RFC 3666

OZEKI OZEKI Phone System
Customizable PBX for Windows

+44 1206 854 512
info@ozekiphone.com

Ozeki Phone System

< RFC 3587 | RFC 3725 >

Network Working Group
Request for Comments: 3666
BCP: 76
Category: Best Current Practice

A. Johnston
MCI
S. Donovan
R. Sparks
C. Cunningham
dynamicsoft
K. Summers
Sonus
December 2003

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Session Initiation Protocol (SIP)

Public Switched Telephone Network (PSTN) Call Flows

Status of this Memo

This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Distribution of this memo is unlimited.

Copyright Notice

Abstract

This document contains best current practice examples of Session Initiation Protocol (SIP) call flows showing interworking with the Public Switched Telephone Network (PSTN). Elements in these call flows include SIP User Agents, SIP Proxy Servers, and PSTN Gateways. Scenarios include SIP to PSTN, PSTN to SIP, and PSTN to PSTN via SIP. PSTN telephony protocols are illustrated using ISDN (Integrated Services Digital Network), ISUP (ISDN User Part), and FGB (Feature Group B) circuit associated signaling. PSTN calls are illustrated using global telephone numbers from the PSTN and private extensions served on by a PBX (Private Branch Exchange). Call flow diagrams and message details are shown.

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Table of Contents

1. Overview
1.1. General Assumptions
1.2. Legend for Message Flows
1.3. SIP Protocol Assumptions
2. SIP to PSTN Dialing
2.1. Successful SIP to ISUP PSTN call
2.2. Successful SIP to ISDN PBX call
2.3. Successful SIP to ISUP PSTN call with overflow
2.4. Session established using ENUM Query
2.5. Unsuccessful SIP to PSTN call: Treatment from PSTN
2.6. Unsuccessful SIP to PSTN: REL w/Cause from PSTN
2.7. Unsuccessful SIP to PSTN: ANM Timeout
3. PSTN to SIP Dialing
3.1. Successful PSTN to SIP call
3.2. Successful PSTN to SIP call, Fast Answer
3.3. Successful PBX to SIP call
3.4. Unsuccessful PSTN to SIP REL, SIP error mapped to REL
3.5. Unsuccessful PSTN to SIP REL, SIP busy mapped to REL
3.6. Unsuccessful PSTN->SIP, SIP error interworking to tones
3.7. Unsuccessful PSTN->SIP, ACM timeout
3.8. Unsuccessful PSTN->SIP, ACM timeout, stateless Proxy
3.9. Unsuccessful PSTN->SIP, Caller Abandonment
4. PSTN to PSTN Dialing via SIP Network
4.1. Successful ISUP PSTN to ISUP PSTN call
4.2. Successful FGB PBX to ISDN PBX call with overflow
5. Security Considerations
6. References
6.1. Normative References
6.2. Informative References
7. Acknowledgments
8. Intellectual Property Statement
9. Authors' Addresses
10. Full Copyright Statement

1 Overview

The call flows shown in this document were developed in the design of a SIP IP communications network. They represent an example of a minimum set of functionality.

It is the hope of the authors that this document will be useful for SIP implementers, designers, and protocol researchers alike and will help further the goal of a standard implementation of RFC 3261 [2]. These flows represent carefully checked and working group reviewed scenarios of the most common SIP/PSTN interworking examples as a companion to the specifications.

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These call flows are based on the current version 2.0 of SIP in RFC 3261 [2] with SDP usage described in RFC 3264 [3]. Other RFCs also comprise the SIP standard but are not used in this set of basic call flows. The SIP/ISUP mapping is based on RFC 3398 [4].

Various PSTN signaling protocols are illustrated in this document: ISDN (Integrated Services Digital Network), ISUP (ISDN User Part) and FGB (Feature Group B) circuit associated signaling. This document shows mainly ANSI ISUP due to its practical origins. However, as used in this document, the usage is virtually identical to the ITU-T International ISUP used as the reference in [4].

Basic SIP call flow examples are contained in a companion document, RFC 3665 [10].

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [1].

1.1 General Assumptions

A number of architecture, network, and protocol assumptions underlie the call flows in this document. Note that these assumptions are not requirements. They are outlined in this section so that they may be taken into consideration and to aid in the understanding of the call flow examples.

The authentication of SIP User Agents in these example call flows is performed using HTTP Digest as defined in [3] and [5].

Some Proxy Servers in these call flows insert Record-Route headers into requests to ensure that they are in the signaling path for future message exchanges.

These flows show TLS, TCP, and UDP for transport. SCTP could also be used. See the discussion in RFC 3261 [2] for details on the transport issues for SIP.

The SIP Proxy Server has access to a Location Service and other databases. Information present in the Request-URI and the context (From header) is sufficient to determine to which proxy or gateway the message should be routed. In most cases, a primary and secondary route will be determined in case of a Proxy or Gateway failure downstream.

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Gateways provide tones (ringing, busy, etc) and announcements to the PSTN side based on SIP response messages, or pass along audio in-band tones (ringing, busy tone, etc.) in an early media stream to the SIP side.

The interactions between the Proxy and Gateway can be summarized as follows:

 
   -  The SIP Proxy Server performs digit analysis and lookup and
      locates the correct gateway.
 
   -  The SIP Proxy Server performs gateway location based on primary
      and secondary routing.

Telephone numbers are usually represented as SIP URIs. Note that an alternative is the use of the tel URI [6].

This document shows typical examples of SIP/ISUP interworking. Although in the spirit of the SIP-T framework [7], these examples do not represent a complete implementation of the framework. The examples here represent more of a minimal set of examples for very basic SIP to ISUP interworking, rather than the more complex goal of ISUP transparency. In particular, there are NO examples of encapsulated ISUP in this document. If present, these messages would show S/MIME encryption due to the sensitive nature of this information, as discussed in the SIP-T Framework security considerations section. (Note - RFC 3204 [8] contains an example of an INVITE with encapsulated ISUP.) See the Security Considerations section for a more detailed discussion on the security of these call flows.

In ISUP, the Calling Party Number is abbreviated as CgPN and the Called Party Number is abbreviated as CdPN. Other abbreviations include Numbering Plan Indicator (NPI) and Nature of Address (NOA).

1.2 Legend for Message Flows

Dashed lines (---) represent signaling messages that are mandatory to the call scenario. These messages can be SIP or PSTN signaling. The arrow indicates the direction of message flow.

 
   Double dashed lines (===) represent media paths between network
   elements.

Messages with parentheses around their name represent optional messages.

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Messages are identified in the Figures as F1, F2, etc. This references the message details in the list that follows the Figure. Comments in the message details are shown in the following form:

 
      /* Comments. */

1.3 SIP Protocol Assumptions

This document does not prescribe the flows precisely as they are shown, but rather the flows illustrate the principles for best practice. They are best practices usages (orderings, syntax, selection of features for the purpose, handling of error) of SIP methods, headers and parameters. IMPORTANT: The exact flows here must not be copied as is by an implementer due to specific incorrect characteristics that were introduced into the document for convenience and are listed below. To sum up, the SIP/PSTN call flows represent well-reviewed examples of SIP usage, which are best common practice according to IETF consensus.

For simplicity in reading and editing the document, there are a number of differences between some of the examples and actual SIP messages. For example, the SIP Digest responses are not actual MD5 encodings. Call-IDs are often repeated, and CSeq counts often begin at 1. Header fields are usually shown in the same order. Usually only the minimum required header field set is shown, others that would normally be present, such as Accept, Supported, Allow, etc. are not shown.

Actors:

 
   Element       Display Name   URI                        IP Address
   -------       ------------   ---                        ----------
 
   User Agent    Alice          sip:alice@a.example.com    192.0.2.101
   User Agent    Bob            sip:bob@b.example.com      192.0.2.200
   Proxy Server                 sip:ss1.a.example.com      192.0.2.111
   User Agent (Gateway)         sip:gw1.a.example.com      192.0.2.201
   User Agent (Gateway)         sip:gw2.a.example.com      192.0.2.202
   User Agent (Gateway)         sip:gw3.a.example.com      192.0.2.203
   User Agent (Gateway)         sip:ngw1.a.example.com     192.0.2.103
   User Agent (Gateway)         sip:ngw2.a.example.com     192.0.2.102

Note that NGW 1 and NGW 2 also have device URIs (Contacts) of sip:ngw1@a.example.com and sip:ngw2@a.example.com which resolve to the Proxy Server sip:ss1.wcom.com using DNS SRV records.

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2 SIP to PSTN Dialing

In the following scenarios, Alice (sip:alice@a.example.com) is a SIP phone or other SIP-enabled device. Bob is reachable via the PSTN at global telephone number +19725552222. Alice places a call to Bob through a Proxy Server, Proxy 1, and a Network Gateway. In other scenarios, Alice places calls to Carol, who is served via a PBX (Private Branch Exchange) and is identified by a private extension 444-3333, or global number +1-918-555-3333. Note that Alice uses his/her global telephone number +1-314-555-1111 in the From header in the INVITE messages. This then gives the Gateway the option of using this header to populate the calling party identification field in subsequent signaling. Left open is the issue of how the Gateway can determine the accuracy of the telephone number which is necessary before passing it as a valid calling party number in the PSTN.

In these scenarios, Alice is a SIP phone or other SIP-enabled device. Alice places a call to Bob in the PSTN or Carol on a PBX through a Proxy Server and a Gateway.

In the failure scenarios, the call does not complete. In some cases however, a media stream is still setup. This is due to the fact that some failures in dialing to the PSTN result in in-band tones (busy, reorder tones or announcements - "The number you have dialed has changed. The new number is..."). The 183 Session Progress response containing SDP media information is used to setup this early media path so that the caller Alice knows the final disposition of the call.

The media stream is either terminated by the caller after the tone or announcement has been heard and understood, or by the Gateway after a timer expires.

In other failure scenarios, a SS7 Release with Cause Code is mapped to a SIP response. In these scenarios, the early media path is not used, but the actual failure code is conveyed to the caller by the SIP User Agent Client.

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2.1 Successful SIP to ISUP PSTN call

 
   Alice           Proxy 1           NGW 1          Switch B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     100  F2    |                |                |
     |<---------------|   INVITE F3    |                |
     |                |--------------->|                |
     |                |     100  F4    |                |
     |                |<---------------|     IAM F5     |
     |                |                |--------------->|
     |                |                |     ACM F6     |
     |                |     183 F7     |<---------------|
     |     183 F8     |<---------------|                |
     |<---------------|                |                |
     |        Both Way RTP Media       |  One Way Voice |
     |<===============================>|<===============|
     |                |                |      ANM F9    |
     |                |    200 F10     |<---------------|
     |     200 F11    |<---------------|                |
     |<---------------|                |                |
     |     ACK F12    |                |                |
     |--------------->|     ACK F13    |                |
     |                |--------------->|                |
     |        Both Way RTP Media       | Both Way Voice |
     |<===============================>|<==============>|
     |     BYE F14    |                |                |
     |--------------->|     BYE F15    |                |
     |                |--------------->|                |
     |                |     200 F16    |                |
     |     200 F17    |<---------------|     REL F18    |
     |<---------------|                |--------------->|
     |                |                |     RLC F19    |
     |                |                |<---------------|
     |                |                |                |

Alice dials the globalized E.164 number +19725552222 to reach Bob. Note that A might have only dialed the last 7 digits, or some other dialing plan. It is assumed that the SIP User Agent Client converts the digits into a global number and puts them into a SIP URI. Note that tel URIs could be used instead of SIP URIs.

