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Some of the information which could possibly introduce privacy concerns is the xCard information as described in section x. In addition, the (text) description field in the Media Capture attribute (section 7.1.1.7) could possibly reveal sensitive information or specific identities. The same would be true for the descriptions in the Capture Scene (section 7.3.1) and Capture Scene Entry (7.3.2) attributes. One other important consideration for the information in the xCard as well as the description field in the Media Capture and Capture Scene Entry attributes is that while the endpoints involved in the session have been authenticated, there is no assurance that the information in the xCard or description fields is authentic. Thus, this information SHOULD not be used to make any authorization decisions and the participants in the sessions SHOULD be made aware of this. -- The document date (May 15, 2014) is 3634 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. 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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 CLUE WG M. Duckworth, Ed. 2 Internet Draft Polycom 3 Intended status: Standards Track A. Pepperell 4 Expires: November 15, 2014 Acano 5 S. Wenger 6 Vidyo 7 May 15, 2014 9 Framework for Telepresence Multi-Streams 10 draft-ietf-clue-framework-15.txt 12 Abstract 14 This document defines a framework for a protocol to enable devices 15 in a telepresence conference to interoperate. The protocol enables 16 communication of information about multiple media streams so a 17 sending system and receiving system can make reasonable decisions 18 about transmitting, selecting and rendering the media streams. 19 This protocol is used in addition to SIP signaling for setting up a 20 telepresence session. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current 30 Internet-Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or obsoleted by other 34 documents at any time. It is inappropriate to use Internet-Drafts 35 as reference material or to cite them other than as "work in 36 progress." 38 This Internet-Draft will expire on November 15, 2014. 40 Copyright Notice 42 Copyright (c) 2013 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with 50 respect to this document. Code Components extracted from this 51 document must include Simplified BSD License text as described in 52 Section 4.e of the Trust Legal Provisions and are provided without 53 warranty as described in the Simplified BSD License. 55 Table of Contents 57 1. Introduction...................................................3 58 2. Terminology....................................................4 59 3. Definitions....................................................4 60 4. Overview & Motivation..........................................7 61 5. Overview of the Framework/Model................................9 62 6. Spatial Relationships.........................................15 63 7. Media Captures and Capture Scenes.............................16 64 7.1. Media Captures...........................................16 65 7.1.1. Media Capture Attributes............................17 66 7.2. Multiple Content Capture.................................22 67 7.2.1. MCC Attributes......................................23 68 7.3. Capture Scene............................................28 69 7.3.1. Capture Scene attributes............................31 70 7.3.2. Capture Scene Entry attributes......................32 71 8. Simultaneous Transmission Set Constraints.....................33 72 9. Encodings.....................................................35 73 9.1. Individual Encodings.....................................35 74 9.2. Encoding Group...........................................36 75 9.3. Associating Captures with Encoding Groups................37 76 10. Consumer's Choice of Streams to Receive from the Provider....38 77 10.1. Local preference........................................41 78 10.2. Physical simultaneity restrictions......................41 79 10.3. Encoding and encoding group limits......................41 80 11. Extensibility................................................42 81 12. Examples - Using the Framework (Informative).................42 82 12.1. Provider Behavior.......................................42 83 12.1.1. Three screen Endpoint Provider.....................43 84 12.1.2. Encoding Group Example.............................49 85 12.1.3. The MCU Case.......................................50 86 12.2. Media Consumer Behavior.................................51 87 12.2.1. One screen Media Consumer..........................51 88 12.2.2. Two screen Media Consumer configuring the example..52 89 12.2.3. Three screen Media Consumer configuring the example53 90 12.3. Multipoint Conference utilizing Multiple Content Captures53 91 12.3.1. Single Media Captures and MCC in the same 92 Advertisement..............................................53 93 12.3.2. Several MCCs in the same Advertisement.............56 94 12.3.3. Heterogeneous conference with switching and 95 composition................................................58 96 13. Acknowledgements.............................................67 97 14. IANA Considerations..........................................67 98 15. Security Considerations......................................68 99 16. Changes Since Last Version...................................69 100 17. Authors' Addresses...........................................75 102 1. Introduction 104 Current telepresence systems, though based on open standards such 105 as RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with 106 each other. A major factor limiting the interoperability of 107 telepresence systems is the lack of a standardized way to describe 108 and negotiate the use of the multiple streams of audio and video 109 comprising the media flows. This document provides a framework for 110 protocols to enable interoperability by handling multiple streams 111 in a standardized way. The framework is intended to support the 112 use cases described in draft-ietf-clue-telepresence-use-cases and 113 to meet the requirements in draft-ietf-clue-telepresence- 114 requirements. 116 The basic session setup for the use cases is based on SIP [RFC3261] 117 and SDP offer/answer [RFC3264]. In addition to basic SIP & SDP 118 offer/answer, CLUE specific signaling is required to exchange the 119 information describing the multiple media streams. The motivation 120 for this framework, an overview of the signaling, and information 121 required to be exchanged is described in subsequent sections of 122 this document. The signaling details and data model are provided 123 in subsequent documents. 125 2. Terminology 127 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 128 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 129 this document are to be interpreted as described in RFC 2119 130 [RFC2119]. 132 3. Definitions 134 The terms defined below are used throughout this document and 135 companion documents and they are normative. In order to easily 136 identify the use of a defined term, those terms are capitalized. 138 Advertisement: a CLUE message a Media Provider sends to a Media 139 Consumer describing specific aspects of the content of the media, 140 the formatting of the media streams it can send, and any 141 restrictions it has in terms of being able to provide certain 142 Streams simultaneously. 144 Audio Capture: Media Capture for audio. Denoted as ACn in the 145 example cases in this document. 147 Camera-Left and Right: For Media Captures, camera-left and camera- 148 right are from the point of view of a person observing the rendered 149 media. They are the opposite of Stage-Left and Stage-Right. 151 Capture: Same as Media Capture. 153 Capture Device: A device that converts audio and video input into 154 an electrical signal, in most cases to be fed into a media encoder. 156 Capture Encoding: A specific encoding of a Media Capture, to be 157 sent by a Media Provider to a Media Consumer via RTP. 159 Capture Scene: a structure representing a spatial region containing 160 one or more Capture Devices, each capturing media representing a 161 portion of the region. The spatial region represented by a Capture 162 Scene MAY or may not correspond to a real region in physical space, 163 such as a room. A Capture Scene includes attributes and one or 164 more Capture Scene Entries, with each entry including one or more 165 Media Captures. 167 Capture Scene Entry (CSE): a list of Media Captures of the same 168 media type that together form one way to represent the entire 169 Capture Scene. 171 Conference: used as defined in [RFC4353], A Framework for 172 Conferencing within the Session Initiation Protocol (SIP). 174 Configure Message: A CLUE message a Media Consumer sends to a Media 175 Provider specifying which content and media streams it wants to 176 receive, based on the information in a corresponding Advertisement 177 message. 179 Consumer: short for Media Consumer. 181 Encoding or Individual Encoding: a set of parameters representing a 182 way to encode a Media Capture to become a Capture Encoding. 184 Encoding Group: A set of encoding parameters representing a total 185 media encoding capability to be sub-divided across potentially 186 multiple Individual Encodings. 188 Endpoint: The logical point of final termination through receiving, 189 decoding and rendering, and/or initiation through capturing, 190 encoding, and sending of media streams. An endpoint consists of 191 one or more physical devices which source and sink media streams, 192 and exactly one [RFC4353] Participant (which, in turn, includes 193 exactly one SIP User Agent). Endpoints can be anything from 194 multiscreen/multicamera rooms to handheld devices. 196 Front: the portion of the room closest to the cameras. In going 197 towards back you move away from the cameras. 199 MCU: Multipoint Control Unit (MCU) - a device that connects two or 200 more endpoints together into one single multimedia conference 201 [RFC5117]. An MCU includes an [RFC4353] like Mixer, without the 202 [RFC4353] requirement to send media to each participant. 204 Media: Any data that, after suitable encoding, can be conveyed over 205 RTP, including audio, video or timed text. 207 Media Capture: a source of Media, such as from one or more Capture 208 Devices or constructed from other Media streams. 210 Media Consumer: an Endpoint or middle box that receives Media 211 streams 213 Media Provider: an Endpoint or middle box that sends Media streams 214 Model: a set of assumptions a telepresence system of a given vendor 215 adheres to and expects the remote telepresence system(s) also to 216 adhere to. 218 Multiple Content Capture: A Capture for audio or video that 219 indicates that the Capture contains multiple audio or video 220 Captures. Single Media Captures may or may not be present in the 221 resultant Capture Encoding depending on time or space. Denoted as 222 MCCn in the example cases in this document. 224 Plane of Interest: The spatial plane containing the most relevant 225 subject matter. 227 Provider: Same as Media Provider. 229 Render: the process of generating a representation from a media, 230 such as displayed motion video or sound emitted from loudspeakers. 232 Simultaneous Transmission Set: a set of Media Captures that can be 233 transmitted simultaneously from a Media Provider. 235 Single Media Capture: A capture which contains media from a single 236 source capture device, i.e. audio capture, video capture. 238 Spatial Relation: The arrangement in space of two objects, in 239 contrast to relation in time or other relationships. See also 240 Camera-Left and Right. 242 Stage-Left and Right: For Media Captures, Stage-left and Stage- 243 right are the opposite of Camera-left and Camera-right. For the 244 case of a person facing (and captured by) a camera, Stage-left and 245 Stage-right are from the point of view of that person. 247 Stream: a Capture Encoding sent from a Media Provider to a Media 248 Consumer via RTP [RFC3550]. 250 Stream Characteristics: the media stream attributes commonly used 251 in non-CLUE SIP/SDP environments (such as: media codec, bit rate, 252 resolution, profile/level etc.) as well as CLUE specific 253 attributes, such as the Capture ID or a spatial location. 255 Video Capture: Media Capture for video. Denoted as VCn in the 256 example cases in this document. 258 Video Composite: A single image that is formed, normally by an RTP 259 mixer inside an MCU, by combining visual elements from separate 260 sources. 262 4. Overview & Motivation 264 This section provides an overview of the functional elements 265 defined in this document to represent a telepresence system. The 266 motivations for the framework described in this document are also 267 provided. 269 Two key concepts introduced in this document are the terms "Media 270 Provider" and "Media Consumer". A Media Provider represents the 271 entity that is sending the media and a Media Consumer represents 272 the entity that is receiving the media. A Media Provider provides 273 Media in the form of RTP packets, a Media Consumer consumes those 274 RTP packets. Media Providers and Media Consumers can reside in 275 Endpoints or in middleboxes such as Multipoint Control Units 276 (MCUs). A Media Provider in an Endpoint is usually associated 277 with the generation of media for Media Captures; these Media 278 Captures are typically sourced from cameras, microphones, and the 279 like. Similarly, the Media Consumer in an Endpoint is usually 280 associated with renderers, such as screens and loudspeakers. In 281 middleboxes, Media Providers and Consumers can have the form of 282 outputs and inputs, respectively, of RTP mixers, RTP translators, 283 and similar devices. Typically, telepresence devices such as 284 Endpoints and middleboxes would perform as both Media Providers 285 and Media Consumers, the former being concerned with those 286 devices' transmitted media and the latter with those devices' 287 received media. In a few circumstances, a CLUE Endpoint middlebox 288 includes only Consumer or Provider functionality, such as 289 recorder-type Consumers or webcam-type Providers. 291 The motivations for the framework outlined in this document 292 include the following: 294 (1) Endpoints in telepresence systems typically have multiple Media 295 Capture and Media Render devices, e.g., multiple cameras and 296 screens. While previous system designs were able to set up calls 297 that would capture media using all cameras and display media on all 298 screens, for example, there is no mechanism that can associate 299 these Media Captures with each other in space and time. 301 (2) The mere fact that there are multiple capture and rendering 302 devices, each of which may be configurable in aspects such as zoom, 303 leads to the difficulty that a variable number of such devices can 304 be used to capture different aspects of a region. The Capture 305 Scene concept allows for the description of multiple setups for 306 those multiple capture devices that could represent sensible 307 operation points of the physical capture devices in a room, chosen 308 by the operator. A Consumer can pick and choose from those 309 configurations based on its rendering abilities and inform the 310 Provider about its choices. Details are provided in section 7. 312 (3) In some cases, physical limitations or other reasons disallow 313 the concurrent use of a device in more than one setup. For 314 example, the center camera in a typical three-camera conference 315 room can set its zoom objective either to capture only the middle 316 few seats, or all seats of a room, but not both concurrently. The 317 Simultaneous Transmission Set concept allows a Provider to signal 318 such limitations. Simultaneous Transmission Sets are part of the 319 Capture Scene description, and discussed in section 8. 321 (4) Often, the devices in a room do not have the computational 322 complexity or connectivity to deal with multiple encoding options 323 simultaneously, even if each of these options is sensible in 324 certain scenarios, and even if the simultaneous transmission is 325 also sensible (i.e. in case of multicast media distribution to 326 multiple endpoints). Such constraints can be expressed by the 327 Provider using the Encoding Group concept, described in section 9. 329 (5) Due to the potentially large number of RTP flows required for a 330 Multimedia Conference involving potentially many Endpoints, each of 331 which can have many Media Captures and media renderers, it has 332 become common to multiplex multiple RTP media flows onto the same 333 transport address, so to avoid using the port number as a 334 multiplexing point and the associated shortcomings such as 335 NAT/firewall traversal. While the actual mapping of those RTP 336 flows to the header fields of the RTP packets is not subject of 337 this specification, the large number of possible permutations of 338 sensible options a Media Provider can make available to a Media 339 Consumer makes a mechanism desirable that allows to narrow down the 340 number of possible options that a SIP offer-answer exchange has to 341 consider. Such information is made available using protocol 342 mechanisms specified in this document and companion documents, 343 although it should be stressed that its use in an implementation is 344 OPTIONAL. Also, there are aspects of the control of both Endpoints 345 and middleboxes/MCUs that dynamically change during the progress of 346 a call, such as audio-level based screen switching, layout changes, 347 and so on, which need to be conveyed. Note that these control 348 aspects are complementary to those specified in traditional SIP 349 based conference management such as BFCP. An exemplary call flow 350 can be found in section 5. 352 Finally, all this information needs to be conveyed, and the notion 353 of support for it needs to be established. This is done by the 354 negotiation of a "CLUE channel", a data channel negotiated early 355 during the initiation of a call. An Endpoint or MCU that rejects 356 the establishment of this data channel, by definition, is not 357 supporting CLUE based mechanisms, whereas an Endpoint or MCU that 358 accepts it is REQUIRED to use it to the extent specified in this 359 document and its companion documents. 361 5. Overview of the Framework/Model 363 The CLUE framework specifies how multiple media streams are to be 364 handled in a telepresence conference. 