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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: March 3, 2012                                            Huawei
                                                         August 31, 2011


               RTCP Extension for Third-party Loss Report
             draft-ietf-avtcore-feedback-supression-rtp-06

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 a
   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
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   This Internet-Draft will expire on March 3, 2012.

Copyright Notice

   Copyright (c) 2011 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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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Protocol Overview  . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Format of RTCP Feedback Messages . . . . . . . . . . . . . . .  6
     4.1.  Transport Layer Feedback:  Third-party Loss Report . . . .  6
     4.2.  Payload Specific Feedback: Third-party Loss Report . . . .  7
   5.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  8
   6.  Example Use Cases  . . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Source Specific Multicast (SSM) use case . . . . . . . . .  9
     6.2.  Unicast based Rapid Acquisition of Multicast Stream
           (RAMS) use case  . . . . . . . . . . . . . . . . . . . . . 10
     6.3.  RTP transport translator use case  . . . . . . . . . . . . 11
     6.4.  Multipoint Control Unit (MCU) use case . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Acknowledgement  . . . . . . . . . . . . . . . . . . . . . . . 13
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     10.2. Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 15
     A.1.  draft-ietf-avtcore-feedback-suppression-rtp-01 . . . . . . 15
     A.2.  draft-ietf-avtcore-feedback-suppression-rtp-02 . . . . . . 15
     A.3.  draft-ietf-avtcore-feedback-suppression-rtp-03 . . . . . . 16
     A.4.  draft-ietf-avtcore-feedback-suppression-rtp-04 . . . . . . 16
     A.5.  draft-ietf-avtcore-feedback-suppression-rtp-05 . . . . . . 16
     A.6.  draft-ietf-avtcore-feedback-suppression-rtp-06 . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17






















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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.
   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 based, sending feedback using RTCP
   NACK messages [RFC4585] without proper dithering of the
   retransmission requests.

   Another use case involves video Fast Update requests.  A storm of
   these feedback messages can occur in conversational multimedia
   scenarios like Topo-Video-switch-MCU [RFC5117].  In this scenario,
   packet loss may happen on an upstream link of an intermediate network
   element such as a Multipoint Control Unit(MCU).  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.

   One approach to this, suggested in [DVB-IPTV], involves sending a
   NACK message to the other clients (or receiver) in the same group as
   the sender of NACK.  However NACK is defined as a receiver report
   sent from a receiver observing a packet loss, therefore it only
   inform others that sender of NACK detected loss while the case the
   sender of the feedback has received reports that the indicated
   packets were lost is not covered.  This document specifies a new
   third-party loss report for this function.  It further is more
   precise in the intended uses and less likely to be confusing to
   receivers.  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.






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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].


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 media source or 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.

   When a receiver gets a Third Party Loss Report message, it should
   refrain from sending a feedback request (e.g., NACK or FIR) for the
   missing packets reported in the message for a certain period of time.
   A receiver may still have sent a Feedback message according to the
   RTP/AVPF scheduling algorithm of [RFC4585]before receiving a Third
   Party Loss Report message, but further feedback messages for those
   sequence numbers will be suppressed by this technique for a certain
   period of time.  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 assume that the use of
   a Third Party Loss Report message actually reduces the amount of
   feedback it receives.

   RTCP Third Party Loss Report follows the similar format of message
   type as RTCP NACK.  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 message is generated by a
   system that has not seen the actual packet loss.  Systems that
   receive a Third Party Loss Report SHOULD NOT initiate their own
   additional Third Party Loss Report messages for the same packet
   sequence numbers.  They may either simply forward the Third Party
   Loss Report message, or 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.

   Since Third Party Loss Report interacts strongly with repair timing,



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   it has to work together with feedback to not adversely impact the
   repair of lost source packets.  One example is the middle box gets
   the retransmitted packet by sending a NACK upstream and sent it
   downstream.  This retransmitted packet was lost on the downstream
   link.  In order to deal with this, the downstream receiver can start
   a timeout in which it expected to get a retransmission packet.  When
   this timeout expires and there is no retransmitted packet or a new
   Third Party Loss Report message, it can take its normal behavior as
   if there is no current retransmission suppression.  In the case when
   the loss was detected and repair initiated much closer to the source,
   the delay for the receiver to recover from packet loss can be reduced
   through the combination of intermediary feedback to the source and
   Third Party Loss Report downstream.


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.

   The FCI field MUST contain one or more entries of transport layer
   third party loss Early Indication (TLLEI).  Each entry applies to a
   different media source, identified by its SSRC.

   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.

         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: Message Format for the Third Party Loss Report



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   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 proceeding 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 [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.

   The FCI field MUST contain a Payload Specific Third Party Loss Early
   Indication (PSLEI) entry.  Each entry applies to a different media
   source, identified by its SSRC.

   The Feedback Control Information (FCI) for PSLEI uses the similar
   format of message Types defined in the section 4.3.1.1 of [RFC5104].
   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                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Seq nr.   |                   Reserved                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

         Figure 2: Message Format for the Third Party Loss Report

   SSRC (32 bits):

      The SSRC value of the media source that is requested to send a
      decoder refresh point.

