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Versions: 00 01 draft-ietf-avt-post-repair-rtcp-xr

AVT                                                             A. Begen
Internet-Draft                                                    D. Hsu
Intended status:  Standards Track                               M. Lague
Expires:  November 26, 2008                                Cisco Systems
                                                            May 25, 2008


           Post-Repair Loss RLE Report Block Type for RTCP XR
                 draft-begen-avt-post-repair-rtcp-xr-01

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document defines a new report block type within the framework of
   RTP Control Protocol (RTCP) Extended Reports (XR).  One of the
   initial XR report block types is the Loss Run Length Encoding (RLE)
   Report Block.  This report conveys the information regarding the
   individual Real-time Transport Protocol (RTP) packet receipt and loss
   events experienced during the RTCP interval preceding the
   transmission of the report.  The new report, which is referred to as



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   the Post-repair Loss RLE Report, carries the information regarding
   the remaining lost packets after all error-repair techniques are
   applied.  By comparing the RTP packet receipts/losses before and
   after the error repair is completed, one can determine the
   effectiveness of the error-repair techniques in an aggregated
   fashion.  This document also defines the signaling of the Post-repair
   Loss RLE Report in the Session Description Protocol (SDP).


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4
   3.  Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4
   4.  Session Description Protocol Signaling  . . . . . . . . . . . . 5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8




























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1.  Introduction

   RTP Control Protocol (RTCP) is the out-of-band control protocol for
   the applications that are using the Real-time Transport Protocol
   (RTP) for media delivery and communications [RFC3550].  RTCP allows
   the RTP entities to monitor the data delivery and provides them
   minimal control functionality via sender and receiver reports as well
   as other control packets.  [RFC3611] expands the RTCP functionality
   further by introducing the RTCP Extended Reports (XR).

   One of the initial XR report block types defined in [RFC3611] is the
   Loss Run Length Encoding (RLE) Report Block.  This report conveys the
   information regarding the individual RTP packet receipt and loss
   events experienced during the RTCP interval preceding the
   transmission of the report.  However, the Loss RLE in an RTCP XR
   report is usually collected only on the primary source stream before
   any error-repair technique is applied.  Once one or more error-repair
   techniques, e.g., Forward Error Correction (FEC)
   [I-D.begen-fecframe-1d2d-parity-scheme] and/or retransmission
   [RFC4588], are applied, some or all of the lost packets on the
   primary source stream may be recovered.  However, the pre-repair Loss
   RLE cannot indicate which source packets were recovered and which are
   still missing.  Thus, the pre-repair Loss RLE cannot specify how well
   the error repair performed.

   This issue can be addressed by generating an additional report block
   (within the same RTCP XR report), which reflects the packet receipt/
   loss events after all error-repair techniques are applied.  This
   report block, which we refer to as the Post-repair Loss RLE,
   indicates the remaining missing, i.e., unrepairable, source packets.
   When the pre- and post-repair Loss RLEs are compared, the RTP sender
   or another 3rd party entity can evaluate the effectiveness of the
   error-repair techniques in an aggregated fashion.

   Note that the idea of using pre- and post-repair Loss RLEs can be
   further extended when multiple sequential error-repair techniques are
   applied to the primary source stream.  Reporting the Loss RLEs before
   and after each error-repair technique can provide specific
   information about the individual performances of these techniques.
   However, it can be a difficult task to quantify the specific
   contribution made by each error-repair technique in hybrid systems,
   where different techniques collectively work together to repair the
   lost source packets.  Thus, in this specification we only consider
   reporting the Loss RLE after all error-repair techniques are applied.
   This document registers a new report block type to cover the Post-
   repair Loss RLE within the framework of RTCP XR.





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2.  Requirements Notation

   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 [RFC2119].


3.  Post-Repair Loss RLE Report Block

   The Post-repair Loss RLE Report Block is similar to the existing Loss
   RLE Report Block defined in [RFC3611].  The report is formatted as
   sketched in Figure 1.

      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=TBD      | rsvd. |   T   |         block length          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                        SSRC of source                         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          begin_seq            |             end_seq           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          chunk 1              |             chunk 2           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     :                              ...                              :
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          chunk n-1            |             chunk n           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Figure 1: Format for the post-repair loss RLE report block

   o  block type (BT):  8 bits
      A Post-repair Loss RLE Report Block is identified by the constant
      TBD.

   o  rsvd.:  4 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.

   o  thinning (T):  4 bits
      The amount of thinning performed on the sequence number space.
      Only those packets with sequence numbers 0 mod 2^T are reported on
      by this block.  A value of 0 indicates that there is no thinning,
      and all packets are reported on.  The maximum thinning is one
      packet in every 32,768 (amounting to two packets within each 16-
      bit sequence space).




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   o  block length:  16 bits
      The length of this report block, including the header, in 32-bit
      words minus one.

   o  SSRC of source:  32 bits

      The SSRC of the RTP data packet source being reported upon by this
      report block.

   o  begin_seq:  16 bits

      The first sequence number that this block reports on.

   o  end_seq:  16 bits

      The last sequence number that this block reports on plus one.

   o  chunk i:  16 bits
      There are three chunk types:  run length, bit vector, and
      terminating null, defined in [RFC3611] (Section 4).  If the chunk
      is all zeroes, then it is a terminating null chunk.  Otherwise,
      the left most bit of the chunk determines its type:  0 for run
      length and 1 for bit vector.


4.  Session Description Protocol Signaling

   A new parameter is defined for the Post-repair Loss RLE Report Block
   to be used with Session Description Protocol (SDP) [RFC4566].  It has
   the following syntax within the "rtcp-xr" attribute:

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

            xr-format = "post-repair-loss-rle" ["=" max-size]

            max-size  = 1*DIGIT ; maximum block size in octets
            DIGIT     = %x30-39
            CRLF      = %d13.10

                                 Figure 2

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


5.  Security Considerations

   The security considerations of [RFC3611] apply.



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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].

   This document assigns the block type value TBD in the RTCP XR Block
   Type Registry to "Post-repair Loss RLE Report Block."  This document
   also registers the SDP [RFC4566] parameter "post-repair-loss-rle" for
   the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry.

   The contact information for the registrations is:

   Ali Begen
   abegen@cisco.com

   170 West Tasman Drive
   San Jose, CA 95134 USA


7.  Acknowledgments

   The authors would like to thank the members of the VQE Team at Cisco
   and Colin Perkins for their inputs and suggestions.


8.  References

8.1.  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.

8.2.  Informative References

   [I-D.begen-fecframe-1d2d-parity-scheme]
              Begen, A. and R. Asati, "1-D and 2-D Parity FEC Scheme for



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              FEC Framework", draft-begen-fecframe-1d2d-parity-scheme-00
              (work in progress), February 2008.

   [RFC4588]  Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
              Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
              July 2006.


Authors' Addresses

   Ali Begen
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email:  abegen@cisco.com


   Dong Hsu
   Cisco Systems
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

   Email:  dohsu@cisco.com


   Michael Lague
   Cisco Systems
   1414 Massachusetts Ave.
   Boxborough, MA  01719
   USA

   Email:  mlague@cisco.com
















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Full Copyright Statement

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