Audio/Video Transport Working                                    G. Hunt
Group                                                                 BT
Internet-Draft                                                  A. Clark
Intended status: Standards Track                                Telchemy
Expires: August 29, November 16, 2009                               February 25,                                  May 15, 2009

       RTCP XR Report Block for Loss Concealment metric Reporting
               draft-ietf-avt-rtcp-xr-loss-conceal-01.txt
               draft-ietf-avt-rtcp-xr-loss-conceal-02.txt

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Abstract

   This document defines an RTCP XR Report Block that allows the
   reporting of Loss Concealment metrics primarily for audio
   applications of RTP.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Loss Concealment Report Block  . . . . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  4
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Loss Concealment Block . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  5
     2.2.  Definition of Fields in Loss Concealment Report Block  . .  5
   3.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
     4.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 10
     4.3.  Contact information for registrations  . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
   7.  Changes from previous version  . . . . . . . . . . . . . . . . 13
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

1.  Introduction

1.1.  Loss Concealment Report Block

   This draft defines a new block type to augment those defined in
   [RFC3611], for use in a range of RTP applications.

   At any instant, the audio output at a receiver may be classified as
   either 'normal' or 'concealed'.  'Normal' refers to playout of audio
   payload received from the remote end, and also includes locally
   generated signals such as announcements, tones and comfort noise.
   Concealment refers to playout of locally-generated signals used to
   mask the impact of network impairments or to reduce the audibility of
   jitter buffer adaptations.

   The new block type provides metrics for actions taken by the receiver
   to mitigate the effect of packet loss and packet discard.
   Specifically, the first metric (On-Time Playout Duration) reports the
   duration of normal playout of data which the receiver obtained from
   the sender's stream.  A second metric (Loss Concealment Duration)
   reports the total time during which the receiver played out media
   data which was manufactured locally, because the sender's data for
   these periods was not available due to packet loss or discard.  A
   similar metric (Buffer Adjustment Concealment Duration) reports the
   duration of playout of locally-manufactured data replacing data which
   is unavailable due to adaptation of an adaptive de-jitter buffer.
   Further metrics (Playout Interrupt Count and Mean Playout Interrupt
   Size) report the number of times normal playout was interrupted, and
   the mean duration of these interruptions.

   Loss Concealment Duration and Buffer Adjustment Concealment Duration
   are reported separately because buffer adjustment is typically
   arranged to occur in silence periods so may have very little impact
   on user experience, whilst loss concealment may occur at any time.

   The metric belongs to the class of transport-related terminal metrics
   defined in [MONARCH] (work in progress).

   Instances of this Metrics Block refer by tag to the separate
   auxiliary Measurement Identity block [MEASIDENT] which contains
   information such as the SSRC of the measured stream, and RTP sequence
   numbers and time intervals indicating the span of the report.

1.2.  RTCP and RTCP XR Reports

   The use of RTCP for reporting is defined in [RFC3550].  [RFC3611]
   defined an extensible structure for reporting using an RTCP Extended
   Report (XR).  This draft defines a new Extended Report block that
   MUST be used as defined in [RFC3550] and [RFC3611].

1.3.  Performance Metrics Framework

   The Performance Metrics Framework [PMOLFRAME] provides guidance on
   the definition and specification of performance metrics.  Metrics
   described in this draft either reference external definitions or
   define metrics generally in accordance with the guidelines in
   [PMOLFRAME].

1.4.  Applicability

   This metric is primarily applicable to audio applications of RTP.
   EDITOR'S NOTE: are there metrics for concealment of transport errors
   for video?

2.  Loss Concealment Block

2.1.  Report Block Structure

      Loss Concealment metrics block
       0               1               2               3
       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    BT=NLC     |I| tag |plc|rsv|       block length=4          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                 On-time Playout Duration                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  Loss Concealment Duration                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |              Buffer Adjustment Concealment Duration           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Playout Interrupt Count    |  Mean Playout Interrupt Size  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

2.2.  Definition of Fields in Loss Concealment Report Block

   block type (BT): 8 bits

      A Loss Concealment Metrics Report Block is identified by the
      constant NLC.

