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Even, Ed. 8 Huawei Technologies 9 December 6, 2013 11 Use Cases for Telepresence Multi-streams 12 draft-ietf-clue-telepresence-use-cases-08.txt 14 Abstract 16 Telepresence conferencing systems seek to create an environment that 17 gives non co-located users or user groups a feeling of co-located 18 presence through multimedia communication including at least audio 19 and video signals of high fidelity. A number of techniques for 20 handling audio and video streams are used to create this experience. 21 When these techniques are not similar, interoperability between 22 different systems is difficult at best, and often not possible. 23 Conveying information about the relationships between multiple 24 streams of media would allow senders and receivers to make choices to 25 allow telepresence systems to interwork. This memo describes the 26 most typical and important use cases for sending multiple streams in 27 a telepresence conference. 29 Status of This Memo 31 This Internet-Draft is submitted in full conformance with the 32 provisions of BCP 78 and BCP 79. 34 Internet-Drafts are working documents of the Internet Engineering 35 Task Force (IETF). Note that other groups may also distribute 36 working documents as Internet-Drafts. The list of current Internet- 37 Drafts is at http://datatracker.ietf.org/drafts/current/. 39 Internet-Drafts are draft documents valid for a maximum of six months 40 and may be updated, replaced, or obsoleted by other documents at any 41 time. It is inappropriate to use Internet-Drafts as reference 42 material or to cite them other than as "work in progress." 44 This Internet-Draft will expire on June 9, 2014. 46 Copyright Notice 47 Copyright (c) 2013 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (http://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 63 2. Telepresence Scenarios Overview . . . . . . . . . . . . . . . 3 64 3. Use Case Scenarios . . . . . . . . . . . . . . . . . . . . . 5 65 3.1. Point to point meeting: symmetric . . . . . . . . . . . . 6 66 3.2. Point to point meeting: asymmetric . . . . . . . . . . . 7 67 3.3. Multipoint meeting . . . . . . . . . . . . . . . . . . . 9 68 3.4. Presentation . . . . . . . . . . . . . . . . . . . . . . 10 69 3.5. Heterogeneous Systems . . . . . . . . . . . . . . . . . . 11 70 3.6. Multipoint Education Usage . . . . . . . . . . . . . . . 12 71 3.7. Multipoint Multiview (Virtual space) . . . . . . . . . . 13 72 3.8. Multiple presentations streams - Telemedicine . . . . . . 14 73 4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 74 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 75 6. Security Considerations . . . . . . . . . . . . . . . . . . . 16 76 7. Informative References . . . . . . . . . . . . . . . . . . . 16 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 17 79 1. Introduction 81 Telepresence applications try to provide a "being there" experience 82 for conversational video conferencing. Often this telepresence 83 application is described as "immersive telepresence" in order to 84 distinguish it from traditional video conferencing, and from other 85 forms of remote presence not related to conversational video 86 conferencing, such as avatars and robots. The salient 87 characteristics of telepresence are often described as: actual sized, 88 immersive video, preserving interpersonal interaction and allowing 89 non-verbal communication. 91 Although telepresence systems are based on open standards such as RTP 92 [RFC3550], SIP [RFC3261], H.264, and the H.323[ITU.H323]suite of 93 protocols, they cannot easily interoperate with each other without 94 operator assistance and expensive additional equipment which 95 translates from one vendor's protocol to another. 97 The basic features that give telepresence its distinctive 98 characteristics are implemented in disparate ways in different 99 systems. Currently Telepresence systems from diverse vendors 100 interoperate to some extent, but this is not supported in a standards 101 based fashion. Interworking requires that translation and 102 transcoding devices be included in the architecture. Such devices 103 increase latency, reducing the quality of interpersonal interaction. 104 Use of these devices is often not automatic; it frequently requires 105 substantial manual configuration and a detailed understanding of the 106 nature of underlying audio and video streams. This state of affairs 107 is not acceptable for the continued growth of telepresence - these 108 systems should have the same ease of interoperability as do 109 telephones. Thus, a standard way of describing the multiple streams 110 constituting the media flows and the fundamental aspects of their 111 behavior, would allow telepresence systems to interwork. 113 This document presents a set of use cases describing typical 114 scenarios. Requirements will be derived from these use cases in a 115 separate document. The use cases are described from the viewpoint of 116 the users. They are illustrative of the user experience that needs 117 to be supported. It is possible to implement these use cases in a 118 variety of different ways. 120 Many different scenarios need to be supported. This document 121 describes in detail the most common and basic use cases. These will 122 cover most of the requirements. There may be additional scenarios 123 that bring new features and requirements which can be used to extend 124 the initial work. 126 Point-to-point and Multipoint telepresence conferences are 127 considered. In some use cases, the number of screens is the same at 128 all sites, in others, the number of screens differs at different 129 sites. Both use cases are considered. Also included is a use case 130 describing display of presentation material or content. 