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'I-D.ietf-clue-datachannel') == Outdated reference: A later version (-17) exists of draft-ietf-clue-data-model-schema-07 == Outdated reference: A later version (-19) exists of draft-ietf-clue-protocol-02 ** Downref: Normative reference to an Experimental draft: draft-ietf-clue-protocol (ref. 'I-D.ietf-clue-protocol') == Outdated reference: A later version (-15) exists of draft-ietf-clue-signaling-04 ** Downref: Normative reference to an Experimental draft: draft-ietf-clue-signaling (ref. 'I-D.ietf-clue-signaling') == Outdated reference: A later version (-14) exists of draft-ietf-clue-rtp-mapping-03 -- Obsolete informational reference (is this intentional?): RFC 5117 (Obsoleted by RFC 7667) Summary: 4 errors (**), 0 flaws (~~), 15 warnings (==), 3 comments (--). 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: July 21, 2015 Acano 5 S. Wenger 6 Vidyo 7 January 21, 2015 9 Framework for Telepresence Multi-Streams 10 draft-ietf-clue-framework-20.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 and SDP 20 negotiation for setting up a 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 July 21, 2015. 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.............................17 64 7.1. Media Captures...........................................17 65 7.1.1. Media Capture Attributes............................18 66 7.2. Multiple Content Capture.................................24 67 7.2.1. MCC Attributes......................................25 68 7.3. Capture Scene............................................30 69 7.3.1. Capture Scene attributes............................33 70 7.3.2. Capture Scene View attributes.......................33 71 7.3.3. Global View List....................................34 72 8. Simultaneous Transmission Set Constraints.....................35 73 9. Encodings.....................................................37 74 9.1. Individual Encodings.....................................37 75 9.2. Encoding Group...........................................38 76 9.3. Associating Captures with Encoding Groups................39 77 10. Consumer's Choice of Streams to Receive from the Provider....40 78 10.1. Local preference........................................43 79 10.2. Physical simultaneity restrictions......................43 80 10.3. Encoding and encoding group limits......................43 81 11. Extensibility................................................44 82 12. Examples - Using the Framework (Informative).................44 83 12.1. Provider Behavior.......................................44 84 12.1.1. Three screen Endpoint Provider.....................44 85 12.1.2. Encoding Group Example.............................51 86 12.1.3. The MCU Case.......................................52 88 12.2. Media Consumer Behavior.................................53 89 12.2.1. One screen Media Consumer..........................53 90 12.2.2. Two screen Media Consumer configuring the example..54 91 12.2.3. Three screen Media Consumer configuring the example55 92 12.3. Multipoint Conference utilizing Multiple Content Captures55 93 12.3.1. Single Media Captures and MCC in the same 94 Advertisement..............................................55 95 12.3.2. Several MCCs in the same Advertisement.............58 96 12.3.3. Heterogeneous conference with switching and 97 composition................................................60 98 12.3.4. Heterogeneous conference with voice activated 99 switching..................................................67 100 13. Acknowledgements.............................................70 101 14. IANA Considerations..........................................70 102 15. Security Considerations......................................70 103 16. Changes Since Last Version...................................72 104 17. Normative References.........................................80 105 18. Informative References.......................................81 106 19. Authors' Addresses...........................................81 108 1. Introduction 110 Current telepresence systems, though based on open standards such 111 as RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with 112 each other. A major factor limiting the interoperability of 113 telepresence systems is the lack of a standardized way to describe 114 and negotiate the use of the multiple streams of audio and video 115 comprising the media flows. This document provides a framework for 116 protocols to enable interoperability by handling multiple streams 117 in a standardized way. The framework is intended to support the 118 use cases described in Use Cases for Telepresence Multistreams 119 [RFC7205] and to meet the requirements in Requirements for 120 Telepresence Multistreams [RFC7262]. 122 This document occasionally refers to the term "CLUE", in capital 123 letters. CLUE is an acronym for "ControLling mUltiple streams for 124 tElepresence", which is the name of the IETF working group in which 125 this document and certain companion documents have been developed. 126 Often, CLUE-something refers to something that has been designed by 127 the CLUE working group; for example, this document may be called 128 the CLUE-framework. 130 The basic session setup for the use cases is based on SIP [RFC3261] 131 and SDP offer/answer [RFC3264]. In addition to basic SIP & SDP 132 offer/answer, CLUE specific signaling is required to exchange the 133 information describing the multiple media streams. The motivation 134 for this framework, an overview of the signaling, and information 135 required to be exchanged is described in subsequent sections of 136 this document. Companion documents describe the signaling details 137 [I-D.ietf-clue-signaling] and the data model [I-D.ietf-clue-data- 138 model-schema] and protocol [I-D.ietf-clue-protocol]. 140 2. Terminology 142 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 143 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 144 this document are to be interpreted as described in RFC 2119 145 [RFC2119]. 147 3. Definitions 149 The terms defined below are used throughout this document and 150 companion documents. In order to easily identify the use of a 151 defined term, those terms are capitalized. 153 Advertisement: a CLUE message a Media Provider sends to a Media 154 Consumer describing specific aspects of the content of the media, 155 and any restrictions it has in terms of being able to provide 156 certain Streams simultaneously. 158 Audio Capture: Media Capture for audio. Denoted as ACn in the 159 examples in this document. 161 Capture: Same as Media Capture. 163 Capture Device: A device that converts physical input, such as 164 audio, video or text, into an electrical signal, in most cases to 165 be fed into a media encoder. 167 Capture Encoding: A specific encoding of a Media Capture, to be 168 sent by a Media Provider to a Media Consumer via RTP. 170 Capture Scene: a structure representing a spatial region captured 171 by one or more Capture Devices, each capturing media representing a 172 portion of the region. The spatial region represented by a Capture 173 Scene MAY correspond to a real region in physical space, such as a 174 room. A Capture Scene includes attributes and one or more Capture 175 Scene Views, with each view including one or more Media Captures. 177 Capture Scene View (CSV): a list of Media Captures of the same 178 media type that together form one way to represent the entire 179 Capture Scene. 181 CLUE-capable device: A device that supports the CLUE data channel 182 [I-D.ietf-clue-datachannel], the CLUE protocol [I-D.ietf-clue- 183 protocol] and the principles of CLUE negotiation, and seeks CLUE- 184 enabled calls. 186 CLUE-enabled call: A call in which two CLUE-capable devices have 187 successfully negotiated support for a CLUE data channel in SDP 188 [RFC4566]. A CLUE-enabled call is not necessarily immediately able 189 to send CLUE-controlled media; negotiation of the data channel and 190 of the CLUE protocol must complete first. Calls between two CLUE- 191 capable devices which have not yet successfully completed 192 negotiation of support for the CLUE data channel in SDP are not 193 considered CLUE- enabled. 195 Conference: used as defined in [RFC4353], A Framework for 196 Conferencing within the Session Initiation Protocol (SIP). 198 Configure Message: A CLUE message a Media Consumer sends to a Media 199 Provider specifying which content and Media Streams it wants to 200 receive, based on the information in a corresponding Advertisement 201 message. 203 Consumer: short for Media Consumer. 205 Encoding: short for Individual Encoding. 207 Encoding Group: A set of encoding parameters representing a total 208 media encoding capability to be sub-divided across potentially 209 multiple Individual Encodings. 211 Endpoint: A CLUE-capable device which is the logical point of final 212 termination through receiving, decoding and rendering, and/or 213 initiation through capturing, encoding, and sending of media 214 streams. An endpoint consists of one or more physical devices 215 which source and sink media streams, and exactly one [RFC4353] 216 Participant (which, in turn, includes exactly one SIP User Agent). 217 Endpoints can be anything from multiscreen/multicamera rooms to 218 handheld devices. 220 Global View: A set of references to one or more Capture Scene Views 221 of the same media type that are defined within Scenes of the same 222 advertisement. A Global View is a suggestion from the Provider to 223 the Consumer for one set of CSVs that provide a useful 224 representation of all the scenes in the advertisement. 226 Global View List: A list of Global Views included in an 227 Advertisement. A Global View List may include Global Views of 228 different media types. 230 Individual Encoding: a set of parameters representing a way to 231 encode a Media Capture to become a Capture Encoding. 233 Multipoint Control Unit (MCU): a CLUE-capable device that connects 234 two or more endpoints together into one single multimedia 235 conference [RFC5117]. An MCU includes an [RFC4353] like Mixer, 236 without the [RFC4353] requirement to send media to each 237 participant. 239 Media: Any data that, after suitable encoding, can be conveyed over 240 RTP, including audio, video or timed text. 242 Media Capture: a source of Media, such as from one or more Capture 243 Devices or constructed from other Media streams. 245 Media Consumer: a CLUE-capable device that intends to receive 246 Capture Encodings. 248 Media Provider: a CLUE-capable device that intends to send Capture 249 Encodings. 251 Multiple Content Capture (MCC): A Capture that mixes and/or 252 switches other Captures of a single type. (E.g. all audio or all 253 video.) Particular Media Captures may or may not be present in the 254 resultant Capture Encoding depending on time or space. Denoted as 255 MCCn in the example cases in this document. 257 Plane of Interest: The spatial plane within a scene containing the 258 most relevant subject matter. 260 Provider: Same as Media Provider. 262 Render: the process of generating a representation from media, such 263 as displayed motion video or sound emitted from loudspeakers. 265 Scene: Same as Capture Scene 267 Simultaneous Transmission Set: a set of Media Captures that can be 268 transmitted simultaneously from a Media Provider. 270 Single Media Capture: A capture which contains media from a single 271 source capture device, e.g. an audio capture from a single 272 microphone, a video capture from a single camera. 274 Spatial Relation: The arrangement in space of two objects, in 275 contrast to relation in time or other relationships. 277 Stream: a Capture Encoding sent from a Media Provider to a Media 278 Consumer via RTP [RFC3550]. 280 Stream Characteristics: the media stream attributes commonly used 281 in non-CLUE SIP/SDP environments (such as: media codec, bit rate, 282 resolution, profile/level etc.) as well as CLUE specific 283 attributes, such as the Capture ID or a spatial location. 285 Video Capture: Media Capture for video. Denoted as VCn in the 286 example cases in this document. 288 Video Composite: A single image that is formed, normally by an RTP 289 mixer inside an MCU, by combining visual elements from separate 290 sources. 292 4. Overview and Motivation 294 This section provides an overview of the functional elements 295 defined in this document to represent a telepresence system. The 296 motivations for the framework described in this document are also 297 provided. 299 Two key concepts introduced in this document are the terms "Media 300 Provider" and "Media Consumer". A Media Provider represents the 301 entity that sends the media and a Media Consumer represents the 302 entity that receives the media. A Media Provider provides Media in 303 the form of RTP packets, a Media Consumer consumes those RTP 304 packets. Media Providers and Media Consumers can reside in 305 Endpoints or in Multipoint Control Units (MCUs). A Media Provider 306 in an Endpoint is usually associated with the generation of media 307 for Media Captures; these Media Captures are typically sourced 308 from cameras, microphones, and the like. Similarly, the Media 309 Consumer in an Endpoint is usually associated with renderers, such 310 as screens and loudspeakers. In MCUs, Media Providers and 311 Consumers can have the form of outputs and inputs, respectively, 312 of RTP mixers, RTP translators, and similar devices. Typically, 313 telepresence devices such as Endpoints and MCUs would perform as 314 both Media Providers and Media Consumers, the former being 315 concerned with those devices' transmitted media and the latter 316 with those devices' received media. In a few circumstances, a 317 CLUE-capable device includes only Consumer or Provider 318 functionality, such as recorder-type Consumers or webcam-type 319 Providers. 321 The motivations for the framework outlined in this document 322 include the following: 324 (1) Endpoints in telepresence systems typically have multiple Media 325 Capture and Media Render devices, e.g., multiple cameras and 326 screens. While previous system designs were able to set up calls 327 that would capture media using all cameras and display media on all 328 screens, for example, there was no mechanism that can associate 329 these Media Captures with each other in space and time, in a cross- 330 vendor interoperable way. 332 (2) The mere fact that there are multiple capturing and rendering 333 devices, each of which may be configurable in aspects such as zoom, 334 leads to the difficulty that a variable number of such devices can 335 be used to capture different aspects of a region. The Capture 336 Scene concept allows for the description of multiple setups for 337 those multiple capture devices that could represent sensible 338 operation points of the physical capture devices in a room, chosen 339 by the operator. A Consumer can pick and choose from those 340 configurations based on its rendering abilities and inform the 341 Provider about its choices. Details are provided in section 7. 343 (3) In some cases, physical limitations or other reasons disallow 344 the concurrent use of a device in more than one setup. For 345 example, the center camera in a typical three-camera conference 346 room can set its zoom objective either to capture only the middle 347 few seats, or all seats of a room, but not both concurrently. The 348 Simultaneous Transmission Set concept allows a Provider to signal 349 such limitations. Simultaneous Transmission Sets are part of the 350 Capture Scene description, and are discussed in section 8. 352 (4) Often, the devices in a room do not have the computational 353 complexity or connectivity to deal with multiple encoding options 354 simultaneously, even if each of these options is sensible in 355 certain scenarios, and even if the simultaneous transmission is 356 also sensible (i.e. in case of multicast media distribution to 357 multiple endpoints). Such constraints can be expressed by the 358 Provider using the Encoding Group concept, described in section 9. 360 (5) Due to the potentially large number of RTP streams required for 361 a Multimedia Conference involving potentially many Endpoints, each 362 of which can have many Media Captures and media renderers, it has 363 become common to multiplex multiple RTP streams onto the same 364 transport address, so to avoid using the port number as a 365 multiplexing point and the associated shortcomings such as 366 NAT/firewall traversal. The large number of possible permutations 367 of sensible options a Media Provider can make available to a Media 368 Consumer makes a mechanism desirable that allows it to narrow down 369 the number of possible options that a SIP offer/answer exchange has 370 to consider. Such information is made available using protocol 371 mechanisms specified in this document and companion documents, 372 although it should be stressed that its use in an implementation is 373 OPTIONAL. Also, there are aspects of the control of both Endpoints 374 and MCUs that dynamically change during the progress of a call, 375 such as audio-level based screen switching, layout changes, and so 376 on, which need to be conveyed. Note that these control aspects are 377 complementary to those specified in traditional SIP based 378 conference management such as BFCP. An exemplary call flow can be 379 found in section 5. 381 Finally, all this information needs to be conveyed, and the notion 382 of support for it needs to be established. This is done by the 383 negotiation of a "CLUE channel", a data channel negotiated early 384 during the initiation of a call. An Endpoint or MCU that rejects 385 the establishment of this data channel, by definition, does not 386 support CLUE based mechanisms, whereas an Endpoint or MCU that 387 accepts it is REQUIRED to use it to the extent specified in this 388 document and its companion documents. 390 5. Description of the Framework/Model 392 The CLUE framework specifies how multiple media streams are to be 393 handled in a telepresence conference. 395 A Media Provider (transmitting Endpoint or MCU) describes specific 396 aspects of the content of the media and the media stream encodings 397 it can send in an Advertisement; and the Media Consumer responds to 398 the Media Provider by specifying which content and media streams it 399 wants to receive in a Configure message. The Provider then 400 transmits the asked-for content in the specified streams. 402 This Advertisement and Configure typically occur during call 403 initiation, after CLUE has been enabled in a call, but MAY also 404 happen at any time throughout the call, whenever there is a change 405 in what the Consumer wants to receive or (perhaps less common) the 406 Provider can send. 408 An Endpoint or MCU typically act as both Provider and Consumer at 409 the same time, sending Advertisements and sending Configurations in 410 response to receiving Advertisements. (It is possible to be just 411 one or the other.) 