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Audio/Video Transport Working Group                             A. Clark
Internet-Draft                                                  Telchemy
Intended status: Standards Track                                 G. Zorn
Expires: June 22, 2013                                       Network Zen
                                                                   Q. Wu
                                                                  Huawei
                                                       December 19, 2012


RTP Control Protocol (RTCP) Extended Report (XR) Block for Discard Count
                            metric Reporting
               draft-ietf-xrblock-rtcp-xr-discard-11.txt

Abstract

   This document defines an RTP Control Protocol(RTCP) Extended Report
   (XR) Block that allows the reporting of a simple discard count metric
   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
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   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on June 22, 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
   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Discard Count 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.  Discard Count Metric Report Block  . . . . . . . . . . . . . .  6
     3.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  6
     3.2.  Definition of Fields in Discard Count Metric Report
           Block  . . . . . . . . . . . . . . . . . . . . . . . . . .  6
   4.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  9
     4.1.  SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . .  9
     4.2.  Offer/Answer Usage . . . . . . . . . . . . . . . . . . . .  9
   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 . . . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 15
     A.1.  draft-ietf-xrblock-rtcp-xr-discard-11  . . . . . . . . . . 15
     A.2.  draft-ietf-xrblock-rtcp-xr-discard-10  . . . . . . . . . . 15
     A.3.  draft-ietf-xrblock-rtcp-xr-discard-09  . . . . . . . . . . 15
     A.4.  draft-ietf-xrblock-rtcp-xr-discard-08  . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16















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1.  Introduction

1.1.  Discard Count Report Block

   This document 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 number of packets which are received
   correctly but are never played out, typically because they arrive too
   late to be played out (buffer underflow) or too early (buffer
   overflow).  The metric is applicable both to systems which use packet
   loss repair techniques (such as forward error correction [RFC5109] or
   retransmission [RFC4588]) and to those which do not.

   This metric is useful for identifying the existence, and
   characterizing the severity, of a packet transport problem which may
   affect users' perception of a service delivered over RTP.

   This block may be used in conjunction with [BGDISCARD] which provides
   additional information on the pattern of discarded packets.  However
   the metric in [BGDISCARD] may be used independently of the metrics in
   this block.

   In case of Discard count Metrics Block sent together with Burst gap
   discard Metrics Block defined in [BGDISCARD] to the media sender or
   RTP based network management system, information carried in the
   discard count Metrics Block and Burst gap discard Metrics Block
   allows them calculate the some bust gap summary statistics, e.g., gap
   discard rate.

   The metric belongs to the class of transport-related end system
   metrics defined in [RFC6792].

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.  The RTP
   Monitoring Architectures [RFC6792] provides guideline for reporting
   block format using RTCP XR.  The Metrics Block described in this
   document are in accordance with the guidelines in [RFC6390] and
   [RFC6792].




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1.4.  Applicability

   This metric is believed to be applicable to a large class of RTP
   applications which use a jitter buffer.

   Discards due to late or early arriving packets affects user
   experience.  The reporting of discards alerts senders and other
   receivers to the need to adjust their transmission or reception
   strategies.  The reports allow network managers to diagnose these
   user experience problems.

   The ability to detect duplicate packets can be used by managers to
   detect network layer or sender behavior which may indicate network or
   device issues.  Based on the reports, these issues may be addressed
   prior to any impact on user experience.




































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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 Discard Count
      Metric counts only discarded packets.  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"
      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.
























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3.  Discard Count Metric Report Block

   Metrics in this block report on the number of packets discarded in
   the stream arriving at the RTP end system.  The measurement of these
   metrics is made at the receiving end of the RTP stream.  Instances of
   this Metrics Block refer by SSRC to the separate auxiliary
   Measurement Information block [RFC6776] which describes measurement
   Intervals in use.  This Metrics Block relies on the measurement
   interval in the Measurement Information block indicating the span of
   the report and should be sent in the same compound RTCP packet as the
   measurement information block.  If the measurement interval is not
   received in the same compound RTCP packet as this Metrics Block, this
   Metrics Block should be discarded.

3.1.  Report Block Structure


        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=PDC    | I |DT |  resv.|      block length = 2         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                        SSRC of Source                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    number of packets discarded                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

3.2.  Definition of Fields in Discard Count Metric Report Block

   Block type (BT): 8 bits

      A Discard Count Metric Report Block is identified by the constant
      PDC.

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


   Interval Metric Flag (I): 2 bits

      This field indicates whether the reported metric is an interval,
      cumulative, or sampled metric [RFC6792].  The Discard Count Metric
      can only be measured over definite intervals, and cannot be
      sampled.  Accordingly, the value I=01, indicating a sampled value,
      MUST NOT be used.  The value I=00 is reserved for future
      definition, and MUST NOT be used.



