Mapping and interworking of Diversion information Between Diversion and History-Info Headers in the Session Initiation Protocol (SIP)
draft-mohali-diversion-history-info-00

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Abstract

Both History-Info and Diversion headers are able to transport diverting information in Session Initiation Protocol (SIP) signaling.
This document proposes a way to map call forwarding information contained in a Diversion header into a History-Info header and vice versa. In addition, an interworking policy is proposed to manage the headers coexistence.
Prior to existence of [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.) describing the History-Info header, there was a draft introducing a header named Diversion for the transport of diversion information.
Since the Diversion header is used in many existing networks implementations and it is not standardized for transport of diversion information, a mapping with the standardized History-Info header is needed.

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] (, “Key words for use in RFCs to Indicate Requirement Levels,” March 1997.).

Table of Contents

1.  Introduction
    1.1.  Overview
    1.2.  Background
2.  Problem Statement
    2.1.  Interworking need
    2.2.  Interworking recommendations
3.  Headers syntaxes reminder
    3.1.  History-Info header syntax
    3.2.  Diversion header syntax
4.  Headers in SIP METHOD
5.  Diversion header to History-Info header
6.  History-Info header to Diversion header
7.  Examples
    7.1.  Example with Diversion header changed into History-Info header
    7.2.  Example with History-Info header changed into Diversion header
    7.3.  Example with two SIP networks using History-Info header interworking with a SIP network using Diversion header
8.  IANA Considerations
9.  Security Considerations
10.  References
    10.1.  Normative References
    10.2.  Informative References
§  Authors' Addresses
§  Intellectual Property and Copyright Statements

1.  Introduction

1.1.  Overview

For enhanced network services (eg. Voicemail, IVR or automatic call distribution), it is necessary for the called SIP user agent to identify from whom and why the session was diverted. In order to be used by various service providers or applications, redirection information needs to pass through the network.
This is possible with two different SIP headers: History-Info [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.) and Diversion [draft‑levy‑sip‑diversion‑08] (, “Diversion Indication in SIP, draft-levy-sip-diversion-08,” August 2004.) which both able to transport diversion information in SIP signaling. Because of this double possibility, it is necessary to map one into the other.
This document provides a standard mechanism of translation between the History-Info header and the Diversion header.

1.2.  Background

To transport diversion information, the History-Info header [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.) and an URI extension [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.) are advocated in the standardized Communication Diversion (CDIV) service Protocol Specifications [TS_183004] (Telecommunications and Internet converged Services and Protocols for Advanced Networking (TISPAN), “PSTN/ISDN simulation services: Communication Diversion (CDIV); Protocol specification, Release 2, ETSI TS 183004,” November 2007.) and [TS_24.604] (3rd Generation Partnership Project, “Technical Specification Group Core Network and Terminals ; Communication Diversion (CDIV) using IP Multimedia (IM)Core Network (CN) subsystem ; Protocol specification (Release 8), 3GPP TS 24.604,” April 2008.).
Because of the implementation of the Diversion header in some SIP networks/terminals and the History-Info header in others, it is necessary to map one to the other.

At first, the Diversion header was described in [draft‑levy‑sip‑diversion‑08] (, “Diversion Indication in SIP, draft-levy-sip-diversion-08,” August 2004.), which is today discarded. This header contains the list of the diverting user(s) with associated information. The top-most diversion entry (first in the list) corresponds to the last diverting user and the bottom-most entry to the first diverting user (see syntax below).

At the same time, the History-Info header was proposed for the transport of "request history" information which allows the receiving application to determine hints about how and why the session arrived at the application/user. As history information is larger than diversion information, diversion information MUST be located and extracted from the History-Info header. This is not the case with the Diversion header. In addition, for diverting information the History-Info header MUST be completed by [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.) for the transport of the diversion reason.

Those headers have different syntaxes described below. Note that the main difference is that the History-Info header is a chronological writing header whereas the Diversion header is the opposite (i.e. the first diversion entry read correspond to the last diverting user).

2.  Problem Statement

2.1.  Interworking need

The Diversion header is used for recording communication diversion information which could be useful to network entities downstream. Today, this SIP header is implemented by several manufacturers and deployed in several networks.

In addition, the History-Info header is standardized, among other needs, for the transportation of diversion information.

As both are answering to call forwarding needs, according to the one created or completed in one side and the one interpreted in the other side, diverting information could be mixed-up if they are both present in the INVITE request. So, Diversion and History-Info headers MUST NOT independently coexist for the session signalling.

