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Versions: (draft-wu-avt-retransmission-supression-rtp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 RFC 6642

Network Working Group                                              Q. Wu
Internet-Draft                                                    F. Xia
Intended status: Standards Track                                 R. Even
Expires: August 13, 2012                                          Huawei
                                                       February 10, 2012


               RTCP Extension for Third-party Loss Report
             draft-ietf-avtcore-feedback-supression-rtp-11

Abstract

   In a large RTP session using the RTCP feedback mechanism defined in
   RFC 4585, a feedback target may experience transient overload if some
   event causes a large number of receivers to send feedback at once.
   This overload is usually avoided by ensuring that feedback reports
   are forwarded to all receivers, allowing them to avoid sending
   duplicate feedback reports.  However, there are cases where it is not
   recommended to forward feedback reports, and this may allow feedback
   implosion.  This memo discusses these cases and defines a new RTCP
   third-party loss report that can be used to inform receivers that the
   feedback target is aware of some loss event, allowing them to
   suppress feedback.  Associated SDP signalling is also defined.

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 13, 2012.

Copyright Notice

   Copyright (c) 2012 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



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   (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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Format of RTCP Feedback Messages . . . . . . . . . . . . . . .  5
     4.1.  Transport Layer Feedback:  Third-party Loss Report . . . .  5
     4.2.  Payload Specific Feedback: Third-party Loss Report . . . .  6
   5.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  Example Use Cases  . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Source Specific Multicast (SSM) use case . . . . . . . . .  8
     6.2.  Unicast based Rapid Acquisition of Multicast Stream
           (RAMS) use case  . . . . . . . . . . . . . . . . . . . . .  8
     6.3.  RTP Transport Translator use case  . . . . . . . . . . . .  9
     6.4.  Multipoint Control Unit (MCU) use case . . . . . . . . . .  9
     6.5.  Mixer use case . . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 11
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     10.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 13
     A.1.  draft-ietf-avtcore-feedback-suppression-rtp-01 . . . . . . 13
     A.2.  draft-ietf-avtcore-feedback-suppression-rtp-02 . . . . . . 13
     A.3.  draft-ietf-avtcore-feedback-suppression-rtp-03 . . . . . . 14
     A.4.  draft-ietf-avtcore-feedback-suppression-rtp-04 . . . . . . 14
     A.5.  draft-ietf-avtcore-feedback-suppression-rtp-05 . . . . . . 14
     A.6.  draft-ietf-avtcore-feedback-suppression-rtp-06 . . . . . . 15
     A.7.  draft-ietf-avtcore-feedback-suppression-rtp-07 . . . . . . 15
     A.8.  draft-ietf-avtcore-feedback-suppression-rtp-08 . . . . . . 15
     A.9.  draft-ietf-avtcore-feedback-suppression-rtp-09 . . . . . . 16
     A.10. draft-ietf-avtcore-feedback-suppression-rtp-10 . . . . . . 16
     A.11. draft-ietf-avtcore-feedback-suppression-rtp-11 . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16







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1.  Introduction

   RTCP feedback messages [RFC4585] allow the receivers in an RTP
   session to report events and ask for action from the media source (or
   a delegated feedback target when using unicast RTCP feedback with SSM
   [RFC5760]).  There are cases where multiple receivers may initiate
   the same, or an equivalent message towards the same media source or
   the same feedback target.  When the receiver count is large, this
   behavior may cause transient overload of the media source, the
   network or both.  This is known as a "feedback storm" or a "NACK
   storm".  One common cause of such a feedback storm is receivers
   utilizing RTP retransmission [RFC4588] as a packet loss recovery
   technique, sending feedback using RTCP NACK messages [RFC4585]
   without proper dithering of the retransmission requests (e.g., not
   implementing the RFC 4585 dithering rules or sending NACKs to a
   feedback target that doesn't redistribute them to other receivers).

   Another use case involves video Fast Update requests.  A storm of
   these feedback messages can occur in conversational multimedia
   scenarios like multipoint video switching conference [RFC4587].  In
   this scenario, the receiver may lose synchronization with the video
   stream when speaker is changed in the middle of session.  Poorly
   designed receivers that blindly issue fast update requests (i.e.,
   Full Intra Request (FIR) described in [RFC5104]), can cause an
   implosion of FIR requests from receivers to the same media source.

