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SIPPING Working Group                                     J. Bakker, Ed.
Internet-Draft                                  Research In Motion (RIM)
Intended status: Experimental                             March 27, 2012
Expires: September 28, 2012


        Specification of 3GPP IM CN Subsystem XML body handling
           draft-bakker-sipping-3gpp-ims-xml-body-handling-08

Abstract

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

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 28, 2012.

Copyright Notice

   Copyright (c) 2012 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
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.


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 field  . . . . . . . . . . . . . . . 4
     4.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . 4
     4.2.  The application/3gpp-ims+xml MIME type with content
           disposition 3gpp-alternative-service  . . . . . . . . . . . 4
       4.2.1.  Example application/3gpp-ims+xml MIME body (part)
               with type XML element set to emergency  . . . . . . . . 5
     4.3.  The application/3gpp-ims+xml MIME type with content
           disposition 3gpp-service-info . . . . . . . . . . . . . . . 5
       4.3.1.  Example application/3gpp-ims+xml body (part)  . . . . . 5

   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5

   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6

   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6

   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7

   Appendix A.  Revision Information . . . . . . . . . . . . . . . . . 7
     A.1.  version 00  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.2.  version 01  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.3.  version 02  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.4.  version 03  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.5.  version 04  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.6.  version 05  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.7.  version 06  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.8.  version 07  . . . . . . . . . . . . . . . . . . . . . . . . 7
     A.9.  version 08  . . . . . . . . . . . . . . . . . . . . . . . . 8

   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 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 field 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 field: 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 field

4.1.  Introduction

   Section 20.11 of [3] specifies that the Content-Disposition header
   field describes how the message body or, for multipart messages, a
   message body part is to be interpreted by the UAC or UAS.  In
   addition, [3] specifies that if this header field is missing, the
   MIME type determines the default content disposition.  If there is
   none, "render" is assumed.

   No default default content disposition has been defined for MIME type
   "application/3gpp-ims+xml" MIME type.  Sections 2.2 and 2.3 show how
   a body (part) according to the MIME type is to be intepreted by
   different entities (UE and AS) in 3GPP IMS.  The difference in
   requirements for UE and AS, coupled with the fact that the Content-
   Disposition header field describes how the message body (part) is to
   be interpreted, implies that a single default content disposition
   value does not cover both cases

4.2.  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) or using
   another registration context, if a type XML element in the MIME body
   (part) is set to "emergency".

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

   It is further possible that one or more UASes in the network
   experience service interuptions, e.g. when forwarding a (non-
   emergency) service request from a UAC.  For example, there is no
   response to the service request and its retransmissions, a 3xx
   response or a 480 (Temporarily Unavailable) response is received for
   the request, the UAS does not have a needed user profile (e.g. due to
   restart or the UAS) and the attempt to retrieve the user profile
   fails.  The UAS then responds with a 504 (Server Time-out), including
   a MIME body (part) and a Content-Type header field set to



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   "application/3gpp-ims+xml".  Upon receiving the response, the UAC
   then creates another registration context in an attempt to restore
   the services, if a type XML element in the MIME body (part) is set to
   "restoration".

   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.

4.2.1.  Example application/3gpp-ims+xml MIME body (part) with type XML
        element set to emergency

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

4.3.  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 (part) of MIME type "application/
   3gpp-ims+xml" in a SIP REGISTER request.  In the example in Section
   4.3.1, an International Mobile Subscriber Identity (IMSI) is
   transferred.

4.3.1.  Example application/3gpp-ims+xml body (part)

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


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



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   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 field that apply to the "application/3gpp-ims+xml"
   body (part) used by 3GPP and are to be registered in the IANA
   registry for Mail Content Disposition Values and Parameters:

      o 3gpp-alternative-service: the body (part) contains 3GPP IM CN
      subsystem XML with the 'alternative-service' XML element as
      described in Section 4.2; and

      o 3gpp-service-info: the body (part) contains 3GPP IM CN subsystem
      XML with the 'service-info' XML element as described in Section
      4.3.


7.  Acknowledgements

   The author would like to thank Andrew Allen, Dean Willis, Cullen
   Jennings, Victor Pascual Avila, Christopher Wong, Gonzalo Camarillo
   and Paul Kyzivat 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.




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   [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 8)", 3GPP TS 24.229 V8.8.0, June 2009.


Appendix A.  Revision Information

A.1.  version 00
   1.  2008-02-12, Initial version

A.2.  version 01
   1.  2008-07-02, Updated reference and further aligned 3GPP TS 24.229
       and this document

A.3.  version 02
   1.  2009-03-01, Corrected "header" into "header field"

A.4.  version 03
   1.  2010-02-23, no changes
   2.  2011-02-09, no changes

A.5.  version 04
   1.  2010-09-28, Introduces the case of addressing the MIME body's use
       for indicating the need to re-register with the IMS
   2.  2010-09-28, Updates the reference to 3GPP TS 24.229
   3.  2010-09-28, Introduces a reference to
       draft-patel-ecrit-sos-parameter-10

A.6.  version 05
   1.  2011-02-09, Editorially correct "registeration context" into
       "registration context"
   2.  2011-02-09, Removed the reference to
       draft-patel-ecrit-sos-parameter-10

A.7.  version 06
   1.  2011-02-21, corrected, and changed, XML element name from "3gpp-
       ims" to "ims-3gpp"
   2.  2011-02-21, Updated address information of author

A.8.  version 07
   1.  2011-12-02, Updated address information of author





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A.9.  version 08
   1.  2012-27-03, Added a new background section 2.1 and renumbered
       existing sections
   2.  2012-27-03, Improved body handling text to not preclude multipart
       bodies
   3.  2012-27-03, Editorials


Author's Address

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

   Phone: unlisted
   Fax:   unlisted
   Email: jbakker@rim.com
































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