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rfc:rfc7003

Internet Engineering Task Force (IETF) A. Clark Request for Comments: 7003 Telchemy Category: Standards Track R. Huang ISSN: 2070-1721 Q. Wu, Ed.

                                                                Huawei
                                                        September 2013
       RTP Control Protocol (RTCP) Extended Report (XR) Block
               for Burst/Gap Discard Metric Reporting

Abstract

 This document defines an RTP Control Protocol (RTCP) Extended Report
 (XR) block that allows the reporting of burst and gap discard metrics
 for use in a range of RTP applications.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7003.

Copyright Notice

 Copyright (c) 2013 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
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Clark, et al. Standards Track [Page 1] RFC 7003 RTCP XR Burst/Gap Discard September 2013

Table of Contents

 1. Introduction ....................................................2
    1.1. Burst/Gap Discard Metrics Block ............................2
    1.2. RTCP and RTCP Extended Reports .............................3
    1.3. Performance Metrics Framework ..............................3
    1.4. Applicability ..............................................3
 2. Terminology .....................................................3
 3. Burst/Gap Discard Metrics Block .................................4
    3.1. Report Block Structure .....................................5
    3.2. Definition of Fields in Burst/Gap Discard Metrics Block ....5
    3.3. Derived Metrics Based on Reported Metrics ..................7
 4. Considerations for Voice-over-IP Applications ...................7
 5. SDP Signaling ...................................................8
    5.1. SDP rtcp-xr Attribute Extension ............................8
    5.2. Offer/Answer Usage .........................................8
 6. IANA Considerations .............................................8
    6.1. New RTCP XR Block Type Value ...............................8
    6.2. New RTCP XR SDP Parameter ..................................9
    6.3. Contact Information for Registrations ......................9
 7. Security Considerations .........................................9
 8. Contributors ....................................................9
 9. Acknowledgments .................................................9
 10. References ....................................................10
    10.1. Normative References .....................................10
    10.2. Informative References ...................................10
 Appendix A.  Metrics Represented Using the Template from RFC 6390..12

1. Introduction

1.1. Burst/Gap Discard Metrics 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 proportion of packets discarded by the
 jitter buffer at the receiver, using packet discard logic according
 to the jitter buffer algorithms.  The discards during discard bursts
 are reported, together with the number of bursts.  This block is
 intended to be used in conjunction with [RFC7002], which provides the
 total packets discarded and on which this block therefore depends.
 However, the metric in [RFC7002] may be used independently of the
 metrics in this block.
 This block provides information on transient IP problems.  Burst/gap
 metrics are typically used in cumulative reports; however, they also
 may be used in interval reports (see the Interval Metric flag in
 Section 3.2).  The burstiness of packet discard affects user
 experience, may influence any sender strategies to mitigate the
 problem, and may also have diagnostic value.

Clark, et al. Standards Track [Page 2] RFC 7003 RTCP XR Burst/Gap Discard September 2013

 The metric belongs to the class of transport-related end-system
 metrics defined in [RFC6792].
 The definitions of "burst", "gap", "loss", and "discard" are
 consistent with the definitions in [RFC3611].  To accommodate the
 range of jitter buffer algorithms and packet discard logic that may
 be used by implementors, the method used to distinguish between
 bursts and gaps shall use an equivalent method to that defined in
 Section 4.7.2 of [RFC3611].  Note that reporting the specific jitter
 buffer algorithms and/or packet discard logic is out of the scope of
 this document.

1.2. RTCP and RTCP Extended 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 Framework [RFC6792] provides guidelines for reporting
 block format using RTCP XR.  The metrics block described in this
 document is in accordance with the guidelines in [RFC6390] and
 [RFC6792].

1.4. Applicability

 These metrics are applicable to a range of RTP applications that
 contain de-jitter buffers [RFC5481] at the receiving end to smooth
 variation in packet-arrival time and don't use stream repair means,
 e.g., Forward Error Correction (FEC) [RFC5109] and/or retransmission
 [RFC4588].

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 RFC 2119 [RFC2119].

