SIPPING Working Group J. Bakker, Ed.
Internet-Draft Research in Motion (RIM)
Intended status: Experimental March 2, 2009
Expires: September 3, 2009
Specification of 3GPP IM CN Subsystem XML body handling
draft-bakker-sipping-3gpp-ims-xml-body-handling-02
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Abstract
This document registers new disposition-types for the Content-
Disposition header field 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.
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. 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
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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. 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">
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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">
262013564857956
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 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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3. 2009-03-01, Corrected "header" into "header field"
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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