XR Block Working Group                                            J. Ott
Internet-Draft                                                  V. Singh
Intended status: Standards Track                        Aalto University
Expires: June 11, August 2, 2012                                        I. Curcio
                                                   Nokia Research Center
                                                        December 9, 2011
                                                        January 30, 2012

 Real-time Transport Control Protocol (RTCP) Extension Report (XR) for
                Run Length Encoding of Discarded Packets


   The Real-time Transport Control Protocol (RTCP) is used in
   conjunction with the Real-time Transport Protocol (RTP) in to provide
   a variety of short-term and long-term reception statistics.  The
   available reporting may include aggregate information across longer
   periods of time as well as individual packet reporting.  This
   document specifies a per-packet report metric capturing individual
   packets discarded from the jitter buffer after successful reception.

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 11, August 2, 2012.

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   Copyright (c) 2011 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  XR Discard RLE Report Block  . . . . . . . . . . . . . . . . .  4
   4.  XR Bytes Discarded Report Block  . . . . . . . . . . . . . . .  5
   5.  Protocol Operation . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Reporting Node (Receiver)  . . . . . . . . . . . . . . . .  6
     5.2.  Media Sender . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  SDP signaling  . . . . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  8
     8.1.  XR Report Block Registration . . . . . . . . . . . . . . .  8
     8.2.  SDP Parameter Registration . . . . . . . . . . . . . . . .  8
     8.3.  Contact information for IANA registrations . . . . . . . .  9  8
   9.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 10
     A.1.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00  . . . . 10
     A.2.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01  . . . . 10
     A.3.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02  . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10

1.  Introduction

   RTP [RFC3550] provides a transport for real-time media flows such as
   audio and video together with the RTP control protocol which provides
   periodic feedback about the media streams received in a specific
   duration.  In addition, RTCP can be used for timely feedback about
   individual events to report (e.g., packet loss) [RFC4585].  Both
   long-term and short-term feedback enable a sender to adapt its media
   transmission and/or encoding dynamically to the observed path

   RFC3611 [RFC3611] defines RTCP eXtension Reports as a detailed
   reporting framework to provide more than just the coarse RR
   statistics.  The detailed reporting may enable a sender to react more
   appropriately to the observed networking conditions as these can be
   characterized better, albeit at the expense of extra overhead.

   Among many other fields, RFC3611 specifies the Loss RLE block which
   define runs of packets received and lost with the granularity of
   individual packets.  This can help both error recovery and path loss
   characterization.  In addition to lost packets, RFC3611 defines the
   notion of "discarded" packets: packets that were received but dropped
   from the jitter buffer because they were either too early (for
   buffering) or too late (for playout).  This metric is part of the
   VoIP metrics report block even though it is not just applicable to
   audio: it is specified as the fraction of discarded packets since the
   beginning of the session.  See section 4.7.1 of RFC3611 [RFC3611].

   Recently proposed extensions to the XR reporting suggest enhancing
   this discard metric:
   o  Reporting the number of discarded packets in a measurement
      interval, i.e., during either the last reporting interval or since
      the beginning of the session, as indicated by a flag in the
      suggested XR report [I-D.ietf-xrblock-rtcp-xr-discard].
   o  Reporting gaps and bursts of discarded packets during a
      measurement interval, i.e., the last reporting interval or
      cumulatively since the beginning of the session

   However, none of these metrics allow a receiver to report precisely
   which packets were discarded.  While this information could in theory
   be derived from high-frequency reporting on the number of discarded
   packets or from the gap/burst report, these two mechanisms do not
   appear feasible: The former would require an unduly high amount of
   reporting which still might not be sufficient due to the non-
   deterministic scheduling of RTCP packets.  The latter incur
   significant complexity and reporting overhead and might still not
   deliver the desired accuracy.

   This document defines a discard report block following the idea of
   the run-length encoding applied for lost and received packets in
   RFC3611 [RFC3611].

   Complementary to or instead of the indication which packets were
   lost, an XR block is defined to indicate the number of bytes lost,
   per interval or for the duration of the session, similar to other XR
   report blocks.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119] and indicate requirement levels for compliant

   The terminology defined in RTP [RFC3550] and in the extensions for XR
   reporting [RFC3611] applies.

3.  XR Discard RLE Report Block

   The XR Discard RLE report block uses the same format as specified for
   the loss and duplicate report blocks in RFC3611 [RFC3611].  Figure
   Figure 1 recaps the packet format.  The fields "BT", "T", "block
   length", "SSRC of source", "begin_seq", and "end_seq" SHALL have the
   same semantics and representation as defined in RFC3611.  The
   "chunks" encoding the run length SHALL have the same representation
   as in RFC3611, but encode discarded packets.

