Internet DRAFT - draft-campbell-sip-service-control

draft-campbell-sip-service-control





Internet Engineering Task Force                              B. Campbell
Internet-Draft                                                 R. Sparks
Expires: July 2, 2001                                        dynamicsoft
                                                            January 2001


            Control of Service Context using SIP Request-URI
                 draft-campbell-sip-service-control-03

Status of this Memo

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

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

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   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

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

   This Internet-Draft will expire on July 2, 2001.

Copyright Notice

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

Abstract

   This memo provides information for the Internet community. It
   describes a useful way to conceptualize the use of the standard SIP
   Request-URI that the authors and many members of the SIP community
   think is suitable as a convention.  It does not define any new
   protocol with respect to RFC 2543. 

   In a conventional telephony environment, extended service
   applications often use call state information, such as calling
   party, called party, reason for forward, etc, to infer application
   context. In a SIP/2.0 call, much of this information may be either
   non-existent or unreliable. This draft proposes a mechanism to
   communicate context information to an application.  Under this


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   proposal, a client or proxy can communicate context through the use
   of a distinctive Request-URI. This draft continues with examples of
   how this mechanism could be used in a voice mail application. 

Table of Contents

   1.      Introduction . . . . . . . . . . . . . . . . . . . . . . .  4
   2.      Example Application  . . . . . . . . . . . . . . . . . . .  4
   2.1     Using URIs to Control Voice Mail Service Behavior  . . . .  4
   3.      Voice Mail Scenario Descriptions . . . . . . . . . . . . .  6
   3.1     Deposits . . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.1.1   Direct Request to Deposit to a particular mailbox  . . . .  6
   3.1.1.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  6
   3.1.1.2 Arbitrary PSTN source  . . . . . . . . . . . . . . . . . .  6
   3.1.1.3 Recognized PSTN source . . . . . . . . . . . . . . . . . .  7
   3.1.2   Direct Request to Deposit, mailbox to be determined  . . .  7
   3.1.2.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.1.2.2 PSTN source  . . . . . . . . . . . . . . . . . . . . . . .  7
   3.1.2.3 Indirect Request to Deposit, due to find-me proxy decision  7
   3.2     Retrievals . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.2.1   Request to Retrieve from a particular mailbox  . . . . . .  8
   3.2.1.1 Trusted SIP source . . . . . . . . . . . . . . . . . . . .  8
   3.2.1.2 Authenticated SIP source . . . . . . . . . . . . . . . . .  8
   3.2.1.3 Unauthenticated SIP source . . . . . . . . . . . . . . . .  8
   3.2.1.4 PSTN source  . . . . . . . . . . . . . . . . . . . . . . .  8
   3.2.2   Request to Retrieve, mailbox to be determined  . . . . . .  8
   3.2.2.1 SIP source . . . . . . . . . . . . . . . . . . . . . . . .  8
   3.2.2.2 Arbitrary PSTN source  . . . . . . . . . . . . . . . . . .  9
   3.2.2.3 Recognized PSTN source . . . . . . . . . . . . . . . . . .  9
   4.      Voice Mail Call Flow Examples  . . . . . . . . . . . . . .  9
   4.1     Generic Scenario . . . . . . . . . . . . . . . . . . . . .  9
   4.1.1   Direct call to the voice mail system . . . . . . . . . . .  9
   4.2     Message Deposit Scenarios  . . . . . . . . . . . . . . . . 14
   4.2.1   Call to known subscriber forwarded on no answer  . . . . . 14
   4.2.2   Call to known subscriber forwarded on busy . . . . . . . . 19
   4.2.3   Direct call to a subscriber's mailbox  . . . . . . . . . . 24
   4.3     Message Retrieval Scenarios  . . . . . . . . . . . . . . . 29
   4.3.1   Call to retrieve messages believed to be from a known        
           subscriber . . . . . . . . . . . . . . . . . . . . . . . . 29
   4.3.2   Call to retrieve messages from an authenticated subscriber 33
   5.      Security Considerations  . . . . . . . . . . . . . . . . . 37
   6.      Acknowledgments  . . . . . . . . . . . . . . . . . . . . . 37
           References . . . . . . . . . . . . . . . . . . . . . . . . 37
           Authors' Addresses . . . . . . . . . . . . . . . . . . . . 37
           Full Copyright Statement . . . . . . . . . . . . . . . . . 38






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1. Introduction

   A communication service should make use of the information it has at
   hand when being accessed. For example, in most current voice mail
   implementations, a subscriber retrieving messages from his own desk
   does not have to reenter his voice mailbox number - the service
   assumes that the store being accessed is the one associated with the
   endpoint being used to access the service. Some services allow the
   user to validate this assumption using IVR techniques before
   prompting for a PIN. 

