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Versions: (draft-sparks-sip-service-examples) 00 01 02 03

Internet Engineering Task Force                          Alan Johnston
Internet Draft                                                WorldCom
Document: draft-ietf-sip-service-examples-01.txt         Robert Sparks
Category: Informational                               Chris Cunningham
March 2001                                               Steve Donovan
Expires: September 2001                                    dynamicsoft
                                                         Kevin Summers
                                                                 Sonus



                          SIP Service Examples


   Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026[1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as 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
   material or to cite them other than as "work in progress."
   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt
   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.



   Abstract

   This informational document gives examples of SIP (Session Initiation
   Protocol) services.  This covers most features offered in so-called
   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 third party call control (3pcc) extensions such as
   the REFER method. These features are not intented to be an exhaustive
   set, but rather show implementations of common features likely to be
   implemented on SIP IP Telephones in a business environment.









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Table of Contents

   1      Overview...................................................3
   1.1Legend for Message Flows ......................................4
   1.2Document History ..............................................4
   2      IP Telephony Services Features Call Flows..................5
   2.1Call Hold .....................................................5
   2.2Music on Hold/Call Park ......................................15
   2.3Consultation Hold ............................................22
   2.4Unattended Transfer ..........................................36
   2.5Attended Transfer ............................................42
   2.6Call Forwarding Unconditional ................................51
   2.7Call Forwarding - Busy .......................................56
   2.8Call Forwarding - No Answer ..................................62
   2.93-way Conference .............................................69
   2.10   Single Line Extension.....................................69
   2.11   Find-Me...................................................70
   2.12   Call Management (Incoming Call Screening).................79
   2.13   Call Management (Outgoing Call Screening).................83
   2.14   Call Pickup...............................................86
   3      References................................................95
   4      Author's Addresses........................................96
































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1  Overview


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

         Call Hold                     Music on Hold/Call Park
         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                   Outgoing Call Screening

   It is the hope of the authors that this document will be useful for
   SIP implementors, users, designers, and protocol researchers alike
   and will help further the goal of a standard SIP implementation for
   IP Telephony.  It is envisioned that as changes to the standard and
   additional RFCs are added that this document will reflect those
   changes and represent the current state of a standard SIP IP
   Telephony implementation.

   These flows assume the functionality described in the SIP Call Flow
   Examples document [2], which explores basic behavior and PSTN
   internetworking. Some of the scenarios described herein make use of
   "SIP Call Control Transfer" [3].

   These flows were prepared assuming a network of proxies, registrars,
   PSTN gateways, and other SIP servers that have a pre-established
   trust relationship with each other, secured through other means than
   SIP. User agents wishing to use the services in this network are
   required to authenticate themselves with an edge proxy using SIP
   Digest. To improve the clarity of this document, authentication of
   User Agents is not explicitly shown in all flows, except where
   authentication directly relates to the service example.

   These flows use SIP as defined by RFC 2543 [4] with some noted
   updates for RFC 2543bis. Note that this document is informational,
   and nothing stated here should be taken as normative.  RFC 2543 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 Back-to-
   Back User Agents (B2BUA) may be more appropriate in some
   circumstances.

   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.





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1.1       Legend for Message Flows

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

1.2       Document History

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

   The next version was combined with the SIP Telephony Call Flows
   document into the "draft-ietf-sip-call-flows-00.txt" April 2000.

   This version is based on Section 7 of that document with many of the
   examples extensively rewritten using the REFER method.


1.3       Changes since 00

   - Moddified all REFER flows to include 202 Accepted and NOTIFY
     result message.

   - Removed "Telephony" from title of document.

   - Added note on 2.9 on use of REFER to exit 3-way conference.

   - Modified Music on Hold/Call Park flow (2.2).

   - Modified order of messages in transfers (2.4 and 2.5) to more
     closely resemble PSTN experience.

   - Added Call Pickup flow (2.13).

   - Added editorial notes on usefulness of Replaces header.







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2  IP Telephony Services Features Call Flows

   These call flows show how a number of standard telephony features can
   be implemented using SIP.  They are not meant to represent a complete
   set.  Some calls make use of SIP Call Control Extensions[3].

2.1       Call Hold

        User A           Proxy          User B
          |                |              |
          |    INVITE F1   |              |
          |--------------->|              |
          |                |   INVITE F2  |
          |(100 Trying) F3 |------------->|
          |<---------------|              |
          |                |180 Ringing F4|
          | 180 Ringing F5 |<-------------|
          |<---------------|              |
          |                |  200 OK F6   |
          |    200 OK F7   |<-------------|
          |<---------------|              |
          |     ACK F8     |              |
          |--------------->|    ACK F9    |
          |                |------------->|
          |    Both way RTP Established   |
          |<=============================>|
          |                |INVITE (c=0) F10
          |INVITE (c=0) 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 |



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          |    200 OK F25  |<-------------|
          |<---------------|              |
          |                |              |

   User A calls User B, User B places call on hold.  User B then takes
   call off hold.  Note that either party can take the other party off
   of hold.  User A hangs up call.


   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy 1 -> B

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103



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


   F3 (100 Trying) Proxy 1 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing B -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content Length:0


   F5 180 Ringing Proxy 1 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content Length: 0


   F6 200 OK B -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp



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   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 ACK Proxy 1 -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>



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   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User B places User A on hold. */

   F10 INVITE B -> Proxy 1

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 INVITE Proxy 1 -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000



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   F12 200 OK A -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F13 200 OK Proxy 1 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F14 ACK B -> Proxy 1

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060



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   Route: <sip:UserB@there.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F15 ACK Proxy 1 -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User B takes the call off hold */

   F16 INVITE B -> Proxy 1

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F17 INVITE Proxy 1 -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159



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   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F18 200 OK A -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F19 200 OK Proxy 1 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...



