



Network Working Group                                          M. Mohali
Internet-Draft                                                    Orange
Obsoletes: 6044 (if approved)                             March 04, 2015
Intended status: Informational
Expires: September 5, 2015


Mapping and interworking of Diversion information Between Diversion and
     History-Info Headers in the Session Initiation Protocol (SIP)
                       draft-mohali-rfc6044bis-02

Abstract

   Although the SIP History-Info header field is the solution adopted in
   IETF, the non-standard Diversion header field is nevertheless already
   implemented and used for conveying call diversion related information
   in the Session Initiation Protocol (SIP) signaling.
   On one hand, the non-standard Diversion header field is described, as
   Historic, in [RFC5806].  On the other hand, the History-Info header
   field is described in [RFC7044] that obsoletes the original[RFC4244]
   describing the History-Info header field.  [RFC7044] defines the SIP
   header field, History-Info, for capturing the history information in
   requests and new SIP header field parameters for the History-Info and
   Contact header fields to tag the method by which the target of a
   request is determined.  [RFC7044] also defines a value for the
   Privacy header field that directs the anonymization of values in the
   History-Info header field.

   Since the Diversion header field is used in existing network
   implementations for the transport of call diversion information, its
   interworking with the SIP History-Info standardized solution is
   needed.  This document describes a recommended interworking guideline
   between the Diversion header field and the History-Info header field
   to handle call diversion information.  In addition, an interworking
   policy is proposed to manage the headers' coexistence.  This work is
   intended to enable the migration from non-standard implementations
   and deployments toward IETF specification-based implementations and
   deployments.
   This document obsoletes [RFC6044]that describes the interworking
   between the Diversion header field [RFC5806] and the obsoleted
   History-Info header field as defined on [RFC4244].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.





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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Background  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.3.  From RFC4244 to RFC7044 . . . . . . . . . . . . . . . . .   4
   2.  Problem Statement . . . . . . . . . . . . . . . . . . . . . .   5
   3.  Interworking recommendations  . . . . . . . . . . . . . . . .   7
     3.1.  General recommendations . . . . . . . . . . . . . . . . .   7
     3.2.  Privacy considerations  . . . . . . . . . . . . . . . . .   7
     3.3.  Headers in SIP Method . . . . . . . . . . . . . . . . . .   9
     3.4.  SIP network/terminal using Diversion to SIP
           network/terminal using History-Info header  . . . . . . .   9
     3.5.  SIP network/terminal using History-Info header to SIP
           network/terminal using Diversion header . . . . . . . . .  11
   4.  Header fields syntaxes reminder . . . . . . . . . . . . . . .  12
     4.1.  History-Info header field syntax  . . . . . . . . . . . .  12
     4.2.  Diversion header field syntax . . . . . . . . . . . . . .  15
   5.  Diversion header to History-Info header . . . . . . . . . . .  15
   6.  History-Info header to Diversion header . . . . . . . . . . .  19
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.1.  Example with Diversion header changed into History-Info
           header  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.2.  Example with History-Info header changed into Diversion



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           header  . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.3.  Example with two SIP networks using History-Info header
           interworking with a SIP network using Diversion header  .  21
     7.4.  Additional interworking Cases . . . . . . . . . . . . . .  23
   8.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .  25
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  25
   11. Acknowlegements . . . . . . . . . . . . . . . . . . . . . . .  25
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     12.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Interworking between Diversion header and Voicemail
                URI  . . . . . . . . . . . . . . . . . . . . . . . .  27
     A.1.  Diversion header field to Voicemail URI . . . . . . . . .  27
     A.2.  Voicemail URI to Diversion header field . . . . . . . . .  27
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  28

1.  Introduction

1.1.  Overview

   For some VoIP-based services (eg.  Voicemail, Interactive Voice
   Recognition (IVR) or automatic call distribution), it is helpful for
   the called SIP user agent to identify from whom and why the session
   was diverted.  For this information to be used in various service
   providers or by applications, it needs to pass through the network.
   This is possible with two different SIP header fields: History-Info
   header field defined in [RFC7044] and the historic Diversion header
   field defined in [RFC5806] which are both able to transport diversion
   information in the SIP signaling.
   Although the Diversion header field is not standardized, it has been
   widely implemented.  Therefore, it is useful to have guidelines to
   make this header field interwork with the standard History-Info
   header field.
   Note that the new implementation and deployment of the Diversion
   header field is strongly discouraged.

   This document provides a mechanism for header fields content
   translation between the Diversion header field and the History-Info
   header field.

1.2.  Background

   The obsoleted History-Info header field [RFC4244] and its extension
   for forming SIP service URIs (including Voicemail URI) [RFC4458] used
   to be recommended by IETF to convey redirection information.  They
   also used to be recommended in the "Communication Diversion (CDIV)
   service" 3GPP specification [TS_24.604].



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   Concerning, the Diversion header field, it was originally described
   in an Internet Draft that was submitted to the SIP Working Group and
   was finally published as [RFC5806] for the historical record and to
   provide a reference for this RFC.

   This header field contains a list of diverting URIs and associated
   information providing specific information as the reason for the call
   diversion.  Most of the first SIP-based implementations have
   implemented the Diversion header field when no standard solution was
   ready to deploy.  The IETF has standardized the History-Info header
   field partly because it can transport general history information.
   This allows the receiving part to determine how and why the session
   is received.  As the History-Info header field may contain further
   information than call diversion information, it is critical to avoid
   losing information and be able to extract the relevant data using the
   retargeting cause URI parameter described in [RFC4458] for the
   transport of the call forwarding reason.

