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Versions: 00 01 02 03 draft-ietf-xrblock-rtcp-xr-loss-conceal

Audio/Video Transport Working Group                              G. Zorn
Internet-Draft                                               Network Zen
Intended status: Standards Track                                   Q. Wu
Expires: April 25, 2013                                           Huawei
                                                                A. Clark
                                                                Telchemy
                                                                   C. Bi
                                                                   STTRI
                                                        October 22, 2012


  RTP Control Protocol (RTCP) Extended Report (XR) Block for Concealed
                        Seconds Metric Reporting
               draft-ietf-xrblock-rtcp-xr-concsec-03.txt

Abstract

   This document defines an RTP Control Protocol(RTCP) Extended Report
   (XR) Block that allows the reporting of Concealed Seconds metrics,
   primarily for audio applications of RTP.

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
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on April 25, 2013.

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
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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



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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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Concealed Seconds Block  . . . . . . . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Standards Language . . . . . . . . . . . . . . . . . . . .  4
   3.  Concealment Seconds Block  . . . . . . . . . . . . . . . . . .  4
     3.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  5
     3.2.  Definition of Fields in Concealed Seconds Metrics Block  .  5
   4.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . .  9
     4.2.  Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 10
   5.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     5.1.  New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
     5.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 10
     5.3.  Contact information for registrations  . . . . . . . . . . 10
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 11
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12



















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1.  Introduction

1.1.  Concealed Seconds Block

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

   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.
   'Concealed' refers to playout of locally-generated signals used to
   mask the impact of network impairments such as lost packets or to
   reduce the audibility of jitter buffer adaptations.
      Editor's Note: For video applications, the output at a receiver
      should also be classified as either normal or concealed.  Should
      this paragraph be clear about this?

   The new block type provides metrics for concealment.  Specifically,
   the first metric (Unimpaired Seconds) reports the number of whole
   seconds occupied only with normal playout of data which the receiver
   obtained from the sender's stream.  The second metric (Concealed
   Seconds) reports the number of whole seconds during which the
   receiver played out any locally-generated media data.  A third metric
   (Severely Concealed Seconds (SCS)) reports the number of whole
   seconds during which the receiver played out locally-generated data
   for longer than SCS Threshold milliseconds.

   The metric belongs to the class of transport-related end system
   metrics defined in Wu, Hunt & Arden [I-D.ietf-avtcore-monarch].

1.2.  RTCP and RTCP XR Reports

   The use of RTCP for reporting is defined in Schulzrinne et al.
   [RFC3550].  Freidman, et al. [RFC3611] defines an extensible
   structure for reporting using an RTCP Extended Report (XR).  This
   draft defines a new Extended Report block that MUST be used as
   specified in RFC 3550 and RFC 3611.

1.3.  Performance Metrics Framework

   The Performance Metrics Framework [RFC6390] provides guidance on the
   definition and specification of performance metrics.  The RTP
   Monitoring Architecture [I-D.ietf-avtcore-monarch] provides
   guidelines for formatting RTCP XR blocks.  The Metrics Block
   described in this document are in accordance with the guidelines in
   [RFC6390] and [I-D.ietf-avtcore-monarch].




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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?

   Editor's Note: note that with video it is possible to use RTP based
   retransmission and also FEC (e.g.  COP3) - typically these would only
   be used with IPTV as this is less delay sensitive than interactive
   services.


2.  Terminology

2.1.  Standards Language

   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 RFC 2119 [RFC2119].

   In addition, the following terms are defined:



      Editor's Note: For Video loss concealment, at least the following
      four methods are used,i.e., Frame freeze,inter-frame
      extrapolation, interpolation, Noise insertation, should this
      section consider giving definition of these four methods for video
      loss concealment?



3.  Concealment Seconds Block

   This block provides a description of potentially audible impairments
   due to lost and discarded packets at the endpoint, expressed on a
   time basis analogous to a traditional PSTN T1/E1 errored seconds
   metric.
      Editor's Note: Should impairment also cover video application?

   The following metrics are based on successive one second intervals as
   declared by a local clock.  This local clock does NOT need to be
   synchronized to any external time reference.  The starting time of
   this clock is unspecified.  Note that this implies that the same loss
   pattern could result in slightly different count values, depending on
   where the losses occur relative to the particular one-second
   demarcation points.  For example, two loss events occurring 50ms



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   apart could result in either one concealed second or two, depending
   on the particular 1000 ms boundaries used.

