XR Block Working Group                                            J. Ott
Internet-Draft                                          Aalto University
Intended status: Standards Track                               I. Curcio
Expires: March 16, 2012                            Nokia Research Center
                                                                V. Singh
                                                        Aalto University
                                                      September 13, 2011


  Real-time Transport Control Protocol Extension Report for Run Length
                     Encoding of Discarded Packets
            draft-ott-xrblock-rtcp-xt-discard-metrics-01.txt

Abstract

   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
   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 March 16, 2012.

Copyright Notice

   Copyright (c) 2011 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



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   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
   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 . . . . . . . . . . . . . . . . . . . . . .  6
     5.1.  Reporting Node (Receiver)  . . . . . . . . . . . . . . . .  7
     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 . . . . . . . . . . . . . . . .  9
     8.3.  Contact information for IANA registrations . . . . . . . .  9
   9.  Normative References . . . . . . . . . . . . . . . . . . . . .  9
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10


























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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 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
   characteristics.

   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, RFC 3611 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 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-avt-rtcp-xr-discard].
   o  Reporting gaps and bursts of discarded packets during the last
      reporting interval or cumulatively since the beginning of the
      session [I-D.ietf-avt-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 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.




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   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
   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",
   "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 [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.




















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       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=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

   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.

   Editor's node: is it acceptable to use one of the 'reserved' bits for
   this purpose or should two block types be used?


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
   [I-D.ietf-pmol-metrics-framework].









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

                 Figure 2: XR Bytes Discarded Report Block

   The Interval Metric flag (I) (1 bit) is used to indicate whether the
   Post-Repair Loss metric is an Interval or a Cumulative metric, that
   is, whether the reported value applies to the most recent measurement
   interval duration between successive metrics reports (I=1) (the
   Interval Duration) or to the accumulation period characteristic of
   cumulative measurements (I=0) (the Cumulative Duration).  Numerical
   values for both these intervals are provided in the Measurement
   Identifier block referenced by the tag field below.

   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.

   The 'number of bytes discarded' is a 32-bit unsigned integer value
   indicating the total number of bytes discarded (I=0) or the number of
   bytes discarded since the last RTCP XR Bytes Discarded block was
   sent.

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

   Editor's note: is it acceptable to use one of the 'reserved' bits for
   this purpose or should two block types be used?


5.  Protocol Operation

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







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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-avt-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.

   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.


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.







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      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, RFC3611, and 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.]




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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.

   [I-D.ietf-avt-rtcp-xr-discard]
              Hunt, G. and A. Clark, "RTCP XR Report Block for Discard
              metric Reporting", draft-ietf-avt-rtcp-xr-discard-02 (work
              in progress), May 2009.

   [I-D.ietf-avt-rtcp-xr-burst-gap-discard]



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              Hunt, G. and A. Clark, "RTCP XR Report Block for Burst/Gap
              Discard metric Reporting",
              draft-ietf-avt-rtcp-xr-burst-gap-discard-02 (work in
              progress), May 2009.

   [I-D.ietf-pmol-metrics-framework]
              Clark, A. and B. Claise, "Guidelines for Considering New
              Performance Metric Development",
              draft-ietf-pmol-metrics-framework-08 (work in progress),
              January 2011.


Authors' Addresses

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

   Email: jo@comnet.tkk.fi


   Igor D.D. Curcio
   Nokia Research Center
   P.O. Box 1000 (Visiokatu 1)
   Tampere, FIN  33721
   Finland

   Email: igor.curcio@nokia.com


   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/










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