   The Diversion header field and the History-Info header field have
   different syntaxes reminded in this document.  Note that the main
   difference is that the History-Info header field is a chronological
   writing header whereas the Diversion header field applies a reverse
   chronology (i.e. the first diversion entry read corresponds to the
   last diverting user).

   The Appendix A provides an interworking guideline between the
   Diversion header field and the Voicemail URI which is another way to
   convey diversion information without using the History-Info header
   field.  The Voicemail URI is defined in [RFC4458].

1.3.  From RFC4244 to RFC7044

   The detail of why and how [RFC4244] has been updated and replaced by
   [RFC7044] is provided in section 16 of [RFC7044].

   Here are the main changes for the History-Info header field
   implementation:

   1.  Added header field parameters "mp", "rc" and "np" to capture the
       specific method by which a target is determined.

   2.  Added a way to indicate a gap in History-Info by adding a "0" in
       the index.

   3.  To apply privacy, entries are anonymized rather than removed.

   4.  Many SHOULD are changed into MUST to have a more reliable header.




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   Backward compatibility aspects are discussed in section 8 of this
   document.

2.  Problem Statement

   This section provides the baseline terminology used in the rest of
   the document and defines the scope of interworking between the
   Diversion header field and the History-Info header field.

   They are many ways in which SIP signaling can be used to modify a
   session destination before it is established and many reasons for
   doing so.  The behavior of the SIP entities that will have to further
   process the session downstream will sometimes vary depending on the
   reasons that lead to changing the destination.  For example, whether
   it is for a simple proxy to route the session or for an application
   server to provide a supplementary service.  The Diversion header
   field and the History-Info header field differ in the approach and
   scope of addressing this problem.


   For clarity, the following vocabulary is used in this document:


   o  Retarget/redirect: these terms refer to the process of a Proxy
      Server/User Agent Client (UAC) changing a Request-URI (Section 7.1
      of [RFC3261]) in a request and thus changing the target of the
      request.  This includes changing the Request-URI due to a location
      service lookup and redirect processing.  This also includes
      internal (to a proxy/SIP intermediary) changes of the URI prior to
      the forwarding of the request.  The retarget term is defined in
      [RFC7044].

   o  Call forwarding/call diversion/communication diversion: these
      terms are equivalent and refer to the Communications Diversion
      (CDIV) supplementary services, based on the ISDN Communication
      diversion supplementary services and defined in 3GPP [TS_24.604].
      They are applicable to entities which are intended to modify the
      original destination of an IP multimedia session during or prior
      to the session establishment.

   This document does not intend to describe when or how History-Info or
   Diversion header fields should be used.  Hereafter is provided
   clarification on the context in which the interworking is required.

   The Diversion header field has exactly the same scope as the call
   diversion service and each header field entry reflects a call
   diversion invocation.  The Diversion header field is used for
   recording call forwarding information which could be useful to



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   network entities downstream.  Today, this SIP header field is
   implemented by several manufacturers and deployed in networks.

   The History-Info header field is used to store all retargeting
   information including call diversion information.  As such, the
   History-Info header field [RFC7044] is used to convey call diversion
   related information by using a cause URI parameter [RFC4458] in the
   relevant entry.
   Note, however, that the use of cause URI parameter [RFC4458] in a
   History-Info entry for a call diversion is specific to the 3GPP
   specification [TS_24.604].  [RFC4458] focuses on retargeting toward
   voicemail server and does not specify whether the cause URI parameter
   should be added in a URI for other cases.  As a consequence,
   implementations that do not use the cause URI parameter for call
   forwarding information, are not considered for the mapping described
   in this document.  Nevertheless, some recommendations are given in
   the next sections on how to avoid the loss of non-mapped information
   at the boundary between a network region using History-Info header
   field and one using the Diversion header field.

   The [RFC7044] defines three header field parameters, "rc", "mp", and
   "np".  The header field parameters "rc" and "mp" indicate the
   mechanism by which a new target for a request is determined.  The
   header field "np" reflects that the target has not changed.  All
   parameters contain an index whose value refers to the hi-index of the
   hi-entry with an hi-targeted-to-uri that represents the Request-URI
   that was retargeted.

   Since both header fields address call forwarding needs, diverting
   information could be mixed-up or be inconsistent if both are present
   in an uncoordinated fashion in the INVITE request.  So, Diversion and
   History-Info header fields must not independently coexist in the same
   session signaling.  This document addresses how to convert
   information between the Diversion header field and the History-Info
   header field, and when and how to preserve both header fields to
   cover additional cases.

   For the transportation of consistent diversion information
   downstream, it is necessary to make the two header fields interwork.
   Interworking between the Diversion header field and the History-Info
   header field is introduced in sections 5 and 6.  Since coexistence
   scenario may vary from one use case to another one, guidelines
   regarding header fields interaction are proposed in section 3.








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3.  Interworking recommendations

3.1.  General recommendations

   Interworking function:

      In a normal case, the network topology assumption is that the
      interworking described in this document should be performed by a
      specific SIP border device which is aware, by configuration, that
      it is at the border between two regions, one using History-Info
      header field and one using Diversion header field.

   As History-Info header field is a standard solution, a network using
   the Diversion header field must be able to provide information to a
   network using the History-Info header field.  In this case, to avoid
   header fields coexistence it is required to replace, as often as
   possible, the Diversion header field with the History-Info header
   field in the INVITE request during the interworking.

