
+---------------------+--------------------+---------+---------+
| CONNECT             |  Mandatory         |  3.1.3  |   3.1   |
+---------------------+--------------------+---------+---------+
| CONNECT ACKNOWLEDGE |  Not supported     |  3.1.4  |   N/A   |
+---------------------+--------------------+---------+---------+
| PROGRESS            |  Not supported     |  3.1.8  |   N/A   |
+---------------------+--------------------+---------+---------+
| SETUP               |  Mandatory         |  3.1.14 |   3.2   |
+---------------------+--------------------+---------+---------+
| SETUP   ACKNOWLEDGE |  Not supported     |  3.1.15 |   N/A   |
+---------------------+--------------------+---------+---------+

Note: (1) It is superfluous because it is assumed that the gateway
automatically generates ACM in response to IAM and at the same time
forwards SETUP to the NAS. It then only needs CONNECT from the NAS
to generate ANM to the SS7 network.


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The following table shows the Q.931 Call information phase messages
and indicates whether ASP supports them.

+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref    |         |
+---------------------+--------------------+---------+---------+
| RESUME              |  Not supported     |  3.1.11 |   N/A   |
+---------------------+--------------------+---------+---------+
| RESUME ACKNOWLEDGE  |  Not supported     |  3.1.12 |   N/A   |
+---------------------+--------------------+---------+---------+
| RESUME REJECT       |  Not supported     |  3.1.13 |   N/A   |
+---------------------+--------------------+---------+---------+
| SUSPEND             |  Not supported     |  3.1.18 |   N/A   |
+---------------------+--------------------+---------+---------+
| SUSPEND ACKNOWLEDGE |  Not supported     |  3.1.19 |   N/A   |
+---------------------+--------------------+---------+---------+
| SUSPEND REJECT      |  Not supported     |  3.1.20 |   N/A   |
+---------------------+--------------------+---------+---------+


The following table shows the Q.931 Call Clearing messages and
indicates whether ASP supports them.

+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref    |         |
+---------------------+--------------------+---------+---------+
| DISCONNECT (Note 1) |  Optional          |  3.1.5  |   6.1   |
+---------------------+--------------------+---------+---------+
| RELEASE             |  Mandatory         |  3.1.9  |   6.2   |
+---------------------+--------------------+---------+---------+
| RELEASE COMPLETE    |  Mandatory         |  3.1.10 |   6.2   |
+---------------------+--------------------+---------+---------+

Note:  1. Both the NAS and the gateway should allow the other side
to start the call clearing sequence by using the RELEASE message,
and respond with RELEASE COMPLETE.














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The following table shows Miscellaneous Q.931 Connection control
messages and indicates whether ASP supports them.

+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref    |         |
+---------------------+--------------------+---------+---------+
| INFORMATION         |  Not supported     |  3.1.6  |   N/A   |
+---------------------+--------------------+---------+---------+
| NOTIFY              |  Not supported     |  3.1.7  |   N/A   |
+---------------------+--------------------+---------+---------+
| STATUS              |  Mandatory         |  3.1.16 |   7.1   |
+---------------------+--------------------+---------+---------+
| STATUS INQUIRY      |  Mandatory         |  3.1.17 |   7.2   |
+---------------------+--------------------+---------+---------+


The following table shows the Q.931 messages with global call
reference and indicate whether ASP supports them

+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref    |         |
+---------------------+--------------------+---------+---------+
| RESTART             |  Mandatory         |  3.4.1  |   8.1   |
+---------------------+--------------------+---------+---------+
| RESTART ACKNOWLEDGE |  Mandatory         |  3.4.2  |   8.2   |
+---------------------+--------------------+---------+---------+
| STATUS              |  Mandatory         |  3.4.3  |   8.3   |
+---------------------+--------------------+---------+---------+




The following messages are extensions to the standard Q.931 message
set. They are sent with a different protocol discriminator (see
8.1). They are used to by the NAS to register its capability, its
interfaces and the state of each channel after an IP connection
between the NAS and the gateway is established. They are also used
by the NAS to report on state changes to an interface or a channel,
or by the gateway to request a state change of an interface or a
channel.










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+---------------------+--------------------+---------+---------+
|                     |  Support by the    |  Q.931  | Section |
|                     |  Gateway and NAS   |  Ref    |         |
+---------------------+--------------------+---------+---------+
| NAS STATUS          |  Mandatory         |  N/A    |   9.1   |
+---------------------+--------------------+---------+---------+
| NAS STATUS ACK      |  Mandatory         |  N/A    |   9.2   |
+---------------------+--------------------+---------+---------+
| INTERFACE STATUS    |  Mandatory         |  N/A    |   9.3   |
+---------------------+--------------------+---------+---------+
| INTERFACE STATUS ACK|  Mandatory         |  N/A    |   9.4   |
+---------------------+--------------------+---------+---------+
| RESOURCE UPDATE     |  Mandatory         |  N/A    |   9.5   |
+---------------------+--------------------+---------+---------+
| RESOURCE UPDATE ACK |  Mandatory         |  N/A    |   9.6   |
+---------------------+--------------------+---------+---------+
| SERVICE             |  Mandatory         |  N/A    |   9.7   |
+---------------------+--------------------+---------+---------+
| SERVICE ACK         |  Mandatory         |  N/A    |   9.8   |
+---------------------+--------------------+---------+---------+
| CONT CHECK RESULT   |  Mandatory         |  N/A    |   9.9   |
+---------------------+--------------------+---------+---------+


5. Call Establishment Messages

The following messages are used to establish a call.