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   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F20 ACK B -> Proxy 1

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 ACK
   Content-Length: 0


   F21 ACK Proxy 1 -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 ACK
   Content-Length: 0


   /* RTP Media stream re-established.  User A disconnects. */

   F22 BYE A -> Proxy 1

   BYE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB@there.com>
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F23 BYE Proxy 1 -> B

   BYE sip:UserB@there.com SIP/2.0



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   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F24 200 OK B -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F25 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0
























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2.2       Music on Hold/Call Park

         User A         User B   Music/Park Server
          |              |              |
          |   INVITE F1  |              |
          |------------->|              |
          |180 Ringing F2|              |
          |<-------------|              |
          |  200 OK F3   |              |
          |<-------------|              |
          |    ACK F4    |              |
          |------------->|              |
          |  RTP Media   |              |
          |<============>|              |
          |      User B Parks Call      |
          |              |   REFER Refer-To: A F5
          |              |------------->|
          |              |    202 F6    |
          |              |------------->|
          |  INVITE F7 Referred-By: B   |
          |<----------------------------|
          |          200 OK F8          |
          |---------------------------->|
          |           ACK F9            |
          |<----------------------------|
          |           RTP Music         |
          |<===========================>|
          |     BYE F10  |              |
          |------------->|  NOTIFY F12  |
          |  200 OK F11  |<-------------|
          |<-------------|  200 OK F13  |
          |              |------------->|
          |   User B picks up the call  |
          |              |              |
          |   INVITE F14 |              |
          |<-------------|              |
          |   200 F15    |              |
          |------------->|              |
          |    ACK F16   |              |
          |<-------------|              |
          |  RTP Media   |              |
          |<============>|              |
          |           BYE F17           |
          |---------------------------->|
          |          200 OK F18         |
          |<----------------------------|
          |       No more RTP Music     |

   In this example, User A calls User B.  User B then parks the call at
   the Music/Park Server by sending a REFER to the Music/Park Server.



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   The server sends an INVITE to A which replaces the session between A
   and B.  The call is accepted by A and causes A to send a BYE to B.
   Note that the Replaces header is needed in this INVITE.  User B
   receives notification of the successful park, and also receives the
   Call-ID in the application/sip body of the NOTIFY response.  When
   User B wishes to retrieve the call, a new INVITE is sent to A which
   replaces the session with the Music/Park Server.  User A accepts the
   call and sends a BYE to the Music/Park Server.  Note that the
   Replaces header is needed in this INVITE as well.  If someone besides
   User B retrieves the call, then this becomes Call Park and Pickup.


   Message Details.


   F1 INVITE A -> B

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 180 Ringing B -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F3 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060



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   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F4 ACK A -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User B REFERs Music Server to establish session with A which
   replaces the established session between A and B */

   F5 REFER B -> Music Server

   REFER sip:music@server.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: Music Server <sip:music@server.com>
   Call-ID: 4802029847@there.com
   CSeq: 1 REFER
   Refer-To: <sip:UserA@here.com>
   Referred-By: <sip:UserB@there.com>
   Content-Length: 0


   F6 202 Accepted Music Server -> B

   SIP/2.0 202 Accepted
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=56323
   To: Music Server <sip:music@server.com>
   Call-ID: 4802029847@there.com



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   CSeq: 1 REFER
   Content-Length: 0


   /* Music Server places call to User A to replace session between A
   and B */

   F7 INVITE Music Server -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP server.com:5060
   From: <sip:music@server.com>
   To: BigGuy <sip:UserA@here.com>
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 INVITE
   Referred-By: <sip:UserB@there.com>
   Contact: <sip:music@server.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=MusicServer 2890844526 2890844526 IN IP4 music.server.com
   s=Session SDP
   c=IN IP4 50.60.70.80
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 200 OK A-> Music Server

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP server.com:5060
   From: <sip:music@server.com>
   To: BigGuy <sip:UserA@here.com>;tag=098594
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000
   a=recvonly





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   F9 ACK Music Server -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP server.com:5060
   From: <sip:music@server.com>
   To: BigGuy <sip:UserA@here.com>;tag=098594
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 BYE A -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F11 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 BYE
   Content-Length: 0


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

   F12 NOTIFY Music Server -> B

   NOTIFY sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   To: LittleGuy <sip:UserB@there.com>
   From: Music Server <sip:music@server.com>;tag=56323
   Call-ID: 4802029847@there.com
   CSeq: 1 NOTIFY
   Event: refer
   Content-Type: application/sip
   Content-Length: ...

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP server.com:5060
   From: <sip:music@server.com>



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   To: BigGuy <sip:UserA@here.com>
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 INVITE
   Contact: <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...


   F13 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   To: LittleGuy <sip:UserB@there.com>
   From: Music Server <sip:music@server.com>;tag=56323
   Call-ID: 4802029847@there.com
   CSeq: 1 NOTIFY
   Content-Length: 0

   /* User A is now parked at the Music Server */

   /* User B picks up the call by sending an INVITE to A which replaces
   the existing session with the Music/Park Server.  Note that B knows
   the Call-ID of the existing session from the NOTIFY response. */

   F14 INVITE B -> A

   INVITE sip:UserA@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 6485356@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F15 200 OK A -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>



Johnston, et al.            Informational                    [Page 20]


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   Call-ID: 6485356@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F16 ACK B -> A

   ACK sip:UserA@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 6485356@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

   F17 BYE A -> Music Server

   BYE sip:music@server.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=098594
   To: <sip:music@server.com>
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 BYE
   Content-Length: 0


