idnits 2.17.1 draft-ietf-clue-framework-17.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 1 instance of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == Line 1117 has weird spacing: '... switch betwe...' == Line 1939 has weird spacing: '...om left bot...' == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: A separate data channel is established to transport the CLUE protocol messages. The contents of the CLUE protocol messages are based on information introduced in this document, which is represented by an XML schema for this information defined in the CLUE data model [ref]. Some of the information which could possibly introduce privacy concerns is the xCard information as described in section 7.1.1.11. In addition, the (text) description field in the Media Capture attribute (section 7.1.1.7) could possibly reveal sensitive information or specific identities. The same would be true for the descriptions in the Capture Scene (section 7.3.1) and Capture Scene View (7.3.2) attributes. One other important consideration for the information in the xCard as well as the description field in the Media Capture and Capture Scene View attributes is that while the endpoints involved in the session have been authenticated, there is no assurance that the information in the xCard or description fields is authentic. Thus, this information SHOULD not be used to make any authorization decisions and the participants in the sessions SHOULD be made aware of this. -- The document date (September 29, 2014) is 3496 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC6351' is mentioned on line 868, but not defined == Missing Reference: 'RFC6350' is mentioned on line 879, but not defined == Missing Reference: 'RFC4566' is mentioned on line 1555, but not defined ** Obsolete undefined reference: RFC 4566 (Obsoleted by RFC 8866) == Missing Reference: 'RFC 6503' is mentioned on line 2967, but not defined == Missing Reference: 'RFC 3261' is mentioned on line 2989, but not defined == Unused Reference: 'I-D.ietf-clue-data-model-schema' is defined on line 3343, but no explicit reference was found in the text == Unused Reference: 'I-D.presta-clue-protocol' is defined on line 3348, but no explicit reference was found in the text == Unused Reference: 'RFC4579' is defined on line 3374, but no explicit reference was found in the text == Outdated reference: A later version (-18) exists of draft-ietf-clue-datachannel-00 ** Downref: Normative reference to an Experimental draft: draft-ietf-clue-datachannel (ref. 'I-D.ietf-clue-datachannel') == Outdated reference: A later version (-17) exists of draft-ietf-clue-data-model-schema-06 -- No information found for draft-prestaclue-protocol - is the name correct? -- Possible downref: Normative reference to a draft: ref. 'I-D.presta-clue-protocol' == Outdated reference: A later version (-15) exists of draft-ietf-clue-signaling-03 ** Downref: Normative reference to an Experimental draft: draft-ietf-clue-signaling (ref. 'I-D.ietf-clue-signaling') -- Obsolete informational reference (is this intentional?): RFC 5117 (Obsoleted by RFC 7667) Summary: 3 errors (**), 0 flaws (~~), 16 warnings (==), 5 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: March 29, 2015 Acano 5 S. Wenger 6 Vidyo 7 September 29, 2014 9 Framework for Telepresence Multi-Streams 10 draft-ietf-clue-framework-17.txt 12 Abstract 14 This document defines a framework for a protocol to enable devices 15 in a telepresence conference to interoperate. The protocol enables 16 communication of information about multiple media streams so a 17 sending system and receiving system can make reasonable decisions 18 about transmitting, selecting and rendering the media streams. 19 This protocol is used in addition to SIP signaling for setting up a 20 telepresence session. 22 Status of this Memo 24 This Internet-Draft is submitted in full conformance with the 25 provisions of BCP 78 and BCP 79. 27 Internet-Drafts are working documents of the Internet Engineering 28 Task Force (IETF). Note that other groups may also distribute 29 working documents as Internet-Drafts. The list of current 30 Internet-Drafts is at http://datatracker.ietf.org/drafts/current/. 32 Internet-Drafts are draft documents valid for a maximum of six 33 months and may be updated, replaced, or obsoleted by other 34 documents at any time. It is inappropriate to use Internet-Drafts 35 as reference material or to cite them other than as "work in 36 progress." 38 This Internet-Draft will expire on March 29, 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.........................................14 63 7. Media Captures and Capture Scenes.............................16 64 7.1. Media Captures...........................................16 65 7.1.1. Media Capture Attributes............................17 66 7.2. Multiple Content Capture.................................23 67 7.2.1. MCC Attributes......................................24 68 7.3. Capture Scene............................................29 69 7.3.1. Capture Scene attributes............................31 70 7.3.2. Capture Scene View attributes.......................32 71 7.3.3. Global View List....................................32 72 8. Simultaneous Transmission Set Constraints.....................33 73 9. Encodings.....................................................35 74 9.1. Individual Encodings.....................................35 75 9.2. Encoding Group...........................................36 76 9.3. Associating Captures with Encoding Groups................37 77 10. Consumer's Choice of Streams to Receive from the Provider....38 78 10.1. Local preference........................................41 79 10.2. Physical simultaneity restrictions......................41 80 10.3. Encoding and encoding group limits......................41 81 11. Extensibility................................................42 82 12. Examples - Using the Framework (Informative).................42 83 12.1. Provider Behavior.......................................42 84 12.1.1. Three screen Endpoint Provider.....................42 85 12.1.2. Encoding Group Example.............................49 86 12.1.3. The MCU Case.......................................50 88 12.2. Media Consumer Behavior.................................51 89 12.2.1. One screen Media Consumer..........................52 90 12.2.2. Two screen Media Consumer configuring the example..52 91 12.2.3. Three screen Media Consumer configuring the example53 92 12.3. Multipoint Conference utilizing Multiple Content Captures53 93 12.3.1. Single Media Captures and MCC in the same 94 Advertisement..............................................53 95 12.3.2. Several MCCs in the same Advertisement.............56 96 12.3.3. Heterogeneous conference with switching and 97 composition................................................58 98 12.3.4. Heterogeneous conference with voice activated 99 switching..................................................65 100 13. Acknowledgements.............................................67 101 14. IANA Considerations..........................................68 102 15. Security Considerations......................................68 103 16. Changes Since Last Version...................................69 104 17. Normative References.........................................76 105 18. Informative References.......................................77 106 19. Authors' Addresses...........................................78 108 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 The basic session setup for the use cases is based on SIP [RFC3261] 123 and SDP offer/answer [RFC3264]. In addition to basic SIP & SDP 124 offer/answer, CLUE specific signaling is required to exchange the 125 information describing the multiple media streams. The motivation 126 for this framework, an overview of the signaling, and information 127 required to be exchanged is described in subsequent sections of 128 this document. Companion documents describe the signaling details 129 [I-D.ietf-clue-signaling] and the data model [I-D.ietf-clue-data- 130 model-schema]. 132 2. Terminology 134 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 135 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in 136 this document are to be interpreted as described in RFC 2119 137 [RFC2119]. 139 3. Definitions 141 The terms defined below are used throughout this document and 142 companion documents and they are normative. In order to easily 143 identify the use of a defined term, those terms are capitalized. 145 Advertisement: a CLUE message a Media Provider sends to a Media 146 Consumer describing specific aspects of the content of the media, 147 and any restrictions it has in terms of being able to provide 148 certain Streams simultaneously. 150 Audio Capture: Media Capture for audio. Denoted as ACn in the 151 examples in this document. 153 Capture: Same as Media Capture. 155 Capture Device: A device that converts physical input, such as 156 audio, video or text, into an electrical signal, in most cases to 157 be fed into a media encoder. 159 Capture Encoding: A specific encoding of a Media Capture, to be 160 sent by a Media Provider to a Media Consumer via RTP. 162 Capture Scene: a structure representing a spatial region captured 163 by one or more Capture Devices, each capturing media representing a 164 portion of the region. The spatial region represented by a Capture 165 Scene MAY or may not correspond to a real region in physical space, 166 such as a room. A Capture Scene includes attributes and one or 167 more Capture Scene Views, with each view including one or more 168 Media Captures. 170 Capture Scene View (CSV): a list of Media Captures of the same 171 media type that together form one way to represent the entire 172 Capture Scene. 174 CLUE-capable device: A device that supports the CLUE data channel 175 [I-D.ietf-clue-datachannel], the CLUE protocol [I-D.presta-clue- 176 protocol] and the principles of CLUE negotiation, and wishes to 177 upgrade the call to CLUE-enabled status. 179 CLUE-enabled call: A call in which two CLUE-capable devices have 180 successfully negotiated support for a CLUE data channel in SDP. A 181 CLUE-enabled call is not necessarily immediately able to send CLUE- 182 controlled media; negotiation of the data channel and of the CLUE 183 protocol must complete first. Calls between two CLUE-capable 184 devices which have not yet successfully completed negotiation of 185 support for the CLUE data channel in SDP are not considered CLUE- 186 enabled. 188 Conference: used as defined in [RFC4353], A Framework for 189 Conferencing within the Session Initiation Protocol (SIP). 191 Configure Message: A CLUE message a Media Consumer sends to a Media 192 Provider specifying which content and media streams it wants to 193 receive, based on the information in a corresponding Advertisement 194 message. 196 Consumer: short for Media Consumer. 198 Encoding or Individual Encoding: a set of parameters representing a 199 way to encode a Media Capture to become a Capture Encoding. 201 Encoding Group: A set of encoding parameters representing a total 202 media encoding capability to be sub-divided across potentially 203 multiple Individual Encodings. 205 Endpoint: A CLUE capable-device which is the logical point of final 206 termination through receiving, decoding and rendering, and/or 207 initiation through capturing, encoding, and sending of media 208 streams. An endpoint consists of one or more physical devices 209 which source and sink media streams, and exactly one [RFC4353] 210 Participant (which, in turn, includes exactly one SIP User Agent). 211 Endpoints can be anything from multiscreen/multicamera rooms to 212 handheld devices. 214 Global View: A set of references to one or more Capture Scene Views 215 of the same media type that are defined within scenes of the same 216 advertisement. Each Global View in the list is a suggestion from 217 the Provider to the Consumer for which CSVs provide a complete 218 representation of the simultaneous captures provided by the 219 Provider, across multiple scenes. 221 MCU: Multipoint Control Unit (MCU) - a CLUE-capable device that 222 connects two or more endpoints together into one single multimedia 223 conference [RFC5117]. An MCU includes an [RFC4353] like Mixer, 224 without the [RFC4353] requirement to send media to each 225 participant. 