366 A Media Provider (transmitting Endpoint or MCU) describes specific 367 aspects of the content of the media and the formatting of the media 368 streams it can send in an Advertisement; and the Media Consumer 369 responds to the Media Provider by specifying which content and 370 media streams it wants to receive in a Configure message. The 371 Provider then transmits the asked-for content in the specified 372 streams. 374 This Advertisement and Configure MUST occur during call initiation 375 but MAY also happen at any time throughout the call, whenever there 376 is a change in what the Consumer wants to receive or (perhaps less 377 common) the Provider can send. 379 An Endpoint or MCU typically act as both Provider and Consumer at 380 the same time, sending Advertisements and sending Configurations in 381 response to receiving Advertisements. (It is possible to be just 382 one or the other.) 384 The data model is based around two main concepts: a Capture and an 385 Encoding. A Media Capture (MC), such as audio or video, describes 386 the content a Provider can send. Media Captures are described in 387 terms of CLUE-defined attributes, such as spatial relationships and 388 purpose of the capture. Providers tell Consumers which Media 389 Captures they can provide, described in terms of the Media Capture 390 attributes. 392 A Provider organizes its Media Captures into one or more Capture 393 Scenes, each representing a spatial region, such as a room. A 394 Consumer chooses which Media Captures it wants to receive from each 395 Capture Scene. 397 In addition, the Provider can send the Consumer a description of 398 the Individual Encodings it can send in terms of the media 399 attributes of the Encodings, in particular, audio and video 400 parameters such as bandwidth, frame rate, macroblocks per second. 401 Note that this is OPTIONAL, and intended to minimize the number of 402 options a later SDP offer-answer would have to include in the SDP 403 in case of complex setups, as should become clearer shortly when 404 discussing an outline of the call flow. 406 The Provider can also specify constraints on its ability to provide 407 Media, and a sensible design choice for a Consumer is to take these 408 into account when choosing the content and Capture Encodings it 409 requests in the later offer-answer exchange. Some constraints are 410 due to the physical limitations of devices--for example, a camera 411 may not be able to provide zoom and non-zoom views simultaneously. 412 Other constraints are system based, such as maximum bandwidth and 413 maximum video coding performance measured in macroblocks/second. 415 The following diagram illustrates the information contained in an 416 Advertisement. 418 ................................................................... 419 . Provider Advertisement . 420 . . 421 . +------------------------+ +--------------------+ . 422 . | Capture Scene N | | Simultaneous | . 423 . +-+----------------------+ | +--------------------+ . 424 . | Capture Scene 2 | | . 425 . +-+----------------------+ | | +----------------------+ . 426 . | Capture Scene 1 | | | | Encoding Group N | . 427 . | +---------------+ | | | +-+--------------------+ | . 428 . | | Attributes | | | | | Encoding Group 2 | | . 429 . | +---------------+ | | | +-+--------------------+ | | . 430 . | | | | | Encoding Group 1 | | | . 431 . | +----------------+ | | | | parameters | | | . 432 . | | E n t r i e s | | | | | | | | . 433 . | | +---------+ | | | | | +-------------------+| | | . 434 . | | |Attribute| | | | | | | V i d e o || | | . 435 . | | +---------+ | | | | | | E n c o d i n g s || | | . 436 . | | | | | | | | Encoding 1 || | | . 437 . | | Entry 1 | | | | | | (parameters) || | | . 438 . | | (list of MCs) | | |-+ | +-------------------+| | | . 439 . | +----|-|--|------+ |-+ | | | | . 440 . +---------|-|--|---------+ | +-------------------+| | | . 441 . | | | | | A u d i o || | | . 442 . | | | | | E n c o d i n g s || | | . 443 . v | | | | Encoding 1 || | | . 444 . +---------|--|--------+ | | (ID,maxBandwidth) || | | . 445 . | Media Capture N |------>| +-------------------+| | | . 446 . +-+---------v--|------+ | | | | | . 447 . | Media Capture 2 | | | | |-+ . 448 . +-+--------------v----+ |-------->| | | . 449 . | Media Capture 1 | | | | |-+ . 450 . | +----------------+ |---------->| | . 451 . | | Attributes | | |_+ +----------------------+ . 452 . | +----------------+ |_+ . 453 . +---------------------+ . 454 . . 455 ................................................................... 456 Figure 1: Advertisement Structure 458 A very brief outline of the call flow used by a simple system (two 459 Endpoints) in compliance with this document can be described as 460 follows, and as shown in the following figure. 462 +-----------+ +-----------+ 463 | Endpoint1 | | Endpoint2 | 464 +----+------+ +-----+-----+ 465 | INVITE (BASIC SDP+CLUECHANNEL) | 466 |--------------------------------->| 467 | 200 0K (BASIC SDP+CLUECHANNEL)| 468 |<---------------------------------| 469 | ACK | 470 |--------------------------------->| 471 | | 472 |<################################>| 473 | BASIC SDP MEDIA SESSION | 474 |<################################>| 475 | | 476 | CONNECT (CLUE CTRL CHANNEL) | 477 |=================================>| 478 | ... | 479 |<================================>| 480 | CLUE CTRL CHANNEL ESTABLISHED | 481 |<================================>| 482 | | 483 | ADVERTISEMENT 1 | 484 |*********************************>| 485 | ADVERTISEMENT 2 | 486 |<*********************************| 487 | | 488 | CONFIGURE 1 | 489 |<*********************************| 490 | CONFIGURE 2 | 491 |*********************************>| 492 | | 493 | REINVITE (UPDATED SDP) | 494 |--------------------------------->| 495 | 200 0K (UPDATED SDP)| 496 |<---------------------------------| 497 | ACK | 498 |--------------------------------->| 499 | | 500 |<################################>| 501 | UPDATED SDP MEDIA SESSION | 502 |<################################>| 503 | | 504 v v 506 Figure 2: Basic Information Flow 508 An initial offer/answer exchange establishes a basic media session, 509 for example audio-only, and a CLUE channel between two Endpoints. 510 With the establishment of that channel, the endpoints have 511 consented to use the CLUE protocol mechanisms and, therefore, MUST 512 adhere to the CLUE protocol suite as outlined herein. 514 Over this CLUE channel, the Provider in each Endpoint conveys its 515 characteristics and capabilities by sending an Advertisement as 516 specified herein. The Advertisement is typically not sufficient to 517 set up all media. The Consumer in the Endpoint receives the 518 information provided by the Provider, and can use it for two 519 purposes. First, it MUST construct and send a CLUE Configure 520 message to tell the Provider what the Consumer wishes to receive. 521 Second, it MAY, but is not necessarily REQUIRED to, use the 522 information provided to tailor the SDP it is going to send during 523 the following SIP offer/answer exchange, and its reaction to SDP it 524 receives in that step. It is often a sensible implementation 525 choice to do so, as the representation of the media information 526 conveyed over the CLUE channel can dramatically cut down on the 527 size of SDP messages used in the O/A exchange that follows. 528 Spatial relationships associated with the Media can be included in 529 the Advertisement, and it is often sensible for the Media Consumer 530 to take those spatial relationships into account when tailoring the 531 SDP. 533 This CLUE exchange MUST be followed by an SDP offer answer exchange 534 that not only establishes those aspects of the media that have not 535 been "negotiated" over CLUE, but has also the side effect of 536 setting up the media transmission itself, involving potentially 537 security exchanges, ICE, and whatnot. This step is plain vanilla 538 SIP, with the exception that the SDP used herein, in most (but not 539 necessarily all) cases can be considerably smaller than the SDP a 540 system would typically need to exchange if there were no pre- 541 established knowledge about the Provider and Consumer 542 characteristics. (The need for cutting down SDP size is not quite 543 obvious for a point-to-point call involving simple endpoints; 544 however, when considering a large multipoint conference involving 545 many multi-screen/multi-camera endpoints, each of which can operate 546 using multiple codecs for each camera and microphone, it becomes 547 perhaps somewhat more intuitive.) 549 During the lifetime of a call, further exchanges MAY occur over the 550 CLUE channel. In some cases, those further exchanges lead to a 551 modified system behavior of Provider or Consumer (or both) without 552 any other protocol activity such as further offer/answer exchanges. 553 For example, voice-activated screen switching, signaled over the 554 CLUE channel, ought not to lead to heavy-handed mechanisms like SIP 555 re-invites. However, in other cases, after the CLUE negotiation an 556 additional offer/answer exchange becomes necessary. For example, 557 if both sides decide to upgrade the call from a single screen to a 558 multi-screen call and more bandwidth is required for the additional 559 video channels compared to what was previously negotiated using 560 offer/answer, a new O/A exchange is REQUIRED. 562 One aspect of the protocol outlined herein and specified in more 563 detail in companion documents is that it makes available 564 information regarding the Provider's capabilities to deliver Media, 565 and attributes related to that Media such as their spatial 566 relationship, to the Consumer. The operation of the renderer 567 inside the Consumer is unspecified in that it can choose to ignore 568 some information provided by the Provider, and/or not render media 569 streams available from the Provider (although it MUST follow the 570 CLUE protocol and, therefore, MUST gracefully receive and respond 571 (through a Configure) to the Provider's information). All CLUE 572 protocol mechanisms are OPTIONAL in the Consumer in the sense that, 573 while the Consumer MUST be able to receive (and, potentially, 574 gracefully acknowledge) CLUE messages, it is free to ignore the 575 information provided therein. Obviously, this is not a 576 particularly sensible design choice in almost all conceivable 577 cases. 579 A CLUE-implementing device interoperates with a device that does 580 not support CLUE, because the non-CLUE device does, by definition, 581 not understand the offer of a CLUE channel in the initial 582 offer/answer exchange and, therefore, will reject it. This 583 rejection MUST be used as the indication to the CLUE-implementing 584 device that the other side of the communication is not compliant 585 with CLUE, and to fall back to behavior that does not require CLUE. 587 As for the media, Provider and Consumer have an end-to-end 588 communication relationship with respect to (RTP transported) media; 589 and the mechanisms described herein and in companion documents do 590 not change the aspects of setting up those RTP flows and sessions. 591 In other words, the RTP media sessions conform to the negotiated 592 SDP whether or not CLUE is used. 594 6. Spatial Relationships 596 In order for a Consumer to perform a proper rendering, it is often 597 necessary or at least helpful for the Consumer to have received 598 spatial information about the streams it is receiving. CLUE 599 defines a coordinate system that allows Media Providers to describe 600 the spatial relationships of their Media Captures to enable proper 601 scaling and spatially sensible rendering of their streams. The 602 coordinate system is based on a few principles: 604 o Simple systems which do not have multiple Media Captures to 605 associate spatially need not use the coordinate model. 607 o Coordinates can be either in real, physical units (millimeters), 608 have an unknown scale or have no physical scale. Systems which 609 know their physical dimensions (for example professionally 610 installed Telepresence room systems) MUST always provide those 611 real-world measurements. Systems which don't know specific 612 physical dimensions but still know relative distances MUST use 613 'unknown scale'. 'No scale' is intended to be used where Media 614 Captures from different devices (with potentially different 615 scales) will be forwarded alongside one another (e.g. in the 616 case of a middle box). 618 * "Millimeters" means the scale is in millimeters. 620 * "Unknown" means the scale is not necessarily millimeters, but 621 the scale is the same for every Capture in the Capture Scene. 623 * "No Scale" means the scale could be different for each 624 capture- an MCU provider that advertises two adjacent 625 captures and picks sources (which can change quickly) from 626 different endpoints might use this value; the scale could be 627 different and changing for each capture. But the areas of 628 capture still represent a spatial relation between captures. 630 o The coordinate system is Cartesian X, Y, Z with the origin at a 631 spatial location of the provider's choosing. The Provider MUST 632 use the same coordinate system with the same scale and origin 633 for all coordinates within the same Capture Scene. 635 The direction of increasing coordinate values is: 636 X increases from Camera-Left to Camera-Right 637 Y increases from front to back 638 Z increases from low to high (i.e. floor to ceiling) 640 7. Media Captures and Capture Scenes 642 This section describes how Providers can describe the content of 643 media to Consumers. 645 7.1. Media Captures 647 Media Captures are the fundamental representations of streams that 648 a device can transmit. What a Media Capture actually represents is 649 flexible: 651 o It can represent the immediate output of a physical source (e.g. 652 camera, microphone) or 'synthetic' source (e.g. laptop computer, 653 DVD player). 655 o It can represent the output of an audio mixer or video composer 657 o It can represent a concept such as 'the loudest speaker' 659 o It can represent a conceptual position such as 'the leftmost 660 stream' 662 To identify and distinguish between multiple Capture instances 663 Captures have a unique identity. For instance: VC1, VC2 and AC1, 664 AC2, where VC1 and VC2 refer to two different video captures and 665 AC1 and AC2 refer to two different audio captures. 667 Some key points about Media Captures: 669 . A Media Capture is of a single media type (e.g. audio or 670 video) 671 . A Media Capture is defined in a Capture Scene and is given an 672 advertisement unique identity. The identity may be referenced 673 outside the Capture Scene that defines it through a Multiple 674 Content Capture (MCC) 675 . A Media Capture is associated with one or more Capture Scene 676 Entries 677 . A Media Capture has exactly one set of spatial information 678 . A Media Capture can be the source of one or more Capture 679 Encodings 681 Each Media Capture can be associated with attributes to describe 682 what it represents. 684 7.1.1. Media Capture Attributes 686 Media Capture Attributes describe information about the Captures. 687 A Provider can use the Media Capture Attributes to describe the 688 Captures for the benefit of the Consumer in the Advertisement 689 message. Media Capture Attributes include: 691 . Spatial information, such as point of capture, point on line 692 of capture, and area of capture, all of which, in combination 693 define the capture field of, for example, a camera; 694 . Capture multiplexing information (mono/stereo audio, maximum 695 number of simultaneous encodings per Capture and so on); and 696 . Other descriptive information to help the Consumer choose 697 between captures (description, presentation, view, priority, 698 language, person information and type). 699 . Control information for use inside the CLUE protocol suite. 701 The sub-sections below define the Capture attributes. 703 7.1.1.1. Point of Capture 705 The Point of Capture attribute is a field with a single Cartesian 706 (X, Y, Z) point value which describes the spatial location of the 707 capturing device (such as camera). 709 7.1.1.2. Point on Line of Capture 711 The Point on Line of Capture attribute is a field with a single 712 Cartesian (X, Y, Z) point value which describes a position in space 713 of a second point on the axis of the capturing device; the first 714 point being the Point of Capture (see above). 716 Together, the Point of Capture and Point on Line of Capture define 717 an axis of the capturing device, for example the optical axis of a 718 camera. The Media Consumer can use this information to adjust how 719 it renders the received media if it so chooses. 721 7.1.1.3. Area of Capture 723 The Area of Capture is a field with a set of four (X, Y, Z) points 724 as a value which describes the spatial location of what is being 725 "captured". By comparing the Area of Capture for different Media 726 Captures within the same Capture Scene a consumer can determine the 727 spatial relationships between them and render them correctly. 729 The four points MUST be co-planar, forming a quadrilateral, which 730 defines the Plane of Interest for the particular media capture. 732 If the Area of Capture is not specified, it means the Media Capture 733 is not spatially related to any other Media Capture. 735 For a switched capture that switches between different sections 736 within a larger area, the area of capture MUST use coordinates for 737 the larger potential area. 739 7.1.1.4. Mobility of Capture 741 The Mobility of Capture attribute indicates whether or not the 742 point of capture, line on point of capture, and area of capture 743 values stay the same over time, or are expected to change 744 (potentially frequently). Possible values are static, dynamic, and 745 highly dynamic. 747 An example for "dynamic" is a camera mounted on a stand which is 748 occasionally hand-carried and placed at different positions in 749 order to provide the best angle to capture a work task. A camera 750 worn by a person who moves around the room is an example for 751 "highly dynamic". In either case, the effect is that the capture 752 point, capture axis and area of capture change with time. 754 The capture point of a static capture MUST NOT move for the life of 755 the conference. The capture point of dynamic captures is 756 categorized by a change in position followed by a reasonable period 757 of stability--in the order of magnitude of minutes. High dynamic 758 captures are categorized by a capture point that is constantly 759 moving. If the "area of capture", "capture point" and "line of 760 capture" attributes are included with dynamic or highly dynamic 761 captures they indicate spatial information at the time of the 762 Advertisement. 