P-Served-User Header Field Parameter for Originating CDIV session case in Session Initiation Protocol (SIP)
draft-mohali-dispatch-originating-cdiv-parameter-00

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Author Marianne Mohali 
Last updated 2016-03-20
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Network Working Group                                          M. Mohali
Internet-Draft                                                    Orange
Updates: 5502 (if approved)                               March 21, 2016
Intended status: Informational
Expires: September 22, 2016

 P-Served-User Header Field Parameter for Originating CDIV session case
                  in Session Initiation Protocol (SIP)
          draft-mohali-dispatch-originating-cdiv-parameter-00

Abstract

   This specification defines a new Session Initiation Protocol (SIP) P-
   Served-User header field parameter, "orig-cdiv-param", which defines
   the session case used by a proxy when handling an originating session
   after Call Diversion (CDIV) services has been invoked for the served
   user.  The P-Served-User header field is defined in [RFC5502].  The
   P-Served-User header field conveys the identity of the served user
   and the session case that applies to this particular communication
   session and application invocation.
   This document updates [RFC5502] in order to add the originating after
   CDIV session case.

Status of This Memo

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   This Internet-Draft will expire on September 22, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents

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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.2.  Use Case  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Proxy behavior and parameter handling . . . . . . . . . . . .   3
   3.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Syntax  . . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  General . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  ABNF  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

1.1.  General

   The P-Served-User header field was defined in [RFC5502] to address an
   issue that was found in the 3rd Generation Partnership Project (3GPP)
   IMS (IP Multimedia Subsystem) between an S-CSCF (Serving Call Session
   Control Function) and an AS (Application Server) on the ISC (IMS
   Service Control) interface.  For more information on the IMS, a
   detailed description can be found in [TS.3GPP.24.229]
   . This header field conveys the identity of the served user and the
   session case that applies to this particular communication session
   and application invocation.
   [RFC5502] defines the originating and terminating session cases for a
   registered or unregistered user.  This document extends the P-Served-
   User header field to include the session case for a forwarded leg
   when a call diversion service (CDIV) has been invoked.
   The generic-param of the P-Served-User is extended by the "orig-cdiv-
   param" created as a new parameter for this Originating_CDIV session
   case.

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   The following section defines the orig-cdiv-param P-Served-User
   header field parameter usage, Section 2 specifies the proxy behavior
   for the new header field parameter handling, and Section 3 discusses
   the applicability and scope of this new header field parameter.
   Section 4 descibes the Syntax, Section 5 registers the orig-cdiv
   header field parameter with the IANA, and Section 6 discusses the
   security properties of the environment where this new header field
   parameter is intended to be used.

1.2.  Use Case

   In the 3GPP IMS (IP Multimedia Subsystem), the S-CSCF (Serving CSCF)
   is a SIP proxy that serves as a registrar and handles originating and
   terminating session states for users allocated to it.  This means
   that any call that is originated by a specific user or any call that
   is terminated to that specific user will pass through the S-CSCF that
   is allocated to that user.

   At the moment that an S-CSCF is allocated for a specific user, a user
   profile is downloaded to the S-CSCF from the HSS (Home Subscriber
   Server), see [TS.3GPP.29.228].

   To be able to determine which responsibilities the S-CSCF has to
   perform and on which user's behalf, the S-CSCF needs to know in which
   situation is the session from its point of view.[RFC5502] defines the
   originating and terminating session cases.

   In the case of a call diversion service, the initially received call
   was considered as a terminating session case and the terminating iFC
   configured in the S-CSCF are performed.  When the call diversion
   service is triggered, the Application Server changes the target
   (Request-URI) of the session and a new call leg is created.  This new
   call leg could be considered as an originating call leg but this is
   not the case.  Indeed, the originating user remains the same and the
   diverting user's originating services do not have to be triggered as
   if it was an originating call.  For instance, the originating user
   identity should not be hidden because the diverting user has a
   privacy service for his/her own identity.  In the same manner, some
   specific services may be triggered when performing a call diversion
   that would not be for a normal originating call.
   For this particular use case, this document created a new parameter
   to be embedded in the P-Served-User header field.

2.  Proxy behavior and parameter handling

   The orig-cdiv-param header filed parameter can be used inside a trust
   domain by proxies that are processing call diversion services.  The

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   following section illustrates how this header field parameter can be
   used in a 3GPP network.

   For a terminating call, when receiving the initial INVITE request,
   the S-CSCF will determines that the session case is for a terminating
   user as described in [RFC5502], then it determines the served user by
   looking at the Request-URI.  Then, the S-CSCF starts the iFC
   processing and triggers the served user Application Server for the
   terminating services to be executed.

