idnits 2.17.1 draft-romanow-clue-telepresence-use-cases-02.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document doesn't use any RFC 2119 keywords, yet seems to have RFC 2119 boilerplate text. -- The document date (May 25, 2011) is 4720 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- -- Obsolete informational reference (is this intentional?): RFC 4582 (Obsoleted by RFC 8855) Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 CLUE WG A. Romanow 3 Internet-Draft Cisco 4 Intended status: Informational S. Botzko 5 Expires: November 26, 2011 M. Duckworth 6 Polycom 7 R. Even 8 Huawei Technologies 9 T. Eubanks 10 Iformata Communications 11 May 25, 2011 13 Use Cases for Telepresence Multi-streams 14 draft-romanow-clue-telepresence-use-cases-02.txt 16 Abstract 18 Telepresence conferencing systems seek to create the sense of really 19 being present. A number of techniques for handling audio and video 20 streams are used to create this experience. When these techniques 21 are not similar, interoperability between different systems is 22 difficult at best, and often not possible. Conveying information 23 about the relationships between multiple streams of media would allow 24 senders and receivers to make choices to allow telepresence systems 25 to interwork. This memo describes the most typical and important use 26 cases for sending multiple streams in a telepresence conference. 28 Status of this Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at http://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on November 26, 2011. 45 Copyright Notice 47 Copyright (c) 2011 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 64 3. Telepresence Scenarios Overview . . . . . . . . . . . . . . . 4 65 4. Use Case Scenarios . . . . . . . . . . . . . . . . . . . . . . 6 66 4.1. Point to point meeting: symmetric . . . . . . . . . . . . 6 67 4.2. Point to point meeting: asymmetric . . . . . . . . . . . . 7 68 4.3. Multipoint meeting . . . . . . . . . . . . . . . . . . . . 9 69 4.4. Presentation . . . . . . . . . . . . . . . . . . . . . . . 10 70 4.5. Heterogeneous Systems . . . . . . . . . . . . . . . . . . 11 71 4.6. Multipoint Education Usage . . . . . . . . . . . . . . . . 12 72 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13 73 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 74 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14 75 8. Informative References . . . . . . . . . . . . . . . . . . . . 14 76 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14 78 1. Introduction 80 Telepresence applications try to provide a "being there" experience 81 for conversational video conferencing. Often this telepresence 82 application is described as "immersive telepresence" in order to 83 distinguish it from traditional video conferencing, and from other 84 forms of remote presence not related to conversational video 85 conferencing, such as avatars and robots. The salient 86 characteristics of telepresence are often described as: full-sized, 87 immersive video, preserving interpersonal interaction and allowing 88 non-verbal communication. 90 Although telepresence systems are based on open standards such as RTP 91 [RFC3550], SIP [RFC3261] , H.264, and the H.323 suite of protocols, 92 they cannot easily interoperate with each other without operator 93 assistance and expensive additional equipment which translates from 94 one vendor to another. A standard way of describing the multiple 95 streams constituting the media flows and the fundamental aspects of 96 their behavior, would allow telepresence systems to interwork. 98 This draft presents a set of use cases describing typical scenarios. 99 Requirements will be derived from these use cases in a separate 100 document. The use cases are described from the viewpoint of the 101 users. They are illustrative of the user experience that needs to be 102 supported. It is possible to implement these use cases in a variety 103 of different ways. 105 Many different scenarios need to be supported. Our strategy in this 106 document is to describe in detail the most common and basic use 107 cases. These will cover most of the requirements. Additional 108 scenarios that bring new features and requirements will be added. 110 We look at telepresence conferences that are point-to-point and 111 multipoint. In some settings, the number of displays is similar at 112 all sites, in others, the number of displays differs at different 113 sites. Both cases are considered. Also included is a use case 114 describing display of presentation or content. 116 The document structure is as follows: Section 2 presents the document 117 terminology, Section 3 gives an overview of the scenarios, and 118 Section 4 describes use cases. 120 2. Terminology 122 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 123 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 124 document are to be interpreted as described in RFC 2119 [RFC2119]. 126 3. Telepresence Scenarios Overview 128 This section describes the general characteristics of the use cases 129 and what the scenarios are intended to show. The typical setting is 130 a business conference, which was the initial focus of telepresence. 