Alice could use either their SIP address (sip:alice@a.example.com) or SIP telephone number (sip:+13145551111@ss1.a.example.com;user=phone) in the From header. In this example, the telephone number is included, and it is shown as being passed as calling party identification through the Network Gateway (NGW 1) to Bob (F5). Note

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that for this number to be passed into the SS7 network, it would have to be somehow verified for accuracy.

In this scenario, Bob answers the call, then Alice disconnects the call. Signaling between NGW 1 and Bob's telephone switch is ANSI ISUP. For the details of SIP to ISUP mapping, refer to [4].

In this flow, notice that the Contact returned by NGW 1 in messages F7-11 is sip:ngw1@a.example.com. This is because NGW 1 only accepts SIP messages that come through Proxy 1 - any direct signaling will be ignored. Since this Contact URI may be used outside of this dialog and must be routable (Section 8.1.1.8 in RFC 3261 [2]) the Contact URI for NGW 1 must resolve to Proxy 1. This Contact URI resolves via DNS to Proxy 1 (sip:ss1.a.example.com) which then resolves it to sip:ngw1.a.example.com which is the address of NGW 1.

This flow shows TCP transport.

Message Details

F1 INVITE Alice -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Proxy-Authorization: Digest username="alice", realm="a.example.com",
    nonce="dc3a5ab25302aa931904ba7d88fa1cf5", opaque="",
    uri="sip:+19725552222@ss1.a.example.com;user=phone",
    response="ccdca50cb091d587421457305d097458c"
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

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F2 100 Trying Proxy 1 -> Alice

SIP/2.0 100 Trying
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

   /* Proxy 1 uses a Location Service function to determine the gateway
   for terminating this call.  The call is forwarded to NGW 1.  Client
   for A prepares to receive data on port 49172 from the
   network.*/

F3 INVITE Proxy 1 -> NGW 1

INVITE sip:+19725552222@ngw1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying NGW 1 -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

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    ;received=192.0.2.111
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 IAM NGW 1 -> Bob

IAM
CdPN=972-555-2222,NPI=E.164,NOA=National
CgPN=314-555-1111,NPI=E.164,NOA=National

F6 ACM Bob -> NGW 1

ACM

F7 183 Session Progress NGW 1 -> Proxy 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* NGW 1 sends PSTN audio (ringing) in the RTP path to A */

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F8 183 Session Progress Proxy 1 -> Alice

SIP/2.0 183 Session Progress
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F9 ANM Bob -> NGW 1

ANM

F10 200 OK NGW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp

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Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F11 200 OK Proxy 1 -> Alice

SIP/2.0 200 OK
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F12 ACK Alice -> Proxy 1

ACK sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK

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Content-Length: 0

F13 ACK Proxy 1 -> NGW 1

ACK sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0
 
   /* Alice Hangs Up with Bob. */

F14 BYE Alice -> Proxy 1

BYE sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F15 BYE Proxy 1 -> NGW 1

BYE sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com

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CSeq: 2 BYE
Content-Length: 0

F16 200 OK NGW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F17 200 OK Proxy 1 -> A

SIP/2.0 200 OK
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F18 REL NGW 1 -> B

REL
CauseCode=16 Normal

F19 RLC B -> NGW 1

RLC

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2.2 Successful SIP to ISDN PBX call

 
   Alice            Proxy 1           GW 1             PBX C
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     100  F2    |                |                |
     |<---------------|   INVITE F3    |                |
     |                |--------------->|                |
     |                |     100  F4    |                |
     |                |<---------------|    SETUP F5    |
     |                |                |--------------->|
     |                |                |  CALL PROC F6  |
     |                |                |<---------------|
     |                |                |   PROGress F7  |
     |                |    180 F8      |<---------------|
     |    180 F9      |<---------------|                |
     |<---------------|                |                |
     |                |                |  One Way Voice |
     |                |                |<===============|
     |                |                |   CONNect F10  |
     |                |                |<---------------|
     |                |                | CONNect ACK F11|
     |                |    200 F12     |--------------->|
     |     200 F13    |<---------------|                |
     |<---------------|                |                |
     |     ACK F14    |                |                |
     |--------------->|     ACK F15    |                |
     |                |--------------->|                |
     |        Both Way RTP Media       | Both Way Voice |
     |<===============================>|<==============>|
     |     BYE F16    |                |                |
     |--------------->|     BYE F17    |                |
     |                |--------------->|                |
     |                |     200 F18    |                |
     |     200 F19    |<---------------| DISConnect F20 |
     |<---------------|                |--------------->|
     |                |                |   RELease F21  |
     |                |                |<---------------|
     |                |                | RELease COM F22|
     |                |                |--------------->|
     |                |                |                |

Alice is a SIP device while Carol is connected via a Gateway (GW 1) to a PBX. The PBX connection is via a ISDN trunk group. Alice dials Carol's telephone number (918-555-3333) which is globalized and put into a SIP URI.

Page 16

The host portion of the Request-URI in the INVITE F3 is used to identify the context (customer, trunk group, or line) in which the private number 444-3333 is valid. Otherwise, this INVITE message could get forwarded by GW 1 and the context of the digits could become lost and the call unroutable.

Proxy 1 looks up the telephone number and locates the gateway that serves Carol. Carol is identified by its extension (444-3333) in the Request-URI sent to GW 1.

Note that the Contact URI for GW 1, as used in messages F8, F9, F12, and F13, is sips:4443333@gw1.a.example.com, which resolves directly to the gateway.

This flow shows the use of Secure SIP (sips) URIs.

Message Details

F1 INVITE Alice -> Proxy 1

INVITE sips:+19185553333@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:alice@client.a.example.com>
   Proxy-Authorization: Digest username="alice",
    realm="a.example.com", nonce="qo0dc3a5ab22aa931904badfa1cf5j9h",
    opaque="", uri="sips:+19185553333@ss1.a.example.com;user=phone",
    response="6c792f5c9fa360358b93c7fb826bf550"
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F2 100 Trying Proxy 1 -> Alice

SIP/2.0 100 Trying

Page 17

Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Content-Length: 0

F3 INVITE Proxy 1 -> GW 1

INVITE sips:4443333@gw1.a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sips:ss1.a.example.com;lr>
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:alice@client.a.example.com>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying GW -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Content-Length: 0

Page 18

F5 SETUP GW 1 -> Carol

Protocol discriminator=Q.931
Message type=SETUP
Bearer capability: Information transfer capability=0 (Speech) or 16 (3.1 kHz audio)
Channel identification=Preferred or exclusive B-channel
Progress indicator=1 (Call is not end-to-end ISDN;further call progress information may be available inband)
Called party number:
Type of number unknown
Digits=444-3333

F6 CALL PROCeeding Carol-> GW 1

Protocol discriminator=Q.931
Message type=CALL PROC
Channel identification=Exclusive B-channel

F7 PROGress Carol-> GW 1

Protocol discriminator=Q.931
Message type=PROG
Progress indicator=1 (Call is not end-to-end ISDN;further call progress information may be available inband)

F8 180 Ringing GW 1 -> Proxy 1

SIP/2.0 180 Ringing
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sips:ss1.a.example.com;lr>
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:4443333@gw1.a.example.com>
   Content-Length: 0

Page 19

F9 180 Ringing Proxy 1 -> Alice

SIP/2.0 180 Ringing
Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sips:ss1.a.example.com;lr>
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:4443333@gw1.a.example.com>
   Content-Length: 0

F10 CONNect Carol-> GW 1

Protocol discriminator=Q.931
Message type=CONN

F11 CONNect ACK GW 1 -> Carol

Protocol discriminator=Q.931
Message type=CONN ACK

F12 200 OK GW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sips:ss1.a.example.com;lr>
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:4443333@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 144

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com

Page 20

s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F13 200 OK Proxy 1 -> Alice

SIP/2.0 200 OK
Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sips:ss1.a.example.com;lr>
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sips:4443333@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 144

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F14 ACK Alice -> Proxy 1

ACK sips:4443333@gw1.a.example.com SIP/2.0
Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <sips:ss1.a.example.com;lr>
From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 ACK
   Content-Length: 0

Page 21

F15 ACK Proxy 1 -> GW 1

ACK sips:4443333@gw1.a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 ACK
   Content-Length: 0
 
   /* Alice Hangs Up with Bob. */

F16 BYE Alice -> Proxy 1

BYE sips:4443333@gw1.a.example.com SIP/2.0
Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <sips:ss1.a.example.com;lr>
From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 3 BYE
   Content-Length: 0

F17 BYE Proxy 1 -> GW 1

BYE sips:4443333@gw1.a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 3 BYE
   Content-Length: 0

Page 22

F18 200 OK GW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 3 BYE
   Content-Length: 0

F19 200 OK Proxy 1 -> A

SIP/2.0 200 OK
Via: SIP/2.0/TLS client.a.example.com:5061;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sips:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Carol <sips:+19185553333@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 3 BYE
   Content-Length: 0

F20 DISConnect GW 1 -> Carol

Protocol discriminator=Q.931
Message type=DISC
Cause=16 (Normal clearing)

F21 RELease Carol-> GW 1

Protocol discriminator=Q.931
Message type=REL

F22 RELease COMplete GW 1 -> Carol

Protocol discriminator=Q.931
Message type=REL COM

Page 23

2.3 Successful SIP to ISUP PSTN call with overflow

 
   Alice          Proxy 1         NGW 1          NGW 2        Switch B
    |              |              |              |              |
    |  INVITE F1   |              |              |              |
    |------------->|              |              |              |
    |              |  INVITE F2   |              |              |
    |    100  F3   |------------->|              |              |
    |<-------------|    503 F4    |              |              |
    |              |<-------------|              |              |
    |              |    ACK F5    |              |              |
    |              |------------->|              |              |
    |              |   INVITE F6                 |              |
    |              |---------------------------->|     IAM F7   |
    |              |                             |------------->|
    |              |                             |     ACM F8   |
    |              |            183 F9           |<-------------|
    |   183 F10    |<----------------------------|              |
    |<-------------|                             |              |
    |               Two Way RTP Media            | One Way Voice|
    |<==========================================>|<=============|
    |              |                             |    ANM F11   |
    |              |           200 F12           |<-------------|
    |    200 F13   |<----------------------------|              |
    |<-------------|                             |              |
    |    ACK F14   |                             |              |
    |------------->|            ACK F15          |              |
    |              |---------------------------->|              |
    |             Both Way RTP Media             |Both Way Voice|
    |<==========================================>|<============>|
    |    BYE F16   |                             |              |
    |------------->|           BYE F17           |              |
    |              |---------------------------->|              |
    |              |           200 F18           |              |
    |    200 F19   |<----------------------------|    REL F20   |
    |<-------------|                             |------------->|
    |              |                             |    RLC F21   |
    |              |                             |<-------------|
    |              |                             |              |

Alice calls Bob through Proxy 1. Proxy 1 tries to route to a Network Gateway NGW 1. NGW 1 is not available and responds with a 503 Service Unavailable (F4). The call is then routed to Network Gateway NGW 2. Bob answers the call. The call is terminated when Alice disconnects the call. NGW 2 and Bob's telephone switch use ANSI ISUP signaling.