       0               1               2               3
       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
      |     BT=DRLE   |rsvd |E|   T   |         block length          |
      |                        SSRC of source                         |
      |          begin_seq            |             end_seq           |
      |          chunk 1              |             chunk 2           |
      :                              ...                              :
      |          chunk n-1            |             chunk n           |

                     Figure 1: XR Discard Report Block

   These reserved bits (2 bits) SHOULD be set to zero by receivers and
   MUST be ignored by senders.

   The 'E' bit is introduced to distinguish between packets discarded
   due to early arrival and those discarded due to late arrival.  The
   'E' bit MUST be set to '1' if the chunks represent packets discarded
   due to too early arrival and MUST be set to '0' otherwise.

   In case both early and late discarded packets shall be reported, two
   Discard RLE report blocks MUST be included; their sequence number
   range MAY overlap, but individual packets MUST only be reported as
   either early or late.  Packets reported in both MUST be considered as
   discarded without further information available, packets reported in
   neither are considered to be properly received and not discarded.

   Discard RLE Report Blocks SHOULD be sent in conjunction with an RTCP
   RR as a compound RTCP packet.

4.  XR Bytes Discarded Report Block

   The XR Bytes Discarded report block uses the following format which
   follows the model of the framework for performance metric development

       0               1               2               3
       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
      |     BT=BDR    | I |E|reserved | Tag |E|res|       block length=2          |
      |                        SSRC of source                         |
      |                  number of bytes discarded                    |

                 Figure 2: XR Bytes Discarded Report Block

   The Interval Metric flag (I) (2 bits) is used to indicate whether the
   discard metric is Sampled, Interval, or a Cumulative metric, that is,
   whether the reported value applies to the most recent measurement
   interval duration between successive reports (I=10, the Interval
   Duration) or to the accumulation period characteristic of cumulative
   measurements (I=11, the Cumulative Duration) or is a sampled value

   The 'E' bit is introduced to distinguish between packets discarded
   due to early arrival and those discarded due to late arrival.  The
   'E' bit MUST be set to '1' if the chunks represent packets discarded
   due to too early arrival and MUST be set to '0' otherwise.  In case
   both early and late discarded packets shall be reported, two Bytes
   Discarded report blocks MUST be included.

   These reserved bits (5 bits) SHOULD be set to zero by receivers and
   MUST be ignored by senders.

   The 'number of bytes discarded' is a 32-bit unsigned integer value
   indicating the total number of bytes discarded discarded.

   If the XR block is not preceded by a measurement identity block
   [I-D.ietf-xrblock-rtcp-xr-meas-identity] then the value indicates the
   bytes lost from from the start of the session (I=11), or the number
   of bytes discarded since the last RTCP XR Bytes Discarded block was
   sent (I=10), or bytes discarded in
   received (I=10).

   If the XR block follows a measurement identity block
   [I-D.ietf-xrblock-rtcp-xr-meas-identity] in an RTCP RR packet then
   the cumulative (I=11) and interval (I=01)
   [I-D.ietf-xrblock-rtcp-xr-meas-identity]. (I=10) correspond to the values in
   the measurement block.

   If the receiver sends the Bytes Discarded Report Blocks SHOULD Block without the
   measurement identity block then the discard block MUST be sent in
   conjunction with an RTCP RR as a compound RTCP packet.

5.  Protocol Operation

   This section describes the behavior of the reporting (= receiver) RTP
   node and the sender RTP node.

5.1.  Reporting Node (Receiver)

   Transmission of RTCP XR Discard RLE Reports is up to the discretion
   of the receiver, as is the reporting granularity.  However, it is
   RECOMMENDED that the receiver signals all discarded packets using the
   method defined in this document.  If all packets over a reporting
   period were lost, the receiver MAY use the Discard Report Block
   [I-D.ietf-xrblock-rtcp-xr-discard] instead.  In case of limited
   available reporting bandwidth, it is up to the receiver whether or
   not to include RTCP XR Discard RLE reports or not. reports.

   The receiver MAY send the Discard RLE Reports as part of the
   regularly scheduled RTCP packets as per RFC3550.  It MAY also include
   Discard RLE Reports in immediate or early feedback packets as per

5.2.  Media Sender

   The media sender MUST be prepared to operate without receiving any
   Discard RLE reports.  If Discard RLE reports are generated by the
   receiver, the sender cannot rely on all these reports being received,
   nor can the sender rely on a regular generation pattern from the
   receiver side.

   However, if the sender receives any RTCP reports but no Discard RLE
   report blocks and is aware that the receiver supports Discard RLE
   report blocks, it MAY assume that no packets were discarded at the

   The sender SHOULD accept the Bytes Discarded Report Block only if it
   is received in a compound RTCP receiver report or if it is preceded
   by a measurement identity block
   [I-D.ietf-xrblock-rtcp-xr-meas-identity].  Under all other
   circumstances it MUST ignore the block.

