Subject: Fwd: mtg notes from May

From: Abel Weinrib <[email-masked]>
Date: Wed, 7 Jul 1993 14:11:13 -0400 (EDT)

Confctrl Meeting over MBONE
                   Wednesday, May 5, 1993

The goal of the meeting was to provide a status report, which mostly
focused on an evolving session control framework.  The main adjustment
has been to the relationship between the session manager and the media
agents.  The organization of the system has moved away from the the
session manager as the center of the architecture, and away from the
idea of the session manager being at one "level" in the layered,
modular architecture and the media agents being at another "level".
The current thinking is that the session manager and media agents have
more or less equal stature in the larger scheme of things.

Discussion also touched on the issue of how the architecture will
support users rendez-vous'ing with other users.  The notion of a per
workstation daemon was raised.  The daemon would be contacted on behalf
of all users whose sessions were rooted at that machine.  Henning
Schulzrinne proposed a framework that includes a per machine forwarding
host for location independence, an agent per user, and an agent per
media handler.  However, as the entry point will influence the
protocol, there was concern that the demultiplexing capability would
hide enough information to change the protocol.  Nonetheless, the issue
of how to find a user needs to be solved.

In discussing the group's charter, several people re-iterated an
interest in providing a membership service that happens also to support
media integration, rather than the other way around (a media
integration service that happens also to support membership).  One
suggestion was to think about the protocol functionality in stages;  
initially, convey membership information beyond what is currently
exchanged in the loosely-controlled protocols in use on the
MBONE, then support an explicit group request-reply service (e.g., the
ability to answer yes/no to participation requests), and finally
include mechanisms for multiparty negotiation.

Thus, the resulting protocol was described as a group negotiation
service.  The protocol would negotiate over membership in the most
common case, but also over other conference needs, such as media
configurations, end-system capabilities, user preferences, and policy
decisions.

Naturally, the larger question was raised about which session model (or
range of session types) are we targeting to support.  Dick Cogger
pointed out that many of the conferences currently happening on the
MBONE entail a few active participants with many more listeners.
Therefore, it is important to study the several-to-many model, and to
consider the impact of receive-only participants.  By considering the
several-to-many model, we can use it as a basis to work toward the
1-to-many and many-to-many cases.

This led into a discussion about session policies, such as who has
permission to send versus receive, and also discussion about
the policy enforcement problem.  Ideally, we would like to devise
a protocol that is largely unaffected by variations in policy.

During a discussion of mappings between session models and their 
underlying session control protocols, reference was made to the paper 
"A Characterization of Multi-Party Interactive Multimedia Applications"
by Szyperski and Ventre of UCB's Tenet group.  This turns out to be a 
good starting point for a taxonomy to describe the various 
session models.

MBONE participation was greatly appreciated; several participants
came forward to offer to help write documents as well.  Unfortunately,
problems with ttl's (experienced by participants at Cornell and 
U.Wisconsin) and with packet loss (experienced by participants at SICS) 
hampered efforts to conduct an entirely error-free telemeeting.

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Notes prepared by Eve Schooler, [email-masked]