Internet DRAFT - draft-bakker-dispatch-3gpp-ims-xml-body-handling
draft-bakker-dispatch-3gpp-ims-xml-body-handling
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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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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