5.1 CONNECT

This message is sent by the gateway to the NAS and by the NAS to
the gateway, in response to SETUP to indicate the acceptance of the
call.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Channel ID      |  10.6    |   M    | both  |   2-*  |
   +-----------------+----------+--------+-------+--------+






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3.2 SETUP

This message is sent by the gateway to the NAS and by the NAS to
the gateway to initiate a call.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Ref.    |  Type  | Direc | Length |
   | element         |          |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Bearer          |  10.7    |   M    | both  | 4-12   |
   | Capability      |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Channel ID      |  10.6    |   O    | both  |   3-*  |
   |                 |          |(note 1)|       |        |
   +-----------------+----------+--------+-------+--------+
   | Calling party   |  10.8    |   O    | both  |   2-*  |
   | number          |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Calling party   |  10.9    |   O    | both  |   2-23 |
   | subaddress      |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Called party    |  10.10   |   M    | both  |   2-*  |
   | number          |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Called party    |  10.11   |   O    | both  |   2-23 |
   | subaddress      |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Transit network |  10.12   |   O    | NAS-> |   2-*  |
   | selection       |          |(note 3)| G/W   |        |
   +-----------------+----------+--------+-------+--------+
   | Low layer       |  10.13   |   O    | both  |   2-18 |
   | compatibility   |          |(note 4)|       |        |
   +-----------------+----------+--------+-------+--------+
   | Shift to        |  10.4    |   O    | G/W-> |   2-*  |
   | codeset 7       |          |(note 2)| NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Original dialed |  10.18   |   O    | G/W-> |   2-*  |
   | number          |          |(note 2)| NAS   |        |
   +-----------------+----------+--------+-------+--------+

NOTES

1) Mandatory in the gateway-NAS direction. Not included in the NAS
to gateway direction - the gateway will select a specific
channel and indicate that in the CONNECT message.

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2) Including by the gateway if this information was provided in the
IAM message, if number translation occurred due to Local Number
Portability requirements.

3) Included by the NAS to select a particular transit network (see
Annex C of Q.931). This Information Element will not be used in
the first release.

4) Included in the NAS to gateway direction when the NAS wants to
pass low layer compatibility information to the called user.
Included in the gateway to NAS direction if the calling user
included a Low layer compatibility information element in the
SETUP message


6. Call Clearing Messages

The following messages are used to tear down calls either in the
process of being established or already established.

6.1 DISCONNECT

The NAS or the gateway sends this message to indicate that the
equipment sending the message (the gateway or the NAS) wishes to
disconnect a particular call.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | both  |  2-32  |
   +-----------------+----------+--------+-------+--------+














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6.2 RELEASE

The NAS or the gateway sends this message to indicate the receipt
of the DISCONNECT, has disconnected the channel (if any) and
intends to release the call reference when it receives RELEASE
COMPLETE.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   O    | both  |  2-32  |
   |                 |          |(note 1)|       |        |
   +-----------------+----------+--------+-------+--------+

Note 1: Mandatory if this is the first message when call clearing.

6.3 RELEASE COMPLETE

The NAS or the gateway sends this message to indicate that the
equipment sending the message (the gateway or the NAS) has released
the channel (if any) and call reference. The channel becomes
available for reuse and the receiving equipment shall release the
reference number.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   O    | both  |  2-32  |
   |                 |          |(note 1)|       |        |
   +-----------------+----------+--------+-------+--------+

Note 1: Mandatory if this is the first message when call clearing.





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7. Miscellaneous Q.931 Connection Control Messages

7.1 STATUS

The gateway or the NAS sends this message in response to the STATUS
ENQUIRY. This message is sent with the Call Reference specific to
the call.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | both  |  4-32  |
   +-----------------+----------+--------+-------+--------+
   | Call state      |  10.15   |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+


7.2 STATUS ENQUIRY

In order to determine the state of a specific call the STATUS
ENQUIRY message may be sent at any time. It will solicit a STATUS
message from the peer. It is mandatory to respond to STATUS
ENQUIRY with STATUS.  This message is sent with the Call Reference
specific to the call.
   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+

8. Q.931 Messages with Global Call Reference

The following messages with global call reference will be
supported.

8.1 RESTART

This message is sent by the NAS or by the gateway to request the

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recipient to restart (i.e. return to an idle condition) the
indicated channel(s) or interface. Any calls established on this
channel or interface will be disconnected.

   +-------------------+----------+--------+-------+--------+
   | Information       |  Refer-  |  Type  | Direc | Length |
   | element           |  ence    |        | tion  |        |
   +-------------------+----------+--------+-------+--------+
   | Protocol          |  10.1    |   M    | both  |   1    |
   | discriminator     |          |        |       |        |
   +-------------------+----------+--------+-------+--------+
   | Call Reference    |  10.2    |   M    | both  |   3    |
   +-------------------+----------+--------+-------+--------+
   | Message type      |  10.3    |   M    | both  |   1    |
   +-------------------+----------+--------+-------+--------+
   | Channel ID        |  10.6    |   M    | both  |  2-*   |
   +-------------------+----------+--------+-------+--------+
   | Restart Indicator |  10.16   |   M    | both  |   3    |
   +-------------------+----------+--------+-------+--------+


8.2 RESTART ACKNOWLEDGE

This message is sent to acknowledge the receipt of the RESTART
message and to indicate that the requested restart is complete.

   +-------------------+----------+--------+-------+--------+
   | Information       |  Refer-  |  Type  | Direc | Length |
   | element           |  ence    |        | tion  |        |
   +-------------------+----------+--------+-------+--------+
   | Protocol          |  10.1    |   M    | both  |   1    |
   | discriminator     |          |        |       |        |
   +-------------------+----------+--------+-------+--------+
   | Call Reference    |  10.2    |   M    | both  |   3    |
   +-------------------+----------+--------+-------+--------+
   | Message type      |  10.3    |   M    | both  |   1    |
   +-------------------+----------+--------+-------+--------+
   | Channel ID        |  10.6    |   M    | both  |  2-*   |
   +-------------------+----------+--------+-------+--------+
   | Restart Indicator |  10.16   |   M    | both  |   3    |
   +-------------------+----------+--------+-------+--------+











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8.3 STATUS

The NAS or the gateway sends this message at any time to
report certain error conditions listed in 10.14. In particular,
this message will be sent if the NAS or the gateway receives an
incorrectly formatted message, or a message which is not permitted
in a given state.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | both  |  4-32  |
   +-----------------+----------+--------+-------+--------+
   | Call state      |  10.15   |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+


9. Maintenance Messages

The following messages were defined as an extension to the standard
Q.931 based messages. The protocol discriminator is used to
distinguish them from the standard set.





















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9.1 NAS STATUS

This message is sent by the NAS to register the fact that it is
operational and whether it is coming out of a cold or warm start.
It can also be used to indicate by the NAS that it wishes to close
the connection with the gateway.
The message will be sent using non-global Call Reference.

