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Versions: (draft-ott-xrblock-rtcp-xt-discard-metrics) 00 01 02 03 04 05 06 07 08 09 RFC 7097

XR Block Working Group                                            J. Ott
Internet-Draft                                                  V. Singh
Intended status: Standards Track                        Aalto University
Expires: January 6, 2013                                       I. Curcio
                                                   Nokia Research Center
                                                            July 5, 2012


   RTP Control Protocol (RTCP) Extended Reports (XR) for  Run Length
                  Encoding (RLE) of Discarded Packets
         draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04.txt

Abstract

   The RTP 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
   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 January 6, 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



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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 . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  XR Discard RLE Report Block  . . . . . . . . . . . . . . . . .  4
   4.  XR Bytes Discarded Report Block  . . . . . . . . . . . . . . .  5
   5.  Protocol Operation . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Reporting Node (Receiver)  . . . . . . . . . . . . . . . .  7
     5.2.  Media Sender . . . . . . . . . . . . . . . . . . . . . . .  7
   6.  SDP signaling  . . . . . . . . . . . . . . . . . . . . . . . .  8
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
     8.1.  XR Report Block Registration . . . . . . . . . . . . . . .  9
     8.2.  SDP Parameter Registration . . . . . . . . . . . . . . . .  9
     8.3.  Contact information for IANA registrations . . . . . . . .  9
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   10. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     10.1. Normative References . . . . . . . . . . . . . . . . . . .  9
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 10
     A.1.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00  . . . . 11
     A.2.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01  . . . . 11
     A.3.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02  . . . . 11
     A.4.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-03  . . . . 11
     A.5.  changes in
           draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04  . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11













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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 (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 characteristics.

   RFC3611 [RFC3611] defines RTCP Extended 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, although at the expense of extra overhead.

   Among many other report blocks, RFC3611 specifies the Loss RLE block
   which reports 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).  The "discard rate" 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].  If an
      endpoint needs to report packet discard due to other reasons than
      early- and late-arrival (for example, discard due to duplication,
      redundancy, etc.) then it should consider using the Discarded
      Packets Report Block [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 the
      duration of the session
      [I-D.ietf-xrblock-rtcp-xr-burst-gap-discard].

   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 [I-D.ietf-xrblock-rtcp-xr-discard] or from the gap/burst
   report [I-D.ietf-xrblock-rtcp-xr-burst-gap-discard], these two



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   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].

   Complementary to or instead of the indication which packets were
   discarded, an XR block is defined to indicate the number of bytes
   discarded, 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",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119] and indicate requirement levels for compliant
   implementations.

   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].  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.














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       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

   Block Type (BT, 8 bits): A Run-length encoded Discarded Packets
   Report Block is identified by the constant DRLE.

   [Note to RFC Editor: please replace DRLE with the IANA provided RTCP
   XR block type for this block.  Please remove this note prior to
   publication as an RFC.]

   rsvd (3 bits): These reserved 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 and not appear marked in both.  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
   [RFC6390].



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       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 |       block length=2          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of source                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                  number of bytes discarded                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 2: XR Bytes Discarded Report Block

   Block Type (BT, 8 bits): A Bytes Discarded Packets Report Block is
   identified by the constant BDR.

   [Note to RFC Editor: please replace BDR with the IANA provided RTCP
   XR block type for this block.  Please remove this note prior to
   publication as an RFC.]

   The Interval Metric flag (I) (2 bits) is used to indicate whether the
   discard metric is 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).  Since the bytes discarded are not
   measured at a particular time instance but over one or several
   reporting intervals, the metric MUST NOT be reported as a Sampled
   Metric (I=01).

   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 it reports bytes discarded due to early
   arrival and MUST be set to '0' if it reports bytes discarded due to
   late arrival.  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.

   block length (16 bits) MUST be set to 2, in accordance with the
   definition of this field in [RFC3611].  The block MUST be discarded
   if the block length is set to a different value.

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

   If Interval Metric flag (I=11) is set, the value in the field
   indicates the number of bytes discarded from the start of the



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   session, if Interval Metric flag (I=01) is set, it indicates the
   number of bytes discarded since the last RTCP XR Byte Discarded Block
   was received.

   If the XR block follows a measurement identity block
   [I-D.ietf-xrblock-rtcp-xr-meas-identity] in the same RTCP compound
   packet then the cumulative (I=11) or the interval (I=10) for this
   report block corresponds to the values of the "measurement duration"
   in the measurement information block.

   If the receiver sends the Bytes Discarded Report 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)
   node and the media sender.

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.

   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
   RFC4585.

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
   receiver.



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   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 reports.

   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 RLE discard metric and bytes discarded
   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 parameter 'discard-rle' MUST be used to indicate support for the
   Discard RLE Report Block defined in Section 3, the parameter
   'discard-bytes' to indicate support for the Bytes Discarded Report
   Block defined in Section 4

   For signaling support of the RLE discard metric and bytes discarded
   metric, the rules defined in RFC3611 apply.  Generally, senders and
   receivers SHOULD indicate this capability if they support these
   metrics 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.



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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
   above.  Please remove this note prior to publication as an RFC.]

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.  Acknowledgements

   Thanks to Qin Wu, Colin Perkins, Dan Romascanu, and Roni Even 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, March 1997.



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

   [I-D.ietf-xrblock-rtcp-xr-meas-identity]
              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-07 (work in
              progress), January 2012.

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

10.2.  Informative References

   [I-D.ietf-xrblock-rtcp-xr-discard]
              Hunt, G., Clark, A., Zorn, G., and W. Wu, "RTCP XR Report
              Block for Discard metric Reporting",
              draft-ietf-xrblock-rtcp-xr-discard-04 (work in progress),
              December 2011.

   [I-D.ietf-xrblock-rtcp-xr-burst-gap-discard]
              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-03 (work in
              progress), October 2011.


Appendix A.  Change Log

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






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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
      block.
   o  Added this section.

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

   o  Removed the measurement identification tag in the bytes discarded
      block.

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

A.4.  changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-03

   o  Added explanation for block length in bytes discarded block
   o  Added an acknowledgement section

A.5.  changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04

   o  Added Block Type definition to each XRBlock
   o  Made changes requested in WGLC


Authors' Addresses

   Joerg Ott
   Aalto University
   Otakaari 5 A
   Espoo, FIN  02150
   Finland

   Email: jo@comnet.tkk.fi














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

   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
   Finland

   Email: igor.curcio@nokia.com

































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