SIPPING Working Group G. Camarillo Internet-Draft G. Blanco Expires: March 16, 2007 Ericsson September 12, 2006 The Session Initiation Protocol (SIP) P-Profile-Key Private Header (P-Header) draft-camarillo-sipping-profile-key-01.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on March 16, 2007. Copyright Notice Copyright (C) The Internet Society (2006). 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. Camarillo & Blanco Expires March 16, 2007 [Page 1] Internet-Draft P-Profile-Key P-Header September 2006 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 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 [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 Camarillo & Blanco Expires March 16, 2007 [Page 2] Internet-Draft P-Profile-Key P-Header September 2006 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 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 avoid storing individual Public Service Identities matching a Wildcarded Public Service Identity in the user database. 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. The augmented Backus-Naur Form (BNF) [2] syntax of the P-Profile-Key Camarillo & Blanco Expires March 16, 2007 [Page 3] Internet-Draft P-Profile-Key P-Header September 2006 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: 6. 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].) Typically, when SIP is used on the Internet, there are no 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 needs to be registered by the IANA ni the SIP Parameters registry under the Header Fields subregistry. Camarillo & Blanco Expires March 16, 2007 [Page 4] Internet-Draft P-Profile-Key P-Header September 2006 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 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 Gacia-Martin performed an expert review on this document on behalf of the SIPPING working group. 10. References 10.1. Normative References [1] 3GPP, "Numbering, addressing and identification", 3GPP TS 23.003 7.0.0, June 2006. [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. Camarillo & Blanco Expires March 16, 2007 [Page 5] Internet-Draft P-Profile-Key P-Header September 2006 10.2. Informative References [5] 3GPP, "IP Multimedia Subsystem (IMS); Stage 2", 3GPP TS 23.228 7.4.0, June 2006. [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 7.4.0, June 2006. [7] Camarillo, G. and G. Blanco, "The Session Initiation Protocol (SIP) P-User-Database Private-Header (P-Header)", RFC 4457, April 2006. Camarillo & Blanco Expires March 16, 2007 [Page 6] Internet-Draft P-Profile-Key P-Header September 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 Camarillo & Blanco Expires March 16, 2007 [Page 7] Internet-Draft P-Profile-Key P-Header September 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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