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Versions: (draft-singh-xrblock-independent-burst-gap-discard) 00 01 02 03 RFC 8015

Audio/Video Transport Working Group                             V. Singh
Internet-Draft                                              callstats.io
Intended status: Standards Track                              C. Perkins
Expires: September 22, 2016                        University of Glasgow
                                                                A. Clark
                                                                Telchemy
                                                                R. Huang
                                                                  Huawei
                                                          March 21, 2016


 RTP Control Protocol (RTCP) Extended Report (XR) Block for Independent
                 Reporting of Burst/Gap Discard Metric
          draft-ietf-xrblock-independent-burst-gap-discard-01

Abstract

   This document defines an RTP Control Protocol (RTCP) Extended Report
   (XR) block that allows the reporting of burst and gap discard metrics
   independently of the 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 September 22, 2016.

Copyright Notice

   Copyright (c) 2016 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



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Burst-Gap Discard Metrics Block . . . . . . . . . . . . .   2
     1.2.  RTCP and RTCP Extended Reports  . . . . . . . . . . . . .   3
     1.3.  Performance Metrics Framework . . . . . . . . . . . . . .   3
     1.4.  Applicability . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Burst/Gap Discard Metrics Block . . . . . . . . . . . . . . .   5
     3.1.  Report Block Structure  . . . . . . . . . . . . . . . . .   5
     3.2.  Definition of Fields in Burst/Gap Discard Metrics Block .   5
     3.3.  Derived Metrics Based on the Reported Metrics . . . . . .   7
   4.  Considerations for Voice-over-IP Applications . . . . . . . .   8
   5.  SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  SDP rtcp-xr Attribute Extension . . . . . . . . . . . . .   8
     5.2.  Offer/Answer Usage  . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     6.1.  New RTCP XR Block Type Value  . . . . . . . . . . . . . .   9
     6.2.  New RTCP XR SDP Parameter . . . . . . . . . . . . . . . .   9
     6.3.  Contact Information for Registrations . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Appendix A.  Metrics Represented Using the Template from RFC 6390  13

1.  Introduction

1.1.  Burst-Gap Discard Metrics Block

   This document defines a new block type that extends the metrics
   defined in [RFC7003].  The new block type reports the proportion of
   packets discarded in a burst by the dejitter buffer at the receiver.
   The number of packets discarded depends on the dejitter buffer
   algorithm implemented by the endpoint.

   The new report block defined in this document is different from the
   one defined in [RFC7003].  The metrics in [RFC7003] depends on the
   metrics in the burst-gap loss metric defined in [RFC6958].
   Consequently, an endpoint using [RFC7003] MUST report it along with



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   [RFC6958] for it to be useful.  The combined usage is useful when an
   endpoint observes correlated packet losses and discard.  However,
   when the burst of packet losses and discards do not occur
   simultaneously, the application may prefer a concise report block
   that just reports the burst-gap of discarded packets.  The report
   block in this document provides the complete information and does not
   require additional report blocks.  That is, this block reports: the
   total number of packets discarded, the total burst duration, and the
   total number of bursts, all of these metrics are missing in
   [RFC7003].

   This block provides information on transient network issues.  Burst/
   gap metrics are typically used in cumulative reports; however, they
   may also be used in interval reports (see the Interval Metric flag in
   Section 3.2).  The variation in the number of packet discards in a
   burst affects the user experience.  Based on the metrics reported in
   the block, the sending endpoint may change the packetization
   interval, vary the bitrate, etc.  The report may additionally be used
   for diagnostics [RFC6792].  The metric belongs to the class of
   transport-related end-system metrics defined in [RFC6792].

   The definitions of "burst", "gap", "loss", and "discard" are
   consistent with the definitions in [RFC3611].  To accommodate a range
   of dejitter buffer algorithms and packet discard logic that may be
   used by implementors, the method used to distinguish between bursts
   and gaps shall use an equivalent method to that defined in
   Section 4.7.2 of [RFC3611].  Note that reporting the specific
   dejitter buffer algorithm and/or the packet discard logic is out of
   the scope of this document.

1.2.  RTCP and RTCP Extended 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.  The RTP
   Monitoring Framework [RFC6792] provides guidelines for reporting
   block format using RTCP XR.  The metrics block described in this
   document is in accordance with the guidelines in [RFC6390] and
   [RFC6792].