   Since, the History-Info header field has a wider scope than the
   Diversion header field, it may be used for other needs and services
   than call diversion.  In addition to trace call diversion
   information, History-Info header field also acts as a session history
   and can store all successive Request-URI values.  Consequently, even
   if it should be better to remove the History-Info header field after
   the creation of the Diversion header field avoiding confusion, the
   History-Info header field must remain unmodified in the SIP signaling
   if it contains supplementary (non-diversion) information.  It is
   possible to have History-Info header fields that do not have values
   that can be mapped into the Diversion header field.  In this case, no
   interworking with Diversion header field should be performed and it
   must be defined per implementation what to do in this case.  This
   point is left out of the scope of this document.

   As a conclusion, it is recommended to have local policies minimizing
   the loss of information and find the best way to keep it up to the
   terminating user agent.

   The following sections describe the basic common use case.
   Additional interworking cases are described in section 7.5.


3.2.  Privacy considerations

   When a SIP message is forwarded to a domain for which the SIP
   intermediary is not responsible, a Privacy Service at the boundary of
   the domain applies the appropriate privacy based on the value of the




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   Privacy header field in the message header or in the privacy
   parameter within concerned header.

   1.  For the History-Info header field, it is the "headers" component
       of the hi-targeted-to-uri in the individual hi-entries with the
       possible priv-value "history".

   2.  For the Diversion header field, it is the diversion-privacy
       parameter "privacy" in each Diversion header field.


   o  For the History-Info header field, as recommended in [RFC7044]:

         - If there is a Privacy header field in the message header of a
         request with a priv-value of "header" or "history", then all
         the hi-targeted-to-uris (in the hi-entries associated with the
         domain for which the SIP intermediary is responsible) are
         anonymized by the Privacy Service.  The Privacy Service must
         change any hi-targeted-to-uri in these hi-entries that have not
         been anonymized to the anonymous SIP URI
         "anonymous@anonymous.invalid" as recommended in sections
         4.1.1.3 and 4.1.1.2 of [RFC3323].

         - If there is a Privacy header field in the "headers" component
         of a hi-targeted-to-uri with a priv-value of "history", then
         all the concerned hi-entries must be anonymized as described
         above prior to forwarding.

      The Privacy Service must remove the Privacy header field from the
      "headers" component of the hi-targeted-to-uris of the concerned
      hi-entries and the priv-value of "history" from the Privacy header
      field in the message header of the request prior to forwarding.
      If there are no remaining priv-values in the Privacy header field,
      the Privacy Service must remove the Privacy header field from the
      request.

   o  For the Diversion header field:

         - If there is a Privacy header field in the message header of a
         request with a priv-value of "header", then all the addresses
         in the Diversion header fields (associated with the domain for
         which the SIP intermediary is responsible) are anonymized by
         the Privacy Service by changing the address to the anonymous
         SIP URI "anonymous@anonymous.invalid" as recommended in
         sections 4.1.1.3 and 4.1.1.2 of [RFC3323] prior to forwarding.

         - For the each Diversion header field or each entry in the
         Diversion header field, if there is a diversion-privacy



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         parameter with a value set to "full", "uri" or "name", then the
         concerned Diversion header field address must be anonymized as
         described above prior to forwarding.

      In the concerned Diversion header field entries, the diversion-
      privacy parameter must be removed from the header.

   The privacy information interworking as described in sections 5 and 6
   must only be considered within a trusted domain that ensure to
   correctly apply the privacy requirements.

3.3.  Headers in SIP Method

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

   In 3xx responses:

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

   In SIP responses other than 100:

      All SIP responses where History-Info could be present are not used
      for the Call Forwarding service and should not be changed into
      Diversion header field.  The destination network must be
      transparent to the received History-Info header field.

   Note: The following mapping is inspired from the ISUP to SIP
   interworking described in [TS_29.163].

3.4.  SIP network/terminal using Diversion to SIP network/terminal using
      History-Info header

   When the Diversion header field is used to create a History-Info
   header field, the Diversion header field must be removed in the
   outgoing INVITE.  It is considered that all the information present
   in the Diversion header field is transferred in the History-Info
   header field.



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   If a History-Info header field is also present in the incoming INVITE
   (in addition to Diversion header field), the Diversion header field
   and History-Info header field present must be mixed and only the
   diversion information not yet present in the History-Info header
   field must be inserted as a last entry (more recent) in the existing
   History-Info header field, following the creation process recommended
   in [RFC7044].


   As an example, this could be the case of an INVITE coming from
   network_2 using Diversion header field but previously passed through
   network_1 using History-Info header field (or the network_2 uses
   History-Info header field to transport successive URI information)
   and going to network_3 using History-Info header field.