227 Media: Any data that, after suitable encoding, can be conveyed over 228 RTP, including audio, video or timed text. 230 Media Capture: a source of Media, such as from one or more Capture 231 Devices or constructed from other Media streams. 233 Media Consumer: a CLUE-capable device that that is capable of 234 receiving Capture Encodings 236 Media Provider: a CLUE-capable device that is capable of sending 237 Capture Encodings 239 Multiple Content Capture (MCC): A Capture that mixes and/or 240 switches other Captures of a single type. (E.g. all audio or all 241 video.) Particular Media Captures may or may not be present in the 242 resultant Capture Encoding depending on time or space. Denoted as 243 MCCn in the example cases in this document. 245 Plane of Interest: The spatial plane containing the most relevant 246 subject matter. 248 Provider: Same as Media Provider. 250 Render: the process of generating a representation from media, such 251 as displayed motion video or sound emitted from loudspeakers. 253 Simultaneous Transmission Set: a set of Media Captures that can be 254 transmitted simultaneously from a Media Provider. 256 Single Media Capture: A capture which contains media from a single 257 source capture device, e.g. an audio capture from a single 258 microphone, a video capture from a single camera. 260 Spatial Relation: The arrangement in space of two objects, in 261 contrast to relation in time or other relationships. 263 Stream: a Capture Encoding sent from a Media Provider to a Media 264 Consumer via RTP [RFC3550]. 266 Stream Characteristics: the media stream attributes commonly used 267 in non-CLUE SIP/SDP environments (such as: media codec, bit rate, 268 resolution, profile/level etc.) as well as CLUE specific 269 attributes, such as the Capture ID or a spatial location. 271 Video Capture: Media Capture for video. Denoted as VCn in the 272 example cases in this document. 274 Video Composite: A single image that is formed, normally by an RTP 275 mixer inside an MCU, by combining visual elements from separate 276 sources. 278 4. Overview & Motivation 280 This section provides an overview of the functional elements 281 defined in this document to represent a telepresence system. The 282 motivations for the framework described in this document are also 283 provided. 285 Two key concepts introduced in this document are the terms "Media 286 Provider" and "Media Consumer". A Media Provider represents the 287 entity that sends the media and a Media Consumer represents the 288 entity that receives the media. A Media Provider provides Media in 289 the form of RTP packets, a Media Consumer consumes those RTP 290 packets. Media Providers and Media Consumers can reside in 291 Endpoints or in Multipoint Control Units (MCUs). A Media Provider 292 in an Endpoint is usually associated with the generation of media 293 for Media Captures; these Media Captures are typically sourced 294 from cameras, microphones, and the like. Similarly, the Media 295 Consumer in an Endpoint is usually associated with renderers, such 296 as screens and loudspeakers. In MCUs, Media Providers and 297 Consumers can have the form of outputs and inputs, respectively, 298 of RTP mixers, RTP translators, and similar devices. Typically, 299 telepresence devices such as Endpoints and MCUs would perform as 300 both Media Providers and Media Consumers, the former being 301 concerned with those devices' transmitted media and the latter 302 with those devices' received media. In a few circumstances, a 303 CLUE-capable device includes only Consumer or Provider 304 functionality, such as recorder-type Consumers or webcam-type 305 Providers. 307 The motivations for the framework outlined in this document 308 include the following: 310 (1) Endpoints in telepresence systems typically have multiple Media 311 Capture and Media Render devices, e.g., multiple cameras and 312 screens. While previous system designs were able to set up calls 313 that would capture media using all cameras and display media on all 314 screens, for example, there was no mechanism that can associate 315 these Media Captures with each other in space and time. 317 (2) The mere fact that there are multiple capturing and rendering 318 devices, each of which may be configurable in aspects such as zoom, 319 leads to the difficulty that a variable number of such devices can 320 be used to capture different aspects of a region. The Capture 321 Scene concept allows for the description of multiple setups for 322 those multiple capture devices that could represent sensible 323 operation points of the physical capture devices in a room, chosen 324 by the operator. A Consumer can pick and choose from those 325 configurations based on its rendering abilities and inform the 326 Provider about its choices. Details are provided in section 7. 328 (3) In some cases, physical limitations or other reasons disallow 329 the concurrent use of a device in more than one setup. For 330 example, the center camera in a typical three-camera conference 331 room can set its zoom objective either to capture only the middle 332 few seats, or all seats of a room, but not both concurrently. The 333 Simultaneous Transmission Set concept allows a Provider to signal 334 such limitations. Simultaneous Transmission Sets are part of the 335 Capture Scene description, and discussed in section 8. 337 (4) Often, the devices in a room do not have the computational 338 complexity or connectivity to deal with multiple encoding options 339 simultaneously, even if each of these options is sensible in 340 certain scenarios, and even if the simultaneous transmission is 341 also sensible (i.e. in case of multicast media distribution to 342 multiple endpoints). Such constraints can be expressed by the 343 Provider using the Encoding Group concept, described in section 9. 345 (5) Due to the potentially large number of RTP flows required for a 346 Multimedia Conference involving potentially many Endpoints, each of 347 which can have many Media Captures and media renderers, it has 348 become common to multiplex multiple RTP media flows onto the same 349 transport address, so to avoid using the port number as a 350 multiplexing point and the associated shortcomings such as 351 NAT/firewall traversal. While the actual mapping of those RTP 352 flows to the header fields of the RTP packets is not subject of 353 this specification, the large number of possible permutations of 354 sensible options a Media Provider can make available to a Media 355 Consumer makes a mechanism desirable that allows to narrow down the 356 number of possible options that a SIP offer-answer exchange has to 357 consider. Such information is made available using protocol 358 mechanisms specified in this document and companion documents, 359 although it should be stressed that its use in an implementation is 360 OPTIONAL. Also, there are aspects of the control of both Endpoints 361 and MCUs that dynamically change during the progress of a call, 362 such as audio-level based screen switching, layout changes, and so 363 on, which need to be conveyed. Note that these control aspects are 364 complementary to those specified in traditional SIP based 365 conference management such as BFCP. An exemplary call flow can be 366 found in section 5. 368 Finally, all this information needs to be conveyed, and the notion 369 of support for it needs to be established. This is done by the 370 negotiation of a "CLUE channel", a data channel negotiated early 371 during the initiation of a call. An Endpoint or MCU that rejects 372 the establishment of this data channel, by definition, does not 373 support CLUE based mechanisms, whereas an Endpoint or MCU that 374 accepts it is REQUIRED to use it to the extent specified in this 375 document and its companion documents. 377 5. Overview of the Framework/Model 379 The CLUE framework specifies how multiple media streams are to be 380 handled in a telepresence conference. 382 A Media Provider (transmitting Endpoint or MCU) describes specific 383 aspects of the content of the media and the media stream encodings 384 it can send in an Advertisement; and the Media Consumer responds to 385 the Media Provider by specifying which content and media streams it 386 wants to receive in a Configure message. The Provider then 387 transmits the asked-for content in the specified streams. 389 This Advertisement and Configure typically occur during call 390 initiation, after CLUE has been enabled in a call, but MAY also 391 happen at any time throughout the call, whenever there is a change 392 in what the Consumer wants to receive or (perhaps less common) the 393 Provider can send. 395 An Endpoint or MCU typically act as both Provider and Consumer at 396 the same time, sending Advertisements and sending Configurations in 397 response to receiving Advertisements. (It is possible to be just 398 one or the other.) 400 The data model is based around two main concepts: a Capture and an 401 Encoding. A Media Capture (MC), such as audio or video, has 402 attributes to describe the content a Provider can send. Media 403 Captures are described in terms of CLUE-defined attributes, such as 404 spatial relationships and purpose of the capture. Providers tell 405 Consumers which Media Captures they can provide, described in terms 406 of the Media Capture attributes. 408 A Provider organizes its Media Captures into one or more Capture 409 Scenes, each representing a spatial region, such as a room. A 410 Consumer chooses which Media Captures it wants to receive from the 411 Capture Scenes. 413 In addition, the Provider can send the Consumer a description of 414 the Individual Encodings it can send in terms of identifiers which 415 relate to items in SDP. 417 The Provider can also specify constraints on its ability to provide 418 Media, and a sensible design choice for a Consumer is to take these 419 into account when choosing the content and Capture Encodings it 420 requests in the later offer-answer exchange. Some constraints are 421 due to the physical limitations of devices--for example, a camera 422 may not be able to provide zoom and non-zoom views simultaneously. 423 Other constraints are system based, such as maximum bandwidth. 425 The following diagram illustrates the information contained in an 426 Advertisement. 428 ................................................................... 429 . Provider Advertisement +--------------------+ . 430 . | Simultaneous Sets | . 431 . +------------------------+ +--------------------+ . 432 . | Capture Scene N | +--------------------+ . 433 . +-+----------------------+ | | Global View List | . 434 . | Capture Scene 2 | | +--------------------+ . 435 . +-+----------------------+ | | +----------------------+ . 436 . | Capture Scene 1 | | | | Encoding Group N | . 437 . | +---------------+ | | | +-+--------------------+ | . 438 . | | Attributes | | | | | Encoding Group 2 | | . 439 . | +---------------+ | | | +-+--------------------+ | | . 440 . | | | | | Encoding Group 1 | | | . 441 . | +----------------+ | | | | parameters | | | . 442 . | | V i e w s | | | | | bandwidth | | | . 443 . | | +---------+ | | | | | +-------------------+| | | . 444 . | | |Attribute| | | | | | | V i d e o || | | . 445 . | | +---------+ | | | | | | E n c o d i n g s || | | . 446 . | | | | | | | | Encoding 1 || | | . 447 . | | View 1 | | | | | | || | | . 448 . | | (list of MCs) | | |-+ | +-------------------+| | | . 449 . | +----|-|--|------+ |-+ | | | | . 450 . +---------|-|--|---------+ | +-------------------+| | | . 451 . | | | | | A u d i o || | | . 452 . | | | | | E n c o d i n g s || | | . 453 . v | | | | Encoding 1 || | | . 454 . +---------|--|--------+ | | || | | . 455 . | Media Capture N |------>| +-------------------+| | | . 456 . +-+---------v--|------+ | | | | | . 457 . | Media Capture 2 | | | | |-+ . 458 . +-+--------------v----+ |-------->| | | . 459 . | Media Capture 1 | | | | |-+ . 460 . | +----------------+ |---------->| | . 461 . | | Attributes | | |_+ +----------------------+ . 462 . | +----------------+ |_+ . 463 . +---------------------+ . 464 . . 465 ................................................................... 466 Figure 1: Advertisement Structure 468 A very brief outline of the call flow used by a simple system (two 469 Endpoints) in compliance with this document can be described as 470 follows, and as shown in the following figure. 