





Internet Engineering Task Force (IETF)                          A. Clark
Request for Comments: 6843                                      Telchemy
Category: Standards Track                                       K. Gross
ISSN: 2070-1721                                             AVA Networks
                                                                   Q. Wu
                                                                  Huawei
                                                            January 2013


            RTP Control Protocol (RTCP) Extended Report (XR)
                    Block for Delay Metric Reporting

Abstract

   This document defines an RTP Control Protocol (RTCP) Extended Report
   (XR) block that allows the reporting of delay metrics for use in a
   range of Real-time Transport Protocol (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/rfc6843.

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.





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Table of Contents

   1. Introduction ....................................................2
      1.1. Packet Delay Metrics Block .................................2
      1.2. RTCP and RTCP XR Reports ...................................2
      1.3. Performance Metrics Framework ..............................3
      1.4. Applicability ..............................................3
   2. Terminology .....................................................3
      2.1. Standards Language .........................................3
   3. Delay Block .....................................................3
      3.1. Report Block Structure .....................................4
      3.2. Definition of Fields in Delay Metrics Report Block .........4
   4. SDP Signaling ...................................................6
      4.1. SDP rtcp-xr-attrib Attribute Extension .....................7
      4.2. Offer/Answer Usage .........................................7
   5. IANA Considerations .............................................7
      5.1. New RTCP XR Block Type Value ...............................7
      5.2. New RTCP XR SDP Parameter ..................................7
      5.3. Contact Information for Registrations ......................7
   6. Security Considerations .........................................8
   7. Contributors ....................................................8
   8. Acknowledgments .................................................8
   9. References ......................................................8
      9.1. Normative References .......................................8
      9.2. Informative References .....................................9

1.  Introduction

1.1.  Packet Delay 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 mean, minimum, and maximum values of
   the network round-trip delay between RTP interfaces in peer RTP end
   systems as measured, for example, using the RTCP method described in
   [RFC3550].  It also supports reporting of the component of the round-
   trip delay internal to the local RTP system.

   The network metrics belong to the class of transport metrics defined
   in [RFC6792].

1.2.  RTCP and RTCP XR 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].




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1.3.  Performance Metrics Framework

   The Performance Metrics Framework [RFC6390] provides guidance on the
   definition and specification of performance metrics.  The RTP
   Monitoring Architectures [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 in which
   this report block would be useful, such as multimedia conferencing
   and streaming audio and video.  Knowledge of the round-trip delay and
   delay characteristics can aid other receivers in sizing their receive
   buffers and selecting a playout delay.  The same information is also
   valuable to network managers in troubleshooting network and user
   experience issues.

2.  Terminology

2.1.  Standards Language

   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].

3.  Delay Block

   Metrics in this block report on packet delay in the stream arriving
   at the RTP system.  The measurement of these metrics is made either
   at the receiving end of the RTP stream or at the sending end of the
   RTP stream.  Instances of this metrics block refer by synchronization
   source (SSRC) to the separate auxiliary Measurement Information block
   [RFC6776], which contains measurement periods (see [RFC6776], Section
   4.2).  This metrics block relies on the measurement period in the
   Measurement Information block indicating the span of the report and
   SHOULD be sent in the same compound RTCP packet as the Measurement
   Information block.  If the measurement period is not received in the
   same compound RTCP packet as this metrics block, this metrics block
   MUST be discarded.










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3.1.  Report Block Structure

   Delay metrics block

        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=16      | I |   resv.   |      block length = 6         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                           SSRC of Source                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  Mean Network Round-Trip Delay                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Min Network Round-Trip Delay                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Max Network Round-Trip Delay                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               End System Delay - Seconds (bit 0-31)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              End System Delay - Fraction (bit 0-31)           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 1: Report Block Structure

3.2.  Definition of Fields in Delay Metrics Report Block

   Block type (BT): 8 bits

      A Delay Report Block is identified by the constant 16.

   Interval Metric flag (I): 2 bit

      This field is used to indicate whether the delay metrics are
      Sampled, Interval or Cumulative metrics:

         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.






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   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 delay block, the block length is equal to 6.

   SSRC of source: 32 bits

      As defined in Section 4.1 of [RFC3611].

   Mean Network Round-Trip Delay: 32 bits

      The Mean Network Round-Trip Delay is the mean value of the RTP-to-
      RTP interface round-trip delay over the measurement period,
      expressed in units of 1/65536 seconds.  This value is typically
      determined using "the NTP timestamp field" in the RTCP sender
      report (SR) and "the last SR (LSR) field","delay since last SR
      (DLSR) field" in the RTCP receiver report (RR) (see [RFC3550],
      Section 6.4.1 and Figure 2).  It also can be determined using "the
      NTP timestamp field" in the RTCP Receiver Reference Time Report
      Block and "last RR (LRR) field", "delay since last RR (DLRR)
      field" in the DLRR Report Block (see [RFC3611], Section 4.5).

