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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-00.txt         Robert Sparks
Category: Informational                               Chris Cunningham
November 2000                                            Steve Donovan
Expires: May 2001                                          dynamicsoft
                                                         Kevin Summers
                                                                   TTI



                     SIP Telephony 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 document gives examples of SIP (Session Initiation Protocol)
   telephony 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
   1.1    Legend for Message Flows...................................3
   1.2    Document History...........................................4
   2      IP Telephony Services Features Call Flows..................5
   2.1    Call Hold..................................................5
   2.2    Music on Hold.............................................15
   2.3    Consultation Hold.........................................24
   2.4    Unattended Transfer.......................................38
   2.5    Attended Transfer.........................................44
   2.6    Call Forwarding Unconditional.............................53
   2.7    Call Forwarding - Busy....................................58
   2.8    Call Forwarding - No Answer...............................64
   2.9    3-way Conference..........................................71
   2.10   Single Line Extension.....................................71
   2.11   Find-Me...................................................72
   2.12   Call Management (Incoming Call Screening).................81
   2.13   Call Management (Outgoing Call Screening).................84
   3      Acknowledgements..........................................88
   4      References................................................89
   5      Author's Addresses........................................90
































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1  Overview


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

         Call Hold (with Music)        Consultation Hold
         Unattended Transfer           Attended Transfer
         Unconditional Call Forwarding Busy Call Forwarding
         No Answer Call Forwarding     3-way Call
         Single-Line Extension         Find-Me
         Incoming Call Screening       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 "SIP Telephony
   Call Flow Examples" [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.

   These flows use SIP as defined by RFC2543 [4].

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


1.1 Legend for Message Flows

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

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




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   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.


































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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.  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
   t=3034423619 0



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   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
   Content-Length: ...



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   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>
   To: LittleGuy <sip:UserB@there.com>;tag=314159



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   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
   Route: <sip:UserB@there.com>



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   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
   To: BigGuy <sip:UserA@here.com>;tag=1234567



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   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
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1



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   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

         User A          User B     Music Server
          |              |              |
          |   INVITE F1  |              |
          |------------->|              |
          | 100 Trying F2|              |
          |<-------------|              |
          |180 Ringing F3|              |
          |<-------------|              |
          |  200 OK F4   |              |
          |<-------------|              |
          |    ACK F5    |              |
          |------------->|              |
          |  RTP Media   |              |
          |<============>|              |
          |              |              |
          |INVITE (c=0) F6              |
          |<-------------|              |
          |   200 OK F7  |              |
          |------------->|              |
          |     ACK F8   |              |
          |<-------------|              |
          |              |              |
          | No RTP Sent! |              |
          |              |              |
          |   REFER Refer-To: sip:music@server.com F9
          |<-------------|              |
          |   100 F10    |              |
          |------------->|              |
          | INVITE F11 Referred-By: B   |
          |---------------------------->|
          |     200 OK a=sendonly F12   |
          |<----------------------------|
          |           ACK F13           |
          |---------------------------->|
          |           RTP Music         |
          |<============================|
          |  200 OK F14  |              |
          |------------->|              |
          |              |              |
          |   User A is taken off Hold  |
          |              |              |
          |   REFER Refer-To: music@server.com;method=BYE F15
          |<-------------|              |
          |   100 F16    |              |
          |------------->|              |
          |           BYE F17           |
          |---------------------------->|
          |          200 OK F18         |



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          |<----------------------------|
          |              |              |
          |       No more RTP Music     |
          |              |              |
          |  200 OK F19  |              |
          |------------->|              |
          |  INVITE F20  |              |
          |<-------------|              |
          |  200 OK F21  |              |
          |------------->|              |
          |    ACK F22   |              |
          |<-------------|              |
          |      RTP     |              |
          |<============>|              |
          |              |              |

   In this example, User A calls User B.  User B then places User A on
   hold, then REFERs User A to a Music Server for the music on hold
   service.  User A agrees to the music on hold and sends an INVITE to
   the Music Server to establish the one way media session.  Before User
   B takes User A off hold, a REFER is sent to tell User A to send a BYE
   to the Music Server to stop the music.  Then User B takes User A off
   hold.


   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 (100 Trying) B -> A




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   SIP/2.0 100 Trying
   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
   Content-Length: 0


   F3 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


   F4 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: 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


   F5 ACK A -> B

   ACK 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
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0




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   /* B places A on hold */

   F6 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>;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


   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=314159
   To: BigGuy <sip:UserA@here.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 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=314159
   To: BigGuy <sip:UserA@here.com>



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   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* User B REFERS User A to a Music On Hold Server */

   F9 REFER B -> A

   REFER 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: 2 REFER
   Refer-To: <sip:music@server.com>
   Content-Length: 0


   F10 (100 Trying) A -> B

   SIP/2.0 100 Trying
   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: 2 REFER
   Content-Length: 0


   /* User A connects to Music On Hold Server */

   F11 INVITE A -> Music Server

   INVITE sip:music@server.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: <sip:music@server.com>
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Contact: BigGuy <sip:UserA@here.com>
   Referred-By: <sip:UserB@there.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
   a=recvonly


