Network Working Group P. Kyzivat Internet-Draft Huawei Updates: 5234 (if approved) January 31, 2013 Intended status: Standards Track Expires: August 4, 2013 CLUE Signaling draft-kyzivat-clue-signaling-00 Abstract This document specifies how signaling is conducted in the course of CLUE sessions. This includes how SIP/SDP signaling is applied to CLUE sessions as well as defining a CLUE-specific signaling protocol that complements SIP/SDP and supports negotiation of CLUE application level data. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. 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." This Internet-Draft will expire on August 4, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as Kyzivat Expires August 4, 2013 [Page 1]
Internet-Draft CLUE Signaling January 2013 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. CLUE-Specific Signaling Protocol . . . . . . . . . . . . . . . 3 3.1. CLUE Messages . . . . . . . . . . . . . . . . . . . . . . . 3 3.1.1. ADVERTISEMENT Message . . . . . . . . . . . . . . . . . 4 3.1.2. CONFIGURE Message . . . . . . . . . . . . . . . . . . . 4 3.1.3. Stand-alone messages or deltas? . . . . . . . . . . . . 4 3.1.4. other . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Message Acknowledgement . . . . . . . . . . . . . . . . . . 4 3.3. Message Sequencing . . . . . . . . . . . . . . . . . . . . 5 3.4. Message Transport . . . . . . . . . . . . . . . . . . . . . 5 3.5. Message Framing . . . . . . . . . . . . . . . . . . . . . . 6 3.6. other . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. CLUE use of SDP O/A . . . . . . . . . . . . . . . . . . . . . . 6 5. Coordination of CLUE protocol and SDP O/A . . . . . . . . . . . 6 6. CLUE requirements on SDP O/A . . . . . . . . . . . . . . . . . 6 7. SIP Signaling . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Interoperation with Legacy SIP Devices . . . . . . . . . . . . 7 9. CLUE over RTCWEB . . . . . . . . . . . . . . . . . . . . . . . 7 10. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . . 7 11. What else? . . . . . . . . . . . . . . . . . . . . . . . . . . 7 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 14. Security Considerations . . . . . . . . . . . . . . . . . . . . 8 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 15.1. Normative References . . . . . . . . . . . . . . . . . . . 8 15.2. Informative References . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Kyzivat Expires August 4, 2013 [Page 2]
Internet-Draft CLUE Signaling January 2013 1. Introduction This document specifies how signaling is conducted in the course of CLUE sessions. This includes how SIP/SDP signaling is applied to CLUE sessions as well as defining a CLUE-specific signaling protocol that complements SIP/SDP and supports negotiation of CLUE application level data. [Yes, this is a dup of the abstract for now. Eventually it should say more.] 2. Terminology 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 [RFC2119]. This document draws liberally from the terminology defined in the CLUE Framework [I-D.ietf-clue-framework]. Other terms introduced here: CLUE Channel: A reliable, bidirectional, transport mechanism used to convey CLUE messages. A CLUE channel consists of one SCTP stream in each direction over a DTLS/SCTP session. 3. CLUE-Specific Signaling Protocol The CLUE Framework [I-D.ietf-clue-framework] mentions a CLUE-specific protocol for the exchange of ADVERTISEMENT and CONFIGURE messages, but gives little detail. The Data Model [I-D.presta-clue-data-model-schema] specifies a model and XML representation for CLUE-related data, but doesn't currently specify exactly what data belongs in each message, or how messages are sequenced. This document provides the detail missing from those documents. 3.1. CLUE Messages CLUE messages are encoded in XML. The Data Model [I-D.presta-clue-data-model-schema] defines many/most of the elements from which CLUE messages are composed. The content of each individual CLUE message could be defined by reference to an XML element type defined in the Data Model. Or this document could itself define an XML element type for each message, with much of the Kyzivat Expires August 4, 2013 [Page 3]
