Internet Draft H. Lu (Editor)
draft-ietf-spirits-implementations-02.txt I. Faynberg
September 2000 J. Voelker
Expires March 2001 M. Weissman
W. Zhang
Lucent Technologies
S. Rhim
J. Hwang
Korea Telecom
S. Ago
S. Moeenuddin
S. Hadvani
NEC
S. Nyckelgard
Telia
J. Yoakum
L. Robart
Nortel Networks
Pre-Spirits Implementations of PSTN-initiated Services
Status of this Memo
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Abstract
This document contains information relevant to the work underway in
The Services in the PSTN/IN Requesting InTernet Services (SPIRITS)
Working Group. It describes four existing implementations of
SPIRITS-like services from Korea Telecom, Lucent Technologies, NEC,
and Telia in cooperation with Nortel Networks. SPIRITS-like services
are those originating in the Public Switched Telephone Network (PSTN)
and necessitating the interactions of the Internet and PSTN.
Surveying the implementations, we can make the following
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SPIRITS [Page 2]
observations:
o The ICW service plays the role of a benchmark service. All four
implementations can support ICW, with three specifically
designed for it.
o Session Initiation Protocol (SIP) is used in most of the imple-
mentations as the base communications protocol between the PSTN
and Internet. (NEC's implementation is the only exception that
uses a proprietary protocol. Nevertheless, NEC has a plan to
support SIP together with the extensions for SPIRITS services.)
o All implementations use IN-based solutions for the PSTN part.
It is clear that not all pre-SPIRITS implementations inter-operate
with each other. It is also clear that not all SIP-based implementa-
tions inter-operate with each other given that they do not support
the same version of SIP. It is a task of the SPIRITS Working Group
to define the inter-networking interfaces that will support inter-
operation of the future implementations of SPIRITS services.
1. Introduction
This document contains information relevant to the work underway in
The Services in the PSTN/IN Requesting InTernet Services (SPIRITS)
Working Group. It describes four existing implementations of
SPIRITS-like services from Korea Telecom, Lucent Technologies, NEC,
and Telia in cooperation with Nortel Networks. SPIRITS-like services
are those originating in the Public Switched Telephone Network (PSTN)
and necessitating the interactions of the Internet and PSTN.
Invariably supported by the implementations examined in this document
is the Internet Call Waiting (ICW) service. With ICW, service sub-
scribers, while using their telephone lines for Internet access, can
be notified of incoming voice calls and specify how to handle the
calls over the same telephone lines.
The document first gives a detailed description of the ICW service.
Then it proceeds to discuss each of the four implementations. The
final sections of the document contains security considerations, the
conclusion and references.
It is important to note that even though the term "SPIRITS server" is
used throughout the document, it has no universal meaning. Its conno-
tation depends on the context and varies from implementation to
implementation.
2. Service Description of Internet Call Waiting
Internet call waiting is the single service that is specifically sup-
ported by all the implementations in question. In a nutshell, the
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service enables a subscriber engaged in an Internet dial-up session
to
o be notified of an incoming call to the very same telephone line
that is being used for the Internet connection;
o specify the desirable treatment of the call; and
o have the call handled as specified.
The details of the ICW service lie in the ways that a waiting call
can be treated, which vary from implementation to implementation. In
this section, we describe the features that are supported by at least
one of the implementations. They are as follows:
o Incoming Call Notification - The subscriber is notified of an
incoming call over the Internet, without having any effect on the
telephone line that is being used by the modem. When a call comes
in, the subscriber is presented with a pop-up dialog box on the PC.
The dialog box may display any combination of the calling party
number, calling party name, and calling time. Note that the display
of the calling party name (or number) requires the availability of
the caller name (or number) delivery feature.
o Online Incoming Call Disposition - Once informed of the incoming
call, the subscriber has various options (indicated in the pop-up
window) for handling the call. Possible options are:
+ Accepting the call over the PSTN line, thus terminating the Inter-
net (modem) connection
+ Accepting the call over the Internet using Voice over IP (VoIP)
+ Rejecting the call
+ Playing a pre-recorded message to the calling party and discon-
necting the call
+ Forwarding the call to voice mail
+ Forwarding the call to another number
+ Rejecting (or Forwarding) on no Response - If the subscriber fails
to respond within a certain period time after the dialog box has
been displayed, the incoming call can be either rejected or han-
dled based the treatment pre-defined by the subscriber.
o Automatic Incoming Call Disposition - Incoming calls are automati-
cally handled based on dispositions pre-defined by the subscriber
without his or her real-time intervention. The subscriber can pre-
define the default disposition (e.g., re-directed to voice mail)
for general calls as well as customized dispositions for calls from
specific numbers. In the latter case, the subscriber selects a par-
ticular disposition for each originating number and stores this
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information in a profile. When a call comes in, the subscriber
won't be presented the call but can examine the treatment and out-
come of the call from the caller log (as described in the call log-
ging bullet). Naturally, this feature also allows the subscriber
to specify the desired treatment for calls originating from private
or unpublished numbers.
o Multiple Call Handling - Multiple calls can arrive during call
disposition processing. With multiple call handling, the subscriber
is notified of the multiple calls one by one.
o Call Logging - A detailed log of the incoming calls processed dur-
ing the ICW service is kept. Typical information recorded in the
log include the incoming call date and time, calling party number,
calling party name, and call disposition.
3. Korea Telecom's ICW Implementation
3.1. Overview
Korea Telecom's ICW implementation supports most of the features
described in Section 2. (The major exception is the feature of
receiving the incoming call over the Internet using voice over IP.)
In addition, the Korea Telecom implementation supports flexible
activation and de-activation of the ICW service:
o Automatic Activation/De-activation - When Internet dial-up connec-
tion is set up, the ICW service is activated or de-activated
automatically.
o Manual Activation/De-activation - The subscriber can de-activate
the ICW service manually when call notification is not desired dur-
ing the Internet dial-up session and activate it when needed.
3.1. Network Architecture
Figure 1 depicts the network architecture of the Korea Telecom ICW
service. The Service Switching Point (SSP), Service Control Point
(SCP), and Intelligent Peripheral (IP) are legacy PSTN IN elements
based on IN CS-1. In contrast, both the ICW Server System and the ICW
Client System are new network elements that are installed in the
Internet domain to support of the ICW service.
PSTN/IN | INTERNET
|
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+---------------------------+ | +--------------+
|+--------+propr-+---------+| PINT | |(Proxy Server)| PINT
||(ICW SL)|ietary|(UAC/UAS)||--- -||-----| ICW |----+
||SCF/SDF |------| SCGF || firewall |Server System | |
|+--------+ i/f +---------+| | +------------- + |
| SCP | | |
+------+--------------+-----+ | |
|INAP |INAP | firewall=====
| | | |
+---+---+ +---+---+ |
| IP | | SSP | |
+-------+ +---+---+ +-------------+
| +---+ | (UAC/UAS) |
+---+---+ || || | ICW |
|---------| LEX |-------------- + + |Client System|
+---+ +-------+ +++++----+-------------+
|| || (callee)
+ + ICW Subscriber's Phone and PC
+++++
(caller)
INAP : Intelligent Network Application Protocol
PINT : PSTN/Internet Interworking Protocol
SL : Service Logic
UAS : User Agent Server
UAC : User Agent Client
Figure 1: Network Architecture of the Korea Telecom ICW Service
3.2. Network Entities
3.2.1. SSP
The SSP performs the Service Switching Function (SSF) and Call Con-
trol Function (CCF). When detecting that the called party is busy
(T_Busy), the SSP sends a query to the SCP and processes the call
under the control of the SCP.
3.2.2. SCP
The SCP performs the Service Control Function (SCF) and Service Data
Function (SDF). It, when queried, instructs the SSP to process the
call based on the service logic. In the case of the ICW service, the
service logic ultimately governs the notification of a waiting call
to an online ICW subscriber and the disposition of the call. In
addition, the SCP performs the Service Control Gateway Function
(SCGF) for protocol inter-working between the PSTN/IN and Internet.
