MMUSIC WG R. Even Internet-Draft Huawei Technologies Intended status: Informational J. Lennox Expires: December 30, 2013 Vidyo Q. Wu Huawei Technologies June 28, 2013 The Session Description Protocol (SDP) Application Token Attribute draft-even-mmusic-application-token-00.txt Abstract The RTP fixed header includes the payload type number and the SSRC values of the RTP stream. RTP defines how you de-multiplex streams within an RTP session, but in some use cases applications need further identifiers in order to identify the application semantics associated with particular streams within the session. This document defines a mechanism to provide the mapping between the SSRCs of RTP streams and the application semantics by defining extensions to RTP and RTCP messages. 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 December 30, 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 Even, et al. Expires December 30, 2013 [Page 1] Internet-Draft SDP application token June 2013 (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 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Proposal for an Application ID token . . . . . . . . . . . . 4 3.1. RTCP SDES message . . . . . . . . . . . . . . . . . . . . 6 3.2. RTP Header Extension . . . . . . . . . . . . . . . . . . 6 4. Using Application ID token . . . . . . . . . . . . . . . . . 7 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 1. Introduction The RTP [RFC3550] header includes the payload type number and the SSRC values of the RTP stream. RTP defines how you de-multiplex streams within an RTP session, but in some use cases, applications need further identifiers in order to identify semantics associated with particular streams within the session. There is ongoing work to define how to support, using SDP [RFC4566], multiple RTP media streams in one or more m-lines that define a single RTP session (as specified in [RFC3550]). The work is addressing the WebRTC architecture [I-D.ietf-rtcweb-overview], and some work will be needed when looking for a general solution in MMUSIC that can be used for non-WebRTC systems. RTCWEB Plan A [I-D.roach-rtcweb-plan-a] that an m-line in SDP represents a single RTP stream. De-multiplexing is done by payload type (PT) number (which MUST be unique), and if unique PTs are not feasible, use SSRC information in the SDP to identify the RTP stream. RTCWEB Plan B [I-D.uberti-rtcweb-plan] takes a different approach, and creates a hierarchy within SDP; an m= line defines an "envelope", specifying codec and transport parameters, and [RFC5576] a=ssrc lines are used to describe individual media sources within that envelope. Even, et al. Expires December 30, 2013 [Page 2] Internet-Draft SDP application token June 2013 Each m-line defines multiple RTP streams. This requires that the SSRCs of all RTP streams in the session are declared before they appear as RTP streams. No plan [I-D.ivov-rtcweb-noplan] proposes using a single m-line for each media type but does not require that all SSRCs will be declared in the SDP. The de-multiplexing is done based on the unique PT numbers and the mapping of SSRC to the application usage may be done by application protocol. In web application, for example, the application specific signaling may use something like { "leftSSRC": "1234", "rightSSRC": "5678" }. Some applications may require more information about the usage of the RTP streams. For example, RTP streams from different cameras that need to be identified by the application in order to render them correctly, or a source that can send multiple versions of the same stream in different resolutions (Simulcast [I-D.westerlund-avtcore-rtp-simulcast]). SDP provides in [RFC4574] a "label" attribute that contains a token defined by an application and is used in its context. "Label" can be attached to m-lines in multiple SDP documents allowing the application to logically identify the media streams across SDP sessions when necessary. The "label" attribute is a token and does not provide any information about the content of the stream. [RFC4796] defines the "content" attribute providing information about the content of the stream, currently there is a small set of values for the content attribute. Both "label" and "content" attribute are SDP media-level attributes, so when an SDP m-line supports multiple RTP streams, this value is applicable to all sources described by the SDP m-line. There is a need to have a token that will allow the mapping between a single source (identified by an SSRC) in an m-line to the application logic (Source may be a single RTP stream identified by a unique SSRC). For example, SSRC1 is the RTP stream from the left camera and SSRC2 is the RTP stream from the right camera both can be specified in a single SDP m-line and may have the same PT number. 