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RFC 5806

Diversion Indication in SIP

Pages: 53
Historic
Errata

Top   ToC   RFC5806 - Page 1
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.
Top   ToC   RFC5806 - Page 2
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.
Top   ToC   RFC5806 - Page 3

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
Top   ToC   RFC5806 - Page 4

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.
Top   ToC   RFC5806 - Page 5
   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.
Top   ToC   RFC5806 - Page 6

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)]
Top   ToC   RFC5806 - Page 7
   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.
Top   ToC   RFC5806 - Page 8

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.
Top   ToC   RFC5806 - Page 9
                     +------------------------+
                     | 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------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |
Top   ToC   RFC5806 - Page 10

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 11

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 12

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 | | | | ;reason=unconditional | | | | | | | |--ACK--------->| | | | | | | | |<-302---------| | | | | Contact: Carol@C | | | | Diversion: Bob@B | | | | ;reason=unconditional | | | | | | | | |--ACK-------->| | | | | | | | | |--INVITE Carol@C------------------------>| | | Diversion: Bob@B | | | | ;reason=unconditional | | | | | | | | |<-200------------------------------------| | | | | | |<-200---------| | | | | | | | | |--ACK-------------------------------------------------->| | | | | | | | | | |
Top   ToC   RFC5806 - Page 13

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 14

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 15

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 16

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 17

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 18

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------------------------------------------------>| | | | | |
Top   ToC   RFC5806 - Page 19

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 20

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------------------------------------------------>| | | | | |
Top   ToC   RFC5806 - Page 21

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 | | | | ;reason=unavailable | | | | | | | |<-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.
Top   ToC   RFC5806 - Page 22
                     +------------------------+
                     | 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------------------------------------------------>|
|              |              |             |          |
|              |              |             |          |
Top   ToC   RFC5806 - Page 23

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------------------------------------------------>| | | | | | | | | | |
Top   ToC   RFC5806 - Page 24

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.
Top   ToC   RFC5806 - Page 25
            +------------------------+     +-------------------------+
            | 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----------------------------------------------------------->|
|              |              |             |          |          |
|              |              |             |          |          |
Top   ToC   RFC5806 - Page 26

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->| | | | | |Diversion: Carol@C | | | | | ;reason=no-answer | | | | | ;privacy="full" | | | | |Diversion: Bob@P2 | | | | | ;reason= unconditional | | | | | | | | | | |<-200------------| | | | | | | | | | |<-200----------| | | | | | | | | | | |<-200---------| | | | | | | | | | | | |<-200---------| | | | | | | | | | | | | |--ACK--------------------------------------------------------->| | | | | | | |
Top   ToC   RFC5806 - Page 27

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.
Top   ToC   RFC5806 - Page 28
                +-------------------------------------+
                | 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
Top   ToC   RFC5806 - Page 29
   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.
Top   ToC   RFC5806 - Page 30
   [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
Top   ToC   RFC5806 - Page 31
   [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?"
Top   ToC   RFC5806 - Page 32
                 +---------------------------------------+
                 | 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"=======|
|               |                |                   |                |
|               |                |                   |                |
Top   ToC   RFC5806 - Page 33
   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
Top   ToC   RFC5806 - Page 34
   [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.
Top   ToC   RFC5806 - Page 35
   [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?"
Top   ToC   RFC5806 - Page 36

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.
Top   ToC   RFC5806 - Page 37
                 +---------------------------------------------+
                 | 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--------------------------------------------------->|
|                  |                  |              |          |
|                  |                  |              |          |
Top   ToC   RFC5806 - Page 38
   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.
Top   ToC   RFC5806 - Page 39
   [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
Top   ToC   RFC5806 - Page 40
   [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
Top   ToC   RFC5806 - Page 41
   [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.).
Top   ToC   RFC5806 - Page 42
   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
Top   ToC   RFC5806 - Page 43
      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.
Top   ToC   RFC5806 - Page 44

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.
Top   ToC   RFC5806 - Page 45
   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.
Top   ToC   RFC5806 - Page 46

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 | |
Top   ToC   RFC5806 - Page 47

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.
Top   ToC   RFC5806 - Page 48
   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.
Top   ToC   RFC5806 - Page 49
   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.
Top   ToC   RFC5806 - Page 50

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.
Top   ToC   RFC5806 - Page 51

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" | |
Top   ToC   RFC5806 - Page 52

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.
Top   ToC   RFC5806 - Page 53

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