SIP Working Group C. Holmberg Internet-Draft Ericsson Expires: February 28, 2009 August 27, 2008 Response Code for Indication of Terminated Dialog draft-ietf-sip-199-01.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 February 28, 2009. 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 to indicate to the UAC that an early dialog has been terminated, before a final response is sent to the UAC. Holmberg Expires February 28, 2009 [Page 1] Internet-Draft 199 August 2008 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Client behavior . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Examples of resource types . . . . . . . . . . . . . . . . 5 5. Server behavior . . . . . . . . . . . . . . . . . . . . . . . 6 6. Proxy behavior . . . . . . . . . . . . . . . . . . . . . . . . 6 7. Backward compability . . . . . . . . . . . . . . . . . . . . . 6 8. 199 Early Dialog Terminated . . . . . . . . . . . . . . . . . 7 9. Usage with SDP offer/answer . . . . . . . . . . . . . . . . . 7 10. Usage with 100rel . . . . . . . . . . . . . . . . . . . . . . 7 11. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. Security Considerations . . . . . . . . . . . . . . . . . . . 8 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 13.1. IANA Registration of the 199 response code . . . . . . . . 8 13.2. IANA Registration of the 199 Option Tag . . . . . . . . . 9 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 15. Normative References . . . . . . . . . . . . . . . . . . . . . 9 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 Intellectual Property and Copyright Statements . . . . . . . . . . 11 Holmberg Expires February 28, 2009 [Page 2] Internet-Draft 199 August 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 can 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. It is possible to receive multiple 2xx final responses. When SIP entities upstream receive the first 2xx final response, and they do not to intend to accept subsequent 2xx final responses, they will automatically terminate other associated outstanding early dialogs. If additional 2xx final responses are received, for INVITE initiated dialogs those SIP entities will normally send a BYE request using the dialog identifier retrieved from the subsequent 2xx final response. NOTE: A UAC can use the Request-Disposition header [RFC3841] to request that proxies do not send CANCEL requests downstream once they have received the first final 2xx response. 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 UAC that initiated the request) do not know that a specific early dialog has Holmberg Expires February 28, 2009 [Page 3] Internet-Draft 199 August 2008 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 and a UAS 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 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 sends an initial request it MUST insert the 199 option- tag in the Supported header, which indicates that the client supports the 199 Early Dialog Terminated response code. When a client receives a 199 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. If multiple usages [RFC5057] are used within an early dialog, and it is not clear which dialogusage the 199 response terminates, SIP entities that keep dialog state SHALL NOT release resources associated with the early dialog when they receive the 199 response. If a client receives a 199 response on a dialog which has not previously been created (this can happen if a 199 response reaches the client before a 18x response) the client SHALL discard the 199 responses. Holmberg Expires February 28, 2009 [Page 4] Internet-Draft 199 August 2008 4.1. Examples of resource types Examples which benefit from resource-release are: 1. codec release - 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. 2. pre-conditions - when the dialog is terminated, procedures and resources associated to the pre-conditions for that dialog can be released. 3. in-band security negotiation - when the dialog is terminated, procedures and resrouces associated with the in-band security negototiation for that dialog can be released. 4. ICE [ref needed] mechanism - when the dialog is terminated, procedures and resrouces associated with the ICE related in-band procedures for that dialog can be released. 5. limited access resources - in case of forking and multiple stream there may not be possible to allow early media on all dialogs, so some dialogs may e.g. be set to "inactive". When a dialog is terminated, media can be allowed on other dialogs. 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. NOTE: When using SRTP [RFC3261], the secure media stream is bound to the crypto context setup for the dialog, and can be identified using the MKI of SRTP. If the client only has a single early dialog (other early dialogs may not have been established, or they may have been established and later terminated) when a 199 response is received for that early dialog, after the client has terminated the early dialog associated with the 199 response it will act as before the first early dialog was established. Holmberg Expires February 28, 2009 [Page 5] Internet-Draft 199 August 2008 5. Server behavior If the received intial request contains an 199 option tag, and the server has established an early dialog with the initiator of the request, the server MAY send a 199 response prior to sending a non- 200 final response towards the initiator of the request. If the server intends to send 199 responses, and if the server supports the procedures defined in [RFC3840], it SHALL during the registration procedure use the sip.extensions feature tag [RFC3840] to indicate support of the 199 response code. 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), and the UAC has indicated support of the 199 response code, the forking proxy 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 and responses associated with the dialog for which the 199 response was sent (a proxy may receive SIP messages from either direction). 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 Holmberg Expires February 28, 2009 [Page 6] Internet-Draft 199 August 2008 that dialog, except for requests which acknowledge reliable responses. 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 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. The To header tag value is used to identify the dialog. 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. NOTE: According to [RFC3262] and [RFC3264], if the INVITE request did not contain an SPD offer, the first relaible response (provisonal or final) MUST contain an SDP offer. However, since 199 is only sent on established early dialog, it will never be the first response sent. 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 [RFC3262] is present in the Require header of the associated request. When a forking proxy triggers a 199 response it MUST NOT be sent reliably. A UAS MAY send a 199 response reliably. 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, Holmberg Expires February 28, 2009 [Page 7] Internet-Draft 199 August 2008 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) ----- --- ACK (leg 2) ----> <-- 199 (leg 2) -- <-- 4xx (leg 3) -------------- --- ACK (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 13. IANA Considerations This section registers a new SIP response code and a new option tag, according to the procedures of RFC 3261. 13.1. IANA Registration of the 199 response code This section registers a new SIP response code, 199. The required information for this registration, as specified in RFC 3261, is: Holmberg Expires February 28, 2009 [Page 8] Internet-Draft 199 August 2008 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 13.2. IANA Registration of the 199 Option Tag This section registers a new SIP option tag, 199. The required information for this registration, as specified in RFC 3261, is: Name: 199 Description: This option tag is for indicating support of the 199 Early Dialog Terminated provisional response code. When present in a Supported header, it indicates that the UA supports the response code. When present in a Require header in a request, it indicates that the UAS MUST support the sending of the response code. 14. Acknowledgements Thanks to Paul Kyzivat, Dale Worley, Gilad Shaham, Francois Audet, Attila Sipos, Robert Sparks and Brett Tate 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. [RFC3420] Sparks, R., "Internet Media Type message/sipfrag", RFC 3420, November 2002. Holmberg Expires February 28, 2009 [Page 9] Internet-Draft 199 August 2008 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [RFC3840] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Indicating User Agent Capabilities in the Session Initiation Protocol (SIP)", RFC 3840, August 2004. [RFC3841] Rosenberg, J., Schulzrinne, H., and P. Kyzivat, "Caller Preferences for the Session Initiation Protocol (SIP)", RFC 3841, August 2004. [RFC5057] Sparks, R., "Multiple Dialog Usages in the Session Initiation Protocol", RFC 5057, November 2007. Author's Address Christer Holmberg Ericsson Hirsalantie 11 Jorvas 02420 Finland Email: christer.holmberg@ericsson.com Holmberg Expires February 28, 2009 [Page 10] Internet-Draft 199 August 2008 Full Copyright Statement Copyright (C) The IETF Trust (2008). 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