131 Recently consumer products are also being developed. We specifically 132 do not include in our scenarios the infrastructure aspects of 133 telepresence, such as room construction, layout and decoration. 135 Telepresence systems are typically composed of one or more video 136 cameras and encoders and one or more display monitors of large size 137 (around 60"). Microphones pick up sound and audio codec(s)produce 138 one or more audio streams. The cameras used to present the 139 telepresence users we will call participant cameras (and likewise for 140 displays). There may also be other cameras, such as for document 141 display. These will be referred to as presentation or content 142 cameras, which generally have different formats, aspect ratios, and 143 frame rates from the participant cameras. The presentation videos 144 may be shown on participant screen, or on auxiliary display screens. 145 A user's computer may also serve as a virtual content camera, 146 generating an animation or playing back a video for display to the 147 remote participants. 149 We describe such a telepresence system as sending M video streams, N 150 audio streams, and D content streams to the remote system(s). (Note 151 that the number of audio streams is generally not the same as the 152 number of video streams.) 154 The fundamental parameters describing today's typical telepresence 155 scenario include: 157 1. The number of participating sites 159 2. The number of visible seats at a site 161 3. The number of cameras 163 4. The number of audio channels 165 5. The screen size 167 6. The display capabilities - such as resolution, frame rate, 168 aspect ratio 170 7. The arrangement of the displays in relation to each other 172 8. Similar or dissimilar number of primary screens at all sites 173 9. Type and number of presentation displays 175 10. Multipoint conference display strategies - for example, the 176 camera-to-display mappings may be static or dynamic 178 11. The camera viewpoint 180 12. The cameras fields of view and how they do or do not overlap 182 The basic features that give telepresence its distinctive 183 characteristics are implemented in disparate ways in different 184 systems. Currently Telepresence systems from diverse vendors 185 interoperate to some extent, but this is not supported in a standards 186 based fashion. Interworking requires that translation and 187 transcoding devices be included in the architecture. Such devices 188 increase latency, reducing the quality of interpersonal interaction. 189 Use of these devices is often not automatic; it frequently requires 190 substantial manual configuration and a detailed understanding of the 191 nature of underlying audio and video streams. This state of affairs 192 is not acceptable for the continued growth of telepresence - we 193 believe telepresence systems should have the same ease of 194 interoperability as do telephones. 196 There is no agreed upon way to adequately describe the semantics of 197 how streams of various media types relate to each other. Without a 198 standard for stream semantics to describe the particular roles and 199 activities of each stream in the conference, interoperability is 200 cumbersome at best. 202 In a multiple screen conference, the video and audio streams sent 203 from remote participants must be understood by receivers so that they 204 can be presented in a coherent and life-like manner. This includes 205 the ability to present remote participants at their true size for 206 their apparent distance, while maintaining correct eye contact, 207 gesticular cues, and simultaneously providing a spatial audio sound 208 stage that is consistent with the video presentation. 210 The receiving device that decides how to display incoming information 211 needs to understand a number of variables such as the spatial 212 position of the speaker, the field of view of the cameras; the camera 213 zoom; which media stream is related to each of the displays; etc. It 214 is not simply that individual streams must be adequately described, 215 to a large extent this already exists, but rather that the semantics 216 of the relationships between the streams must be communicated. Note 217 that all of this is still required even if the basic aspects of the 218 streams, such as the bit rate, frame rate, and aspect ratio, are 219 known. Thus, this problem has aspects considerably beyond those 220 encountered in interoperation of single-node video conferencing 221 units. 223 4. Use Case Scenarios 225 Our development of use cases is staged, initially focusing on what is 226 currently typical and important. Use cases that add future or more 227 specialized features will be added later as needed. Also, there are 228 a number of possible variants for these use cases, for example, the 229 audio supported may differ at the end points (such as mono or stereo 230 versus surround sound), etc. 232 The use cases here are intended to be hierarchical, in that the 233 earlier use cases describe basics of telepresence that will also be 234 used by later use cases. 236 Many of these systems offer a full conference room solution where 237 local participants sit on one side of a table and remote participants 238 are displayed as if they are sitting on the other side of the table. 