Page 24

NGW 2 also only accepts SIP messages that come through Proxy 1, so the Contact URI sip:ngw2@a.example.com is used in this flow.

This flow shows UDP transport.

Message Details

F1 INVITE Alice -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com>
   Proxy-Authorization: Digest username="alice",
    realm="a.example.com", nonce="b59311c3ba05b401cf80b2a2c5ac51b0",
    opaque="", uri="sip:+19725552222@ss1.a.example.com;user=phone",
    response="ba6ab44923fa2614b28e3e3957789ab0"
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Proxy 1 receives a primary route NGW 1 and a secondary
   route NGW 2.  NGW 1 is tried first */

F2 INVITE Proxy 1 -> NGW 1

INVITE sip:+19725552222@ngw1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl

Page 25

To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 2xTb9vxSit55XU7p8@a.example.com
CSeq: 1 INVITE
Contact: <sip:alice@client.a.example.com>
Content-Type: application/sdp
Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F3 100 Trying Proxy 1 -> Alice

SIP/2.0 100 Trying
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F4 503 Service Unavailable NGW 1 -> Proxy 1

SIP/2.0 503 Service Unavailable
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

Page 26

F5 ACK Proxy 1 -> NGW 1

ACK sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com>;user=phone>
    ;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0
 
   /* Proxy 1 now tries secondary route to NGW 2 */

F6 INVITE Proxy 1 -> NGW 2

INVITE sip:+19725552222@ngw2.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F7 IAM NGW 2 -> Bob

IAM
CdPN=972-555-2222,NPI=E.164,NOA=National
CgPN=314-555-1111,NPI=E.164,NOA=National

Page 27

F8 ACM Bob -> NGW 2

ACM

F9 183 Session Progress NGW 2 -> Proxy 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw2@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw2.a.example.com
s=-
c=IN IP4 ngw2.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* RTP packets are sent by GW to A for audio (e.g. ring tone) */

F10 183 Session Progress Proxy 1 -> Alice

SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw2@a.example.com>
   Content-Type: application/sdp

Page 28

Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw2.a.example.com
s=-
c=IN IP4 ngw2.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F11 ANM Bob -> NGW 2

ANM

F12 200 OK NGW 2 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw2@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw2.a.example.com
s=-
c=IN IP4 ngw2.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F13 200 OK Proxy 1 -> Alice

SIP/2.0 200 OK
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101

Page 29

Record-Route: <sip:ss1.a.example.com;lr>
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw2@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw2.a.example.com
s=-
c=IN IP4 ngw2.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F14 ACK Alice -> Proxy 1

ACK sip:ngw2@a.example.com SIP/2.0
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <ss1.a.example.com;lr>
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F15 ACK Proxy 1 -> NGW 2

ACK sip:ngw2@a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK

Page 30

Content-Length: 0

 
   /* RTP streams are established between A and B(via the GW) */
 
   /* Alice Hangs Up with Bob. */

F16 BYE Alice -> Proxy 1

BYE sip:ngw2@a.example.com SIP/2.0
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
Route: <ss1.a.example.com;lr>
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F17 BYE Proxy 1 -> NGW 2

BYE sip:ngw2@a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F18 200 OK NGW 2 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>

Page 31

 
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F19 200 OK Proxy 1 -> Alice

SIP/2.0 200 OK
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F20 REL NGW 2 -> B

REL
CauseCode=16 Normal

F21 RLC B -> NGW 2

RLC

Page 32

2.4 Successful SIP to SIP using ENUM Query

 
   Alice         DNS Server         Proxy 3            Bob
     |                |                |                |
     |  ENUM Query F1 |                |                |
     |--------------->|                |                |
     |   Response F2  |                |                |
     |<---------------|                |                |
     |            INVITE F3            |                |
     |-------------------------------->|    INVITE F4   |
     |             100 F5              |--------------->|
     |<--------------------------------|      180 F6    |
     |             180 F7              |<---------------|
     |<--------------------------------|                |
     |                                 |     200 F8     |
     |             200 F9              |<---------------|
     |<--------------------------------|                |
     |             ACK F10             |                |
     |-------------------------------->|     ACK F11    |
     |                                 |--------------->|
     |                Both Way RTP Media                |
     |<================================================>|
     |                                 |     BYE F12    |
     |             BYE F13             |<---------------|
     |<--------------------------------|                |
     |             200 F14             |                |
     |-------------------------------->|     200 F15    |
     |                                 |--------------->|
     |                                 |                |

In this scenario, Alice places a call to Bob by dialing Bob's telephone number (9725552222). Alice's UA converts the phone number to an E.164 number (+19725552222), and performs an ENUM query [9] on the E.164 number (2.2.2.2.5.5.5.2.7.9.1.e164.arpa), which returns a NAPTR record containing a SIP AOR URI for Bob
(sip:+19725552222@b.example.com). As a result, Alice's UA sends an INVITE and the call completes over IP bypassing the PSTN.

The call is terminated when Bob sends a BYE message.

Message Details

F1 ENUM Query Alice -> DNS Server

2.2.2.2.5.5.5.2.7.9.1.e164.arpa

Page 33

F2 ENUM NAPTR Set DNS Server -> Alice

$ORIGIN 2.2.2.2.5.5.5.2.7.9.1.e164.arpa.
IN NAPTR 100 10 "u" "sip+E2U"
"!^.*$!sip:+19725552222@b.example.com!".

F3 INVITE Alice -> Proxy 3

INVITE sip:+19725552222@b.example.com SIP/2.0
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
To: <tel:+19725552222>
Call-ID: 2xTb9vxSit55XU7p8@a.example.com
CSeq: 2 INVITE
Contact: <sip:+13145551111@client.a.example.com>
Content-Type: application/sdp
Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 INVITE Proxy 3 -> Bob

INVITE sip:+19725552222@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss3.b.example.com;lr>
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sip:+13145551111@client.a.example.com>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=UserA 2890844526 2890844526 IN IP4 client.a.example.com s=-

Page 34

c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F5 100 Trying Proxy 3 -> Alice

SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Content-Length: 0

F6 180 Ringing B -> Proxy 3

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1

 
    ;received=192.0.2.233
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss3.b.example.com;lr>
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sip:+19725552222@client.b.example.com>
   Content-Length: 0

F7 180 Ringing Proxy 3 -> Alice

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss3.b.example.com;lr>
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sip:+19725552222@client.b.example.com>
   Content-Length: 0

Page 35

F8 200 OK Bob -> Proxy 3

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1

 
    ;received=192.0.2.233
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss3.b.example.com;lr>
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sip:+19725552222@client.b.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F9 200 OK Proxy -> Alice

SIP/2.0 200 OK
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss3.b.example.com;lr>
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 INVITE
   Contact: <sip:+19725552222@client.b.example.com>
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 192.0.2.100
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Page 36

F10 ACK Alice -> Proxy 3

ACK sip:+19725552222@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bq9 Max-Forwards: 70
Route: <sip:ss3.b.example.com;lr>
From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
To: <tel:+19725552222>;tag=314159
Call-ID: 2xTb9vxSit55XU7p8@a.example.com
CSeq: 2 ACK
Content-Length: 0

F11 ACK Proxy 3 -> Bob

ACK sip:+19725552222@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bq9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   From: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   To: <tel:+19725552222>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 2 ACK
   Content-Type: application/sdp
   Content-Length: 0
 
   /* RTP streams are established between A and B*/
 
   /* User B Hangs Up with User A. */

F12 BYE Bob -> Proxy 3

BYE sip:+13145551111@client.a.example.com SIP/2.0
Via: SIP/2.0/UDP client.b.example.com:5060;branch=z9hG4bKfgaw2 Max-Forwards: 70
Route: <sip:ss3.b.example.com;lr>
From: <tel:+19725552222>;tag=314159
To: <sip:+13145551111@a.example.com>;tag=9fxced76sl
Call-ID: 2xTb9vxSit55XU7p8@a.example.com
CSeq: 1 BYE
Content-Length: 0

F13 BYE Proxy 3 -> Alice

BYE sip:+13145551111@client.a.example.com SIP/2.0

Page 37

Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1

 
    ;received=192.0.2.100
   Via: SIP/2.0/UDP client.b.example.com:5060;branch=z9hG4bKfgaw2
   Max-Forwards: 69
   From: <tel:+19725552222>;tag=314159
   To: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 BYE
   Content-Length: 0

F14 200 OK Alice -> Proxy 3

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss3.b.example.com:5060;branch=z9hG4bK721e418c4.1

 
    ;received=192.0.2.233
   Via: SIP/2.0/UDP client.b.example.com:5060;branch=z9hG4bKfgaw2
    ;received=192.0.2.100
   From: <tel:+19725552222>;tag=314159
   To: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 BYE
   Content-Length: 0

F15 200 OK Proxy 3 -> Bob

SIP/2.0 200 OK
Via: SIP/2.0/UDP client.b.example.com:5060;branch=z9hG4bKfgaw2

 
    ;received=192.0.2.100
   From: <tel:+19725552222>;tag=314159
   To: <sip:+13145551111@a.example.com>;tag=9fxced76sl
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 BYE
   Content-Length: 0

Page 38

2.5 Unsuccessful SIP to PSTN call: Treatment from PSTN

 
   Alice            Proxy 1           NGW 1            Bob
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     100  F2    |                |                |
     |<---------------|   INVITE F3    |                |
     |                |--------------->|                |
     |                |     100  F4    |                |
     |                |<---------------|     IAM F5     |
     |                |                |--------------->|
     |                |                |     ACM F6     |
     |                |     183 F7     |<---------------|
     |     183 F8     |<---------------|                |
     |<---------------|                |                |
     |         Two Way RTP Media       |  One Way Voice |
     |<===============================>|<===============|
     |                 Treatment Applied                |
     |<=================================================|
     |   CANCEL F9    |                |                |
     |--------------->|                |                |
     |     200 F10    |                |                |
     |<---------------|   CANCEL F11   |                |
     |                |--------------->|                |
     |                |     200 F12    |                |
     |                |<---------------|     REL F13    |
     |                |                |--------------->|
     |                |                |     RLC F14    |
     |                |     487 F15    |<---------------|
     |                |<---------------|                |
     |                |     ACK F16    |                |
     |     487 F17    |--------------->|                |
     |<---------------|                |                |
     |     ACK F18    |                |                |
     |--------------->|                |                |
     |                |                |                |

Alice calls Bob in the PSTN through a proxy server Proxy 1 and a Network Gateway NGW 1. The call is rejected by the PSTN with an in-band treatment (tone or recording) played. Alice hears the treatment and then hangs up, which results in a CANCEL (F9) being sent to terminate the call. (A BYE is not sent since no final response was ever received by Alice.)