764 7.1.1.5. Audio Channel Format 766 The Audio Channel Format attribute is a field with enumerated 767 values which describes the method of encoding used for audio. A 768 value of 'mono' means the Audio Capture has one channel. 'stereo' 769 means the Audio Capture has two audio channels, left and right. 771 This attribute applies only to Audio Captures. A single stereo 772 capture is different from two mono captures that have a left-right 773 spatial relationship. A stereo capture maps to a single Capture 774 Encoding, while each mono audio capture maps to a separate Capture 775 Encoding. 777 7.1.1.6. Max Capture Encodings 779 The Max Capture Encodings attribute is an optional attribute 780 indicating the maximum number of Capture Encodings that can be 781 simultaneously active for the Media Capture. The number of 782 simultaneous Capture Encodings is also limited by the restrictions 783 of the Encoding Group for the Media Capture. 785 7.1.1.7. Description 787 The Description attribute is a human-readable description of the 788 Capture, which could be in multiple languages. 790 7.1.1.8. Presentation 792 The Presentation attribute indicates that the capture originates 793 from a presentation device, that is one that provides supplementary 794 information to a conference through slides, video, still images, 795 data etc. Where more information is known about the capture it MAY 796 be expanded hierarchically to indicate the different types of 797 presentation media, e.g. presentation.slides, presentation.image 798 etc. 800 Note: It is expected that a number of keywords will be defined that 801 provide more detail on the type of presentation. 803 7.1.1.9. View 805 The View attribute is a field with enumerated values, indicating 806 what type of view the Capture relates to. The Consumer can use 807 this information to help choose which Media Captures it wishes to 808 receive. The value MUST be one of: 810 Room - Captures the entire scene 812 Table - Captures the conference table with seated people 814 Individual - Captures an individual person 816 Lectern - Captures the region of the lectern including the 817 presenter, for example in a classroom style conference room 818 Audience - Captures a region showing the audience in a classroom 819 style conference room 821 7.1.1.10. Language 823 The language attribute indicates one or more languages used in the 824 content of the Media Capture. Captures MAY be offered in different 825 languages in case of multilingual and/or accessible conferences. A 826 Consumer can use this attribute to differentiate between them and 827 pick the appropriate one. 829 Note that the Language attribute is defined and meaningful both for 830 audio and video captures. In case of audio captures, the meaning 831 is obvious. For a video capture, "Language" could, for example, be 832 sign interpretation or text. 834 7.1.1.11. Person Information 836 The person information attribute allows a Provider to provide 837 specific information regarding the people in a Capture (regardless 838 of whether or not the capture has a Presentation attribute). The 839 Provider may gather the information automatically or manually from 840 a variety of sources however the xCard [RFC6351] format is used to 841 convey the information. This allows various information such as 842 Identification information (section 6.2/[RFC6350]), Communication 843 Information (section 6.4/[RFC6350]) and Organizational information 844 (section 6.6/[RFC6350]) to be communicated. A Consumer may then 845 automatically (i.e. via a policy) or manually select Captures 846 based on information about who is in a Capture. It also allows a 847 Consumer to render information regarding the people participating 848 in the conference or to use it for further processing. 850 The Provider may supply a minimal set of information or a larger 851 set of information. However it MUST be compliant to [RFC6350] and 852 supply a "VERSION" and "FN" property. A Provider may supply 853 multiple xCards per Capture of any KIND (section 6.1.4/[RFC6350]). 855 In order to keep CLUE messages compact the Provider SHOULD use a 856 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 857 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 858 message. 860 7.1.1.12. Person Type 862 The person type attribute indicates the type of people contained in 863 the capture in the conference with respect to the meeting agenda 864 (regardless of whether or not the capture has a Presentation 865 attribute). As a capture may include multiple people the attribute 866 may contain multiple values. However values shall not be repeated 867 within the attribute. 869 An Advertiser associates the person type with an individual capture 870 when it knows that a particular type is in the capture. If an 871 Advertiser cannot link a particular type with some certainty to a 872 capture then it is not included. A Consumer on reception of a 873 capture with a person type attribute knows with some certainly that 874 the capture contains that person type. The capture may contain 875 other person types but the Advertiser has not been able to 876 determine that this is the case. 878 The types of Captured people include: 880 . Chairman - the person responsible for running the conference 881 according to the agenda. 882 . Vice-Chairman - the person responsible for assisting the 883 chairman in running the meeting. 884 . Minute Taker - the person responsible for recording the 885 minutes of the conference 886 . Member - the person has no particular responsibilities with 887 respect to running the meeting. 888 . Presenter - the person is scheduled on the agenda to make a 889 presentation in the meeting. Note: This is not related to any 890 "active speaker" functionality. 891 . Translator - the person is providing some form of translation 892 or commentary in the meeting. 893 . Timekeeper - the person is responsible for maintaining the 894 meeting schedule. 896 Furthermore the person type attribute may contain one or more 897 strings allowing the Provider to indicate custom meeting specific 898 roles. 900 7.1.1.13. Priority 902 The priority attribute indicates a relative priority between 903 different Media Captures. The Provider sets this priority, and the 904 Consumer MAY use the priority to help decide which captures it 905 wishes to receive. 907 The "priority" attribute is an integer which indicates a relative 908 priority between Captures. For example it is possible to assign a 909 priority between two presentation Captures that would allow a 910 remote endpoint to determine which presentation is more important. 911 Priority is assigned at the individual capture level. It represents 912 the Provider's view of the relative priority between Captures with 913 a priority. The same priority number MAY be used across multiple 914 Captures. It indicates they are equally important. If no priority 915 is assigned no assumptions regarding relative important of the 916 Capture can be assumed. 918 7.1.1.14. Embedded Text 920 The Embedded Text attribute indicates that a Capture provides 921 embedded textual information. For example the video Capture MAY 922 contain speech to text information composed with the video image. 923 This attribute is only applicable to video Captures and 924 presentation streams with visual information. 926 7.1.1.15. Related To 928 The Related To attribute indicates the Capture contains additional 929 complementary information related to another Capture. The value 930 indicates the identity of the other Capture to which this Capture 931 is providing additional information. 933 For example, a conference can utilize translators or facilitators 934 that provide an additional audio stream (i.e. a translation or 935 description or commentary of the conference). Where multiple 936 captures are available, it may be advantageous for a Consumer to 937 select a complementary Capture instead of or in addition to a 938 Capture it relates to. 940 7.2. Multiple Content Capture 942 The MCC indicates that one or more Single Media Captures are 943 contained in one Media Capture. Only one Capture type (i.e. audio, 944 video, etc.) is allowed in each MCC instance. The MCC may contain 945 a reference to the Single Media Captures (which may have their own 946 attributes) as well as attributes associated with the MCC itself. 947 A MCC may also contain other MCCs. The MCC MAY reference Captures 948 from within the Capture Scene that defines it or from other Capture 949 Scenes. No ordering is implied by the order that Captures appear 950 within a MCC. A MCC MAY contain no references to other Captures to 951 indicate that the MCC contains content from multiple sources but no 952 information regarding those sources is given. 954 One or more MCCs may also be specified in a CSE. This allows an 955 Advertiser to indicate that several MCC captures are used to 956 represent a capture scene. Table 14 provides an example of this 957 case. 959 As outlined in section 7.1. each instance of the MCC has its own 960 Capture identity i.e. MCC1. It allows all the individual captures 961 contained in the MCC to be referenced by a single MCC identity. 963 The example below shows the use of a Multiple Content Capture: 965 +-----------------------+---------------------------------+ 966 | Capture Scene #1 | | 967 +-----------------------|---------------------------------+ 968 | VC1 | {attributes} | 969 | VC2 | {attributes} | 970 | VCn | {attributes} | 971 | MCC1(VC1,VC2,...VCn) | {attributes} | 972 | CSE(MCC1) | | 973 +---------------------------------------------------------+ 975 Table 1: Multiple Content Capture concept 977 This indicates that MCC1 is a single capture that contains the 978 Captures VC1, VC2 and VC3 according to any MCC1 attributes. 980 7.2.1. MCC Attributes 982 Attributes may be associated with the MCC instance and the Single 983 Media Captures that the MCC references. A provider should avoid 984 providing conflicting attribute values between the MCC and Single 985 Media Captures. Where there is conflict the attributes of the MCC 986 override any that may be present in the individual captures. 988 A Provider MAY include as much or as little of the original source 989 Capture information as it requires. 991 There are MCC specific attributes that MUST only be used with 992 Multiple Content Captures. These are described in the sections 993 below. The attributes described in section 7.1.1. MAY also be used 994 with MCCs. 996 The spatial related attributes of an MCC indicate its area of 997 capture and point of capture within the scene, just like any other 998 media capture. The spatial information does not imply anything 999 about how other captures are composed within an MCC. 1001 For example: A virtual scene could be constructed for the MCC 1002 capture with two Video Captures with a "MaxCaptures" attribute set 1003 to 2 and an "Area of Capture" attribute provided with an overall 1004 area. Each of the individual Captures could then also include an 1005 "Area of Capture" attribute with a sub-set of the overall area. 1006 The Consumer would then know how each capture is related to others 1007 within the scene, but not the relative position of the individual 1008 captures within the composed capture. 1010 +-----------------------+---------------------------------+ 1011 | Capture Scene #1 | | 1012 +-----------------------|---------------------------------+ 1013 | VC1 | AreaofCapture=(0,0,0)(9,0,0) | 1014 | | (0,0,9)(9,0,9) | 1015 | VC2 | AreaofCapture=(10,0,0)(19,0,0) | 1016 | | (10,0,9)(19,0,9) | 1017 | MCC1(VC1,VC2) | MaxCaptures=2 | 1018 | | AreaofCapture=(0,0,0)(19,0,0) | 1019 | | (0,0,9)(19,0,9) | 1020 | CSE(MCC1) | | 1021 +---------------------------------------------------------+ 1023 Table 2: Example of MCC and Single Media Capture attributes 1025 The sections below describe the MCC only attributes. 1027 7.2.1.1. Maximum Number of Captures within a MCC 1029 The Maximum Number of Captures MCC attribute indicates the maximum 1030 number of individual captures that may appear in a Capture Encoding 1031 at a time. The actual number at any given time can be less than 1032 this maximum. It may be used to derive how the Single Media 1033 Captures within the MCC are composed / switched with regards to 1034 space and time. 1036 A Provider can indicate that the number of captures in a MCC 1037 capture encoding is equal "=" to the MaxCaptures value or that 1038 there may be any number of captures up to and including "<=" the 1039 MaxCaptures value. This allows a Provider to distinguish between a 1040 MCC that purely represents a composition of sources versus a MCC 1041 that represents switched or switched and composed sources. 1043 MaxCaptures MAY be set to one so that only content related to one 1044 of the sources are shown in the MCC Capture Encoding at a time or 1045 it may be set to any value up to the total number of Source Media 1046 Captures in the MCC. 1048 The bullets below describe how the setting of MaxCapture versus the 1049 number of captures in the MCC affects how sources appear in a 1050 capture encoding: 1052 . When MaxCaptures is set to <= 1 and the number of captures in 1053 the MCC is greater than 1 (or not specified) in the MCC this 1054 is a switched case. Zero or 1 captures may be switched into 1055 the capture encoding. Note: zero is allowed because of the 1056 "<=". 1057 . When MaxCaptures is set to = 1 and the number of captures in 1058 the MCC is greater than 1 (or not specified) in the MCC this 1059 is a switched case. Only one capture source is contained in a 1060 capture encoding at a time. 1061 . When MaxCaptures is set to <= N (with N > 1) and the number of 1062 captures in the MCC is greater than N (or not specified) this 1063 is a switched and composed case. The capture encoding may 1064 contain purely switched sources (i.e. <=2 allows for 1 source 1065 on its own), or may contain composed and switched sources 1066 (i.e. a composition of 2 sources switched between the 1067 sources). 1068 . When MaxCaptures is set to = N (with N > 1) and the number of 1069 captures in the MCC is greater than N (or not specified) this 1070 is a switched and composed case. The capture encoding contains 1071 composed and switched sources (i.e. a composition of N sources 1072 switched between the sources). It is not possible to have a 1073 single source. 1074 . When MaxCaptures is set to <= to the number of captures in the 1075 MCC this is a switched and composed case. The capture encoding 1076 may contain media switched between any number (up to the 1077 MaxCaptures) of composed sources. 1078 . When MaxCaptures is set to = to the number of captures in the 1079 MCC this is a composed case. All the sources are composed into 1080 a single capture encoding. 1082 If this attribute is not set then as default it is assumed that all 1083 source content can appear concurrently in the Capture Encoding 1084 associated with the MCC. 1086 For example: The use of MaxCaptures equal to 1 on a MCC with three 1087 Video Captures VC1, VC2 and VC3 would indicate that the Advertiser 1088 in the capture encoding would switch between VC1, VC2 or VC3 as 1089 there may be only a maximum of one capture at a time. 1091 7.2.1.2. Policy 1093 The Policy MCC Attribute indicates the criteria that the Provider 1094 uses to determine when and/or where media content appears in the 1095 Capture Encoding related to the MCC. 1097 The attribute is in the form of a token that indicates the policy 1098 and index representing an instance of the policy. 1100 The tokens are: 1102 SoundLevel - This indicates that the content of the MCC is 1103 determined by a sound level detection algorithm. For example: the 1104 loudest (active) speaker is contained in the MCC. 1106 RoundRobin - This indicates that the content of the MCC is 1107 determined by a time based algorithm. For example: the Provider 1108 provides content from a particular source for a period of time and 1109 then provides content from another source and so on. 1111 An index is used to represent an instance in the policy setting. A 1112 index of 0 represents the most current instance of the policy, i.e. 1113 the active speaker, 1 represents the previous instance, i.e. the 1114 previous active speaker and so on. 1116 The following example shows a case where the Provider provides two 1117 media streams, one showing the active speaker and a second stream 1118 showing the previous speaker. 