239 The cameras and screens are typically arranged to provide a panoramic 240 (left to right from the local user view point) view of the remote 241 room. 243 The sense of immersion and non-verbal communication is fostered by a 244 number of technical features, such as: 246 1. Good eye contact, which is achieved by careful placement of 247 participants, cameras and screens. 249 2. Camera field of view and screen sizes are matched so that the 250 images of the remote room appear to be full size. 252 3. The left side of each room is presented on the right display at 253 the far end; similarly the right side of the room is presented on 254 the left display. The effect of this is that participants of 255 each site appear to be sitting across the table from each other. 256 If two participants on the same site glance at each other, all 257 participants can observe it. Likewise, if a participant on one 258 site gestures to a participant on the other site, all 259 participants observe the gesture itself and the participants it 260 includes. 262 4.1. Point to point meeting: symmetric 264 In this case each of the two sites has an identical number of 265 screens, with cameras having fixed fields of view, and one camera for 266 each screen. The sound type is the same at each end. As an example, 267 there could be 3 cameras and 3 screens in each room, with stereo 268 sound being sent and received at each end. 270 The important thing here is that each of the 2 sites has the same 271 number of screens. Each screen is paired with a corresponding 272 camera. Each camera / screen pair is typically connected to a 273 separate codec, producing a video encoded stream for transmission to 274 the remote site, and receiving a similarly encoded stream from the 275 remote site. 277 Each system has one or multiple microphones for capturing audio. In 278 some cases, stereophonic microphones are employed. In other systems, 279 a microphone may be placed in front of each participant (or pair of 280 participants). In typical systems all the microphones are connected 281 to a single codec that sends and receives the audio streams as either 282 stereo or surround sound. The number of microphones and the number 283 of audio channels are often not the same as the number of cameras. 284 Also the number of microphones is often not the same as the number of 285 loudspeakers. 287 The audio may be transmitted as multi-channel (stereo/surround sound) 288 or as distinct and separate monophonic streams. Audio levels should 289 be matched, so the sound levels at both sites are identical. 290 Loudspeaker and microphone placements are chosen so that the sound 291 "stage" (orientation of apparent audio sources) is coordinated with 292 the video. That is, if a participant on one site speaks, the 293 participants at the remote site perceive her voice as originating 294 from her visual image. In order to accomplish this, the audio needs 295 to be mapped at the received site in the same fashion as the video. 296 That is, audio received from the right side of the room needs to be 297 output from loudspeaker(s) on the left side at the remote site, and 298 vice versa. 300 4.2. Point to point meeting: asymmetric 302 In this case, each site has a different number of screens and cameras 303 than the other site. The important characteristic of this scenario 304 is that the number of displays is different between the two sites. 305 This creates challenges which are handled differently by different 306 telepresence systems. 308 This use case builds on the basic scenario of 3 screens to 3 screens. 309 Here, we use the common case of 3 screens and 3 cameras at one site, 310 and 1 screen and 1 camera at the other site, connected by a point to 311 point call. The display sizes and camera fields of view at both 312 sites are basically similar, such that each camera view is designed 313 to show two people sitting side by side. Thus the 1 screen room has 314 up to 2 people seated at the table, while the 3 screen room may have 315 up to 6 people at the table. 317 The basic considerations of defining left and right and indicating 318 relative placement of the multiple audio and video streams are the 319 same as in the 3-3 use case. However, handling the mismatch between 320 the two sites of the number of displays and cameras requires more 321 complicated maneuvers. 323 For the video sent from the 1 camera room to the 3 screen room, 324 usually what is done is to simply use 1 of the 3 displays and keep 325 the second and third displays inactive, or put up the date, for 326 example. This would maintain the "full size" image of the remote 327 side. 329 For the other direction, the 3 camera room sending video to the 1 330 screen room, there are more complicated variations to consider. Here 331 are several possible ways in which the video streams can be handled. 