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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 6958

Audio/Video Transport Working Group                             A. Clark
Internet-Draft                                                  Telchemy
Intended status: Standards Track                           S. Zhang, Ed.
Expires: April 14, 2013                                          J. Zhao
                                                                   STTRI
                                                                   Q. Wu
                                                                  Huawei
                                                        October 11, 2012


  RTP Control Protocol (RTCP) Extended Report (XR) Block for Burst/Gap
                         Loss metric Reporting
            draft-ietf-xrblock-rtcp-xr-burst-gap-loss-04.txt

Abstract

   This document defines an RTP Control Protocol (RTCP) Extended Report
   (XR) Block that allows the reporting of Burst and Gap Loss metrics
   for use in a range of RTP applications.

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 April 14, 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   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.  Burst and Gap Loss Report Block  . . . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
     2.1.  Standards Language . . . . . . . . . . . . . . . . . . . .  5
   3.  Burst/Gap Loss Block . . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  6
     3.2.  Definition of Fields in Burst/Gap Loss Report Block  . . .  6
     3.3.  Derived metrics based on reported metrics  . . . . . . . .  9
   4.  Considerations for Voice-over-IP applications  . . . . . . . . 10
   5.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.1.  SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 11
     5.2.  Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  New RTCP XR Block Type value . . . . . . . . . . . . . . . 12
     6.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 12
     6.3.  Contact information for registrations  . . . . . . . . . . 12
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
   8.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 15
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     10.2. Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 17
     A.1.  draft-ietf-xrblock-rtcp-xr-burst-gap-loss-04 . . . . . . . 17
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18
















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1.  Introduction

1.1.  Burst and Gap Loss Report Block

   This draft defines a new block type to augment those defined in
   [RFC3611] for use in a range of RTP applications.  The new block type
   supports the reporting of the proportion of packets lost by the
   network.  The losses during loss bursts are reported, together with
   the number of bursts and additional data allowing the calculation of
   statistical parameters (mean and variance) of the distribution of
   burst lengths.  Some uses of these metrics depend on the availability
   of the metric "cumulative number of packets lost" from RTCP
   [RFC3550].

   This block provides information on transient IP problems.  Burst/Gap
   metrics are typically used in Cumulative reports however MAY be used
   in Interval reports.  The burstiness of packet loss affects user
   experience, may influence any sender strategies to mitigate the
   problem, and may also have diagnostic value.

   The metric belongs to the class of transport-related end system
   metrics defined in [MONARCH].

   The definitions of Burst, Gap, Loss and Discard are consistent with
   definitions in [RFC3611].  To accommodate the range of jitter buffer
   algorithms and packet discard logic that may be used by implementors,
   the method used to distinguish between bursts and gaps may be an
   equivalent method to that defined in [RFC3611].  The method used
   SHOULD produce the same result as that defined in [RFC3611] for
   conditions of burst packet loss, but MAY produce different results
   for conditions of time varying jitter.

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 document defines a new Extended Report block for
   use with [RFC3550] and [RFC3611].

1.3.  Performance Metrics Framework

   The Performance Metrics Framework [RFC6390] 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
   [RFC6390].





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1.4.  Applicability

   These metrics are applicable to a range of RTP applications which
   don't use stream repair means.















































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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:

   Received, Lost and Discarded

      A packet shall be regarded as lost if it fails to arrive within an
      implementation-specific time window.  A packet that arrives within
      this time window but is too early or late to be played out or
      thrown away before playout due to packet duplication or redundancy
      shall be regarded as discarded.  A packet shall be classified as
      one of received (or OK), discarded or lost.  The metric
      "cumulative number of packets lost" defined in [RFC3550] reports a
      count of packets lost from the media stream (single SSRC within
      single RTP session).  Similarly the metric "number of packets
      discarded" defined in [DISCARD] reports a count of packets
      discarded from the media stream (single SSRC within single RTP
      session) arriving at the receiver.  Another metric defined in
      [RFC5725] is available to report on packets which are not
      recovered by any repair techniques which may be in use.