For the transportation of consistent diversion information downstream, it is necessary to make the two headers interwork. Mapping between the Diversion header and the History-Info header is presented in sections 5 and 6.

2.2.  Interworking recommendations

To avoid the two headers coexisting it would be better to replace one by the other during the interworking, but this may not be possible due to the information that History-Info header may carry.
Indeed, the History-Info header is larger than Diversion header and is used for other services than call diversion: in addition to trace call forwarding information, it is acting as a session history and could store all successive R-URI values. So, sometimes, it will not be possible to suppress the History-Info header after the Diversion header has been created.

SIP network/terminal using Diversion to SIP network/terminal using History-Info header:

When the Diversion header is mapped into a History-Info header, the Diversion header MUST be suppressed in the outgoing INVITE. It is considered that all information present in the Diversion header is transferred in the History-Info header.

If a History-Info header is present in the incoming INVITE (in addition to Diversion header), the Diversion header and History-Info header present MUST be mixed and only the diversion information not yet present in the History-Info header MUST be inserted as a last entry (more recent) in the existing History-Info header as recommended in [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.).
As an example, this could be the case of an INVITE coming from a network_2 using Diversion header but before passed through a network_1 using History-Info header (or the network_2 uses History-Info header to transport successive URI information) and going to a network_3 using History-Info header. In that case, the incoming INVITE contains a Diversion header and a History-info header. So that, it is necessary to create, for network_3, a single History-Info header gathering existing information in the History-Info header received and those present in the Diversion header. Then network_3 could use call forwarding information that are present in a single header and add its own diversion information if necessary.

Note that the chronological order could not be certified. If previous policy recommendations are applied, the chronological order is respected as Diversion entries are inserted at the end of the History-Info header taking into account the Diversion internal chronology.

SIP network/terminal using History-Info header to SIP network/terminal using Diversion header:

When the History-Info header is mapped into a Diversion header, some precautions MUST be taken.
If the History-Info header contains only communication diversion information, then it MUST be suppressed after the mapping.
If the History-Info header contains other information, then only the information of concern to the diverting user MUST be used to create entries in the Diversion header and the History-Info header MUST be kept as received in the INVITE forwarded downstream.

Note: The History-Info header could be used for other reasons than CDIV services, for example by a service which need to know if a specific AS had yet been invoked in the signalling path. If the call is after forwarded to a network using History-Info header, it would be better to not loose history information due to passing though the network which only support Diversion header. A recommended solution MUST NOT disrupt the standard behaviour and networks which not implement History-Info header MUST be transparent to an incoming History-Info header.

If a Diversion header is already presents in the incoming INVITE (in addition to History-Info header), only diversion information present in the History-Info header but not in the Diversion header MUST be inserted from the last entry (more recent) into the existing Diversion header as recommended in the Diversion draft [draft‑levy‑sip‑diversion‑08] (, “Diversion Indication in SIP, draft-levy-sip-diversion-08,” August 2004.). Note that the chronological order could not be certified. If previous policy recommendations are respected, this case SHOULD NOT happen.


Forking case:
The History-Info header enables the recording of sequential forking for the same served-user. During a mapping from the History-Info header to Diversion header, the History-Info entries contaning a forking situation (with an incremented "index" parameter) could be either mapped for each entry with a call forwarding "cause" parameter, the interworking entity could choose to create only one Diversion entry or to not apply the mapping. The choice could be done according a local policy.

3.  Headers syntaxes reminder

3.1.  History-Info header syntax

History-Info = "History-Info" HCOLON hi-entry *(COMMA hi-entry)
hi-entry = hi-targeted-to-uri *( SEMI hi-param )
hi-targeted-to-uri= name-addr
hi-param = hi-index / hi-extension
hi-index = "index" EQUAL 1*DIGIT *(DOT 1*DIGIT)
hi-extension = generic-param


The History-Info header is specified in [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.). Amongst the information contained in the header list is the diversion information with a specific cause code mentioning the diversion reason. These optional cause codes are defined in [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.). It is also possible to introduce the Privacy header defined in [RFC3323] (, “A Privacy Mechanism for the Session Initiation Protocol (SIP),” November 2002.) for diversion information. The top-most History-Info entry (first in the list) corresponds to the oldest history information.
A diverting user information is identifiable by the History-Info entry containing a cause-param with cause value as listed in [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.) and by the entry just before. The last diversion target is identifiable by the last History-Info entries containing a cause-param with cause value as listed in RFC 4458.
The cause-param is inserted in the hi-targeted-to-uri of the address were the communication is diverted to. The index parameter is a string of digits, separated by dots to indicate the number of forward hops and retargets.