   The seconds in this sub-block are not necessarily calendar seconds.
   At the tail end of a session, periods of time of less than 1000ms
   shall be incorporated into these counts if they exceed 500ms and
   shall be disregarded if they are less than 500ms.

3.1.  Report Block Structure

   Concealed Seconds Metrics Block

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    BT=NCS     | I |plc|Rserved|       block length=4          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                         SSRC of Source                        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Unimpaired Seconds                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                    Concealed Seconds                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Severely Concealed Seconds    |    RESERVED   | SCS Threshold |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

3.2.  Definition of Fields in Concealed Seconds Metrics Block

   Block type (BT): 8 bits

      A Concealed Seconds Metrics Report Block is identified by the
      constant <NCS>.

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

   Interval Metric flag (I): 2 bit

      This field is used to indicate whether the Concealed Seconds
      metrics are Sampled, Interval or Cumulative metrics, that is,
      whether the reported values applies to the most recent measurement
      interval duration between successive metrics reports (I=10) (the
      Interval Duration) or to the accumulation period characteristic of
      cumulative measurements (I=11) (the Cumulative Duration) or is a
      sampled instantaneous value (I=01) (Sampled Value).




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   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
            Other values reserved
               Editor's Note 1 : In the packet loss concealment
               methods,"Enhanced" is defines as one new Packet loss
               Concealment method?  However it is not clear what this
               packet loss concealment method looks like?
               Editor's Note 2: For Video loss concealment, there are a
               range of methods used, for example:
                  (i) Frame freeze In this case the impaired video frame
                  is not displayed and the previously displayed frame is
                  hence "frozen" for the duration of the loss event
                  (ii) Inter-frame extrapolation If an area of the video
                  frame is damaged by loss, the same area from the
                  previous frame(s) can be used to estimate what the
                  missing pixels would have been.  This can work well in
                  a scene with no motion but can be very noticeable if
                  there is significant movement from one frame to
                  another.  Simple decoders may simply re-use the pixels
                  that were in the missing area, more complex decoders
                  may try to use several frames to do a more complex
                  extrapolation.
                  (iii) Interpolation A decoder may use the undamaged
                  pixels in the image to estimate what the missing block
                  of image should have
                  (iv) Noise insertion A decoder may insert random pixel
                  values - which would generally be less noticeable than
                  a blank rectangle in the image.
               Therefore more text required in the future draft to
               discuss Techniques for Video Loss Concealment method in
               this document.

   Reserved (resv): 4 bits

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








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   Block Length: 16 bits

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

   SSRC of source: 32 bits

      As defined in Section 4.1 of RFC 3611.

   Unimpaired Seconds: 32 bits

      A count of the number of unimpaired Seconds that have occurred.

      An unimpaired Second is defined as a continuous period of 1000ms
      during which no frame loss or discard due to late arrival has
      occurred.  Every second in a session must be classified as either
      OK or Concealed.

      If voice activity detection [VAD] is used, normal playout of
      comfort noise or other silence concealment signals during periods
      of talker silence SHALL be counted as unimpaired seconds.
         Editor's Note: It should be clear that voice activity detection
         does not apply to video.
      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.

   Concealed Seconds: 32 bits

      A count of the number of Concealed Seconds that have occurred.

      A Concealed Second is defined as a continuous period of 1000ms
      during which any frame loss or discard due to late arrival has
      occurred.

      Equivalently, a concealed second is one in which some Loss-type
      concealment has occurred.  Buffer adjustment-type concealment
      SHALL NOT cause Concealed Seconds to be incremented, with the
      following exception.  An implementation MAY cause Concealed
      Seconds to be incremented for 'emergency' buffer adjustments made
      during talkspurts.

      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



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      generally formed, at the decoder or elsewhere, to reduce audible
      impairment.

      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.  For
      these reasons, buffer adjustment-type concealment MAY be exempted
      from inclusion in calculations of Concealed Seconds and Severely
      Concealed Seconds.
         Editor's Note: In this document, two kind of concealments are
         defined: a.  Loss-type concealment b.  Buffer Adjustment-type
         concealment Loss-type concealment is applicable to both audio
         and video.  However Buffer Adjustment-type concealment is
         usually applied to audio.  Should this section be clear about
         this?