   RTCP feedback storms may cause short term overload, and in extreme
   cases to pose a possible risk of increasing network congestion on the
   control channel (e.g.  RTCP feedback), the data channel, or both.  It
   is therefore desirable to provide a way of suppressing unneeded
   feedback.  This document specifies a new third-party loss report for
   this function.  It supplements the existing the use of RTCP NACK
   packet and further is more precise in the uses where the network is
   active to suppress feedback.  It tells receivers explicitly that
   feedback for a particular packet or frame loss is not needed for a
   period of time and can provide an early indication before the
   receiver reacts to the loss and invokes its packet loss repair
   machinery.  Section 6 provides some examples of when to send the
   Third Party Loss Report message.


2.  Terminology

   The keywords "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].





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3.  Protocol Overview

   This document extends the RTCP feedback messages defined in the
   Audio-Visual Profile with feedback (RTP/AVPF) [RFC4585] defining a
   Third Party Loss Report message.  The Third Party Loss Report message
   can be used by the intermediaries to inform the receiver that the
   sender of the Third Party Loss Report has received reports that the
   indicated packets were lost, and asks the receiver not to send
   feedback to it regarding these packets.  Intermediaries are variously
   referred to as Distribution source, Burst/Retransmission Sources
   (BRS), MCUs, RTP translator, or RTP mixers, depending on the precise
   use case described in section 6.

   RTCP Third Party Loss Report follows the similar format of message
   type as RTCP NACK or Full Intra Request Command.  However, the Third
   Party Loss Report is defined as an indication that the sender of the
   feedback has received reports that the indicated packets were lost,
   while NACK [RFC4585] just indicates that the sender of the NACK
   observed that these packets were lost.  The Third Party Loss Report
   (TPLR) message is generated by an intermediary that may not seen the
   actual packet loss.  It is sent following the same timing rule as
   sending NACK defined in [RFC4585].  The TPLR feedback message may be
   sent in a regular full compound RTCP packet or in an early RTCP
   packet, as per the RTP/AVPF rules.  Intermediaries in the network
   that receive a Third Party Loss Report SHOULD NOT send their own
   additional Third Party Loss Report messages for the same packet
   sequence numbers.  They should simply forward the Third Party Loss
   Report message received from upstream direction to the receiver(s),
   additionally, they may generate their own Third Party Loss Report
   that reports a set of the losses they see, which are different from
   ones reported in the Third Party Loss report they received.  The
   Third Party Loss Report does not have the retransmission request
   [RFC4588] semantics.

   When a receiver gets a Third Party Loss Report message, it should
   follow the rules for NACK suppression in RFC 4585 and refrain from
   sending a feedback request (e.g., NACK or FIR) for the missing
   packets reported in the message,which is dealt with in the same way
   as receiving NACK.

   To increase the robustness to the loss of a TPLR, TPLR may be
   retransmitted.  If the additional TPLR arrives at receiver, the
   receiver should deal with the additional TPLR in the same way as
   receiving the first TPLR for the same packet and no additional
   behavior for receiver is required.

   A receiver may have sent a Feedback message according to the RTP/AVPF
   scheduling algorithm of [RFC4585] before receiving a Third Party Loss



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   Report message, but further feedback messages for those sequence
   numbers SHOULD be suppressed for a period of time after receiving the
   TPLR.  Nodes that do not understand the Third Party Loss Report
   message will ignore it, and might therefore still send feedback
   according to the AVPF scheduling algorithm of [RFC4585].  The media
   source or intermediate nodes cannot be certain that the use of a
   Third Party Loss Report message actually reduces the amount of
   feedback it receives.


4.  Format of RTCP Feedback Messages

   This document registers two new RTCP Feedback messages for Third
   Party Loss Report.  Applications that are employing one or more loss-
   repair methods MAY use the Third Party Loss Report together with
   their existing loss-repair methods either for every packet they
   expect to receive, or for an application-specific subset of the RTP
   packets in a session.  In other words, receivers MAY ignore Third
   Party Loss Report messages, but SHOULD react to them unless they have
   good reason to still send feedback messages despite having been
   requested to suppress them.

4.1.  Transport Layer Feedback:  Third-party Loss Report

   This Third Party Loss Report message is an extension to the RTCP
   Transport Layer Feedback Report and identified by RTCP packet type
   value PT=RTPFB and FMT=TBD.

   Within the common packet header for feedback messages (as defined in
   section 6.1 of [RFC4585]), the "SSRC of packet sender" field
   indicates the source of the request, and the "SSRC of media source"
   denotes the media sender of the flow for which the indicated losses
   are being suppressed.

