RFC 4597

RFC 4597: Conferencing Scenarios 💖

okay bestie, this one is from July 2006 and it's an Informational RFC from the Network Working Group 🎀 It was written by R. Even at Polycom and N. Ismail at Cisco Systems, Inc. It doesn't obsolete or update any other RFCs, since the header doesn't list any. It's basically a collection of real-life conferencing setups so the XCON working group could figure out what their protocols needed to do 🧚

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).

Abstract

This doc is all about multimedia conferencing scenarios 🎬 It covers basic ones and advanced ones, and they involve voice, video, text, and interactive text sessions. The whole point is to help define and evaluate the protocols that the centralized conferencing XCON working group was building 🦋

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

1. Introduction ✨

So this document describes multimedia conferencing scenarios 🎀 The whole reason we're doing this is to help define and evaluate the requirements for the centralized conferencing (XCON) working group. It uses some definitions and conventions from the SIP Conferencing Framework document [1], but these scenarios are not specific to SIP, so don't get it twisted 🙈 It covers basic and advanced conferencing scenarios. The advanced ones assume the user agents support the set of XCON protocols from the Framework and Data Model for Centralized Conferencing [3], so they can actually use the conference features. BUT, and this is a big but, lots of these features can already be done today with an interactive voice response (IVR) or web interface controlling the conferencing app 💅

The entities in the Conferencing System are the conference, which is the center point for signaling, and the participants. The participant who started the conference is called the initiating participant 👑

The scenarios show off different conferencing services. These services can be offered in a multimedia environment where the user agents help out a bit, which makes conferencing more robust and easier to use 🌸 It's totally up to the conferencing system manufacturers and the conferencing service provider to decide what gets built and which services end users actually get 🫶

The scenarios are written with multimedia examples, but they also apply to audio-only conferences as well as audio and video ones 🦋

Multimedia conferences can mix any combination of media types, like audio, video, text, interactive text, or presentation graphics. The scenarios are pretty similar across the board, but how the media gets handled can depend on the media type 🍓

2. Basic Conferencing Scenarios 🎧

These scenarios let a conference-unaware participant create, join, and take part in a conference 💖 The participant may use out-of-band signaling to take part, but that isn't mandatory. The Conferencing System has everything it needs to supply the service to participants. The typical minimum is that the participant can support dual-tone multi-frequency (DTMF) tones or signal, or give voice responses to an IVR system 🔥

2.1. Ad Hoc Conferences 📞

Here's the deal: a participant has a service set up for them that lets them start an ad hoc conference whenever they call the Conferencing System ✨ When they want to start a conference, they just call the conference service. The participant can be identified in different ways: by the request destination, by their authenticated identity, or by an IVR system using DTMF. The conference gets created automatically with the predefined functionality. The participant who has this service tells everyone else how to call in, using external means like instant message or email 💌

The participant might also have Conferencing System functionality on their own user agent, so they can create an ad hoc conference right from their device 💅 For example, a participant with a service that starts a conference when they call a specific URI can run an audio conference. The conference might get created when the first person calls that URI, or only after the owner is authenticated through an IVR system. In the second case, the other participants may hear an announcement, and they get placed on hold if they call the conference before the owner shows up 😭

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

This is a basic case 🎀 The initiating participant (PA) is on a point-to-point call with another participant (PB). PA wants to add a third participant (PC) to the call. PA can't provide Conferencing System functionality on their user agent, and neither can PB. PA and PB don't support call transfer either. PA does have a conferencing service that uses the methods from 2.1. So PA tells PB the conference info during the point-to-point call. Both participants disconnect and call the Conferencing System 📱 The Conferencing System may support dial-out (for example, via DTMF), which lets PA call the third party PC through the Conferencing System 🧚

2.3. Reserved Conferences 📅

Reservations for this kind of conference are usually made out-of-band, in advance of the actual conference time 🌈 The conference identification, which can be a URI or a phone number with a PIN, is allocated by the reservation system. It gets sent to all participants through email, IM, and so on. Participants join by using that conference identification. The conference identification must be routable, so the system can allocate a conference with free resources at the time the conference actually runs ⭐ The Conferencing System can also dial out to the conference participants 💜 The participants may not be told they're in a conference, since their User Agent isn't conference aware 🙈 They might find out from an announcement by the Conferencing System that they're in a conference, and who the other participants are 🎁

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

Okay so, to get the conference started, 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 ✨. For a reserved conference, the Conferencing System starts the conference at the scheduled time ⏰. Participants may join by calling the conference URI, or the Conferencing System may call them 🦋. The conference may have privilege levels tied to a specific conference or participant 👑. The privileges are for the initiating participant and for a regular participant, and 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 in this section, when we talk about a participant that has a functionality, we mean 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, just some examples of how specific functions may be used in a conference 🧚.