It translates the SIP message from the ICW Server to the service con-
trol interface message and vise versa. The SCGF is an IP end point
and behaves as a UAS (User Agent server) or UAC (User Agent client).
3.2.3. IP
The IP contains Service Resource Function (SRF). It, when necessary,
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plays announcements to the calling party during the ICW service
before/after receiving the response from the ICW subscriber and
records the calling party number or voice message from the calling
party when the call is forwarded to the Voice Mail System (VMS).
3.2.4. ICW Server System
The ICW Server system serves as a SIP proxy or a redirect server for
message routing between the ICW Client and SCGF. The ICW Server is
also responsible for managing the ICW Clients that are connected to
it. When an ICW Client (subscriber) sends a registration request for
the ICW service, the ICW Server relays that request to the SCP, waits
for the result of authorization from the SCP, and registers the
authorized subscriber in its data base. In addition, the ICW Server
monitors the connection status of the registered ICW Clients. As
soon as a client deactivates the ICW service or terminates the Inter-
net connection, the ICW Server detects the status change and de-
activates the ICW service for the client. Finally, the ICW Server
manages profiles for each ICW subscribers as well as logs all the
call processing results.
3.2.5. ICW Client System
The ICW Client System is an application program running on the
subscriber's PC. Launched as soon as the subscriber powers on the PC,
it monitors the Internet connection status of the PC (or subscriber).
Upon the subscriber's connection to the Internet, the ICW Client
sends a REGISTRATION request to the SCGF via the ICW Server and then
eventually to the SCP. In this capacity, the ICW Client acts as a UAC
to the SCGF, which acts as a UAS. Thereafter it notifies the ICW
Server periodically of the connection status of the subscriber.
The ICW Client is also responsible for popping up a dialog box on the
subscriber's PC to announce an incoming call. The dialog box displays
the number and name of calling party, calling time, and the call pro-
cessing options (including Accept, Reject, Forward to another number
or VMS). After the subscriber selects the option, the ICW Client
sends it to the SCP. In this capacity, the ICW Client acts as a UAS.
Depending on the pre-defined ICW Service Profile, the ICW Client may
screen the incoming call before notifying the subscriber.
The ICW Client manages the ICW Service Profile, which contains the
following fields:
o Subscriber Information (including, Name, Directory Number, Pass-
word)
o Service Status (Activation/De-activation)
o Automatic Call Processing Method
+ Call Processing Method on No Answer (Reject/Forward/VMS) - The
call is automatically handled by the method if the subscriber
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doesn't respond after a pre-defined period of time.
+ Do Not Disturb Mode (On/Off) - When this is set on, the sub-
scriber won't be notified of the incoming calls.
+ Call Processing Method on Do Not Disturb (Reject/Forward/VMS)
+ Call Processing List by Calling Party Numbers
(Accept/Reject/Forward/VMS) - Calls originated from a number on
the list are handled by the associated call processing method.
o The ICW Client records the call processing method and the result
for each incoming call in a log file on the subscriber's PC. The
call record in the call log contains the following information:
- Calling Time
- Calling Party Number
- Calling Party Name (optional)
- Call Processing Method (Accept/Reject/Forward/Forward to VMS)
- Result (Success/Fail)
3.2.6. Firewall
Packet Filtering Firewall Systems are between the ICW server and
clients as well as between the SCGF and ICW server for accessing the
Korea Telecom IN Nodes.
3.3. Network Interfaces
o The SCF-SDF, SCF-SSF, and SCF-SRF interfaces are the same as exist-
ing PSTN IN Interfaces based on the KT INAP CS-1.
o The SCGF-SCF interface relays requests either from the IN or the
Internet and is implemented based on the internal API of the SCP.
o The SCGF-ICW Server and ICW Server-ICW Client interfaces are imple-
mented based on the PINT Service Protocol V.1. We adopted UAS-
Proxy-UAC relationships as shown in Figure 2.
+---------+ +-------------+ +---------+
|(UAC/UAS)|PINT 1.0| (Proxy) |PINT 1.0|(UAC/UAS)|
| |--------| ICW |--------| ICW |
| SCGF | | Server | | Client |
+---------+ +-------------+ +---------+
Figure 2: PINT Protocol Architecture
3.4. Protocols
3.4.1. Intelligent Network Application Part Protocol (INAP)
The SCP, SSP, and IP support the KT INAP V1.0, which is based on
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ITU-T INAP CS-1 with the incorporation of two INAP CS-2 messages [PRM
(PromptAndReceiveMessage) and EM (EraseMessage)] for recording the
voice message.
3.4.2. PINT Protocol
The ICW service uses the PINT Service Protocol 1.0 [1] for communica-
tions between the SCP and the ICW Server System, and between the ICW
Server System and the ICW Client System. Developed in the IETF PINT
Working Group for invoking telephone services from an IP network, the
PINT Service Protocol 1.0 specifies a set of enhancements to SIP 2.0
and SDP.
Summarized below are the elements of the PINT Service Protocol 1.0
relevant to the Korea Telecom ICW implementation:
o REGISTER
The REGISTER method is used to inform the SCP of the connection
status of an ICW subscriber. With this method, the ICW Client sends
to the ICW Server the IP address (of the PC) and phone number of the
subscriber when the subscriber is first connected to the
Internet. The ICW server relays the information to the SCP, which
updates the data base (if the subscriber is authorized), and in the
end sends a registration acknowledgement to the ICW Server and then
the Client. After the subscriber is connected to the Internet, the
ICW Client sends a REGISTER request to the ICW Server periodically
at a pre-defined interval (e.g., 20 seconds) to indicate its
connection status. The request is not relayed to the SCP. The ICW
Server only checks if it is from the authorized subscriber. Finally,
when the subscriber terminates the Internet connection, the Client
sends the last REGISTER request to the SCP via the ICW Server. If
the REGISTER request does not arrive during the pre-defined interval,
the ICW Server can also detect the change of the connection status
of the ICW Client.
o INVITE
The SCP uses the INVITE method to notify the ICW Client, via the ICW
Server, of an incoming call.
o ACK
Both the SCP and the ICW Server use the ACK method to confirm the
receipt of the final responses to their requests.
o BYE
The BYE method terminates a service session. In addition to this
original usage, we use the value (success or failure) of the Subject
header to indicate the result of the desired disposition of an
incoming call in the PSTN.
o CANCEL
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When the calling party releases the call before the called party
responds, the SCP sends a CANCEL request to the ICW Client
to cancel the INVITE request that it sent previously.
o OPTION
This method is not used in the KT implementation.
o Responses
The SCP responds to a REGISTER request with one of the status codes
and associated comments below:
. 100 Trying: Trying
. 200 OK: Registered
The ICW Client responds to an INVITE request with one of the
status codes and associated comments below:
. 100 Trying: Trying
. 200 OK: Accept the Call
. 303 see other: Forward the Call to Another Number
. 380 alternative service: Forward the Call to the VMS
. 603 decline: Reject the Call
3.5. Example Scenarios
3.5.1. ICW Service Subscription
Access to the Korea Telecom ICW service is by subscription. Here
Korea Telecom serves as both the PSTN operator and IN-based ICW ser-
vice provider. Note that the subscription data need to be loaded onto
the relevant SSPs, including the local ones that may not be operated
by Korea Telecom.
3.5.2. ICW Client Installation
An ICW subscriber should install the ICW Client program in his or her
PC. The ICW Client is automatically activated to run as a daemon pro-
cess when the subscriber's PC is turned on. The Client monitors the
Internet connection status of the subscriber.
3.5.3. ICW Service Activation
When the subscriber initiates the Internet connection or activates
the ICW service manually, the ICW service is activated. That is done
by sending a REGISTER request with the directory number and IP
address from the ICW Client to the SCP through the ICW Server.