   F12 200 OK Music Server -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: <sip:music@server.com>;tag=se83kw1
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   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
   a=sendonly


   F13 ACK A -> Music Server

   ACK sip:music@server.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: <sip:music@server.com>;takg=se83kw1
   Call-ID: 12345601@here.com
   CSeq: 2 ACK
   Content-Length: 0


   /* User A now has Music and reports success back to B */

   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>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 2 REFER
   Content-Length: 0


   /* User B prepares to take A off hold by first stopping music */



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   F15 REFER B -> A

   REFER 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>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 3 REFER
   Refer-To: <sip:music@server.com?method=BYE>
   Content-Length: 0


   F16 (100 Trying) A -> B

   SIP/2.0 100 Trying
   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: 3 REFER
   Content-Length: 0


   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>
   To: <sip:music@server.com>;tag=se83kw1
   Call-ID: 12345601@here.com
   CSeq: 3 BYE
   Contact: BigGuy <sip:UserA@here.com>
   Referred-By: <sip:UserB@there.com>
   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>
   To: <sip:music@server.com>;tag=se83kw1
   Call-ID: 12345601@here.com
   CSeq: 3 BYE
   Content-Length: 0


   /* Music is stopped, User A reports to B success */

   F19 200 OK A -> B



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   SIP/2.0 200 OK
   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: 3 REFER
   Content-Length: 0


   /* B now takes A off hold and continues session */

   F20 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>;tag=314159
   To: BigGuy <sip:UserA@here.com>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 4 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


   F21 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>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 4 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


   F22 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>;tag=1234567
   Call-ID: 12345601@here.com
   CSeq: 4 ACK
   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, after that call is finished User B take the call with User A off
   hold.

   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



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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











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2.4 Unattended Transfer

   This example is taken directly from "SIP Call Control Transfer"[3]
   section 4.4.1.

       User A              User B               User C
         |      INVITE F1     |                    |
         |<-------------------|                    |
         |      200 OK F2     |                    |
         |------------------->|                    |
         |        ACK F3      |                    |
         |<-------------------|                    |
         |        RTP         |                    |
         |<==================>|                    |
         |                    |                    |
         |  INVITE (hold) F4  |                    |
         |------------------->|                    |
         |     200 OK F5      |                    |
         |<-------------------|                    |
         |       ACK F6       |                    |
         |------------------->|                    |
         |                    |                    |
         |    No RTP Sent!    |                    |
         |                    |                    |
         |    REFER Refer-To: C F7                 |
         |------------------->|                    |
         |    100 Trying F8   |                    |
         |<-------------------|                    |
         |                    |     INVITE F9      |
         |                    |------------------->|
         |                    |     200 OK F10     |
         |                    |<-------------------|
         |                    |       ACK F11      |
         |                    |------------------->|
         |                    |        RTP         |
         |                    |<==================>|
         |      200 OK F12    |                    |
         |<-------------------|                    |
         |       BYE F13      |                    |
         |------------------->|                    |
         |     200 OK F14     |                    |
         |<-------------------|                    |
         |                    |                    |


   User B call User A.  User B then transfers User A to User C.  User B
   hangs up the call.






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


   F3 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



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   To: BigGuy <sip:UserA@here.com>
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* Session is established between A and B.  User B then places User A
   on hold */

   F4 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>;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 0.0.0.0
   t=3034423619
   m=audio 49170 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F5 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: 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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   F6 ACK A -> B

   ACK 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
   Call-ID: 12345601@here.com
   CSeq: 1 ACK
   Content-Length: 0


   /* B is now on hold.  A transfers B to C */

   F7 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>
   Content-Length: 0


   F8 (100 Trying) B -> A

   SIP/2.0 100 Trying
   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


   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: 12345601@here.com
   CSeq: 2 INVITE
   Contact: LittleGuy <sip:UserB@there.com>
   Content-Type: application/sdp
   Content-Length: ...

   v=0
   o=UserB 2890844539 2890844539 IN IP4 client.there.com
   s=Session SDP



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   c=IN IP4 110.111.112.113
   t=3034423821 0
   m=audio 3458 RTP/AVP 0
   a=rtpmap:0 PCMU/8000


   F10 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=928287
   Call-ID: 12345601@here.com
   CSeq: 2 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


   F11 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: 12345601@here.com
   CSeq: 2 ACK
   Content-Length: 0


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

   F12 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 REFER
   Content-Length: 0





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   /* A now disconnects with B */

   F13 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
   Call-ID: 12345601@here.com
   CSeq: 3 BYE
   Content-Length: 0


   F14 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
































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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 to C F14 |              |
          |<---------------|              |
          |(100 Trying) F15|              |
          |--------------->|              |
          |            INVITE F16         |
          |------------------------------>|
          |            200 OK F17         |
          |<------------------------------|
          |             ACK F18           |
          |------------------------------>|
          |               RTP             |
          |<=============================>|
          |   200 OK F19   |              |
          |--------------->|              |



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

   User A calls User B.  User B puts User A on hold, and Calls user C to
   announce transfer.  User B transfers User A to User C while
   maintaining sessions with both A and C.  Once the session between A
   and C is successfully established, User B hangs up on both A and C.

