1. RFC 4597
Network Working Group                                            R. Even
Request for Comments: 4597                                       Polycom
Category: Informational                                        N. Ismail
                                                     Cisco Systems, Inc.
                                                               July 2006

                         Conferencing Scenarios

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document describes multimedia conferencing scenarios.  It
   describes both basic and advanced conferencing scenarios involving
   voice, video, text, and interactive text sessions.  These scenarios
   will help with the definition and evaluation of the protocols being
   developed in the centralized conferencing XCON working group.

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Table of Contents

   1. Introduction ....................................................3
   2. Basic Conferencing Scenarios ....................................3
      2.1. Ad Hoc Conferences .........................................4
      2.2. Extension of a Point-to-Point Call to a Multipoint Call ....4
      2.3. Reserved Conferences .......................................4
   3. Advanced Conferencing Scenarios .................................5
      3.1. Extending a Point-to-Point Call to a Multipoint Call .......5
      3.2. Lecture Mode Conferences ...................................5
      3.3. Conference with Conference-Aware and Unaware Participants ..6
      3.4. A Reserved or Ad Hoc Conference with
           Conference-Aware Participants ..............................6
      3.5. Advanced Conference Features ...............................6
   4. Scenarios for Media Policy Control ..............................9
      4.1. Video Mixing Scenarios ....................................10
      4.2. Typical Video Conferencing Scenario .......................11
      4.3. Conference Sidebar Scenario ...............................11
      4.4. Coaching Scenario .........................................12
      4.5. Presentation and Q & A Session ............................12
      4.6. Presence-Enabled Ad Hoc Conference ........................13
      4.7. Group Chat Text Conferencing ..............................13
      4.8. Interactive Text ..........................................13
      4.9. Moderated Group Chat ......................................14
      4.10. Text Sidebars ............................................14
      4.11. Conference Announcements .................................14
   5. Security Considerations ........................................14
   6. Acknowledgements ...............................................15
   7. Informative References .........................................15

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1.  Introduction

   This document describes multimedia conferencing scenarios.  The
   development of these scenarios is intended to help with the
   definition and evaluation of the requirements for the centralized
   conferencing (XCON) working group.  Although this document uses some
   definitions and conventions described in the SIP Conferencing
   Framework document [1], these scenarios are not specific to SIP.  The
   document describes basic and advanced conferencing scenarios.  The
   advanced scenarios assume that the user agents support the set of
   XCON protocols, identified in the Framework and Data Model for
   Centralized Conferencing [3], in order to take advantage of the
   conference functionality.  However, note that many of these features
   can be implemented today by using an interactive voice response (IVR)
   or web interface to control the conferencing application.

   The entities comprising the Conferencing System are the conference
   that is the center point for signaling and the participants.  The
   participant who initiated the conference is called the initiating

   The scenarios described here demonstrate different conferencing
   services.  These services can be offered in a multimedia environment
   that benefits from having some support in the user agents that enable
   more robust and easier-to-use conferencing services.  It is up to the
   conferencing system manufacturers and the conferencing service
   provider to decide what services can be built and which services are
   offered to the end users.

   The scenarios describe multimedia examples, but they are applicable
   to audio only as well as to audio and video conferences.

   Multimedia conferences may include any combination of different media
   types such as audio, video, text, interactive text, or presentation
   graphics.  The conference scenarios are similar, but the media
   handling may be dependent on the media type.

2.  Basic Conferencing Scenarios

   These scenarios enable a conference-unaware participant to create,
   join, and participate in a conference.  The participant may use out-
   of-band signaling to participate in a conference, but this is not
   mandatory.  The Conferencing System has all the functionality it
   needs in order to supply the service offered to the participants.
   Typical minimum requirements are that the participant support dual-
   tone multi-frequency (DTMF) tones/signal or provide voice responses
   to an IVR system.

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2.1.  Ad Hoc Conferences

   A participant has a service provisioned to him that enables him to
   start an ad hoc conference when he calls the Conferencing System.
   When the participant wants to start a conference, he calls the
   conference service.  The participant may be identified by different
   means, including request destination, authenticated identity, or an
   IVR system using DTMF.  The conference is created automatically with
   the predefined functionality.  The participant who has such a service
   notifies the other participants how to call the conference via
   external means such as instant message or email.