   The FCI field MUST contain one or more entries of transport layer
   third party loss Early Indication (TLLEI).  Each entry applies to the
   same media source identified by the SSRC contained in the SSRC of
   media source field of Feedback header.  The length of the TLLEI
   feedback message MUST be set to 2+1*N, where N is the number of FCI
   entries.

   The Feedback Control Information (FCI) for TLLEI uses the similar
   format of message Types defined in the section 6.2.1 of [RFC4585].
   The format is shown in Figure 1.







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         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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            PID                |             BLP               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Figure 1: Syntax of an FCI Entry in the TLLEI Feedback Message

   Packet ID (PID): 16 bits

      The PID field is used to specify a lost packet.  The PID field
      refers to the RTP sequence number of the lost packet.

   bitmask of lost packets (BLP): 16 bits

      The BLP allows for reporting losses of any of the 16 RTP packets
      immediately following the RTP packet indicated by the PID.  The
      BLP's definition is identical to that given in the section 6.2.1
      of [RFC4585].


4.2.  Payload Specific Feedback: Third-party Loss Report

   This message is an extension to the RTCP Payload Specific Feedback
   report and identified by RTCP packet type value PT=PSFB and FMT=TBD,
   which is used to suppress FIR [RFC5104]and PLI [RFC4585].

   Within the common packet header for feedback messages (as defined in
   section 6.1 of [RFC4585]), the "SSRC of packet sender" field
   indicates the source of the request, and the "SSRC of media source"
   is not used and SHALL be set to 0.  The SSRCs of the media senders to
   which this message applies are in the corresponding FCI entries.

   The Feedback Control Information (FCI) for a Payload Specific Third
   Party Loss Early Indication (PSLEI) consists one or more FCI entries.
   Each entry applies to a different media Source, identified by its
   SSRC. the content of which is depicted in Figure 2.  The length of
   the PSLEI feedback message MUST be set to 2+1*N, where N is the
   number of FCI entries.

   The format is shown in Figure 2.

         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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                              SSRC                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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      Figure 2: Syntax of an FCI Entry in the PSLEI Feedback Message

   Synchronization source (SSRC):32 bits

      The SSRC value of the media source that has already been aware the
      receiver lost synchronization with the video stream and signal to
      the receiver not sending a decoder refresh point.



5.  SDP Signaling

   The Session Description Protocol (SDP) [RFC4566] attribute, rtcp-fb,
   is defined in the Section 4 of [RFC4585] and may be used to negotiate
   the capability to handle specific AVPF commands and indications.  The
   ABNF for rtcp-fb is described in section 4.2 of [RFC4585].  In this
   section, we extend the rtcp-fb attribute to include the commands and
   indications that are described for third party loss report in the
   present document.

   In the ABNF [RFC5234] for rtcp-fb-val defined in [RFC4585], the
   feedback type "nack", without parameters, indicates use of the
   Generic NACK feedback format as defined in Section 6.2.1of [RFC4585].
   In this document, we define two parameters that indicate the third
   party loss supported for use with "nack", namely:

   o  "tllei" denotes support of transport layer third party loss early
      indication.

   o  "pslei" denotes support of payload specific third party loss early
      indication.

   The ABNF for these two parameters for "nack" is defined here (please
   refer to section 4.2 of [RFC4585] for complete ABNF syntax).

           rtcp-fb-val        =/ "nack" rtcp-fb-nack-param
           rtcp-fb-nack-param = SP "tllei"
                                   ;transport layer third party
                                   ; loss early indication
                               / SP "pslei"
                                   ;payload specific third party
                                   ; loss early indication
                               / SP token [SP byte-string]
                                   ; for future commands/indications
           token =     <as defined in section 9 of [RFC4566]>
           byte-string = <as defined in section 4.2 of [RFC4585] >

   Refer to Section 4.2 of [RFC4585] for a detailed description and the



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   full syntax of the "rtcp-fb" attribute.


6.  Example Use Cases

   The operation of feedback suppression is similar for all types of RTP
   sessions and topologies [RFC5117], however the exact messages used
   and the scenarios in which suppression is employed differ for various
   use cases.  The following sections outline some of the intended use
   cases for using the Third Party Loss Report for feedback suppression
   and give an overview of the particular mechanisms.

6.1.  Source Specific Multicast (SSM) use case

   In SSM RTP sessions as described in "RTP Control Protocol (RTCP)
   Extensions for Single-Source Multicast Sessions with Unicast
   Feedback" [RFC5760], one or more Media Sources send RTP packets to a
   Distribution Source.  The Distribution Source relays the RTP packets
   to the receivers using a source- specific multicast group.