132 The document structure is as follows: Section 2 gives an overview of 133 scenarios, and Section 3 describes use cases. 135 2. Telepresence Scenarios Overview 137 This section describes the general characteristics of the use cases 138 and what the scenarios are intended to show. The typical setting is 139 a business conference, which was the initial focus of telepresence. 140 Recently consumer products are also being developed. We specifically 141 do not include in our scenarios the physical infrastructure aspects 142 of telepresence, such as room construction, layout and decoration. 143 Furthermore, these use cases do not describe all the aspects needed 144 to create the best user experience. 146 We also specifically do not attempt to precisely define the 147 boundaries between telepresence systems and other systems, nor do we 148 attempt to identify the "best" solution for each presented scenario. 150 Telepresence systems are typically composed of one or more video 151 cameras and encoders and one or more display screens of large size 152 (diagonal around 60"). Microphones pick up sound and audio codec(s) 153 and produce one or more audio streams. The cameras used to capture 154 the telepresence users are referred to as participant cameras (and 155 likewise for screens). There may also be other cameras, such as for 156 document display. These will be referred to as presentation or 157 content cameras, which generally have different formats, aspect 158 ratios, and frame rates from the participant cameras. The 159 presentation streams may be shown on participant screen, or on 160 auxiliary display screens. A user's computer may also serve as a 161 virtual content camera, generating an animation or playing a video 162 for display to the remote participants. 164 We describe such a telepresence system as sending one or more video 165 streams, audio streams, and presentation streams to the remote 166 system(s). (Note that the number of audio, video or presentation 167 streams is generally not identical.) 169 The fundamental parameters describing today's typical telepresence 170 scenarios include: 172 1. The number of participating sites 174 2. The number of visible seats at a site 176 3. The number of cameras 178 4. The number and type of microphones 180 5. The number of audio channels 182 6. The screen size 184 7. The screen capabilities - such as resolution, frame rate, aspect 185 ratio 187 8. The arrangement of the screens in relation to each other 189 9. The number of primary screens at each sites 191 10. Type and number of presentation screens 193 11. Multipoint conference display strategies - for example, the 194 camera-to-screen mappings may be static or dynamic 196 12. The camera point of capture. 198 13. The cameras fields of view and how they spatially relate to each 199 other. 201 As discussed in the introduction, the basic features that give 202 telepresence its distinctive characteristics are implemented in 203 disparate ways in different systems. 205 There is no agreed upon way to adequately describe the semantics of 206 how streams of various media types relate to each other. Without a 207 standard for stream semantics to describe the particular roles and 208 activities of each stream in the conference, interoperability is 209 cumbersome at best. 211 In a multiple screen conference, the video and audio streams sent 212 from remote participants must be understood by receivers so that they 213 can be presented in a coherent and life-like manner. This includes 214 the ability to present remote participants at their actual size for 215 their apparent distance, while maintaining correct eye contact, 216 gesticular cues, and simultaneously providing a spatial audio sound 217 stage that is consistent with the displayed video. 219 The receiving device that decides how to render incoming information 220 needs to understand a number of variables such as the spatial 221 position of the speaker, the field of view of the cameras, the camera 222 zoom, which media stream is related to each of the screens, etc. It 223 is not simply that individual streams must be adequately described, 224 to a large extent this already exists, but rather that the semantics 225 of the relationships between the streams must be communicated. Note 226 that all of this is still required even if the basic aspects of the 227 streams, such as the bit rate, frame rate, and aspect ratio, are 228 known. Thus, this problem has aspects considerably beyond those 229 encountered in interoperation of single camera/screen video 230 conferencing systems. 232 3. Use Case Scenarios 233 The use case scenarios focus on typical implementations. There are a 234 number of possible variants for these use cases, for example, the 235 audio supported may differ at the end points (such as mono or stereo 236 versus surround sound), etc. 238 Many of these systems offer a full conference room solution where 239 local participants sit at one side of a table and remote participants 240 are displayed as if they are sitting on the other side of the table. 