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SIP                                                           Steve Levy
Internet-Draft                                                J. R. Yang
draft-levy-sip-diversion-08.txt                            Cisco Systems
                                                            Bryan Byerly

Expires: February 25,2005                               August  25, 2004


                      Diversion Indication in SIP
                      draft-levy-sip-diversion-08

Status of this Memo

   This document is an Internet-Draft and is subject to 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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   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
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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 February 25, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2004). All Rights Reserved.

Abstract

  This document proposes an extension to the Session Initiation
  Protocol (SIP).  This extension provides the ability for
  the called SIP user agent to identify from whom the call
  was diverted and why the call was diverted.

  The extension defines a general header, Diversion, which
  conveys the diversion information from other SIP user agents
  and proxies to the called user agent.

  This extension allows enhanced support for various features,
  including Unified Messaging, Third-Party Voicemail, and Automatic Call
  Distribution (ACD).  SIP user agents and SIP proxies which receive
  diversion information may use this as supplemental information for
  feature invocation decisions.



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1 Introduction

In the legacy telephony network, redirection information is
passed through the network in ISDN/ISUP signaling messages.
This information is used by various service providers and
business applications to support enhanced features for the end user.

An analogous mechanism of providing redirection information would enable
such enhanced features for SIP users.

The Diversion header allows implementation of feature logic
based on from whom the call was diverted.

Version 06 (and forward) of the draft adds support for privacy and
screening information.


2 Definitions

    diversion:      A change to the ultimate destination endpoint
                    of a request.  A change in the Request-URI of a
                    request that was not caused by a routing decision.
                    This is also sometimes called a deflection or
                    redirection.

                    A diversion can occur when the "user" portion of the
                    Request-URI is changed for a reason other than
                    expansion or translation.

                    A diversion can occur when only the "host" portion of
                    the Request-URI has changed if the change was due to
                    a non-routing decision.

    divertor:       The entity which diverted the call.

    recursing:      A SIP proxy or user agent which handles a received
                    or internally generated 3xx response by forking
                    new request(s) itself.

    non-recursing:  A SIP proxy or user agent which handles a
                    received or internally generated 3xx response
                    by forwarding it upstream.

3 Abbreviations

    CFUNC:          Call Forward Unconditional

    CFTOD:          Call Forward Time-of-Day

    CFB:            Call Forward on Busy

    CFNA:           Call Forward on No Answer

    CFUNV:          Call Forward Unavailable

    ACD:            Automatic Call Distribution

4 Overview

  In order to implement certain third-party features such as
  third-party voicemail and Automatic Call Distribution (ACD)
  applications, diversion information needs to be given to the
  called third-party so that he may respond to the caller
  intelligently.

  In these situations, the party receiving a diverted call
  needs answers for two questions:

  Question 1: From whom was the request diverted?
  Question 2: Why was the request diverted?

  This document proposes usage of the Diversion header to answer
  these questions for the party receiving the diverted call.

  Insertion of the previous Request-URI (before the diversion
  occurred) into the Diversion header answers question 1.

  Insertion of the "reason" tag into the Diversion header
  (by the divertor) answers question 2.


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4.1 When is the Diversion header used?

    The Diversion header SHOULD be added when a SIP proxy server,
    SIP redirect server, or SIP user agent changes the ultimate
    endpoint which will receive the call.

    Diversion information SHOULD NOT be added for normal call routing
    changes to the Request-URI.  Thus, the Diversion header is not
    added when features such as speed dial change the Request-URI.

    When a diversion occurs, a Diversion header SHOULD be added
    to the forwarded request or forwarded 3xx response.
    The Diversion header MUST contain the Request-URI of the request
    prior to the diversion.  The Diversion header SHOULD contain
    a reason that the diversion occurred.

    Existing Diversion headers received in an incoming request
    MUST NOT be removed or changed in forwarded requests.

    Existing Diversion headers received in an incoming response
    MUST NOT be removed or changed in the forwarded response.

    A Diversion header is added when features such as
    call forwarding or call deflection change the Request-URI.


5 Extension Syntax

  The syntax of the Diversion header is:

    Diversion = "Diversion" ":" 1# (name-addr *( ";" diversion_params ))
    diversion-params = diversion-reason | diversion-counter |
                       diversion-limit | diversion-privacy |
                       diversion-screen | diversion-extension
    diversion-reason = "reason" "="
                    ( "unknown" | "user-busy" | "no-answer" |
                      "unavailable" | "unconditional" |
                      "time-of-day" | "do-not-disturb" |
                      "deflection" | "follow-me" |
                      "out-of-service" | "away" |
                      token | quoted-string )
    diversion-counter = "counter" "=" 1*2DIGIT
    diversion-limit = "limit" "=" 1*2DIGIT
    diversion-privacy = "privacy" "=" ( "full" | "name" |
                        "uri" | "off" | token | quoted-string )
    diversion-screen = "screen" "=" ( "yes" | "no" | token |
                                         quoted-string )
    diversion-extension = token ["=" (token | quoted-string)]


  The following is an extension of tables 4 and 5 in [SIP] for
  the Diversion header:

                            where  enc.  e-e ACK BYE CAN INV OPT REG
       _____________________________________________________________
       Diversion              R           h   -   -   -   o   -   -
       Diversion             3xx          h   -   -   -   o   -   -


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6 Detailed Semantics

6.1 UAS Behavior

    A SIP UAS which receives a request and returns a 3xx SHOULD
    add a Diversion header containing the previous Request-URI
    and the reason for the diversion.

6.2 UAC Behavior

    A SIP UAC which receives a 3xx containing a Diversion header
    SHOULD copy the Diversion header into each downstream forked
    request which resulted from the 3xx.

6.3 Redirect Server Behavior

    A SIP redirect server which receives a request and returns a
    3xx containing a Contact which diverts the request to a
    different endpoint SHOULD add a Diversion header containing
    the Request-URI from the incoming request and the reason for
    the diversion.

6.4 Proxy Server Behavior

    A non-recursing SIP proxy which receives a 3xx containing a
    Diversion header SHOULD forward the 3xx containing the Diversion
    header upstream unchanged.

    A SIP proxy which receives a request and invokes a feature which
    changes the Request-URI of the forwarded request in order to divert
    the request to a different endpoint SHOULD add a Diversion header
    containing the Request-URI from the incoming request and the reason
    for the diversion.

    A SIP proxy which receives a request and returns a 3xx containing
    a Contact which diverts the request to a different endpoint SHOULD
    add a Diversion header containing the Request-URI from the incoming
    request and the reason for the diversion.

6.4.1 Proxy Logic for Diversion header

    if (pdu.is_request()) {
        if (request-URI is changed due to a called feature) {
            if (proxy.is_recursing()) {
                Add the Diversion header (indicating the reason
                  that the call has been diverted) to
                  the downstream forwarded request(s).
            } else {
                Add the Diversion header (indicating the reason
                  that the call has been diverted) to
                  the upstream forwarded 3xx response.
            }
        }
    } else if (pdu.is_response()) {
        if (pdu.is_3xx()) {
            if (proxy.is_recursing()) {
              Copy Diversion header into forwarded INVITE(s).
            } else {
              Forward response upstream.
            }
        }
    }

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7 Examples using Diversion header

  There are several implementations of call forwarding features
  that can be implemented by either recursing or non-recursing
  SIP proxies or SIP user agents.