   Bursts and Gaps

      The terms Burst and Gap are used in a manner consistent with that
      of RTCP XR [RFC3611].  RTCP XR views a RTP stream as being divided
      into bursts, which are periods during which the loss rate is high
      enough to cause noticeable quality degradation (generally over 5
      percent loss rate), and gaps, which are periods during which lost
      packets are infrequent and hence quality is generally acceptable.















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3.  Burst/Gap Loss Block

   Metrics in this block report on Burst/Gap Loss in the stream arriving
   at the RTP system.

3.1.  Report Block Structure

   Burst/Gap Loss 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=NBGL    | I |C|  resv.  |      block length = 5         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        SSRC of Source                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Threshold     |         Sum of Burst Durations (ms)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |            Packets Lost in Bursts             |    Total...   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | ...Packets expected in bursts |    Number of bursts   | Sum of|
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                ...Squares of Burst Durations (ms-squared)     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

3.2.  Definition of Fields in Burst/Gap Loss Report Block

   Block type (BT): 8 bits

      A Burst/Gap Loss Report Block is identified by the constant NBGL.

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


   Interval Metric flag (I): 2 bits

      This field is used to indicate whether the Burst/Gap Loss 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).  In this
      document, Burst/Gap Loss Metric is not measured at a particular
      time instant but over one or several reporting intervals.



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      Therefore Burst/Gap Loss Metric MUST not be chosen as Sampled
      Metric.  In this document, Burst/Gap Loss Metric is not measured
      at a particular time instant but over one or several reporting
      intervals.  Therefore Burst/Gap Loss Metric MUST NOT be chosen as
      Sampled Metric.


    Loss and Discard Combination flag (C): 1 bit

      The 'C' flag is used to indicate whether combining loss/discard
      report is needed.  This field MUST be set to '1' if the burst gap
      loss report is present in conjunction with the burst gap discard
      report in the same compound RTCP packet and MUST be set to '0'
      otherwise.  If the burst gap discard is not sent with the burst
      gap loss, then the receiver MUST discard the burst gap loss with
      'C' flag set to 1.  If the 'C' flag is set to 0, then receiver
      MUST NOT discard the burst gap loss metric block when the burst
      gap discard is not received.


   Reserved (resv): 5 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 Burst/Gap Loss block, the block length is equal to 5.


   SSRC of source: 32 bits

      As defined in Section 4.1 of [RFC3611].


   Threshold: 8 bits

      The Threshold is equivalent to Gmin in [RFC3611], i.e. the number
      of successive packets that must be received prior to and following
      a lost packet in order for this lost packet to be regarded as part
      of a gap.








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   Sum of Burst Durations (ms): 24 bits

      The total duration of bursts of lost packets in the period of the
      report (Interval or Cumulative).

      If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD
      be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFF SHOULD be reported.


   Packets lost in bursts: 24 bits

      The total number of packets lost during loss bursts.

      If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD
      be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFF SHOULD be reported.


   Total packets expected in bursts: 24 bits

      The total number of packets expected during loss bursts (that is,
      the sum of received packets and lost packets).

      If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD
      be reported to indicate an over-range measurement.  If the
      measurement is unavailable, the value 0xFFFFFF SHOULD be reported.


   Number of bursts: 16 bits

      The number of bursts in the period of the report (Interval or
      Cumulative).

      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.


   Sum of Squares of Burst Durations (ms-squared): 36 bits

      The sum of the squares of burst durations (where individual burst
      durations are expressed in ms) over in the period of the report
      (Interval or Cumulative).  The units for this quantity are
      milliseconds-squared.

      If the measured value exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE
      SHOULD be reported to indicate an over-range measurement.  If the



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      measurement is unavailable, the value 0xFFFFFFFFF SHOULD be
      reported.


3.3.  Derived metrics based on reported metrics

   The metrics described here are intended to be used as described in
   this section, in conjunction with information from the Measurement
   Information block [MEASID] (which MUST be present in the same RTCP
   packet as the Burst/Gap Loss block) and also with the metric
   "cumulative number of packets lost" provided in standard RTCP
   [RFC3550].

