2.8.2 Centralized Conferencing (xcon)

NOTE: This charter is a snapshot of the 58th IETF Meeting in Minneapolis, Minnesota USA. It may now be out-of-date.

Last Modified: 2003-10-20

Adam Roach <adam@dynamicsoft.com>
Alan Johnston <alan.johnston@mci.com>
Transport Area Director(s):
Allison Mankin <mankin@psg.com>
Jon Peterson <jon.peterson@neustar.biz>
Transport Area Advisor:
Allison Mankin <mankin@psg.com>
Mailing Lists:
General Discussion: xcon@ietf.org
To Subscribe: https://www1.ietf.org/mailman/listinfo/xcon
Archive: http://www1.ietf.org/mail-archive/working-groups/xcon/current/
Description of Working Group:
The focus of this working group is to develop a standardized suite of protocols for tightly-coupled multimedia conferences, where strong security and authorization requirements are integral to the solution. Tightly-coupled conferences have a central point of control and authorization (known as a focus) so they can enforce specific media and membership relationships, and provide an accurate roster of participants. The media mixing or combining function of a tightly-coupled conference need not be performed centrally, however.

The scope of this effort is intentionally more narrow than previous attempts to standardize conferencing (e.g. centralized control), and is intended to enable interoperability in a commercial environment which already has a number of non-standard implementations using some of the protocols.

Privacy, security, and authorization mechanisms are integral to the solution generated by the working group. This includes allowing participants to be invisible to all but the conference owner, or to be visible but participate anonymously with respect to some or all of the other participants.

Authorization rules allow for participants and non-participants to have roles (ex: speaker, moderator, owner), and to be otherwise authorized to perform membership and media manipulation for or on behalf of other participants. In order to preserve these properties, the protocols used will require implementation of channel security and authentication services.

Due to the centralized architecture of the WG, XCON's mechanisms will place requirements on the signaling protocol used between the focus and the participants. At a high level, the signaling protocol must be able to establish, tear down, modify, and perform call control operations on multimedia streams, including voice, video, and instant messaging, in both a centralized and distributed mixing architecture. SIP will be the reference session signaling protocol used for examples; however, none of the XCON solutions themselves will be signaling protocols, nor will XCON extend existing signaling protocols. Other signaling protocols than SIP may be used between the focus and participants, including non-IETF protocols, but the requirements and possible extensions needed for other signaling protocols to utilize the full functionality of the XCON architecture is outside the scope of XCON.

The deliverables for the group will be: - A mechanism for membership and authorization control - A mechanism to manipulate and describe media "mixing" or "topology" for multiple media types (audio, video, text) - A mechanism for notification of conference related events/changes (for example a floor change) - A basic floor control protocol

The initial set of protocols will be developed for use in unicast media conferences. The working group will perform a second round of work to enhance the set of protocols as necessary for use with multicast media after their initial publication.

The following items are specifically out-of-scope: - Voting - Fully distributed conferences - Loosely-coupled conferences (no central point of control) - Far-end device control - Protocol used between the conference controller and the mixer(s) - Capabilities negotiation of the mixer(s) - Master-slave cascaded conferences

The working group will coordinate closely with the SIPPING and MMUSIC working groups. In addition the working group will cooperate with other groups as needed, including SIP, MSEC, AVT, and the W3C SMIL working groups. In addition, the working group will consider a number of existing drafts as input to the working group.

Goals and Milestones:
Oct 03  Submit Requirements for Membership Manipulation for publication as Informational
Oct 03  Submit Requirements for Basic Floor Control for publication as Informational
Nov 03  Submit Conferencing Scenarios document for publication as Informational
Nov 03  Submit Use Cases for Media Topology Control for publication as Informational
Dec 03  Submit Requirements for Media Topology Control for publication as Informational
Feb 04  Submit Basic Floor Control Protocol for publication as PS
Mar 04  Submit Notification Event package extension for conference related events for publication as PS
May 04  Submit Membership Manipulation Protocol for publication as PS
Jul 04  Submit Protocol for Media Topology Control for publication
No Current Internet-Drafts
No Request For Comments

Current Meeting Report


Could you post these notes (after reviewing) on the supplemental page and  
forward to the IESG.

Thanks, Alan.

- - - - - -

Reviewed charter milestones. Noted that this is first meeting of the WG and  
we're already behind.

draft-even-xcon-conference-scenarios-00. There were questions  about 
adequacy of scenarios, especially regarding text media. * Cullen 
Jennings agreed to contribute some text on that subject. * Room polled for 
consensus: should we accept this draft as a   WG item? Hum indicated 

Joerg Ott discussed 
draft-koskelainen-xcon-floor-control-req-00. There was  question by 
Jonathan Rosenberg about relationship to focus - not covered by  
document. Roni Even and Rohan Mahy also asked about positioning re the  
conferencing framework. (There seemed to be sentiment for better  
positioning of this doc) Dean Willis asked if the protocol will allow  
selection of a particular floor - Joerg said yes.  Juhe Garg raised 
concern  with the number of protocols that conference participants must 
implement.  Answer was that this doc is just requirements, not 
specification of a  protocol. Nermeen Ismail asked whether 
participants are notified who has  the floor. Answer was there is a 
requirement for this. Cullen Jennings  asked for way for requestor to know 
what status is of request for floor.