1120 +-----------------------+---------------------------------+ 1121 | Capture Scene #1 | | 1122 +-----------------------|---------------------------------+ 1123 | VC1 | | 1124 | VC2 | | 1125 | MCC1(VC1,VC2) | Policy=SoundLevel:0 | 1126 | | MaxCaptures=1 | 1127 | MCC2(VC1,VC2) | Policy=SoundLevel:1 | 1128 | | MaxCaptures=1 | 1129 | CSE(MCC1,MCC2) | | 1130 +---------------------------------------------------------+ 1132 Table 3: Example Policy MCC attribute usage 1134 7.2.1.3. Synchronisation Identity 1136 The Synchronisation Identity MCC attribute indicates how the 1137 individual captures in multiple MCC captures are synchronised. To 1138 indicate that the Capture Encodings associated with MCCs contain 1139 captures from the source at the same time a Provider should set the 1140 same Synchronisation Identity on each of the concerned MCCs. It is 1141 the provider that determines what the source for the Captures is, 1142 so a provider can choose how to group together Single Media 1143 Captures for the purpose of keeping them synchronized according to 1144 the SynchronisationID attribute. For example when the provider is 1145 in an MCU it may determine that each separate CLUE endpoint is a 1146 remote source of media. The Synchronisation Identity may be used 1147 across media types, i.e. to synchronize audio and video related 1148 MCCs. 1150 Without this attribute it is assumed that multiple MCCs may provide 1151 content from different sources at any particular point in time. 1153 For example: 1155 +=======================+=================================+ 1156 | Capture Scene #1 | | 1157 +-----------------------|---------------------------------+ 1158 | VC1 | Description=Left | 1159 | VC2 | Description=Centre | 1160 | VC3 | Description=Right | 1161 | AC1 | Description=room | 1162 | CSE(VC1,VC2,VC3) | | 1163 | CSE(AC1) | | 1164 +=======================+=================================+ 1165 | Capture Scene #2 | | 1166 +-----------------------|---------------------------------+ 1167 | VC4 | Description=Left | 1168 | VC5 | Description=Centre | 1169 | VC6 | Description=Right | 1170 | AC2 | Description=room | 1171 | CSE(VC4,VC5,VC6) | | 1172 | CSE(AC2) | | 1173 +=======================+=================================+ 1174 | Capture Scene #3 | | 1175 +-----------------------|---------------------------------+ 1176 | VC7 | | 1177 | AC3 | | 1178 +=======================+=================================+ 1179 | Capture Scene #4 | | 1180 +-----------------------|---------------------------------+ 1181 | VC8 | | 1182 | AC4 | | 1183 +=======================+=================================+ 1184 | Capture Scene #3 | | 1185 +-----------------------|---------------------------------+ 1186 | MCC1(VC1,VC4,VC7) | SynchronisationID=1 | 1187 | | MaxCaptures=1 | 1188 | MCC2(VC2,VC5,VC8) | SynchronisationID=1 | 1189 | | MaxCaptures=1 | 1190 | MCC3(VC3,VC6) | MaxCaptures=1 | 1191 | MCC4(AC1,AC2,AC3,AC4) | SynchronisationID=1 | 1192 | | MaxCaptures=1 | 1193 | CSE(MCC1,MCC2,MCC3) | | 1194 | CSE(MCC4) | | 1195 +=======================+=================================+ 1197 Table 4: Example Synchronisation Identity MCC attribute usage 1199 The above Advertisement would indicate that MCC1, MCC2, MCC3 and 1200 MCC4 make up a Capture Scene. There would be four capture 1201 encodings (one for each MCC). Because MCC1 and MCC2 have the same 1202 SynchronisationID, each encoding from MCC1 and MCC2 respectively 1203 would together have content from only Capture Scene 1 or only 1204 Capture Scene 2 or the combination of VC7 and VC8 at a particular 1205 point in time. In this case the provider has decided the sources 1206 to be synchronized are Scene #1, Scene #2, and Scene #3 and #4 1207 together. The encoding from MCC3 would not be synchronised with 1208 MCC1 or MCC2. As MCC4 also has the same Synchronisation Identity 1209 as MCC1 and MCC2 the content of the audio encoding will be 1210 synchronised with the video content. 1212 7.3. Capture Scene 1214 In order for a Provider's individual Captures to be used 1215 effectively by a Consumer, the provider organizes the Captures into 1216 one or more Capture Scenes, with the structure and contents of 1217 these Capture Scenes being sent from the Provider to the Consumer 1218 in the Advertisement. 1220 A Capture Scene is a structure representing a spatial region 1221 containing one or more Capture Devices, each capturing media 1222 representing a portion of the region. A Capture Scene includes one 1223 or more Capture Scene entries, with each entry including one or 1224 more Media Captures. A Capture Scene represents, for example, the 1225 video image of a group of people seated next to each other, along 1226 with the sound of their voices, which could be represented by some 1227 number of VCs and ACs in the Capture Scene Entries. A middle box 1228 can also describe in Capture Scenes what it constructs from media 1229 Streams it receives. 1231 A Provider MAY advertise one or more Capture Scenes. What 1232 constitutes an entire Capture Scene is up to the Provider. A 1233 simple Provider might typically use one Capture Scene for 1234 participant media (live video from the room cameras) and another 1235 Capture Scene for a computer generated presentation. In more 1236 complex systems, the use of additional Capture Scenes is also 1237 sensible. For example, a classroom may advertise two Capture 1238 Scenes involving live video, one including only the camera 1239 capturing the instructor (and associated audio), the other 1240 including camera(s) capturing students (and associated audio). 1242 A Capture Scene MAY (and typically will) include more than one type 1243 of media. For example, a Capture Scene can include several Capture 1244 Scene Entries for Video Captures, and several Capture Scene Entries 1245 for Audio Captures. A particular Capture MAY be included in more 1246 than one Capture Scene Entry. 1248 A provider MAY express spatial relationships between Captures that 1249 are included in the same Capture Scene. However, there is not 1250 necessarily the same spatial relationship between Media Captures 1251 that are in different Capture Scenes. In other words, Capture 1252 Scenes can use their own spatial measurement system as outlined 1253 above in section 6. 1255 A Provider arranges Captures in a Capture Scene to help the 1256 Consumer choose which captures it wants to render. The Capture 1257 Scene Entries in a Capture Scene are different alternatives the 1258 Provider is suggesting for representing the Capture Scene. Each 1259 Capture Scene Entry is given an advertisement unique identity. The 1260 order of Capture Scene Entries within a Capture Scene has no 1261 significance. The Media Consumer can choose to receive all Media 1262 Captures from one Capture Scene Entry for each media type (e.g. 1263 audio and video), or it can pick and choose Media Captures 1264 regardless of how the Provider arranges them in Capture Scene 1265 Entries. Different Capture Scene Entries of the same media type 1266 are not necessarily mutually exclusive alternatives. Also note 1267 that the presence of multiple Capture Scene Entries (with 1268 potentially multiple encoding options in each entry) in a given 1269 Capture Scene does not necessarily imply that a Provider is able to 1270 serve all the associated media simultaneously (although the 1271 construction of such an over-rich Capture Scene is probably not 1272 sensible in many cases). What a Provider can send simultaneously 1273 is determined through the Simultaneous Transmission Set mechanism, 1274 described in section 8. 1276 Captures within the same Capture Scene entry MUST be of the same 1277 media type - it is not possible to mix audio and video captures in 1278 the same Capture Scene Entry, for instance. The Provider MUST be 1279 capable of encoding and sending all Captures (that have an encoding 1280 group) in a single Capture Scene Entry simultaneously. The order 1281 of Captures within a Capture Scene Entry has no significance. A 1282 Consumer can decide to receive all the Captures in a single Capture 1283 Scene Entry, but a Consumer could also decide to receive just a 1284 subset of those captures. A Consumer can also decide to receive 1285 Captures from different Capture Scene Entries, all subject to the 1286 constraints set by Simultaneous Transmission Sets, as discussed in 1287 section 8. 1289 When a Provider advertises a Capture Scene with multiple entries, 1290 it is essentially signaling that there are multiple representations 1291 of the same Capture Scene available. In some cases, these multiple 1292 representations would typically be used simultaneously (for 1293 instance a "video entry" and an "audio entry"). In some cases the 1294 entries would conceptually be alternatives (for instance an entry 1295 consisting of three Video Captures covering the whole room versus 1296 an entry consisting of just a single Video Capture covering only 1297 the center of a room). In this latter example, one sensible choice 1298 for a Consumer would be to indicate (through its Configure and 1299 possibly through an additional offer/answer exchange) the Captures 1300 of that Capture Scene Entry that most closely matched the 1301 Consumer's number of display devices or screen layout. 1303 The following is an example of 4 potential Capture Scene Entries 1304 for an endpoint-style Provider: 1306 1. (VC0, VC1, VC2) - left, center and right camera Video Captures 1307 2. (VC3) - Video Capture associated with loudest room segment 1309 3. (VC4) - Video Capture zoomed out view of all people in the room 1311 4. (AC0) - main audio 1313 The first entry in this Capture Scene example is a list of Video 1314 Captures which have a spatial relationship to each other. 1315 Determination of the order of these captures (VC0, VC1 and VC2) for 1316 rendering purposes is accomplished through use of their Area of 1317 Capture attributes. The second entry (VC3) and the third entry 1318 (VC4) are alternative representations of the same room's video, 1319 which might be better suited to some Consumers' rendering 1320 capabilities. The inclusion of the Audio Capture in the same 1321 Capture Scene indicates that AC0 is associated with all of those 1322 Video Captures, meaning it comes from the same spatial region. 1323 Therefore, if audio were to be rendered at all, this audio would be 1324 the correct choice irrespective of which Video Captures were 1325 chosen. 1327 7.3.1. Capture Scene attributes 1329 Capture Scene Attributes can be applied to Capture Scenes as well 1330 as to individual media captures. Attributes specified at this 1331 level apply to all constituent Captures. Capture Scene attributes 1332 include 1334 . Human-readable description of the Capture Scene, which could 1335 be in multiple languages; 1336 . xCard scene information 1337 . Scale information (millimeters, unknown, no scale), as 1338 described in Section 6. 1340 7.3.1.1. Scene Information 1342 The Scene information attribute provides information regarding the 1343 Capture Scene rather than individual participants. The Provider 1344 may gather the information automatically or manually from a 1345 variety of sources. The scene information attribute allows a 1346 Provider to indicate information such as: organizational or 1347 geographic information allowing a Consumer to determine which 1348 Capture Scenes are of interest in order to then perform Capture 1349 selection. It also allows a Consumer to render information 1350 regarding the Scene or to use it for further processing. 1352 As per 7.1.1.11. the xCard format is used to convey this 1353 information and the Provider may supply a minimal set of 1354 information or a larger set of information. 1356 In order to keep CLUE messages compact the Provider SHOULD use a 1357 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 1358 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 1359 message. 1361 7.3.2. Capture Scene Entry attributes 1363 A Capture Scene can include one or more Capture Scene Entries in 1364 addition to the Capture Scene wide attributes described above. 1365 Capture Scene Entry attributes apply to the Capture Scene Entry as 1366 a whole, i.e. to all Captures that are part of the Capture Scene 1367 Entry. 1369 Capture Scene Entry attributes include: 1371 . Human-readable description of the Capture Scene Entry, which 1372 could be in multiple languages; 1374 7.3.3. Global Capture Scene Entry List 1376 An Advertisement can include an optional global Capture Scene 1377 Entry list. Each item in this list is a set of one or more 1378 Capture Scene Entries of the same media type. Each set of CSEs in 1379 the list is a suggestion from the Provider to the Consumer for 1380 which CSEs provide a complete representation of the simultaneous 1381 captures provided by the provider, across multiple scenes. The 1382 Provider can include multiple sets, to allow a consumer to choose 1383 sets of captures appropriate to its capabilities or application. 1384 The choice of how to make these suggestions in the Global CSE list 1385 for what represents all the scenes for which the provider can send 1386 media is up to the provider. This is very similar to how each CSE 1387 represents a particular scene. 1389 As an example, suppose an advertisement has three scenes, and each 1390 scene has three CSEs, ranging from one to three video captures in 1391 each CSE. The provider is advertising a total of nine video 1392 captures across three scenes. The provider can use the Global CSE 1393 list to suggest alternatives for consumers that can't receive all 1394 nine video captures as separate media streams. For accommodating 1395 a consumer that wants to receive three video captures, a provider 1396 might suggest a single CSE with three captures and nothing from 1397 the other two scenes. Or a provider might suggest three different 1398 CSEs, one from each scene, with a single video capture in each. 1400 Some additional rules: 1402 . The ordering of items (sets of CSEs) in the global CSE list 1403 is not important. 1404 . The ordering of CSEs within each set is not important. 1405 . A particular CSE may be used in multiple sets. 1406 . The Provider must be capable of encoding and sending all 1407 Captures within the CSEs of a given set simultaneously. 1409 8. Simultaneous Transmission Set Constraints 1411 In many practical cases, a Provider has constraints or limitations 1412 on its ability to send Captures simultaneously. One type of 1413 limitation is caused by the physical limitations of capture 1414 mechanisms; these constraints are represented by a simultaneous 1415 transmission set. The second type of limitation reflects the 1416 encoding resources available, such as bandwidth or video encoding 1417 throughput (macroblocks/second). This type of constraint is 1418 captured by encoding groups, discussed below. 1420 Some Endpoints or MCUs can send multiple Captures simultaneously; 1421 however sometimes there are constraints that limit which Captures 1422 can be sent simultaneously with other Captures. A device may not 1423 be able to be used in different ways at the same time. Provider 1424 Advertisements are made so that the Consumer can choose one of 1425 several possible mutually exclusive usages of the device. This 1426 type of constraint is expressed in a Simultaneous Transmission Set, 1427 which lists all the Captures of a particular media type (e.g. 1428 audio, video, text) that can be sent at the same time. There are 1429 different Simultaneous Transmission Sets for each media type in the 1430 Advertisement. This is easier to show in an example. 1432 Consider the example of a room system where there are three cameras 1433 each of which can send a separate capture covering two persons 1434 each- VC0, VC1, VC2. The middle camera can also zoom out (using an 1435 optical zoom lens) and show all six persons, VC3. But the middle 1436 camera cannot be used in both modes at the same time - it has to 1437 either show the space where two participants sit or the whole six 1438 seats, but not both at the same time. As a result, VC1 and VC3 1439 cannot be sent simultaneously. 1441 Simultaneous Transmission Sets are expressed as sets of the Media 1442 Captures that the Provider could transmit at the same time (though, 1443 in some cases, it is not intuitive to do so). If a Multiple 1444 Content Capture is included in a Simultaneous Transmission Set it 1445 indicates that the Capture Encoding associated with it could be 1446 transmitted as the same time as the other Captures within the 1447 Simultaneous Transmission Set. It does not imply that the Single 1448 Media Captures contained in the Multiple Content Capture could all 1449 be transmitted at the same time. 1451 In this example the two simultaneous sets are shown in Table 1. If 1452 a Provider advertises one or more mutually exclusive Simultaneous 1453 Transmission Sets, then for each media type the Consumer MUST 1454 ensure that it chooses Media Captures that lie wholly within one of 1455 those Simultaneous Transmission Sets. 1457 +-------------------+ 1458 | Simultaneous Sets | 1459 +-------------------+ 1460 | {VC0, VC1, VC2} | 1461 | {VC0, VC3, VC2} | 1462 +-------------------+ 1464 Table 5: Two Simultaneous Transmission Sets 1466 A Provider OPTIONALLY can include the simultaneous sets in its 1467 provider Advertisement. These simultaneous set constraints apply 1468 across all the Capture Scenes in the Advertisement. It is a syntax 1469 conformance requirement that the simultaneous transmission sets 1470 MUST allow all the media captures in any particular Capture Scene 1471 Entry to be used simultaneously. Similarly, the simultaneous 1472 transmission sets MUST reflect the simultaneity expressed by any 1473 global CSE sets. 1475 For shorthand convenience, a Provider MAY describe a Simultaneous 1476 Transmission Set in terms of Capture Scene Entries and Capture 1477 Scenes. If a Capture Scene Entry is included in a Simultaneous 1478 Transmission Set, then all Media Captures in the Capture Scene 1479 Entry are included in the Simultaneous Transmission Set. If a 1480 Capture Scene is included in a Simultaneous Transmission Set, then 1481 all its Capture Scene Entries (of the corresponding media type) are 1482 included in the Simultaneous Transmission Set. The end result 1483 reduces to a set of Media Captures in either case. 1485 If an Advertisement does not include Simultaneous Transmission 1486 Sets, then the Provider MUST be able to provide all Capture Scenes 1487 simultaneously. If multiple capture Scene Entries are in a Capture 1488 Scene then the Consumer chooses at most one Capture Scene Entry per 1489 Capture Scene for each media type. Likewise, if there are no 1490 Simultaneous Transmission Sets and there is a global CSE list, then 1491 the Consumer chooses at most one set of CSEs of each media type, 1492 from the global CSE list. 1494 If an Advertisement includes multiple Capture Scene Entries in a 1495 Capture Scene then the Consumer MAY choose one Capture Scene Entry 1496 for each media type, or MAY choose individual Captures based on the 1497 Simultaneous Transmission Sets. 1499 9. Encodings 1501 Individual encodings and encoding groups are CLUE's mechanisms 1502 allowing a Provider to signal its limitations for sending Captures, 1503 or combinations of Captures, to a Consumer. Consumers can map the 1504 Captures they want to receive onto the Encodings, with encoding 1505 parameters they want. As for the relationship between the CLUE- 1506 specified mechanisms based on Encodings and the SIP Offer-Answer 1507 exchange, please refer to section 4. 1509 9.1. Individual Encodings 1511 An Individual Encoding represents a way to encode a Media Capture 1512 to become a Capture Encoding, to be sent as an encoded media stream 1513 from the Provider to the Consumer. An Individual Encoding has a 1514 set of parameters characterizing how the media is encoded. 1516 Different media types have different parameters, and different 1517 encoding algorithms may have different parameters. An Individual 1518 Encoding can be assigned to at most one Capture Encoding at any 1519 given time. 1521 The parameters of an Individual Encoding represent the maximum 1522 values for certain aspects of the encoding. A particular 1523 instantiation into a Capture Encoding MAY use lower values than 1524 these maximums if that is applicable for the media in question. 