472 +-----------+ +-----------+ 473 | Endpoint1 | | Endpoint2 | 474 +----+------+ +-----+-----+ 475 | INVITE (BASIC SDP+CLUECHANNEL) | 476 |--------------------------------->| 477 | 200 0K (BASIC SDP+CLUECHANNEL)| 478 |<---------------------------------| 479 | ACK | 480 |--------------------------------->| 481 | | 482 |<################################>| 483 | BASIC SDP MEDIA SESSION | 484 |<################################>| 485 | | 486 | CONNECT (CLUE CTRL CHANNEL) | 487 |=================================>| 488 | ... | 489 |<================================>| 490 | CLUE CTRL CHANNEL ESTABLISHED | 491 |<================================>| 492 | | 493 | ADVERTISEMENT 1 | 494 |*********************************>| 495 | ADVERTISEMENT 2 | 496 |<*********************************| 497 | | 498 | CONFIGURE 1 | 499 |<*********************************| 500 | CONFIGURE 2 | 501 |*********************************>| 502 | | 503 | REINVITE (UPDATED SDP) | 504 |--------------------------------->| 505 | 200 0K (UPDATED SDP)| 506 |<---------------------------------| 507 | ACK | 508 |--------------------------------->| 509 | | 510 |<################################>| 511 | UPDATED SDP MEDIA SESSION | 512 |<################################>| 513 | | 514 v v 516 Figure 2: Basic Information Flow 518 An initial offer/answer exchange establishes a basic media session, 519 for example audio-only, and a CLUE channel between two Endpoints. 520 With the establishment of that channel, the endpoints have 521 consented to use the CLUE protocol mechanisms and, therefore, MUST 522 adhere to the CLUE protocol suite as outlined herein. 524 Over this CLUE channel, the Provider in each Endpoint conveys its 525 characteristics and capabilities by sending an Advertisement as 526 specified herein. The Advertisement is typically not sufficient to 527 set up all media. The Consumer in the Endpoint receives the 528 information provided by the Provider, and can use it for two 529 purposes. First, it MUST construct and send a CLUE Configure 530 message to tell the Provider what the Consumer wishes to receive. 531 Second, it MAY, but is not necessarily REQUIRED to, use the 532 information provided to tailor the SDP it is going to send during 533 the following SIP offer/answer exchange, and its reaction to SDP it 534 receives in that step. It is often a sensible implementation 535 choice to do so, as the representation of the media information 536 conveyed over the CLUE channel can dramatically cut down on the 537 size of SDP messages used in the O/A exchange that follows. 538 Spatial relationships associated with the Media can be included in 539 the Advertisement, and it is often sensible for the Media Consumer 540 to take those spatial relationships into account when tailoring the 541 SDP. 543 This CLUE exchange MUST be followed by an SDP offer answer exchange 544 that not only establishes those aspects of the media that have not 545 been "negotiated" over CLUE, but has also the side effect of 546 setting up the media transmission itself, involving potentially 547 security exchanges, ICE, and whatnot. This step is plain vanilla 548 SIP, with the exception that the SDP used herein, in most (but not 549 necessarily all) cases can be considerably smaller than the SDP a 550 system would typically need to exchange if there were no pre- 551 established knowledge about the Provider and Consumer 552 characteristics. (The need for cutting down SDP size is not quite 553 obvious for a point-to-point call involving simple endpoints; 554 however, when considering a large multipoint conference involving 555 many multi-screen/multi-camera endpoints, each of which can operate 556 using multiple codecs for each camera and microphone, it becomes 557 perhaps somewhat more intuitive.) 559 During the lifetime of a call, further exchanges MAY occur over the 560 CLUE channel. In some cases, those further exchanges lead to a 561 modified system behavior of Provider or Consumer (or both) without 562 any other protocol activity such as further offer/answer exchanges. 563 For example, voice-activated screen switching, signaled over the 564 CLUE channel, ought not to lead to heavy-handed mechanisms like SIP 565 re-invites. However, in other cases, after the CLUE negotiation an 566 additional offer/answer exchange becomes necessary. For example, 567 if both sides decide to upgrade the call from a single screen to a 568 multi-screen call and more bandwidth is required for the additional 569 video channels compared to what was previously negotiated using 570 offer/answer, a new O/A exchange is REQUIRED. 572 One aspect of the protocol outlined herein and specified in more 573 detail in companion documents is that it makes available 574 information regarding the Provider's capabilities to deliver Media, 575 and attributes related to that Media such as their spatial 576 relationship, to the Consumer. The operation of the renderer 577 inside the Consumer is unspecified in that it can choose to ignore 578 some information provided by the Provider, and/or not render media 579 streams available from the Provider (although it MUST follow the 580 CLUE protocol and, therefore, MUST gracefully receive and respond 581 (through a Configure) to the Provider's information). All CLUE 582 protocol mechanisms are OPTIONAL in the Consumer in the sense that, 583 while the Consumer MUST be able to receive (and, potentially, 584 gracefully acknowledge) CLUE messages, it is free to ignore the 585 information provided therein. 587 A CLUE-implementing device interoperates with a device that does 588 not support CLUE, because the non-CLUE device does, by definition, 589 not understand the offer of a CLUE channel in the initial 590 offer/answer exchange and, therefore, will reject it. This 591 rejection MUST be used as the indication to the CLUE-implementing 592 device that the other side of the communication is not compliant 593 with CLUE, and to fall back to behavior that does not require CLUE. 595 As for the media, Provider and Consumer have an end-to-end 596 communication relationship with respect to (RTP transported) media; 597 and the mechanisms described herein and in companion documents do 598 not change the aspects of setting up those RTP flows and sessions. 599 In other words, the RTP media sessions conform to the negotiated 600 SDP whether or not CLUE is used. 602 6. Spatial Relationships 604 In order for a Consumer to perform a proper rendering, it is often 605 necessary or at least helpful for the Consumer to have received 606 spatial information about the streams it is receiving. CLUE 607 defines a coordinate system that allows Media Providers to describe 608 the spatial relationships of their Media Captures to enable proper 609 scaling and spatially sensible rendering of their streams. The 610 coordinate system is based on a few principles: 612 o Simple systems which do not have multiple Media Captures to 613 associate spatially need not use the coordinate model. 615 o Coordinates can be either in real, physical units (millimeters), 616 have an unknown scale or have no physical scale. Systems which 617 know their physical dimensions (for example professionally 618 installed Telepresence room systems) MUST always provide those 619 real-world measurements. Systems which don't know specific 620 physical dimensions but still know relative distances MUST use 621 'unknown scale'. 'No scale' is intended to be used where Media 622 Captures from different devices (with potentially different 623 scales) will be forwarded alongside one another (e.g. in the 624 case of an MCU). 626 * "Millimeters" means the scale is in millimeters. 628 * "Unknown" means the scale is not necessarily millimeters, but 629 the scale is the same for every Capture in the Capture Scene. 631 * "No Scale" means the scale could be different for each 632 capture- an MCU Provider that advertises two adjacent 633 captures and picks sources (which can change quickly) from 634 different endpoints might use this value; the scale could be 635 different and changing for each capture. But the areas of 636 capture still represent a spatial relation between captures. 638 o The coordinate system is right-handed Cartesian X, Y, Z with the 639 origin at a spatial location of the Provider's choosing. The 640 Provider MUST use the same coordinate system with the same scale 641 and origin for all coordinates within the same Capture Scene. 643 The direction of increasing coordinate values is: 644 X increases from left to right, from the point of view of an 645 observer at the front of the room looking toward the back 646 Y increases from the front of the room to the back of the room 647 Z increases from low to high (i.e. floor to ceiling) 649 Cameras in a scene typically point in the direction of increasing 650 Y, from front to back. But there could be multiple cameras 651 pointing in different directions. If the physical space does not 652 have a well-defined front and back, the provider chooses any 653 direction for X and Y consistent with right-handed coordinates. 655 7. Media Captures and Capture Scenes 657 This section describes how Providers can describe the content of 658 media to Consumers. 660 7.1. Media Captures 662 Media Captures are the fundamental representations of streams that 663 a device can transmit. What a Media Capture actually represents is 664 flexible: 666 o It can represent the immediate output of a physical source (e.g. 667 camera, microphone) or 'synthetic' source (e.g. laptop computer, 668 DVD player). 670 o It can represent the output of an audio mixer or video composer 672 o It can represent a concept such as 'the loudest speaker' 674 o It can represent a conceptual position such as 'the leftmost 675 stream' 677 To identify and distinguish between multiple Capture instances 678 Captures have a unique identity. For instance: VC1, VC2 and AC1, 679 AC2, where VC1 and VC2 refer to two different video captures and 680 AC1 and AC2 refer to two different audio captures. 682 Some key points about Media Captures: 684 . A Media Capture is of a single media type (e.g. audio or 685 video) 686 . A Media Capture is defined in a Capture Scene and is given an 687 advertisement unique identity. The identity may be referenced 688 outside the Capture Scene that defines it through a Multiple 689 Content Capture (MCC) 690 . A Media Capture may be associated with one or more Capture 691 Scene Views 692 . A Media Capture has exactly one set of spatial information 693 . A Media Capture can be the source of one or more Capture 694 Encodings 696 Each Media Capture can be associated with attributes to describe 697 what it represents. 699 7.1.1. Media Capture Attributes 701 Media Capture Attributes describe information about the Captures. 702 A Provider can use the Media Capture Attributes to describe the 703 Captures for the benefit of the Consumer of the Advertisement 704 message. Media Capture Attributes include: 706 . Spatial information, such as point of capture, point on line 707 of capture, and area of capture, all of which, in combination 708 define the capture field of, for example, a camera 709 . Other descriptive information to help the Consumer choose 710 between captures (description, presentation, view, priority, 711 language, person information and type) 712 . Control information for use inside the CLUE protocol suite 714 The sub-sections below define the Capture attributes. 716 7.1.1.1. Point of Capture 718 The Point of Capture attribute is a field with a single Cartesian 719 (X, Y, Z) point value which describes the spatial location of the 720 capturing device (such as camera). For an Audio Capture with 721 multiple microphones, the Point of Capture defines the nominal mid- 722 point of the microphones. 724 7.1.1.2. Point on Line of Capture 726 The Point on Line of Capture attribute is a field with a single 727 Cartesian (X, Y, Z) point value which describes a position in space 728 of a second point on the axis of the capturing device, toward the 729 direction it is pointing; the first point being the Point of 730 Capture (see above). 732 Together, the Point of Capture and Point on Line of Capture define 733 the direction and axis of the capturing device, for example the 734 optical axis of a camera or the axis of a microphone. The Media 735 Consumer can use this information to adjust how it renders the 736 received media if it so chooses. 