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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 5359

SIPPING Working Group                                        A. Johnston
Internet-Draft                                                       MCI
Expires: August 17, 2005                                       R. Sparks
                                                           C. Cunningham
                                                              S. Donovan
                                                             dynamicsoft
                                                              K. Summers
                                                                   Sonus
                                                       February 13, 2005


              Session Initiation Protocol Service Examples
                 draft-ietf-sipping-service-examples-08

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 17, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   This document gives examples of Session Initiation Protocol (SIP)



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   services.  This covers most features offered in so-called IP Centrex
   offerings from local exchange carriers and PBX (Private Branch
   Exchange) features.  Most of the services shown in this document are
   implemented in the SIP User Agents, although some require the
   assistance of a SIP Proxy.  Some require some extensions to SIP
   including the REFER, SUBSCRIBE, and NOTIFY methods and the Replaces
   and Join headers.  These features are not intended to be an
   exhaustive set, but rather show implementations of common features
   likely to be implemented on SIP IP telephones in a business
   environment.

Table of Contents

   1.   Overview . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.   Service Examples . . . . . . . . . . . . . . . . . . . . . .   4
     2.1  Call Hold  . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2  Consultation Hold  . . . . . . . . . . . . . . . . . . . .  16
     2.3  Music On Hold  . . . . . . . . . . . . . . . . . . . . . .  33
     2.4  Transfer - Unattended  . . . . . . . . . . . . . . . . . .  41
     2.5  Transfer - Attended  . . . . . . . . . . . . . . . . . . .  48
     2.6  Transfer - Instant Messaging . . . . . . . . . . . . . . .  61
     2.7  Call Forwarding Unconditional  . . . . . . . . . . . . . .  66
     2.8  Call Forwarding - Busy . . . . . . . . . . . . . . . . . .  72
     2.9  Call Forwarding - No Answer  . . . . . . . . . . . . . . .  78
     2.10   3-way Conference - Third Party is Added  . . . . . . . .  87
     2.11   3-way Conference - Third Party Joins . . . . . . . . . .  93
     2.12   Single Line Extension  . . . . . . . . . . . . . . . . .  98
     2.13   Find-Me  . . . . . . . . . . . . . . . . . . . . . . . . 116
     2.14   Call Management (Incoming Call Screening)  . . . . . . . 126
     2.15   Call Management (Outgoing Call Screening)  . . . . . . . 134
     2.16   Call Park  . . . . . . . . . . . . . . . . . . . . . . . 137
     2.17   Call Pickup  . . . . . . . . . . . . . . . . . . . . . . 146
     2.18   Automatic Redial . . . . . . . . . . . . . . . . . . . . 154
     2.19   Click to Dial  . . . . . . . . . . . . . . . . . . . . . 159
   3.   Security Considerations  . . . . . . . . . . . . . . . . . . 163
   4.   IANA Considerations  . . . . . . . . . . . . . . . . . . . . 163
   5.   Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 163
   6.   Document History . . . . . . . . . . . . . . . . . . . . . . 164
     6.1  Changes since -07  . . . . . . . . . . . . . . . . . . . . 164
   7.   References . . . . . . . . . . . . . . . . . . . . . . . . . 164
     7.1  Normative References . . . . . . . . . . . . . . . . . . . 164
     7.2  Informative References . . . . . . . . . . . . . . . . . . 165
        Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 166
        Intellectual Property and Copyright Statements . . . . . . . 167







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1.  Overview

   This document provides example call flows detailing a SIP
   implementation of the following traditional telephony services:

            Call Hold                     Music on Hold
            Unattended Transfer           Consultation Hold
            Unconditional Call Forwarding Attended Transfer
            No Answer Call Forwarding     Busy Call Forwarding
            Single-Line Extension         3-way Call
            Incoming Call Screening       Find-Me
            Call Pickup                   Call Park
            Outgoing Call Screening       Automatic Redial
            Click to Dial

   The call flows shown in this document were developed in the design of
   a SIP IP communications network.  They represent an example set of
   so-called IP Centrex services or PBX services.

   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 SIP service examples as a companion to the
   specifications.

   These call flows are based on the current version 2.0 of SIP in RFC
   3261 [2] with SDP usage described in RFC 3264 [5] Other RFCs also
   comprise the SIP standard and are used and references in these call
   flows.

   The SIP specification and the other referenced documents are
   definitive as far as protocol issues are concerned.  Also, these
   flows do not represent the only way to implement these services -
   other approaches such as 3pcc (Third Party Call Control) [17] or
   Back-to-Back User Agents (B2BUA) may be more appropriate in some
   circumstances.  The peer-to-peer design and principles of these
   service examples are described in the Multiparty Framework document
   [12].

   These flows assume the functionality described in the SIP Call Flow
   Examples document [16], which explores basic SIP behavior.  Some of
   the scenarios described herein make use of the SIP method extension
   REFER [3] and the SIP header extension Replaces [4], the SIP header
   extension Join [9], and some of the concepts in the 3pcc (third party
   call control) [17] document.  The SIP Events document [6] describes
   the use of SUBSCRIBE and NOTIFY while the SIP Dialog Event Package



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   [8] document describes the dialog event package.  Some examples make
   use the GRUU (Globally Routable User Agent URI) [20] extension.

   These flows were prepared assuming a network of proxies, registrars,
   PSTN gateways, and other SIP servers.  The use of Secure SIP URIs
   (sips) is shown throughout this document with assumed certificate
   validation for security.  However, other security approaches such as
   Digest challenges can be used.

   Each call flow is presented with a textual description of the
   scenario, a message flow diagram showing the messages exchanged
   between separate network elements, and the detailed contents of each
   message shown in the diagram.

   1.1 Legend for Message Flows

   Dashed lines (---) represent control messages that are mandatory to
   the call scenario.  These control messages can be SIP signaling.

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

   Messages with parenthesis around name represent optional control
   messages.

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

   /* Comments.  */

2.  Service Examples

2.1  Call Hold

            Alice           Proxy            Bob
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             |                |   INVITE F2  |
             |(100 Trying) F3 |------------->|
             |<---------------|              |
             |                |180 Ringing F4|
             | 180 Ringing F5 |<-------------|
             |<---------------|              |
             |                |  200 OK F6   |
             |    200 OK F7   |<-------------|
             |<---------------|              |



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             |     ACK F8     |              |
             |--------------->|    ACK F9    |
             |                |------------->|
             |    Both way RTP Established   |
             |<=============================>|
             |                |INVITE(hold) F10
             |INVITE(hold) F11|<-------------|
             |<---------------|              |
             |    200 OK F12  |              |
             |--------------->|   200 OK F13 |
             |                |------------->|
             |                |     ACK F14  |
             |     ACK F15    |<-------------|
             |<---------------|              |
             |           No RTP Sent!        |
             |                |  INVITE F16  |
             |   INVITE F17   |<-------------|
             |<---------------|              |
             |   200 OK F18   |              |
             |--------------->|  200 OK F19  |
             |                |------------->|
             |                |    ACK F20   |
             |     ACK F21    |<-------------|
             |<---------------|              |
             |    Both way RTP Established   |
             |<=============================>|
             |     BYE F22    |              |
             |--------------->|   BYE F23    |
             |                |------------->|
             |                |   200 OK F24 |
             |    200 OK F25  |<-------------|
             |<---------------|              |
             |                |              |

   In this scenario, Alice calls Bob, then Bob places the call on hold.
   Bob then takes call off hold.  Alice hangs up call.  Note that hold
   is unidirectional in nature.  However, a UA that places the other
   party on hold will generally also stop sending media, resulting in no
   media exchange between the UAs.  Older UAs may set the connection
   address to 0.0.0.0 when initiating hold.  However, this behavior has
   been deprecated in favor of using the a=sendonly SDP attribute.

   Message Details


      F1 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy 1 -> Bob

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000





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      F3 (100 Trying) Proxy 1 -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 180 Ringing Bob -> Proxy 1

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length:0


      F5 180 Ringing Proxy 1 -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length: 0


      F6 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9



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       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F7 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 ACK Alice -> Proxy 1




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      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf92
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F9 ACK Proxy 1 -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837492.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf92
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Bob places Alice on hold.  Note that the version is


         incremented in the o= field of the SDP  */

      F10 INVITE Bob -> Proxy 1

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp



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      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F11 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      /* A replies to hold */

      F12 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7



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       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F13 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly





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      F14 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds72
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F15 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds72
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /*   Bob takes the call off hold */

      F16 INVITE Bob -> Proxy 1


      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds73
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp



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      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F17 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837493.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds73
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F18 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837493.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds73
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F19 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds73
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F20 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds74
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70



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      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F21 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837494.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds74
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* RTP Media stream re-established.   Alice disconnects. */

      F22 BYE Alice -> Proxy 1

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf97
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F23 BYE Proxy 1 -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837497.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf97
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F24 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK


      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837497.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf97
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F25 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf97
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


2.2  Consultation Hold

           Alice            Proxy           Bob                Carol
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|   INVITE F2  |                   |
             |                |------------->|                   |
             |(100 Trying) F3 |              |                   |
             |<---------------|180 Ringing F4|                   |
             |                |<-------------|                   |
             | 180 Ringing F5 |              |                   |
             |<---------------|  200 OK F6   |                   |
             |                |<-------------|                   |
             |    200 OK F7   |              |                   |



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             |<---------------|              |                   |
             |     ACK F8     |              |                   |
             |--------------->|     ACK F9   |                   |
             |                |------------->|                   |
             |     Both way RTP Established  |                   |
             |<=============================>|                   |
             |                |INVITE(hold) F10                  |
             |INVITE(hold) F11|<-------------|                   |
             |<---------------|              |                   |
             |    200 OK F12  |              |                   |
             |--------------->|   200 OK F13 |                   |
             |                |------------->|                   |
             |                |     ACK F14  |                   |
             |                |<-------------|                   |
             |    ACK F15     |              |                   |
             |<---------------|              |                   |
             |         No RTP Sent!          |                   |
             |                |   INVITE F16 |                   |
             |                |<-------------|                   |
             |                |              |    INVITE F17     |
             |                |--------------------------------->|
             |                |(100 Trying) F18                  |
             |                |------------->|                   |
             |                |              | 180 Ringing F19   |
             |                |<---------------------------------|
             |                | 180 Ringing F20                  |
             |                |------------->|                   |
             |                |              |    200 OK F21     |
             |                |<---------------------------------|
             |                |   200 OK F22 |                   |
             |                |------------->|                   |
             |                |    ACK F23   |                   |
             |                |<-------------|                   |
             |                |              |      ACK F24      |
             |                |--------------------------------->|
             |                |         Both way RTP Established |
             |                |              |<=================>|
             |                |   BYE F25    |                   |
             |                |<-------------|                   |
             |                |              |       BYE F26     |
             |                |--------------------------------->|
             |                |              |    200 OK F27     |
             |                |<---------------------------------|
             |                |   200 OK F28 |                   |
             |                |------------->|                   |
             |                |   INVITE F29 |                   |
             |    INVITE F30  |<-------------|                   |
             |<---------------|              |                   |



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             |    200 OK F31  |              |                   |
             |--------------->|   200 OK F32 |                   |
             |                |------------->|                   |
             |                |     ACK F33  |                   |
             |                |<-------------|                   |
             |    ACK F34     |              |                   |
             |<---------------|              |                   |
             |     Both way RTP Established  |                   |
             |<=============================>|                   |
             |    BYE F35     |              |                   |
             |--------------->|    BYE F36   |                   |
             |                |------------->|                   |
             |                |   200 OK F37 |                   |
             |                |<-------------|                   |
             |  200 OK F38    |              |                   |
             |<---------------|              |                   |
             |                |              |                   |

   In this scenario, Alice calls Bob.  Bob places call on hold.  Bob
   calls Carol.  Bob then disconnects with Carol, then takes the call
   with Alice off hold.  The call ends when Alice hangs up.

