Request for Comments: 4597 Polycom
Category: Informational N. Ismail
Cisco Systems, Inc.
July 2006
Conferencing Scenarios
Status of This Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes multimedia conferencing scenarios. It
describes both basic and advanced conferencing scenarios involving
voice, video, text, and interactive text sessions. These scenarios
will help with the definition and evaluation of the protocols being
developed in the centralized conferencing XCON working group.
Table of Contents
1. Introduction ....................................................3
2. Basic Conferencing Scenarios ....................................3
2.1. Ad Hoc Conferences .........................................4
2.2. Extension of a Point-to-Point Call to a Multipoint Call ....4
2.3. Reserved Conferences .......................................4
3. Advanced Conferencing Scenarios .................................5
3.1. Extending a Point-to-Point Call to a Multipoint Call .......5
3.2. Lecture Mode Conferences ...................................5
3.3. Conference with Conference-Aware and Unaware Participants ..6
3.4. A Reserved or Ad Hoc Conference with
Conference-Aware Participants ..............................6
3.5. Advanced Conference Features ...............................6
4. Scenarios for Media Policy Control ..............................9
4.1. Video Mixing Scenarios ....................................10
4.2. Typical Video Conferencing Scenario .......................11
4.3. Conference Sidebar Scenario ...............................11
4.4. Coaching Scenario .........................................12
4.5. Presentation and Q & A Session ............................12
4.6. Presence-Enabled Ad Hoc Conference ........................13
4.7. Group Chat Text Conferencing ..............................13
4.8. Interactive Text ..........................................13
4.9. Moderated Group Chat ......................................14
4.10. Text Sidebars ............................................14
4.11. Conference Announcements .................................14
5. Security Considerations ........................................14
6. Acknowledgements ...............................................15
7. Informative References .........................................15
1. Introduction
This document describes multimedia conferencing scenarios. The
development of these scenarios is intended to help with the
definition and evaluation of the requirements for the centralized
conferencing (XCON) working group. Although this document uses some
definitions and conventions described in the SIP Conferencing
Framework document [1], these scenarios are not specific to SIP. The
document describes basic and advanced conferencing scenarios. The
advanced scenarios assume that the user agents support the set of
XCON protocols, identified in the Framework and Data Model for
Centralized Conferencing [3], in order to take advantage of the
conference functionality. However, note that many of these features
can be implemented today by using an interactive voice response (IVR)
or web interface to control the conferencing application.
The entities comprising the Conferencing System are the conference
that is the center point for signaling and the participants. The
participant who initiated the conference is called the initiating
participant.
The scenarios described here demonstrate different conferencing
services. These services can be offered in a multimedia environment
that benefits from having some support in the user agents that enable
more robust and easier-to-use conferencing services. It is up to the
conferencing system manufacturers and the conferencing service
provider to decide what services can be built and which services are
offered to the end users.
The scenarios describe multimedia examples, but they are applicable
to audio only as well as to audio and video conferences.
Multimedia conferences may include any combination of different media
types such as audio, video, text, interactive text, or presentation
graphics. The conference scenarios are similar, but the media
handling may be dependent on the media type.
2. Basic Conferencing Scenarios
These scenarios enable a conference-unaware participant to create,
join, and participate in a conference. The participant may use out-
of-band signaling to participate in a conference, but this is not
mandatory. The Conferencing System has all the functionality it
needs in order to supply the service offered to the participants.
Typical minimum requirements are that the participant support dual-
tone multi-frequency (DTMF) tones/signal or provide voice responses
to an IVR system.
2.1. Ad Hoc Conferences
A participant has a service provisioned to him that enables him to
start an ad hoc conference when he calls the Conferencing System.
When the participant wants to start a conference, he calls the
conference service. The participant may be identified by different
means, including request destination, authenticated identity, or an
IVR system using DTMF. The conference is created automatically with
the predefined functionality. The participant who has such a service
notifies the other participants how to call the conference via
external means such as instant message or email.