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1.4.  Applicability

   These metrics are applicable to a range of RTP applications that
   contain dejitter buffers [RFC5481] at the receiving end to smooth
   variation in packet-arrival time and don't use stream repair means,
   e.g., Forward Error Correction (FEC)
   [I-D.ietf-payload-flexible-fec-scheme] and/or retransmission
   [RFC4588].

2.  Terminology

   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 to be played out, too
      late to be played out, or thrown away before playout due to packet
      duplication or redundancy shall be regarded as discarded.  A
      packet shall not be regarded as discarded if it arrives within
      this time window but is dropped during decoding by some higher-
      layer decoder, e.g., due to a decoding error.  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
      synchronization source (SSRC) within a single RTP session).
      Similarly, the metric "number of packets discarded" defined in
      [RFC7002] reports a count of packets discarded from the media
      stream (single SSRC within a single RTP session) arriving at the
      receiver.  Another metric, defined in [RFC5725], is available to
      report on packets that are not recovered by any repair techniques
      that may be in use.  Note that the term "discard" defined here
      builds on the "discard" definition in [RFC3611] but extends the
      concept to take into account packet duplication and reports
      different types of discard counts [RFC7002].

   Bursts and Gaps

      The terms "burst" and "gap" are used in a manner consistent with
      that of RTCP XR [RFC3611].  RTCP XR views an RTP stream as being
      divided into bursts, which are periods during which the discard
      rate is high enough to cause noticeable quality degradation
      (generally over 5 percent discard rate), and gaps, which are



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      periods during which discarded packets are infrequent and hence
      quality is generally acceptable.  [RFC3611] RECOMMENDS a Gmin
      value of 16.

3.  Burst/Gap Discard Metrics Block

   Metrics in this block report on burst/gap discard in the stream
   arriving at the RTP system.  Measurements of these metrics are made
   at the receiving end of the RTP stream.  Instances of this metrics
   block use the synchronization source (SSRC) to refer to the separate
   auxiliary Measurement Information Block [RFC6776], which describes
   measurement periods in use (see [RFC6776], Section 4.2).

   This metrics block relies on the measurement period in the
   Measurement Information Block indicating the span of the report.
   Senders MUST send this block in the same compound RTCP packet as the
   Measurement Information Block.  Receivers MUST verify that the
   measurement period is received in the same compound RTCP packet as
   this metrics block.  If not, this metrics block MUST be discarded.

3.1.  Report Block Structure

   The structure of the Burst/Gap Discard Metrics Block is as follows.

       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=IBGD    | I |   resv    |      Block Length = 5         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of Source                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Threshold   |         Sum of Burst Durations (ms)           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Packets Discarded in Bursts          |    Number of  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Bursts     |           Total Packets Expected in Bursts    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Discard Count                          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 1: Report Block Structure

3.2.  Definition of Fields in Burst/Gap Discard Metrics Block

   Block Type (BT): 8 bits





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      A Burst/Gap Discard Metrics Block is identified by the constant
      IBGD.

      [Note to RFC Editor: Please replace IBGD 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 discard
      metrics are Sampled, Interval, or Cumulative metrics [RFC6792]:

         I=10: Interval Duration - the reported value applies to the
         most recent measurement interval duration between successive
         metrics reports.

         I=11: Cumulative Duration - the reported value applies to the
         accumulation period characteristic of cumulative measurements.

         I=01: Sampled Value - the reported value is a sampled
         instantaneous value.

      In this document, burst/gap discard metrics can only be measured
      over definite intervals and cannot be sampled.  Also, the value
      I=00 is reserved for future use.  Senders MUST NOT use the values
      I=00 or I=01.  If a block is received with I=00 or I=01, the
      receiver MUST discard the block.

   Reserved (resv): 6 bits

      These bits are reserved.  They MUST be set to zero by senders and
      ignored by receivers (see [RFC6709], Section 4.2).

   block length: 16 bits

      The length of this report block in 32-bit words, minus one.  For
      the Burst/Gap Discard Metrics Block, the block length is equal to
      5.  The block MUST be discarded if the block length is set to a
      different value.