                       IWF*                                  IWF*
     network1           |                network_2            |network_3
    History-Info        |                 Diversion           |using
                        |                                     |Hist-Info
                        |                                     |
UA A    P1     AS B     |       P2     AS C    UA C   AS D    |     UA E
|       |       |       |       |       |       |     |       |        |
|INVITE |       |       |       |       |       |     |       |        |
|------>|       |       |       |       |       |     |       |        |
|       |       |       |       |       |       |     |       |        |
|       |INVITE |       |       |       |       |     |       |        |
|       |------>|       |       |       |       |     |       |        |
|       |Supported: histinfo    |       |       |     |       |        |
|       | History-Info:         |       |       |     |       |        |
|       | <sip:proxyP1>; index=1,       |       |     |       |        |
|       | <sip:userB >; index=1.1;rc=1  |       |     |       |        |
|       |       |       |       |       |       |     |       |        |
|       |       |INVITE |       |       |       |     |       |        |
|       |       |------>|       |       |       |     |       |        |
|       |       |History-Info:  |       |       |     |       |        |
|       |       |<sip:proxyP1>; index=1,|       |     |       |        |
|       |       |<sip:userB>; index=1.1;rc=1,   |     |       |        |
|       |       |<sip:userC; cause=302>; index=1.1.1;mp=1.1   |        |

   In this case, the incoming INVITE contains a Diversion header field
   and a History-Info header field.  Therefore, as recommended in this
   document, it is necessary to create for network_3, a single History-
   Info header field gathering existing information from both the
   History-Info and the Diversion header fields received.  Anyway, it is
   required from network_2 (ie.IWF) to remove the Diversion header field
   when the message is going to a network not using the Diversion header



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   field.  Then network_3 could use call forwarding information that is
   present in a single header field and add its own diversion
   information if necessary.

   Notes:

   1.  If a network is not able either to use only one header field each
       time, or to maintain both header fields up to date, the
       chronological order can not be certified.

   2.  It is not possible to have only Diversion header field when the
       History-Info header field contains more than call diversion
       information.  If previous policy recommendations are applied, the
       chronological order is respected as Diversion entries are
       inserted at the end of the History-Info header field taking into
       account the Diversion internal chronology.

3.5.  SIP network/terminal using History-Info header to SIP network/
      terminal using Diversion header

   When the History-Info header field is interpreted to create a
   Diversion header field, some precautions must be taken.
   If the History-Info header field contains only call forwarding
   information, then it must be deleted after the interworking.
   If the History-Info header field contains other information, then
   only the information of concern to the diverting user must be used to
   create entries in the Diversion header field and the History-Info
   header field must be kept as received in the INVITE and forwarded
   downstream.

   Note: The History-Info header field could be used for other reasons
   than call diversion services, for example by a service which need to
   know if a specific AS had yet been invoked in the signaling path.  If
   the call is later forwarded to a network using History-Info header
   field, it would be better not to lose history information due to
   passing though the network which only support Diversion header field.
   A recommended solution must not disrupt the standard behavior and
   networks which do not implement the History-Info header field must be
   transparent to a received History-Info header field.

   If a Diversion header field is present in the incoming INVITE (in
   addition to History-Info header field), only diversion information
   present in the History-Info header field but not in the Diversion
   header field must be inserted from the last entry (more recent) into
   the existing Diversion header field as recommended in the [RFC5806].






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   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 field enables the recording of sequential
      forking for the same served-user.  During an interworking, from
      the History-Info header field to Diversion header field, the
      History-Info entries containing a forking situation (with an
      incremented "index" parameter) could possibly be mapped if it
      contains a call forwarding "cause" parameter.  The interworking
      entity could choose to create only a Diversion entry or not apply
      the interworking.  The choice could be done according a local
      policy.

   The same logic is applied for an interworking with Voicemail URI (see
   the Appendix A).

4.  Header fields syntaxes reminder

4.1.  History-Info header field syntax

   The ABNF syntax [RFC5234] for the History-Info header field and
   header field parameters is as follows:

   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-target-param/hi-extension
     hi-index           = "index" EQUAL index-val
     index-val          =  number *("." number)
     number             =  [ %x31-39 *DIGIT ] DIGIT
     hi-target-param    = rc-param / mp-param / np-param
     rc-param           = "rc" EQUAL index-val
     mp-param           = "mp" EQUAL index-val
     np-param           = "np" EQUAL index-val
     hi-extension       = generic-param

   The ABNF definitions for "generic-param", "name-addr", "HCOLON",
   "COMMA", "SEMI", and "EQUAL" are from[RFC3261].


   The History-Info header field is specified in [RFC7044].  The top-
   most History-Info entry (first in the list) corresponds to the oldest
   history information.



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   Cause URI parameter:

      A hi-entry may contain a cause URI parameter expressing the
      diversion reason.  This cause URI parameter is defined in
      [RFC4458].  The ABNF grammar [RFC5234] for the cause-param
      parameter is reminded below as it has been subject to Errata [ID:
      1409] in [RFC4458].  The Status-Code is defined in [RFC3261].

      cause-param = "cause=" Status-Code

      This parameter is also named cause-param is a SIP/SIPS URI
      parameter and should be inserted in the History-Info entry (URI)
      of the diverted-to user in case of call diversion as recommended
      in the 3GPP CDIV specification [TS_24.604].  The cause values used
      in the cause-param for the diverting reason are listed in
      [RFC4458] .  Because it is a parameter dedicated to call
      forwarding service, its presence is used to determine that a hi-
      entry is a diverting user.  More precisely, each diverting user is
      located in the hi-entry before the one containing a cause-param
      with cause value as listed in [RFC4458].

   Reason header field:

      Moreover, the Reason header field defined in [RFC3326] should be
      escaped in the hi-entry of the diverting user when the call
      diversion is due to a received SIP response.  The Reason header
      field contains a cause parameter set to the true SIP response code
      received (Status-Code).
      Therefore, in case of call diversion due to a SIP response, both
      cause parameters should be used.  The complexity is that these
      parameters could be used at the same time in the History-Info
      header field but not in the same hi-entry and not with the same
      meaning.  Only the cause-param is dedicated to call diversion
      service.  The 'cause' Reason header field parameter is not taken
      into account in the mapping with a Diversion header field.

