CURRENT MEETING REPORT
Reported by Eve Schooler,
Minutes of the Multiparty
Multimedia Session Control Working Group (MMUSIC)
MMUSIC met during two sessions
at the 35th IETF, both of which were multicast. A summary of each
of the talks given and a report of any follow-up action items
follows. An on-line copy of these minutes and the accompanying
PostScript slides are available from ftp://ftp.isi.edu/confctrl/minutes
in the files ietf.3.96 and slides.3.96.{tar, tar.Z}. These notes
were prepared by Ruth Lang.
Mark Handley (UCL) gave a
presentation and solicited additional input on open issues on
the Session Description Protocol (sdp.3.96.ps). The issues reviewed
include expression of RTP profiles and payload types, format lists,
format groups, and a proposed change to the "media"
and "connection" lines which allow more general expression
of connection topologies and media relationships (e.g., for layered
encodings). Sufficient input was received to resolve some of the
issues, but discussion will continue on the mailing list on others.
Specifically, RTP profiles will be expressed on the "protocol"
line of the description (i.e., rtp/profile); supporting dynamic
RTP payload types was left as an open issue dependent on further
discussions in AVT regarding the definition of a registration
mechanism for them; the idea of re-introducing format groups was
discouraged in favor of retaining explicit descriptions of a group
of encodings; and changes to the "media2 and "connection"
lines were left as an open issue. A revised Internet draft will
be issued soon and the goal of issuing "last call" before
the next IETF meeting was set.
Mark Handley (UCL) gave a
presentation on the design goals and issues for a Session Directory
Announcement Protocol (SDAP) (sdap.3.96.ps). This protocol was
originally envisioned to only support wide-area multicast of SDP
packets, but has been divided into a wide-area (server to server)
and local-area (client to server) portions. The division was made
to facilitate a segregation between session directory management
and maintenance functions (e.g., multicast address allocation)
and user-oriented functions (e.g., instantiating tools). It was
noted that the Service Location Protocol could provide a means
to locate directory servers, but lacked support for asynchronous
update. Mark has proposed to write an Internet-Draft describing
SDAP for review and discussion before the next IETF.
Mark Handley (UCL) provided
an overview of the motivations for the creation of the Internet
Multimedia Conferencing Architecture document (confarch.3.96.ps).
This document describes the "big picture" which is driving
the development of the MMUSIC protocols, and the relationship
among the protocols in terms of a conference lifecycle. Allison
Mankin (Transport Area Chair) encouraged that 1) the document
be made an Informational RFC with note that the document is intended
to change, and 2) MMUSIC formally ask the Security Area for a
formal consultation. Additional comments received included an
encouragement that this document be used to note the relationship
between MMUSIC and the ITU work on session control, and that the
document should provide descriptions of yet unchartered (by MMUSIC)
technical challenges.
Ross Finlayson (Live Networks)
gave a presentation aimed at motivating more general thinking
about the use of the MBONE as a general groupware framework (groupware.3.96/1-10.ps).
Some ideas Ross suggested for further thought include: developing
a way to share more than just media (i.e., workspace sharing),
a generalization in how sessions are managed (e.g., multiple directories),
use of object inheritance models in describing sessions, supporting
additional persistence models in describing sessions (e.g., personal
directories). Some discussion centered around the use of multiple
directories and their similarity to net news. No action items
followed from this presentation.
Rob Williams (Microsoft) and
Eve Schooler (Cal Tech) each gave presentations on the topic of
User Location [(uls.3.96.ps) and (userdir.3.96.ps) respectively].
Rob's presentation described a service that has been developed
at Microsoft for which an MMUSIC Internet-Draft has been created.
This User Location Service provides a means for users to build
a common directory of information regarding the running applications
that can be used for collaboration. The User Location Service
I-D describes the client-side protocol for add/delete/refresh/query
operations to a database of tagged records. Rob outlined several
issues that the Internet-Draft does not yet cover; examples include
defining identifiers for common schema elements, integration with
DNS (seen as way to find User Location Servers), and security.