413 The data model [I-D.ietf-clue-data-model-schema]is based around two 414 main concepts: a Capture and an Encoding. A Media Capture (MC), 415 such as of type audio or video, has attributes to describe the 416 content a Provider can send. Media Captures are described in terms 417 of CLUE-defined attributes, such as spatial relationships and 418 purpose of the capture. Providers tell Consumers which Media 419 Captures they can provide, described in terms of the Media Capture 420 attributes. 422 A Provider organizes its Media Captures into one or more Capture 423 Scenes, each representing a spatial region, such as a room. A 424 Consumer chooses which Media Captures it wants to receive from the 425 Capture Scenes. 427 In addition, the Provider can send the Consumer a description of 428 the Individual Encodings it can send in terms of identifiers which 429 relate to items in SDP [RFC4566]. 431 The Provider can also specify constraints on its ability to provide 432 Media, and a sensible design choice for a Consumer is to take these 433 into account when choosing the content and Capture Encodings it 434 requests in the later offer/answer exchange. Some constraints are 435 due to the physical limitations of devices--for example, a camera 436 may not be able to provide zoom and non-zoom views simultaneously. 437 Other constraints are system based, such as maximum bandwidth. 439 The following diagram illustrates the information contained in an 440 Advertisement. 442 ................................................................... 443 . Provider Advertisement +--------------------+ . 444 . | Simultaneous Sets | . 445 . +------------------------+ +--------------------+ . 446 . | Capture Scene N | +--------------------+ . 447 . +-+----------------------+ | | Global View List | . 448 . | Capture Scene 2 | | +--------------------+ . 449 . +-+----------------------+ | | +----------------------+ . 450 . | Capture Scene 1 | | | | Encoding Group N | . 451 . | +---------------+ | | | +-+--------------------+ | . 452 . | | Attributes | | | | | Encoding Group 2 | | . 453 . | +---------------+ | | | +-+--------------------+ | | . 454 . | | | | | Encoding Group 1 | | | . 455 . | +----------------+ | | | | parameters | | | . 456 . | | V i e w s | | | | | bandwidth | | | . 457 . | | +---------+ | | | | | +-------------------+| | | . 458 . | | |Attribute| | | | | | | V i d e o || | | . 459 . | | +---------+ | | | | | | E n c o d i n g s || | | . 460 . | | | | | | | | Encoding 1 || | | . 461 . | | View 1 | | | | | | || | | . 462 . | | (list of MCs) | | |-+ | +-------------------+| | | . 463 . | +----|-|--|------+ |-+ | | | | . 464 . +---------|-|--|---------+ | +-------------------+| | | . 465 . | | | | | A u d i o || | | . 466 . | | | | | E n c o d i n g s || | | . 467 . v | | | | Encoding 1 || | | . 468 . +---------|--|--------+ | | || | | . 469 . | Media Capture N |------>| +-------------------+| | | . 470 . +-+---------v--|------+ | | | | | . 471 . | Media Capture 2 | | | | |-+ . 472 . +-+--------------v----+ |-------->| | | . 473 . | Media Capture 1 | | | | |-+ . 474 . | +----------------+ |---------->| | . 475 . | | Attributes | | |_+ +----------------------+ . 476 . | +----------------+ |_+ . 477 . +---------------------+ . 478 . . 479 ................................................................... 481 Figure 1: Advertisement Structure 483 A very brief outline of the call flow used by a simple system (two 484 Endpoints) in compliance with this document can be described as 485 follows, and as shown in the following figure. 487 +-----------+ +-----------+ 488 | Endpoint1 | | Endpoint2 | 489 +----+------+ +-----+-----+ 490 | INVITE (BASIC SDP+CLUECHANNEL) | 491 |--------------------------------->| 492 | 200 0K (BASIC SDP+CLUECHANNEL)| 493 |<---------------------------------| 494 | ACK | 495 |--------------------------------->| 496 | | 497 |<################################>| 498 | BASIC SDP MEDIA SESSION | 499 |<################################>| 500 | | 501 | CONNECT (CLUE CTRL CHANNEL) | 502 |=================================>| 503 | ... | 504 |<================================>| 505 | CLUE CTRL CHANNEL ESTABLISHED | 506 |<================================>| 507 | | 508 | ADVERTISEMENT 1 | 509 |*********************************>| 510 | ADVERTISEMENT 2 | 511 |<*********************************| 512 | | 513 | CONFIGURE 1 | 514 |<*********************************| 515 | CONFIGURE 2 | 516 |*********************************>| 517 | | 518 | REINVITE (UPDATED SDP) | 519 |--------------------------------->| 520 | 200 0K (UPDATED SDP)| 521 |<---------------------------------| 522 | ACK | 523 |--------------------------------->| 524 | | 525 |<################################>| 526 | UPDATED SDP MEDIA SESSION | 527 |<################################>| 528 | | 529 v v 531 Figure 2: Basic Information Flow 533 An initial offer/answer exchange establishes a basic media session, 534 for example audio-only, and a CLUE channel between two Endpoints. 535 With the establishment of that channel, the endpoints have 536 consented to use the CLUE protocol mechanisms and, therefore, MUST 537 adhere to the CLUE protocol suite as outlined herein. 539 Over this CLUE channel, the Provider in each Endpoint conveys its 540 characteristics and capabilities by sending an Advertisement as 541 specified herein. The Advertisement is typically not sufficient to 542 set up all media. The Consumer in the Endpoint receives the 543 information provided by the Provider, and can use it for two 544 purposes. It uses it, along with information from an offer/answer 545 exchange, to construct a CLUE Configure message to tell the 546 Provider what the Consumer wishes to receive. Also, the Consumer 547 MAY use the information provided to tailor the SDP it is going to 548 send during any following SIP offer/answer exchange, and its 549 reaction to SDP it receives in that step. It is often a sensible 550 implementation choice to do so. Spatial relationships associated 551 with the Media can be included in the Advertisement, and it is 552 often sensible for the Media Consumer to take those spatial 553 relationships into account when tailoring the SDP. The Consumer 554 can also limit the number of encodings it must set up resources to 555 receive, and not waste resources on unwanted encodings, because it 556 has the Provider's Advertisement information ahead of time to 557 determine what it really wants to receive. 559 This initial CLUE exchange is followed by an SDP offer/answer 560 exchange that not only establishes those aspects of the media that 561 have not been "negotiated" over CLUE, but has also the side effect 562 of setting up the media transmission itself, involving potentially 563 security exchanges, ICE, and whatnot. This step is plain vanilla 564 SIP. 566 During the lifetime of a call, further exchanges MAY occur over the 567 CLUE channel. In some cases, those further exchanges lead to a 568 modified system behavior of Provider or Consumer (or both) without 569 any other protocol activity such as further offer/answer exchanges. 570 For example, a Configure Message requesting the Provider to place a 571 different Capture source into a Capture Encoding, signaled over the 572 CLUE channel, ought not to lead to heavy-handed mechanisms like SIP 573 re-invites. However, in other cases, after the CLUE negotiation an 574 additional offer/answer exchange becomes necessary. For example, 575 if both sides decide to upgrade the call from a single screen to a 576 multi-screen call and more bandwidth is required for the additional 577 video channels compared to what was previously negotiated using 578 offer/answer, a new O/A exchange is REQUIRED. 580 One aspect of the protocol outlined herein and specified in more 581 detail in companion documents is that it makes available 582 information regarding the Provider's capabilities to deliver Media, 583 and attributes related to that Media such as their spatial 584 relationship, to the Consumer. The operation of the renderer 585 inside the Consumer is unspecified in that it can choose to ignore 586 some information provided by the Provider, and/or not render media 587 streams available from the Provider (although it MUST follow the 588 CLUE protocol and, therefore, MUST gracefully receive and respond 589 (through a Configure) to the Provider's information). All CLUE 590 protocol mechanisms are OPTIONAL in the Consumer in the sense that, 591 while the Consumer MUST be able to receive (and, potentially, 592 gracefully acknowledge) CLUE messages, it is free to ignore the 593 information provided therein. 595 A CLUE-capable device interoperates with a device that does not 596 support CLUE. The CLUE-capable device can determine, by the result 597 of the initial offer/answer exchange, if the other device supports 598 and wishes to use CLUE. The specific mechanism for this is 599 described in [I-D.ietf-clue-signaling]. If the other device does 600 not use CLUE, then the CLUE-capable device falls back to behavior 601 that does not require CLUE. 603 As for the media, Provider and Consumer have an end-to-end 604 communication relationship with respect to (RTP transported) media; 605 and the mechanisms described herein and in companion documents do 606 not change the aspects of setting up those RTP flows and sessions. 607 In other words, the RTP media sessions conform to the negotiated 608 SDP whether or not CLUE is used. 610 6. Spatial Relationships 612 In order for a Consumer to perform a proper rendering, it is often 613 necessary or at least helpful for the Consumer to have received 614 spatial information about the streams it is receiving. CLUE 615 defines a coordinate system that allows Media Providers to describe 616 the spatial relationships of their Media Captures to enable proper 617 scaling and spatially sensible rendering of their streams. The 618 coordinate system is based on a few principles: 620 o Each Capture Scene has a distinct coordinate system, unrelated 621 to the coordinate systems of other scenes. 623 o Simple systems which do not have multiple Media Captures to 624 associate spatially need not use the coordinate model, although 625 it can still be useful to provide an Area of Capture. 627 o Coordinates can be either in real, physical units (millimeters), 628 have an unknown scale or have no physical scale. Systems which 629 know their physical dimensions (for example professionally 630 installed Telepresence room systems) MUST provide those real- 631 world measurements to enable the best user experience for 632 advanced receiving systems that can utilize this information. 633 Systems which don't know specific physical dimensions but still 634 know relative distances MUST use 'unknown scale'. 'No scale' is 635 intended to be used only where Media Captures from different 636 devices (with potentially different scales) will be forwarded 637 alongside one another (e.g. in the case of an MCU). 639 * "Millimeters" means the scale is in millimeters. 641 * "Unknown" means the scale is not necessarily millimeters, but 642 the scale is the same for every Capture in the Capture Scene. 644 * "No Scale" means the scale could be different for each 645 capture- an MCU Provider that advertises two adjacent 646 captures and picks sources (which can change quickly) from 647 different endpoints might use this value; the scale could be 648 different and changing for each capture. But the areas of 649 capture still represent a spatial relation between captures. 651 o The coordinate system is right-handed Cartesian X, Y, Z with the 652 origin at a spatial location of the Provider's choosing. The 653 Provider MUST use the same coordinate system with the same scale 654 and origin for all coordinates within the same Capture Scene. 656 The direction of increasing coordinate values is: 657 X increases from left to right, from the point of view of an 658 observer at the front of the room looking toward the back 659 Y increases from the front of the room to the back of the room 660 Z increases from low to high (i.e. floor to ceiling) 662 Cameras in a scene typically point in the direction of increasing 663 Y, from front to back. But there could be multiple cameras 664 pointing in different directions. If the physical space does not 665 have a well-defined front and back, the provider chooses any 666 direction for X and Y consistent with right-handed coordinates. 668 7. Media Captures and Capture Scenes 670 This section describes how Providers can describe the content of 671 media to Consumers. 673 7.1. Media Captures 675 Media Captures are the fundamental representations of streams that 676 a device can transmit. What a Media Capture actually represents is 677 flexible: 679 o It can represent the immediate output of a physical source (e.g. 680 camera, microphone) or 'synthetic' source (e.g. laptop computer, 681 DVD player) 683 o It can represent the output of an audio mixer or video composer 685 o It can represent a concept such as 'the loudest speaker' 687 o It can represent a conceptual position such as 'the leftmost 688 stream' 690 To identify and distinguish between multiple Capture instances 691 Captures have a unique identity. For instance: VC1, VC2 and AC1, 692 AC2, where VC1 and VC2 refer to two different video captures and 693 AC1 and AC2 refer to two different audio captures. 695 Some key points about Media Captures: 697 . A Media Capture is of a single media type (e.g. audio or 698 video) 699 . A Media Capture is defined in a Capture Scene and is given an 700 Advertisement unique identity. The identity may be referenced 701 outside the Capture Scene that defines it through a Multiple 702 Content Capture (MCC) 703 . A Media Capture may be associated with one or more Capture 704 Scene Views 705 . A Media Capture has exactly one set of spatial information 706 . A Media Capture can be the source of at most one Capture 707 Encoding 709 Each Media Capture can be associated with attributes to describe 710 what it represents. 712 7.1.1. Media Capture Attributes 714 Media Capture Attributes describe information about the Captures. 715 A Provider can use the Media Capture Attributes to describe the 716 Captures for the benefit of the Consumer of the Advertisement 717 message. All these attributes are optional. Media Capture 718 Attributes include: 720 . Spatial information, such as point of capture, point on line 721 of capture, and area of capture, all of which, in combination 722 define the capture field of, for example, a camera 723 . Other descriptive information to help the Consumer choose 724 between captures (e.g. description, presentation, view, 725 priority, language, person information and type) 727 The sub-sections below define the Capture attributes. 729 7.1.1.1. Point of Capture 731 The Point of Capture attribute is a field with a single Cartesian 732 (X, Y, Z) point value which describes the spatial location of the 733 capturing device (such as camera). For an Audio Capture with 734 multiple microphones, the Point of Capture defines the nominal mid- 735 point of the microphones. 737 7.1.1.2. Point on Line of Capture 739 The Point on Line of Capture attribute is a field with a single 740 Cartesian (X, Y, Z) point value which describes a position in space 741 of a second point on the axis of the capturing device, toward the 742 direction it is pointing; the first point being the Point of 743 Capture (see above). 745 Together, the Point of Capture and Point on Line of Capture define 746 the direction and axis of the capturing device, for example the 747 optical axis of a camera or the axis of a microphone. The Media 748 Consumer can use this information to adjust how it renders the 749 received media if it so chooses. 751 For an Audio Capture, the Media Consumer can use this information 752 along with the Audio Capture Sensitivity Pattern to define a 3- 753 dimensional volume of capture where sounds can be expected to be 754 picked up by the microphone providing this specific audio capture. 755 If the Consumer wants to associate an Audio Capture with a Video 756 Capture, it can compare this volume with the area of capture for 757 video media to provide a check on whether the audio capture is 758 indeed spatially associated with the video capture. For example, a 759 video area of capture that fails to intersect at all with the audio 760 volume of capture, or is at such a long radial distance from the 761 microphone point of capture that the audio level would be very low, 762 would be inappropriate. 764 7.1.1.3. Area of Capture 766 The Area of Capture is a field with a set of four (X, Y, Z) points 767 as a value which describes the spatial location of what is being 768 "captured". This attribute applies only to video captures, not 769 other types of media. By comparing the Area of Capture for 770 different Video Captures within the same Capture Scene a Consumer 771 can determine the spatial relationships between them and render 772 them correctly. 774 The four points MUST be co-planar, forming a quadrilateral, which 775 defines the Plane of Interest for the particular Media Capture. 777 If the Area of Capture is not specified, it means the Video Capture 778 is not spatially related to any other Video Capture. 780 For a switched Capture that switches between different sections 781 within a larger area, the area of capture MUST use coordinates for 782 the larger potential area. 784 7.1.1.4. Mobility of Capture 786 The Mobility of Capture attribute indicates whether or not the 787 point of capture, line on point of capture, and area of capture 788 values stay the same over time, or are expected to change 789 (potentially frequently). Possible values are static, dynamic, and 790 highly dynamic. 792 An example for "dynamic" is a camera mounted on a stand which is 793 occasionally hand-carried and placed at different positions in 794 order to provide the best angle to capture a work task. A camera 795 worn by a person who moves around the room is an example for 796 "highly dynamic". In either case, the effect is that the capture 797 point, capture axis and area of capture change with time. 799 The capture point of a static Capture MUST NOT move for the life of 800 the conference. The capture point of dynamic Captures is 801 categorized by a change in position followed by a reasonable period 802 of stability--in the order of magnitude of minutes. High dynamic 803 captures are categorized by a capture point that is constantly 804 moving. If the "area of capture", "capture point" and "line of 805 capture" attributes are included with dynamic or highly dynamic 806 Captures they indicate spatial information at the time of the 807 Advertisement. 809 7.1.1.5. Audio Capture Sensitivity Pattern 811 The Audio Capture Sensitivity Pattern attribute applies only to 812 audio captures. This attribute gives information about the nominal 813 sensitivity pattern of the microphone which is the source of the 814 Capture. Possible values include patterns such as omni, shotgun, 815 cardioid, hyper-cardioid. 817 7.1.1.6. Description 819 The Description attribute is a human-readable description (which 820 could be in multiple languages) of the Capture. 