The participant may have Conferencing System functionality and thus
can create an ad hoc conference using his own user agent. An example
of such a conference is an audio conference initiated by a
participant who has a conference service that enables him to start a
conference when he calls a specific URI. The conference may be
created by the first person calling this URI, or it may be created
only after the owner is authenticated using an IVR system. In the
latter case, the other participants may get an announcement and are
placed on hold if they call the conference before the owner.
2.2. Extension of a Point-to-Point Call to a Multipoint Call
This is a basic case. The initiating participant (PA) is in a
point-to-point call with another participant (PB). PA wants to add a
third participant (PC) to the call. PA cannot provide the
Conferencing System functionality on his user agent nor can the other
participant PB. PA and PB do not support call transfer. PA has a
conferencing service that uses the methods described in 2.1. PA
conveys the conference information to PB in the point-to-point call.
Both participants disconnect and call the Conferencing System. The
Conferencing System may support dial-out (for example, via DTMF),
allowing the initiating participant PA to call the third party PC
through the Conferencing System.
2.3. Reserved Conferences
The reservation for this type of conference is typically done by an
out-of-band mechanism in advance of the actual conference time. The
conference identification, which may be a URI or a phone number with
a pin number, is allocated by the reservation system. It is sent to
all participants through email, IM, etc. The participants join by
using the conference identification. The conference identification
must be routable, enabling the allocation of a conference with free
resources at the time when the conference actually runs. The
Conferencing System can also dial out to the conference participants.
The participants may not be informed that they are in a conference,
since their User Agent is not conference aware. The participants may
know, via announcement from the Conferencing System, that they are in
a conference and who the other participants are.
3. Advanced Conferencing Scenarios
These scenarios assume user agents that support at least call
transfer service and a way to communicate information on events from
the Conferencing System to the user agent. The Conferencing System
may have the ability to discover the capabilities of the
participants, for example, whether they support call transfer. This
section specifies the dependencies in each scenario. An advanced
conference can be initiated only by a user agent that has advanced
features, but some user agents in the conference may have less
functionality.
3.1. Extending a Point-to-Point Call to a Multipoint Call
The initiating participant PA is in a point-to-point call and wants
to add a third participant. PA can start a multipoint call on a
conferencing bridge known to him. The extension can be without
consultation, which means that PA moves the point-to-point call to
the Conferencing System and then adds the third party (this can be
done in various ways). Alternatively the extension can be done with
consultation, which means that PA puts his current party on hold,
calls the third party, asks him to join the conference, and then
transfers all the participants to the Conferencing System.
3.2. Lecture Mode Conferences
This conference scenario enables a conference with a lecturer who
presents a topic and can allow questions. The lecturer needs to know
who the participants are and needs to be able to give them the right
to speak. The right to speak can be based on floor control or an
out-of-band mechanism.
In general, the lecturer is seen/heard by the conference participants
and often shares a presentation or application with the other
participants.
A participant joining this type of conference can get the identity of
the lecturer and often the identities of the audience participants.
This type of conference may have multiple media streams. For
example, if simultaneous language translation is available, a
participant has the option of selecting the appropriate language
audio stream. Multiple video streams could include the speaker’s
face and a whiteboard/demonstration stream.
3.3. Conference with Conference-Aware and Unaware Participants
A conference can include a mix of participants that are conference-
aware and unaware. Conference-unaware participants may be using a
proxy function that proxies the advanced functionality between the
different protocols and the Conferencing System. For example, an IVR
system or a web page interface can be used to provide additional
functionality.
3.4. A Reserved or Ad Hoc Conference with Conference-Aware Participants
In order to start the conference, the initiating participant calls
the Conferencing System using, for example, a unique identifier. The
Conferencing System may use some authenticating method to qualify the
participant. The other participants may call the Conferencing System
and join the conference. The Conferencing System is able to find the
capabilities of the participants. In case of a reserved conference,
the Conferencing System starts the conference at the scheduled time.
The participants may join by calling the conference URI, or the
Conferencing System may call them. The conference may have privilege
levels associated with a specific conference or participant. The
privileges are for the initiating participant and for a regular
participant; the initiating participant may delegate privileges to
the other participants. The privileges allow functionality as
defined in the next section.