  A SIP proxy or user agent which generates or forwards 3xx's
  upstream is non-recursing.  A SIP proxy or user agent which handles
  received (or internally generated) 3xx's itself is recursing.

  The following examples illustrate usage of the Diversion header
  for some of the variants of recursing and non-recursing proxies
  and user agents.


7.1 Call Forward Unconditional

    Usage of the Diversion header is shown below for several
    variant implementations of Call Forward Unconditional.

7.1.1 Network Call Forward Unconditional, P2 recursing

      In this message flow, the call would normally be
      routed to Bob@B.  However, Proxy 2 (P2) recursively
      implements Call Forward Unconditional (CFUNC) to
      Carol@C.


                     +------------------------+
                     | Bob@P2: CFUNC->Carol@C |
                     +------+-----------------+
                             \
                              \
A             P1              P2            B          C
                            recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INVITE Carol@C------->|
|              |              |  Diversion: Bob@P2     |
|              |              |    ;reason=unconditional
|              |              |             |          |
|              |              |<-200-------------------|
|              |              |             |          |
|              |<-200---------|             |          |
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.1.2 Network Call Forward Unconditional, P1 non-recursing
                                          P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward Unconditional (CFUNC) to Carol@C.  Proxy 1 (P1)
      is non-recursing.


                     +------------------------+
                     | Bob@P2: CFUNC->Carol@C |
                     +------+-----------------+
                             \
                              \
A              P1             P2            B          C
            non-recursing  non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unconditional   |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|<-302---------|              |             |          |
|  Contact: Carol@C           |             |          |
|  Diversion: Bob@P2          |             |          |
|    ;reason=unconditional    |             |          |
|              |              |             |          |
|--ACK-------->|              |             |          |
|              |              |             |          |
|--INVITE Carol@C------------------------------------->|
|  Diversion: Bob@P2          |             |          |
|    ;reason=unconditional    |             |          |
|              |              |             |          |
|<-200-------------------------------------------------|
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.1.3 Network Call Forward Unconditional, P1 recursing
                                          P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward Unconditional (CFUNC) to Carol@C.  Proxy 1 (P1)
      is recursing.

                     +------------------------+
                     | Bob@P2: CFUNC->Carol@C |
                     +------+-----------------+
                             \
                              \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unconditional   |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unconditional   |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.1.4 Endpoint Call Forward Unconditional, P1 recursing
                                           P2 non-recursing

      In this message flow, user agent server B (B) non-recursively
      implements Call Forward Unconditional (CFUNC) to Carol@C.
      Proxy 2 (P2) is  non-recursing.  Proxy 1 (P1) is recursing.


                                    +-----------------------+
                                    | Bob@B: CFUNC->Carol@C |
                                    +------+----------------+
                                            \
                                             \
A              P1             P2              B          C
            recursing      non-recursing
|              |              |               |          |
|--INV Bob@P1->|              |               |          |
|              |              |               |          |
|              |--INV Bob@P2->|               |          |
|              |              |--INV Bob@B--->|          |
|              |              |               |          |
|              |              |<-302----------|          |
|              |              |  Contact: Carol@C        |
|              |              |  Diversion: Bob@B        |
|              |              |    ;reason=unconditional
|              |              |               |          |
|              |              |--ACK--------->|          |
|              |              |               |          |
|              |<-302---------|               |          |
|              |  Contact: Carol@C            |          |
|              |  Diversion: Bob@B            |          |
|              |    ;reason=unconditional     |          |
|              |              |               |          |
|              |--ACK-------->|               |          |
|              |              |               |          |
|              |--INVITE Carol@C------------------------>|
|              |  Diversion: Bob@B            |          |
|              |    ;reason=unconditional     |          |
|              |              |               |          |
|              |<-200------------------------------------|
|              |              |               |          |
|<-200---------|              |               |          |
|              |              |               |          |
|--ACK-------------------------------------------------->|
|              |              |               |          |
|              |              |               |          |


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7.2 Call Forward on Busy

    Usage of the Diversion header is shown below for several
    variant implementations of Call Forward on Busy.

7.2.1 Network Call Forward on Busy, P2 recursing

      In this message flow, Proxy 2 (P2) recursively implements
      Call Forward on Busy (CFB) to Carol@C.

                     +----------------------+
                     | Bob@P2: CFB->Carol@C |
                     +------+---------------+
                             \
                              \
A              P1             P2            B          C
                           recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-486--------|          |
|              |              |             |          |
|              |              |--ACK------->|          |
|              |              |             |          |
|              |              |--INVITE Carol@C------->|
|              |              |  Diversion: Bob@P2     |
|              |              |    ;reason=user-busy   |
|              |              |             |          |
|              |              |<-200-------------------|
|              |              |             |          |
|              |<-200---------|             |          |
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.2.2 Network Call Forward on Busy, P1 non-recursing
                                    P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on Busy (CFB) to Carol@C.  Proxy 1 (P1) is
      non-recursing.

                     +----------------------+
                     | Bob@P2: CFB->Carol@C |
                     +------+---------------+
                             \
                              \
A              P1             P2            B          C
            non-recursing  non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-486--------|          |
|              |              |             |          |
|              |              |--ACK------->|          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=user-busy       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|<-302---------|              |             |          |
|  Contact: Carol@C           |             |          |
|  Diversion: Bob@P2          |             |          |
|    ;reason=user-busy        |             |          |
|              |              |             |          |
|--ACK-------->|              |             |          |
|              |              |             |          |
|--INVITE Carol@C------------------------------------->|
|  Diversion: Bob@P2          |             |          |
|    ;reason=user-busy        |             |          |
|              |              |             |          |
|<-200-------------------------------------------------|
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.2.3 Network Call Forward on Busy, P1 recursing
                                    P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on Busy (CFB) to Carol@C.  Proxy 1 (P1) is recursing.

                     +----------------------+
                     | Bob@P2: CFB->Carol@C |
                     +------+---------------+
                             \
                              \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-486--------|          |
|              |              |             |          |
|              |              |--ACK------->|          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=user-busy       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=user-busy       |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.2.4 Endpoint Call Forward on Busy, P1 recursing
                                     P2 non-recursing

      In this message flow, user agent server B (B) non-recursively
      implements Call Forward on Busy (CFB) to Carol@C.
      Proxy 2 (P2) is non-recursing.  Proxy 1 (P1) is recursing.

                               +---------------------+
                               | Bob@B: CFB->Carol@C |
                               +------+--------------+
                                          \
                                           \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-302--------|          |
|              |              |  Contact: Carol@C      |
|              |              |  Diversion: Bob@B      |
|              |              |    ;reason=user-busy   |
|              |              |             |          |
|              |              |--ACK------->|          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@B          |          |
|              |    ;reason=user-busy       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@B          |          |
|              |    ;reason-user-busy       |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.3 Call Forward on No-Answer

    Usage of the Diversion header is shown below for several
    variant implementations of Call Forward on No-Answer.