Page 39

Message Details

F1 INVITE Alice -> Proxy 1

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com>
   Proxy-Authorization: Digest username="alice",
    realm="a.example.com", nonce="01cf8311c3b0b2a2c5ac51bb59a05b40",
    opaque="", uri="sip:+19725552222@ss1.a.example.com;user=phone",
    response="e178fbe430e6680a1690261af8831f40"
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F2 100 Trying Proxy 1 -> A

SIP/2.0 100 Trying
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to NGW
   1.  Client for A prepares to receive data on port 49172 from the
   network. */

Page 40

F3 INVITE Proxy 1 -> NGW 1

INVITE sip:+19725552222@ngw1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying NGW 1 -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 IAM NGW 1 -> Bob

IAM
CdPN=972-555-2222,NPI=E.164,NOA=National
CgPN=314-555-1111,NPI=E.164,NOA=National

Page 41

F6 ACM Bob -> NGW 1

ACM

F7 183 Session Progress NGW 1 -> Proxy 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F8 183 Session Progress Proxy 1 -> Alice

SIP/2.0 183 Session Progress
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

Page 42

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Caller hears the recorded announcement, then hangs up */

F9 CANCEL Alice -> Proxy 1

CANCEL sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

F10 200 OK Proxy 1 -> A

SIP/2.0 200 OK
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

F11 CANCEL Proxy 1 -> NGW 1

CANCEL sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

Page 43

F12 200 OK NGW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

F13 REL NGW 1 -> B

REL
CauseCode=18 No user responding

F14 RLC B -> NGW 1

RLC

F15 487 Request Terminated NGW 1 -> Proxy 1

SIP/2.0 487 Request Terminated
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F16 ACK Proxy 1 -> NGW 1

ACK sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>

Page 44

 
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F17 487 Request Terminated Proxy 1 -> A

SIP/2.0 487 Request Terminated
Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F18 ACK Alice -> Proxy 1

ACK sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

Page 45

2.6 Unsuccessful SIP to PSTN: REL w/Cause from PSTN

 
   Alice            Proxy 1           NGW 1           Switch B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     100  F2    |                |                |
     |<---------------|   INVITE F3    |                |
     |                |--------------->|                |
     |                |     100  F4    |                |
     |                |<---------------|     IAM F5     |
     |                |                |--------------->|
     |                |                |    REL(1) F6   |
     |                |                |<---------------|
     |                |                |     RLC F7     |
     |                |     404 F8     |--------------->|
     |                |<---------------|                |
     |                |     ACK F9     |                |
     |                |--------------->|                |
     |     404 F10    |                |                |
     |<---------------|                |                |
     |     ACK F11    |                |                |
     |--------------->|                |                |
     |                |                |                |

Alice calls PSTN Bob through a Proxy Server Proxy 1 and a Network Gateway NGW 1. The call is rejected by the PSTN with a ANSI ISUP Release message REL containing a specific Cause code. This cause value (1) is mapped by the Gateway to a SIP 404 Address Incomplete response which is proxied back to Alice. For more details of ISUP cause value to SIP response mapping, refer to [4].

Message Details

F1 INVITE Alice -> Proxy 1

INVITE sip:+44-1234@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Proxy-Authorization: Digest username="alice",
    realm="a.example.com", nonce="j1c3b0b01cf832da2c5ac51bb59a05b40",
    opaque="", uri="sip:+44-1234@ss1.a.example.com;user=phone",

Page 46

response="a451358d46b55512863efe1dccaa2f42"
Content-Type: application/sdp
Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F2 100 Trying Proxy 1 -> A

SIP/2.0 100 Trying
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to NGW1.
   Client for A prepares to receive data on port 49172 from the network.
   */

F3 INVITE Proxy 1 -> NGW 1

INVITE sip:+44-1234@ngw1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 154

Page 47

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying NGW 1 -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 IAM NGW 1 -> Bob

IAM
CdPN=44-1234,NPI=E.164,NOA=International
CgPN=314-555-1111,NPI=E.164,NOA=National

F6 REL Bob -> NGW 1

REL
CauseValue=1 Unallocated number

F7 RLC NGW 1 -> Bob

RLC

 
   /* Network Gateway maps CauseValue=1 to the SIP message 404 Not
      Found */

Page 48

F8 404 Not Found NGW 1 -> Proxy 1

SIP/2.0 404 Not Found
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:not-found-ann@ann.a.example.com>
   Content-Length: 0

F9 ACK Proxy 1 -> NGW 1

ACK sip:+44-1234@ngw1.a.example.com;user=phone SIP/2.0
Max-Forwards: 70
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F10 404 Not Found Proxy 1 -> Alice

SIP/2.0 404 Not Found
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:not-found-ann@ann.a.example.com>
   Content-Length: 0

F11 ACK Alice -> Proxy 1

ACK sip:+44-1234@ss1.a.example.com;user=phone SIP/2.0
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 Max-Forwards: 70

Page 49

From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+44-1234@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

2.7 Unsuccessful SIP to PSTN: ANM Timeout

 
   Alice           Proxy 1           NGW 1           Switch B
     |                |                |                |
     |   INVITE F1    |                |                |
     |--------------->|                |                |
     |     100  F2    |                |                |
     |<---------------|   INVITE F3    |                |
     |                |--------------->|                |
     |                |     100  F4    |                |
     |                |<---------------|     IAM F5     |
     |                |                |--------------->|
     |                |                |     ACM F6     |
     |                |      183 F7    |<---------------|
     |     183 F8     |<---------------|                |
     |<---------------|                |                |
     |                |      Timer on NGW 1 Expires     |
     |                |                |                |
     |                |                |     REL F9     |
     |                |                |--------------->|
     |                |                |    RLC F10     |
     |                |     480 F11    |<---------------|
     |                |<---------------|                |
     |                |     ACK F12    |                |
     |                |--------------->|                |
     |     480 F13    |                |                |
     |<---------------|                |                |
     |     ACK F14    |                |                |
     |--------------->|                |                |

Alice calls Bob in the PSTN through a proxy server Proxy 1 and Network Gateway NGW 1. The call is released by the Gateway after a timer expires due to no ANswer Message (ANM) being received. The Gateway sends an ISUP Release REL message to the PSTN and a 480 Temporarily Unavailable response to Alice in the SIP network.

Page 50

Message Details

F1 INVITE Alice -> Proxy 1

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Proxy-Authorization: Digest username="alice",
    realm="a.example.com", nonce="da2c5ac51bb59a05j1c3b0b01cf832b40",
    opaque="", uri="sip:+19725552222@ss1.a.example.com;user=phone",
    response="579cb9db184cdc25bf816f37cbc03c7d"
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to NGW
   1.  Client for A prepares to receive data on port 49172 from the
   network.*/

F2 100 Trying Proxy 1 -> A

SIP/2.0 100 Trying
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

Page 51

F3 INVITE Proxy 1 -> NGW 1

INVITE sip:+19725552222@ngw1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:alice@client.a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 154

v=0
o=alice 2890844526 2890844526 IN IP4 client.a.example.com s=-
c=IN IP4 client.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying NGW 1 -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 IAM NGW 1 -> Bob

IAM
CdPN=972-555-2222,NPI=E.164,NOA=National
CgPN=314-555-1111,NPI=E.164,NOA=National

Page 52

F6 ACM Bob -> NGW 1

ACM

F7 183 Session Progress NGW 1 -> Proxy 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F8 183 Session Progress Proxy 1 -> Alice

SIP/2.0 183 Session Progress
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   Record-Route: <sip:ss1.a.example.com;lr>
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

Page 53

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* After NGW 1's timer expires, Network Gateway sends REL to ISUP
   network and 480 to SIP network */

F9 REL NGW 1 -> Bob

REL

CauseCode=18 No user responding

F10 RLC Bob -> NGW 1

RLC

F11 480 Temporarily Unavailable NGW 1 -> Proxy 1

SIP/2.0 480 Temporarily Unavailable
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:temp-unavail-ann@ann.a.example.com>
   Content-Length: 0

F12 ACK Proxy 1 -> NGW 1

ACK sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl

Page 54

To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>

 
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F13 480 Temporarily Unavailable F13 Proxy 1 -> Alice

SIP/2.0 480 Temporarily Unavailable
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9

 
    ;received=192.0.2.101
   From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:temp-unavail-ann@ann.a.example.com>
   Content-Length: 0

F14 ACK Alice -> Proxy 1

ACK sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Max-Forwards: 70
Via: SIP/2.0/TCP client.a.example.com:5060;branch=z9hG4bK74bf9 From: Alice <sip:+13145551111@ss1.a.example.com;user=phone>

 
    ;tag=9fxced76sl
   To: Bob <sip:+19725552222@ss1.a.example.com;user=phone>
    ;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@a.example.com
   CSeq: 1 ACK
   Content-Length: 0

3 PSTN to SIP Dialing

In these scenarios, Alice is placing calls from the PSTN to Bob in a SIP network. Alice's telephone switch signals to a Network Gateway (NGW 1) using ANSI ISUP.

Since the called SIP User Agent does not send in-band signaling information, no early media path needs to be established on the IP side. As a result, the 183 Session Progress response is not used. However, NGW 1 will establish a one way speech path prior to call completion, and generate ringing for the PSTN caller. Any tones or

Page 55

recordings are generated by NGW 1 and played in this speech path. When the call completes successfully, NGW 1 bridges the PSTN speech path with the IP media path.

To reduce the number of messages, only a single proxy server is shown in these flows, which means that the a.example.com proxy server has access to the b.example.com location service.

3.1 Successful PSTN to SIP call

 
   Switch A          NGW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F5    |
     |                |    180 F6      |<---------------|
     |     ACM F7     |<---------------|                |
     |<---------------|                |                |
     |  One Way Voice |                |                |
     |<===============|                |                |
     |  Ringing Tone  |                |      200 F8    |
     |<===============|    200 F9      |<---------------|
     |                |<---------------|                |
     |                |     ACK F10    |                |
     |     ANM F12    |--------------->|     ACK F11    |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     REL F13    |                |                |
     |--------------->|                |                |
     |     RLC F14    |                |                |
     |<---------------|     BYE F15    |                |
     |                |--------------->|     BYE F16    |
     |                |                |--------------->|
     |                |                |     200 F17    |
     |                |     200 F18    |<---------------|
     |                |<---------------|                |
     |                |                |                |

In this scenario, Alice from the PSTN calls Bob through a Network Gateway NGW1 and Proxy Server Proxy 1. When Bob answers the call, the media path is setup end-to-end. The call terminates when Alice hangs up the call, with Alice's telephone switch sending an ISUP RELease message that is mapped to a BYE by NGW 1.