   F18 200 OK Music Server -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=098594
   To: <sip:music@server.com>
   Call-ID: a5-75-34-12-76@server.com
   CSeq: 1 BYE
   Content-Length: 0





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2.3       Consultation Hold

       User A           Proxy          User B              User C
          |                |              |                   |
          |    INVITE F1   |              |                   |
          |--------------->|   INVITE F2  |                   |
          |                |------------->|                   |
          |(100 Trying) F3 |              |                   |
          |<---------------|180 Ringing F4|                   |
          |                |<-------------|                   |
          | 180 Ringing F5 |              |                   |
          |<---------------|  200 OK F6   |                   |
          |                |<-------------|                   |
          |    200 OK F7   |              |                   |
          |<---------------|              |                   |
          |     ACK F8     |              |                   |
          |--------------->|     ACK F9   |                   |
          |                |------------->|                   |
          |     Both way RTP Established  |                   |
          |<=============================>|                   |
          |                |INVITE (c=0) F10                  |
          |INVITE (c=0) 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 |



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          |                |              |<=================>|
          |                |   BYE F25    |                   |
          |                |<-------------|                   |
          |                |              |       BYE F26     |
          |                |--------------------------------->|
          |                |              |    200 OK F27     |
          |                |<---------------------------------|
          |                |   200 OK F28 |                   |
          |                |------------->|                   |
          |                |   INVITE F29 |                   |
          |    INVITE F30  |<-------------|                   |
          |<---------------|              |                   |
          |    200 OK F31  |              |                   |
          |--------------->|   200 OK F32 |                   |
          |                |------------->|                   |
          |                |     ACK F33  |                   |
          |                |<-------------|                   |
          |    ACK F34     |              |                   |
          |<---------------|              |                   |
          |     Both way RTP Established  |                   |
          |<=============================>|                   |
          |    BYE F35     |              |                   |
          |--------------->|    BYE F36   |                   |
          |                |------------->|                   |
          |                |   200 OK F37 |                   |
          |                |<-------------|                   |
          |  200 OK F38    |              |                   |
          |<---------------|              |                   |
          |                |              |                   |

   User A calls user B.  User B places call on hold.  User B calls User
   C.  User B then disconnects with C, then takes the call with User A
   off hold.  The call ends with B hangs up.

   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com



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   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy 1 -> B

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3(100 Trying) Proxy 1 -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing B -> Proxy 1

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content Length:0



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   F5 180 Ringing Proxy 1 -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content Length: 0


   F6 200 OK B -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com



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   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 ACK Proxy 1 -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User B places User A on hold. */

   F10 INVITE B -> Proxy 1

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0



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


   F11 INVITE Proxy 1 -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F12 200 OK A -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F13 200 OK Proxy 1 -> B



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   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F14 ACK B -> Proxy 1

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F15 ACK Proxy 1 -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F16 INVITE B -> Proxy 1

   INVITE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>



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   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844526 2890844526 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 50170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F17 INVITE Proxy 1 -> C

   INVITE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserC@anywhere.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844526 2890844526 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 50170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F18 (100 Trying) Proxy 1 -> B

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Content-Length: 0


   F19 180 Ringing C -> Proxy 1




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   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@here.com
   CSeq: 1 INVITE
   Content Length:0


   F20 180 Ringing Proxy 1 -> B

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Content Length: 0


   F21 200 OK C -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserC@anywhere.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserC 2890844527 2890844527 IN IP4 client.anywhere.com
   s=Session SDP
   c=IN IP4 120.121.122.123
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F22 200 OK Proxy 1 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserC@anywhere.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654



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   Call-ID: 9876543210@there.com
   CSeq: 1 INVITE
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserC 2890844527 2890844527 IN IP4 client.anywhere.com
   s=Session SDP
   c=IN IP4 120.121.122.123
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F23 ACK B -> Proxy 1

   ACK sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserC@anywhere.com>
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 1 ACK
   Content-Length: 0


   F24 ACK Proxy 1 -> C

   ACK sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 1 ACK
   Content-Length: 0


   F25 BYE B -> Proxy 1

   BYE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserC@anywhere.com>
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 2 BYE
   Content-Length: 0





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   F26 BYE Proxy 1 -> C

   BYE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 2 BYE
   Content-Length: 0


   F27 200 OK C -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 2 BYE
   Content-Length: 0


   F28 200 OK Proxy 1 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=456654
   Call-ID: 9876543210@there.com
   CSeq: 2 BYE
   Content-Length: 0


   /* User B takes the call off hold */

   F29 INVITE B -> Proxy 1

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0



Johnston, et al.            Informational                    [Page 32]


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   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F30 INVITE Proxy 1 -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F31 200 OK A -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0



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   a=rtpmap:0 PCMU/8000


   F32 200 OK Proxy 1 -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   Record-Route: <sip:UserA@here.com;maddr=ss1.wcom.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F33 ACK B -> Proxy 1

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 ACK
   Content-Length: 0


   F34 ACK Proxy 1 -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 2 ACK
   Content-Length: 0


   F35 BYE A -> Proxy 1




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   BYE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB@there.com>
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F36 BYE Proxy 1 -> B

   BYE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F37 200 OK B -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F38 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=1234567
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0











Johnston, et al.            Informational                    [Page 35]


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2.4       Unattended Transfer


