Subject: MMUSIC Minutes

From: Mark Handley <[email-masked]>
Date: Tue, 25 Jul 95 16:47:11 +0100

Multiparty Multimedia Session Control Working Group (MMUSIC)
                   Minutes from the 33rd IETF
                       Stockholm, Sweden
                         18th July 1995

                             Chairs

                Mark Handley, [email-masked]
                      Ruth Lang, [email-masked]
                Eve Schooler, [email-masked]

These notes were prepared by Mark Handley.  An on-line copy of the
minutes and the accompanying PostScript slides will shortly be
available from ftp://ftp.isi.edu/confctrl/minutes in the files
ietf.7.95 and slides.7.95.tar.

The Multiparty Multimedia Session Control Working Group (MMUSIC) met
for two sessions on July 17 and 18 at the 33rd IETF.

Carsten Bormann gave a presentation (slides.7.95.a) of the
possibilities for interworking between the ITU T.120 family for
multimedia conferencing and internet based approaches to conferencing.
The ITU appears to be moving towards using RTP or an RTP like protocol
for media data streams, but it is unclear how the conference control
functionality encompassed in the T.120 suite would be achieved over
the wide area internet.  Initially the ITU seems to be interested only
in LAN interoperability.

Three interoperability scenarios were presented, and the implications
examined:

1. T.120 terminal phones in to "classical" IETF multicast session

2. Internet protocols only used locally behind a gateway

3. Tight interworking with the illusion of homogeneity

The issues where there are potential incompatibilities include:

- Resource Control
- Addressing: use of multicast
- Session setup: Prescriptive session description vs negotiated
- Security: cryptography vs link setup authentication

The details of these interoperability scenarios are discussed in more
detail in draft-bormann-mmusic-itu-interop-00.txt.

This presentation was followed by a discussion of how the MMUSIC
working group should relate to the T.120 work.  The rough consensus
was that we should pay attention to the ITU work, and not needlessly
replicate T.120's conference control functionality in an incompatible
way.  However, the opinion was expressed that the group's current
emphasis on wide area scalable multicast based conferencing was
desirable, and that we shouldn't sacrifice the benefits of multicast
based sessions to conform to the ITU tightly coupled model.  No real
conclusion was reached, except that a building blocks approach was
advocated.  

Joerg Ott gave a presentation (slides.7.95.b) of two vertical control
protocols (control protocols between local applications and
controllers) developed at TU Berlin: The LASSO Dictionary and the
Conference Information and Request Protocol (CIRP).  Unlike CCCP and
the control architecture described by Henning Schulzrinne (see
minutes.4.95), these consist of a central (for each participant)
information store, and an access protocol to this data store.  The
dictionaries object store is an acyclic directed graph, which is
sufficient to reflect T.120 conference data, as well as more loosely
couple conferences.  CIRP complements the dictionary and allows a more
flexible asynchronous event triggered interaction style, but still
requires a single conference controller per user.  Work is currently
in progress to unify the dictionary and CIRP.

Mark Handley presented the changes that have been made to the Session
Description Protocol since the Danvers IETF (slides.7.95.c).  The
current version of the draft is available from
http://www.cs.ucl.ac.uk/staff/M.Handley/sdp.01.ps.

The main changes are:
- SDP is longer a superset of the sd protocol.
- the "c" fields have been split into channel and time fields.
- repeat time fields have been completely re-worked.
- origin fields have been completely re-worked, and now uniquely identify
  a session announcement.
- bandwidth fields have been reworked somewhat.
- media fields have been reworked somewhat.
- the Session Description Protocol has been separated into a separate
  draft from the announcement protocol that carries it.

In general the changes attempt to make the protocol more generic and 
more widely applicable.

A number of minor problems with the protocol or the description in the
current draft were noted.  All these changes are fairly minor, but the
most significant are:

- the "o" field allows spaces in the address.  The "c" field does not.
  The incompatibility should be resolved.
- For unicast, the existing "c" field may not be sufficient to
  identify whether the address is to send to or receive from or some
  other semantics.  This should be investigated further.
- <address type> in "o" and "c" fields should probably be two fields:
  <network type> and <address type>
- For unicast, hierarchical encodings need to be able to use multiple
  ports (for multicast they use multiple multicast addresses).  The 
  notation <base address>/<number of addresses> should be extended to
  ports in the media field.

A new draft will be released shortly addressing these issues.
Assuming this does not raise new objections, the consensus of the
group was that we should submit SDP for consideration as a proposed
standard around the time of the Dallas IETF.

It was also flagged that the Agreement Protocol is now available as an
internet draft: draft-ietf-mmusic-agree.{txt,ps}