Independent Submission S. Levy

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 |
| | | ;reason=unconditional
| | | | |
| | |<-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 |
| | | ;reason=unconditional
| | | | |
| | |--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 |
| | | ;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.

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->|
| | | | |Diversion: Carol@C
| | | | | ;reason=no-answer
| | | | | ;privacy="full"
| | | | |Diversion: Bob@P2
| | | | | ;reason= unconditional
| | | | | |
| | | | |<-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:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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:[email protected] SIP/2.0
Via: SIP/2.0/UDP p1.isp.com
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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:[email protected] 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:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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:[email protected] 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:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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----->|
| | | Diversion: WeSellFlowers@P4
| | | ;reason=time-of-day
| | | |
| | | |<-[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:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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:[email protected] SIP/2.0
Via: SIP/2.0/UDP p1.isp.com
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=p4
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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:[email protected]
To: <sip:[email protected]>;tag=p4
Call-ID: [email protected]
CSeq: 1 INVITE

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

INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP p1.isp.com
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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:[email protected] 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:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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
[email protected]. 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->[email protected] |
+--------------------------------------+------+
\
\
UAC1 P1 P2 UAS1 UAS2
Voicemail.com
| | | | |
|--[1] INV Bob@P1->| | | |
| | | | |
| |--[2] INV Bob@P2->| | |
| | | | |
| | [3] INV Bob@uas1->| |
| | | | |
| | [4] <- 302-------| |
| | Contact: [email protected] |
| | Diversion: Bob@uas1 |
| | ;reason=do-not-disturb |
| | | | |
| | |[5] ACK------>| |
| | | | |
| |<-[6] 302---------| | |
| | Contact: [email protected] | |
| | Diversion: Bob@uas1 | |
| | ;reason=do-not-disturb | |
| | | | |
| |--[7] ACK-------->| | |
|<-[8] 302---------| | | |
| Contact: [email protected] | | |
| Diversion: Bob@uas1 | | |
| ;reason=do-not-disturb | | |
| | | | |
|--[9] ACK-------->| | | |
| | | | |
|--[10] INVITE [email protected]>|
| 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:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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:[email protected] SIP/2.0
Via: SIP/2.0/UDP p1.isp.com
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Content-Type: application/sdp

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

INVITE sip:[email protected] 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:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;reason=do-not-disturb

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

ACK sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP p2.isp.com
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;reason=do-not-disturb

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

ACK sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP p1.isp.com
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;reason=do-not-disturb

[9] SIP UAC to SIP proxy server 1:

ACK sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas1
Call-ID: [email protected]
CSeq: 1 INVITE

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

INVITE sip:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: sip:[email protected]
Call-ID: [email protected]
CSeq: 1 INVITE
Diversion: <sip:[email protected]>
;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: [email protected]
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas2
Call-ID: [email protected]
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:[email protected] SIP/2.0
Via: SIP/2.0/UDP alice-pc.isp.com
From: sip:[email protected]
To: <sip:[email protected]>;tag=uas2
Call-ID: [email protected]
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
[email protected] becomes a configuration problem at
[email protected] and is prone to namespace collision.

Support for Diversion headers enables Bob to contract a third-
party service ([email protected]) with a single globally
significant URL for his voice mailbox ([email protected]).

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: [email protected]

Marianne Mohali (editor)
Orange Labs
38-40 rue du General Leclerc
Issy-Les-Moulineaux Cedex 9 92794
France

Phone: +33145294514
EMail: [email protected]

Levy & Mohali Historic [Page 53]