7.3.1 Network Call Forward on No-Answer, P2 recursing

      In this message flow, Proxy 2 (P2) recursively implements
      Call Forward on No Answer (CFNA) to Carol@C.

                     +-----------------------+
                     | Bob@P2: CFNA->Carol@C |
                     +------+----------------+
                             \
                              \
A              P1             P2            B          C
                           recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-180--------|          |
|              |              |             |          |
|              |              |             |          |
|              |              |             |          |
|              |           timeout          |          |
|              |              |--INVITE Carol@C------->|
|              |              |  Diversion: Bob@P2     |
|              |              |    ;reason=no-answer   |
|              |              |             |          |
|              |              |<-200-------------------|
|              |              |             |          |
|              |<-200---------|             |          |
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.3.2 Network Call Forward on No-Answer, P1 non-recursing
                                         P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on No Answer (CFNA) to Carol@C.  Proxy 1 (P1) is
      non-recursing.

                     +-----------------------+
                     | Bob@P2: CFNA->Carol@C |
                     +------+----------------+
                             \
                              \
A              P1             P2            B          C
            non-recursing  non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-180--------|          |
|              |              |             |          |
|              |              |             |          |
|              |              |             |          |
|              |           timeout          |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=no-answer       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|<-302---------|              |             |          |
|  Contact: Carol@C           |             |          |
|  Diversion: Bob@P2          |             |          |
|    ;reason=no-answer        |             |          |
|              |              |             |          |
|--ACK-------->|              |             |          |
|              |              |             |          |
|--INVITE Carol@C------------------------------------->|
|  Diversion: Bob@P2          |             |          |
|    ;reason=no-answer        |             |          |
|              |              |             |          |
|<-200-------------------------------------------------|
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.3.3 Network Call Forward on No Answer, P1 recursing
                                         P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on No Answer (CFNA) to Carol@C.  Proxy 1 (P1) is
      recursing.

                     +-----------------------+
                     | Bob@P2: CFNA->Carol@C |
                     +------+----------------+
                             \
                              \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |<-180--------|          |
|              |              |             |          |
|              |              |             |          |
|              |              |             |          |
|              |            timeout         |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=no-answer       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=no-answer       |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.3.4 Endpoint Call Forward on No-Answer, P1 recursing,
                                          P2 non-recursing
                                          B non-recursing

      In this message flow, user agent server B (B) non-recursively
      implements Call Forward on No Answer (CFNA) to Carol@C.
      Proxy 2 (P2) is non-recursing.  Proxy 1 (P1) is recursing.

                                  +----------------------+
                                  | Bob@B: CFNA->Carol@C |
                                  +------+---------------+
                                          \
                                           \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |             |          |
|              |              |             |          |
|              |              |             |          |
|              |              |          timeout       |
|              |              |<-302--------|          |
|              |              |  Contact: Carol@C      |
|              |              |  Diversion: Bob@B      |
|              |              |    ;reason=no-answer   |
|              |              |             |          |
|              |              |--ACK------->|          |
|              |              |             |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@B          |          |
|              |    ;reason=no-answer       |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@B          |          |
|              |    ;reason-no-answer       |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.4 Call Forward on Unavailable

    Usage of the Diversion header is shown below for several
    variant implementations of Call Forward on Unavailable.

7.4.1 Network Call Forward on Unavailable, P2 recursing

    In this message flow, Proxy 2 (P2) recursively implements
    Call Forward on Unavailable (CFUNV) to Carol@C.

                     +------------------------+
                     | Bob@P2: CFUNV->Carol@C |
                     +------+-----------------+
                             \
                              \
A              P1             P2            B          C
                           recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|<-100---------|              |             |          |
|              |--INV Bob@P2->|             |          |
|              |<-100---------|             |          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |  ...        |          |
|              |              |--INV Bob@B->|          |
|              |           timeout          |          |
|              |              |--INVITE Carol@C------->|
|              |              |  Diversion: Bob@P2     |
|              |              |    ;reason=unavailable
|              |              |             |          |
|              |              |<-200-------------------|
|              |              |             |          |
|              |<-200---------|             |          |
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.4.2 Network Call Forward on Unavailable, P1 non-recursing
                                           P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on Unavailable (CFUNV) to Carol@C.  Proxy 1 (P1)
      is non-recursing.

                     +------------------------+
                     | Bob@P2: CFUNV->Carol@C |
                     +------+-----------------+
                             \
                              \
A              P1             P2            B          C
            non-recursing  non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|              |              |             |          |
|              |--INV Bob@P2->|             |          |
|              |              |             |          |
|              |<-100---------|             |          |
|              |              |             |          |
|<-100---------|              |             |          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |  ...        |          |
|              |              |--INV Bob@B->|          |
|              |           timeout          |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unavailable     |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|<-302---------|              |             |          |
|  Contact: Carol@C           |             |          |
|  Diversion: Bob@P2          |             |          |
|    ;reason=unavailable      |             |          |
|              |              |             |          |
|--ACK-------->|              |             |          |
|              |              |             |          |
|--INVITE Carol@C------------------------------------->|
|  Diversion: Bob@P2          |             |          |
|    ;reason=unavailable      |             |          |
|              |              |             |          |
|<-200-------------------------------------------------|
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |


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7.4.3 Network Call Forward on Unavailable, P1 recursing
                                           P2 non-recursing

      In this message flow, Proxy 2 (P2) non-recursively implements
      Call Forward on Unavailable (CFUNV) to Carol@C.  Proxy 1 (P1)
      is recursing.

                     +------------------------+
                     | Bob@P2: CFUNV->Carol@C |
                     +------+-----------------+
                             \
                              \
A              P1             P2            B          C
            recursing      non-recursing
|              |              |             |          |
|--INV Bob@P1->|              |             |          |
|<-100---------|              |             |          |
|              |--INV Bob@P2->|             |          |
|              |<-100---------|             |          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |--INV Bob@B->|          |
|              |              |  ...        |          |
|              |              |--INV Bob@B->|          |
|              |           timeout          |          |
|              |<-302---------|             |          |
|              |  Contact: Carol@C          |          |
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unavailable     |          |
|              |              |             |          |
|              |--ACK-------->|             |          |
|              |              |             |          |
|              |--INVITE Carol@C---------------------->|
|              |  Diversion: Bob@P2         |          |
|              |    ;reason=unavailable     |          |
|              |              |             |          |
|              |<-200----------------------------------|
|              |              |             |          |
|<-200---------|              |             |          |
|              |              |             |          |
|--ACK------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |

7.5 Multiple Diversions

    Usage of the Diversion header when multiple diversions
    occur are shown the following two examples.


    7.5.1 Call Forward Unconditional and Call Forward Busy

    In this message flow, Proxy 2 (P2) implements Call
    Forward Unconditional (CFUNC) to Carol@C.  C then
    implements Call Forward on Busy (CFB) to 5551234@D.  P2 is
    non-recursing.  P1 is recursing.  C is non-recursing.