822 7.1.1.7. Presentation 824 The Presentation attribute indicates that the capture originates 825 from a presentation device, that is one that provides supplementary 826 information to a conference through slides, video, still images, 827 data etc. Where more information is known about the capture it MAY 828 be expanded hierarchically to indicate the different types of 829 presentation media, e.g. presentation.slides, presentation.image 830 etc. 832 Note: It is expected that a number of keywords will be defined that 833 provide more detail on the type of presentation. 835 7.1.1.8. View 837 The View attribute is a field with enumerated values, indicating 838 what type of view the Capture relates to. The Consumer can use 839 this information to help choose which Media Captures it wishes to 840 receive. The value MUST be one of: 842 Room - Captures the entire scene 843 Table - Captures the conference table with seated people 845 Individual - Captures an individual person 847 Lectern - Captures the region of the lectern including the 848 presenter, for example in a classroom style conference room 850 Audience - Captures a region showing the audience in a classroom 851 style conference room 853 7.1.1.9. Language 855 The Language attribute indicates one or more languages used in the 856 content of the Media Capture. Captures MAY be offered in different 857 languages in case of multilingual and/or accessible conferences. A 858 Consumer can use this attribute to differentiate between them and 859 pick the appropriate one. 861 Note that the Language attribute is defined and meaningful both for 862 audio and video captures. In case of audio captures, the meaning 863 is obvious. For a video capture, "Language" could, for example, be 864 sign interpretation or text. 866 The Language attribute is coded per [RFC5646]. 868 7.1.1.10. Person Information 870 The Person Information attribute allows a Provider to provide 871 specific information regarding the people in a Capture (regardless 872 of whether or not the capture has a Presentation attribute). The 873 Provider may gather the information automatically or manually from 874 a variety of sources however the xCard [RFC6351] format is used to 875 convey the information. This allows various information such as 876 Identification information (section 6.2/[RFC6350]), Communication 877 Information (section 6.4/[RFC6350]) and Organizational information 878 (section 6.6/[RFC6350]) to be communicated. A Consumer may then 879 automatically (i.e. via a policy) or manually select Captures 880 based on information about who is in a Capture. It also allows a 881 Consumer to render information regarding the people participating 882 in the conference or to use it for further processing. 884 The Provider may supply a minimal set of information or a larger 885 set of information. However it MUST be compliant to [RFC6350] and 886 supply a "VERSION" and "FN" property. A Provider may supply 887 multiple xCards per Capture of any KIND (section 6.1.4/[RFC6350]). 889 In order to keep CLUE messages compact the Provider SHOULD use a 890 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 891 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 892 message. 894 7.1.1.11. Person Type 896 The Person Type attribute indicates the type of people contained in 897 the capture in the conference with respect to the meeting agenda 898 (regardless of whether or not the capture has a Presentation 899 attribute). As a capture may include multiple people the attribute 900 may contain multiple values. However values MUST NOT be repeated 901 within the attribute. 903 An Advertiser associates the person type with an individual capture 904 when it knows that a particular type is in the capture. If an 905 Advertiser cannot link a particular type with some certainty to a 906 capture then it is not included. A Consumer on reception of a 907 capture with a person type attribute knows with some certainly that 908 the capture contains that person type. The capture may contain 909 other person types but the Advertiser has not been able to 910 determine that this is the case. 912 The types of Captured people include: 914 . Chairman - the person responsible for running the conference 915 according to the agenda. 916 . Vice-Chairman - the person responsible for assisting the 917 chairman in running the meeting. 918 . Minute Taker - the person responsible for recording the 919 minutes of the conference. 920 . Attendee - the person has no particular responsibilities with 921 respect to running the meeting. 922 . Observer - an Attendee without the right to influence the 923 discussion. 924 . Presenter - the person is scheduled on the agenda to make a 925 presentation in the meeting. Note: This is not related to any 926 "active speaker" functionality. 927 . Translator - the person is providing some form of translation 928 or commentary in the meeting. 929 . Timekeeper - the person is responsible for maintaining the 930 meeting schedule. 932 Furthermore the person type attribute may contain one or more 933 strings allowing the Provider to indicate custom meeting specific 934 roles. 936 7.1.1.12. Priority 938 The Priority attribute indicates a relative priority between 939 different Media Captures. The Provider sets this priority, and the 940 Consumer MAY use the priority to help decide which Captures it 941 wishes to receive. 943 The "priority" attribute is an integer which indicates a relative 944 priority between Captures. For example it is possible to assign a 945 priority between two presentation Captures that would allow a 946 remote Endpoint to determine which presentation is more important. 947 Priority is assigned at the individual Capture level. It represents 948 the Provider's view of the relative priority between Captures with 949 a priority. The same priority number MAY be used across multiple 950 Captures. It indicates they are equally important. If no priority 951 is assigned no assumptions regarding relative important of the 952 Capture can be assumed. 954 7.1.1.13. Embedded Text 956 The Embedded Text attribute indicates that a Capture provides 957 embedded textual information. For example the video Capture MAY 958 contain speech to text information composed with the video image. 959 This attribute is only applicable to video Captures and 960 presentation streams with visual information. 962 7.1.1.14. Related To 964 The Related To attribute indicates the Capture contains additional 965 complementary information related to another Capture. The value 966 indicates the identity of the other Capture to which this Capture 967 is providing additional information. 969 For example, a conference can utilize translators or facilitators 970 that provide an additional audio stream (i.e. a translation or 971 description or commentary of the conference). Where multiple 972 captures are available, it may be advantageous for a Consumer to 973 select a complementary Capture instead of or in addition to a 974 Capture it relates to. 976 7.2. Multiple Content Capture 978 The MCC indicates that one or more Single Media Captures are 979 multiplexed (temporally and/or spatially) in one Media Capture. 980 Only one Capture type (i.e. audio, video, etc.) is allowed in each 981 MCC instance. The MCC may contain a reference to the Single Media 982 Captures (which may have their own attributes) as well as 983 attributes associated with the MCC itself. A MCC may also contain 984 other MCCs. The MCC MAY reference Captures from within the Capture 985 Scene that defines it or from other Capture Scenes. No ordering is 986 implied by the order that Captures appear within a MCC. A MCC MAY 987 contain no references to other Captures to indicate that the MCC 988 contains content from multiple sources but no information regarding 989 those sources is given. MCCs either contain the referenced Captures 990 and no others, or have no referenced captures and therefore may 991 contain any Capture. 993 One or more MCCs may also be specified in a CSV. This allows an 994 Advertiser to indicate that several MCC captures are used to 995 represent a capture scene. Table 14 provides an example of this 996 case. 998 As outlined in section 7.1. each instance of the MCC has its own 999 Capture identity i.e. MCC1. It allows all the individual captures 1000 contained in the MCC to be referenced by a single MCC identity. 1002 The example below shows the use of a Multiple Content Capture: 1004 +-----------------------+---------------------------------+ 1005 | Capture Scene #1 | | 1006 +-----------------------|---------------------------------+ 1007 | VC1 | {attributes} | 1008 | VC2 | {attributes} | 1009 | VCn | {attributes} | 1010 | MCC1(VC1,VC2,...VCn) | {attributes} | 1011 | CSV(MCC1) | | 1012 +---------------------------------------------------------+ 1014 Table 1: Multiple Content Capture concept 1016 This indicates that MCC1 is a single capture that contains the 1017 Captures VC1, VC2 and VC3 according to any MCC1 attributes. 1019 7.2.1. MCC Attributes 1021 Attributes may be associated with the MCC instance and the Single 1022 Media Captures that the MCC references. A Provider should avoid 1023 providing conflicting attribute values between the MCC and Single 1024 Media Captures. Where there is conflict the attributes of the MCC 1025 override any that may be present in the individual Captures. 1027 A Provider MAY include as much or as little of the original source 1028 Capture information as it requires. 1030 There are MCC specific attributes that MUST only be used with 1031 Multiple Content Captures. These are described in the sections 1032 below. The attributes described in section 7.1.1. MAY also be used 1033 with MCCs. 1035 The spatial related attributes of an MCC indicate its area of 1036 capture and point of capture within the scene, just like any other 1037 media capture. The spatial information does not imply anything 1038 about how other captures are composed within an MCC. 1040 For example: A virtual scene could be constructed for the MCC 1041 capture with two Video Captures with a "MaxCaptures" attribute set 1042 to 2 and an "Area of Capture" attribute provided with an overall 1043 area. Each of the individual Captures could then also include an 1044 "Area of Capture" attribute with a sub-set of the overall area. 1045 The Consumer would then know how each capture is related to others 1046 within the scene, but not the relative position of the individual 1047 captures within the composed capture. 1049 +-----------------------+---------------------------------+ 1050 | Capture Scene #1 | | 1051 +-----------------------|---------------------------------+ 1052 | VC1 | AreaofCapture=(0,0,0)(9,0,0) | 1053 | | (0,0,9)(9,0,9) | 1054 | VC2 | AreaofCapture=(10,0,0)(19,0,0) | 1055 | | (10,0,9)(19,0,9) | 1056 | MCC1(VC1,VC2) | MaxCaptures=2 | 1057 | | AreaofCapture=(0,0,0)(19,0,0) | 1058 | | (0,0,9)(19,0,9) | 1059 | CSV(MCC1) | | 1060 +---------------------------------------------------------+ 1062 Table 2: Example of MCC and Single Media Capture attributes 1064 The sections below describe the MCC only attributes. 1066 7.2.1.1. Maximum Number of Captures within a MCC 1068 The Maximum Number of Captures MCC attribute indicates the maximum 1069 number of individual Captures that may appear in a Capture Encoding 1070 at a time. The actual number at any given time can be less than 1071 this maximum. It may be used to derive how the Single Media 1072 Captures within the MCC are composed / switched with regards to 1073 space and time. 1075 A Provider can indicate that the number of Captures in a MCC 1076 Capture Encoding is equal "=" to the MaxCaptures value or that 1077 there may be any number of Captures up to and including "<=" the 1078 MaxCaptures value. This allows a Provider to distinguish between a 1079 MCC that purely represents a composition of sources versus a MCC 1080 that represents switched or switched and composed sources. 1082 MaxCaptures MAY be set to one so that only content related to one 1083 of the sources are shown in the MCC Capture Encoding at a time or 1084 it may be set to any value up to the total number of Source Media 1085 Captures in the MCC. 1087 The bullets below describe how the setting of MaxCapture versus the 1088 number of Captures in the MCC affects how sources appear in a 1089 Capture Encoding: 1091 . When MaxCaptures is set to <= 1 and the number of Captures in 1092 the MCC is greater than 1 (or not specified) in the MCC this 1093 is a switched case. Zero or 1 Captures may be switched into 1094 the Capture Encoding. Note: zero is allowed because of the 1095 "<=". 1096 . When MaxCaptures is set to = 1 and the number of Captures in 1097 the MCC is greater than 1 (or not specified) in the MCC this 1098 is a switched case. Only one Capture source is contained in a 1099 Capture Encoding at a time. 1100 . When MaxCaptures is set to <= N (with N > 1) and the number of 1101 Captures in the MCC is greater than N (or not specified) this 1102 is a switched and composed case. The Capture Encoding may 1103 contain purely switched sources (i.e. <=2 allows for 1 source 1104 on its own), or may contain composed and switched sources 1105 (i.e. a composition of 2 sources switched between the 1106 sources). 1107 . When MaxCaptures is set to = N (with N > 1) and the number of 1108 Captures in the MCC is greater than N (or not specified) this 1109 is a switched and composed case. The Capture Encoding contains 1110 composed and switched sources (i.e. a composition of N sources 1111 switched between the sources). It is not possible to have a 1112 single source. 1113 . When MaxCaptures is set to <= to the number of Captures in the 1114 MCC this is a switched and composed case. The Capture Encoding 1115 may contain media switched between any number (up to the 1116 MaxCaptures) of composed sources. 1117 . When MaxCaptures is set to = to the number of Captures in the 1118 MCC this is a composed case. All the sources are composed into 1119 a single Capture Encoding. 1121 If this attribute is not set then as default it is assumed that all 1122 source content can appear concurrently in the Capture Encoding 1123 associated with the MCC. 1125 For example: The use of MaxCaptures equal to 1 on a MCC with three 1126 Video Captures VC1, VC2 and VC3 would indicate that the Advertiser 1127 in the Capture Encoding would switch between VC1, VC2 or VC3 as 1128 there may be only a maximum of one Capture at a time. 1130 7.2.1.2. Policy 1132 The Policy MCC Attribute indicates the criteria that the Provider 1133 uses to determine when and/or where media content appears in the 1134 Capture Encoding related to the MCC. 1136 The attribute is in the form of a token that indicates the policy 1137 and an index representing an instance of the policy. The same 1138 index value can be used for multiple MCCs. 1140 The tokens are: 1142 SoundLevel - This indicates that the content of the MCC is 1143 determined by a sound level detection algorithm. The loudest 1144 (active) speaker (or a previous speaker, depending on the index 1145 value) is contained in the MCC. 1147 RoundRobin - This indicates that the content of the MCC is 1148 determined by a time based algorithm. For example: the Provider 1149 provides content from a particular source for a period of time and 1150 then provides content from another source and so on. 1152 An index is used to represent an instance in the policy setting. An 1153 index of 0 represents the most current instance of the policy, i.e. 1155 the active speaker, 1 represents the previous instance, i.e. the 1156 previous active speaker and so on. 1158 The following example shows a case where the Provider provides two 1159 media streams, one showing the active speaker and a second stream 1160 showing the previous speaker. 1162 +-----------------------+---------------------------------+ 1163 | Capture Scene #1 | | 1164 +-----------------------|---------------------------------+ 1165 | VC1 | | 1166 | VC2 | | 1167 | MCC1(VC1,VC2) | Policy=SoundLevel:0 | 1168 | | MaxCaptures=1 | 1169 | MCC2(VC1,VC2) | Policy=SoundLevel:1 | 1170 | | MaxCaptures=1 | 1171 | CSV(MCC1,MCC2) | | 1172 +---------------------------------------------------------+ 1174 Table 3: Example Policy MCC attribute usage 1176 7.2.1.3. Synchronisation Identity 1178 The Synchronisation Identity MCC attribute indicates how the 1179 individual Captures in multiple MCC Captures are synchronised. To 1180 indicate that the Capture Encodings associated with MCCs contain 1181 Captures from the same source at the same time a Provider should 1182 set the same Synchronisation Identity on each of the concerned 1183 MCCs. It is the Provider that determines what the source for the 1184 Captures is, so a Provider can choose how to group together Single 1185 Media Captures into a combined "source" for the purpose of 1186 switching them together to keep them synchronized according to the 1187 SynchronisationID attribute. For example when the Provider is in 1188 an MCU it may determine that each separate CLUE Endpoint is a 1189 remote source of media. The Synchronisation Identity may be used 1190 across media types, i.e. to synchronize audio and video related 1191 MCCs. 1193 Without this attribute it is assumed that multiple MCCs may provide 1194 content from different sources at any particular point in time. 1196 For example: 1198 +=======================+=================================+ 1199 | Capture Scene #1 | | 1200 +-----------------------|---------------------------------+ 1201 | VC1 | Description=Left | 1202 | VC2 | Description=Centre | 1203 | VC3 | Description=Right | 1204 | AC1 | Description=Room | 1205 | CSV(VC1,VC2,VC3) | | 1206 | CSV(AC1) | | 1207 +=======================+=================================+ 1208 | Capture Scene #2 | | 1209 +-----------------------|---------------------------------+ 1210 | VC4 | Description=Left | 1211 | VC5 | Description=Centre | 1212 | VC6 | Description=Right | 1213 | AC2 | Description=Room | 1214 | CSV(VC4,VC5,VC6) | | 1215 | CSV(AC2) | | 1216 +=======================+=================================+ 1217 | Capture Scene #3 | | 1218 +-----------------------|---------------------------------+ 1219 | VC7 | | 1220 | AC3 | | 1221 +=======================+=================================+ 1222 | Capture Scene #4 | | 1223 +-----------------------|---------------------------------+ 1224 | VC8 | | 1225 | AC4 | | 1226 +=======================+=================================+ 1227 | Capture Scene #5 | | 1228 +-----------------------|---------------------------------+ 1229 | MCC1(VC1,VC4,VC7) | SynchronisationID=1 | 1230 | | MaxCaptures=1 | 1231 | MCC2(VC2,VC5,VC8) | SynchronisationID=1 | 1232 | | MaxCaptures=1 | 1233 | MCC3(VC3,VC6) | MaxCaptures=1 | 1234 | MCC4(AC1,AC2,AC3,AC4) | SynchronisationID=1 | 1235 | | MaxCaptures=1 | 1236 | CSV(MCC1,MCC2,MCC3) | | 1237 | CSV(MCC4) | | 1238 +=======================+=================================+ 1240 Table 4: Example Synchronisation Identity MCC attribute usage 1242 The above Advertisement would indicate that MCC1, MCC2, MCC3 and 1243 MCC4 make up a Capture Scene. There would be four Capture 1244 Encodings (one for each MCC). Because MCC1 and MCC2 have the same 1245 SynchronisationID, each Encoding from MCC1 and MCC2 respectively 1246 would together have content from only Capture Scene 1 or only 1247 Capture Scene 2 or the combination of VC7 and VC8 at a particular 1248 point in time. In this case the Provider has decided the sources 1249 to be synchronized are Scene #1, Scene #2, and Scene #3 and #4 1250 together. The Encoding from MCC3 would not be synchronised with 1251 MCC1 or MCC2. As MCC4 also has the same Synchronisation Identity 1252 as MCC1 and MCC2 the content of the audio Encoding will be 1253 synchronised with the video content. 