   Target URI parameter:

      The [RFC4458] also defines the 'target' URI parameter which could
      be inserted in a Request-URI and consequently in the hi-targeted-
      to-uri.  This parameter is used to keep the diverting user address
      in the downstream INVITE request in Voicemail URI implementation.
      As this information is already present in the hi-entries, the
      'target' URI parameter is not taken into account regarding the
      interworking with the Diversion header field.  From the Diversion
      header field, it could be possible to create the 'target' URI
      parameter in the hi-entries and/or in the Request-URI but this




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      possibility is based on local policies not described in this
      document.

   Privacy header field:

      A Privacy header field as defined in [RFC3323] could also be
      embeded in hi-entries with the 'history' value defined in
      [RFC7044].

   Index header field parameter:

      The index parameter is a string of digits, separated by dots to
      indicate the number of forward hops and retargets.


   Note: A history entry could contain the "gr" parameter.  Regardless
   the rules concerning "gr" parameter defined in [TS_24.604] which must
   be applied, this parameter has no impact on the mapping and must only
   be copied with the served user address.

   Missing entry:

      If the request clearly has a gap in the hi-entry (i.e., the last
      hi-entry and Request-URI differ), the entity adding an hi-entry
      must add a single index with a value of "0" (i.e., the nonnegative
      integer zero) prior to adding the appropriate index for the action
      to be taken (eg.  Index=1.1.2.0.1).  Prior to any application
      usage of the History-Info header field parameters, the SIP entity
      that processes the hi-entries must evaluate the hi-entries and
      determine if there are any gaps in the hi-entries.

   "histinfo" option tag:

      According to [RFC7044], a proxy that receives a Request with the
      "histinfo" option tag in the Supported header field should return
      captured History-Info in subsequent, provisional and final
      responses to the Request.  The behavior depends upon whether the
      local policy supports the capture of History-Info or not.


   Example:

   History-Info:
   <sip:diverting_user1_addr?Privacy=none&Reason=SIP%3Bcause%3D302>;
   index=1,
   <sip:diverting_user2_addr;cause=480?Privacy=history>;index=1.1;mp=1,
   <sip:last_diversion_target;cause=486>; index=1.1.1;mp=1.1




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4.2.  Diversion header field syntax

   The following text is restating the exact syntax that the production
   rules in [RFC5806] define, but using [RFC5234] ABNF:


   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 field 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].


   Example:

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



5.  Diversion header to History-Info header

   The following text is valid only if no History-Info is present in the
   INVITE request.  If at least one History-Info header field is




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   present, the interworking function must adapt its behavior to respect
   the chronological order.  For more information, see section 3.

   Concerning the privacy information in the Diversion header field, the
   following mapping only applies within a trusted domain, otherwise see
   the privacy considerations in section 3.2.

   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.  Each Diversion entry shall be mapped
   into a History-Info entry.  An additional History-Info entry (the
   last one) must be created with the diverted-to party address present
   in the Request-URI of the received INVITE.  The mapping is described
   in the table hereafter.

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

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

      - if a privacy parameter is present in the bottom-most Diversion
      entry, then a Privacy header field must be escaped in the History-
      Info header field as described in the table hereafter,

      - a hi-index set to 1.


   For each following Diversion entry (from bottom to top), the History-
   info entries are created as following (from top to bottom):

 Source                                   Destination
 Diversion header component:              History-Info header component:
 =======================================================================
 Name-addr                                Hi-target-to-uri

 =======================================================================
 Reason of the previous                   Cause URI parameter
 Diversion entry                          A cause-param "cause" is
                                          added in each hi-entry
                                          (except the first one)
 "unknown"----------------------------------404 (default 'cause' value)
 "unconditional"----------------------------302
 "user-busy"--------------------------------486
 "no-answer"--------------------------------408
 "deflection "------------------------------480 or 487
 "unavailable"------------------------------503
 "time-of-day"------------------------------404 (default)



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 "do-not-disturb"---------------------------404 (default)
 "follow-me"--------------------------------404 (default)
 "out-of-service"---------------------------404 (default)
 "away"-------------------------------------404 (default)

 ======================================================================
 Counter                                  Hi-index
 "1" or parameter ------------------------The previous created index
 no present                               is incremented with ".1"
 Superior to "1" -------------------------Create N-1 placeholder History
 (i.e. N)                                 entry with the previous index
                                          extended with ".1"
                                          Then the History-Info header
                                          created with the Diversion
                                          entry with the previous index
                                          extended with ".1"
 ======================================================================
 Privacy                                  Privacy header escaped in the
                                          hi-targeted-to-uri
 "full"-----------------------------------"history"
 "Off"------------------------------------Privacy header field
                                          absent or "none"
 "name"-----------------------------------"history"
 "uri"------------------------------------"history"
 ======================================================================
                                          hi-target-param
                                          A mp-param "mp" is added in
                                          each created hi-entry
                                          (except the first one)
                                          The "mp" parameter is set to
                                          the index value of the
                                          preceding hi-entry.
 =======================================================================

   A last History-Info entry is created and contains:

      - a hi-target-to-uri with the Request-URI of the INVITE request,

      - a cause-param from the top-most Diversion entry, mapped from the
      diversion-reason as described above,

      - an index set to the previous created index extended with a new
      level ".1" added at the end,

      - a hi-target-param set to "mp" equals to the index value of the
      previous preceding hi-entry.

   Notes:



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   1.  For other optional Diversion parameters, there is no
       recommendation as History-Info header field does not provide
       equivalent parameters.