Clark, et al. Standards Track [Page 3] RFC 7003 RTCP XR Burst/Gap Discard September 2013

 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 to be played out, too
    late to be played out, or thrown away before playout due to packet
    duplication or redundancy shall be regarded as discarded.  A
    packet shall not be regarded as discarded if it arrives within
    this time window but is dropped during decoding by some higher-
    layer decoder, e.g., due to a decoding error.  A packet shall be
    classified as one of received (or OK), discarded, or lost.  The
    metric "cumulative number of packets lost" defined in [RFC3550]
    reports a count of packets lost from the media stream (single
    synchronization source (SSRC) within a single RTP session).
    Similarly, the metric "number of packets discarded" defined in
    [RFC7002] reports a count of packets discarded from the media
    stream (single SSRC within a single RTP session) arriving at the
    receiver.  Another metric, defined in [RFC5725], is available to
    report on packets that are not recovered by any repair techniques
    that may be in use.  Note that the term "discard" defined here
    builds on the "discard" definition in [RFC3611] but extends the
    concept to take into account packet duplication and reports
    different types of discard counts [RFC7002].
 Bursts and Gaps
    The terms "burst" and "gap" are used in a manner consistent with
    that of RTCP XR [RFC3611].  RTCP XR views an RTP stream as being
    divided into bursts, which are periods during which the discard
    rate is high enough to cause noticeable quality degradation
    (generally over 5 percent discard rate), and gaps, which are
    periods during which discarded packets are infrequent and hence
    quality is generally acceptable.

3. Burst/Gap Discard Metrics Block

 Metrics in this block report on burst/gap discard in the stream
 arriving at the RTP system.  Measurements of these metrics are made
 at the receiving end of the RTP stream.  Instances of this metrics
 block use the synchronization source (SSRC) to refer to the separate
 auxiliary Measurement Information Block [RFC6776], which describes
 measurement periods in use (see [RFC6776], Section 4.2).
 This metrics block relies on the measurement period in the
 Measurement Information Block indicating the span of the report.
 Senders MUST send this block in the same compound RTCP packet as the

Clark, et al. Standards Track [Page 4] RFC 7003 RTCP XR Burst/Gap Discard September 2013

 Measurement Information Block.  Receivers MUST verify that the
 measurement period is received in the same compound RTCP packet as
 this metrics block.  If not, this metrics block MUST be discarded.

3.1. Report Block Structure

 The structure of the Burst/Gap Discard Metrics Block is as follows.
     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=20     | I |   resv    |      Block Length = 3         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        SSRC of Source                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Threshold   |         Packets Discarded in Bursts           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       Total Packets Expected in Bursts        |   Reserved    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 1: Report Block Structure

3.2. Definition of Fields in Burst/Gap Discard Metrics Block

 Block Type (BT): 8 bits
    A Burst/Gap Discard Metrics Block is identified by the constant
    20.
 Interval Metric flag (I): 2 bits
    This field is used to indicate whether the burst/gap discard
    metrics are Sampled, Interval, or Cumulative metrics [RFC6792]:
       I=10: Interval Duration - the reported value applies to the
       most recent measurement interval duration between successive
       metrics reports.
       I=11: Cumulative Duration - the reported value applies to the
       accumulation period characteristic of cumulative measurements.
       I=01: Sampled Value - the reported value is a sampled
       instantaneous value.

Clark, et al. Standards Track [Page 5] RFC 7003 RTCP XR Burst/Gap Discard September 2013

    In this document, burst/gap discard metrics can only be measured
    over definite intervals and cannot be sampled.  Also, the value
    I=00 is reserved for future use.  Senders MUST NOT use the values
    I=00 or I=01.  If a block is received with I=00 or I=01, the
    receiver MUST discard the block.
 Reserved (resv): 6 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.  For
    the Burst/Gap Discard Metrics Block, the block length is equal to
    3.  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].
 Threshold: 8 bits
    The Threshold is equivalent to Gmin in [RFC3611], i.e., the number
    of successive packets that must not be discarded prior to and
    following a discard packet in order for this discarded packet to
    be regarded as part of a gap.  Note that the Threshold is set in
    accordance with the Gmin calculation defined in Section 4.7.2 of
    [RFC3611].
 Packets Discarded in Bursts: 24 bits
    The total number of packets discarded during discard bursts.
    The measured value is unsigned value.  If the measured value
    exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate
    an over-range measurement.  If the measurement is unavailable, the
    value 0xFFFFFF MUST be reported.
 Total Packets Expected in Bursts: 24 bits
    The total number of packets expected during discard bursts (that
    is, the sum of received packets and lost packets).

