DISPATCH Working Group                                    J. Bakker, Ed.
Internet-Draft                                  Research In Motion (RIM)
Intended status: Standards Track                       September 4, 2012
Expires: March 8, 2013


        Specification of 3GPP IM CN Subsystem XML body handling
          draft-bakker-dispatch-3gpp-ims-xml-body-handling-00

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 [5].  The applicability of these content-
   disposition values are limited to 3GPP IMS [5].  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

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   This Internet-Draft will expire on March 8, 2013.

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   to this document.  Code Components extracted from this document must
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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 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.  General . . . . . . . . . . . . . . . . . . . . . . . . 4
       4.2.2.  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.  General . . . . . . . . . . . . . . . . . . . . . . . . 5
       4.3.2.  Example application/3gpp-ims+xml body (part)  . . . . . 6

   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 6

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

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

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

   Appendix A.  Revision Information . . . . . . . . . . . . . . . . . 7
     A.1.  version 00  . . . . . . . . . . . . . . . . . . . . . . . . 7

   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7










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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 (3GPP) 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) [6] 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 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 content disposition has been defined for MIME type
   "application/3gpp-ims+xml" MIME type [5].  Sections 4.2 and 4.3 below
   show how a body (part) according to the MIME type is interpreted by
   different entities (UE and AS) in 3GPP IMS (each entity having a
   different content handler for the same MIME media type tag).  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 interpreted, implies that a single default content
   disposition value does not cover both cases.

   NOTE: An alternative with a more general applicable approach could
         e.g. be unique MIME media type tags, each associated with a
         content handler.  However, having unique MIME media type tags
         at this stage raises backwards compatibility concerns for the
         IP multimedia subsystem (IMS) [6].

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

4.2.1.  General

   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 can detect the emergency call and 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".




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   It is further possible that one or more UASes in the network
   experience service interruptions, e.g. when forwarding a (non-
   emergency) service request from a UAC.  Examples of this are when
   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 of the UAS) and the attempt to retrieve the user
   profile fails.  In such situations the UAS responds with a 504
   (Server Time-out), including a MIME body (part) and a Content-Type
   header field set to "application/3gpp-ims+xml".  Upon receiving this
   response, the UAC can create 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.  Security issues with usage of this mechanism in
   the general internet have not been evaluated.

4.2.2.  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

4.3.1.  General

   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
   4.3.2, an International Mobile Subscriber Identity (IMSI) is
   transferred.







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4.3.2.  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
   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,
   Paul Kyzivat, and Atle Monrad for their guidance and comments that
   contributed to the progression of this work.


8.  References



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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]  IANA, "Registry for Application Media Types".

   [6]  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 V8.20.0, June 2012.


Appendix A.  Revision Information

A.1.  version 00
   1.  Initial version for consideration by dispatch, based upon
       draft-bakker-sipping-3gpp-ims-xml-body-handling-08
   2.  Changed references to section 2.2 and 2.3 into 4.2 and 4.3,
       respectively.
   3.  Updated abstract and section 2 and section 4.1 to reflect
       discussions on the list
   4.  Various editorial comments
















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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

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








































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