333 1. The 1 screen system might simply show only 1 of the 3 camera 334 images, since the receiving side has only 1 screen. Two people 335 are seen at full size, but 4 people are not seen at all. The 336 choice of which 1 of the 3 streams to display could be fixed, or 337 could be selected by the users. It could also be made 338 automatically based on who is speaking in the 3 screen room, such 339 that the people in the 1 screen room always see the person who is 340 speaking. If the automatic selection is done at the sender, the 341 transmission of streams that are not displayed could be 342 suppressed, which would avoid wasting bandwidth. 344 2. The 1 screen system might be capable of receiving and decoding 345 all 3 streams from all 3 cameras. The 1 screen system could then 346 compose the 3 streams into 1 local image for display on the 347 single screen. All six people would be seen, but smaller than 348 full size. This could be done in conjunction with reducing the 349 image resolution of the streams, such that encode/decode 350 resources and bandwidth are not wasted on streams that will be 351 downsized for display anyway. 353 3. The 3 screen system might be capable of including all 6 people in 354 a single stream to send to the 1 screen system. For example, it 355 could use PTZ (Pan Tilt Zoom) cameras to physically adjust the 356 cameras such that 1 camera captures the whole room of six people. 357 Or it could recompose the 3 camera images into 1 encoded stream 358 to send to the remote site. These variations also show all six 359 people, but at a reduced size. 361 4. Or, there could be a combination of these approaches, such as 362 simultaneously showing the speaker in full size with a composite 363 of all the 6 participants in smaller size. 365 The receiving telepresence system needs to have information about the 366 content of the streams it receives to make any of these decisions. 367 If the systems are capable of supporting more than one strategy, 368 there needs to be some negotiation between the two sites to figure 369 out which of the possible variations they will use in a specific 370 point to point call. 372 4.3. Multipoint meeting 374 In a multipoint telepresence conference, there are more than two 375 sites participating. Additional complexity is required to enable 376 media streams from each participant to show up on the displays of the 377 other participants. 379 Clearly, there are a great number of topologies that can be used to 380 display the streams from multiple sites participating in a 381 conference. 383 One major objective for telepresence is to be able to preserve the 384 "Being there" user experience. However, in multi-site conferences it 385 is often (in fact usually) not possible to simultaneously provide 386 full size video, eye contact, common perception of gestures and gaze 387 by all participants. Several policies can be used for stream 388 distribution and display: all provide good results but they all make 389 different compromises. 391 One common policy is called site switching. Let's say the speaker is 392 at site A and everyone else is at a "remote" site. When the room at 393 site A shown, all the camera images from site A are forwarded to the 394 remote sites. Therefore at each receiving remote site, all the 395 screens display camera images from site A. This can be used to 396 preserve full size image display, and also provide full visual 397 context of the displayed far end, site A. In site switching, there is 398 a fixed relation between the cameras in each room and the displays in 399 remote rooms. The room or participants being shown is switched from 400 time to time based on who is speaking or by manual control, e.g., 401 from site A to site B. 403 Segment switching is another policy choice. Still using site A as 404 where the speaker is, and "remote" to refer to all the other sites, 405 in segment switching, rather than sending all the images from site A, 406 only the speaker at site A is shown. The camera images of the 407 current speaker and previous speakers (if any) are forwarded to the 408 other sites in the conference. Therefore the screens in each site 409 are usually displaying images from different remote sites - the 410 current speaker at site A and the previous ones. This strategy can 411 be used to preserve full size image display, and also capture the 412 non-verbal communication between the speakers. In segment switching, 413 the display depends on the activity in the remote rooms - generally, 414 but not necessarily based on audio / speech detection). 416 A third possibility is to reduce the image size so that multiple 417 camera views can be composited onto one or more screens. This does 418 not preserve full size image display, but provides the most visual 419 context (since more sites or segments can be seen). Typically in 420 this case the display mapping is static, i.e., each part of each room 421 is shown in the same location on the display screens throughout the 422 conference. 424 Other policies and combinations are also possible. For example, 425 there can be a static display of all screens from all remote rooms, 426 with part or all of one screen being used to show the current speaker 427 at full size. 429 4.4. Presentation 431 In addition to the video and audio streams showing the participants, 432 additional streams are used for presentations. 