Marcus Brunner discussed 
draft-brunner-xcon-fc-issues-00. This draft  asserts floor control 
mechanism must be independent of policy; policy is  instead part of the 
conference application. Question by chair if this could  be 
incorporated into the floor control requirements document. Joerg and  
author had discussion of fine points of this. Decided this should be taken  
to the mailing list. Brian Rosen expressed opinion that the 
requirements  were verging on too much for initial work - should remove 
rather than add  requirements.

* On hum, agreed to accept the combination of these two documents as WG 
doc. * Room polled for consensus: should we accept the combinations of 
these   two documents a WG item? Hum indicated support.

Hisham Khartabil presented 
draft-koskelainen-xcon-cpcp-reqs-01. Juhe Garg  requested addition of 
requirement to control when a conference ends.

* Room polled for consensus: should we accept this draft as a   WG item? Hum 
indicated support.

Hisham also discussed 
draft-koskelainen-xcon-xcap-cpcp-usage-01: asked for  opinions on use of 
XCAP for this. The people present were not prepared to  commit on this.

Orit Levin presented draft-levin-xcon-cpcp-00 (apparently an 
alternative to  
draft-koskelainen-xcon-xcap-cpcp-usage-01.) She had some issues with XCAP -  
expressed opinion it would unduly influence schema - preferred focusing on  
xml schema independent of transport used to manage it - open to http, sip,  
soap. Discussion continued on both documents. Cullen Jennings thought  
things don't hang together very well yet - need more work. Alan 
Johnston  complained that he hadn't seen anything on list about it - 
asserted not  ready to decide on one approach vs the other - need to take 
this to the  list.  Lisa Dusseault mentioned new ACL Webdav 
extensions.  Chairs  requested people to read and comment on the 

* Cullen Jennings, Eric Burger, and others agreed to do so.

Rohan discussed 
draft-mahy-xcon-media-policy-control-00. It raises issue of  what level of 
abstraction does the wg want to work at. There was very  lively 
discussion of this, only slightly captured here. Got to question of  
whether the application deals with application specific roles, and they are  
the subjects in interaction with media policy, or whether the 
application  must itself map its notion of role onto some 
non-application-specific  notation of media streams, etc. Cullen 
Jennings thought roles of  participants can change - wasn't sure if 
everybody on same page. Doesn't  want it to be hard to figure out roles. He 
also doesn't know how an  "application" relates to the model, but 
apparently it is important. Nermeen  Ismail reiterated desire to make 
policy engine unaware of significance of  particular roles. She feels 
"media policy" is a bad term.  Eric Burger  wanted something fairly high 
level - gave analogy - assembly language is  more flexible than Java, but 
would prefer to use Java. Eric also said even  MGCP would be preferred to 
the logical model proposed.  Rohan and Eric  debated on connections 
between media and conference policy. Rohan thinks  there are cases where 
changes to role of a participant in conf policy also  affect media 
policy. Eric says "not necessarily" - it is up to  "application" to 
decide if both should be changed. Alan raised issue that  changes to media 
policy must be able to be reflected back to users - need  some way to 
reverse engineer the changes to something user meaningful. Also  
commented that the "application" is the user interface. Thought that the  
conceptual approach was better than the logical (Rohan) approach for this.  
Juhe Garg wanted to remove term "roles" - focus only on 
"permissions". Eric  really didn't like this. Rohan felt use cases are 
needed. Nermeen wanted  better requirements. Rohan then showed a 
strawman definition of a  subconference - asserting it is a 

Brian Rosen then showed a couple of slides  
(jennings-xconMediaPolicyRan.pdf) of rebutal to Rohan's, asking what is the  
problem we are trying to solve. Asserted  
draft-mahy-xcon-media-policy-control-00 is too complicated, and doesn't  
address the problem directly. Its a language to describe media flow 
graphs,  not one to control them. Not facilitating interoperable 
implementations.  Brian proposed templates instead. Rohan was 
concerned with how to map  templates for media control onto 
conference control. Brian gave an example  of a mix-minus mixer. Said 
#input audio streams, #output audio streams  (max) are bound at conf 
creation. This raised a lot of concerns from  audience. People felt this was 
almost what Rohan was proposing. Rohan  asserted that any proposal must 
address how it interacts with conf policy.  And Cullen wanted to be sure it 
covers all the requirements. Jonathan  didn't think it was necessary to 
solve all problems as long as there is  extensibility.

Media policy requirements draft by Roni Even mentioned: hasn't changed  
since last meeting.

See everyone next time! 


Conferencing Scenarios
Requirements for Floor Control Protocol
Policy-Free Floor Control
Conference Policy
Conference Policy Control Protocol xcon-6 Media Policy Issues
What is the problem we are solving?
Conferencing media policy requirements