1525 For example, most video codec specifications require a conformant 1526 decoder to decode resolutions and frame rates smaller than what has 1527 been negotiated as a maximum, so downgrading the CLUE maximum 1528 values for macroblocks/second is appropriate. On the other hand, 1529 downgrading the sample rate of G.711 audio below 8kHz is not 1530 specified in G.711 and therefore not applicable in the sense 1531 described here. 1533 Individual Encoding parameters are represented in SDP [RFC4566], 1534 not in CLUE messages. For example, for a video encoding using 1535 H.26x compression technologies, this can include parameters such 1536 as: 1538 . Maximum bandwidth; 1539 . Maximum picture size in pixels; 1540 . Maxmimum number of pixels to be processed per second; 1542 The bandwidth parameter is the only one that specifically relates 1543 to a CLUE Advertisement, as it can be further constrained by the 1544 maximum group bandwidth in an Encoding Group. 1546 9.2. Encoding Group 1548 An Encoding Group includes a set of one or more Individual 1549 Encodings, and parameters that apply to the group as a whole. By 1550 grouping multiple individual Encodings together, an Encoding Group 1551 describes additional constraints on bandwidth for the group. 1553 The Encoding Group data structure contains: 1555 . Maximum bitrate for all encodings in the group combined; 1556 . A list of identifiers for audio and video encodings, 1557 respectively, belonging to the group. 1559 When the Individual Encodings in a group are instantiated into 1560 Capture Encodings, each Capture Encoding has a bitrate that MUST be 1561 less than or equal to the max bitrate for the particular individual 1562 encoding. The "maximum bitrate for all encodings in the group" 1563 parameter gives the additional restriction that the sum of all the 1564 individual capture encoding bitrates MUST be less than or equal to 1565 the this group value. 1567 The following diagram illustrates one example of the structure of a 1568 media provider's Encoding Groups and their contents. 1570 ,-------------------------------------------------. 1571 | Media Provider | 1572 | | 1573 | ,--------------------------------------. | 1574 | | ,--------------------------------------. | 1575 | | | ,--------------------------------------. | 1576 | | | | Encoding Group | | 1577 | | | | ,-----------. | | 1578 | | | | | | ,---------. | | 1579 | | | | | | | | ,---------.| | 1580 | | | | | Encoding1 | |Encoding2| |Encoding3|| | 1581 | `.| | | | | | `---------'| | 1582 | `.| `-----------' `---------' | | 1583 | `--------------------------------------' | 1584 `-------------------------------------------------' 1586 Figure 3: Encoding Group Structure 1588 A Provider advertises one or more Encoding Groups. Each Encoding 1589 Group includes one or more Individual Encodings. Each Individual 1590 Encoding can represent a different way of encoding media. For 1591 example one Individual Encoding may be 1080p60 video, another could 1592 be 720p30, with a third being CIF, all in, for example, H.264 1593 format. 1594 While a typical three codec/display system might have one Encoding 1595 Group per "codec box" (physical codec, connected to one camera and 1596 one screen), there are many possibilities for the number of 1597 Encoding Groups a Provider may be able to offer and for the 1598 encoding values in each Encoding Group. 1600 There is no requirement for all Encodings within an Encoding Group 1601 to be instantiated at the same time. 1603 9.3. Associating Captures with Encoding Groups 1605 Each Media Capture MAY be associated with at least one Encoding 1606 Group, which is used to instantiate that Capture into one or more 1607 Capture Encodings. Typically MCCs are assigned an Encoding Group 1608 and thus become a Capture Encoding. The Captures (including other 1609 MCCs) referenced by the MCC do not need to be assigned to an 1610 Encoding Group. This means that all the Media Captures referenced 1611 by the MCC will appear in the Capture Encoding according to any MCC 1612 attributes. This allows an Advertiser to specify Capture attributes 1613 associated with the Media Captures without the need to provide an 1614 individual Capture Encoding for each of the inputs. 1616 If an Encoding Group is assigned to a Media Capture referenced by 1617 the MCC it indicates that this Capture may also have an individual 1618 Capture Encoding. 1620 For example: 1622 +--------------------+------------------------------------+ 1623 | Capture Scene #1 | | 1624 +--------------------+------------------------------------+ 1625 | VC1 | EncodeGroupID=1 | 1626 | VC2 | | 1627 | MCC1(VC1,VC2) | EncodeGroupID=2 | 1628 | CSE(VC1) | | 1629 | CSE(MCC1) | | 1630 +--------------------+------------------------------------+ 1632 Table 6: Example usage of Encoding with MCC and source Captures 1634 This would indicate that VC1 may be sent as its own Capture 1635 Encoding from EncodeGroupID=1 or that it may be sent as part of a 1636 Capture Encoding from EncodeGroupID=2 along with VC2. 1638 More than one Capture MAY use the same Encoding Group. 1640 The maximum number of streams that can result from a particular 1641 Encoding Group constraint is equal to the number of individual 1642 Encodings in the group. The actual number of Capture Encodings 1643 used at any time MAY be less than this maximum. Any of the 1644 Captures that use a particular Encoding Group can be encoded 1645 according to any of the Individual Encodings in the group. If 1646 there are multiple Individual Encodings in the group, then the 1647 Consumer can configure the Provider, via a Configure message, to 1648 encode a single Media Capture into multiple different Capture 1649 Encodings at the same time, subject to the Max Capture Encodings 1650 constraint, with each capture encoding following the constraints of 1651 a different Individual Encoding. 1653 It is a protocol conformance requirement that the Encoding Groups 1654 MUST allow all the Captures in a particular Capture Scene Entry to 1655 be used simultaneously. 1657 10. Consumer's Choice of Streams to Receive from the Provider 1659 After receiving the Provider's Advertisement message (that includes 1660 media captures and associated constraints), the Consumer composes 1661 its reply to the Provider in the form of a Configure message. The 1662 Consumer is free to use the information in the Advertisement as it 1663 chooses, but there are a few obviously sensible design choices, 1664 which are outlined below. 1666 If multiple Providers connect to the same Consumer (i.e. in a n 1667 MCU-less multiparty call), it is the responsibility of the Consumer 1668 to compose Configures for each Provider that both fulfill each 1669 Provider's constraints as expressed in the Advertisement, as well 1670 as its own capabilities. 1672 In an MCU-based multiparty call, the MCU can logically terminate 1673 the Advertisement/Configure negotiation in that it can hide the 1674 characteristics of the receiving endpoint and rely on its own 1675 capabilities (transcoding/transrating/...) to create Media Streams 1676 that can be decoded at the Endpoint Consumers. The timing of an 1677 MCU's sending of Advertisements (for its outgoing ports) and 1678 Configures (for its incoming ports, in response to Advertisements 1679 received there) is up to the MCU and implementation dependent. 1681 As a general outline, A Consumer can choose, based on the 1682 Advertisement it has received, which Captures it wishes to receive, 1683 and which Individual Encodings it wants the Provider to use to 1684 encode the Captures. 1686 On receipt of an Advertisement with an MCC the Consumer treats the 1687 MCC as per other non-MCC Captures with the following differences: 1689 - The Consumer would understand that the MCC is a Capture that 1690 includes the referenced individual Captures and that these 1691 individual Captures are delivered as part of the MCC's Capture 1692 Encoding. 1694 - The Consumer may utilise any of the attributes associated with 1695 the referenced individual Captures and any Capture Scene attributes 1696 from where the individual Captures were defined to choose Captures 1697 and for rendering decisions. 1699 - The Consumer may or may not choose to receive all the indicated 1700 captures. Therefore it can choose to receive a sub-set ofCaptures 1701 indicated by the MCC. 1703 For example if the Consumer receives: 1705 MCC1(VC1,VC2,VC3){attributes} 1707 A Consumer could choose all the Captures within a MCCs however if 1708 the Consumer determines that it doesn't want VC3 it can return 1709 MCC1(VC1,VC2). If it wants all the individual Captures then it 1710 returns only the MCC identity (i.e. MCC1). If the MCC in the 1711 advertisement does not reference any individual captures, then the 1712 Consumer cannot choose what is included in the MCC, it is up to the 1713 Provider to decide. 1715 A Configure Message includes a list of Capture Encodings. These 1716 are the Capture Encodings the Consumer wishes to receive from the 1717 Provider. Each Capture Encoding refers to one Media Capture, one 1718 Individual Encoding, and includes the encoding parameter values. A 1719 Configure Message does not include references to Capture Scenes or 1720 Capture Scene Entries. 1722 For each Capture the Consumer wants to receive, it configures one 1723 or more of the encodings in that capture's encoding group. The 1724 Consumer does this by telling the Provider, in its Configure 1725 Message, parameters such as the resolution, frame rate, bandwidth, 1726 etc. for each Capture Encodings for its chosen Captures. Upon 1727 receipt of this Configure from the Consumer, common knowledge is 1728 established between Provider and Consumer regarding sensible 1729 choices for the media streams and their parameters. The setup of 1730 the actual media channels, at least in the simplest case, is left 1731 to a following offer-answer exchange. Optimized implementations 1732 MAY speed up the reaction to the offer-answer exchange by reserving 1733 the resources at the time of finalization of the CLUE handshake. 1735 CLUE advertisements and configure messages don't necessarily 1736 require a new SDP offer-answer for every CLUE message 1737 exchange. But the resulting encodings sent via RTP must conform to 1738 the most recent SDP offer-answer result. 1740 In order to meaningfully create and send an initial Configure, the 1741 Consumer needs to have received at least one Advertisement from the 1742 Provider. 1744 In addition, the Consumer can send a Configure at any time during 1745 the call. The Configure MUST be valid according to the most 1746 recently received Advertisement. The Consumer can send a Configure 1747 either in response to a new Advertisement from the Provider or on 1748 its own, for example because of a local change in conditions 1749 (people leaving the room, connectivity changes, multipoint related 1750 considerations). 1752 When choosing which Media Streams to receive from the Provider, and 1753 the encoding characteristics of those Media Streams, the Consumer 1754 advantageously takes several things into account: its local 1755 preference, simultaneity restrictions, and encoding limits. 1757 10.1. Local preference 1759 A variety of local factors influence the Consumer's choice of 1760 Media Streams to be received from the Provider: 1762 o if the Consumer is an Endpoint, it is likely that it would 1763 choose, where possible, to receive video and audio Captures that 1764 match the number of display devices and audio system it has 1766 o if the Consumer is a middle box such as an MCU, it MAY choose to 1767 receive loudest speaker streams (in order to perform its own 1768 media composition) and avoid pre-composed video Captures 1770 o user choice (for instance, selection of a new layout) MAY result 1771 in a different set of Captures, or different encoding 1772 characteristics, being required by the Consumer 1774 10.2. Physical simultaneity restrictions 1776 Often there are physical simultaneity constraints of the Provider 1777 that affect the Provider's ability to simultaneously send all of 1778 the captures the Consumer would wish to receive. For instance, a 1779 middle box such as an MCU, when connected to a multi-camera room 1780 system, might prefer to receive both individual video streams of 1781 the people present in the room and an overall view of the room 1782 from a single camera. Some Endpoint systems might be able to 1783 provide both of these sets of streams simultaneously, whereas 1784 others might not (if the overall room view were produced by 1785 changing the optical zoom level on the center camera, for 1786 instance). 1788 10.3. Encoding and encoding group limits 1790 Each of the Provider's encoding groups has limits on bandwidth and 1791 computational complexity, and the constituent potential encodings 1792 have limits on the bandwidth, computational complexity, video 1793 frame rate, and resolution that can be provided. When choosing 1794 the Captures to be received from a Provider, a Consumer device 1795 MUST ensure that the encoding characteristics requested for each 1796 individual Capture fits within the capability of the encoding it 1797 is being configured to use, as well as ensuring that the combined 1798 encoding characteristics for Captures fit within the capabilities 1799 of their associated encoding groups. In some cases, this could 1800 cause an otherwise "preferred" choice of capture encodings to be 1801 passed over in favor of different Capture Encodings--for instance, 1802 if a set of three Captures could only be provided at a low 1803 resolution then a three screen device could switch to favoring a 1804 single, higher quality, Capture Encoding. 1806 11. Extensibility 1808 One important characteristics of the Framework is its 1809 extensibility. Telepresence is a relatively new industry and 1810 while we can foresee certain directions, we also do not know 1811 everything about how it will develop. The standard for 1812 interoperability and handling multiple streams must be future- 1813 proof. The framework itself is inherently extensible through 1814 expanding the data model types. For example: 1816 o Adding more types of media, such as telemetry, can done by 1817 defining additional types of Captures in addition to audio and 1818 video. 1820 o Adding new functionalities, such as 3-D, say, may require 1821 additional attributes describing the Captures. 1823 o Adding a new codecs, such as H.265, can be accomplished by 1824 defining new encoding variables. 1826 The infrastructure is designed to be extended rather than 1827 requiring new infrastructure elements. Extension comes through 1828 adding to defined types. 1830 12. Examples - Using the Framework (Informative) 1832 This section gives some examples, first from the point of view of 1833 the Provider, then the Consumer, then some multipoint scenarios 1835 12.1. Provider Behavior 1837 This section shows some examples in more detail of how a Provider 1838 can use the framework to represent a typical case for telepresence 1839 rooms. First an endpoint is illustrated, then an MCU case is 1840 shown. 1842 12.1.1. Three screen Endpoint Provider 1844 Consider an Endpoint with the following description: 1846 3 cameras, 3 displays, a 6 person table 1848 o Each camera can provide one Capture for each 1/3 section of the 1849 table 1851 o A single Capture representing the active speaker can be provided 1852 (voice activity based camera selection to a given encoder input 1853 port implemented locally in the Endpoint) 1855 o A single Capture representing the active speaker with the other 1856 2 Captures shown picture in picture within the stream can be 1857 provided (again, implemented inside the endpoint) 1859 o A Capture showing a zoomed out view of all 6 seats in the room 1860 can be provided 1862 The audio and video Captures for this Endpoint can be described as 1863 follows. 1865 Video Captures: 1867 o VC0- (the camera-left camera stream), encoding group=EG0, 1868 view=table 1870 o VC1- (the center camera stream), encoding group=EG1, view=table 1872 o VC2- (the camera-right camera stream), encoding group=EG2, 1873 view=table 1875 o MCC3- (the loudest panel stream), encoding group=EG1, 1876 view=table, MaxCaptures=1 1878 o MCC4- (the loudest panel stream with PiPs), encoding group=EG1, 1879 view=room, MaxCaptures=3 1881 o VC5- (the zoomed out view of all people in the room), encoding 1882 group=EG1, view=room 1884 o VC6- (presentation stream), encoding group=EG1, presentation 1885 The following diagram is a top view of the room with 3 cameras, 3 1886 displays, and 6 seats. Each camera is capturing 2 people. The 1887 six seats are not all in a straight line. 1889 ,-. d 1890 ( )`--.__ +---+ 1891 `-' / `--.__ | | 1892 ,-. | `-.._ |_-+Camera 2 (VC2) 1893 ( ).' ___..-+-''`+-+ 1894 `-' |_...---'' | | 1895 ,-.c+-..__ +---+ 1896 ( )| ``--..__ | | 1897 `-' | ``+-..|_-+Camera 1 (VC1) 1898 ,-. | __..--'|+-+ 1899 ( )| __..--' | | 1900 `-'b|..--' +---+ 1901 ,-. |``---..___ | | 1902 ( )\ ```--..._|_-+Camera 0 (VC0) 1903 `-' \ _..-''`-+ 1904 ,-. \ __.--'' | | 1905 ( ) |..-'' +---+ 1906 `-' a 1907 Figure 4: Room Layout 1909 The two points labeled b and c are intended to be at the midpoint 1910 between the seating positions, and where the fields of view of the 1911 cameras intersect. 1913 The plane of interest for VC0 is a vertical plane that intersects 1914 points 'a' and 'b'. 1916 The plane of interest for VC1 intersects points 'b' and 'c'. The 1917 plane of interest for VC2 intersects points 'c' and 'd'. 1919 This example uses an area scale of millimeters. 1921 Areas of capture: 1923 bottom left bottom right top left top right 1924 VC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757) 1925 VC1 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757) 1926 VC2 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757) 1927 MCC3(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1928 MCC4(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1929 VC5 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1930 VC6 none 1932 Points of capture: 1933 VC0 (-1678,0,800) 1934 VC1 (0,0,800) 1935 VC2 (1678,0,800) 1936 MCC3 none 1937 MCC4 none 1938 VC5 (0,0,800) 1939 VC6 none 1941 In this example, the right edge of the VC0 area lines up with the 1942 left edge of the VC1 area. It doesn't have to be this way. There 1943 could be a gap or an overlap. One additional thing to note for 1944 this example is the distance from a to b is equal to the distance 1945 from b to c and the distance from c to d. All these distances are 1946 1346 mm. This is the planar width of each area of capture for VC0, 1947 VC1, and VC2. 