738 For an Audio Capture, the Media Consumer can use this information 739 along with the Audio Capture Sensitivity Pattern to define a 3- 740 dimensional volume of capture where sounds can be expected to be 741 picked up by the microphone providing this specific audio capture. 742 If the Consumer wants to associate an Audio Capture with a Video 743 Capture, it can compare this volume with the area of capture for 744 video media to provide a check on whether the audio capture is 745 indeed spatially associated with the video capture. For example, a 746 video area of capture that fails to intersect at all with the audio 747 volume of capture, or is at such a long radial distance from the 748 microphone point of capture that the audio level would be very low, 749 would be inappropriate. 751 7.1.1.3. Area of Capture 753 The Area of Capture is a field with a set of four (X, Y, Z) points 754 as a value which describes the spatial location of what is being 755 "captured". This attribute applies only to video captures, not 756 other types of media. By comparing the Area of Capture for 757 different Video Captures within the same Capture Scene a Consumer 758 can determine the spatial relationships between them and render 759 them correctly. 761 The four points MUST be co-planar, forming a quadrilateral, which 762 defines the Plane of Interest for the particular media capture. 764 If the Area of Capture is not specified, it means the Video Capture 765 is not spatially related to any other Video Capture. 767 For a switched capture that switches between different sections 768 within a larger area, the area of capture MUST use coordinates for 769 the larger potential area. 771 7.1.1.4. Mobility of Capture 773 The Mobility of Capture attribute indicates whether or not the 774 point of capture, line on point of capture, and area of capture 775 values stay the same over time, or are expected to change 776 (potentially frequently). Possible values are static, dynamic, and 777 highly dynamic. 779 An example for "dynamic" is a camera mounted on a stand which is 780 occasionally hand-carried and placed at different positions in 781 order to provide the best angle to capture a work task. A camera 782 worn by a person who moves around the room is an example for 783 "highly dynamic". In either case, the effect is that the capture 784 point, capture axis and area of capture change with time. 786 The capture point of a static capture MUST NOT move for the life of 787 the conference. The capture point of dynamic captures is 788 categorized by a change in position followed by a reasonable period 789 of stability--in the order of magnitude of minutes. High dynamic 790 captures are categorized by a capture point that is constantly 791 moving. If the "area of capture", "capture point" and "line of 792 capture" attributes are included with dynamic or highly dynamic 793 captures they indicate spatial information at the time of the 794 Advertisement. 796 7.1.1.5. Audio Capture Sensitivity Pattern 798 The Audio Capture Sensitivity Pattern attribute applies only to 799 audio captures. This is an optional attribute. This attribute 800 gives information about the nominal sensitivity pattern of the 801 microphone which is the source of the capture. Possible values 802 include patterns such as omni, shotgun, cardioid, hyper-cardioid. 804 7.1.1.6. Max Capture Encodings 806 The Max Capture Encodings attribute is an optional attribute 807 indicating the maximum number of Capture Encodings that can be 808 simultaneously active for the Media Capture. The number of 809 simultaneous Capture Encodings is also limited by the restrictions 810 of the Encoding Group for the Media Capture. 812 7.1.1.7. Description 814 The Description attribute is a human-readable description (which 815 could be in multiple languages) of the Capture. 817 7.1.1.8. Presentation 819 The Presentation attribute indicates that the capture originates 820 from a presentation device, that is one that provides supplementary 821 information to a conference through slides, video, still images, 822 data etc. Where more information is known about the capture it MAY 823 be expanded hierarchically to indicate the different types of 824 presentation media, e.g. presentation.slides, presentation.image 825 etc. 827 Note: It is expected that a number of keywords will be defined that 828 provide more detail on the type of presentation. 830 7.1.1.9. View 832 The View attribute is a field with enumerated values, indicating 833 what type of view the Capture relates to. The Consumer can use 834 this information to help choose which Media Captures it wishes to 835 receive. The value MUST be one of: 837 Room - Captures the entire scene 839 Table - Captures the conference table with seated people 841 Individual - Captures an individual person 843 Lectern - Captures the region of the lectern including the 844 presenter, for example in a classroom style conference room 846 Audience - Captures a region showing the audience in a classroom 847 style conference room 849 7.1.1.10. Language 851 The language attribute indicates one or more languages used in the 852 content of the Media Capture. Captures MAY be offered in different 853 languages in case of multilingual and/or accessible conferences. A 854 Consumer can use this attribute to differentiate between them and 855 pick the appropriate one. 857 Note that the Language attribute is defined and meaningful both for 858 audio and video captures. In case of audio captures, the meaning 859 is obvious. For a video capture, "Language" could, for example, be 860 sign interpretation or text. 862 7.1.1.11. Person Information 864 The person information attribute allows a Provider to provide 865 specific information regarding the people in a Capture (regardless 866 of whether or not the capture has a Presentation attribute). The 867 Provider may gather the information automatically or manually from 868 a variety of sources however the xCard [RFC6351] format is used to 869 convey the information. This allows various information such as 870 Identification information (section 6.2/[RFC6350]), Communication 871 Information (section 6.4/[RFC6350]) and Organizational information 872 (section 6.6/[RFC6350]) to be communicated. A Consumer may then 873 automatically (i.e. via a policy) or manually select Captures 874 based on information about who is in a Capture. It also allows a 875 Consumer to render information regarding the people participating 876 in the conference or to use it for further processing. 878 The Provider may supply a minimal set of information or a larger 879 set of information. However it MUST be compliant to [RFC6350] and 880 supply a "VERSION" and "FN" property. A Provider may supply 881 multiple xCards per Capture of any KIND (section 6.1.4/[RFC6350]). 883 In order to keep CLUE messages compact the Provider SHOULD use a 884 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 885 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 886 message. 888 7.1.1.12. Person Type 890 The person type attribute indicates the type of people contained in 891 the capture in the conference with respect to the meeting agenda 892 (regardless of whether or not the capture has a Presentation 893 attribute). As a capture may include multiple people the attribute 894 may contain multiple values. However values shall not be repeated 895 within the attribute. 897 An Advertiser associates the person type with an individual capture 898 when it knows that a particular type is in the capture. If an 899 Advertiser cannot link a particular type with some certainty to a 900 capture then it is not included. A Consumer on reception of a 901 capture with a person type attribute knows with some certainly that 902 the capture contains that person type. The capture may contain 903 other person types but the Advertiser has not been able to 904 determine that this is the case. 906 The types of Captured people include: 908 . Chairman - the person responsible for running the conference 909 according to the agenda. 910 . Vice-Chairman - the person responsible for assisting the 911 chairman in running the meeting. 912 . Minute Taker - the person responsible for recording the 913 minutes of the conference 914 . Member - the person has no particular responsibilities with 915 respect to running the meeting. 916 . Presenter - the person is scheduled on the agenda to make a 917 presentation in the meeting. Note: This is not related to any 918 "active speaker" functionality. 920 . Translator - the person is providing some form of translation 921 or commentary in the meeting. 922 . Timekeeper - the person is responsible for maintaining the 923 meeting schedule. 925 Furthermore the person type attribute may contain one or more 926 strings allowing the Provider to indicate custom meeting specific 927 roles. 929 7.1.1.13. Priority 931 The priority attribute indicates a relative priority between 932 different Media Captures. The Provider sets this priority, and the 933 Consumer MAY use the priority to help decide which captures it 934 wishes to receive. 936 The "priority" attribute is an integer which indicates a relative 937 priority between Captures. For example it is possible to assign a 938 priority between two presentation Captures that would allow a 939 remote endpoint to determine which presentation is more important. 940 Priority is assigned at the individual capture level. It represents 941 the Provider's view of the relative priority between Captures with 942 a priority. The same priority number MAY be used across multiple 943 Captures. It indicates they are equally important. If no priority 944 is assigned no assumptions regarding relative important of the 945 Capture can be assumed. 947 7.1.1.14. Embedded Text 949 The Embedded Text attribute indicates that a Capture provides 950 embedded textual information. For example the video Capture MAY 951 contain speech to text information composed with the video image. 952 This attribute is only applicable to video Captures and 953 presentation streams with visual information. 955 7.1.1.15. Related To 957 The Related To attribute indicates the Capture contains additional 958 complementary information related to another Capture. The value 959 indicates the identity of the other Capture to which this Capture 960 is providing additional information. 962 For example, a conference can utilize translators or facilitators 963 that provide an additional audio stream (i.e. a translation or 964 description or commentary of the conference). Where multiple 965 captures are available, it may be advantageous for a Consumer to 966 select a complementary Capture instead of or in addition to a 967 Capture it relates to. 969 7.2. Multiple Content Capture 971 The MCC indicates that one or more Single Media Captures are 972 contained in one Media Capture. Only one Capture type (i.e. audio, 973 video, etc.) is allowed in each MCC instance. The MCC may contain 974 a reference to the Single Media Captures (which may have their own 975 attributes) as well as attributes associated with the MCC itself. 976 A MCC may also contain other MCCs. The MCC MAY reference Captures 977 from within the Capture Scene that defines it or from other Capture 978 Scenes. No ordering is implied by the order that Captures appear 979 within a MCC. A MCC MAY contain no references to other Captures to 980 indicate that the MCC contains content from multiple sources but no 981 information regarding those sources is given. 983 One or more MCCs may also be specified in a CSV. This allows an 984 Advertiser to indicate that several MCC captures are used to 985 represent a capture scene. Table 14 provides an example of this 986 case. 988 As outlined in section 7.1. each instance of the MCC has its own 989 Capture identity i.e. MCC1. It allows all the individual captures 990 contained in the MCC to be referenced by a single MCC identity. 992 The example below shows the use of a Multiple Content Capture: 994 +-----------------------+---------------------------------+ 995 | Capture Scene #1 | | 996 +-----------------------|---------------------------------+ 997 | VC1 | {attributes} | 998 | VC2 | {attributes} | 999 | VCn | {attributes} | 1000 | MCC1(VC1,VC2,...VCn) | {attributes} | 1001 | CSV(MCC1) | | 1002 +---------------------------------------------------------+ 1004 Table 1: Multiple Content Capture concept 1006 This indicates that MCC1 is a single capture that contains the 1007 Captures VC1, VC2 and VC3 according to any MCC1 attributes. 