XCON R. Even
Internet-Draft Polycom
Expires: November 30, 2004 N. Ismail
Cisco Systems, Inc.
June 2004
Conferencing Scenarios
draft-ietf-xcon-conference-scenarios-01.txt
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Abstract
This document describes multimedia conferencing scenarios. It
describes both basic and advance conferencing scenarios involving
voice, video, text and interactive text sessions. These conferencing
scenarios will help with the definition and evaluation of the
protocols being developed in the centralized conferencing XCON
working group.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Simple Conferencing scenarios . . . . . . . . . . . . . . . 3
2.1 Ad-hoc conference . . . . . . . . . . . . . . . . . . . . 4
2.2 Extension of a Point to point calls to a multipoint call . 4
2.3 Reserved conference . . . . . . . . . . . . . . . . . . . 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 simple and advanced participants . . . . . 5
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 . . . . . . . . . . . . . 8
4.1 Video mixing scenarios . . . . . . . . . . . . . . . . . . 9
4.2 Typical video conferencing scenario . . . . . . . . . . . 10
4.3 Conference Sidebar scenario . . . . . . . . . . . . . . . 10
4.4 Coaching scenario . . . . . . . . . . . . . . . . . . . . 11
4.5 Presentation and QA session . . . . . . . . . . . . . . . 11
4.6 Presence enabled ad-hoc conference . . . . . . . . . . . . 12
4.7 Group chat text conferencing . . . . . . . . . . . . . . . 12
4.8 Interactive text . . . . . . . . . . . . . . . . . . . . . 12
4.9 Moderated group chat . . . . . . . . . . . . . . . . . . . 13
4.10 Text sidebars . . . . . . . . . . . . . . . . . . . . . 13
4.11 Advanced media control features . . . . . . . . . . . . 13
5. Security Considerations . . . . . . . . . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . 14
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
8. Informative References . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . 15
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1. Introduction
This document describes multimedia conferencing scenarios. The
development of these conferencing scenarios is intended to help with
definition and evaluation of the requirements for the centralized
conferencing (XCON) working group. Although this document uses
definitions, conventions and architectures described in the SIP
Conferencing Framework document[1], these scenarios are not
SIP-specific. The document describes basic and advance conferencing
scenarios. The advanced scenarios will assume that the endpoint
functionality is based on the future set of XCON protocols that will
be needed in order to participate in the conference and take
advantage of the conference functionality. However, note that many
of these features can be implemented today using an IVR or web
interface to control the conferencing application.
The entities comprising the conference will be the "focus" that is
the center point for signaling and the participants. A special
participant is the participant who initiated the conference. The
scenarios described are to demonstrate different conferencing
services that can be offered in a multimedia environment that will
benefit from having some support in the endpoints that will enable
more robust and easier to use conferencing services. It will be up
to the conferencing bridge manufacturers and the service provider to
decide what services can be built and which services will be offered
to the end users.
The scenarios will describe multimedia examples but they are
applicable to audio only as well as for audio and video conferences.
Multimedia conferences may include any combination of different media
types like audio, video, text, interactive text, or presentations
graphics. The conference scenarios are similar but the media
handling may be dependent on the media type.
2. Simple Conferencing scenarios
These scenarios enable a basic endpoint without any specific
conferencing extensions to create, join and participate in a
conference. The endpoint may use out of band signaling to
participate in a conference but this is not a mandatory requirement.
The focus will have all the functionality it needs in order to supply
the service offered to the participants. A typical minimum
requirement is that the participant support DTMF tones/signal or
provide voice responses to an IVR system.
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2.1 Ad-hoc conference
A user has a service provisioned to him that enables him to start an
ad-hoc conference when he calls the focus. 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 the
functionality of a focus and thus can create ad-hoc conference using
his own endpoint functionality. An example of such a conference is
an audio conference initiated by one of the participants 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, 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 calls to a multipoint call
This is a simple case. The initiating participant is in a call with
one party and wants to add another party to the call. The initiating
participant cannot provide the focus functionality on his endpoint
nor can the other participant. If neither also support call
transfer, the only way to create this conference is by disconnecting
and using the methods described in 2.1. The information about the
conference will be conveyed in the point-to-point call. The focus
may support dial out allowing the initiating participant to call the
third party.
2.3 Reserved conference
The reservation for this type of conference is typically done by an
out of band mechanism and 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 using email, IM, etc. The participants join
using the conference identification. The conference identification
must be routable enabling the allocation of a focus with free
resources at the time when the conference will actually run. The
focus can also dial out to the conference participants. The
endpoints may not be aware that they are in a conference. The
participants may know via announcement from the conference that they
are in a conference and who are the other participants.