   +-------------------+----------+--------+-------+--------+
   | Information       |  Refer-  |  Type  | Direc | Length |
   | element           |  ence    |        | tion  |        |
   +-------------------+----------+--------+-------+--------+
   | Protocol          |  10.1    |   M    | NAS-> |   1    |
   | discriminator     |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Call Reference    |  10.2    |   M    | NAS-> |   3    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Message type      |  10.3    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Shift to Codeset 7|  10.4    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | NAS status info   |  10.19   |   M    | NAS-> |   3    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+

9.2 NAS STATUS ACK

This message is sent by the gateway to NAS in response to NAS
STATUS. It will also indicate whether the gateway will allow the
NAS to receive only or also generate calls using the Cause
Information Element.

This message will be sent using non-global Call Reference.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | G/W-> |   1    |
   | discriminator   |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | G/W-> |   3    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | G/W-> |   1    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | G/W-> |  2-32  |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+

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9.3 INTERFACE STATUS

This message is sent by the NAS to the gateway to register the
available interfaces and to indicate the status of each channel on
that interface. Changes in the state of any interface or any
channel must be reported to the gateway using the SERVICE message.
Also, any call tear-down originated by NAS must be reported to the
gateway.

The gateway must process and respond to the INTERFACE STATUS
message before requesting any interface or channel state changes
using the SERVICE message. Once it responds to the INTERFACE STATUS
message, the gateway can also start originating and terminating
calls.

This message will use non-global Call Reference.

   +-------------------+----------+--------+-------+--------+
   | Information       |  Refer-  |  Type  | Direc | Length |
   | element           |  ence    |        | tion  |        |
   +-------------------+----------+--------+-------+--------+
   | Protocol          |  10.1    |   M    | NAS-> |   1    |
   | discriminator     |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Call Reference    |  10.2    |   M    | NAS-> |   3    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Message type      |  10.3    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Shift to Codeset 7|  10.4    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Interface status  |  10.21   |   M    | NAS-> |  17-21 |
   | info              |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+

9.4 INTERFACE STATUS ACK

This message is sent by the Gateway in response to INTERFACE STATUS
message. The Cause Information Element indicates the
success/failure of the interface registration operation.

This response will use non-global Call Reference.







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   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | G/W-> |   1    |
   | discriminator   |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | G/W-> |   3    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | G/W-> |   1    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | G/W-> |  2-32  |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+


9.5 RESOURCE UPDATE

This message is sent by the NAS to register the resources it
controls. The NAS will also send this message whenever the number
of resources has changed as a result of failure or administrator
action (e.g. modem failure).

The message will be sent using non-global Call Reference.
   +-------------------+----------+--------+-------+--------+
   | Information       |  Refer-  |  Type  | Direc | Length |
   | element           |  ence    |        | tion  |        |
   +-------------------+----------+--------+-------+--------+
   | Protocol          |  10.1    |   M    | NAS-> |   1    |
   | discriminator     |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Call Reference    |  10.2    |   M    | NAS-> |   3    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Message type      |  10.3    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | Shift to Codeset 7|  10.4    |   M    | NAS-> |   1    |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | NAS resource 1    |  10.20   |   M    | NAS-> |        |
   | (note 1)          |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+
   | ...               |          |        |       |        |
   +-------------------+----------+--------+-------+--------+
   | NAS resource n    |  10.20   |   O    | NAS-> |        |
   |                   |          |        | G/W   |        |
   +-------------------+----------+--------+-------+--------+

(1)  This information element can be repeated 1 to n times.

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9.6 RESOURCE UPDATE ACK

This message is sent by the gateway to NAS in response to RESOURCE
UPDATE.  This message will be sent using non-global Call Reference.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | G/W-> |   1    |
   | discriminator   |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | G/W-> |   3    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | G/W-> |   1    |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+
   | Cause           |  10.14   |   M    | G/W-> |  2-32  |
   |                 |          |        | NAS   |        |
   +-----------------+----------+--------+-------+--------+

9.7 SERVICE

The gateway sends this message to request a change of the current
status of an interface or channel. The NAS sends this message to
report to the gateway the change in status of a particular
interface or channel.

This message might result in SS7 Blocking or Unblocking messages
to be sent to the switch.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Channel ID      |  10.6    |   M    | both  |  3-6   |
   +-----------------+----------+--------+-------+--------+
   | Shift to        |  10.4    |   M    | both  |   1    |
   | Codeset 7       |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Change status   |  10.17   |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+


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9.8 SERVICE ACK

This message is sent as an acknowledgment to the SERVICE message.
If sent be the NAS, it indicates that the NAS is processing the
SERVICE request. If sent by the gateway, it indicates that the
gateway has recorded the change in status.

   +-----------------+----------+--------+-------+--------+
   | Information     |  Refer-  |  Type  | Direc | Length |
   | element         |  ence    |        | tion  |        |
   +-----------------+----------+--------+-------+--------+
   | Protocol        |  10.1    |   M    | both  |   1    |
   | discriminator   |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Call Reference  |  10.2    |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+
   | Message type    |  10.3    |   M    | both  |   1    |
   +-----------------+----------+--------+-------+--------+
   | Channel ID      |  10.6    |   M    | both  |  3-6   |
   +-----------------+----------+--------+-------+--------+
   | Shift to        |  10.4    |   M    | both  |   1    |
   | Codeset 7       |          |        |       |        |
   +-----------------+----------+--------+-------+--------+
   | Change status   |  10.17   |   M    | both  |   3    |
   +-----------------+----------+--------+-------+--------+


9.9 CONTINUITY CHECK RESULT

The NAS sends this message to report to the gateway the result of
continuity check for a particular channel.

   +-------------------+----------+--------+----------+--------+
   | Information       |  Refer-  |  Type  | Direc    | Length |
   | element           |  ence    |        | tion     |        |
   +-------------------+----------+--------+----------+--------+
   | Protocol          |  10.1    |   M    | NAS->G/W |   1    |
   | discriminator     |          |        |          |        |
   +-------------------+----------+--------+----------+--------+
   | Call Reference    |  10.2    |   M    | NAS->G/W |   3    |
   +-------------------+----------+--------+----------+--------+
   | Message type      |  10.3    |   M    | NAS->G/W |   1    |
   +-------------------+----------+--------+----------+--------+
   | Channel ID        |  10.6    |   M    | NAS->G/W |  3-6   |
   +-------------------+----------+--------+----------+--------+
   | Shift to Codeset 7|  10.4    |   M    | NAS->G/W |   1    |
   +-------------------+----------+--------+----------+--------+
   | Continuity result |  10.22   |   M    | NAS->G/W |   3    |
   +-------------------+----------+--------+----------+--------+


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10. Information Elements

10.1 Protocol Discriminator

The protocol discriminator is the first field (1 byte) of every
message. Two protocol discriminator values will be supported:
- Q.931 user-network call control messages. The value used will
be hex 08.
- Maintenance messages defined in section 7. The value used will
be hex 03.