Clark, et al. Standards Track [Page 6] RFC 7003 RTCP XR Burst/Gap Discard September 2013

    The measured value is unsigned value.  If the measured value
    exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate
    an over-range measurement.  If the measurement is unavailable, the
    value 0xFFFFFF MUST be reported.
 Reserved: 8 bits
    These bits are reserved.  They MUST be set to zero by senders and
    ignored by receivers (See [RFC6709], Section 4.2).

3.3. Derived Metrics Based on Reported Metrics

 The metrics described here are intended to be used in conjunction
 with information from the Measurement Information Block [RFC6776] and
 also with the metric "number of packets discarded" provided in the
 RTCP XR Discard Count Metrics Block [RFC7002].
 These metrics provide the following information relevant to
 statistical parameters, including:
 o  The fraction of packets discarded during bursts (Burst Discard
    Rate in [RFC7004]), which can be calculated using the metric
    "Packets Discarded in Bursts" and the metric "Total Packets
    Expected in Bursts" provided in the Burst/Gap Discard Metrics
    Block.
 o  The fraction of packets discarded during gaps (Gap Discard Rate in
    [RFC7004]), which can be calculated using the metric "Packets
    Discarded in Bursts" and the metric "Total Packets Expected in
    Bursts" provided in the Burst/Gap Discard Metrics Block.
 The details on calculation these parameters in the metrics are
 described in [RFC7004].

4. Considerations for Voice-over-IP Applications

 This metrics block is applicable to a broad range of RTP
 applications.  Where the metric is used with a Voice-over-IP (VoIP)
 application and the stream repair means is not available, the
 following considerations apply.
 RTCP XR views a call as being divided into bursts, which are periods
 during which the discard rate is high enough to cause noticeable call
 quality degradation (generally over 5 percent discard rate) and gaps,
 which are periods during which discarded packets are infrequent and
 hence call quality is generally acceptable.

Clark, et al. Standards Track [Page 7] RFC 7003 RTCP XR Burst/Gap Discard September 2013

 If voice activity detection is used, the burst and gap duration shall
 be determined as if silence packets had been sent, i.e., a period of
 silence in excess of Gmin packets will terminate a burst condition.
 The recommended value for the threshold Gmin in [RFC3611] results in
 a burst being a period of time during which the call quality is
 degraded to a similar extent to a typical pulse code modulation (PCM)
 severely errored second.

5. SDP Signaling

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

5.1. SDP rtcp-xr 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.  The
 ABNF [RFC5234] syntax is as follows.
 xr-format =/ xr-bgd-block
 xr-bgd-block = "burst-gap-discard"

5.2. 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 in Offer/Answer for unilateral
 parameters, refer to Section 5.2 of [RFC3611].

6. 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].

6.1. New RTCP XR Block Type Value

 This document assigns the block type value 20 in the IANA "RTP
 Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
 the "Burst/Gap Discard Metrics Block".

Clark, et al. Standards Track [Page 8] RFC 7003 RTCP XR Burst/Gap Discard September 2013

6.2. New RTCP XR SDP Parameter

 This document also registers a new parameter "burst-gap-discard" in
 the "RTP Control Protocol Extended Reports (RTCP XR) Session
 Description Protocol (SDP) Parameters Registry".

6.3. Contact Information for Registrations

 The contact information for the registrations is:
 Qin Wu (sunseawq@huawei.com)
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China

7. Security Considerations

 It is believed that this RTCP XR 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.

8. Contributors

 Geoff Hunt wrote the initial draft of this document.

9. Acknowledgments

 The authors gratefully acknowledge reviews and feedback provided by
 Bruce Adams, Philip Arden, Amit Arora, Claire Bi, Bob Biskner, Benoit
 Claise, Kevin Connor, Claus Dahm, Randy Ethier, Roni Even, Stephen
 Farrell, Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus,
 Paul Jones, Rajesh Kumar, Paul Kyzivat, Keith Lantz, Mohamed Mostafa,
 Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Dan
 Romascanu, Albrecht Schwarz, Tom Taylor, and Hideaki Yamada.