Page 56

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE Alice -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:ngw1@a.example.com>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to NGW
   1.  NGW 1  prepares to receive data on port 3456 from Alice.*/

Page 57

F3 INVITE Proxy 1 -> Bob

INVITE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying Bob -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 180 Ringing Bob -> Proxy 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals

Page 58

To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:bob@client.b.example.com>
Content-Length: 0

F6 180 Ringing Proxy 1 -> NGW 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0

F7 ACM NGW 1 -> Alice

ACM

F8 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   Contact: <sip:bob@client.b.example.com>
   CSeq: 1 INVITE
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0

Page 59

a=rtpmap:0 PCMU/8000

F9 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F10 ACK NGW 1 -> Proxy 1

ACK sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F11 ACK Proxy 1 -> Bob

ACK sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159

Page 60

Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F12 ANM Bob -> NGW 1

ANM

 
   /* RTP streams are established between A and B (via the GW) */
 
   /* Alice Hangs Up with Bob. */

F13 REL Alice -> NGW 1

REL
CauseCode=16 Normal

F14 RLC NGW 1 -> Alice

RLC

F15 BYE NGW 1-> Proxy 1

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 2 BYE
Content-Length: 0

F16 BYE Proxy 1 -> Bob

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com

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CSeq: 2 BYE
Content-Length: 0

F17 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F18 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

Page 62

3.2 Successful PSTN to SIP call, Fast Answer

 
   Switch A           NGW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      200 F5    |
     |                |     200 F6     |<---------------|
     |                |<---------------|                |
     |                |     ACK F7     |                |
     |     ANM F9     |--------------->|     ACK F8     |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     |     REL F10    |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|     BYE F12    |                |
     |                |--------------->|     BYE F13    |
     |                |                |--------------->|
     |                |                |     200 F14    |
     |                |     200 F15    |<---------------|
     |                |<---------------|                |
     |                |                |                |

This "fast answer" scenario is similar to 3.1., except that Bob immediately accepts the call, sending a 200 OK (F5) without sending a 180 Ringing response. The Gateway then sends an Answer Message (ANM) without sending an Address Complete Message (ACM). Note that for ETSI and some other ISUP variants, a CONnect message (CON) would be sent instead of the ANM.

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE NGW 1 -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

Page 63

Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:ngw1@a.example.com;transport=tcp>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Based upon location analysis the call is forwarded to User
   B.  Bob  prepares to receive data on port 3456 from Alice.*/

F3 INVITE Proxy 1 -> Bob

INVITE bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Page 64

F4 100 Trying Proxy 1 -> NGW 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F6 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com;transport=tcp>

Page 65

Content-Type: application/sdp
Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F7 ACK NGW 1 -> Proxy 1

ACK bob@client.b.example.com SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F8 ACK Proxy 1 -> Bob

ACK bob@client.b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=130.131.132.14
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F9 ANM Bob -> NGW 1

ANM

 
   /* RTP streams are established between A and B (via the GW) */
 
   /* Alice Hangs Up with Bob. */

Page 66

F10 REL ser Alice -> NGW 1

REL
CauseCode=16 Normal

F11 RLC NGW 1 -> Alice

RLC

F12 BYE NGW 1 -> Proxy 1

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 2 BYE
Content-Length: 0

F13 BYE Proxy 1 -> Bob

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F14 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com

Page 67

CSeq: 2 BYE
Content-Length: 0

F15 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

Page 68

3.3 Successful PBX to SIP call

 
   PBX A            GW 1           Proxy 1           Bob
     |                |                |                |
     |    Seizure     |                |                |
     |--------------->|                |                |
     |      Wink      |                |                |
     |<---------------|                |                |
     |  MF Digits F1  |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F5    |
     |                |    180 F6      |<---------------|
     |                |<---------------|                |
     |  One Way Voice |                |                |
     |<===============|                |                |
     |  Ringing Tone  |                |      200 F7    |
     |<===============|     200 F8     |<---------------|
     |                |<---------------|                |
     |                |     ACK F9     |                |
     |     Seizure    |--------------->|     ACK F10    |
     |<---------------|                |--------------->|
     | Both Way Voice |        Both Way RTP Media       |
     |<==============>|<===============================>|
     | Seizure Removal|                |                |
     |--------------->|                |                |
     | Seizure Removal|                |                |
     |<---------------|     BYE F11    |                |
     |                |--------------->|     BYE F12    |
     |                |                |--------------->|
     |                |                |     200 F13    |
     |                |     200 F14    |<---------------|
     |                |<---------------|                |
     |                |                |                |

In this scenario, Alice dials from PBX A to Bob through GW 1 and Proxy 1. This is an example of a call that appears destined for the PSTN but is instead routed to a SIP Client.

Signaling between PBX A and GW 1 is Feature Group B (FGB) circuit associated signaling, in-band Mult-Frequency (MF) outpulsing. After the receipt of the 180 Ringing from Bob, GW 1 generates a ringing tone for Alice.

Bob answers the call by sending a 200 OK. The call terminates when Alice hangs up, causing GW1 to send a BYE.

Page 69

The Gateway can only identify the trunk group that the call came in on; it cannot identify the individual line on PBX A that is placing the call. The SIP URI used to identify the caller is shown in these flows as sip:551313@gw1.a.example.com.

Message Details

PBX Alice -> GW 1

Seizure

GW 1 -> PBX A

Wink

F1 MF Digits PBX Alice -> GW 1

KP 1 972 555 2222 ST

F2 INVITE GW 1 -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65 Max-Forwards: 70
From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:551313@gw1.a.example.com;user=phone>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine where the
   phone number +19725552222 is located.  Based upon location
   analysis the call is forwarded to SIP Bob. */

Page 70

F3 INVITE Proxy 1 -> Bob

INVITE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying Proxy 1 -> GW 1

SIP/2.0 100 Trying
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 180 Ringing Bob -> Proxy 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com

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CSeq: 1 INVITE
Contact: <sip:bob@client.b.example.com>
Content-Length: 0

F6 180 Ringing Proxy 1 -> GW 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0
 
   /* One way Voice path is established between GW and the PBX for
   ringing. */

F7 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   Contact: <sip:bob@client.b.example.com>
   CSeq: 1 INVITE
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Page 72

F8 200 OK Proxy 1 -> GW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Type: application/sdp
   Content-Length: 151

v=0
o=bob 2890844527 2890844527 IN IP4 client.b.example.com
s=-
c=IN IP4 client.b.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F9 ACK GW 1 -> Proxy 1

ACK sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F10 ACK Proxy 1 -> Bob

ACK sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

Page 73

 
   /* RTP streams are established between A and B (via the GW) */
 
   /* Alice Hangs Up with Bob. */

F11 BYE GW 1 -> Proxy 1

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
CSeq: 2 BYE
Content-Length: 0

F12 BYE Proxy 1 -> Bob

BYE sip:bob@client.b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

F13 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

Page 74

F14 200 OK Proxy 1 -> GW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com;user=phone>;tag=jwdkallkzm
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 2 BYE
   Content-Length: 0

3.4 Unsuccessful PSTN to SIP REL, SIP error mapped to REL

 
   Switch A            GW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|                |
     |                |     604 F3     |                |
     |                |<---------------|                |
     |                |     ACK F4     |                |
     |                |--------------->|                |
     |     REL F5     |                |                |
     |<---------------|                |                |
     |     RLC F6     |                |                |
     |--------------->|                |                |
     |                |                |                |

Alice attempts to place a call through Gateway GW 1 and Proxy 1, which is unable to find any routing for the number. The call is rejected by Proxy 1 with a REL message containing a specific Cause value mapped by the gateway based on the SIP error.

Message Details

F1 IAM Alice -> GW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-9999,NPI=E.164,NOA=National

F2 INVITE Alice -> Proxy 1

INVITE sip:+1972559999@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s

Page 75

To: <sip:+1972559999@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
CSeq: 1 INVITE
Contact:

 
   <sip:+13145551111@gw1.a.example.com;user=phone;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 144

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service to find a route to +1-972-555-
   9999.  A route is not found, so Proxy 1 rejects the call. */

F3 604 Does Not Exist Anywhere Proxy 1 -> GW 1

SIP/2.0 604 Does Not Exist Anywhere
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s
   To: <sip:+1972559999@ss1.a.example.com;user=phone>;tag=6a34d410
   Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
   CSeq: 1 INVITE
   Error-Info: <sip:does-not-exist@ann.a.example.com>
   Content-Length: 0

F4 ACK GW 1 -> Proxy 1

ACK sip:+1972559999@ss1.a.example.com;user=phone SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@gw1.a.example.com;user=phone>;tag=076342s To: <sip:+1972559999@ss1.a.example.com;user=phone>;tag=6a34d410 Call-ID: 4Fde34wkd11wsGFDs3@gw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

Page 76

F5 REL GW 1 -> Alice

REL
CauseCode=1

F6 RLC Alice -> GW 1

RLC

3.5 Unsuccessful PSTN to SIP REL, SIP busy mapped to REL

 
   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      600 F5    |
     |                |                |<---------------|
     |                |                |      ACK F6    |
     |                |     600 F7     |--------------->|
     |                |<---------------|                |
     |                |     ACK F8     |                |
     |                |--------------->|                |
     |   REL(17) F9   |                |                |
     |<---------------|                |                |
     |     RLC F10    |                |                |
     |<-------------->|                |                |
     |                |                |                |

In this scenario, Alice calls Bob through Network Gateway NGW 1 and Proxy 1. The call is routed to Bob by Proxy 1. The call is rejected by Bob who sends a 600 Busy Everywhere response. The Gateway sends a REL message containing a specific Cause value mapped by the gateway based on the SIP error.

Since no interworking is indicated in the IAM (F1), the busy tone is generated locally by Alice's telephone switch. In some scenarios, the busy signal is generated by the Gateway since interworking is indicated. For more discussion on interworking, refer to [4].

