Internet DRAFT - draft-finlayson-avt-mpa-robust-interoperability

draft-finlayson-avt-mpa-robust-interoperability




Network Working Group                                   Ross Finlayson
INTERNET-DRAFT                                          LIVE.COM
Expires: February 5, 2004                               October 5, 2004

         Interoperability of the "audio/mpa-robust" RTP Payload Format
           <draft-finlayson-avt-mpa-robust-interoperability-01.txt>

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Abstract

    In order for the "audio/mpa-robust" RTP payload format specification
    to advance from Proposed Standard to Draft Standard, it is required
    to demonstrate interoperability for all functionality described by
    the specification.  This document describes the interoperability
    shown between different implementations of this specification.


1.  Introduction

    The "audio/mpa-robust" RTP payload format for MP3 audio is described
    in RFC 3119 [3119] (and updated in [3119BIS] to correct typographical
    errors).  This payload format is an alternative to the format
    described in RFC 2250 [2250], and performs better if there is
    packet loss.

    This RTP payload format specification is currently at Proposed
    Standard.  In order to advance to Draft Standard, the Internet
    standards process [2026] requires "at least two independent and
    interoperable implementations from different code bases," and that
    interoperability be shown for "all of the options and features of
    the specification."  This document describes the interoperability
    shown between three independent implementations:
          1/ "LIVE.COM Streaming Media" project's "testMP3Streamer"
            application [LIVEMEDIA].
          2/ RealNetworks' "RealPlayer 9" media player [REAL].
          3/ The "MPEG4IP" project's "mp4player" media player [MPEG4IP].
            (Despite its name, this player plays MP3 audio in addition
             to MPEG-4 formats.)


2.  Features Tested for Interoperability

    RTP payloads conforming to this specification can vary in the
    following ways:

    1/ Descriptor size.
       As specified by the "T" (descriptor type) flag in each ADU
       descriptor, the descriptor size can be either 1 byte (for ADU
       frame sizes < 64), or 2 bytes.

    2/ Fragmentation.
       If an "ADU frame" is too large to fit within a RTP packet, it
       is fragmented across more than one RTP packet (each beginning with
       an ADU descriptor.  The fragmentation is indicated by the "C"
       (continuation) flag in each ADU descriptor.

    3/ Interleaving.
       The high-order 11 bits of each MPEG header ('syncword') can either
       remain at 0xFFE - which indicates that no ADU frame interleaving
       is performed - or it can consist of an "Interleaving Sequence
       Number" - which indicates that ADU frames are rearranged in an
       interleaving pattern.

    As described in the next section, we demonstrated interoperability
    by testing each combination of these three variables.


3.  Test Results

    The results of the interoperability tests are shown in the table
    below.  In each case, the LIVE.COM "testMP3Streamer" application
    was used as the transmitter, and one (or both) of the "RealPlayer 9"
    and MPEG4IP "mp4player" applications was used as the receiver.

+-----------------+----------------+---------------++------+-----------+
|                   Stream Features                ||     Receiver     |
+-----------------+----------------+---------------++------+-----------+
| descriptor size | fragmentation? | interleaving? || Real | mp4player |
+-----------------+----------------+---------------++------+-----------+
|      1 byte     |      no        |      no       || Yes  | Yes       |
|      1 byte     |      no        |      yes      || Yes  | Yes       |
|      1 byte     |      yes       |      no       || No   | Yes       |
|      1 byte     |      yes       |      yes      || No   | Yes       |
|      2 bytes    |      no        |      no       || Yes  | Yes       |
|      2 bytes    |      no        |      yes      || Yes  | Yes       |
|      2 bytes    |      yes       |      no       || No   | Yes       |
|      2 bytes    |      yes       |      yes      || No   | Yes       |
+-----------------+----------------+---------------++------+-----------+

Note: As noted in the table, "RealPlayer 9" was unable to handle
fragmented ADU frames.  However, because "mp4player" was able to play
fragmented frames from the LIVE.COM "testMP3Streamer" application,
this is sufficient to demonstrate interoperability of this feature
between two independent implementations.


4. Security Considerations

    Not applicable.


5. Normative References

    [3119]       Finlayson, R., "A More Loss-Tolerant RTP Payload
                 Format for MP3 Audio," RFC 3119, June 2001.

    [2026]       Bradner, S., "The Internet Standards Process
                 -- Revision 3," RFC 2026, October 1996.


6. Informative References

    [3119BIS]    Finlayson, R., "A More Loss-Tolerant RTP Payload
                 Format for MP3 Audio,"
                 draft-ietf-avt-rfc3119bis-02.txt,
                 Work in progress, February 2004.

    [2250]       Hoffman, D., Fernando, G., Goyal, V. and M. Civanlar,
                 "RTP Payload Format for MPEG1/MPEG2 Video", RFC 2250,
                 January 1998.

    [LIVEMEDIA]  "LIVE.COM Streaming Media," Live Networks, Inc.,
                 <http://www.live.com/liveMedia/>.

    [REAL]       RealNetworks, Inc., <http://www.real.com/>.

    [MPEG4IP]    The "MPEG4IP Open Streaming Video and Audio" project,
                 <http://mpeg4ip.sourceforge.net/>.


7. Author's Address

    Ross Finlayson,
    Live Networks, Inc. (LIVE.COM)
    650 Castro St., suite 120-196
    Mountain View, CA 94041

    EMail: finlayson (at) live.com
    WWW: http://www.live.com/


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Expires: Febrary 5, 2005