   This concept of context-awareness can be captured in a voice mail
   service implementing SIP as defined in RFC 2543[1], without
   modification, through the standard use of that protocol's
   Request-URI. Furthermore, the concept is applicable to any SIP-based
   service where initial application state should be determined from
   context. 

   This concept is a usage convention of standard SIP as defined in RFC
   2543[1] and does not modify or extend that protocol in any way. 

2. Example Application

   In this draft, we use the example of voice mail to illustrate the
   technique. One motivation for applying this technique to this
   problem is allowing a proxy or location server to control the
   initial state of a voice service.  For example, a voice client might
   register a contact list ending with the URL that would accept voice
   messages for the client. 

2.1 Using URIs to Control Voice Mail Service Behavior

   Many conventional voice mail systems use call state information,
   such as the calling party, called party, reason for forward, etc, to
   decide the initial application state.  For example, it might play
   one outgoing message if the call reached voice mail because the
   called party did not answer and another if the line was busy.  It
   decides whom the message is for based on the called party
   information. If the call originated from a subscriber's phone
   number, it might authenticate the caller and then go directly to the
   message retrieval and account maintenance menu. 

   When a new subscriber is added to a system, a set of identities
   could be generated, each given a unique sip URI. The following
   tables show some of the identities that might be generated (it is
   not exhaustive). The example schemes show that the URIs could, but
   don't necessarily have to, have mnemonic value. 

   In practical applications, it is important that an application does


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   not apply semantic rules to the various URIs. Instead, it should
   allow any arbitrary string to be provisioned, and map the string to
   the desired behavior. The owner of the system may choose to
   provision mnemonic strings, but the application should not require
   it. In any large installation, the system owner is likely to have
   pre-existing rules for mnemonic URIs, and any attempt by an
   application to define its own rules may create a conflict. For our
   example, this means a voice mail system should allow an arbitrary
   mix of URLs from these schemes, or any other scheme that renders
   valid SIP URIs to be provisioned, rather than enforce one particular
   scheme. 

     URI Identity       Example Scheme 1
                             Example Scheme 2
                                  Example Scheme 3

     Deposit with       sip:sub-rjs-deposit@vm.wcom.com
     standard greeting       sip:677283@vm.wcom.com
                                  sip:rjs@vm.wcom.com;mode=deposit


     Deposit with on    sip:sub-rjs-deposit-busy.vm.wcom.com
     phone greeting          sip:677372@vm.wcom.com
                                  sip:rjs@vm.wcom.com;mode=3991243

     Deposit with       sip:sub-rjs-deposit-sg@vm.wcom.com
     special greeting        sip:677384@vm.wcom.com
                                  sip:rjs@vm.wcom.com;mode=sg

     Retrieve - SIP     sip:sub-rjs-retrieve@vm.wcom.com
     authentication          sip:677405@vm.wcom.com
                                  sip:rjs@vm.wcom.com;mode=retrieve

     Retrieve - prompt  sip:sub-rjs-retrieve-inpin.vm.wcom.com
     for PIN in-band         sip:677415@vm.wcom.com
                                  sip:rjs@vm.wcom.com;mode=inpin


   When a service is first set up, identities such as the following
   could be created. 