       User A              User B               User C
         |      INVITE F1     |                    |
         |<-------------------|                    |
         |   180 Ringing F2   |                    |
         |------------------->|                    |
         |      200 OK F3     |                    |
         |------------------->|                    |
         |        ACK F4      |                    |
         |<-------------------|                    |
         |        RTP         |                    |
         |<==================>|                    |
         |                    |                    |
         |  A performs unattended transfer         |
         |                    |                    |
         | REFER Refer-To:C F5|                    |
         |------------------->|                    |
         |  202 Accepted F6   |                    |
         |<-------------------|                    |
         |       BYE F7       |                    |
         |------------------->|                    |
         |     200 OK F8      |                    |
         |<-------------------|                    |
         |   No RTP Session   | INVITE Referred-By: A F9
         |                    |------------------->|
         |                    |   180 Ringing F10  |
         |                    |<-------------------|
         |                    |     200 OK F11     |
         |                    |<-------------------|
         |                    |       ACK F12      |
         |                    |------------------->|
         |                    |        RTP         |
         |                    |<==================>|
         |      NOTIFY F13    |                    |
         |<-------------------|                    |
         |      200 OK F14    |                    |
         |------------------->|                    |
         |                    |                    |


   User B call User A.  User A then transfers User B to User C, then
   User A disconnects with User B.  User B establishes the session to C
   then reports the success  back to A in the NOTIFY.  If the transfer
   fails, User B can send a new INVITE back to A to re-establish the
   session.






Johnston, et al.            Informational                    [Page 36]


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   Message Details

   F1 INVITE B -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 180 Ringing A -> B

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F3 200 OK A -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0



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


   F4 ACK B -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* Session is established between A and B. */

   /* A peforms unattended transfer of B to C */

   F5 REFER A -> B

   REFER sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 REFER
   Refer-To: <sip:UserC@anywhere.com>
   Referred-By: <UserA@here.com>
   Content-Length: 0


   F6 202 Accepted B -> A

   SIP/2.0 202 Accepted
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 2 REFER
   Content-Length: 0


   /* A now disconnects with B */

   F7 BYE A -> B

   BYE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159



Johnston, et al.            Informational                    [Page 38]


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   Call-ID: 12345601@here.com
   CSeq: 3 BYE
   Content-Length: 0


   F8 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345601@here.com
   CSeq: 3 BYE
   Content-Length: 0


   /* B attempts the transfer to C */

   F9 INVITE B -> C

   INVITE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: 7436222@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Referred-By: <UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844539 2890844539 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423821 0
   m=audio 3458 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 180 Ringing C -> B

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=928287
   Call-ID: 7436222@here.com
   CSeq: 1 INVITE


   F11 200 OK C -> B



Johnston, et al.            Informational                    [Page 39]


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   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=928287
   Call-ID: 7436222@here.com
   CSeq: 1 INVITE
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserC 2890844527 2890844527 IN IP4 client.anywhere.com
   s=Session SDP
   c=IN IP4 120.121.122.123
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F12 ACK B -> C

   ACK sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=928287
   Call-ID: 7436222@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* B and C now have established a session.  B reports success to A
   which A probably ignores. */

   F13 NOTIFY B -> A

   NOTIFY sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 NOTIFY
   Event: refer
   Content-Type: application/sip
   Content-Length: ...

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=928287
   Call-ID: 7436222@here.com



Johnston, et al.            Informational                    [Page 40]


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   CSeq: 1 INVITE
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   F14 200 OK A -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=314159
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 NOTIFY
   Content-Length: 0








































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2.5       Attended Transfer


         User A          User B        User C
          |                |              |
          |    INVITE F1   |              |
          |--------------->|              |
          |(100 Trying) F2 |              |
          |<---------------|              |
          | 180 Ringing F3 |              |
          |<---------------|              |
          |    200 OK F4   |              |
          |<---------------|              |
          |     ACK F5     |              |
          |--------------->|              |
          |       RTP      |              |
          |<==============>|              |
          |  INVITE c=0 F6 |              |
          |<---------------|              |
          |    200 OK F7   |              |
          |--------------->|              |
          |     ACK F8     |              |
          |<---------------|              |
          |  No RTP Sent!  |              |
          |                |  INVITE F9   |
          |                |------------->|
          |                |(100 Trying) F10
          |                |<-------------|
          |                | 180 Ringing F11
          |                |<-------------|
          |                | 200 OK F12   |
          |                |<-------------|
          |                |    ACK F13   |
          |                |------------->|
          |                |     RTP      |
          |                |<============>|
          |                | REFER Refer-To: A F14
          |                |------------->|
          |                |202 Accepted F15
          |                |<-------------|
          |    INVITE Referred-By: B F16  |
          |<------------------------------|
          |            200 OK F17         |
          |------------------------------>|
          |             ACK F18           |
          |<------------------------------|
          |               RTP             |
          |<=============================>|
          |     BYE F19    |              |
          |--------------->|              |



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          |   200 OK F20   |              |
          |<---------------|              |
          |                |  NOTIFY F21  |
          |                |<-------------|
          |                |  200 OK F22  |
          |                |------------->|
          |                |   BYE F23    |
          |                |------------->|
          |                |  200 OK F24  |
          |                |<-------------|

   User A calls User B.  User B puts User A on hold then calls User C to
   announce transfer.  User B transfers User C to User A which replaces
   the session between A and B.  B then disconnects session with A. C
   reports success of transfer to B who then disconnects with C.

   Note: the Replaces header would be very useful in this example.

