<pre>Internet Engineering Task Force (IETF)                        A. Romanow
Request for Comments: 7205                                         Cisco
Category: Informational                                        S. Botzko
ISSN: 2070-1721                                             M. Duckworth
                                                                 Polycom
                                                            R. Even, Ed.
                                                     Huawei Technologies
                                                              April 2014


                <span class="h1">Use Cases for Telepresence Multistreams</span>

Abstract

   Telepresence conferencing systems seek to create an environment that
   gives users (or user groups) that are not co-located a feeling of co-
   located presence through multimedia communication that includes at
   least audio and video signals of high fidelity.  A number of
   techniques for handling audio and video streams are used to create
   this experience.  When these techniques are not similar,
   interoperability between different systems is difficult at best, and
   often not possible.  Conveying information about the relationships
   between multiple streams of media would enable senders and receivers
   to make choices to allow telepresence systems to interwork.  This
   memo describes the most typical and important use cases for sending
   multiple streams in a telepresence conference.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see <a href="./rfc5741#section-2">Section&nbsp;2 of RFC 5741</a>.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   <a href="http://www.rfc-editor.org/info/rfc7205">http://www.rfc-editor.org/info/rfc7205</a>.









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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   <a href="#section-1">1</a>.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-3">3</a>
   <a href="#section-2">2</a>.  Overview of Telepresence Scenarios  . . . . . . . . . . . . .   <a href="#page-4">4</a>
   <a href="#section-3">3</a>.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   <a href="#page-6">6</a>
     <a href="#section-3.1">3.1</a>.  Point-to-Point Meeting: Symmetric . . . . . . . . . . . .   <a href="#page-7">7</a>
     <a href="#section-3.2">3.2</a>.  Point-to-Point Meeting: Asymmetric  . . . . . . . . . . .   <a href="#page-7">7</a>
     <a href="#section-3.3">3.3</a>.  Multipoint Meeting  . . . . . . . . . . . . . . . . . . .   <a href="#page-9">9</a>
     <a href="#section-3.4">3.4</a>.  Presentation  . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-10">10</a>
     <a href="#section-3.5">3.5</a>.  Heterogeneous Systems . . . . . . . . . . . . . . . . . .  <a href="#page-11">11</a>
     <a href="#section-3.6">3.6</a>.  Multipoint Education Usage  . . . . . . . . . . . . . . .  <a href="#page-12">12</a>
     <a href="#section-3.7">3.7</a>.  Multipoint Multiview (Virtual Space)  . . . . . . . . . .  <a href="#page-14">14</a>
     <a href="#section-3.8">3.8</a>.  Multiple Presentation Streams - Telemedicine  . . . . . .  <a href="#page-15">15</a>
   <a href="#section-4">4</a>.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-16">16</a>
   <a href="#section-5">5</a>.  Security Considerations . . . . . . . . . . . . . . . . . . .  <a href="#page-16">16</a>
   <a href="#section-6">6</a>.  Informative References  . . . . . . . . . . . . . . . . . . .  <a href="#page-16">16</a>




















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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   Telepresence applications try to provide a "being there" experience
   for conversational video conferencing.  Often, this telepresence
   application is described as "immersive telepresence" in order to
   distinguish it from traditional video conferencing and from other
   forms of remote presence not related to conversational video
   conferencing, such as avatars and robots.  The salient
   characteristics of telepresence are often described as: being actual
   sized, providing immersive video, preserving interpersonal
   interaction, and allowing non-verbal communication.

   Although telepresence systems are based on open standards such as RTP
   [<a href="./rfc3550" title="&quot;RTP: A Transport Protocol for Real-Time Applications&quot;">RFC3550</a>], SIP [<a href="./rfc3261" title="&quot;SIP: Session Initiation Protocol&quot;">RFC3261</a>], H.264 [<a href="#ref-ITU.H264" title="&quot;Advanced video coding for generic audiovisual services&quot;">ITU.H264</a>], and the H.323 [<a href="#ref-ITU.H323" title="&quot;Packet-based Multimedia Communications Systems&quot;">ITU.H323</a>]
   suite of protocols, they cannot easily interoperate with each other
   without operator assistance and expensive additional equipment that
   translates from one vendor's protocol to another.