            +------------------------+     +-------------------------+
            | Bob@P2: CFUNC->Carol@C |     | Carol@C: CFB->5551234@D |
            +---------------+--------+     +--------+----------------+
                             \                       \
                              \                       \
A              P1             P2            B          C          D
            recursing      non-recursing          non-recursing
|              |              |             |          |          |
|--INV Bob@P1->|              |             |          |          |
|              |              |             |          |          |
|              |--INV Bob@P2->|             |          |          |
|              |              |             |          |          |
|              |<-302---------|             |          |          |
|              |  Contact: Carol@C          |          |          |
|              |  Diversion: Bob@P2         |          |          |
|              |    ;reason=unconditional   |          |          |
|              |              |             |          |          |
|              |--ACK-------->|             |          |          |
|              |              |             |          |          |
|              |--INVITE Carol@C---------------------->|          |
|              |  Diversion: Bob@P2         |          |          |
|              |    ;reason=unconditional   |          |          |
|              |              |             |          |          |
|              |<-302----------------------------------|          |
|              |  Contact: 5551234@D        |          |          |
|              |  Diversion: Carol@C        |          |          |
|              |    ;reason=user-busy       |          |          |
|              |    ;privacy="full"         |          |          |
|              |  Diversion: Bob@P2         |          |          |
|              |    ;reason=unconditional   |          |          |
|              |              |             |          |          |
|              |--ACK--------------------------------->|          |
|              |              |             |          |          |
|              |--INVITE 5551234@D------------------------------->|
|              |  Diversion: Carol@C        |          |          |
|              |    ;reason=user-busy       |          |          |
|              |    ;privacy="full"         |          |          |
|              |  Diversion: Bob@P2         |          |          |
|              |    ;reason=unconditional   |          |          |
|              |              |             |          |          |
|              |<-200---------------------------------------------|
|              |              |             |          |          |
|<-200---------|              |             |          |          |
|              |              |             |          |          |
|--ACK----------------------------------------------------------->|
|              |              |             |          |          |
|              |              |             |          |          |


    7.5.2 Call Forward Unconditional and Call Forward No Answer

    In this message flow, Proxy 2 (P2) implements Call
    Forward Unconditional (CFUNC) to Carol@C.  (P2 would normally
    have routed the call to B).  C then implements Call Forward
    on No Answer (CFNA) to 5551234@D.  P2 is recursing.
    C is recursing.

         +------------------------+  +--------------------------+
         | Bob@P2: CFUNC->Carol@C |  | Carol@C: CFNA->5551234@D |
         +------------------+-----+  +-----+--------------------+
                             \              \
                              \              \
A              P1             P2       B      C                 D
                            recursing       recursing
|              |              |        |      |                 |
|--INV Bob@P1->|              |        |      |                 |
|              |              |        |      |                 |
|              |--INV Bob@P2->|        |      |                 |
|              |              |        |      |                 |
|              |              |--INV Carol@C->|                 |
|              |              |  Diversion: Bob@P2              |
|              |              |    ;reason=unconditional        |
|              |              |        |      |                 |
|              |              |<--180---------|                 |
|              |              |        |      |                 |
|              |<-180---------|        |      |                 |
|              |              |        |      |                 |
|<-180---------|              |        |      |                 |
|              |              |        |      |                 |
|              |              |        |      |                 |
|              |              |        |    timeout             |
|              |              |        |      |--INV 5551234@D->|
|              |              |        |      |Diversion: Carol@C
|              |              |        |      |  ;reason=no-answer
|              |              |        |      |  ;privacy="full"
|              |              |        |      |Diversion: Bob@P2
|              |              |        |      |  ;reason= unconditional

|              |              |        |      |                 |
|              |              |        |      |<-200------------|
|              |              |        |      |         |       |
|              |              |<-200----------|         |       |
|              |              |        |      |         |       |
|              |<-200---------|        |      |         |       |
|              |              |        |      |         |       |
|<-200---------|              |        |      |         |       |
|              |              |        |      |         |       |
|--ACK--------------------------------------------------------->|
|              |              |        |      |         |       |
|              |              |        |      |         |       |


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8 Security Considerations

  There are some privacy considerations when using the Diversion
  header.

  Usage of the Diversion header implies that the diverting UAS
  trusts the diverted-to UAS.

  Usage of the Diversion header by SIP proxies or SIP user
  agents can cause information leakage of route information and
  called information to untrusted SIP proxies and untrusted callers
  in upstream 3xx's.

  Leakage of this information can be mitigated by having
  a recursing trusted upstream proxy server.

  For a SIP network architecture where all proxies are required
  to be non-recursive, Diversion header hiding may be considered
  necessary in order to prevent leakage of route information
  to the caller.  To accomplish Diversion header hiding, a
  trusted upstream proxy would add a Record-Route header and
  use a secret key to encrypt the contents of the Diversion header
  in 3xx's which are forwarded upstream.  On receipt of re-INVITEs
  the proxy would decrypt the contents of the Diversion header
  (using its secret key) and forward the INVITE.

  There is no currently defined interaction of the Diversion
  and Hide headers.

  Question: Should there be?



9 Further Examples

Only the relevant headers have been included in the following
examples.  The contents of the SDPs has also been omitted.

9.1 Night Service/Automatic Call Distribution (ACD) using Diversion header

    In the following 2 message flows two separate companies,
    WeSellPizza.com and WeSellFlowers.com, have contracted with a third
    company, NightService.com to provide nighttime support for their
    incoming voice calls.

    In the first flow, Alice calls out for pizza.  In the second flow,
    Alice calls for roses.  In both instances, the same night service
    company (and receptionist, Carol) answers the call.  However, because
    the Diversion header is used, Carol is able to customize her greeting
    to the caller.

                 +-------------------------------------+
                 | WeSellPizza@P2: CFTOD->nightserv@P3 |
                 +-------------+-----------------------+
                                \
                                 \
UAC              P1               P2                 P3                  UAS1
                          (WeSellPizza.com)  (NightService.com)
                                                    (ACD)
| [1]            |                |                   |                     |
|-INV pizza@P1-->|                |                   |                     |
|                |                |                   |                     |
|                |                |                   |                     |
|                | [2] INVITE WeSellPizza@P2          |                     |
|                |--------------->|                   |                     |
|                |                |                   |                     |
|                |                | [3]               |                     |
|                |                |-INV nightserv@P3->|                     |
|                |                | Diversion: WeSellPizza@P2               |
|                |                |   ;reason=time-of-day                   |
|                |                |                   |                     |
|                |                |                   | [4]                 |
|                |                |                   |-INV Carol@uas1----->|
|                |                |               Diversion: WeSellPizza@P2 |
|                |                |                 ;reason=time-of-day     |
|                |                |                   |                     |
|                |                |                   |<-[5] 200------------|
|                |                |<-[6] 200----------|                     |
|                |<-[7] 200-------|                   |                     |
|<-[8] 200-------|                |                   |                     |
|                |                |                   |                     |
|--[9] ACK----------------------------------------------------------------->|
|                |                |                   |                     |
|<============================================="Hello, WeSellPizza"=========|
|                |                |                   |                     |
|                |                |                   |                     |

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     Alice calls for pizza.