1949 Note the text in parentheses (e.g. "the camera-left camera 1950 stream") is not explicitly part of the model, it is just 1951 explanatory text for this example, and is not included in the 1952 model with the media captures and attributes. Also, MCC4 doesn't 1953 say anything about how a capture is composed, so the media 1954 consumer can't tell based on this capture that MCC4 is composed of 1955 a "loudest panel with PiPs". 1957 Audio Captures: 1959 o AC0 (camera-left), encoding group=EG3, channel format=mono 1961 o AC1 (camera-right), encoding group=EG3, channel format=mono 1963 o AC2 (center) encoding group=EG3, channel format=mono 1965 o AC3 being a simple pre-mixed audio stream from the room (mono), 1966 encoding group=EG3, channel format=mono 1968 o AC4 audio stream associated with the presentation video (mono) 1969 encoding group=EG3, presentation, channel format=mono 1971 Areas of capture: 1973 bottom left bottom right top left top right 1975 AC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757) 1976 AC1 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757) 1977 AC2 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757) 1978 AC3 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1979 AC4 none 1981 The physical simultaneity information is: 1983 Simultaneous transmission set #1 {VC0, VC1, VC2, MCC3, MCC4, 1984 VC6} 1986 Simultaneous transmission set #2 {VC0, VC2, VC5, VC6} 1988 This constraint indicates it is not possible to use all the VCs at 1989 the same time. VC5 cannot be used at the same time as VC1 or MCC3 1990 or MCC4. Also, using every member in the set simultaneously may 1991 not make sense - for example MCC3(loudest) and MCC4 (loudest with 1992 PIP). (In addition, there are encoding constraints that make 1993 choosing all of the VCs in a set impossible. VC1, MCC3, MCC4, 1994 VC5, VC6 all use EG1 and EG1 has only 3 ENCs. This constraint 1995 shows up in the encoding groups, not in the simultaneous 1996 transmission sets.) 1997 In this example there are no restrictions on which audio captures 1998 can be sent simultaneously. 2000 Encoding Groups: 2002 This example has three encoding groups associated with the video 2003 captures. Each group can have 3 encodings, but with each 2004 potential encoding having a progressively lower specification. In 2005 this example, 1080p60 transmission is possible (as ENC0 has a 2006 maxPps value compatible with that). Significantly, as up to 3 2007 encodings are available per group, it is possible to transmit some 2008 video captures simultaneously that are not in the same entry in 2009 the capture scene. For example VC1 and MCC3 at the same time. 2011 It is also possible to transmit multiple capture encodings of a 2012 single video capture. For example VC0 can be encoded using ENC0 2013 and ENC1 at the same time, as long as the encoding parameters 2014 satisfy the constraints of ENC0, ENC1, and EG0, such as one at 2015 4000000 bps and one at 2000000 bps. 2017 encodeGroupID=EG0, maxGroupBandwidth=6000000 2018 encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2019 maxPps=124416000, maxBandwidth=4000000 2020 encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2021 maxPps=27648000, maxBandwidth=4000000 2022 encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30, 2023 maxPps=15552000, maxBandwidth=4000000 2024 encodeGroupID=EG1 maxGroupBandwidth=6000000 2025 encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2026 maxPps=124416000, maxBandwidth=4000000 2027 encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2028 maxPps=27648000, maxBandwidth=4000000 2029 encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30, 2030 maxPps=15552000, maxBandwidth=4000000 2031 encodeGroupID=EG2 maxGroupBandwidth=6000000 2032 encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2033 maxPps=124416000, maxBandwidth=4000000 2034 encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2035 maxPps=27648000, maxBandwidth=4000000 2036 encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30, 2037 maxPps=15552000, maxBandwidth=4000000 2039 Figure 5: Example Encoding Groups for Video 2041 For audio, there are five potential encodings available, so all 2042 five audio captures can be encoded at the same time. 2044 encodeGroupID=EG3, maxGroupBandwidth=320000 2045 encodeID=ENC9, maxBandwidth=64000 2046 encodeID=ENC10, maxBandwidth=64000 2047 encodeID=ENC11, maxBandwidth=64000 2048 encodeID=ENC12, maxBandwidth=64000 2049 encodeID=ENC13, maxBandwidth=64000 2051 Figure 6: Example Encoding Group for Audio 2053 Capture Scenes: 2055 The following table represents the capture scenes for this 2056 provider. Recall that a capture scene is composed of alternative 2057 capture scene entries covering the same spatial region. Capture 2058 Scene #1 is for the main people captures, and Capture Scene #2 is 2059 for presentation. 2061 Each row in the table is a separate Capture Scene Entry 2063 +------------------+ 2064 | Capture Scene #1 | 2065 +------------------+ 2066 | VC0, VC1, VC2 | 2067 | MCC3 | 2068 | MCC4 | 2069 | VC5 | 2070 | AC0, AC1, AC2 | 2071 | AC3 | 2072 +------------------+ 2074 +------------------+ 2075 | Capture Scene #2 | 2076 +------------------+ 2077 | VC6 | 2078 | AC4 | 2079 +------------------+ 2081 Table 7: Example Capture Scene Entries 2083 Different capture scenes are unique to each other, non- 2084 overlapping. A consumer can choose an entry from each capture 2085 scene. In this case the three captures VC0, VC1, and VC2 are one 2086 way of representing the video from the endpoint. These three 2087 captures should appear adjacent next to each other. 2088 Alternatively, another way of representing the Capture Scene is 2089 with the capture MCC3, which automatically shows the person who is 2090 talking. Similarly for the MCC4 and MCC5 alternatives. 2092 As in the video case, the different entries of audio in Capture 2093 Scene #1 represent the "same thing", in that one way to receive 2094 the audio is with the 3 audio captures (AC0, AC1, AC2), and 2095 another way is with the mixed AC3. The Media Consumer can choose 2096 an audio capture entry it is capable of receiving. 2098 The spatial ordering is understood by the media capture attributes 2099 Area of Capture and Point of Capture. 2101 A Media Consumer would likely want to choose a capture scene entry 2102 to receive based in part on how many streams it can simultaneously 2103 receive. A consumer that can receive three people streams would 2104 probably prefer to receive the first entry of Capture Scene #1 2105 (VC0, VC1, VC2) and not receive the other entries. A consumer 2106 that can receive only one people stream would probably choose one 2107 of the other entries. 2109 If the consumer can receive a presentation stream too, it would 2110 also choose to receive the only entry from Capture Scene #2 (VC6). 2112 12.1.2. Encoding Group Example 2114 This is an example of an encoding group to illustrate how it can 2115 express dependencies between encodings. 2117 encodeGroupID=EG0 maxGroupBandwidth=6000000 2118 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2119 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2120 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2121 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2122 encodeID=AUDENC0, maxBandwidth=96000 2123 encodeID=AUDENC1, maxBandwidth=96000 2124 encodeID=AUDENC2, maxBandwidth=96000 2126 Here, the encoding group is EG0. Although the encoding group is 2127 capable of transmitting up to 6Mbit/s, no individual video 2128 encoding can exceed 4Mbit/s. 2130 This encoding group also allows up to 3 audio encodings, AUDENC<0- 2131 2>. It is not required that audio and video encodings reside 2132 within the same encoding group, but if so then the group's overall 2133 maxBandwidth value is a limit on the sum of all audio and video 2134 encodings configured by the consumer. A system that does not wish 2135 or need to combine bandwidth limitations in this way should 2136 instead use separate encoding groups for audio and video in order 2137 for the bandwidth limitations on audio and video to not interact. 2139 Audio and video can be expressed in separate encoding groups, as 2140 in this illustration. 2142 encodeGroupID=EG0 maxGroupBandwidth=6000000 2143 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2144 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2145 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2146 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2147 encodeGroupID=EG1 maxGroupBandwidth=500000 2148 encodeID=AUDENC0, maxBandwidth=96000 2149 encodeID=AUDENC1, maxBandwidth=96000 2150 encodeID=AUDENC2, maxBandwidth=96000 2152 12.1.3. The MCU Case 2154 This section shows how an MCU might express its Capture Scenes, 2155 intending to offer different choices for consumers that can handle 2156 different numbers of streams. A single audio capture stream is 2157 provided for all single and multi-screen configurations that can 2158 be associated (e.g. lip-synced) with any combination of video 2159 captures at the consumer. 2161 +-----------------------+---------------------------------+ 2162 | Capture Scene #1 | | 2163 +-----------------------|---------------------------------+ 2164 | VC0 | VC for a single screen consumer | 2165 | VC1, VC2 | VCs for a two screen consumer | 2166 | VC3, VC4, VC5 | VCs for a three screen consumer | 2167 | VC6, VC7, VC8, VC9 | VCs for a four screen consumer | 2168 | AC0 | AC representing all participants| 2169 | CSE(VC0) | | 2170 | CSE(VC1,VC2) | | 2171 | CSE(VC3,VC4,VC5) | | 2172 | CSE(VC6,VC7,VC8,VC9) | | 2173 | CSE(AC0) | | 2174 +-----------------------+---------------------------------+ 2175 Table 8: MCU main Capture Scenes 2177 If / when a presentation stream becomes active within the 2178 conference the MCU might re-advertise the available media as: 2180 +------------------+--------------------------------------+ 2181 | Capture Scene #2 | note | 2182 +------------------+--------------------------------------+ 2183 | VC10 | video capture for presentation | 2184 | AC1 | presentation audio to accompany VC10 | 2185 | CSE(VC10) | | 2186 | CSE(AC1) | | 2187 +------------------+--------------------------------------+ 2189 Table 9: MCU presentation Capture Scene 2191 12.2. Media Consumer Behavior 2193 This section gives an example of how a Media Consumer might behave 2194 when deciding how to request streams from the three screen 2195 endpoint described in the previous section. 2197 The receive side of a call needs to balance its requirements, 2198 based on number of screens and speakers, its decoding capabilities 2199 and available bandwidth, and the provider's capabilities in order 2200 to optimally configure the provider's streams. Typically it would 2201 want to receive and decode media from each Capture Scene 2202 advertised by the Provider. 2204 A sane, basic, algorithm might be for the consumer to go through 2205 each Capture Scene in turn and find the collection of Video 2206 Captures that best matches the number of screens it has (this 2207 might include consideration of screens dedicated to presentation 2208 video display rather than "people" video) and then decide between 2209 alternative entries in the video Capture Scenes based either on 2210 hard-coded preferences or user choice. Once this choice has been 2211 made, the consumer would then decide how to configure the 2212 provider's encoding groups in order to make best use of the 2213 available network bandwidth and its own decoding capabilities. 2215 12.2.1. One screen Media Consumer 2217 MCC3, MCC4 and VC5 are all different entries by themselves, not 2218 grouped together in a single entry, so the receiving device should 2219 choose between one of those. The choice would come down to 2220 whether to see the greatest number of participants simultaneously 2221 at roughly equal precedence (VC5), a switched view of just the 2222 loudest region (MCC3) or a switched view with PiPs (MCC4). An 2223 endpoint device with a small amount of knowledge of these 2224 differences could offer a dynamic choice of these options, in- 2225 call, to the user. 2227 12.2.2. Two screen Media Consumer configuring the example 2229 Mixing systems with an even number of screens, "2n", and those 2230 with "2n+1" cameras (and vice versa) is always likely to be the 2231 problematic case. In this instance, the behavior is likely to be 2232 determined by whether a "2 screen" system is really a "2 decoder" 2233 system, i.e., whether only one received stream can be displayed 2234 per screen or whether more than 2 streams can be received and 2235 spread across the available screen area. To enumerate 3 possible 2236 behaviors here for the 2 screen system when it learns that the far 2237 end is "ideally" expressed via 3 capture streams: 2239 1. Fall back to receiving just a single stream (MCC3, MCC4 or VC5 2240 as per the 1 screen consumer case above) and either leave one 2241 screen blank or use it for presentation if / when a 2242 presentation becomes active. 2244 2. Receive 3 streams (VC0, VC1 and VC2) and display across 2 2245 screens (either with each capture being scaled to 2/3 of a 2246 screen and the center capture being split across 2 screens) or, 2247 as would be necessary if there were large bezels on the 2248 screens, with each stream being scaled to 1/2 the screen width 2249 and height and there being a 4th "blank" panel. This 4th panel 2250 could potentially be used for any presentation that became 2251 active during the call. 2253 3. Receive 3 streams, decode all 3, and use control information 2254 indicating which was the most active to switch between showing 2255 the left and center streams (one per screen) and the center and 2256 right streams. 2258 For an endpoint capable of all 3 methods of working described 2259 above, again it might be appropriate to offer the user the choice 2260 of display mode. 2262 12.2.3. Three screen Media Consumer configuring the example 2264 This is the most straightforward case - the Media Consumer would 2265 look to identify a set of streams to receive that best matched its 2266 available screens and so the VC0 plus VC1 plus VC2 should match 2267 optimally. The spatial ordering would give sufficient information 2268 for the correct video capture to be shown on the correct screen, 2269 and the consumer would either need to divide a single encoding 2270 group's capability by 3 to determine what resolution and frame 2271 rate to configure the provider with or to configure the individual 2272 video captures' encoding groups with what makes most sense (taking 2273 into account the receive side decode capabilities, overall call 2274 bandwidth, the resolution of the screens plus any user preferences 2275 such as motion vs sharpness). 2277 12.3. Multipoint Conference utilizing Multiple Content Captures 2279 The use of MCCs allows the MCU to construct outgoing Advertisements 2280 describing complex and media switching and composition scenarios. 2281 The following sections provide several examples. 2283 Note: In the examples the identities of the CLUE elements (e.g. 2284 Captures, Capture Scene) in the incoming Advertisements overlap. 2285 This is because there is no co-ordination between the endpoints. 2286 The MCU is responsible for making these unique in the outgoing 2287 advertisement. 2289 12.3.1. Single Media Captures and MCC in the same Advertisement 2291 Four endpoints are involved in a Conference where CLUE is used. An 2292 MCU acts as a middlebox between the endpoints with a CLUE channel 2293 between each endpoint and the MCU. The MCU receives the following 2294 Advertisements. 2296 +-----------------------+---------------------------------+ 2297 | Capture Scene #1 | Description=AustralianConfRoom | 2298 +-----------------------|---------------------------------+ 2299 | VC1 | Description=Audience | 2300 | | EncodeGroupID=1 | 2301 | CSE(VC1) | | 2302 +---------------------------------------------------------+ 2304 Table 10: Advertisement received from Endpoint A 2306 +-----------------------+---------------------------------+ 2307 | Capture Scene #1 | Description=ChinaConfRoom | 2308 +-----------------------|---------------------------------+ 2309 | VC1 | Description=Speaker | 2310 | | EncodeGroupID=1 | 2311 | VC2 | Description=Audience | 2312 | | EncodeGroupID=1 | 2313 | CSE(VC1, VC2) | | 2314 +---------------------------------------------------------+ 2316 Table 11: Advertisement received from Endpoint B 2318 +-----------------------+---------------------------------+ 2319 | Capture Scene #1 | Description=USAConfRoom | 2320 +-----------------------|---------------------------------+ 2321 | VC1 | Description=Audience | 2322 | | EncodeGroupID=1 | 2323 | CSE(VC1) | | 2324 +---------------------------------------------------------+ 2326 Table 12: Advertisement received from Endpoint C 2328 Note: Endpoint B above indicates that it sends two streams. 2330 If the MCU wanted to provide a Multiple Content Capture containing 2331 a round robin switched view of the audience from the 3 endpoints 2332 and the speaker it could construct the following advertisement: 2334 Advertisement sent to Endpoint F 2336 +=======================+=================================+ 2337 | Capture Scene #1 | Description=AustralianConfRoom | 2338 +-----------------------|---------------------------------+ 2339 | VC1 | Description=Audience | 2340 | CSE(VC1) | | 2341 +=======================+=================================+ 2342 | Capture Scene #2 | Description=ChinaConfRoom | 2343 +-----------------------|---------------------------------+ 2344 | VC2 | Description=Speaker | 2345 | VC3 | Description=Audience | 2346 | CSE(VC2, VC3) | | 2347 +=======================+=================================+ 2348 | Capture Scene #3 | Description=USAConfRoom | 2349 +-----------------------|---------------------------------+ 2350 | VC4 | Description=Audience | 2351 | CSE(VC4) | | 2352 +=======================+=================================+ 2353 | Capture Scene #4 | | 2354 +-----------------------|---------------------------------+ 2355 | MCC1(VC1,VC2,VC3,VC4) | Policy=RoundRobin:1 | 2356 | | MaxCaptures=1 | 2357 | | EncodingGroup=1 | 2358 | CSE(MCC1) | | 2359 +=======================+=================================+ 2361 Table 13: Advertisement sent to Endpoint F - One Encoding 2363 Alternatively if the MCU wanted to provide the speaker as one media 2364 stream and the audiences as another it could assign an encoding 2365 group to VC2 in Capture Scene 2 and provide a CSE in Capture Scene 2366 #4 as per the example below. 