3.5. Advanced Conference Features
The following features can be used in all the advanced conferencing
scenarios. In the examples given in this section, when referring to
a participant that has a functionality, it means a participant with
the right privileges. These scenarios may be available in the
advanced conferencing scenarios and are common in many conferencing
applications. This is not a requirement list, rather some examples
of how specific functions may be used in a conference.
o Add Participants - A participant may add a new participant to the
conference. This can be done, for example, by instructing the
Conferencing System to call the participant or by the first
participant calling the new participant and pointing him to the
conference.
o Delete Participant - A participant may delete participants from
the conference if he can identify them.
o Changing User Agent/Modes - During the course of a conference, a
participant may switch between user agents with different
capabilities while still remaining part of the conference. For
example, a participant may initially join using a mobile phone and
then switch to a desktop phone. Or a participant may join with a
phone, discover that the conference has video streams available,
and switch to a video phone.
o Changing Media - During the conference, a participant may be able
to select different media streams than the one he had when he
joined the conference. An example is a participant that initially
joined the conference as an audio participant. The participant is
unable to understand the conversation properly, and he learns that
there is also an interactive text available. He will ask to
receive the text stream also.
o Authenticate participants - A participant can authenticate other
participants who want to join the conference. This can be done,
for example, in a video conferencing session by creating a sidebar
between the two participants, allowing the authenticating
participant to talk with the new participant and verify his
identity.
o Authorize participants - A participant can authorize other
participants in order to allow them to join the conference. This
can be done implicitly by assigning a password to the conference
or to each participant and letting the Conferencing System decide
if the new participant is allowed to join. The authorization can
be done explicitly by directing the entered password to the
initiating participant who will authorize each participant. The
conferencing system may use an authentication mechanism to
authenticate the participants.
o Controlling the presentation of media - During the conference, the
participant may be able to manage whose media is being sent to
each participant. For example, the participant may be able to
decide that he wants to be the speaker and all the rest to be
listeners; he may also specify whose media he wants to receive.
The participant may be able to mute a media stream during the
conference.
o Giving privileges - During the conference, the participant may
want to give a privilege to another participant. The assigning of
privileges may be implicit when requested or explicit by asking
the participant to grant a privilege.
o Side conferences or sidebars - The participant may want to create
a side conference that include some of the main conference
participants. When the side conference is finished, the
participants return to the main conference. A sidebar may have
the same functionality as the main conference. There can be
several sidebar scenarios:
1. A basic sidebar requires that two participants have the
capability to have two calls at the same time, with a point-
to-point call in parallel to the main conference. It is user
agent implementation-specific whether both calls’ streams are
mixed automatically or the participants are allowed to
manually switch between them.
2. A conferencing-system-based sidebar uses the Conferencing
System to create the sidebar and compose the relevant sidebar
stream mixes. These mixes can include the main conference as
an incoming stream to the mix. Mechanisms to signal the
creation of the sidebar, invite participants, and control the
mixes should be available.
For example, participants in an audio sidebar may not be heard
by the rest of the conference. However, the main conference
audio may be mixed in the sidebar, but at a lower volume, or
in a different channel. As another example, a sidebar can
have a different media type from the main conference: a video
call can have an audio sidebar where the other participants
can see the sidebar participants talking but cannot hear them;
or an audio or video conference may have a text sidebar.
o Conference information - When a participant joins the conference,
he is announced to the participants. An announcement may be
available when he leaves the conference. The participants may
query the conferencing system for the current participants of a
specific conference. This conference information may include
other information, for example, the media streams available in the
conference.
o Extending of a conference - Reserved conferences and ad hoc
conferences may have a time limit. The Conferencing System
informs the participants when the limit is approaching and may
allow the extension of the conference.
o Adding and removing a media type to the conference - A participant
may want to start a data presentation during a conference. He may
want to distribute this new media to all the participants. The
participant asks the Conferencing System to start the new media
channel and to allow him to send data in the new channel.
o Audio-only participants - In a multimedia conference, some of the
participants who want to join may have no way to send and receive
all the media types. Typically, they can send and receive audio.
Such participants join the conference as audio-only participants.