1255 7.2.1.4. Allow Subset Choice 1257 The Allow Subset Choice MCC attribute is a boolean value, 1258 indicating whether or not the Provider allows the Consumer to 1259 choose a specific subset of the Captures referenced by the MCC. 1260 If this attribute is true, and the MCC references other Captures, 1261 then the Consumer MAY select (in a Configure message) a specific 1262 subset of those Captures to be included in the MCC, and the 1263 Provider MUST then include only that subset. If this attribute is 1264 false, or the MCC does not reference other Captures, then the 1265 Consumer MUST NOT select a subset. 1267 7.3. Capture Scene 1269 In order for a Provider's individual Captures to be used 1270 effectively by a Consumer, the Provider organizes the Captures into 1271 one or more Capture Scenes, with the structure and contents of 1272 these Capture Scenes being sent from the Provider to the Consumer 1273 in the Advertisement. 1275 A Capture Scene is a structure representing a spatial region 1276 containing one or more Capture Devices, each capturing media 1277 representing a portion of the region. A Capture Scene includes one 1278 or more Capture Scene Views (CSV), with each CSV including one or 1279 more Media Captures of the same media type. There can also be 1280 Media Captures that are not included in a Capture Scene View. A 1281 Capture Scene represents, for example, the video image of a group 1282 of people seated next to each other, along with the sound of their 1283 voices, which could be represented by some number of VCs and ACs in 1284 the Capture Scene Views. An MCU can also describe in Capture 1285 Scenes what it constructs from media Streams it receives. 1287 A Provider MAY advertise one or more Capture Scenes. What 1288 constitutes an entire Capture Scene is up to the Provider. A 1289 simple Provider might typically use one Capture Scene for 1290 participant media (live video from the room cameras) and another 1291 Capture Scene for a computer generated presentation. In more 1292 complex systems, the use of additional Capture Scenes is also 1293 sensible. For example, a classroom may advertise two Capture 1294 Scenes involving live video, one including only the camera 1295 capturing the instructor (and associated audio), the other 1296 including camera(s) capturing students (and associated audio). 1298 A Capture Scene MAY (and typically will) include more than one type 1299 of media. For example, a Capture Scene can include several Capture 1300 Scene Views for Video Captures, and several Capture Scene Views for 1301 Audio Captures. A particular Capture MAY be included in more than 1302 one Capture Scene View. 1304 A Provider MAY express spatial relationships between Captures that 1305 are included in the same Capture Scene. However, there is no 1306 spatial relationship between Media Captures from different Capture 1307 Scenes. In other words, Capture Scenes each use their own spatial 1308 measurement system as outlined above in section 6. 1310 A Provider arranges Captures in a Capture Scene to help the 1311 Consumer choose which captures it wants to render. The Capture 1312 Scene Views in a Capture Scene are different alternatives the 1313 Provider is suggesting for representing the Capture Scene. Each 1314 Capture Scene View is given an advertisement unique identity. The 1315 order of Capture Scene Views within a Capture Scene has no 1316 significance. The Media Consumer can choose to receive all Media 1317 Captures from one Capture Scene View for each media type (e.g. 1318 audio and video), or it can pick and choose Media Captures 1319 regardless of how the Provider arranges them in Capture Scene 1320 Views. Different Capture Scene Views of the same media type are 1321 not necessarily mutually exclusive alternatives. Also note that 1322 the presence of multiple Capture Scene Views (with potentially 1323 multiple encoding options in each view) in a given Capture Scene 1324 does not necessarily imply that a Provider is able to serve all the 1325 associated media simultaneously (although the construction of such 1326 an over-rich Capture Scene is probably not sensible in many cases). 1327 What a Provider can send simultaneously is determined through the 1328 Simultaneous Transmission Set mechanism, described in section 8. 1330 Captures within the same Capture Scene View MUST be of the same 1331 media type - it is not possible to mix audio and video captures in 1332 the same Capture Scene View, for instance. The Provider MUST be 1333 capable of encoding and sending all Captures (that have an encoding 1334 group) in a single Capture Scene View simultaneously. The order of 1335 Captures within a Capture Scene View has no significance. A 1336 Consumer can decide to receive all the Captures in a single Capture 1337 Scene View, but a Consumer could also decide to receive just a 1338 subset of those captures. A Consumer can also decide to receive 1339 Captures from different Capture Scene Views, all subject to the 1340 constraints set by Simultaneous Transmission Sets, as discussed in 1341 section 8. 1343 When a Provider advertises a Capture Scene with multiple CSVs, it 1344 is essentially signaling that there are multiple representations of 1345 the same Capture Scene available. In some cases, these multiple 1346 views would be used simultaneously (for instance a "video view" and 1347 an "audio view"). In some cases the views would conceptually be 1348 alternatives (for instance a view consisting of three Video 1349 Captures covering the whole room versus a view consisting of just a 1350 single Video Capture covering only the center of a room). In this 1351 latter example, one sensible choice for a Consumer would be to 1352 indicate (through its Configure and possibly through an additional 1353 offer/answer exchange) the Captures of that Capture Scene View that 1354 most closely matched the Consumer's number of display devices or 1355 screen layout. 1357 The following is an example of 4 potential Capture Scene Views for 1358 an endpoint-style Provider: 1360 1. (VC0, VC1, VC2) - left, center and right camera Video Captures 1362 2. (MCC3) - Video Capture associated with loudest room segment 1364 3. (VC4) - Video Capture zoomed out view of all people in the room 1366 4. (AC0) - main audio 1368 The first view in this Capture Scene example is a list of Video 1369 Captures which have a spatial relationship to each other. 1370 Determination of the order of these captures (VC0, VC1 and VC2) for 1371 rendering purposes is accomplished through use of their Area of 1372 Capture attributes. The second view (MCC3) and the third view 1373 (VC4) are alternative representations of the same room's video, 1374 which might be better suited to some Consumers' rendering 1375 capabilities. The inclusion of the Audio Capture in the same 1376 Capture Scene indicates that AC0 is associated with all of those 1377 Video Captures, meaning it comes from the same spatial region. 1378 Therefore, if audio were to be rendered at all, this audio would be 1379 the correct choice irrespective of which Video Captures were 1380 chosen. 1382 7.3.1. Capture Scene attributes 1384 Capture Scene Attributes can be applied to Capture Scenes as well 1385 as to individual media captures. Attributes specified at this 1386 level apply to all constituent Captures. Capture Scene attributes 1387 include 1389 . Human-readable description of the Capture Scene, which could 1390 be in multiple languages; 1391 . xCard scene information 1392 . Scale information (millimeters, unknown, no scale), as 1393 described in Section 6. 1395 7.3.1.1. Scene Information 1397 The Scene information attribute provides information regarding the 1398 Capture Scene rather than individual participants. The Provider 1399 may gather the information automatically or manually from a 1400 variety of sources. The scene information attribute allows a 1401 Provider to indicate information such as: organizational or 1402 geographic information allowing a Consumer to determine which 1403 Capture Scenes are of interest in order to then perform Capture 1404 selection. It also allows a Consumer to render information 1405 regarding the Scene or to use it for further processing. 1407 As per 7.1.1.10. the xCard format is used to convey this 1408 information and the Provider may supply a minimal set of 1409 information or a larger set of information. 1411 In order to keep CLUE messages compact the Provider SHOULD use a 1412 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 1413 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 1414 message. 1416 7.3.2. Capture Scene View attributes 1418 A Capture Scene can include one or more Capture Scene Views in 1419 addition to the Capture Scene wide attributes described above. 1420 Capture Scene View attributes apply to the Capture Scene View as a 1421 whole, i.e. to all Captures that are part of the Capture Scene 1422 View. 1424 Capture Scene View attributes include: 1426 . Human-readable description (which could be in multiple 1427 languages) of the Capture Scene View 1429 7.4. Global View List 1431 An Advertisement can include an optional Global View list. Each 1432 item in this list is a Global View. The Provider can include 1433 multiple Global Views, to allow a Consumer to choose sets of 1434 captures appropriate to its capabilities or application. The 1435 choice of how to make these suggestions in the Global View list 1436 for what represents all the scenes for which the Provider can send 1437 media is up to the Provider. This is very similar to how each CSV 1438 represents a particular scene. 1440 As an example, suppose an advertisement has three scenes, and each 1441 scene has three CSVs, ranging from one to three video captures in 1442 each CSV. The Provider is advertising a total of nine video 1443 Captures across three scenes. The Provider can use the Global 1444 View list to suggest alternatives for Consumers that can't receive 1445 all nine video Captures as separate media streams. For 1446 accommodating a Consumer that wants to receive three video 1447 Captures, a Provider might suggest a Global View containing just a 1448 single CSV with three Captures and nothing from the other two 1449 scenes. Or a Provider might suggest a Global View containing 1450 three different CSVs, one from each scene, with a single video 1451 Capture in each. 1453 Some additional rules: 1455 . The ordering of Global Views in the Global View list is 1456 insignificant. 1457 . The ordering of CSVs within each Global View is 1458 insignificant. 1459 . A particular CSV may be used in multiple Global Views. 1460 . The Provider must be capable of encoding and sending all 1461 Captures within the CSVs of a given Global View 1462 simultaneously. 1464 The following figure shows an example of the structure of Global 1465 Views in a Global View List. 1467 ........................................................ 1468 . Advertisement . 1469 . . 1470 . +--------------+ +-------------------------+ . 1471 . |Scene 1 | |Global View List | . 1472 . | | | | . 1473 . | CSV1 (v)<----------------- Global View (CSV 1) | . 1474 . | <-------. | | . 1475 . | | *--------- Global View (CSV 1,5) | . 1476 . | CSV2 (v) | | | | . 1477 . | | | | | . 1478 . | CSV3 (v)<---------*------- Global View (CSV 3,5) | . 1479 . | | | | | | . 1480 . | CSV4 (a)<----------------- Global View (CSV 4) | . 1481 . | <-----------. | | . 1482 . +--------------+ | | *----- Global View (CSV 4,6) | . 1483 . | | | | | . 1484 . +--------------+ | | | +-------------------------+ . 1485 . |Scene 2 | | | | . 1486 . | | | | | . 1487 . | CSV5 (v)<-------' | | . 1488 . | <---------' | . 1489 . | | | (v) = video . 1490 . | CSV6 (a)<-----------' (a) = audio . 1491 . | | . 1492 . +--------------+ . 1493 `......................................................' 1495 Figure 3: Global View List Structure 1497 8. Simultaneous Transmission Set Constraints 1499 In many practical cases, a Provider has constraints or limitations 1500 on its ability to send Captures simultaneously. One type of 1501 limitation is caused by the physical limitations of capture 1502 mechanisms; these constraints are represented by a Simultaneous 1503 Transmission Set. The second type of limitation reflects the 1504 encoding resources available, such as bandwidth or video encoding 1505 throughput (macroblocks/second). This type of constraint is 1506 captured by Individual Encodings and Encoding Groups, discussed 1507 below. 1509 Some Endpoints or MCUs can send multiple Captures simultaneously; 1510 however sometimes there are constraints that limit which Captures 1511 can be sent simultaneously with other Captures. A device may not 1512 be able to be used in different ways at the same time. Provider 1513 Advertisements are made so that the Consumer can choose one of 1514 several possible mutually exclusive usages of the device. This 1515 type of constraint is expressed in a Simultaneous Transmission Set, 1516 which lists all the Captures of a particular media type (e.g. 1517 audio, video, text) that can be sent at the same time. There are 1518 different Simultaneous Transmission Sets for each media type in the 1519 Advertisement. This is easier to show in an example. 1521 Consider the example of a room system where there are three cameras 1522 each of which can send a separate Capture covering two persons 1523 each- VC0, VC1, VC2. The middle camera can also zoom out (using an 1524 optical zoom lens) and show all six persons, VC3. But the middle 1525 camera cannot be used in both modes at the same time - it has to 1526 either show the space where two participants sit or the whole six 1527 seats, but not both at the same time. As a result, VC1 and VC3 1528 cannot be sent simultaneously. 1530 Simultaneous Transmission Sets are expressed as sets of the Media 1531 Captures that the Provider could transmit at the same time (though, 1532 in some cases, it is not intuitive to do so). If a Multiple 1533 Content Capture is included in a Simultaneous Transmission Set it 1534 indicates that the Capture Encoding associated with it could be 1535 transmitted as the same time as the other Captures within the 1536 Simultaneous Transmission Set. It does not imply that the Single 1537 Media Captures contained in the Multiple Content Capture could all 1538 be transmitted at the same time. 1540 In this example the two Simultaneous Transmission Sets are shown in 1541 Table 5. If a Provider advertises one or more mutually exclusive 1542 Simultaneous Transmission Sets, then for each media type the 1543 Consumer MUST ensure that it chooses Media Captures that lie wholly 1544 within one of those Simultaneous Transmission Sets. 1546 +-------------------+ 1547 | Simultaneous Sets | 1548 +-------------------+ 1549 | {VC0, VC1, VC2} | 1550 | {VC0, VC3, VC2} | 1551 +-------------------+ 1553 Table 5: Two Simultaneous Transmission Sets 1555 A Provider OPTIONALLY can include the Simultaneous Transmission 1556 Sets in its Advertisement. These constraints apply across all the 1557 Capture Scenes in the Advertisement. It is a syntax conformance 1558 requirement that the Simultaneous Transmission Sets MUST allow all 1559 the media Captures in any particular Capture Scene View to be used 1560 simultaneously. Similarly, the Simultaneous Transmission Sets MUST 1561 reflect the simultaneity expressed by any Global View. 1563 For shorthand convenience, a Provider MAY describe a Simultaneous 1564 Transmission Set in terms of Capture Scene Views and Capture 1565 Scenes. If a Capture Scene View is included in a Simultaneous 1566 Transmission Set, then all Media Captures in the Capture Scene View 1567 are included in the Simultaneous Transmission Set. If a Capture 1568 Scene is included in a Simultaneous Transmission Set, then all its 1569 Capture Scene Views (of the corresponding media type) are included 1570 in the Simultaneous Transmission Set. The end result reduces to a 1571 set of Media Captures, of a particular media type, in either case. 1573 If an Advertisement does not include Simultaneous Transmission 1574 Sets, then the Provider MUST be able to simultaneously provide all 1575 the Captures from any one CSV of each media type from each Capture 1576 Scene. Likewise, if there are no Simultaneous Transmission Sets 1577 and there is a Global View list, then the Provider MUST be able to 1578 simultaneously provide all the Captures from any particular Global 1579 View (of each media type) from the Global View list. 1581 If an Advertisement includes multiple Capture Scene Views in a 1582 Capture Scene then the Consumer MAY choose one Capture Scene View 1583 for each media type, or MAY choose individual Captures based on the 1584 Simultaneous Transmission Sets. 1586 9. Encodings 1588 Individual encodings and encoding groups are CLUE's mechanisms 1589 allowing a Provider to signal its limitations for sending Captures, 1590 or combinations of Captures, to a Consumer. Consumers can map the 1591 Captures they want to receive onto the Encodings, with the encoding 1592 parameters they want. As for the relationship between the CLUE- 1593 specified mechanisms based on Encodings and the SIP offer/answer 1594 exchange, please refer to section 5. 1596 9.1. Individual Encodings 1598 An Individual Encoding represents a way to encode a Media Capture 1599 to become a Capture Encoding, to be sent as an encoded media stream 1600 from the Provider to the Consumer. An Individual Encoding has a 1601 set of parameters characterizing how the media is encoded. 1603 Different media types have different parameters, and different 1604 encoding algorithms may have different parameters. An Individual 1605 Encoding can be assigned to at most one Capture Encoding at any 1606 given time. 1608 Individual Encoding parameters are represented in SDP [RFC4566], 1609 not in CLUE messages. For example, for a video encoding using 1610 H.26x compression technologies, this can include parameters such 1611 as: 1613 . Maximum bandwidth; 1614 . Maximum picture size in pixels; 1615 . Maxmimum number of pixels to be processed per second; 1617 The bandwidth parameter is the only one that specifically relates 1618 to a CLUE Advertisement, as it can be further constrained by the 1619 maximum group bandwidth in an Encoding Group. 