SIP Working Group C. Holmberg Internet-Draft Ericsson Intended status: Informational May 15, 2008 Expires: November 16, 2008 Response Code for Indication of Terminated Dialog draft-ietf-sip-199-00.txt 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 November 16, 2008. Abstract This specification defines a new SIP response code, 199 Early Dialog Terminated, which a SIP entity can use to indicate upstream that an early dialog has been terminated. The response code can be used by a SIP entity, normally a forking SIP proxy, to allow the UAC to know that an early dialog has been terminated before it a final response is sent to the request. Holmberg Expires November 16, 2008 [Page 1] Internet-Draft 199 May 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Client behavior . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Server behavior . . . . . . . . . . . . . . . . . . . . . . . . 5 6. Proxy behavior . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Backward compability . . . . . . . . . . . . . . . . . . . . . 5 8. 199 Early Dialog Terminated . . . . . . . . . . . . . . . . . . 6 9. Usage with SDP offer/answer . . . . . . . . . . . . . . . . . . 6 10. Usage with 100rel . . . . . . . . . . . . . . . . . . . . . . . 6 11. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 15. Normative References . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . . 9 Holmberg Expires November 16, 2008 [Page 2] Internet-Draft 199 May 2008 1. Introduction As defined in SIP (Session Initiation Protocol) specification [RFC3261], an early SIP dialog is created when a non-100 provisional response is sent to the dialog initiation request (e.g. INVITE). The dialog is considered to be in early state until a final response is sent. When a proxy receives an initial request (outside an existing dialog, and without a pre-defined route set), it MAY forward it towards multiple remote destinations. When the proxy does that, it performs forking. When a forking proxy receives non-100 provisional responses, it forwards the responses upstream towards the sender of the associated request. When a forking proxy receives a 2xx final response, it forwards the response upstream towards the sender of the associated request. At that point the proxy normally sends a CANCEL request downstream towards all remote destinations where it previously sent the request associated with the 2xx final response, and from which it has yet not received a final response, in order to terminate associated outstanding early dialogs. When SIP entities upstream receive the 2xx final response they will automatically terminate other associated outstanding early dialogs. When a forking proxy receives a non-2xx final response, it does not always immediately forward the response upstream towards the sender of the associated request. Instead, the forking proxy "stores" it and waits for further final responses from remote destinations where the forked request was forwarded. At some point the proxy uses a specified mechanism to determine the "best" final response code, and forwards that final response upstream towards the sender of the associated request. When SIP entities upstream receive the non-2xx final response they will automatically terminate the session setup and all associated early dialogs. Since the forking proxy does not always immediately forward non-2xx final responses, SIP entities upstream (including the UA that initiated the request) do not know that a specific early dialog has been terminated, and the SIP entities keep possible resources associated with the early dialog until they receive a final response from the forking proxy. This specification defines a new SIP response code, 199 Early Dialog Terminated, which a forking proxy can use to indicate upstream that an early dialog has been terminated. The 199 response can also be sent by an UAS, prior to sending a non-2xx final response. SIP entities that receive the 199 provisional response MAY release Holmberg Expires November 16, 2008 [Page 3] Internet-Draft 199 May 2008 resources associated with the specific early dialog. 2. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119]. 3. Requirements REQ 1: It must be possible to indicate to the UAC that an early dialog has been terminated before a final response is sent. 4. Client behavior When a client receives a 199 Early Dialog Terminated provisional response it MAY release resources and procedures associated with the early dialog the 199 response is received on. Examples of resources and procedures are e.g. procedures for the establishment of media plane resources (bandwidth, radio, codecs etc), media security procedures or procedures related to NAT traversal. One example is when resources for a specific codec has been reserved only for the stream that is terminated. In that case the resources associated with that codec can be released. Another example is when pre-conditions are used. When the dialog is terminated, procedures and resources associated to the pre-conditions for that dialog can be released. Another example is when in-band security negotiation is used. When the dialog is terminated, procedures and resrouces associated with the in-band security negototiation for that dialog can be released. If the client is able to associate the 199 response with a specific media stream, it MAY choose to discard media on that specific media stream, it MAY release all resources associated with that media stream and it MAY start to process media streams received on other early diaogs. When the P-Early-Media header is used, a UA may trigger different actions depending on whether the header has been used for the terminated dialog. How the association between the dialog and the associated media stream is done is outside the scope of this document. Holmberg Expires November 16, 2008 [Page 4] Internet-Draft 199 May 2008 The UAC MAY use additional information (for example the final response which triggered the 199 response) received in the 199 response when initiating new sessions, if it is possible to avoid the new session initation request to be rejected. 5. Server behavior When a UAS wants to terminate a dialog it sends a non-2xx SIP final response, as specified in [RFC3261]. In addition, prior to sending the non-2xx SIP final response, the UAS MAY send a 199 response to indicate that the dialog is being terminated. 