   2.  For values of the diversion-reason which are mapped with a
       recommended default value, it could also be possible to choose
       another value.  The cause-param URI parameter offers less
       possible values than the diversion-reason parameter.  However, it
       has been considered that cause-param values list was sufficient
       to implement CDIV service as defined in 3GPP[TS_24.604] as it
       cover a large portion of cases.

   3.  The Diversion header field can contain a "tel" URI as defined in
       [RFC3966]in the name-addr parameter.  The History-Info header
       field can also contain an address that is a "tel" URI but if this
       hi-entry has to be completed with either a SIP header field (eg.
       Reason or Privacy) or a SIP URI parameter (eg. 'cause' or
       'target'); the "tel" URI must be converted into a SIP URI.
       [RFC3261] gives an indication as to the mapping between sip: and
       tel: URIs but in this particular case it is difficult to assign a
       valid hostport as the diversion has occurred in a previous
       network and a valid hostport is difficult to determine.  So, it
       is suggested that in case of "tel" URI in the Diversion header
       field, the History-Info header field should be created with a SIP
       URI with user=phone and a domain set to "unknow.invalid".

   4.  The Diversion header field allows the carrying of a counter that
       retains the information about the number of successive
       redirections.  History-Info does not have an equivalent because
       to trace and count the number of diversion it is necessary to
       count cause parameter containing a value associated to a call
       diversion listed in[RFC4458].  Read the index value is not
       enough.  With the use of the "placeholder" entry the History-info
       header field entries could reflect the real number of diversion
       occurred still thanks to the cause-param.


   Example of placeholder entry in the History-Info header field:

      <sip:unknown@unknown.invalid;cause=xxx>;index=1.1

      <sip:bob_addr;cause=404>;index=1.1.1;mp=1.1

   "cause=xxx" reflects the diverting reason of a previous diverting
   user.  For a placeholder hi-entry the value "404" must be taken for
   the cause-param and so, located in the next hi-entry.





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   Concerning local policies recommendations about header fields
   coexistence in the INVITE request, see sections 3 and 7.5.

6.  History-Info header to Diversion header

   Concerning the privacy information for the History-Info header field,
   the following mapping only applies within a trusted domain, otherwise
   see the privacy considerations in section 3.2.

   To create the Diversion entries in the same order than during a
   session establishment, the History-Info entries must be mapped from
   the top-most until the bottom-most.  The first History-Info header
   field entry selected will be mapped into the last Diversion header
   field entry and so on.  One Diversion header field entry must be
   created for each History-Info entry having cause-param with a value
   listed in [RFC4458].

   Diversion information:

   The Target_entry and the Diverting_entry terms defined below are used
   to ease the mapping understanding of the History-Info header field.

   The diversion information can be identified by finding the following
   hi-entries:

   o  Target_entry: hi-entries containing a cause-param URI parameter
      with a value listed in [RFC4458]will contain the diversion reason
      and the address of the target of the concerned call forwarding.
      Following the [RFC7044]these hi-entries may also contain a hi-
      target-param set to "mp".

   o  Diverting_entry:
      For each previously identified hi-entry:

         - If there is a "mp" header field parameter, the hi-entry whose
         hi-index matches the value of the hi-target-param "mp" will
         contain the diverting party address, its possible privacy and/
         or SIP reason when the retargeting has been caused by a
         received SIP response.

         - If there is no "mp" header field parameter, the information
         of the diverting party address, privacy and/or SIP reason will
         be found in the hi-entry that precede this identified hi-entry.

   Note: Following [RFC7044], all retargeting entries must point to a
   hi-entry that contain a "mp" parameter but for backward compatibility
   reasons, it may be absent from some of the received hi-entries.  You




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   can find more information on the backward compatibility aspects in
   section 8.

   The History-Info header field must be mapped into the Diversion
   header field as following:

   Source                                    Destination
   History-Info header component:            Diversion header component:
   =====================================================================
   Hi-target-to-uri                          Name-addr
   of the Diverting_entry.

   =====================================================================
   Cause-param                               Reason
   of the Target_entry
   404---------------------------------------"unknown" (default value)
   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 header field escaped              Privacy
   in the hi-targeted-to-uri
   of the Diverting_entry
   "history"----------------------------------"full"
   Privacy header field ----------------------"Off"
   Absent or "none"
   =====================================================================

   Note: For other optional History-Info parameters, there is no
   recommendation as Diversion header field does not provide equivalent
   parameters.

   Concerning local policies recommendations about header fields
   coexistence in the INVITE request, see section 3.









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7.  Examples

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

   INVITE sip:last_diverting_target
   Diversion:
   <sip:diverting_user3_address>;reason=unconditional;counter=1;
   privacy=off,
   <sip:diverting_user2_address>;reason=user-busy;counter=1;
   privacy=full,
   <sip: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;
   cause=408?privacy=history>;index=1.1;mp=1,
   <sip:diverting_user3_address;
   cause=486?privacy=none>;index=1.1.1;mp=1.1,
   <sip:last_diverting_target; cause=302>;index=1.1.1.1;mp=1.1.1

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

   INVITE sip:last_diverting_target; cause=486
   History-Info:
   <sip:diverting_user1_address?privacy=history>; index=1,
   <sip:diverting_user2_address; cause=302?
   privacy=none>;index=1.1;mp=1,
   <sip:last_diverting_target; cause=486>;index=1.1.1;mp=1.1

   Mapped into:

   Diversion:
   <sip:diverting_user2_address>; reason=user-busy; counter=1;
   privacy=off,
   <sip: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.