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     URI Identity       Example Scheme 1
                             Example Scheme 2
                                  Example Scheme 3

     Deposit -          sip:deposit@vm.wcom.com
     identify target         sip:670001@vm.wcom.com
     mailbox by To:               sip:deposit@vm.wcom.com

     Retrieve -         sip:retrieve@vm.wcom.com
     identify target         sip:670002@vm.wcom.com
     mailbox by SIP               sip:retrieve@vm.wcom.com
     authentication

     Deposit - prompt   sip:deposit-in@vm.wcom.com
     for target              sip:670003@vm.wcom.com
     mailbox in-band              sip:deposit@vm.wcom.com;mode=inband

     Retrieve - prompt  sip:retrieve-in@vm.wcom.com
     for target              sip:670004@vm.wcom.com
     mailbox and PIN              sip:retrieve@vm.wcom.com;mode=inband
     in-band

   In addition to providing this set of URIs to the subscriber (to use
   as he sees fit), an integrated service provider could add these to
   the set of contacts in a find-me proxy. The proxy could then route
   calls to the appropriate URI based on the origin of the request, the
   subscriber's preferences and current state. 

3. Voice Mail Scenario Descriptions

   In each of these scenarios, the PSTN gateway is configured to
   communicate only with a particular proxy-registrar. 

3.1 Deposits

3.1.1 Direct Request to Deposit to a particular mailbox

3.1.1.1 SIP source

   A SIP client that knew the URI for a particular deposit mailbox
   (sip:sub-rjs-deposit@vm.wcom.com) could place a direct invitation to
   the voicemail service, or through a protecting proxy. The proxy
   could restrict access to deposit identities with special greetings
   by authenticating the requester. 

3.1.1.2 Arbitrary PSTN source

   The gateway's proxy would map a call from an unrecognized PSTN
   number to a number associated with a subscriber's mailbox into an


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   invite to the deposit with standard greeting URI
   (sip:sub-rjs-deposit@vm.wcom.com). 

3.1.1.3 Recognized PSTN source

   The gateway's proxy would map a call from a recognized (exact or
   pattern match) PSTN number to a number associated with a
   subscriber's mailbox into an invite to the appropriate special
   greeting URI (sip:sub-rjs-deposit-sg@vm.wcom.com). The gateway's
   ability to identify the calling party (using calling party number)
   is trusted, so no further authentication of the requester is
   performed. 

3.1.2 Direct Request to Deposit, mailbox to be determined

3.1.2.1 SIP source

   A voice mail service or its protecting proxy could expose a generic
   deposit URL for use when a caller wished to go directly to voice
   mail. The service would likely play an IVR dialog to determine what
   message store to deposit a message into. 

   An application designer may be tempted to attempt to match the To:
   and From: headers on a call to infer information.  However, this
   approach could cause complications when multiple proxy forwards
   occur in a call.  For example, A calls B, who has all calls
   forwarded to C.  C forwards the call to her voice mail service.  If
   the voice mail service matches the To: header to determine the
   message store, it will get the information for B instead of C.  But
   there is no reason to assume that C's voice mail service has any
   knowledge of B. 

3.1.2.2 PSTN source

   The gateway's proxy would map a call from an unrecognized PSTN
   number to the top level voice mail service access number to an
   invite to the Deposit - prompt for target mailbox in-band URI
   (sip:deposit-in@vm.wcom.com for example). Getting the call to the
   target mailbox would proceed as in the SIP source case. 

3.1.2.3 Indirect Request to Deposit, due to find-me proxy decision

   A find-me proxy could map an invitation to a subscriber
   (sip:rjs@wcom.com) to the appropriate voice mail service URI
   depending on the subscriber's current state. The normal deposit URI
   could be chosen if the subscriber's contact list has been otherwise
   exhausted with no answer. The busy-announcement URI would be chosen
   when a busy everywhere response is received from one of the
   contacts. A DND announcement URI could be selected if the subscriber


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   had activated DND. Calls to sip:receptionist@wcom.com could be
   configured to roll to sip:deposit@wcom.com 

3.2 Retrievals

3.2.1 Request to Retrieve from a particular mailbox

3.2.1.1 Trusted SIP source

   A request to retrieve the contents of a particular mailbox
   (sip:sub-rjs-retrieve@vm.wcom.com) coming from a trusted source
   could be honored without further authentication checks. A trusted
   source is one with which the voice mail service has secure
   communications, and to which it is willing to delegate
   authentication. This could be the service's protecting proxy for
   example. 

3.2.1.2 Authenticated SIP source

   A service, or its protecting proxy, could choose to honor a retrieve
   request for a particular mailbox (sip:sub-rjs-retrieve@vm.wcom.com)
   based on SIP authentication. If SIP level authentication failed, the
   service or proxy could be configured to send the call to the in-band
   pin prompting URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com). 