10.2 Call Reference

Call reference is always the second field of every message.
The purpose of the call reference is to identify the call or
facility registration/cancellation request at the local gateway to
NAS interface to which the particular message applies. A sequence
of Call reference values will be allocated for each TCP/IP
connection. For the detail format of the information element refer
to Q.931 specification

Global Call Reference values will be supported.

The protocol between the gateway and NAS will always use Call
reference with length of 2.

10.3 Message Type

The message type is the third field. For the individual values of
Q.931 defined fields refer to section 4.4 of the Q.931
specification.

In the case when the protocol discriminator indicates Maintenance
message, the value of the message type will be:


















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   +------------------------------+--------+
   |    Message                   |  Hex   |
   |                              | Value  |
   +------------------------------+--------+
   |  NAS STATUS                  |   01   |
   +------------------------------+--------+
   |  NAS STATUS ACK              |   02   |
   +------------------------------+--------+
   |  INTERFACE STATUS            |   03   |
   +------------------------------+--------+
   |  INTERFACE STATUS ACK        |   04   |
   +------------------------------+--------+
   |  RESOURCE UPDATE             |   05   |
   +------------------------------+--------+
   |  RESOURCE UPDATE ACK         |   06   |
   +------------------------------+--------+
   |  SERVICE                     |   0F   |
   +------------------------------+--------+
   |  SERVICE ACK                 |   07   |
   +------------------------------+--------+
   |  CONTINUITY CHECK RESULT     |   08   |
   +------------------------------+--------+

10.4 Extension to Codesets

Refer to section 4.5.2 of the Q.931 for the definition of codeset
change procedures. The ASP will use the locking procedure to
codeset 7 (user defined) to define the Information Elements
specific to the
ASP.

10.5 Coding of Other Information Elements

All other Information Elements will be coded using the coding
rules for variable length information elements defined in section
4.5.1 of the Q.931 specification.  The Information Element
Identifier values for standard Q.931 elements are defined in
section 4 of the Q.931 specification.

The values of Information Elements identifiers defined specifically
in this document will be specified using locking shift into codeset
7. They are:











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   +------------------------------+--------+
   |    Information Element       |  Hex   |
   |                              | Value  |
   +------------------------------+--------+
   |  Original Dialed Number      |   01   |
   +------------------------------+--------+
   |  NAS Status Info             |   02   |
   +------------------------------+--------+
   |  NAS Resources               |   03   |
   +------------------------------+--------+
   |  Interface Status Info       |   04   |
   +------------------------------+--------+
   |  Change Status               |   05   |
   +------------------------------+--------+
   |  Continuity Result           |   07   |
   +------------------------------+--------+


10.6 Channel Identification

This information element will be coded according to the general
coding rules defined in section 4.5.1 of the Q.931 specification.
The specific definition of the coding of this element is in section
4.5.13 of the Q.931 specification.  The information element will be
coded as follows:



























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+-----+----------+----+---------+-------------------------+
|Octet| Field    |Bits| Value   |  Explanation            |
+-----+----------+----+---------+-------------------------+
|  1  |Extension | 8  |  0      | Multiple octets in      |
|     |          |    |         | element                 |
|     +----------+----+---------+-------------------------+
|     |IE Iden-  |7-1 | 0011000 | Channel Identification  |
+-----+----------+----+---------+-------------------------+
|  2  |Length    |8-1 | Binary  | Length of IE            |
+-----+----------+----+---------+-------------------------+
|  3  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Interface | 7  |   1     |Interface explicitly     |
|     |ID present|    |         |defined by this IE       |
|     +----------+----+---------+-------------------------+
|     |Interface | 6  |   1     |Primary rate             |
|     |type      |    |         |                         |
|     +----------+----+---------+-------------------------+
|     |Spare     | 5  |   0     |Spare                    |
|     +----------+----+---------+-------------------------+
|     |Preferred/| 4  |   1     |Exclusive; only the      |
|     |exclusive |    |         |indicated channel is     |
|     |          |    |         |acceptable               |
|     +----------+----+---------+-------------------------+
|     |D-channel | 3  |   0     |This is not D-channel    |
|     +----------+----+---------+-------------------------+
|     |Info      |2-1 |   00    |No channel specified -   |
|     |channel   |    |         |the message applies to   |
|     |selection |    |         | whole interface (1)     |
|     |          |    +---------+-------------------------+
|     |          |    |   01    |Channel defined in the   |
|     |          |    |         |following octets         |
+-----+----------+----+---------+-------------------------+
|  4  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Interface |7-1 | Binary  |Number assigned to       |
|     |          |    |         |interface (note 2)       |
+-----+----------+----+---------+-------------------------+
|  5  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Coding std|7-6 |   00    |ITU standardized         |
|     +----------+----+---------+-------------------------+
|     |Number/map| 5  |   0     |Channel is indicated     |
|     |          |    |         |by number                |
|     |          |    +---------+-------------------------+
|     |          |    |   1     |Channel is indicated by  |
|     |          |    |         |by slot map              |
|     +----------+----+---------+-------------------------+
|     |Channel   |4-1 |  0011   |B channel units          |
|     |type      |    |         |                         |
                     continued

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+-----+----------+----+---------+-------------------------+
| 6-n |Channel   |8-1 | Binary  |Binary number assigned to|
|     |number/   |    |         |the channel (note 3)     |
|     |slot map  |    |         |                         |
|     |          |    +---------+-------------------------+
|     |          |    | Binary  |Bit position in slot map |
|     |          |    |         |corresponding to the time|
|     |          |    |         |slots used by the channels|
|     |          |    |         |are set to 1 (note 4)    |
+-----+----------+----+---------+-------------------------+

Note:
(1) If the Info Channel Selection field is set to 00 (no channel
specified), the information element will end with octet 4. If
the field is set to 01, octets 5 onwards will be present.
(2) Interface identifier will be agreed between the gateway and
the NAS and configured on both. The gateway will be configured
to map interface numbers (with local meaning) to CICs.
(3) If the channel is indicated by number, the bit 8 will be used
as an extension bit and will be set to 1 to indicate that this
is the last octet of description.
(4) Refer to the Q.931 time-slot map definition for T1 and E1.
Bit map will not be implemented in the first release.