   The basic features that give telepresence its distinctive
   characteristics are implemented in disparate ways in different
   systems.  Currently, telepresence systems from diverse vendors
   interoperate to some extent, but this is not supported in a
   standards-based fashion.  Interworking requires that translation and
   transcoding devices be included in the architecture.  Such devices
   increase latency, reducing the quality of interpersonal interaction.
   Use of these devices is often not automatic; it frequently requires
   substantial manual configuration and a detailed understanding of the
   nature of underlying audio and video streams.  This state of affairs
   is not acceptable for the continued growth of telepresence -- these
   systems should have the same ease of interoperability as do
   telephones.  Thus, a standard way of describing the multiple streams
   constituting the media flows and the fundamental aspects of their
   behavior would allow telepresence systems to interwork.

   This document presents a set of use cases describing typical
   scenarios.  Requirements will be derived from these use cases in a
   separate document.  The use cases are described from the viewpoint of
   the users.  They are illustrative of the user experience that needs
   to be supported.  It is possible to implement these use cases in a
   variety of different ways.

   Many different scenarios need to be supported.  This document
   describes in detail the most common and basic use cases.  These will
   cover most of the requirements.  There may be additional scenarios
   that bring new features and requirements that can be used to extend
   the initial work.





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   Point-to-point and multipoint telepresence conferences are
   considered.  In some use cases, the number of screens is the same at
   all sites; in others, the number of screens differs at different
   sites.  Both use cases are considered.  Also included is a use case
   describing display of presentation material or content.

   The multipoint use cases may include a variety of systems from
   conference room systems to handheld devices, and such a use case is
   described in the document.

   This document's structure is as follows: <a href="#section-2">Section 2</a> gives an overview
   of scenarios, and <a href="#section-3">Section 3</a> describes use cases.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Overview of Telepresence Scenarios</span>

   This section describes the general characteristics of the use cases
   and what the scenarios are intended to show.  The typical setting is
   a business conference, which was the initial focus of telepresence.
   Recently, consumer products are also being developed.  We
   specifically do not include in our scenarios the physical
   infrastructure aspects of telepresence, such as room construction,
   layout, and decoration.  Furthermore, these use cases do not describe
   all the aspects needed to create the best user experience (for
   example, the human factors).

   We also specifically do not attempt to precisely define the
   boundaries between telepresence systems and other systems, nor do we
   attempt to identify the "best" solution for each presented scenario.

   Telepresence systems are typically composed of one or more video
   cameras and encoders and one or more display screens of large size
   (diagonal around 60 inches).  Microphones pick up sound, and audio
   codec(s) produce one or more audio streams.  The cameras used to
   capture the telepresence users are referred to as "participant
   cameras" (and likewise for screens).  There may also be other
   cameras, such as for document display.  These will be referred to as
   "presentation cameras" or "content cameras", which generally have
   different formats, aspect ratios, and frame rates from the
   participant cameras.  The presentation streams may be shown on
   participant screens or on auxiliary display screens.  A user's
   computer may also serve as a virtual content camera, generating an
   animation or playing a video for display to the remote participants.

   We describe such a telepresence system as sending one or more video
   streams, audio streams, and presentation streams to the remote
   system(s).





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   The fundamental parameters describing today's typical telepresence
   scenarios include:

   1.   The number of participating sites

   2.   The number of visible seats at a site

   3.   The number of cameras

   4.   The number and type of microphones

   5.   The number of audio channels

   6.   The screen size

   7.   The screen capabilities -- such as resolution, frame rate,
        aspect ratio

   8.   The arrangement of the screens in relation to each other

   9.   The number of primary screens at each site

   10.  Type and number of presentation screens

   11.  Multipoint conference display strategies -- for example, the
        camera-to-screen mappings may be static or dynamic

   12.  The camera point of capture

   13.  The cameras fields of view and how they spatially relate to each
        other

   As discussed in the introduction, the basic features that give
   telepresence its distinctive characteristics are implemented in
   disparate ways in different systems.