6. Proxy behavior When a proxy receives a 199 provisional response, the proxy MUST process the response as any other non-100 provisional responses. The proxy MUST forward the response upstream towards the sender of the associated request. The proxy MAY release resources it has reserved associated with the early dialog on which the response is received. When a forking proxy receives a non-2xx final response which terminates one or more early dialogs and the proxy does not intend to forward the final response immediately (due to the rules for a forking proxy) it MUST send a 199 provisional response, for each associated early dialog that it can associate with the final response, upstream towards the sender of the associated request. The 199 provisional response MUST contain a To header tag parameter, which identifies the early dialog that has been terminated. NOTE: Since the forking proxy is not required to maintain state of all forked legs, it may not be able to send a 199 provisional response for each early dialog associated with the received non-2xx final response. 7. Backward compability Since all SIP entities involved in a session setup do not necessarily support the specific meaning of the 199 Early Dialog Terminated provisional response, the sender of the response MUST be prepared to receive SIP requests associated with the dialog for which the 199 response was sent. If such request is received, and the receiver maintains state of the dialogs, the receiver MUST reply to such requests with a 481 final response. A UAC that receives a 199 response for an early dialog MUST NOT send any further requests on that dialog, except for a PRACK if the 199 response was sent Holmberg Expires November 16, 2008 [Page 5] Internet-Draft 199 May 2008 reliably, and PRACKs for other reliable provisional responses that are to be acknowledged. The 199 Early Dialog Terminated response code MUST NOT "replace" a final response. A final response MUST always be sent, after one or many 199 Early Dialog Terminated provisional responses have been sent. 8. 199 Early Dialog Terminated The 199 Early Dialog Terminated response code allows a SIP entity to indicate upstream that a specific dialog has been terminated, before a final response is sent by the entity. OPEN ISSUE: We need to discuss whether the To tag in the 199 identifies the dialog that has been terminated, and/or if some additional information element (e.g. SIP header) can be used, which would allow to indicate the termination of multiple dialogs in a single 199 response. OPEN ISSUE: We need to discuss whether, in addition to the dialog identifier, some additional information (e.g. the non-2xx final response which triggered the 199 response) should be provided in the 199 response. 9. Usage with SDP offer/answer A 199 Early Dialog Terminated provisional response MUST NOT contain a new SDP offer/answer message body, but the sender of the response MAY insert a copy of a previously sent offer/answer message body as otherwise allowed by the offer/answer rules for a provisional response. A forking proxy or a UAS MUST NOT trigger and send a 199 Early Dialog Terminated provisional response reliably in a situation where a reliable provisional response is required to contain an SDP offer/ answer message body, according to [RFC3262] and [RFC3264]. 10. Usage with 100rel When a 199 Early Dialog Terminated provisional response is sent, since it is only used for information purpose, the sender is not required to send it reliably [RFC3262] even if the 100rel option tag is present in the Require header of the associated request. Holmberg Expires November 16, 2008 [Page 6] Internet-Draft 199 May 2008 OPEN ISSUE: We need to discuss whether a proxy should send 199 reliably at all, since the proxy would have to terminate the associated PRACK, and support the logic associated with 100rel. If not sent, how would required 100rel affect the usage of 199? 11. Example The figure shows an example, where a proxy (P1) forks an INVITE received from UAC. The forked INVITE reaches UAS_2, UAS_3 and UAS_4, which send 18x provisional responses in order to create early dialogs between themselves and the UAC. UAS_2 and UAS_3 rejects the INVITE by sending a 4xx error response. When P1 receives the 4xx responses it immediately sends 199 Early Dialog Terminated responses, associated with the dialogs where the 4xx responses were received, towards the UAC. UAC P1 UAS_2 UAS_3 UAS_4 --- INVITE ------> --- INVITE (leg 2) -> --- INVITE (leg 3) ----------> --- INVITE (leg 4) -------------------> <-- 18x (leg 2) ----- <-- 18x (leg 2) -- <-- 18x (leg 3) -------------- <-- 18x (leg 3) -- <-- 18x (leg 4) ----------------------- <-- 18x (leg 4) -- <-- 4xx (leg 2) ----- <-- 199 (leg 2) -- <-- 4xx (leg 3) -------------- <-- 199 (leg 3) -- <-- 200 (leg 4) ----------------------- <-- 200 (leg 4) -- --- ACK (leg 4) -> --- ACK (leg 4) ----------------------> Figure 1: Example call flow 12. Security Considerations TBD Holmberg Expires November 16, 2008 [Page 7] Internet-Draft 199 May 2008 13. IANA Considerations This section registers a new SIP response code according to the procedures of RFC 3261. RFC Number: RFC XXXX [[NOTE TO IANA: Please replace XXXX with the RFC number of this specification]] Response Code Number: 199 Default Reason Phrase: Early Dialog Terminated 14. Acknowledgements Thanks to Paul Kyzivat, Dale Worley and Gilad Shaham for their input on the SIPPING mailing list. 15. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3261] 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. [RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of Provisional Responses in Session Initiation Protocol (SIP)", RFC 3262, June 2002. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. Author's Address Christer Holmberg Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: christer.holmberg@ericsson.com Holmberg Expires November 16, 2008 [Page 8] Internet-Draft 199 May 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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. 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, THE IETF TRUST 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. Intellectual Property 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. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Holmberg Expires November 16, 2008 [Page 9]