XR Block Working Group                                     V. Singh, Ed.
Internet-Draft                                                    J. Ott
Intended status: Standards Track                        Aalto University
Expires: May 08, August 30, 2014                                       I. Curcio
                                                   Nokia Research Center
                                                       November 04, 2013
                                                       February 26, 2014

  RTP Control Protocol (RTCP) Extended Report (XR) for Bytes Discarded


   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 report
   computing the bytes discarded from the de-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 May 08, August 30, 2014.

Copyright Notice

   Copyright (c) 2013 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  XR Bytes Discarded Report Block . . . . . . . . . . . . . . .   4
   4.  Protocol Operation  . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Reporting Node (Receiver) . . . . . . . . . . . . . . . .   5
     4.2.  Media Sender  . . . . . . . . . . . . . . . . . . . . . .   6
   5.  SDP signaling . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7   8
     7.1.  XR Report Block Registration  . . . . . . . . . . . . . .   7   8
     7.2.  SDP Parameter Registration  . . . . . . . . . . . . . . .   7   8
     7.3.  Contact information for IANA registrations  . . . . . . .   8
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Appendix A.  Metrics represented using RFC6390 Template . . . . .   9  10
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  10
     B.1.  changes in            draft-singh-xrblock-rtcp-xr-bytes-
           discarded-metric-01 . . . . . . . . . . . . . . . . . . .  10
     B.2.  changes in            draft-ietf-xrblock-rtcp-xr-bytes-            draft-singh-xrblock-rtcp-xr-bytes-
           discarded-metric-00 . . . . . . . . . . . . . . . . . . .  10  11
     B.3.  changes in            draft-ietf-xrblock-rtcp-xr-bytes-
           discarded-metric-00 . . . . . . . . . . . . . . . . . . .  11
     B.4.  changes in            draft-ietf-xrblock-rtcp-xr-bytes-
           discarded-metric-01 . . . . . . . . . . . . . . . . . . .  10  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   RTP [RFC3550] provides a transport for real-time media flows such as
   audio and video together with the RTP control protocol (RTCP) (RTCP), 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 media sender to adapt
   its media transmission and/or encoding dynamically to the observed
   path characteristics.


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

   In addition to lost packets, RFC3611 [RFC3611] defines the notion of
   "discarded" packets: packets that were received but dropped from the
   de-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].  The
   discard metric is believed to be applicable to a large class of RTP
   applications which use a de-jitter buffer RFC5481 [RFC5481].

   Recently proposed extensions to the Extended Reports (XR) reporting
   suggest enhancing this the 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 [RFC7002].  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

   o  Reporting gaps and bursts of discarded packets during a
      measurement interval, i.e., the last reporting interval or the
      duration of the session [RFC7003].

   o  Reporting run-length encoding of discarded packet during a
      measurement interval, i.e., between a set of sequence numbers

   However, none of these metrics allow a receiver to report precisely
   the number of RTP payload bytes that were discarded.  While this
   information could in theory be derived from high-frequency reporting
   on the number of discarded packets [RFC7002] or from the Discard RLE
   report [I-D.ietf-xrblock-rtcp-xr-discard-rle-metrics], [RFC7097], these two mechanisms do not appear feasible: The 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 incurs significant complexity (by storing a
   map of sequence numbers and packet sizes) and reporting overhead.

   An XR block is defined in this document to indicate the number of RTP
   payload bytes discarded, per interval or for the duration of the
   session, similar to the 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].

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

3.  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 |       block length=2          |
   |                        SSRC of source                         |
   |             number of RTP payload bytes discarded             |

                 Figure 1: 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).  In addition, the value I=00 is reserved and MUST NOT
   be sent, and MUST be discarded when received.

   The 'E' bit is introduced to distinguish between packets discarded
   due to early arrival and those discarded due to late arrival.  The
   'E' bit is set to '1' if it reports bytes discarded due to early
   arrival and is set to '0' if it reports bytes discarded due to late
   arrival.  If a duplicate packet is received and discarded, these
   duplicate packets are ignored and not reported.  In case both early
   and late discarded packets shall be reported, two Bytes Discarded
   report blocks MUST be included.

   reserved (5 bits): This field is reserved for future definition.  In
   the absence of such definition, the bits in this field MUST be set to
   zero and MUST be ignored by the receiver.

   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 RTP payload bytes discarded' is a 32-bit unsigned
   integer value indicating the total number of bytes discarded.  Bytes
   discarded corresponds to the RTP payload size of every RTP packet
   that is discarded (due to early or late arrival).  Hence, the bytes
   discarded ignores the size of any RTP header extensions and the size
   of the padding bits.  Also the discarded packet is associated to the
   interval in which it was discarded and not when it was expected.

