Colin Perkins
                                   University College London

               RTP Interoperability Statement

                 draft-ietf-avt-rtp-interop-01.txt
              draft-ietf-avt-rtp-interop-02.txt

                    Status of this memo

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                         Abstract

    It is required to demonstrate interoperability of RTP implementations
    in order to move the RTP specification to draft standard.  This memo
    outlines those features to be tested, as the first stage of an
    interoperability statement.

1  Introduction

The Internet standards process [1] places a number of requirements
on a standards track protocol specification.  In particular, when
advancing a protocol from proposed standard to draft standard it
is necessary to demonstrate at least two independent and interoperable
implementations, from different code bases, of all options and features
of that protocol.  Further, in cases where one or more options or
features have not been demonstrated in at least two interoperable

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implementations, the specification may advance to the draft standard
level only if those options or features are removed.  The Real-time
Transport Protocol, RTP, was originally specified in RFC1889 as a
proposed standard [2].  The revision of this specification for draft
standard status is now well underway, so it has become necessary
to conduct such an interoperability demonstration.

This memo describes the set of features and options of the RTP specification
which need to be tested as a basis for this demonstration.  Due to the
nature of RTP there are necessarily two types of test described: those
which directly affect the interoperability of implementations at a ``bits
on the wire level'' and those which affect scalability and safety of the
protocol but do not directly affect interoperability.  A related memo [4]
describes a testing framework which may aid with interoperability testing.

This memo is for information only and does not specify a standard
of any kind.

2  Features and options required to demonstrate interoperability

In order to demonstrate interoperability it is required to produce
a statement of interoperability for each feature noted below.  Such
a statement should note the pair of implementations tested, including
version numbers, and a pass/fail statement for each feature.  It
is not expected that every implementation will implement every feature,
but each feature needs to be demonstrated by some pair of applications.
Note that some of these tests depend on the particular profile used,
or upon options in that profile.  For example, it will be necessary
to test audio and video applications operating under [3] separately.

  1. Interoperable

  1.Interoperable exchange of data packets using the basic RTP header
    with no header extension, padding or CSRC list.

  2. Interoperable

  2.Interoperable exchange of data packets which use padding

  3. Interoperable padding.

  3.Interoperable exchange of data packets which use a header extension.
    There are three possibilities here:  a) if both implementations
    use a header extension in the same manner, it should be verified
    that the receiver correctly receives the information contained
    in the extension header; b) If the sender uses a header extension
    and the receiver does not, it should be verified that the receiver
    ignores the extension; c) If neither implementation implements
    an extended header, this test is considered a failure.

  4. Interoperable

  4.Interoperable exchange of data packets using the marker bit as
    specified in the profile.

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  5. Interoperable

  5.Interoperable exchange of data packets using the payload type
    field to differentiate multiple payload formats according to
    a profile definition.

  6. Interoperable

  6.Interoperable exchange of data packets containing a CSRC list

  7. Interoperable list.

  7.Interoperable exchange of RTCP packets, which must be compound
    packets containing at least an initial SR or RR packet and an
    SDES CNAME packet.

  8. Interoperable  Other RTCP packet types may be included,
    but this is not required for this test.

  8.Interoperable exchange of sender report packets when the receiver
    of the sender reports is not also a sender (ie:  sender reports
    which only contain sender info, with no report blocks).

  9. Interoperable

  9.Interoperable exchange of sender report packets when the receiver
    of the sender reports is also a sender (ie:  sender reports which
    contain one or more report blocks).

 10. Interoperable

 10.Interoperable exchange of receiver report packets.

 11. Interoperable

 11.Interoperable exchange of receiver report packets when not receiving
    data (ie:  the empty receiver report which has to be sent first
    in each compound RTCP packet when no-participants are transmitting
    data).

 12. Interoperable

 12.Interoperable and correct choice of CNAME, according to the rules
    in the RTP specification and profile.

 13. Interoperable profile (applications using the
    audio/video profile [3] under IPv4 should typically generate
    a CNAME of the form `example@10.0.0.1', or `10.0.0.1' if they
    are on a machine which no concept of usernames).

 13.Interoperable exchange of source description packets containing
    a CNAME item.

 14. Interoperable

 14.Interoperable exchange of source description packets containing
    a NAME item.

 15. Interoperable

 15.Interoperable exchange of source description packets containing
    an EMAIL item.

 16. Interoperable

 16.Interoperable exchange of source description packets containing
    a PHONE item.

 17. Interoperable

 17.Interoperable exchange of source description packets containing
    a LOC item.