   Message Details


   F1 INVITE A -> B

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 (100 Trying B -> A)

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0



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   F3 180 Ringing B -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=23431
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=23431
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 ACK A -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User A and User B have established a session.  User B puts User A
   on Hold */

   F6 INVITE B -> A

   INVITE sip:UserA@here.com SIP/2.0



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   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=23431
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1024 INVITE
   Contact: BigGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 200 OK A -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=23431
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1024 INVITE
   Contact: LittleGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 0.0.0.0
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 ACK B -> A

   ACK sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=23431
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1024 ACK
   Content-Length: 0


   /* User B calls User C  */



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   F9 INVITE B -> C

   INVITE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 42 INVITE
   Contact: BigGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844528 2890844528 IN IP4 client.there.com
   s=Session SDP
   c=IN IP4 110.111.112.113
   t=3034423645 0
   m=audio 3458 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 (100 Trying C -> B)

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 42 INVITE
   Content-Length: 0


   F11 180 Ringing C -> B

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 42 INVITE
   Content-Length: 0


   F12 200 OK C -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com



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   CSeq: 42 INVITE
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserC 2890844527 2890844527 IN IP4 client.anywhere.com
   s=Session SDP
   c=IN IP4 120.121.122.123
   t=3034423619 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F13 ACK B -> C

   ACK sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 42 ACK
   Content-Length: 0


   /* User B Transfers User C to User A  */

   F14 REFER B -> C

   REFER sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 43 REFER
   Refer-To: <sip:UserB@here.com?Accept-Contact=sip:UserB@here.com;
    only=true>
   Referred-By: <sip:UserB@there.com>
   Content-Length: 0


   F15 202 Accepted A -> B

   SIP/2.0 202 Accepted
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 43 REFER
   Content-Length: 0




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   /* User C establishes session with User A which replaces the session
   between User A and User B */

   F16 INVITE C -> A

   INVITE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP anywhere.com:5060
   From: OtherGuy <sip:UserC@anywhere.com>
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 9435674543@anywhere.com
   CSeq: 1 INVITE
   Referred-By: <sip:UserB@there.com>
   Accept-Contact: sip:UserB@here.com;only=true
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserC 2890844529 2890844529 IN IP4 client.anywhere.com
   s=Session SDP
   c=IN IP4 120.121.122.123
   t=3034423643 0
   m=audio 3458 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F17 200 OK A -> C

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP anywhere.com:5060
   From: OtherGuy <sip:UserC@anywhere.com>
   To: BigGuy <sip:UserA@here.com>;tag=ff3a
   Call-ID: 9435674543@anywhere.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844538 2890844538 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423452 0
   m=audio 49172 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F18 ACK C -> A

   ACK sip:UserC@anywhere.com SIP/2.0



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   Via: SIP/2.0/UDP anywhere.com:5060
   From: OtherGuy <sip:UserC@anywhere.com>
   To: BigGuy <sip:UserA@here.com>;tag=ff3a
   Call-ID: 9435674543@anywhere.com
   CSeq: 1 INVITE
   Content-Length: 0


   /* User A then disconnects from User B */

   F19 BYE A -> B

   BYE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=23431
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F20 200 OK B -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>;tag=23431
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   /* User C tells User B that the call has been successfully
   transferred */

   F21 NOTIFY C -> B

   NOTIFY sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   ToLittleGuy <sip:UserB@there.com>
   From: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 1 NOTIFY
   Content-Type: application/sdp
   Content-Length: ...

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP anywhere.com:5060
   From: OtherGuy <sip:UserC@anywhere.com>
   To: BigGuy <sip:UserA@here.com>;tag=ff3a
   Call-ID: 9435674543@anywhere.com



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   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   F22 200 OK B -> C

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   ToLittleGuy <sip:UserB@there.com>
   From: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: sdjfdjfskdf@there.com
   CSeq: 1 NOTIFY
   Content-Length: 0


   /* User B disconnects with User C */

   F23 BYE B -> C

   BYE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: 12345600@here.com
   CSeq: 44 BYE
   Content-Length: 0


   F24 200 OK C -> B

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=5f35a3
   Call-ID: 12345601@here.com
   CSeq: 44 BYE
   Content-Length: 0
















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2.6       Call Forwarding Unconditional


         User A           Proxy          Gateway
          |                |              |
          |    INVITE F1   |              |
          |--------------->|   INVITE F2  |
          |(100 Trying) F3 |------------->|
          |<---------------|180 Ringing F4|
          | 180 Ringing F5 |<-------------|
          |<---------------|  200 OK F6   |
          |    200 OK F7   |<-------------|
          |<---------------|              |
          |     ACK F8     |              |
          |--------------->|    ACK F9    |
          |                |------------->|
          |    Both way RTP Established   |
          |<=============================>|
          |     BYE F10    |              |
          |--------------->|   BYE F11    |
          |                |------------->|
          |                |   200 OK F12 |
          |    200 OK F13  |<-------------|
          |<---------------|              |
          |                |              |

   User B wants all calls forwarded to the PSTN.  User A calls User B.
   The Proxy server rewrites the request URI, and forwards the INVITE to
   a Gateway.  Details of messaging behind the Gateway are not shown.

   Message Details


   F1 INVITE A -> Proxy

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0



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


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

   F2 INVITE Proxy -> Gateway

   INVITE sip:+19727293660@gw1.wcom.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 (100 Trying) Proxy -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing Gateway -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content Length:0




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   F5 180 Ringing Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content Length: 0


   F6 200 OK Gateway -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: <sip:+19727293660@gw1.wcom.com;user=phone>
   Content-Type: application/sdp
   Content-Length: ...