   Message Details


      F1 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000




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      F2 INVITE Proxy 1 -> Bob

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F3(100 Trying) Proxy 1 -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 180 Ringing Bob -> Proxy 1

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length:0


      F5 180 Ringing Proxy 1 -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content Length: 0


      F6 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000





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      F7 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 ACK Alice -> Proxy 1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf45
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F9 ACK Proxy 1 -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837494.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf45
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Bob  places  Alice on hold. */

      F10 INVITE Bob -> Proxy 1

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F11 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837497.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE



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      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F12 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837497.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F13 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7



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       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F14 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdsg
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F15 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8374.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdsg
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK



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      Content-Length: 0


      F16 INVITE Bob -> Proxy 1

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844834 2890844834 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 50170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F17 INVITE Proxy 1 -> Carol

      INVITE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749a.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844834 2890844834 IN IP4 client.biloxi.example.com
      s=Session SDP



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      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 50170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F18 (100 Trying) Proxy 1 -> Bob

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE

      Content-Length: 0



      F19 180 Ringing Carol -> Proxy 1

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749a.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content Length:0


      F20 180 Ringing Proxy 1 -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=client.chicago.example.com
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content Length: 0



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      F21 200 OK Carol -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749a.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F22 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds22
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0



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      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F23 ACK Bob -> Proxy 1

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds24
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F24 ACK Proxy 1 -> Carol

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749b.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds24
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F25 BYE Bob -> Proxy 1

      BYE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7j
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654


      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0



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      F26 BYE Proxy 1 -> Carol

      BYE sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749k.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F27 200 OK Carol -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749k.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F28 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7j
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=456654
      Call-ID: 9876543210@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      /* Bob  takes the call off hold */


      F29 INVITE Bob -> Proxy 1

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7b
      Route: <sips:ss1.example.com;lr>



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      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F30 INVITE Proxy 1 -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749q.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F31 200 OK Alice -> Proxy 1

      SIP/2.0 200 OK



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      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749q.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F32 200 OK Proxy 1 -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7b
       ;received=192.0.2.105
      Record-Route: <sips:ss1.example.com;lr>
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000




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      F33 ACK Bob -> Proxy 1

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7d7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F34 ACK Proxy 1 -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8374.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7d7
       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F35 BYE Alice -> Proxy 1

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf10
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F36 BYE Proxy 1 -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8379.1



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F37 200 OK Bob -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8379.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F38 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf10
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


2.3  Music On Hold


           Alice             Bob       Music Server
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             | 180 Ringing F2 |              |
             |<---------------|              |
             |    200 OK F3   |              |
             |<---------------|              |
             |     ACK F4     |              |



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             |--------------->|              |
             |       RTP      |              |
             |<==============>|              |
             |                |              |
             | Bob places Alice on hold with music
             |                |              |
             |                | INVITE no sdp F5
             |                |------------->|
             |                |200 OK sdpM F6|
             |                |<-------------|
             |INVITE (hold) F7|              |
             |<---------------|              |
             | 200 OK sdpA F8 |              |
             |--------------->|              |
             |     ACK F9     |              |
             |<---------------|              |
             |                | ACK sdpA F10 |
             |                |------------->|
             |               RTP             |
             |<==============================|
             |                |              |
             |    Bob Picks up the Call      |
             |                |    BYE F11   |
             |                |------------->|
             |                | 200 OK F12   |
             |                |<-------------|
             |    INVITE F13  |              |
             |<---------------|              |
             |    200 OK F14  |              |
             |--------------->|              |
             |     ACK F15    |              |
             |<---------------|              |
             |       RTP      |              |
             |<==============>|              |

   In this flow, Bob places Alice on hold with music.  This is performed
   by Bob acting as a 3pcc (third party call controller) [17] to INVITE
   a Music Server into the session, which sends RTP music to Alice.  Bob
   picks the call up from hold by sending a BYE to the music server and
   taking Alice off of hold.

   Note that if Alice responds to the INVITE with hold SDP with hold SDP
   in the 200 OK, this call flow will not work properly.

   Note also that Alice will receive RTP packets from two different IP
   addresses during this call flow.  Alice could refuse the music by
   sending a re-INVITE changing the session to a=inactive.




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   Message Details



      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0



      F3 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 ACK Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfd
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0



      /* Bob  places Alice on hold with music by acting as a 3pcc and
         sending an INVITE to the Music Server  */

      F5 INVITE Bob -> Music Server

      INVITE sips:music@server.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Music <sips:music@server.example.com>
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces



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      Content-Length: 0


      F6 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Music <sips:music@server.example.com>;tag=90210
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:music@server.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=MusicServer 2890844576 2890844577 IN IP4 music.server.example.com
      s=Session SDP
      c=IN IP4 music.server.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly

      /* Bob re-INVITEs Alice on hold */

      F7 INVITE Bob -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf5
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 music.server.example.com



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      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F8 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf5
       ;received=192.0.2.103
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F9 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfy
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Bob passes SDP of Alice to the Music Server to allow music to be sent
         from Bob to Alice */




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      F10 ACK Bob -> Music Server

      ACK sips:music@server.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds3
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Music <sips:music@server.example.com>;tag=90210
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      /* RTP music is now sent from the Music Server to Alice */

      /* Bob picks up the call from the Music Server */

      F11 BYE Bob -> Music Server

      BYE sips:music@server.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds0
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Music <sips:music@server.example.com>;tag=90210
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F12 200 OK Music Server -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds0
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Music <sips:music@server.example.com>;tag=90210
      Call-ID: sdjfdjfskdf@biloxi.example.com



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      CSeq: 2 BYE
      Content-Length:0


      /* B re-INVITEs taking A off hold */

      F13 INVITE Bob -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...


      v=0
      o=bob 2890844527 2890844529 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F14 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b
       ;received=192.0.2.103
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:bob@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844528 IN IP4 client.atlanta.example.com



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      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F15 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b5
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com

      CSeq: 2 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Normal media session between A and B is resumed */



2.4  Transfer - Unattended


          Alice                 Bob                 Carol
            |      INVITE F1     |                    |
            |<-------------------|                    |
            |   180 Ringing F2   |                    |
            |------------------->|                    |
            |      200 OK F3     |                    |
            |------------------->|                    |
            |        ACK F4      |                    |
            |<-------------------|                    |
            |        RTP         |                    |
            |<==================>|                    |
            |                    |                    |
            |  Alice performs unattended transfer     |
            |                    |                    |
            | REFER Refer-To:C F5|                    |
            |------------------->|                    |
            |  202 Accepted F6   |                    |
            |<-------------------|                    |
            |      NOTIFY F7     |                    |



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            |<-------------------|                    |
            |      200 OK F8     |                    |
            |------------------->|                    |
            |       BYE F9       |                    |
            |------------------->|                    |
            |     200 OK F10     |                    |
            |<-------------------|                    |
            |   No RTP Session   | INVITE Referred-By: A F11
            |                    |------------------->|
            |                    |   180 Ringing F12  |
            |                    |<-------------------|
            |                    |     200 OK F13     |
            |                    |<-------------------|
            |                    |       ACK F14      |
            |                    |------------------->|
            |                    |        RTP         |
            |                    |<==================>|
            |      NOTIFY F14    |                    |


            |<-------------------|                    |
            |      200 OK F15    |                    |
            |------------------->|                    |
            |                    |                    |

   In this scenario, Bob calls Alice.  Alice then transfers Bob to
   Carol, then Alice disconnects with Bob.  Bob establishes the session
   to Carol then reports the success  back to Alice in the NOTIFY in
   F14.  If the transfer fails, Bob can send a new INVITE back to Alice
   to re-establish the session.

   Despite the BYE sent by Alice in F9, the dialog between Alice and Bob
   still exists until the subscription created by the REFER has
   terminated (either due to a NOTIFY containing a Subscription-State:
   terminated;reason=noresource header field, as in F14, or a 481
   response to a NOTIFY).

   For more about call transfer see the transfer [7] document.

   Message Details


      F1 INVITE Bob -> Alice

      INVITE sips:alice@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159



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      To: Alice <sips:alice@atlanta.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Alice -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Length: 0


      F3 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com



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      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000



      F4 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds2
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Session is established between Alice and Bob. */

      /* Alice peforms unattended transfer of Bob to Carol */

      F5 REFER Alice -> Bob

      REFER sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds8
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 REFER
      Refer-To: <sips:carol@chicago.example.com>
      Referred-By: <alice@atlanta.example.com>
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Length: 0


      F6 202 Accepted Bob -> Alice

      SIP/2.0 202 Accepted
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds8
       ;received=192.0.2.113
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159



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      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 REFER
      Content-Length: 0


      F7 NOTIFY Bob -> Alice

      NOTIFY sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds32
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 NOTIFY
      Event: refer
      Subscription-State: active;expires=60
      Content-Type: message/sipfrag
      Content-Length: ...


      SIP/2.0 100 Trying


      F8 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds32
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0


      /* Alice now disconnects with Bob. */

      F9 BYE Alice -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds43
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 BYE
      Content-Length: 0




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      F10 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds43
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 BYE
      Content-Length: 0


      /* Bob attempts the transfer to Carol */

      F11 INVITE Bob -> Carol

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds1
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Referred-By: <alice@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844539 2890844539 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423821 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F12 180 Ringing Carol -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE



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      Contact: <sips:carol@client.chicago.example.com>
      Content-Length: 0


      F13 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844527 2890844527 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F14 ACK Bob -> Carol

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds9
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* Bob and Carol now have established a session.  Bob reports success to Alice which Alice probably ignores. */

      F15 NOTIFY Bob -> Alice

      NOTIFY sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds67
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159



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      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 NOTIFY
      Event: refer
      Subscription-State: terminated;reason=noresource
      Content-Type: message/sipfrag
      Content-Length: ...

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds1
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content-Type: application/sdp
      Content-Length: ...


      F16 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds6
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 3 NOTIFY
      Content-Length: 0


2.5  Transfer - Attended


           Alice             Bob          Carol
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             | 180 Ringing F2 |              |
             |<---------------|              |
             |    200 OK F3   |              |
             |<---------------|              |
             |     ACK F4     |              |
             |--------------->|              |
             |       RTP      |              |
             |<==============>|              |
             |INVITE (hold) F5|              |



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             |<---------------|              |
             |    200 OK F6   |              |
             |--------------->|              |
             |     ACK F7     |              |
             |<---------------|              |
             |     No RTP     |              |
             |                |  INVITE F8   |
             |                |------------->|
             |                | 180 Ringing F9
             |                |<-------------|
             |                |  200 OK F10  |
             |                |<-------------|
             |                |    ACK F11   |
             |                |------------->|
             |                |     RTP      |
             |                |<============>|
             |                |INVITE (hold) F12
             |                |------------->|
             |                | 200 OK F13   |
             |                |<-------------|
             |                |    ACK F14   |
             |                |------------->|
             |                |     No RTP   |
             | REFER Refer-To: C F15         |
             |<---------------|              |
             |202 Accepted F16|              |
             |--------------->|              |
             |   NOTIFY F17   |              |
             |--------------->|              |
             |   200 OK F18   |              |
             |<---------------|              |
             |     INVITE Replaces: B F19    |
             |------------------------------>|
             |            200 OK F20         |
             |<------------------------------|
             |             ACK F21           |
             |------------------------------>|
             |               RTP             |
             |<=============================>|
             |                |    BYE F22   |
             |                |<-------------|
             |                |  200 OK F23  |
             |                |------------->|
             |   NOTIFY F24   |              |
             |--------------->|              |
             |   200 OK F25   |              |
             |<---------------|              |
             |    BYE F26     |              |



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             |<---------------|              |
             |   200 OK F27   |              |
             |--------------->|              |

   In this scenario, Alice calls Bob.  Bob puts Alice on hold then calls
   Carol to announce transfer, then places Carol on hold.  Bob
   transfers  Alice to Carol which replaces the session between Bob and
   Carol.  Carol then disconnects session with Bob.  Alice reports
   success of transfer to Bob, who then disconnects with Alice.  In this
   example, the Replaces header field [4] is inserted into the Refer-To
   URI by Bob.  Note that the Refer-To URI is the Contact URI returned
   by Carol in the 200 OK response F10.  This ensures that only the
   correct instance of Carol is reached.  The presence of the Supported:
   gruu header field in message F10 indicates that the Contact URI is,
   in fact, a GRUU [20] and will be globally routable outside of the
   dialog.  Without knowing the Contact URI is a gruu, Bob must be
   prepared, if the triggered INVITE had fails, to retry the REFER with
   a Refer-To URI of the URI used to reach Carol but with a Require:
   replaces header escaped in the Refer-To header field, as discussed in
   the transfer [7] document.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0

      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000




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      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F3 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000



      F4 ACK Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY



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      Supported: replaces
      Content-Length: 0


      /*  Alice and Bob  have established a session.  Bob puts Alice on Hold */

      F5 INVITE Bob -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Type: application/sdp
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F6 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com



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      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F7 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds3
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 ACK
      Content-Length: 0


      /* Bob calls Carol  */

      F8 INVITE Bob -> Carol

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 28908445834 2890844834 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423645 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F9 180 Ringing Carol -> Bob




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      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE
      Contact: <sips:39itp34klkd@chicago.example.com>
      Content-Length: 0


      F10 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE
      Contact: <sips:39itp34klkd@chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F11 ACK Bob -> Carol

      ACK sips:39itp34klkd@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd5
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 ACK
      Content-Length: 0


      /* Bob  puts Carol on hold */



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      F12 INVITE Bob -> Carol

      INVITE sips:39itp34klkd@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds0
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 43 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 289084834 2890844835 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423645 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F13 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds0
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 43 INVITE
      Contact: <sips:39itp34klkd@chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844923 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly



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      F14 ACK Bob -> Carol

      ACK sips:39itp34klkd@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash334
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 43 ACK
      Content-Length: 0


      /* Bob  Transfers  Alice to Carol.  */

      F15 REFER Bob -> Alice

      REFER sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds2g
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1025 REFER
      Refer-To: <sips:39itp34klkd@chicago.example.com?Replaces=
       sdjfdjfskdf%40biloxi.example.com%3Bto-tag%3D5f35a3%3Bfrom-tag%3D8675309>
      Referred-By: <sips:bob@biloxi.example.com>
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F16 202 Accepted Alice -> Bob

      SIP/2.0 202 Accepted
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds2g
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=1234567
      To: Alice <sips:alice@atlanta.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1025 REFER
      Content-Length: 0


      F17 NOTIFY Alice -> Bob

      NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfK
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 NOTIFY
      Contact: <sips:bob@client.biloxi.example.com>
      Event: refer
      Subscription-State: active;expires=60
      Content-Type: message/sipfrag
      Content-Length: ...