241 The cameras and screens are typically arranged to provide a panoramic 242 (left to right from the local user view point) view of the remote 243 room. 245 The sense of immersion and non-verbal communication is fostered by a 246 number of technical features, such as: 248 1. Good eye contact, which is achieved by careful placement of 249 participants, cameras and screens. 251 2. Camera field of view and screen sizes are matched so that the 252 images of the remote room appear to be full size. 254 3. The left side of each room is presented on the right screen at 255 the far end; similarly the right side of the room is presented on 256 the left screen. The effect of this is that participants of each 257 site appear to be sitting across the table from each other. If 258 two participants on the same site glance at each other, all 259 participants can observe it. Likewise, if a participant at one 260 site gestures to a participant on the other site, all 261 participants observe the gesture itself and the participants it 262 includes. 264 3.1. Point to point meeting: symmetric 266 In this case each of the two sites has an identical number of 267 screens, with cameras having fixed fields of view, and one camera for 268 each screen. The sound type is the same at each end. As an example, 269 there could be 3 cameras and 3 screens in each room, with stereo 270 sound being sent and received at each end. 272 The important thing here is that each of the 2 sites has the same 273 number of screens. Each screen is paired with a corresponding 274 camera. Each camera / screen pair is typically connected to a 275 separate codec, producing a video encoded stream for transmission to 276 the remote site, and receiving a similarly encoded stream from the 277 remote site. 279 Each system has one or multiple microphones for capturing audio. In 280 some cases, stereophonic microphones are employed. In other systems, 281 a microphone may be placed in front of each participant (or pair of 282 participants). In typical systems all the microphones are connected 283 to a single codec that sends and receives the audio streams as either 284 stereo or surround sound. The number of microphones and the number 285 of audio channels are often not the same as the number of cameras. 286 Also the number of microphones is often not the same as the number of 287 loudspeakers. 289 The audio may be transmitted as multi-channel (stereo/surround sound) 290 or as distinct and separate monophonic streams. Audio levels should 291 be matched, so the sound levels at both sites are identical. 292 Loudspeaker and microphone placements are chosen so that the sound 293 "stage" (orientation of apparent audio sources) is coordinated with 294 the video. That is, if a participant at one site speaks, the 295 participants at the remote site perceive her voice as originating 296 from her visual image. In order to accomplish this, the audio needs 297 to be mapped at the received site in the same fashion as the video. 298 That is, audio received from the right side of the room needs to be 299 output from loudspeaker(s) on the left side at the remote site, and 300 vice versa. 302 3.2. Point to point meeting: asymmetric 304 In this case, each site has a different number of screens and cameras 305 than the other site. The important characteristic of this scenario 306 is that the number of screens is different between the two sites. 307 This creates challenges which are handled differently by different 308 telepresence systems. 310 This use case builds on the basic scenario of 3 screens to 3 screens. 311 Here, we use the common case of 3 screens and 3 cameras at one site, 312 and 1 screen and 1 camera at the other site, connected by a point to 313 point call. The screen sizes and camera fields of view at both sites 314 are basically similar, such that each camera view is designed to show 315 two people sitting side by side. Thus the 1 screen room has up to 2 316 people seated at the table, while the 3 screen room may have up to 6 317 people at the table. 319 The basic considerations of defining left and right and indicating 320 relative placement of the multiple audio and video streams are the 321 same as in the 3-3 use case. However, handling the mismatch between 322 the two sites of the number of screens and cameras requires more 323 complicated maneuvers. 325 For the video sent from the 1 camera room to the 3 screen room, 326 usually what is done is to simply use 1 of the 3 screens and keep the 327 second and third screens inactive or, for example, put up the current 328 date. This would maintain the "full size" image of the remote side. 330 For the other direction, the 3 camera room sending video to the 1 331 screen room, there are more complicated variations to consider. Here 332 are several possible ways in which the video streams can be handled. 334 1. The 1 screen system might simply show only 1 of the 3 camera 335 images, since the receiving side has only 1 screen. Two people 336 are seen at full size, but 4 people are not seen at all. The 337 choice of which 1 of the 3 streams to display could be fixed, or 338 could be selected by the users. It could also be made 339 automatically based on who is speaking in the 3 screen room, such 340 that the people in the 1 screen room always see the person who is 341 speaking. If the automatic selection is done at the sender, the 342 transmission of streams that are not displayed could be 343 suppressed, which would avoid wasting bandwidth. 