XCON R. Even
Internet-Draft Polycom
Expires: May 1, 2004 N. Ismail
Cisco Systems, Inc.
November 2003
Conferencing Scenarios
draft-ietf-xcon-conference-scenarios-00.txt
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Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This document describes SIP conferencing scenarios. It will describe
basic and advance conferencing scenarios. These conferencing
scenarios will help with definition and evaluation of the
requirements for SIP conferencing framework and the protocol
associated with the framework.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Simple Conferencing scenarios . . . . . . . . . . . . . . . 3
2.1 Ad-hoc conference . . . . . . . . . . . . . . . . . . . . . 3
2.2 Extension of a Point to point calls to a multipoint call . . 4
2.3 Reserved conference . . . . . . . . . . . . . . . . . . . . 4
3. Advanced Conferencing scenarios . . . . . . . . . . . . . . 4
3.1 Extending a point-to-point call to a multipoint call . . . . 5
3.2 Lecture mode conferences . . . . . . . . . . . . . . . . . . 5
3.3 Conference with non-SIP participants . . . . . . . . . . . . 5
3.4 A reserved or ad-hoc conference with conference aware
participants. . . . . . . . . . . . . . . . . . . . . . . . 5
3.5 Advanced conference features . . . . . . . . . . . . . . . . 6
4. Scenarios for media policy control . . . . . . . . . . . . . 8
4.1 Video mixing scenarios . . . . . . . . . . . . . . . . . . . 8
4.2 Typical video conferencing scenario . . . . . . . . . . . . 9
4.3 Conference Sidebar scenario . . . . . . . . . . . . . . . . 10
4.4 Coaching scenario . . . . . . . . . . . . . . . . . . . . . 10
4.5 Presentation and QA session . . . . . . . . . . . . . . . . 11
4.6 Presence enabled ad-hoc conference . . . . . . . . . . . . . 11
4.7 Group chat text conferencing . . . . . . . . . . . . . . . . 11
4.8 Moderated group chat . . . . . . . . . . . . . . . . . . . . 12
4.9 Text sidebars . . . . . . . . . . . . . . . . . . . . . . . 12
4.10 Advanced media control features . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
References . . . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . 14
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1. Introduction
This document describes SIP 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. This document uses definitions, conventions
and architectures described in the SIP Conferencing Framework
document[1]. 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 composing 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 the SIP environment that will benefit
from having some support in the UAs 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.
2. Simple Conferencing scenarios
These scenarios will assume a UA that support basic SIP functionality
as described in RFC3261[2] and RFC3264 [3] . The reason for these
scenarios is to enable a basic UA without any specific conferencing
extensions to create, join and participate in a conference. The UA
may use an 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..
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 the
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Request-URI or To header fields, the Contact or From header fields 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 UA 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 functioality on his UA 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 desribed 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 out
of band mechanism and in advance of the actual conference time. The
conference identification, which may 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
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 UA. 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
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dependencies. An advance conference can be initiated by a UA that
has advanced features but some UAs in the conference may have lesser
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 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
speakerÇÖs face and a whiteboard/demonstration stream.
3.3 Conference with non-SIP participants
A focus can include participants that are not SIP UAs that are
joining the focus via a gateway function. Those participants may be
basic participants or the GW function will proxy the advanced
functionality between the different protocols and the SIP 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.
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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. These are not a requirement list but some examples of
how specific functionality is 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 participant
and pointing him to the conference. The participant may delete
participants from the focus if he can identify them.
Changing Devices/Modes Çô 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 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.
Authenticate participants - A participant can authenticate
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
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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 and 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. The 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 be a
different media type from the main conference Çô 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
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.
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Audio only participants - In a multimedia conference some of the
users who wants to join has no way to send and receive all the media.
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.
4. Scenarios for media policy control
On going conferences 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.
The scenarios apply to audio conferences as well as to multimedia
conferences. There are some specific information about the mixed
video layout 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
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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
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
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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.
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.
User with the right authorization can move another participant into
the sidebar with no indication in which case the user will suddenly
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
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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.
4.6 Presence enabled ad-hoc conference
A presence enabled ad-hoc conference, sometimes described as Push To
Talk (PTT) 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, as implemented
in cell phones, 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.
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
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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 to text.
4.8 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).
4.9 Text sidebars
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.
4.10 Advanced media control features
The following features can be used in all the conferenceing
scenarios.
Announcement - The conference moderator may be able to play
announcments to all the conference participants. The announcement
may be pre-recorded or composed by the moderator before sending them.
The annoucments 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
No specific security considerations for this draft. Security
consideration will be available in the relevant drafts that will
compose the suggested solution
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6. Acknowledgements
Thanks to Brian Rosen for contributing conferencing scenarios.
Thanks to Alan Johnston for going over the document and adding some
more scenarios.
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] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
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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