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Versions: (draft-asaeda-xrblock-rtcp-xr-synchronization) 00 01 04 05 06 07 08 09 02 RFC 7244

Network Working Group                                          H. Asaeda
Internet-Draft                                                      NICT
Intended status: Standards Track                                R. Huang
Expires: August 5, 2013                                            Q. Wu
                                                                  Huawei
                                                        February 1, 2013


      RTP Control Protocol (RTCP) Extended Report (XR) Blocks for
           Synchronization Delay and Offset Metrics Reporting
             draft-ietf-xrblock-rtcp-xr-synchronization-02

Abstract

   This document defines two RTP Control Protocol (RTCP) Extended Report
   (XR) Blocks that allow the reporting of synchronization delay and
   offset metrics for use in a range of RTP applications.

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
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   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 August 5, 2013.

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
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   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Synchronization Delay and Offset Metrics Reporting
           Blocks . . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  Standards Language . . . . . . . . . . . . . . . . . . . .  4
   3.  RTP Flows Initial Synchronization Delay Report Block . . . . .  5
     3.1.  Metric Block Structure . . . . . . . . . . . . . . . . . .  5
     3.2.  Definition of Fields in RTP Flow Initial
           Synchronization Delay Metrics Block  . . . . . . . . . . .  5
   4.  RTP Flows Synchronization Offset Metrics Block . . . . . . . .  6
     4.1.  Metric Block Structure . . . . . . . . . . . . . . . . . .  7
     4.2.  Definition of Fields in RTP Flow General
           Synchronization Offset Metrics Block . . . . . . . . . . .  7
   5.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . .  8
     5.2.  Offer/Answer Usage . . . . . . . . . . . . . . . . . . . .  9
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 11
   Appendix A.  Change Log  . . . . . . . . . . . . . . . . . . . . . 11
     A.1.  draft-ietf-xrblock-rtcp-xr-syncronization-02 . . . . . . . 11
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11


















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1.  Introduction

1.1.  Synchronization Delay and Offset Metrics Reporting Blocks

   This draft defines two new block types to augment those defined in
   [RFC3611], for use in a range of RTP applications.

   The first new block type supports reporting of Initial
   Synchronization Delay to establish multimedia session.  Information
   is recorded about time difference between the start of RTP sessions
   and the time the RTP receiver acquires all components of RTP sessions
   in the multimedia session [RFC6051].

   The second new block type supports reporting of the relative
   synchronization offset time of two arbitrary streams (e.g., between
   audio and video streams), with the same RTCP CNAME included in RTCP
   SDES packets [RFC3550].  Information is recorded about the
   synchronization offset time of each RTP stream relative to the
   reference RTP stream with the same CNAME and General Synchronization
   Offset of zero.

   These metrics belong to the class of transport level 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].

1.3.  Performance Metrics Framework

   The RTP Monitoring Architectures [RFC6792] provides guideline for
   reporting block format using RTCP XR.  The new report block described
   in this memo is in compliance with the monitoring architecture
   specified in [RFC6792].

1.4.  Applicability

   When joining each session in layered video sessions [RFC6190] or the
   multimedia session, a receiver may not synchronize playout across the
   multimedia session or layered video session until RTCP SR packets
   have been received on all components of RTP sessions.  The component
   RTP session are referred to as each RTP session for each media type
   in multimedia session or separate RTP session for each layer in the
   layered video session.  For multicast session, the initial
   synchronization delay metric varies with the session bandwidth, the



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   number of members, and the number of senders in the session.  The RTP
   flow Initial synchronization delay block defined in this document can
   be used to report such metric, i.e., the initial synchronization
   delay to receive all the RTP streams belonging to the same multimedia
   session or layered video session.  In the absence of packet loss, the
   initial synchronization delay equals to the average time taken to
   receive the first RTCP packet in the RTP session with the longest
   RTCP reporting interval.  In the presence of packet loss, the media
   synchronization should rely on the in-band mapping of RTP and NTP-
   format timestamps [RFC6051] or wait until the reporting interval has
   passed, and the next RTCP SR packet is sent.

   Receivers of the RTP flow initial synchronization delay block could
   use this metric to compare with targets (i.e., Service Level
   Agreement or thresholds of the system) to help ensure the quality of
   real-time application performance.