   These metrics provides information relevant to statistical
   parameters, including:

   o  The fraction of packets lost during bursts (i.e., Burst Loss Rate
      in [SUMSTAT])

   o  The fraction of packets lost during gaps (i.e., Gap Loss Rate in
      [SUMSTAT])

   o  burst duration mean [SUMSTAT]

   o  burst duration variance [SUMSTAT]

   The details on calculation these parameters in the metrics are
   described in [SUMSTAT].























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4.  Considerations for Voice-over-IP applications

   This metric block is applicable to a broad range of RTP applications.
   Where the metric is used with a Voice-overIP (VoIP) application and
   the stream repair means is not available, the following
   considerations apply.

   RTCP XR views a call as being divided into bursts, which are periods
   during which the loss rate is high enough to cause noticeable call
   quality degradation (generally over 5 percent loss rate), and gaps,
   which are periods during which lost packets are infrequent and hence
   call quality is generally acceptable.

   If Voice Activity Detection is used the Burst and Gap Duration shall
   be determined as if silence packets had been sent, i.e. a period of
   silence in excess of Gmin packets MUST terminate a burst condition.

   The recommended value for the threshold Gmin in [RFC3611] results in
   a Burst being a period of time during which the call quality is
   degraded to a similar extent to a typical PCM Severely Errored Second
   [PSES].






























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5.  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.

5.1.  SDP rtcp-xr-attrib Attribute Extension

   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.

   xr-format =/ xr-bgl-block

   xr-bgl-block = "brst-gap-loss"

5.2.  Offer/Answer Usage

   When SDP is used in offer-answer context, the SDP Offer/Answer usage
   defined in [RFC3611] applies.































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6.  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].

6.1.  New RTCP XR Block Type value

   This document assigns the block type value NDEL in the IANA "RTCP XR
   Block Type Registry" to the "Burst/Gap Loss Metrics Block".

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

6.2.  New RTCP XR SDP Parameter

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

6.3.  Contact information for registrations


   The contact information for the registrations is:

    Qin Wu (sunseawq@huawei.com)

    101 Software Avenue, Yuhua District
    Nanjing, Jiangsu  210012
    China






















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7.  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.












































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8.  Contributors

   Geoff Hunt wrote the initial draft of this document.
















































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9.  Acknowledgments

   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.











































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10.  References

10.1.  Normative References

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

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

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

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

   [RFC5725]  Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
              Report Block Type for RTP Control Protocol (RTCP) Extended
              Reports (XRs)", RFC 5725, February 2020.

10.2.  Informative References

   [DISCARD]  Hunt, G., "RTCP XR Report Block for Discard metric
              Reporting", ID draft-ietf-xrblock-rtcp-xr-discard-06,
              October 2012.

   [MEASID]   Wu, Q., "Measurement Identity and information Reporting
              using SDES item and XR Block",
              ID draft-ietf-xrblock-rtcp-xr-meas-identity-10,
              August 2012.

   [MONARCH]  Hunt, G., "Monitoring Architectures for RTP",
              ID draft-ietf-avtcore-monarch-22, September 2012.

   [PSES]     "URL",  http://www.its.bldrdoc.gov/projects/devglossary/
              _severely_errored_second.html, October 2011.

   [RFC6390]  Clark, A. and B. Claise, "Framework for Performance Metric
              Development", RFC 6390, July 2011.

   [SUMSTAT]  Zorn, G., "RTCP XR for Summary Statistics Metrics
              Reporting", ID draft-zorn-xrblock-rtcp-xr-al-stat-06,
              July 2012.








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Appendix A.  Change Log

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

A.1.  draft-ietf-xrblock-rtcp-xr-burst-gap-loss-04

   The following are the major changes compared to previous version:

   o  Outdated reference update.

   o  Editorial changes based on comments that applied to PDV and Delay
      drafts.






































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Authors' Addresses

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

   Email: alan.d.clark@telchemy.com


   Sunshine Zhang (editor)
   Shanghai Research Institure of China Telecom Corporation Limited
   No.1835,South Pudong Road
   Shanghai  200122
   China

   Email: zhangyx@sttri.com.cn


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

   Email: zhaojing@sttri.com.cn


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

   Email: sunseawq@huawei.com















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