   As outlined in the [RFC5760], there are two Unicast Feedback models
   that may be used for reporting, the Simple Feedback model and the
   Distribution Source Feedback Summary Model.  In the simple Feedback
   Model, there's no need for distribution source to create the Third
   Party Loss Report, instead, NACKs are reflected by the distribution
   source to the other Receivers.  However in the Distribution Source
   Feedback Summary model, the distribution source will not redistribute
   the NACK for some reason(e.g., to prevent revealing the identity or
   existence of a system sending NACK)and may send a Third Party Loss
   Report to the systems that were unable to receive the NACK, and won't
   receive the NACK via other means.  Since the summary feedback does
   not mandate the forwarding of NACK downstream.  The Third Party Loss
   Report can be generated at the distribution source when downstream
   loss is told (e.g., downstream loss report is received), which
   indicates to the receivers that they should not transmit feedback
   messages for the same loss event for a certain time.  Therefore the
   distribution source in the feedback summary model can be reasonably
   certain that it will help the situation by sending this Third Party
   Loss Report message to all the relevant receivers impacted by the
   packet loss.

6.2.  Unicast based Rapid Acquisition of Multicast Stream (RAMS) use
      case

   The typical RAMS architecture [RFC6285] may have several Burst/
   Retransmission Sources(BRS) behind the multicast source (MS) placed
   at the same level.  These BRSes will receive the primary multicast
   RTP stream from the media source and cache most recent packets after



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   joining multicast session.  If packet loss happens at the upstream of
   all the BRSs or the downstream of BRSes.  One of the BRSes or all the
   BRSes may send a NACK or TPLR message to the DS, where the SSRC in
   this NACK or TPLR message is the BRS that is sending the message.
   The DS forwards/reflects this message down on the primary SSM.  The
   details on how DS deal with this message is specified in
   [RETRANSMISSION-FOR-SSM].

6.3.  RTP Transport Translator use case

   A Transport Translator (Topo-Trn-Translator), as defined in [RFC5117]
   is typically forwarding the RTP and RTCP traffic between RTP clients,
   for example converting from multicast to unicast for domains that do
   not support multicast.  The translator may suffer a loss of important
   video packets.  In this case, the translator may forward TPLR message
   received from upstream in the same way as forwarding other RTCP
   traffic.  If the translator acting as the monitor [MONARCH]is aware
   of packet loss, it may use the SSRC of monitor as packet sender SSRC
   to create NACK message and send it to the receivers that is not aware
   of packet loss.

6.4.  Multipoint Control Unit (MCU) use case

   When the speaker is changed in a voice-activated multipoint video
   switching conference [RFC4587], an RTP mixer can be used to select
   the available input streams and forward them to each participants.
   If the MCU is doing a blind switch without waiting for a
   synchronization point on the new stream it can send a FIR to the new
   video source.  In this case the MCU should send a FIR suppression
   message to the new receivers. e.g., when the RTP Mixer starts to
   receive FIR from some participants it can suppress the remaining
   session participants from sending FIR by sending out a Third party
   Loss report message.

6.5.  Mixer use case

   A Mixer, in accordance with [RFC5117], aggregates multiple RTP
   streams from other session participants and generates a new RTP
   stream sent to the session participants.  In some cases, the video
   frames may get badly screwed up between media source and the mixer.
   In such case, the mixer need to check if the packet loss will result
   in PLI or FIR transmissions from most of the group by analyzing the
   received video.  If so the mixer may initiate FIR or PLI towards the
   media source on behalf of all the session participants and send out a
   Third party Loss report message to these session participants that
   may or are expected to send a PLI or FIR.  Alternatively, when the
   mixer starts to receive FIR or PLI from some participants and like to
   suppress the remaining session participants from sending FIR or PLI



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   by forwarding the FIR/PLI from one session participant to others.


7.  Security Considerations

   The defined messages have certain properties that have security
   implications.  These must be addressed and taken into account by
   users of this protocol.

   Spoofed or maliciously created feedback messages of the type defined
   in this specification can have the following implications:

   Sending the spurious Third Party Loss Report (e.g., the Third Party
   Loss Report with the wrong sequence number of lost packet) that
   causes missing RTP packets to not be repaired in a timely fashion.

