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rfc:rfc5806

Independent Submission S. Levy Request for Comments: 5806 Cisco Systems Category: Historic M. Mohali, Ed. ISSN: 2070-1721 Orange Labs

                                                            March 2010
                    Diversion Indication in SIP

Abstract

 This RFC, which contains the text of an Internet Draft that was
 submitted originally to the SIP Working Group, is being published now
 for the historical record and to provide a reference for later
 Informational RFCs.  The original Abstract follows.
 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 that
 receive diversion information may use this as supplemental
 information for feature invocation decisions.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for the historical record.
 This document defines a Historic Document for the Internet community.
 This is a contribution to the RFC Series, independently of any other
 RFC stream.  The RFC Editor has chosen to publish this document at
 its discretion and makes no statement about its value for
 implementation or deployment.  Documents approved for publication by
 the RFC Editor are not a candidate for any level of Internet
 Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc5806.

Levy & Mohali Historic [Page 1] RFC 5806 Diversion Indication in SIP March 2010

IESG Note

 This document contains an early proposal to the IETF SIP Working
 Group that was not chosen for standardization.  Discussions on the
 topic resulted in the informational RFC 3325, "Private Extensions to
 the Session Initiation Protocol (SIP) for Asserted Identity within
 Trusted Networks", and the standard solution that was chosen can be
 found in RFC 4244, "An Extension to the Session Initiation Protocol
 (SIP) for Request History Information".

Copyright Notice

 Copyright (c) 2010 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.

Levy & Mohali Historic [Page 2] RFC 5806 Diversion Indication in SIP March 2010

Table of Contents

 1. Introduction ....................................................4
 2. Terminology .....................................................4
    2.1. Requirements Language ......................................4
    2.2. Definitions ................................................4
    2.3. Abbreviations ..............................................5
 3. Overview ........................................................5
    3.1. When Is the Diversion Header Used? .........................6
 4. Extension Syntax ................................................6
 5. Detailed Semantics ..............................................7
    5.1. UAS Behavior ...............................................7
    5.2. UAC Behavior ...............................................7
    5.3. Redirect Server Behavior ...................................7
    5.4. Proxy Server Behavior ......................................7
 6. Examples Using Diversion Header .................................8
    6.1. Call Forward Unconditional .................................8
    6.2. Call Forward on Busy ......................................13
    6.3. Call Forward on No-Answer .................................17
    6.4. Call Forward on Unavailable ...............................21
    6.5. Multiple Diversions .......................................24
 7. Security Considerations ........................................27
 8. Further Examples ...............................................27
    8.1. Night Service/Automatic Call Distribution (ACD)
         Using Diversion Header ....................................27
    8.2. Voicemail Service Using Diversion Header ..................36
    8.3. Questions and Answers on Alternative Approaches ...........41

9. Mapping ISUP/ISDN Redirection Information to SIP

    Diversion Header ...............................................42
    9.1. Mapping ISUP/ISDN Diversion Reason Codes ..................42
    9.2. Mapping ISUP Redirection Information to SIP
         Diversion Header ..........................................43
    9.3. Mapping ISDN Redirection Information to SIP
         Diversion Header ..........................................47
    9.4. Information Loss in SIP to ISUP/ISDN Translation ..........52
 10. Contributors ..................................................53
 11. Acknowledgements ..............................................53
 12. Normative References ..........................................53

Levy & Mohali Historic [Page 3] RFC 5806 Diversion Indication in SIP March 2010

1. Introduction

 This RFC, which contains the text of an Internet Draft that was
 submitted originally to the SIP Working Group, is being published now
 for the historical record and to provide a reference for later
 Informational RFCs.
 In the legacy telephony network, redirection information is passed
 through the network in ISDN/ISUP (ISDN User Part) 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.

2. Terminology

2.1. Requirements Language

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

2.2. 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 that diverted the call.

Levy & Mohali Historic [Page 4] RFC 5806 Diversion Indication in SIP March 2010

 recursing:
    A SIP proxy or user agent that handles a received or internally
    generated 3xx response by forking new request(s) itself.
 non-recursing:
    A SIP proxy or user agent that handles a received or internally
    generated 3xx response by forwarding it upstream.

2.3. 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

3. 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.

Levy & Mohali Historic [Page 5] RFC 5806 Diversion Indication in SIP March 2010

3.1. 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 that
 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.

4. 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)]

Levy & Mohali Historic [Page 6] RFC 5806 Diversion Indication in SIP March 2010

 The following is an extension of tables 4 and 5 in [RFC3261] for the
 Diversion header:
                     where  enc.  e-e ACK BYE CAN INV OPT REG
 _____________________________________________________________
 Diversion              R           h   -   -   -   o   -   -
 Diversion             3xx          h   -   -   -   o   -   -

5. Detailed Semantics

5.1. UAS Behavior

 A SIP User Agent Service (UAS) that receives a request and returns a
 3xx SHOULD add a Diversion header containing the previous Request-URI
 and the reason for the diversion.