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   Discard Type (DT): 2bits

      This field is used to identify the discard type used in this
      report block.  The discard type is defined as follows:

         00: Report packet discarded or being thrown away before playout
         due to packets duplication.

         01: Report packet discarded due to too early to be played out.

         10: Report packet discarded due to too late to be played out.


      The value DT=11 is reserved for future definition and MUST NOT be
      used.

      An endpoint MAY report any combination of discard types in each
      reporting interval by including several Discard Count Metric
      Report Blocks in a single RTCP XR packet.

      Some systems send duplicate RTP packets for robustness or error
      resilience.  This is NOT RECOMMENDED since it breaks RTCP packet
      statistics.  If duplication is desired for error resilience, the
      mechanism described in [RTPDUP] can be used, since this will not
      cause breakage of RTP streams or RTCP statistics.


   Reserved (resv): 4 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, in
      accordance with the definition in[RFC3611] .  This field MUST be
      set to 2 to match the fixed length of the report block.  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].







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   number of packets discarded: 32 bits

      Number of packets discarded over the period (Interval or
      Cumulative) covered by this report.

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

      Note that the number of packets expected in the period associated
      with this metric (whether interval or cumulative) is available
      from the difference between a pair of extended sequence numbers in
      the Measurement Information block [RFC6776], so need not be
      repeated in this block.





































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4.  SDP Signaling

   [RFC3611] defines the use of SDP (Session Description Protocol)
   [RFC4566] for signaling the use of XR blocks.  However XR blocks MAY
   be used without prior signaling (see section 5 of RFC3611).

4.1.  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-pdc-block

    xr-pdc-block = "pkt-dscrd-count"

4.2.  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 of Offer/Answer for unilateral
   parameter, refer to section 5.2 of [RFC3611].





























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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
   [RFC3611].

5.1.  New RTCP XR Block Type value

   This document assigns the block type value PDC in the IANA " RTP
   Control Protocol Extended Reports (RTCP XR) Block Type Registry " to
   the "Discard Count Metrics Block".

   [Note to RFC Editor: please replace PDC 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 "pkt-dscrd-count" in the
   " RTP Control Protocol Extended Reports (RTCP XR) Session Description
   Protocol (SDP) Parameters Registry ".

5.3.  Contact information for registrations


   The following contact information is provided for all
   registrations in this document:

   Qin Wu (sunseawq@huawei.com)

   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China



















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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 [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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7.  Contributors

   Geoff Hunt wrote the initial draft of this document.
















































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8.  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,Kevin
   Gross, Varun Singh, Claire Bi, Roni Even, Dan Romascanu and Jonathan
   Lennox.









































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9.  References

9.1.  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.

   [RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
              Considerations for Protocol Extensions", RFC 6709,
              September 2012.

   [RFC6776]  Hunt, G., "Measurement Identity and information Reporting
              using SDES item and XR Block", RFC 6776, October 2012.

9.2.  Informative References

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

   [RFC4588]  Rey, J., "RTP Retransmission Payload Format", RFC 4588,
              July 2006.

   [RFC5109]  Li, A., "RTP Payload Format for Generic Forward Error
              Correction", RFC 5109, July 2006.

   [RFC5725]  Begen, A., "RTCP XR Report Block for Post-Repair Loss
              metric Reporting", RFC 5725, February 2010.

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

   [RFC6792]  Wu, Q., "Monitoring Architectures for RTP", RFC 6792,
              November 2012.

   [RTPDUP]   Begen, A. and C. Perkins, "Duplicating RTP Streams",
              ID draft-ietf-avtext-rtp-duplication-00, 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-discard-11

   The following are the major changes compared to previous version:

   o  Editorial change t based on SDP Directorate and Colin's Review.

A.2.  draft-ietf-xrblock-rtcp-xr-discard-10

   The following are the major changes compared to previous version:

   o  Editorial change to get in line with recently discussed drafts.

   o  Remove DT=3 based on the discussion to summary statistics draft.

A.3.  draft-ietf-xrblock-rtcp-xr-discard-09

   The following are the major changes compared to previous version:

   o  SDP Duplicated Parameter Deleting.

A.4.  draft-ietf-xrblock-rtcp-xr-discard-08

   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


   Glen Zorn
   Network Zen
   77/440 Soi Phoomjit, Rama IV Road
   Phra Khanong, Khlong Toie
   Bangkok  10110
   Thailand

   Phone: +66 (0) 87 502 4274
   Email: gwz@net-zen.net


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

   Email: sunseawq@huawei.com






















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