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[RFC2119] and indicate requirement levels for compliant RTP implementations. Even, et al. Expires December 30, 2013 [Page 3] Internet-Draft SDP application token June 2013 3. Proposal for an Application ID token As we saw in the previous section, there are tokens defined that could be used for the mapping, but they have existing usages and semantics, and tend to apply at media-level rather than source-level. In order to avoid overload of existing attributes, it is better to have a new token attribute that can identify a specific source corresponding to the application. This document defines such a new token, called "AppID". AppID is a general-purpose token associated with an RTP stream, allowing the semantics of the stream with a token to be defined by the application. This token may be mapped, for example, to a CLUE media capture using CLUE protocol [I-D.ietf-clue-framework], or to a specific resolution in a simulcast application described in the SDP . The token is chosen by the sender, and represents the RTP stream that will be sent to the receiver. The proposed token can be sent using SDP, RTCP SDES messages [RFC3550], or an RTP header extension [RFC5285] The SSRC mapping may be available to the receiver when receiving the RTP stream through the RTP header extension, but may also be available ahead of time via an RTCP SDES message conveyed before the source started sending, even if the receiver has not seen any RTP packets from this source like in a multipoint conference or in the SDP description. The receiver can receive new sources that may be of two kinds. o A new RTP stream replacing an existing RTP stream, in which case the AppID of the replaced RTP stream will be assigned to the new SSRC. o A new RTP stream requiring a different AppID, for example, when adding a presentation stream to an existing call with two video cameras from a room. The solution should support a RTP session as described using SDP. The RTP session may be specified using a single SDP m-line, or using Bundle [I-D.ietf-mmusic-sdp-bundle-negotiation], using more than one m-line. In the latter case, if the SSRCs of all RTP streams are not known in advance, the AppIDs associated with each m-line need to be available to the receiver in order to map each SSRC to a specific m-line configuration. Even, et al. Expires December 30, 2013 [Page 4] Internet-Draft SDP application token June 2013 To support these cases the document defines a new SDP media level attribute a=appID that can be used to list all the appIDs that an application may use. The appID syntax provides a token identifier and optional SDP attributes that describe the application usage if exists in SDP. Application usage in SDP may be, for example, an image attribute describing a simulcast application usage [I-D.westerlund-avtcore-rtp-simulcast]. Each value of the AppID maps to one SSRC at a time. When a new SSRC is mapped to an existing AppID using an RTP header extension or SDES message, it replaces the previous RTP stream for this application usage. The formal representation of the appID token is: appid-attribute = "appID:" tokenlist [SP attribute] tokenlist = token *("," token) ; The base definition of "attribute" is in [RFC4566]. ; (It is the content of "a=" lines.) Examples: The SSRCs of the streams are not known when the SDP offer is sent, two appID are specified and can be used for mapping to specific SSRCs in the application. m=video 49200 RTP/AVP 99 a=rtpmap:99 H264/90000 a=appID:2,3 The second example is when the application usage of the RTP steam is specified using SDP to provide different image resolutions. m=video 49200 RTP/AVP 98, 99 a=rtpmap:98 H264/90000 a=rtpmap:99 H264/90000 a=appID:2 imageattr:98 send [x=480,y=320] recv * Even, et al. Expires December 30, 2013 [Page 5] Internet-Draft SDP application token June 2013 a=appID:3 imageattr:99 send [x=800,y=640] recv * 3.1. RTCP SDES message The document specify a new RTCP SDES message 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AppID = XXX | length |AppID token +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | .... This AppID is the same token as defined in the new SDP attribute and will also be used in the RTP header extension. This SDES message MAY be sent in a compound RTCP packet based on the application need. 3.2. RTP Header Extension The Application ID could be carried within the RTP header extension field, using [RFC5285] two bytes header extension. This is negotiated within the SDP i.e. a=extmap:1 urn:ietf:params:rtp-hdrext:App-ID Packets tagged by the sender with the AppID will then contain a header extension as shown below 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=1 | Len-1 | AppID +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AppID .............. | +-+-+-+-+-+-+-+-+ To add or modify the AppID by an intermediary can be an expensive operation, particularly if SRTP is used to authenticate the packet. Modification to the contents of the RTP header requires a re- authentication of the complete packet, and this could prove to be a limiting factor in the throughput of a multipoint device. Even, et al. Expires December 30, 2013 [Page 6] Internet-Draft SDP application token June 2013 There is no need to send the AppID header extension with all RTP packets. Senders MAY choose to send it only when a new SSRC is sent, or when an SSRC changes its association to an AppID. If such a mode is being used, the header extension SHOULD be sent in the first few RTP packets to reduce the risk of losing it due to packet loss. For codecs with decoder refresh points (such as I-Frames in video codecs), senders also SHOULD send the AppID header extension along with the packets carrying the decoder refresh. 