   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


   F3 180 Ringing B -> A

   SIP/2.0 180 Ringing



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   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
   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



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   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  */

   F9 INVITE B -> A

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



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   From: LittleGuy <sip:UserB@there.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: 12345600@here.com
   CSeq: 1025 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: 12345600@here.com
   CSeq: 1025 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: 12345600@here.com
   CSeq: 1025 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: 12345600@here.com
   CSeq: 1025 INVITE
   Contact: OtherGuy <sip:UserC@anywhere.com>
   Content-Type: application/sdp
   Content-Length: ...




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   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: 12345600@here.com
   CSeq: 1025 ACK
   Content-Length: 0


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

   F14 REFER B -> A

   REFER 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>;tag=23431
   Call-ID: 12345600@here.com
   CSeq: 1026 REFER
   Refer-To: <sip:UserC@anywhere.com>
   Content-Length: 0


   F15 (100 Trying) A -> B

   SIP/2.0 100 Trying
   Via: SIP/2.0/UDP there.com:5060
   From: LittleGuy <sip:UserB@there.com>
   To: BigGuy <sip:UserA@here.com>;tag=23431
   Call-ID: 12345600@here.com
   CSeq: 1026 REFER
   Content-Length: 0


   /* User A calls User C */

   F16 INVITE A -> C

   INVITE sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060



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   From: BigGuy <sip:UserA@here.com>
   To: OtherGuy <sip:UserC@anywhere.com>
   Call-ID: 12345600@here.com
   CSeq: 2 INVITE
   Referred-By: <sip:UserB@there.com>
   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


   F17 200 OK C -> A

   SIP/2.0 200 OK
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=ff3a
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   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


   F18 ACK A -> C

   ACK sip:UserC@anywhere.com SIP/2.0
   Via: SIP/2.0/UDP here.com:5060
   From: BigGuy <sip:UserA@here.com>
   To: OtherGuy <sip:UserC@anywhere.com>;tag=ff3a
   Call-ID: 12345601@here.com
   CSeq: 2 INVITE
   Content-Length: 0






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

   F19 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=23431
   Call-ID: 12345600@here.com
   CSeq: 1026 REFER
   Content-Length: 0


   /* User B then disconnects from both User A and User C */

   F20 BYE B -> A

   BYE 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>;tag=23431
   Call-ID: 12345600@here.com
   CSeq: 1027 BYE
   Content-Length: 0


   F21 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=23431
   Call-ID: 12345600@here.com
   CSeq: 1027 BYE
   Content-Length: 0


   F22 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: 1028 BYE
   Content-Length: 0


   F23 200 OK C -> B




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   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: 1028 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


   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


   F5 180 Ringing Proxy -> A



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   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: LittleGuy <sip:7773660,phone-
   context=p1234@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



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   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
   Content-Length: 0



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   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































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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>



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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



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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



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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: ...




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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




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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























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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

   INVITE sip:UserB@there.com SIP/2.0



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   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




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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




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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>
   To: LittleGuy <sip:UserB@there.com>;tag=123456



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   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
   Content-Length: ...



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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


   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




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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.



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
   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


   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
   Via: SIP/2.0/UDP ss1.wcom.com:5060;branch=83749.1



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   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
   CSeq: 1 INVITE



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   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: ...

   v=0



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   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
   a=rtpmap:0 PCMU/8000



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   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

   SIP/2.0 200 OK



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



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   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: 2 BYE
   Content-Length: 0













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2.12
    Call Management (Incoming Call Screening)

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

   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.

   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>
   Call-ID: 12345600@here.com
   CSeq: 1 INVITE
   Proxy-Authenticate: Digest realm="MCI WorldCom SIP",
   domain="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>
   Call-ID: 12345600@here.com
   CSeq: 1 ACK
   Content-Length:0


   /* User A responds by 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="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
   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 (Terminating) Proxy 1 -> A



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   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: 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=ffe254
   Call-ID: 12345600@here.com
   CSeq: 2 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="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:UserB@there.com;maddr=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





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

   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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3  Acknowledgements


   The authors wish to thank the following individuals for their
   assistance and review of this call flows document: Rohan Mahey,
   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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4  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 Telephony Call Flow
       Examples", Internet Draft, Internet Engineering Task Force,
       November 2000, Work in Progress.

   [3] R. Sparks, "SIP Call Control Transfer", Internet Draft,
       Internet Engineering Task Force, September 2000,
       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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5  Author's Addresses


   Alan Johnston               Email: alan.johnston@wcom.com

   Robert Sparks               Email: rsparks@dynamicsoft.com

   Chris Cunningham            Email: ccunningham@dynamicsoft.com

   Steve Donovan               Email: sdonovan@dynamicsoft.com

   Kevin Summers               Email: kevin.summers@ttimail.com



   Copyright Notice

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   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
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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