5.2. UAC Behavior

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

5.3. Redirect Server Behavior

 A SIP redirect server that receives a request and returns a 3xx
 containing a Contact that 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.

5.4. Proxy Server Behavior

 A non-recursing SIP proxy that receives a 3xx containing a Diversion
 header SHOULD forward the 3xx containing the Diversion header
 upstream unchanged.
 A SIP proxy that receives a request and invokes a feature that
 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 that receives a request and returns a 3xx containing a
 Contact that 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.

Levy & Mohali Historic [Page 7] RFC 5806 Diversion Indication in SIP March 2010

5.4.1. 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.
            }
        }
    }

6. 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 that generates or forwards 3xxs upstream is
 non-recursing.  A SIP proxy or user agent that handles received (or
 internally generated) 3xxs 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.

6.1. Call Forward Unconditional

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

6.1.1. 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.

Levy & Mohali Historic [Page 8] RFC 5806 Diversion Indication in SIP March 2010

                   +------------------------+
                   | Bob@P2: CFUNC->Carol@C |
                   +------+-----------------+
                           \
                            \

A P1 P2 B C

                          recursing

| | | | |

–INV Bob@P1→
–INV Bob@P2→
–INVITE Carol@C——→
Diversion: Bob@P2
←200——————-
←200———
←200———
–ACK————————————————>

Levy & Mohali Historic [Page 9] RFC 5806 Diversion Indication in SIP March 2010

6.1.2. 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————————————————>

Levy & Mohali Historic [Page 10] RFC 5806 Diversion Indication in SIP March 2010

6.1.3. 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————————————————>

Levy & Mohali Historic [Page 11] RFC 5806 Diversion Indication in SIP March 2010

6.1.4. 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
–ACK———>
←302———
Contact: Carol@C
Diversion: Bob@B
;reason=unconditional
–ACK——–>
–INVITE Carol@C————————>
Diversion: Bob@B
;reason=unconditional
←200————————————
←200———
–ACK————————————————–>

Levy & Mohali Historic [Page 12] RFC 5806 Diversion Indication in SIP March 2010

6.2. Call Forward on Busy

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

6.2.1. 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————————————————>

Levy & Mohali Historic [Page 13] RFC 5806 Diversion Indication in SIP March 2010

6.2.2. 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————————————————>

Levy & Mohali Historic [Page 14] RFC 5806 Diversion Indication in SIP March 2010

6.2.3. 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————————————————>

Levy & Mohali Historic [Page 15] RFC 5806 Diversion Indication in SIP March 2010

6.2.4. 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————————————————>

Levy & Mohali Historic [Page 16] RFC 5806 Diversion Indication in SIP March 2010

6.3. Call Forward on No-Answer

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

6.3.1. 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————————————————>

Levy & Mohali Historic [Page 17] RFC 5806 Diversion Indication in SIP March 2010

6.3.2. 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————————————————>

Levy & Mohali Historic [Page 18] RFC 5806 Diversion Indication in SIP March 2010

6.3.3. 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————————————————>

Levy & Mohali Historic [Page 19] RFC 5806 Diversion Indication in SIP March 2010

6.3.4. 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————————————————>

Levy & Mohali Historic [Page 20] RFC 5806 Diversion Indication in SIP March 2010

6.4. Call Forward on Unavailable

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

6.4.1. 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
←200——————-
←200———
←200———
–ACK————————————————>

6.4.2. 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.

Levy & Mohali Historic [Page 21] RFC 5806 Diversion Indication in SIP March 2010

                   +------------------------+
                   | 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————————————————>

Levy & Mohali Historic [Page 22] RFC 5806 Diversion Indication in SIP March 2010

6.4.3. 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————————————————>

Levy & Mohali Historic [Page 23] RFC 5806 Diversion Indication in SIP March 2010

6.5. Multiple Diversions

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

6.5.1. 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.

Levy & Mohali Historic [Page 24] RFC 5806 Diversion Indication in SIP March 2010

          +------------------------+     +-------------------------+
          | 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———————————————————–>

Levy & Mohali Historic [Page 25] RFC 5806 Diversion Indication in SIP March 2010

6.5.2. 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→
←200————
←200———-
←200———
←200———
–ACK———————————————————>

Levy & Mohali Historic [Page 26] RFC 5806 Diversion Indication in SIP March 2010

7. 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 3xxs.  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 3xxs that 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?

8. Further Examples

 Only the relevant headers have been included in the following
 examples.  The contents of the Session Description Protocols (SDPs)
 have also been omitted.

8.1. Night Service/Automatic Call Distribution (ACD) Using Diversion

    Header
 In the following two 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.

Levy & Mohali Historic [Page 27] RFC 5806 Diversion Indication in SIP March 2010

              +-------------------------------------+
              | 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"======
 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

Levy & Mohali Historic [Page 28] RFC 5806 Diversion Indication in SIP March 2010

 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 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.

Levy & Mohali Historic [Page 29] RFC 5806 Diversion Indication in SIP March 2010

 [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
 [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

Levy & Mohali Historic [Page 30] RFC 5806 Diversion Indication in SIP March 2010

 [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?"