Page 77

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE Alice -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:ngw1@a.example.com;transport=tcp>
Content-Type: application/sdp
Content-Length: 144

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */

F3 INVITE F3 Proxy 1 -> Bob

INVITE bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp

Page 78

Content-Length: 144

v=0
o=GW 2890844527 2890844527 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying Proxy 1 -> NGW 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 600 Busy Everywhere Bob -> Proxy 1

SIP/2.0 600 Busy Everywhere
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F6 ACK Proxy 1 -> Bob

ACK bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

Page 79

F7 600 Busy Everywhere Proxy 1 -> NGW 1

SIP/2.0 600 Busy Everywhere
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F8 ACK NGW 1 -> Proxy 1

ACK bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F9 REL NGW 1 -> Alice

REL
CauseCode=17 Busy

F10 RLC Alice -> NGW 1

RLC

Page 80

3.6 Unsuccessful PSTN->SIP, SIP error interworking to tones

 
   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      600 F5    |
     |                |                |<---------------|
     |                |                |      ACK F6    |
     |                |     600 F7     |--------------->|
     |                |<---------------|                |
     |                |     ACK F8     |                |
     |     ACM F9     |--------------->|                |
     |<---------------|                |                |
     | One Way Voice  |                |                |
     |<===============|                |                |
     |    Busy Tone   |                |                |
     |<===============|                |                |
     |   REL(16) F10  |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|                |                |
     |                |                |                |

In this scenario, Alice calls Bob through Network Gateway NGW 1 and Proxy 1. The call is routed to Bob by Proxy 1. The call is rejected by the Bob client. NGW 1 sets up a two way voice path to Alice and plays busy tone. The caller then disconnects

NGW 1 plays the busy tone since the IAM (F1) indicates the interworking is present. In scenario 5.2.2., with no interworking, the busy indication is carried in the REL Cause value and is generated locally instead.

Again, note that for ETSI or ITU ISUP, a CONnect message would be sent instead of the Answer Message.

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National
Interworking=encountered

Page 81

F2 INVITE NGW1 -> Proxy 1

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */

F3 INVITE Proxy 1 -> Bob

INVITE bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com;transport=tcp>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0

Page 82

a=rtpmap:0 PCMU/8000

F4 100 Trying Bob -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 600 Busy Everywhere Bob -> Proxy 1

SIP/2.0 600 Busy Everywhere
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F6 ACK Proxy 1 -> Bob

Page 83

F7 600 Busy Everywhere Proxy 1 -> NGW 1

SIP/2.0 600 Busy Everywhere
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F8 ACK NGW 1 -> Proxy 1

ACK sip:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F9 ACM NGW 1 -> Alice

ACM

 
   /* A one way speech path is established between NGW 1 and Alice. */
 
   /* Call Released after Alice hangs up. */

F10 REL Alice -> NGW 1

REL
CauseCode=16

F11 RLC NGW 1 -> Alice

RLC

Page 84

3.7 Unsuccessful PSTN->SIP, ACM timeout

 
   Switch A          NGW 1           Proxy 1          Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |   INVITE F5    |
     |                |                |--------------->|
     |                |                |   INVITE F6    |
     |                |                |--------------->|
     |                |                |   INVITE F7    |
     |                |                |--------------->|
     |                |                |   INVITE F8    |
     |                |                |--------------->|
     |                |                |   INVITE F9    |
     |                |                |--------------->|
     |     REL F10    |                |                |
     |--------------->|                |                |
     |     RLC F11    |                |                |
     |<---------------|                |                |
     |                |   CANCEL F12   |                |
     |                |--------------->|                |
     |                |     200 F13    |                |
     |                |<---------------|                |

Alice calls Bob through NGW 1 and Proxy 1. Proxy 1 re-sends the INVITE after the expiration of SIP timer T1 without receiving any response from Bob. Bob never responds with 180 Ringing or any other response (it is reachable but unresponsive). After the expiration of a timer, Alice's network disconnects the call by sending a Release message REL. The Gateway maps this to a CANCEL.

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE Alice -> Proxy 1

INVITE sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

Page 85

Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:ngw1@a.example.com>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */

F3 INVITE Proxy 1 -> Bob

INVITE sip:bob@b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
c c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Page 86

F4 100 Trying Proxy 1 -> NGW 1

SIP/2.0 100 Trying
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 INVITE Proxy 1 -> Bob

Same as Message F3

F6 INVITE Proxy 1 -> Bob

Same as Message F3

F7 INVITE Proxy 1 -> Bob

Same as Message F3

F8 INVITE Proxy 1 -> Bob

Same as Message F3

F9 INVITE Proxy 1 -> Bob

Same as Message F3

 
   /* Timer expires in Alice's access network. */

F10 REL Alice -> NGW 1

REL
CauseCode=16 Normal

F11 RLC NGW 1 -> Alice

RLC

Page 87

F12 CANCEL NGW 1 -> Proxy 1

CANCEL sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 CANCEL
Content-Length: 0

F13 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

Page 88

3.8 Unsuccessful PSTN->SIP, ACM timeout, stateless Proxy

 
   Switch A          NGW 1      Stateless Proxy 1     Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |   INVITE F4    |--------------->|
     |                |--------------->|   INVITE F5    |
     |                |   INVITE F6    |--------------->|
     |                |--------------->|   INVITE F7    |
     |                |   INVITE F8    |--------------->|
     |                |--------------->|   INVITE F9    |
     |                |   INVITE F10   |--------------->|
     |                |--------------->|   INVITE F11   |
     |                |   INVITE F12   |--------------->|
     |                |--------------->|   INVITE F13   |
     |                |                |--------------->|
     |     REL F14    |                |                |
     |--------------->|                |                |
     |     RLC F15    |                |                |
     |<---------------|                |                |

In this scenario, Alice calls Bob through NGW 1 and Proxy 1. Since Proxy 1 is stateless (it does not send a 100 Trying response), NGW 1 re-sends the INVITE message after the expiration of SIP timer T1. Bob does not respond with 180 Ringing. Alice's network disconnects the call with a release REL (CauseCode=102 Timeout).

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE NGW 1 -> Proxy 1

Page 89

Contact: <sip:ngw1@a.example.com>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */

F3 INVITE Proxy 1 -> Bob

INVITE sip:bob@b.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.201
   Max-Forwards: 69
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 INVITE NGW 1 -> Proxy 1

Same as Message F2

F5 INVITE Proxy 1 -> Bob

Same as Message F3

Page 90

F6 INVITE NGW 1 -> Proxy 1

Same as Message F2

F7 INVITE Proxy 1 -> Bob

Same as Message F3

F8 INVITE NGW 1 -> Proxy 1

Same as Message F2

F9 INVITE Proxy 1 -> Bob

Same as Message F3

F10 INVITE NGW 1 -> Proxy 1

Same as Message F2

F11 INVITE Proxy 1 -> Bob

Same as Message F3

F12 INVITE NGW 1 -> Proxy 1

Same as Message F2

F13 INVITE Proxy 1 -> Bob

Same as Message F3

 
   /* A timer expires in Alice's access network. */

F14 REL Alice -> NGW 1

REL
CauseCode=102 Timeout

Page 91

F15 RLC NGW 1 -> Alice

RLC

3.9 Unsuccessful PSTN->SIP, Caller Abandonment

 
   Switch A          NGW 1          Proxy 1           Bob
     |                |                |                |
     |     IAM F1     |                |                |
     |--------------->|   INVITE F2    |                |
     |                |--------------->|   INVITE F3    |
     |                |     100  F4    |--------------->|
     |                |<---------------|                |
     |                |                |      180 F5    |
     |                |    180 F6      |<---------------|
     |     ACM F7     |<---------------|                |
     |<---------------|                |                |
     |  One Way Voice |                |                |
     |<===============|                |                |
     |  Ringing Tone  |                |                |
     |<===============|                |                |
     |                |                |                |
     |     REL F8     |                |                |
     |--------------->|                |                |
     |     RLC F9     |                |                |
     |<---------------|   CANCEL F10   |                |
     |                |--------------->|                |
     |                |     200 F11    |                |
     |                |<---------------|                |
     |                |                |   CANCEL F12   |
     |                |                |--------------->|
     |                |                |     200 F13    |
     |                |                |<---------------|
     |                |                |     487 F14    |
     |                |                |<---------------|
     |                |                |     ACK F15    |
     |                |     487 F16    |--------------->|
     |                |<---------------|                |
     |                |     ACK F17    |                |
     |                |--------------->|                |
     |                |                |                |

In this scenario, Alice calls Bob through NGW 1 and Proxy 1. Bob does not respond with 200 OK. NGW 1 plays ringing tone since the ACM indicates that interworking has been encountered. Alice disconnects the call with a Release message REL which is mapped by NGW 1 to a

Page 92

CANCEL. Note that if Bob had sent a 200 OK response after the REL, NGW 1 would have sent an ACK and then a BYE to properly terminate the call.

Message Details

F1 IAM Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=972-555-2222,NPI=E.164,NOA=National

F2 INVITE Alice -> Proxy 1

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 uses a Location Service function to determine a route for
   +19725552222.  The call is then forwarded to Bob. */

F3 INVITE Proxy 1 -> Bob

INVITE sip:bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>

Page 93

Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:ngw1@a.example.com;transport=tcp>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844527 2890844527 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 100 Trying Bob -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.201
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 180 Ringing Bob -> Proxy 1

SIP/2.0 180 Ringing
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com;transport=tcp>
   Content-Length: 0

F6 180 Ringing Proxy 1 -> NGW 1

SIP/2.0 180 Ringing

Page 94

Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:bob@client.b.example.com>
   Content-Length: 0

F7 ACM NGW 1 -> Alice

ACM

 
   /* Alice hangs up */

F8 REL Alice -> NGW 1

REL
CauseCode=16 Normal

F9 RLC NGW 1 -> Alice

RLC

F10 CANCEL NGW 1 -> Proxy 1

CANCEL sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 CANCEL
Content-Length: 0

F11 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>

Page 95

Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 CANCEL
Content-Length: 0

F12 CANCEL Proxy 1 -> Bob

CANCEL sip:bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>
Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 CANCEL
Content-Length: 0

F13 200 OK Bob -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 CANCEL
   Content-Length: 0

F14 487 Request Terminated Bob -> Proxy 1

SIP/2.0 487 Request Terminated
Via: SIP/2.0/TCP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F15 ACK Proxy 1 -> Bob

ACK sip:bob@b.example.com SIP/2.0
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70

Page 96

From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F16 487 Request Terminated Proxy 1 -> NGW 1

SIP/2.0 487 Request Terminated
Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F17 ACK NGW 1 -> Proxy 1

ACK sip:+19725552222@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TCP ngw1.a.example.com:5060;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sip:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sip:+19725552222@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 4Fde34wkd11wsGFDs3@ngw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

4 PSTN to PSTN Dialing via SIP Network

In these scenarios, both the caller and the called party are in the telephone network, either normal PSTN subscribers or PBX extensions. The calls route through two Gateways and at least one SIP Proxy Server. The Proxy Server performs the authentication and location of the Gateways.

Again it is noted that the intent of this call flows document is not to provide a detailed parameter level mapping of SIP to PSTN protocols. For information on SIP to ISUP mapping, the reader is referred to other references [4].

In these scenarios, the call is successfully completed between the two Gateways, allowing the PSTN or PBX users to communicate. The 183 Session Progress response is used to indicate that in-band alerting may flow from the called party telephone switch to the caller.