   There is no agreed upon way to adequately describe the semantics of
   how streams of various media types relate to each other.  Without a
   standard for stream semantics to describe the particular roles and
   activities of each stream in the conference, interoperability is
   cumbersome at best.

   In a multiple-screen conference, the video and audio streams sent
   from remote participants must be understood by receivers so that they
   can be presented in a coherent and life-like manner.  This includes
   the ability to present remote participants at their actual size for
   their apparent distance, while maintaining correct eye contact,




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   gesticular cues, and simultaneously providing a spatial audio sound
   stage that is consistent with the displayed video.

   The receiving device that decides how to render incoming information
   needs to understand a number of variables such as the spatial
   position of the speaker, the field of view of the cameras, the camera
   zoom, which media stream is related to each of the screens, etc.  It
   is not simply that individual streams must be adequately described,
   to a large extent this already exists, but rather that the semantics
   of the relationships between the streams must be communicated.  Note
   that all of this is still required even if the basic aspects of the
   streams, such as the bit rate, frame rate, and aspect ratio, are
   known.  Thus, this problem has aspects considerably beyond those
   encountered in interoperation of video conferencing systems that have
   a single camera/screen.

<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Use Cases</span>

   The use cases focus on typical implementations.  There are a number
   of possible variants for these use cases; for example, the audio
   supported may differ at the end points (such as mono or stereo versus
   surround sound), etc.

   Many of these systems offer a "full conference room" solution, where
   local participants sit at one side of a table and remote participants
   are displayed as if they are sitting on the other side of the table.
   The cameras and screens are typically arranged to provide a panoramic
   view of the remote room (left to right from the local user's
   viewpoint).

   The sense of immersion and non-verbal communication is fostered by a
   number of technical features, such as:

   1.  Good eye contact, which is achieved by careful placement of
       participants, cameras, and screens.

   2.  Camera field of view and screen sizes are matched so that the
       images of the remote room appear to be full size.

   3.  The left side of each room is presented on the right screen at
       the far end; similarly, the right side of the room is presented
       on the left screen.  The effect of this is that participants of
       each site appear to be sitting across the table from each other.
       If 2 participants on the same site glance at each other, all
       participants can observe it.  Likewise, if a participant at one
       site gestures to a participant on the other site, all
       participants observe the gesture itself and the participants it
       includes.



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<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>.  Point-to-Point Meeting: Symmetric</span>

   In this case, each of the 2 sites has an identical number of screens,
   with cameras having fixed fields of view, and 1 camera for each
   screen.  The sound type is the same at each end.  As an example,
   there could be 3 cameras and 3 screens in each room, with stereo
   sound being sent and received at each end.

   Each screen is paired with a corresponding camera.  Each camera/
   screen pair is typically connected to a separate codec, producing an
   encoded stream of video for transmission to the remote site, and
   receiving a similarly encoded stream from the remote site.

   Each system has one or multiple microphones for capturing audio.  In
   some cases, stereophonic microphones are employed.  In other systems,
   a microphone may be placed in front of each participant (or pair of
   participants).  In typical systems, all the microphones are connected
   to a single codec that sends and receives the audio streams as either
   stereo or surround sound.  The number of microphones and the number
   of audio channels are often not the same as the number of cameras.
   Also, the number of microphones is often not the same as the number
   of loudspeakers.

   The audio may be transmitted as multi-channel (stereo/surround sound)
   or as distinct and separate monophonic streams.  Audio levels should
   be matched, so the sound levels at both sites are identical.
   Loudspeaker and microphone placements are chosen so that the sound
   "stage" (orientation of apparent audio sources) is coordinated with
   the video.  That is, if a participant at one site speaks, the
   participants at the remote site perceive her voice as originating
   from her visual image.  In order to accomplish this, the audio needs
   to be mapped at the received site in the same fashion as the video.
   That is, audio received from the right side of the room needs to be
   output from loudspeaker(s) on the left side at the remote site, and
   vice versa.

