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Versions: (draft-berger-avtext-framemarking) 00 01 02 03 04 05 06 07 08

Network Working Group                                          E. Berger
Internet-Draft                                             S. Nandakumar
Intended status: Standards Track                               M. Zanaty
Expires: January 19, 2017                                  Cisco Systems
                                                           July 18, 2016


                   Frame Marking RTP Header Extension
                   draft-ietf-avtext-framemarking-02

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 January 19, 2017.

Copyright Notice

   Copyright (c) 2016 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



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   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.  Key Words for Normative Requirements  . . . . . . . . . . . .   4
   3.  Frame Marking RTP Header Extension  . . . . . . . . . . . . .   4
     3.1.  Mandatory Extension . . . . . . . . . . . . . . . . . . .   4
     3.2.  Layer ID Mappings . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  H265 LID Mapping  . . . . . . . . . . . . . . . . . .   5
       3.2.2.  VP9 LID Mapping . . . . . . . . . . . . . . . . . . .   5
       3.2.3.  VP8 LID Mapping . . . . . . . . . . . . . . . . . . .   6
       3.2.4.  H264-SVC LID Mapping  . . . . . . . . . . . . . . . .   6
       3.2.5.  H264 (AVC) LID Mapping  . . . . . . . . . . . . . . .   6
     3.3.  Signaling information . . . . . . . . . . . . . . . . . .   6
     3.4.  Considerations on use . . . . . . . . . . . . . . . . . .   6
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   Many widely deployed RTP [RFC3550] 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",




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   "source forwarding unit/middlebox" and "video switching MCU" as
   discussed in [I-D.ietf-avtcore-rtp-topologies-update].

            +---+      +------------+      +---+
            | 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.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.








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2.  Key Words for Normative Requirements

   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].

3.  Frame Marking RTP Header Extension

   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 an RTP switch to do generic selective
   forwarding of video streams encoded with potentially different video
   codecs.

3.1.  Mandatory Extension

   The following information are extracted from the media payload and
   sent in the Frame Marking RTP header extension.

   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 layer starts with 0,
      and increases with 1 for each higher temporal layer/sub-layer.
   o  LID: Layer ID (8 bits) - Identifies the spatial and quality layer
      encoded.
   o  TL0PICIDX: Temporal Layer 0 Picture Index (8 bits) - Running index
      of base temporal layer 0 frames when TID is 0.  When TID is not 0,
      this indicates a dependency on the given index.

   The layer information contained in TID and LID convey useful aspects
   of the layer structure that can be utilized in selective forwarding.
   Without further information about the layer structure, these
   identifiers can only be used for relative priority of layers.  They
   convey a layer hierarchy with TID=0 and LID=0 identifying the base
   layer.  Higher values of TID identify higher temporal layers with
   higher frame rates.  Higher values of LID identify higher spatial or
   quality layers with higher resolutions and bitrates.




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   With further information, for example, possible future RTCP SDES
   items that convey full layer structure information, it may be
   possible to map these TIDs and LIDs to specific frame rates,
   resolutions and bitrates.  Such additional layer information may be
   useful to forwarding decisions in the RTP switch, but is beyond the
   scope of this memo.  The relative layer information is still useful
   for many selective forwarding decisions even without such additional
   layer information.

   The Frame Marking RTP header extension is encoded using the one-byte
   header or two-byte header as described in [RFC5285].  The one-byte
   header format is shown below and used for examples in this memo.  The
   two-byte header format is used when other two-byte header extensions
   are present in the same RTP packet, since mixing one-byte and two-
   byte extensions is not possible in the same RTP packet.

    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=2 |  L=2  |S|E|I|D|B| TID |   LID         |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



3.2.  Layer ID Mappings

3.2.1.  H265 LID Mapping

   The following shows H265-LayerID (6 bits) mapped to the generic LID
   field.

    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=2 |  L=2  |S|E|I|D|B| TID |0|0|  LayerID  |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.2.  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                   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=2 |  L=2  |S|E|I|D|B| TID |0|0|0|0| RS| RQ|    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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3.2.3.  VP8 LID Mapping

   The following shows the header extension for VP8 that contains no
   layer information.

    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=2 |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.4.  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                   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=2 |  L=2  |S|E|I|D|B| TID |0| DID |  QID  |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.5.  H264 (AVC) LID Mapping

   The following shows the header extension for H264 (AVC) that contains
   no layer information.

    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=2 |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.3.  Signaling information

   The URI for declaring this header extension in an extmap attribute is
   "urn:ietf:params:rtp-hdrext:framemarking".  It does not contain any
   extension attributes.

   An example attribute line in SDP:

      a=extmap:3 urn:ietf:params:rtp-hdrext:framemarking

3.4.  Considerations on use

   The header extension values MUST represent what is already in the RTP
   payload.




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   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.

4.  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.

5.  Acknowledgements

   Many thanks to Bernard Aboba, Jonathan Lennox, and Stephan Wenger for
   their inputs.

6.  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: espeberg@cisco.com
   Reference: RFC XXXX

   Note to RFC Editor: please replace RFC XXXX with the number of this
   RFC.

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.





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7.2.  Informative References

   [I-D.ietf-avtcore-rtp-topologies-update]
              Westerlund, M. and S. Wenger, "RTP Topologies", draft-
              ietf-avtcore-rtp-topologies-update-10 (work in progress),
              July 2015.

   [I-D.aboba-avtcore-sfu-rtp]
              Aboba, B., "Codec-Independent Selective Forwarding",
              draft-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>.

   [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: espeberg@cisco.com








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   Suhas Nandakumar
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Email: snandaku@cisco.com


   Mo Zanaty
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Email: mzanaty@cisco.com



































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