      SIP/2.0 100 Trying


      F18 200 OK Bob -> Carol

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfK
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=1234567
      From: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0


      /*  Alice establishes session with Carol which replaces the session
          between Bob and Carol */

      F19 INVITE Alice -> Carol

      INVITE sips:39itp34klkd@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKadfe4ko
      To: Carol <sips:39itp34klkd@chicago.example.com>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=3461
      Call-ID: 9435674543@atlanta.example.com
      CSeq: 1 INVITE
      Referred-By: <sips:bob@biloxi.example.com>
      Replaces: sdjfdjfskdf@biloxi.example.com;to-tag=5f35a3;from-tag=8675309
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844989 2890844989 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com



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      t=3034423643 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F20 200 OK Carol -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKadfe4ko
       ;received=192.0.2.123
      To: Carol <sips:39itp34klkd@chicago.example.com>;tag=ff3a
      From: Alice <sips:alice@atlanta.example.com>;tag=3461
      Call-ID: 9435674543@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:39itp34klkd@chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844221 2890844221 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423452 0
      m=audio 49172 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F21 ACK Alice -> Carol

      ACK sips:39itp34klkd@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKadfe4kU3
      To: Carol <sips:39itp34klkd@chicago.example.com>;tag=ff3a
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=3461
      Call-ID: 9435674543@atlanta.example.com
      CSeq: 1 INVITE
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      /* Carol then disconnects from Bob */

      F22 BYE Carol -> Bob

      BYE sips:bob@client.biloxi.example.com SIP/2.0



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfE
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 1 BYE
      Content-Length: 0


      F23 200 OK Bob -> Carol

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfE
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      From: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 1 BYE
      Content-Length: 0



      /*  Alice tells Bob  that the call has been successfully transferred */

      F24 NOTIFY Alice -> Bob

      NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf2N
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 3 NOTIFY
      Event: refer
      Subscription-State: terminated;reason=noresource
      Content-Type: message/sipfrag
      Content-Length: ...

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKadfe4ko
       ;received=192.0.2.123
      From: Carol <sips:carol@chicago.example.com>;tag=ff3a
      To: Alice <sips:alice@atlanta.example.com>;tag=3461
      Call-ID: 9435674543@chicago.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>





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      F25 200 OK Bob -> Carol

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=1234567
      From: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: 12345600@atlanta.example.com
      CSeq: 3 NOTIFY
      Content-Length: 0


      /* Bob disconnects with  Alice */

      F26 BYE Bob -> Alice

      BYE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7P
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1026 BYE
      Content-Length: 0


      F27 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7P
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1026 BYE
      Content-Length: 0















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2.6  Transfer - Instant Messaging


            Alice          Bob                Carol
             |              |                   |
             |   INVITE F1  |                   |
             |------------->|                   |
             | 180 Ringing F2                   |
             |<-------------|                   |
             |  200 OK F3   |                   |
             |<-------------|                   |
             |    ACK F4    |                   |
             |------------->|                   |
             |  Both way RTP Established        |
             |<============>|                   |
             |              |     MESSAGE F5    |
             |              |------------------>|
             |              |     200 OK F6     |
             |              |<------------------|
             |              |                   |
             |       INVITE Replaces:A-B F7     |
             |<---------------------------------|
             |            200 OK F8             |
             |--------------------------------->|
             |               ACK F9             |
             |<---------------------------------|
             |   Both way RTP Established       |
             |<================================>|
             |    BYE F10   |                   |
             |------------->|                   |
             |  200 OK F11  |                   |
             |<-------------|                   |
             |                                  |

   In this scenario, Alice and Bob establish a session between them.
   Bob wants Carol to take the call so sends an Instant Message (IM) to
   Carol containing Alice's URI and an embedded Replaces header field.
   If Carol clicks on the URI, Carol's SIP UA sends an INVITE to Alice
   which replaces the session with Bob.

   This scenario shows the use of the SIP MESSAGE [15] method to pass
   the URI.  However, another IM protocol or other method could have
   been used to pass the URI from Bob to Carol.

   Message Details


      F1 INVITE Alice -> Bob



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      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@client.biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F3 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      Contact: <sips:bob@client.biloxi.example.com>
      CSeq: 1 INVITE
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE
      Supported: replaces
      Content-Type: application/sdp



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      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000



      F4 ACK Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74r
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      CSeq: 1 ACK
      Content-Length: 0


      /* Bob IMs Carol  */

      F5 MESSAGE Bob -> Carol


      MESSAGE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 MESSAGE
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE
      Supported: replaces
      Content-Type: text/html
      Content-Length: ...

      <HTML>Do you want to take this call from
      <A HREF="sips:a8342043f@atlanta.example.com?Replaces=
       12345600@atlanta.example.com%3Bfrom-tag%3D314159%3Bto-tag%3D1234567">
       Alice</A>? </HTML>




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      F6 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=5f35a3
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 MESSAGE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE
      Supported: replaces
      Content-Length: 0



   /* Carol takes the call from Bob */

      F7 INVITE  Carol -> Alice

      INVITE sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74HH
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Alice <sips:a8342043f@atlanta.example.com>
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 INVITE
      Replaces: 12345600@atlanta.example.com;to-tag=314578;from-tag=1234567
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY, MESSAGE
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890843122 2890843122 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 5342 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Alice matches the dialog information in the Replaces header and accepts
         the INVITE */

      F8 200 OK Alice -> Carol




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      SIP/2.0 200 OK
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74HH
       ;received=192.0.2.114
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Alice <sips:a8342043f@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 289084543 289084543 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49172 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F9 ACK  Carol -> Alice

      ACK sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS b2.biloxi.example.com:5061;branch=z9hG4bK7435
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Alice <sips:a8342043f@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* RTP streams are established between Alice and Carol.
         Alice Hangs Up with Bob due to the Replaces header field. */

      F10 BYE Alice -> Bob

      BYE sips:carol@client.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
      Max-Forwards: 70
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      From: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0




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      F11 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      From: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq:  2 BYE
      Content-Length: 0






2.7  Call Forwarding Unconditional


            Alice           Proxy          Gateway
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             |(100 Trying) F2 |              |
             |<---------------|              |
             | (181 Call Is Being Forwarded) F3
             |<---------------|   INVITE F4  |
             |                |------------->|
             |                |180 Ringing F5|
             | 180 Ringing F6 |<-------------|
             |<---------------|  200 OK F7   |
             |    200 OK F8   |<-------------|
             |<---------------|              |
             |     ACK F9     |              |
             |--------------->|    ACK F10   |
             |                |------------->|
             |    Both way RTP Established   |
             |<=============================>|
             |     BYE F11    |              |
             |--------------->|   BYE F12    |
             |                |------------->|
             |                |   200 OK F13 |
             |    200 OK F14  |<-------------|
             |<---------------|              |
             |                |              |

   Bob wants all calls forwarded to the PSTN (which is just another URI
   to the proxy server).  Alice calls Bob.  The proxy server rewrites



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   the Request URI, and forwards the INVITE to a Gateway.  Details of
   messaging behind the Gateway are not shown.

   Note that the 181 Call is Being Forwarded response does not have a To
   tag added as the proxy does not wish to establish an early dialog
   with Alice.

   Note also that forwarding could be accomplished using a redirect (302
   Moved Temporarily response).

   Message Details


      F1 INVITE Alice -> Proxy

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 (100 Trying) Proxy -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F3 (181 Call is Being Forwarded) Proxy -> Alice



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      SIP/2.0 181 Call is Being Forwarded
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0

      /* Proxy forwards call by rewriting Request-URI */

      F4 INVITE Proxy -> Gateway

      INVITE sips:+19727293660@gw1.example.com;user=phone SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F5 180 Ringing Gateway -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE



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      Contact: <sips:+19727293660@gw1.example.com;user=phone>
      Content Length:0


      F6 180 Ringing Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:+19727293660@gw1.example.com;user=phone>
      Content Length: 0


      F7 200 OK Gateway -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:+19727293660@gw1.example.com;user=phone>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=GATEWAY1 2890844527 2890844527 IN IP4 gatewayone.example.com
      s=Session SDP
      c=IN IP4 gatewayone.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103



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      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:+19727293660@gw1.example.com;user=phone>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=GATEWAY1 2890844527 2890844527 IN IP4 gatewayone.example.com
      s=Session SDP
      c=IN IP4 gatewayone.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F9 ACK Alice -> Proxy

      ACK sips:+19727293660@gw1.example.com;user=phone SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf31
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F10 ACK Proxy -> Gateway

      ACK sips:+19727293660@gw1.example.com;user=phone SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749ws.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf31
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F11 BYE Alice -> Proxy 1

      BYE sips:+19727293660@gw1.example.com;user=phone SIP/2.0



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfJe
      Route: <sips:+19727293660@gw1.example.com;user=phone>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F12 BYE Proxy 1 -> Gateway

      BYE sips:+19727293660@gw1.example.com;user=phone SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749G1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfJe
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F13 200 OK Gateway -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749G
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfJe
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F14 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfJe
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345600@atlanta.example.com
      CSeq:  2 BYE
      Content-Length: 0



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2.8  Call Forwarding - Busy


           Alice            Proxy          User B1             User B2
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|   INVITE F2  |                   |
             |                |------------->|                   |
             |(100 Trying) F3 |              |                   |
             |<---------------|  486 Busy F4 |                   |
             |                |<-------------|                   |
             |                |     ACK F5   |                   |
             |                |------------->|                   |
             |(181 Call is Being Forwarded) F6                   |
             |<---------------|              |    INVITE F7      |
             |                |--------------------------------->|
             |                |              | 180 Ringing F8    |
             |                |<---------------------------------|
             | 180 Ringing F9 |              |                   |
             |<---------------|              |      200 OK F10   |
             |                |<---------------------------------|
             |    200 OK F11  |              |                   |
             |<---------------|              |                   |
             |     ACK F12    |              |                   |
             |--------------->|              |     ACK F13       |
             |                |--------------------------------->|
             |               Both way RTP Established            |
             |<=================================================>|
             |    BYE F14     |              |                   |
             |--------------->|              |      BYE F15      |
             |                |--------------------------------->|
             |                |              |    200 OK F16     |
             |  200 OK F17    |<---------------------------------|
             |<---------------|              |                   |
             |                |              |                   |

   Bob wants calls to B1 forwarded to B2 if B1 is busy (this information
   is known to the proxy).  Alice calls B1, B1 is busy, the proxy server
   places call to B2.