     [1] SIP UAC to SIP proxy server 1:

          INVITE sip:pizza@p1.isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:pizza@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     The ISP's originating proxy translated the keyword pizza to the
     company WeSellPizza.com

     [2] SIP proxy server 1 to SIP proxy server 2 (WeSellPizza.com):

          INVITE sip:WeSellPizza@p2.isp.com SIP/2.0
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:pizza@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     It's after midnight and the pizza people are in bed.  Fortunately,
     WeSellPizza.com has contracted with NightService.com to answer
     their nighttime calls.   Thus, P2 implements CFTOD to
     to NightService.com.

     [3] SIP proxy server 2 (WeSellPizza.com) to
         SIP proxy server 3 (NightService.com):

          INVITE sip:NightService@p3.isp.com SIP/2.0
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:pizza@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:WeSellPizza@p2.isp.com>
            ;reason=time-of-day
          Content-Type: application/sdp

     Carol is available to receive the incoming call.

     [4] SIP proxy server 3 (NightService.com) to UAS1 (Carol):

          INVITE sip:carol@uas1.nightservice.com SIP/2.0
          Via: SIP/2.0/UDP p3.isp.com
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:pizza@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:WeSellPizza@p2.isp.com>
            ;reason=time-of-day
          Content-Type: application/sdp

     The ACD keys off the Diversion header to pull up the WeSellPizza FAQ
     on Carol's web browser.

     [5] UAS1 to SIP proxy server 3:

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP p3.isp.com
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:pizza@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

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     [6] SIP proxy server 3 to SIP proxy server 2:

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:pizza@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [7] SIP proxy server 2 to SIP proxy server 1:

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:pizza@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [8] SIP proxy server 1 to UAC

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:pizza@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [9] SIP UAC to UAS1:

          ACK sip:uas1.nightservice.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: <sip:pizza@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     The RTP flows begin and Carol answers "Hello, WeSellPizza.
     How may I help you?"


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     Alice now calls for roses:

                 +---------------------------------------+
                 | WeSellFlowers@P4: CFTOD->nightserv@P3 |
                 +-------------+-------------------------+
                                \
                                 \
UAC             P1               P4                 P3              UAS1
                         (WeSellFlowers.com)  (NightService.com)
                                                   (ACD)
| [1]           |                |                   |                |
|-INV roses@P1->|                |                   |                |
|               |                |                   |                |
|               | [2] INVITE WeSellFlowers@P4        |                |
|               |--------------->|                   |                |
|               |                |                   |                |
|               | [3]            |                   |                |
|               |<-302-----------|                   |                |
|               |  Contact: nightservice@P3          |                |
|               |  Diversion: WeSellFlowers@P4       |                |
|               |    ;reason=time-of-day             |                |
|               |                |                   |                |
|               |--[4] ACK------>|                   |                |
|               |                |                   |                |
|               | [5]            |                   |                |
|               |-INVITE nightservice@P3------------>|                |
|               | Diversion: WeSellFlowers@P4        |                |
|               |   ;reason=time-of-day              |                |
|               |                |                   |                |
|               |                |                   | [6]            |
|               |                |               -INV Carol@uas1----->|
|               |                |          Diversion: WeSellFlowers@P4
|               |                |            ;reason=time-of-day
|               |                |                                    |
|               |                |              |<-[7] 200------------|
|               |<-[8] 200---------------------------|                |
|<-[9] 200------|                |                   |                |
|               |                |                   |                |
|--[10] ACK---------------------------------------------------------->|
|               |                |                   |                |
|<======================================="Hello, WeSellFlowers"=======|
|               |                |                   |                |
|               |                |                   |                |

     Alice calls for roses.

     [1] SIP UAC to SIP proxy server 1:

          INVITE sip:roses@p1.isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:roses@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     The ISP's originating proxy translated the keyword roses to the
     company WeSellFlowers.com


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     [2] SIP proxy server 1 to SIP proxy server 4 (WeSellFlowers.com):

          INVITE sip:WeSellFlowers@p4.isp.com SIP/2.0
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:roses@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     It's now 1am and the florists are also in bed.  Fortunately,
     WeSellFlowers.com has contracted with NightService.com to answer
     their nighttime calls, too.  Thus, P4 implements CFTOD to
     to NightService.com.

     [3] SIP proxy server 4 (WeSellFlowers.com) to
         SIP proxy server 1 (NightService.com):

          SIP/2.0 302 Moved Temporarily
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: NightService@p3.isp.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=p4
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:WeSellFlowers@p4.isp.com>
            ;reason=time-of-day

     [4] SIP proxy server 1 to SIP proxy server 4 (WeSellFlowers.com):
          ACK sip:uas1.nightservice.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=p4
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     [5] SIP proxy server 1 (WeSellFlowers.com) to
         SIP proxy server 3 (NightService.com):

          INVITE sip:NightService@p3.isp.com SIP/2.0
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:roses@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:WeSellFlowers@p4.isp.com>
            ;reason=time-of-day
          Content-Type: application/sdp

     Carol is available to receive the incoming call.

     [6] SIP proxy server 3 (NightService.com) to UAS1 (Carol):

          INVITE sip:carol@uas1.nightservice.com SIP/2.0
          Via: SIP/2.0/UDP p3.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:roses@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:WeSellFlowers@p4.isp.com>
            ;reason=time-of-day
          Content-Type: application/sdp

     The ACD keys off the Diversion header to pull up
     the WeSellFlowers FAQ on Carol's web browser.

     [7] SIP UAS1 to SIP proxy server 3:

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP p3.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

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     [8] SIP proxy server 3 to SIP proxy server 1:

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [9] SIP proxy server 1 to UAC

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: carol@uas1.nightservice.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [10] SIP UAC to SIP UAS1:

          ACK sip:uas1.nightservice.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: <sip:roses@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     The RTP flows begin and Carol answers "Hello, WeSellFlowers.
     How may I help you?"


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9.2 Voicemail Service using Diversion header

    Bob has contracted his Voicemail to a third-party company,
    Voicemail.com.  In this message flow, Bob has hit the Do-Not-Disturb
    button on his phone.  The Do-Not-Disturb functionality of Bob's phone
    is configured to CFUNC (Call Forward Unconditional) to
    voicemail@isp.com.  Because the Diversion header is used,
    Voicemail.com is able to place the incoming call into
    Bob's voice mailbox.

