SIP Working Group O. Levin Internet-Draft Microsoft Corporation Updates: 3515 (if approved) A. Johnston Expires: January 6, 2006 MCI July 5, 2005 Conveying Feature Tags with Session Initiation Protocol REFER Method draft-ietf-sip-refer-feature-param-00 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 January 6, 2006. Copyright Notice Copyright (C) The Internet Society (2005). Abstract This document extends the SIP REFER method, defined in RFC 3515, to convey feature parameters defined in RFC 3840. 1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this Levin & Johnston Expires January 6, 2006 [Page 1] Internet-Draft Feature Tags with SIP REFER July 2005 document are to be interpreted as described in RFC 2119 [1]. To simplify discussions of the REFER method and its extensions, three new terms are being used throughout the document: o REFER-Issuer: the UA issuing the REFER request o REFER-Recipient: the UA receiving the REFER request o REFER-Target: the UA designated in the Refer-To URI 2. Introduction This document extends the SIP [2] REFER method defined in RFC 3515 [3] to be used with feature parameters defined in RFC 3840 [4]. Feature tags are used by a SIP User Agent (UA) to convey to another UA information about capabilities and features. This information can be shared by a UA using a number of mechanisms including registration requests, OPTIONS responses, or shared in the context of a dialog by inclusion with a remote target URI (Uniform Resource Identifier), such as a Contact URI. Feature tag information can be very useful to another UA. It is especially useful prior to the establishment of a session. For example, if a UA knows (through an OPTIONS query, for example) that the remote UA supports both video and audio, the calling UA might call offering video in its session description. Another example is when a UA knows that a remote UA is acting as a focus and hosting a conference. In this case, the UA might first subscribe to the conference URI and find out details about the conference prior to sending an INVITE to join. This extension to the REFER method provides a mechanism by which the REFER-Issuer can provide this useful information about the REFER- Target capabilities and functionality to the REFER-Recipient by including feature tags in the Refer-To header field in a REFER request. 3. Definitions The Refer-To BNF from RFC 3515: Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) *(SEMI generic-param) is extended to: Refer-To = ("Refer-To" / "r") HCOLON ( name-addr / addr-spec ) *(SEMI refer-param) refer-param = generic-param / feature-param Levin & Johnston Expires January 6, 2006 [Page 2] Internet-Draft Feature Tags with SIP REFER July 2005 where feature-param is defined in Section 9 of RFC 3840 [4]. Note that if any URI parameters are present, the entire URI must be enclosed in "<" and ">". If no "<" and ">" are present, all parameters after the URI are header parameters, not URI parameters. 4. Examples 4.1 isfocus Feature Tag Usage The example below shows how the "isfocus" feature tag can be used by REFER-Issuer to tell the REFER-Recipient that the REFER-Target is a conference focus and, consequently, sending an INVITE will bring the REFER-Recipient into the conference: Refer-To: ;isfocus 4.2 Voice and Video Feature Tags Usage The example below shows how a REFER-Issuer can tell the REFER- Recipient that the REFER-Target supports audio and video and, consequently, that a video and audio session can be established by sending an INVITE to the REFER-Target: Refer-To: "Alice's Videophone" ;audio;video 4.3 Example with URI parameters and multiple feature tags The example below shows how the REFER-Issuer can tell the REFER- Recipient that the REFER-Target is a voicemail server. Note that the transport URI parameter is enclosed within the "<" and ">" so that it is not interpreted as a header parameter. Refer-To: ;actor="msg-taker";automata;audio 5. IANA Considerations This document requires no actions by IANA. Note that this document does not define any elements in the SIP Header Parameter Registry [5], since it incorporates media feature parameters instead of SIP header parameters. Levin & Johnston Expires January 6, 2006 [Page 3] Internet-Draft Feature Tags with SIP REFER July 2005 6. Security Considerations Feature tags can provide sensitive information about a user or a UA. As such, RFC 3840 cautions against providing sensitive information to another party. Once this information is given out, any use may be made of it, including relaying to a third party as in this specification. As a result, it is NOT RECOMMENDED that all feature tag information be passed using the mechanism described in this specification. Instead, only feature tags that directly relate to a requested operation should be used. For example, the "isfocus" feature tag has clear operation semantics and utility. However, the "mobility" or "class" feature tags have no obvious use in a REFER scenario and should not be included unless their application is defined in the future. A feature tag provided by a REFER-Issuer can not be authenticated or certified directly from the REFER request. As such, the REFER- Recipient MUST treat the information as hint. If the REFER-Recipient application logic or user's action depends on the presence of the expressed feature, the feature tag can be verified. For example, in order to do so, the REFER-Recipient can directly send an OPTIONS query to the REFER-Target over a secure (e.g. mutually authenticated and integrity protected) connection. This protects the REFER- Recipient against incorrect or malicious feature tags being sent. A REFER-Issuer MUST NOT create or guess feature tags - instead a feature tag included in a REFER SHOULD have been discovered in an authenticated and secure method (such as an OPTIONS response or from a remote target URI in a dialog) directly from the REFER-Target. 7. Acknowledgements The authors would like to thank Jonathan Rosenberg for providing helpful guidance to this work. 8. References 8.1 Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] 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. Levin & Johnston Expires January 6, 2006 [Page 4] Internet-Draft Feature Tags with SIP REFER July 2005 [3] Sparks, R., "The Session Initiation Protocol (SIP) Refer Method", RFC 3515, April 2003. [4] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. 8.2 Informative References [5] Camarillo, G., "The Internet Assigned Number Authority (IANA) Header Field Parameter Registry for the Session Initiation Protocol (SIP)", BCP 98, RFC 3968, December 2004. Authors' Addresses Orit Levin Microsoft Corporation One Microsoft Way Redmond, WA 98052 USA Phone: 425-722-2225 Email: oritl@microsoft.com Alan Johnston MCI 100 South 4th Street St. Louis, MO 63102 Email: alan.johnston@mci.com Levin & Johnston Expires January 6, 2006 [Page 5] Internet-Draft Feature Tags with SIP REFER July 2005 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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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2005). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Levin & Johnston Expires January 6, 2006 [Page 6]