3.2.1.3 Unauthenticated SIP source

   A service, or its protecting proxy, receiving a retrieve request for
   a particular mailbox (sip:sub-rjs-retrieve@vm.wcom.com) with no
   other method of authenticating the requestor could send the request
   to the in-band pin prompting URI
   (sip:sub-rjs-retrieve-inpin@vm.wcom.com). 

3.2.1.4 PSTN source

   This scenario assumes that the service provider's network has been
   configured such that a PSTN number could be dialed explicitly for
   retrieving messages from a particular mailbox. Such services
   currently exist, but are not common. In such a network, the
   gateway's proxy would map the call to the in-band pin prompting URI
   (sip:sub-rjs-retrieve-inpin@vm.wcom.com). 

3.2.2 Request to Retrieve, mailbox to be determined

3.2.2.1 SIP source

   As in the Request to Deposit scenario, when a service receives a
   request for the top level retrieve URI it would most likely need to
   use in-band IVR techniques to determine the target mailbox and


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   authenticate the caller. 

3.2.2.2 Arbitrary PSTN source

   This scenario assumes there is a single PSTN number that subscribers
   dial to access the voice mail service to retrieve messages. This is
   the most common access method provided by current voice mail
   services. 

   The gateway's proxy would map a call to the top level PSTN number to
   the top level retrieve in-band prompting URI
   (sip:retrieve-in@vm.wcom.com). Once the system identifies the target
   mailbox, the call would be transferred to the appropriate in-band
   pin prompting URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com). 

3.2.2.3 Recognized PSTN source

   This scenario also assumes there is a single PSTN number that
   subscribers dial to access the voice mail service to retrieve
   messages. 

   The gateway's proxy would recognize the calling party number as a
   subscriber, and map the call to the subscriber's in-band prompting
   URI (sip:sub-rjs-retrieve-inpin@vm.wcom.com) 

4. Voice Mail Call Flow Examples

   The following section describes some example call flows for a
   hypothetical voice mail service, with the host name of vm.wcom.com.
   All the call flows assume that a proxy protects the voice mail
   service and that a trust relationship exists between the voice mail
   service and the proxy. 

4.1 Generic Scenario

4.1.1 Direct call to the voice mail system

   User A calls the voice mail system directly. The voice mail system
   invokes the top-level menu, which might prompt the caller for an
   extension or the first few letters of a name. 











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            User A              Proxy               VM Service
              |                   |                       |
              |  INVITE F1        |                       |
              |------------------>|                       |
              |                   |  INVITE F2            |
              | (100 Trying) F3   |---------------------->|
              |<------------------|                       |
              |                   |  180 Ringing F4       |
              |  180 Ringing F5   |<----------------------|
              |<------------------|                       |
              |                   |  200 OK F6            |
              |  200 OK F6        |<----------------------|
              |<------------------|                       |
              |                   |                       |
              |  ACK F8           |                       |
              |------------------>|  ACK F9               |
              |                   |---------------------->|
              |                   |                       |
              |      RTP Established- Play top level menu |
              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                   |                       |
              |  BYE F10          |                       |
              |------------------>|  BYE F11              |
              |                   |---------------------->|
              |                   |                       |
              |                   |  200 OK F12           |
              |                   |<----------------------|
              |  200 OK F13       |                       |
              |<------------------|                       |
              |                   |                       |



     Flow Id                            Comments

    INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserA",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cc4e341ae6cbe5a359", opaque="",
                  uri="sip:VoiceMail@wcom.com", response=<appropriately
                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>


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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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:top@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    180 Ringing   SIP/2.0 180 Ringing
    F4            Via: SIP/2.0/UDP wcom.com:5060; branch=1
    VM->Proxy     Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    180 Ringing   SIP/2.0 180 Ringing


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    F5            Via: SIP/2.0/UDP here.com:5060
    Proxy->A      From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    200 OK F6     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: VoiceMailSystem <sip:top@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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


    200 OK F7     SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact VoiceMailSystem <sip:top@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F8        ACK sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060


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                  Route:<sip:top@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F9        ACK sip:top@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

                  /* RTP streams are established between A and VM.  VM
                  system starts IVR dialog for top level menu */

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/

    BYE F10       BYE sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip: top@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F11       BYE sip: top@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F12    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0



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    200 OK F13    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0


4.2 Message Deposit Scenarios

4.2.1 Call to known subscriber forwarded on no answer

   User A attempts to call UserB, who does not answer.  The call is
   forwarded to UserB's mailbox, and the voice mail system plays
   UserB's outgoing message for a ring-no-answer. The flow assumes that
   the URL of "sip:UserB-dep-fna@vm.wcom.com maps" to the desired
   behavior for depositing a message on a forward-no-answer. 