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ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
| | | | | |
0A | | | | |
0BREG(DN1,IP1)| | | | |
1 |----------->|REG(DN1,IP1)| | | |
2 | |----------->| | | |
| | 2A | | |
| | |reg(DN1,IP1)| | |
3 | | |-.-.-.-.-.->| | |
| | | 3A | |
| | | reg ok 3B | |
4 | | |<-.-.-.-.-.-| | |
| | 200 OK 4A | | |
5 | |<-----------| | | |
| 200 OK 5A | | | |
6 |<-----------| | | | |
6A | | | | |
| | | | | |
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 3: ICW Service Activation
As depicted in Figure 3, the relevant information flows are as follows:
(0A) The ICW subscriber dials the ISP access number and establishes a
PPP connection.
(0B) The ICW Client detects the PPP connection.
1. The ICW Client sends a registration request to the ICW Server in order
to register the IP address-DN relationship for the dial-up connection.
2. The ICW Server relays registration request to the SCGF.
2A. The SCGF translates the user registration information from the SIP
message to the SCP internal API message.
3. The SCGF relays the user registration message to the SCF/SDF.
3A. The SCF/SDF authorizes the subscriber with the directory number
based on the user registration information.
3B. The SCF/SDF stores the IP address of the ICW Client
and sets the status to "Internet on-line."
4. The SCF/SDF sends the result of registration to the SCF/SCGF.
4A. The SCGF translates the user registration response of the SCP
internal API message to the PINT message.
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5. The SCGF relays the user registration response to the ICW Server.
5A. The ICW Server records the user registration information and the
Internet on-line status for the subscriber in the data base.
6. The ICW Server sends the user registration response to the ICW
Client.
6A. The ICW Client notifies the subscriber that the registration is
completed successfully and the ICW service is in the active state.
3.5.4. Incoming Call Notification
When a calling party makes a call to the ICW subscriber, the SCP
notifies the ICW Client of the incoming call and waits for the
subscriber's response.
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
| | | | | |
| | | | setup(DN1,DN2)|
1 | | | | |<+++++++++++|
| | | | 1A |
| | | IDP(T-busy,DN1)| |
2 | | | |<--.--.--.--| |
| | | 2A | |
| | | 2B | |
| | | 2C | |
| | noti(DN1,IP1,DN2)| | |
3 | | |<-.-.-.-.-.-| | |
| | 3A | | |
| INV(DN1,IP1,DN2)| | | |
4 | |<-----------| | | |
| 4A | | | |
| | 100 Trying | | | |
5 | |----------->| | | |
INV(DN1,IP1,DN2)| | | | |
6 |<-----------| | | | |
6A | | | | |
| 100 Trying | | | | |
7 |----------->| | | | |
| | | | | |
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 4: Incoming Call Notification
As depicted in Figure 4, the relevant information flows are as follows:
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1. The calling party at DN2 (a telephone user) makes a call to the ICW
subscriber (PC user) at DN1. The connection is set up using the existing
ISDN signaling.
1A. The SSF/CCF detects that the callee (the ICW subscriber) is busy.
2. The SSF/CCF sends InitialDP (T_Busy) to the SCF/SDF.
2A. The SCF/SDF determines whether the user at DN1 is PSTN on-line
or Internet on-line. (The SCF/SDF executes the KT Telephone Mail
Service logic in the PSTN on-line case and the ICW service Logic in the
Internet on-line case.)
2B. The SCF/SDF retrieves the IP address corresponding to DN1.
2C. The SCF/SDF may play an announcement to the calling party, while
waiting for the response of the called party.
3. The SCF sends an incoming call notification to the SCGF.
3A. The SCGF translates the incoming call notification from the SCP
internal format to the PINT format.
4. The SCGF relays the notification to the ICW Server.
4A. The ICW Server double-checks the subscriber's status using the
ICW subscribers profile in its own data base.
5. The ICW Server sends trying message to the SCGF.
6. The ICW Server relays the notification to the ICW Client.
6A. The ICW Client consults the ICW service profile to see if there
is a pre-defined call disposition for the incoming call. If so, then
the procedure for automatic call processing is performed.
6B. If there is no pre-defined call disposition for the incoming call,
the subscriber is notified of the call via a pop-up dialog box.
7. The ICW Client sends trying message to the ICW Server.
3.5.5. Incoming Call Processing
The incoming call can be accepted, rejected, forwarded to another
number, or forwarded to the VMS depending on the on-the-fly or pre-
defined choice of the subscriber. This section describes the informa-
tion flows for the cases of "Accept the call" and "Forward the call
to another number."
3.5.5.1. Accept the Call
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ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
| | | | | |
0A 200 OK | | | | |
1 |----------->| | | | |
1A | | | | |
1B | 200 OK | | | |
2 | |----------->| | | |
| | ACK 2A | | |
3 | |<-----------| | | |
| | |Accept(DN1,IP1,DN2) | |
4 | | |-.-.-.-.-.->| | |
| | | |Connect(DN1,DN2) |
5 | | | |--.--.--.-->| |
| | | Setup(DN1,DN2)| |
6 |<++++++++++++++++++++++++++++++++++++++++++++++++++| |
|<==============================6A==============================>|
| | | | ERB | |
7 | | | |<--.--.--.--| |
| | | ok | | |
8 | | |<-.-.-.-.-.-| | |
| | 8A | | |
| | BYE | | | |
9 | |<-----------| | | |
| 9A | | | |
| | | | | |
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 5: Incoming Call Processing - Accept the Call
As depicted in Figure 5, the relevant information flows are as follows:
0A. The ICW subscriber chooses to "Accept" the incoming call.
1. The ICW Client sends the "Accept" indication to the ICW Server.
1A. The ICW Client records the subscriber's selection for the incoming
call in the call log.
1B. The ICW Client terminates the subscriber's Internet connection.
2. The ICW Server sends an "Accept" message to the SCGF.
2A. The SCGF translates the "Accept" message to an SCP internal
API message.
3. The SCGF sends an "ACK" message to the ICW Server.
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4. The SCGF sends the "Accept" message to the SCF.
5. The SCF instructs the SSF/CCF to route the call to DN1.
6. The SSF/CCF initiates the connection setup to DN1.
6A. The bearer connection between the calling party (DN2) and the
ICW subscriber(DN1) is set up.
7. The connection result is returned to the SCF through ERB.
8. The SCF sends a call completion message to the SCGF.
8A. The SCGF translates the call completion message to a PINT
message.
9. The SCGF sends a "BYE" message to the ICW Server.
9A. The ICW Server records the call completion result in the log file.
3.5.5.2. Forward the Call to Another Number
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling Another
ICW Client party Phone
(DN1/IP1) (IP2) (IP3) (DN2) (DN3)
| | | | | | |
0A | | | | | |
|303 SeeOther | | | | |
1 |--------->| | | | | |
1A ACK | | | | | |
2 |<---------|303 SeeOther | | | |
3 | |--------->| | | | |
| | ACK 3A | | | |
4 | |<---------|Connect(DN2,DN3) | | |
5 | | |-.-.-.-.->| | | |
| | | |Connect(DN2,DN3) | |
6 | | | |.--.--.-->| | |
| | | | |Setup(DN2,DN3) |
7 | | | | ++++++++++++++++++++>|
8 | | | | ERB | |<===5A==>|
| | | |<--.--.--.| | |
| | | ok | | | |
9 | | |<-.-.-.-.-| | | |
| | BYE 9A | | | |
10 | |<---------| | | | |
| BYE 10A | | | | |
11 |<---------| | | | | |
11A | | | | | |
| | | | | | |
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
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=====> Bearer
Figure 6: Incoming Call Processing - Forward the Call to Another
As depicted in Figure 6, the relevant information flows are as follows:
0A. The ICW subscriber chooses to "Forward to another number (DN3)"
for the incoming call.
1. The ICW Client sends the "Forward to another number" indication to
the ICW Server.
1A. The ICW Client records the subscriber's selection for the incoming
call in the call log.
2. The ICW Server sends an "ACK" message to the ICW Client.
3. The ICW Server relays the "Forward to another number" message to the
SCGF.
