Internet Engineering Task Force Flemming Andreasen MMUSIC Working Group Dave Oran INTERNET-DRAFT Dan Wing EXPIRES: August 2004 Cisco Systems February, 2004 Connectivity Preconditions for Session Description Protocol Media Streams 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 cite them other than as "work in progress". The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/lid-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This document defines a new connectivity precondition for the Session Description Protocol precondition framework described in RFC 3312. A connecitivity precondition can be used to delay session establishment or modification until media stream connectivity has been verified successfully. INTERNET-DRAFT Connectivity Preconditions February, 2004 1. Notational Conventions..........................................2 2. Introduction....................................................2 3. Connectivity Precondition Definition............................2 4. Examples........................................................3 5. Security Considerations.........................................5 6. IANA Considerations.............................................5 7. Acknowledgements................................................5 8. Authors' Addresses..............................................6 9. Normative References............................................6 10. Informative References..........................................6 Intellectual Property Statement......................................7 Acknowledgement......................................................8 1. Notational Conventions The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Introduction RFC 3312 defines the concept of a Session Description Protocol (SDP) [SDP] precondition, which is a condition that has to be satisfied for a given media stream in order for session establishment or modification to proceed. When the precondition is not met, session progress is delayed until the precondition is satisfied, or the session establishment fails. For example, RFC 3312 defines the Quality of Service precondition, which is used to ensure availability of network resources prior to establishing (i.e. alerting) a call. SIP sessions are typically established in order to setup one or more media streams. Even though a media stream may be negotiated successfully, the actual media stream itself may fail. For example, when there is a NAT or firewall in the media path, the media stream may not be received. The connectivity precondition defined in this document ensures, that session progress is delayed until media stream connectivity is established, or the session itself is abandoned. 3. Connectivity Precondition Definition The connectivity precondition type is defined by the string "con" and hence we modify the grammar found in RFC 3312 as follows: precondition-type = "con" | "qos" | token RFC 3312 defines support for two kinds of status types, namely segmented and end-to-end. The connectivity precondition-type Andreasen, Oran, Wing [Page 2] INTERNET-DRAFT Connectivity Preconditions February, 2004 defined here MUST be used with the end-to-end status type; use of the segmented status type is undefined. An entity that wishes to delay session establishment or modification until media stream connectivity has been established uses this precondition-type in an offer. When a connectivity precondition is received in an offer, session establishment or modification MUST be delayed until the connectivity precondition has been met, i.e. media stream connectivity has been established in the desired direction(s). The direction attributes are interpreted as follows: * send: The offerer/answerer is sending media stream packets to the other party, and the offerer/answer knows the other party is receiving those media stream packets. * recv: The offerer/answerer knows that the other party has ascertained media stream connectivity to it. If media stream connectivity in both directions is required, the desired status should be set to "sendrecv". Media stream connectivity can be ascertained in different ways and this document does not mandate any particular mechanism for doing so. It is however RECOMMENDED that the No-Op RTP payload format defined in [no-op] is supported by entities that support connectivity preconditions. This will ensure that all entities that support the connectivity preconditions have at least one common way of ascertaining connectivity. 