Page 97

4.1 Successful ISUP PSTN to ISUP PSTN call

 
   Switch A       NGW 1         Proxy 1         GW 2         Switch C
    |              |              |              |              |
    |     IAM F1   |              |              |              |
    |------------->|              |              |              |
    |              |  INVITE F2   |              |              |
    |              |------------->|  INVITE F3   |              |
    |              |              |------------->|     IAM F4   |
    |              |              |              |------------->|
    |              |              |              |     ACM F5   |
    |              |              |   183 F6     |<-------------|
    |              |    183 F7    |<-------------|              |
    |    ACM F8    |<-------------|              |              |
    |<-------------|              |              |              |
    | One Way Voice|      Two Way RTP Media      | One Way Voice|
    |<=============|<===========================>|<=============|
    |              |              |              |    ANM F9    |
    |              |              |   200 F10    |<-------------|
    |              |    200 F11   |<-------------|              |
    |    ANM F12   |<-------------|              |              |
    |<-------------|              |              |              |
    |              |    ACK F13   |              |              |
    |              |------------->|    ACK F14   |              |
    |              |              |------------->|              |
    |Both Way Voice|     Both Way RTP Media      |Both Way Voice|
    |<=============|<===========================>|<=============|
    |              |              |              |    REL F15   |
    |              |              |              |<-------------|
    |              |              |   BYE F16    |              |
    |              |    BYE F18   |<-------------|    RLC F17   |
    |              |<-------------|              |------------->|
    |              |              |              |              |
    |              |    200 F19   |              |              |
    |              |------------->|    200 F20   |              |
    |              |              |------------->|              |
    |    REL F21   |              |              |              |
    |<-------------|              |              |              |
    |    RLC F22   |              |              |              |
    |------------->|              |              |              |
    |              |              |              |              |

In this scenario, Alice in the PSTN calls Carol who is an extension on a PBX. Alice's telephone switch signals via SS7 to the Network Gateway NGW 1, while Carol's PBX signals via SS7 with the Gateway GW 2. The CdPN and CgPN are mapped by GW 1 into SIP URIs and placed in the To and From headers. Proxy 1 looks up the dialed digits in the Request-URI and maps the digits to the PBX extension of Carol, which

Page 98

is served by GW 2. The Proxy in F3 uses the host portion of the Request-URI to identify what private dialing plan is being referenced. The INVITE is then forwarded to GW 2 for call completion. An early media path is established end-to-end so that Alice can hear the ringing tone generated by PBX C.

Carol answers the call and the media path is cut through in both directions. Bob hangs up terminating the call.

Message Details

F1 IAM Switch Alice -> NGW 1

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=918-555-3333,NPI=E.164,NOA=National

F2 INVITE NGW 1 -> Proxy 1

INVITE sips:+19185553333@ss1.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2 Max-Forwards: 70
From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sips:+19185553333@ss1.a.example.com;user=phone>
Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
CSeq: 1 INVITE
Contact: <sips:ngw1@a.example.com>
Content-Type: application/sdp
Content-Length: 146

v=0
o=GW 2890844526 2890844526 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* Proxy 1 consults Location Service and translates the dialed number
   to a private number in the Request-URI*/

F3 INVITE Proxy 1 -> GW 2

INVITE sips:4443333@gw2.a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKwqwee65

Page 99

 
    ;received=192.0.2.103
   Max-Forwards: 69
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:ngw1@a.example.com>
   Content-Type: application/sdp
   Content-Length: 146

v=0
o=GW 2890844526 2890844526 IN IP4 ngw1.a.example.com
s=-
c=IN IP4 ngw1.a.example.com
t=0 0
m=audio 3456 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 IAM GW 2 -> Switch C

IAM
CgPN=314-555-1111,NPI=E.164,NOA=National
CdPN=444-3333,NPI=Private,NOA=Subscriber

F5 ACM Switch C -> GW 2

ACM

 
   /* Based on the ACM message, GW 2 returns a 183 response.  In-band
   call progress indications are sent to Alice through NGW 1. */

F6 183 Session Progress GW 2 -> Proxy 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>

Page 100

Content-Type: application/sdp
Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw2.a.example.com
s=-
c=IN IP4 gw2.a.example.com
t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F7 183 Session Progress Proxy 1 -> GW 1

SIP/2.0 183 Session Progress
Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw2.a.example.com
s=-
c=IN IP4 gw2.a.example.com
t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

 
   /* NGW 1 receives packets from GW 2 with encoded ringback, tones or
   other audio.  NGW 1 decodes this and places it on the originating
   trunk. */

F8 ACM NGW 1 -> Switch A

ACM

 
   /* Bob answers */

Page 101

F9 ANM Switch C -> GW 2

ANM

F10 200 OK GW 2 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw2.a.example.com
s=-
c=IN IP4 gw2.a.example.com
t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F11 200 OK Proxy 1 -> NGW 1

SIP/2.0 200 OK
Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Record-Route: <sips:ss1.a.example.com;lr>
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sips:4443333@gw2.a.example.com>
   Content-Type: application/sdp
   Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw2.a.example.com
s=-
c=IN IP4 gw2.a.example.com

Page 102

t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F12 ANM NGW 1 -> Switch A

ANM

F13 ACK NGW 1 -> Proxy 1

ACK sips:4443333@gw2.a.example.com SIP/2.0
Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2 Max-Forwards: 70
Route: <sips:ss1.a.example.com;lr>
From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159 Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F14 ACK Proxy 1 -> GW 2

ACK sips:4443333@gw2.a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS ngw1.a.example.com:5061;branch=z9hG4bKlueha2

 
    ;received=192.0.2.103
   Max-Forwards: 69
   From: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   To: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0
 
   /* RTP streams are established between NGW 1 and GW 2. */
 
   /* Bob Hangs Up with Alice. */

F15 REL Switch C -> GW 2

REL
CauseCode=16 Normal

Page 103

F16 BYE GW 2 -> Proxy 1

BYE sips:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6 Max-Forwards: 70
Route: <sips:ss1.a.example.com;lr>
From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159 To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
CSeq: 4 BYE
Content-Length: 0

F17 RLC GW 2 -> Switch C

RLC

F18 BYE Proxy 1 -> NGW 1

BYE sips:ngw1@a.example.com SIP/2.0
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1 Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6

 
    ;received=192.0.2.202
   Max-Forwards: 69
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0

F19 200 OK NGW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/TLS ss1.a.example.com:5061;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6
    ;received=192.0.2.202
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0

Page 104

F20 200 OK Proxy 1 -> GW 2

SIP/2.0 200 OK
Via: SIP/2.0/TLS gw2.a.example.com:5061;branch=z9hG4bKtexx6

 
    ;received=192.0.2.202
   From: <sips:+19185553333@ss1.a.example.com;user=phone>;tag=314159
   To: <sips:+13145551111@ngw1.a.example.com;user=phone>;tag=7643kals
   Call-ID: 2xTb9vxSit55XU7p8@ngw1.a.example.com
   CSeq: 4 BYE
   Content-Length: 0

F21 REL Switch C -> GW 2

REL
CauseCode=16 Normal

F22 RLC GW 2 -> Switch C

RLC

Page 105

4.2 Successful FGB PBX to ISDN PBX call with overflow

 
   PBX A       GW 1        Proxy 1        GW 2         GW 3        PBX C
     |            |            |            |            |            |
     |  Seizure   |            |            |            |            |
     |----------->|            |            |            |            |
     |    Wink    |            |            |            |            |
     |<-----------|            |            |            |            |
     |MF Digits F1|            |            |            |            |
     |----------->|            |            |            |            |
     |            | INVITE F2  |            |            |            |
     |            |----------->| INVITE F3  |            |            |
     |            |            |----------->|            |            |
     |            |            |   503 F4   |            |            |
     |            |            |<-----------|            |            |
     |            |            |   ACK F5   |            |            |
     |            |            |----------->|            |            |
     |            |            |  INVITE F6              |            |
     |            |            |------------------------>|  SETUP F7  |
     |            |            |          100  F8        |----------->|
     |            |            |<------------------------|CALL PROC F9|
     |            |            |                         |<-----------|
     |            |            |                         | ALERT F10  |
     |            |            |          180 F11        |<-----------|
     |            |  180 F12   |<------------------------|            |
     |            |<-----------|                         |            |
     | Ringtone   |            |                         |OneWay Voice|
     |<===========|            |                         |<===========|
     |            |            |                         | CONNect F13|
     |            |            |         200 F14         |<-----------|
     |            |  200 F15   |<------------------------|            |
     |  Seizure   |<-----------|                         |            |
     |<-----------|  ACK F16   |                         |            |
     |            |----------->|         ACK F17         |            |
     |            |            |------------------------>|CONN ACK F18|
     |            |            |                         |----------->|
     |BothWayVoice|          Both Way RTP Media          |BothWayVoice|
     |<==========>|<====================================>|<==========>|
     |            |            |                         |  DISC F19  |
     |            |            |                         |<-----------|
     |            |            |         BYE F20         |            |
     |            |  BYE F21   |<------------------------|  REL F22   |
     |Seiz Removal|<-----------|                         |----------->|
     |<-----------|  200 F23   |                         |            |
     |Seiz Removal|----------->|         200 F24         |            |
     |----------->|            |------------------------>| REL COM F25|
     |            |            |                         |<-----------|
     |            |            |                         |            |

Page 106

PBX Alice calls PBX Carol via Gateway GW 1 and Proxy 1. During the attempt to reach Carol via GW 2, an error is encountered - Proxy 1 receives a 503 Service Unavailable (F4) response to the forwarded INVITE. This could be due to all circuits being busy, or some other outage at GW 2. Proxy 1 recognizes the error and uses an alternative route via GW 3 to terminate the call. From there, the call proceeds normally with Carol answering the call. The call is terminated when Carol hangs up.