   If Interval Metric flag (I=11) is set, the value in the field
   indicates the number of RTP payload bytes discarded from the start of
   the session, if Interval Metric flag (I=01) (I=10) is set, it indicates the
   number of bytes discarded since in the last RTCP XR Byte Discarded Block
   was received. most recent reporting interval.

   If the XR block follows a measurement identity block [RFC6776] 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 Receiver Report (RR) as a compound RTCP

4.  Protocol Operation

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

4.1.  Reporting Node (Receiver)
   The media receiver MAY send the Bytes Discard Reports as part of the
   regularly scheduled RTCP packets as per RFC3550.  It MAY also include
   Bytes Discard Reports in immediate or early feedback packets as per

   Transmission of RTCP XR Bytes Discarded Report is up to the
   discretion of the media receiver, as is the reporting granularity.
   However, it is RECOMMENDED that the media receiver signals all the bytes
   discarded packets using the method defined in this document.  When
   reporting several metrics in a single RTCP packet, the reporting
   intervals for the report blocks are synchronized, therefore the media
   receiver may choose to additionally send the Discarded Packets
   [RFC7002] or Discard RLE [RFC7097] Report Block to assist the media
   sender in correlating the bytes discarded to the packets discarded in
   that particular interval.

   If all packets over a reporting period were discarded, the media
   receiver MAY use the Discard Discarded Packets Report Block [RFC7002]

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

4.2.  Media Sender

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

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

   The media 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 [RFC6776].  Under all other
   circumstances it MUST ignore the block.

5.  SDP signaling

   A participant of a media session MAY use SDP to signal its support
   for the report block specified in this document or use them without
   any prior signaling (see section 5 of [RFC3611]).

   For signaling in SDP, the RTCP XR attribute as defined in [RFC3611]
   MUST be used.  The SDP [RFC4566] attribute 'xr-format' defined in
   RFC3611 is augmented as described in the following to indicate the
   bytes discarded metric.

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

      xr-format       =/ xr-discard-bytes

      xr-discard-bytes = "discard-bytes"

   The parameter 'discard-bytes' to indicate support for the Bytes
   Discarded Report Block defined in Section 3.

   When SDP is used in Offer/Answer context, the mechanism defined in
   [RFC3611] for unilateral "rtcp-xr" attribute parameters applies (see
   section 5.2 of [RFC3611]).

6.  Security Considerations

   The Bytes Discarded block does not provide per-packet statistics,
   hence the risk to confidentiality documented in Section 7, paragraph
   3 of [RFC3611] does not apply.  In some situations, returning very
   detailed error information (e.g., over-range measurement or
   measurement unavailable) using this report block can provide an
   attacker with insight into the security processing.  For example,
   assume that the attacker sends a packet with a stale timestamp (i.e.,
   time in the past) to the receiver.  If the receiver now sends a
   discard report with the same number of bytes as the payload of the
   injected packet, the attacker can infer that no security processing
   was performed.  If, on the other hand, the attacker does not receive
   a discard report, it can equivalently assume that the security
   procedures were performed on the packet.

   Implementers should therefore consider the guidance in
   [I-D.ietf-avt-srtp-not-mandatory] for using appropriate security
   mechanisms, i.e., where security is a concern, the implementation
   should apply encryption and authentication to the report block.  For
   example this can be achieved by using the AVPF profile together with
   the Secure RTP profile as defined in [RFC3711]; an appropriate
   combination of the two profiles (an "SAVPF") is specified in
   [RFC5124].  However, other mechanisms also exist (documented in
   [I-D.ietf-avtcore-rtp-security-options]) and might be more suitable.


   The discarded bytes report is employed by the sender to perform
   congestion control, typically, for calculating goodput.  In these
   cases an attacker MAY drive the endpoint to lower its sending rate
   and under-utilised the link, therefore media senders should choose
   appropriate security measures to mitigate such attacks.

   Lastly, the security considerations of [RFC3550], [RFC3611], and
   [RFC4585] apply.

7.  IANA Considerations

   New block types for RTCP XR are subject to IANA registration.  For
   general guidelines on IANA considerations for RTCP XR, refer to

7.1.  XR Report Block Registration

   This document extends the IANA "RTP Control Protocol Extended Reports
   (RTCP XR) Block Type Registry" by a new value: BDR (Bytes Discarded

   [Note to RFC Editor: please replace 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.]