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


   F7 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: <sip:+19727293660@gw1.wcom.com;user=phone>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=GATEWAY1 2890844527 2890844527 IN IP4 gatewayone.wcom.com
   s=Session SDP



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   c=IN IP4 gatewayone.wcom.com
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F8 ACK A -> Proxy

   ACK sip:+19727293660@gw1.wcom.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:+19727293660@gw1.wcom.com;user=phone>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F9 ACK Proxy -> Gateway

   ACK sip:+19727293660@gw1.wcom.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 BYE A -> Proxy 1

   BYE sip:+19727293660@gw1.wcom.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:+19727293660@gw1.wcom.com;user=phone>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F11 BYE Proxy 1 -> Gateway

   BYE sip:+19727293660@gw1.wcom.com;user=phone SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE



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   Content-Length: 0


   F12 200 OK Gateway -> Proxy 1

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F13 200 OK Proxy 1 -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314159
   Call-ID: 12345600@here.com
   CSeq:  2 BYE
   Content-Length: 0






























Johnston, et al.            Informational                    [Page 55]


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2.7       Call Forwarding - Busy

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

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

   Message Details


   F1 INVITE A -> Proxy

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>



Johnston, et al.            Informational                    [Page 56]


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

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy -> B1

   INVITE sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 (100 Trying) Proxy -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 486 Busy Here B1 -> Proxy

   SIP/2.0 486 Busy Here
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060



Johnston, et al.            Informational                    [Page 57]


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   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 ACK Proxy -> B1

   ACK sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

   F6 INVITE Proxy -> B2

   INVITE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F7 180 Ringing B2 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com



Johnston, et al.            Informational                    [Page 58]


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   CSeq: 1 INVITE
   Content-Length: 0


   F8 180 Ringing Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp
   Content-Length: ...




Johnston, et al.            Informational                    [Page 59]


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   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 ACK A -> Proxy

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F12 ACK Proxy -> B2

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

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

   F13 BYE A -> Proxy

   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F14 BYE Proxy -> B2




Johnston, et al.            Informational                    [Page 60]


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   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F15 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F16 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq:  2 BYE
   Content-Length: 0























Johnston, et al.            Informational                    [Page 61]


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2.8       Call Forwarding - No Answer

         User A           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   |                   |
          |                |------------->|                   |
          |                |              |    INVITE F10     |
          |                |--------------------------------->|
          |                |              | 180 Ringing F11   |
          | 180 Ringing F12|<---------------------------------|
          |<---------------|              |      200 OK F13   |
          |                |<---------------------------------|
          |   200 OK F14   |              |                   |
          |<---------------|              |                   |
          |     ACK F15    |              |                   |
          |--------------->|              |     ACK F16       |
          |                |--------------------------------->|
          |               Both way RTP Established            |
          |<=================================================>|
          |    BYE F17     |              |                   |
          |--------------->|              |      BYE F18      |
          |                |--------------------------------->|
          |                |              |    200 OK F19     |
          |  200 OK F20    |<---------------------------------|
          |<---------------|              |                   |
          |                |              |                   |

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


   Message Details

   F1 INVITE A -> Proxy




Johnston, et al.            Informational                    [Page 62]


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   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy -> B1

   INVITE sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 (100 Trying) Proxy -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0



Johnston, et al.            Informational                    [Page 63]


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   F4 180 Ringing B1 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 180 Ringing Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   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 sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F7 200 OK B1 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F8 487 Request Cancelled B1 -> Proxy



Johnston, et al.            Informational                    [Page 64]


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   SIP/2.0 487 Request Cancelled
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 ACK Proxy -> B1

   ACK sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 INVITE Proxy -> B2

   INVITE sip:UserB4@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F11 180 Ringing B2 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>



Johnston, et al.            Informational                    [Page 65]


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   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F12 180 Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F13 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F14 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp



Johnston, et al.            Informational                    [Page 66]


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   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F15 ACK A -> Proxy

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F16 ACK Proxy -> B2

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

   F17 BYE A -> Proxy

   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F18 BYE Proxy -> B2



Johnston, et al.            Informational                    [Page 67]


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   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F19 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F20 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq:  2 BYE
   Content-Length: 0






















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2.9  3-way Conference

   User A calls User B, User B then invites user C to a 3-way call. User
   B will mix the audio streams (act as the conference bridge).  If user
   B drops out of the call then the entire call is dropped.  This is not
   a fully meshed conference, and does not make use of the concepts in
   the call control draft.

   The signaling for this scenario is as follows:  User A calls User B,
   this establishes the call between A and B.  User B calls User C, this
   establishes the call between B and C.  User B will mix the audio
   streams, sending media originating at A to C, and media originating
   at C to A.  There is no SIP signaling relationship between User A and
   User C.

   The REFER method with the Replaces header could be used by User B to
   drop out of the call without disconnecting A and C.


2.10
    Single Line Extension

   Single Line Extension (Sequential, First Wins implementation), a call
   will ring several extensions in sequence.  The extension to answer
   the call becomes the active set, no other sets may join the call.

   The signaling is described in Section 2.11 of this document.  It is
   anticipated that Single Line Extension will be associated with help
   desk/call center applications rather then individual users.  The
   signaling for this implementation of Single Line Extension and Find-
   Me is the same, the difference may be in the provisioning of the
   service.

   Note that the call flows for a Home Extension have not yet been
   designed.



















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2.11
    Find-Me

         User A           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|      |      |
          |                |-------------------->|      |      |
          |                |          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    |<----------------------------------|
          |<---------------|                                   |



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          |    200 OK F25  |                                   |
          |--------------->|                 200 OK F26        |
          |                |---------------------------------->|
          |                |                                   |

   A call to a user will 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.

   It is anticipated that the Find-me feature will be associated with
   individual users.  The signaling for the implementation of Single
   Line Extension and Find-Me is the same, the difference may be in the
   provisioning of the service.


   Message Details


   F1 INVITE A -> Proxy

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t= 0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy -> B1

   INVITE sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp



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   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t= 0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 (100 Trying) Proxy -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing B1 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 180 Ringing Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   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 sip:UserB1@there.com SIP/2.0



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   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F7 200 OK B1 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F8 487 Request Cancelled B1 -> Proxy

   SIP/2.0 487 Request Cancelled
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F9 ACK Proxy -> B1

   ACK sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F10 INVITE Proxy -> B2

   INVITE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com



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   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   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/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314756
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F12 ACK Proxy -> B2

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=314756
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F13 INVITE Proxy -> B3

   INVITE sip:UserB3@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.3
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...