1009 7.2.1. MCC Attributes 1011 Attributes may be associated with the MCC instance and the Single 1012 Media Captures that the MCC references. A Provider should avoid 1013 providing conflicting attribute values between the MCC and Single 1014 Media Captures. Where there is conflict the attributes of the MCC 1015 override any that may be present in the individual captures. 1017 A Provider MAY include as much or as little of the original source 1018 Capture information as it requires. 1020 There are MCC specific attributes that MUST only be used with 1021 Multiple Content Captures. These are described in the sections 1022 below. The attributes described in section 7.1.1. MAY also be used 1023 with MCCs. 1025 The spatial related attributes of an MCC indicate its area of 1026 capture and point of capture within the scene, just like any other 1027 media capture. The spatial information does not imply anything 1028 about how other captures are composed within an MCC. 1030 For example: A virtual scene could be constructed for the MCC 1031 capture with two Video Captures with a "MaxCaptures" attribute set 1032 to 2 and an "Area of Capture" attribute provided with an overall 1033 area. Each of the individual Captures could then also include an 1034 "Area of Capture" attribute with a sub-set of the overall area. 1035 The Consumer would then know how each capture is related to others 1036 within the scene, but not the relative position of the individual 1037 captures within the composed capture. 1039 +-----------------------+---------------------------------+ 1040 | Capture Scene #1 | | 1041 +-----------------------|---------------------------------+ 1042 | VC1 | AreaofCapture=(0,0,0)(9,0,0) | 1043 | | (0,0,9)(9,0,9) | 1044 | VC2 | AreaofCapture=(10,0,0)(19,0,0) | 1045 | | (10,0,9)(19,0,9) | 1046 | MCC1(VC1,VC2) | MaxCaptures=2 | 1047 | | AreaofCapture=(0,0,0)(19,0,0) | 1048 | | (0,0,9)(19,0,9) | 1049 | CSV(MCC1) | | 1050 +---------------------------------------------------------+ 1052 Table 2: Example of MCC and Single Media Capture attributes 1054 The sections below describe the MCC only attributes. 1056 7.2.1.1. Maximum Number of Captures within a MCC 1058 The Maximum Number of Captures MCC attribute indicates the maximum 1059 number of individual captures that may appear in a Capture Encoding 1060 at a time. The actual number at any given time can be less than 1061 this maximum. It may be used to derive how the Single Media 1062 Captures within the MCC are composed / switched with regards to 1063 space and time. 1065 A Provider can indicate that the number of captures in a MCC 1066 capture encoding is equal "=" to the MaxCaptures value or that 1067 there may be any number of captures up to and including "<=" the 1068 MaxCaptures value. This allows a Provider to distinguish between a 1069 MCC that purely represents a composition of sources versus a MCC 1070 that represents switched or switched and composed sources. 1072 MaxCaptures MAY be set to one so that only content related to one 1073 of the sources are shown in the MCC Capture Encoding at a time or 1074 it may be set to any value up to the total number of Source Media 1075 Captures in the MCC. 1077 The bullets below describe how the setting of MaxCapture versus the 1078 number of captures in the MCC affects how sources appear in a 1079 capture encoding: 1081 . When MaxCaptures is set to <= 1 and the number of captures in 1082 the MCC is greater than 1 (or not specified) in the MCC this 1083 is a switched case. Zero or 1 captures may be switched into 1084 the capture encoding. Note: zero is allowed because of the 1085 "<=". 1086 . When MaxCaptures is set to = 1 and the number of captures in 1087 the MCC is greater than 1 (or not specified) in the MCC this 1088 is a switched case. Only one capture source is contained in a 1089 capture encoding at a time. 1090 . When MaxCaptures is set to <= N (with N > 1) and the number of 1091 captures in the MCC is greater than N (or not specified) this 1092 is a switched and composed case. The capture encoding may 1093 contain purely switched sources (i.e. <=2 allows for 1 source 1094 on its own), or may contain composed and switched sources 1095 (i.e. a composition of 2 sources switched between the 1096 sources). 1097 . When MaxCaptures is set to = N (with N > 1) and the number of 1098 captures in the MCC is greater than N (or not specified) this 1099 is a switched and composed case. The capture encoding contains 1100 composed and switched sources (i.e. a composition of N sources 1101 switched between the sources). It is not possible to have a 1102 single source. 1103 . When MaxCaptures is set to <= to the number of captures in the 1104 MCC this is a switched and composed case. The capture encoding 1105 may contain media switched between any number (up to the 1106 MaxCaptures) of composed sources. 1107 . When MaxCaptures is set to = to the number of captures in the 1108 MCC this is a composed case. All the sources are composed into 1109 a single capture encoding. 1111 If this attribute is not set then as default it is assumed that all 1112 source content can appear concurrently in the Capture Encoding 1113 associated with the MCC. 1115 For example: The use of MaxCaptures equal to 1 on a MCC with three 1116 Video Captures VC1, VC2 and VC3 would indicate that the Advertiser 1117 in the capture encoding would switch between VC1, VC2 or VC3 as 1118 there may be only a maximum of one capture at a time. 1120 7.2.1.2. Policy 1122 The Policy MCC Attribute indicates the criteria that the Provider 1123 uses to determine when and/or where media content appears in the 1124 Capture Encoding related to the MCC. 1126 The attribute is in the form of a token that indicates the policy 1127 and index representing an instance of the policy. 1129 The tokens are: 1131 SoundLevel - This indicates that the content of the MCC is 1132 determined by a sound level detection algorithm. For example: the 1133 loudest (active) speaker is contained in the MCC. 1135 RoundRobin - This indicates that the content of the MCC is 1136 determined by a time based algorithm. For example: the Provider 1137 provides content from a particular source for a period of time and 1138 then provides content from another source and so on. 1140 An index is used to represent an instance in the policy setting. A 1141 index of 0 represents the most current instance of the policy, i.e. 1142 the active speaker, 1 represents the previous instance, i.e. the 1143 previous active speaker and so on. 1145 The following example shows a case where the Provider provides two 1146 media streams, one showing the active speaker and a second stream 1147 showing the previous speaker. 1149 +-----------------------+---------------------------------+ 1150 | Capture Scene #1 | | 1151 +-----------------------|---------------------------------+ 1152 | VC1 | | 1153 | VC2 | | 1154 | MCC1(VC1,VC2) | Policy=SoundLevel:0 | 1155 | | MaxCaptures=1 | 1156 | MCC2(VC1,VC2) | Policy=SoundLevel:1 | 1157 | | MaxCaptures=1 | 1158 | CSV(MCC1,MCC2) | | 1159 +---------------------------------------------------------+ 1161 Table 3: Example Policy MCC attribute usage 1163 7.2.1.3. Synchronisation Identity 1165 The Synchronisation Identity MCC attribute indicates how the 1166 individual captures in multiple MCC captures are synchronised. To 1167 indicate that the Capture Encodings associated with MCCs contain 1168 captures from the same source at the same time a Provider should 1169 set the same Synchronisation Identity on each of the concerned 1170 MCCs. It is the Provider that determines what the source for the 1171 Captures is, so a Provider can choose how to group together Single 1172 Media Captures into a combined "source" for the purpose of 1173 switching them together to keep them synchronized according to the 1174 SynchronisationID attribute. For example when the Provider is in 1175 an MCU it may determine that each separate CLUE Endpoint is a 1176 remote source of media. The Synchronisation Identity may be used 1177 across media types, i.e. to synchronize audio and video related 1178 MCCs. 1180 Without this attribute it is assumed that multiple MCCs may provide 1181 content from different sources at any particular point in time. 1183 For example: 1185 +=======================+=================================+ 1186 | Capture Scene #1 | | 1187 +-----------------------|---------------------------------+ 1188 | VC1 | Description=Left | 1189 | VC2 | Description=Centre | 1190 | VC3 | Description=Right | 1191 | AC1 | Description=room | 1192 | CSV(VC1,VC2,VC3) | | 1193 | CSV(AC1) | | 1194 +=======================+=================================+ 1195 | Capture Scene #2 | | 1196 +-----------------------|---------------------------------+ 1197 | VC4 | Description=Left | 1198 | VC5 | Description=Centre | 1199 | VC6 | Description=Right | 1200 | AC2 | Description=room | 1201 | CSV(VC4,VC5,VC6) | | 1202 | CSV(AC2) | | 1203 +=======================+=================================+ 1204 | Capture Scene #3 | | 1205 +-----------------------|---------------------------------+ 1206 | VC7 | | 1207 | AC3 | | 1208 +=======================+=================================+ 1209 | Capture Scene #4 | | 1210 +-----------------------|---------------------------------+ 1211 | VC8 | | 1212 | AC4 | | 1213 +=======================+=================================+ 1214 | Capture Scene #3 | | 1215 +-----------------------|---------------------------------+ 1216 | MCC1(VC1,VC4,VC7) | SynchronisationID=1 | 1217 | | MaxCaptures=1 | 1218 | MCC2(VC2,VC5,VC8) | SynchronisationID=1 | 1219 | | MaxCaptures=1 | 1220 | MCC3(VC3,VC6) | MaxCaptures=1 | 1221 | MCC4(AC1,AC2,AC3,AC4) | SynchronisationID=1 | 1222 | | MaxCaptures=1 | 1223 | CSV(MCC1,MCC2,MCC3) | | 1224 | CSV(MCC4) | | 1225 +=======================+=================================+ 1227 Table 4: Example Synchronisation Identity MCC attribute usage 1229 The above Advertisement would indicate that MCC1, MCC2, MCC3 and 1230 MCC4 make up a Capture Scene. There would be four capture 1231 encodings (one for each MCC). Because MCC1 and MCC2 have the same 1232 SynchronisationID, each encoding from MCC1 and MCC2 respectively 1233 would together have content from only Capture Scene 1 or only 1234 Capture Scene 2 or the combination of VC7 and VC8 at a particular 1235 point in time. In this case the Provider has decided the sources 1236 to be synchronized are Scene #1, Scene #2, and Scene #3 and #4 1237 together. The encoding from MCC3 would not be synchronised with 1238 MCC1 or MCC2. As MCC4 also has the same Synchronisation Identity 1239 as MCC1 and MCC2 the content of the audio encoding will be 1240 synchronised with the video content. 1242 7.3. Capture Scene 1244 In order for a Provider's individual Captures to be used 1245 effectively by a Consumer, the Provider organizes the Captures into 1246 one or more Capture Scenes, with the structure and contents of 1247 these Capture Scenes being sent from the Provider to the Consumer 1248 in the Advertisement. 1250 A Capture Scene is a structure representing a spatial region 1251 containing one or more Capture Devices, each capturing media 1252 representing a portion of the region. A Capture Scene includes one 1253 or more Capture Scene Views (CSV), with each CSV including one or 1254 more Media Captures of the same media type. There can also be 1255 Media Captures that are not included in a Capture Scene View. A 1256 Capture Scene represents, for example, the video image of a group 1257 of people seated next to each other, along with the sound of their 1258 voices, which could be represented by some number of VCs and ACs in 1259 the Capture Scene Views. An MCU can also describe in Capture 1260 Scenes what it constructs from media Streams it receives. 1262 A Provider MAY advertise one or more Capture Scenes. What 1263 constitutes an entire Capture Scene is up to the Provider. A 1264 simple Provider might typically use one Capture Scene for 1265 participant media (live video from the room cameras) and another 1266 Capture Scene for a computer generated presentation. In more 1267 complex systems, the use of additional Capture Scenes is also 1268 sensible. For example, a classroom may advertise two Capture 1269 Scenes involving live video, one including only the camera 1270 capturing the instructor (and associated audio), the other 1271 including camera(s) capturing students (and associated audio). 