   Message Details


      F1 INVITE Alice -> Proxy

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70



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      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy -> B1

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F3 (100 Trying) Proxy -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 486 Busy Here B1 -> Proxy

      SIP/2.0 486 Busy Here
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0



      F5 ACK Proxy -> B1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F6 (181 Call is Being Forwarded) Proxy -> Alice

      SIP/2.0 181 Call is Being Forwarded
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      /* The proxy now forwards the call to B2 */

      F7 INVITE Proxy -> B2



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      INVITE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 180 Ringing B2 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Length: 0


      F9 180 Ringing Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com



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      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Length: 0


      F10 200 OK B2 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0

      a=rtpmap:0 PCMU/8000


      F11 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP



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      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F12 ACK Alice -> Proxy

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfX
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com


      F13 ACK Proxy -> B2

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83731
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfX
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* RTP streams are established between A and B2 */

      /*  Alice eventually hangs up with User B2. */

      F14 BYE Alice -> Proxy

      BYE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bW4
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0





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      F15 BYE Proxy -> B2

      BYE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837493
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bW4
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0



      F16 200 OK B2 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837493
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bW4
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F17 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bW4
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq:  2 BYE
      Content-Length: 0



2.9  Call Forwarding - No Answer








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           Alice            Proxy         User B1             User B2
             |                |              |                   |
             |    INVITE F1   |              |                   |
             |--------------->|   INVITE F2  |                   |
             |(100 Trying) F3 |------------->|                   |
             |<---------------|180 Ringing F4|                   |
             | 180 Ringing F5 |<-------------|                   |
             |<---------------|              |                   |
             |                 Request Timeout                   |
             |                |              |                   |
             |                |   CANCEL F6  |                   |
             |                |------------->|                   |
             |                |   200 OK F7  |                   |
             |                |<-------------|                   |
             |                |     487 F8   |                   |
             |                |<-------------|                   |
             |                |     ACK F9   |                   |
             |                |------------->|                   |
             |(181 Call is Being Forwarded) F10                  |
             |<---------------|              |    INVITE F11     |
             |                |--------------------------------->|
             |                |              | 180 Ringing F12   |
             | 180 Ringing F13|<---------------------------------|
             |<---------------|              |      200 OK F14   |
             |                |<---------------------------------|
             |   200 OK F15   |              |                   |
             |<---------------|              |                   |
             |     ACK F16    |              |                   |
             |--------------->|              |     ACK F17       |
             |                |--------------------------------->|
             |               Both way RTP Established            |
             |<=================================================>|
             |    BYE F18     |              |                   |
             |--------------->|              |      BYE F19      |
             |                |--------------------------------->|
             |                |              |    200 OK F20     |
             |  200 OK F21    |<---------------------------------|
             |<---------------|              |                   |
             |                |              |                   |

   Bob  wants calls to B1 forwarded to B2 if B1 is not answered
   (information is known to the proxy server).  Alice calls B1 and no
   one answers.  The proxy server then places the call to B2.

   Message Details


      F1 INVITE Alice -> Proxy



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      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy -> B1

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F3 (100 Trying) Proxy -> Alice

      SIP/2.0 100 Trying



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 180 Ringing B1 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F5 180 Ringing Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      /* B1 rings until a configurable timer expires in the Proxy. The
      Proxy sends Cancel and proceeds down the list of routes. */

      F6 CANCEL Proxy -> B1

      CANCEL sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F7 200 OK B1 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      From: Alice <sips:alice@atlanta.example.com>
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F8 487 Request Terminated B1 -> Proxy

      SIP/2.0 487 Request Terminated
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F9 ACK Proxy -> B1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F10 (181 Call is Being Forwarded) Proxy -> Alice

      SIP/2.0 181 Call is Being Forwarded
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9



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       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F11 INVITE Proxy -> B2

      INVITE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F12 180 Ringing B2 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Length: 0




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      F13 180 Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Length: 0


      F14 200 OK B2 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000



      F15 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432



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      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F16 ACK Alice -> Proxy

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf3
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F17 ACK Proxy -> B2

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8374.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf3
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* RTP streams are established between A and B2.   Alice Hangs Up with User B2. */

      F18 BYE Alice -> Proxy

      BYE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b3f



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      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0



      F19 BYE Proxy -> B2

      BYE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b3f
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F20 200 OK B2 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK837.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b3f
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F21 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b3f
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq:  2 BYE
      Content-Length: 0



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2.10  3-way Conference - Third Party is Added


            Alice           Bob            Carol
             |    INVITE F1   |              |
             |--------------->|              |
             | 180 Ringing F2 |              |
             |<---------------|              |
             |    200 OK F3   |              |
             |<---------------|              |
             |     ACK F4     |              |
             |--------------->|              |
             |       RTP      |              |
             |<==============>|              |
             |   INVITE F5    |              |
             |<---------------|              |
             |    200 OK F6   |              |
             |--------------->|              |
             |     ACK F7     |              |
             |<---------------|  INVITE F8   |
             |                |------------->|
             |                |    180 F9    |
             |                |<-------------|
             |                |  200 OK F10  |
             |                |<-------------|
             |                |  ACK F11     |
             |                |------------->|
             |                |       RTP    |
             |                |<============>|

   In this scenario, Alice and Bob are in a 2-party call (session) when
   Bob wishes to add Carol into the conversation.  Bob is capable of
   media mixing in a 3-party call.  Bob first sends a re-INVITE to Alice
   changing Contact URIs to one that indicates Alice's mixer and acts
   like a focus.  As a result, Bob includes the "isfocus" feature tag
   [10] as described in [11].  Bob then INVITEs Carol using the same
   Contact URI.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>



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      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:b54gh42f5@biloxi.example.com>
      Content-Length: 0


      F3 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:b54gh42f5@biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP



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      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 ACK Alice -> Bob

      ACK sips:b54gh42f5@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfL
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /*  Alice and Bob  have established a session.  Bob  re-INVITEs changing
          Contact URIs */


      F5 INVITE Bob -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE
      Contact: <sips:bob-Mixer@client.biloxi.example.com>;isfocus
      Content-Type: application/sdp
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 49172 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=sendonly


      F6 200 OK Alice -> Bob



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      SIP/2.0 200 OK

      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly



      F7 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash3G
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 ACK
      Content-Length: 0


      /* Bob calls Carol  */

      F8 INVITE Bob -> Carol

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashJfd
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE



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      Contact: <sips:bob-Mixer@client.biloxi.example.com>;isfocus
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 28908445834 2890844834 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423645 0
      m=audio 48174 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F9 180 Ringing Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashJfd
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=341313
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F10 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashJfd
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=341313
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP



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      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000



      F11 ACK Bob -> Carol

      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash431
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=341313
      Call-ID: sdjfdjfskdf@biloxi.example.com
      CSeq: 42 ACK
      Content-Length: 0


      /* User B's mixer know mixes media from both A and C to create the 3-way conference.  */































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2.11  3-way Conference - Third Party Joins


            Alice           Bob            Carol
             |    INVITE F1   |              |
             |--------------->|              |
             | 180 Ringing F2 |              |
             |<---------------|              |
             |    200 OK F3   |              |
             |<---------------|              |
             |     ACK F4     |              |
             |--------------->|              |
             |       RTP      |              |
             |<==============>|  INVITE Join:A-B F5
             |                |<-------------|
             |                |    180 F6    |
             |                |------------->|
             |   INVITE F7    |              |
             |<---------------|              |
             |    200 OK F8   |              |
             |--------------->|              |
             |     ACK F9     |              |
             |<---------------|              |
             |                |  200 OK F10  |
             |                |------------->|
             |                |  ACK F11     |
             |                |<-------------|
             |                |       RTP    |
             |                |<============>|


   In this scenario, Alice and Bob are in a 2 party call and Carol
   wishes to join resulting in a three party call.  Carol could have
   learned Bobs conference URI using some non-SIP means, or possibly
   from a NOTIFY with the dialog package sent by Bob.  Carol sends an
   INVITE to Bob containing a Join header identifying the dialog between
   Alice and Bob.  Bob re-INVITEs Alice to switch to focus mode and
   includes the "isfocus" feature tag [10] as described in [11].  Bob
   then accepts the INVITE from Carol, resulting in the 3-way call.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70



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      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0

      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:b54gh42f5@biloxi.example.com>
      Content-Length: 0


      F3 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:b54gh42f5@biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, join, gruu
      Content-Type: application/sdp
      Content-Length: ...




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      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 ACK Alice -> Bob

      ACK sips:b54gh42f5@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf6
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /*  Alice and Bob  have established a session.  Carol requests to join the session */

      F5 INVITE Carol -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 452k499sk@chicago.example.com
      CSeq: 99 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, join
      Join: 12345600@atlanta.example.com;from-tag=1234567;to-tag=23431
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000





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      F6 180 Ringing Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKnashds7
       ;received=120.
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>;tag=0982
      Call-ID: 452k499sk@chicago.example.com
      CSeq: 99 INVITE
      Contact: <sips:bob-Mixer@client.biloxi.example.com>;isfocus
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Length: 0


      F7 INVITE Bob -> Alice

      INVITE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdyKL
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE
      Contact: <sips:bob-Mixer@client.biloxi.example.com>;isfocus
      Content-Type: application/sdp
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, join, gruu
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844528 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 49172 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdyKL
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 INVITE



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      Contact: <sips:alice@client.atlanta.example.com>;isfocus
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY

      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F9 ACK Bob -> Alice

      ACK sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnash3g
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=23431
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1024 ACK
      Content-Length: 0


      F10 200 OK Bob -> Carol

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKnashds7
       ;received=120.
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>;tag=0982
      Call-ID: 452k499sk@chicago.example.com
      CSeq: 99 INVITE
      Contact: <sips:bob-Mixer@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, join, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 28908445834 2890844834 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423645 0



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      m=audio 48174 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F11 ACK OK Bob -> Carol

      ACK sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bKnash4Gf
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>;tag=0982
      Call-ID: 452k499sk@chicago.example.com
      CSeq: 99 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, join
      Content-Length:0



2.12  Single Line Extension


             Alice      Forking Proxy       User   User   User
                                             B1     B2     B3
             |                |              |      |      |
             |    INVITE F1   |              |      |      |
             |--------------->|   INVITE F2  |      |      |
             |                |------------->|      |      |
             |                |       INVITE F3     |      |
             |                |-------------------->|      |
             |                |          INVITE F4  |      |
             |                |--------------------------->|
             | 100 Trying F5  |              |      |      |
             |<---------------|180 Ringing F6|      |      |
             |                |<-------------|      |      |
             | 180 Ringing F7 |              |      |      |
             |<---------------|              |      |      |
             |                | 480 Not Logged In F8|      |
             |                |<--------------------|      |
             |                |              ACK F9 |      |
             |                |-------------------->|      |
             |                |         180 Ringing F10    |
             |     180 F11    |<---------------------------|
             |<---------------|            200 OK F12      |
             |   200 OK F13   |<---------------------------|
             |<---------------|              |      |      |
             |                |   CANCEL 14  |      |      |
             |                |------------->|      |      |



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             |                |  200 OK F15  |      |      |
             |                |<-------------|      |      |
             |                |    487 F16   |      |      |
             |                |<-------------|      |      |
             |                |    ACK F17   |      |      |
             |                |------------->|      |      |
             |     ACK F18    |              |      |      |
             |--------------->|           ACK F19   |      |
             |                |--------------------------->|
             |               Both way RTP Established      |
             |<===========================================>|
             |                |          NOTIFY F20        |
             |                |<---------------------------|
             |                |   NOTIFY F21 |      |      |
             |                |------------->|      |      |
             |                |       NOTIFY F22    |      |
             |                |-------------------->|      |
             |                |          NOTIFY F23 |      |
             |                |--------------------------->|
             |                |   200 OK F24 |      |      |
             |                |<-------------|      |      |
             |                |          200 OK F25        |
             |                |--------------------------->|
             |                |   200 OK F26 |      |
             |                |<--------------------|      |
             |                |     482 Loop Detected F27  |
             |                |<---------------------------|
             |                |                            |
             |         User B2 wants to join the call      |
             |                |                            |
             |                |   INVITE Join:A-B3 F28     |
             |                |<--------------------|      |
             |                |   INVITE Join: A-B3 F29    |
             |                |------------->|      |      |
             |                |      INVITE Join: A-B3 F30 |
             |                |-------------------->|      |
             |                |          INVITE Join: A-B3 F31
             |                |--------------------------->|
             |                |    100 Trying F32   |      |
             |                |-------------------->|      |
             |                | 481 Dialog Does Not Exist F33
             |                |<-------------|      |      |
             |                |     ACK F34  |      |      |
             |                |------------->|      |      |
             |                | 482 Loop Detected F35      |
             |                |<--------------------|      |
             |                |            ACK F36  |      |
             |                |-------------------->|      |



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             |                |               200 OK F37   |
             |                |<---------------------------|
             |                |          200 OK F38 |      |
             |                |-------------------->|      |
             |                |                     |ACK F39
             |                |                     |----->|
             |                |             Both way RTP Established
             |                |                     |<====>|  B3 mixes RTP
             |                |                     |      |

   In Single Line Extension a call will ring several extensions at the
   same time (forking).  The first extension to answer the call becomes
   the active set.  If other extensions pick up, the call becomes a
   conference call.

   The grouping of multiple UAs with a single URI is possible in SIP by
   registering multiple Contact URIs against a single address of record.
   For the group of UAs to learn the dialog state of each other to
   enable a Join request to be formulated, a full mesh of dialog package
   subscriptions could be used.  A new UA being added to the group would
   register with the group AOR then subscribe to the registration
   package [19] to find out the other registered members.  However, when
   the Nth UA joins the group, it will cause an additional 2(N-1) new
   subscriptions to be created.  An INVITE forked to all N group members
   will result in N(N-1) NOTIFYs being sent among the group.  To avoid
   this scaling issue, this flow uses an implicit subscription between
   each of the group members and a simple forking proxy.