<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>.  Point-to-Point Meeting: Asymmetric</span>

   In this case, each site has a different number of screens and cameras
   than the other site.  The important characteristic of this scenario
   is that the number of screens is different between the 2 sites.  This
   creates challenges that are handled differently by different
   telepresence systems.

   This use case builds on the basic scenario of 3 screens to 3 screens.
   Here, we use the common case of 3 screens and 3 cameras at one site,
   and 1 screen and 1 camera at the other site, connected by a point-to-
   point call.  The screen sizes and camera fields of view at both sites



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   are basically similar, such that each camera view is designed to show
   2 people sitting side by side.  Thus, the 1-screen room has up to 2
   people seated at the table, while the 3-screen room may have up to 6
   people at the table.

   The basic considerations of defining left and right and indicating
   relative placement of the multiple audio and video streams are the
   same as in the 3-3 use case.  However, handling the mismatch between
   the 2 sites of the number of screens and cameras requires more
   complicated maneuvers.

   For the video sent from the 1-camera room to the 3-screen room,
   usually what is done is to simply use 1 of the 3 screens and keep the
   second and third screens inactive or, for example, put up the current
   date.  This would maintain the "full-size" image of the remote side.

   For the other direction, the 3-camera room sending video to the
   1-screen room, there are more complicated variations to consider.
   Here are several possible ways in which the video streams can be
   handled.

   1.  The 1-screen system might simply show only 1 of the 3 camera
       images, since the receiving side has only 1 screen.  2 people are
       seen at full size, but 4 people are not seen at all.  The choice
       of which one of the 3 streams to display could be fixed, or could
       be selected by the users.  It could also be made automatically
       based on who is speaking in the 3-screen room, such that the
       people in the 1-screen room always see the person who is
       speaking.  If the automatic selection is done at the sender, the
       transmission of streams that are not displayed could be
       suppressed, which would avoid wasting bandwidth.

   2.  The 1-screen system might be capable of receiving and decoding
       all 3 streams from all 3 cameras.  The 1-screen system could then
       compose the 3 streams into 1 local image for display on the
       single screen.  All 6 people would be seen, but smaller than full
       size.  This could be done in conjunction with reducing the image
       resolution of the streams, such that encode/decode resources and
       bandwidth are not wasted on streams that will be downsized for
       display anyway.

   3.  The 3-screen system might be capable of including all 6 people in
       a single stream to send to the 1-screen system.  For example, it
       could use PTZ (Pan Tilt Zoom) cameras to physically adjust the
       cameras such that 1 camera captures the whole room of 6 people.
       Or, it could recompose the 3 camera images into 1 encoded stream
       to send to the remote site.  These variations also show all 6
       people but at a reduced size.



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   4.  Or, there could be a combination of these approaches, such as
       simultaneously showing the speaker in full size with a composite
       of all 6 participants in a smaller size.

   The receiving telepresence system needs to have information about the
   content of the streams it receives to make any of these decisions.
   If the systems are capable of supporting more than one strategy,
   there needs to be some negotiation between the 2 sites to figure out
   which of the possible variations they will use in a specific point-
   to-point call.

<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>.  Multipoint Meeting</span>

   In a multipoint telepresence conference, there are more than 2 sites
   participating.  Additional complexity is required to enable media
   streams from each participant to show up on the screens of the other
   participants.

   Clearly, there are a great number of topologies that can be used to
   display the streams from multiple sites participating in a
   conference.

   One major objective for telepresence is to be able to preserve the
   "being there" user experience.  However, in multi-site conferences,
   it is often (in fact, usually) not possible to simultaneously provide
   full-size video, eye contact, and common perception of gestures and
   gaze by all participants.  Several policies can be used for stream
   distribution and display: all provide good results, but they all make
   different compromises.

   One common policy is called site switching.  Let's say the speaker is
   at site A and the other participants are at various "remote" sites.
   When the room at site A shown, all the camera images from site A are
   forwarded to the remote sites.  Therefore, at each receiving remote
   site, all the screens display camera images from site A.  This can be
   used to preserve full-size image display, and also provide full
   visual context of the displayed far end, site A.  In site switching,
   there is a fixed relation between the cameras in each room and the
   screens in remote rooms.  The room or participants being shown are
   switched from time to time based on who is speaking or by manual
   control, e.g., from site A to site B.

