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Versions: 00 01 02 03 04 05 rfc4597                                     
XCON                                                             R. Even
Internet-Draft                                                   Polycom
Expires: September 26, 2005                                    N. Ismail
                                                     Cisco Systems, Inc.
                                                          March 28, 2005

                         Conferencing Scenarios

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of section 3 of RFC 3667.  By submitting this Internet-Draft, each
   author represents that any applicable patent or other IPR claims of
   which he or she is aware have been or will be disclosed, and any of
   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 26, 2005.

Copyright Notice

   Copyright (C) The Internet Society (2005).


   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 advanced 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 in order to demonstrate different
   conferencing services.  These conferencing services 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 presentation
   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.  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 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 supports 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 the other participants are.

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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 call
   transfer.  This section will specify in each scenario the
   dependencies.  An advanced conference can be initiated only by an
   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).  Alternatively 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 who
   presents a topic and can allow questions.  The lecturer needs to know
   who the participants are and 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 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 calling 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 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 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 first 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 receive
   also the text stream.  The text sidebar may be using RFC 2973
   interactive text.

   Authenticate participants - A participant can authenticate other
   participants who 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 sidebar 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.  This is an end point implementation
   specific, 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.
   For 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 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

   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 approaching and may allow the
   extension of the conference.

   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 will ask 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 may have 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, but 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 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.

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 sizes.  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.  Other aspects like number
   of different mixes in the conference and a custom mix for each
   participant, these functionalities are applicable also to audio
   mixing and are based on server capabilities and authorization.

   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

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   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 4/9 of the screen while the
   other five occupy 1/9 of the screen each.

4.2  Typical video conferencing scenario

   In this scenario the audio is typically an n-1 audio mix.  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 if
   it was part of the sidebar mix.

   A 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

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   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 who can monitor the conference.  There are the supervised
   users that may be the call center operators or the teachers.  A
   participant is the conference may be a supervised user or a

   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

   The supervisor listens/sees to the session but can only be heard/seen
   by the supervised user.

   The 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 an 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

   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
   be used to represent the audio in the conference using some
   translation services.  There can be more than 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 who at the same time are
   following the main conference.

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,
   asserted identity, etc.  These conference-specific security

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   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; to Keith Lantz for carefully reading the document.

8  Informative References

   [1]  Rosenberg, J., "A Framework for Conferencing with the Session
        Initiation Protocol",
        draft-ietf-sipping-conferencing-framework-04 (work in progress),
        October 2003.

   [2]  Hellstrom, G., "RTP Payload for Text Conversation", RFC 2793,
        May 2000.

Authors' Addresses

   Roni Even
   94 Derech Em Hamoshavot
   Petach Tikva  49130

   EMail: roni.even@polycom.co.il

   Nermeen Ismail
   Cisco Systems, Inc.
   170 West Tasman Drive
   San Jose  95134

   EMail: nismail@cisco.com

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Internet-Draft            Conference Scenarios                March 2005

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