Editor's Note: The CONFCTRL BOF became the MMUSIC WG on 6/24/93. CURRENT_MEETING_REPORT_ Reported by Eve Schooler/Information Sciences Institute Minutes of the Conferencing Control BOF (CONFCTRL) These Minutes were prepared by Eve Schooler from notes provided by Abel Weinrib of Bellcore and Deborah Estrin of USC/ISI. Introduction and Presentations Two CONFCTRL sessions were held at the Columbus IETF. The first meeting was used to provide an overview of Conference Control efforts both within and outside of the IETF. Inside the IETF, the CONFCTRL Group was spawned by the Remote Conferencing Architecture BOF (REMCONF). Outside the IETF, interest in conference control, sometimes referred to as connection management, has been ongoing for some time. Thus far, the CONFCTRL mailing list has collected a sizable bibliography containing references to many of the early and ongoing research projects in this area. Most of the first session was used for presentations on different CONFCTRL schemes. The intent of the presentations was to flesh out design assumptions, tradeoffs, complexity, scalability, etc. The systems were classified according to several parameters: whether they (1) concentrate more on groupware conferencing (shared editors, whiteboards) than on real-time audio/video conferencing, (2) provide session control of packet-based real-time media versus analog real-time media, (3) rely on centralized versus distributed session management, and/or (4) observe loose versus tight session control. o Ruth Lang of SRI reported on the Collaborative Environment for Concurrent Engineering Design (CECED). o Abel Weinrib of Bellcore focused on the session elements and functions supported by Bellcore's Touring Machine. o Hans Eriksson of SICS discussed the CoDesk architecture. o Don Hoffman of Sun Microsystems outlined the model used for the COCO project. o Chip Elliott of BBN presented his work on VideoTeam and the Sticky CONFCTRL protocol on which it relies. o Lakshman Krishnamurthy of University of Kentucky summarized the versatile Multi-flow Conversation Protocol. o Eve Schooler of ISI gave an overview of the MMCC tool and its Conference Control Protocol. 1 o Thierry Turletti's ivs program was discussed as a contrasting example that uses loose-style session management. Synthesis of CONFCTRL approaches The second session was used to identify pervasive CONFCTRL themes, and to question the applicability of the various solutions to the Internet. The main objective was to narrow the scope of the problem en route to the design of a generic CONFCTRL protocol. Observations were culled not only from the presentations at the IETF but also from templates that were filled out prior to the meeting. The templates included Dave Lewis' write up of the UCL PREPARE project, a description of the ZAPT project by Joe Touch of ISI, a contribution from Jack Jansen of CWI about the Meeting project, and Fengmin Gong's template on the MCNC CONCERT Video Network Migration effort. Of particular interest were implementors' comments about the aspects of their approaches which were hard, easy, or warranted change. Except for a lone comment about the ease of implementation of floor control, there were several recurrent themes regarding implementation difficulties: o It is difficult to design a CONFCTRL protocol that balances simplicity with a high degree of semantic flexibility, e.g., Jansen of CWI concluded that different conferencing styles require entirely separate CONFCTRL protocols. o A distributed model comes with distributed system complexities: - Support for causality of multiway message exchanges. - Recovery from temporary network failures. - Propagation of consistent state information. The solutions proved to be cumbersome, unexpectedly hard and often times ``tricky''. o The underlying transport (that carries session control information) comes at a price, e.g., the overhead of one RPC implementation led the PREPARE project to shift to a different, lighter implementation. o There is room for improved media integration, e.g., asymmetric flows are difficult to characterize at setup, there is a need for more powerful control over presentation of media streams. Most experimental systems either are or began as LAN-based conferencing systems. However, it is clear that many, if not all, are aiming for WAN operation. Although the tools that currently populate the MBONE rely on loose-style session control, in the past most experimentation has taken place with tightly controlled session models -- though this is clearly changing. The Group speculated that the predominance of tight-control 2 systems may be a function of the interest in supporting ``coordinated'' telecollaborations, which are readily modeled using a tight-control framework, whereas the emergence of