3A. The SCGF translates the "Forward to another number" message to
an SCP internal API message.
4. The SCGF sends an "ACK" message to the ICW Server.
5. The SCGF sends the "Forward to another number" message to the SCF.
6. The SCF instructs the SSF/CCF to route the call to DN3.
7. The SSF/CCF initiates the connection setup to DN3.
7A. The bearer connection between the calling party (DN2) and the
new termination number (DN3) is set up.
8. The connection result is returned to the SCF through ERB.
9. The SCF sends a call completion message to the SCGF.
9A. The SCGF translates the call completion message to a PINT
message.
10. The SCGF sends the call completion message to the ICW Server.
10A. The ICW Server records the call completion result in the log file.
11. The ICW Server sends the success of "Forwarding to another number"
to the ICW Client.
11A. The ICW Client records the call completion result in the log file.
3.5.6. ICW service De-activation
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The SCP de-activates the ICW service for a subscriber either upon the
termination of the subscriber's Internet connection or upon the
subscriber's manual request. In this section, we illustrate the
former scenario.
ICW Subscriber ICW Server SCGF SCF/SDF SSF/CCF Calling
ICW Client party
(DN1/IP1) (IP2) (IP3) (DN2)
| | | | | |
0A | | | | |
| 0B | | | |
| |Unreg(DN1,IP1) | | |
1 | |----------->| | | |
| | 1A | | |
| | |Unreg(DN1,IP1) | |
2 | | |-.-.-.-.-.->| | |
| | | 2A | |
| | | ok 2B | |
3 | | |<-.-.-.-.-.-| | |
| | 3A | | |
| | 200 OK | | | |
4 | |<-----------| | | |
| 4A | | | |
| | | | | |
-----> PINT Protocol -.-.-> SCP Internal API
--.--> INAP Protocol +++++> ISUP Protocol
=====> Bearer
Figure 7: ICW Service De-activation
As depicted in Figure 7, the relevant information flows are as follows:
0A. The ICW subscriber terminates the Internet connection.
0B. The ICW Server determines that the Internet connection has been
terminated when it does not receive the periodic on-line notification
from the ICW Client.
1. The ICW Server sends an un-register message to the SCGF.
1A. The SCGF translates the un-register message to an SCP internal
API message.
2. The SCGF sends the un-register message to the SCF.
2A. The SCF/SDF authorizes the subscriber with the directory number
based on the un-registration information.
2B. The SCF/SDF records the Internet off-line status for that ICW
Client.
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SPIRITS [Page 17]
3. The SCF/SDF sends a user un-registration response to the SCF/SCGF.
3B. The SCGF translates the user un-registration response to a PINT
message.
4. The SCGF relays the user un-registration response to the
ICW Server.
4A. The ICW Server records the Internet off-line status for the
ICW Client (subscriber) in the data base.
4. The Lucent Technologies Online Communications Center
4.1 Overview
The Lucent Technologies Online Communications Center (OCC) is an
Intelligent Network (IN)-based platform that supports the Internet
call waiting service. Its basic components are the OCC Server and OCC
Client, which are described in detail in the Architecture section.
The OCC Server interacts with the PSTN entities over the secure
intranet via plain-text Session Initiation Protocol (SIP) messages
[2]. With the PC Client, the OCC Server interacts via encrypted SIP
messages.
The OCC Server run-time environment effectively consists of two
multi-threaded processes responsible for Call Registration and Call
Notification services, respectively.
OCC call registration services are initiated from an end-user's PC
(or Internet appliance). With those, a subscriber registers his or
her end-points and activates the notification services. (The regis-
tration services are not, strictly speaking, SPIRITS services but
rather have a flavor of PINT services.)
All OCC call notification services are PSTN-initiated. One common
feature of these services is that of informing the user of the incom-
ing telephone call via the Internet, without having any effect on the
line already used by the modem. (A typical call waiting tone would
interrupt the Internet connection, and it is a standard practice to
disable the "old" PSTN call waiting service for the duration of the
call in support of the Internet connection between the end-user and
the ISP.)
When a call comes in, the user is presented with a pop-up dialog box,
which displays the caller's number (if available), name (again, if
available), as well as the time of the call. If the called party does
not initiate an action within a specified period of time the call is
rejected.
As far as the disposition of the call is concerned, OCC supports all
the features described in Section 2.
4.2. Architecture
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+------------+
| Compact | +-------------+
| Service | | Service |
+-----| Node (CSN) | | Management |
| | OCC Server | | System (SMS)|
| | OCC CSN SPA| +-------------+
| +-------:--|-+ |
| | +-------------[ IP INTRANET ]---------+
===== firewall : |
| | |
| +-------+ +-------+
| |Central|-..-..-..-..-..-..-..-..-..-..-|Service|
| +-%-|Office |-..-..-: |Control|
| | +---|---+ | |Point |
| % | : | (SCP) |
| | +--|---+ +-------+ +----------+ |OCC SCP|
| % | PC | | VoIP | | VoIP | | SPA |
| | |OCC Cl| |Gateway| |Gatekeeper| +-------+
| % +------+ +---|---+ +-----|----+
| | ===== firewall =====
| % | |
| | +---------------|---+ |
| +-%-| |----------+
+----------| I N T E R N E T |
| |
+-------------------+
Figure 8: The Lucent OCC Physical Architecture
Figure 8 depicts the joint PSTN/Internet physical architecture
relevant to the OCC operation. The Compact Service Node (CSN) and SCP
are Lucent's implementations of the ITU-T IN Recommendations (in par-
ticular, the Recommendation Q.1205 where these entities are defined)
augmented by the requirements of Bellcore's Advanced Intelligent Net-
work (AIN) Release 1.0) and equipped with other features. The Central
Office (CO) may be any switch supporting the Integrated Services
Digital Network (ISDN) Primary Rate Interface (PRI) and the call for-
warding feature that would allow it to interwork with the CSN. Alter-
natively, in order to interwork with the SCP, it needs to be an IN
Service Switching Point (SSP). In the latter case, the central
office is connected to the SCP via the signaling system No. 7 (SS7)
and INAP at the application layer.
The Service Management System (SMS) is responsible for provisioning
of the SCPs, CSNs, and central offices. In particular, for IN support
of the Internet Call Waiting, it must provision the Central Office to
direct a terminating attempt query to the subsystem number
corresponding to the OCC SCP SPA based on the Termination Attempt
Trigger (TAT). In addition, the Subscriber Directory Number (DN),
Personal Identification Number (PIN) and Language ID are provisioned
for each subscriber into the OCC Subscriber entry of the SCP Real
Time Data Base (RTDB). Figure 9 shows the structure of an RTDB entry.
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+-------------------------------------------------------+
|DN | PIN | IP Address | Session Key | CNF | Language ID|
+-------------------------------------------------------+
Field Descriptions:
(DN) Directory Number - the subscriber's telephone number
(PIN) Personal Identification Number - the subscriber's password
IP Address - Internet Protocol Address of the subscriber
(CNF) Call Notification In Progress Flag (boolean) - the flag
indicating if an attempt to notify the subscriber of a call is
currently in progress
Session Key - unique identifier for the current registration session
of the subscriber
Language ID - language identifier for the subscriber
Figure 9: Structure of the RTDB Subscriber Record
The Central Office, SMS, CSN, and SCP are the only PSTN elements of
the architecture. The other elements are VoIP Gateway and Gatekeeper
defined in the ITU-T Recommendation H.323, whose roles are to estab-
lish and provide the part of the voice path over IP. The Central
Office is explicitly connected to the VoIP Gateway via the ISDN PRI
connection. In this architecture, CSN, VoIP Gateway, and VoIP Gate-
keeper are the only entities connected to the Internet, with each
respective connection protected by a firewall. The CSN and SCP are
interconnected via a secure IP Intranet. There may be more than one
CSN or SCP (or both) (and the SCPs come in mated pairs interconnected
by X.25, anyway) in a network, but these details are not essential to
the level of description chosen for this document. However, we note
that load balancing and adaptation to failures by the use of alterna-
tive nodes is incorporated into the architecture.
