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SIPPING Working Group                                     J. Bakker, Ed.
Internet-Draft                                  Research in Motion (RIM)
Intended status: Experimental                             August 7, 2008
Expires: February 8, 2009


        Specification of 3GPP IM CN Subsystem XML body handling
           draft-bakker-sipping-3gpp-ims-xml-body-handling-01

Status of this Memo

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Abstract

   This document registers new disposition-types for the Content-
   Disposition header that apply to the application/3gpp-ims+xml body
   used by 3GPP.  The applicability of these content-disposition values
   are limited to 3GPP IMS.  The application/3gpp-ims+xml body has the
   following two distinct uses: (1) for redirecting the emergency
   session to use a different domain (e.g. using a Circuit Switched
   call), and (2) for delivering user profile specific information from
   the SIP registrar to an Application Server.







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Table of Contents

   1.  Overall Applicability . . . . . . . . . . . . . . . . . . . . . 3
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Background for the new disposition-types for the
       Content-Disposition header  . . . . . . . . . . . . . . . . . . 4
     4.1.  The application/3gpp-ims+xml MIME type with content
           disposition 3gpp-alternative-service  . . . . . . . . . . . 4
       4.1.1.  Example application/3gpp-ims+xml body . . . . . . . . . 4
     4.2.  The application/3gpp-ims+xml MIME type with content
           disposition 3gpp-service-info . . . . . . . . . . . . . . . 5
       4.2.1.  Example application/3gpp-ims+xml body . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Appendix A.  Revision Information . . . . . . . . . . . . . . . . . 6
     A.1.  version 00  . . . . . . . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8




























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1.  Overall Applicability

   This document makes certain assumptions regarding network topology
   and the existence of transitive trust.  These assumptions are
   generally NOT APPLICABLE in the Internet as a whole.  The mechanism
   specified here was designed to satisfy the requirements specified by
   the 3rd Generation Partnership Project for IP multimedia subsystem
   (IMS) for which either no general-purpose solution was found, where
   insufficient operational experience was available to understand if a
   general solution is needed, or where a more general solution is not
   yet mature.


2.  Introduction

   New disposition-types for the Content-Disposition header can only be
   registered with IANA according to procedures defined in Section 9 of
   [1].

   The 3rd Generation Partnership Project (3GPP) (http://www.3gpp.org)
   is specifying the IP multimedia subsystem (IMS) where SIP is the
   protocol used to establish media sessions across different
   participants.

   This document registers new disposition-types for the Content-
   Disposition header: 3gpp-alternative-service and 3gpp-service-info,
   to address specific requirements of the IMS.  The new disposition-
   types may not be applicable to the general Internet.  The new
   disposition types are applicable to the "application/3gpp-ims+xml"
   MIME type [5].


3.  Terminology

   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 [2].

   The term "Application Server" (AS) is introduced in this document.

   An "Application Server" as referred to here is a SIP network server
   that performs network based functions.  The AS can act as a SIP Proxy
   as defined in [3] or a back-to-back UA (B2BUA) as defined in [3]
   based on the functions it needs to perform.  There can be one or more
   ASes involved in a SIP session.






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4.  Background for the new disposition-types for the Content-Disposition
    header

4.1.  The application/3gpp-ims+xml MIME type with content disposition
      3gpp-alternative-service

   In the IMS it is possible that a UA attempts to place an emergency
   call when the IMS network does not support emergency services.  The
   edge proxy detects the emergency call and can redirect the UE using a
   SIP 380 (Alternative Service) to place the emergency call using
   another domain (e.g. using a Circuit Switched network).

   Section 21.3.5 of [3] specifies that, for the SIP 380 (Alternative
   Service) response, alternative services are described in the message
   body of the response.  In IMS, for the purpose of indicating
   alternative domains, a SIP 380 (Alternative Service) response will
   include a MIME body and a Content-Type header field set to
   "application/3gpp-ims+xml".

   The "application/3gpp-ims+xml" MIME type with content disposition
   3gpp-alternative-service is applicable in the following
   circumstances:

      o Where the invitee UA originates a SIP request containing in the
      R-URI a URI that identifies this request as an emergency session
      request;

      o The network also contains intermediate network SIP servers that
      are trusted;

      o The edge proxy has knowledge of the network's capability or
      policy to handle the requested (type of) emergency session.

   Such configurations are generally not applicable to the internet as a
   whole where such trust relationships do not exist.

   In addition security issues have only been considered for networks
   which are trusted and use hop by hop security mechanisms with
   transitive trust and security issues with usage of this mechanism in
   the general internet have not been evaluated.

4.1.1.  Example application/3gpp-ims+xml body

      <3gpp-ims version="1">
         <alternative-service>
            <type>





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               <emergency/>
            </type>
            <reason/>
         </alternative-service>
      </3gpp-ims>

4.2.  The application/3gpp-ims+xml MIME type with content disposition
      3gpp-service-info

   In 3GPP IMS the SIP registrar (S-CSCF) can perform a third party
   registration to an AS.  The SIP registrar downloads User Profile
   information and can transparently transfer User Profile specific
   information to the AS using a body of MIME type "application/
   3gpp-ims+xml" in a SIP REGISTER request.  In the example in Section
   4.2.1, an International Mobile Subscriber Identity (IMSI) is
   transferred.

4.2.1.  Example application/3gpp-ims+xml body

      <3gpp-ims version="1">
         <service-info>
            262013564857956
         </service-info>
      </3gpp-ims>


5.  Security Considerations

   It is necessary to protect the messages between proxies;
   implementation SHOULD use a transport that provides integrity and
   confidentially between the signaling hops.  The Transport Layer
   Security (TLS) [4] based signaling in SIP can be used to provide this
   protection.

   Security issues have only been considered for networks which are
   trusted and use hop by hop security mechanisms with transitive trust
   and security issues with usage of this mechanism in the general
   internet have not been evaluated.


6.  IANA Considerations

   This document registers new disposition-types for the Content-
   Disposition header that apply to the "application/3gpp-ims+xml" body
   used by 3GPP and are to be registered in the IANA registry for Mail
   Content Disposition Values and Parameters:





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      o 3gpp-alternative-service: the body contains 3GPP IM CN subsystem
      XML with the 'alternative-service' XML element as described in
      Section 4.1; and

      o 3gpp-service-info: the body contains 3GPP IM CN subsystem XML
      with the 'service-info' XML element as described in Section 4.2.


7.  Acknowledgements

   The author would like to thank Andrew Allen, Dean Willis, Cullen
   Jennings for their guidance and comments that contributed to the
   progression of this work.


8.  References

8.1.  Normative References

   [1]  Troost, R., Dorner, S., and K. Moore, "Communicating
        Presentation Information in Internet Messages: The Content-
        Disposition Header Field", RFC 2183, August 1997.

   [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [3]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [4]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)
        Protocol Version 1.1", RFC 4346, April 2006.

8.2.  Informative References

   [5]  3GPP, "IP Multimedia Call Control Protocol based on Session
        Initiation Protocol (SIP) and Session Description Protocol
        (SDP); Stage 3 (Release 5)", 3GPP TS 24.229 V8.4.1, June 2008.


Appendix A.  Revision Information

A.1.  version 00
   1.  2008-02-12, Initial version
   2.  2008-07-02, Updated reference and further aligned 3GPP TS 24.229
       and this document





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Author's Address

   John-Luc Bakker (editor)
   Research in Motion (RIM)
   5000 Riverside Drive, building 6, suite 100
   Irving, Texas  75039
   USA

   Email: jbakker@rim.com










































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