Network Working Group A. B. Roach Internet-Draft dynamicsoft Expires: February 3, 2004 August 5, 2003 A "Conflict" Response Code for the Session Initiation Protocol (SIP) draft-roach-sip-409-00 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 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 February 3, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document proposes an addition of a "409 Conflict" response code for the Session Initiation protocol. This response code is required for a number of application-specific purposes, and is expected to be useful in future extensions to the protocol. 1. Introduction The first published version of SIP, RFC 2543, included a "409 Conflict" response code borrowed from HTTP/1.1 [2]. When copied into SIP, however, this response code was unfortunately defined to apply to an extremely narrow use case. This single use case was subsequently deprecated by RFC 3261 [1]; seeing no further use for Roach Expires February 3, 2004 [Page 1] Internet-Draft SIP 409 Response Code August 2003 the 409 response code, the authors elected to removed it at the same time. Operational experience has demonstrated that various specialized applications occasionally encounter circumstances in which a request cannot be processed because doing so would result in an inconsistent or disallowed state. This document seeks to reinstate the 409 response code in a more general form so that such situations can be accurately signalled to UACs. 2. "409 Conflict" Response Code The 409 response is added to the "Client-Error" header field definition. "409 Conflict" is used to indicate that the request could not be completed due to a conflict with the current state of the resource. This code is only allowed in situations where it is expected that the user might be able to resolve the conflict and resubmit the request. Conflicts are most likely to occur in response to requests that create state in the network, such as REGISTER and SUBSCRIBE. The circumstances under which a 409 response code is returned are expected to be highly dependent on the application that the UAS provides. 3. Backwards Compatibility It should be noted that section 8.1.3.2 of RFC 3261 [1] defines UAC behavior upon receipt of an unrecognized response code. Under the behavior specified therein, a 409 response will be treated by a client that does not understand it as if it were a "400 Bad Request" response. The semantics defined for that response indicate that the UAC should not retry the same request without modification, which is generally a reasonable course of action to take in the case of a conflict. 4. Security Considerations It is not beleived that the addition of the described 409 response code has the ability to reveal sensitive information or provide any additional avenues for attack. 5. IANA Considerations This document defines an additional SIP response code, which is to be added to the method and response-code sub-registry under http:// www.iana.org/assignments/sip-parameters. Roach Expires February 3, 2004 [Page 2] Internet-Draft SIP 409 Response Code August 2003 Response Code Number: 409 Default Reason Phrase: Conflict References [1] 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. [2] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999. Author's Address Adam Roach dynamicsoft 5100 Tennyson Pkwy Suite 1200 Plano, TX 75024 US EMail: adam@dynamicsoft.com Roach Expires February 3, 2004 [Page 3] Internet-Draft SIP 409 Response Code August 2003 Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Roach Expires February 3, 2004 [Page 4]