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                          IWF*                                IWF*
     SIP network using     |           SIP network using       |SIP net.
       History-Info        |                Diversion          |using
                           |                                   Hist-Info
                           |                                   |
   UA A    P1     AS B     |      P2     AS C    UA C   AS D   |    UA E
   |       |       |       |      |       |       |     |      |       |
   |INV B  |       |       |      |       |       |     |      |       |
   |------>|       |       |      |       |       |     |      |       |
   |       |       |       |      |       |       |     |      |       |
   |       |INV B  |       |      |       |       |     |      |       |
   |       |------>|       |      |       |       |     |      |       |
   |       |Supported: histinfo   |       |       |     |      |       |
   |       | History-Info:        |       |       |     |      |       |
   |       | <sip:proxyP1>; index=1,      |       |     |      |       |
   |       | <sip:userB>; index=1.1; rc=1 |       |     |      |       |
   |       |       |       |      |       |       |     |      |       |
   |       |       |INV C  |      |       |       |     |      |       |
   |       |       |------>|      |       |       |     |      |       |
   |       |       |History-Info: |       |       |     |      |       |
   |       |       <sip:proxyP1>; index=1,|       |     |      |       |
   |       |       <sip:userB>; index=1.1; rc=1,  |     |      |       |
   |       |       <sip:proxyP2; cause=302>; index=1.1.1; mp=1.1       |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |INV C |       |       |     |      |       |
   |       |       |       |----->|       |       |     |      |       |
   |       |       | Diversion:   |       |       |     |      |       |
   |       |       | userB; reason=unconditional; counter=1; privacy=off
   |       |       |       |History-Info: |       |     |      |       |
   |       |       |       <sip:proxyP1>; index=1,|     |      |       |
   |       |       |       <sip:userB>; index=1.1; rc=1,|      |       |
   |       |       |       <sip:proxyP2; cause=302>; index=1.1.1; mp=1.1
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |INV C  |       |     |      |       |
   |       |       |       |      |------>|       |     |      |       |
   |       |       |       |     No modification of Diversion header   |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |       |INV C  |     |      |       |
   |       |       |       |      |       |------>|     |      |       |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |       |<--180-|     |      |       |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |  No response timer expires |       |
   |       |       |       |      |       |---INV D --->|      |       |
   |       |       |Diversion:                          |      |       |
   |       |       |userC; reason=no-answer; counter=1; privacy=full,  |
   |       |       |userB; reason=unconditional; counter=1; privacy=off,
   |       |       |    History-Info:                   |      |       |



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   |       |       |    <sip:proxyP1>; index=1,         |      |       |
   |       |       |    <sip:userB>; index=1.1; rc=1,   |      |       |
   |       |       |    <sip:proxyP2; cause=302>; index=1.1.1; mp=1.1  |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |       |       |     |INV E |       |
   |       |       |       |      |       |       |     |----->|       |
   |       |       |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; rc=1,         |       |
   |       |       |     <sip:proxyP2; cause=302>; index=1.1.1; mp=1.1 |
   |       |       |       |      |       |       |     |      |       |
   |       |       |       |      |       |       |     |      | INV E |
   |       |       |       |      |       |       |     |      |------>|
   |       |   History-Info:      |       |       |     |      |       |
   |       |   <sip:proxyP1>; index=1,    |       |     |      |       |
   |       |   <sip:userB>; index=1.1; rc=1,      |     |      |       |
   |       |   <sip:proxyP2; cause=302>; index=1.1.1; mp=1.1,  |       |
   |       |   <sip:userC ?privacy=history>; index=1.1.1.0.1,  |       |
   |<sip:userD;cause=408?privacy=none>;index=1.1.1.0.1.1; mp=1.1.1.0.1,|
   |       |<sip:userE; cause=404>; index=1.1.1.0.1.1.1; mp=1.1.1.0.1.1|
   |       |       |       |      |       |       |     |       |      |
   |       |       |       |      |       |       |     |       |      |

   * Note: The IWF is an interworking function which could be a stand-
    alone equipment not defined in this document (it could be a proxy).

7.4.  Additional interworking Cases

   Even if for particular cases in which both header fields could
   coexist, it should be the network local policy responsibility to make
   it work together.  Here are described some situations and some
   recommendations on the behavior to follow.

   In the case where there is one network which includes different
   nodes, some of them supporting Diversion header field and other ones
   supporting History-info header field, there is a problem when any
   node handling a message does not know the next node that will handle
   the message.  This case can occur when the network has new and old
   nodes, the older ones using Diversion header field and the more
   recent History-Info header field.

   While a network replacement may be occurring there will be a time
   when both nodes coexist in the network.  If the different nodes are
   being used to support different subscriber types due to different



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   node capabilities then the problem is more important.  In this case
   there is a need to pass both History-Info header field and Diversion
   header field within the core network.