            User A            Proxy              User B         VM System
              |                 |                  |                |
              |  INVITE F1      |                  |                |
              |---------------->|  INVITE F2       |                |
              |                 |----------------->|                |
              | (100 Trying) F3 |                  |                |
              |<----------------| 180 Ringing F4   |                |
              |                 |<-----------------|                |
              |  180 Ringing F5 |                  |                |
              |<----------------| (Request Timeout)|                |
              |                 |                  |                |
              |                 | Cancel F6        |                |
              |                 |----------------->|                |
              |                 |                  |                |
              |                 | 200 OK F7        |                |
              |                 |<-----------------|                |
              |                 |                  |                |
              |                 |         INVITE F8                 |
              |                 |---------------------------------->|
              |                 |                  |                |
              |                 |         200 OK F9|                |
              |  200 OK F10     |<----------------------------------|
              |<----------------|                  |                |
              |                 |                  |                |
              |  ACK F11        |                  |                |
              |---------------->|         ACK F12  |                |
              |                 |---------------------------------->|
              |                 |                  |                |
              |    RTP Established Both Ways-Deposit Msg for B      |


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              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                 |                  |                |
              |  BYE F13        |                  |                |
              |---------------->|         BYE F14  |                |
              |                 |---------------------------------->|
              |                 |                  |                |
              |                 |         OK F15   |                |
              |  OK F16         |<----------------------------------|
              |<----------------|                  |                |
              |                 |                  |                |




     Flow Id                            Comments

    INVITE F1     INVITE sip:UserB@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserA",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                  uri="sip:UserB@wcom.com", response=<appropriately
                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:UserB1@somewhere.wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com


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

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    180 Ringing   SIP/2.0 180 Ringing
    F4            Via: SIP/2.0/UDP wcom.com:5060; branch=1
    B1->Proxy     Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    180 Ringing   SIP/2.0 180 Ringing
    F5            Via: SIP/2.0/UDP here.com:5060
    Proxy->A      From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

                  /* B1 rings for 9 seconds, this duration is a
                  configurable parameter in the Proxy Server.  Proxy
                  sends Cancel and proceeds down the list of routes,
                  eventually hitting the voice mail URI for forward no
                  answer */

    CANCEL F6     CANCEL sip:UserB1@wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com


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                  CSeq: 1 CANCEL
                  Content-Length: 0

    200 OK F7     SIP/2.0 200 OK
    B1->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 CANCEL
                  Content-Length: 0


    INVITE F8     INVITE sip:UserB-dep-fna@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060;branch=2
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    200 OK F9     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=2
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                  fna@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                  s=Session SDP
                  c=IN IP4 110.111.112.114


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


    200 OK F10    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                  fna@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F11       ACK sip:UserB@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip: UserB-dep-fna@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F12       ACK sip:UserB-dep-fna@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

                  /* RTP streams are established between A and B2.  VM
                  system starts IVR dialog for message-deposit on no-
                  answer for UserB */

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/


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    BYE F13       BYE sip:UserB@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip: UserB-dep-fna@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F14       BYE sip: UserB-dep-fna@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F15    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F16    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0

4.2.2 Call to known subscriber forwarded on busy

   User A attempts to call UserB, who is busy.  The call is forwarded
   to UserB's mailbox, and the voice mail system plays UserB's outgoing
   message for a busy. This flow assumes that
   "sip:UserB-dep-fb@vm.wcom.com" maps to UserB's mailbox and the
   behavior of "deposit message on busy." 