434 In systems available today, generally only one additional video 435 stream is available for presentations. Often this presentation 436 stream is half-duplex in nature, with presenters taking turns. The 437 presentation video may be captured from a PC screen, or it may come 438 from a multimedia source such as a document camera, camcorder or a 439 DVD. In a multipoint meeting, the presentation streams for the 440 currently active presentation are always distributed to all sites in 441 the meeting, so that the presentations are viewed by all. 443 Some systems display the presentation video on a screen that is 444 mounted either above or below the three participant screens. Other 445 systems provide monitors on the conference table for observing 446 presentations. If multiple presentation monitors are used, they 447 generally display identical content. There is considerable variation 448 in the placement, number, and size or presentation displays. 450 In some systems presentation audio is pre-mixed with the room audio. 451 In others, a separate presentation audio stream is provided (if the 452 presentation includes audio). 454 In H.323 systems, H.239 is typically used to control the video 455 presentation stream. In SIP systems, similar control mechanisms can 456 be provided using BFCP [RFC4582] for presentation token. These 457 mechanisms are suitable for managing a single presentation stream. 459 Although today's systems remain limited to a single video 460 presentation stream, there are obvious uses for multiple presentation 461 streams. 463 1. Frequently the meeting convener is following a meeting agenda, 464 and it is useful for her to be able to show that agenda to all 465 participants during the meeting. Other participants at various 466 remote sites are able to make presentations during the meeting, 467 with the presenters taking turns. The presentations and the 468 agenda are both shown, either on separate displays, or perhaps 469 re-scaled and shown on a single display. 471 2. A single multimedia presentation can itself include multiple 472 video streams that should be shown together. For instance, a 473 presenter may be discussing the fairness of media coverage. In 474 addition to slides which support the presenter's conclusions, she 475 also has video excerpts from various news programs which she 476 shows to illustrate her findings. She uses a DVD player for the 477 video excerpts so that she can pause and reposition the video as 478 needed. Another example is an educator who is presenting a 479 multi-screen slide show. This show requires that the placement 480 of the images on the multiple displays at each site be 481 consistent. 483 There are many other examples where multiple presentation streams are 484 useful. 486 4.5. Heterogeneous Systems 488 It is common in meeting scenarios for people to join the conference 489 from a variety of environments, using different types of endpoint 490 devices. In a multi-screen immersive telepresence conference may 491 include someone on a PC-based video conferencing system, a 492 participant calling in by phone, and (soon) someone on a handheld 493 device. 495 What experience/view will each of these devices have? 497 Some may be able to handle multiple streams and others can handle 498 only a single stream. (We are not here talking about legacy systems, 499 but rather systems built to participate in such a conference, 500 although they are single stream only.) In a single video stream , 501 the stream may contain one or more compositions depending on the 502 available screen space on the device. In most cases a transcoding 503 intermediate device will be relied upon to produce a single stream, 504 perhaps with some kind of continuous presence. 506 Bit rates will vary - the handheld and phone having lower bit rates 507 than PC and multi-screen systems. 509 Layout is accomplished according to different policies. For example, 510 a handheld and PC may receive the active speaker stream. The 511 decision can either be made explicitly by the receiver or by the 512 sender if it can receive some kind of rendering hint. The same is 513 true for audio -- i. e., that it receives a mixed stream or a number 514 of the loudest speakers if mixing is not available in the network. 516 For the software conferencing participant, the user's experience 517 depends on the application. It could be single stream, similar to a 518 handheld but with a bigger screen. Or, it could be multiple streams, 519 similar to an immersive but with a smaller screen. Control for 520 manipulation of streams can be local in the software application, or 521 in another location and sent to the application over the network. 523 The handheld device is the most extreme. How will that participant 524 be viewed and heard? it should be an equal participant, though the 525 bandwidth will be significantly less than an immersive system. A 526 receiver may choose to display output coming from a handheld 527 differently based on the resolution, but that would be the case with 528 any low resolution video stream, e. g., from a powerful PC on a bad 529 network. 