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3. Advanced Conferencing scenarios
These scenarios will assume endpoints that support at least call
transfer service and a way to communicate information on events from
the focus to the endpoint. The focus has the ability to discover the
capabilities of the participants, to identify if they support the
call transfer. This section will specify in each scenario the
dependencies. An advance conference can be initiated by a endpoint
that has advanced features but some endpoints in the conference may
have less functionality.
3.1 Extending a point-to-point call to a multipoint call
The initiating participant is in a point-to-point call and want to
add a third participant. The initiating participant can start a
multipoint call on a conferencing bridge known to him. The extension
can be without consultation, which means that he moves the
point-to-point call to the focus and then adds the third party (this
can be done in various ways). The extension can be done with
consultation, which means that he puts his current party on hold
calls, the third party and asks him to join the conference and then
transfers all the participants to the conferencing bridge.
3.2 Lecture mode conferences
This conference scenario enables a conference with a lecturer that
present a topic and can allow questions. The lecturer needs to know
who are the participants and to be able to give them the right to
speak. The right to speak can be based on floor control but can also
be based on an out of band mechanism.
In general, the lecturer will be seen/heard by the conference
participants and often will share 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 will have 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 simple and advanced participants
A focus can include participants that are a mix of simple and
advanced participants. Those participants may be basic participants
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or the GW function may proxy the advanced functionality between the
different protocols and the focus. 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.
The initiating participant will call the focus using for example a
unique identifier in order to start the conference. The focus may
use some authenticating method to qualify the participant. The other
participants may call the focus and join the conference. The focus
will be able to find the capabilities of the participants. In case
of a reserved conference the focus will start the conference at the
scheduled time. The participants may join by call the conference URI
or the focus may call them. The conference may have privilege levels
associated with a specific conference or participant. The privileges
will be for the initiating participant and for a regular participant;
the initiating participant may delegate privileges to the other
participants. The privileges will allow functionality as defined in
the next section.
3.5 Advanced conference features
The following scenarios can be used in all the advance 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 but some examples of
how specific functionality are being used in a conference.
Add Participants - A participant may add a new participant to the
focus. This can be done, for example, by instructing the focus to
call the participant or by the participant calling the new
participant and pointing him to the conference. The participant may
delete participants from the focus if he can identify them.
Changing Devices/Modes - During the course of a conference, a
participant may switch between devices 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 desk top phone. Or a participant may join with a phone,
discover that the conference has video streams available, and switch
to a video phone.
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 was not able to
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understand the conversation properly and he learned that there is
also an interactive text available, the participant asked to get also
the text stream. The text sidebar may be using RFC 2973 interactive
text.
Authenticate participants - A participant can authenticate other
participants that want to join the focus. This can be done
implicitly by assigning a password to the conference and letting the
focus authenticate the new participants or explicitly by directing
the authentication requests to the initiating participant who will
authenticate each user.
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 are listeners he may also
specify whose media he wants to receive. The participant may be able
to mute a media stream during the conference.
Giving privileges - the participant may want, during the conference,
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.
Side conferences or sidebars - the participant may want to create a
side conference that include some of the participants. When the side
conference is done the participants will return to the main
conference. A side bar may have the same functionality as the main
conference. There can be some sidebars scenarios. The simple one
will be based on capabilities of two participants to have two calls
at the same time and they will have a point to point call in parallel
to the main conference, it is an end point implementation to decide
if to mix both calls streams or to enable the user to switch between
them. The sidebar scenario that will use the focus will use the same
call he is in and let the focus create the sidebar and compose the
relevant sidebar stream mixes. These mixes can include the main
conference as an incoming stream to the mix. A way to signal the
creation of the sidebar and how to invite participants and control
the mixes should be available. For example, participants in an audio
sidebar can generally not be heard by the rest of the conference.
However, the main conference audio may be mixed in the sidebar, but
at a low volume, or in a different channel. 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 can not hear them. Or an audio or video
conference may have a text sidebar.
Focus information - When a participant joins the focus he is
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announced to the participants. An announcement may be available when
he leaves the focus. The participants may query the focus for its
current participants. This presence information can be used by
applications.
Extending of a conference - Reserved conferences and ad-hoc
conferences may have a time limit. The focus will inform the
participants when the limit is close and may allow the extension of
the conference.