      If only one measurement of Round-Trip Delay is available for the
      time span of the report (i.e., the measurement period) (whether
      Interval or Cumulative), this single value SHOULD be reported as
      the mean value.

      If the measurement is unavailable, the value of this field with
      all bits set to 1 MUST be reported.

   Min Network Round-Trip Delay: 32 bits

      The Min Network Round Trip Delay is the minimum value of the RTP-
      to-RTP interface round-trip delay over the measurement period,
      expressed in units of 1/65536 seconds.  This value is typically
      determined using the NTP timestamp field in the RTCP SR and LSR
      field and DLSR field in the RTCP RR.  It also can be determined
      using the NTP timestamp field in the RTCP Receiver Reference Time
      Report Block and LRR field and DLRR field in the DLRR Report
      Block.






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      If only one measurement of Round Trip Delay is available for the
      time span of the report (i.e., the measurement period) (whether
      Interval or Cumulative), this single value SHOULD be reported as
      the minimum value.

      If the measurement is unavailable, the value of this field with
      all bits set to 1 MUST be reported.

   Max Network Round-Trip Delay: 32 bits

      The Max Network Round-Trip Delay is the maximum value of the RTP-
      to-RTP interface round-trip delay over the measurement period,
      expressed in units of 1/65536 seconds.  This value is typically
      determined using the NTP timestamp field in the RTCP SR and LSR
      field and DLSR field in the RTCP RR.  It also can be determined
      using the NTP timestamp field in the RTCP Receiver Reference Time
      Report Block and LRR field and DLRR field in the DLRR Report
      Block.

      If only one measurement of Round-Trip Delay is available for the
      time span of the report (i.e.,the measurement period) (whether
      Interval or Cumulative), this single value SHOULD be reported as
      the maximum value.

      If the measurement is unavailable, the value of this field with
      all bits set to 1 MUST be reported.

   End System Delay: 64 bits

      The End System Delay is the internal round-trip delay within the
      reporting endpoint, calculated using the nominal value of the
      jitter buffer delay plus the accumulation/encoding and decoding/
      playout delay associated with the codec being used.  The value of
      this field is represented using a 64-bit NTP-format timestamp as
      defined in [RFC5905], which is a 64-bit unsigned fixed-point
      number with the integer part in the first 32 bits and the
      fractional part in the last 32 bits.

      If the measurement is unavailable, the value of this field with
      all bits set to 1 MUST be reported.

4.  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.





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4.1.  SDP rtcp-xr-attrib 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.

   xr-format =/ xr-delay-block

   xr-delay-block ="delay"

4.2.  Offer/Answer Usage

   When SDP is used in offer/answer context, the SDP Offer/Answer usage
   defined in [RFC3611] applies.

5.  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].

5.1.  New RTCP XR Block Type Value

   This document assigns the block type value 16 in the IANA "RTP
   Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
   the "Delay Metrics Block".

5.2.  New RTCP XR SDP Parameter

   This document also registers a new parameter "delay" in the "RTP
   Control Protocol Extended Reports (RTCP XR) Session Description
   Protocol (SDP) Parameters" registry.

5.3.  Contact Information for Registrations

      The contact information for the registrations is:

      Qin Wu (sunseawq@huawei.com)
      Huawei
      101 Software Avenue, Yuhua District
      Nanjing, Jiangsu  210012
      China









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6.  Security Considerations

   It is believed that this proposed RTCP XR report 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.

7.  Contributors

   Geoff Hunt wrote the initial version of this document.

8.  Acknowledgments

   The authors gratefully acknowledge the comments and contributions
   made by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin
   Connor, Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert
   Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith
   Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho,
   Ravi Raviraj, Albrecht Schwarz, Tom Taylor, and Hideaki Yamada, Jing
   Zhao, Kevin Gross, Colin Perkins, Charles Eckel, Glen Zorn, Shida
   Schubert, Barry Leiba, Sean Turner, Robert Sparks, Benoit Claise, and
   Stephen Farrell.

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 2003.

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

   [RFC5905]  Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
              Time Protocol Version 4: Protocol and Algorithms
              Specification", RFC 5905, June 2010.






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   [RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
              Considerations for Protocol Extensions", RFC 6709,
              September 2012.

9.2.  Informative References

   [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.

   [RFC6792]  Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
              RTP Monitoring Framework", RFC 6792, November 2012.

Authors' Addresses

   Alan Clark
   Telchemy Incorporated
   2905 Premiere Parkway, Suite 280
   Duluth, GA  30097
   USA

   EMail: alan.d.clark@telchemy.com


   Kevin Gross
   AVA Networks

   EMail: kevin.gross@avanw.com


   Qin Wu
   Huawei
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   EMail: sunseawq@huawei.com










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