   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 not be discarded prior to and
      following a discard packet in order for this discarded packet to



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      be regarded as part of a gap.  Note that the Threshold is set in
      accordance with the Gmin calculation defined in Section 4.7.2 of
      [RFC3611].

    Sum of Burst Durations (ms): 24 bits

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

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

   Packets Discarded in Bursts: 24 bits

      The total number of packets discarded during discard bursts, as
      defined in Section 3.2 of [RFC7002].

   Number of Bursts: 16 bits

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

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

   Total Packets Expected in Bursts: 24 bits

      The total number of packets expected during the discard bursts
      (that is, the sum of received packets and lost packets).  The
      metric is defined in [RFC7003].

   Discard Count: 32 bits

      Number of packets discarded over the period (Interval or
      Cumulative) covered by this report, as defined in Section 3.2 of
      [RFC7002].

3.3.  Derived Metrics Based on the Reported Metrics

   The metrics described here are intended to be used in conjunction
   with information from the Measurement Information Block [RFC6776].






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   These metrics provide the following information relevant to
   statistical parameters (depending on cumulative of interval
   measures), for example:

   o  The average discarded burst size, which can be calculated by
      dividing the metric "Packets Discarded in Bursts" by the "Number
      of Bursts".

   o  The average burst duration, which can be calculated by dividing
      the metric "Sum of Burst Durations (ms)" by the "Number of
      bursts".

4.  Considerations for Voice-over-IP Applications

   This metrics block is applicable to a broad range of RTP
   applications.  Where the metric is used with a Voice-over-IP (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 discard rate is high enough to cause noticeable call
   quality degradation (generally over 5 percent discard rate) and gaps,
   which are periods during which discarded 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 will 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 pulse code modulation (PCM)
   severely errored second.

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 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.  The
   ABNF [RFC5234] syntax is as follows.





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   xr-format =/ xr-ind-bgd-block

   xr-ind-bgd-block = "ind-burst-gap-discard"

5.2.  Offer/Answer Usage

   When SDP is used in Offer/Answer context, the SDP Offer/Answer usage
   defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters
   applies.  For detailed usage in Offer/Answer for unilateral
   parameters, refer to Section 5.2 of [RFC3611].

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 IBGD in the IANA "RTP
   Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
   the "Burst/Gap Discard Metrics Block".

   [Note to RFC Editor: Please replace IBGD 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 "ind-burst-gap-discard"
   in the "RTP Control Protocol Extended Reports (RTCP XR) Session
   Description Protocol (SDP) Parameters Registry".

6.3.  Contact Information for Registrations

   The contact information for the registrations is:

      ART Area Directors <art-ads@tools.ietf.org>

7.  Security Considerations

   It is believed that this RTCP XR 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

   Qin Wu, Rachel Huang, and Alan Clark wrote RFC7003, which this
   document extends.

9.  Acknowledgments

   The authors would like to thank Paul Kyzivat, Jan Novak, Dan
   Romascanu for providing valuable feedback on earlier versions of this
   draft.

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <http://www.rfc-editor.org/info/rfc3550>.

   [RFC3611]  Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
              "RTP Control Protocol Extended Reports (RTCP XR)", RFC
              3611, DOI 10.17487/RFC3611, November 2003,
              <http://www.rfc-editor.org/info/rfc3611>.

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
              July 2006, <http://www.rfc-editor.org/info/rfc4566>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/
              RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [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, DOI 10.17487/RFC5725, February
              2010, <http://www.rfc-editor.org/info/rfc5725>.








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   [RFC6776]  Clark, A. and Q. Wu, "Measurement Identity and Information
              Reporting Using a Source Description (SDES) Item and an
              RTCP Extended Report (XR) Block", RFC 6776, DOI 10.17487/
              RFC6776, October 2012,
              <http://www.rfc-editor.org/info/rfc6776>.

   [RFC7003]  Clark, A., Huang, R., and Q. Wu, Ed., "RTP Control
              Protocol (RTCP) Extended Report (XR) Block for Burst/Gap
              Discard Metric Reporting", RFC 7003, DOI 10.17487/RFC7003,
              September 2013, <http://www.rfc-editor.org/info/rfc7003>.