loose-control systems may be a reflection of the relative ease with which they are implemented. Systems were clearly differentiated in their approaches to interconnectivity among participants, both for session and for media topology. In certain cases, symmetry exists for N-way communication capabilities, while in other cases conferees are asymmetrically interconnected, relying on an initiator, moderator, filter/reflector or a privileged set of designees to coordinate communication on behalf of others. Explicit versus implicit communication is another distinguishing feature; this relates to whether or not the session has policies attached to it, such as who dictates membership rules, the extent to which session information is disseminated or if participant information is meant to be kept globally coherent. Finally, it was observed that the decision to model the system in a centralized or distributed fashion influenced the degree of messaging synchrony and causality. Group Scope, Framework and Functional Taxonomy There was rough consensus on the definition of conference control as the management and coordination of multiple sessions and their multiple users in multiple media. It was also agreed that the focus of the Group is to design a ``session layer'' protocol to perform these functions. However, the Group debated the utility of designing a ``teleconferencing'' session protocol specifically for the coordination of users' ``media'' versus designing a Group negotiation protocol that is extensible to act as a conduit for media details. The Group recognizes that it cannot set out to support all conferencing scenarios. However, it proposes to support one loose style protocol (a la Xerox PARC's nv, INRIA's ivs, BBN's dvc, LBL's vat, UMass' nevot) and one tight style protocol (for negotiated and potentially private sessions). How loose and how tight? To answer this, the list of conversation styles must be mapped (from the last IETF Minutes) into their underlying CONFCTRL session protocols. As an example of how a tight-control approach to session management might integrate with already existing MBONE tools, an X-based version of ISI's MMCC conference control tool was demonstrated at the IETF. MMCC was used to explicitly invite a specific set of participants (versus having a wide-open session), to distribute multicast addresses and a shared encryption key among those participants, and to initiate as well as tear down sessions comprised of nv, vat and/or BBN's newly released PictureWindow. Although it was emphasized that the goal of the Group is to design a session protocol, the Group conceded that there is a need for a common framework within which it can talk about conferencing control. The framework that arose from discussion, looked as follows: 3 User A User B +-------------+ +-------------+ | | | | | Application | | Application | | | | | +------+------+ +------+------+ | | +------+------+ +------+------+ | | | | | Session |<----------------------------->| Session | | | "Session Protocol" | | +---+--+--+---+ +---+--+--+---+ / | \ / | \ / ... \ / ... \ +-------+ +-------+ +-------+ +-------+ | Media | ... | Media |<---------------------->| Media | | Media | | Agent | | Agent | "Media Stream" | Agent | | Agent | +-------+ +-------+ +-------+ +-------+ The premise is that the session protocol would be distributed in nature, and would accommodate multiple user sessions (even though the diagram depicts only two conferees). There is a firm separation between the session protocol and media transport protocols. Thus, it is immaterial whether the media transport is packet-based or analog. Generic session state would include membership and policy information. Application-domain specific state might include media interconnectivity (topology) and media configuration (data encodings, rates). Although needing further refinment, the list of session functionality provided to the end systems and reflected in the session protocol would encompass: o Create/Destroy Session o Add/Delete Member o Set Policy - Who may join - Who may invite - Who may set policies - Etc. o Add/Change Application-Domain Specific State - Media interconnectivity - Media configuration o Floor Control? o Prescheduling? Polling the interest of the BOF participants, it was found that 75% were 4 interested in solving the session protocol problem, 40% also would be interested in defining or standardizing the media-agent-to-session-entity interface, and 30% were interested in configuration management issues. Terminology It became evident that there are no set definitions for terms such as conference, connection, session, media agents, etc. Many of the systems presented during the BOF and described in the templates used these terms differently. Thus, a CONFCTRL terminology