10.7 Bearer Capability

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.5 of the Q.931 specification.

This information element will be coded as follows.



















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+-----+----------+----+---------+-------------------------+
|Octet| Field    |Bits| Value   |  Explanation            |
+-----+----------+----+---------+-------------------------+
|  1  |Extension | 8  |  0      | Multiple octets in      |
|     |          |    |         | element                 |
|     +----------+----+---------+-------------------------+
|     |IE Iden-  |7-1 | 0000100 | Bearer Capability       |
|     |tifier    |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  2  |Length    |8-1 | Binary  | Length of IE            |
+-----+----------+----+---------+-------------------------+
|  3  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Coding    |7-6 |   00    |ITU-T standardized       |
|     |standard  |    |         |                         |
|     +----------+----+---------+-------------------------+
|     |Inform.   |5-1 | 00000   |Speech                   |
|     |transfer  |    +---------+-------------------------+
|     |capability|    | 01000   |Unrestricted digital info|
|     |          |    +---------+-------------------------+
|     |          |    | 01001   |Restricted digital info  |
|     |          |    +---------+-------------------------+
|     |          |    | 10000   |3.1 khz audio            |
+-----+----------+----+---------+-------------------------+
|  4  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Transfer  |7-6 |   00    |Circuit mode             |
|     |mode      |    |         |                         |
|     +----------+----+---------+-------------------------+
|     |Info      |5-1 | 10000   |64 kbit/s - circuit mode |
|     |transfer  |    |         |                         |
|     |rate      |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  5  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Layer 1   |7-6 |   01    |Layer 1 identification   |
|     |identif.  |    |         |coding                   |
|     +----------+----+---------+-------------------------+
|     |Layer 1   |5-1 |  00001  |rate adaption            |
|     |protocol  |    +---------+-------------------------+
|     |          |    |  00010  |u-law encoding           |
|     |          |    +---------+-------------------------+
|     |          |    |  00011  |a-law encoding           |
+-----+----------+----+---------+-------------------------+

Note:

(1) additional octets will be required to support V.110 rate
adaption, including the 56 K rate. For details refer to the
Q.931 specification.


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10.8 Calling Party Number

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.10 of the Q.931 specification.


10.9 Calling Party Subaddress

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.11 of the Q.931 specification.


10.10 Called Party Number

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.8 of the Q.931 specification.


10.11 Called Party Subaddress

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.9 of the Q.931 specification.


10.12 Transit Network Selection

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.29 of the Q.931 specification.


10.13 Low Layer Compatibility

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.19 of the Q.931 specification.






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10.14 Cause

This information element will be coded as follows:

+-----+----------+----+---------+-------------------------+
|Octet| Field    |Bits| Value   |  Explanation            |
+-----+----------+----+---------+-------------------------+
|  1  |Extension | 8  |  0      | Multiple octets in      |
|     |          |    |         | element                 |
|     +----------+----+---------+-------------------------+
|     |IE Iden-  |7-1 | 0001000 | Cause                   |
|     |tifier    |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  2  |Length    |8-1 | Binary  | Length of IE            |
+-----+----------+----+---------+-------------------------+
|  3  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Coding    |7-6 |   11    |Standard specific to     |
|     |standard  |    |         |location                 |
|     +----------+----+---------+-------------------------+
|     |Spare     | 5  |    0    |Spare                    |
|     |----------+----+---------+-------------------------+
|     |Location  |4-1 |  0001   |Private network serving  |
|     |          |    |         |local user               |
+-----+----------+----+---------+-------------------------+
|  4  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Cause     |7-1 |  Binary |See table below          |
|     |value     |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  5  |Diagnostic|8-1 | Binary  |See table below          |
| etc |          |    |         |                         |
+-----+----------+----+---------+-------------------------+



















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The following cause values will be used:
+--------+--------------------------------+--------------+
| Number |  Explanation                   | Diagnostics  |
+--------+--------------------------------+--------------+
|  01    | Unallocated (unassigned) number| None         |
+--------+--------------------------------+--------------+
|  06    | Channel unacceptable           | None         |
+--------+--------------------------------+--------------+
|  16    | Normal Call clearing           | None         |
+--------+--------------------------------+--------------+
|  17    | User busy                      | None         |
+--------+--------------------------------+--------------+
|  18    | No user responding             | None         |
+--------+--------------------------------+--------------+
|  21    | Call rejected                  | None         |
+--------+--------------------------------+--------------+
|  28    | Invalid number format          | Number IE    |
+--------+--------------------------------+--------------+
|  44    | Requested circuit/channel      | None         |
|        |  not available                 |              |
+--------+--------------------------------+--------------+
|  52    | Outgoing call barred           | None         |
+--------+--------------------------------+--------------+
|  54    | Incoming call barred           | None         |
+--------+--------------------------------+--------------+
|  65    | Bearer capability not implem.  | None         |
+--------+--------------------------------+--------------+
|  69    | Channel type not implemented   | None         |
+--------+--------------------------------+--------------+
|  81    | Invalid call reference         | None         |
+--------+--------------------------------+--------------+
|  96    | Mandatory Info Element missing | IE identifier|
+--------+--------------------------------+--------------+
|  97    | Message type non-existent or   | Message type |
|        |  not implemented               |              |
+--------+--------------------------------+--------------+
|  98    | Message not compatible with the| Message type |
|        | call state or message type not |              |
|        | existent or not implemented    |              |
+--------+--------------------------------+--------------+
|  99    | Information element non-       | IE identifier|
|        |  existent or not implemented   |              |
+--------+--------------------------------+--------------+
|  100   | Invalid IE Contents            | IE identifier|
+--------+--------------------------------+--------------+
|  125   | NAS registered for incoming    | None         |
|        |calls only                      |              |
+--------+--------------------------------+--------------+
|  126   | NAS registered for incoming    | None         |
|        |  and outgoing calls            |              |
+--------+--------------------------------+--------------+
|  127   | NAS registration rejected      | None         |
+--------+--------------------------------+--------------+

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10.15 Call State

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.7 of the Q.931 specification.

10.16 Restart Indicator

This information element will be coded according to the coding
rules defined in section 4.5.1 of the Q.931 specification.  The
specific definition of the coding of this element is in section
4.5.25 of the Q.931 specification.

All the specified values (indicated channel, single interface, all
interfaces) will be supported.

10.17 Change Status

This information element will be coded as follows.