345 2. The 1 screen system might be capable of receiving and decoding 346 all 3 streams from all 3 cameras. The 1 screen system could then 347 compose the 3 streams into 1 local image for display on the 348 single screen. All six people would be seen, but smaller than 349 full size. This could be done in conjunction with reducing the 350 image resolution of the streams, such that encode/decode 351 resources and bandwidth are not wasted on streams that will be 352 downsized for display anyway. 354 3. The 3 screen system might be capable of including all 6 people in 355 a single stream to send to the 1 screen system. For example, it 356 could use PTZ (Pan Tilt Zoom) cameras to physically adjust the 357 cameras such that 1 camera captures the whole room of six people. 358 Or it could recompose the 3 camera images into 1 encoded stream 359 to send to the remote site. These variations also show all six 360 people, but at a reduced size. 362 4. Or, there could be a combination of these approaches, such as 363 simultaneously showing the speaker in full size with a composite 364 of all the 6 participants in smaller size. 366 The receiving telepresence system needs to have information about the 367 content of the streams it receives to make any of these decisions. 368 If the systems are capable of supporting more than one strategy, 369 there needs to be some negotiation between the two sites to figure 370 out which of the possible variations they will use in a specific 371 point to point call. 373 3.3. Multipoint meeting 375 In a multipoint telepresence conference, there are more than two 376 sites participating. Additional complexity is required to enable 377 media streams from each participant to show up on the screens of the 378 other participants. 380 Clearly, there are a great number of topologies that can be used to 381 display the streams from multiple sites participating in a 382 conference. 384 One major objective for telepresence is to be able to preserve the 385 "Being there" user experience. However, in multi-site conferences it 386 is often (in fact usually) not possible to simultaneously provide 387 full size video, eye contact, common perception of gestures and gaze 388 by all participants. Several policies can be used for stream 389 distribution and display: all provide good results but they all make 390 different compromises. 392 One common policy is called site switching. Let's say the speaker is 393 at site A and everyone else is at a "remote" site. When the room at 394 site A shown, all the camera images from site A are forwarded to the 395 remote sites. Therefore at each receiving remote site, all the 396 screens display camera images from site A. This can be used to 397 preserve full size image display, and also provide full visual 398 context of the displayed far end, site A. In site switching, there 399 is a fixed relation between the cameras in each room and the screens 400 in remote rooms. The room or participants being shown is switched 401 from time to time based on who is speaking or by manual control, 402 e.g., from site A to site B. 404 Segment switching is another policy choice. Still using site A as 405 where the speaker is, and "remote" to refer to all the other sites, 406 in segment switching, rather than sending all the images from site A, 407 only the speaker at site A is shown. The camera images of the 408 current speaker and previous speakers (if any) are forwarded to the 409 other sites in the conference. Therefore the screens in each site 410 are usually displaying images from different remote sites - the 411 current speaker at site A and the previous ones. This strategy can 412 be used to preserve full size image display, and also capture the 413 non-verbal communication between the speakers. In segment switching, 414 the display depends on the activity in the remote rooms - generally, 415 but not necessarily based on audio / speech detection). 417 A third possibility is to reduce the image size so that multiple 418 camera views can be composited onto one or more screens. This does 419 not preserve full size image display, but provides the most visual 420 context (since more sites or segments can be seen). Typically in 421 this case the display mapping is static, i.e., each part of each room 422 is shown in the same location on the display screens throughout the 423 conference. 425 Other policies and combinations are also possible. For example, 426 there can be a static display of all screens from all remote rooms, 427 with part or all of one screen being used to show the current speaker 428 at full size. 430 3.4. Presentation 432 In addition to the video and audio streams showing the participants, 433 additional streams are used for presentations. 435 In systems available today, generally only one additional video 436 stream is available for presentations. Often this presentation 437 stream is half-duplex in nature, with presenters taking turns. The 438 presentation stream may be captured from a PC screen, or it may come 439 from a multimedia source such as a document camera, camcorder or a 440 DVD. In a multipoint meeting, the presentation streams for the 441 currently active presentation are always distributed to all sites in 442 the meeting, so that the presentations are viewed by all. 444 Some systems display the presentation streams on a screen that is 445 mounted either above or below the three participant screens. Other 446 systems provide screens on the conference table for observing 447 presentations. If multiple presentation screens are used, they 448 generally display identical content. There is considerable variation 449 in the placement, number, and size or presentation screens. 