1621 9.2. Encoding Group 1623 An Encoding Group includes a set of one or more Individual 1624 Encodings, and parameters that apply to the group as a whole. By 1625 grouping multiple individual Encodings together, an Encoding Group 1626 describes additional constraints on bandwidth for the group. A 1627 single Encoding Group MAY refer to Encodings for different media 1628 types. 1630 The Encoding Group data structure contains: 1632 . Maximum bitrate for all encodings in the group combined; 1633 . A list of identifiers for the Individual Encodings belonging 1634 to the group. 1636 When the Individual Encodings in a group are instantiated into 1637 Capture Encodings, each Capture Encoding has a bitrate that MUST be 1638 less than or equal to the max bitrate for the particular Individual 1639 Encoding. The "maximum bitrate for all encodings in the group" 1640 parameter gives the additional restriction that the sum of all the 1641 individual Capture Encoding bitrates MUST be less than or equal to 1642 this group value. 1644 The following diagram illustrates one example of the structure of a 1645 media Provider's Encoding Groups and their contents. 1647 ,-------------------------------------------------. 1648 | Media Provider | 1649 | | 1650 | ,--------------------------------------. | 1651 | | ,--------------------------------------. | 1652 | | | ,--------------------------------------. | 1653 | | | | Encoding Group | | 1654 | | | | ,-----------. | | 1655 | | | | | | ,---------. | | 1656 | | | | | | | | ,---------.| | 1657 | | | | | Encoding1 | |Encoding2| |Encoding3|| | 1658 | `.| | | | | | `---------'| | 1659 | `.| `-----------' `---------' | | 1660 | `--------------------------------------' | 1661 `-------------------------------------------------' 1663 Figure 4: Encoding Group Structure 1665 A Provider advertises one or more Encoding Groups. Each Encoding 1666 Group includes one or more Individual Encodings. Each Individual 1667 Encoding can represent a different way of encoding media. For 1668 example one Individual Encoding may be 1080p60 video, another could 1669 be 720p30, with a third being CIF, all in, for example, H.264 1670 format. 1671 While a typical three codec/display system might have one Encoding 1672 Group per "codec box" (physical codec, connected to one camera and 1673 one screen), there are many possibilities for the number of 1674 Encoding Groups a Provider may be able to offer and for the 1675 encoding values in each Encoding Group. 1677 There is no requirement for all Encodings within an Encoding Group 1678 to be instantiated at the same time. 1680 9.3. Associating Captures with Encoding Groups 1682 Each Media Capture, including MCCs, MAY be associated with one 1683 Encoding Group. To be eligible for configuration, a Media Capture 1684 MUST be associated with one Encoding Group, which is used to 1685 instantiate that Capture into a Capture Encoding. When an MCC is 1686 configured all the Media Captures referenced by the MCC will appear 1687 in the Capture Encoding according to the attributes of the chosen 1688 encoding of the MCC. This allows an Advertiser to specify encoding 1689 attributes associated with the Media Captures without the need to 1690 provide an individual Capture Encoding for each of the inputs. 1692 If an Encoding Group is assigned to a Media Capture referenced by 1693 the MCC it indicates that this Capture may also have an individual 1694 Capture Encoding. 1696 For example: 1698 +--------------------+------------------------------------+ 1699 | Capture Scene #1 | | 1700 +--------------------+------------------------------------+ 1701 | VC1 | EncodeGroupID=1 | 1702 | VC2 | | 1703 | MCC1(VC1,VC2) | EncodeGroupID=2 | 1704 | CSV(VC1) | | 1705 | CSV(MCC1) | | 1706 +--------------------+------------------------------------+ 1708 Table 6: Example usage of Encoding with MCC and source Captures 1710 This would indicate that VC1 may be sent as its own Capture 1711 Encoding from EncodeGroupID=1 or that it may be sent as part of a 1712 Capture Encoding from EncodeGroupID=2 along with VC2. 1714 More than one Capture MAY use the same Encoding Group. 1716 The maximum number of Capture Encodings that can result from a 1717 particular Encoding Group constraint is equal to the number of 1718 individual Encodings in the group. The actual number of Capture 1719 Encodings used at any time MAY be less than this maximum. Any of 1720 the Captures that use a particular Encoding Group can be encoded 1721 according to any of the Individual Encodings in the group. 1723 It is a protocol conformance requirement that the Encoding Groups 1724 MUST allow all the Captures in a particular Capture Scene View to 1725 be used simultaneously. 1727 10. Consumer's Choice of Streams to Receive from the Provider 1729 After receiving the Provider's Advertisement message (that includes 1730 media captures and associated constraints), the Consumer composes 1731 its reply to the Provider in the form of a Configure message. The 1732 Consumer is free to use the information in the Advertisement as it 1733 chooses, but there are a few obviously sensible design choices, 1734 which are outlined below. 1736 If multiple Providers connect to the same Consumer (i.e. in an MCU- 1737 less multiparty call), it is the responsibility of the Consumer to 1738 compose Configures for each Provider that both fulfill each 1739 Provider's constraints as expressed in the Advertisement, as well 1740 as its own capabilities. 1742 In an MCU-based multiparty call, the MCU can logically terminate 1743 the Advertisement/Configure negotiation in that it can hide the 1744 characteristics of the receiving endpoint and rely on its own 1745 capabilities (transcoding/transrating/...) to create Media Streams 1746 that can be decoded at the Endpoint Consumers. The timing of an 1747 MCU's sending of Advertisements (for its outgoing ports) and 1748 Configures (for its incoming ports, in response to Advertisements 1749 received there) is up to the MCU and implementation dependent. 1751 As a general outline, a Consumer can choose, based on the 1752 Advertisement it has received, which Captures it wishes to receive, 1753 and which Individual Encodings it wants the Provider to use to 1754 encode the Captures. 1756 On receipt of an Advertisement with an MCC the Consumer treats the 1757 MCC as per other non-MCC Captures with the following differences: 1759 - The Consumer would understand that the MCC is a Capture that 1760 includes the referenced individual Captures (or any Captures, if 1761 none are referenced) and that these individual Captures are 1762 delivered as part of the MCC's Capture Encoding. 1764 - The Consumer may utilise any of the attributes associated with 1765 the referenced individual Captures and any Capture Scene attributes 1766 from where the individual Captures were defined to choose Captures 1767 and for rendering decisions. 1769 - If the MCC attribute Allow Subset Choice is true, then the 1770 Consumer may or may not choose to receive all the indicated 1771 Captures. It can choose to receive a sub-set of Captures indicated 1772 by the MCC. 1774 For example if the Consumer receives: 1776 MCC1(VC1,VC2,VC3){attributes} 1778 A Consumer could choose all the Captures within a MCC however if 1779 the Consumer determines that it doesn't want VC3 it can return 1780 MCC1(VC1,VC2). If it wants all the individual Captures then it 1781 returns only the MCC identity (i.e. MCC1). If the MCC in the 1782 advertisement does not reference any individual captures, or the 1783 Allow Subset Choice attribute is false, then the Consumer cannot 1784 choose what is included in the MCC, it is up to the Provider to 1785 decide. 1787 A Configure Message includes a list of Capture Encodings. These 1788 are the Capture Encodings the Consumer wishes to receive from the 1789 Provider. Each Capture Encoding refers to one Media Capture and 1790 one Individual Encoding. 1792 For each Capture the Consumer wants to receive, it configures one 1793 of the Encodings in that Capture's Encoding Group. The Consumer 1794 does this by telling the Provider, in its Configure Message, which 1795 Encoding to use for each chosen Capture. Upon receipt of this 1796 Configure from the Consumer, common knowledge is established 1797 between Provider and Consumer regarding sensible choices for the 1798 media streams. The setup of the actual media channels, at least in 1799 the simplest case, is left to a following offer/answer exchange. 1800 Optimized implementations MAY speed up the reaction to the 1801 offer/answer exchange by reserving the resources at the time of 1802 finalization of the CLUE handshake. 1804 CLUE advertisements and configure messages don't necessarily 1805 require a new SDP offer/answer for every CLUE message 1806 exchange. But the resulting encodings sent via RTP must conform to 1807 the most recent SDP offer/answer result. 1809 In order to meaningfully create and send an initial Configure, the 1810 Consumer needs to have received at least one Advertisement, and an 1811 SDP offer defining the Individual Encodings, from the Provider. 1813 In addition, the Consumer can send a Configure at any time during 1814 the call. The Configure MUST be valid according to the most 1815 recently received Advertisement. The Consumer can send a Configure 1816 either in response to a new Advertisement from the Provider or on 1817 its own, for example because of a local change in conditions 1818 (people leaving the room, connectivity changes, multipoint related 1819 considerations). 1821 When choosing which Media Streams to receive from the Provider, and 1822 the encoding characteristics of those Media Streams, the Consumer 1823 advantageously takes several things into account: its local 1824 preference, simultaneity restrictions, and encoding limits. 1826 10.1. Local preference 1828 A variety of local factors influence the Consumer's choice of 1829 Media Streams to be received from the Provider: 1831 o if the Consumer is an Endpoint, it is likely that it would 1832 choose, where possible, to receive video and audio Captures that 1833 match the number of display devices and audio system it has 1835 o if the Consumer is an MCU, it MAY choose to receive loudest 1836 speaker streams (in order to perform its own media composition) 1837 and avoid pre-composed video Captures 1839 o user choice (for instance, selection of a new layout) MAY result 1840 in a different set of Captures, or different encoding 1841 characteristics, being required by the Consumer 1843 10.2. Physical simultaneity restrictions 1845 Often there are physical simultaneity constraints of the Provider 1846 that affect the Provider's ability to simultaneously send all of 1847 the captures the Consumer would wish to receive. For instance, an 1848 MCU, when connected to a multi-camera room system, might prefer to 1849 receive both individual video streams of the people present in the 1850 room and an overall view of the room from a single camera. Some 1851 Endpoint systems might be able to provide both of these sets of 1852 streams simultaneously, whereas others might not (if the overall 1853 room view were produced by changing the optical zoom level on the 1854 center camera, for instance). 1856 10.3. Encoding and encoding group limits 1858 Each of the Provider's encoding groups has limits on bandwidth, 1859 and the constituent potential encodings have limits on the 1860 bandwidth, computational complexity, video frame rate, and 1861 resolution that can be provided. When choosing the Captures to be 1862 received from a Provider, a Consumer device MUST ensure that the 1863 encoding characteristics requested for each individual Capture 1864 fits within the capability of the encoding it is being configured 1865 to use, as well as ensuring that the combined encoding 1866 characteristics for Captures fit within the capabilities of their 1867 associated encoding groups. In some cases, this could cause an 1868 otherwise "preferred" choice of capture encodings to be passed 1869 over in favor of different Capture Encodings--for instance, if a 1870 set of three Captures could only be provided at a low resolution 1871 then a three screen device could switch to favoring a single, 1872 higher quality, Capture Encoding. 1874 11. Extensibility 1876 One important characteristics of the Framework is its 1877 extensibility. The standard for interoperability and handling 1878 multiple streams must be future-proof. The framework itself is 1879 inherently extensible through expanding the data model types. For 1880 example: 1882 o Adding more types of media, such as telemetry, can done by 1883 defining additional types of Captures in addition to audio and 1884 video. 1886 o Adding new functionalities, such as 3-D video Captures, say, may 1887 require additional attributes describing the Captures. 1889 The infrastructure is designed to be extended rather than 1890 requiring new infrastructure elements. Extension comes through 1891 adding to defined types. 1893 12. Examples - Using the Framework (Informative) 1895 This section gives some examples, first from the point of view of 1896 the Provider, then the Consumer, then some multipoint scenarios 1898 12.1. Provider Behavior 1900 This section shows some examples in more detail of how a Provider 1901 can use the framework to represent a typical case for telepresence 1902 rooms. First an endpoint is illustrated, then an MCU case is 1903 shown. 1905 12.1.1. Three screen Endpoint Provider 1907 Consider an Endpoint with the following description: 1909 3 cameras, 3 displays, a 6 person table 1911 o Each camera can provide one Capture for each 1/3 section of the 1912 table 1914 o A single Capture representing the active speaker can be provided 1915 (voice activity based camera selection to a given encoder input 1916 port implemented locally in the Endpoint) 1918 o A single Capture representing the active speaker with the other 1919 2 Captures shown picture in picture within the stream can be 1920 provided (again, implemented inside the endpoint) 1922 o A Capture showing a zoomed out view of all 6 seats in the room 1923 can be provided 1925 The video and audio Captures for this Endpoint can be described as 1926 follows. 1928 Video Captures: 1930 o VC0- (the left camera stream), encoding group=EG0, view=table 1932 o VC1- (the center camera stream), encoding group=EG1, view=table 1934 o VC2- (the right camera stream), encoding group=EG2, view=table 1936 o MCC3- (the loudest panel stream), encoding group=EG1, 1937 view=table, MaxCaptures=1 1939 o MCC4- (the loudest panel stream with PiPs), encoding group=EG1, 1940 view=room, MaxCaptures=3 1942 o VC5- (the zoomed out view of all people in the room), encoding 1943 group=EG1, view=room 1945 o VC6- (presentation stream), encoding group=EG1, presentation 1947 The following diagram is a top view of the room with 3 cameras, 3 1948 displays, and 6 seats. Each camera is capturing 2 people. The 1949 six seats are not all in a straight line. 1951 ,-. d 1952 ( )`--.__ +---+ 1953 `-' / `--.__ | | 1954 ,-. | `-.._ |_-+Camera 2 (VC2) 1955 ( ).' <--(AC1)-+-''`+-+ 1956 `-' |_...---'' | | 1957 ,-.c+-..__ +---+ 1958 ( )| ``--..__ | | 1959 `-' | ``+-..|_-+Camera 1 (VC1) 1960 ,-. | <--(AC2)..--'|+-+ ^ 1961 ( )| __..--' | | | 1962 `-'b|..--' +---+ |X 1963 ,-. |``---..___ | | | 1964 ( )\ ```--..._|_-+Camera 0 (VC0) | 1965 `-' \ <--(AC0) ..-''`-+ | 1966 ,-. \ __.--'' | | <----------+ 1967 ( ) |..-'' +---+ Y 1968 `-' a (0,0,0) origin is under Camera 1 1970 Figure 5: Room Layout Top View 1972 The two points labeled b and c are intended to be at the midpoint 1973 between the seating positions, and where the fields of view of the 1974 cameras intersect. 1976 The plane of interest for VC0 is a vertical plane that intersects 1977 points 'a' and 'b'. 1979 The plane of interest for VC1 intersects points 'b' and 'c'. The 1980 plane of interest for VC2 intersects points 'c' and 'd'. 1982 This example uses an area scale of millimeters. 1984 Areas of capture: 1986 bottom left bottom right top left top right 1987 VC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757) 1988 VC1 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757) 1989 VC2 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757) 1990 MCC3(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1991 MCC4(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1992 VC5 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1993 VC6 none 1995 Points of capture: 1996 VC0 (-1678,0,800) 1997 VC1 (0,0,800) 1998 VC2 (1678,0,800) 1999 MCC3 none 2000 MCC4 none 2001 VC5 (0,0,800) 2002 VC6 none 2004 In this example, the right edge of the VC0 area lines up with the 2005 left edge of the VC1 area. It doesn't have to be this way. There 2006 could be a gap or an overlap. One additional thing to note for 2007 this example is the distance from a to b is equal to the distance 2008 from b to c and the distance from c to d. All these distances are 2009 1346 mm. This is the planar width of each area of capture for VC0, 2010 VC1, and VC2. 2012 Note the text in parentheses (e.g. "the left camera stream") is 2013 not explicitly part of the model, it is just explanatory text for 2014 this example, and is not included in the model with the media 2015 captures and attributes. Also, MCC4 doesn't say anything about 2016 how a capture is composed, so the media consumer can't tell based 2017 on this capture that MCC4 is composed of a "loudest panel with 2018 PiPs". 2020 Audio Captures: 2022 Three ceiling microphones are located between the cameras and the 2023 table, at the same height as the cameras. The microphones point 2024 down at an angle toward the seating positions. 2026 o AC0 (left), encoding group=EG3 2028 o AC1 (right), encoding group=EG3 2030 o AC2 (center) encoding group=EG3 2032 o AC3 being a simple pre-mixed audio stream from the room (mono), 2033 encoding group=EG3 2035 o AC4 audio stream associated with the presentation video (mono) 2036 encoding group=EG3, presentation 2038 Point of capture: Point on Line of Capture: 2040 AC0 (-1342,2000,800) (-1342,2925,379) 2041 AC1 ( 1342,2000,800) ( 1342,2925,379) 2042 AC2 ( 0,2000,800) ( 0,3000,379) 2043 AC3 ( 0,2000,800) ( 0,3000,379) 2044 AC4 none 2046 The physical simultaneity information is: 2048 Simultaneous transmission set #1 {VC0, VC1, VC2, MCC3, MCC4, 2049 VC6} 2051 Simultaneous transmission set #2 {VC0, VC2, VC5, VC6} 2053 This constraint indicates it is not possible to use all the VCs at 2054 the same time. VC5 cannot be used at the same time as VC1 or MCC3 2055 or MCC4. Also, using every member in the set simultaneously may 2056 not make sense - for example MCC3(loudest) and MCC4 (loudest with 2057 PIP). In addition, there are encoding constraints that make 2058 choosing all of the VCs in a set impossible. VC1, MCC3, MCC4, 2059 VC5, VC6 all use EG1 and EG1 has only 3 ENCs. This constraint 2060 shows up in the encoding groups, not in the simultaneous 2061 transmission sets. 2063 In this example there are no restrictions on which Audio Captures 2064 can be sent simultaneously. 