Internet Engineering Task Force                                P. Koskelainen
Internet Draft                                                          Nokia
draft-koskelainen-mmusic-floor-req-01.txt                      H. Schulzrinne
October 31, 2002                                                  Columbia U.
Expires: May 2003                                                      J. Ott
                                                          Universitaet Bremen

                     Requirements for Floor Control


   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress".

   The list of current Internet-Drafts can be accessed at

   To view the list Internet-Draft Shadow Directories, see


   This document defines the requirements for floor control.

1 Introduction

   Multimedia conferences often contain shared resources such as the
   right to talk, input access to a limited-bandwidth video channel, or
   a pointer or input focus in a shared application.

   In many cases, it is desirable to be able to control who can provide
   input (send/write/control, depending on the application) to the
   shared resource.

   Floor control enables applications or users to gain safe and mutually
   exclusive or non-exclusive input access to the shared object or

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 1]

Internet Draft            Floor control reqs.           October 31, 2002

   resource. We define a floor as the temporary permission for a
   conference participant to access or manipulate a specific shared
   resource or group of resources [2].

   Floor control is an optional feature of conferences. SIP [4]
   conferencing applications may decide not to support this feature at
   all. Some applications of floor control, such as write access to a
   shared document, are useful even for "conferences" with two members,
   while other resources, such as an audio channel, may only make floor
   control worthwhile for larger groups.

   Earlier work on this topic (e.g., [3], [5], [6], [2]) can serve as
   useful input for the SIP standardization efforts.

   In general, floor control is closely related to the management of
   shared resources in operating systems and distributed systems.
   Synchronization, mutual exclusion and the reader-writer problem have
   become standard tools in those areas. However, floor control differs
   in that it generally involves managing access by human participants,
   with a much stronger emphasis on policies.

   This work supports on-going SIPPING conferencing work [1], and [7].

2 Conventions of This Document

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   and "OPTIONAL" are to be interpreted as described in RFC 2119 [8].

3 Definitions

        Focus: The focus is a SIP user agent that is addressed by a
             conference URI. The focus maintains a SIP signaling
             relationship with each participant in the conference. The
             focus is responsible for ensuring, in some way, that each
             participant receives the media that make up the conference.
             The focus also implements conference policies.  The focus
             is a logical role.

        Floor: A floor is a set of shared resources within a conference.
             A single conference may have multiple floors.

        Conference members: A conference member or participant that has
             a signaling relationship with the conference focus and
             receives one or more of the media streams that are part of
             the conference.

        Conference owner: A conference owner is a privileged user who

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 2]

Internet Draft            Floor control reqs.           October 31, 2002

             defines rules for running the conference. By default, the
             conference creator becomes the owner, but the role can be
             delegated to another entity. Among other roles, the
             conference owner also establishes rules for floor control,
             by creating floors, assigning and removing floor chairs.
             The conference owner may delegate some of these
             responsibilities to another party. The conference owner
             does not have to be a member in the conference.

        Chair: A user (or an entity) who manages one floor by granting,
             denying or revoking access privileges. The chair does not
             have to be a member of the conference. The chair is
             sometimes also referred to as the moderator. Different
             floors within a conference may have different chairs.
             Chairs may change during a conference.

        Floor control: Floor control is a mechanism that enables
             applications or users to gain safe and mutually exclusive
             or non-exclusive access to the shared object or resource.

        Floor controller: A floor controller is a logical entity that
             manages floors. It receives requests from conference
             participants, the conference owner and the floor chair and
             issues protocol requests to affect conference and floor
             status. Depending on floor policy, the floor controller may
             ask the chair to approve decisions.

        Floor policy: The floor policy is the set of rules and
             attributes governing operation of the floor controller. The
             floor policy is defined upon creation of a floor and may be
             modified by an authorized participant.

4 Model

   A floor control protocol is used to convey the floor control messages
   among the floor chairs (moderators) of the conference, the floor
   controller, the focus and the participants of the conference.

   Floor control can operate at the origin of data, at a redistribution
   point or at the destination. At the origin of data, floor control can
   ask the sender, via signaling, to surpress the generation of data. At
   the redistribution point, the floor controller can modify the mixing
   matrix, so that only media streams from certain participants are
   delivered to other participants. At the destination, floor control
   can filter incoming media or messages, so that only floor holders can
   affect the state of the shared resource.

   We can also distinguish cooperative and coercive floor control.