451 In some systems presentation audio is pre-mixed with the room audio. 452 In others, a separate presentation audio stream is provided (if the 453 presentation includes audio). 455 In H.323[ITU.H323] systems, H.239[ITU.H239] is typically used to 456 control the video presentation stream. In SIP systems, similar 457 control mechanisms can be provided using BFCP [RFC4582] for 458 presentation token. These mechanisms are suitable for managing a 459 single presentation stream. 461 Although today's systems remain limited to a single video 462 presentation stream, there are obvious uses for multiple presentation 463 streams: 465 1. Frequently the meeting convener is following a meeting agenda, 466 and it is useful for her to be able to show that agenda to all 467 participants during the meeting. Other participants at various 468 remote sites are able to make presentations during the meeting, 469 with the presenters taking turns. The presentations and the 470 agenda are both shown, either on separate screens, or perhaps re- 471 scaled and shown on a single screen. 473 2. A single multimedia presentation can itself include multiple 474 video streams that should be shown together. For instance, a 475 presenter may be discussing the fairness of media coverage. In 476 addition to slides which support the presenter's conclusions, she 477 also has video excerpts from various news programs which she 478 shows to illustrate her findings. She uses a DVD player for the 479 video excerpts so that she can pause and reposition the video as 480 needed. 482 3. An educator who is presenting a multi-screen slide show. This 483 show requires that the placement of the images on the multiple 484 screens at each site be consistent. 486 There are many other examples where multiple presentation streams are 487 useful. 489 3.5. Heterogeneous Systems 491 It is common in meeting scenarios for people to join the conference 492 from a variety of environments, using different types of endpoint 493 devices. A multi-screen immersive telepresence conference may 494 include someone on a PC-based video conferencing system, a 495 participant calling in by phone, and (soon) someone on a handheld 496 device. 498 What experience/view will each of these devices have? 500 Some may be able to handle multiple streams and others can handle 501 only a single stream. (We are not here talking about legacy systems, 502 but rather systems built to participate in such a conference, 503 although they are single stream only.) In a single video stream , 504 the stream may contain one or more compositions depending on the 505 available screen space on the device. In most cases an intermediate 506 transcoding device will be relied upon to produce a single stream, 507 perhaps with some kind of continuous presence. 509 Bit rates will vary - the handheld and phone having lower bit rates 510 than PC and multi-screen systems. 512 Layout is accomplished according to different policies. For example, 513 a handheld and PC may receive the active speaker stream. The 514 decision can either be made explicitly by the receiver or by the 515 sender if it can receive some kind of rendering hint. The same is 516 true for audio -- i.e., that it receives a mixed stream or a number 517 of the loudest speakers if mixing is not available in the network. 519 For the PC based conferencing participant, the user's experience 520 depends on the application. It could be single stream, similar to a 521 handheld but with a bigger screen. Or, it could be multiple streams, 522 similar to an immersive telepresence system but with a smaller 523 screen. Control for manipulation of streams can be local in the 524 software application, or in another location and sent to the 525 application over the network. 527 The handheld device is the most extreme. How will that participant 528 be viewed and heard? It should be an equal participant, though the 529 bandwidth will be significantly less than an immersive system. A 530 receiver may choose to display output coming from a handheld 531 differently based on the resolution, but that would be the case with 532 any low resolution video stream, e.g., from a powerful PC on a bad 533 network. 535 The handheld will send and receive a single video stream, which could 536 be a composite or a subset of the conference. The handheld could say 537 what it wants or could accept whatever the sender (conference server 538 or sending endpoint) thinks is best. The handheld will have to 539 signal any actions it wants to take the same way that immersive 540 system signals actions. 