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rfc:rfc5002

Network Working Group G. Camarillo Request for Comments: 5002 G. Blanco Category: Informational Ericsson

                                                           August 2007
               The Session Initiation Protocol (SIP)
              P-Profile-Key Private Header (P-Header)

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

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.

Table of Contents

 1. Introduction ....................................................2
 2. Terminology .....................................................2
 3. Scenario ........................................................2
 4. Requirements ....................................................3
 5. P-Profile-Key Header Field Definition ...........................3
 6. Applicability ...................................................4
 7. IANA Considerations .............................................4
 8. Security Considerations .........................................5
 9. Acknowledgements ................................................5
 10. References .....................................................5
    10.1. Normative References ......................................5
    10.2. Informative References ....................................6

Author* Informational [Page 1] RFC 5002 P-Profile-Key P-Header August 2007

1. Introduction

 The 3rd-Generation Partnership Project (3GPP) IMS (IP Multimedia
 Subsystem) uses SIP [RFC3261] as its main signalling protocol.  (For
 more information on the IMS, a detailed description can be found in
 3GPP TS 23.228 [3GPP.23.228] and 3GPP TS 24.229 [3GPP.24.229]).  3GPP
 has identified a set of requirements that can be met, according to
 the procedures in [RFC3427], by defining a new SIP P-header.
 The remainder of this document is organized as follows.  Section 3
 describes the scenario considered by 3GPP and Section 4 discusses the
 requirements derived from this scenario.  Section 5 defines the P-
 Profile-Key header field, which meets those requirements, and Section
 6 discusses the applicability and scope of this new header field.
 Section 7 registers the P-Profile-Key header field with the IANA and
 Section 8 discusses the security properties of the environment where
 this header field is intended to be used.

2. Terminology

 HSS:     Home Subscriber Server.
 I-CSCF:  Interrogating - Call/Session Control Function.
 Public Service Identity:
          A SIP URI that refers to a service instead of a user.
 S-CSCF:  Serving - Call/Session Control Function.
 Wildcarded Public Service Identity:
          A set of Public Service Identities that match a regular
          expression and share the same profile.

3. 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
 [RFC4457].  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

Author* Informational [Page 2] RFC 5002 P-Profile-Key P-Header August 2007

 '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 [3GPP.23.003].
 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.  For
 example, if the user database receives a query for
 'sip:chatroom-657@example.com', the user database needs to go through
 all the Wildcarded Public Service Identity it has until it finds a
 matching one; in this case, 'sip:chatroom-!.*!@example.com'.  The
 process to find a matching 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 Service Identity, the
 user database needs to perform the matching process twice.  Having to
 perform that process twice can be avoided by having the first proxy
 obtain the Wildcarded Public Service 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 Service 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.

4. 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 keep the user database's size and maintenance
     manageable (e.g., storing individual Public Service Identities
     matching a Wildcarded Public Service Identity in the user
     database is not believed to be an acceptable solution).

5. 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.

Author* Informational [Page 3] RFC 5002 P-Profile-Key P-Header August 2007

 The augmented Backus-Naur Form (BNF) [RFC4234] 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 [RFC3261].  The format of Wildcarded Public Service
 Identities is defined in 3GPP TS 23.003 [3GPP.23.003].  They take the
 form of Extended Regular Expressions (ERE) as defined in Chapter 9 of
 IEEE 1003.1-2004 Part 1 [IEEE.1003.1-2004].
 The following is an example of a P-Profile-Key header field that
 contains a Wildcarded Public Service Identity:
    P-Profile-Key: <sip:chatroom-!.*!@example.com>

6. Applicability

 According to [RFC3427], 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 [RFC4457].)
 Typically, when SIP is used on the Internet, there are not multiple
 proxies with a trust relationship between them querying the same user
 database.  Consequently, the P-Profile-Key header field does not seem
 useful in a general Internet environment.

7. IANA Considerations

 This document defines a new SIP header field: P-Profile-Key.  This
 header field has been registered by the IANA in the SIP Parameters
 registry under the Header Fields subregistry.

Author* Informational [Page 4] RFC 5002 P-Profile-Key P-Header August 2007

8. 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.  The P-Profile-Key header field
 MUST NOT be used in environments that do not have these
 characteristics.
 The P-Profile-Key header field needs to be integrity protected to
 keep attackers from modifying its contents.  An attacker able to
 modify the contents of this header field could make the network apply
 a different service than the one corresponding to the request
 carrying the P-Profile-Key header field.
 The contents of the P-Profile-Key field need to be kept confidential.
 An attacker able to access the contents of this header field would
 obtain certain knowledge about the way services are structured in a
 given domain.

9. Acknowledgements

 Alf Heidermark and Timo Forsman provided input to this document.
 Miguel Angel Garcia-Martin performed an expert review on this
 document on behalf of the SIPPING working group.  Jon Peterson
 provided comments on this document.

10. References

10.1. Normative References

 [RFC3261]           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.
 [RFC3427]           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.
 [RFC4234]           Crocker, D. and P. Overell, "Augmented BNF for
                     Syntax Specifications: ABNF", RFC 4234, October
                     2005.

Author* Informational [Page 5] RFC 5002 P-Profile-Key P-Header August 2007

 [3GPP.23.003]       3GPP, "Numbering, addressing and identification",
                     3GPP TS 23.003 3.15.0, October 2006.
 [IEEE.1003.1-2004]  "Standard for information technology - portable
                     operating system interface (POSIX).  Base
                     definitions", IEEE  1003.1-2004, 2004.

10.2. Informative References

 [RFC4457]           Camarillo, G. and G. Blanco, "The Session
                     Initiation Protocol (SIP) P-User-Database
                     Private-Header (P-Header)", RFC 4457, April 2006.
 [3GPP.23.228]       3GPP, "IP Multimedia Subsystem (IMS); Stage 2",
                     3GPP TS 23.228 5.15.0, June 2006.
 [3GPP.24.229]       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 5.18.0, October
                     2006.

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

Author* Informational [Page 6] RFC 5002 P-Profile-Key P-Header August 2007

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 Copyright (C) The IETF Trust (2007).
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 contained in BCP 78, and except as set forth therein, the authors
 retain all their rights.
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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Author* Informational [Page 7]

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