   [Note to RFC Editor: please replace NLC with the IANA provided RTCP
   XR block type for this block.]

   Interval Metric flag (I): 1 bit

      This field is used to indicate whether the Loss Concealment metric
      block is an Interval or a Cumulative report, that is, whether the
      reported values apply to the most recent measurement interval
      duration between successive metrics reports (I=1) (the Interval
      Duration) or to the accumulation period characteristic of
      cumulative measurements (I=0) (the Cumulative Duration).
      Numerical values for both these intervals are provided in the
      Measurement Identifier block referenced by the tag field below.

   Measurement Identifier association (tag): 3 bits

      This field is used to identify the Measurement Identifier block
      [MEASIDENT] which describes this measurement.  The relevant
      Measurement Identifier block has the same tag value as the Loss
      Concealment Metrics block.  Note that there may be more than one
      Measurement Identifier block per RTCP packet.

   Packet Loss Concealment Method (plc): 2 bits

      This field is used to identify the packet loss concealment method
      in use at the receiver, according to the following code:

           bits 014-015
                 0 = silence insertion
                 1 = simple replay, no attenuation
                 2 = simple replay, with attenuation
                 3 = enhanced

   Reserved (rsv): 2 bits

      These bits are reserved.  They SHOULD be set to zero by senders
      and MUST be ignored by receivers.

   block length: 16 bits

      The length of this report block in 32-bit words, minus one.  For
      the Loss Concealment Metrics block, the block length is equal to
      4.

   On-time Playout Duration (ms): 32 bits

      'On-time' playout is the uninterrupted, in-sequence playout of
      valid decoded audio information originating from the remote
      endpoint.  This includes comfort noise during periods of remote
      talker silence, if VAD is used, and locally generated or
      regenerated tones and announcements.

      An equivalent definition is that on-time playout is playout of any
      signal other than those used for concealment.

      On-time playout duration MUST include both speech and silence
      intervals, whether VAD is used or not.  This duration is reported
      in millisecond units.

      If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
      SHOULD be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFFFF SHOULD be
      reported.

   Loss Concealment Duration (ms): 32 bits
      The duration, in milliseconds, of audio playout corresponding to
      Loss-type concealment.

      Loss-type concealment is reactive insertion or deletion of samples
      in the audio playout stream due to effective frame loss at the
      audio decoder.  "Effective frame loss" is the event in which a
      frame of coded audio is simply not present at the audio decoder
      when required.  In this case, substitute audio samples are
      generally formed, at the decoder or elsewhere, to reduce audible
      impairment.

      If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
      SHOULD be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFFFF SHOULD be
      reported.

   Buffer Adjustment Concealment Duration (ms): 32 bits

      The duration, in milliseconds, of audio playout corresponding to
      Buffer Adjustment-type concealment, if known.

      If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
      SHOULD be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFFFF SHOULD be
      reported.

      Buffer Adjustment-type concealment is proactive or controlled
      insertion or deletion of samples in the audio playout stream due
      to jitter buffer adaptation, re-sizing or re-centering decisions
      within the endpoint.

      Because this insertion is controlled, rather than occurring
      randomly in response to losses, it is typically less audible than
      loss-type concealment.  For example, jitter buffer adaptation
      events may be constrained to occur during periods of talker
      silence, in which case only silence duration is affected, or
      sophisticated time-stretching methods for insertion/deletion
      during favorable periods in active speech may be employed.

      Concealment events which cannot be classified as Buffer
      Adjustment- type MUST be classified as Loss-type.

   Playout Interrupt Count: 16 bits

      The number of interruptions to normal playout which occurred
      during the reporting period.