   In this flow, Alice calls Bob using his AOR URI which results in the
   INVITE being forked to three devices, B1, B2, and B3.  In this
   example, B3 answers the call and is connected to Alice.  B3 sends a
   NOTIFY containing the dialog information to the AOR for Bob, which is
   forked to B1 and B2.  (The service-unaware forking proxy actually
   forks it back to B3 as well, but B3 simply discards with a 482 Loop
   Detected response.)  Later in the example, B2 wishes to join the call
   and sends an INVITE with a Join header field to Bob's AOR URI to
   request this.  This INVITE is forked and is accepted by B3 who then
   performs the mixing function.  The INVITE is rejected by both B1 and
   B2.

   Note that this call flow requires B1, B2, and B3 have an implicit
   subscription with Bob's AOR.

   Note that if B3 is not capable of mixing the media, B3 would transfer
   both Alice and B2 to a conferencing bridge which would perform the
   mixing.

   This flow requires reliable transport such as TCP since the forking



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   proxy only guarantees that one UA receives each NOTIFY, not every UA.
   (This is because it only waits for one final response, not N, before
   completing the transaction.

   The use of SUBSCRIBE and NOTIFY is defined in [6] while the dialog
   Event package is defined in [8].

   Message Details


      F1 INVITE Alice -> Proxy

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t= 0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy -> B1

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0



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      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t= 0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F3 INVITE Proxy -> B2

      INVITE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 INVITE Proxy -> B3

      INVITE sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.3
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0



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      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F5 100 Trying Proxy -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F6 180 Ringing B1 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F7 180 Ringing Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0





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      F8 480 Not Logged In B2 -> Proxy

      SIP/2.0 480 Not Logged In
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314756
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F9 ACK Proxy -> B2

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314756
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F10 180 Ringing B3 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=83749.3
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client3.biloxi.example.com>
      Content-Length: 0


      F11 180 Ringing B3 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136



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      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client3.biloxi.example.com>
      Content-Length: 0


      F12 200 OK B3 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=83749.3
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client3.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client3.biloxi.example.com
      s=Session SDP
      c=IN IP4 client3.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F13 200 OK Proxy -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com.115>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...



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      v=0
      o=bob 2890844527 2890844527 IN IP4 client3.biloxi.example.com
      s=Session SDP
      c=IN IP4 client3.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Forking Proxy cancels pending branch B1 */

      F14 CANCEL Proxy -> B1

      CANCEL sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F15 200 OK B1 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      From: Alice <sips:alice@atlanta.example.com>
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F16 487 Request Terminated B1 -> Proxy

      SIP/2.0 487 Request Terminated
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0




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      F17 ACK Proxy -> B1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F18 ACK Alice -> Proxy

      ACK sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf3
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK

      Content-Length: 0


      F19 ACK Proxy -> B3

      ACK sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83742
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf3
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com


      CSeq: 1 ACK
      Content-Length: 0


      /* RTP streams are established between A and B3*/

      /* User B3 sends a NOTIFY to the group with established dialog information. */

      F20 NOTIFY B3 -> Proxy

      NOTIFY sips:bob@biloxi.example.com SIP/2.0



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      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="partial" entity="sips:bob@biloxi.example.com">
      <dialog id="2393lds3204" call-id="12345600@atlanta.example.com"
         local-tag="7137136" remote-tag="1234567" direction="recipient">
      <state event="2xx">confirmed</state>
      </dialog>
      </dialog-info>


      F21 NOTIFY Proxy -> B1

      NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="partial" entity="sips:bob@biloxi.example.com">
      <dialog id="2393lds3204" call-id="12345600@atlanta.example.com"
         local-tag="7137136" remote-tag="1234567" direction="recipient">
      <state event="2xx">confirmed</state>
      </dialog>
      </dialog-info>


      F22 Proxy -> B2



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      NOTIFY sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.2
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="partial" entity="sips:bob@biloxi.example.com">
      <dialog id="2393lds3204" call-id="12345600@atlanta.example.com"
         local-tag="7137136" remote-tag="1234567" direction="recipient">

      <state event="2xx">confirmed</state>
      </dialog>
      </dialog-info>


      F23 NOTIFY Proxy-> B3

      NOTIFY sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.3
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com


      CSeq: 1 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="partial" entity="sips:bob@biloxi.example.com">
      <dialog id="2393lds3204" call-id="12345600@atlanta.example.com"
         local-tag="7137136" remote-tag="1234567" direction="recipient">



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      <state event="2xx">confirmed</state>
      </dialog>
      </dialog-info>


      F24 200 OK B1 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      F25 200 OK Proxy -> B3

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      F26 200 OK B2 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      F27 200 OK B3 -> Proxy

      SIP/2.0 482 Loop Detected



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      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558a.3
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewlk
       ;received=192.0.2.115
      From: Bob <sips:bob@biloxi.example.com>;tag=w2Hu8sj
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 8458999275@biloxi.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      /* User B2 decided to join the call.  */

      F28 INVITE B2 -> Proxy

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Join: 12345600@atlanta.example.com;to-tag=765432;from-tag=1234567
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F29 INVITE Proxy -> B1

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.1
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>



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      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Join: 12345600@atlanta.example.com;to-tag=765432;from-tag=1234567
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F30 INVITE Proxy -> B2

      INVITE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.2
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Join: 12345600@atlanta.example.com;to-tag=765432;from-tag=1234567
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000






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      F31 INVITE Proxy -> B3

      INVITE sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.3
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client2.biloxi.example.com>
      Join: 12345600@atlanta.example.com;to-tag=765432;from-tag=1234567
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client2.biloxi.example.com
      s=Session SDP
      c=IN IP4 client2.biloxi.example.com
      t=0 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F32 100 Trying Proxy -> B2

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Content-Length: 0



      /* B1 does not have an established dialog, so it returns a 481 */

      F33 481 Dialog Does Not Exist B1 -> Proxy

      SIP/2.0 481 Dialog Does Not Exist
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.1
       ;received=192.0.2.54



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      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=68324lk42jd
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F34 ACK Proxy -> B1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.1
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=68324lk42jd
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F35 482 Loop Detected B2 -> Proxy

      SIP/2.0 482 Loop Detected
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=134lkwe
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F36 ACK Proxy -> B2

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.2
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=134lkwe
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* B3 has an existing dialog and agrees to mix B2 into the session. */

      F37 200 OK User B3 -> Proxy



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      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK4558ab.3
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=3891908734
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client3.biloxi.example.com>;isfocus
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client3.biloxi.example.com
      s=Session SDP
      c=IN IP4 client3.biloxi.example.com
      t=0 0
      m=audio 3460 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F38 200 OK User B3 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ewl
       ;received=192.0.2.114
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=3891908734
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client3.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Allow-Event: dialog
      Supported: replaces, join
      Content-Type: application/sdp
      Content-Length: ...

      v=0


      o=bob 2890844527 2890844527 IN IP4 client3.biloxi.example.com
      s=Session SDP
      c=IN IP4 client3.biloxi.example.com



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      t=0 0
      m=audio 3460 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F39 ACK B2 -> B3

      ACK sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKq0qwli6ew4
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=4524524312
      To: Bob <sips:bob@biloxi.example.com>;tag=3891908734
      Call-ID: 524251233@biloxi.example.com
      CSeq: 1 ACK
      Content-Length: 0



2.13  Find-Me


             Alice           Proxy           User   User   User   User
                                              B1     B2     B3     B4
             |                |              |      |      |      |
             |    INVITE F1   |              |      |      |      |
             |--------------->|   INVITE F2  |      |      |      |
             |                |------------->|      |      |      |
             |(100 Trying) F3 |              |      |      |      |
             |<---------------|180 Ringing F4|      |      |      |
             |                |<-------------|      |      |      |
             | 180 Ringing F5 |              |      |      |      |
             |<---------------|              |      |      |      |
             |                |    Timeout   |      |      |      |
             |                |              |      |      |      |
             |                |   CANCEL F6  |      |      |      |
             |                |------------->|      |      |      |
             |                |   200 OK F7  |      |      |      |
             |                |<-------------|      |      |      |
             |                |     487 F8   |      |      |      |
             |                |<-------------|      |      |      |
             |                |     ACK F9   |      |      |      |
             |                |------------->|      |      |      |
             |                |     INVITE F10      |      |      |
             |                |-------------------->|      |      |
             |                |480 Not Logged In F11|      |      |
             |                |<--------------------|      |      |
             |                |              ACK F12|      |      |
             |                |-------------------->|      |      |



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             |                |          INVITE F13        |      |
             |                |--------------------------->|      |
             |                |      486 Busy Here F14     |      |
             |                |<---------------------------|      |
             |                |            ACK F15         |      |
             |                |--------------------------->|      |
             |                |              INVITE F16           |
             |                |---------------------------------->|
             |                |            180 Ringing F17        |
             |     180 F18    |<----------------------------------|
             |<---------------|               200 OK F19          |
             |   200 OK F20   |<----------------------------------|
             |<---------------|                                   |
             |     ACK F21    |                                   |
             |--------------->|                 ACK F22           |
             |                |---------------------------------->|
             |               Both way RTP Established             |
             |<==================================================>|
             |                |                  BYE F23          |
             |     BYE F24    |<----------------------------------|
             |<---------------|                                   |
             |    200 OK F25  |                                   |
             |--------------->|                 200 OK F26        |
             |                |---------------------------------->|
             |                |                                   |

   Alice's call to Bob will result in an attempt to locate that user by
   calling locations from a list of contacts.  The location to answer
   the call becomes the active set, no other sets may join the call.

   While this flow shows a sequential search, the search could be
   accomplished using parallel forking, as in the previous example.

   Message Details


      F1 INVITE Alice -> Proxy

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...



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      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t= 0 0
      m=audio 49170 RTP/AVP 0

      a=rtpmap:0 PCMU/8000


      F2 INVITE Proxy -> B1

      INVITE sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t= 0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F3 (100 Trying) Proxy -> Alice

      SIP/2.0 100 Trying
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F4 180 Ringing B1 -> Proxy



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      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F5 180 Ringing Proxy -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      /* B1 rings for until a configurable timer in the Proxy expires. The
      Proxy then sends Cancel and proceeds down the list of routes. */

      F6 CANCEL Proxy -> B1

      CANCEL sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F7 200 OK B1 -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54



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      From: Alice <sips:alice@atlanta.example.com>
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F8 487 Request Terminated B1 -> Proxy

      SIP/2.0 487 Request Terminated
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F9 ACK Proxy -> B1

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=765432
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F10 INVITE Proxy -> B2


      INVITE sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9


       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE



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      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F11 480 Not Logged In B2 -> Proxy

      SIP/2.0 480 Not Logged In
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314756
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F12 ACK Proxy -> B2

      ACK sips:bob@client2.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.2
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314756
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F13 INVITE Proxy -> B3

      INVITE sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.3
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F14 486 Busy Here B3 -> Proxy

      SIP/2.0 486 Busy Here
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.3
       ;received=192.0.2.54
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F15 ACK Proxy -> B3

      ACK sips:bob@client3.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.3
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7654321
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F16 INVITE Proxy -> B4

      INVITE sips:bob@client4.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=83749.4
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      Max-Forwards: 69



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      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F17 180 Ringing B4 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=83749.4
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client4.biloxi.example.com>
      Content-Length: 0


      F18 180 Ringing B4 -> Proxy

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client4.biloxi.example.com>
      Content-Length: 0



      F19 200 OK B4 -> Proxy



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      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=83749.4
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client4.biloxi.example.com>
      Content-Type: application/sdp
      Content-Length: ...


      v=0
      o=bob 2890844527 2890844527 IN IP4 client4.biloxi.example.com
      s=Session SDP
      c=IN IP4 client4.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F20 200 OK Proxy -> Alice


      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      Record-Route: <sips:ss1.example.com;lr>
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com.116>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client4.biloxi.example.com
      s=Session SDP
      c=IN IP4 client4.biloxi.example.com
      t=0 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F21 ACK Alice -> Proxy



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      ACK sips:bob@client4.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F22 ACK Proxy -> B4

      ACK sips:bob@client4.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK8374
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7137136
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0



      /* RTP streams are established between A and B4*/

      /* User B4 Hangs Up with User A. */

      F23 BYE B4 -> Proxy

      BYE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Route: <sips:ss1.example.com;lr>
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=7137136
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 BYE
      Content-Length: 0


      F24 BYE Proxy -> Alice

      BYE sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83754
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7



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       ;received=192.0.2.105
      Max-Forwards: 69
      From: Bob <sips:bob@biloxi.example.com>;tag=7137136
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 BYE
      Content-Length: 0


      F25 200 OK Alice -> Proxy

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83754
       ;received=192.0.2.54
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=7137136
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 BYE
      Content-Length: 0


      F26 200 OK Proxy -> B4

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=7137136
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 BYE
      Content-Length: 0


2.14  Call Management (Incoming Call Screening)















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                                                                    Announcement
           Alice           Proxy            Bob           Server
             |                |              |              |
             |    INVITE F1   |              |              |
             |------------------------------>|              |
             | 305 Use Proxy F2              |              |
             |<------------------------------|              |
             |     ACK F3     |              |              |
             |------------------------------>|              |
             |    INVITE F4   |              |              |
             |--------------->|              |              |
             | 407 Proxy Authorization F5    |              |
             |<---------------|              |              |
             |     ACK F6     |              |              |
             |--------------->|              |              |
             |    INVITE F7   |              |              |
             |--------------->|              |              |
             | 403 Screening Failure (Terminating) Error-Info: URI F8
             |<---------------|              |              |
             |     ACK F9     |              |              |
             |--------------->|              |              |
             |    INVITE F10  |              |              |
             |--------------->|  INVITE F11                 |
             |                |---------------------------->|
             |                |   200 OK F12                |
             |    200 OK F13  |<----------------------------|
             |<---------------|                             |
             |     ACK F14    |                             |
             |--------------------------------------------->|
             |          Announcement Played to Caller       |
             |<============================================>|
             |                                    BYE F15   |
             |<---------------------------------------------|
             |     200 OK F16                               |
             |--------------------------------------------->|
             |                                              |
             |                                              |
             |                                              |

   Bob  has an incoming call screening list,  Alice is included on the
   list of addresses Bob  will not accept calls from.  Alice attempts to
   call user B.  Messages F1, F2, and F3 are included to show that Bob
   does not accept INVITEs that have not been screened by the proxy.

