Transport Area H. Schulzrinne
Internet-Draft X. Wu
Expires: July 8, 2004 Columbia University
P. Koskelainen
Nokia
J. Ott
Uni Bremen TZI
January 8, 2004
Requirements for Floor Control Protocol
draft-ietf-xcon-floor-control-req-00
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This document is an Internet-Draft and is in full conformance with
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Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines the requirements for floor control in a
multi-party conference environment.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Integration with Conferencing . . . . . . . . . . . . . . . . 7
6. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 8
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
Normative References . . . . . . . . . . . . . . . . . . . . . 12
Informative References . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . 15
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1. Introduction
Conference applications often have 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
resource. The floor is an individual temporary access or manipulation
permission for a specific shared resource (or group of resources)
[7].
Floor control is an optional feature for conferencing applications.
SIP [2] conferencing applications may also decide not to support this
feature at all. Two-party applications may use floor control outside
conferencing, although the usefulness of this kind of scenario is
limited. Floor control may be used together with conference policy
control protocol (CPCP) [8], or it may be used as independent
standalone protocol, e.g. with SIP but without CPCP.
Floor control has been studied extensively over the years, (e.g. [9],
[7], [6]) therefore earlier work can be leveraged here.
The present document describes the requirements for a floor control
protocol. As a requirements specification, the document makes no
assumptions about the later implementation of the respective
requirements as parts of one or more protocols and about the entities
implementing it/them and their roles.
This document may be used in conjunction with other documents, such
as the Conferencing framework document [3]. In particular, when
speaking about a floor control server, this entity may be identical
to or co-located with the focus or a conference policy server defined
in the framework document, while participants and floor chairs
referred to in this specificiation may be regular participants as
introduced in the conferencing framework document. The term "floor
control protocol" is used in an abstract sense in this specification
and may ultimately be mapped to any of the existing conference
control or other signaling protocols (including CPCP and SIP). But
defining those relationships is left to a concrete floor control
protocol specification.
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2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119.
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3. Terminology
This document uses the definitions from [3].
Additional definitions:
Floor: A permission to temporarily access or manipulate a specific
shared resource or set of resources.
Conference owner: A privileged user who controls the conference,
creates floors and assigns and deassigns floor chairs. The
conference owner does not have to be a member in a conference.
Floor chair: A user (or an entity) who manages one floor (grants,
denies or revokes a floor). The floor chair does not have to be a
member in a conference.
Floor control: A mechanism that enables applications or users to gain
safe and mutually exclusive or non-exclusive input access to the
shared object or resource.
Floor control server: A logical entity that maintains the state of
the floor(s) including which floors exists, who the floor chairs are,
who holds a floor, etc. Requests to manipulate a floor are directed
at the floor control server.
Floor request set: A logical data structure holding all requests for
a particular floor at a given point in time.
Floor holder set: A logical data structure identifying all
participants who currently hold the floor.
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4. Model
The model for floor control comprises three logical entities: a
single floor control server, one or more floor chairs (moderators),
and any number of regular conference participants.
A floor control protocol is used to convey the floor control messages
among the floor chairs (moderators) of the conference, the floor
control server, and the participants of the conference. A centralized
architecture is assumed in which all messages go via one point, the
floor control server. Processing (granting or rejecting) floor
control requests is done by the one or more floor chairs or by the
server itself, depending on the policy.
Floor requests from the participants are received by the floor
control server and kept in an -- at the level of the floor control
protocol -- "unordered" floor request set. The current floor holders
are reflected in a current floor holder set. Floor chairs are
capable of manipulating both sets to e.g. grant, revoke, reject, and
pass the floor.
The order in which requests are processed, whether they are granted
or rejected, how many participants obtain a floor simultaneously, is
determined by a higher layer application operating on these sets and
is not confined by the floor control protocol.