   Based on some criteria, the diversion service concludes that the
   request needs to be diverted to another user or application and the
   served user address is deleted from the Request-URI and replaced with
   the new diverted-to address.  The Application Server stores the
   served user address by adding a new History-Info header field entry
   [RFC7044].  The served user address is tagged thanks to the mp-param
   header field parameter added in the History-Info entry associated to
   the diverted-to address created.
   The AS changes the P-Served-User header field content by replacing
   the received "sescase" header field parameter set to "term" by the
   "orig-cdiv" header field parameter.
   Then the AS routes the INVITE request back to the S-CSCF.

   When the S-CSCF receives the INVITE, it can see that the topmost
   Route header contains its own hostname.  Receiving the P-Served-User
   header field containing the "orig-cdiv" parameter, the S-CSCF
   concludes that the INVITE request should be handled as if a call is
   originated after a call diversion (CDIV) service.

   Then the procedure would continue forwarding the INVITE request over
   to an AS that hosts the originating services of the served user that
   specifically need to be executed on the forwarded leg after a call
   diversion service.

   When the AS receives the INVITE request, it determines that the
   session case is for "orig-cdiv" session case and will perform the
   related services for the served user.

3.  Applicability

   The use of the P-Served-User header field extensions is only
   applicable inside a Trust Domain for served user.  Nodes in such a
   Trust Domain explicitly trust each other to convey the served user
   and to be responsible for withholding that information outside of the
   Trust Domain.  The means by which the network determines the served
   user and the policies that are executed for a specific served user is
   outside the scope of this document.

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4.  Syntax

4.1.  General

   The orig-cdiv-param parameter is defined as an instance of generic-
   param from the current served-user-param component of P-Served-User
   header field.

   Following is a reminder of the P-Served-User syntax:

     P-Served-User            = "P-Served-User" HCOLON PServedUser-value
                                *(SEMI served-user-param)
     served-user-param        = sessioncase-param
                                / registration-state-param
                                / generic-param
     PServedUser-value        = name-addr / addr-spec
     sessioncase-param        = "sescase" EQUAL "orig" / "term"
     registration-state-param = "regstate" EQUAL "unreg" / "reg"

   EQUAL, HCOLON, SEMI, name-addr, addr-spec, and generic-param are
   defined in [RFC3261].

4.2.  ABNF

   The augmented Backus-Naur Form (BNF) [RFC5234] syntax of the P-
   Served-User header field is described in [RFC5502].
   The P-Served-User header syntax is extended as follows:

      served-user-param        =/ orig-cdiv-param

      orig-cdiv-param          = "orig-cdiv"

   The following is an example of a P-Served-User header field:

   P-Served-User: <sip:user@example.com>; orig-cdiv; regstate=reg

5.  IANA Considerations

   This specification defines a new P-Served-User header field parameter
   called orig-cdiv-param in the "Header Field Parameters and Parameter
   Values" sub-registry as per the registry created by [RFC3968].
   The syntax is defined in Section 4.

   The required information is:

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                   Header Name                References
                   --------------         -----------------
                   P-Served-User          [RFC5502][RFCxxxx]

   Note to RFC Editor: Please replace RFC XXXX with the RFC number of
   this specification.

6.  Security Considerations

   The security considerations in [RFC5502] apply.

   As the orig-cdiv-param P-Served-User header field parameter can be
   used to trigger applications, it is important to ensure that the
   parameter has not been added to the SIP message by an unauthorized
   SIP entity.

7.  Acknowledgments

   TBD

8.  References

8.1.  Normative References

   [RFC2119]  "Key words for use in RFCs to Indicate Requirement
              Levels", RFC 2119, March 1997.

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

   [RFC3968]  "The Internet Assigned Number Authority (IANA) Header
              Field Parameter Registry for the Session Initiation
              Protocol (SIP)", RFC 3968, December 2004.

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

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

8.2.  Informative References

   [RFC5502]  "The SIP P-Served-User Private-Header (P-Header) for the
              3GPP IP Multimedia (IM) Core Network (CN) Subsystem",
              RFC 5502, April 2009.

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   [TS.3GPP.24.229]
              3GPP, "IP multimedia call control protocol based on
              Session Initiation Protocol (SIP) and Session Description
              Protocol (SDP);Stage 3", 3GPP TS 24.229 x.x.x.

   [TS.3GPP.29.228]
              3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
              Signalling flows and message contents", 3GPP TS 29.228
              x.x.x.

Author's Address

   Marianne Mohali
   Orange
   Orange Gardens, 44 avenue de la Republique
   Chatillon  92326
   France

   Email: marianne.mohali@orange.com

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