   Note that call screening can not be done using the From header -
   instead some form of authentication credentials must be used.

   The screening proxy inserts an announcement URI in an Error-Info



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   header field which Alice accesses by sending an INVITE to listen to
   the Announcement.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Bob  only accepts INVITEs that have been screened by the proxy */

      F2 305 Use Proxy Bob -> Alice

      SIP/2.0 305 Use Proxy
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=342123
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:ss1.example.com>
      Content-Length: 0


      F3 ACK Alice -> Bob

      ACK sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70



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      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=342123
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* A retries the call through the proxy */

      F4 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf0
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Proxy 1 challenges  Alice for authentication */


      F5 407 Proxy Authorization Required Proxy 1 -> Alice

      SIP/2.0 407 Proxy Authorization Required
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf0
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7886765
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Proxy-Authenticate: Digest realm="example.com",
       domain="sips:ss1.example.com", nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
       opaque="", stale=FALSE, algorithm=MD5
      Content-Length: 0




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      F6 ACK Alice -> Proxy 1

      ACK sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf0
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=7886765
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Content-Length: 0


      /*  Alice responds by sending an INVITE with authentication
      credentials in it.  */


      F7 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf2
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 3 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Proxy-Authorization: Digest username="alice",
       realm="example.com", nonce="ae9137be1c87d175c2dd63302a0d6e0a",
       opaque="", uri="sips:bob@biloxi.example.com",
       response="bbaec39f943bdcb3620d90afc548a45c"
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 403 Screening Failure (Terminating) Proxy 1 -> Alice

      SIP/2.0 403 Screening Failure (Terminating)
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf2
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>;tag=ffe254
      Call-ID: 12345600@atlanta.example.com
      CSeq: 3 INVITE
      Error-Info: <sips:screen-failure-term-ann@annoucement.example.com>
      Content-Length: 0


      F9 ACK Alice -> Proxy 1

      ACK sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf2
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=ffe254
      Call-ID: 12345600@atlanta.example.com
      Proxy-Authorization: Digest username="alice",
       realm="example.com", nonce="ae9137be1c87d175c2dd63302a0d6e0a",
       opaque="", uri="sips:bob@biloxi.example.com",
       response="bbaec39f943bdcb3620d90afc548a45c"
      CSeq: 3 ACK
      Content-Length: 0


   /* To hear the recording, Alice connects to the Error-Info URI */

      F10 INVITE Alice -> Proxy 1


      INVITE sips:screen-failure-term-ann@annoucement.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfj
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 4 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000





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      F11 INVITE Proxy 1 -> Announcement Server


      INVITE sips:screen-failure-term-ann@annoucement.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83743
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfj
       ;received=192.0.2.103
      Max-Forwards: 69
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 4 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F12 200 OK Announcement Server -> Proxy 1

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83743
       ;received=192.0.2.100
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfj
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=234934
      Call-ID: 12345600@atlanta.example.com
      CSeq: 4 INVITE
      Contact: <sips:announce.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=annc 2890844543 2890844543 IN IP4 announcement.example.com
      s=Session SDP
      c=IN IP4 announcement.example.com
      t=0 0
      m=audio 49174 RTP/AVP 0
      a=rtpmap:0 PCMU/8000




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      F13 200 OK Proxy 1 -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfj
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=234934
      Call-ID: 12345600@atlanta.example.com
      CSeq: 4 INVITE
      Contact: <sips:announce.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=annc 2890844543 2890844543 IN IP4 announcement.example.com
      s=Session SDP
      c=IN IP4 announcement.example.com
      t=0 0
      m=audio 49174 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F14 ACK Alice -> Announcement Server


      ACK sips:annoucement.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b32
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=234934
      Call-ID: 12345600@atlanta.example.com
      CSeq: 4 ACK
      Content-Length: 0


     /* Announcement Server plays announcement then disconnects */

      F15 BYE Announcement Server -> Alice

      BYE sips:alice@client.Atlanta.com SIP/2.0
      Via: SIP/2.0/TLS announcement.example.com:5061;branch=z9hG4bK74bKS
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=234934
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2334 BYE
      Content-Length: 0




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      F16 200 OK Alice -> Announcement Server

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS announcement.example.com:5061;branch=z9hG4bK74bKS
        ;received=192.0.2.103
      From: Bob <sips:bob@biloxi.example.com>;tag=234934
      To: Alice <sips:alice@atlanta.example.com>;tag=1234567
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2334 BYE
      Content-Length: 0



2.15  Call Management (Outgoing Call Screening)


           Alice            Proxy           Bob
             |                |              |
             |    INVITE F1   |              |
             |--------------->|              |
             | 407 Proxy Authorization F2    |
             |<---------------|              |
             |     ACK F3     |              |
             |--------------->|              |
             |    INVITE F4   |              |
             |--------------->|              |
             | 403 Screening Failure (Originating) F5
             |<---------------|              |
             |     ACK F6     |              |
             |--------------->|              |
             |                |              |

   Alice has an outgoing call screening list, Bob is included on the
   list of addresses Alice will not be able to place a call to.  Alice
   attempts to call Bob.

   Alice could establish a session to listen to the announcement in the
   Error-Info header field.

   Message Details


      F1 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567



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      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Proxy 1 challenges  Alice for authentication */

      F2 407 Proxy Authorization Required Proxy 1 -> Alice

      SIP/2.0 407 Proxy Authorization Required
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=90210
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Proxy-Authenticate: Digest realm="example.com",
       domain="sips:ss1.example.com", nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
       opaque="", stale=FALSE, algorithm=MD5
      Content-Length: 0


      F3 ACK Alice -> Proxy 1

      ACK sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=90210
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /*  Alice responds be sending an INVITE with authentication
      credentials in it.  */




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      F4 INVITE Alice -> Proxy 1

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b4
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Proxy-Authorization: Digest username="alice", realm="example.com",
       nonce="cb360afc54bbaec39f943bd820d9a45c", opaque="",
       uri="sips:bob@biloxi.example.com",
       response="b9d2e5bcdec9f69ab2a9b44f270285a6"
      Content-Type: application/sdp
      Content-Length: ...


      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F5 403 Screening Failure (Originating) Proxy 1 -> Alice

      SIP/2.0 403 Screening Failure (Originating)
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b4
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=18017
      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 INVITE
      Error-Info: <sips:screen-failure-orig-ann@annoucement.example.com>
      Content-Length: 0


      F6 ACK Alice -> Proxy 1

      ACK sips:bob@biloxi.example.com SIP/2.0

      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b4
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=18017



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      Call-ID: 12345600@atlanta.example.com
      CSeq: 2 ACK
      Proxy-Authorization: Digest username="alice", realm="example.com",
       nonce="cb360afc54bbaec39f943bd820d9a45c", opaque="",
       uri="sips:bob@biloxi.example.com",
       response="b9d2e5bcdec9f69ab2a9b44f270285a6"
      Content-Length: 0


2.16  Call Park


           Alice           Bob        Park Server       Carol
             |              |              |              |
             |   INVITE F1  |              |              |
             |------------->|              |              |
             |180 Ringing F2|              |              |
             |<-------------|              |              |
             |  200 OK F3   |              |              |
             |<-------------|              |              |
             |    ACK F4    |              |              |
             |------------->|              |              |
             |  RTP Media   |              |              |
             |<============>|              |              |
             |      Bob Parks Call         |              |
             |              |   REFER Refer-To: A F5      |
             |              |------------->|              |
             |              |    202 F6    |              |
             |              |<-------------|              |
             |              |   NOTIFY F7  |              |
             |              |<-------------|              |
             |              |    200 F8    |              |
             |              |------------->|              |
             |  INVITE F9 Replaces: B      |              |
             |<----------------------------|              |
             |          200 OK F10         |              |
             |---------------------------->|              |
             |           ACK F11           |              |
             |<----------------------------|              |
             |           RTP Music         |              |
             |<===========================>|              |
             |     BYE F12  |              |              |
             |------------->|  NOTIFY F14  |              |
             |  200 OK F13  |<-------------|              |
             |<-------------|  200 OK F15  |              |
             |              |------------->|              |
             |              |   Carol picks up the call   |
             |              |              |              |



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             |           INVITE Replaces: Park Server F16 |
             |<-------------------------------------------|
             |              |              |   200 F17    |
             |------------------------------------------->|
             |              |              |    ACK F18   |
             |<-------------------------------------------|
             |                  RTP Media                 |
             |<==========================================>|
             |           BYE F19           |              |
             |---------------------------->|              |
             |          200 OK F20         |              |
             |<----------------------------|              |
             |       No more RTP Music     |              |

   In this example, Alice calls Bob.  Bob then parks the call at the
   Park Server by sending a REFER to the Park Server.  The server sends
   an INVITE to Alice which replaces the session between Alice and Bob.
   The call is accepted by Alice and causes Alice to send a BYE to Bob.
   Bob receives notification of the successful park, and also receives
   the dialog identifiers in the application/sip body of the NOTIFY
   response.  Carol wishes to retrieve the call, a new INVITE is sent to
   Alice which replaces the session with the Park Server.  Alice accepts
   the call and sends a BYE to the Park Server.  Note that if the Park
   Server did not return the dialog identifiers (Call-ID, To and From
   tags) in the NOTIFY, Carol could send a SUBSCRIBE to retrieve this
   information.

   Note that this call is a special case of call transfer.

   Note also that this flow could also be used for Music on Hold.

   Message Details.


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...



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      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F3 200 OK Bob -> Alice


      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F4 ACK Alice -> Bob



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      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 ACK
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Length: 0


      /*   Bob REFERs Park Server to establish session with A which replaces the established session between A and B.  Note that there is no session established between B and the Park Server. */

      F5 REFER Bob -> Park Server

      REFER sips:park@server.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds9
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=02134
      To: Park Server <sips:park@server.example.com>
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 1 REFER
      Refer-To: <sips:a8342043f@atlanta.example.com?Replaces=
       12345601%40atlanta.example.com%3Bfrom-tag%3D314159%3Bto-tag%3D1234567>
      Referred-By: <sips:bob@biloxi.example.com>
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F6 202 Accepted Park Server -> Bob

      SIP/2.0 202 Accepted
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds9
       ;received=192.0.2.105
      From: Bob <sips:bob@biloxi.example.com>;tag=02134
      To: Park Server <sips:park@server.example.com>;tag=56323
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 1 REFER
      Content-Length: 0


      F7 NOTIFY Park Server -> Bob

      NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bT6
      To: Bob <sips:bob@biloxi.example.com>;tag=02134
      Max-Forwards: 70



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      From: Park Server <sips:park@server.example.com>;tag=56323
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 1 NOTIFY
      Event: refer
      Subscription-State: active;expires=60
      Content-Type: message/sipfrag
      Content-Length: ...