   Seq nr:8bits  Command sequence number.  The sequence number space is
      unique for each pairing of the SSRC of command source and the SSRC
      of the command target.  The sequence number SHALL be increased by
      1 modulo 256 for each new request.







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   Reserved: 24 bits

      All bits SHALL be set to 0 by the media source and SHALL be
      ignored on reception.



5.  SDP Signaling

   A new feedback value "tplr" needs to be defined for the Third Party
   Loss Report message to be used with Session Description Protocol
   (SDP) [RFC4566] using the Augmented Backus-Naur Form (ABNF)
   [RFC4585].

   The "tplr" feedback value SHOULD be used with parameters that
   indicate the third party loss supported.  In this document, we define
   two such parameter, 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.

   In the ABNF for rtcp-fb-val defined in [RFC4585], there is a
   placeholder called rtcp-fb-id to define new feedback types. "tplr" is
   defined as a new feedback type in this document, and the ABNF for the
   parameters for tplr is defined here (please refer to section 4.2 of
   [RFC4585] for complete ABNF syntax).

         rtcp-fb-val        =/ "tplr" rtcp-fb-tplr-param
         rtcp-fb-tplr-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
      byte-string = <as defined in section 4.2 of [RFC4585] >

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



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   and give an overview of the particular mechanisms.

6.1.  Source Specific Multicast (SSM) use case

   In SSM RTP sessions as described in [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.  Note that each receiver sending multicast
   NACK to its group may still need to send unicast NACK addressed to
   the media source or distribution source for lost packets, this may
   lead to a NACK storm if feedback suppression is not performed and if
   the RTCP bandwidth limit is misconfigured.

   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, NACKs are reflected by the distribution source to the other
   receivers, and there's no need for distribution source to create the
   Third Party Loss Report.  The Third Party Loss Report may be
   generated at the distribution source when downstream loss report is
   received in the Distribution Source Feedback Summary model, since
   this summary feedback does not mandate the forwarding of NACK
   downstream.

   In order to observe packet loss before the receivers perceive it, one
   or more intermediate nodes may be placed between the media source and
   the receivers.  These intermediaries monitor for upstream packet loss
   .  These intermediates may be Distribution source, MCUs, RTP
   translator, or RTP mixers, depending on the precise implementation.
   If an intermediary notices the loss itself, then it may send a NACK
   both downstream towards the receivers and upstream towards the media
   source, to indicate that it has noticed the loss, and to suppress
   feedback from other downstream receivers.  In the SSM case, If the
   distribution source ,using the simple feedback model, receives a NACK
   from another system (e.g.,an intermediary), it should redistribute
   that NACK to all other systems that would not otherwise receive it.
   If the distribution source, using the summary feedback model,
   receives a NACK from another system, but, for some reason(e.g., to
   prevent revealing the identity or existence of a system sending
   NACK), cannot redistribute that NACK, then it 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.  Therefore the intermediate
   node can be reasonably certain that it will help the situation by
   sending a Third Party Loss Report message to all the relevant
   receivers, thereby indicating to the receivers that they should not
   transmit feedback messages for a certain period of time.  The
   intermediate node needs to take into account such factors as the
   tolerable application delay, packet loss recovery techniques, the



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   network dynamics, and the media type.  Loss-repair methods such as
   retransmission and Forward Error Correction may be used to recover
   the missing packet.

   Alternatively, the media source may directly monitor the amount of
   feedback reports it receives from downstream.  If the media source
   notices the loss itself, then it may send a NACK downstream towards
   the receivers to suppress feedback.  If the media source receives a
   NACK from another system, it should redistribute that NACK to all
   other systems that would not otherwise receive it.  If the media
   source receives a NACK from another system, but, for some reason
   (e.g., hiding identity or existing a system sending NACK ), cannot
   redistribute that NACK, then it 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.

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 multicast SSM stream
   from the media source.  If one of the BRSes receives downstream loss
   report (i.e., First loss in Figure 3) on its downstream link, but the
   others BRSes have not, as the packet loss took place on the SSM tree
   branch that does not impact the other BRSes.  In such case, the BRSes
   not being impacted are not aware of downstream loss at their
   downstream link, therefore these BRSes will not create a new Third
   Party Loss Report message and send it to receivers in their
   downstream path.  If the BRS impacted by packet loss has been told
   the actual packet loss, the BRS MAY choose to create new Third Party
   Loss Report message and send it to the receivers in the downstream
   link.  Note that BRS must use its own SSRC as packet sender SSRC for
   transmitting the feedback suppress message.

   The BRS may also send a NACK upstream to request the retransmitted
   packet.  Upon receiving the retransmitted packet, the BRS sent it
   downstream.  Note that this retransmitted packet may get lost (i.e.,
   second loss in the Figure 3) on the downstream link.  In order to
   deal with this issue, the downstream receiver can start a timeout
   clock in which it expected to get a retransmission packet.  When this
   timeout expires and there is no retransmitted packet or a new Third
   Party Loss Report message, it can take its normal behavior as if
   there is no current retransmission suppression in place.