   In an RTP multimedia session, there can be an arbitrary number of
   streams carried in different RTP sessions, with the same RTCP CNAME.
   These streams may be not synchronized with each other.  For example,
   one audio stream and one video stream belong to the same session, and
   the audio stream is transmitted lagging behind video stream for
   multiple tens of milliseconds [TR-126].  The RTP Flows
   Synchronization Offset block can be used to report such
   synchronization offset between video stream and audio stream.  The
   metrics defined in the RTP flows synchronization Offset block can be
   used by network manager for trouble shooting and dealing with 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].

   In addition, the following terms are defined:

   Initial Synchronization Delay:

      A multimedia session comprises a set of concurrent RTP sessions
      among a common group of participants, using one RTP session for
      each media type.  The initial synchronization Delay is the average
      time for receiver to synchronize all components of a multimedia
      session [RFC6051].




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   Synchronization Offset:

      Synchronization between two media streams must be maintained to
      ensure satisfactory QoE.  Two media streams can be of the same
      media type belonging to one RTP session or in different media
      types belonging to one multimedia session.  The Synchronization
      Offset is the relative time difference of the two media streams
      that need to be synchronized.



3.  RTP Flows Initial Synchronization Delay Report Block

   This block is sent by RTP receivers and reports Initial
   synchronization delay beyond the information carried in the standard
   RTCP packet format.  Information is recorded about time difference
   between the start of multimedia session and the time when the RTP
   receiver acquires all components of RTP sessions [RFC6051].

3.1.  Metric Block Structure

   The RTP Flows Initial Synchronization Delay Report Block has the
   following format:

       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=RFISD   |   Reserved    |         Block length=2        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                      SSRC of Source                           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |               Initial Synchronization Delay                   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.  Definition of Fields in RTP Flow Initial Synchronization Delay
      Metrics Block

   Block type (BT): 8 bits

      The RTP Flows Initial Synchronization Delay Report Block is
      identified by the constant <RFISD>.

   Reserved: 8 bits

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




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   Block length: 16 bits

      The constant 2, in accordance with the definition of this field in
      Section 3 of RFC 3611 [RFC3611].

   SSRC of source: 32 bits

      The SSRC of the media source SHALL be set to the value of the SSRC
      identifier carried in any arbitrary component of RTP sessions
      belonging to the same multimedia session.

   Initial Synchronization Delay: 32 bits

      The average delay, expressed in units of 1/65536 seconds, from the
      beginning of multimedia session [RFC6051] to the time when RTCP
      packets are received on all of the components RTP sessions.  It is
      recommended that the beginning of multimedia session is chosen as
      the time when the receiver has joined the first RTP session of the
      multimedia session.  The value of the initial synchronization
      delay is calculated based on received RTCP SR packets or the RTP
      header extension containing in-band mapping of RTP and NTP-format
      timestamps [RFC6051].  If there is no packet loss, the initial
      synchronization delay is expected to be equal to the average time
      taken to receive the first RTCP packet in the RTP session with the
      longest RTCP reporting interval or the average time taken to
      receive the first RTP header extension containing in-band mapping
      of RTP and NTP- format timestamps.

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


4.  RTP Flows Synchronization Offset Metrics Block

   In the RTP multimedia sessions, there can be an arbitrary number of
   Media streams and each media stream (e.g., audio stream or video
   stream) is sent in a separate RTP stream.  The receiver associates
   RTP streams to be synchronized by means of RTCP CNAME contained in
   the RTCP Source Description (SDES) packets [RFC3550].

   This block is sent by RTP receivers and reports synchronization
   offset of the arbitrary two RTP streams that needs to be synchronized
   in the RTP multimedia session.  Information is recorded about the
   relative average time difference between the reporting stream and the
   reference stream with the same CNAME.  For multimedia session with
   multiple media types (e.g., audio and video), it is recommended to
   choose the stream with the lower bandwidth as the reference stream.
   For layered video sessions, it is recommended to use the base layer



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   stream as the reference stream.

4.1.  Metric Block Structure

   The RTP Flow General Synchronization Offset Report Block has the
   following format:

       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=RFSO    |   Reserved    |         Block length=4        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of source                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of reference                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Synchronization Offset, most significant word         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Synchronization Offset, least significant word        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2.  Definition of Fields in RTP Flow General Synchronization Offset
      Metrics Block

   Block type (BT): 8 bits

      The RTP Flow General Synchronization Offset Report Block is
      identified by the constant <RFSO>.

   Reserved: 8 bits

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

   Block length: 16 bits

      The constant 4, in accordance with the definition of this field in
      Section 3 of RFC 3611 [RFC3611].

   SSRC of Source: 32 bits

      The SSRC of the media source SHALL be set to the value of the SSRC
      identifier of the reporting RTP stream to which the XR relates.







