Frame Marking RTP Header Extension
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This is an older version of an Internet-Draft whose latest revision state is "Active".
|Authors||Espen Berger , Suhas Nandakumar , Mo Zanaty|
|Last updated||2015-10-20 (Latest revision 2015-10-19)|
|RFC stream||Internet Engineering Task Force (IETF)|
ARTART Last Call review (of -13) by Martin Thomson Ready w/issues
|Additional resources||Mailing list discussion|
|Stream||WG state||WG Document|
|Associated WG milestone||
|IESG||IESG state||I-D Exists|
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Network Working Group E. Berger Internet-Draft S. Nandakumar Intended status: Standards Track M. Zanaty Expires: April 21, 2016 Cisco Systems October 19, 2015 Frame Marking RTP Header Extension draft-ietf-avtext-framemarking-00 Abstract This document describes a Frame Marking RTP header extension used to convey information about video frames that is critical for error recovery and packet forwarding in RTP middleboxes or network nodes. It is most useful when media is encrypted, and essential when the middlebox or node has no access to the media encryption keys. It is also useful for codec-agnostic processing of encrypted or unencrypted media, while it also supports extensions for codec-specific information. 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 April 21, 2016. Copyright Notice Copyright (c) 2015 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 Berger, et al. Expires April 21, 2016 [Page 1] Internet-Draft Frame Marking October 2015 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. Solution . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Mandatory Extension . . . . . . . . . . . . . . . . . . . 4 2.2. Layer ID Mappings . . . . . . . . . . . . . . . . . . . . 4 2.2.1. H265 LID Mapping . . . . . . . . . . . . . . . . . . 4 2.2.2. VP9 LID Mapping . . . . . . . . . . . . . . . . . . . 5 2.2.3. VP8 LID Mapping . . . . . . . . . . . . . . . . . . . 5 2.2.4. H264-SVC LID Mapping . . . . . . . . . . . . . . . . 5 2.2.5. H264 (AVC) LID Mapping . . . . . . . . . . . . . . . 5 2.3. Signaling information . . . . . . . . . . . . . . . . . . 6 2.4. Considerations on use . . . . . . . . . . . . . . . . . . 6 3. Security Considerations . . . . . . . . . . . . . . . . . . . 6 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 6.1. Normative References . . . . . . . . . . . . . . . . . . 7 6.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Many widely deployed RTP topologies used in modern voice and video conferencing systems include a centralized component that acts as an RTP switch. It receives voice and video streams from each participant, which may be encrypted using SRTP [RFC3711], or extensions that provide participants with private media via end-to- end encryption that excludes the switch. The goal is to provide a set of streams back to the participants which enable them to render the right media content. In a simple video configuration, for example, the goal will be that each participant sees and hears just the active speaker. In that case, the goal of the switch is to receive the voice and video streams from each participant, determine the active speaker based on energy in the voice packets, possibly using the client-to-mixer audio level RTP header extension, and select the corresponding video stream for transmission to participants; see Figure 1. In this document, an "RTP switch" is used as a common short term for the terms "switching RTP mixer", "source projecting middlebox", "source forwarding unit/middlebox" and "video switching MCU" as discussed in [I-D.ietf-avtcore-rtp-topologies-update]. Berger, et al. Expires April 21, 2016 [Page 2] Internet-Draft Frame Marking October 2015 +---+ +------------+ +---+ | A |<---->| |<---->| B | +---+ | | +---+ | RTP | +---+ | Switch | +---+ | C |<---->| |<---->| D | +---+ +------------+ +---+ Figure 1: RTP switch In order to properly support switching of video streams, the RTP switch typically needs some critical information about video frames in order to start and stop forwarding streams. o Because of inter-frame dependencies, it should ideally switch video streams at a point where the first frame from the new speaker can be decoded by recipients without prior frames, e.g switch on an intra-frame. o In many cases, the switch may need to drop frames in order to realize congestion control techniques, and needs to know which frames can be dropped with minimal impact to video quality. o Furthermore, it is highly desirable to do this in a way which is not specific to the video codec. Nearly all modern video codecs share common concepts around frame types. o It is also desirable to be able to do this for SRTP without requiring the video switch to decrypt the packets. SRTP will encrypt the RTP payload format contents and consequently this data is not usable for the switching function without decryption, which may not even be possible in the case of end-to-end encryption of private media. A comprehensive discussion of SFU considerations around codec agnostic selective forwarding of RTP media is described in [I-D.draft-aboba-avtcore-sfu-rtp] By providing meta-information about the RTP streams outside the encrypted media payload an RTP switch can do selective forwarding without decrypting the payload. This document provides a solution to this problem. 