1273 A Capture Scene MAY (and typically will) include more than one type 1274 of media. For example, a Capture Scene can include several Capture 1275 Scene Views for Video Captures, and several Capture Scene Views for 1276 Audio Captures. A particular Capture MAY be included in more than 1277 one Capture Scene View. 1279 A Provider MAY express spatial relationships between Captures that 1280 are included in the same Capture Scene. However, there is no 1281 spatial relationship between Media Captures from different Capture 1282 Scenes. In other words, Capture Scenes each use their own spatial 1283 measurement system as outlined above in section 6. 1285 A Provider arranges Captures in a Capture Scene to help the 1286 Consumer choose which captures it wants to render. The Capture 1287 Scene Views in a Capture Scene are different alternatives the 1288 Provider is suggesting for representing the Capture Scene. Each 1289 Capture Scene View is given an advertisement unique identity. The 1290 order of Capture Scene Views within a Capture Scene has no 1291 significance. The Media Consumer can choose to receive all Media 1292 Captures from one Capture Scene View for each media type (e.g. 1293 audio and video), or it can pick and choose Media Captures 1294 regardless of how the Provider arranges them in Capture Scene 1295 Views. Different Capture Scene Views of the same media type are 1296 not necessarily mutually exclusive alternatives. Also note that 1297 the presence of multiple Capture Scene Views (with potentially 1298 multiple encoding options in each view) in a given Capture Scene 1299 does not necessarily imply that a Provider is able to serve all the 1300 associated media simultaneously (although the construction of such 1301 an over-rich Capture Scene is probably not sensible in many cases). 1302 What a Provider can send simultaneously is determined through the 1303 Simultaneous Transmission Set mechanism, described in section 8. 1305 Captures within the same Capture Scene View MUST be of the same 1306 media type - it is not possible to mix audio and video captures in 1307 the same Capture Scene View, for instance. The Provider MUST be 1308 capable of encoding and sending all Captures (that have an encoding 1309 group) in a single Capture Scene View simultaneously. The order of 1310 Captures within a Capture Scene View has no significance. A 1311 Consumer can decide to receive all the Captures in a single Capture 1312 Scene View, but a Consumer could also decide to receive just a 1313 subset of those captures. A Consumer can also decide to receive 1314 Captures from different Capture Scene Views, all subject to the 1315 constraints set by Simultaneous Transmission Sets, as discussed in 1316 section 8. 1318 When a Provider advertises a Capture Scene with multiple CSVs, it 1319 is essentially signaling that there are multiple representations of 1320 the same Capture Scene available. In some cases, these multiple 1321 views would typically be used simultaneously (for instance a "video 1322 view" and an "audio view"). In some cases the views would 1323 conceptually be alternatives (for instance a view consisting of 1324 three Video Captures covering the whole room versus a view 1325 consisting of just a single Video Capture covering only the center 1326 of a room). In this latter example, one sensible choice for a 1327 Consumer would be to indicate (through its Configure and possibly 1328 through an additional offer/answer exchange) the Captures of that 1329 Capture Scene View that most closely matched the Consumer's number 1330 of display devices or screen layout. 1332 The following is an example of 4 potential Capture Scene Views for 1333 an endpoint-style Provider: 1335 1. (VC0, VC1, VC2) - left, center and right camera Video Captures 1337 2. (VC3) - Video Capture associated with loudest room segment 1339 3. (VC4) - Video Capture zoomed out view of all people in the room 1341 4. (AC0) - main audio 1343 The first view in this Capture Scene example is a list of Video 1344 Captures which have a spatial relationship to each other. 1345 Determination of the order of these captures (VC0, VC1 and VC2) for 1346 rendering purposes is accomplished through use of their Area of 1347 Capture attributes. The second view (VC3) and the third view (VC4) 1348 are alternative representations of the same room's video, which 1349 might be better suited to some Consumers' rendering capabilities. 1350 The inclusion of the Audio Capture in the same Capture Scene 1351 indicates that AC0 is associated with all of those Video Captures, 1352 meaning it comes from the same spatial region. Therefore, if audio 1353 were to be rendered at all, this audio would be the correct choice 1354 irrespective of which Video Captures were chosen. 1356 7.3.1. Capture Scene attributes 1358 Capture Scene Attributes can be applied to Capture Scenes as well 1359 as to individual media captures. Attributes specified at this 1360 level apply to all constituent Captures. Capture Scene attributes 1361 include 1363 . Human-readable description of the Capture Scene, which could 1364 be in multiple languages; 1365 . xCard scene information 1366 . Scale information (millimeters, unknown, no scale), as 1367 described in Section 6. 1369 7.3.1.1. Scene Information 1371 The Scene information attribute provides information regarding the 1372 Capture Scene rather than individual participants. The Provider 1373 may gather the information automatically or manually from a 1374 variety of sources. The scene information attribute allows a 1375 Provider to indicate information such as: organizational or 1376 geographic information allowing a Consumer to determine which 1377 Capture Scenes are of interest in order to then perform Capture 1378 selection. It also allows a Consumer to render information 1379 regarding the Scene or to use it for further processing. 1381 As per 7.1.1.11. the xCard format is used to convey this 1382 information and the Provider may supply a minimal set of 1383 information or a larger set of information. 1385 In order to keep CLUE messages compact the Provider SHOULD use a 1386 URI to point to any LOGO, PHOTO or SOUND contained in the xCARD 1387 rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE 1388 message. 1390 7.3.2. Capture Scene View attributes 1392 A Capture Scene can include one or more Capture Scene Views in 1393 addition to the Capture Scene wide attributes described above. 1394 Capture Scene View attributes apply to the Capture Scene View as a 1395 whole, i.e. to all Captures that are part of the Capture Scene 1396 View. 1398 Capture Scene View attributes include: 1400 . Human-readable description (which could be in multiple 1401 languages) of the Capture Scene View 1403 7.3.3. Global View List 1405 An Advertisement can include an optional Global View list. Each 1406 item in this list is a Global View. A Global View is a set of 1407 references to one or more Capture Scene Views of the same media 1408 type that are defined within scenes of the same advertisement. 1409 Each Global View in the list is a suggestion from the Provider to 1410 the Consumer for which CSVs provide a complete representation of 1411 the simultaneous captures provided by the Provider, across 1412 multiple scenes. The Provider can include multiple Global Views, 1413 to allow a Consumer to choose sets of captures appropriate to its 1414 capabilities or application. The choice of how to make these 1415 suggestions in the Global View list for what represents all the 1416 scenes for which the Provider can send media is up to the 1417 Provider. This is very similar to how each CSV represents a 1418 particular scene. 1420 As an example, suppose an advertisement has three scenes, and each 1421 scene has three CSVs, ranging from one to three video captures in 1422 each CSV. The Provider is advertising a total of nine video 1423 Captures across three scenes. The Provider can use the Global 1424 View list to suggest alternatives for Consumers that can't receive 1425 all nine video Captures as separate media streams. For 1426 accommodating a Consumer that wants to receive three video 1427 Captures, a Provider might suggest a Global View containing just a 1428 single CSV with three Captures and nothing from the other two 1429 scenes. Or a Provider might suggest a Global View containing 1430 three different CSVs, one from each scene, with a single video 1431 Capture in each. 1433 Some additional rules: 1435 . The ordering of Global Views in the Global View list is not 1436 important. 1437 . The ordering of CSVs within each Global View is not 1438 important. 1439 . A particular CSV may be used in multiple Global Views. 1440 . The Provider must be capable of encoding and sending all 1441 Captures within the CSVs of a given Global View 1442 simultaneously. 1444 8. Simultaneous Transmission Set Constraints 1446 In many practical cases, a Provider has constraints or limitations 1447 on its ability to send Captures simultaneously. One type of 1448 limitation is caused by the physical limitations of capture 1449 mechanisms; these constraints are represented by a simultaneous 1450 transmission set. The second type of limitation reflects the 1451 encoding resources available, such as bandwidth or video encoding 1452 throughput (macroblocks/second). This type of constraint is 1453 captured by encoding groups, discussed below. 1455 Some Endpoints or MCUs can send multiple Captures simultaneously; 1456 however sometimes there are constraints that limit which Captures 1457 can be sent simultaneously with other Captures. A device may not 1458 be able to be used in different ways at the same time. Provider 1459 Advertisements are made so that the Consumer can choose one of 1460 several possible mutually exclusive usages of the device. This 1461 type of constraint is expressed in a Simultaneous Transmission Set, 1462 which lists all the Captures of a particular media type (e.g. 1463 audio, video, text) that can be sent at the same time. There are 1464 different Simultaneous Transmission Sets for each media type in the 1465 Advertisement. This is easier to show in an example. 1467 Consider the example of a room system where there are three cameras 1468 each of which can send a separate capture covering two persons 1469 each- VC0, VC1, VC2. The middle camera can also zoom out (using an 1470 optical zoom lens) and show all six persons, VC3. But the middle 1471 camera cannot be used in both modes at the same time - it has to 1472 either show the space where two participants sit or the whole six 1473 seats, but not both at the same time. As a result, VC1 and VC3 1474 cannot be sent simultaneously. 