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   SSRC of Reference: 32 bits

      The SSRC of the reference stream SHALL be set to the value of the
      SSRC identifier of the reference RTP stream to which the XR
      relates.

   Synchronization Offset: 64 bits

      The synchronization offset of the reporting RTP stream relative to
      the reference RTP stream with the same CNAME.  The calculation of
      Synchronization Offset is similar to Difference D calculation in
      the RFC3550.  That is to say, if Si is the NTP timestamp from the
      reporting RTP packet i, and Ri is the time of arrival in NTP
      timestamp units for reporting RTP packet i, Sj is the NTP
      timestamp from the reference RTP packet j, and Rj is the time of
      arrival in NTP timestamp units for reference RTP packet j, then
      the value of the synchronization offset D may be expressed as

         D(i,j) = (Rj - Ri) - (Sj - Si) = (Rj - Sj) - (Ri - Si)

      If in-band delivery of NTP-format timestamps is supported
      [RFC6051], Si and Sj should be obtained directly from the RTP
      packets where NTP timestamps are available.  If not, Si and Sj
      should be calculated from their corresponding RTP timestamps.  The
      value of the synchronization offset is represented using a 64- bit
      signed NTP-format timestamp as defined in [RFC5905], which is 64-
      bit signed fixed-point number with the integer part in the first
      32 bits and the fractional part in the last 32 bits.  A positive
      value of the synchronization offset means that the reporting
      stream leads before the reference stream, while a negative value
      means that the reporting stream lags behind the reference stream.

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


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-attrib Attribute Extension

   Two new parameters are defined for the two report blocks defined in
   this document to be used with Session Description Protocol (SDP)
   [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC5234].
   They have the following syntax within the "rtcp-xr" attribute



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   [RFC3611]:

   xr-format = xr-rfisd-block
             / xr-rfso-block

   xr-rfisd-block = " init-syn-delay"
   xr-rfso-block = " syn-offset"

   Refer to Section 5.1 of RFC 3611 [RFC3611] for a detailed description
   and the full syntax of the "rtcp-xr" attribute.

5.2.  Offer/Answer Usage

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


6.  IANA Considerations

   New report block types for RTCP XR are subject to IANA registration.
   For general guidelines on IANA allocations for RTCP XR, refer to
   Section 6.2 of [RFC3611].

   This document assigns two new block type values in the RTCP XR Block
   Type Registry:

      Name:       RFISD
      Long Name:  RTP Flows Initial Synchronization Delay
      Value       <RFISD>
      Reference:  Section 3

      Name:       RFSO
      Long Name:  RTP Flows Synchronization Offset Metrics Block
      Value       <RFSO>
      Reference:  Section 4


   This document also registers two new SDP [RFC4566] parameters for the
   "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry:

      *  "xr-rfisd "
      *  "xr-rfso"

   The contact information for the registrations is:







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


7.  Security Considerations

   The new RTCP XR report blocks proposed in this document introduces no
   new security considerations beyond those described in [RFC3611].


8.  Acknowledgements

   The authors would like to thank Bill Ver Steeg, David R Oran, Ali
   Begen, Colin Perkins, Roni Even, Kevin Gross, Jing Zhao, Fernando
   Boronat Segui, Mario Montagud Climent, Youqing Yang, Wenxiao Yu and
   Yinliang Hu for their valuable comments and suggestions on this
   document.


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.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

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

   [RFC6051]  Perkins, C. and T. Schierl, "Rapid Synchronisation of RTP
              Flows", RFC 6051, November 2010.



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   [RFC6190]  Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis,
              "RTP Payload Format for Scalable Video Coding", RFC 6190,
              May 2011.

   [TR-126]   BBF Forum, "Triple-play Services Quality of Experience
              (QoE) Requirements", December 2006.

9.2.  Informative References

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

   [Y.1540]   ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and
              availability performance parameters", November 2007.


Appendix A.  Change Log

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

A.1.  draft-ietf-xrblock-rtcp-xr-syncronization-02

   The following are the major changes compared to previous version:

      Editorial change based on comments raised on the list and in the
      IETF85 meeting


Authors' Addresses

   Hitoshi Asaeda
   National Institute of Information and Communications Technology
   4-2-1 Nukui-Kitamachi
   Koganei, Tokyo  184-8795
   Japan

   Email: asaeda@nict.go.jp


   Rachel Huang
   Huawei Technologies Co., Ltd.
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: Rachel@huawei.com




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   Qin Wu
   Huawei Technologies Co., Ltd.
   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

   Email: sunseawq@huawei.com












































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