A floor is associated with one or more media sessions. The
centralized conference server manages the floors and thus controls
access to the media sessions. There are two aspects to this: 1) The
server maintains and distributes consistent state information about
who has a certain floor at a certain point in time and does so
following some rule set. This provides all participants with the
necessary information about who is allowed to e.g. speak, but relies
on a cooperative behavior among all participants. 2) In addition, to
prevent individuals from ignoring the "hints" given by the floor
control server, the latter may -- e.g. in cooperation with other
functional entities -- enforce compliance with floor status, e.g. by
blocking media streams from participants not entitled to speak. The
floor control server controls the floors at least at the signaling
level (1); actively controlling also the actual (physical) media
resources (2) is highly recommended, but beyond the scope of this
document.
As noted in the introduction, an actual protocol specification
fulfilling the requirements defined in this memo may map the
components of the above model onto the conferencing components
defined in the conferencing framework document. Some of these
aspects are discussed briefly in the next subsection.
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5. Integration with Conferencing
Floor control itself does not support privileges such as creating
floors and appointing floor chairs, handing over chair privileges to
other users (or taking them away). Instead, some external mechanism,
such as conference management (e.g. CPCP or web interface for policy
manipulation) is used for that.
The conference policy (and thus the conference owner or creator)
defines whether floor control is in use or not. Actually enforcing
conference media distribution in line with the respective media's
floor status (e.g. controlling an audio bridge) is beyond the scope
of this document. Floor control itself does not define media
enforcement. It is up to the conference and media policies to define
which media streams may be used in a conference and which ones are
floor controlled.
Typically, the conference owner creates the floor(s) using conference
policy control protocol (or some other mechanism) and appoints the
floor chair. The conference owner can remove the floor anytime (so
that a media session is not floor-controlled anymore) or change floor
chair or floor parameters.
The floor chair just controls the access to the floor(s), according
to the conference policy.
A floor control server is a separate logical entity, typically
co-located with focus and/or conference policy server. Therefore,
the floor control server can interact with focus, conference Policy
Server and media servers as needed. Communication mechanisms between
floor control server and other central conferencing entities are not
defined at this point.
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6. Requirements
REQ-1: It MUST be possible to announce to participants that a
particular media session (or group of media sessions) is
floor-controlled.
(This is a requirement for session protocol, i.e. SIP. SDP's "a" line
offers one possible indication.)
REQ-2: It MUST be possible to group several media sessions in a
conference together so that one floor applies to the group.
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 authorize other
entities, via the conference policy.
(This is a requirement for CPCP rather than an FCP requirement.)
REQ-4: It MUST be possible to use a chair-controlled floor policy in
which the floor control server 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
the floor chair, or it may do filtering and send only occasional
notifications to the chair.
REQ-5: Participants MUST be able to request (claim) a floor.
REQ-6: It SHOULD be possible for a user requesting a floor to give
additional information about the request, such as the topic of the
question for an audio floor. In some scenarios, the floor chair may
use this information when granting the floor to the user, or when
making manipulation to the floor sets at the server.
REQ-7: It MUST be possible to grant a floor to a participant.
REQ-8: A participant MUST be informed that she has been granted the
floor.
REQ-9: It MUST be possible to reject a participant's floor request.
REQ-10: A participant MUST be informed that his floor request has
been rejected.
REQ-11: The floor chair or moderator MUST be able to revoke a floor
from (one of) its current holder(s).
REQ-12: A participant MUST be informed that the floor was revoked
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from her.
REQ-13: A participant SHOULD be informed that her floor request is
pending and will be processed later.
REQ-14: A floor holder MUST be able to release a floor.
REQ-15: It SHOULD be possible to get and set various floor related
parameters. Note that not all parameters maintained for a floor are
also interpreted by the floor control protocol (e.g. floor policy
descriptions may be stored associated with a floor but may be
interpreted by a higher layer application.
(For example, it may be useful to see who the floor chair is, what
kind of policy is in use, time limits, number of simultanous floor
holders and current floor holder.)
REQ-16: It MUST be possible for a user with appropriate conference
privileges to change the chair for a floor.