Example:

History-Info:
<sip: diverting_user1_addr; Privacy=none >;index=1,
<sip: diverting_user2_addr; Privacy=history; Reason=SIP;cause=302>index=1.1,
<sip:last_diversion_target;Reason=SIP;cause=486>; index=1.1.1,


Policy concerning "histinfo" option tag in Supported header:
According to [RFC4244] (, “An Extension to the Session Initiation Protocol (SIP) for Request History Information,” November 2005.), a proxy that receives a Request with the "histinfo" option tag in the Supported header should return captured History-Info in subsequent, provisional and final responses to the Request. The behaviour depend whether the local policy support the capture of History-Info or not.

3.2.  Diversion header syntax

It seems that there is some few mistakes in the Diversion syntax, so it would be better to use the following syntax:

Diversion = "Diversion" HCOLON diversion-params *(COMMA diversion-params)
diversion-params = name-addr *(SEMI (diversion-reason / diversion-counter / diversion-limit / diversion-privacy / diversion-screen / diversion-extension))
diversion-reason = "reason" EQUAL ("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" EQUAL 1*2DIGIT
diversion-limit = "limit" EQUAL 1*2DIGIT
diversion-privacy = "privacy" EQUAL ("full" / "name" / "uri" / "off" / token / quoted-string)
diversion-screen = "screen" EQUAL ("yes" / "no" / token / quoted-string)
diversion-extension = token [EQUAL (token / quoted-string)]


Note: The Diversion header could be used in the comma-separated format as described below and in a header-separated format. Both formats could be combined a received INVITE as RECOMMENDED in [RFC3261] (, “SIP: Session Initiation Protocol,” June 2002.).


Example:

Diversion:
diverting_user2_addr; reason="user-busy"; counter=1; privacy=full,
diverting_user1_addr; reason="unconditional"; counter=1; privacy=off

4.  Headers in SIP METHOD

You can find here a reminder of History-Info header field and Diversion header field in relation to methods. As those headers does not have the same capabilities, it is necessary to clarify the interworking.

Use of History-Info header field:

Header field where proxy ACK BYE CAN INV OPT REG MSG
------------ ----- ----- --- --- --- --- --- --- ---
History-Info        amdr   -   -   -  o   o   o   o
                         SUB NOT REF INF UPD PRA PUB
                         --- --- --- --- --- --- ---
History-Info        amdr o    o   o   -   -   -   o


Use of Diversion header field:

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

The recommended interworking presented in this document SHOULD apply only for INVITE requests.

In 3xx responses, both headers could be present.
When a proxy wants to interwork with a network supporting the other header field, it SHOULD apply the mapping between Diversion header and History-Info header in the 3xx response.
When a recursing proxy redirects an initial INVITE after receving a 3xx response, it SHOULD add as a last entry either a Diversion header or History-Info header (according its capabilities) in the forwarded INVITE. Local policies could apply to send the received header in the next INVITE or not.

Other messages where History-Info could be present are not used for the Call Forwarding service and SHOULD NOT be changed into Diversion header. The destination network MUST be transparent the received History-Info header.

5.  Diversion header to History-Info header

For N Diversion entries N+1 History-Info entries MUST be created. To create the History-Info entries in the same order than during a session establishment, the Diversion entries MUST be mapped from the bottom-most until the top-most.

The first entry created in the History-Info header contains:

- a hi-target-to-uri with the name-addr parameter of the bottom-most Diversion header

- the privacy entry mapping the privacy parameter of the bottom-most Diversion header,

- an index set to 1.

For the each Diversion header, the next History-info entries are mapped as following:

Source                                         Destination
Diversion header component:                    History-Info header component:
=============================================================================
Name-addr of the previous                      Hi-target-to-uri
(on top) Diversion header.
If there is no previous(top-most),
it is the Request-URI address.

=============================================================================
Reason                                         Cause
“unknown”--------------------------------------404
"unconditional"--------------------------------302
"user-busy"------------------------------------486
"No-answer"------------------------------------408
"deflection "----------------------------------480
"Unavailable"----------------------------------503
"time-of-day"----------------------------------404 (default) or 302
"do-not-disturb"-------------------------------404 (default) or 302
"follow-me"------------------------------------404 (default) or 302
"out-of-service"-------------------------------404 (default)
"away"-----------------------------------------404 (default) or 302

=============================================================================
Counter                                         Hi-index
"1" or parameter ------------------------------The previous created index
no present                                     is incremented with ".1"
Superior to "1" -------------------------------1+[(N-1)*".1"]
(i.e. N)

=============================================================================
Privacy of the previous                        Privacy escaped in the
(on top) Diversion header.                     hi-targeted-to-uri
If there is no previous(top-most),
no privacy parameter is created.
"full"-----------------------------------------"history"
"Off"------------------------------------------Privacy header field
                                               absent or "none"
"name"-----------------------------------------"history"
"uri"------------------------------------------"history"
=============================================================================

Note: For other optional Diversion parameters, there is no recommendation.
Note: For values of the "reason" parameter which are mapped with a recommended default value, it could also be possible to choose an other value or to omit the parameter.