2066 Encoding Groups: 2068 This example has three encoding groups associated with the video 2069 captures. Each group can have 3 encodings, but with each 2070 potential encoding having a progressively lower specification. In 2071 this example, 1080p60 transmission is possible (as ENC0 has a 2072 maxPps value compatible with that). Significantly, as up to 3 2073 encodings are available per group, it is possible to transmit some 2074 video Captures simultaneously that are not in the same view in the 2075 Capture Scene. For example VC1 and MCC3 at the same time. 2077 encodeGroupID=EG0, maxGroupBandwidth=6000000 2078 encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2079 maxPps=124416000, maxBandwidth=4000000 2080 encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2081 maxPps=27648000, maxBandwidth=4000000 2082 encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30, 2083 maxPps=15552000, maxBandwidth=4000000 2084 encodeGroupID=EG1 maxGroupBandwidth=6000000 2085 encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2086 maxPps=124416000, maxBandwidth=4000000 2087 encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2088 maxPps=27648000, maxBandwidth=4000000 2089 encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30, 2090 maxPps=15552000, maxBandwidth=4000000 2091 encodeGroupID=EG2 maxGroupBandwidth=6000000 2092 encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2093 maxPps=124416000, maxBandwidth=4000000 2094 encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2095 maxPps=27648000, maxBandwidth=4000000 2096 encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30, 2097 maxPps=15552000, maxBandwidth=4000000 2099 Figure 6: Example Encoding Groups for Video 2101 For audio, there are five potential encodings available, so all 2102 five Audio Captures can be encoded at the same time. 2104 encodeGroupID=EG3, maxGroupBandwidth=320000 2105 encodeID=ENC9, maxBandwidth=64000 2106 encodeID=ENC10, maxBandwidth=64000 2107 encodeID=ENC11, maxBandwidth=64000 2108 encodeID=ENC12, maxBandwidth=64000 2109 encodeID=ENC13, maxBandwidth=64000 2111 Figure 7: Example Encoding Group for Audio 2113 Capture Scenes: 2115 The following table represents the Capture Scenes for this 2116 provider. Recall that a Capture Scene is composed of alternative 2117 Capture Scene Views covering the same spatial region. Capture 2118 Scene #1 is for the main people captures, and Capture Scene #2 is 2119 for presentation. 2121 Each row in the table is a separate Capture Scene View 2123 +------------------+ 2124 | Capture Scene #1 | 2125 +------------------+ 2126 | VC0, VC1, VC2 | 2127 | MCC3 | 2128 | MCC4 | 2129 | VC5 | 2130 | AC0, AC1, AC2 | 2131 | AC3 | 2132 +------------------+ 2134 +------------------+ 2135 | Capture Scene #2 | 2136 +------------------+ 2137 | VC6 | 2138 | AC4 | 2139 +------------------+ 2141 Table 7: Example Capture Scene Views 2143 Different Capture Scenes are distinct from each other, and are 2144 non-overlapping. A consumer can choose a view from each Capture 2145 Scene. In this case the three Captures VC0, VC1, and VC2 are one 2146 way of representing the video from the Endpoint. These three 2147 Captures should appear adjacent next to each other. 2148 Alternatively, another way of representing the Capture Scene is 2149 with the capture MCC3, which automatically shows the person who is 2150 talking. Similarly for the MCC4 and VC5 alternatives. 2152 As in the video case, the different views of audio in Capture 2153 Scene #1 represent the "same thing", in that one way to receive 2154 the audio is with the 3 Audio Captures (AC0, AC1, AC2), and 2155 another way is with the mixed AC3. The Media Consumer can choose 2156 an audio CSV it is capable of receiving. 2158 The spatial ordering is understood by the Media Capture attributes 2159 Area of Capture and Point of Capture and Point on Line of Capture. 2161 A Media Consumer would likely want to choose a Capture Scene View 2162 to receive based in part on how many streams it can simultaneously 2163 receive. A consumer that can receive three video streams would 2164 probably prefer to receive the first view of Capture Scene #1 2165 (VC0, VC1, VC2) and not receive the other views. A consumer that 2166 can receive only one video stream would probably choose one of the 2167 other views. 2169 If the consumer can receive a presentation stream too, it would 2170 also choose to receive the only view from Capture Scene #2 (VC6). 2172 12.1.2. Encoding Group Example 2174 This is an example of an Encoding Group to illustrate how it can 2175 express dependencies between Encodings. The information below 2176 about Encodings is a summary of what would be conveyed in SDP, not 2177 directly in the CLUE Advertisement. 2179 encodeGroupID=EG0 maxGroupBandwidth=6000000 2180 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2181 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2182 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2183 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2184 encodeID=AUDENC0, maxBandwidth=96000 2185 encodeID=AUDENC1, maxBandwidth=96000 2186 encodeID=AUDENC2, maxBandwidth=96000 2188 Here, the Encoding Group is EG0. Although the Encoding Group is 2189 capable of transmitting up to 6Mbit/s, no individual video 2190 Encoding can exceed 4Mbit/s. 2192 This encoding group also allows up to 3 audio encodings, AUDENC<0- 2193 2>. It is not required that audio and video encodings reside 2194 within the same encoding group, but if so then the group's overall 2195 maxBandwidth value is a limit on the sum of all audio and video 2196 encodings configured by the consumer. A system that does not wish 2197 or need to combine bandwidth limitations in this way should 2198 instead use separate encoding groups for audio and video in order 2199 for the bandwidth limitations on audio and video to not interact. 2201 Audio and video can be expressed in separate encoding groups, as 2202 in this illustration. 2204 encodeGroupID=EG0 maxGroupBandwidth=6000000 2205 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2206 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2207 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2208 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2209 encodeGroupID=EG1 maxGroupBandwidth=500000 2210 encodeID=AUDENC0, maxBandwidth=96000 2211 encodeID=AUDENC1, maxBandwidth=96000 2212 encodeID=AUDENC2, maxBandwidth=96000 2214 12.1.3. The MCU Case 2216 This section shows how an MCU might express its Capture Scenes, 2217 intending to offer different choices for consumers that can handle 2218 different numbers of streams. Each MCC is for video. A single 2219 Audio Capture is provided for all single and multi-screen 2220 configurations that can be associated (e.g. lip-synced) with any 2221 combination of Video Captures (the MCCs) at the consumer. 2223 +-----------------------+---------------------------------+ 2224 | Capture Scene #1 | | 2225 +-----------------------|---------------------------------+ 2226 | MCC | for a single screen consumer | 2227 | MCC1, MCC2 | for a two screen consumer | 2228 | MCC3, MCC4, MCC5 | for a three screen consumer | 2229 | MCC6, MCC7, MCC8, MCC9| for a four screen consumer | 2230 | AC0 | AC representing all participants| 2231 | CSV(MCC0) | | 2232 | CSV(MCC1,MCC2) | | 2233 | CSV(MCC3,MCC4,MCC5) | | 2234 | CSV(MCC6,MCC7, | | 2235 | MCC8,MCC9) | | 2236 | CSV(AC0) | | 2237 +-----------------------+---------------------------------+ 2238 Table 8: MCU main Capture Scenes 2240 If / when a presentation stream becomes active within the 2241 conference the MCU might re-advertise the available media as: 2243 +------------------+--------------------------------------+ 2244 | Capture Scene #2 | note | 2245 +------------------+--------------------------------------+ 2246 | VC10 | video capture for presentation | 2247 | AC1 | presentation audio to accompany VC10 | 2248 | CSV(VC10) | | 2249 | CSV(AC1) | | 2250 +------------------+--------------------------------------+ 2252 Table 9: MCU presentation Capture Scene 2254 12.2. Media Consumer Behavior 2256 This section gives an example of how a Media Consumer might behave 2257 when deciding how to request streams from the three screen 2258 endpoint described in the previous section. 2260 The receive side of a call needs to balance its requirements, 2261 based on number of screens and speakers, its decoding capabilities 2262 and available bandwidth, and the provider's capabilities in order 2263 to optimally configure the provider's streams. Typically it would 2264 want to receive and decode media from each Capture Scene 2265 advertised by the Provider. 2267 A sane, basic, algorithm might be for the consumer to go through 2268 each Capture Scene View in turn and find the collection of Video 2269 Captures that best matches the number of screens it has (this 2270 might include consideration of screens dedicated to presentation 2271 video display rather than "people" video) and then decide between 2272 alternative views in the video Capture Scenes based either on 2273 hard-coded preferences or user choice. Once this choice has been 2274 made, the consumer would then decide how to configure the 2275 provider's encoding groups in order to make best use of the 2276 available network bandwidth and its own decoding capabilities. 2278 12.2.1. One screen Media Consumer 2280 MCC3, MCC4 and VC5 are all different views by themselves, not 2281 grouped together in a single view, so the receiving device should 2282 choose between one of those. The choice would come down to 2283 whether to see the greatest number of participants simultaneously 2284 at roughly equal precedence (VC5), a switched view of just the 2285 loudest region (MCC3) or a switched view with PiPs (MCC4). An 2286 endpoint device with a small amount of knowledge of these 2287 differences could offer a dynamic choice of these options, in- 2288 call, to the user. 2290 12.2.2. Two screen Media Consumer configuring the example 2292 Mixing systems with an even number of screens, "2n", and those 2293 with "2n+1" cameras (and vice versa) is always likely to be the 2294 problematic case. In this instance, the behavior is likely to be 2295 determined by whether a "2 screen" system is really a "2 decoder" 2296 system, i.e., whether only one received stream can be displayed 2297 per screen or whether more than 2 streams can be received and 2298 spread across the available screen area. To enumerate 3 possible 2299 behaviors here for the 2 screen system when it learns that the far 2300 end is "ideally" expressed via 3 capture streams: 2302 1. Fall back to receiving just a single stream (MCC3, MCC4 or VC5 2303 as per the 1 screen consumer case above) and either leave one 2304 screen blank or use it for presentation if / when a 2305 presentation becomes active. 2307 2. Receive 3 streams (VC0, VC1 and VC2) and display across 2 2308 screens (either with each capture being scaled to 2/3 of a 2309 screen and the center capture being split across 2 screens) or, 2310 as would be necessary if there were large bezels on the 2311 screens, with each stream being scaled to 1/2 the screen width 2312 and height and there being a 4th "blank" panel. This 4th panel 2313 could potentially be used for any presentation that became 2314 active during the call. 2316 3. Receive 3 streams, decode all 3, and use control information 2317 indicating which was the most active to switch between showing 2318 the left and center streams (one per screen) and the center and 2319 right streams. 2321 For an endpoint capable of all 3 methods of working described 2322 above, again it might be appropriate to offer the user the choice 2323 of display mode. 2325 12.2.3. Three screen Media Consumer configuring the example 2327 This is the most straightforward case - the Media Consumer would 2328 look to identify a set of streams to receive that best matched its 2329 available screens and so the VC0 plus VC1 plus VC2 should match 2330 optimally. The spatial ordering would give sufficient information 2331 for the correct Video Capture to be shown on the correct screen, 2332 and the consumer would either need to divide a single encoding 2333 group's capability by 3 to determine what resolution and frame 2334 rate to configure the provider with or to configure the individual 2335 Video Captures' Encoding Groups with what makes most sense (taking 2336 into account the receive side decode capabilities, overall call 2337 bandwidth, the resolution of the screens plus any user preferences 2338 such as motion vs. sharpness). 2340 12.3. Multipoint Conference utilizing Multiple Content Captures 2342 The use of MCCs allows the MCU to construct outgoing Advertisements 2343 describing complex media switching and composition scenarios. The 2344 following sections provide several examples. 2346 Note: In the examples the identities of the CLUE elements (e.g. 2347 Captures, Capture Scene) in the incoming Advertisements overlap. 2348 This is because there is no co-ordination between the endpoints. 2349 The MCU is responsible for making these unique in the outgoing 2350 advertisement. 2352 12.3.1. Single Media Captures and MCC in the same Advertisement 2354 Four endpoints are involved in a Conference where CLUE is used. An 2355 MCU acts as a middlebox between the endpoints with a CLUE channel 2356 between each endpoint and the MCU. The MCU receives the following 2357 Advertisements. 2359 +-----------------------+---------------------------------+ 2360 | Capture Scene #1 | Description=AustralianConfRoom | 2361 +-----------------------|---------------------------------+ 2362 | VC1 | Description=Audience | 2363 | | EncodeGroupID=1 | 2364 | CSV(VC1) | | 2365 +---------------------------------------------------------+ 2367 Table 10: Advertisement received from Endpoint A 2369 +-----------------------+---------------------------------+ 2370 | Capture Scene #1 | Description=ChinaConfRoom | 2371 +-----------------------|---------------------------------+ 2372 | VC1 | Description=Speaker | 2373 | | EncodeGroupID=1 | 2374 | VC2 | Description=Audience | 2375 | | EncodeGroupID=1 | 2376 | CSV(VC1, VC2) | | 2377 +---------------------------------------------------------+ 2379 Table 11: Advertisement received from Endpoint B 2381 +-----------------------+---------------------------------+ 2382 | Capture Scene #1 | Description=USAConfRoom | 2383 +-----------------------|---------------------------------+ 2384 | VC1 | Description=Audience | 2385 | | EncodeGroupID=1 | 2386 | CSV(VC1) | | 2387 +---------------------------------------------------------+ 2389 Table 12: Advertisement received from Endpoint C 2391 Note: Endpoint B above indicates that it sends two streams. 2393 If the MCU wanted to provide a Multiple Content Capture containing 2394 a round robin switched view of the audience from the 3 endpoints 2395 and the speaker it could construct the following advertisement: 2397 Advertisement sent to Endpoint F 2398 +=======================+=================================+ 2399 | Capture Scene #1 | Description=AustralianConfRoom | 2400 +-----------------------|---------------------------------+ 2401 | VC1 | Description=Audience | 2402 | CSV(VC1) | | 2403 +=======================+=================================+ 2404 | Capture Scene #2 | Description=ChinaConfRoom | 2405 +-----------------------|---------------------------------+ 2406 | VC2 | Description=Speaker | 2407 | VC3 | Description=Audience | 2408 | CSV(VC2, VC3) | | 2409 +=======================+=================================+ 2410 | Capture Scene #3 | Description=USAConfRoom | 2411 +-----------------------|---------------------------------+ 2412 | VC4 | Description=Audience | 2413 | CSV(VC4) | | 2414 +=======================+=================================+ 2415 | Capture Scene #4 | | 2416 +-----------------------|---------------------------------+ 2417 | MCC1(VC1,VC2,VC3,VC4) | Policy=RoundRobin:1 | 2418 | | MaxCaptures=1 | 2419 | | EncodingGroup=1 | 2420 | CSV(MCC1) | | 2421 +=======================+=================================+ 2423 Table 13: Advertisement sent to Endpoint F - One Encoding 2425 Alternatively if the MCU wanted to provide the speaker as one media 2426 stream and the audiences as another it could assign an encoding 2427 group to VC2 in Capture Scene 2 and provide a CSV in Capture Scene 2428 #4 as per the example below. 2430 Advertisement sent to Endpoint F 2431 +=======================+=================================+ 2432 | Capture Scene #1 | Description=AustralianConfRoom | 2433 +-----------------------|---------------------------------+ 2434 | VC1 | Description=Audience | 2435 | CSV(VC1) | | 2436 +=======================+=================================+ 2437 | Capture Scene #2 | Description=ChinaConfRoom | 2438 +-----------------------|---------------------------------+ 2439 | VC2 | Description=Speaker | 2440 | | EncodingGroup=1 | 2441 | VC3 | Description=Audience | 2442 | CSV(VC2, VC3) | | 2443 +=======================+=================================+ 2444 | Capture Scene #3 | Description=USAConfRoom | 2445 +-----------------------|---------------------------------+ 2446 | VC4 | Description=Audience | 2447 | CSV(VC4) | | 2448 +=======================+=================================+ 2449 | Capture Scene #4 | | 2450 +-----------------------|---------------------------------+ 2451 | MCC1(VC1,VC3,VC4) | Policy=RoundRobin:1 | 2452 | | MaxCaptures=1 | 2453 | | EncodingGroup=1 | 2454 | MCC2(VC2) | MaxCaptures=1 | 2455 | | EncodingGroup=1 | 2456 | CSV2(MCC1,MCC2) | | 2457 +=======================+=================================+ 2459 Table 14: Advertisement sent to Endpoint F - Two Encodings 2461 Therefore a Consumer could choose whether or not to have a separate 2462 speaker related stream and could choose which endpoints to see. If 2463 it wanted the second stream but not the Australian conference room 2464 it could indicate the following captures in the Configure message: 2466 +-----------------------+---------------------------------+ 2467 | MCC1(VC3,VC4) | Encoding | 2468 | VC2 | Encoding | 2469 +-----------------------|---------------------------------+ 2470 Table 15: MCU case: Consumer Response 2472 12.3.2. Several MCCs in the same Advertisement 2474 Multiple MCCs can be used where multiple streams are used to carry 2475 media from multiple endpoints. For example: 2477 A conference has three endpoints D, E and F. Each end point has 2478 three video captures covering the left, middle and right regions of 2479 each conference room. The MCU receives the following 2480 advertisements from D and E. 2482 +-----------------------+---------------------------------+ 2483 | Capture Scene #1 | Description=AustralianConfRoom | 2484 +-----------------------|---------------------------------+ 2485 | VC1 | CaptureArea=Left | 2486 | | EncodingGroup=1 | 2487 | VC2 | CaptureArea=Centre | 2488 | | EncodingGroup=1 | 2489 | VC3 | CaptureArea=Right | 2490 | | EncodingGroup=1 | 2491 | CSV(VC1,VC2,VC3) | | 2492 +---------------------------------------------------------+ 2494 Table 16: Advertisement received from Endpoint D 2496 +-----------------------+---------------------------------+ 2497 | Capture Scene #1 | Description=ChinaConfRoom | 2498 +-----------------------|---------------------------------+ 2499 | VC1 | CaptureArea=Left | 2500 | | EncodingGroup=1 | 2501 | VC2 | CaptureArea=Centre | 2502 | | EncodingGroup=1 | 2503 | VC3 | CaptureArea=Right | 2504 | | EncodingGroup=1 | 2505 | CSV(VC1,VC2,VC3) | | 2506 +---------------------------------------------------------+ 2508 Table 17: Advertisement received from Endpoint E 2510 The MCU wants to offer Endpoint F three Capture Encodings. Each 2511 Capture Encoding would contain all the Captures from either 2512 Endpoint D or Endpoint E depending based on the active speaker. 