542 3.6. Multipoint Education Usage 544 The importance of this example is that the multiple video streams are 545 not used to create an immersive conferencing experience with 546 panoramic views at all the sites. Instead the multiple streams are 547 dynamically used to enable full participation of remote students in a 548 university class. In some instances the same video stream is 549 displayed on multiple screens in the room, in other instances an 550 available stream is not displayed at all. 552 The main site is a university auditorium which is equipped with three 553 cameras. One camera is focused on the professor at the podium. A 554 second camera is mounted on the wall behind the professor and 555 captures the class in its entirety. The third camera is co-located 556 with the second, and is designed to capture a close up view of a 557 questioner in the audience. It automatically zooms in on that 558 student using sound localization. 560 Although the auditorium is equipped with three cameras, it is only 561 equipped with two screens. One is a large screen located at the 562 front so that the class can see it. The other is located at the rear 563 so the professor can see it. When someone asks a question, the front 564 screen shows the questioner. Otherwise it shows the professor 565 (ensuring everyone can easily see her). 567 The remote sites are typical immersive telepresence room with three 568 camera/screen pairs. 570 All remote sites display the professor on the center screen at full 571 size. A second screen shows the entire classroom view when the 572 professor is speaking. However, when a student asks a question, the 573 second screen shows the close up view of the student at full size. 574 Sometimes the student is in the auditorium; sometimes the speaking 575 student is at another remote site. The remote systems never display 576 the students that are actually in that room. 578 If someone at the remote site asks a question, then the screen in the 579 auditorium will show the remote student at full size (as if they were 580 present in the auditorium itself). The screen in the rear also shows 581 this questioner, allowing the professor to see and respond to the 582 student without needing to turn her back on the main class. 584 When no one is asking a question, the screen in the rear briefly 585 shows a full-room view of each remote site in turn, allowing the 586 professor to monitor the entire class (remote and local students). 587 The professor can also use a control on the podium to see a 588 particular site - she can choose either a full-room view or a single 589 camera view. 591 Realization of this use case does not require any negotiation between 592 the participating sites. Endpoint devices (and an MCU if present) - 593 need to know who is speaking and what video stream includes the view 594 of that speaker. The remote systems need some knowledge of which 595 stream should be placed in the center. The ability of the professor 596 to see specific sites (or for the system to show all the sites in 597 turn) would also require the auditorium system to know what sites are 598 available, and to be able to request a particular view of any site. 599 Bandwidth is optimized if video that is not being shown at a 600 particular site is not distributed to that site. 602 3.7. Multipoint Multiview (Virtual space) 604 This use case describes a virtual space multipoint meeting with good 605 eye contact and spatial layout of participants. The use case was 606 proposed very early in the development of video conferencing systems 607 as described in 1983 by Allardyce and Randal [virtualspace]. The use 608 case is illustrated in figure 2-5 of their report. The virtual space 609 expands the point to point case by having all multipoint conference 610 participants "seat" in a virtual room. In this case each participant 611 has a fixed "seat" in the virtual room so each participant expects to 612 see a different view having a different participant on his left and 613 right side. Today, the use case is implemented in multiple 614 telepresence type video conferencing systems on the market. The term 615 "virtual space" was used in their report. The main difference 616 between the result obtained with modern systems and those from 1983 617 are larger screen sizes. 619 Virtual space multipoint as defined here assumes endpoints with 620 multiple cameras and screens. Usually there is the same number of 621 cameras and screens at a given endpoint. A camera is positioned 622 above each screen. A key aspect of virtual space multipoint is the 623 details of how the cameras are aimed. The cameras are each aimed on 624 the same area of view of the participants at the site. Thus each 625 camera takes a picture of the same set of people but from a different 626 angle. Each endpoint sender in the virtual space multipoint meeting 627 therefore offers a choice of video streams to remote receivers, each 628 stream representing a different view point. For example a camera 629 positioned above a screen to a participant's left may take video 630 pictures of the participant's left ear while at the same time, a 631 camera positioned above a screen to the participant's right may take 632 video pictures of the participant's right ear. 634 Since a sending endpoint has a camera associated with each screen, an 635 association is made between the receiving stream output on a 636 particular screen and the corresponding sending stream from the 637 camera associated with that screen. These associations are repeated 638 for each screen/camera pair in a meeting. The result of this system 639 is a horizontal arrangement of video images from remote sites, one 640 per screen. The image from each screen is paired with the camera 641 output from the camera above that screen resulting in excellent eye 642 contact. 