The general case is that participants may send and receive only
part of the media streams available in the multimedia conference.
o Passive participants - In a conference, some participants may be
listeners to all or part of the media streams, but may be
invisible to all other participants.
o Recorders - A recorder can be added to the conference. A recorder
can record all streams or a subset of the streams. Recorders may
be turned on and off during the conference. Recorders may be used
for a "role call" scenario in order to record a participant’s
name. This name can be announced at a later stage automatically
or based on a participant request. A recorder is a case of a
passive participant.
o Whisper/Private Message - A participant can send a one-way message
(text, audio, or even some other media) to another participant
that is immediately rendered. This differs from a sidebar in that
it is immediate and creates no long-lived session.
o Human operator - A participant may ask for assistance from a human
operator during the conference.
4. Scenarios for Media Policy Control
During a conference, media streams may be controlled by authorized
participants using either a media control protocol or a third-party
application. This section describes some typical media control
scenarios. The conference can be of any size. Some of the media
control scenarios are typical of specific conference sizes. As a
general rule, larger conferences scenarios tend to be more centrally
managed or structured.
The mixing of media in a conference may start when the conference
starts or when the initiating participant joins. In the later case,
early participants may be put on hold and get "music on hold".
The scenarios apply to audio conferences as well as to multimedia
conferences. In the sections below, there is some specific
information about the mixed video layout and interactive text.
4.1. Video Mixing Scenarios
For video, the participant selects one of a set of predefined video
presentations offered by the server. Each video presentation is
identified by a textual description as well as an image specifying
how the presentation appears on the screen. In this scenario, by
choosing a video presentation, the participant chooses how many video
streams (participants) are viewed at once and the layout of these
video streams on the screen.
The contents of each sub-window can be defined by a conference policy
and/or controlled by authorized participants. It may also be
possible to have multiple mixes per conference, possibly as many as
there are participants. (Note that the same flexibility may be
afforded to audio mixes as well.)
The following is a list of typical video presentations. Other
layouts are available today in commercial products.
- Single view: This presentation typically shows the video of the
loudest speaker.
- Dual view: This presentation shows two streams. If the streams are
to be multiplexed in one image (typical of centralized servers),
the multiplexing can be:
1. Side-by-side windows, with no altered aspect ratio. Thus,
blanking of parts of the image might be necessary if the
streams are to be combined as one image.
2. Side-by-side windows, with altered aspect ratios. Thus,
blanking parts of the image is not necessary. The mixer
handles the cropping of the images.
3. One window above the other, with no altered aspect ratio.
4. One window above the other, with altered aspect ratios.
- Quadrate view: This presentation shows 4 streams. If the streams
are multiplexed into one image (centralized server), they are
arranged in a 2x2 style. Note that in this style the aspect ratios
are maintained.
- 9 sub-picture view: This presentation shows 9 streams. If the
streams are to be multiplexed in one image, they are arranged in a
3x3 style. In the multiplexing case, cropping is performed under
the discretion of the mixer.
- 16 sub-picture view: This presentation shows 16 streams. If the
streams are to be multiplexed into one image, they are arranged in
a 4x4 style. In this style, the aspect ratios are maintained, and
no cropping or blanking is needed.
- 5+1 sub-picture view: This presentation shows 6 streams. If the
streams are to be multiplexed into one image, then the pictures are
laid so that one sub-window occupies 4/9 of the screen while each
of the other five occupies 1/9 of the screen.
4.2. Typical Video Conferencing Scenario
This scenario is known as voice-activated video switch. Every
participant hears the N loudest participants but does not hear
himself. All the participants see the loudest speaker; the loudest
speaker may see the previous loudest speaker. This mode is typical
for a small conference.
A participant with proper authorization can exclude one or more
participants from the audio or video mix. An indication that they
are not being seen/heard might be displayed to the affected
participants.
A participant with proper authorization can manipulate the gain level
associated with one or more audio streams in the mix.
4.3. Conference Sidebar Scenario
An authorized participant creates a sidebar. The participant selects
whether the sidebar should include the media from the main conference
or not and the audio gain level associated with the main conference