1476 Simultaneous Transmission Sets are expressed as sets of the Media 1477 Captures that the Provider could transmit at the same time (though, 1478 in some cases, it is not intuitive to do so). If a Multiple 1479 Content Capture is included in a Simultaneous Transmission Set it 1480 indicates that the Capture Encoding associated with it could be 1481 transmitted as the same time as the other Captures within the 1482 Simultaneous Transmission Set. It does not imply that the Single 1483 Media Captures contained in the Multiple Content Capture could all 1484 be transmitted at the same time. 1486 In this example the two simultaneous sets are shown in Table 5. If 1487 a Provider advertises one or more mutually exclusive Simultaneous 1488 Transmission Sets, then for each media type the Consumer MUST 1489 ensure that it chooses Media Captures that lie wholly within one of 1490 those Simultaneous Transmission Sets. 1492 +-------------------+ 1493 | Simultaneous Sets | 1494 +-------------------+ 1495 | {VC0, VC1, VC2} | 1496 | {VC0, VC3, VC2} | 1497 +-------------------+ 1499 Table 5: Two Simultaneous Transmission Sets 1501 A Provider OPTIONALLY can include the simultaneous sets in its 1502 Advertisement. These simultaneous set constraints apply across all 1503 the Capture Scenes in the Advertisement. It is a syntax 1504 conformance requirement that the simultaneous transmission sets 1505 MUST allow all the media captures in any particular Capture Scene 1506 View to be used simultaneously. Similarly, the simultaneous 1507 transmission sets MUST reflect the simultaneity expressed by any 1508 Global View. 1510 For shorthand convenience, a Provider MAY describe a Simultaneous 1511 Transmission Set in terms of Capture Scene Views and Capture 1512 Scenes. If a Capture Scene View is included in a Simultaneous 1513 Transmission Set, then all Media Captures in the Capture Scene View 1514 are included in the Simultaneous Transmission Set. If a Capture 1515 Scene is included in a Simultaneous Transmission Set, then all its 1516 Capture Scene Views (of the corresponding media type) are included 1517 in the Simultaneous Transmission Set. The end result reduces to a 1518 set of Media Captures, of a particular media type, in either case. 1520 If an Advertisement does not include Simultaneous Transmission 1521 Sets, then the Provider MUST be able to simultaneously provide all 1522 the captures from any one CSV of each media type from each capture 1523 scene. Likewise, if there are no Simultaneous Transmission Sets 1524 and there is a Global View list, then the Provider MUST be able to 1525 simultaneously provide all the captures from any particular Global 1526 View (of each media type) from the Global View list. 1528 If an Advertisement includes multiple Capture Scene Views in a 1529 Capture Scene then the Consumer MAY choose one Capture Scene View 1530 for each media type, or MAY choose individual Captures based on the 1531 Simultaneous Transmission Sets. 1533 9. Encodings 1535 Individual encodings and encoding groups are CLUE's mechanisms 1536 allowing a Provider to signal its limitations for sending Captures, 1537 or combinations of Captures, to a Consumer. Consumers can map the 1538 Captures they want to receive onto the Encodings, with encoding 1539 parameters they want. As for the relationship between the CLUE- 1540 specified mechanisms based on Encodings and the SIP Offer-Answer 1541 exchange, please refer to section 5. 1543 9.1. Individual Encodings 1545 An Individual Encoding represents a way to encode a Media Capture 1546 to become a Capture Encoding, to be sent as an encoded media stream 1547 from the Provider to the Consumer. An Individual Encoding has a 1548 set of parameters characterizing how the media is encoded. 1550 Different media types have different parameters, and different 1551 encoding algorithms may have different parameters. An Individual 1552 Encoding can be assigned to at most one Capture Encoding at any 1553 given time. 1555 Individual Encoding parameters are represented in SDP [RFC4566], 1556 not in CLUE messages. For example, for a video encoding using 1557 H.26x compression technologies, this can include parameters such 1558 as: 1560 . Maximum bandwidth; 1561 . Maximum picture size in pixels; 1562 . Maxmimum number of pixels to be processed per second; 1564 The bandwidth parameter is the only one that specifically relates 1565 to a CLUE Advertisement, as it can be further constrained by the 1566 maximum group bandwidth in an Encoding Group. 1568 9.2. Encoding Group 1570 An Encoding Group includes a set of one or more Individual 1571 Encodings, and parameters that apply to the group as a whole. By 1572 grouping multiple individual Encodings together, an Encoding Group 1573 describes additional constraints on bandwidth for the group. A 1574 single Encoding Group MAY refer to encodings for different media 1575 types. 1577 The Encoding Group data structure contains: 1579 . Maximum bitrate for all encodings in the group combined; 1580 . A list of identifiers for the Individual Encodings belonging 1581 to the group. 1583 When the Individual Encodings in a group are instantiated into 1584 Capture Encodings, each Capture Encoding has a bitrate that MUST be 1585 less than or equal to the max bitrate for the particular individual 1586 encoding. The "maximum bitrate for all encodings in the group" 1587 parameter gives the additional restriction that the sum of all the 1588 individual capture encoding bitrates MUST be less than or equal to 1589 this group value. 1591 The following diagram illustrates one example of the structure of a 1592 media Provider's Encoding Groups and their contents. 1594 ,-------------------------------------------------. 1595 | Media Provider | 1596 | | 1597 | ,--------------------------------------. | 1598 | | ,--------------------------------------. | 1599 | | | ,--------------------------------------. | 1600 | | | | Encoding Group | | 1601 | | | | ,-----------. | | 1602 | | | | | | ,---------. | | 1603 | | | | | | | | ,---------.| | 1604 | | | | | Encoding1 | |Encoding2| |Encoding3|| | 1605 | `.| | | | | | `---------'| | 1606 | `.| `-----------' `---------' | | 1607 | `--------------------------------------' | 1608 `-------------------------------------------------' 1610 Figure 3: Encoding Group Structure 1612 A Provider advertises one or more Encoding Groups. Each Encoding 1613 Group includes one or more Individual Encodings. Each Individual 1614 Encoding can represent a different way of encoding media. For 1615 example one Individual Encoding may be 1080p60 video, another could 1616 be 720p30, with a third being CIF, all in, for example, H.264 1617 format. 1618 While a typical three codec/display system might have one Encoding 1619 Group per "codec box" (physical codec, connected to one camera and 1620 one screen), there are many possibilities for the number of 1621 Encoding Groups a Provider may be able to offer and for the 1622 encoding values in each Encoding Group. 1624 There is no requirement for all Encodings within an Encoding Group 1625 to be instantiated at the same time. 1627 9.3. Associating Captures with Encoding Groups 1629 Each Media Capture, including MCCs, MAY be associated with one or 1630 more Encoding Groups. To be eligible for configuration, a Media 1631 Capture MUST be associated with at least one Encoding Group, which 1632 is used to instantiate that Capture into one or more Capture 1633 Encodings. When an MCC is configured all the Media Captures 1634 referenced by the MCC will appear in the Capture Encoding according 1635 to the attributes of the chosen encoding of the MCC. This allows an 1636 Advertiser to specify encoding attributes associated with the Media 1637 Captures without the need to provide an individual Capture Encoding 1638 for each of the inputs. 1640 If an Encoding Group is assigned to a Media Capture referenced by 1641 the MCC it indicates that this Capture may also have an individual 1642 Capture Encoding. 1644 For example: 1646 +--------------------+------------------------------------+ 1647 | Capture Scene #1 | | 1648 +--------------------+------------------------------------+ 1649 | VC1 | EncodeGroupID=1 | 1650 | VC2 | | 1651 | MCC1(VC1,VC2) | EncodeGroupID=2 | 1652 | CSV(VC1) | | 1653 | CSV(MCC1) | | 1654 +--------------------+------------------------------------+ 1656 Table 6: Example usage of Encoding with MCC and source Captures 1658 This would indicate that VC1 may be sent as its own Capture 1659 Encoding from EncodeGroupID=1 or that it may be sent as part of a 1660 Capture Encoding from EncodeGroupID=2 along with VC2. 1662 More than one Capture MAY use the same Encoding Group. 1664 The maximum number of streams that can result from a particular 1665 Encoding Group constraint is equal to the number of individual 1666 Encodings in the group. The actual number of Capture Encodings 1667 used at any time MAY be less than this maximum. Any of the 1668 Captures that use a particular Encoding Group can be encoded 1669 according to any of the Individual Encodings in the group. If 1670 there are multiple Individual Encodings in the group, then the 1671 Consumer can configure the Provider, via a Configure message, to 1672 encode a single Media Capture into multiple different Capture 1673 Encodings at the same time, subject to the Max Capture Encodings 1674 constraint, with each capture encoding following the constraints of 1675 a different Individual Encoding. 1677 It is a protocol conformance requirement that the Encoding Groups 1678 MUST allow all the Captures in a particular Capture Scene View to 1679 be used simultaneously. 1681 10. Consumer's Choice of Streams to Receive from the Provider 1683 After receiving the Provider's Advertisement message (that includes 1684 media captures and associated constraints), the Consumer composes 1685 its reply to the Provider in the form of a Configure message. The 1686 Consumer is free to use the information in the Advertisement as it 1687 chooses, but there are a few obviously sensible design choices, 1688 which are outlined below. 1690 If multiple Providers connect to the same Consumer (i.e. in a n 1691 MCU-less multiparty call), it is the responsibility of the Consumer 1692 to compose Configures for each Provider that both fulfill each 1693 Provider's constraints as expressed in the Advertisement, as well 1694 as its own capabilities. 1696 In an MCU-based multiparty call, the MCU can logically terminate 1697 the Advertisement/Configure negotiation in that it can hide the 1698 characteristics of the receiving endpoint and rely on its own 1699 capabilities (transcoding/transrating/...) to create Media Streams 1700 that can be decoded at the Endpoint Consumers. The timing of an 1701 MCU's sending of Advertisements (for its outgoing ports) and 1702 Configures (for its incoming ports, in response to Advertisements 1703 received there) is up to the MCU and implementation dependent. 1705 As a general outline, a Consumer can choose, based on the 1706 Advertisement it has received, which Captures it wishes to receive, 1707 and which Individual Encodings it wants the Provider to use to 1708 encode the Captures. 1710 On receipt of an Advertisement with an MCC the Consumer treats the 1711 MCC as per other non-MCC Captures with the following differences: 1713 - The Consumer would understand that the MCC is a Capture that 1714 includes the referenced individual Captures and that these 1715 individual Captures are delivered as part of the MCC's Capture 1716 Encoding. 1718 - The Consumer may utilise any of the attributes associated with 1719 the referenced individual Captures and any Capture Scene attributes 1720 from where the individual Captures were defined to choose Captures 1721 and for rendering decisions. 1723 - The Consumer may or may not choose to receive all the indicated 1724 captures. Therefore it can choose to receive a sub-set ofCaptures 1725 indicated by the MCC. 1727 For example if the Consumer receives: 1729 MCC1(VC1,VC2,VC3){attributes} 1731 A Consumer could choose all the Captures within a MCCs however if 1732 the Consumer determines that it doesn't want VC3 it can return 1733 MCC1(VC1,VC2). If it wants all the individual Captures then it 1734 returns only the MCC identity (i.e. MCC1). If the MCC in the 1735 advertisement does not reference any individual captures, then the 1736 Consumer cannot choose what is included in the MCC, it is up to the 1737 Provider to decide. 1739 A Configure Message includes a list of Capture Encodings. These 1740 are the Capture Encodings the Consumer wishes to receive from the 1741 Provider. Each Capture Encoding refers to one Media Capture and 1742 one Individual Encoding. A Configure Message does not include 1743 references to Capture Scenes or Capture Scene Views. 1745 For each Capture the Consumer wants to receive, it configures one 1746 or more of the Encodings in that Capture's Encoding Group. The 1747 Consumer does this by telling the Provider, in its Configure 1748 Message, which Encoding to use for each chosen Capture. Upon 1749 receipt of this Configure from the Consumer, common knowledge is 1750 established between Provider and Consumer regarding sensible 1751 choices for the media streams. The setup of the actual media 1752 channels, at least in the simplest case, is left to a following 1753 offer-answer exchange. Optimized implementations MAY speed up the 1754 reaction to the offer-answer exchange by reserving the resources at 1755 the time of finalization of the CLUE handshake. 1757 CLUE advertisements and configure messages don't necessarily 1758 require a new SDP offer-answer for every CLUE message 1759 exchange. But the resulting encodings sent via RTP must conform to 1760 the most recent SDP offer-answer result. 1762 In order to meaningfully create and send an initial Configure, the 1763 Consumer needs to have received at least one Advertisement, and an 1764 SDP offer defining the Individual Encodings, from the Provider. 