2368 Advertisement sent to Endpoint F 2370 +=======================+=================================+ 2371 | Capture Scene #1 | Description=AustralianConfRoom | 2372 +-----------------------|---------------------------------+ 2373 | VC1 | Description=Audience | 2374 | CSE(VC1) | | 2375 +=======================+=================================+ 2376 | Capture Scene #2 | Description=ChinaConfRoom | 2377 +-----------------------|---------------------------------+ 2378 | VC2 | Description=Speaker | 2379 | | EncodingGroup=1 | 2380 | VC3 | Description=Audience | 2381 | CSE(VC2, VC3) | | 2382 +=======================+=================================+ 2383 | Capture Scene #3 | Description=USAConfRoom | 2384 +-----------------------|---------------------------------+ 2385 | VC4 | Description=Audience | 2386 | CSE(VC4) | | 2387 +=======================+=================================+ 2388 | Capture Scene #4 | | 2389 +-----------------------|---------------------------------+ 2390 | MCC1(VC1,VC3,VC4) | Policy=RoundRobin:1 | 2391 | | MaxCaptures=1 | 2392 | | EncodingGroup=1 | 2393 | MCC2(VC2) | MaxCaptures=1 | 2394 | | EncodingGroup=1 | 2395 | CSE2(MCC1,MCC2) | | 2396 +=======================+=================================+ 2398 Table 14: Advertisement sent to Endpoint F - Two Encodings 2400 Therefore a Consumer could choose whether or not to have a separate 2401 speaker related stream and could choose which endpoints to see. If 2402 it wanted the second stream but not the Australian conference room 2403 it could indicate the following captures in the Configure message: 2405 +-----------------------+---------------------------------+ 2406 | MCC1(VC3,VC4) | Encoding | 2407 | VC2 | Encoding | 2408 +-----------------------|---------------------------------+ 2409 Table 15: MCU case: Consumer Response 2411 12.3.2. Several MCCs in the same Advertisement 2413 Multiple MCCs can be used where multiple streams are used to carry 2414 media from multiple endpoints. For example: 2416 A conference has three endpoints D, E and F. Each end point has 2417 three video captures covering the left, middle and right regions of 2418 each conference room. The MCU receives the following 2419 advertisements from D and E. 2421 +-----------------------+---------------------------------+ 2422 | Capture Scene #1 | Description=AustralianConfRoom | 2423 +-----------------------|---------------------------------+ 2424 | VC1 | CaptureArea=Left | 2425 | | EncodingGroup=1 | 2426 | VC2 | CaptureArea=Centre | 2427 | | EncodingGroup=1 | 2428 | VC3 | CaptureArea=Right | 2429 | | EncodingGroup=1 | 2430 | CSE(VC1,VC2,VC3) | | 2431 +---------------------------------------------------------+ 2433 Table 16: Advertisement received from Endpoint D 2435 +-----------------------+---------------------------------+ 2436 | Capture Scene #1 | Description=ChinaConfRoom | 2437 +-----------------------|---------------------------------+ 2438 | VC1 | CaptureArea=Left | 2439 | | EncodingGroup=1 | 2440 | VC2 | CaptureArea=Centre | 2441 | | EncodingGroup=1 | 2442 | VC3 | CaptureArea=Right | 2443 | | EncodingGroup=1 | 2444 | CSE(VC1,VC2,VC3) | | 2445 +---------------------------------------------------------+ 2447 Table 17: Advertisement received from Endpoint E 2449 The MCU wants to offer Endpoint F three Capture Encodings. Each 2450 Capture Encoding would contain all the Captures from either 2451 Endpoint D or Endpoint E depending based on the active speaker. 2452 The MCU sends the following Advertisement: 2454 +=======================+=================================+ 2455 | Capture Scene #1 | Description=AustralianConfRoom | 2456 +-----------------------|---------------------------------+ 2457 | VC1 | | 2458 | VC2 | | 2459 | VC3 | | 2460 | CSE(VC1,VC2,VC3) | | 2461 +=======================+=================================+ 2462 | Capture Scene #2 | Description=ChinaConfRoom | 2463 +-----------------------|---------------------------------+ 2464 | VC4 | | 2465 | VC5 | | 2466 | VC6 | | 2467 | CSE(VC4,VC5,VC6) | | 2468 +=======================+=================================+ 2469 | Capture Scene #3 | | 2470 +-----------------------|---------------------------------+ 2471 | MCC1(VC1,VC4) | CaptureArea=Left | 2472 | | MaxCaptures=1 | 2473 | | SynchronisationID=1 | 2474 | | EncodingGroup=1 | 2475 | MCC2(VC2,VC5) | CaptureArea=Centre | 2476 | | MaxCaptures=1 | 2477 | | SynchronisationID=1 | 2478 | | EncodingGroup=1 | 2479 | MCC3(VC3,VC6) | CaptureArea=Right | 2480 | | MaxCaptures=1 | 2481 | | SynchronisationID=1 | 2482 | | EncodingGroup=1 | 2483 | CSE(MCC1,MCC2,MCC3) | | 2484 +=======================+=================================+ 2485 Table 17: Advertisement received from Endpoint E 2487 12.3.3. Heterogeneous conference with switching and composition 2489 Consider a conference between endpoints with the following 2490 characteristics: 2492 Endpoint A - 4 screens, 3 cameras 2494 Endpoint B - 3 screens, 3 cameras 2496 Endpoint C - 3 screens, 3 cameras 2498 Endpoint D - 3 screens, 3 cameras 2500 Endpoint E - 1 screen, 1 camera 2502 Endpoint F - 2 screens, 1 camera 2504 Endpoint G - 1 screen, 1 camera 2506 This example focuses on what the user in one of the 3-camera multi- 2507 screen endpoints sees. Call this person User A, at Endpoint A. 2508 There are 4 large display screens at Endpoint A. Whenever somebody 2509 at another site is speaking, all the video captures from that 2510 endpoint are shown on the large screens. If the talker is at a 3- 2511 camera site, then the video from those 3 cameras fills 3 of the 2512 screens. If the talker is at a single-camera site, then video from 2513 that camera fills one of the screens, while the other screens show 2514 video from other single-camera endpoints. 2516 User A hears audio from the 4 loudest talkers. 2518 User A can also see video from other endpoints, in addition to the 2519 current talker, although much smaller in size. Endpoint A has 4 2520 screens, so one of those screens shows up to 9 other Media Captures 2521 in a tiled fashion. When video from a 3 camera endpoint appears in 2522 the tiled area, video from all 3 cameras appears together across 2523 the screen with correct spatial relationship among those 3 images. 2525 +---+---+---+ +-------------+ +-------------+ +-------------+ 2526 | | | | | | | | | | 2527 +---+---+---+ | | | | | | 2528 | | | | | | | | | | 2529 +---+---+---+ | | | | | | 2530 | | | | | | | | | | 2531 +---+---+---+ +-------------+ +-------------+ +-------------+ 2532 Figure 7: Endpoint A - 4 Screen Display 2534 User B at Endpoint B sees a similar arrangement, except there are 2535 only 3 screens, so the 9 other Media Captures are spread out across 2536 the bottom of the 3 displays, in a picture-in-picture (PIP) format. 2537 When video from a 3 camera endpoint appears in the PIP area, video 2538 from all 3 cameras appears together across a single screen with 2539 correct spatial relationship. 2541 +-------------+ +-------------+ +-------------+ 2542 | | | | | | 2543 | | | | | | 2544 | | | | | | 2545 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2546 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2547 +-------------+ +-------------+ +-------------+ 2548 Figure 8: Endpoint B - 3 Screen Display with PiPs 2550 When somebody at a different endpoint becomes the current talker, 2551 then User A and User B both see the video from the new talker 2552 appear on their large screen area, while the previous talker takes 2553 one of the smaller tiled or PIP areas. The person who is the 2554 current talker doesn't see themselves; they see the previous talker 2555 in their large screen area. 2557 One of the points of this example is that endpoints A and B each 2558 want to receive 3 capture encodings for their large display areas, 2559 and 9 encodings for their smaller areas. A and B are be able to 2560 each send the same Configure message to the MCU, and each receive 2561 the same conceptual Media Captures from the MCU. The differences 2562 are in how they are rendered and are purely a local matter at A and 2563 B. 2565 The Advertisements for such a scenario are described below. 2567 +-----------------------+---------------------------------+ 2568 | Capture Scene #1 | Description=Endpoint x | 2569 +-----------------------|---------------------------------+ 2570 | VC1 | EncodingGroup=1 | 2571 | VC2 | EncodingGroup=1 | 2572 | VC3 | EncodingGroup=1 | 2573 | AC1 | EncodingGroup=2 | 2574 | CSE1(VC1, VC2, VC3) | | 2575 | CSE2(AC1) | | 2576 +---------------------------------------------------------+ 2578 Table 19: Advertisement received at the MCU from Endpoints A to D 2580 +-----------------------+---------------------------------+ 2581 | Capture Scene #1 | Description=Endpoint y | 2582 +-----------------------|---------------------------------+ 2583 | VC1 | EncodingGroup=1 | 2584 | AC1 | EncodingGroup=2 | 2585 | CSE1(VC1) | | 2586 | CSE2(AC1) | | 2587 +---------------------------------------------------------+ 2589 Table 20: Advertisement received at the MCU from Endpoints E to F 2591 Rather than considering what is displayed the CLUE concentrates 2592 more on what the MCU sends. The MCU doesn't know anything about 2593 the number of screens an endpoint has. 2595 As Endpoints A to D each advertise that three Captures make up a 2596 Capture Scene, the MCU offers these in a "site" switching mode. 2597 That is that there are three Multiple Content Captures (and 2598 Capture Encodings) each switching between Endpoints. The MCU 2599 switches in the applicable media into the stream based on voice 2600 activity. Endpoint A will not see a capture from itself. 2602 Using the MCC concept the MCU would send the following 2603 Advertisement to endpoint A: 2605 +=======================+=================================+ 2606 | Capture Scene #1 | Description=Endpoint B | 2607 +-----------------------|---------------------------------+ 2608 | VC4 | Left | 2609 | VC5 | Center | 2610 | VC6 | Right | 2611 | AC1 | | 2612 | CSE(VC4,VC5,VC6) | | 2613 | CSE(AC1) | | 2614 +=======================+=================================+ 2615 | Capture Scene #2 | Description=Endpoint C | 2616 +-----------------------|---------------------------------+ 2617 | VC7 | Left | 2618 | VC8 | Center | 2619 | VC9 | Right | 2620 | AC2 | | 2621 | CSE(VC7,VC8,VC9) | | 2622 | CSE(AC2) | | 2623 +=======================+=================================+ 2624 | Capture Scene #3 | Description=Endpoint D | 2625 +-----------------------|---------------------------------+ 2626 | VC10 | Left | 2627 | VC11 | Center | 2628 | VC12 | Right | 2629 | AC3 | | 2630 | CSE(VC10,VC11,VC12) | | 2631 | CSE(AC3) | | 2632 +=======================+=================================+ 2633 | Capture Scene #4 | Description=Endpoint E | 2634 +-----------------------|---------------------------------+ 2635 | VC13 | | 2636 | AC4 | | 2637 | CSE(VC13) | | 2638 | CSE(AC4) | | 2639 +=======================+=================================+ 2640 | Capture Scene #5 | Description=Endpoint F | 2641 +-----------------------|---------------------------------+ 2642 | VC14 | | 2643 | AC5 | | 2644 | CSE(VC14) | | 2645 | CSE(AC5) | | 2646 +=======================+=================================+ 2647 | Capture Scene #6 | Description=Endpoint G | 2648 +-----------------------|---------------------------------+ 2649 | VC15 | | 2650 | AC6 | | 2651 | CSE(VC15) | | 2652 | CSE(AC6) | | 2653 +=======================+=================================+ 2655 Table 21: Advertisement sent to endpoint A - Source Part 2657 The above part of the Advertisement presents information about the 2658 sources to the MCC. The information is effectively the same as the 2659 received Advertisements except that there are no Capture Encodings 2660 associated with them and the identities have been re-numbered. 2662 In addition to the source Capture information the MCU advertises 2663 "site" switching of Endpoints B to G in three streams. 2665 +=======================+=================================+ 2666 | Capture Scene #7 | Description=Output3streammix | 2667 +-----------------------|---------------------------------+ 2668 | MCC1(VC4,VC7,VC10, | CaptureArea=Left | 2669 | VC13) | MaxCaptures=1 | 2670 | | SynchronisationID=1 | 2671 | | Policy=SoundLevel:0 | 2672 | | EncodingGroup=1 | 2673 | | | 2674 | MCC2(VC5,VC8,VC11, | CaptureArea=Center | 2675 | VC14) | MaxCaptures=1 | 2676 | | SynchronisationID=1 | 2677 | | Policy=SoundLevel:0 | 2678 | | EncodingGroup=1 | 2679 | | | 2680 | MCC3(VC6,VC9,VC12, | CaptureArea=Right | 2681 | VC15) | MaxCaptures=1 | 2682 | | SynchronisationID=1 | 2683 | | Policy=SoundLevel:0 | 2684 | | EncodingGroup=1 | 2685 | | | 2686 | MCC4() (for audio) | CaptureArea=whole scene | 2687 | | MaxCaptures=1 | 2688 | | Policy=SoundLevel:0 | 2689 | | EncodingGroup=2 | 2690 | | | 2691 | MCC5() (for audio) | CaptureArea=whole scene | 2692 | | MaxCaptures=1 | 2693 | | Policy=SoundLevel:1 | 2694 | | EncodingGroup=2 | 2695 | | | 2696 | MCC6() (for audio) | CaptureArea=whole scene | 2697 | | MaxCaptures=1 | 2698 | | Policy=SoundLevel:2 | 2699 | | EncodingGroup=2 | 2700 | | | 2701 | MCC7() (for audio) | CaptureArea=whole scene | 2702 | | MaxCaptures=1 | 2703 | | Policy=SoundLevel:3 | 2704 | | EncodingGroup=2 | 2705 | | | 2706 | CSE(MCC1,MCC2,MCC3) | | 2707 | CSE(MCC4,MCC5,MCC6, | | 2708 | MCC7) | | 2709 +=======================+=================================+ 2711 Table 22: Advertisement send to endpoint A - switching part 2713 The above part describes the switched 3 main streams that relate to 2714 site switching. MaxCaptures=1 indicates that only one Capture from 2715 the MCC is sent at a particular time. SynchronisationID=1 indicates 2716 that the source sending is synchronised. The provider can choose to 2717 group together VC13, VC14, and VC15 for the purpose of switching 2718 according to the SynchronisationID. Therefore when the provider 2719 switches one of them into an MCC, it can also switch the others 2720 even though they are not part of the same Capture Scene. 2722 All the audio for the conference is included in this Scene #7. 2723 There isn't necessarily a one to one relation between any audio 2724 capture and video capture in this scene. Typically a change in 2725 loudest talker will cause the MCU to switch the audio streams more 2726 quickly than switching video streams. 2728 The MCU can also supply nine media streams showing the active and 2729 previous eight speakers. It includes the following in the 2730 Advertisement: 2732 +=======================+=================================+ 2733 | Capture Scene #8 | Description=Output9stream | 2734 +-----------------------|---------------------------------+ 2735 | MCC8(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2736 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:0 | 2737 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2738 | | | 2739 | MCC9(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2740 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:1 | 2741 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2742 | | | 2743 to to | 2744 | | | 2745 | MCC16(VC4,VC5,VC6,VC7,| MaxCaptures=1 | 2746 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:8 | 2747 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2748 | | | 2749 | CSE(MCC8,MCC9,MCC10, | | 2750 | MCC11,MCC12,MCC13,| | 2751 | MCC14,MCC15,MCC16)| | 2752 +=======================+=================================+ 2754 Table 23: Advertisement sent to endpoint A - 9 switched part 2756 The above part indicates that there are 9 capture encodings. Each 2757 of the Capture Encodings may contain any captures from any source 2758 site with a maximum of one Capture at a time. Which Capture is 2759 present is determined by the policy. The MCCs in this scene do not 2760 have any spatial attributes. 2762 Note: The Provider alternatively could provide each of the MCCs 2763 above in its own Capture Scene. 2765 If the MCU wanted to provide a composed Capture Encoding containing 2766 all of the 9 captures it could Advertise in addition: 2768 +=======================+=================================+ 2769 | Capture Scene #9 | Description=NineTiles | 2770 +-----------------------|---------------------------------+ 2771 | MCC13(MCC8,MCC9,MCC10,| MaxCaptures=9 | 2772 | MCC11,MCC12,MCC13,| EncodingGroup=1 | 2773 | MCC14,MCC15,MCC16)| | 2774 | | | 2775 | CSE(MCC13) | | 2776 +=======================+=================================+ 2778 Table 24: Advertisement sent to endpoint A - 9 composed part 2780 As MaxCaptures is 9 it indicates that the capture encoding contains 2781 information from 9 sources at a time. 2783 The Advertisement to Endpoint B is identical to the above other 2784 than the captures from Endpoint A would be added and the captures 2785 from Endpoint B would be removed. Whether the Captures are rendered 2786 on a four screen display or a three screen display is up to the 2787 Consumer to determine. The Consumer wants to place video captures 2788 from the same original source endpoint together, in the correct 2789 spatial order, but the MCCs do not have spatial attributes. So the 2790 Consumer needs to associate incoming media packets with the 2791 original individual captures in the advertisement (such as VC4, 2792 VC5, and VC6) in order to know the spatial information it needs for 2793 correct placement on the screens. 2795 Editor's note: this is an open issue, about how to associate 2796 incoming packets with the original capture that is a constituent of 2797 an MCC. This document probably should mention it in an earlier 2798 section, after the solution is worked out in the other CLUE 2799 documents. 2801 12.3.4. Heterogeneous conference with voice activated switching 2803 This example illustrates how multipoint "voice activated switching" 2804 behavior can be realized, with an endpoint making its own decision 2805 about which of its outgoing video streams is considered the "active 2806 talker" from that endpoint. Then an MCU can decide which is the 2807 active talker among the whole conference. 