Internet-Draft CLUE Signaling January 2013 content of those elements being drawn from the Data Model. Which approach to follow is TBD. 3.1.1. ADVERTISEMENT Message Most of the content needed for the ADVERTISEMENT message is already defined in the Data Model. But the Data Model has't been constructed with that in mind. So either the Data Model needs revision with a focus on the needs of signaling, or else additional schema is needed here. 3.1.2. CONFIGURE Message The CONFIGURE message should probably also be based primarily on data elements defined in the Data Model. The CONFIGURE message must make reference (explicitly or implicitly) to the ADVERTISEMENT message on which it is based. The mechanism for doing this must be specified. 3.1.3. Stand-alone messages or deltas? Each message exchanged within a CLUE session could contain a complete description of the state it wishes to achieve. Or each message could describe just the changes that it wishes to make to the current state. Or the protocol could support both message forms. Which direction to pursue is TBD. [Paul: while this does need to be decided, it is fundamentally just an optimization. IMO it does not have major impact on the other parts of this document, so I would prefer to continue deferring it until we are so far along with the remainder of the document that we can no longer defer it.] 3.1.4. other 3.2. Message Acknowledgement The CLUE channel is reliable, so there is no need for acknowledgement to guarantee delivery. But there is still a need for application-to- application acknowledgement to report that the message has been received, parsed, and found to be of an acceptable format. One possibility is to introduce separate ACK and/or NAK messages. Another possibility is to add a confirmation element to each CLUE message, so that confirmation can be piggybacked on the basic messages. Something concrete needs to be proposed. Kyzivat Expires August 4, 2013 [Page 4]
Internet-Draft CLUE Signaling January 2013 3.3. Message Sequencing There is a very basic introduction to this topic in section 9.4 (Message Flow) of the CLUE Framework [I-D.ietf-clue-framework]. That still mentions the Consumer Capability message, which we have decided to drop. Without that it would look like: Media Consumer Media Provider -------------- ------------ | | |<----- ADVERTISEMENT message --------| | | | | |-------- CONFIGURE message --------->| | | But we need much more than this, to show multiple CONFIGUREs per ADVERTISEMENT, interleaving of ADVERTISEMENTs and CONFIGUREs in both directions, etc. Message sequencing needs to be described at two levels: o Basic sequencing of the CLUE messages themselves, without regard for the SIP/SDP signaling that may be going on at the same time. This is useful to cover the basic concepts. That should be covered in this section. It provides context for understanding the more detailed treatment later. This could include some simple state machines. o In reality there is a complex dependency between CLUE signaling and SDP Offer/Answer exchanges carried in SIP signaling. So there is a need to describe the valid ways in which these two forms of signaling interact. That is covered in Section 5. 3.4. Message Transport CLUE messages are transported over CLUE channels. In a two-party CLUE session, a CLUE channel connects the two endpoints. In a CLUE conference, each endpoint has a CLUE channel connecting it to an MCU. (In conferences with cascaded mixers [RFC4353], two MCUs will be connected by a CLUE channel.) The transport mechanism used for CLUE messages is DTLS/SCTP as specified in [I-D.tuexen-tsvwg-sctp-dtls-encaps] and [I-D.ietf-mmusic-sctp-sdp]. A CLUE channel consists of one SCTP stream in each direction over a DTLS/SCTP session. The mechanism for establishing the DTLS/SCTP session is described in Section 4. Kyzivat Expires August 4, 2013 [Page 5]
