Network Working Group M. Garcia Internet Draft Ericsson Expires: October 2002 April 2002 Private SIP extension for Associated URI Status of this memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This document is an individual submission to the IETF. Comments should be directed to the authors. Abstract This memo describes a private extension to SIP in the form of a P-Associated-URI header. A UAC registers a URI to a registrar. Then the registrar informs the UAC of the associated URIs to its registered URI. This information is conveyed in the P-Associated-URI header, carried in a 200 OK response to a REGISTER request. Table of contents 1. Introduction......................................................2 2. Applicability statement...........................................2 3. The Associated URI header.........................................2 4. Syntax and definition.............................................2 Network Working Group Expiration 10/30/02 Page 1 Garcia The SIP Associated URL header April 2002 5. Usage.............................................................3 5.1 Procedures at the UA.............................................3 5.2 Procedures at the registrar......................................3 5.3 Procedures at the proxy..........................................3 6. Security Considerations...........................................3 7. IANA Considerations...............................................3 8. Author's Addresses................................................4 9. Acknowledgements..................................................4 10. References.......................................................4 10.1 Normative references............................................4 10.2 Informative references..........................................4 1. Introduction A UAC registers a SIP or SIPS URI to a registrar. The registrar may be aware of one or more associated SIP or SIPS URIs to the registered one. The registrar considers the associated URIs alias of the registered one. A subscriber typically is assigned with one or more URIs. This may be in the form of a SIP or SIPS URI. Typically a user will group some of this URIs, so that when one of them registers, the other are automatically associated at the registrar, and the user is allowed to insert any of them into the From header of any request. The effect is that the associated URIs are aliases of the registered URI. 2. Applicability statement The P-Associated-URI is applicable whenever the following circumstances are met: 1. The UAC sends a REGISTER message in order to register a URI. 2. The user has one or more URIs associated to the one that is registering. 3. The registrar wants to inform the user of the other associated URIs. 3. The Associated URI header The registrar inserts the P-Associated-URI header into the 200 OK response to a REGISTER request. The header is populated with a list of URIs that are associated to the registered URI. If the registrar supports the P-Associated-URI header, it always insert it in a 200 OK response to a REGISTER request, no matter whether the REGISTER was an initial registration, re-registration, or de-registration. 4. Syntax and definition Network Working Group Expiration 10/30/02 Page 2 Garcia The SIP Associated URL header April 2002 The P-Associated-URI is a SIP extension header. The syntax of the P- Associated-URI header is based on the ABNF of SIP [1] and its syntax is described as follows: P-Associated-URI = "P-Associated-URI" HCOLON addr-spec *(COMMA addr-spec) A P-Associated-URI header may be inserted into a 200 OK response for a REGISTER request. The allowable usage of headers is described in Table 2 of SIP [1]. The following additions to this table are needed for the P-Associated-URI header. Addition of P-Associated-URI to SIP Table 2: Header field where proxy ACK BYE CAN INV OPT REG PRA SUB NOT _____________________________________________________________________ P-Associated-URI 200 - - - - - - o - - - 5. Usage 5.1 Procedures at the UA A UAC may receive a P-Associated-URI header in the 200 OK response for a REGISTER. The header contains a list of associated URIs. The UAC can use any of the associated URIs to populate the From header field in a subsequent dialog. 5.2 Procedures at the registrar A registrar that receives and authorizes a REGISTER request, may automatically associate one or more URIs with the registered URI. The registrar, includes a P-Associated-URI header in the 200 OK response, and populates it with the list of associated URIs to the registered request. 5.3 Procedures at the proxy This memo does not define any procedures at the proxy. 6. Security Considerations The information returned in the header is not viewed as particularly sensitive. Rather, it is simply informational in nature, providing openness to the UE with regard to the automatic association performed by the registrar. If end-to-end protection is not used at the SIP layer, it is possible for proxies between the registrar and the UA to modify the contents of the header. This attack, while potentially annoying, should not have significant impacts. 7. IANA Considerations Network Working Group Expiration 10/30/02 Page 3 Garcia The SIP Associated URL header April 2002 This document defines the SIP extension header "P-Associated-URI" which should be included in the registry of SIP headers defined in SIP [1]. As required by the SIP change process [3] the SIP extension header name "Associated-URI" should also be registered in association with this extension. 8. Author's Addresses Miguel A. Garcia Ericsson FIN-02420, Jorvas, Finland Tel: +358 9299 3553 e-mail: miguel.a.garcia@ericsson.com 9. Acknowledgements The author would like to thank Andrew Allen, Gabor Bajko, Gonzalo Camarillo, Keith Drage, Georg Mayer, Dean Willis and the 3GPP CN1 WG members for the comments on this document. 10. References 10.1 Normative references 1. J. Rosenberg, H. S., etc, Session Initiation Protocol, RFC 3261 March 2002. 10.2 Informative references 2. M. Garcia et al, 3GPP requirements on SIP, draft-sipping-garcia- 3gpp-reqs-03.txt, work in progress. 3. S. Bradner, R. Mahy, A. Mankin, J. Ott, B. Rosen, D. Willis, SIP change process, draft-tsvarea-sipchange-01.txt, February 2002, work in progress. Network Working Group Expiration 10/30/02 Page 4