   The participant may have Conferencing System functionality and thus
   can create an ad hoc conference using his own user agent.  An example
   of such a conference is an audio conference initiated by a
   participant who has a conference service that enables him to start a
   conference when he calls a specific URI.  The conference may be
   created by the first person calling this URI, or it may be created
   only after the owner is authenticated using an IVR system.  In the
   latter case, the other participants may get an announcement and are
   placed on hold if they call the conference before the owner.

2.2.  Extension of a Point-to-Point Call to a Multipoint Call

   This is a basic case.  The initiating participant (PA) is in a
   point-to-point call with another participant (PB).  PA wants to add a
   third participant (PC) to the call.  PA cannot provide the
   Conferencing System functionality on his user agent nor can the other
   participant PB.  PA and PB do not support call transfer.  PA has a
   conferencing service that uses the methods described in 2.1.  PA
   conveys the conference information to PB in the point-to-point call.
   Both participants disconnect and call the Conferencing System.  The
   Conferencing System may support dial-out (for example, via DTMF),
   allowing the initiating participant PA to call the third party PC
   through the Conferencing System.

2.3.  Reserved Conferences

   The reservation for this type of conference is typically done by an
   out-of-band mechanism in advance of the actual conference time.  The
   conference identification, which may be a URI or a phone number with
   a pin number, is allocated by the reservation system.  It is sent to
   all participants through email, IM, etc.  The participants join by
   using the conference identification.  The conference identification
   must be routable, enabling the allocation of a conference with free
   resources at the time when the conference actually runs.  The
   Conferencing System can also dial out to the conference participants.
   The participants may not be informed that they are in a conference,

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   since their User Agent is not conference aware.  The participants may
   know, via announcement from the Conferencing System, that they are in
   a conference and who the other participants are.

3.  Advanced Conferencing Scenarios

   These scenarios assume user agents that support at least call
   transfer service and a way to communicate information on events from
   the Conferencing System to the user agent.  The Conferencing System
   may have the ability to discover the capabilities of the
   participants, for example, whether they support call transfer.  This
   section specifies the dependencies in each scenario.  An advanced
   conference can be initiated only by a user agent that has advanced
   features, but some user agents in the conference may have less

3.1.  Extending a Point-to-Point Call to a Multipoint Call

   The initiating participant PA is in a point-to-point call and wants
   to add a third participant.  PA can start a multipoint call on a
   conferencing bridge known to him.  The extension can be without
   consultation, which means that PA moves the point-to-point call to
   the Conferencing System and then adds the third party (this can be
   done in various ways).  Alternatively the extension can be done with
   consultation, which means that PA puts his current party on hold,
   calls the third party, asks him to join the conference, and then
   transfers all the participants to the Conferencing System.

3.2.  Lecture Mode Conferences

   This conference scenario enables a conference with a lecturer who
   presents a topic and can allow questions.  The lecturer needs to know
   who the participants are and needs to be able to give them the right
   to speak.  The right to speak can be based on floor control or an
   out-of-band mechanism.

   In general, the lecturer is seen/heard by the conference participants
   and often shares a presentation or application with the other

   A participant joining this type of conference can get the identity of
   the lecturer and often the identities of the audience participants.

   This type of conference may have multiple media streams.  For
   example, if simultaneous language translation is available, a
   participant has the option of selecting the appropriate language
   audio stream.  Multiple video streams could include the speaker's
   face and a whiteboard/demonstration stream.

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3.3.  Conference with Conference-Aware and Unaware Participants

   A conference can include a mix of participants that are conference-
   aware and unaware.  Conference-unaware participants may be using a
   proxy function that proxies the advanced functionality between the
   different protocols and the Conferencing System.  For example, an IVR
   system or a web page interface can be used to provide additional

3.4.  A Reserved or Ad Hoc Conference with Conference-Aware Participants

   In order to start the conference, the initiating participant calls
   the Conferencing System using, for example, a unique identifier.  The
   Conferencing System may use some authenticating method to qualify the
   participant.  The other participants may call the Conferencing System
   and join the conference.  The Conferencing System is able to find the
   capabilities of the participants.  In case of a reserved conference,
   the Conferencing System starts the conference at the scheduled time.
   The participants may join by calling the conference URI, or the
   Conferencing System may call them.  The conference may have privilege
   levels associated with a specific conference or participant.  The
   privileges are for the initiating participant and for a regular
   participant; the initiating participant may delegate privileges to
   the other participants.  The privileges allow functionality as
   defined in the next section.