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   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   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/UDP ss1.wcom.com:5060;branch=83749.3
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F15 ACK Proxy -> B3

   ACK sip:UserB3@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.3
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7654321
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F16 INVITE Proxy -> B4

   INVITE sip:UserB4@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.4
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0



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   a=rtpmap:0 PCMU/8000


   F17 180 Ringing B4 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.4
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F18 180 Ringing B4 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F19 200 OK B4 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.4
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB4@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client4.there.com
   s=Session SDP
   c=IN IP4 110.111.112.116
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F20 200 OK Proxy -> A




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   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB4@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client4.there.com
   s=Session SDP
   c=IN IP4 110.111.112.116
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F21 ACK A -> Proxy

   ACK sip:UserB4@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <UserB4@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F22 ACK Proxy -> B4

   ACK sip:UserB4@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7137136
   Call-ID: 12345600@here.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 sip:UserA@here.com SIP/2.0



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   Via: SIP/2.0/UDP there.com:5060
   Route: <sip:UserA@here.com>
   From: LittleGuy <sip:UserB@there.com>;tag=7137136
   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345600@here.com
   CSeq: 1 BYE
   Content-Length: 0


   F24 BYE Proxy -> A

   BYE sip:UserA@here.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=7137136
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 BYE
   Content-Length: 0


   F25 200 OK A -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=7137136
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 BYE
   Content-Length: 0


   F26 200 OK Proxy -> B4

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>;tag=7137136
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345600@here.com
   CSeq: 1 BYE
   Content-Length: 0












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2.12
    Call Management (Incoming Call Screening)

         User A           Proxy          User B
          |                |              |
          |    INVITE F1   |              |
          |------------------------------>|
          | 305 Use Proxy F2              |
          |<------------------------------|
          |     ACK F3     |              |
          |------------------------------>|
          |    INVITE F4   |              |
          |--------------->|              |
          | 407 Proxy Authorization F5    |
          |<---------------|              |
          |     ACK F6     |              |
          |--------------->|              |
          |    INVITE F7   |              |
          |--------------->|              |
          | 403 Screening Failure (Terminating) F8
          |<---------------|              |
          |     ACK F9     |              |
          |--------------->|              |
          |                |              |

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

   Message Details


   F1 INVITE A -> B

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0



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


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

   F2 305 Use Proxy B -> A

   SIP/2.0 305 Use Proxy
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=342123
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: <sip:ss1.wcom.com>
   Content-Length: 0


   F3 ACK A -> B

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=342123
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* A retries the call through the proxy */

   F4 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000



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   /* Proxy 1 challenges User A for authentication */

   F5 407 Proxy Authorization Required Proxy 1 -> A

   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7886765
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Proxy-Authenticate: Digest realm="MCI WorldCom SIP",
    domain="sip:ss1.wcom.com", nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F6 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=7886765
   Call-ID: 12345600@here.com
   CSeq: 2 ACK
   Content-Length: 0


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

   F7 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 3 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Proxy-Authorization: DIGEST username="UserA",
    realm="MCI WorldCom SIP", nonce="ae9137be1c87d175c2dd63302a0d6e0a",
    opaque="", uri="sip:ss1.wcom.com",
    response="bbaec39f943bdcb3620d90afc548a45c"
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP



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   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


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

   SIP/2.0 403 Screening Failure (Terminating)
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=ffe254
   Call-ID: 12345600@here.com
   CSeq: 3 INVITE
   Content-Length: 0


   F9 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=ffe254
   Call-ID: 12345600@here.com
   CSeq: 3 ACK
   Content-Length: 0




























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2.13
    Call Management (Outgoing Call Screening)

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

   User A has an outgoing call screening list, User B is included on the
   list of addresses User A will not be able to place a call to.  User A
   attempts to call user B.

   Message Details


   F1 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* Proxy 1 challenges User A for authentication */

   F2 407 Proxy Authorization Required Proxy 1 -> A




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   SIP/2.0 407 Proxy Authorization Required
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=90210
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Proxy-Authenticate: Digest realm="MCI WorldCom SIP",
    domain="sip:ss1.wcom.com", nonce="ea9c8e88df84f1cec4341ae6cbe5a359",
    opaque="", stale=FALSE, algorithm=MD5
   Content-Length: 0


   F3 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=90210
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

   F4 INVITE A -> Proxy 1

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Proxy-Authorization: DIGEST username="UserA", realm="MCI WorldCom
    SIP", nonce="cb360afc54bbaec39f943bd820d9a45c", opaque="",
    uri="sip:ss1.wcom.com", response="b9d2e5bcdec9f69ab2a9b44f270285a6"
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=3034423619 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


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



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   SIP/2.0 403 Screening Failure (Originating)
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=18017
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Content-Length: 0


   F6 ACK A -> Proxy 1

   ACK sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=18017
   Call-ID: 12345600@here.com
   CSeq: 2 ACK
   Content-Length: 0



