   Segment switching is another policy choice.  In segment switching
   (assuming still that site A is where the speaker is, and "remote"
   refers to all the other sites), rather than sending all the images
   from site A, only the speaker at site A is shown.  The camera images
   of the current speaker and previous speakers (if any) are forwarded
   to the other sites in the conference.  Therefore, the screens in each



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   site are usually displaying images from different remote sites -- the
   current speaker at site A and the previous ones.  This strategy can
   be used to preserve full-size image display and also capture the non-
   verbal communication between the speakers.  In segment switching, the
   display depends on the activity in the remote rooms (generally, but
   not necessarily based on audio/speech detection).

   A third possibility is to reduce the image size so that multiple
   camera views can be composited onto one or more screens.  This does
   not preserve full-size image display, but it provides the most visual
   context (since more sites or segments can be seen).  Typically in
   this case, the display mapping is static, i.e., each part of each
   room is shown in the same location on the display screens throughout
   the conference.

   Other policies and combinations are also possible.  For example,
   there can be a static display of all screens from all remote rooms,
   with part or all of one screen being used to show the current speaker
   at full size.

<span class="h3"><a class="selflink" id="section-3.4" href="#section-3.4">3.4</a>.  Presentation</span>

   In addition to the video and audio streams showing the participants,
   additional streams are used for presentations.

   In systems available today, generally only one additional video
   stream is available for presentations.  Often, this presentation
   stream is half-duplex in nature, with presenters taking turns.  The
   presentation stream may be captured from a PC screen, or it may come
   from a multimedia source such as a document camera, camcorder, or a
   DVD.  In a multipoint meeting, the presentation streams for the
   currently active presentation are always distributed to all sites in
   the meeting, so that the presentations are viewed by all.

   Some systems display the presentation streams on a screen that is
   mounted either above or below the 3 participant screens.  Other
   systems provide screens on the conference table for observing
   presentations.  If multiple presentation screens are used, they
   generally display identical content.  There is considerable variation
   in the placement, number, and size of presentation screens.

   In some systems, presentation audio is pre-mixed with the room audio.
   In others, a separate presentation audio stream is provided (if the
   presentation includes audio).







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   In H.323 [<a href="#ref-ITU.H323" title="&quot;Packet-based Multimedia Communications Systems&quot;">ITU.H323</a>] systems, H.239 [<a href="#ref-ITU.H239" title="&quot;Role management and additional media channels for H.300-series terminals&quot;">ITU.H239</a>] is typically used to
   control the video presentation stream.  In SIP systems, similar
   control mechanisms can be provided using the Binary Floor Control
   Protocol (BFCP) [<a href="./rfc4582" title="&quot;The Binary Floor Control Protocol (BFCP)&quot;">RFC4582</a>] for the presentation token.  These
   mechanisms are suitable for managing a single presentation stream.

   Although today's systems remain limited to a single video
   presentation stream, there are obvious uses for multiple presentation
   streams:

   1.  Frequently, the meeting convener is following a meeting agenda,
       and it is useful for her to be able to show that agenda to all
       participants during the meeting.  Other participants at various
       remote sites are able to make presentations during the meeting,
       with the presenters taking turns.  The presentations and the
       agenda are both shown, either on separate screens, or perhaps
       rescaled and shown on a single screen.

   2.  A single multimedia presentation can itself include multiple
       video streams that should be shown together.  For instance, a
       presenter may be discussing the fairness of media coverage.  In
       addition to slides that support the presenter's conclusions, she
       also has video excerpts from various news programs that she shows
       to illustrate her findings.  She uses a DVD player for the video
       excerpts so that she can pause and reposition the video as
       needed.

   3.  An educator who is presenting a multiscreen slide show.  This
       show requires that the placement of the images on the multiple
       screens at each site be consistent.

   There are many other examples where multiple presentation streams are
   useful.