3.5.  Advanced Conference Features

   The following features can be used in all the advanced conferencing
   scenarios.  In the examples given in this section, when referring to
   a participant that has a functionality, it means a participant with
   the right privileges.  These scenarios may be available in the
   advanced conferencing scenarios and are common in many conferencing
   applications.  This is not a requirement list, rather some examples
   of how specific functions may be used in a conference.

   o  Add Participants - A participant may add a new participant to the
      conference.  This can be done, for example, by instructing the
      Conferencing System to call the participant or by the first
      participant calling the new participant and pointing him to the

   o  Delete Participant - A participant may delete participants from
      the conference if he can identify them.

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   o  Changing User Agent/Modes - During the course of a conference, a
      participant may switch between user agents with different
      capabilities while still remaining part of the conference.  For
      example, a participant may initially join using a mobile phone and
      then switch to a desktop phone.  Or a participant may join with a
      phone, discover that the conference has video streams available,
      and switch to a video phone.

   o  Changing Media - During the conference, a participant may be able
      to select different media streams than the one he had when he
      joined the conference.  An example is a participant that initially
      joined the conference as an audio participant.  The participant is
      unable to understand the conversation properly, and he learns that
      there is also an interactive text available.  He will ask to
      receive the text stream also.

   o  Authenticate participants - A participant can authenticate other
      participants who want to join the conference.  This can be done,
      for example, in a video conferencing session by creating a sidebar
      between the two participants, allowing the authenticating
      participant to talk with the new participant and verify his

   o  Authorize participants - A participant can authorize other
      participants in order to allow them to join the conference.  This
      can be done implicitly by assigning a password to the conference
      or to each participant and letting the Conferencing System decide
      if the new participant is allowed to join.  The authorization can
      be done explicitly by directing the entered password to the
      initiating participant who will authorize each participant.  The
      conferencing system may use an authentication mechanism to
      authenticate the participants.

   o  Controlling the presentation of media - During the conference, the
      participant may be able to manage whose media is being sent to
      each participant.  For example, the participant may be able to
      decide that he wants to be the speaker and all the rest to be
      listeners; he may also specify whose media he wants to receive.
      The participant may be able to mute a media stream during the

   o  Giving privileges - During the conference, the participant may
      want to give a privilege to another participant.  The assigning of
      privileges may be implicit when requested or explicit by asking
      the participant to grant a privilege.

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   o  Side conferences or sidebars - The participant may want to create
      a side conference that include some of the main conference
      participants.  When the side conference is finished, the
      participants return to the main conference.  A sidebar may have
      the same functionality as the main conference.  There can be
      several sidebar scenarios:

      1.  A basic sidebar requires that two participants have the
          capability to have two calls at the same time, with a point-
          to-point call in parallel to the main conference.  It is user
          agent implementation-specific whether both calls' streams are
          mixed automatically or the participants are allowed to
          manually switch between them.

      2.  A conferencing-system-based sidebar uses the Conferencing
          System to create the sidebar and compose the relevant sidebar
          stream mixes.  These mixes can include the main conference as
          an incoming stream to the mix.  Mechanisms to signal the
          creation of the sidebar, invite participants, and control the
          mixes should be available.

          For example, participants in an audio sidebar may not be heard
          by the rest of the conference.  However, the main conference
          audio may be mixed in the sidebar, but at a lower volume, or
          in a different channel.  As another example, a sidebar can
          have a different media type from the main conference: a video
          call can have an audio sidebar where the other participants
          can see the sidebar participants talking but cannot hear them;
          or an audio or video conference may have a text sidebar.

   o  Conference information - When a participant joins the conference,
      he is announced to the participants.  An announcement may be
      available when he leaves the conference.  The participants may
      query the conferencing system for the current participants of a
      specific conference.  This conference information may include
      other information, for example, the media streams available in the

   o  Extending of a conference - Reserved conferences and ad hoc
      conferences may have a time limit.  The Conferencing System
      informs the participants when the limit is approaching and may
      allow the extension of the conference.

   o  Adding and removing a media type to the conference - A participant
      may want to start a data presentation during a conference.  He may
      want to distribute this new media to all the participants.  The
      participant asks the Conferencing System to start the new media
      channel and to allow him to send data in the new channel.