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            User A            Proxy              User B         VM System
              |                 |                  |                |
              |  INVITE F1      |                  |                |
              |---------------->|  INVITE F2       |                |
              |                 |----------------->|                |
              | (100 Trying) F3 |                  |                |
              |<----------------| 486 Busy Here F4 |                |
              |                 |<-----------------|                |
              |                 |                  |                |
              |                 |  ACK F5          |                |
              |                 |----------------->|                |
              |                 |                  |                |
              |                 |         INVITE F6                 |
              |                 |---------------------------------->|
              |                 |                  |                |
              |                 |         200 OK F7|                |
              |  200 OK F8      |<----------------------------------|
              |<----------------|                  |                |
              |                 |                  |                |
              |  ACK F9         |                  |                |
              |---------------->|         ACK F10  |                |
              |                 |---------------------------------->|
              |                 |                  |                |
              |    RTP Established Both Ways-Deposit Msg for B      |
              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                 |                  |                |
              |  BYE F11        |                  |                |
              |---------------->|         BYE F12  |                |
              |                 |---------------------------------->|
              |                 |                  |                |
              |                 |         OK F13   |                |
              |  OK F14         |<----------------------------------|
              |<----------------|                  |                |
              |                 |                  |                |


     Flow Id                            Comments

    INVITE F1     INVITE sip:UserB@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserA",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                  uri="sip:UserB@wcom.com", response=<appropriately


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                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:UserB1@somewhere.wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    486 Busy      SIP/2.0 486 Busy Here
    Here F4       Via: SIP/2.0/UDP wcom.com:5060;branch=1
    B1->Proxy     Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com


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                  CSeq: 1 INVITE
                  Content-Length: 0

    ACK F5        ACK sip: UserB1@wcom.com SIP/2.0
    Proxy->B      Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=123456
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    INVITE F6     INVITE sip:UserB-dep-fb@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060;branch=2
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    200 OK F7     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=2
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheLittleGuyVoiceMail <sip:UserB-dep-
                  fb@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.com
                  s=Session SDP
                  c=IN IP4 110.111.112.114
                  t=0 0


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

    200 OK F8     SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact TheLittleGuyVoiceMail <sip:UserB-dep-
                  fb@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F9        ACK sip:UserB@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserB-dep-fb@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F10       ACK sip:UserB-dep-fb@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

                  /* RTP streams are established between A and B2.  VM
                  system starts IVR dialog for message-deposit on busy
                  for UserB */

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/

    BYE F11       BYE sip:UserB@wcom.com SIP/2.0


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    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route: <sip:UserB-dep-fnb@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F12       BYE sip: UserB-dep-fnb@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F13    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F14    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuy <sip:UserB@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0

4.2.3 Direct call to a subscriber's mailbox

   User A calls UserB's mailbox directly. This flow assumes that
   "sip:UserB-dep@vm.wcom.com" maps to UserB's mailbox and the behavior
   of "generic message deposit" 












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            User A              Proxy                VM Service
              |                   |                       |
              |  INVITE F1        |                       |
              |------------------>|                       |
              |                   |  INVITE F2            |
              | (100 Trying) F3   |---------------------->|
              |<------------------|                       |
              |                   |  200 OK F4            |
              |  200 OK F5        |<----------------------|
              |<------------------|                       |
              |                   |                       |
              |  ACK F6           |                       |
              |------------------>|  ACK F7               |
              |                   |---------------------->|
              |                   |                       |
              |      RTP Both Ways - Deposit Msg for B    |
              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                   |                       |
              |  BYE F8           |                       |
              |------------------>|  BYE F9               |
              |                   |---------------------->|
              |                   |                       |
              |                   |  200 OK F10           |
              |                   |<----------------------|
              |  200 OK F11       |                       |
              |<------------------|                       |
              |                   |                       |


     Flow Id                            Comments

    INVITE F1     INVITE sip:UserB-VM@vm.wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-VM@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserA",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                  uri="sip:UserB-VM@wcom.com", response=<appropriately
                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

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


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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:UserB-dep@vm.wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB-VM@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-VM@vm.wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-VM@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    200 OK F4     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB-VM@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheLittleGuyVoiceMail <sip:UserB-
                  dep@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>


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                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    200 OK F5     SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:UserB-VM@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact TheLittleGuyVoiceMail <sip:UserB-
                  dep@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F6        ACK sip:UserB-VM@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserB-dep@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F7        ACK sip:UserB-dep@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0