                 +---------------------------------------------+
                 | Bob@UAS1: CFDoNotDisturb->voicemail@isp.com |
                 +--------------------------------------+------+
                                                         \
                                                          \
UAC1               P1                P2            UAS1        UAS2
                                                          (Voicemail.com)
|                  |                  |              |          |
|--[1] INV Bob@P1->|                  |              |          |
|                  |                  |              |          |
|                  |--[2] INV Bob@P2->|              |          |
|                  |                  |              |          |
|                  |               [3] INV Bob@uas1->|          |
|                  |                  |              |          |
|                  |                [4] <- 302-------|          |
|                  |               Contact: voicemail@isp.com   |
|                  |               Diversion: Bob@uas1          |
|                  |                 ;reason=do-not-disturb     |
|                  |                  |              |          |
|                  |                  |[5] ACK------>|          |
|                  |                  |              |          |
|                  |<-[6] 302---------|              |          |
|                  |  Contact: voicemail@isp.com     |          |
|                  |  Diversion: Bob@uas1            |          |
|                  |    ;reason=do-not-disturb       |          |
|                  |                  |              |          |
|                  |--[7] ACK-------->|              |          |
|<-[8] 302---------|                  |              |          |
|  Contact: voicemail@isp.com         |              |          |
|  Diversion: Bob@uas1                |              |          |
|    ;reason=do-not-disturb           |              |          |
|                  |                  |              |          |
|--[9] ACK-------->|                  |              |          |
|                  |                  |              |          |
|--[10] INVITE voicemail@isp.com------------------------------->|
|  Diversion: Bob@uas1                |              |          |
|    ;reason=do-not-disturb           |              |          |
|                  |                  |              |          |
|<--[11] 200----------------------------------------------------|
|                  |                  |              |          |
|---[12] ACK--------------------------------------------------->|
|                  |                  |              |          |
|                  |                  |              |          |


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     Alice calls Bob.

     [1] SIP UAC to SIP proxy server 1:

          INVITE sip:Bob@p1.isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:Bob@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     The ISP's originating proxy routes the request to proxy 2 (P2)

     [2] SIP proxy server 1 to SIP proxy server 2:

          INVITE sip:Bob@p2.isp.com SIP/2.0
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:Bob@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     [3] SIP proxy server 2 to UAS1 (Bob's SIP phone):

          INVITE sip:Bob@uas1.isp.com SIP/2.0
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:Bob@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp

     Since Bob had hit the Do-Not-Disturb button on his SIP phone,
     Bob's phone forwards the call to his voicemail service.

     [4] User agent server 1 (UAS1) to SIP proxy server 2 (P2)

          SIP/2.0 302 Moved Temporarily
          Via: SIP/2.0/UDP p2.isp.com
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: Voicemail@isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:Bob@uas1.isp.com>
            ;reason=do-not-disturb

     [5] SIP proxy server 2 to UAS1 (Bob's SIP phone):
          ACK sip:Bob@uas1.isp.com SIP/2.0
          Via: SIP/2.0/UDP p2.isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE


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     [6] SIP proxy server 2 (P2) to SIP proxy server 1 (P1):

          SIP/2.0 302 Moved Temporarily
          Via: SIP/2.0/UDP p1.isp.com
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: Voicemail@isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:Bob@uas1.isp.com>
            ;reason=do-not-disturb

     [7] SIP proxy server 1 to SIP proxy server 2:

          ACK sip:Bob@p2.isp.com SIP/2.0
          Via: SIP/2.0/UDP p1.isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     [8] SIP proxy server 1 (P1) to UAC (alice-pc):

          SIP/2.0 302 Moved Temporarily
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: Voicemail@isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:Bob@uas1.isp.com>
            ;reason=do-not-disturb

     [9] SIP UAC to SIP proxy server 1:

          ACK sip:Bob@p1.isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas1
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     [10] SIP UAC (alice-pc) to Voicemail server.

          INVITE sip:Voicemail@isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: sip:Bob@p1.isp.com
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Diversion: <sip:Bob@uas1.isp.com>
            ;reason=do-not-disturb
          Content-Type: application/sdp

     [11] Voicemail server to SIP UAC (alice-pc):

          SIP/2.0 200 OK
          Via: SIP/2.0/UDP alice-pc.isp.com
          Contact: Voicemail@isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas2
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE
          Content-Type: application/sdp


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     [12] SIP UAC to Voicemail server:

          ACK sip:Voicemail@isp.com SIP/2.0
          Via: SIP/2.0/UDP alice-pc.isp.com
          From: sip:alice@isp.com
          To: <sip:Bob@p1.isp.com>;tag=uas2
          Call-ID: 12345600@alice-pc.isp.com
          CSeq: 1 INVITE

     Because the Diversion header is present, the Voicemail
     server is able to place Alice's message into Bob's voice
     mailbox.


9.3 Q&A on alternative approaches

    Question 1:
        Why do we need the Diversion header when we can see the
        To: header?
    Answer:
        a) The To: header is not guaranteed to have significance
           to the called party.

           For example, the To: header may contain a locally
           significant URL (to the caller) such as a private numbering
           plan, speed dial digits, telephony escape digits, or
           telephony prefix digits.

           Without a Diversion header, enumerating all possible locally
           significant To: headers that anyone might use to contact
           Bob@uas1.isp.com becomes a configuration problem at
           Voicemail@isp.com and is prone to namespace collision.

           Support for Diversion headers enables Bob to contract
           a third-party service (Voicemail@isp.com) with a single
           globally significant URL for his voice mailbox
           (Bob@uas1.isp.com).

        b) Given a set of multiple diversions, there is a policy
           decision of which Diversion header takes precedence
           for service logic.

           Different services (or even different users for the same
           service) may want to configure this policy differently
           (first, last,second to last, etc).

    Question 2:
        Why do we need the Diversion header when we can see the
        Via: header?
    Answer:
        The Via header does not contain information about
        servers whom have deflected the call (using a 3xx).


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10 Mapping ISUP/ISDN Redirection information to SIP Diversion header

   The discussions below regarding ISUP/ISDN reflect generic elements
   in ISUP/ISDN.  In some variations of ISUP/ISDN, the information
   elements are represented differently.  Regardless of the ISUP/ISDN
   variant, translation should be performed for the "first redirecting
   number" and the "last redirecting number".

   In order to prevent ambiguity, it is important to highlight a
   terminology mismatch between ISUP/ISDN and SIP.  In SIP, a "redirect"
   indicates the act of returning a 3xx response.  In ISUP/ISDN a
   "redirection" is diversion of a call by a network entity.  In
   ISUP/ISDN a call may also be deflected (by an endpoint).
   Diversion is the more generic term which refers to either the act of
   an network redirection or endpoint deflection.

   In SIP, Diversion can be implemented as either an upstream 3xx
   (non-recursive) or an additionally forked downstream request
   (recursive).  In the following text, a lower-case "redirect"
   indicates the SIP usage, while an uppercase "Redirect" indicates
   ISUP usage.

10.1 Mapping ISUP/ISDN Diversion Reason codes

     ISUP and ISDN define the following diversion reasons:

     0000 = Unknown
     0001 = Call forwarding busy or called DTE busy
     0010 = Call forwarding no reply
     1111 = Call forwarding unconditional or systematic call redirection
     1010 = Call deflection or call forwarding by the called DTE
     1001 = Call forwarding DTE out of order

     Mapping of ISUP/ISDN reason codes to Diversion reason codes is
     performed as follows:

     ISUP/ISDN reason code       Diversion reason code
     0001                        "user-busy"
     0010                        "no-answer"
     1111                        "unconditional"
     1010                        "deflection"
     1001                        "unavailable"
     0000                        all others


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10.2 Mapping ISUP Redirection information to SIP Diversion header

     This section describes how generic ISUP diversion information
     elements may be translated across an ISUP/SIP gateway.