4. Examples The call flow of Figure 1 shows a basic session establishment using connectivity preconditions and using RTP no-op. Note that not all SDP details are provided in the following. SDP1: A includes the end-to-end connectivity precondition with a desired status of "sendrecv"; this will ensure media stream connectivity in both directions before continuing with the session setup. Since media stream connectivity in either direction is unknown at this point, the current status is set to "none": m=audio 20000 RTP/AVP 0 96 c=IN IP4 192.0.2.1 a=rtpmap:96 no-op/8000 a=curr:con e2e none a=des:con mandatory e2e sendrecv SDP2: When B receives the offer, B sees the bidirectional connectivity preconditions. B can ascertain connectivity to A by Andreasen, Oran, Wing [Page 3] INTERNET-DRAFT Connectivity Preconditions February, 2004 use of the RTP no-op, however B needs A to inform it about connectivity in the other direction. Consequently, B includes a request for confirmation in the "receive" direction: m=audio 30000 RTP/AVP 0 96 a=rtpmap:96 no-op/8000 c=IN IP4 192.0.2.4 a=curr:con e2e none a=des:con mandatory e2e sendrecv a=conf:con e2e recv Meanwhile, B performs a connectivity check to A, which succeeds. Also, A performs a connectivity check to B, which also succeeds. SDP3: A now sends an UPDATE (5) to B to confirm the connectivity from A to B, as requested by B: m=audio 20000 RTP/AVP 0 96 a=rtpmap:96 no-op/8000 c=IN IP4 192.0.2.1 a=curr:con e2e send a=des:qos mandatory e2e sendrecv SDP4: Upon receiving the updated offer, B now knows that there is connectivity from A to B; connectivity from B to A was verified earlier. B therefore responds with an answer (6) which contains the current status of the connectivity precondition (i.e., sendrecv) from B's point of view: m=audio 30000 RTP/AVP 0 96 a=rtpmap:96 no-op/8000 c=IN IP4 192.0.2.4 a=curr:con e2e sendrecv a=des:con mandatory e2e sendrecv At this point in time, session establishment resumes and B returns a 180 (Ringing) response (7). Andreasen, Oran, Wing [Page 4] INTERNET-DRAFT Connectivity Preconditions February, 2004 A B | | |-------------(1) INVITE SDP1--------------->| | | |<------(2) 183 Session Progress SDP2--------| | | |<~~~~~ Connectivity check to A ~~~~~~~~~~~~~| | | |----------------(3) PRACK------------------>| | | |~~~~~ Connectivity to A OK ~~~~~~~~~~~~~~~~>| | | |<-----------(4) 200 OK (PRACK)--------------| | | |~~~~~ Connectivity check to B ~~~~~~~~~~~~~>| |<~~~~ Connectivity to B OK ~~~~~~~~~~~~~~~~~| | | |-------------(5) UPDATE SDP3--------------->| | | |<--------(6) 200 OK (UPDATE) SDP4-----------| | | |<-------------(7) 180 Ringing---------------| | | | | | | Figure 1: Example using the connectivity precondition 5. Security Considerations TBD 6. IANA Considerations IANA is hereby requested to register a RFC 3312 precondition type called "con" with the name "Connectivity precondition". The reference for this precondition type is the current document. 7. Acknowledgements The concept of a "connectivity precondition" is the result of discussions with numerous people over a long period of time; the authors greatly appreciate these contributions. Andreasen, Oran, Wing [Page 5] INTERNET-DRAFT Connectivity Preconditions February, 2004 8. Authors' Addresses Flemming Andreasen Cisco Systems, Inc. 499 Thornall Street, 8th Floor Edison, New Jersey 08837 USA EMail: fandreas@cisco.com David Oran Cisco Systems, Inc. 7 Ladyslipper Lane Acton, MA 01720 USA EMail: oran@cisco.com Dan Wing Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134 USA EMail: dwing@cisco.com 9. Normative References [RFC3312] G. Camarillo, W. Marshall, J. Rosenberg, "Integration of Resource Management and Session Initiation Protocol (SIP)", RFC 3312, October 2002. [RFC2327] M. Handley and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. 10. Informative References [RFC3551] H. Schulzrinne, and S. Casner "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 3550, July 2003. [NO-OP] F. Andreasen, D. Oran, and D. Wing, "RTP No-Op Payload Format", February 2004, http://search.ietf.org/internet-drafts/ draft-wing-avt-rtp-noop-00.txt, Work in Progress Andreasen, Oran, Wing [Page 6] INTERNET-DRAFT Connectivity Preconditions February, 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication 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 implementors or users of this specification can be obtained from the IETF Secretariat. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director. Full Copyright Statement Copyright(C) The Internet Society 2004. All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 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. Andreasen, Oran, Wing [Page 7] INTERNET-DRAFT Connectivity Preconditions February, 2004 Acknowledgement Funding for the RFC Editor function is currently provided by the Internet Society. Andreasen, Oran, Wing [Page 8]