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                  /* RTP streams are established between A and VM.  VM
                  system starts IVR dialog for generic message-deposit
                  for UserB */

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/

    BYE F8        BYE sip:UserB-VM@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserB-dep@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F9        BYE sip: UserB-dep@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F10    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F11    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: TheLittleGuyVoiceMail <sip:UserB-
                  VM@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0






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4.3 Message Retrieval Scenarios

4.3.1 Call to retrieve messages believed to be from a known subscriber

   Some user uses a SIP client on UserA's desk to call the voice mail
   system to retrieve messages. The SIP client has authenticated itself
   to the proxy using credentials assigned to the device. The proxy can
   make a weak assumption that the caller is the device owner. The URI
   of "sip:UserA-retrieve@vm.wcom.com" maps to UserA's mailbox and the
   behavior of "retrieve messages after prompting for and verifying
   PIN." The VM System trusts the proxy, and will not accept calls from
   an untrusted source. The proxy will not allow direct calls to
   UserA-retrieve@vm.wcom.com. The proxy will forward calls placed to
   VoiceMail@wcom.com to UserA-retrieve@vm.wcom.com only for calls
   placed from a client device assigned to UserA. 

            User A              Proxy                VM Service
              |                   |                       |
              |  INVITE F1        |                       |
              |------------------>|                       |
              |                   |  INVITE F2            |
              | (100 Trying) F3   |---------------------->|
              |<------------------|                       |
              |                   |  200 OK F4            |
              |  200 OK F5        |<----------------------|
              |<------------------|                       |
              |                   |                       |
              |  ACK F6           |                       |
              |------------------>|  ACK F7               |
              |                   |---------------------->|
              |                   |                       |
              |      RTP Both Ways - VM prompts for PIN
              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                   |                       |
              |  BYE F8           |                       |
              |------------------>|  BYE F9               |
              |                   |---------------------->|
              |                   |                       |
              |                   |  200 OK F10           |
              |                   |<----------------------|
              |  200 OK F11       |                       |
              |<------------------|                       |
              |                   |                       |


     Flow Id                            Comments

    INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060


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                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserAPhone",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                  uri="sip:VoiceMail@wcom.com", response=<appropriately
                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:UserA-retrieve@vm.wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com


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                  CSeq: 1 INVITE
                  Content-Length: 0

    200 OK F4     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: VoiceMailSystem <sip:UserA-
                  retrieve@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    200 OK F5     SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact VoiceMailSystem <sip: UserA-
                  retrieve@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F6        ACK sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserA-retrieve@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678


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                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F7        ACK sip:UserA-retrieve@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

                  /* RTP streams are established between A and VM.  VM
                  determines that the call is likely from UserA, and
                  starts a message retrieval session, prompting for
                  PIN*/

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/

    BYE F8        BYE sip: VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserA-retrieve@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F9        BYE sip: UserA-retrieve@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F10    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F11    SIP/2.0 200 OK


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    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0

4.3.2 Call to retrieve messages from an authenticated subscriber

   UserA to call the voice mail system to retrieve messages.
   Assumptions: The caller is authenticated using UserA's credentials.
   "sip:UserA-retrieve-auth@vm.wcom.com" maps to UserA's mailbox and
   the behavior of "retrieve messages." The voice mail service trusts
   the proxy not to forward any calls to that URI unless the call is
   authenticated to be from UserA. 

   Given these assumptions, The VM service may choose not require a PIN
   for calls to this URI. 

            User A              Proxy                VM Service
              |                   |                       |
              |  INVITE F1        |                       |
              |------------------>|                       |
              |                   |  INVITE F2            |
              | (100 Trying) F3   |---------------------->|
              |<------------------|                       |
              |                   |  200 OK F4            |
              |  200 OK F5        |<----------------------|
              |<------------------|                       |
              |                   |                       |
              |  ACK F6           |                       |
              |------------------>|  ACK F7               |
              |                   |---------------------->|
              |                   |                       |
              |      RTP Both Ways - Deposit Msg for B    |
              |<-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m-m->|
              |                   |                       |
              |  BYE F8           |                       |
              |------------------>|  BYE F9               |
              |                   |---------------------->|
              |                   |                       |
              |                   |  200 OK F10           |
              |                   |<----------------------|
              |  200 OK F11       |                       |
              |<------------------|                       |
              |                   |                       |