 18. Interoperable

 18.Interoperable exchange of source description packets containing
    a TOOL item.

 19. Interoperable

 19.Interoperable exchange of source description packets containing
    a NOTE item.

 20. Interoperable

 20.Interoperable exchange of source description packets containing
    a PRIV item.

 21. Interoperable

 21.Interoperable exchange of BYE packets.

 22. Interoperable packets containing a single SSRC.

 22.Interoperable exchange of BYE packets containing multiple SSRCs.

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 23. Interoperable

 23.Interoperable exchange of BYE packets containing the optional
    reason for leaving text.

 24. Interoperable

 24.Interoperable exchange of BYE packets containing the optional
    reason for leaving text and multiple SSRCs.

 25.Interoperable exchange of application defined RTCP packets.  As
    with the RTP header extension this test takes two forms:  if
    both implementations implement the same application defined packet
    it should be verified that those packets can be interoperably
    exchanged.  If only one implementation uses application defined
    packets, it should be verified that the other implementation
    can receive compound RTCP packets containing an APP packet whilst
    ignoring the APP packet.  If neither implementation implements
    APP packets this test is considered a failure.

 25. Interoperable

 26.Interoperable exchange of encrypted RTP packets using DES encryption
    in CBC mode.

 26. Interoperable

 27.Interoperable exchange of encrypted RTCP packets using DES encryption
    in CBC mode.

3  Features and options relating to scalability

In addition to the basic interoperability tests, RTP includes a number
of features relating to scaling of the protocol to large groups.
Since these features are those which have undergone the greatest
change in the update of the RTP specification, it is considered important
to demonstrate their correct implementation.  However, since these
changes do not affect the bits-on-the-wire behaviour of the protocol,
it is not possible to perform a traditional interoperability test.
As an alternative to such testing we require that multiple independent
implementations complete the following demonstrations.

  1. Demonstrate

  1.Demonstrate correct implementation of basic RTCP transmission
    rules:  periodic transmission of RTCP packets at the minimum
    (5 second) interval and randomisation of the transmission interval.

  2. Demonstrate

  2.Demonstrate correct implementation of the RTCP step join backoff
    algorithm as a receiver.

  3. Demonstrate

  3.Demonstrate correct implementation of the RTCP step join backoff
    algorithm as a sender.

  4. Demonstrate

  4.Demonstrate correct steady state scaling of the RTCP interval
    acording to the group size.

  5. Demonstrate

  5.Demonstrate correct steady state scaling of the RTCP interval
    acording to the group size with compensation for the number of
    senders.

  6. Demonstrate

  6.Demonstrate correct implementation of the RTCP reverse reconsideration
    algorithm.

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  7. Demonstrate

  7.Demonstrate correct implementation of the RTCP BYE reconsideration
    algorithm.

  8. Demonstrate

  8.Demonstrate correct implementation of the RTCP member timeout
    algorithm.

  9. Demonstrate

  9.Demonstrate random choice of SSRC.

 10. Demonstrate

 10.Demonstrate random selection of initial RTP sequence number.

 11. Demonstrate

 11.Demonstrate random selection of initial RTP timestamp.

 12. Demonstrate

 12.Demonstrate correct implementation of the SSRC collision/loop
    detection algorithm.

 13. Demonstrate

 13.Demonstrate correct generation of reception report statistics
    in SR/RR packets.

 14. Demonstrate

 14.Demonstrate correct generation of the sender info block in SR
    packets.

4  Author's Address

Colin Perkins
Department of Computer Science
University College London
Gower Street
London WC1E 6BT
United Kingdom

Email:  c.perkins@cs.ucl.ac.uk

5  Acknowledgments

Thanks to Steve Casner, Jonathan Rosenberg and Bill Fenner for their
helpful feedback.

6  References

[1] S. Bradner, ``The Internet Standards Process -- Revision 3'',
    RFC2026, Internet Engineering Task Force, October 1996.

[2] H. Schulzrinne, S. Casner, R. Frederick and V. Jacobson, ``RTP:
    A Transport Protocol to Real-Time Applications'', RFC1889, Internet
    Engineering Task Force, January 1996.

[3] H. Schulzrinne, ``RTP Profile for Audio and Video Conferences with
    Minimal Control'', draft-ietf-avt-profile-new-05.txt, February 1999.

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[4] C. S. Perkins, J. Rosenberg and H. Schulzrinne, ``RTP Testing
    Strategies'', draft-ietf-avt-rtptest-01.txt, August 1999.

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