Clark, et al. Standards Track [Page 9] RFC 7003 RTCP XR Burst/Gap Discard September 2013

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.
 [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
            2003.
 [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
            Description Protocol", RFC 4566, July 2006.
 [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234, January 2008.
 [RFC5725]  Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
            Report Block Type for RTP Control Protocol (RTCP) Extended
            Reports (XRs)", RFC 5725, February 2010.
 [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) for Discard Count Metric
            Reporting", RFC 7002, September 2013.
 [RFC7004]  Zorn, G., Schott, R., Wu, Q., Ed., and R. Huang, "RTP
            Control Protocol (RTCP) Extended Report (XR) Blocks for
            Summary Statistics Metrics Reporting", RFC 7004, September
            2013.

10.2. Informative References

 [RFC4588]  Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
            Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
            July 2006.
 [RFC5109]  Li, A., "RTP Payload Format for Generic Forward Error
            Correction", RFC 5109, December 2007.

Clark, et al. Standards Track [Page 10] RFC 7003 RTCP XR Burst/Gap Discard September 2013

 [RFC5481]  Morton, A. and B. Claise, "Packet Delay Variation
            Applicability Statement", RFC 5481, March 2009.
 [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
            Performance Metric Development", BCP 170, RFC 6390,
            October 2011.
 [RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
            Considerations for Protocol Extensions", RFC 6709,
            September 2012.
 [RFC6792]  Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
            RTP Monitoring Framework", RFC 6792, November 2012.

Clark, et al. Standards Track [Page 11] RFC 7003 RTCP XR Burst/Gap Discard September 2013

Appendix A. Metrics Represented Using the Template from RFC 6390

 a.  Burst/Gap Discard Threshold in RTP Metric
  • Metric Name: Burst/gap discard threshold in RTP
  • Metric Description: The Threshold is equivalent to Gmin in

[RFC3611], i.e., the number of successive packets that must

        not be discarded prior to and following a discard packet in
        order for this discarded packet to be regarded as part of a
        gap.
  • Method of Measurement or Calculation: See Section 3.2,

Threshold definition.

  • Units of Measurement: See Section 3.2, Threshold definition.
  • Measurement Point(s) with Potential Measurement Domain: See

Section 3, 1st paragraph.

  • Measurement Timing: See Section 3, 2nd paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 b.  Packets Discarded in Bursts Metric
  • Metric Name: RTP packets discarded in bursts
  • Metric Description: The total number of RTP packets discarded

during discard bursts.

  • Method of Measurement or Calculation: See Section 3.2, Packets

Discarded in Bursts definition.

  • Units of Measurement: See Section 3.2, Packets Discarded in

Bursts definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 3, 1st paragraph.

  • Measurement Timing: See Section 3, 2nd paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

Clark, et al. Standards Track [Page 12] RFC 7003 RTCP XR Burst/Gap Discard September 2013

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 c.  Total Packets Expected in Discard Bursts Metric
  • Metric Name: Total RTP packets expected in discard bursts
  • Metric Description: The total number of packets expected

during discard bursts (that is, the sum of received packets

        and lost packets).
  • Method of Measurement or Calculation: See Section 3.2, Total

Packets Expected in Bursts definition.

  • Units of Measurement: See Section 3.2, Total Packets Expected

in Bursts definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 3, 1st paragraph.

  • Measurement Timing: See Section 3, 2nd paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.

Clark, et al. Standards Track [Page 13] RFC 7003 RTCP XR Burst/Gap Discard September 2013

Authors' Addresses

 Alan Clark
 Telchemy Incorporated
 2905 Premiere Parkway, Suite 280
 Duluth, GA  30097
 USA
 EMail: alan.d.clark@telchemy.com
 Rachel Huang
 Huawei Technologies Co., Ltd.
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China
 EMail: Rachel@huawei.com
 Qin Wu (editor)
 Huawei
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China
 EMail: sunseawq@huawei.com

Clark, et al. Standards Track [Page 14]

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