Network Working Group M. Garcia Internet Draft Ericsson Expires: November 2002 May 2002 Private Session Initiation Protocol extension for Associated Uniform Resource Identifiers 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 [1] that allows a registrar to return a set of Associated URIs to a UAC. We define the P-Associated-URI header, used in the 200 OK response to a REGISTER request or 200-class response to a SUBSCRIBE. The P-Associated-URI header transports the set of Associated URIs to the SIP URI that has been registered or subscribed. Table of contents 1. Introduction......................................................2 2. Applicability statement...........................................2 3. The Associated URI header.........................................2 Network Working Group Expiration 11/30/02 Page 1 Garcia The SIP Associated URI header May 2002 4. Syntax and definition.............................................3 5. Usage.............................................................3 5.1 Procedures at the UA.............................................3 5.2 Procedures at the registrar......................................4 5.3 Procedures at the proxy..........................................4 5.4 Procedures at the subscriber.....................................4 5.5 Procedures at the notifier.......................................4 6. Security Considerations...........................................4 7. IANA Considerations...............................................4 8. Author's Addresses................................................5 9. Acknowledgements..................................................5 10. References.......................................................5 10.1 Normative references............................................5 10.2 Informative references..........................................5 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 user 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 these 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. In a similar fashion, a subscriber may get the set of associated URIs to the subscribed one, in the 200-class response to the SUBSCRIBE request. 2. Applicability statement The P-Associated-URI is applicable when the following circumstances are met: 1. The UAC sends a REGISTER request in order to register a URI. 2. The registered URI has one or more URIs associated to him. 3. The registrar wants to inform the user of the other associated URIs. When used within the SIP-specific event notification [4], the P- Associated-URI is applicable when the following circumstances are met: 1. A subscriber sends a SUBSCRIBE request to a notifier. 2. The subscribed URI has one or more URIs associated to him. 3. The notifier wants to inform the subscriber of the other associated URIs. 3. The Associated URI header Network Working Group Expiration 11/30/02 Page 2 Garcia The SIP Associated URI header May 2002 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 inserts it in a 200 OK response to a REGISTER request, regardless of whether the REGISTER was an initial registration, re-registration, or de-registration. When the P-Associated-URI header is used within the SIP-specific event notification framework [4], then the notifier inserts it into the 200 OK or 202 Accepted response for a SUBSCRIBE request. The header is populated with a list of URIs that are associated to the subscribed URI. 4. Syntax and definition 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 or a 200-class response to a SUBSCRIBE request. The allowable usage of headers is described in Table 2 of SIP [1]. Addition of P-Associated-URI to the Table 2 in SIP [1], section 4.1 of the SIP-specific event notification [4], tables 1 and 2 in the SIP INFO method [5], tables 1 and 2 in Reliability of provisional responses in SIP [6], tables 1 and 2 in the SIP UPDATE method [7], tables 1 and 2 in the SIP extension for Instant Messaging [8] and table 1 in the SIP REFER method [9]: Addition of P-Associated-URI to SIP Table 2: Header field where proxy ACK BYE CAN INV OPT REG ___________________________________________________________ P-Associated-URI 2xx - - - - - o Header field SUB NOT PRA INF UPD MES REF _______________________________________________________________ P-Associated-URI o - - - - - - 5. Usage 5.1 Procedures at the UA Network Working Group Expiration 11/30/02 Page 3 Garcia The SIP Associated URI header May 2002 A UAC may receive a P-Associated-URI header in the 200 OK response for a REGISTER. The header value contains a list of associated URIs to the one that was registered. The UAC MAY use any of the associated URIs to populate the From header value, or any other SIP header value that provides information of the identity of the calling party, 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, MAY include a P-Associated-URI header in the 200 OK response, and populates it with the list of associated URIs to the registered URI. 5.3 Procedures at the proxy This memo does not define any procedures at the proxy. 5.4 Procedures at the subscriber A subscriber may receive a P-Associated-URI header in the 200-class response to a SUBSCRIBE request. The header value contains a list of associated URIs to the subscribed one. 5.5 Procedures at the notifier A notifier that supports this extension MAY insert the P-Associated- URI header in the 200-class response to a SUBSCRIBE requiest. The notifier populates it with the list of associated URIs to the subscribed URI. 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. The lack of encryption, either end-to-end or hop-by-hop, may lead to leak some privacy regarding the list of authorized identities. An eavesdropper could collect this information. Therefore it is RECOMMENDED that this extension is used in a secured environment, where encryption of SIP messages is provided either end-to-end or hop- by-hop. 7. IANA Considerations Network Working Group Expiration 11/30/02 Page 4 Garcia The SIP Associated URI header May 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, Rohan Mahy 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. 4. A. Roach, SIP-Specific Event Notification, RFC 3265, March 2002. 5. S. Donovan, The SIP INFO method, RFC 2976, October 2000. 6. J. Rosenberg, H. Schulzrinne, Reliability of Provisional Responses in SIP, RFC 3262, March 2002. 7. J. Rosenberg, The Session Initiation Protocol UPDATE Method, draft-ietf-sip-update-02.txt, April 2002, work in progress. 8. B. Campbell, J. Rosenberg, H. Schulzrinne, C. Huitema, D. Gurle, Session Initiation Protocol Extension for Instant Messaging, draft-ietf-sip-message-04, May 2002, work in progress. 9. R. Sparks, The REFER method, draft-sparks-sip-refer-split-00.txt, April 2002, work in progress. Network Working Group Expiration 11/30/02 Page 5 Garcia The SIP Associated URI header May 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. 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