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2.14
    Call Pickup

         User A           Proxy          User B1             User B2
          |                |              |                   |
          |    INVITE F1   |              |                   |
          |--------------->|   INVITE F2  |                   |
          |(100 Trying) F3 |------------->|                   |
          |<---------------|180 Ringing F4|                   |
          | 180 Ringing F5 |<-------------|                   |
          |<---------------|              |                   |
          |                |              |   REGISTER F6     |
          |                |<---------------------------------|
          |                |              |    200 OK F7      |
          |                |--------------------------------->|
          |                |              |    INVITE F8      |
          |                |--------------------------------->|
          |                |              | 180 Ringing F9    |
          | 180 Ringing F10|<---------------------------------|
          |<---------------|              |      200 OK F11   |
          |                |<---------------------------------|
          |   200 OK F12   |  CANCEL F13  |                   |
          |<---------------|------------->|                   |
          |     ACK F15    |  200 OK F14  |                   |
          |--------------->|<-------------|                   |
          |                |              |     ACK F16       |
          |                |--------------------------------->|
          |                |    487 F17   |                   |
          |                |<-------------|                   |
          |                |    ACK F18   |                   |
          |                |------------->|                   |
          |               Both way RTP Established            |
          |<=================================================>|
          |    BYE F19     |              |                   |
          |--------------->|              |      BYE F20      |
          |                |--------------------------------->|
          |                |              |    200 OK F21     |
          |  200 OK F22    |<---------------------------------|
          |<---------------|              |                   |
          |                |              |                   |

   User B1 and B2 are part of a work group that can pick up each others
   calls. User A calls B1 who does not answer.  User B2 wishes to pick
   up the call and sends a REGISTER with Expires:0 to the proxy which
   recognizes this as a call pickup not a register based on the Request-
   URI.  The proxy server then forks the INVITE by sending it to B2 who
   answers.  The proxy then cancels the B1 fork of the INVITE.


   Message Details




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   F1 INVITE A -> Proxy

   INVITE sip:UserB@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F2 INVITE Proxy -> B1

   INVITE sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F3 (100 Trying) Proxy -> A

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com



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   CSeq: 1 INVITE
   Content-Length: 0


   F4 180 Ringing B1 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F5 180 Ringing Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   /* User B2 decides to pick up the call */

   F6 REGISTER  B2 -> Proxy

   REGISTER sip:pickupgroup37.ss1.wcom.com SIP/2.0
   Via: SIP/2.0/UDP b2.there.com:5060
   From: LittleGuy <sip:UserB2@there.com>
   To: LittleGuy <sip:UserB2@there.com>
   Call-ID: 563456212@b2.there.com
   CSeq: 1 REGISTER
   Contact: BigGuy <sip:UserB2@there.com>
   Expires: 0
   Content-Length: 0


   F7 200 OK  Proxy -> B2

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP b2.there.com:5060
   From: LittleGuy <sip:UserB2@there.com>
   To: LittleGuy <sip:UserB2@there.com>
   Call-ID: 563456212@b2.there.com
   CSeq: 1 REGISTER
   Contact: BigGuy <sip:UserB2@there.com>



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   Expires: 0
   Content-Length: 0


   /* Proxy recognizes the REGISTER directed at pickgroup37.ss1.wcom.com
   as being a call pickup attempt for the pending INVITE to B1.  The
   proxy then forks the INVITE and sends it to B2. */

   F8 INVITE Proxy -> B2

   INVITE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserA 2890844526 2890844526 IN IP4 client.here.com
   s=Session SDP
   c=IN IP4 100.101.102.103
   t=0 0
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F9 180 Ringing B2 -> Proxy

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F10 180 Proxy -> A

   SIP/2.0 180 Ringing
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE



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   Content-Length: 0


   F11 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.2
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F12 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   Record-Route: <sip:UserB@there.com;maddr=ss1.wcom.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Contact: LittleGuy <sip:UserB2@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844527 2890844527 IN IP4 client2.there.com
   s=Session SDP
   c=IN IP4 110.111.112.114
   t=0 0
   m=audio 3456 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   /* The Proxy detects the answer by B2 and cancels the B1 branch */

   F13 CANCEL Proxy -> B1



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   CANCEL sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F14 200 OK B1 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>
   Call-ID: 12345600@here.com
   CSeq: 1 CANCEL
   Content-Length: 0


   F15 ACK A -> Proxy

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F16 ACK Proxy -> B2

   ACK sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


   F17 487 Request Cancelled B1 -> Proxy

   SIP/2.0 487 Request Cancelled
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>



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   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Content-Length: 0


   F18 ACK Proxy -> B1

   ACK sip:UserB1@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=3145678
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length: 0


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

   F19 BYE A -> Proxy

   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   Route: <sip:UserB2@there.com>
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F20 BYE Proxy -> B2

   BYE sip:UserB2@there.com SIP/2.0
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F21 200 OK B2 -> Proxy

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456



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   Call-ID: 12345600@here.com
   CSeq: 2 BYE
   Content-Length: 0


   F22 200 OK Proxy -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: LittleGuy <sip:UserB@there.com>;tag=123456
   Call-ID: 12345600@here.com
   CSeq:  2 BYE
   Content-Length: 0








































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   Acknowledgements

   The authors wish to thank the following individuals for their
   assistance and review of this call flows 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.











































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3  References


   [1] S. Bradner, "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

   [2] A. Johnston, S. Donovan, R. Sparks, C. Cunningham, D. Willis, J.
       Rosenberg, and H. Schulzrinne, "SIP Call Flow Examples", Internet
       Draft, Internet Engineering Task Force, March 2001, Work in
       Progress.

   [3] R. Sparks, "SIP Call Control Transfer", Internet Draft,
       Internet Engineering Task Force, February 2001,
       Work in Progress.

   [4] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
       Session Initiation Protocol", RFC 2543, March 1999.





































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4  Author's Addresses


   Alan Johnston               Email: alan.johnston@wcom.com
                               sip:alan@digitalari.com

   Robert Sparks               Email: rsparks@dynamicsoft.com

   Chris Cunningham            Email: ccunningham@dynamicsoft.com

   Steve Donovan               Email: sdonovan@dynamicsoft.com

   Kevin Summers               Email: kevin.summers@sonusnet.com



   Copyright Notice

   "Copyright (C) The Internet Society 2001. All Rights Reserved.

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

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

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











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