2513 The MCU sends the following Advertisement: 2515 +=======================+=================================+ 2516 | Capture Scene #1 | Description=AustralianConfRoom | 2517 +-----------------------|---------------------------------+ 2518 | VC1 | | 2519 | VC2 | | 2520 | VC3 | | 2521 | CSV(VC1,VC2,VC3) | | 2522 +=======================+=================================+ 2523 | Capture Scene #2 | Description=ChinaConfRoom | 2524 +-----------------------|---------------------------------+ 2525 | VC4 | | 2526 | VC5 | | 2527 | VC6 | | 2528 | CSV(VC4,VC5,VC6) | | 2529 +=======================+=================================+ 2530 | Capture Scene #3 | | 2531 +-----------------------|---------------------------------+ 2532 | MCC1(VC1,VC4) | CaptureArea=Left | 2533 | | MaxCaptures=1 | 2534 | | SynchronisationID=1 | 2535 | | EncodingGroup=1 | 2536 | MCC2(VC2,VC5) | CaptureArea=Centre | 2537 | | MaxCaptures=1 | 2538 | | SynchronisationID=1 | 2539 | | EncodingGroup=1 | 2540 | MCC3(VC3,VC6) | CaptureArea=Right | 2541 | | MaxCaptures=1 | 2542 | | SynchronisationID=1 | 2543 | | EncodingGroup=1 | 2544 | CSV(MCC1,MCC2,MCC3) | | 2545 +=======================+=================================+ 2547 Table 17: Advertisement received from Endpoint E 2549 12.3.3. Heterogeneous conference with switching and composition 2551 Consider a conference between endpoints with the following 2552 characteristics: 2554 Endpoint A - 4 screens, 3 cameras 2556 Endpoint B - 3 screens, 3 cameras 2558 Endpoint C - 3 screens, 3 cameras 2559 Endpoint D - 3 screens, 3 cameras 2561 Endpoint E - 1 screen, 1 camera 2563 Endpoint F - 2 screens, 1 camera 2565 Endpoint G - 1 screen, 1 camera 2567 This example focuses on what the user in one of the 3-camera multi- 2568 screen endpoints sees. Call this person User A, at Endpoint A. 2569 There are 4 large display screens at Endpoint A. Whenever somebody 2570 at another site is speaking, all the video captures from that 2571 endpoint are shown on the large screens. If the talker is at a 3- 2572 camera site, then the video from those 3 cameras fills 3 of the 2573 screens. If the talker is at a single-camera site, then video from 2574 that camera fills one of the screens, while the other screens show 2575 video from other single-camera endpoints. 2577 User A hears audio from the 4 loudest talkers. 2579 User A can also see video from other endpoints, in addition to the 2580 current talker, although much smaller in size. Endpoint A has 4 2581 screens, so one of those screens shows up to 9 other Media Captures 2582 in a tiled fashion. When video from a 3 camera endpoint appears in 2583 the tiled area, video from all 3 cameras appears together across 2584 the screen with correct spatial relationship among those 3 images. 2586 +---+---+---+ +-------------+ +-------------+ +-------------+ 2587 | | | | | | | | | | 2588 +---+---+---+ | | | | | | 2589 | | | | | | | | | | 2590 +---+---+---+ | | | | | | 2591 | | | | | | | | | | 2592 +---+---+---+ +-------------+ +-------------+ +-------------+ 2593 Figure 8: Endpoint A - 4 Screen Display 2595 User B at Endpoint B sees a similar arrangement, except there are 2596 only 3 screens, so the 9 other Media Captures are spread out across 2597 the bottom of the 3 displays, in a picture-in-picture (PIP) format. 2598 When video from a 3 camera endpoint appears in the PIP area, video 2599 from all 3 cameras appears together across a single screen with 2600 correct spatial relationship. 2602 +-------------+ +-------------+ +-------------+ 2603 | | | | | | 2604 | | | | | | 2605 | | | | | | 2606 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2607 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2608 +-------------+ +-------------+ +-------------+ 2609 Figure 9: Endpoint B - 3 Screen Display with PiPs 2611 When somebody at a different endpoint becomes the current talker, 2612 then User A and User B both see the video from the new talker 2613 appear on their large screen area, while the previous talker takes 2614 one of the smaller tiled or PIP areas. The person who is the 2615 current talker doesn't see themselves; they see the previous talker 2616 in their large screen area. 2618 One of the points of this example is that endpoints A and B each 2619 want to receive 3 capture encodings for their large display areas, 2620 and 9 encodings for their smaller areas. A and B are be able to 2621 each send the same Configure message to the MCU, and each receive 2622 the same conceptual Media Captures from the MCU. The differences 2623 are in how they are rendered and are purely a local matter at A and 2624 B. 2626 The Advertisements for such a scenario are described below. 2628 +-----------------------+---------------------------------+ 2629 | Capture Scene #1 | Description=Endpoint x | 2630 +-----------------------|---------------------------------+ 2631 | VC1 | EncodingGroup=1 | 2632 | VC2 | EncodingGroup=1 | 2633 | VC3 | EncodingGroup=1 | 2634 | AC1 | EncodingGroup=2 | 2635 | CSV1(VC1, VC2, VC3) | | 2636 | CSV2(AC1) | | 2637 +---------------------------------------------------------+ 2639 Table 19: Advertisement received at the MCU from Endpoints A to D 2640 +-----------------------+---------------------------------+ 2641 | Capture Scene #1 | Description=Endpoint y | 2642 +-----------------------|---------------------------------+ 2643 | VC1 | EncodingGroup=1 | 2644 | AC1 | EncodingGroup=2 | 2645 | CSV1(VC1) | | 2646 | CSV2(AC1) | | 2647 +---------------------------------------------------------+ 2649 Table 20: Advertisement received at the MCU from Endpoints E to F 2651 Rather than considering what is displayed CLUE concentrates more 2652 on what the MCU sends. The MCU doesn't know anything about the 2653 number of screens an endpoint has. 2655 As Endpoints A to D each advertise that three Captures make up a 2656 Capture Scene, the MCU offers these in a "site" switching mode. 2657 That is that there are three Multiple Content Captures (and 2658 Capture Encodings) each switching between Endpoints. The MCU 2659 switches in the applicable media into the stream based on voice 2660 activity. Endpoint A will not see a capture from itself. 2662 Using the MCC concept the MCU would send the following 2663 Advertisement to endpoint A: 2665 +=======================+=================================+ 2666 | Capture Scene #1 | Description=Endpoint B | 2667 +-----------------------|---------------------------------+ 2668 | VC4 | Left | 2669 | VC5 | Center | 2670 | VC6 | Right | 2671 | AC1 | | 2672 | CSV(VC4,VC5,VC6) | | 2673 | CSV(AC1) | | 2674 +=======================+=================================+ 2675 | Capture Scene #2 | Description=Endpoint C | 2676 +-----------------------|---------------------------------+ 2677 | VC7 | Left | 2678 | VC8 | Center | 2679 | VC9 | Right | 2680 | AC2 | | 2681 | CSV(VC7,VC8,VC9) | | 2682 | CSV(AC2) | | 2683 +=======================+=================================+ 2684 | Capture Scene #3 | Description=Endpoint D | 2685 +-----------------------|---------------------------------+ 2686 | VC10 | Left | 2687 | VC11 | Center | 2688 | VC12 | Right | 2689 | AC3 | | 2690 | CSV(VC10,VC11,VC12) | | 2691 | CSV(AC3) | | 2692 +=======================+=================================+ 2693 | Capture Scene #4 | Description=Endpoint E | 2694 +-----------------------|---------------------------------+ 2695 | VC13 | | 2696 | AC4 | | 2697 | CSV(VC13) | | 2698 | CSV(AC4) | | 2699 +=======================+=================================+ 2700 | Capture Scene #5 | Description=Endpoint F | 2701 +-----------------------|---------------------------------+ 2702 | VC14 | | 2703 | AC5 | | 2704 | CSV(VC14) | | 2705 | CSV(AC5) | | 2706 +=======================+=================================+ 2707 | Capture Scene #6 | Description=Endpoint G | 2708 +-----------------------|---------------------------------+ 2709 | VC15 | | 2710 | AC6 | | 2711 | CSV(VC15) | | 2712 | CSV(AC6) | | 2713 +=======================+=================================+ 2715 Table 21: Advertisement sent to endpoint A - Source Part 2717 The above part of the Advertisement presents information about the 2718 sources to the MCC. The information is effectively the same as the 2719 received Advertisements except that there are no Capture Encodings 2720 associated with them and the identities have been re-numbered. 2722 In addition to the source Capture information the MCU advertises 2723 "site" switching of Endpoints B to G in three streams. 2725 +=======================+=================================+ 2726 | Capture Scene #7 | Description=Output3streammix | 2727 +-----------------------|---------------------------------+ 2728 | MCC1(VC4,VC7,VC10, | CaptureArea=Left | 2729 | VC13) | MaxCaptures=1 | 2730 | | SynchronisationID=1 | 2731 | | Policy=SoundLevel:0 | 2732 | | EncodingGroup=1 | 2733 | | | 2734 | MCC2(VC5,VC8,VC11, | CaptureArea=Center | 2735 | VC14) | MaxCaptures=1 | 2736 | | SynchronisationID=1 | 2737 | | Policy=SoundLevel:0 | 2738 | | EncodingGroup=1 | 2739 | | | 2740 | MCC3(VC6,VC9,VC12, | CaptureArea=Right | 2741 | VC15) | MaxCaptures=1 | 2742 | | SynchronisationID=1 | 2743 | | Policy=SoundLevel:0 | 2744 | | EncodingGroup=1 | 2745 | | | 2746 | MCC4() (for audio) | CaptureArea=whole scene | 2747 | | MaxCaptures=1 | 2748 | | Policy=SoundLevel:0 | 2749 | | EncodingGroup=2 | 2750 | | | 2751 | MCC5() (for audio) | CaptureArea=whole scene | 2752 | | MaxCaptures=1 | 2753 | | Policy=SoundLevel:1 | 2754 | | EncodingGroup=2 | 2755 | | | 2756 | MCC6() (for audio) | CaptureArea=whole scene | 2757 | | MaxCaptures=1 | 2758 | | Policy=SoundLevel:2 | 2759 | | EncodingGroup=2 | 2760 | | | 2761 | MCC7() (for audio) | CaptureArea=whole scene | 2762 | | MaxCaptures=1 | 2763 | | Policy=SoundLevel:3 | 2764 | | EncodingGroup=2 | 2765 | | | 2766 | CSV(MCC1,MCC2,MCC3) | | 2767 | CSV(MCC4,MCC5,MCC6, | | 2768 | MCC7) | | 2769 +=======================+=================================+ 2771 Table 22: Advertisement send to endpoint A - switching part 2773 The above part describes the switched 3 main streams that relate to 2774 site switching. MaxCaptures=1 indicates that only one Capture from 2775 the MCC is sent at a particular time. SynchronisationID=1 indicates 2776 that the source sending is synchronised. The provider can choose to 2777 group together VC13, VC14, and VC15 for the purpose of switching 2778 according to the SynchronisationID. Therefore when the provider 2779 switches one of them into an MCC, it can also switch the others 2780 even though they are not part of the same Capture Scene. 2782 All the audio for the conference is included in this Scene #7. 2783 There isn't necessarily a one to one relation between any audio 2784 capture and video capture in this scene. Typically a change in 2785 loudest talker will cause the MCU to switch the audio streams more 2786 quickly than switching video streams. 2788 The MCU can also supply nine media streams showing the active and 2789 previous eight speakers. It includes the following in the 2790 Advertisement: 2792 +=======================+=================================+ 2793 | Capture Scene #8 | Description=Output9stream | 2794 +-----------------------|---------------------------------+ 2795 | MCC8(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2796 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:0 | 2797 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2798 | | | 2799 | MCC9(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2800 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:1 | 2801 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2802 | | | 2803 to to | 2804 | | | 2805 | MCC16(VC4,VC5,VC6,VC7,| MaxCaptures=1 | 2806 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:8 | 2807 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2808 | | | 2809 | CSV(MCC8,MCC9,MCC10, | | 2810 | MCC11,MCC12,MCC13,| | 2811 | MCC14,MCC15,MCC16)| | 2812 +=======================+=================================+ 2814 Table 23: Advertisement sent to endpoint A - 9 switched part 2816 The above part indicates that there are 9 capture encodings. Each 2817 of the Capture Encodings may contain any captures from any source 2818 site with a maximum of one Capture at a time. Which Capture is 2819 present is determined by the policy. The MCCs in this scene do not 2820 have any spatial attributes. 2822 Note: The Provider alternatively could provide each of the MCCs 2823 above in its own Capture Scene. 2825 If the MCU wanted to provide a composed Capture Encoding containing 2826 all of the 9 captures it could advertise in addition: 2828 +=======================+=================================+ 2829 | Capture Scene #9 | Description=NineTiles | 2830 +-----------------------|---------------------------------+ 2831 | MCC13(MCC8,MCC9,MCC10,| MaxCaptures=9 | 2832 | MCC11,MCC12,MCC13,| EncodingGroup=1 | 2833 | MCC14,MCC15,MCC16)| | 2834 | | | 2835 | CSV(MCC13) | | 2836 +=======================+=================================+ 2838 Table 24: Advertisement sent to endpoint A - 9 composed part 2840 As MaxCaptures is 9 it indicates that the capture encoding contains 2841 information from 9 sources at a time. 2843 The Advertisement to Endpoint B is identical to the above other 2844 than the captures from Endpoint A would be added and the captures 2845 from Endpoint B would be removed. Whether the Captures are rendered 2846 on a four screen display or a three screen display is up to the 2847 Consumer to determine. The Consumer wants to place video captures 2848 from the same original source endpoint together, in the correct 2849 spatial order, but the MCCs do not have spatial attributes. So the 2850 Consumer needs to associate incoming media packets with the 2851 original individual captures in the advertisement (such as VC4, 2852 VC5, and VC6) in order to know the spatial information it needs for 2853 correct placement on the screens. The Provider can use the RTCP 2854 CaptureId SDES item and associated RTP header extension, as 2855 described in [I-D.ietf-clue-rtp-mapping], to convey this 2856 information to the Consumer. 2858 12.3.4. Heterogeneous conference with voice activated switching 2860 This example illustrates how multipoint "voice activated switching" 2861 behavior can be realized, with an endpoint making its own decision 2862 about which of its outgoing video streams is considered the "active 2863 talker" from that endpoint. Then an MCU can decide which is the 2864 active talker among the whole conference. 2866 Consider a conference between endpoints with the following 2867 characteristics: 2869 Endpoint A - 3 screens, 3 cameras 2871 Endpoint B - 3 screens, 3 cameras 2873 Endpoint C - 1 screen, 1 camera 2875 This example focuses on what the user at endpoint C sees. The 2876 user would like to see the video capture of the current talker, 2877 without composing it with any other video capture. In this 2878 example endpoint C is capable of receiving only a single video 2879 stream. The following tables describe advertisements from A and B 2880 to the MCU, and from the MCU to C, that can be used to accomplish 2881 this. 2883 +-----------------------+---------------------------------+ 2884 | Capture Scene #1 | Description=Endpoint x | 2885 +-----------------------|---------------------------------+ 2886 | VC1 | CaptureArea=Left | 2887 | | EncodingGroup=1 | 2888 | VC2 | CaptureArea=Center | 2889 | | EncodingGroup=1 | 2890 | VC3 | CaptureArea=Right | 2891 | | EncodingGroup=1 | 2892 | MCC1(VC1,VC2,VC3) | MaxCaptures=1 | 2893 | | CaptureArea=whole scene | 2894 | | Policy=SoundLevel:0 | 2895 | | EncodingGroup=1 | 2896 | AC1 | CaptureArea=whole scene | 2897 | | EncodingGroup=2 | 2898 | CSV1(VC1, VC2, VC3) | | 2899 | CSV2(MCC1) | | 2900 | CSV3(AC1) | | 2901 +---------------------------------------------------------+ 2903 Table 25: Advertisement received at the MCU from Endpoints A and B 2905 Endpoints A and B are advertising each individual video capture, 2906 and also a switched capture MCC1 which switches between the other 2907 three based on who is the active talker. These endpoints do not 2908 advertise distinct audio captures associated with each individual 2909 video capture, so it would be impossible for the MCU (as a media 2910 consumer) to make its own determination of which video capture is 2911 the active talker based just on information in the audio streams. 2913 +-----------------------+---------------------------------+ 2914 | Capture Scene #1 | Description=conference | 2915 +-----------------------|---------------------------------+ 2916 | MCC1() | CaptureArea=Left | 2917 | | MaxCaptures=1 | 2918 | | SynchronisationID=1 | 2919 | | Policy=SoundLevel:0 | 2920 | | EncodingGroup=1 | 2921 | | | 2922 | MCC2() | CaptureArea=Center | 2923 | | MaxCaptures=1 | 2924 | | SynchronisationID=1 | 2925 | | Policy=SoundLevel:0 | 2926 | | EncodingGroup=1 | 2927 | | | 2928 | MCC3() | CaptureArea=Right | 2929 | | MaxCaptures=1 | 2930 | | SynchronisationID=1 | 2931 | | Policy=SoundLevel:0 | 2932 | | EncodingGroup=1 | 2933 | | | 2934 | MCC4() | CaptureArea=whole scene | 2935 | | MaxCaptures=1 | 2936 | | Policy=SoundLevel:0 | 2937 | | EncodingGroup=1 | 2938 | | | 2939 | MCC5() (for audio) | CaptureArea=whole scene | 2940 | | MaxCaptures=1 | 2941 | | Policy=SoundLevel:0 | 2942 | | EncodingGroup=2 | 2943 | | | 2944 | MCC6() (for audio) | CaptureArea=whole scene | 2945 | | MaxCaptures=1 | 2946 | | Policy=SoundLevel:1 | 2947 | | EncodingGroup=2 | 2948 | CSV1(MCC1,MCC2,MCC3 | | 2949 | CSV2(MCC4) | | 2950 | CSV3(MCC5,MCC6) | | 2951 +---------------------------------------------------------+ 2952 Table 26: Advertisement sent from the MCU to C 2954 The MCU advertises one scene, with four video MCCs. Three of them 2955 in CSV1 give a left, center, right view of the conference, with 2956 "site switching". MCC4 provides a single video capture 2957 representing a view of the whole conference. The MCU intends for 2958 MCC4 to be switched between all the other original source 2959 captures. In this example advertisement the MCU is not giving all 2960 the information about all the other endpoints' scenes and which of 2961 those captures is included in the MCCs. The MCU could include all 2962 that information if it wants to give the consumers more 2963 information, but it is not necessary for this example scenario. 