531 The handheld will send and receive a single video stream, which could 532 be a composite or a subset of the conference. The handheld could say 533 what it wants or could accept whatever the sender (conference server 534 or sending endpoint) thinks is best. The handheld will have to 535 signal any actions it wants to take the same way that immersive 536 signals. 538 4.6. Multipoint Education Usage 540 The importance of this example is that the multiple video streams are 541 not used to create an immersive conferencing experience with 542 panoramic views at all the site. Instead the multiple streams are 543 dynamically used to enable full participation of remote students in a 544 university class. In some instances the same video stream is 545 displayed on multiple displays in the room, in other instances an 546 available stream is not displayed at all. 548 The main site is a university auditorium which is equipped with three 549 cameras. One camera is focused on the professor at the podium. A 550 second camera is mounted on the wall behind the professor and 551 captures the class in its entirety. The third camera is co-located 552 with the second, and is designed to capture a close up view of a 553 questioner in the audience. It automatically zooms in on that 554 student using sound localization. 556 Although the auditorium is equipped with three cameras, it is only 557 equipped with two screens. One is a large screen located at the 558 front so that the class can see it. The other is located at the rear 559 so the professor can see it. When someone asks a question, the front 560 screen shows the questioner. Otherwise it shows the professor 561 (ensuring everyone can easily see her). 563 The remote sites are typical immersive telepresence room with three 564 camera/screen pairs. 566 All remote sites display the professor on the center screen at full 567 size. A second screen shows the entire classroom view when the 568 professor is speaking. However, when a student asks a question, the 569 second screen shows the close up view of the student at full size. 570 Sometimes the student is in the auditorium; sometimes the speaking 571 student is at another remote site. The remote systems never display 572 the students that are actually in that room. 574 If someone at the remote site asks a question, then the screen in the 575 auditorium will show the remote student at full size (as if they were 576 present in the auditorium itself). The display in the rear also 577 shows this questioner, allowing the professor to see and respond to 578 the student without needing to turn her back on the main class. 580 When no one is asking a question, the screen in the rear briefly 581 shows a full-room view of each remote site in turn, allowing the 582 professor to monitor the entire class (remote and local students). 583 The professor can also use a control on the podium to see a 584 particular site - she can choose either a full-room view or a single 585 camera view. 587 Realization of this use case does not require any negotiation between 588 the participating sites. Endpoint devices (and an MCU if present) - 589 need to know who is speaking and what video stream includes the view 590 of that speaker. The remote systems need some knowledge of which 591 stream should be placed in the center. The ability of the professor 592 to see specific sites (or for the system to show all the sites in 593 turn) would also require the auditorium system to know what sites are 594 available, and to be able to request a particular view of any site. 595 Bandwidth is optimized if video that is not being shown at a 596 particular site is not distributed to that site. 598 5. Acknowledgements 600 The draft has benefitted from input from a number of people including 601 Alex Eleftheriadis, Tommy Andre Nyquist, Mark Gorzynski, Charles 602 Eckel, Nermeen Ismail, Mary Barnes, Pascal Buhler, Jim Cole. 604 6. IANA Considerations 606 This document contains no IANA considerations. 608 7. Security Considerations 610 While there are likely to be security considerations for any solution 611 for telepresence interoperability, this document has no security 612 considerations. 614 8. Informative References 616 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 617 Requirement Levels", BCP 14, RFC 2119, March 1997. 619 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 620 A., Peterson, J., Sparks, R., Handley, M., and E. 621 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 622 June 2002. 624 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 625 Jacobson, "RTP: A Transport Protocol for Real-Time 626 Applications", STD 64, RFC 3550, July 2003. 628 [RFC4582] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor 629 Control Protocol (BFCP)", RFC 4582, November 2006. 631 Authors' Addresses 633 Allyn Romanow 634 Cisco 635 San Jose, CA 95134 636 US 638 Email: allyn@cisco.com 640 Stephen Botzko 641 Polycom 642 Andover, MA 01810 643 US 645 Email: stephen.botzko@polycom.com 646 Mark Duckworth 647 Polycom 648 Andover, MA 01810 649 US 651 Email: mark.duckworth@polycom.com 653 Roni Even 654 Huawei Technologies 655 Tel Aviv, 656 Israel 658 Email: even.roni@huawei.com 660 Marshall Eubanks 661 Iformata Communications 662 Dayton, Ohio 45402 663 US 665 Email: marshall.eubanks@ilformata.com