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   o  Audio-only participants - In a multimedia conference, some of the
      participants who want to join may have no way to send and receive
      all the media types.  Typically, they can send and receive audio.
      Such participants join the conference as audio-only participants.
      The general case is that participants may send and receive only
      part of the media streams available in the multimedia conference.

   o  Passive participants - In a conference, some participants may be
      listeners to all or part of the media streams, but may be
      invisible to all other participants.

   o  Recorders - A recorder can be added to the conference.  A recorder
      can record all streams or a subset of the streams.  Recorders may
      be turned on and off during the conference.  Recorders may be used
      for a "role call" scenario in order to record a participant's
      name.  This name can be announced at a later stage automatically
      or based on a participant request.  A recorder is a case of a
      passive participant.

   o  Whisper/Private Message - A participant can send a one-way message
      (text, audio, or even some other media) to another participant
      that is immediately rendered.  This differs from a sidebar in that
      it is immediate and creates no long-lived session.

   o  Human operator - A participant may ask for assistance from a human
      operator during the conference.

4.  Scenarios for Media Policy Control

   During a conference, media streams may be controlled by authorized
   participants using either a media control protocol or a third-party
   application.  This section describes some typical media control
   scenarios.  The conference can be of any size.  Some of the media
   control scenarios are typical of specific conference sizes.  As a
   general rule, larger conferences scenarios tend to be more centrally
   managed or structured.

   The mixing of media in a conference may start when the conference
   starts or when the initiating participant joins.  In the later case,
   early participants may be put on hold and get "music on hold".

   The scenarios apply to audio conferences as well as to multimedia
   conferences.  In the sections below, there is some specific
   information about the mixed video layout and interactive text.

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4.1.  Video Mixing Scenarios

   For video, the participant selects one of a set of predefined video
   presentations offered by the server.  Each video presentation is
   identified by a textual description as well as an image specifying
   how the presentation appears on the screen.  In this scenario, by
   choosing a video presentation, the participant chooses how many video
   streams (participants) are viewed at once and the layout of these
   video streams on the screen.

   The contents of each sub-window can be defined by a conference policy
   and/or controlled by authorized participants.  It may also be
   possible to have multiple mixes per conference, possibly as many as
   there are participants.  (Note that the same flexibility may be
   afforded to audio mixes as well.)

   The following is a list of typical video presentations.  Other
   layouts are available today in commercial products.

   - Single view: This presentation typically shows the video of the
     loudest speaker.

   - Dual view: This presentation shows two streams.  If the streams are
     to be multiplexed in one image (typical of centralized servers),
     the multiplexing can be:

     1.  Side-by-side windows, with no altered aspect ratio.  Thus,
         blanking of parts of the image might be necessary if the
         streams are to be combined as one image.

     2.  Side-by-side windows, with altered aspect ratios.  Thus,
         blanking parts of the image is not necessary.  The mixer
         handles the cropping of the images.

     3.  One window above the other, with no altered aspect ratio.

     4.  One window above the other, with altered aspect ratios.

   - Quadrate view: This presentation shows 4 streams.  If the streams
     are multiplexed into one image (centralized server), they are
     arranged in a 2x2 style.  Note that in this style the aspect ratios
     are maintained.

   - 9 sub-picture view: This presentation shows 9 streams.  If the
     streams are to be multiplexed in one image, they are arranged in a
     3x3 style.  In the multiplexing case, cropping is performed under
     the discretion of the mixer.

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   - 16 sub-picture view: This presentation shows 16 streams.  If the
     streams are to be multiplexed into one image, they are arranged in
     a 4x4 style.  In this style, the aspect ratios are maintained, and
     no cropping or blanking is needed.

   - 5+1 sub-picture view: This presentation shows 6 streams.  If the
     streams are to be multiplexed into one image, then the pictures are
     laid so that one sub-window occupies 4/9 of the screen while each
     of the other five occupies 1/9 of the screen.

4.2.  Typical Video Conferencing Scenario

   This scenario is known as voice-activated video switch.  Every
   participant hears the N loudest participants but does not hear
   himself.  All the participants see the loudest speaker; the loudest
   speaker may see the previous loudest speaker.  This mode is typical
   for a small conference.