      However, an implementation SHOULD include buffer-type concealment
      in counts of Concealed Seconds and Severely Concealed Seconds if
      the event occurs at an 'inopportune' moment, with an emergency or
      large, immediate adaptation during active speech, or for
      unsophisticated adaptation during speech without regard for the
      underlying signal, in which cases the assumption of low-audibility
      cannot hold.  In other words, jitter buffer adaptation events
      which may be presumed to be audible SHOULD be included in
      Concealed Seconds and Severely Concealed Seconds counts.
      Concealment events which cannot be classified as Buffer
      Adjustment- type MUST be classified as Loss-type.
      For clarification, the count of Concealed Seconds MUST include the
      count of Severely Concealed Seconds.
      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.

   Severely Concealed Seconds: 16 bits

      A count of the number of Severely Concealed Seconds.

      A Severely Concealed Second is defined as a non-overlapping period



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      of 1000 ms during which the cumulative amount of time that has
      been subject to frame loss or discard due to late arrival, exceeds
      the SCS Threshold.

      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.

   Reserved: 8 bits

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

   SCS Threshold: 8 bits

      The SCS Threshold defines the amount of time corresponding to lost
      or discarded frames that must occur within a one second period in
      order for the second to be classified as a Severely Concealed
      Second.  This is expressed in milliseconds and hence can represent
      a range of 0.1 to 25.5 percent loss or discard.

      A default threshold of 50ms (5% effective frame loss per second)
      is suggested.



4.  SDP Signaling

   RFC 3611 defines the use of Session Description Protocol (SDP,
   [RFC4566] for signaling the use of XR blocks.  XR blocks MAY be used
   without prior signaling.

4.1.  SDP rtcp-xr-attrib Attribute Extension

   This section augments the SDP attribute "rtcp-xr" defined in Section
   5.1 of RFC 3611 by providing an additional value of "xr-format" to
   signal the use of the report block defined in this document.

   The SDP attribute for the block has an additional optional paremeter,
   "thresh", used to supply a value for the SCS Threshold parameter.  If
   this parameter is present, the RTP system receiving the SDP SHOULD
   use this value for the current session.  If the parameter is not
   present, the RTP system SHOULD use a locally configured value.








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   xr-format =/ xr-conc-sec-block

   xr-conc-sec-block = "conc-sec" ["=" thresh]

   thresh      = 1*DIGIT          ; threshold for SCS (ms)
   DIGIT          = <as defined in Section 3.4 of [RFC5234]>

4.2.  Offer/Answer Usage

   When SDP is used in offer-answer context, the SDP Offer/Answer usage
   defined in Section 5.2 of RFC 3611 applies.


5.  IANA Considerations

   New block types for RTCP XR are subject to IANA registration.  For
   general guidelines on IANA considerations for RTCP XR, refer to
   Section 6 of RFC 3611.

5.1.  New RTCP XR Block Type value

   This document assigns the block type value <NCS> in the IANA "RTCP XR
   Block Type Registry" to the "Concealed Seconds Metrics Block".

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

5.2.  New RTCP XR SDP Parameter

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

5.3.  Contact information for registrations


      The contact information for the registrations is:

      Alan Clark (alan.d.clark@telchemy.com)

      2905 Premiere Parkway, Suite 280
      Duluth, GA  30097
      USA









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6.  Security Considerations

   It is believed that this proposed RTCP XR report block introduces no
   new security considerations beyond those described in RFC 3611.  This
   block does not provide per-packet statistics so the risk to
   confidentiality documented in Section 7, paragraph 3 of [RFC3611]
   does not apply.


7.  Contributors

   Geoff Hunt wrote the initial draft of this document.


8.  Acknowledgements

   The authors gratefully acknowledge reviews and feedback provided 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.


9.  References

9.1.  Normative References

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

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

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

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

9.2.  Informative References

   [I-D.ietf-avtcore-monarch]
              Wu, W., Hunt, G., and P. Arden, "Guidelines for Use of the
              RTP Monitoring Framework", draft-ietf-avtcore-monarch-22
              (work in progress), September 2012.



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   [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development", BCP 170, RFC 6390,
              October 2011.

   [VAD]      "http://en.wikipedia.org/wiki/Voice_activity_detection".


Authors' Addresses

   Glen Zorn
   Network Zen
   227/358 Thanon Sanphawut
   Bang Na, Bangkok  10260
   Thailand

   Phone: +66 (0) 909-0201060
   Email: glenzorn@gmail.com


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

   Email: sunseawq@huawei.com


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

   Email: alan.d.clark@telchemy.com


   Claire Bi
   Shanghai Research Institure of China Telecom Corporation Limited
   No.1835,South Pudong Road
   Shanghai  200122
   China

   Email: bijy@sttri.com.cn







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