      SIP/2.0 100 Trying



      F8 200 OK Bob -> Park Server

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bT6
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=02134
      From: Park Server <sips:park@server.example.com>;tag=56323
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      /* Park Server places call to Alice to replace session between Alice and Bob */

      F9 INVITE Park Server -> Alice


      INVITE sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS server.example.com:5061;branch=z9hG4bK74rf
      Max-Forwards: 70
      From: <sips:park@server.example.com>;tag=0111


      To: <sips:a8342043f@atlanta.example.com>
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 1 INVITE
      Referred-By: <sips:bob@biloxi.example.com>
      Contact: <sips:park@server.example.com>
      Replaces: 12345601@atlanta.example.com;from-tag=314159;to-tag=1234567
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0



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      o=ParkServer 2890844576 2890844576 IN IP4 Park.server.example.com
      s=Session SDP
      c=IN IP4 music.server.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F10 200 OK Alice -> Park Server

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS music.server.example.com:5061;branch=z9hG4bK74rf
      From: <sips:park@server.example.com>;tag=0111
      To: Alice <sips:a8342043f@atlanta.example.com>;tag=098594
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000
      a=recvonly


      F11 ACK Park Server -> Alice

      ACK sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS music.server.example.com:5061;branch=z9hG4bK7rfF
      Max-Forwards: 70
      From: <sips:park@server.example.com>;tag=0111
      To: Alice <sips:a8342043f@atlanta.example.com>;tag=098594
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F12 BYE Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7



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      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159


      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE

      Content-Length: 0



      F13 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.105
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com
      CSeq: 2 BYE
      Content-Length: 0


      /*  Park Server reports success back to B by returning all the SIP headers in 200 OK response  */

      F14 NOTIFY Park Server -> Bob


      NOTIFY sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      To: Bob <sips:bob@biloxi.example.com>;tag=02134
      Max-Forwards: 70
      From: Park Server <sips:park@server.example.com>;tag=56323
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 1 NOTIFY
      Event: refer
      Subscription-State: terminated;reason=noresource
      Content-Type: message/sipfrag
      Content-Length: ...

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS music.server.example.com:5061
      From: <sips:park@server.example.com>;tag=0111
      To: Alice <sips:a8342043f@atlanta.example.com>;tag=098594
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 2 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>



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      F15 200 OK Bob -> Park Server

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=02134
      From: Park Server <sips:park@server.example.com>;tag=56323
      Call-ID: 4802029847@biloxi.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0


      /*  Alice is now parked at the Park Server */

      /* Carol picks up the call by sending an INVITE to A which replaces
         the existing session with the Park/Park Server.  Carol needs to know
         the dialog information to construct the Replaces header. */

      F16 INVITE Carol -> Alice

      INVITE sips:alice@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS chicago.example.com:5061;branch=z9hG4bK74bQ2
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=5893461
      To: Alice <sips:alice@atlanta.example.com>
      Call-ID: 6485356@chicago.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Replaces: a5-75-34-12-76@server.example.com;from-tag=098594;to-tag=0111
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844922 2890844922 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F17 200 OK Alice -> Carol

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bQ2
       ;received=192.0.2.105



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      From: Carol <sips:carol@chicago.example.com>;tag=5893461
      To: Alice <sips:alice@atlanta.example.com>;tag=222
      Call-ID: 6485356@chicago.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...


      v=0
      o=alice 2890844527 2890844527 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F18 ACK Carol -> Alice

      ACK sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bJ0
      Max-Forwards: 70
      From: Carol <sips:carol@chicago.example.com>;tag=5893461
      To: Alice <sips:alice@atlanta.example.com>;tag=222
      Call-ID: 6485356@chicago.example.com
      CSeq: 1 ACK
      Content-Length: 0



      /* A replaces the session to the Park Server with the new session with C and generates a BYE to disconnect the Park Server */

      F19 BYE Alice -> Park Server

      BYE sips:park@server.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b4N
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=098594
      To: <sips:park@server.example.com>;tag=0111
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 1 BYE
      Content-Length: 0


      F20 200 OK Park Server -> Alice



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      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b4N
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=098594
      To: <sips:park@server.example.com>;tag=0111
      Call-ID: a5-75-34-12-76@server.example.com
      CSeq: 1 BYE
      Content-Length: 0


2.17  Call Pickup


            Alice          Bob                Bill
             |              |                   |
             |   INVITE F1  |                   |
             |------------->|                   |
             |180 Ringing F2|                   |
             |<-------------|                   |
             |              |   SUBSCRIBE F3    |
             |              |<------------------|
             |              |     200 OK F4     |
             |              |------------------>|
             |              |     NOTIFY F5     |
             |              |------------------>|
             |              |     200 OK F6     |
             |              |<------------------|
             |          INVITE Replaces:Bob  F7 |
             |<---------------------------------|
             |              |     200 OK F8     |
             |--------------------------------->|
             |   CANCEL F9  |                   |
             |------------->|                   |
             |  200 OK F10  |                   |
             |<-------------|                   |
             |    487 F11   |                   |
             |<-------------|                   |
             |    ACK F12   |                   |
             |------------->|                   |
             |                    ACK F13       |
             |<---------------------------------|
             |              |     NOTIFY F14    |
             |              |------------------>|
             |              |       481 F15     |
             |              |<------------------|
             |                                  |
             |   Both way RTP Established       |
             |<================================>|



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             |                     BYE F16      |
             |--------------------------------->|
             |                   200 OK F17     |
             |<---------------------------------|

             |                                  |

   Bob and Bill are part of a work group at example.com that can pick up
   each others calls.  Alice calls Bob who does not answer.  Bill wishes
   to pick up the call and sends a SUBSCRIBE to Bob to retrieve the
   dialog information.  Bill then generates an INVITE with a Replaces to
   Alice.  Alice answers the INVITE and sends a CANCEL to stop Bob's
   phone ringing.  Note that the order of the CANCEL/ACK sequence in F11
   through F20 is not significant.

   This call flow shows the use of the "early-only" parameter [4] in the
   Replaces header field of F7.  This parameter prevents Alice from
   accepting the INVITE if Bob has already accepted the INVITE.  If Bill
   had wished to "take" the call from Bob regardless of whether he had
   answered, the parameter would not have been present in F7.

   Also note that the subscription between Bob and Carol could have been
   established prior to Alice's call.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49170 RTP/AVP 0



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      a=rtpmap:0 PCMU/8000



      F2 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0



      /*   Bill decides to pick up the call */

      F3 SUBSCRIBE  Bill -> Bob

      SUBSCRIBE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74bf
      Max-Forwards: 70
      From: Bill <sips:bill@biloxi.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 1 SUBSCRIBE
      Contact: <sips:bill@pc.biloxi.example.com>
      Event: dialog
      Subscription-State: active;expires=3600
      Accept: application/dialog-info+xml
      Content-Length: 0


      F4 200 OK Bob -> Bill

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74bf
       ;received=192.0.2.114
      Max-Forwards: 70
      From: Bill <sips:bill@biloxi.example.com>;tag=8675309
      To: Bob <sips:bob@biloxi.example.com>;tag=31451098
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 1 SUBSCRIBE
      Content-Length: 0




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      F5 NOTIFY  Bob -> Bill

      NOTIFY sips:bill@pc.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bK74br
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=31451098
      To: Bill <sips:bill@biloxi.example.com>;tag=8675309
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 1 NOTIFY
      Contact: <sips:bob@client.biloxi.example.com>
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="full" entity="sips:bob@biloxi.example.com">
      <dialog id="94992014524" call-id="12345600@atlanta.example.com"
         local-tag="3145678" remote-tag="1234567" direction="recipient"
         remote-uri="alice@atlanta.example.com"
         remote-target="alice@client.atlanta.example.com">
      <state>early</state>
      </dialog>
      </dialog-info>


      F6 200 OK  Bill -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bK74br
      From: Bob <sips:bob@biloxi.example.com>;tag=31451098
      To: Bill <sips:bill@biloxi.example.com>;tag=8675309
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 1 NOTIFY
      Contact: <sips:bill@pc.biloxi.example.com>
      Content-Length: 0


      F7 INVITE  Bill -> Alice

      INVITE sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74HH
      Max-Forwards: 70
      From: Bill <sips:bill@biloxi.example.com>;tag=8675309
      To: Alice <sips:alice@atlanta.example.com>
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 INVITE



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      Replaces: 12345600@atlanta.example.com;to-tag=314578;from-tag=1234567
       ;early-only
      Contact: <sips:bill@pc.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=bob 2890843122 2890843122 IN IP4 pc.biloxi.example.com
      s=Session SDP
      c=IN IP4 pc.biloxi.example.com
      t=3034423619 0
      m=audio 5342 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Alice matches the dialog information in the Replaces header and accepts
         the INVITE */

      F8 200 OK  Alice -> Bill

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bK74HH
       ;received=192.0.2.114
      From: Bill <sips:bill@biloxi.example.com>;tag=8675309
      To: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 INVITE
      Contact: <sips:a8342043f@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces, gruu
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 289084543 289084543 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=0 0
      m=audio 49172 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      /* Alice stops Bob's phone from ringing by sending a CANCEL */

      F9 CANCEL Alice -> Bob




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      CANCEL sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F10 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 CANCEL
      Content-Length: 0


      F11 487 Request Terminated Bob -> Alice

      SIP/2.0 487 Request Terminated
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F12 ACK Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS ss1.example.com:5061;branch=z9hG4bK83749.1
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=3145678
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F13 ACK  Bill -> Alice




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      ACK sips:a8342043f@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS b2.biloxi.example.com:5061;branch=z9hG4bK7435
      Max-Forwards: 70
      From: Bill <sips:bill@biloxi.example.com>;tag=8675309
      To: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F14 NOTIFY  Bob -> Bill

      NOTIFY sips:bill@pc.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bK749X
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=31451098
      To: Bill <sips:bill@biloxi.example.com>;tag=8675309
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 2 NOTIFY
      Contact: <sips:bob@client.biloxi.example.com>
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="1" state="partial" entity="sips:bob@biloxi.example.com">
      <dialog id="94992014524" call-id="12345600@atlanta.example.com"
         local-tag="3145678" remote-tag="1234567" direction="recipient">
      <state>terminated</state>
      </dialog>
      </dialog-info>


      F15 481 Dialog Does Not Exist  Bill -> Bob

      SIP/2.0 481 Dialog Does Not Exist
      Via: SIP/2.0/TLS bob.biloxi.example.com:5061;branch=z9hG4bK749X
      From: Bob <sips:bob@biloxi.example.com>;tag=31451098
      To: Bill <sips:bill@biloxi.example.com>;tag=8675309
      Call-ID: rt4353gs2egg@pc.biloxi.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0



      /* RTP streams are established between Alice and Bill.



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         Alice Hangs Up with Bob. */

      F16 BYE Alice -> Bob

      BYE sips:carol@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
      Max-Forwards: 70
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      From: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq: 2 BYE
      Content-Length: 0


      F17 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf
       ;received=192.0.2.103
      To: Bob <sips:bob@biloxi.example.com>;tag=8675309
      From: Alice <sips:alice@atlanta.example.com>;tag=131256
      Call-ID: 563456212@b2.biloxi.example.com
      CSeq:  2 BYE
      Content-Length: 0



























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2.18  Automatic Redial


           Alice             Bob
             |                |
             |    INVITE F1   |
             |--------------->|
             |486 Busy Here F2|
             |<---------------|    Bob is busy
             |     ACK F3     |
             |--------------->|
             |  SUBSCRIBE F4  |
             |--------------->|
             |   200 OK F5    |
             |<---------------|
             |    NOTIFY F6   |
             |<---------------|
             |   200 OK F7    |
             |--------------->|
             |                |
             |    NOTIFY F8   |    Bob is now available
             |<---------------|
             |   200 OK F9    |
             |--------------->|
             |                |
             |   INVITE F10   |
             |--------------->|   Session setup successfully
             | 180 Ringing F11|
             |<---------------|
             |   200 OK F12   |
             |<---------------|
             |     ACK F13    |
             |--------------->|
             |  Media Session |
             |<==============>|
             |                |

   Bob is initially busy when  Alice calls.  Alice subscribes to User
   B's call state using a SUBSCRIBE F4.  Bob sends a NOTIFY F8 when Bob
   is available.  A is alerted, then Alice sends an INVITE to B to
   establish the session.

   Message Details


      F1 INVITE Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0



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      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000




      F2 486 Busy Here

      SIP/2.0 486 Busy Here
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=982039i4
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 INVITE
      Content-Length: 0


      F3 ACK Alice -> Bob

      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bf9
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=982039i4
      Call-ID: 12345600@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      F4 SUBSCRIBE Alice -> Bob




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      SUBSCRIBE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b8G
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=837348234
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 1 SUBSCRIBE
      Contact: alice@client.atlanta.example.com
      Event: dialog
      Accept: application/dialog-info+xml
      Content-Length: 0


      F5 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74b8G
      From: Alice <sips:alice@atlanta.example.com>;tag=837348234
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 1 SUBSCRIBE
      Contact: alice@client.biloxi.example.com
      Content-Length: 0



      F6 NOTIFY Bob -> Alice


      NOTIFY sips:alice@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bn2
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=341123
      To: Alice <sips:alice@atlanta.example.com>;tag=837348234
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 1 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

      <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="full" entity="sips:bob@biloxi.example.com">
      <dialog id="562623442g3">
      <state>confirmed</state>
      </dialog>
      </dialog-info>



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      F7 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bn2
      From: Bob <sips:bob@biloxi.example.com>;tag=341123
      To: Alice <sips:alice@atlanta.example.com>;tag=837348234
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      /*   Bob is now available */

      F8 NOTIFY Bob -> Alice

      NOTIFY sips:alice@atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bVi
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=341123
      To: Alice <sips:alice@atlanta.example.com>;tag=837348234
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 2 NOTIFY
      Event: dialog
      Subscription-State: active;expires=3600
      Content-Type: application/dialog-info+xml
      Content-Length: ...