Eve provided an overview of a multicast-based user directory she
has developed. Goals of the effort are to enable a simple method
for registering user communities, combine dynamic and static approaches
of session management, and take advantage of other user information
on "closeness" to bound scope of media relations for
sessions. This user directory employs an announce/listen paradigm
- everyone using same multicast addr/port is loosely bound; the
scope of reception of the user announcement also defines the scope
of reception of the session itself. Eve has implemented a prototype
which will be released with the next release of MMCC. No specific
action items were generated as a result of these two talks. It
was later identified by the chairs that this topic is of interest
to the working group and that a more thorough review of the problem
area and options for providing such a service (e.g., based on
already-developed Internet protocols) was needed and will be scheduled
as an agenda item for the next IETF.
Eve Schooler (Cal Tech) presented
the motivations for and specifics of the Session Invitation Protocol
(SIP) (sip.3.96.ps). This protocol is targeted to complement the
advertisement mechanism provided by tools such as sd and sdr by
enabling the joining of users (as compared to users joining a
session address). It can be used in the context of both tightly-
and loosely-controlled sessions and is intended for transmission
among peer user agents (or proxies for them). SIP uses SDP as
a means of describing the sessions for which an invitation is
being issues. It is meant to be conveyed over UDP and is therefore
minimally stateful -- request/response pair messages are mandatory,
but progress reports and acks are optional. Issues regarding the
choice of transport mechanism of UDP as compared to TCP or remote
procedure calls were discussed, and set-up delay imposed by timer-based
retransmissions were discussed.
Henning Schulzrinne (Fokus
GMD) presented the motivations for and specifics of the Simple
Conference Invitation Protocol (SCIP) (scip.3.96.ps). This protocol
is also aimed at complementing advertisement mechanisms but was
developed with an eye towards supporting telephony functionality.
The models and goals of the two protocols are similar, but SCIP
can be contrasted with SIP by its use of TCP as a transport mechanism,
leveraged use of HTTP and SMTP, and use of an alternate session
description format (i.e., not SDP), etc. Some discussion on UDP
vs TCP (T/TCP) vs RPC etc. occurred but no resolution was reached
regarding a choice of a single transport mechanism for conveyance
of an invitation protocol. It is expected that discussion of issues
will be carried on the group's mailing list and an effort to resolve
differences between these two approaches will be undertaken.
Carsten Bormann (Univ. Bremenn)
provided an overview of the Simple Conference Control Protocol
(SCCP) which is a protocol between conference control agents (horizontal)
for orchestrating tightly-coupled conferences (sccp.3.96.ps).
The protocol is intended to support managing a membership list
including per-member capabilities, application/media sessions,
floor control, and conductorship. It does not duplicate session
advertisement or invitation functions and supports session control
only. The protocol distinguishes protocol structure and protocol
semantics (a document describing the latter was proposed as a
complement to SCCP), and is intended to support bridging to T.120.
Design goals for the protocol included simplicity and generality,
but scalability to "large" groups (e.g., IETF broadcasts
over the Mbone) was excluded. No discussion regarding the protocol
occurred in the meeting due to lack of time. The draft document
circulated informally to the mailing list will be revised and
submitted as an Internet-draft.
Jim Toga (Intel) provided
an overview of the ITU H.323 protocol and highlighted its ability
to operate over the Internet (h323.3.96.ps). Specifically, H.323
supports having two (or more) H.323 terminals be interconnected
by an IP cloud. It supports the establishment of tightly-controlled
conferences which can be centralized (hub) or distributed (peer-to-
peer). H.323 is based on family of ITU protocols and interoperability
among them is important. Thus the standard contains many guidelines
for interoperation via gateways. No discussion regarding H.323's
use on the Internet and potential impact on protocols being developed
by this group occurred due to lack of time. This will be carried
on the mailing list.
Ed Ellesson (IBM) provided an overview of Internet Telephony and highlighted the impact on conference control as well as other IETF- and Internet-related areas (AVT, Integrated Services). Ed proposed questions such as whether solving issues regarding the lack of interoperability among the Internet Telephone tools was the purview of MMUSIC and pointed out that regardless, these tools in widespread use would have a significant impact on traffic congestion on the Internet. Ed offered to bring Internet phone vendors into the IETF for joint discussions on this issue. Discussion regarding the seemed mismatch between the bandwidth most Internet Telephone users have (e.g., 14.4 kb/sec) and the size of Internet protocols, whether the Internet should work to accommodate this type of traffic flow (vs emphasize its ability to carry multicast traffic), etc. occurred. No specific conclusions were reached in this meeting.