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Roach 3 Internet-Draft dynamicsoft 4 Expires: February 3, 2004 August 5, 2003 6 A "Conflict" Response Code for the Session Initiation Protocol (SIP) 7 draft-roach-sip-409-00 9 Status of this Memo 11 This document is an Internet-Draft and is in full conformance with 12 all provisions of Section 10 of RFC2026. 14 Internet-Drafts are working documents of the Internet Engineering 15 Task Force (IETF), its areas, and its working groups. Note that 16 other groups may also distribute working documents as Internet- 17 Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at http:// 25 www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 This Internet-Draft will expire on February 3, 2004. 32 Copyright Notice 34 Copyright (C) The Internet Society (2003). All Rights Reserved. 36 Abstract 38 This document proposes an addition of a "409 Conflict" response code 39 for the Session Initiation protocol. This response code is required 40 for a number of application-specific purposes, and is expected to be 41 useful in future extensions to the protocol. 43 1. Introduction 45 The first published version of SIP, RFC 2543, included a "409 46 Conflict" response code borrowed from HTTP/1.1 [2]. When copied into 47 SIP, however, this response code was unfortunately defined to apply 48 to an extremely narrow use case. This single use case was 49 subsequently deprecated by RFC 3261 [1]; seeing no further use for 50 the 409 response code, the authors elected to removed it at the same 51 time. 53 Operational experience has demonstrated that various specialized 54 applications occasionally encounter circumstances in which a request 55 cannot be processed because doing so would result in an inconsistent 56 or disallowed state. This document seeks to reinstate the 409 57 response code in a more general form so that such situations can be 58 accurately signalled to UACs. 60 2. "409 Conflict" Response Code 62 The 409 response is added to the "Client-Error" header field 63 definition. "409 Conflict" is used to indicate that the request 64 could not be completed due to a conflict with the current state of 65 the resource. This code is only allowed in situations where it is 66 expected that the user might be able to resolve the conflict and 67 resubmit the request. 69 Conflicts are most likely to occur in response to requests that 70 create state in the network, such as REGISTER and SUBSCRIBE. The 71 circumstances under which a 409 response code is returned are 72 expected to be highly dependent on the application that the UAS 73 provides. 75 3. Backwards Compatibility 77 It should be noted that section 8.1.3.2 of RFC 3261 [1] defines UAC 78 behavior upon receipt of an unrecognized response code. Under the 79 behavior specified therein, a 409 response will be treated by a 80 client that does not understand it as if it were a "400 Bad Request" 81 response. The semantics defined for that response indicate that the 82 UAC should not retry the same request without modification, which is 83 generally a reasonable course of action to take in the case of a 84 conflict. 86 4. Security Considerations 88 It is not beleived that the addition of the described 409 response 89 code has the ability to reveal sensitive information or provide any 90 additional avenues for attack. 92 5. IANA Considerations 94 This document defines an additional SIP response code, which is to be 95 added to the method and response-code sub-registry under http:// 96 www.iana.org/assignments/sip-parameters. 98 Response Code Number: 409 100 Default Reason Phrase: Conflict 102 References 104 [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., 105 Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: 106 Session Initiation Protocol", RFC 3261, June 2002. 108 [2] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., Masinter, L., 109 Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol -- 110 HTTP/1.1", RFC 2616, June 1999. 112 Author's Address 114 Adam Roach 115 dynamicsoft 116 5100 Tennyson Pkwy 117 Suite 1200 118 Plano, TX 75024 119 US 121 EMail: adam@dynamicsoft.com 123 Full Copyright Statement 125 Copyright (C) The Internet Society (2003). All Rights Reserved. 127 This document and translations of it may be copied and furnished to 128 others, and derivative works that comment on or otherwise explain it 129 or assist in its implementation may be prepared, copied, published 130 and distributed, in whole or in part, without restriction of any 131 kind, provided that the above copyright notice and this paragraph are 132 included on all such copies and derivative works. However, this 133 document itself may not be modified in any way, such as by removing 134 the copyright notice or references to the Internet Society or other 135 Internet organizations, except as needed for the purpose of 136 developing Internet standards in which case the procedures for 137 copyrights defined in the Internet Standards process must be 138 followed, or as required to translate it into languages other than 139 English. 141 The limited permissions granted above are perpetual and will not be 142 revoked by the Internet Society or its successors or assigns. 144 This document and the information contained herein is provided on an 145 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 146 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 147 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 148 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 149 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 151 Acknowledgement 153 Funding for the RFC Editor function is currently provided by the 154 Internet Society.