<span class="h3"><a class="selflink" id="section-3.5" href="#section-3.5">3.5</a>.  Heterogeneous Systems</span>

   It is common in meeting scenarios for people to join the conference
   from a variety of environments, using different types of endpoint
   devices.  A multiscreen immersive telepresence conference may include
   someone on a PC-based video conferencing system, a participant
   calling in by phone, and (soon) someone on a handheld device.

   What experience/view will each of these devices have?

   Some may be able to handle multiple streams, and others can handle
   only a single stream.  (Here, we are not talking about legacy
   systems, but rather systems built to participate in such a
   conference, although they are single stream only.)  In a single video



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   stream, the stream may contain one or more compositions depending on
   the available screen space on the device.  In most cases, an
   intermediate transcoding device will be relied upon to produce a
   single stream, perhaps with some kind of continuous presence.

   Bit rates will vary -- the handheld device and phone having lower bit
   rates than PC and multiscreen systems.

   Layout is accomplished according to different policies.  For example,
   a handheld device and PC may receive the active speaker stream.  The
   decision can either be made explicitly by the receiver or by the
   sender if it can receive some kind of rendering hint.  The same is
   true for audio -- i.e., that it receives a mixed stream or a number
   of the loudest speakers if mixing is not available in the network.

   For the PC-based conferencing participant, the user's experience
   depends on the application.  It could be single stream, similar to a
   handheld device but with a bigger screen.  Or, it could be multiple
   streams, similar to an immersive telepresence system but with a
   smaller screen.  Control for manipulation of streams can be local in
   the software application, or in another location and sent to the
   application over the network.

   The handheld device is the most extreme.  How will that participant
   be viewed and heard?  It should be an equal participant, though the
   bandwidth will be significantly less than an immersive system.  A
   receiver may choose to display output coming from a handheld device
   differently based on the resolution, but that would be the case with
   any low-resolution video stream, e.g., from a powerful PC on a bad
   network.

   The handheld device will send and receive a single video stream,
   which could be a composite or a subset of the conference.  The
   handheld device could say what it wants or could accept whatever the
   sender (conference server or sending endpoint) thinks is best.  The
   handheld device will have to signal any actions it wants to take the
   same way that an immersive system signals actions.

<span class="h3"><a class="selflink" id="section-3.6" href="#section-3.6">3.6</a>.  Multipoint Education Usage</span>

   The importance of this example is that the multiple video streams are
   not used to create an immersive conferencing experience with
   panoramic views at all the sites.  Instead, the multiple streams are
   dynamically used to enable full participation of remote students in a
   university class.  In some instances, the same video stream is
   displayed on multiple screens in the room; in other instances, an
   available stream is not displayed at all.




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   The main site is a university auditorium that is equipped with 3
   cameras.  One camera is focused on the professor at the podium.  A
   second camera is mounted on the wall behind the professor and
   captures the class in its entirety.  The third camera is co-located
   with the second and is designed to capture a close-up view of a
   questioner in the audience.  It automatically zooms in on that
   student using sound localization.

   Although the auditorium is equipped with 3 cameras, it is only
   equipped with 2 screens.  One is a large screen located at the front
   so that the class can see it.  The other is located at the rear so
   the professor can see it.  When someone asks a question, the front
   screen shows the questioner.  Otherwise, it shows the professor
   (ensuring everyone can easily see her).

   The remote sites are typical immersive telepresence rooms, each with
   3 camera/screen pairs.

   All remote sites display the professor on the center screen at full
   size.  A second screen shows the entire classroom view when the
   professor is speaking.  However, when a student asks a question, the
   second screen shows the close-up view of the student at full size.
   Sometimes the student is in the auditorium; sometimes the speaking
   student is at another remote site.  The remote systems never display
   the students that are actually in that room.

   If someone at a remote site asks a question, then the screen in the
   auditorium will show the remote student at full size (as if they were
   present in the auditorium itself).  The screen in the rear also shows
   this questioner, allowing the professor to see and respond to the
   student without needing to turn her back on the main class.

   When no one is asking a question, the screen in the rear briefly
   shows a full-room view of each remote site in turn, allowing the
   professor to monitor the entire class (remote and local students).
   The professor can also use a control on the podium to see a
   particular site -- she can choose either a full-room view or a
   single-camera view.