When someone attempts to call the subscriber, the central office
serving that subscriber interrupts normal termination processing and
notifies the SCP which, in turn, can check whether that subscriber
has registered that he (or she) is logged onto the Internet.
Exploiting the standardized layering of service logic that character-
izes the intelligent network, the central office will do this without
requiring the installation or development of any central office
software specific to OCC. The central office is simply provisioned to
query the SCP when there is a termination attempt (i.e., TAT)
directed to the subscriber's directory number. (Note that the Central
Office has no bearer circuit connection to the SCP, only a signaling
one over SS7).
TCP/IP communication between the SCP and CSN utilizes a secure
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intranet. The subscriber, of course, is assumed to have access only
to the Internet.
The intelligent network entities, the SCP and CSN, do have OCC
related software. The OCC server is implemented on the CSN. In
addition, one service package application (SPA) is installed on the
SCP. Another SPA is located in the CSN and is needed only when the
subscriber elects to accept an incoming call using voice over IP.
The OCC Server is a collection of Java servers on the CSN whose
responsibilities include:
o Listening for incoming Call Notification (TCP/IP) messages from the
SCP SPA.
o De-multiplexing/multiplexing incoming Call Notification messages
sent from the SCP SPA.
o Relaying messages between the OCC Client and the SCP SPA.
o Listening for and authentication of OCC Client requests for service
registration.
o Handling encryption/decryption of messages exchanged with the OCC
Client, and generating session-specific encryption/decryption keys.
The OCC Client is a collection of software components that run on the
Subscriber's PC. Its components include the SIP User Agent Server
(which handles the exchange of SIP messages with the OCC Server and
invokes the Call Notification pop-up window) and a daemon process
that monitors the Point-to-Point Protocol (PPP) actions and is
responsible for starting and stopping the SIP User Agent Server.
4.3. Protocol and Operations Considerations
The OCC Server uses distinct TCP/IP ports configured on the CSN to
o Listen for incoming SIP REGISTER messages (in support of registra-
tion service) sent from the OCC Client.
o Listen for incoming SIP INVITE messages (in support of call notifi-
cation service) sent from the SCP.
During call notification, the SCP SPA is the client and thus is
started after the OCC Server has been started. The SCP SPA and OCC
Server exchange SIP messages over TCP/IP (via the Secure Intranet)
using a "nailed-up" connection which is initiated by the SCP SPA.
This connection is initiated at the time the SCP SPA receives the
very first SIP REGISTER request from the OCC Server, and must prevail
for as long as the SPA is in the in-service state. The SCP SPA also
supports restarting the connection after any failure condition.
The OCC Server supports multithreading. For each Call
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Notification/Call Disposition event, a separate thread is used to
handle the call. This model supports multi-threading on a "per mes-
sage" basis where every start message (SIP INVITE) received from the
SCP SPA uses a separate thread of control to handle the call. Subse-
quent messages containing the same session Call-ID (which includes
the SPA's instance known as "call_index" and the SCP hostname) as the
original start message is routed to the same thread that previously
handled the respective initiating message.
The OCC Server dynamically opens a new TCP/IP socket with the OCC
Client for each Call Notification/Call Disposition session. This
socket connection uses the IP address and a pre-configured port on
the PC running the OCC Client software.
For session registration, the OCC Server dynamically opens TCP/IP
sessions with the SCP SPA. The SCP SPA listens at a pre-configured
port to incoming SIP REGISTER messages sent by OCC Clients via the
OCC Server. To exchange SIP messages with the OCC Server, the OCC
Client dynamically opens a TCP/IP socket connection with the OCC
Server using a pre-configured port number on the CSN and the CSN's IP
address.
For the VoIP Scenario, the CSN SPA, acting as a client, dynamically
opens TCP/IP sessions with the SCP that handled the initial TAT
query. As soon as the CSN SPA has successfully made the correlation
and connected the two incoming call legs pertaining to a VoIP call
back, the SIP 180 RINGING message will be sent back to the SCP SPA
running on the actual SCP that instructed the SSP to forward the
Caller to the CSN. This SIP message, which contains the VoIP Call
Back DN dialed by one of the bridged call legs, is an indication to
the SCP SPA that the VoIP Call Back DN is freed up.
A typical subscription scenario works like as follows:
1. Each VoIP Gateway is provisioned with a list of authorized VoIP
Call Back DNs, each terminating on a particular CSN. These spe-
cial DNs are used when an on-line subscriber elects to receive an
incoming call via VoIP. In particular, they assist in routing an
outgoing call from the subscriber's NetMeeting to the particular
CSN to which the SCP is (roughly concurrently) forwarding the
incoming call. (These two calls are joined in the CSN to connect
the incoming call to the subscriber's Netmeeting client.) Furth-
ermore, these special DNs permits that CSN to associate, and hence
bridge, the correct pair of call legs to join the party calling
the subscriber to the call from the subscriber's NetMeeting
client.
2. The subscriber calls a PSTN service provider and signs up for the
service.
3. An active Terminating Attempt Trigger (TAT) is assigned to the
subscriber's DN at the subscriber's central office.
4. The PSTN service provider uses the SMS to create a record for the
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subscriber and provision the Subscriber DN and PIN in the OCC RTDB
table in the SCP.
5. The subscriber is provided with the OCC Client software, a PIN and
a file containing the OCC Server IP Addresses.
Finally, we describe the particular scenario of the OCC Call Disposi-
tion that involves voice over IP, which proceeds as follows:
1. The OCC subscriber clicks on "Accept VoIP".
2. The OCC Client sends a "SIP 380 Alternative Service" message to
the OCC Server. This message includes a reference to the Call
Back DN which will ultimately be used by the CSN to associate the
call leg (soon to be initiated by the subscriber's NetMeeting)
connecting to the subscriber (via the VoIP gateway) with the PSTN
call leg connecting to the calling party.
3. The OCC Server closes the TCP/IP session with the OCC Client and
sends to the SCP SPA the "SIP 380 Alternative Service" message
which includes the Call Back DN.
4. The SCP SPA instructs the Central Office to forward the call
incoming to the subscriber to the CSN. This instruction includes
the Call Back DN.
5. The SSP forwards the Caller to the CSN referencing the Call Back
DN. Note that the Call Back DN, originally assigned to the OCC
client by the SCP when the subscriber was alerted to the presence
of an incoming call attempt, flowed next to the OCC server when
the client elected to receive the call via VoIP, then to the SCP,
then to the central office in association with a SCP command to
forward the incoming call to the CSN, then to the OCC server on
the CSN in association with that forwarded call.
6. Meanwhile, the OCC Client extracts 1) the VoIP Call Back DN from
the SIP INVITE message received during Call Notification and 2)
the H323UID and H323PIN values from its properties file and
updates the 'netmtg.cnf' file.
7. The NetMeeting application is launched and sets up a connection
with the VoIP Gateway.
8. Once a connection is established between NetMeeting and the VoIP
Gateway, NetMeeting initiates a phone call - passing to the VoIP
Gateway the Call Back DN as the destination DN.
9. The VoIP Gateway consults the VoIP Gatekeeper and authenticates
the NetMeeting call by verifying the H323UID and H323PIN values,
and by ensuring the called DN (i.e., Call Back DN) is authorized
for use.
10. After passing the authentication step, the VoIP Gateway dials (via
PSTN) the Call Back DN and gets connected to the CSN. The CSN
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SPIRITS [Page 23]
notes that it was reached by the particular Call Back DN.
11. The CSN bridges the Calling and Called parties together by match-
ing on the basis of the Call Back DN.
12. The CSN notifies the SCP (SIP 180 Ringing) of status and refer-
ences the Call Back DN so that the SCP can reuse it for other
calls.
13. If the central office supports that two B-channel transfer
(Lucent, Nortel, and perhaps other central office vender's do), an
optimization is possible. The CSN can have the central office
rearrange the topology of the newly connected call in such a way
that it flows only through the central office and no longer
through the CSN.