Message Details

PBX Alice -> GW 1

Seizure

GW 1 -> PBX A

Wink

F1 MF Digits PBX Alice -> GW 1

KP 444 3333 ST

F2 INVITE GW 1 -> Proxy 1

INVITE sip:4443333@ss1.a.example.com SIP/2.0
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65 Max-Forwards: 70
From: <sip:551313@gw1.a.example.com>;tag=63412s
To: <sip:4443333@ss1.a.example.com>
Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:551313@gw1.a.example.com>
Content-Type: application/sdp
Content-Length: 155

v=0
o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

Page 107

 
   /* Proxy 1 uses a Location Service function to determine where B is
   located.  Response is returned listing alternative routes, GW2 and
   GW3, which are then tried sequentially. */

F3 INVITE Proxy 1 -> GW 2

INVITE sip:4443333@gw2.a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 155

v=0
o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F4 503 Service Unavailable GW 2 -> Proxy 1

SIP/2.0 503 Service Unavailable
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F5 ACK Proxy 1 -> GW 2

ACK sip:4443333@ss1.a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.1

Page 108

Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forward: 70
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=314159
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

F6 INVITE Proxy 1 -> GW 3

INVITE sip:+19185553333@gw3.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:551313@gw1.a.example.com>
   Content-Type: application/sdp
   Content-Length: 155

v=0
o=GW 2890844526 2890844526 IN IP4 gw1.a.example.com
s=-
c=IN IP4 gw1.a.example.com
t=0 0
m=audio 49172 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F7 SETUP GW 3 -> PBX C

Protocol discriminator=Q.931
Message type=SETUP
Bearer capability: Information transfer capability=0 (Speech) or 16 (3.1 kHz audio)
Channel identification=Preferred or exclusive B-channel
Progress indicator=1 (Call is not end-to-end ISDN; further call progress information may be available inband)
Called party number:
Type of number and numbering plan ID=33 (National number in ISDN numbering plan)
Digits=918-555-3333

Page 109

F8 100 Trying GW 3 -> Proxy 1

SIP/2.0 100 Trying
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Content-Length: 0

F9 CALL PROCeeding PBX C -> GW 3

Protocol discriminator=Q.931
Message type=CALL PROC

F10 ALERT PBX C -> GW 3

Protocol discriminator=Q.931
Message type=PROG

 
   /* Based on ALERT message, GW 3 returns a 180 response. */

F11 180 Ringing GW 3 -> Proxy 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Length: 0

F12 180 Ringing Proxy 1 -> GW 1

SIP/2.0 180 Ringing
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

Page 110

 
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Length: 0

F13 CONNect PBX C -> GW 3

Protocol discriminator=Q.931
Message type=CONN

F14 200 OK GW 3 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 INVITE
   Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
   Content-Type: application/sdp
   Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw3.a.example.com
s=-
c=IN IP4 gw3.a.example.com
t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

F15 200 OK Proxy 1 -> GW 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Record-Route: <sip:ss1.a.example.com;lr>
   From: <sip:551313@gw1.a.example.com>;tag=63412s

Page 111

To: <sip:4443333@ss1.a.example.com>;tag=123456789
Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
CSeq: 1 INVITE
Contact: <sip:+19185553333@gw3.a.example.com;user=phone>
Content-Type: application/sdp
Content-Length: 143

v=0
o=GW 987654321 987654321 IN IP4 gw3.a.example.com
s=-
c=IN IP4 gw3.a.example.com
t=0 0
m=audio 14918 RTP/AVP 0
a=rtpmap:0 PCMU/8000

GW 1 -> PBX A

Seizure

F16 ACK GW 1 -> Proxy 1

ACK sip:+19185553333@gw3.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65 Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:551313@gw1.a.example.com>;tag=63412s
To: <sip:4443333@ss1.a.example.com>;tag=123456789
Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
CSeq: 1 ACK
Content-Length: 0

F17 ACK Proxy 1 -> GW 3

ACK sip:+19185553333@gw3.a.example.com;user=phone SIP/2.0 Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP gw1.a.example.com:5060;branch=z9hG4bKwqwee65

 
    ;received=192.0.2.201
   Max-Forwards: 69
   From: <sip:551313@gw1.a.example.com>;tag=63412s
   To: <sip:4443333@ss1.a.example.com>;tag=123456789
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 ACK
   Content-Length: 0

Page 112

F18 CONNect ACK GW 3 -> PBX C

Protocol discriminator=Q.931
Message type=CONN ACK

 
   /* RTP streams are established between GW 1 and GW 3. */
 
   /* Bob Hangs Up with Alice. */

F19 DISConnect PBX C -> GW 3

Protocol discriminator=Q.931
Message type=DISC
Cause=16 (Normal clearing)

F20 BYE GW 3 -> Proxy 1

BYE sip:551313@gw1.a.example.com SIP/2.0
Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq Max-Forwards: 70
Route: <sip:ss1.a.example.com;lr>
From: <sip:4443333@ss1.a.example.com>;tag=123456789
To: <sip:551313@gw1.a.example.com>;tag=63412s
Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
CSeq: 1 BYE
Content-Length: 0

F21 BYE Proxy 1 -> GW 1

BYE sip:551313@gw1.a.example.com SIP/2.0
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2 Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq

 
    ;received=192.0.2.203
   Max-Forwards: 69
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0

GW 1 -> PBX A

Seizure removal

Page 113

F22 RELease GW 3 -> PBX C

Protocol discriminator=Q.931
Message type=REL

F23 200 OK GW 1 -> Proxy 1

SIP/2.0 200 OK
Via: SIP/2.0/UDP ss1.a.example.com:5060;branch=z9hG4bK2d4790.2

 
    ;received=192.0.2.111
   Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq
    ;received=192.0.2.203
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0

F24 200 OK Proxy 1 -> GW 3

SIP/2.0 200 OK
Via: SIP/2.0/UDP gw3.a.example.com:5060;branch=z9hG4bKkdjuwq

 
    ;received=192.0.2.203
   From: <sip:4443333@ss1.a.example.com>;tag=123456789
   To: <sip:551313@gw1.a.example.com>;tag=63412s
   Call-ID: 2xTb9vxSit55XU7p8@gw1.a.example.com
   CSeq: 1 BYE
   Content-Length: 0

F25 RELease COMplete PBX C -> GW 3

Protocol discriminator=Q.931
Message type=REL COM

PBX Alice -> GW 1

Seizure removal

5 Security Considerations

This document provides examples of mapping from SIP to ISUP and ISUP to SIP. The gateways in these examples are compliant with the Security Considerations Section of RFC 3398 [4] which is summarized here.

Page 114

There are few security concerns relating to the mapping of ISUP to SIP besides privacy considerations in the calling party number passing. Some concerns relating to the mapping from tel URI parameters to ISUP include the user creation of parameters and codes relating to called number and local number portability (LNP). An operator of a gateway should use policies similar to those present in PSTN switches to avoid security problems.

The mapping from a SIP response code to an ISUP Cause Code presents a theoretical risk, so a gateway operator may implement policies controlling this mapping. Gateways should also not rely on the contents of the From header field for identity information, as it may be arbitrarily populated by a user. Instead, some sort of cryptographic authentication and authorization should be used for identity determination. These flows show both HTTP Digest for authentication of users, although for brevity, the challenge is not always shown.

The early media cut-through shown in some flows is another potential security risk, but it is also required for proper interaction with the PSTN. Again, a gateway operator should use proper policies relating to early media to prevent fraud and misuse. Finally, a user agent (even a properly authenticated one) can launch multiple simultaneous requests through a gateway, constituting a denial of service attack. The adoption of policies to limit the number of simultaneous requests from a single entity may be used to prevent this attack.

As discussed in the SIP-T framework [7], SIP/ISUP interworking can be employed as an interdomain signaling mechanism that may be subject to pre-existing trust relationships between administrative domains. Any administrative domain implementing SIP-T or SIP/ISUP interworking should have an adequate security apparatus (including elements that manage any appropriate policies to manage fraud and billing in an interdomain environment) in place to ensure that the translation of ISUP information does not result in any security violations.

Although no examples of this are shown in this document, transporting ISUP in SIP bodies may provide opportunities for abuse, fraud, and privacy concerns, especially when SIP-T requests can be generated, inspected or modified by arbitrary SIP endpoints. ISUP MIME bodies should be secured (preferably with S/MIME as detailed in RFC 3261 [2]) to alleviate this concern. Authentication properties provided by S/MIME would allow the recipient of a SIP-T message to ensure that the ISUP MIME body was generated by an authorized entity. Encryption would ensure that only carriers possessing a particular decryption key are capable of inspecting encapsulated ISUP MIME bodies in a SIP request.

Page 115

6 References

6.1 Normative References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[2] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. E. and Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002.

[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002.

[4] Camarillo, G., Roach, A. B., Peterson, J. and L. Ong, "Integrated Services Digital Network (ISDN) User Part (ISUP) to Session Initiation Protocol (SIP) Mapping", RFC 3398, December 2002.

[5] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S., Leach, P., Luotonen, A. and L. Stewart, "HTTP Authentication: Basic and Digest Access Authentication", RFC 2617, June 1999.

[6] Vaha-Sipila, A., "URLs for Telephone Calls", RFC 2806, April 2000.

[7] Vemuri, A. and J. Peterson, "Session Initiation Protocol for Telephones (SIP-T): Context and Architectures", BCP 63, RFC 3372, September 2002.

[8] Zimmerer, E., Peterson, J., Vemuri, A., Ong, L., Audet, F., Watson, M. and M. Zonoun, "MIME media types for ISUP and QSIG Objects", RFC 3204, December 2001.

[9] Faltstrom, P., "E.164 number and DNS", RFC 2916, September 2000.

6.2 Informative References

[10] Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K. Summers, "Session Initiation Protocol (SIP) Basic Call Flow Examples", RFC 3665, December 2003.

Page 116

7 Acknowledgments

Thanks to Rohan Mahy, Adam Roach, Gonzalo Camarillo, Cullen Jennings, and Tom Taylor for their detailed comments during the final review. Thanks to Dean Willis for his early contributions to the development of this document. Thanks to Jon Peterson for his help on the security section.

The authors wish to thank Kundan Singh for performing parser validation of messages.

The authors wish to thank the following individuals for their participation in a detailed review of this call flows document: Aseem Agarwal, Rafi Assadi, Ben Campbell, Sunitha Kumar, Jon Peterson, Marc Petit-Huguenin, Vidhi Rastogi, and Bodgey Yin Shaohua.

The authors also wish to thank the following individuals for their assistance: Jean-Francois Mule, Hemant Agrawal, Henry Sinnreich, David Devanatham, Joe Pizzimenti, Matt Cannon, John Hearty, the whole MCI WorldCom IPOP Design team, Scott Orton, Greg Osterhout, Pat Sollee, Doug Weisenberg, Danny Mistry, Steve McKinnon, and Denise Ingram, Denise Caballero, Tom Redman, Ilya Slain, Pat Sollee, John Truetken, and others from MCI WorldCom, 3Com, Cisco, Lucent and Nortel.

8 Intellectual Property Statement

The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat.

The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director.

Page 117

9 Authors' Addresses

All listed authors actively contributed large amounts of text to this document.

Alan Johnston
MCI
100 South 4th Street
St. Louis, MO 63102
USA

EMail: alan.johnston@mci.com

Steve Donovan
dynamicsoft, Inc.
5100 Tennyson Parkway
Suite 1200
Plano, Texas 75024
USA

EMail: sdonovan@dynamicsoft.com

Robert Sparks
dynamicsoft, Inc.
5100 Tennyson Parkway
Suite 1200
Plano, Texas 75024
USA

EMail: rsparks@dynamicsoft.com

Chris Cunningham
dynamicsoft, Inc.
5100 Tennyson Parkway
Suite 1200
Plano, Texas 75024
USA

EMail: ccunningham@dynamicsoft.com

Kevin Summers
Sonus
1701 North Collins Blvd, Suite 3000
Richardson, TX 75080
USA

EMail: kevin.summers@sonusnet.com

Page 118

10 Full Copyright Statement

This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English.

The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees.

This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

Funding for the RFC Editor function is currently provided by the Internet Society.

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