10.2.1 ISUP Definitions

       Called party number          The number of the party to which the
                                    call is currently being routed.


       Redirecting number           The number to which the call was
                                    being routed when the last diversion
                                    occurred.

       Redirecting reason           The reason that the last diversion
                                    occurred.


       Original called number       The number to which the call was
                                    being routed when the first
                                    diversion occurred.

       Original redirecting reason  The reason that the first diversion
                                    occurred.

       Redirection counter          The count of the total number of
                                    diversions that have occurred.

       Address Presentation         Indication of whether presentation
                                    is allowed or restricted.



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10.2.2 ISUP parameters


       When a SIP call transits a SIP/ISUP gateway, the following
       information in the ISUP message should be examined/set when
       translating SIP Diversion headers to ISUP diversion information:
         1) Redirecting Number
         2) Redirecting reason
         3) Redirecting address presentation
         4) Original called number
         5) Original redirecting reason
         6) Original address presentation
         7) Redirection counter.

       An ISUP message contains information on the first and last
       diversions that occurred.  The Redirection Number is to which the
       call was being routed when the last diversion occurred.
       The Redirecting Reason is the reason that the last diversion
       occurred.

       The Original Called Number is the number to which the call was
       being routed when the first diversion occurred.  The Original
       Redirecting Reason is the reason that the first diversion
       occurred.

       When only one Diversion has occurred, the number to which
       the call was being routed when the diversion occurred is
       in the Redirecting Number and the reason for that diversion is
       carried in the Redirect Reason.

10.2.3 ISUP to SIP translation

       The ISUP Redirecting Number SHOULD be used to set the value of
       the name-addr of the top-most Diversion header. The ISUP
       Redirecting Number address presentation SHOULD be used to set
       the value of the diversion-privacy of the top-most Diversion
       header. The ISUP Redirecting Reason SHOULD be used to set the
       value of the diversion-reason of the top-most Diversion header.
       When present, the Original Called Number SHOULD be used to set
       the name-addr of the bottom-most Diversion header.  When
       present, the Original Redirecting Reason SHOULD be used to set
       the diversion-reason of the bottom-most Diversion header.When
       present, the Original address presentation SHOULD be used to set
       the diversion-privacy of the bottom-most Diversion header.

       The Redirect Counter value minus 1 SHOULD be stored in the
       diversion-counter associated with the top-most Diversion
       header.  Presence of the diversion-counter for the bottom-most
       Diversion header is optional.  If present the diversion-counter
       of the bottom-most Diversion header SHOULD be 1.

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10.2.4 SIP to ISUP translation

       The name-addr of the top-most Diversion header SHOULD be used
       to set the ISUP Redirecting Number.  The diversion-reason of
       the top-most Diversion header SHOULD be used to set the ISUP
       Redirecting Reason.The diversion-privacy of the top-most
       Diversion header SHOULD be used to set the ISUP
       Redirecting Address Presentation.

       When multiple Diversion headers are present, the name-addr of
       the bottom-most Diversion header SHOULD be used to set
       the ISUP Original Redirecting Number.  When multiple Diversion
       headers are present, the diversion-reason of the bottom-most
       Diversion header SHOULD be used to set the ISUP Original
       Redirecting Reason. When multiple Diversion headers are
       present, the diversion-privacy of the bottom-most
       Diversion header SHOULD be used to set the ISUP Original
       Redirecting Address Presentation.

       The ISUP Redirection counter SHOULD be set equal to the
       sum of the counters of all Diversion headers in the SIP
       message.  A Diversion header which does not explicitly specify
       a diversion-counter tag counts as 1.


10.2.5 Example of ISUP to SIP translation


                                   ISUP/SIP GW
                                       |
--IAM--------------------------------->|
  Called Party Number    =+19195551004 |
  Redirecting Number     =+19195551002 |
    Address Presentation =presentation restricted
  Original Called Number =+19195551001 |
  RedirectionInformation:              |
    Original redirecting reason = Unconditional (1111)
    Redirecting Reason = User busy (0001)
    Redirection counter = 5            |
                                       |
                                       |--INVITE +19195551004------>
                                       |  Diversion: <tel:+19195551002>
                                       |    ;reason=user-busy
                                       |    ;privacy="full"
                                       |    ;counter=4
                                       |  Diversion: <tel:+19195551001>
                                       |    ;reason=unconditional
                                       |    ;counter=1
                                       |
                                       |

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10.2.6 Example of SIP to ISUP translation

                                   ISUP/SIP GW
                                       |
                                       |<--INVITE +19195551004------
                                       |  Diversion: <tel:+19195551002>
                                       |    ;reason=user-busy
                                       |    ;privacy="full"
                                       |    ;counter=4
                                       |  Diversion: <tel:+19195551001>
                                       |    ;reason=unconditional
                                       |    ;counter=1
                                       |
                                       |
                                       |
<--IAM---------------------------------|
  Called Party Number    =+19195551004 |
  Redirecting Number     =+19195551002 |
    Address Presentation =presentation restricted
  Original Called Number =+19195551001 |
  RedirectionInformation:              |
    Original redirecting reason = Unconditional (1111)
    Redirecting Reason = User busy (0001)
    Redirection counter = 5            |



10.3 Mapping ISDN Redirection information to SIP Diversion header

     An ISDN message can contain up to two instances of a Redirecting
     number information element.  When a diversion occurs, an
     additional Redirection number information element is added.
     When a third (or greater) diversion occurs, the new
     Redirecting number information element replaces the bottom-most
     Redirection number information element.

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10.3.1 ISDN Definitions

       Called party number          The number of the party to which the
                                    call is currently being routed.

       Redirecting number
       information element          Aggregate information element
                                    which contains Redirecting number
                                    and Reason for diversion.


       Redirecting number           The number to which the call was
                                    being routed when the last diversion
                                    occurred.

       Reason for diversion         The reason that the last diversion
                                    occurred.

       Origin of Number             Indicates whether number is user
                                    provided and screened or network
                                    provided

       Presentation Status          Indicates if presentation is
                                    allowed or prohibited


10.3.2 ISDN parameters

       When a SIP call transits a SIP/ISDN gateway, the following
       information in the ISDN message should be examined/set when
       translating SIP Diversion headers to ISDN diversion information:
         1) Redirecting number of the top-most Redirecting number
            information element
         2) Reason for diversion of the top-most Redirection number
            information element
         3) Origin of Number and Presentation Status of the top-most
            Redirection number information element
         4) Redirection number of the bottom-most Redirection number
            information element
         5) Reason for diversion of the bottom-most Redirection number
            information element.
         6) Origin of Number and Presentation Status of the bottom-most
            Redirection number information element


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       An ISDN message contains information on the first and last
       diversions that occurred.  The top-most Redirection number
       information element contains information (including the
       Redirecting number, Origin of Number, Presentation Status,
       and Reason for diversion) about the last diversion that occurred.
       The bottom-most Redirection number information element contains
       information (including the Redirecting number, Origin of Number,
       Presentation Status,and Reason for diversion) about the
       first diversion that occurred.