5. NEC's Implementation
5.1. Overview
The NEC implementation of the ICW service is based on IN. Via a SPIR-
ITS server and an ICW client, incoming calls will be presented to the
user via a pop-up screen dialogue box. This dialogue box informs the
user of the call arrival time and the calling party's number and name
(if available). The arrival of the call is also indicated with an
accompanied audible indication.
The pop-up dialogue box offers the user various call management
options. Selecting a call management option allows the user to
answer the call, forward it to another destination or to voice mail,
or ignore it.
The user will be able to customize their service through various ser-
vice set-up options. All calls presented to the user during an
Internet session will be recorded in a call log.
Other features include Multiple call arrival management with which
each new call arrival will generate its own pop-up dialogue box and
audible indication.
5.2. Architecture and Overall Call Flow
Figure 10 depicts the NEC ICW system.
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SPIRITS [Page 24]
====================================
|| I n t e r n e t ||
|| ||
====================================
/ | \
: (p1) : : (p2)
/ | \
+-------+ +------------+ +-----+
|SPIRITS| | ISP | | W3S |
|Server | | ISP | | W3S |
+-------+ +------------+ +-----+
: :
Internet | :
PSTN/IN |(p0) :
: :
| ============:======
+------+ (p3) || +-----+ : ||
| SCP |-..-..-..-| SSP | : ||
+------+ || +-----+ : ||
|| (p4)| : ||
+-------+ || : : ||
| ICW | (p1)+-----+ || | : ||
|Client |.....| M/D |............+------+ ||
+-------+ (p2)+-----+ || | CO | ||
--------------------| |-------
/ || +------+ || \
/--\ / || P S T N || \ /--\
()/\() / =================== \ ()/\()
_/__\___/ \______/__\_
ICW Subscriber Calling Party
Legend:
ISP : Internet Service Provider
W3S : WWW Server
SCP : Service Control Point(acts as SPIRITS Client)
SSP : Service Switching Point
CO : Central Office
M/D : Modem
Traffic:
--- : PSTN Voice Traffic
... : PPP(IP traffic)
-..-: Signaling Traffic
Interfaces:
p0 : SPIRITS Server-SCP(SPIRITS Client) interface
p1 : SPIRITS Server-ICW Client interface
p2 : ICW Client-W3S interface
(Web access through HTTP)
p3 : SCP-SSP interface(INAP)
p4 : SSP-CO interface(ISUP)
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Figure 10: the NEC ICW system
The description below provides the necessary steps to initiate the
ICW service on a CO line, and how the ICW service is applied to an
incoming call based on the above architecture:
1. The CO line is primed for the ICW service when the customer con-
nects to their ISP by inserting a special activation code (e.g.,
*54) prefix in front of the ISP Directory Number.
2. The ICW service is activated when the user opens a secured session
from an ICW client to the SPIRITS server. Once a session is open,
the SPIRITS server will know the relationship between the line and
the PC (i.e., it will know the Directory Number of the user's
Internet line and the user's IP Address).
3. When a call arrives at a busy Internet line, the SSP will trigger
the ICW service. The SCP which acts as the SPIRITS client will
inform the SPIRITS server that a call is terminating to a busy
Internet line. The message will include the Caller ID and Calling
Line Identify Restriction (CLIR) Status of the calling party, and
DN of the busy line.
4. The SPIRITS server will verify that if an ICW session has been
established for the busy line. If so, the SPIRITS server will com-
municate with the user's ICW client application. The user will
receive a real-time pop-up dialogue box including the Calling Name
and Number of the Calling Party if available. The user will then
select one of the following call management options:
- Answer the call (the Internet connection will be automatically
dropped and the phone will ring)
- Send the call to Voice Mail
- Forward the call to another destination
- Ignore the call
5. When the Internet user has made a selection, the ICW client appli-
cation will transmit this to the SPIRITS server. The SPIRITS
server will instruct the PSTN via the SCP how to handle the call.
5.3. Interfaces and Protocols
5.3.1. SCP (SPIRITS Client)-SPIRITS Server Interface
5.3.1.1. Connecting to SPIRITS Services
The physical connection between the SCP and the SPIRITS server will
be via a LAN/WAN. The logical connection will use the UDP/IP commun-
ications as defined in RFC 768 and RFC 1122.
If a socket connection is not currently established, the SCP will
periodically try to open a connection. The SCP routing tables will
be configured so that all available connections to a SPIRITS server
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SPIRITS [Page 26]
are used.
5.3.1.2. Message Types
Two different types of message are used between the SCP and the SPIR-
ITS server: "Connection Management Message Type" and the "Data Mes-
sage Type". These messages will carry the remote operation messages
which are based on ITU-T Q.1228 SCF-SCF interface with some NEC
proprietary extensions.
NEC also has a plan to support SIP/SDP-based protocols for the SPIR-
ITS client-server interface in the near future.
5.3.1.2.1 Connection Management Message Type
Connection management messages are to support functions related to
the opening and closing of connections and monitoring connections to
ensure reliable communications are maintained between the SCP and a
SPIRITS server. The SCP is responsible for establishing a connection
to a SPIRITS server. A connection can be closed by either the SCP or
the SPIRITS server.
The "Connection Management Message Type" includes the following
operations:
- scfBind
- scfUnbind
- activitytest
Opening a Connection
If a connection is not open to an SPIRITS server, the SCP will
periodically try to open a connection until it is opened. If after a
pre-determined number of attempts the connection is not opened, the
socket connection will be released and then re-established and then
the attempt to open the connection will be repeated.
The sequence for opening a connection is:
1. SCP will transmit a scfBind invokation message to the SPIRITS
server. This message also carries the version information and
activity test interval.
2. The SPIRITS server, upon receiving an invokation of the scfBind
from a particular SCP, will reset all the data concerning the connec-
tion and then responds with either a return result containing the Web
Server Identification number or a return error with a reason.
3. When the SCP receives a return result, if the ID number does not
match the number configured in the SCP, then a scfUnbind will be sent
indicating the wrong ID number. If the SCP receives nothing or a
return error is received, then the scfBind will be retried after a
pre-determined period of time.
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4. Once the SCP has received a return result, the SCP will send Han-
dling Information Request or Activity Test.
Upon receiving an invokation of activityTest, the SPIRITS server
should reply with a return result of activityTest. If the SPIRITS
server does not receive any invokation messages of Handling Informa-
tion Request or Activity Test from the SCP for four times the
Activity Test Interval value in milliseconds, the SPIRITS server
should then close the connection.
To close a connection an invokation of the scfUnbind is sent by
either the SCP or SPIRITS server to the remote end. When an invoka-
tion message of the scfUnbind is received, the receiving end should
terminate the connection.
scfBind
The scfBind operation is used to open the connection between the SCP
and the SPIRITS server. The SCP will send the SPIRITS server an invo-
kation of the scfBind to establish an association. If the SPIRITS
server is ready to handle the request then it should respond with a
return result.
The return result of scfBind contains the identifier of the SPIRITS
server. If the SCP receives the return result where the identifica-
tion of the SPIRITS server does not match that registered against the
SPIRITS server, then the SCP will send an invokation of the scfUnbind
indicating an incorrect identifier was received.
If the SPIRITS server is not ready to handle the request or cannot
handle the version, then it should respond with a return error.
scfUnbind
The scfUnbind operation is used to close the connection between the
SCP and the SPIRITS server. Either the SCP or the SPIRITS server can
invoke this operation.
Upon receiving an invokation message the receiving end should ter-
minate the connection.
activityTest
If the SCP has not sent a Data Message for the time period specified
by the "Activity Test Interval", it will send an invokation message
of activityTest. When the SPIRITS server receives such an invokation,
it will reply with a return result message of activityTest.
Its contents should be retained by the SPIRITS server. They are to be
echoed back in the return result so that the message reply time can
be calculated.