Concerning local policies recommendations about headers coexistence in the INVITE request, see section 2.2.

6.  History-Info header to Diversion header

As each previous diverting user MUST be present in the received History-Info header, one Diversion header entry per diverting user MUST be created in order to not to loose any diverting information.

For each History-Info header containing a cause-param with cause value as listed in the [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.); a Diversion header entry MUST be created. The first History-Info header entry selected will be mapped into the last Diversion header entry and so on.

In this case, the History-Info header MUST be mapped into the Diversion header as following:

Source                                         Destination
History-Info header component:                 Diversion header component:
============================================================================
Hi-target-to-uri of the                        Name-addr
History-Info which precedes the one
containing a diverting cause-param

============================================================================
Cause                                          Reason
404--------------------------------------------"unknown"
302--------------------------------------------"unconditional"
486--------------------------------------------"user-busy"
408--------------------------------------------"No-answer"
480 or 487-------------------------------------"deflection "
503--------------------------------------------"Unavailable"

============================================================================
Hi-index                                        Counter
Mandatory parameter for-------------------------The counter is set to "1".
History-Info reflecting
the chronological order
of the information.
============================================================================
Privacy escaped in the                          Privacy
hi-targeted-to-uri of the
History-Info which precedes the one
containing a diverting cause-param.
Optional parameter for History-Info,
this Privacy indicates that this
specific History-Info header SHOULD
not be forwarded.
"history"---------------------------------------"full"
Privacy header field ---------------------------"Off"
Absent or "none"

============================================================================
Privacy header [RFC3323]                        Privacy
The Privacy indicates that all
History-Info headers SHOULD NOT
be forwarded.
"history"---------------------------------------"full"
============================================================================

Concerning local policies recommendations about headers coexistence in the INVITE request, see section 2.2.


Editor's note: Iinterworking with Voicemail URI, defined in [RFC4458] (, “Session Initiation Protocol (SIP) URIs for Applications such as Voicemail and Interactive Voice Response (IVR),” April 2006.), will be added in the next release of the document.

7.  Examples

7.1.  Example with Diversion header changed into History-Info header

INVITE last_diverting_target
Diversion:
diverting_user3_address;reason="unconditional";counter=1;privacy=off,
diverting_user2_address;reason="user-busy";counter=1;privacy=full,
diverting_user1_address;reason="no-answer";counter=1;privacy=off

Mapped into:

History-Info:
<sip: diverting_user1_address; privacy=none >; index=1,
<sip: diverting_user2_address; privacy=history, reason=SIP; cause=408>index=1.1,
<sip: diverting_user3_address; privacy=none, reason=SIP; cause=486>index=1.1.1,
<sip: last_diverting_target; Reason=SIP; cause=302>index=1.1.1.1,

7.2.  Example with History-Info header changed into Diversion header

History-Info:
<sip: diverting_user1_address ;Privacy=history >; index=1,
<sip: diverting_user2_address; Privacy=none; Reason=SIP; cause=302>index=1.1,
<sip: last_diverting_target; Reason=SIP; cause=486>index=1.1.1

Mapped into:

Diversion:
diverting_user2_address; reason="user-busy"; counter=1; privacy=off,
diverting_user1_address; reason="unconditional"; counter=1; privacy=full

7.3.  Example with two SIP networks using History-Info header interworking with a SIP network using Diversion header

A -> P1 -> B -> C -> P2 -> D-> E
A, B, C, D and E are users.
B, C and D have Call Forwarding service invoked.
P1 and P2 are proxies.
Only relevant information is shown on the following call flow.