(This is rather a requirement for the conference policy control
protocol than for the floor control protocol.)
REQ-17: Bandwidth and terminal limitations SHOULD be taken into
account in order to ensure that floor control can be efficiently used
in mobile environments.
It should be noted that efficient communication by means of minimal
sized messages may contradict the desire to express reasons for
requesting a floor (as per REQ-6) along with other information.
Therefore, a floor control protocol SHOULD be designed in a way that
it allow for expressive as well as minimal messaging, as (negotiable)
configuration option and/or selectable on a per-message basis.
REQ-18: Conference members and the chair MUST have the capability to
learn who has the floor and who has requested the floor. (Note:
Conference policy may prevent members seeing this.)
REQ-19: It MUST be possible to notify conference members and chair
about the floorholder changes and when a new floor request is being
made. (Note: Conference policy may prevent members seeing this.)
REQ-20: There MAY be operations to manipulate the request set
available for floor chair(s).
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7. Open Issues
- Support for privacy, e.g. the following: floor claimer must be able
to indicate privacy preference, and the ability to hide floor chair's
identity.
Preliminary proposal:
RRQ-a: It MUST be possible for the floor requester to indicate her
privacy preference. The privacy preferences MUST include the
following options:
anonymous: the participants (including the floor chair) cannot see
the floor requester's identity. The floor chair grant the floor based
on the claim id and the topic of the claim.
known to the floor chair: only the floor chair is able to see the
floor requester's identity; all other participants do not obtain this
information.
public: all the participants can see the floor requester's identity.
RRQ-b: It MUST be possible to hide the identity of a floor chair from
a subset or all participants of a conference.
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8. Acknowledgements
The authors would like to thank IETF conferencing design team and
Marcus Brunner, Keith Drage, Sanjoy Sen, Eric Burger, Brian Rosen,
and Nermeen Ismail for their feedback.
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Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCD 14, March 1997.
[2] Rosenberg et al., J., "SIP: Session Initiation Protocol", RFC
3261, June 2002.
[3] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol",
draft-rosenberg-sipping-conferencing-framework-01 (work in
progress), February 2003.
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Informative References
[4] Koskelainen, P., Schulzrinne, H. and X. Wu, "Additional
Requirements to Conferencing", October 2002.
[5] Wu, X., Schulzrinne, H. and P. Koskelainen, "Use of SIP and SOAP
for conference floor control", January 2003.
[6] Koskelainen, P., Schulzrinne, H. and X. Wu, "A sip-based
conference control framework", Nossdav'2002 Miami Beach, May
2002.
[7] Dommel, H. and J. Garcia-Luna-Aceves, "Floor control for
activity coordination in networked multimedia applications",
Proc. of 2nd Asian-pacific Conference on Communications APPC,
Osaka Japan, June 1995.
[8] Koskelainen, P. and H. Khartabil, "An Extensible Markup Language
(XML) Configuration Access Protocol (XCAP) Usage for Conference
Policy Manipulation", draft-koskelainen-xcon-xcap-cpcp-usage-01
(work in progress), October 2003.
[9] Borman, C., Kutchner, D., Ott, J. and D. Trossen, "Simple
conference control protocol service specification",
draft-ietf-mmusic-sccp-00 (work in progress), March 2001.
Authors' Addresses
Henning Schulzrinne
Columbia University
1214 Amsterdam Avenue
New York 10027
USA
EMail: hgs@cs.columbia.edu
Xiaotao Wu
Columbia University
1214 Amsterdam Avenue
New York 10027
USA
EMail: xiaotaow@cs.columbia.edu
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Petri Koskelainen
Nokia
P.O. Box 100 (Visiokatu 1)
Tampere FIN-33721
Finland
EMail: petri.koskelainen@nokia.com
Joerg Ott
Uni Bremen TZI
Bibliothekstr. 1
Bremen D-28359
Germany
EMail: jo@tzi.uni-bremen.de
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