5.3.1.2.2. Data Message Type
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SCPs use the following operations, which are sent to the SPIRITS
server via a Data-Message-Type message, to request execution of some
service procedure or notification of an event that takes place at the
SCPs:
o handlingInformationRequest
The handlingInformationRequest message will request a SPIRITS
server the execution of some service procedure.
o handlingInformationResult
The handlingInformationResult message will show the SCP the result
of the execution, which was carried out by the SPIRITS server.
o confirmedNotificationProvided
The confirmedNotificationProvided message will indicate to the
SPIRITS server of an event, which takes place at the SCP. If the
confirmedNotificationProvided indicating 'caller abandon' is
received, the SPIRITS server will inform the client of the caller
abandon and send the SCP a return result for the confirmedNotifica-
tionProvided.
The invoked operation has always a response which is either a
return result of the operation or an invokation of another opera-
tion.
If a Data Message is not replied to within a pre-determined time
out period then the message will be resent a number of specified
times. Once the number of times has been exceeded, if another node
exists, the message will be sent to another node if it is avail-
able. If all available SPIRITS servers have been queried then Mes-
sage Time out will be returned to the calling process.
If an invokation of the handlingInformationResult is received with
the cause=63 (Service not available), the handlingInformationRe-
quest will be sent to another node if it is available. If all
available SPIRITS severs have been queried then cause=63 will be
returned to the calling process.
5.3.2. SPIRITS Server-ICW Client Application Interface
The following is a list of the application messages that are sent via
the secure protocol (refer to section 5.3.3):
o VersionInfo (ICW client -> SPIRITS server)
Indicate the current version of ICW client software. The SPIRITS
server uses this information to determine if the client software is
out of date.
o VersionInfoAck (SPIRITS server -> ICW client)
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If the VersionInfo message from an ICW client indicates to a SPIR-
ITS server that it is an out of date version, the URL information
is returned within the VersionInfoAck message for use in download-
ing the newer version. If the client software is up to date, the
message simply indicates so and does not include any URL informa-
tion.
o CallArrival (SPIRITS server -> ICW client)
Sent by the server to tell the client someone has called the DN.
o CallID
An identifier for this call. Unique in the domain of this
client/server session.
o CallingNumber
o CallingName
The name of the calling party is sent to the Client Application
from the SPIRITS server. When available, the name is sent as a 15-
character string. If the name is unavailable it is sent as "Name
Unavailable". If the calling party has CLIR set, it is sent as
empty (" ").
o CallConnect (ICW client -> SPIRITS server)
If a corresponding CallConnect is not received within a certain
period after sending a CallArrival, the SPIRITS server will behave
as though a CallConnect, Handling=Ignore had been received.
o CallLost (SPIRITS server -> ICW client)
Sent by server to cancel a CallArrival before a CallConnect is
received by the server.
5.3.3. Secure Reliable Hybrid Datagram Session Protocol (SRHDSP) for Use
Between ICW Client Application and SPIRITS Server
5.3.3.1. Overview
In principle the solution involves session initiation over SSL (meet-
ing requirements for standards based security) after which the SSL
session is closed, thereby reducing the number of simultaneous TCP/IP
sessions. The rest of the session is communicated over UDP/IP,
secured using keys and other parameters exchanged securely during the
SSL session.
5.3.3.2. Session Initiation
The ICW client initiates an SRHDSP session, by reserving a UDP/IP
port, and opening an SSL session with the service (e.g., ICW) on the
service's well known SSL/TCP port. After establishing the SSL
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Session, the ICW client sends the server its IP address, the reserved
UDP port number, and the set of supported symmetric key algorithms.
The server responds with a symmetric key algorithm chosen from the
set, the server's UDP port for further communication, heartbeat
period, and the value to use for the sequencing window.
The client then generates a symmetric key using the selected algo-
rithm and transmits this to the server. The SSL session is then
closed and the SRHDSP session is considered open.
5.3.3.3. Secure Reliable Datagram Transport
Application, and subsequent session management messages use symmetric
signaling. That is, the signaling is the same whether the client is
sending a message or the server is sending a message.
The message packets are transmitted securely. The protocol corrects
for lost, duplicated and out of sequence packets.
5.3.3.4. Session closure
The client or server may close the session.
A session is closed using a Close message including the next sequence
number, and encrypted with the agreed key.
The receiver, on processing (as opposed to receiving) a Close mes-
sage, should set a timer, when the timer expires all details of the
session should be forgotten. The timer is to allow for re-
transmission of the close if the Ack gets lost, we still need to be
able to decrypt the subsequent retransmission and re-acknowledgement.
If any message other than a close is received after a close is pro-
cessed, it is ignored.
6. Telia/Nortel's Implementation
6.1. Overview
The system implemented by Telia in cooperation with Nortel Networks
is designed to support services that execute before the end-to-end
media sessions are established. These services include, for example:
- call transfer and number portability for redirecting calls
- call waiting and call offering for announcing a pending call
- call screening and don't disturb for filtering incoming calls
- automatic call distribution and 800-services for selecting
termination point
The Telia/Nortel system aims to allow service providers to develop
the services mentioned above. Presently, prototypes for online incom-
ing call diposition and automatic incoming call disposition
(described in Section 2) have been developed to prove the concept.
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In the Telia/Nortel architecture, services run on top of SIP Redirect
Servers. The distributed nature of SIP enables these servers to be
hosted, for example, by an enterprise server, a Service Provider's
server cluster, a user's desktop PC, or even by a hand-held cordless
device.
The SIP Redirect Server receives a SIP INVITE message for each call
regardless of which network the call is being set up in. The server
MAY apply any kind of service logic in order to decide on how to
respond to the invitation. Service logic may interact with the user
to allow the user to specify how to handle a call such as described
in Section 2. This, however, is not the focus of the Telia/Nortel
system.
6.2. Architecture and Protocols
The general idea behind the architecture is to create services as if
all communication was based on IP and all clients and servers were
SIP enabled. This of cause is not true in existing telecommunications
networks. Hence, a new type of network element, the Service Control
Gateways (SCG) hides the true situation from the services.
SCGs convert network-specific call control signaling to SIP messages
and vice versa. A SCG behaves as a regular SIP User Agent (UA)
towards the services and as a network-specific service control node
in the network where the call is being set up. For example, when con-
necting to a GSM network, the SCG can play the role of an SCP or a
MAP or an ISUP proxy. The specific role depends on what service
triggers are being used in the GSM network.
SCGs handle protocol conversions but not address translation, such as
telephone number to SIP URL, which is handled by a regular SIP Server
to keep the SCG as simple as possible.
Consider a service example of number portability. A conventional
number portability implementation in a mobile Circuit Switched Net-
work (CSN) uses INAP messages to carry number queries to a network-
internal data base application. Here, a SCG and a high- performance
SIP Redirect Server, referred to as the Number Server (NS), have
replaced the data base typically located in an SCP. (See Figure 11.)
+-----------+ INAP +-----+ SIP +--------------------------+
| CSN node |--------| SCG |-------| NS (SIP Redirect Server) |
+-----------+ +-----+ +--------------------------+
Figure 11: An Architecture for Number Portability
The INAP IDP message that carries the number query is converted to a
SIP INVITE message by the SCG and is then forwarded to the NS (SIP
Redirect Server).
If the called number is not registered, then the NS will return "404
Not Found". The SCG interprets this as "non ported number" and
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returns a CON message to the CSN network, making it connect the call
to the called number.
If the number is ported and hence registered, then the NS will return
"301 Moved Permanently" with a TEL URL (routing number) in the con-
tact field. The SCG then returns a CON message to the CSN network,
making it connect the call to the number that was conveyed in the
contact field.
The solution above enables the same Number Server to provide Number
Portability to multiple networks by means of using multiple SCGs.
If we make the SIP server in the number portability example operate
in proxy mode for selected numbers, then it will become a kind of
service router, able to relay number queries to any SIP-Redirect-
Server-based service anywhere, provided there is an IP connection to
the host in concern. Figure 12 shows the arrangement.