     Flow Id                            Comments


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    INVITE F1     INVITE sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Proxy-Authorization:Digest username="UserA",
                  realm="MCI WorldCom SIP",
                  nonce="ea9c8e88df84f1cec4341ae6cbe5a359", opaque="",
                  uri="sip:VoiceMail@wcom.com", response=<appropriately
                  calculated hash goes here>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

                  /*Client for A prepares to receive data on port 49170
                  from the network. */

    INVITE F2     INVITE sip:UserA-retrieve-auth@vm.wcom.com SIP/2.0
    Proxy->B1     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: TheBigGuy <sip:UserA@here.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  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

    (100 Trying   SIP/2.0 100 Trying
    F3            Via: SIP/2.0/UDP here.com:5060
    Proxy->A)     From: TheBigGuy <sip:UserA@here.com>


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                  To: VoiceMail <sip:VoiceMail@wcom.com>
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Content-Length: 0

    200 OK F4     SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060; branch=1
                  Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact: VoiceMailSystem <sip:UserA-retrieve-
                  auth@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    200 OK F5     SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  Record-Route: <sip:VoiceMail@wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 INVITE
                  Contact VoiceMailSystem <sip: UserA-retrieve-
                  auth@vm.wcom.com>
                  Content-Type: application/sdp
                  Content-Length: <appropriate value>

                  v=0
                  o=UserB 2890844527 2890844527 IN IP4 vm.wcom.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

    ACK F6        ACK sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route: <sip:UserA-retrieve-auth@vm.wcom.com>


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                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

    ACK F7        ACK sip:UserA-retrieve-auth@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>; tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 1 ACK
                  Content-Length: 0

                  /* RTP streams are established between A and VM.  VM
                  determines that the call is likely from UserA, and
                  starts a message retrieval session.  Since the proxy
                  has already authenticated the identity of UserA, the
                  VM does not need to prompt for PIN. */

                  /* User A Hangs Up with VM system. Alternatively, the
                  VM system could initiate the BYE*/

    BYE F8        BYE sip:VoiceMail@wcom.com SIP/2.0
    A->Proxy      Via: SIP/2.0/UDP here.com:5060
                  Route:<sip:UserA-retrieve-auth@vm.wcom.com>
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    BYE F9        BYE sip: UserA-retrieve-auth@vm.wcom.com SIP/2.0
    Proxy->VM     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE
                  Content-Length: 0

    200 OK F10    SIP/2.0 200 OK
    VM->Proxy     Via: SIP/2.0/UDP wcom.com:5060
                  Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq: 2 BYE


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                  Content-Length: 0

    200 OK F11    SIP/2.0 200 OK
    Proxy->A      Via: SIP/2.0/UDP here.com:5060
                  From: TheBigGuy <sip:UserA@here.com>
                  To: VoiceMail <sip:VoiceMail@wcom.com>;tag=3145678
                  Call-Id: 12345600@here.com
                  CSeq:  2 BYE
                  Content-Length: 0

5. Security Considerations

   This document discusses a usage of SIP/2.0 as defined by RFC
   2543[1]. It introduces no additions, modifications, or restrictions
   to the protocol defined therein. Any implementation of the concepts
   in this document is subject to the issues discussed there. 

6. Acknowledgments

   The authors would like to thank Chris Cunningham, Steve Donovan,
   Alan Johnston, Henry Sinnreich, Kevin Summers, John Truetken, and 
   Dean Willis for their discussion of and contribution to this work. 

References

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


Authors' Addresses

   Ben Campbell
   dynamicsoft
   5100 Tennyson Parkway
   Suite 1200
   Plano, TX  75024

   email: bcampbell@dynamicsoft.com


   Robert J. Sparks
   dynamicsoft
   5100 Tennyson Parkway
   Suite 1200
   Plano, TX  75024

   email: rsparks@dynamicsoft.com




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Full Copyright Statement

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

   This document and translations of it may be copied and furnished to
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   or assist in its implementation may be prepared, copied, published
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   The limited permissions granted above are perpetual and will not be
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Acknowledgement

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



















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