                       IWF*                                    IWF*
  SIP network using     |            SIP network using          |SIP network
    History-Info        |                 Diversion             |using
                        |                                       |History-Info
                        |                                       |
UA A    P1     AS B     |       P2     AS C    UE C   AS D      |      UE E
|       |       |       |       |       |       |       |       |         |
|INVITE |       |       |       |       |       |       |       |         |
|------>|       |       |       |       |       |       |       |         |
|       |       |       |       |       |       |       |       |         |
|       |INVITE |       |       |       |       |       |       |         |
|       |------>|       |       |       |       |       |       |         |
|       |Supported: histinfo    |       |       |       |       |         |
|       | History-Info:         |       |       |       |       |         |
|       | <sip:proxyP1>; index=1,       |       |       |       |         |
|       | <sip:userB >; index=1.1       |       |       |       |         |
|       |       |       |       |       |       |       |       |         |
|       |       |INVITE |       |       |       |       |       |         |
|       |       |------>|       |       |       |       |       |         |
|       |       |History-Info:  |       |       |       |       |         |
|       |       |<sip:proxyP1>; index=1,|       |       |       |         |
|       |       |<sip:userB>; index=1.1 |       |       |       |         |
|       |       |<sip:userC>; cause=302; index=1.1.1    |       |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |INVITE |       |       |       |       |         |
|       |       |       |------>|       |       |       |       |         |
|       |       |       |Diversion:     |       |       |       |         |
|       |       |       |B reason= unconditional counter=1      |         |
|       |       |       |History-Info:  |       |       |       |         |
|       |       |       |<sip:proxyP1>; index=1,|       |       |         |
|       |       |       |<sip:userB>; index=1.1 |       |       |         |
|       |       |       |<sip:proxyP2>; cause=302; index=1.1.1  |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |INVITE |       |       |       |         |
|       |       |       |       |------>|       |       |       |         |
|       |       |       |       |No modification of Diversion due to P2   |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |       |INVITE |       |       |         |
|       |       |       |       |       |------>|       |       |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |       |<--180-|       |       |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |  No response timer expire     |         |
|       |       |       |       |       |---INVITE----->|       |         |
|       |       |       Diversion:                      |       |         |
|       |       |       userC; reason=no-answer; counter=1; privacy=full,
|       |       |       userB; reason=unconditional; counter=1; privacy=off,
|       |       |       History-Info:                   |       |         |
|       |       |       <sip:proxyP1>; index=1,         |       |         |
|       |       |       <sip:userB>; index=1.1          |       |         |
|       |       |       <sip:proxyP2>; cause=302; index=1.1.1   |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |       |       |       |INVITE |         |
|       |       |       |       |       |       |       |------>|         |
|       |       |       Diversion:                              |         |
|       |       |       userD; reason=time-of-day; counter=1; privacy=off |
|       |       |       userC; reason=no-answer; counter=1; privacy=full, |
|       |       |       userB; reason=unconditional; counter=1; privacy=off,
|       |       |       History-Info:                           |         |
|       |       |       <sip:proxyP1>; index=1,                 |         |
|       |       |       <sip:userB>; index=1.1                  |         |
|       |       |       <sip:proxyP2>; cause=302; index=1.1.1   |         |
|       |       |       |       |       |       |       |       |         |
|       |       |       |       |       |       |       |       | INVITE  |
|       |       |       |       |       |       |       |       |-------->|
|       |       |       History-Info:                                     |
|       |       |       <sip:proxyP1>; index=1,                           |
|       |       |       <sip:userB>; index=1.1; privacy=none,             |
|       |       |       <sip:proxyP2>; cause=302; index=1.1.1,            |
|       |       |       <sip:userC>; privacy=history; index=1.1.1.1,      |
|       |       |      <sip:userD>; cause=408; privacy=none; index=1.1.1.1.1,
|       |       |       <sip:userE>; cause=404; index=1.1.1.1.1.1         |
|       |       |       |       |       |       |       |        |        |
|       |       |       |       |       |       |       |        |        |

* Note: The IWF is an interworking function which could be a stand-alone equipment not defined in this draft.

8.  IANA Considerations

This document makes no request of IANA.

9.  Security Considerations

The use of Diversion header or History-Info header require to apply the requested privacy and integrity asked by each diverting user or entity. Without integrity, the requested privacy functions could be downgraded or eliminated, potentially exposing identity information. Without confidentiality, eavesdroppers on the network (or any intermediaries between the user and the privacy service) could see the very personal information that the user has asked the privacy service to obscure. Unauthorised insertion, deletion of modification of those headers can provide misleading information to users and applications. A SIP entity that can provide a redirection reason in a History-Info header or Diversion header SHOULD be able to suppress this in accordance with privacy requirements of the user concerned.

10.  References

10.1. Normative References

10.2. Informative References

Authors' Addresses

Full Copyright Statement

Copyright © The IETF Trust (2008).

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

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