+------+ INAP +-----+ SIP +----------------+ SIP +----------+
| CSN |------| SCG |-----| NS |-----| Service |
| node | | | |(redirect/proxy)| |(redirect)|
+------+ +-----+ +----------------+ +----------+
Figure 12: SIP-Based Service Router
Suppose that we connect a value-added service, such as a Personal
Call Filtering service hosted by a user's desktop PC, to a certain
telephone number. The INAP IDP message is converted to a SIP INVITE
message by the SCG and is then forwarded to the NS, just as in the
previous example. However, in this case, the number is registered
with a reference to a SIP URL. This makes the Number Server proxy the
SIP INVITE message to the registered URL, which is the address of the
service.
The service responds as a SIP Redirect Server and the Personal Call
Filtering service logic determines the response. The NS sends the
response back to the SCG which converts the response to an appropri-
ate INAP message. The response from the service is typically "302
Moved Temporarily" with a telephone number in the Contact field.
If the response is 301 or 302, as the examples above suggest, then a
telephone number is carried in the contact field. If the user can be
reached via several different addresses, then all of them SHOULD be
added to the response by means of multiple contact fields. The SCG
then selects an address that is valid for the node or application
that issued the number query.
As illustrated by the service examples, the Telia/Nortel system aims
to allow the introduction of multi-network services without requiring
multi-protocol support. The services hence operate in the same way
regardless of in which network the call is made and common IP ser-
vices can be shared across heterogeneous networks.
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SPIRITS [Page 33]
+-----------+ +-------+ SIP +----+ ...... SIP +-----------+
| Network 1 |---| SCG 1 |-----| |---: :-----| Service A |
+-----------+ +-------+ | | : : +-----------+
| | : :
+-----------+ +-------+ SIP | | : : SIP +-----------+
| Network 2 |---| SCG 2 |-----| NS |---: :-----| Service B |
+-----------+ +-------+ | | : Any : +-----------+
| | : IP :
+-----------+ +-------+ SIP | | : net- : SIP +-----------+
| Network n |---| SCG n |-----| |---: work :-----| Service C |
+-----------+ +-------+ +----+ : : +-----------+
: :
+--------+ SIP : : SIP +-----------+
| SIP UA |-----------------------------: :-----| Service x |
+--------+ '......' +-----------+
Figure 13: Interconnecting Heterogeneous Networks via SIP
6.3. Security
The Telia/Nortel architecture uses security mechanisms available to
ordinary SIP services, implemented as they would be in a pure SIP
network. The architecture described here does not impose any addi-
tional security considerations.
General security issues that must be considered include interconnec-
tion of two different networks. SCGs must therefore include mechan-
isms that prevent destructive service control signaling from one net-
work to the other. For example, a firewall-type mechanism that can
block a denial-of- service attack from an Internet user toward the
PSTN.
7. Security Considerations
Overall, the SPIRITS security requirements are essentially the same
as those for PINT [3, 4], which include, for example:
+ Protection of the PSTN from attacks from the Internet.
+ Peer entity authentication to allow a communicating entity to prove
its identity to another in the network.
+ Authorization and access control to verify if a network entity
is allowed to use a network resource.
+ Confidentiality to avoid disclosure of information (e.g., the end
user profile information and data) without the permission of its
owner.
+ Non-repudiation to account for all operations in case of doubt or
dispute.
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As seen in the previous sections, most implementations examined in
this document have employed means (e.g., firewalls and encryption) to
meet these requirements. The means are, however, different from
implementation to implementation.
8. Conclusion
This document has provided information relevant to the development of
inter-networking interfaces between the PSTN and Internet for sup-
porting SPIRITS services. Specifically, it described four existing
implementations of SPIRITS-like services. Surveying these implementa-
tions, we can make the following observations:
o The ICW service plays the role of a benchmark service. All four
implementations can support ICW, with three specifically designed
for it.
o SIP is used in most of the implementations as the based communica-
tions protocol between the PSTN and Internet. (NEC's implementation
is the only exception that uses a proprietary protocol. Neverthe-
less, NEC has a plan to support SIP together with the extensions
for SPIRITS services.)
o All implementations use IN-based solutions for the PSTN part.
It is clear that not all pre-SPIRITS implementations inter-operate
with each other. It is also clear that not all SIP-based implementa-
tions inter-operate with each other given that they do not support
the same version of SIP. It is a task of the SPIRITS Working Group
to define the inter-networking interfaces that will support inter-
operation of the future implementations of SPIRITS services.
8. References
[1] Petrack, S. and L. Conroy, The PINT Service Protocol: Extensions
to SIP and SDP for IP Access to Telephone Call Services. <draft-
ietf-pint-protocol-02.txt>. Work in Progress. October, 1999
[2] Handley, H., H. Schulzrinne, E. Schooler, and J. Rosenberg. SIP:
Session Initiation Protocol. RFC 2543. March, 1999
[3] Lu, H. (Ed.), M. Krishnaswamy, L. Conroy, S. Bellovin, F. Burg,
A. DeSimone, K. Tewani, P. Davidson, H. Schulzrinne and K.
Vishwanathan, Toward the PSTN/Internet Inter-Networking--Pre- PINT
Implementations". RFC 2458. November 1998.
[4] Petrack, S. and L. Conroy, The PINT Service Protocol: Exten-
sions to SIP and SDP for IP Access to Telephone Call Services. RFC
2848. June, 2000
9. Authors' Addresses
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Igor Faynberg
Lucent Technologies
Room 4L-334
101 Crawfords Corner Road
Holmdel, NJ 07733-3030 US
E-mail: faynberg@lucent.com
Telephone: +1 732 949 0137
Hui-Lan Lu
Lucent Technologies
Room 4L-317
101 Crawfords Corner Road
Holmdel, NJ 07733-3030 US
E-mail: huilanlu@lucent.com
Telephone: +1 732 949 0321
John Voelker
Lucent Technologies
Room 1A-417
263 Shuman Blvd PO Box 3050
Naperville, IL 60566-7050
E-mail: jvoelker@lucent.com
Telephone: +1 630 713 5538
Mark Weissman
Lucent Technologies
SUITE 500
2000 Regency Pky
Cary, NC 27511-8506 US
E-mail: maw1@lucent.com
Telephone: +1 919 380 6813
Weizhong Zhang
Lucent Technologies
Room 01-A5-17
2000 Regency Parkway
Cary, NC 27511-8506
E-Mail: wzz@lucent.com
Telephone: +1 919 380-6638
Sung-Yurn Rhim
Korea Telecom
17 Woomyun-dong
Seocho-gu, Seoul, Korea
E-mail: syrhim@kt.co.kr
Telephone: +82 2 526 6172
Jinkyung Hwang
Korea Telecom
17 Woomyun-dong
Seocho-gu, Seoul, Korea
E-mail: jkhwang@kt.co.kr
Telephone: +82 2 526 6830
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SPIRITS [Page 36]
Shinji.Ago
NEC Corporation
1131, Hinode, Abiko,
Chiba, 270-1198, JAPAN
E-mail: ago@ssf.abk.nec.co.jp
Telephone: +81 471 85 7412
S. Moeenuddin
NEC America, Inc
1525 Walnut Hill Lane,
Irving TX 75038
E-mail: moeen@asl.dl.nec.com
Telephone: +1 972 518 5102
S. Hadvani
NEC America, Inc
1525 Walnut Hill Lane,
Irving TX 75038
E-mail: hadvani@asl.dl.nec.com
Telephone: +1 972 518 3628
Soren Nyckelgard
Telia Research
Chalmers Teknikpark
41288 Gothenburg
Sweden
E-mail: soren.m.nyckelgard@telia.se
John Yoakum
Nortel Networks
507 Airport Blvd, Suite 115,
Morrisville, NC, USA 27560
E-mail: yoakum@nortelnetworks.com
Lewis Robart
Nortel Networks
P.O. Box 402
Ogdensburg, NY, USA 13669
E-mail: robart@nortelnetworks.com
Pre-SPIRITS Implementations September 2000