6.  SDP signaling

   The report blocks specified in this document define extensions to
   RTCP XR reporting.  Whether or not this specific extended report is
   sent is left to the discretion of the receiver.  Its presence may
   enable better operation of the sender since more detailed information
   is available.  Not providing this information will make the sender
   rely on other RTCP report metrics.

   A participant of a media session MAY use SDP to signal its support
   for this attribute.  In this case, the RTCP XR attribute as defined
   in RFC3611 [RFC3611] MUST be used.  The SDP RFC4566 [RFC4566]
   attribute 'xr-format' defined in RFC3611 is augmented as described in
   the following to indicate the discard metric.

      rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)]
                       CRLF   ; defined in [RFC3611]

      xr-format       =/ xr-discard-rle
                       / xr-discard-bytes

      xr-discard-rle   = "discard-rle"
      xr-discard-bytes = "discard-bytes"

   The literal 'discard-rle' MUST be used to indicate support for the
   Discard RLE Report Block defined in section Section 3, the literal
   'discard-bytes' to indicate support for the Bytes Discarded Report
   Block defined in section Section 4

   For signaling support for the discard metric, the rules defined in
   RFC3611 apply.  Generally, senders and receivers SHOULD indicate this
   capability if they support this metric and would like to use it in
   the specific media session being signaled.  The receiver MAY decide
   not to send discard information unless it knows about the sender's
   support to save on RTCP reporting bandwidth.

   A participant in a media session MAY use the two report blocks
   specified in this document without any explicit (SDP) signaling.

7.  Security Considerations

   The security considerations of RFC3550 [RFC3550], RFC3611 [RFC3611],
   and RFC4585 [RFC4585] apply.  Since this document offers only a more
   precise reporting for an already existing metric, no further security
   implications are foreseen.

8.  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 [RFC3611].

8.1.  XR Report Block Registration

   This document extends the IANA "RTCP XR Block Type Registry" by two
   new values: DRLE and BDR.

   [Note to RFC Editor: please replace DRLE and BDR with the IANA
   provided RTCP XR block type for this block here and in the diagrams

8.2.  SDP Parameter Registration

   This document registers two new parameters for the Session
   Description Protocol (SDP), "discard-rle" and "discard-bytes", in the
   "RTCP XR SDP Parameters Registry".

8.3.  Contact information for IANA registrations

   Joerg Ott (jo@comnet.tkk.fi)

   Aalto University Comnet, Otakaari 5A, 02150 Espoo, Finland.

9.  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.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
              July 2006.

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

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

   [RFC5760]  Ott, J., Chesterfield, J., and E. Schooler, "RTP Control
              Protocol (RTCP) Extensions for Single-Source Multicast
              Sessions with Unicast Feedback", RFC 5760, February 2010.

              Hunt, G., Clark, A., Zorn, G., and W. Wu, "RTCP XR Report
              Block for Discard metric Reporting",
              draft-ietf-xrblock-rtcp-xr-discard-00 (work in progress),
              October 2011.

              Hunt, G., Clark, A., Huang, R., and W. Wu, "RTCP XR Report
              Block for Burst/Gap Discard metric Reporting",
              draft-ietf-xrblock-rtcp-xr-burst-gap-discard-00 (work in
              progress), October 2011.

              Hunt, G., Clark, A., and W. Wu, "Measurement Identity and
              information Reporting using SDES item and XR Block",
              draft-ietf-xrblock-rtcp-xr-meas-identity-01 (work in
              progress), October 2011.

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

Appendix A.  Change Log

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

A.1.  changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00

   o  Changed the interval flag from 1 to 2 bits in the discarded bytes
      report.  Also added the measurement identification tag to the
   o  Added this section.

A.2.  changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01

   o  Removed the measurement identification tag to in the bytes discarded

A.3.  changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02

   o  Removed the extra Tag bits from the Discarded bytes XR block.
   o  Clarified use of measurement identity block in Section 4 and 5.2

Authors' Addresses

   Joerg Ott
   Aalto University
   Otakaari 5 A
   Espoo, FIN  02150

   Email: jo@comnet.tkk.fi

   Varun Singh
   Aalto University
   School of Science and Technology
   Otakaari 5 A
   Espoo, FIN  02150

   Email: varun@comnet.tkk.fi
   URI:   http://www.netlab.tkk.fi/~varun/
   Igor D.D. Curcio
   Nokia Research Center
   P.O. Box 1000 (Visiokatu 1)
   Tampere, FIN  33721

   Email: igor.curcio@nokia.com