Levy & Mohali Historic [Page 31] RFC 5806 Diversion Indication in SIP March 2010

               +---------------------------------------+
               | 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—–>
←[7] 200————
←[8] 200—————————
←[9] 200——
–[10] ACK———————————————————→
⇐======================================"Hello, WeSellFlowers"=======

Levy & Mohali Historic [Page 32] RFC 5806 Diversion Indication in SIP March 2010

 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
 [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 1 a.m. 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
 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

Levy & Mohali Historic [Page 33] RFC 5806 Diversion Indication in SIP March 2010

 [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.

Levy & Mohali Historic [Page 34] RFC 5806 Diversion Indication in SIP March 2010

 [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
 [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?"

Levy & Mohali Historic [Page 35] RFC 5806 Diversion Indication in SIP March 2010

8.2. 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.

Levy & Mohali Historic [Page 36] RFC 5806 Diversion Indication in SIP March 2010

               +---------------------------------------------+
               | 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—————————————————>

Levy & Mohali Historic [Page 37] RFC 5806 Diversion Indication in SIP March 2010

 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.

Levy & Mohali Historic [Page 38] RFC 5806 Diversion Indication in SIP March 2010

 [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
 [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

Levy & Mohali Historic [Page 39] RFC 5806 Diversion Indication in SIP March 2010

 [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

Levy & Mohali Historic [Page 40] RFC 5806 Diversion Indication in SIP March 2010

 [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.

8.3. Questions and Answers 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.).

Levy & Mohali Historic [Page 41] RFC 5806 Diversion Indication in SIP March 2010

 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).

9. 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 that 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 lowercase "redirect" indicates the SIP
 usage, while an uppercase "Redirect" indicates ISUP usage.

9.1. 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

Levy & Mohali Historic [Page 42] RFC 5806 Diversion Indication in SIP March 2010

    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

9.2. 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.

9.2.1. 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.

Levy & Mohali Historic [Page 43] RFC 5806 Diversion Indication in SIP March 2010

9.2.2. 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 the number 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.

9.2.3. 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.

Levy & Mohali Historic [Page 44] RFC 5806 Diversion Indication in SIP March 2010

 The Redirection 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.

9.2.4. 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 that does not explicitly specify a diversion-counter tag
 counts as 1.

Levy & Mohali Historic [Page 45] RFC 5806 Diversion Indication in SIP March 2010

9.2.5. 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
                                     |
                                     |

Levy & Mohali Historic [Page 46] RFC 5806 Diversion Indication in SIP March 2010

9.2.6. 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            |

9.3. 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.

9.3.1. 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 that
                              contains Redirecting number and Reason
                              for diversion.

Levy & Mohali Historic [Page 47] RFC 5806 Diversion Indication in SIP March 2010

 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 the number is user
                              provided and screened or network
                              provided.
 Presentation Status          Indicates if presentation is allowed or
                              prohibited.

9.3.2. 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
 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.

Levy & Mohali Historic [Page 48] RFC 5806 Diversion Indication in SIP March 2010

 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).

9.3.3. 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.

Levy & Mohali Historic [Page 49] RFC 5806 Diversion Indication in SIP March 2010

9.3.4. 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.

Levy & Mohali Historic [Page 50] RFC 5806 Diversion Indication in SIP March 2010

9.3.5. 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"
                                     |
                                     |

Levy & Mohali Historic [Page 51] RFC 5806 Diversion Indication in SIP March 2010

9.3.6. 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 prohibited
                                     |
                                     |<--INVITE tel:+19195551004----
                                     |  Diversion: <tel:+19195551002>
                                     |    ;reason=user-busy
                                     |    ;screen="yes"
                                     |    ;privacy="off
                                     |  Diversion: <tel:+19195551001>
                                     |    ;reason=unconditional
                                     |    ;screen="yes"
                                     |    ;privacy="full"
                                     |

9.4. 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.

9.4.1. 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.

9.4.2. 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.

Levy & Mohali Historic [Page 52] RFC 5806 Diversion Indication in SIP March 2010

9.4.3. 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.

10. Contributors

 Special acknowledgement to both Bryan Byerly and JR Yang.  As
 original authors of this document, both were instrumental is getting
 this document written.

11. Acknowledgements

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

12. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
            A., Peterson, J., Sparks, R., Handley, M., and E.
            Schooler, "SIP: Session Initiation Protocol", RFC 3261,
            June 2002.

Authors' Addresses

 Steve Levy
 Cisco Systems
 7025 Kit Creek Road P.O. Box 14987 Research Triangle Park,
 NC  27709
 USA
 EMail: stlevy@cisco.com
 Marianne Mohali (editor)
 Orange Labs
 38-40 rue du General Leclerc
 Issy-Les-Moulineaux Cedex 9  92794
 France
 Phone: +33145294514
 EMail: marianne.mohali@orange-ftgroup.com

Levy & Mohali Historic [Page 53]

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