+-----+----------+----+---------+-------------------------+
|Octet| Field    |Bits| Value   |  Explanation            |
+-----+----------+----+---------+-------------------------+
|  1  |Extension | 8  |  0      | Multiple octets in      |
|     |          |    |         | element                 |
|     +----------+----+---------+-------------------------+
|     |IE Iden-  |7-1 |         | Change Status           |
|     |tifier    |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  2  |Length    |8-1 | Binary  | Length of IE            |
+-----+----------+----+---------+-------------------------+
|  3  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Preference| 7  |   0     |Interface specified by   |
|     |          |    |         |Channel Identification IE|
|     |          |    +---------+-------------------------+
|     |          |    |  1      |Specific Channel speci-  |
|     |          |    |         |fied by                  |
|     |          |    |         |Channel Identification IE|
|     +----------+----+---------+-------------------------+
|     |Spare     |6-4 |  0000   |Spare                    |
|     +----------+----+---------+-------------------------+
|     |New Status|3-1 |   000   |In service               |
|     |          |    +---------+-------------------------+
|     |          |    |   001   |Loop back                |
|     |          |    +---------+-------------------------+
|     |          |    |   010   |Out of service           |
|     |          |    +---------+-------------------------+
|     |          |    |   011   |Request continuity check |
|     |          |    +---------+-------------------------+
|     |          |    |   100   |Graceful shutdown        |
+-----+----------+----+---------+-------------------------+

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The following table shows the relationship between the 'Preference"
field and the 'New Status' field when the request is originated by
the SS7 Gateway.

+------------+--------------------------+-------------------------+
|            | Interface Specified      | Channel Specified       |
+------------+--------------------------+-------------------------+
| In Service | The NAS will attempt to  | The NAS will mark the   |
|            | bring the T1/E1 into ser-| channel as available.   |
|            | vice.  The NAS will      | Established calls will  |
|            | respond with 'Out of     | not be affected.        |
|            | Service' if the T1/E1 is |                         |
|            | down (not framing).      |                         |
+------------+--------------------------+-------------------------+
| Loop Back  | The T1/E1 will be placed | The NAS will place the  |
|            | into loopback.  All esta-| DS0 into loopback state |
|            | blished calls will be    | if there is no esta-    |
|            | torn down.               | blished call.  The NAS  |
|            |                          | will respond with 'In   |
|            |                          | Service' if a call is   |
|            |                          | in progress.            |
+------------+--------------------------+-------------------------+
| Out of     | The NAS will place the   | The NAS will mark the   |
| Service    | T1/E1 into this state.   | DS0 and tear down any   |
|            | All established calls    | if there is no esta-    |
|            | will be torn down.       | established calls.      |
+------------+--------------------------+-------------------------+
| Request    | The NAS will reject this | The NAS will execute the|
| Continuity | message and send STATUS  | continuity check if     |
| Check      | message.                 | there is no established |
|            |                          | call.  The NAS will res-|
|            |                          | pond with 'In Service'  |
|            |                          | if a call is in progress|
+------------+--------------------------+-------------------------+
| Graceful   | The NAS will mark the    | The NAS will mark the   |
| Shutdown   | T1/E1.  It will not tear | DS0, but will not tear  |
|            | down any established     | down any established    |
|            | calls.                   | calls.                  |
+------------+--------------------------+-------------------------+













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The following shows the relationship between the "Preference" field
and "New Status" field when the request is originated by the NAS.

+------------+--------------------------+-------------------------+
|            | Interface Specified      | Channel Specified       |
+------------+--------------------------+-------------------------+
| In Service | The NAS will send this   | The NAS can send this   |
|            | message when the T1/E1   | request for Channels it |
|            | framing is achieved. The | previously took "Out of |
|            | Gateway should not change| Service".  The Gateway  |
|            | the state of any esta-   | should not change the   |
|            | blished call.            | state of any            |
|            |                          | established call.       |
+------------+--------------------------+-------------------------+
| Loop Back  | The NAS will not generate| The NAS will not gene-  |
|            | this request.  The Gate- | rate this request.  The |
|            | way should respond with  | Gateway should respond  |
|            | STATUS.                  | with STATUS.            |
+------------+--------------------------+-------------------------+
| Out of     | The NAS will place the   | The NAS will send this  |
| Service    | T1/E1 into this state if | message in the case of  |
|            | T1/E1 framing is lost or | modem failure.  Any     |
|            | if requested by the      | established call will   |
|            | operator.  All esta-     | be torn down.           |
|            | blished calls will be    |                         |
|            | torn down.               |                         |
+------------+--------------------------+-------------------------+
| Request    | The NAS will not send    | The NAS will use this   |
| Continuity | this message.  The Gate- | request as a result of  |
| Check      | way should respond with  | an operator request.    |
|            | STATUS.                  |                         |
+------------+--------------------------+-------------------------+
| Graceful   | The NAS will issue this  | The NAS will not issue  |
| Shutdown   | request as a result of an| this message.  The Gate-|
|            | operator request. Any    | way should reject this  |
|            | call in progress should  | message using the       |
|            | not be affected.         | STATUS message.         |
+------------+--------------------------+-------------------------+



10.18 Original Dialed Number

The format of this Information Element will be the same as for the
Called Party Number Information Element specified in section 4.5.8
of the Q.931.






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10.19 NAS Status Info

The format of this information element will be as follows:

+-----+----------+----+---------+-----------------------+
|Octet| Field    |Bits| Value   |  Explanation          |
+-----+----------+----+---------+-----------------------+
|  1  |Extension | 8  |  0      | Multiple octets in    |
|     |          |    |         | element               |
|     +----------+----+---------+-----------------------+
|     |IE Iden-  |7-1 |         | NAS Status Info       |
|     |tifier    |    |         |                       |
+-----+----------+----+---------+-----------------------+
|  2  |Length    |8-1 |   1     | Length of IE          |
+-----+----------+----+---------+-----------------------+
|  3  |Extension | 8  |   1     |Last octet             |
|     +----------+----+---------+-----------------------+
|     |Spare     |7-3 |  00000  |Spare                  |
|     +----------+----+---------+-----------------------+
|     |Status    |2-1 |   00    |Cold start: NAS coming |
|     |          |    |         | up after booting      |
|     |          |    +---------+-----------------------+
|     |          |    |   01    |Warm start: NAS is     |
|     |          |    |         | reestablishing gateway|
|     |          |    |         | connectivity          |
|     |          |    +---------+-----------------------+
|     |          |    |   10    |Hot shutdown: NAS will |
|     |          |    |         | disconnect abruptly.  |
|     |          |    |         | All calls should be   |
|     |          |    |         | terminated.           |
|     |          |    +---------+-----------------------+
|     |          |    |   11    |Soft shutdown: NAS will|
|     |          |    |         |shutdown when all calls|
|     |          |    |         | have terminated.      |
+-----+----------+----+---------+-----------------------+


















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10.20 NAS Resource

This information provides information regarding the NAS available
resources.