• 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 them to the conference 📲.
• Delete Participant - A participant may delete participants from the conference if they can identify them 🙅‍♀️.
• Changing User Agent/Modes - During the course of a conference, a participant may switch between user agents with different capabilities while still staying 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 📱➡️🎥.
• Changing Media - During the conference, a participant may be able to select different media streams than the ones they had when they joined. An example is a participant who initially joined the conference as an audio participant. They can't understand the conversation properly, and they learn that there is also an interactive text available. They will ask to receive the text stream too 📝😭.
• 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, which lets the authenticating participant talk with the new participant and verify their identity 🔐.
• Authorize participants - A participant can authorize other participants so they're allowed 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 whether the new participant is allowed in 🔑. The authorization can also be done explicitly by directing the entered password to the initiating participant, who will authorize each participant one by one. The conferencing system may use an authentication mechanism to authenticate the participants 🛂.
• Controlling the presentation of media - During the conference, the participant may be able to manage whose media is sent to each participant. For example, they may be able to decide that they want to be the speaker and everyone else is a listener 🎤. They may also specify whose media they want to receive. The participant may be able to mute a media stream during the conference 🔇.
• Giving privileges - During the conference, the participant may want to give a privilege to another participant. Assigning 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 includes 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 running 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 switch between them manually 🔀.
  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 into the sidebar, but at a lower volume or on 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 can't hear them 👀; or an audio or video conference may have a text sidebar 💬.

• Conference information - When a participant joins the conference, they are announced to the participants. An announcement may also be made when they leave. 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 conference 📋.
• 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 conference to be extended ⌛.
• Adding and removing a media type to the conference - A participant may want to start a data presentation during a conference. They 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 let them send data in it 📊.
• 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 some of the media streams available in the multimedia conference.
• 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 👻.
• Recorders - A recorder can be added to the conference. A recorder can record all streams or a subset of them. Recorders may be turned on and off during the conference. Recorders may be used for a "role call" scenario to record a participant's name. That name can be announced at a later stage automatically or based on a participant's request 📼. 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 rendered immediately. This differs from a sidebar in that it is immediate and creates no long-lived session 🤍.
• Human operator - A participant may ask for assistance from a human operator during the conference 🙋‍♀️.

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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, and some of the media control scenarios are typical of specific conference sizes. As a general rule, larger conference 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 latter 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 📺💬.

4.1. Video Mixing Scenarios ✨

Okay so for video, the participant picks one of a set of predefined video presentations that the server offers 🎀 Each presentation comes with a textual description and an image showing how it looks on the screen 🖼️ By choosing a presentation, the participant decides how many video streams (participants) they see at once, and how those streams are laid out on the screen 💅

The contents of each sub-window can be set by a conference policy, controlled by authorized participants, or both 🌸 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 given to audio mixes too, fr.)

Here's a list of typical video presentations 📋 Other layouts are out there in commercial products rn.

• 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.
• 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 one is called voice-activated video switch 🎙️ Every participant hears the N loudest participants but does not hear themselves. Everyone sees the loudest speaker, and 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 participants 🙈

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 🧁 They pick whether the sidebar should include the media from the main conference or not, plus the audio gain level for the main conference audio.

A participant invites others to the sidebar, and once they accept, they start receiving the sidebar media as the sidebar creator specified. If the new participant isn't in the conference and is only in the sidebar, they only receive the sidebar media, without the main conference media 💌

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

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

A participant can be in more than one sidebar but can only actively participate in one 🦋 They can also 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's 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 "customer" 💁

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 them 🌟

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 presentation ends, 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 🙌

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're 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, which is why presence is needed to make sure the other participants are still available 🕰️ The ad hoc nature of the conference means the participant list can be changed at any time 🔄 Floor control can be used to let other participants speak, since the conference is usually half-duplex in nature 🎙️

4.7. Group Chat Text Conferencing 💬

Group chat is a super common text messaging scenario 💖 A participant joins (or enters) a chat room where text messages from participants are rendered in a single window and attributed to whoever sent them. Changes in conference membership are often announced right in the text window (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, which gives real-time interactivity, as described in RFC 4103 [2] ⚡ The interactive text session may be the main conference itself, or it may be used alongside 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 for 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 🤓

Conference participants should be able to pick whether they receive text streams with the conference audio or without it 💅

4.9. Moderated Group Chat 🛡️

A moderated group chat is similar to group chat, but all text messages sent to the group are filtered/approved by a moderator. The moderator can be a human or an application 🤖 The moderator also often has the ability to remove participants and give feedback on their submissions (e.g., 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 perks to having text sessions be a sidebar, and therefore part of the main conference ✨ For example, a conference that provides 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's sent. Announcements may be text, audio, or audio-visual 🎞️ For example, picture 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 🔐✨

Okay bestie, security time, and it's SERIOUS 😭 Conferences usually have authorization rules about who can or can't join, what kinds of media can or can't be used, and so on. That info, which people sometimes call the conference policy or common conference information, is what the Conferencing System uses to let people in or keep them out 🚪. For the policy to actually work, the Conferencing System needs to be able to authenticate potential participants. The method depends on the signaling protocols the conference uses. It can be a challenge/response mechanism, certificates, a shared secret, asserted identity, etc. 🔑

Conferences often need their content to stay confidential 🤫. Also, secure authorization of participants is incomplete if unauthorized people can still get to the media, so the Conferencing System needs to provide functions for securing the media and for key management and distribution to authorized participants. Sometimes the functions used for participant authorization can be reused for this too 🔁.

Privacy is a huge deal in conferencing 💜. Users might want to join a conference without anyone knowing they joined, like silently listening in 👂. In other apps, a participant might just want to hide their identity from everyone else while still letting them know they're there. The Conferencing System needs to provide these functions too.

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 even more scenarios 🌸. Also thanks to Keith Lantz, Mary Barnes, and Dave Morgan for reading the document super carefully 👑.

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.

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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