644 3.8. Multiple presentations streams - Telemedicine 645 This use case describes a scenario where multiple presentation 646 streams are used. In this use case, the local site is a surgery room 647 connected to one or more remote sites that may have different 648 capabilities. At the local site three main cameras capture the whole 649 room (typical 3 camera Telepresence case). Also multiple 650 presentation inputs are available: a surgery camera which is used to 651 provide a zoomed view of the operation, an endoscopic monitor, an 652 X-ray CT image output device, a B-ultrasonic apparatus, a cardiogram 653 generator, an MRI image instrument, etc. These devices are used to 654 provide multiple local video presentation streams to help the surgeon 655 monitor the status of the patient and assist in the surgical process. 657 The local site may have three main screens and one (or more) 658 presentation screen(s). The main screens can be used to display the 659 remote experts. The presentation screen(s) can be used to display 660 multiple presentation streams from local and remote sites 661 simultaneously. The three main cameras capture different parts of 662 the surgery room. The surgeon can decide the number, the size and 663 the placement of the presentations displayed on the local 664 presentation screen(s). He can also indicate which local 665 presentation captures are provided for the remote sites. The local 666 site can send multiple presentation captures to remote sites and it 667 can receive multiple presentations related to the patient or the 668 procedure from them. 670 One type of remote site is a single or dual screen and one camera 671 system used by a consulting expert. In the general case the remote 672 sites can be part of a multipoint Telepresence conference. The 673 presentation screens at the remote sites allow the experts to see the 674 details of the operation and related data. Like the main site, the 675 experts can decide the number, the size and the placement of the 676 presentations displayed on the presentation screens. The 677 presentation screens can display presentation streams from the 678 surgery room or from other remote sites and also local presentation 679 streams. Thus the experts can also start sending presentation 680 streams, which can carry medical records, pathology data, or their 681 reference and analysis, etc. 683 Another type of remote site is a typical immersive Telepresence room 684 with three camera/screen pairs allowing more experts to join the 685 consultation. These sites can also be used for education. The 686 teacher, who is not necessarily the surgeon, and the students are in 687 different remote sites. Students can observe and learn the details 688 of the whole procedure, while the teacher can explain and answer 689 questions during the operation. 691 All remote education sites can display the surgery room. Another 692 option is to display the surgery room on the center screen, and the 693 rest of the screens can show the teacher and the student who is 694 asking a question. For all the above sites, multiple presentation 695 screens can be used to enhance visibility: one screen for the zoomed 696 surgery stream and the others for medical image streams, such as MRI 697 images, cardiogram, B-ultrasonic images and pathology data. 699 4. Acknowledgements 701 The document has benefitted from input from a number of people 702 including Alex Eleftheriadis, Marshall Eubanks, Tommy Andre Nyquist, 703 Mark Gorzynski, Charles Eckel, Nermeen Ismail, Mary Barnes, Pascal 704 Buhler, Jim Cole. 706 Special acknowledgement to Lennard Xiao who contributed the text for 707 the telemedicine use case and to Claudio Allocchio for his detailed 708 review of the document. 710 5. IANA Considerations 712 This document contains no IANA considerations. 714 6. Security Considerations 716 While there are likely to be security considerations for any solution 717 for telepresence interoperability, this document has no security 718 considerations. 720 7. Informative References 722 [ITU.H239] 723 , "Role management and additional media channels for 724 H.300-series terminals", ITU-T Recommendation H.239, 725 September 2005. 727 [ITU.H323] 728 , "Packet-based Multimedia Communications Systems", ITU-T 729 Recommendation H.323, December 2009. 731 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 732 A., Peterson, J., Sparks, R., Handley, M., and E. 733 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 734 June 2002. 736 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 737 Jacobson, "RTP: A Transport Protocol for Real-Time 738 Applications", STD 64, RFC 3550, July 2003. 740 [RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor 741 Control Protocol (BFCP)", RFC 4582, November 2006. 743 [virtualspace] 744 Allardyce, and Randall, "Development of Teleconferencing 745 Methodologies With Emphasis on Virtual Space Videe and 746 Interactive Graphics", 1983. 748 Authors' Addresses 750 Allyn Romanow 751 Cisco 752 San Jose, CA 95134 753 US 755 Email: allyn@cisco.com 757 Stephen Botzko 758 Polycom 759 Andover, MA 01810 760 US 762 Email: stephen.botzko@polycom.com 764 Mark Duckworth 765 Polycom 766 Andover, MA 01810 767 US 769 Email: mark.duckworth@polycom.com 771 Roni Even (editor) 772 Huawei Technologies 773 Tel Aviv 774 Israel 776 Email: roni.even@mail01.huawei.com