10.2.  Informative References

   [I-D.ietf-payload-flexible-fec-scheme]
              Singh, V., Begen, A., Zanaty, M., and G. Mandyam, "RTP
              Payload Format for Flexible Forward Error Correction
              (FEC)", draft-ietf-payload-flexible-fec-scheme-01 (work in
              progress), October 2015.

   [RFC4588]  Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
              Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
              DOI 10.17487/RFC4588, July 2006,
              <http://www.rfc-editor.org/info/rfc4588>.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
              March 2009, <http://www.rfc-editor.org/info/rfc5481>.

   [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development", BCP 170, RFC 6390, DOI
              10.17487/RFC6390, October 2011,
              <http://www.rfc-editor.org/info/rfc6390>.

   [RFC6709]  Carpenter, B., Aboba, B., Ed., and S. Cheshire, "Design
              Considerations for Protocol Extensions", RFC 6709, DOI
              10.17487/RFC6709, September 2012,
              <http://www.rfc-editor.org/info/rfc6709>.

   [RFC6792]  Wu, Q., Ed., Hunt, G., and P. Arden, "Guidelines for Use
              of the RTP Monitoring Framework", RFC 6792, DOI 10.17487/
              RFC6792, November 2012,
              <http://www.rfc-editor.org/info/rfc6792>.

   [RFC6958]  Clark, A., Zhang, S., Zhao, J., and Q. Wu, Ed., "RTP
              Control Protocol (RTCP) Extended Report (XR) Block for
              Burst/Gap Loss Metric Reporting", RFC 6958, DOI 10.17487/
              RFC6958, May 2013,
              <http://www.rfc-editor.org/info/rfc6958>.



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   [RFC7002]  Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol
              (RTCP) Extended Report (XR) Block for Discard Count Metric
              Reporting", RFC 7002, DOI 10.17487/RFC7002, September
              2013, <http://www.rfc-editor.org/info/rfc7002>.















































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Appendix A.  Metrics Represented Using the Template from RFC 6390

   a.  Threshold Metric

       *  Defined in Appendix A.a of [RFC7003].

   b.  Sum of burst durations (ms)

       *  Metric Name: Sum of Burst Durations with Discarded RTP
          Packets.

       *  Metric Description: The total duration of bursts of discarded
          RTP packets in the period of the report.

       *  Method of Measurement or Calculation: See Section 3.1, Sum of
          Burst Durations definition.

       *  Units of Measurement: See Section 3.1, Sum of Burst Durations
          definition.

       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 3, 1st paragraph.

       *  Measurement Timing: See Section 3, 2nd paragraph for
          measurement timing and Section 3.1 for Interval Metric flag.

       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

   c.  Packets Discarded in Bursts Metric

       *  Defined in Appendix A.b of [RFC7003].

   d.  Number of bursts

       *  Metric Name: Number of discard bursts in RTP.

       *  Metric Description: The total number of bursts with discarded
          RTP packets in the period of the report.

       *  Method of Measurement or Calculation: See Section 3.1, Number
          of discard bursts definition.

       *  Units of Measurement: See Section 3.1 for the Number of bursts
          definition.





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       *  Measurement Point(s) with Potential Measurement Domain: See
          Section 3, 1st paragraph.

       *  Measurement Timing: See Section 3, 2nd paragraph for
          measurement timing and Section 3.1 for Interval Metric flag.

       *  Use and Applications: See Section 1.4.

       *  Reporting Model: See RFC 3611.

   e.  Total Packets Expected in Bursts Metric

       *  Defined in Appendix A.c of [RFC7003].

   f.  Discard Count

       *  Defined in Appendix A.a of [RFC7002].

Authors' Addresses

   Varun Singh
   Nemu Dialogue Systems Oy
   Runeberginkatu 4c A 4
   Helsinki  00100
   Finland

   EMail: varun.singh@iki.fi
   URI:   http://www.callstats.io/


   Colin Perkins
   University of Glasgow
   School of Computing Science
   Glasgow  G12 8QQ
   United Kingdom

   EMail: csp@csperkins.org


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

   EMail: alan.d.clark@telchemy.com





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   Rachel Huang
   Huawei Technologies Co., Ltd.
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: Rachel@huawei.com












































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