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 3]

Internet Draft            Floor control reqs.           October 31, 2002

   Cooperative floor control relies on the cooperation of the data
   source, while coercive floor control does not; it can function even
   if a participant is malicious or malfunctioning. Among the three
   locations of floor control, floor control at the redistribution point
   and at the receiver can be made coercive, while floor control at the
   sender is by necessity cooperative.

   A floor is always coupled to one or more media sessions. The manner
   of creating a media session itself is defined elsewhere. A
   participant with appropriate privileges may create a floor by
   defining that one or more media sessions are now floor-controlled. As
   part of the creation of a floor, a chair needs to be appointed. (In
   some cases, the chair is an automaton, rather than a human

5 Integration with Conferencing

   We assume that the ability of users to create floors is governed by
   the conference policy. For simplicity, we assume that a chair can
   delegate his or her responsibility to any other member of the

   The conference policy and thus, indirectly, the conference owner
   defines whether or not floor control is in use and for which
   resources. If floor control is enabled for a particular resource or
   set of resources, the conference policy also defines for which
   resources the use of floor control is mandatory and for which it is
   optional. [TBD: Not clear what mandatory and optional means.]

   Typically, the conference owner creates a floor using a yet-to-be-
   defined mechanism and appoints the floor chair. The conference owner
   can remove the floor at any time (so that the resources are no longer
   floor-controlled), change the chair or the floor parameters.

   The chair just controls the access to the floor, according to the
   conference policy.

   Figure 1 depicts how floor control integrates into the overall
   conferencing architecture.

6 Requirements

        REQ-1: It MUST be possible to announce to participants that a
             particular media session (or group of media session) is
             floor-controlled and where requests for the floor should be
             addressed to.

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 4]

Internet Draft            Floor control reqs.           October 31, 2002

                                     |                        |
          +-------+                  |   +------------------+ |
          |Floor  |                  |   | Conference Policy| |
          |Control| ---              |   |       Server     | |
          |Server |    ------        |   +------------------+ |
          +-------+          -----   |                        |
              .  .   .            ---+--    +-------------+   |
              .   .   ..             |  --- | Media Policy|   |
              .    ..   ..           |      |   Server    |   |
              .      .    .          |      +-------------+   |
              .       .    ..        |                        |
        Floor .        .     ..      | +---------+  +-----+   |
      Control .         ..     .     | |Focus    |  |Mixer|   |
      Protocols.          .     ..   | +---------+  +-----+   |
    (SUB/NOT & .           .      .. +-----/-----------------+
     controls) .            .       .---- /            |
               .             .   ----..  /             |
               .             ----      ./            dialogs
               .         ----   .       /.             |
               .     ----        .     /  ..           |
                  ---                 /     ..         |
            +-------+            +-------+    .      +-------+
            |       |            |       |     ..    |       |
            | Client|            | Client|       ..  | Client|
            |       |            |       |         . |       |
            |       |            |       |           |       |
            |       |            |       |           |       |
            +-------+            +-------+           +-------+

   Figure 1: Floor control integration into Conferencing

             SDP's "a" line offers one possible indication.

        REQ-2: It MUST be possible to group more than one media sessions
             together so that one floor applies to the group.

             The SDP "fid" extension may serve this purpose.

        REQ-3: It MUST be possible to define who is allowed to create,
             change and remove a floor in a conference. We assume that
             the conference owner always has this privilege and may also

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 5]

Internet Draft            Floor control reqs.           October 31, 2002

             authorize other entities, via conference policy.

        REQ-4: A participant with appropriate privileges MUST be able to
             create a floor with specific parameters, such as how many
             simultaneous users are allowed to access the resource. It
             MUST be possible to modify these parameters during the
             lifetime of a floor.

        REQ-5: It MUST be possible to use a chair-controlled floor
             policy in which the floor controller notifies the floor
             chair and waits for the chair to make a decision. This
             enables the chair to fully control who has the floor. The
             server MAY forward all requests immediately to chair, or it
             may do filtering and send only occasional notifications to

        REQ-6: Participants MUST be able to request (claim) a floor and
             give additional information about the request, such as the
             topic of the question for an audio floor.

        REQ-7: A floor holder MUST be able to release a floor.

        REQ-8: The chair or controller MUST be able to revoke a floor
             from its current holder.

        REQ-9: It MUST be possible to grant a floor to a participant.

        REQ-10: It MUST be possible to get and set at least the
             following floor parameters:

             - who is floor control chair (this does not have to be the
               conference owner);

             - floor control policy (such as chair-controlled, first-
               come first-served, random);

             - the number of simultaneous floor holders.

