XCON BOF R. Even
Internet-Draft Polycom
Expires: December 21, 2003 N. Ismail
Cisco Systems, Inc.
June 22, 2003
Conferencing Scenarios
draft-even-xcon-conference-scenarios- 00.txt
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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.
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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. Advance Conferencing scenarios . . . . . . . . . . . . . . . . 4
3.1 Extending a point-to-point call to a multipoint call . . . . . 4
3.2 Lecture mode conferences . . . . . . . . . . . . . . . . . . . 5
3.3 Conference with non-SIP members . . . . . . . . . . . . . . . 5
3.4 A reserved or ad-hoc conference with conference aware
members. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5 Advanced conference features . . . . . . . . . . . . . . . . . 5
4. Scenarios for media policy control . . . . . . . . . . . . . . 7
4.1 Video mixing scenarios . . . . . . . . . . . . . . . . . . . . 7
4.2 Typical video conferencing scenario . . . . . . . . . . . . . 8
4.3 Conference Sidebar scenario . . . . . . . . . . . . . . . . . 9
4.4 Coaching scenario . . . . . . . . . . . . . . . . . . . . . . 9
4.5 Presentation and QA session . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . 12
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1. Introduction
This document describes SIP conferencing scenarios. It will describe
basic and advance conferencing scenarios. These conferencing
scenarios will help with the definition and the evaluation of the
requirements for SIP conferencing framework. The advanced scenarios
will assume the UA functionality based on relevant SIP RFCs that will
be needed in order to participate in the conference and take
advantage of the conference functionality. The entities composing
the conference will be the "focus" that is the center point for
signaling and the members. A special member is the member 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.
2. Simple Conferencing scenarios
These scenarios will assume a UA that support basic SIP functionality
as described in RFC3261[1] and RFC3264 [2] . 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
members. The UA shall be able to provide DTMF tones.
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 member wants to
start a conference he calls the conference service. The member may
be identified by different means including the called number, the
calling number or an IVR system using in-band DTMF tones. The
conference is created automatically with the predefined
functionality. The member who has such a service notifies the other
participants how to call the conference via an external mean like
email. The member 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
members who has a conference service that enables him to start a
conference when he calls a specific number (or URI). The conference
may be created by the first person calling this number 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
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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 member is in a call with one
party and wants to add another party to the call. The initiating
member cannot handle the focus on his UA nor can the other member.
Both of them cannot support call transfer. The way to do this
conference is by disconnecting and using the above method. The
information about the conference will be conveyed in the
point-to-point call. The focus may support dial out allowing the
initiating member to call the third party.
2.3 Reserved conference
The reservation was done by out of band mechanism. The conference
identification is allocated by the reservation system. It is sent to
all participants. 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 members. The UAs will 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
members
3. Advance Conferencing scenarios
These scenarios will assume UAs that support at least call transfer
service and a way to communicate information on events from the focus
to the UA. The focus will be able to know the capabilities of the
members to identify if they support the call transfer. The section
will specify in each scenario the 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 member is in a point-to-point call and want to add a
third member. The initiating member 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 members to the
conferencing bridge.
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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.
3.3 Conference with non-SIP members
A focus can include participants that are not SIP UAs that are
joining the focus via a gateway function. Those members may be basic
participants or the GW function will proxy the advanced functionality
between the different protocols and the SIP focus.
3.4 A reserved or ad-hoc conference with conference aware members.
The initiating member 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 member. The other participants
may call the focus and join the conference. The focus will be able
to find the capabilities of the members. In case of a reserved
conference the focus will start the conference at the scheduled time.
The members may join by call the conference ID or the focus may call
them. The conference may have privilege levels associated with a
specific conference or member. The privileges will be for the
initiating member and for a regular member; the initiating member may
delegate privileges to the other members. 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 member that has a functionality it means a member 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 member may add a new member to the focus. This
can be done, for example, by instructing the focus to call the
participant or by the member calling the participant and pointing him
to the conference. The member may delete participants from the focus
if he can identify them.
Authenticate participants - A member can authenticate members that
want to join the focus. This can be done implicitly by assigning a
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password to the conference and letting the focus authenticate the new
members or explicitly by directing the authentication requests to the
initiating member who will authenticate each user.
Controlling the presentation of media - during the conference the
member may be able to manage whose media is being sent to each
participant. For example the member 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 member may be able to
mute a media stream during the conference.
Giving privileges - the member may want, during the conference, to
give a privilege to another member. The assigning of privileges may
be implicit when requested or explicit by asking the member to grant
a privilege.
Side conferences or sidebars - the member may want to create a side
conference that include some of the participants and when the side
conference is done the members 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 members and control the mixes should be
available.
Focus information - When a member joins the focus he is announced to
the members. An announcement may be available when he leaves the
focus. The members may query the focus for its current members.
Extending of a conference - Reserved conferences and ad-hoc
conferences may have a time limit. The focus will inform the members
when the limit is close and may allow the extension of the
conference.
Adding and removing a media type to the conference - a member may
want to start a power point presentation during a conference. He may
want to distribute this new media to all the members. The member
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
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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
support the media presentation of the conference, the participant can
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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
participant will get a mixed audio of N loudest participants but his
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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 member 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
the supervisor has joined. The other participants do not hear the
announcement.
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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 members 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.
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
References
[1] 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.
[2] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
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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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