Adding and removing a media type to the conference - a participant
may want to start a power point presentation during a conference. He
may want to distribute this new media to all the participants. The
participant will request from the focus to start the new media
channel and to allow him to send data in the new channel.
Audio only participants - In a multimedia conference some of the
users who want to join has no way to send and receive all the media
types. Typically they can send and receive audio. Such participants
will join the conference as audio only participants. The general
case is that users may send and receive only part of the media
streams available in the multi media conference.
Passive participants - In a conference some participants may be
listeners to all or part of the media streams. They may be invisible
to all the other participants.
Recorders - A recorder can be added to the conference. A recorder
can record all streams or a subset of the streams. A recorder is a
case of a passive participant.
Whisper/Private Message - A participant can send 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.
4. Scenarios for media policy control
During a conference media streams may be controlled by authorized
users using either a media control protocol or a third party
application. This section will describe some typical media control
scenarios. The conference can be of any size starting from small
conferences (3-5 participants) through medium size of up to 16
participants and large conferences. Some of the media control
scenarios are typical to specific conference size. As a general rule
larger conferences scenarios tend to be more centrally managed or
structured.
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The scenarios apply to audio conferences as well as to multimedia
conferences. There are some specific information about the mixed
video layout and about interactive text discussed bellow.
4.1 Video mixing scenarios
For video the user selects one of a set of pre-defined video
presentations offered by the server. Each video presentation is
identified by a textual description as well as an image specifying
how the presentation looks like on the screen. In this scenario by
choosing a video presentation the user chooses how many video streams
(participants) will be 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
or controlled by authorized participants. In other aspects like
number of different mixes in the conference and a custom mix for each
user, these functionality are similar to audio mixing and are based
on server capabilities and authorization.
Note that for non-centralized mixing if the endpoint mixer does not
support the media presentation of the conference, the participant can
get the default media presentation offered by the endpoint mixer.
The following are a list of typical video presentations; there are
other layouts 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 with no altered aspect ratio and hence 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 and hence
blanking parts of the image is not necessary. The mixer handles the
cropping of the images.
3. One above the other windows with no altered aspect ratio
4. One above the other windows with altered aspect ratio
- Quadrate view: This presentation shows 4 streams. If the streams
are to be multiplexed into one image (centralized server) they will
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be 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 will be 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 will be 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 four ninth of the screen while
the other five occupy a ninth of the screen each.
4.2 Typical video conferencing scenario
In this scenario the audio is typically an n-1 audio mixing. Every
participant will get a mixed audio of N loudest participants but his
own audio will not be part of the received mix. All the participants
will see the current speaker and he will see the previous speaker.
This mode is typical to small conference.
User with correct authorization can exclude one or more users from
the audio or video mix. An indication might be displayed to the
affected users indicating that they are not being seen/heard.
User with correct authorization can manipulate the gain level
associated with one or more audio streams in the mix.
4.3 Conference Sidebar scenario
An authorized user creates a side bar. The user selects whether the
sidebar should include the media from the main conference or not and
the audio gain level associated with the main conference audio.
A user invites participants to the sidebar and upon acceptance they
start receiving the sidebar media as specified by the sidebar
creator. If the new participant is not a participant of the
conference but rather just the sidebar the participant will only
receive the sidebar media without the media of the main conference
being mixed.
A user with the right authorization can move another participant into
the sidebar with no indication in which case the user will suddenly
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start receiving the sidebar media.
Sidebar participants with the right authorization can select to hear
or not hear the main conference audio mixed with the sidebar audio
A participant can be a participant to more than one sidebar but can
only actively participate in one.
A participant can jump back and forth between the main conference and
one or more sidebars to actively participate.
4.4 Coaching scenario
This is a call center or a remote training session where there is a
supervisor that can monitor. There are the supervised users that may
be the call center operators or the teachers
The supervisor will be a hidden participant and will not be part of
the participant roster.
The supervised users might get an announcement/tone indicating that
the supervisor has joined. The other participants do not hear the
announcement.
Supervisor listens/sees to the session but can only be heard/seen by
the supervised user.
Supervisor can become a normal participant in which case the
participants will see the supervisor as part of the roster and will
start hearing and seeing him.
4.5 Presentation and QA session
An example is a panel earning call scenario in which a group of
presenters deliver material to a group of people. After the
presentation is finished a QA session is opened.
The conference is created as a panel and the panel participants are
identified. Only their streams will be mixed.
After the end of the presentation the session chair changes the
conference type to normal and now streams from all users may be
mixed.