2965 The Provider advertises MCC5 and MCC6 for audio. Both are 2966 switched captures, with different SoundLevel policies indicating 2967 they are the top two dominant talkers. The Provider advertises 2968 CSV3 with both MCCs, suggesting the Consumer should use both if it 2969 can. 2971 Endpoint C, in its configure message to the MCU, requests to 2972 receive MCC4 for video, and MCC5 and MCC6 for audio. In order for 2973 the MCU to get the information it needs to construct MCC4, it has 2974 to send configure messages to A and B asking to receive MCC1 from 2975 each of them, along with their AC1 audio. Now the MCU can use 2976 audio energy information from the two incoming audio streams from 2977 A and B to determine which of those alternatives is the current 2978 talker. Based on that, the MCU uses either MCC1 from A or MCC1 2979 from B as the source of MCC4 to send to C. 2981 13. Acknowledgements 2983 Allyn Romanow and Brian Baldino were authors of early versions. 2984 Mark Gorzynski also contributed much to the initial approach. 2985 Many others also contributed, including Christian Groves, Jonathan 2986 Lennox, Paul Kyzivat, Rob Hansen, Roni Even, Christer Holmberg, 2987 Stephen Botzko, Mary Barnes, John Leslie, Paul Coverdale. 2989 14. IANA Considerations 2991 None. 2993 15. Security Considerations 2995 There are several potential attacks related to telepresence, and 2996 specifically the protocols used by CLUE, in the case of 2997 conferencing sessions, due to the natural involvement of multiple 2998 endpoints and the many, often user-invoked, capabilities provided 2999 by the systems. 3001 An MCU involved in a CLUE session can experience many of the same 3002 attacks as that of a conferencing system such as that enabled by 3003 the XCON framework [RFC 6503]. Examples of attacks include the 3004 following: an endpoint attempting to listen to sessions in which 3005 it is not authorized to participate, an endpoint attempting to 3006 disconnect or mute other users, and theft of service by an 3007 endpoint in attempting to create telepresence sessions it is not 3008 allowed to create. Thus, it is RECOMMENDED that an MCU 3009 implementing the protocols necessary to support CLUE, follow the 3010 security recommendations specified in the conference control 3011 protocol documents. In the case of CLUE, SIP is the conferencing 3012 protocol, thus the security considerations in RFC 4579 MUST be 3013 followed. 3015 One primary security concern, surrounding the CLUE framework 3016 introduced in this document, involves securing the actual 3017 protocols and the associated authorization mechanisms. These 3018 concerns apply to endpoint to endpoint sessions, as well as 3019 sessions involving multiple endpoints and MCUs. Figure 2 in 3020 section 5 provides a basic flow of information exchange for CLUE 3021 and the protocols involved. 3023 As described in section 5, CLUE uses SIP/SDP to establish the 3024 session prior to exchanging any CLUE specific information. Thus 3025 the security mechanisms recommended for SIP [RFC 3261], including 3026 user authentication and authorization, SHOULD be followed. In 3027 addition, the media is based on RTP and thus existing RTP security 3028 mechanisms SHOULD be supported, and DTLS/SRTP MUST be supported. 3029 Media security is also discussed in [I-D.ietf-clue-signaling] and 3030 [I-D.ietf-clue-rtp-mapping]. 3032 A separate data channel is established to transport the CLUE 3033 protocol messages. The contents of the CLUE protocol messages are 3034 based on information introduced in this document. The CLUE data 3035 model [I-D.ietf-clue-data-model-schema] defines through an XML 3036 schema the syntax to be used. Some of the information which could 3037 possibly introduce privacy concerns is the xCard information as 3038 described in section 7.1.1.11. In addition, the (text) 3039 description field in the Media Capture attribute (section 7.1.1.7) 3040 could possibly reveal sensitive information or specific 3041 identities. The same would be true for the descriptions in the 3042 Capture Scene (section 7.3.1) and Capture Scene View (7.3.2) 3043 attributes. One other important consideration for the 3044 information in the xCard as well as the description field in the 3045 Media Capture and Capture Scene View attributes is that while the 3046 endpoints involved in the session have been authenticated, there 3047 is no assurance that the information in the xCard or description 3048 fields is authentic. Thus, this information MUST NOT be used to 3049 make any authorization decisions. 3051 While other information in the CLUE protocol messages does not 3052 reveal specific identities, it can reveal characteristics and 3053 capabilities of the endpoints. That information could possibly 3054 uniquely identify specific endpoints. It might also be possible 3055 for an attacker to manipulate the information and disrupt the CLUE 3056 sessions. It would also be possible to mount a DoS attack on the 3057 CLUE endpoints if a malicious agent has access to the data 3058 channel. Thus, it MUST be possible for the endpoints to establish 3059 a channel which is secure against both message recovery and 3060 message modification. Further details on this are provided in the 3061 CLUE data channel solution document. 3063 There are also security issues associated with the authorization 3064 to perform actions at the CLUE endpoints to invoke specific 3065 capabilities (e.g., re-arranging screens, sharing content, etc.). 3066 However, the policies and security associated with these actions 3067 are outside the scope of this document and the overall CLUE 3068 solution. 3070 16. Changes Since Last Version 3072 NOTE TO THE RFC-Editor: Please remove this section prior to 3073 publication as an RFC. 3075 Changes from 19 to 20: 3077 1. Define term "CLUE" in introduction. 3078 2. Add MCC attribute Allow Subset Choice. 3079 3. Remove phrase about reducing SDP size, replace with 3080 potentially saving consumer resources. 3081 4. Change example of a CLUE exchange that does not require SDP 3082 exchange. 3083 5. Language attribute uses RFC5646. 3085 6. Change Member person type to Attendee. Add Observer type. 3086 7. Clarify DTLS/SRTP MUST be supported. 3087 8. Change SHOULD NOT to MUST NOT regarding using xCard or 3088 description information for authorization decisions. 3089 9. Clarify definition of Global View. 3090 10. Refer to signaling doc regarding interoperating with a 3091 device that does not support CLUE. 3092 11. Various minor editorial changes from working group last call 3093 feedback. 3094 12. Capitalize defined terms. 3096 Changes from 18 to 19: 3098 1. Remove the Max Capture Encodings media capture attribute. 3099 2. Refer to RTP mapping document in the MCC example section. 3100 3. Update references to current versions of drafts in progress. 3102 Changes from 17 to 18: 3104 1. Add separate definition of Global View List. 3105 2. Add diagram for Global View List structure. 3106 3. Tweak definitions of Media Consumer and Provider. 3108 Changes from 16 to 17: 3110 1. Ticket #59 - rename Capture Scene Entry (CSE) to Capture 3111 Scene View (CSV) 3113 2. Ticket #60 - rename Global CSE List to Global View List 3115 3. Ticket #61 - Proposal for describing the coordinate system. 3116 Describe it better, without conflicts if cameras point in 3117 different directions. 3119 4. Minor clarifications and improved wording for Synchronisation 3120 Identity, MCC, Simultaneous Transmission Set. 3122 5. Add definitions for CLUE-capable device and CLUE-enabled 3123 call, taken from the signaling draft. 3125 6. Update definitions of Capture Device, Media Consumer, Media 3126 Provider, Endpoint, MCU, MCC. 3128 7. Replace "middle box" with "MCU". 3130 8. Explicitly state there can also be Media Captures that are 3131 not included in a Capture Scene View. 3133 9. Explicitly state "A single Encoding Group MAY refer to 3134 encodings for different media types." 3136 10. In example 12.1.1 add axes and audio captures to the 3137 diagram, and describe placement of microphones. 3139 11. Add references to data model and signaling drafts. 3141 12. Split references into Normative and Informative sections. 3142 Add heading number for references section. 3144 Changes from 15 to 16: 3146 1. Remove Audio Channel Format attribute 3148 2. Add Audio Capture Sensitivity Pattern attribute 3150 3. Clarify audio spatial information regarding point of capture 3151 and point on line of capture. Area of capture does not apply 3152 to audio. 3154 4. Update section 12 example for new treatment of audio spatial 3155 information. 3157 5. Clean up wording of some definitions, and various places in 3158 sections 5 and 10. 3160 6. Remove individual encoding parameter paragraph from section 3161 9. 3163 7. Update Advertisement diagram. 3165 8. Update Acknowledgements. 3167 9. References to use cases and requirements now refer to RFCs. 3169 10. Minor editorial changes. 3171 Changes from 14 to 15: 3173 1. Add "=" and "<=" qualifiers to MaxCaptures attribute, and 3174 clarify the meaning regarding switched and composed MCC. 3176 2. Add section 7.3.3 Global Capture Scene Entry List, and a few 3177 other sentences elsewhere that refer to global CSE sets. 3179 3. Clarify: The Provider MUST be capable of encoding and sending 3180 all Captures (*that have an encoding group*) in a single 3181 Capture Scene Entry simultaneously. 3183 4. Add voice activated switching example in section 12. 3185 5. Change name of attributes Participant Info/Type to Person 3186 Info/Type. 3188 6. Clarify the Person Info/Type attributes have the same meaning 3189 regardless of whether or not the capture has a Presentation 3190 attribute. 3192 7. Update example section 12.1 to be consistent with the rest of 3193 the document, regarding MCC and capture attributes. 3195 8. State explicitly each CSE has a unique ID. 3197 Changes from 13 to 14: 3199 1. Fill in section for Security Considerations. 3201 2. Replace Role placeholder with Participant Information, 3202 Participant Type, and Scene Information attributes. 3204 3. Spatial information implies nothing about how constituent 3205 media captures are combined into a composed MCC. 3207 4. Clean up MCC example in Section 12.3.3. Clarify behavior of 3208 tiled and PIP display windows. Add audio. Add new open 3209 issue about associating incoming packets to original source 3210 capture. 3212 5. Remove editor's note and associated statement about RTP 3213 multiplexing at end of section 5. 3215 6. Remove editor's note and associated paragraph about 3216 overloading media channel with both CLUE and non-CLUE usage, 3217 in section 5. 3219 7. In section 10, clarify intent of media encodings conforming 3220 to SDP, even with multiple CLUE message exchanges. Remove 3221 associated editor's note. 3223 Changes from 12 to 13: 3225 1. Added the MCC concept including updates to existing sections 3226 to incorporate the MCC concept. New MCC attributes: 3227 MaxCaptures, SynchronisationID and Policy. 3229 2. Removed the "composed" and "switched" Capture attributes due 3230 to overlap with the MCC concept. 3232 3. Removed the "Scene-switch-policy" CSE attribute, replaced by 3233 MCC and SynchronisationID. 3235 4. Editorial enhancements including numbering of the Capture 3236 attribute sections, tables, figures etc. 3238 Changes from 11 to 12: 3240 1. Ticket #44. Remove note questioning about requiring a 3241 Consumer to send a Configure after receiving Advertisement. 3243 2. Ticket #43. Remove ability for consumer to choose value of 3244 attribute for scene-switch-policy. 3246 3. Ticket #36. Remove computational complexity parameter, 3247 MaxGroupPps, from Encoding Groups. 3249 4. Reword the Abstract and parts of sections 1 and 4 (now 5) 3250 based on Mary's suggestions as discussed on the list. Move 3251 part of the Introduction into a new section Overview & 3252 Motivation. 3254 5. Add diagram of an Advertisement, in the Overview of the 3255 Framework/Model section. 3257 6. Change Intended Status to Standards Track. 3259 7. Clean up RFC2119 keyword language. 3261 Changes from 10 to 11: 3263 1. Add description attribute to Media Capture and Capture Scene 3264 Entry. 3266 2. Remove contradiction and change the note about open issue 3267 regarding always responding to Advertisement with a Configure 3268 message. 3270 3. Update example section, to cleanup formatting and make the 3271 media capture attributes and encoding parameters consistent 3272 with the rest of the document. 3274 Changes from 09 to 10: 3276 1. Several minor clarifications such as about SDP usage, Media 3277 Captures, Configure message. 3279 2. Simultaneous Set can be expressed in terms of Capture Scene 3280 and Capture Scene Entry. 3282 3. Removed Area of Scene attribute. 3284 4. Add attributes from draft-groves-clue-capture-attr-01. 3286 5. Move some of the Media Capture attribute descriptions back 3287 into this document, but try to leave detailed syntax to the 3288 data model. Remove the OUTSOURCE sections, which are already 3289 incorporated into the data model document. 3291 Changes from 08 to 09: 3293 1. Use "document" instead of "memo". 3295 2. Add basic call flow sequence diagram to introduction. 3297 3. Add definitions for Advertisement and Configure messages. 3299 4. Add definitions for Capture and Provider. 3301 5. Update definition of Capture Scene. 3303 6. Update definition of Individual Encoding. 3305 7. Shorten definition of Media Capture and add key points in the 3306 Media Captures section. 3308 8. Reword a bit about capture scenes in overview. 3310 9. Reword about labeling Media Captures. 3312 10. Remove the Consumer Capability message. 3314 11. New example section heading for media provider behavior 3316 12. Clarifications in the Capture Scene section. 3318 13. Clarifications in the Simultaneous Transmission Set section. 3320 14. Capitalize defined terms. 3322 15. Move call flow example from introduction to overview section 3324 16. General editorial cleanup 3326 17. Add some editors' notes requesting input on issues 3328 18. Summarize some sections, and propose details be outsourced 3329 to other documents. 3331 Changes from 06 to 07: 3333 1. Ticket #9. Rename Axis of Capture Point attribute to Point 3334 on Line of Capture. Clarify the description of this 3335 attribute. 3337 2. Ticket #17. Add "capture encoding" definition. Use this new 3338 term throughout document as appropriate, replacing some usage 3339 of the terms "stream" and "encoding". 3341 3. Ticket #18. Add Max Capture Encodings media capture 3342 attribute. 3344 4. Add clarification that different capture scene entries are 3345 not necessarily mutually exclusive. 3347 Changes from 05 to 06: 3349 1. Capture scene description attribute is a list of text strings, 3350 each in a different language, rather than just a single string. 3352 2. Add new Axis of Capture Point attribute. 3354 3. Remove appendices A.1 through A.6. 3356 4. Clarify that the provider must use the same coordinate system 3357 with same scale and origin for all coordinates within the same 3358 capture scene. 3360 Changes from 04 to 05: 3362 1. Clarify limitations of "composed" attribute. 3364 2. Add new section "capture scene entry attributes" and add the 3365 attribute "scene-switch-policy". 3367 3. Add capture scene description attribute and description 3368 language attribute. 3370 4. Editorial changes to examples section for consistency with the 3371 rest of the document. 3373 Changes from 03 to 04: 3375 1. Remove sentence from overview - "This constitutes a significant 3376 change ..." 3378 2. Clarify a consumer can choose a subset of captures from a 3379 capture scene entry or a simultaneous set (in section "capture 3380 scene" and "consumer's choice..."). 3382 3. Reword first paragraph of Media Capture Attributes section. 3384 4. Clarify a stereo audio capture is different from two mono audio 3385 captures (description of audio channel format attribute). 3387 5. Clarify what it means when coordinate information is not 3388 specified for area of capture, point of capture, area of scene. 3390 6. Change the term "producer" to "provider" to be consistent (it 3391 was just in two places). 3393 7. Change name of "purpose" attribute to "content" and refer to 3394 RFC4796 for values. 3396 8. Clarify simultaneous sets are part of a provider advertisement, 3397 and apply across all capture scenes in the advertisement. 3399 9. Remove sentence about lip-sync between all media captures in a 3400 capture scene. 3402 10. Combine the concepts of "capture scene" and "capture set" 3403 into a single concept, using the term "capture scene" to 3404 replace the previous term "capture set", and eliminating the 3405 original separate capture scene concept. 3407 17. Normative References 3409 [I-D.ietf-clue-datachannel] 3410 Holmberg, C., "CLUE Protocol Data Channel", draft- 3411 ietf-clue-datachannel-05 (work in progress), November 3412 2014. 3414 [I-D.ietf-clue-data-model-schema] 3415 Presta, R., Romano, S P., "An XML Schema for the CLUE 3416 data model", draft-ietf-clue-data-model-schema-07 (work 3417 in progress), September 2014. 3419 [I-D.ietf-clue-protocol] 3420 Presta, R. and S. Romano, "CLUE protocol", draft- 3421 ietf-clue-protocol-02 (work in progress), October 2014. 3423 [I-D.ietf-clue-signaling] 3424 Kyzivat, P., Xiao, L., Groves, C., Hansen, R., "CLUE 3425 Signaling", draft-ietf-clue-signaling-04 (work in 3426 progress), October 2014. 3428 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3429 Requirement Levels", BCP 14, RFC 2119, March 1997. 3431 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., 3432 Johnston, 3433 A., Peterson, J., Sparks, R., Handley, M., and E. 3434 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 3435 June 2002. 3437 [RFC3264] Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model 3438 with the Session Description Protocol (SDP)", RFC 3264, 3439 June 2002. 3441 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 3442 Jacobson, "RTP: A Transport Protocol for Real-Time 3443 Applications", STD 64, RFC 3550, July 2003. 3445 [RFC4579] Johnston, A., Levin, O., "SIP Call Control - 3446 Conferencing for User Agents", RFC 4579, August 2006 3448 18. Informative References 3450 [I-D.ietf-clue-rtp-mapping] 3451 Even, R., Lennox, J., "Mapping RP streams to CLUE media 3452 captures", draft-ietf-clue-rtp-mapping-03 (work in 3453 progress), October 2014. 3455 [RFC4353] Rosenberg, J., "A Framework for Conferencing with the 3456 Session Initiation Protocol (SIP)", RFC 4353, 3457 February 2006. 3459 [RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 3460 5117, January 2008. 3462 [RFC5646] Phillips, A., Davis, M., "Tags for Identifying 3463 Languages", RFC 5646, September 2009 3465 [RFC7205] Romanow, A., Botzko, S., Duckworth, M., Even, R., 3466 "Use Cases for Telepresence Multistreams", RFC 7205, 3467 April 2014. 3469 [RFC7262] Romanow, A., Botzko, S., Barnes, M., "Requirements 3470 for Telepresence Multistreams", RFC 7262, June 2014. 3472 19. Authors' Addresses 3474 Mark Duckworth (editor) 3475 Polycom 3476 Andover, MA 01810 3477 USA 3479 Email: mark.duckworth@polycom.com 3480 Andrew Pepperell 3481 Acano 3482 Uxbridge, England 3483 UK 3485 Email: apeppere@gmail.com 3487 Stephan Wenger 3488 Vidyo, Inc. 3489 433 Hackensack Ave. 3490 Hackensack, N.J. 07601 3491 USA 3493 Email: stewe@stewe.org