   Realization of this use case does not require any negotiation between
   the participating sites.  Endpoint devices (and a Multipoint Control
   Unit (MCU), if present) need to know who is speaking and what video
   stream includes the view of that speaker.  The remote systems need
   some knowledge of which stream should be placed in the center.  The
   ability of the professor to see specific sites (or for the system to
   show all the sites in turn) would also require the auditorium system





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   to know what sites are available and to be able to request a
   particular view of any site.  Bandwidth is optimized if video that is
   not being shown at a particular site is not distributed to that site.

<span class="h3"><a class="selflink" id="section-3.7" href="#section-3.7">3.7</a>.  Multipoint Multiview (Virtual Space)</span>

   This use case describes a virtual space multipoint meeting with good
   eye contact and spatial layout of participants.  The use case was
   proposed very early in the development of video conferencing systems
   as described in 1983 by Allardyce and Randal [<a href="#ref-virtualspace">virtualspace</a>].  The use
   case is illustrated in Figure 2-5 of their report.  The virtual space
   expands the point-to-point case by having all multipoint conference
   participants "seated" in a virtual room.  In this case, each
   participant has a fixed "seat" in the virtual room, so each
   participant expects to see a different view having a different
   participant on his left and right side.  Today, the use case is
   implemented in multiple telepresence-type video conferencing systems
   on the market.  The term "virtual space" was used in their report.
   The main difference between the result obtained with modern systems
   and those from 1983 are larger screen sizes.

   Virtual space multipoint as defined here assumes endpoints with
   multiple cameras and screens.  Usually, there is the same number of
   cameras and screens at a given endpoint.  A camera is positioned
   above each screen.  A key aspect of virtual space multipoint is the
   details of how the cameras are aimed.  The cameras are each aimed on
   the same area of view of the participants at the site.  Thus, each
   camera takes a picture of the same set of people but from a different
   angle.  Each endpoint sender in the virtual space multipoint meeting
   therefore offers a choice of video streams to remote receivers, each
   stream representing a different viewpoint.  For example, a camera
   positioned above a screen to a participant's left may take video
   pictures of the participant's left ear; while at the same time, a
   camera positioned above a screen to the participant's right may take
   video pictures of the participant's right ear.

   Since a sending endpoint has a camera associated with each screen, an
   association is made between the receiving stream output on a
   particular screen and the corresponding sending stream from the
   camera associated with that screen.  These associations are repeated
   for each screen/camera pair in a meeting.  The result of this system
   is a horizontal arrangement of video images from remote sites, one
   per screen.  The image from each screen is paired with the camera
   output from the camera above that screen, resulting in excellent eye
   contact.






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<span class="h3"><a class="selflink" id="section-3.8" href="#section-3.8">3.8</a>.  Multiple Presentation Streams - Telemedicine</span>

   This use case describes a scenario where multiple presentation
   streams are used.  In this use case, the local site is a surgery room
   connected to one or more remote sites that may have different
   capabilities.  At the local site, 3 main cameras capture the whole
   room (the typical 3-camera telepresence case).  Also, multiple
   presentation inputs are available: a surgery camera that is used to
   provide a zoomed view of the operation, an endoscopic monitor, a
   flouroscope (X-ray imaging), an ultrasound diagnostic device, an
   electrocardiogram (ECG) monitor, etc.  These devices are used to
   provide multiple local video presentation streams to help the surgeon
   monitor the status of the patient and assist in the surgical process.

   The local site may have 3 main screens and one (or more) presentation
   screen(s).  The main screens can be used to display the remote
   experts.  The presentation screen(s) can be used to display multiple
   presentation streams from local and remote sites simultaneously.  The
   3 main cameras capture different parts of the surgery room.  The
   surgeon can decide the number, the size, and the placement of the
   presentations displayed on the local presentation screen(s).  He can
   also indicate which local presentation captures are provided for the
   remote sites.  The local site can send multiple presentation captures
   to remote sites, and it can receive from them multiple presentations
   related to the patient or the procedure.

