P-Served-User Header Field Parameter for Originating CDIV session case in Session Initiation Protocol (SIP)
draft-mohali-dispatch-originating-cdiv-parameter-02

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Author Marianne Mohali 
Last updated 2016-09-27
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Network Working Group                                          M. Mohali
Internet-Draft                                                    Orange
Updates: 5502 (if approved)                           September 27, 2016
Intended status: Informational
Expires: March 31, 2017

 P-Served-User Header Field Parameter for Originating CDIV session case
                  in Session Initiation Protocol (SIP)
          draft-mohali-dispatch-originating-cdiv-parameter-02

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

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

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   This Internet-Draft will expire on March 31, 2017.

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 . . . . . . . . . . . .   4
   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 and the
   Application Server haves to perform and on which user's behalf, it is
   necessary to know in which situation is the session and who is the
   current served user.[RFC5502] defines the originating and terminating
   session cases.

   In the case of a call diversion service, the received request is
   first considered as a terminating session case and the terminating
   iFC configured in the S-CSCF are performed.  Receiving the call
   initiation request, the Application Server is able to determine the
   served user and the session case (here "term") from the received P-
   Served-User header field content and to execute terminating services.
   When the call diversion service is executed, 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.

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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
   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 and saves this 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
   received Request-URI is replaced with the new diverted-to address.
   The Application Server stores the Request-URI(s) by adding one or two
   new History-Info header field entry(ies) [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.
   Then the AS forwards the INVITE request back to the S-CSCF.

   When the S-CSCF receives the INVITE, it can see that the topmost
   Route header field contains its own hostname but the Request-URI does
   not match the saved Request-URI.  In that case, the S-CSCF updates
   the P-Served-User header field content by removing both "sescase" and
   "regstate" header field parameters and inserting the "orig-cdiv"
   header field parameter.

   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
   originating services to be executed after retargeting 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

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   user and the policies that are executed for a specific served user is
   outside the scope of this document.

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 as defined in
   [RFC5502]:

    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 (ABNF) [RFC5234] syntax of the P-
   Served-User header field is described in [RFC5502].
   The existing P-Served-User header field ABNF 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].

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   The syntax is defined in Section 4.

   The required information is:

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

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

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

   [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 v11.

   [TS.3GPP.29.228]
              3GPP, "IP Multimedia (IM) Subsystem Cx and Dx interfaces;
              Signalling flows and message contents", 3GPP TS 29.228
              v11.

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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