SIPPING Working Group G. Camarillo
Internet-Draft G. Blanco
Expires: December 2, 2006 Ericsson
May 31, 2006
The Session Initiation Protocol (SIP) P-Profile-Key Private Header
(P-Header)
draft-camarillo-sipping-profile-key-00.txt
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Abstract
This document specifies the SIP P-Profile-Key P-header. This header
field is used in the 3rd-Generation Partnership Project (3GPP) IMS
(IP Multimedia Subsystem) to provide SIP registrars and SIP proxy
servers with the key of the profile corresponding to the destination
SIP URI of a particular SIP request.
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1. Introduction
The 3rd-Generation Partnership Project (3GPP) IMS (IP Multimedia
Subsystem) uses SIP [3] as its main signalling protocol. (For more
information on the IMS, a detailed description can be found in 3GPP
TS 23.228 [5] and 3GPP TS 24.229 [6]). 3GPP has identified a set of
requirements that can be met, according to the procedures in RFC 3427
[4], by defining a new SIP P-header.
The remainder of this document is organized as follows. Section 2
describes the scenario considered by 3GPP and Section 3 discusses the
requirements derived from this scenario. Section 4 defines the
P-Profile-Key header field, which meets those requirements, and
Section 5 discusses the applicability and scope of this new header
field. Section 6 registers the P-Profile-Key header field with the
IANA and Section 7 discusses the security properties of the
environment where this header field is intended to be used.
2. Scenario
In the 3GPP IMS, there are scenarios where a set of proxies handling
a request need to consult the same user database, as described in
[7]. Those proxies typically use the destination SIP URI of the
request as the key for their database queries. Nevertheless, when a
proxy handles a Wildcarded Public Service Identity, the key to be
used in its database query is not the destination SIP URI of the
request, but a regular expression instead.
Public Service Identities are SIP URIs that refer to services instead
of users. That is, they address a specific application in an
Application Server. Wildcarded Public Service Identities are a set
of Public Service Identities that match a regular expression and
share the same profile. For example, the Public Service Identities
'sip:chatroom-12@example.com' and 'sip:chatroom-657@example.com'
would match the Wildcarded Public Service Identity 'sip:chatroom-
!.*!@example.com'. For a description of Wildcarded Public Service
Identities, see 3GPP TS 23.003 [1].
When a proxy queries the user database for a Public Service Identity
for which there is no profile in the user database, the user database
needs to find its matching Wildcarded Public Service Identity. The
process of finding a matching a Wildcarded Public Service Identity
can be computationally expensive, time consuming, or both.
When two proxies query the user database for the same Public Service
Identity, which matches a Wildcarded Public User Identity, the user
database needs to perform the matching process twice. Having to
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perform that process twice can be avoided by having the first proxy
obtain the Wildcarded Public User Identity from the user database and
transfer it, piggy-backed in the SIP message, to the second proxy.
This way, the second proxy can query the user database using the
Wildcarded Public User Identity directly.
An alternative, but undesirable, solution would consist of having the
user database store every Public Service Identity and its matching
Wildcarded Public Service Identity. The scalability and
manageability properties of this approach are considerably worse than
those of the approach described earlier.
3. Requirements
This section lists the requirements derived from the previous
scenario:
1. It is necessary to optimize the response time for session
establishment in the 3GPP IMS.
2. It is necessary to avoid storing individual Public Service
Identities matching a Wildcarded Public Service Identity in the
user database.
4. P-Profile-Key header field definition
This document defines the SIP P-Profile-Key P-header. The P-Profile-
Key P-header contains the key to be used by a proxy to query the user
database for a given profile.
The augmented Backus-Naur Form (BNF) [2] syntax of the P-Profile-Key
header field is the following:
P-Profile-Key = "P-Profile-Key" HCOLON (name-addr / addr-spec)
*( SEMI generic-param )
The format of HCOLON, name-addr, addr-spec, and generic-param are
defined in RFC 3261 [3]. The format of Wildcarded Public Service
Identities is defined in 3GPP TS 23.003 [1].
The following is an example of a P-Profile-Key header field that
contains a Wildcarded Public Service Identity:
P-Profile-Key: <chatroom-!.*!@example.com>
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5. Applicability
According to RFC 3427 [4], P-headers have a limited applicability.
Specifications of P-headers such as this RFC need to clearly document
the useful scope of the proposal, and explain its limitations and why
it is not suitable for the general use of SIP on the Internet.
The P-Profile-Key header field is intended to be used in 3GPP IMS
networks. This header field carries the key of a service profile,
that is stored in a user database referred to as HSS, between two
proxies, which are referred to as I-CSCF and S-CSCF. The I-CSCF and
the S-CSCF belong to the same administrative domain and share a
common frame of reference to the user database. The I-CSCF inserts
the P-Profile-Key header field into a SIP request and the S-CSCF
removes it before routing the request further. (For a description of
how an I-CSCF and an S-CSCF query the same user database for a single
request, see [7].)
When SIP is used on the Internet, there are typically no proxies
querying a user database between the UA sending an INVITE request and
the registrar. Consequently, the P-Profile-Key header field does not
seem useful in a general Internet environment.
6. IANA Considerations
This document defines a new SIP header field: P-Profile-Key. This
header field needs to be registered by the IANA ni the SIP Parameters
registry under the Header Fields subregistry.
7. Security Considerations
The P-Profile-Key defined in this document is to be used in an
environment where elements are trusted and where attackers are not
supposed to have access to the protocol messages between those
elements. Traffic protection between network elements is sometimes
achieved by using IPsec and sometimes by physically protecting the
network. In any case, the environment where the P-Profile-Key header
field will be used ensures the integrity and the confidentiality of
the contents of this header field.
8. Acknowledgements
Alf Heidermark and Timo Forsman provided input to this document.
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9. References
9.1. Normative References
[1] 3GPP, "Numbering, addressing and identification", 3GPP TS 23.003
3.14.0, January 2004.
[2] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 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] Mankin, A., Bradner, S., Mahy, R., Willis, D., Ott, J., and B.
Rosen, "Change Process for the Session Initiation Protocol
(SIP)", BCP 67, RFC 3427, December 2002.
9.2. Informative References
[5] 3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP TS 23.228
5.14.0, October 2005.
[6] 3GPP, "Internet Protocol (IP) multimedia call control protocol
based on Session Initiation Protocol (SIP) and Session
Description Protocol (SDP); Stage 3", 3GPP TS 24.229 5.16.0,
March 2006.
[7] Camarillo, G. and G. Blanco, "The Session Initiation Protocol
(SIP) P-User-Database Private-Header (P-Header)", RFC 4457,
April 2006.
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Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: Gonzalo.Camarillo@ericsson.com
German Blanco
Ericsson
Via de los Poblados 13
Madrid 28033
Spain
Email: German.Blanco@ericsson.com
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