2. Solution The solution uses RTP header extensions as defined in [RFC5285]. A subset of meta-information from the video stream is provided as an RTP header extension to allow a RTP switch to do generic video switching handling of video streams encoded with different video codecs. Berger, et al. Expires April 21, 2016 [Page 3] Internet-Draft Frame Marking October 2015 2.1. Mandatory Extension The following information are extracted from the media payload: o S: Start of Frame (1 bit) - MUST be 1 in the first packet in a frame within a layer; otherwise MUST be 0. o E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame within a layer; otherwise MUST be 0. o I: Independent Frame (1 bit) - MUST be 1 for frames that can be decoded independent of prior frames, e.g. intra-frame, VPx keyframe, H.264 IDR [RFC6184], H.265 CRA/BLA; otherwise MUST be 0. o D: Discardable Frame (1 bit) - MUST be 1 for frames that can be dropped, and still provide a decodable media stream; otherwise MUST be 0. o B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends on the base layer; otherwise MUST be 0. o TID: Temporal ID (3 bits) - The base temporal quality starts with 0, and increases with 1 for each temporal layer/sub-layer. o LID: Layer ID (8 bits) - Identifies the spatial and quality layer encoded. NOTE:Given the opaque nature of the LID, consider having the layer structure information as RTCP SDES item (either in the RTCP SDES message or as the RTP SDES Header extension) to map the LIDs to specific resolutions and bitrates thus enabling the RTP Switch to make informed decisions The values of frame information can be carried as RTP header extensions encoded using the one-byte header as described in [RFC5285] as shown below. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID | LID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2. Layer ID Mappings 2.2.1. H265 LID Mapping The following shows H265-LayerID (6 bits) mapped to the generic LID field. Berger, et al. Expires April 21, 2016 [Page 4] Internet-Draft Frame Marking October 2015 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID |0|0| LayerID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2.2. VP9 LID Mapping The following shows VP9 Layer encoding information (4 bits for spatial and quality) mapped to the generic LID field. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0| RS| RQ| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2.3. VP8 LID Mapping The following shows the header extension for VP8 that contains no layer information. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2.4. H264-SVC LID Mapping The following shows H264-SVC Layer encoding information (3 bits for spatial and 4 bits quality) mapped to the generic LID field. 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID |0| DID | QID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.2.5. H264 (AVC) LID Mapping The following shows the header extension for H264 (AVC) that contains no layer information. Berger, et al. Expires April 21, 2016 [Page 5] Internet-Draft Frame Marking October 2015 0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ID=2 | L=1 |S|E|I|D|B| TID |0|0|0|0|0|0|0|0| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2.3. Signaling information The URI for declaring this header extension in an extmap attribute is "urn:ietf:params:rtp-hdrext:framemarkinginfo". It does not contain any extension attributes. An example attribute line in SDP: a=extmap:3 urn:ietf:params:rtp-hdrext:framemarkinginfo 2.4. Considerations on use The header extension values MUST represent what is already in the RTP payload. When a RTP switch needs to discard a received video frame due to congestion control considerations, it is RECOMMENDED that it preferably drop frames marked with the "discardable" bit. When a RTP switch wants to forward a new video stream to a receiver, it is RECOMMENDED to select the new video stream from the first switching point (I bit set) and forward the same. A RTP switch can request a media source to generate a switching point for H.264 by sending Full Intra Request (RTCP FIR) as defined in [RFC5104], for example. 3. Security Considerations In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP header extensions are authenticated but not encrypted. When header extensions are used some of the payload type information are exposed and is visible to middle boxes. The encrypted media data is not exposed, so this is not seen as a high risk exposure. 4. Acknowledgements Many thanks to Bernard Aboba, Jonathan Lennox for their inputs. Berger, et al. Expires April 21, 2016 [Page 6] Internet-Draft Frame Marking October 2015 5. IANA Considerations This document defines a new extension URI to the RTP Compact HeaderExtensions sub-registry of the Real-Time Transport Protocol (RTP) Parameters registry, according to the following data: Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo Description: Frame marking information for video streams Contact: email@example.com Reference: RFC XXXX Note to RFC Editor: please replace RFC XXXX with the number of this RFC. 6. References 6.1. Normative References [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 6.2. Informative References [I-D.ietf-avtcore-rtp-topologies-update] Westerlund, M. and S. Wenger, "RTP Topologies", draft- ietf-avtcore-rtp-topologies-update (work in progress), April 2013. [I-D.draft-aboba-avtcore-sfu-rtp] Aboba, B., "Codec-Independent Selective Forwarding", raft- aboba-avtcore-sfu-rtp-00 (work in progress), July 2015. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, July 2003, <http://www.rfc-editor.org/info/rfc3550>. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, DOI 10.17487/RFC3711, March 2004, <http://www.rfc-editor.org/info/rfc3711>. [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, "Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, February 2008, <http://www.rfc-editor.org/info/rfc5104>. Berger, et al. Expires April 21, 2016 [Page 7] Internet-Draft Frame Marking October 2015 [RFC5285] Singer, D. and H. Desineni, "A General Mechanism for RTP Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July 2008, <http://www.rfc-editor.org/info/rfc5285>. [RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP Payload Format for H.264 Video", RFC 6184, DOI 10.17487/ RFC6184, May 2011, <http://www.rfc-editor.org/info/rfc6184>. Authors' Addresses Espen Berger Cisco Systems Phone: +47 98228179 Email: firstname.lastname@example.org Suhas Nandakumar Cisco Systems 170 West Tasman Drive San Jose, CA 95134 US Email: email@example.com Mo Zanaty Cisco Systems 170 West Tasman Drive San Jose, CA 95134 US Email: firstname.lastname@example.org Berger, et al. Expires April 21, 2016 [Page 8]