       If only one Diversion has occurred, only one Redirection
       number information element is present.

       The Redirecting Number information element has the same Type of
       Number/Numbering Plan, and Digits as the Calling Party Number
       information element.

       There is no Redirection counter associated with this ISDN
       information element.

       Notice that the order of the Redirection number information
       elements in an ISDN message (top=first, bottom=last)
       is reversed from the order of Diversion headers in
       a SIP message (top=last, bottom=first).


10.3.3 ISDN to SIP translation

       The Redirecting number of the top-most ISDN Redirecting
       number information element SHOULD be used to set the value of
       the name-addr of the bottom-most Diversion header.  The Reason
       for Diversion of the top-most ISDN Redirecting number
       information element SHOULD be used to set the value of the
       diversion-reason of the bottom-most Diversion header.
       The Origin of Number of the top-most ISDN Redirecting number
       information element SHOULD be used to set the value of the
       diversion-screen of the bottom-most Diversion header.
       The Presentation Status of the top-most ISDN Redirecting number
       information element SHOULD be used to set the value of the
       diversion-privacy of the bottom-most Diversion header.

       The Redirecting number of the bottom-most ISDN Redirecting
       number information element SHOULD be used to set the value of
       the name-addr of the top-most Diversion header.  The Reason
       for Diversion of the bottom-most ISDN Redirecting number
       information element SHOULD be used to set the value of the
       diversion-reason of the top-most Diversion header.
       The Origin of Number of the bottom-most ISDN Redirecting number
       information element SHOULD be used to set the value of the
       diversion-screen of the top-most Diversion header.
       The Presentation Status of the bottom-most ISDN Redirecting
       number information element SHOULD be used to set the value of the
       diversion-privacy of the top-most Diversion header.

       Presence of the diversion-counter in each of the Diversion
       headers is optional.  If present, the diversion-counter of each
       Diversion header SHOULD be 1.


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10.3.4 SIP to ISDN translation

       The name-addr of the top-most Diversion header SHOULD
       be used to set the Redirecting number of the bottom-most
       ISDN Redirecting number information element.  The
       diversion-reason of the top-most Diversion header SHOULD
       be used to set the Reason for Diversion of the bottom-most
       ISDN Redirecting number information element. The
       diversion-screen of the top-most Diversion header SHOULD
       be used to set the Origin of Number of the bottom-most
       ISDN Redirecting number information element. The
       diversion-privacy of the top-most Diversion header SHOULD
       be used to set the Presentation Status of the bottom-most
       ISDN Redirecting number information element.


       The name-addr of the bottom-most Diversion header SHOULD
       be used to set the Redirecting number of the top-most
       ISDN Redirecting number information element.  The
       diversion-reason of the bottom-most Diversion header SHOULD
       be used to set the Reason for Diversion of the top-most
       ISDN Redirecting number information element. The
       diversion-screen of the bottom-most Diversion header SHOULD
       be used to set the Origin of Number of the top-most
       ISDN Redirecting number information element. The
       diversion-privacy of the bottom-most Diversion header SHOULD
       be used to set the Presentation Status of the top-most
       ISDN Redirecting number information element.

10.3.5 Example of ISDN to SIP translation


                                   ISDN/SIP GW
                                       |
--Setup------------------------------->|
  Called party number      =+19195551004
  Redirecting number information element:
    Redirecting number     =+19195551001
    Reason for redirection = Unconditional (1111)
    Origin of Number       = passed network screening
    Presentation Status    = presentation allowed
  Redirecting number information element:
    Redirecting number     =+19195551002
    Reason for redirection = User busy (0001)
    Origin of Number       = passed network screening
    Presentation Status    = presentation prohibited
                                       |
                                       |--INVITE tel:+19195551004---->
                                       |  Diversion: <tel:+19195551002>
                                       |    ;reason=user-busy
                                       |    ;screen="yes"
                                       |    ;privacy="off"
                                       |  Diversion: <tel:+19195551001>
                                       |    ;reason=unconditional
                                       |    ;screen="yes"
                                       |    ;privacy="full"
                                       |
                                       |

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10.3.6 Example of SIP to ISDN translation

                                   ISDN/SIP GW
                                       |
<--Setup-------------------------------|
  Called party number      =+19195551004
  Redirecting number information element:
    Redirecting number     =+19195551001
    Reason for redirection = Unconditional (1111)
    Origin of Number       = passed network screening
    Presentation Status    = presentation allowed
  Redirecting number information element:
    Redirecting number     =+19195551002
    Reason for redirection = User busy (0001)
    Origin of Number       = passed network screening
    Presentation Status    = presentation prhibited
                                       |
                                       |<--INVITE tel:+19195551004----
                                       |  Diversion: <tel:+19195551002>
                                       |    ;reason=user-busy
                                       |    ;screen="yes"
                                       |    ;privacy="off
                                       |  Diversion: <tel:+19195551001>
                                       |    ;reason=unconditional
                                       |    ;screen="yes"
                                       |    ;privacy="full"
                                       |


10.4 Information loss in SIP to ISUP/ISDN translation

     Because ISUP and ISDN only support a subset of the information
     in a SIP Diversion header, information loss occurs during
     translation at a SIP/ISUP or SIP/ISDN boundary.

     10.4.1 Loss of diversion URI information

            Because ISUP and ISDN only support a subset of URI types,
            (specifically tel: URIs and sip:x@y;user=phone URIs)
            Diversion information occurring for other URI types
            may be lost when crossing from SIP to ISDN or ISUP.

     10.4.2 Loss of diversion reason information

            Because ISUP and ISDN only support a subset of the reason
            codes supported by the Diversion header, specific reason
            code information may be lost when crossing from SIP to
            ISDN or ISUP.


     10.4.3 Loss of diversion counter information
            Because ISDN does not support a counter field (indicating
            the number of diversions that have occurred), counter
            information may be lost when crossing from SIP to ISDN.

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11 Acknowledgments

  We would like to thank David Williams, Ameet Kher, Satya Khatter,
  Manoj Bhatia, Shail Bhatnagar, Denise Caballero-Mccann,
  Kara Adams, and Charles Eckel of Cisco Systems and Bert Culpepper of
  InterVoice-Brite for their insights, inputs, and comments.

12 References

[SIP]  J. Rosenberg, et al. "SIP: Session Initiation Protocol",
        RFC 3261, June 2002.

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













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Authors' Addresses

   Steve Levy
   Cisco Systems
   7025 Kit Creek Road
   P.O. Box 14987
   Research Triangle Park, NC 27709
   USA
   Email: stlevy@cisco.com

   Bryan J. Byerly

   J. R. Yang
   Cisco Systems
   7025 Kit Creek Road
   P.O. Box 14987
   Research Triangle Park, NC 27709
   USA
   Email: jryang@cisco.com






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