4. Using Application ID token The usage of mapping may depend on the de-multiplexing of the RTP streams in the SDP m-lines. Currently we have three options discussed based on input from the RTCweb WG. For plan A [I-D.roach-rtcweb-plan-a], since each RTP stream is described by a specific m-line it will be enough to have a media level token for mapping the sent stream. Only need for example: m=video 49200 RTP/AVP 99 a=rtpmap:99 H264/90000 a=appID 2 For plan B [I-D.uberti-rtcweb-plan] which adds another level of RTP stream description, the mapping of SSRC to the application will need to be at the SSRC level base on [RFC5576] since all SSRCs are specified in the m-line. The document addresses the mapping of SSRCs using the SSRC attribute but uses the msid [I-D.ietf-mmusic-msid] that defines a specific semantics for each SSRC. The following offer example is using RFC5576 to provide source specific attribute identifier. m=video 49200 RTP/AVP a=rtpmap:99 H264/90000 a=max-send-ssrc:{*:3} a=max-recv-ssrc:{*:3} a=ssrc:11111 AppID:1 a=ssrc:22222 AppID:2 Even, et al. Expires December 30, 2013 [Page 7] Internet-Draft SDP application token June 2013 a=ssrc:33333 AppID:3 When using noplan [I-D.ivov-rtcweb-noplan] in MMUSIC, not all SSRCs will be known ahead of time. For example, in the following SDP the offer offers either two streams with the same resolution (for example two cameras) or two streams with different resolutions. m=video 5002 RTP/SAVPF 98 a=rtpmap:98 H264/90000 a= appID 1,2 imageattr:98 send [x=800,y=640,sar=1.1,q=0.6] recv * a= appID 3,4 imageattr:98 send [x=480,y=320] recv * a=max-send-ssrc:{*:2} In the CLUE WG case the mapping is from an RTP stream to a CLUE media capture specified in the CLUE framework [I-D.ietf-clue-framework]. The SSRCs of all streams may be known like in PLAN B but there are cases where the SDP may not be available so a pre-announce is recommended like in the following example. m=video 49200 RTP/AVP a=rtpmap:99 H264/90000 a=max-send-ssrc:{*:5} a=max-recv-ssrc:{*:3} a=ssrc:11111 AppID:1 a=ssrc:22222 AppID:2 a=ssrc:33333 AppID:3 a=appID 4, 5 The pre-announce is needed since the new RTCP SDES message includes only the SSRC and the appID but not the PT. A receiver of the SDES message will be able to map the SSRC to a codec configuration based on the SDP pre-announced tokens. 5. Acknowledgements Place Holder Even, et al. Expires December 30, 2013 [Page 8] Internet-Draft SDP application token June 2013 6. IANA Considerations TBD 7. Security Considerations TBD. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, July 2008. 8.2. Informative References [I-D.ietf-clue-framework] Duckworth, M., Pepperell, A., and S. Wenger, "Framework for Telepresence Multi-Streams", draft-ietf-clue- framework-10 (work in progress), May 2013. [I-D.ietf-mmusic-msid] Alvestrand, H., "Cross Session Stream Identification in the Session Description Protocol", draft-ietf-mmusic- msid-00 (work in progress), February 2013. [I-D.ietf-mmusic-sdp-bundle-negotiation] Holmberg, C., Alvestrand, H., and C. Jennings, "Multiplexing Negotiation Using Session Description Protocol (SDP) Port Numbers", draft-ietf-mmusic-sdp- bundle-negotiation-04 (work in progress), June 2013. [I-D.ietf-rtcweb-overview] Alvestrand, H., "Overview: Real Time Protocols for Brower- based Applications", draft-ietf-rtcweb-overview-06 (work in progress), February 2013. [I-D.ivov-rtcweb-noplan] Ivov, E., Marocco, E., and P. Thatcher, "No Plan: Economical Use of the Offer/Answer Model in WebRTC Even, et al. Expires December 30, 2013 [Page 9] Internet-Draft SDP application token June 2013 Sessions with Multiple Media Sources", draft-ivov-rtcweb- noplan-01 (work in progress), June 2013. [I-D.roach-rtcweb-plan-a] Roach, A. and M. Thomson, "Using SDP with Large Numbers of Media Flows", draft-roach-rtcweb-plan-a-00 (work in progress), May 2013. [I-D.uberti-rtcweb-plan] Uberti, J., "Plan B: a proposal for signaling multiple media sources in WebRTC.", draft-uberti-rtcweb-plan-00 (work in progress), May 2013. [I-D.westerlund-avtcore-rtp-simulcast] Westerlund, M., Lindqvist, M., and F. Jansson, "Using Simulcast in RTP Sessions", draft-westerlund-avtcore-rtp- simulcast-02 (work in progress), February 2013. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. [RFC4574] Levin, O. and G. Camarillo, "The Session Description Protocol (SDP) Label Attribute", RFC 4574, August 2006. [RFC4575] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session Initiation Protocol (SIP) Event Package for Conference State", RFC 4575, August 2006. [RFC4796] Hautakorpi, J. and G. Camarillo, "The Session Description Protocol (SDP) Content Attribute", RFC 4796, February 2007. [RFC5576] Lennox, J., Ott, J., and T. Schierl, "Source-Specific Media Attributes in the Session Description Protocol (SDP)", RFC 5576, June 2009. Authors' Addresses Roni Even Huawei Technologies Tel Aviv Israel Email: roni.even@mail01.huawei.com Even, et al. Expires December 30, 2013 [Page 10] Internet-Draft SDP application token June 2013 Jonathan Lennox Vidyo, Inc. 433 Hackensack Avenue Seventh Floor Hackensack, NJ 07601 US Email: jonathan@vidyo.com Qin Wu Huawei Technologies Email: bill.wu@huawei.com Even, et al. Expires December 30, 2013 [Page 11]