2809 Consider a conference between endpoints with the following 2810 characteristics: 2812 Endpoint A - 3 screens, 3 cameras 2814 Endpoint B - 3 screens, 3 cameras 2816 Endpoint C - 1 screen, 1 camera 2818 This example focuses on what the user at endpoint C sees. The 2819 user would like to see the video capture of the current talker, 2820 without composing it with any other video capture. In this 2821 example endpoint C is capable of receiving only a single video 2822 stream. The following tables describe advertisements from A and B 2823 to the MCU, and from the MCU to C, that can be used to accomplish 2824 this. 2826 +-----------------------+---------------------------------+ 2827 | Capture Scene #1 | Description=Endpoint x | 2828 +-----------------------|---------------------------------+ 2829 | VC1 | CaptureArea=Left | 2830 | | EncodingGroup=1 | 2831 | VC2 | CaptureArea=Center | 2832 | | EncodingGroup=1 | 2833 | VC3 | CaptureArea=Right | 2834 | | EncodingGroup=1 | 2835 | MCC1(VC1,VC2,VC3) | MaxCaptures=1 | 2836 | | CaptureArea=whole scene | 2837 | | Policy=SoundLevel:0 | 2838 | | EncodingGroup=1 | 2839 | AC1 | CaptureArea=whole scene | 2840 | | EncodingGroup=2 | 2841 | CSE1(VC1, VC2, VC3) | | 2842 | CSE2(MCC1) | | 2843 | CSE3(AC1) | | 2844 +---------------------------------------------------------+ 2846 Table 25: Advertisement received at the MCU from Endpoints A and B 2848 Endpoints A and B are advertising each individual video capture, 2849 and also a switched capture MCC1 which switches between the other 2850 three based on who is the active talker. These endpoints do not 2851 advertise distinct audio captures associated with each individual 2852 video capture, so it would be impossible for the MCU (as a media 2853 consumer) to make its own determination of which video capture is 2854 the active talker based just on information in the audio streams. 2856 +-----------------------+---------------------------------+ 2857 | Capture Scene #1 | Description=conference | 2858 +-----------------------|---------------------------------+ 2859 | MCC1() | CaptureArea=Left | 2860 | | MaxCaptures=1 | 2861 | | SynchronisationID=1 | 2862 | | Policy=SoundLevel:0 | 2863 | | EncodingGroup=1 | 2864 | | | 2865 | MCC2() | CaptureArea=Center | 2866 | | MaxCaptures=1 | 2867 | | SynchronisationID=1 | 2868 | | Policy=SoundLevel:0 | 2869 | | EncodingGroup=1 | 2870 | | | 2871 | MCC3() | CaptureArea=Right | 2872 | | MaxCaptures=1 | 2873 | | SynchronisationID=1 | 2874 | | Policy=SoundLevel:0 | 2875 | | EncodingGroup=1 | 2876 | | | 2877 | MCC4() | CaptureArea=whole scene | 2878 | | MaxCaptures=1 | 2879 | | Policy=SoundLevel:0 | 2880 | | EncodingGroup=1 | 2881 | | | 2882 | MCC5() (for audio) | CaptureArea=whole scene | 2883 | | MaxCaptures=1 | 2884 | | Policy=SoundLevel:0 | 2885 | | EncodingGroup=2 | 2886 | | | 2887 | MCC6() (for audio) | CaptureArea=whole scene | 2888 | | MaxCaptures=1 | 2889 | | Policy=SoundLevel:1 | 2890 | | EncodingGroup=2 | 2891 | CSE1(MCC1,MCC2,MCC3 | | 2892 | CSE2(MCC4) | | 2893 | CSE3(MCC5,MCC6) | | 2894 +---------------------------------------------------------+ 2896 Table 26: Advertisement sent from the MCU to C 2898 The MCU advertises one scene, with four video MCCs. Three of them 2899 in CSE1 give a left, center, right view of the conference, with 2900 "site switching". MCC4 provides a single video capture 2901 representing a view of the whole conference. The MCU intends for 2902 MCC4 to be switched between all the other original source 2903 captures. In this example advertisement the MCU is not giving all 2904 the information about all the other endpoints' scenes and which of 2905 those captures is included in the MCCs. The MCU could include all 2906 that information if it wants to give the consumers more 2907 information, but it is not necessary for this example scenario. 2909 The Provider advertises MCC5 and MCC6 for audio. Both are 2910 switched captures, with different SoundLevel policies indicating 2911 they are the top two dominant talkers. The Provider advertises 2912 CSE3 with both MCCs, suggesting the Consumer should use both if it 2913 can. 2915 Endpoint C, in its configure message to the MCU, requests to 2916 receive MCC4 for video, and MCC5 and MCC6 for audio. In order for 2917 the MCU to get the information it needs to construct MCC4, it has 2918 to send configure messages to A and B asking to receive MCC1 from 2919 each of them, along with their AC1 audio. Now the MCU can use 2920 audio energy information from the two incoming audio streams from 2921 A and B to determine which of those alternatives is the current 2922 talker. Based on that, the MCU uses either MCC1 from A or MCC1 2923 from B as the source of MCC4 to send to C. 2925 13. Acknowledgements 2927 Allyn Romanow and Brian Baldino were authors of early versions. 2928 Mark Gorzyinski contributed much to the approach. We want to 2929 thank Stephen Botzko for helpful discussions on audio. 2931 14. IANA Considerations 2933 None. 2935 15. Security Considerations 2937 There are several potential attacks related to telepresence, and 2938 specifically the protocols used by CLUE, in the case of 2939 conferencing sessions, due to the natural involvement of multiple 2940 endpoints and the many, often user-invoked, capabilities provided 2941 by the systems. 2943 A middle box involved in a CLUE session can experience many of the 2944 same attacks as that of a conferencing system such as that enabled 2945 by the XCON framework [RFC 6503]. Examples of attacks include the 2946 following: an endpoint attempting to listen to sessions in which 2947 it is not authorized to participate, an endpoint attempting to 2948 disconnect or mute other users, and theft of service by an 2949 endpoint in attempting to create telepresence sessions it is not 2950 allowed to create. Thus, it is RECOMMENDED that a middle box 2951 implementing the protocols necessary to support CLUE, follow the 2952 security recommendations specified in the conference control 2953 protocol documents. In the case of CLUE, SIP is the default 2954 conferencing protocol, thus the security considerations in RFC 2955 4579 MUST be followed. 2957 One primary security concern, surrounding the CLUE framework 2958 introduced in this document, involves securing the actual 2959 protocols and the associated authorization mechanisms. These 2960 concerns apply to endpoint to endpoint sessions, as well as 2961 sessions involving multiple endpoints and middle boxes. Figure 2 2962 in section 5 provides a basic flow of information exchange for 2963 CLUE and the protocols involved. 2965 As described in section 5, CLUE uses SIP/SDP to establish the 2966 session prior to exchanging any CLUE specific information. Thus 2967 the security mechanisms recommended for SIP [RFC 3261], including 2968 user authentication and authorization, SHOULD be followed. In 2969 addition, the media is based on RTP and thus existing RTP security 2970 mechanisms, such as DTLS/SRTP, MUST be supported. 2972 A separate data channel is established to transport the CLUE 2973 protocol messages. The contents of the CLUE protocol messages are 2974 based on information introduced in this document, which is 2975 represented by an XML schema for this information defined in the 2976 CLUE data model [ref]. Some of the information which could 2977 possibly introduce privacy concerns is the xCard information as 2978 described in section x. In addition, the (text) description field 2979 in the Media Capture attribute (section 7.1.1.7) could possibly 2980 reveal sensitive information or specific identities. The same 2981 would be true for the descriptions in the Capture Scene (section 2982 7.3.1) and Capture Scene Entry (7.3.2) attributes. One other 2983 important consideration for the information in the xCard as well 2984 as the description field in the Media Capture and Capture Scene 2985 Entry attributes is that while the endpoints involved in the 2986 session have been authenticated, there is no assurance that the 2987 information in the xCard or description fields is authentic. 2988 Thus, this information SHOULD not be used to make any 2989 authorization decisions and the participants in the sessions 2990 SHOULD be made aware of this. 2992 While other information in the CLUE protocol messages does not 2993 reveal specific identities, it can reveal characteristics and 2994 capabilities of the endpoints. That information could possibly 2995 uniquely identify specific endpoints. It might also be possible 2996 for an attacker to manipulate the information and disrupt the CLUE 2997 sessions. It would also be possible to mount a DoS attack on the 2998 CLUE endpoints if a malicious agent has access to the data 2999 channel. Thus, It MUST be possible for the endpoints to establish 3000 a channel which is secure against both message recovery and 3001 message modification. Further details on this are provided in the 3002 CLUE data channel solution document. 3004 There are also security issues associated with the authorization 3005 to perform actions at the CLUE endpoints to invoke specific 3006 capabilities (e.g., re-arranging screens, sharing content, etc.). 3007 However, the policies and security associated with these actions 3008 are outside the scope of this document and the overall CLUE 3009 solution. 3011 16. Changes Since Last Version 3013 NOTE TO THE RFC-Editor: Please remove this section prior to 3014 publication as an RFC. 3016 Changes from 14 to 15: 3018 1. Add "=" and "<=" qualifiers to MaxCaptures attribute, and 3019 clarify the meaning regarding switched and composed MCC. 3021 2. Add section 7.3.3 Global Capture Scene Entry List, and a few 3022 other sentences elsewhere that refer to global CSE sets. 3024 3. Clarify: The Provider MUST be capable of encoding and sending 3025 all Captures (*that have an encoding group*) in a single 3026 Capture Scene Entry simultaneously. 3028 4. Add voice activated switching example in section 12. 3030 5. Change name of attributes Participant Info/Type to Person 3031 Info/Type. 3033 6. Clarify the Person Info/Type attributes have the same meaning 3034 regardless of whether or not the capture has a Presentation 3035 attribute. 3037 7. Update example section 12.1 to be consistent with the rest of 3038 the document, regarding MCC and capture attributes. 3040 8. State explicitly each CSE has a unique ID. 3042 Changes from 13 to 14: 3044 1. Fill in section for Security Considerations. 3046 2. Replace Role placeholder with Participant Information, 3047 Participant Type, and Scene Information attributes. 3049 3. Spatial information implies nothing about how constituent 3050 media captures are combined into a composed MCC. 3052 4. Clean up MCC example in Section 12.3.3. Clarify behavior of 3053 tiled and PIP display windows. Add audio. Add new open 3054 issue about associating incoming packets to original source 3055 capture. 3057 5. Remove editor's note and associated statement about RTP 3058 multiplexing at end of section 5. 3060 6. Remove editor's note and associated paragraph about 3061 overloading media channel with both CLUE and non-CLUE usage, 3062 in section 5. 3064 7. In section 10, clarify intent of media encodings conforming 3065 to SDP, even with multiple CLUE message exchanges. Remove 3066 associated editor's note. 3068 Changes from 12 to 13: 3070 1. Added the MCC concept including updates to existing sections 3071 to incorporate the MCC concept. New MCC attributes: 3072 MaxCaptures, SynchronisationID and Policy. 3074 2. Removed the "composed" and "switched" Capture attributes due 3075 to overlap with the MCC concept. 3077 3. Removed the "Scene-switch-policy" CSE attribute, replaced by 3078 MCC and SynchronisationID. 3080 4. Editorial enhancements including numbering of the Capture 3081 attribute sections, tables, figures etc. 3083 Changes from 11 to 12: 3085 1. Ticket #44. Remove note questioning about requiring a 3086 Consumer to send a Configure after receiving Advertisement. 3088 2. Ticket #43. Remove ability for consumer to choose value of 3089 attribute for scene-switch-policy. 3091 3. Ticket #36. Remove computational complexity parameter, 3092 MaxGroupPps, from Encoding Groups. 3094 4. Reword the Abstract and parts of sections 1 and 4 (now 5) 3095 based on Mary's suggestions as discussed on the list. Move 3096 part of the Introduction into a new section Overview & 3097 Motivation. 3099 5. Add diagram of an Advertisement, in the Overview of the 3100 Framework/Model section. 3102 6. Change Intended Status to Standards Track. 3104 7. Clean up RFC2119 keyword language. 3106 Changes from 10 to 11: 3108 1. Add description attribute to Media Capture and Capture Scene 3109 Entry. 3111 2. Remove contradiction and change the note about open issue 3112 regarding always responding to Advertisement with a Configure 3113 message. 3115 3. Update example section, to cleanup formatting and make the 3116 media capture attributes and encoding parameters consistent 3117 with the rest of the document. 3119 Changes from 09 to 10: 3121 1. Several minor clarifications such as about SDP usage, Media 3122 Captures, Configure message. 3124 2. Simultaneous Set can be expressed in terms of Capture Scene 3125 and Capture Scene Entry. 3127 3. Removed Area of Scene attribute. 3129 4. Add attributes from draft-groves-clue-capture-attr-01. 3131 5. Move some of the Media Capture attribute descriptions back 3132 into this document, but try to leave detailed syntax to the 3133 data model. Remove the OUTSOURCE sections, which are already 3134 incorporated into the data model document. 3136 Changes from 08 to 09: 3138 1. Use "document" instead of "memo". 3140 2. Add basic call flow sequence diagram to introduction. 3142 3. Add definitions for Advertisement and Configure messages. 3144 4. Add definitions for Capture and Provider. 3146 5. Update definition of Capture Scene. 3148 6. Update definition of Individual Encoding. 3150 7. Shorten definition of Media Capture and add key points in the 3151 Media Captures section. 3153 8. Reword a bit about capture scenes in overview. 3155 9. Reword about labeling Media Captures. 3157 10. Remove the Consumer Capability message. 3159 11. New example section heading for media provider behavior 3161 12. Clarifications in the Capture Scene section. 3163 13. Clarifications in the Simultaneous Transmission Set section. 3165 14. Capitalize defined terms. 3167 15. Move call flow example from introduction to overview section 3169 16. General editorial cleanup 3171 17. Add some editors' notes requesting input on issues 3173 18. Summarize some sections, and propose details be outsourced 3174 to other documents. 3176 Changes from 06 to 07: 3178 1. Ticket #9. Rename Axis of Capture Point attribute to Point 3179 on Line of Capture. Clarify the description of this 3180 attribute. 3182 2. Ticket #17. Add "capture encoding" definition. Use this new 3183 term throughout document as appropriate, replacing some usage 3184 of the terms "stream" and "encoding". 3186 3. Ticket #18. Add Max Capture Encodings media capture 3187 attribute. 3189 4. Add clarification that different capture scene entries are 3190 not necessarily mutually exclusive. 3192 Changes from 05 to 06: 3194 1. Capture scene description attribute is a list of text strings, 3195 each in a different language, rather than just a single string. 3197 2. Add new Axis of Capture Point attribute. 3199 3. Remove appendices A.1 through A.6. 3201 4. Clarify that the provider must use the same coordinate system 3202 with same scale and origin for all coordinates within the same 3203 capture scene. 3205 Changes from 04 to 05: 3207 1. Clarify limitations of "composed" attribute. 3209 2. Add new section "capture scene entry attributes" and add the 3210 attribute "scene-switch-policy". 3212 3. Add capture scene description attribute and description 3213 language attribute. 3215 4. Editorial changes to examples section for consistency with the 3216 rest of the document. 3218 Changes from 03 to 04: 3220 1. Remove sentence from overview - "This constitutes a significant 3221 change ..." 3223 2. Clarify a consumer can choose a subset of captures from a 3224 capture scene entry or a simultaneous set (in section "capture 3225 scene" and "consumer's choice..."). 3227 3. Reword first paragraph of Media Capture Attributes section. 3229 4. Clarify a stereo audio capture is different from two mono audio 3230 captures (description of audio channel format attribute). 3232 5. Clarify what it means when coordinate information is not 3233 specified for area of capture, point of capture, area of scene. 3235 6. Change the term "producer" to "provider" to be consistent (it 3236 was just in two places). 3238 7. Change name of "purpose" attribute to "content" and refer to 3239 RFC4796 for values. 3241 8. Clarify simultaneous sets are part of a provider advertisement, 3242 and apply across all capture scenes in the advertisement. 3244 9. Remove sentence about lip-sync between all media captures in a 3245 capture scene. 3247 10. Combine the concepts of "capture scene" and "capture set" 3248 into a single concept, using the term "capture scene" to 3249 replace the previous term "capture set", and eliminating the 3250 original separate capture scene concept. 3252 Informative References 3254 Edt. Note: Decide which of these really are Normative References. 3256 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3257 Requirement Levels", BCP 14, RFC 2119, March 1997. 3259 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., 3260 Johnston, 3261 A., Peterson, J., Sparks, R., Handley, M., and E. 3262 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 3263 June 2002. 3265 [RFC3264] Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model 3266 with the Session Description Protocol (SDP)", RFC 3264, 3267 June 2002. 3269 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 3270 Jacobson, "RTP: A Transport Protocol for Real-Time 3271 Applications", STD 64, RFC 3550, July 2003. 3273 [RFC4353] Rosenberg, J., "A Framework for Conferencing with the 3274 Session Initiation Protocol (SIP)", RFC 4353, 3275 February 2006. 3277 [RFC4579] Johnston, A., Levin, O., "SIP Call Control - 3278 Conferencing for User Agents", RFC 4579, August 2006 3280 [RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 3281 5117, 3282 January 2008. 3284 17. Authors' Addresses 3286 Mark Duckworth (editor) 3287 Polycom 3288 Andover, MA 01810 3289 USA 3290 Email: mark.duckworth@polycom.com 3292 Andrew Pepperell 3293 Acano 3294 Uxbridge, England 3295 UK 3297 Email: apeppere@gmail.com 3299 Stephan Wenger 3300 Vidyo, Inc. 3301 433 Hackensack Ave. 3302 Hackensack, N.J. 07601 3303 USA 3305 Email: stewe@stewe.org