   To prevent these attacks, there is a need to apply authentication and
   integrity protection of the feedback messages.  This can be
   accomplished against threats external to the current RTP session
   using the RTP profile that combines Secure RTP [RFC3711] and AVPF
   into SAVPF [RFC5124].

   Note that intermediaries that are not visible at the RTP layer that
   wish to send the Third Party Loss Reports on behalf of the media
   source can only do so if they spoof the SSRC of the media source.
   This is difficult in case SRTP is in use.  If the intermediary is
   visible at the RTP layer, this is not an issue, provided the
   intermediary is part of the security context for the session.

   Also note that endpoints that receive a Third Party Loss Report would
   be well-advised to ignore it, unless the security is in place to
   authenticate the sender of the Third Party Loss Report.  Accepting
   Third Party Loss Report from un-authenticated sender can lead to a
   denial of service attack, where the endpoint accepts poor quality
   media that could be repaired.


8.  IANA Consideration

   For use with "nack" [RFC4585], a joint sub-registry has been set up
   that registers the following two values:










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  The value registration for the attribute value "nack":

       Value name:     tllei
       Long name:      Transport Layer Third Party Loss Early Indication
       Usable with:    nack
       Reference:      RFC 4585.

       Value name:     pslei
       Long name:      Payload Specific Third Party
       Usable with:    nack
       Reference:      RFC 4585.

   The following value have been registered as one FMT value in the "FMT
   Values for RTPFB Payload Types" registry located at the time of
   publication at: http://www.iana.org/assignments/rtp-parameters

      RTPFB range
      Name           Long Name                         Value  Reference
      -------------- --------------------------------- -----  ---------
      TLLEI         Transport Layer Third Party         TBA1   [RFCXXXX]
                    Loss Early Indication

   The following value have been registered as one FMT value in the "FMT
   Values for PSFB Payload Types" registry located at the time of
   publication at: http://www.iana.org/assignments/rtp-parameters

   PSFB range
   Name           Long Name                             Value  Reference
   -------------- ---------------------------------     ----- ---------
   PSLEI         Payload Specific Third Party           TBA2   [RFCXXXX]
                 Loss Early Indication


9.  Acknowledgement

   The authors would like to thank David R Oran, Magnus Westerlund,
   Colin Perkins, Ali C. Begen, Tom VAN CAENEGEM, Ingemar Johansson S,
   Bill Ver Steeg, Jonathan Lennox, WeeSan Lee for their valuable
   comments and suggestions on this document.


10.  References

10.1.  Normative References

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.



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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              July 2006.

   [RFC4588]  Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
              Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
              July 2006.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
              "Codec Control Messages in the RTP Audio-Visual Profile
              with Feedback (AVPF)", RFC 5104, February 2008.

10.2.  Informative References

   [RFC5740]  Adamson, B., Bormann, C., Handley, M., and J. Macker,
              "NACK-Oriented Reliable Multicast (NORM) Transport
              Protocol", November 2009.

   [RFC6285]  Steeg, B., Begen, A., Caenegem, T., and Z. Vax, "Unicast-
              Based Rapid Acquisition of Multicast RTP Sessions",
              June 2011.

   [MONARCH]  Wu, Q., Hunt, G., and P. Arden, "Monitoring Architectures
              for RTP", June 2011.

   [RETRANSMISSION-FOR-SSM]
              Caenegem, T., Steeg, B., and A. Begen, "Retransmission for
              Source-Specific Multicast (SSM) Sessions", May 2011.

   [RFC5117]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 5117,
              January 2008.

   [RFC4587]  Even, R., "RTP Payload Format for H.261 Video Streams",
              RFC 4587, August 2006.

   [RFC5760]  Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
              Protocol (RTCP) Extensions for Single-Source Multicast
              Sessions with Unicast Feedback", RFC 5760, February 2010.



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   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, February 2008.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.


Appendix A.  Change Log

   Note to the RFC-Editor: please remove this section prior to
   publication as an RFC.

A.1.  draft-ietf-avtcore-feedback-suppression-rtp-01

   The following are the major changes compared to previous version:

   o  Remove the merge report from SSM use case and additional text to
      address report merging issue.

   o  Revise section 3 and section 6 to address FEC packet dealing issue
      and Leave how to repair packet loss beyond the scope.

   o  Modify the SSM use case and RAMS use case to focus on uses.

   o  Other Editorial changes.