        REQ-11: Floor policies MAY support time limits that
             automatically pass the floor to the next-in-line after a
             preset time interval.

        REQ-12: It MUST be possible for a user with appropriate
             conference privileges to change the chair for a floor.

        REQ-13: It MAY be possible for a user to request that a media
             session should be floor-controlled. The requestor does not
             necessarily become the floor chair. (For example, a

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 6]

Internet Draft            Floor control reqs.           October 31, 2002

             conference creator may designate a set of media as a latent
             floor that automatically becomes floor controlled as soon
             as a member requests it.)

        REQ-14: Different floors may have different chairs.

        REQ-15: Bandwidth and terminal limitations SHOULD be taken into
             account in order to ensure that floor control can be
             efficiently used in mobile environments.

        REQ-16: Conference members and the chair MUST be able to
             determine who has the floor and who has requested the

        REQ-17: Conference members and the chair MUST be able to be
             notified when the floorholder changes and when a new floor
             request is being made.

        REQ-18: It should be possible to name custom floor control
             policies, both with local meaning only and global

        REQ-19: It may be desirable to support a floor control mechanism
             where users without specialized software can request the
             floor. (For example, a floor control mechanism could
             utilize specific instant messages.)

7 Open Issues

        o Support multiple simultaneous chairs for one floor?

        o Support for privacy (especially for REQ-16)

8 Acknowledgements

   The authors would like to thank Xiaotao Wu, Sanjoy Sen, Jonathan
   Rosenberg, Brian Rosen, Nermeen Ismail, Rohan Mahy, and Orit Levin
   for their comments.

9 Authors' Addresses

   Petri Koskelainen
   Visiokatu 1,
   33720 Tampere
   electronic mail:

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 7]

Internet Draft            Floor control reqs.           October 31, 2002

   Henning Schulzrinne
   Dept. of Computer Science
   Columbia University
   1214 Amsterdam Avenue, MC 0401
   New York, NY 10027
   electronic mail:

   Joerg Ott <>
   Universitaet Bremen
   MZH 5180
   Bibliothekstr. 1
   D-28359 Bremen

10 Bibliography

   [1] J. Rosenberg, "A Framework for Conferencing with the Session
   Initiation Protocol, " Internet Draft, Internet Engineering Task
   Force, Oct 2002, Work in progress.

   [2] Dommel, H.-P., and Garcia-Luna-Aceves, J., "Floor control for
   activity coordination in networked multimedia applications.," In
   Proc. of 2nd Asian-Pacific Conference on Communications (APCC (Osaka,
   Japan, June 1995).

   [3] P. Koskelainen, H. Schulzrinne, and X. Wu, "A sip-based
   conference control framework," in The 12nd International Workshop on
   Network and Operating System Support for Digital Audio and Video
   (NOSSDAV) , (Miami Beach, Florida), May 2002.

   [4] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
   Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP: session
   initiation protocol," RFC 3261, Internet Engineering Task Force, June

   [5] C. Bormann, D. Kutscher, J. Ott, and D. Trossen, "Simple
   conference control protocol service specification," Internet Draft,
   Internet Engineering Task Force, Mar. 2001.  Work in progress.

   [6] X. Wu, P. Koskelainen, H. Schulzrinne, and C. Chen, "Use SIP and
   SOAP for conference floor control," Internet Draft, Internet
   Engineering Task Force, Apr. 2002.  Work in progress.

   [7] O. Levin et al.  , "Requirements for tightly coupled SIP
   conferencing," Internet Draft, Internet Engineering Task Force, July

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 8]

Internet Draft            Floor control reqs.           October 31, 2002

   2002.  Work in progress.

   [8] S. Bradner, "Key words for use in RFCs to indicate requirement
   levels," RFC 2119, Internet Engineering Task Force, Mar. 1997.

   Full Copyright Statement

   Copyright (c) The Internet Society (2002). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein is provided on an

                           Table of Contents

   1          Introduction ........................................    1
   2          Conventions of This Document ........................    2
   3          Definitions .........................................    2
   4          Model ...............................................    3
   5          Integration with Conferencing .......................    4
   6          Requirements ........................................    4
   7          Open Issues .........................................    7

P. Koskelainen/H. Schulzrinne/J. Ott                          [Page 9]

Internet Draft            Floor control reqs.           October 31, 2002

   8          Acknowledgements ....................................    7
   9          Authors' Addresses ..................................    7
   10         Bibliography ........................................    8

P. Koskelainen/H. Schulzrinne/J. Ott                         [Page 10]