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                                     +------------+ First Loss +----------+
                                     |Burst and   |Second Loss |          |
                         +-----------| Retrans.   |----X--X--->|          |
                         | Upstream  |Source1(BRS)| Downstream |          |
           Link close    | link 1    +------------+ link 1     |          |
           to multicast  |                                     |          |
           source        |                                     |          |
                |        |                                     |          |
                |        |           +------------+            |   RTP    |
   +---------+  |  +-----++          |Burst and   |            | Receiver |
   |Multicast|  V| |      +----------| Retrans.   |----------->|          |
   | Source  +-----|Router|Upstream  |Source2(BRS)| Downstream |  RTP_Rx  |
   +---------+     |      |link 2    +------------+ link 2     |          |
                   +-----++                                    |          |
                         |                                     |          |
                         |                                     |          |
                         |                                     |          |
                         |           +------------+            |          |
                         |           |Burst and   |            |          |
                         +-----------+ Retrans.   |----------->|          |
                           Upstream  |Source k(BRS| Downstream |          |
                           link k    +------------+ link k     +----------+

                          Figure 3: RAMS Use Case

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 between multicast and unicast for domains that
   do not support multicast.  The translator can identify packet loss
   using co-located monitor [I-D.ietf-avtcore-monarch] by receiving a
   NACK from another system and then the monitor can use it's own SSRC
   as packet sender SSRC for transmitting the Third Party Loss Report
   message and send this message to the unicast receivers that is not
   aware of packet loss.

6.4.  Multipoint Control Unit (MCU) use case

   In point to multipoint topologies using video switching MCU (Topo-
   Video-switch-MCU) [RFC5117], the MCU typically forwards a single
   media stream to each participant, selected from the available input
   streams.  The selection of the input stream is often based on voice
   activity in the audio-visual conference, but other conference
   management mechanisms (like presentation mode or explicit floor
   control) exist as well.

   In this case the MCU may identify packet loss by receiving a NACK



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   from another system or may decide to switch to a new source.  In both
   cases the receiver may lose synchronization with the video stream and
   may send a FIR request.  If the MCU itself can detect the mis-
   synchronization of the video, the MCU can send the FIR suppression
   message to the receivers and send a FIR request to the video source.
   As suggested in RFC 5117, this topology is better implemented as an
   Topo-Mixer, in which case the mixer's SSRC is used as packet sender
   SSRC for transmitting the Third Party Loss Report message.


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 Third Party Loss Report with wrong sequence number of
   lost packet that makes missing RTP packets can not be compensated.

   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 middleboxes 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 middlebox is visible at the
   RTP layer, this is not an issue, provided the middlebox 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 it is authenticated via SRTCP or
   similar.  Accepting un-authenticated Third Party Loss Report can lead
   to a denial of service attack, where the endpoint accepts poor
   quality media that could be repaired.


8.  IANA Consideration

   New feedback type and New parameters for RTCP Third Party Loss Report
   are subject to IANA registration.  For general guidelines on IANA
   considerations for RTCP feedback, refer to [RFC4585].




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   This document assigns one new feedback type value in the RTCP
   feedback report registry to "Third Party Loss Report" with the
   following registrations format:

                    Name:            TPLR
                    Long Name:       Third Party Loss Report
                    Value:           TBD
                    Reference:       This document.

   This document also assigns the parameter value in the RTCP TPLR
   feedback report Registry to " Transport Layer Third Party Loss Early
   Indication ", with the following registrations format:

        Name:           TLLEI
        Long name:      Transport Layer Third Party Loss Early Indication
        Value:          TBD
        Reference:      this document.

   This document also assigns the parameter value in the RTCP TPLR
   feedback report Registry to "Payload Specific Third Party Loss Early
   Indication ", with the following registrations format:

        Name:           PSLEI
        Long name:      Payload Specific Third Party Loss Early Indication
        Value:          TBD
        Reference:      this document.

   The contact information for the registrations is:

     Qin Wu
     sunseawq@huawei.com
     101 Software Avenue, Yuhua District
     Nanjing, Jiangsu  210012, China


9.  Acknowledgement

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


10.  References







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10.1.  Normative References

   [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.

   [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.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

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

   [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.

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

   [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.

10.2.  Informative References

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



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   [DVB-IPTV]
              ETSI Standard, "Digital Video Broadcasting(DVB); Transport
              of MPEG-2 TS Based DVB Services over IP Based Networks",
              ETSI TS 102 034, V1.4.1 , August 2009.

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

   [I-D.ietf-avtcore-monarch]
              Wu, Q., Hunt, G., and P. Arden, "Monitoring Architectures
              for RTP", June 2011.

   [I-D.ietf-pmol-metrics-framework]
              Clark, A. and B. Claise, "Framework for Performance Metric
              Development", January 2011.


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.





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   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.

   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.




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   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.

   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.


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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