Internet-Draft CLUE Signaling January 2013 3.5. Message Framing Message framing is provided by the SCTP transport protocol. Each CLUE message is carried in one SCTP message. 3.6. other 4. CLUE use of SDP O/A The CLUE channel is usually offered in the first SIP O/A exchange between two parties in an intended CLUE session. The offer of the CLUE channel is the indicator that this SIP session is proposing to establish a CLUE session. (However it is also acceptable to start with a non-CLUE SIP session and upgrade it to a CLUE session later.) The mechanism for negotiating a DTLS/SCTP connection is specified in [I-D.ietf-mmusic-sctp-sdp]. We need to specify how to select the specific pair of SCTP streams that comprise the CLUE channel. Any specific usage/conventions required for coordination of SDP offers and answers with the CLUE messages should also be described here. (We have a draft [I-D.even-clue-sdp-clue-relation] that can contribute to this.) 5. Coordination of CLUE protocol and SDP O/A This should include state machines and/or call flows. These will illustrate, and then provide normative rules for valid sequences of messages of both types. For instance this needs to show when SDP offers and answers must occur relative to an ADVERTISEMENT or CONFIGURE message that requires SDP changes. [THIS IS A VERY IMPORTANT PART OF THIS DOCUMENT!] 6. CLUE requirements on SDP O/A Any SDP extensions required by CLUE should be specified here. Then we will need to take action within MMUSIC to make those happen. This section should be empty and removed before this document becomes an RFC. Kyzivat Expires August 4, 2013 [Page 6]
Internet-Draft CLUE Signaling January 2013 7. SIP Signaling (Placeholder) This may be unremarkable. If so we can drop it. 8. Interoperation with Legacy SIP Devices This may just describe how the degenerate form of the general mechanisms work for legacy devices. Or it may describe special case handling that we mandate as part of CLUE. Or it may just discuss non-normative things for implementors should consider. 9. CLUE over RTCWEB We may want to rule this out of scope for now. But we should be thinking about this. 10. Open Issues Here are issues pertinent to signaling that need resolution. Resolution will probably result in changes somewhere in this document, but may also impact other documents. o While the preference is to multiplex multiple capture encodings over a single RTP session, this will not always be desirable or possible. The factors that prevent multiplexing may come from either the provider or the consumer. So the extent of multiplexing must be negotiated. The decision about how to multiplex affects the number and grouping of m-lines in the SDP. The endpoint of a CLUE session that sends an offer needs to know the mapping of capture encodings to m-lines for both sides. AFAIK this issue hasn't yet been considered at all. 11. What else? 12. Acknowledgements The team focusing on this draft consists of: Roni Even, Rob Hansen, Christer Holmberg, Paul Kyzivat, Simon Pietro-Romano, Roberta Presta. Paul's contributions are supported by collaboration with colleague Lennard Xiao on the study of CLUE signaling. Kyzivat Expires August 4, 2013 [Page 7]
Internet-Draft CLUE Signaling January 2013 The author list should be updated as people contribute substantial text to this document. 13. IANA Considerations TBD 14. Security Considerations TBD 15. References 15.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [I-D.ietf-clue-framework] Duckworth, M., Pepperell, A., and S. Wenger, "Framework for Telepresence Multi-Streams", draft-ietf-clue-framework-08 (work in progress), December 2012. [I-D.presta-clue-data-model-schema] Presta, R. and S. Romano, "An XML Schema for the CLUE data model", draft-presta-clue-data-model-schema-01 (work in progress), October 2012. [I-D.ietf-mmusic-sctp-sdp] Loreto, S. and G. Camarillo, "Stream Control Transmission Protocol (SCTP)-Based Media Transport in the Session Description Protocol (SDP)", draft-ietf-mmusic-sctp-sdp-03 (work in progress), January 2013. [I-D.tuexen-tsvwg-sctp-dtls-encaps] Jesup, R., Loreto, S., Stewart, R., and M. Tuexen, "DTLS Encapsulation of SCTP Packets for RTCWEB", draft-tuexen-tsvwg-sctp-dtls-encaps-01 (work in progress), July 2012. 15.2. Informative References [RFC4353] Rosenberg, J., "A Framework for Conferencing with the Session Initiation Protocol (SIP)", RFC 4353, Kyzivat Expires August 4, 2013 [Page 8]
Internet-Draft CLUE Signaling January 2013 February 2006. [I-D.even-clue-sdp-clue-relation] Even, R., "Signalling of CLUE and SDP offer/answer", draft-even-clue-sdp-clue-relation-01 (work in progress), October 2012. Author's Address Paul Kyzivat Huawei Email: pkyzivat@alum.mit.edu Kyzivat Expires August 4, 2013 [Page 9]