   A participant with proper authorization can exclude one or more
   participants from the audio or video mix.  An indication that they
   are not being seen/heard might be displayed to the affected

   A participant with proper authorization can manipulate the gain level
   associated with one or more audio streams in the mix.

4.3.  Conference Sidebar Scenario

   An authorized participant creates a sidebar.  The participant selects
   whether the sidebar should include the media from the main conference
   or not and the audio gain level associated with the main conference

   A participant 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 is just a participant of the sidebar, the participant
   only receives the sidebar media without the media of the main

   A participant with the right authorization can move another
   participant into the sidebar with no indication, in which case the
   participant suddenly starts receiving the sidebar media.

   Sidebar participants with the right authorization can select to hear
   or not to hear the main conference audio mixed with the sidebar

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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.

4.4.  Coaching Scenario

   This is a call center or a remote training session where there is a
   supervisor who can monitor the conference.  The supervised
   participants may be the call center operators or the teachers.  A
   participant in the conference may be a supervised participant or a

   The supervisor is a hidden participant and is not part of the
   participant roster.

   The supervised participants might get an announcement/tone indicating
   that the supervisor has joined.  The other participants do not hear
   the announcement.

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

   The supervisor can become a normal participant, in which case the
   participants see the supervisor as part of the roster and start
   hearing and seeing him.

4.5.  Presentation and Q & A Session

   An example is an earning call scenario in which a group of presenters
   delivers material to a group of people.  After the presentation is
   finished, a Q & A session is opened.

   The conference is created as a panel, and the panel participants are
   identified.  Only their streams are mixed.

   After the end of the presentation, the session chair changes the
   conference type to normal, and now streams from all participants may
   be mixed.  Alternatively, a floor control protocol can be used.  The
   chair can grant the right to speak by adding the participant, whose
   turn it 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; as a result, the media is 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.  "Nicknames"
   or aliases are often chosen by participants or assigned by the
   Conferencing System and used as handles within the room.

4.8.  Interactive Text

   Interactive text uses RTP to carry text one character at a time,
   providing real-time interactivity, as described in RFC 4103 [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.  These transcoders
   have similar functionality to transcoders between different audio or
   video algorithms.

   The conference participants should be able to select to receive text
   streams with the conference audio or those 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 all text messages sent to the group are 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 that 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 Conferencing System.

   Another use of a text sidebar is a text-only conversation/discussion
   between two or more conference participants who are following the
   main conference at the same time.

4.11.  Conference Announcements

   The conference moderator may be able to play announcements to all the
   conference participants.  An announcement may be prerecorded or
   composed by the moderator before it is sent.  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, 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 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 or
   common conference information, is used by the Conferencing System to
   admit or deny participation in a conference.  For the conference
   policy to be implemented, the Conferencing System needs to be able to
   authenticate potential participants.  The methods used depend on the
   signaling protocols used by the conference.  This can include a
   challenge/response mechanism, certificates, shared secret, asserted
   identity, etc.

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   Conferences often require that their content be confidential.  In
   addition, secure authorization of participants is incomplete if
   access to the media can be gained by unauthorized participants.
   Functions for securing the media and for key management and
   distribution to authorized participants need to be provided by the
   Conferencing System.  In some cases, the functions used for
   participant authorization can be leveraged for this purpose.

   Privacy is an important aspect of conferencing.  Users may wish to
   join a conference without anyone knowing that they have joined, in
   order to silently listen in.  In other applications, a participant
   may wish just to hide their identity from other participants, but
   otherwise let them know of their presence.  These functions need to
   be provided by the Conferencing System.

   These conference-specific security requirements are discussed further
   in the XCON framework document.

6.  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, Mary Barnes, and Dave Morgan for
   carefully reading the document.

7.  Informative References

   [1]  Rosenberg, J., "A Framework for Conferencing with the Session
        Initiation Protocol (SIP)", RFC 4353, February 2006.

   [2]  Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation",
        RFC 4103, June 2005.

   [3]  Barnes, M., "A Framework and Data Model for Centralized
        Conferencing", Work in Progress, June 2006.

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RFC 4597                  Conference Scenarios                 July 2006

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

Even & Ismail                Informational                     [Page 16]
RFC 4597                  Conference Scenarios                 July 2006

Full Copyright Statement

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  1. RFC 4597