   One type of remote site is a single- or dual-screen and one-camera
   system used by a consulting expert.  In the general case, the remote
   sites can be part of a multipoint telepresence conference.  The
   presentation screens at the remote sites allow the experts to see the
   details of the operation and related data.  Like the main site, the
   experts can decide the number, the size, and the placement of the
   presentations displayed on the presentation screens.  The
   presentation screens can display presentation streams from the
   surgery room, from other remote sites, or from local presentation
   streams.  Thus, the experts can also start sending presentation
   streams that can carry medical records, pathology data, or their
   references and analysis, etc.

   Another type of remote site is a typical immersive telepresence room
   with 3 camera/screen pairs, allowing more experts to join the
   consultation.  These sites can also be used for education.  The
   teacher, who is not necessarily the surgeon, and the students are in
   different remote sites.  Students can observe and learn the details
   of the whole procedure, while the teacher can explain and answer
   questions during the operation.





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   All remote education sites can display the surgery room.  Another
   option is to display the surgery room on the center screen, and the
   rest of the screens can show the teacher and the student who is
   asking a question.  For all the above sites, multiple presentation
   screens can be used to enhance visibility: one screen for the zoomed
   surgery stream and the others for medical image streams, such as MRI
   images, cardiograms, ultrasonic images, and pathology data.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Acknowledgements</span>

   The document has benefitted from input from a number of people
   including Alex Eleftheriadis, Marshall Eubanks, Tommy Andre Nyquist,
   Mark Gorzynski, Charles Eckel, Nermeen Ismail, Mary Barnes, Pascal
   Buhler, and Jim Cole.

   Special acknowledgement to Lennard Xiao, who contributed the text for
   the telemedicine use case, and to Claudio Allocchio for his detailed
   review of the document.

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Security Considerations</span>

   While there are likely to be security considerations for any solution
   for telepresence interoperability, this document has no security
   considerations.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Informative References</span>

   [<a id="ref-ITU.H239">ITU.H239</a>]  ITU-T, "Role management and additional media channels for
               H.300-series terminals", ITU-T Recommendation H.239,
               September 2005.

   [<a id="ref-ITU.H264">ITU.H264</a>]  ITU-T, "Advanced video coding for generic audiovisual
               services", ITU-T Recommendation H.264, April 2013.

   [<a id="ref-ITU.H323">ITU.H323</a>]  ITU-T, "Packet-based Multimedia Communications Systems",
               ITU-T Recommendation H.323, December 2009.

   [<a id="ref-RFC3261">RFC3261</a>]   Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
               A., Peterson, J., Sparks, R., Handley, M., and E.
               Schooler, "SIP: Session Initiation Protocol", <a href="./rfc3261">RFC 3261</a>,
               June 2002.

   [<a id="ref-RFC3550">RFC3550</a>]   Schulzrinne, H., Casner, S., Frederick, R., and V.
               Jacobson, "RTP: A Transport Protocol for Real-Time
               Applications", STD 64, <a href="./rfc3550">RFC 3550</a>, July 2003.

   [<a id="ref-RFC4582">RFC4582</a>]   Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
               Control Protocol (BFCP)", <a href="./rfc4582">RFC 4582</a>, November 2006.



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   [<a id="ref-virtualspace">virtualspace</a>]
               Allardyce, L. and L. Randall, "Development of
               Teleconferencing Methodologies with Emphasis on Virtual
               Space Video and Interactive Graphics", April 1983,
               &lt;<a href="http://www.dtic.mil/docs/citations/ADA127738">http://www.dtic.mil/docs/citations/ADA127738</a>&gt;.

Authors' Addresses

   Allyn Romanow
   Cisco
   San Jose, CA  95134
   US

   EMail: allyn@cisco.com


   Stephen Botzko
   Polycom
   Andover, MA  01810
   US

   EMail: stephen.botzko@polycom.com


   Mark Duckworth
   Polycom
   Andover, MA  01810
   US

   EMail: mark.duckworth@polycom.com


   Roni Even (editor)
   Huawei Technologies
   Tel Aviv
   Israel

   EMail: roni.even@mail01.huawei.com













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