reference guide needs to be developed. The Group had been interchanging the phrases session control, session management, connection control and connection management, but later agreed that ``connection'' is too ambiguous since it is used at any number of levels in the protocol stack. Connection was replaced by the term ``session'', and was broadly defined as an association of members for control purposes. However, it was later argued that session looks too much like an OSI term. The term ``conference'' was also felt to be too application specific. Therefore, the Group is open to suggestions for a better name. It was suggested (although not entirely resolved) that ``media agents'' handle the media specifics associated with a session. ``Media'' could be considered any data streams that involve communication. It was also suggested that floor control is deemed the responsibility of a media agent when it concerns a single media agent, but the responsibility of the session entity when it requires coordination across different media agents (e.g., video to follow audio). The Group also differentiated between two meanings of configuration; the static end-system description, including hardware and software capabilities, and the per-session description. Liaisons The CONFCTRL Group is committed to tracking the progress of related efforts, both within and outside the IETF. An important IETF linkage is to leverage off ongoing work in the Audio/Video Transport Working Group (AVT), which is nearing completion of the Real-time Transport Protocol (RTP) specification. During the first two AVT sessions, there was considerable discussion about RTCP, the control protocol associated with RTP. Certain functions in RTCP were felt to violate ``layering''; they do not belong in the transport, but would live comfortably within the session level, e.g., text strings of session participants. The Group will need to follow closely the outcome of these developments, especially if certain services are assumed to percolate into the session layer. The MBONE is another strategic testing ground for a CONFCTRL solution, although its use should not preclude use of these ideas elsewhere, nor 5 should these ideas be tailored specifically to the MBONE. By mentioning MBONE it is really meant that the Group expects, in the long term, to have access to networks that support multicast and in the longer term to support real-time services. The general Internet should suffice for now. Individuals who volunteered to track developments in related areas include: Ruth Lang Directory Services Hans Eriksson Multicast Developments Fengmin Gong Resource Management/QoS Steve Casner Audio/Video Transport Eve Schooler Audio/Video Transport Paul Lambert Security Stuart Stubblebine Security Yee-Hsiang Chang ATM Peter Kirstein MIBs Action Items o Make CONFCTRL bibliography available. o Documentation: - Terminology reference guide. - Refinement of functional taxonomy. - Turn Minutes into issues/framework document. - Mapping of conversation styles into session protocols. - Collect suggestions for a Group name change. Attendees Lou Berger lberger@bbn.com Monroe Bridges monroe@cup.hp.com Al Broscius broscius@bellcore.com Randy Butler rbutler@ncsa.uiuc.edu Yee-Hsiang Chang yhc@hpl.hp.com Brian Coan coan@faline.bellcore.com Richard Cogger R.Cogger@cornell.edu Simon Coppins coppins@arch.adelaide.edu.au Dave Cullerot cullerot@ctron.com 6 Steve DeJarnett steve@ibmpa.awdpa.ibm.com Ed Ellesson ellesson@vnet.ibm.com Chip Elliott celliot@bbn.com Hans Eriksson hans@sics.se Deborah Estrin estrin@isi.edu Francois Fluckiger fluckiger@vxcern.cern.ch Jerry Friesen jafries@sandia.llnl.gov Fengmin Gong gong@concert.net Kenneth Goodwin goodwin@a.psc.edu Mark Green markg@apple.com Russ Hobby rdhobby@ucdavis.edu Don Hoffman hoffman@eng.sun.com Frank Hoffmann hoffmann@dhdibm1.bitnet Michael Khalandovsky mlk@ftp.com Peter Kirstein P.Kirstein@cs.ucl.ac.uk Jim Knowles jknowles@binky.arc.nasa.gov Lakshman Krishnamurthy lakashman@ms.uky.edu Giri Kuthethoor giri@ms.uky.edu Paul Lambert paul_lambert@email.mot.com Ruth Lang rlang@nisc.sri.com Patrick Leung patrickl@eicon.qc.ca Allison Mankin mankin@cmf.nrl.navy.mil Donald Merritt Don@brl.mil Paul Milazzo milazzo@bbn.com Robert Mines rfm@sandia.llnl.gov Joseph Pang pang@bodega.stanford.edu Geir Pedersen Geir.Pedersen@usit.uio.no John Penners jpenners@advtech.uswest.com Bala Rajagopalan braja@qsun.att.com Michael Safly saf@tank1.msfc.nasa.gov Eve Schooler schooler@isi.edu Michael St. Johns stjohns@darpa.mil Stuart Stubblebine stubblebine@isi.edu Sally Tarquinio sallyt@gateway.mitre.org Claudio Topolcic topolcic@cnri.reston.va.us Mario Vecchi mpv@thumper.bellcore.com Abel Weinrib abel@bellcore.com John Wroclawski jtw@lcs.mit.edu Yow-Wei Yao yao@chang.austin.ibm.com 7