A floor control protocol can be used instead of changing the
conference type. The chair can grant the right to speak by adding
just the participant whose turn is to ask a question to the
conference mix.
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4.6 Presence enabled ad-hoc conference
A presence enabled ad-hoc conference, sometimes described as "walkie
talkie" service is a scenario in which a participant sends media to
the other participants of the conference after receiving a
confirmation of the other participants availability. For example, a
participant presses a talk button which checks the presence of the
participants to see if they are available for communication. If they
are, a confirmation tone is played and the participant can then talk,
which results in the media being sent to the other participants in
the conference. These types of conferences tend to be long lived,
hence the need for presence to ensure that the other participants are
still available. The ad-hoc nature of the conference means that the
participant list can be changed at any time. Floor control can be
used to allow other participants to speak, as the conference is
usually half-duplex in nature.
4.7 Group chat text conferencing
Group chat is a common scenario for text messaging in which a
participant joins (or enters) a chat room in which text messages from
participants are rendered in a single window and attributed to the
participant that sent the message. Changes in conference membership
are often announced in the text window itself (e.g. "Alice has just
entered the room. Bob has just departed.") Note that a real-time
transcription/closed captioning service can provide a similar window
in which audio media is converted into interactive text. "Nick
names" or aliases are often chosen by participants or assigned by the
focus and used as handles within the room.
4.8 Interactive text
Interactive text is using RTP to carry text one character at a time
providing real-time interactivity, as described in RFC2793. [2] The
interactive text session may be the main conference itself, or it may
be used in conjunction with other media types. Interactive text may
serve as text stream representing the audio in the conference using
some translation services. There can be more then one such stream
where each text stream is in a different language. These text
streams may be used as subtitles to the audio stream. The
translation from to text to speech and back is done by transcoders.
Those transcoder have similar functionality to transcoders between
different audio or video algorithms.
The conference participants should be able to select to receive those
text streams with the conference audio or without it.
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4.9 Moderated group chat
A moderated group chat scenario for text messaging is similar to
group chat but with all text messages sent to the group being
filtered/approved by a moderator. Note that the moderator can be a
human or an application. The moderator also often has the ability to
remove participants and provide feedback on their submissions (e.g.
provide warnings before removal).
4.10 Text sidebars
Interactive text or instant messaging sidebars are perhaps the most
common sidebars in conferences today. Often the text sessions are
separate from the conference. However, there are some advantages to
having text sessions be a sidebar and as a result a part of the main
conference. For example, a conference which is providing anonymity/
aliases to participants can also provide anonymous/alias sidebars. A
text sidebar can also benefit from other security/logging/recording
services provided by the focus.
Another use of a text sidebar is a text only conversation/discussion
between two or more conference participants while at the same time
following the main conference without being distracted by additional
audio.
4.11 Advanced media control features
The following features can be used in all the conferencing scenarios.
Announcement - The conference moderator may be able to play
announcements to all the conference participants. The announcement
may be pre-recorded or composed by the moderator before sending them.
The announcements may be text, audio or audio visual. An example is
a conference with several audio break out sessions going on. At some
point in the time, the moderator wants to record an audio message
like "in 5 minutes, everyone please come back to the main meeting"
and then play that message to all of the breakout sessions.
5. Security Considerations
Conferences generally have authorization rules about who may or may
not join a conference, what type of media may or may not be used,
etc. This information, sometimes called the conference policy, is
used by the focus to admit or deny participation in a conference.
For the conference policy to be implemented, the focus needs to be
able to authenticate potential participants. The methods used will
depend on the signaling protocols used by the focus. This can
include a challenge/response mechanism, certificates, shared secret,
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asserted identity, etc. These conference specific security
requirements are discussed further in the XCON requirements and
framework documents.
6. IANA Considerations
There are no IANA considerations associated with this specification.
7. Acknowledgements
Thanks to Brian Rosen for contributing conferencing scenarios.
Thanks to Alan Johnston for going over the document and adding some
more scenarios.
8 Informative References
[1] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol", draft-
ietf-sipping-conferencing-framework-01 (work in progress),
October 2003.
[2] Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793,
May 2000.
Authors' Addresses
Roni Even
Polycom
94 Derech Em Hamoshavot
Petach Tikva 49130
Israel
EMail: roni.even@polycom.co.il
Nermeen Ismail
Cisco Systems, Inc.
170 West Tasman Drive
San Jose 95134
CA USA
EMail: nismail@cisco.com
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