A.2.  draft-ietf-avtcore-feedback-suppression-rtp-02

   The following are the major changes compared to previous version:

   o  In Section 4.1, fix typo: Section 4.3.1.1 of section [RFC5104]->
      section 6.2.1 of [RFC4585].

   o  In Section 3: Clarify how to deal with downstream loss using Third
      party loss report and upstream loss using NACK.

   o  Update title and abstract to focus on third party loss report.

   o  In Section 6.1: Update this section to explain how third party
      loss report is used to deal with downstream loss.

   o  In section 6.1.2: Update this section to explain how third party
      loss report is used to deal with downstream loss.






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   o  In section 6.2: Rephrase the text to discuss how BRS deal with the
      third party loss report.

A.3.  draft-ietf-avtcore-feedback-suppression-rtp-03

   The following are the major changes compared to previous version:

   o  In Appendix A, fix typo: Appendix A.  Appendix A.  -> Appendix A.

   o  Update abstract to clarify when third-party loss reports should be
      sent instead of NACKs.

   o  Update section 3 Paragraph 2 to differentiate when a third-party
      loss report should be used compared to a NACK.

   o  Update section 3 Paragraph 3 to explain when media source to send
      a third-party loss.

   o  Move specific rules for section 6.1.1 and section 6.1.2 to section
      6.1 as generic rules and delete section 6.1.1.

A.4.  draft-ietf-avtcore-feedback-suppression-rtp-04

   The following are the major changes compared to previous version:
   o  Reference Update.

   o  Clarify the use of the third party loss report in section 3 and
      section 6.1.1.

A.5.  draft-ietf-avtcore-feedback-suppression-rtp-05

   The following are the major changes compared to previous version:
   o  Remove 3rd and 4th paragraphs of section 6.1 and replaced them
      with 2nd and 3rd paragraphs of section 3.

   o  Remove section 6.1.1.1.

   o  Revise the last paragraph of section 1 to clarify the rationale of
      using new message.

   o  Update RTP transport translator case in section 6.3 to correct the
      use of the third party loss report.

   o  Update MCU case in section 6.4 to correct the use of the third
      party loss report.






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   o  Revise SSM use case to address multiple DS issue.

   o  References Update.

   o  Move one rationale on preventing sending unicast NACK in
      introduction section to SSM case section.

   o  Other Editorial changes to section 6.1, 6.1.1, 6.2.

A.6.  draft-ietf-avtcore-feedback-suppression-rtp-06

   The following are the major changes compared to previous version:

   o  A few Editorial changes to the whole document.

A.7.  draft-ietf-avtcore-feedback-suppression-rtp-07

   The following are the major changes compared to previous version:

   o  Restructuring the protocol overview section to clarify the round
      trip time calculation and receiver behavior to the additional
      TPLR.

   o  Restructuring the SSM use case section to focus on the use of
      TPLR.

   o  Editorial changes to the abstract, introduction, message format,
      use cases and IANA sections.

   o  References update

A.8.  draft-ietf-avtcore-feedback-suppression-rtp-08

   The following are the major changes compared to previous version:

   o  Clarify which RTT is used and how timer is refreshed in the
      section 3.

   o  Editorial changes to the Introduction, Protocol Overview, SDP
      Signaling, Message Format, Use case,Security Consideration and
      IANA sections.

   o  Remove Seq Nr field in the figure 2 for payload specific feedback.

   o  References reorganizing.






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A.9.  draft-ietf-avtcore-feedback-suppression-rtp-09

   The following are the major changes compared to previous version:

   o  Clarify to suppression interval with regard to how long to receive
      the retransmitted packet.  Treating TPLR in the same way as
      receiving NACK .Replace timer based approach with timeless based
      approach

A.10.  draft-ietf-avtcore-feedback-suppression-rtp-10

   The following are the major changes compared to previous version:

   o  Fix the definition of Synchronization source for TPLR in section
      4.2.
   o  Associate SDP parameters tllei and pslei with "nack".
   o  Remove the packet loss recovery from TPLR loss handling part.
   o  Other typo fixed.

A.11.  draft-ietf-avtcore-feedback-suppression-rtp-11

   The following are the major changes compared to previous version:

   o  Additional Editorial changes.


Authors' Addresses

   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: sunseawq@huawei.com


   Frank Xia
   Huawei
   1700 Alma Dr. Suite 500
   Plano, TX 75075
   USA

   Phone: +1 972-509-5599
   Email: xiayangsong@huawei.com






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   Roni Even
   Huawei
   14 David Hamelech
   Tel Aviv 64953
   Israel

   Email: even.roni@huawei.com












































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