+-----+----------+----+---------+----------------------+
|Octet| Field    |Bits| Value   |  Explanation         |
+-----+----------+----+---------+----------------------+
|  1  |Extension | 8  |  0      | Multiple octets in   |
|     |          |    |         | element              |
|     +----------+----+---------+----------------------+
|     |IE Iden-  |7-1 |         | NAS Resources        |
|     |tifier    |    |         |                      |
+-----+----------+----+---------+----------------------+
|  2  |Length    |8-1 |   2     | Length of IE         |
+-----+----------+----+---------+----------------------+
|  3  |Extension | 8  |   1     |Last octet            |
|     +----------+----+---------+----------------------+
|     |Category  |7-5 |   001   |Modems                |
|     |          |    +---------+----------------------+
|     |          |    |   010   | HDLC channels        |
|     +----------+----+---------+----------------------+
|     |State     |4-1 |  0001   |Available             |
+-----+----------+----+---------+----------------------+
|  4  |Extension | 8  |   1     |Last octet            |
|     +----------+----+---------+----------------------+
|     |Capacity  |7-1 | Binary  |Count of resources in |
|     |          |    |         | that category        |
+-----+----------+----+---------+----------------------+























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10.21 Interface Status Info

This information element is used to specify the status of a given
interface and the status of all the associated channels.
+-----+----------+----+---------+-------------------------+
|Octet| Field    |Bits| Value   |  Explanation            |
+-----+----------+----+---------+-------------------------+
|  1  |Extension | 8  |  0      | Multiple octets in      |
|     |          |    |         | element                 |
|     +----------+----+---------+-------------------------+
|     |IE Iden-  |7-1 |         | Interface Status Info   |
|     |tifier    |    |         |                         |
+-----+----------+----+---------+-------------------------+
|  2  |Length    |8-1 | Binary  | Length of IE            |
+-----+----------+----+---------+-------------------------+
|  3  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Interface |7-1 |  Binary |Interface number         |
+-----+----------+----+---------+-------------------------+
|  4  |Extension | 8  |   1     |Last octet of description|
|     +----------+----+---------+-------------------------+
|     |Spare     |7-3 | 00000   |Spare                    |
|     +----------+----+---------+-------------------------+
|     |Interface |2-1 |   00    |In Service (up)          |
|     | status   |    +---------+-------------------------+
|     |          |    |   01    |Maintenance (loopback)(1)|
|     |          |    +---------+-------------------------+
|     |          |    |   10    |Out of Service (down)(1) |
+-----+----------+----+---------+-------------------------+
|  5  |Extension | 8  |   1     |Last octet               |
|     +----------+----+---------+-------------------------+
|     |Chan Count|7-1 | Binary  |Count of channels sup-   |
|     |          |    |         |ported by interface      |
+-----+----------+----+---------+-------------------------+
|  6  |Chan 1    |8-5 |  0000   |Idle - no existing calls |
|     |Status    |    +---------+-------------------------+
|     |          |    |  0001   |Unavailable/blocked      |
|     |          |    +---------+-------------------------+
|     |          |    |  0010   |Call in progress         |
|     +----------+----+---------+-------------------------+
|     |Chan 2    |4-1 |  0000   |Idle - no existing calls |
|     |Status    |    +---------+-------------------------+
|     |          |    |  0001   |Unavailable/blocked      |
|     |          |    +---------+-------------------------+
|     |          |    |  0010   |Call in progress         |
+-----+----------+----+---------+-------------------------+

Octet 6 is repeated until all channels defined by octet 5 are
specified.

Note 1:If the interface status is either Maintenance or Out of
Service, octets 6 onwards are not provided. Their state is implied
from the state of the interface.

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10.22 Continuity Result

This Information element is used to report the result of continuity
check performed by the NAS. The format will be as follows:

+-----+----------+----+---------+-----------------------+
|Octet| Field    |Bits| Value   |  Explanation          |
+-----+----------+----+---------+-----------------------+
|  1  |Extension | 8  |  0      | Multiple octets in    |
|     |          |    |         | element               |
|     +----------+----+---------+-----------------------+
|     |IE Iden-  |7-1 |         | Continuity Result     |
|     |tifier    |    |         |                       |
+-----+----------+----+---------+-----------------------+
|  2  |Length    |8-1 |   1     | Length of IE          |
+-----+----------+----+---------+-----------------------+
|  3  |Extension | 8  |   1     |Last octet             |
|     +----------+----+---------+-----------------------+
|     |Spare     |7-2 | 0000000 |Spare                  |
|     +----------+----+---------+-----------------------+
|     |Result    | 1  | 0       |Continuity Check failed|
|     |          |    +---------+-----------------------+
|     |          |    | 1       |Continuity Check suc-  |
|     |          |    |         |ceeded                 |
+-----+----------+----+---------+-----------------------+


























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11. Examples of Timing Diagrams

11.1 NAS Registers with Gateway for Service

The following timing diagram shows that the NAS is responsible for
the registration of the interfaces under its control.

NAS                            Gateway
|                               |
| NAS STATUS (cold start)       |
|------------------------------>|
| NAS STATUS ACK                |
|<------------------------------|
|                               |
| INTERFACE STATUS (i/f 1 up)   |
|------------------------------>|
| INTERFACE STATUS ACK          |
|<------------------------------|
|                               |
| INTERFACE STATUS (i/f 2 down) |
|------------------------------>|
| INTERFACE STATUS ACK          |
|<------------------------------|
|                               |
| RESOURCE UPDATE               |
|------------------------------>|
| RESOURCE UPDATE ACK           |
|<------------------------------|


11.2 Gateway Originated Normal Call Setup and Release

The following diagram shows successful Call establishment
for gateway originated calls.