7.2.  SDP Parameter Registration

   This document registers a new parameters for the Session Description
   Protocol (SDP), "discard-bytes" in the "RTP Control Protocol Extended
   Reports (RTCP XR) Session Description Protocol (SDP) Parameters

7.3.  Contact information for IANA registrations

   Varun Singh (varun.singh@iki.fi)

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

   RAI Area Directors: rai-ads@tools.ietf.org

8.  Acknowledgments

   The authors would like to thank Alan Clark, Benoit Claise, Roni Even,
   Vijay Gurbani, Sam Hartman, Vinayak Hegde, Jeffrey Hutzelman, Barry
   Leiba, Colin Perkins, Dan Romascanu, Dan Wing, and Qin Wu for
   providing valuable feedback on earlier versions of this draft.

9.  References

9.1.  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.

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

   [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

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

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

   [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, October 2012.

   [RFC7002]  Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol
              (RTCP) Extended Report (XR) Block for Discard Count Metric
              Reporting", RFC 7002, September 2013.

9.2.  Informative References

   [RFC7003]  Clark, A., Huang, R., and Q. Wu, "RTP Control Protocol
              (RTCP) Extended Report (XR) Block for Burst/Gap Discard
              Metric Reporting", RFC 7003, September 2013.


   [RFC7097]  Ott, J., Singh, V., and I. Curcio, "RTP Control Protocol
              (RTCP) Extended Reports Report (XR) for Run Length Encoding (RLE) RLE of Discarded Packets", draft-ietf-xrblock-rtcp-xr-discard-
              rle-metrics-06 (work in progress), July 2013.
              RFC 7097, January 2014.

   [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
              Applicability Statement", RFC 5481, March 2009.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC5124]  Ott, J. and E. Carrara, "Extended Secure RTP Profile for
              Real-time Transport Control Protocol (RTCP)-Based Feedback
              (RTP/SAVPF)", RFC 5124, February 2008.

              Perkins, C. and M. Westerlund, "Securing the RTP Protocol
              Framework: Why RTP Does Not Mandate a Single Media
              Security Solution", draft-ietf-avt-srtp-not-mandatory-13 draft-ietf-avt-srtp-not-mandatory-16
              (work in progress), May 2013. January 2014.

              Westerlund, M. and C. Perkins, "Options for Securing RTP
              Sessions", draft-ietf-avtcore-rtp-security-options-04 draft-ietf-avtcore-rtp-security-options-10
              (work in progress), July 2013. January 2014.

Appendix A.  Metrics represented using RFC6390 Template

   RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC
   number, when assigned.

   a.  RTP Payload Bytes Discarded Metric

       *  Metric Name: RTP Payload Bytes Discarded Metric

       *  Metric Description: Total number of RTP Payload bytes
          discarded over the period covered by this report.

       *  Method of Measurement or Calculation: See section 4, number of
          bytes discarded definition in [RFCXXXX].

       *  Units of Measurement: See section 4, number of RTP payload
          bytes discarded definition in [RFCXXXX].

       *  Measurement Point(s) with Potential Measurement Domain: See
          section 4, 1st paragraph of [RFCXXXX].

       *  Measurement Timing: See section 4, last three paragraphs of
          [RFCXXXX] for measurement timing and for the Interval Metric

       *  Use and applications: See section 1, paragraph 1 of [RFCXXXX].

       *  Reporting model: See RFC3611.

Appendix B.  Change Log

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

B.1.  changes in draft-singh-xrblock-rtcp-xr-bytes-discarded-metric-01

   o  Address SEC-DIR and Gen-art review.

   o  Incorporate IESG comments.

B.2.  changes in draft-singh-xrblock-rtcp-xr-bytes-discarded-metric-00

   o  Bytes discarded metric split from

B.2. [I-D.ietf-xrblock-rtcp-xr-
      discard-rle-metrics] />.

B.3.  changes in draft-ietf-xrblock-rtcp-xr-bytes-discarded-metric-00

   o  Submitted as a WG draft.


B.4.  changes in draft-ietf-xrblock-rtcp-xr-bytes-discarded-metric-01

   o  Editorial fixes: Updated references from drafts to RFCs.

   o  Updated fields in the RFC6390 template.

   o  Changed 'number of bytes discarded' to 'number of RTP payload
      bytes discarded'.

Authors' Addresses

   Varun Singh (editor)
   Aalto University
   School of Electrical Engineering
   Otakaari 5 A
   Espoo, FIN  02150

   Email: varun@comnet.tkk.fi
   URI:   http://www.netlab.tkk.fi/~varun/

   Joerg Ott
   Aalto University
   School of Electrical Engineering
   Otakaari 5 A
   Espoo, FIN  02150

   Email: jo@comnet.tkk.fi

   Igor D.D. Curcio
   Nokia Research Center
   P.O. Box 1000 (Visiokatu 3)
   Tampere, FIN  33721

   Email: igor.curcio@nokia.com