   These header fields need to be equivalent to ensure that, whatever
   the node receiving the message, the correct diversion information is
   received.  This requires that whatever the received header field,
   there is a requirement to be able to compare the header fields and to
   convert the header fields.  Depending upon the node capability, it
   may be possible to make assumptions as to how this is handled.


   o  If it is known that the older Diversion header field supporting
      nodes do not pass on any received History-Info header field then
      the interworking becomes easier.  If a message is received with
      only Diversion header fields then it has originated from an 'old'
      node.  The equivalent History-Info entries can be created and
      these can then be passed as well as the Diversion header field.

   o  If the node creates a new History-Info header field for a call
      diversion, then an additional Diversion header field must be
      created.

   o  If the next node is an 'old' node then the Diversion header field
      will be used by that node and the History-Info entries will be
      removed from the message when it is passed on.

   o  If the next node is a new node then the presence of both Diversion
      header field and History-Info header field means that interworking
      has already occurred and the Diversion and History-Info entries
      must be considered equivalent.

   o  If both nodes pass on both History-Info header field and Diversion
      header field but only actively use one, then both types of node
      need to perform the interworking and must maintain equivalence
      between the header fields.  This will eventually result in the use
      of Diversion header field being deprecated when all nodes in the
      network support History-Info header field.

   o  If a gap is identified in the History-Info header field by a node
      that would create a new entry, it shall add a single index with a
      value of "0" prior to adding the appropriate index for the action
      to be taken.








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8.  Backward Compatibility

   The backward compatibility aspects are due to the changes on the
   History-Info header field evolution from [RFC4244] to [RFC7044]that
   are described in section 1.3 of this document.  The backawrd
   compatibility is taken into account throughout this document for the
   interworking with the Diversion header field.  More details are
   provided in the backward compatibility section of [RFC7044].

9.  IANA Considerations

   This document makes no request of IANA.

10.  Security Considerations

   The security considerations in [RFC7044] and [RFC5806] apply.

   The privacy considerations described in section 3.2 apply.

   The use of Diversion header field or History-Info header field
   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 header fields can provide
   misleading information to users and applications.  A SIP entity that
   can provide a redirection reason in a History-Info header field or
   Diversion header field should be able to suppress this in accordance
   with privacy requirements of the user concerned.

11.  Acknowlegements

   The editor would like to acknowledge the constructive feedback and
   support provided by Steve Norreys, Jan Van Geel, Martin Dolly,
   Francisco Silva, Guiseppe Sciortino, Cinza Amenta, Christer Holmberg,
   Ian Elz, Jean-Francois Mule, Mary Barnes, Francois Audet, Erick
   Sasaki, Shida Schubert, Joel M.  Halpern, Bob Braden and Robert
   Sparks.  Merci a Lionel Morand, Xavier Marjou et Philippe Fouquart.

12.  References








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12.1.  Normative References

   [RFC3261]  "SIP: Session Initiation Protocol", RFC 3261, June 2002.

   [RFC3323]  "A Privacy Mechanism for the Session Initiation Protocol
              (SIP)", RFC 3323, November 2002.

   [RFC3326]  "The Reason Header Field for the Session Initiation
              Protocol (SIP)", RFC 3326, December 2002.

   [RFC3966]  "The tel URI for Telephone Numbers", RFC 3966, December
              2004.

   [RFC4244]  "An Extension to the Session Initiation Protocol (SIP) for
              Request History Information", RFC 4244, November 2005.

   [RFC5806]  "Diversion Indication in SIP", March 2010.

   [RFC7044]  "An Extension to the Session Initiation Protocol (SIP) for
              Request History Information", RFC 7044, February 2014.

12.2.  Informative References

   [RFC4458]  "Session Initiation Protocol (SIP) URIs for Applications
              such as Voicemail and Interactive Voice Response (IVR)",
              RFC 4458, April 2006.

   [RFC5234]  "Augmented BNF for Syntax Specifications: ABNF", RFC 5234,
              January 2008.

   [RFC6044]  "Mapping and Interworking of Diversion Information between
              Diversion and History-Info Headers in the Session
              Initiation Protocol (SIP)", RFC 6044, October 2010.

   [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", December 2008.

   [TS_29.163]
              3rd Generation Partnership Project, "Technical
              Specification Group Core Network and Terminals ;
              Interworking between the IP Multimedia (IM) Core Network
              (CN) Subsystem and Circuit Switched (CS) networks (Release
              8)", December 2008.




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Appendix A.  Interworking between Diversion header and Voicemail URI

   Voicemail URI is a mechanism described in [RFC4458] to provide a
   simple way to transport only one redirecting user address and the
   reason why the diversion occurred in the Request-URI of the INVITE
   request.  This mechanism is mainly used for call diversion to a
   voicemail.


A.1.  Diversion header field to Voicemail URI

   Received:
   Diversion: userA-address;reason=user-busy;counter=1;privacy=full

   Sent (Voicemail URI created in the R-URI line of the INVITE):
   sip: voicemail@example.com;target=userA-address;cause=486 SIP/2.0

   Mapping of the Redirection Reason is the same as for History-Info
   header field with a default value set to 404.
   If the Diversion header field contains more than one Diversion entry,
   the choice of the redirecting user information inserted in the URI is
   in charge of the network local policy.  For example, the choice
   criterion of the redirecting information inserted in the URI could be
   the destination of forwarded INVITE request (if the voicemail serves
   this user or not).

   Note: This interworking could be done in addition to the interworking
   of the Diversion header field into the History-Info header field.

A.2.  Voicemail URI to Diversion header field

   In case of real Voicemail, this way of interworking should not
   happen.  However, if for any reason it occurs, it is recommended to
   do it as following:

   Received:
   INVITE sip: voicemail@example.com;\
   target=sip:+33145454500%40example.com;user=phone;\
   cause=302 SIP/2.0

   Sent in the forwarded INVITE:
   Diversion: sip:+33145454500%40example.com;user=phone;
   reason=unconditional;counter=1








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Author's Address

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

   Phone: +33 1 45 29 45 14
   Email: marianne.mohali@orange.com









































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