NAS                            Gateway
|                               |
| SETUP  (Channel ID = n)       |
|<------------------------------|
| CONNECT                       |
|------------------------------>|
|                               |
| DISCONNECT                    |
|------------------------------>|
| RELEASE                       |
|<------------------------------|
| RELEASE COMPLETE              |
|------------------------------>|

Note: The disconnect sequence can be initiated by either the NAS or
by the gateway to hang-up the call.

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11.3 Call Setup with Alternative Call Clearing

The following diagram shows successful Call establishment
for gateway originated calls, using an alternative call clearing
sequence that is also allowed in the protocol.

NAS                            Gateway
|                               |
| SETUP (Channel ID = n)        |
|<------------------------------|
| CONNECT                       |
|------------------------------>|
|                               |
| RELEASE                       |
|<------------------------------|
| RELEASE COMPLETE              |
|------------------------------>|



11.4 NAS Originated Normal Call Setup

The following diagram shows successful Call establishment
for NAS originated calls.  For NAS originated calls, the Gateway
selects the channel to be used in the call.

NAS                            Gateway
|                               |
| SETUP(channel not specified)  |
|------------------------------>|
| CONNECT ( Channel ID = n )    |
|<------------------------------|
|                               |
| DISCONNECT                    |
|------------------------------>|
| RELEASE                       |
|<------------------------------|
| RELEASE COMPLETE              |
|------------------------------>|

Note: The disconnect sequence can be initiated by either the NAS or
by the gateway to hang-up the call.  Disconnection can be initiated
by either the DISCONNECT or RELEASE message.








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11.5 Unsuccessful Call Establishment Sequence

The following sequence illustrates when a call is rejected by the
NAS.

NAS                            Gateway
|                               |
| SETUP                         |
|<------------------------------|
| RELEASE COMPLETE              |
|------------------------------>|



11.6 Continuity check test as part of Incoming Call Setup - Success

The following sequence illustrates when the gateway receives an IAM
message indicating that a continuity test should be performed on
the circuit prior to the call establishment.

NAS                            Gateway
|                               |
| SERVICE (chan n loop back)    |
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|
|                               |
| SETUP                         |
|<------------------------------|
| CONNECT                       |
|------------------------------>|

Per Q.699 (3.1.18) continuity checking should be performed before
the SETUP is sent to the terminating end-point. SERVICE message
from the gateway to the NAS is used to initiate the loopback. If
the remote end-point indicates to the gateway that the continuity
check succeeded, the gateway proceeds with SETUP.















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11.6 Continuity check test as part of Incoming Call Setup - Failure

If the remote end indicates failure, the gateway will send SERVICE
message to the NAS requesting that the channel be placed into the
in service state.

NAS                            Gateway
|                               |
| SERVICE (chan n loop back)    |
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|
|                               |
| SERVICE (chan n in service)   |
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|



11.7 Continuity check test as part of Outgoing Call Setup - Success

The following sequence illustrates when the NAS initiates call
setup and the SS7 Gateway determines that continuity test should be
performed on the circuit prior to the call establishment.

NAS                            Gateway
|                               |
| SETUP (channel not specified) |
|------------------------------>|
|                               |
| SERVICE (chan n request       |
|             continuity check) |
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|
| CONTINUITY CHECK RESULT       |
|------------------------------>|
|                               |
| CONNECT (Channel ID = n)      |
|<------------------------------|











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11.8 Continuity check test initiated by the SS7 gateway operator

The gateway sends a SERVICE message to initiate the continuity
check. The NAS performs continuity check and reports the result
using the CONTINUITY CHECK RESULT.

NAS                            Gateway
|                               |
| SERVICE (chan n request       |
|             continuity check) |
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|
|                               |
| CONTINUITY CHECK RESULT       |
|------------------------------>|


11.7 NAS detects bearer T1/E1 line down (LOS, Red Alarm)


If the NAS detects that a particular T1/E1 line failed, it sends a
SERVICE message to the gateway. Established calls will be torn down
as part of normal processing - i.e the NAS modems will detect loss
of connection and the NAS will disconnect the call. The gateway
will request blocking of CICs associated with the particular T1/E1
using an SS7 Blocking or Circuit Group Blocking Message.

NAS                            Gateway
|                               |
| SERVICE (i/f 1 out-of-service)|
|------------------------------>|
| SERVICE ACK                   |
|<------------------------------|


11.8 Individual bearer channel taken out-of-service by NAS

NAS                            Gateway
|                               |
| SERVICE(chan n out-of-service)|
|------------------------------>|
| SERVICE ACK                   |
|<------------------------------|








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11.9 Individual bearer channel taken out-of-service by Gateway
operator

NAS                            Gateway
|                               |
| SERVICE(chan n out-of-service)|
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|


11.10 Bearer T1/E1 trunk abrupt shutdown initiated by Gateway
operator

NAS                            Gateway
|                               |
| SERVICE (i/f n out-of-service)|
|<------------------------------|
| SERVICE ACK                   |
|------------------------------>|


11.11 Bearer T1/E1 trunk abrupt shutdown initiated by NAS

NAS                            Gateway
|                               |
| SERVICE (i/f n out-of-service)|
|------------------------------>|

| SERVICE ACK                   |
|<------------------------------|


11.12 Bearer T1/E1 trunk graceful shutdown initiated by Gateway
operator

NAS                               Gateway
|                                   |
| SERVICE (i/f n graceful shutdown) |
|<----------------------------------|
| SERVICE ACK                       |
|---------------------------------->|


11.13 Bearer T1/E1 trunk graceful shutdown initiated by NAS

NAS                               Gateway
|                                   |

| SERVICE (i/f n graceful shutdown) |
|---------------------------------->|
| SERVICE ACK                       |
|<----------------------------------|

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10. Error Handling


Refer to section 3.7.8 of TR 41459 ATT Network ISDN Primary Rate
Interface. This section defines how to handle error conditions such
as Call reference errors, message type errors , etc. The ASP will
use the error procedures.


11. Timers

To be provided.


12. State Diagrams

To be provided.


13. Acknowledgements

The authors would like to acknowledge Mehdi Ghasem, Wan Man and Ki
Suh of Stratus Computer, as well as Miguel Sasson of Bay Networks
for their helpful review and comments on this protocol specification.


14. Contact Information

Jiri Matousek          Lyndon Ong
Bay Networks, Inc.     Bay Networks, Inc.
5 Federal Street       4401 Gt America Pkwy
Billerica, MA 01821    Santa Clara, CA 95052

jiri@baynetworks.com   long@baynetworks.com




           EXPIRES JANUARY 1999













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