         <?xml version="1.0"?>
      <dialog-info xmlns="urn:ietf:params:xml:ns:dialog-info"
         version="0" state="full" entity="sips:bob@biloxi.example.com">
      <dialog id="562623442g3">
      <state>terminated</state>
      </dialog>
      </dialog-info>


      F9 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bVi
      From: Bob <sips:bob@biloxi.example.com>;tag=341123
      To: Alice <sips:alice@atlanta.example.com>;tag=837348234
      Call-ID: 4524526232@atlanta.example.com
      CSeq: 2 NOTIFY
      Content-Length: 0


      F10 INVITE Alice -> Bob



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      INVITE sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfq
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=f23fkg14k
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: aoij4i9okitr@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:alice@client.atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=alice 2890844526 2890844526 IN IP4 client.atlanta.example.com
      s=Session SDP
      c=IN IP4 client.atlanta.example.com
      t=3034423619 0
      m=audio 49170 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F11 180 Ringing Bob -> Alice

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfq
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=f23fkg14k
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: aoij4i9okitr@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Content-Length: 0


      F12 200 OK Bob -> Alice

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bfq
       ;received=192.0.2.103
      From: Alice <sips:alice@atlanta.example.com>;tag=f23fkg14k
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: aoij4i9okitr@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, SUBSCRIBE, NOTIFY
      Supported: replaces
      Content-Type: application/sdp



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      Content-Length: ...

      v=0
      o=bob 2890844527 2890844527 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F13 ACK Alice -> Bob

      ACK sips:bob@client.biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS client.atlanta.example.com:5061;branch=z9hG4bK74bLBJ
      Max-Forwards: 70
      From: Alice <sips:alice@atlanta.example.com>;tag=f23fkg14k
      To: Bob <sips:bob@biloxi.example.com>;tag=23431
      Call-ID: aoij4i9okitr@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0



2.19  Click to Dial


        Bob's PC                Bob                Carol
            | REFER Refer-To:Carol F1                 |
            |------------------->|                    |
            |  202 Accepted F2   |                    |
            |<-------------------|                    |
            |      NOTIFY F3     |                    |
            |<-------------------|                    |
            |      200 OK F4     |                    |
            |------------------->|                    |
            |                    |     INVITE F5      |
            |                    |------------------->|
            |                    |   180 Ringing F6   |
            |                    |<-------------------|
            |                    |     200 OK F7      |
            |                    |<-------------------|
            |                    |       ACK F8       |
            |                    |------------------->|
            |                    |         RTP        |
            |                    |<==================>|
            |                    |                    |




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   In this example, while browsing the web on his PC, Bob clicks on
   Carol's SIP URI intending to establish a session with Carol.  Bob's
   web browser passes the SIP URI to the SIP client on Bob's PC.  The PC
   client is configured with the URI of Bob's SIP phone.  A REFER is
   sent to the SIP phone which results in the establishment of the
   session between Bob and Carol.

   Note that Bob's SIP phone immediately terminates the dialog by
   indicating in the NOTIFY (F3) that the subscription is terminated.

   This flow is preferable to the 3pcc flow because the end-to-end SIP
   signaling is not interrupted by the 3pcc controller, and because
   Bob's experience of the call will not be marred by the lack of
   ringback tone or possible clipping.  Suitable authorization of the
   REFER and explicit authorization of the triggered INVITE by Bob is
   necessary.

   Message Details

   /* Bob's PC SIP Client sends a REFER to Bob's SIP phone */




      F1 REFER PC -> Bob


      REFER sips:bob@biloxi.example.com SIP/2.0
      Via: SIP/2.0/TLS pc.biloxi.example.com:5061;branch=z9hG4bKnashds7
      Max-Forwards: 70
      From: <sips:pc.biloxi.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 REFER
      Refer-To: <sips:carol@chicago.example.com>
      Contact: <sips:pc.client.atlanta.example.com>
      Content-Length: 0


      F2 202 Accepted Bob -> PC


      SIP/2.0 202 Accepted
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds7
       ;received=192.0.2.113
      From: <sips:pc.biloxi.example.com>;tag=1234567
      To: Bob <sips:bob@biloxi.example.com>;tag=314159
      Call-ID: 12345601@atlanta.example.com



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      CSeq: 1 REFER
      Content-Length: 0


      F3 NOTIFY Bob -> Alice

      NOTIFY sips:alice@client.atlanta.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds9
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: <sips:pc.biloxi.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 NOTIFY
      Event: refer
      Subscription-State: terminated;reason=noresource
      Content-Type: message/sipfrag
      Content-Length: ...

      SIP/2.0 100 Trying


      F4 200 OK Alice -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashds9
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=314159
      To: <sips:pc.biloxi.example.com>;tag=1234567
      Call-ID: 12345601@atlanta.example.com
      CSeq: 1 NOTIFY
      Content-Length: 0


      F5 INVITE Bob -> Carol

      INVITE sips:carol@chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdK9
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:bob@client.biloxi.example.com>
      Referred-By: <alice@atlanta.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...



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      v=0
      o=bob 2890844539 2890844539 IN IP4 client.biloxi.example.com
      s=Session SDP
      c=IN IP4 client.biloxi.example.com
      t=3034423821 0
      m=audio 3458 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F6 180 Ringing Carol -> Bob

      SIP/2.0 180 Ringing
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdK9
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Content-Length: 0


      F7 200 OK Carol -> Bob

      SIP/2.0 200 OK
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashdK9
       ;received=192.0.2.113
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 INVITE
      Contact: <sips:carol@client.chicago.example.com>
      Allow: INVITE, ACK, CANCEL, OPTIONS, BYE, REFER, NOTIFY
      Supported: replaces
      Content-Type: application/sdp
      Content-Length: ...

      v=0
      o=carol 2890844527 2890844527 IN IP4 client.chicago.example.com
      s=Session SDP
      c=IN IP4 client.chicago.example.com
      t=3034423619 0
      m=audio 3456 RTP/AVP 0
      a=rtpmap:0 PCMU/8000


      F8 ACK Bob -> Carol




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      ACK sips:carol@client.chicago.example.com SIP/2.0
      Via: SIP/2.0/TLS client.biloxi.example.com:5061;branch=z9hG4bKnashd43
      Max-Forwards: 70
      From: Bob <sips:bob@biloxi.example.com>;tag=8675309
      To: Carol <sips:carol@chicago.example.com>;tag=928287
      Call-ID: 7436222@atlanta.example.com
      CSeq: 1 ACK
      Content-Length: 0


      /* Bob and Carol now have established a session. */


3.  Security Considerations

   Since many of the examples in this document involve SIP call control,
   either peer-to-peer or 3pcc, the security considerations in the
   Multiparty Framework document [12] apply.

   Many of the services shown in this document rely on a particular user
   agent being part of a group.  Members of a group could be, for
   example, employees within a particular department, a set of home
   phone extensions, members of a call center, etc.  As such, user
   agents which are part of the group permit other group members special
   privileges and features.  For example, while a user agent may not in
   general allow another user agent to learn detailed dialog
   information, this information might be shared with another group
   member in order to facilitate a service such as call pickup.  Group
   members must be authenticated using normal SIP means such as
   certificates or shared secrets.

   The service examples in this document make extensive use of the SIP
   call control primitives REFER, Replaces, Join, and the dialog
   package.  The security considerations associated with each of these
   extensions apply to the scenarios in this document.

4.  IANA Considerations

   None.

5.  Acknowledgements

   The Transfer - Instant Messaging call flow is based on the
   "IM-a-call" call flow by Jonathan Rosenberg and Henning Schulzrinne.
   The Automatic Call Back call flow is based on a call flow by Adam
   Roach.  The Single Line Extension call flow is based on a call flow
   by Jonathan Rosenberg.  The authors wish to thank the following
   individuals for their assistance and review of this call flows



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   document: Rohan Mahey, Jonathan Rosenberg, Hemant Agrawal, Henry
   Sinnreich, Dean Willis, 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.

6.  Document History

   The first version of this document was the Internet-Draft
   draft-sparks-sip-service-examples October 1999.

   The next version was combined with the SIP Telephony Call Flows
   document into the draft-ietf-sip-call-flows April 2000.

   The current version was renamed as a work item of the SIPPING WG.

6.1  Changes since -07

   - Minor corrects.  - Updated references.

7.  References

7.1  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. and E. Schooler, "SIP:
         Session Initiation Protocol", RFC 3261, June 2002.

   [3]   Sparks, R., "The Session Initiation Protocol (SIP) Refer
         Method", RFC 3515, April 2003.

   [4]   Mahy, R., Biggs, B. and R. Dean, "The Session Initiation
         Protocol (SIP) "Replaces" Header", RFC 3891, September 2004.

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

   [6]   Roach, A., "Session Initiation Protocol (SIP)-Specific Event
         Notification", RFC 3265, June 2002.

   [7]   Sparks, R. and A. Johnston, "Session Initiation Protocol Call
         Control - Transfer",
         Internet-Draft draft-ietf-sipping-cc-transfer-03, October 2004.



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   [8]   Rosenberg, J., "An INVITE Inititiated Dialog Event Package for
         the Session Initiation  Protocol (SIP)",
         Internet-Draft draft-ietf-sipping-dialog-package-05, November
         2004.

   [9]   Mahy, R. and D. Petrie, "The Session Initiation Protocol (SIP)
         "Join" Header", RFC 3911, October 2004.

   [10]  Rosenberg, J., Schulzrinne, H. and P. Kyzivat, "Indicating User
         Agent Capabilities in the Session Initiation Protocol (SIP)",
         RFC 3840, August 2004.

   [11]  Johnston, A. and O. Levin, "Session Initiation Protocol Call
         Control - Conferencing for User Agents",
         Internet-Draft draft-ietf-sipping-cc-conferencing-06, November
         2004.

   [12]  Mahy, R., "A Call Control and Multi-party usage framework for
         the Session Initiation  Protocol (SIP)",
         Internet-Draft draft-ietf-sipping-cc-framework-03, October
         2003.

   [13]  Campbell, B. and R. Sparks, "Control of Service Context using
         SIP Request-URI", RFC 3087, April 2001.

   [14]  Sparks, R., "Internet Media Type message/sipfrag", RFC 3420,
         November 2002.

   [15]  Campbell, B., Rosenberg, J., Schulzrinne, H., Huitema, C. and
         D. Gurle, "Session Initiation Protocol (SIP) Extension for
         Instant Messaging", RFC 3428, December 2002.

7.2  Informative References

   [16]  Johnston, A., Donovan, S., Sparks, R., Cunningham, C. and K.
         Summers, "Session Initiation Protocol (SIP) Basic Call Flow
         Examples", BCP 75, RFC 3665, December 2003.

   [17]  Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo,
         "Best Current Practices for Third Party Call Control (3pcc) in
         the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April
         2004.

   [18]  Rosenberg, J., "A Session Initiation Protocol (SIP) Event
         Package for Conference State",
         Internet-Draft draft-ietf-sipping-conference-package-08,
         December 2004.




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   [19]  Rosenberg, J., "A Session Initiation Protocol (SIP) Event
         Package for Registrations", RFC 3680, March 2004.

   [20]  Rosenberg, J., "Obtaining and Using Globally Routable User
         Agent (UA) URIs (GRUU) in the  Session Initiation Protocol
         (SIP)", Internet-Draft draft-ietf-sip-gruu-02, July 2004.


Authors' Addresses

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

   Email: alan.johnston@mci.com


   Robert Sparks
   dynamicsoft
   5100 Tennyson Parkway, Suite 1200
   Plano, TX  75023

   Email: rsparks@dynamicsoft.com


   Chris Cunningham
   dynamicsoft
   5100 Tennyson Parkway, Suite 1200
   Plano, TX  75023

   Email: ccunningham@dynamicsoft.com


   Steve Donovan
   dynamicsoft
   5100 Tennyson Parkway, Suite 1200
   Plano, TX  75023

   Email: sdonovan@dynamicsoft.com


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

   Email: kevin.summers@sonusnet.com



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   This document and the information contained herein are provided on an
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Acknowledgment

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