      If the measured value exceeds 0xFFFD, the value 0xFFFE SHOULD be
      reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFF SHOULD be reported.

   Mean Playout Interrupt Size (ms): 16 bits

      The mean duration, in ms, of interruptions to normal playout which
      occurred during the reporting period.

      If the measured value exceeds 0xFFFD, the value 0xFFFE SHOULD be
      reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFF SHOULD be reported.

3.  SDP Signaling

   [RFC3611] defines the use of SDP (Session Description Protocol)
   [RFC4566] for signaling the use of XR blocks.  XR blocks MAY be used
   without prior signaling.

   This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
   in [RFC3611] by providing an additional value of "xr-format" to
   signal the use of the report block defined in this document.

   rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF

   (defined in [RFC3611])

   xr-format = xr-format / =/ xr-conceal-block

   xr-conceal-block = "loss-conceal"

4.  IANA Considerations

   New block types for RTCP XR are subject to IANA registration.  For
   general guidelines on IANA considerations for RTCP XR, refer to
   [RFC3611].

4.1.  New RTCP XR Block Type value

   This document assigns the block type value NLC in the IANA "RTCP XR
   Block Type Registry" to the "Loss Concealment Metrics Block".

   [Note to RFC Editor: please replace NLC with the IANA provided RTCP
   XR block type for this block.]

4.2.  New RTCP XR SDP Parameter

   This document also registers a new parameter "loss-conceal" in the
   "RTCP XR SDP Parameters Registry".

4.3.  Contact information for registrations

   The contact information for the registrations is:

   Geoff Hunt (geoff.hunt@bt.com)

   Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United
   Kingdom

5.  Security Considerations

   It is believed that this proposed RTCP XR report block introduces no
   new security considerations beyond those described in [RFC3611].
   This block does not provide per-packet statistics so the risk to
   confidentiality documented in Section 7, paragraph 3 of [RFC3611]
   does not apply.

6.  Contributors

   The authors gratefully acknowledge the comments and contributions
   made by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin
   Connor, Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert
   Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith
   Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho,
   Ravi Raviraj, Albrecht Schwarz, Tom Taylor, and Hideaki Yamada.

7.  Changes from previous version

   Expanded and clarified IANA Considerations section

   Changed SDP tag BNF for block to "loss-conceal" SDP following Christian Groves' and Tom Taylor's
   comments (4th and 5th May 2009), now aligned with RFC 5234 section
   3.3 "Incremental Alternatives".

   Updated references

8.  References

8.1.  Normative References

   [MEASIDENT]
              Hunt, G., "RTCP XR Measurement Identifier Block",
              ID draft-ietf-avt-rtcp-xr-measid-01, February draft-ietf-avt-rtcp-xr-meas-identity-02, May 2009.

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

   [RFC3550]  Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
              Applications", RFC 3550, July 2003.

   [RFC3611]  Friedman, T., "RTP Control Protocol Extended Reports (RTCP
              XR)", RFC 3611, November 2003.

   [RFC4566]  Handley, M., "SDP: Session Description Protocol",
              RFC 4566, July 2006.

8.2.  Informative References

   [MONARCH]  Hunt, G., "Monitoring Architectures for RTP",
              ID draft-hunt-avt-monarch-01, August 2008.

   [PMOLFRAME]
              Clark, A., "Framework for Performance Metric Development",
              ID draft-ietf-pmol-metrics-framework-00, July 2008. draft-ietf-pmol-metrics-framework-02, March 2009.

Authors' Addresses

   Geoff Hunt
   BT
   Orion 2 PP3
   Adastral Park
   Martlesham Heath
   Ipswich, Suffolk  IP5 3RE
   United Kingdom

   Phone: +44 1473 651704
   Email: geoff.hunt@bt.com

   Alan Clark
   Telchemy Incorporated
   2905 Premiere Parkway, Suite 280
   Duluth, GA  30097
   USA

   Email: alan.d.clark@telchemy.com