1766 In addition, the Consumer can send a Configure at any time during 1767 the call. The Configure MUST be valid according to the most 1768 recently received Advertisement. The Consumer can send a Configure 1769 either in response to a new Advertisement from the Provider or on 1770 its own, for example because of a local change in conditions 1771 (people leaving the room, connectivity changes, multipoint related 1772 considerations). 1774 When choosing which Media Streams to receive from the Provider, and 1775 the encoding characteristics of those Media Streams, the Consumer 1776 advantageously takes several things into account: its local 1777 preference, simultaneity restrictions, and encoding limits. 1779 10.1. Local preference 1781 A variety of local factors influence the Consumer's choice of 1782 Media Streams to be received from the Provider: 1784 o if the Consumer is an Endpoint, it is likely that it would 1785 choose, where possible, to receive video and audio Captures that 1786 match the number of display devices and audio system it has 1788 o if the Consumer is an MCU, it MAY choose to receive loudest 1789 speaker streams (in order to perform its own media composition) 1790 and avoid pre-composed video Captures 1792 o user choice (for instance, selection of a new layout) MAY result 1793 in a different set of Captures, or different encoding 1794 characteristics, being required by the Consumer 1796 10.2. Physical simultaneity restrictions 1798 Often there are physical simultaneity constraints of the Provider 1799 that affect the Provider's ability to simultaneously send all of 1800 the captures the Consumer would wish to receive. For instance, an 1801 MCU, when connected to a multi-camera room system, might prefer to 1802 receive both individual video streams of the people present in the 1803 room and an overall view of the room from a single camera. Some 1804 Endpoint systems might be able to provide both of these sets of 1805 streams simultaneously, whereas others might not (if the overall 1806 room view were produced by changing the optical zoom level on the 1807 center camera, for instance). 1809 10.3. Encoding and encoding group limits 1811 Each of the Provider's encoding groups has limits on bandwidth and 1812 computational complexity, and the constituent potential encodings 1813 have limits on the bandwidth, computational complexity, video 1814 frame rate, and resolution that can be provided. When choosing 1815 the Captures to be received from a Provider, a Consumer device 1816 MUST ensure that the encoding characteristics requested for each 1817 individual Capture fits within the capability of the encoding it 1818 is being configured to use, as well as ensuring that the combined 1819 encoding characteristics for Captures fit within the capabilities 1820 of their associated encoding groups. In some cases, this could 1821 cause an otherwise "preferred" choice of capture encodings to be 1822 passed over in favor of different Capture Encodings--for instance, 1823 if a set of three Captures could only be provided at a low 1824 resolution then a three screen device could switch to favoring a 1825 single, higher quality, Capture Encoding. 1827 11. Extensibility 1829 One important characteristics of the Framework is its 1830 extensibility. The standard for interoperability and handling 1831 multiple streams must be future-proof. The framework itself is 1832 inherently extensible through expanding the data model types. For 1833 example: 1835 o Adding more types of media, such as telemetry, can done by 1836 defining additional types of Captures in addition to audio and 1837 video. 1839 o Adding new functionalities, such as 3-D, say, may require 1840 additional attributes describing the Captures. 1842 The infrastructure is designed to be extended rather than 1843 requiring new infrastructure elements. Extension comes through 1844 adding to defined types. 1846 12. Examples - Using the Framework (Informative) 1848 This section gives some examples, first from the point of view of 1849 the Provider, then the Consumer, then some multipoint scenarios 1851 12.1. Provider Behavior 1853 This section shows some examples in more detail of how a Provider 1854 can use the framework to represent a typical case for telepresence 1855 rooms. First an endpoint is illustrated, then an MCU case is 1856 shown. 1858 12.1.1. Three screen Endpoint Provider 1860 Consider an Endpoint with the following description: 1862 3 cameras, 3 displays, a 6 person table 1864 o Each camera can provide one Capture for each 1/3 section of the 1865 table 1867 o A single Capture representing the active speaker can be provided 1868 (voice activity based camera selection to a given encoder input 1869 port implemented locally in the Endpoint) 1871 o A single Capture representing the active speaker with the other 1872 2 Captures shown picture in picture within the stream can be 1873 provided (again, implemented inside the endpoint) 1875 o A Capture showing a zoomed out view of all 6 seats in the room 1876 can be provided 1878 The audio and video Captures for this Endpoint can be described as 1879 follows. 1881 Video Captures: 1883 o VC0- (the left camera stream), encoding group=EG0, view=table 1885 o VC1- (the center camera stream), encoding group=EG1, view=table 1887 o VC2- (the right camera stream), encoding group=EG2, view=table 1889 o MCC3- (the loudest panel stream), encoding group=EG1, 1890 view=table, MaxCaptures=1 1892 o MCC4- (the loudest panel stream with PiPs), encoding group=EG1, 1893 view=room, MaxCaptures=3 1895 o VC5- (the zoomed out view of all people in the room), encoding 1896 group=EG1, view=room 1898 o VC6- (presentation stream), encoding group=EG1, presentation 1900 The following diagram is a top view of the room with 3 cameras, 3 1901 displays, and 6 seats. Each camera is capturing 2 people. The 1902 six seats are not all in a straight line. 1904 ,-. d 1905 ( )`--.__ +---+ 1906 `-' / `--.__ | | 1907 ,-. | `-.._ |_-+Camera 2 (VC2) 1908 ( ).' <--(AC1)-+-''`+-+ 1909 `-' |_...---'' | | 1910 ,-.c+-..__ +---+ 1911 ( )| ``--..__ | | 1912 `-' | ``+-..|_-+Camera 1 (VC1) 1913 ,-. | <--(AC2)..--'|+-+ ^ 1914 ( )| __..--' | | | 1915 `-'b|..--' +---+ |X 1916 ,-. |``---..___ | | | 1917 ( )\ ```--..._|_-+Camera 0 (VC0) | 1918 `-' \ <--(AC0) ..-''`-+ | 1919 ,-. \ __.--'' | | <----------+ 1920 ( ) |..-'' +---+ Y 1921 `-' a (0,0,0) origin is under Camera 1 1923 Figure 4: Room Layout Top View 1925 The two points labeled b and c are intended to be at the midpoint 1926 between the seating positions, and where the fields of view of the 1927 cameras intersect. 1929 The plane of interest for VC0 is a vertical plane that intersects 1930 points 'a' and 'b'. 1932 The plane of interest for VC1 intersects points 'b' and 'c'. The 1933 plane of interest for VC2 intersects points 'c' and 'd'. 1935 This example uses an area scale of millimeters. 1937 Areas of capture: 1939 bottom left bottom right top left top right 1940 VC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757) 1941 VC1 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757) 1942 VC2 ( 673,3000,0) (2011,2850,0) ( 673,3000,757) (2011,3000,757) 1943 MCC3(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1944 MCC4(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1945 VC5 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757) 1946 VC6 none 1948 Points of capture: 1949 VC0 (-1678,0,800) 1950 VC1 (0,0,800) 1951 VC2 (1678,0,800) 1952 MCC3 none 1953 MCC4 none 1954 VC5 (0,0,800) 1955 VC6 none 1957 In this example, the right edge of the VC0 area lines up with the 1958 left edge of the VC1 area. It doesn't have to be this way. There 1959 could be a gap or an overlap. One additional thing to note for 1960 this example is the distance from a to b is equal to the distance 1961 from b to c and the distance from c to d. All these distances are 1962 1346 mm. This is the planar width of each area of capture for VC0, 1963 VC1, and VC2. 1965 Note the text in parentheses (e.g. "the left camera stream") is 1966 not explicitly part of the model, it is just explanatory text for 1967 this example, and is not included in the model with the media 1968 captures and attributes. Also, MCC4 doesn't say anything about 1969 how a capture is composed, so the media consumer can't tell based 1970 on this capture that MCC4 is composed of a "loudest panel with 1971 PiPs". 1973 Audio Captures: 1975 Three ceiling microphones are located between the cameras and the 1976 table, at the same height as the cameras. The microphones point 1977 down at an angle toward the seating positions. 1979 o AC0 (left), encoding group=EG3 1981 o AC1 (right), encoding group=EG3 1983 o AC2 (center) encoding group=EG3 1985 o AC3 being a simple pre-mixed audio stream from the room (mono), 1986 encoding group=EG3 1988 o AC4 audio stream associated with the presentation video (mono) 1989 encoding group=EG3, presentation 1991 Point of capture: Point on Line of Capture: 1993 AC0 (-1342,2000,800) (-1342,2925,379) 1994 AC1 ( 1342,2000,800) ( 1342,2925,379) 1995 AC2 ( 0,2000,800) ( 0,3000,379) 1996 AC3 ( 0,2000,800) ( 0,3000,379) 1997 AC4 none 1999 The physical simultaneity information is: 2001 Simultaneous transmission set #1 {VC0, VC1, VC2, MCC3, MCC4, 2002 VC6} 2004 Simultaneous transmission set #2 {VC0, VC2, VC5, VC6} 2006 This constraint indicates it is not possible to use all the VCs at 2007 the same time. VC5 cannot be used at the same time as VC1 or MCC3 2008 or MCC4. Also, using every member in the set simultaneously may 2009 not make sense - for example MCC3(loudest) and MCC4 (loudest with 2010 PIP). (In addition, there are encoding constraints that make 2011 choosing all of the VCs in a set impossible. VC1, MCC3, MCC4, 2012 VC5, VC6 all use EG1 and EG1 has only 3 ENCs. This constraint 2013 shows up in the encoding groups, not in the simultaneous 2014 transmission sets.) 2016 In this example there are no restrictions on which audio captures 2017 can be sent simultaneously. 2019 Encoding Groups: 2021 This example has three encoding groups associated with the video 2022 captures. Each group can have 3 encodings, but with each 2023 potential encoding having a progressively lower specification. In 2024 this example, 1080p60 transmission is possible (as ENC0 has a 2025 maxPps value compatible with that). Significantly, as up to 3 2026 encodings are available per group, it is possible to transmit some 2027 video captures simultaneously that are not in the same view in the 2028 capture scene. For example VC1 and MCC3 at the same time. 2030 It is also possible to transmit multiple capture encodings of a 2031 single video capture. For example VC0 can be encoded using ENC0 2032 and ENC1 at the same time, as long as the encoding parameters 2033 satisfy the constraints of ENC0, ENC1, and EG0, such as one at 2034 4000000 bps and one at 2000000 bps. 2036 encodeGroupID=EG0, maxGroupBandwidth=6000000 2037 encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2038 maxPps=124416000, maxBandwidth=4000000 2039 encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2040 maxPps=27648000, maxBandwidth=4000000 2041 encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30, 2042 maxPps=15552000, maxBandwidth=4000000 2043 encodeGroupID=EG1 maxGroupBandwidth=6000000 2044 encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2045 maxPps=124416000, maxBandwidth=4000000 2046 encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2047 maxPps=27648000, maxBandwidth=4000000 2048 encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30, 2049 maxPps=15552000, maxBandwidth=4000000 2050 encodeGroupID=EG2 maxGroupBandwidth=6000000 2051 encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60, 2052 maxPps=124416000, maxBandwidth=4000000 2053 encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30, 2054 maxPps=27648000, maxBandwidth=4000000 2055 encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30, 2056 maxPps=15552000, maxBandwidth=4000000 2058 Figure 5: Example Encoding Groups for Video 2060 For audio, there are five potential encodings available, so all 2061 five audio captures can be encoded at the same time. 2063 encodeGroupID=EG3, maxGroupBandwidth=320000 2064 encodeID=ENC9, maxBandwidth=64000 2065 encodeID=ENC10, maxBandwidth=64000 2066 encodeID=ENC11, maxBandwidth=64000 2067 encodeID=ENC12, maxBandwidth=64000 2068 encodeID=ENC13, maxBandwidth=64000 2070 Figure 6: Example Encoding Group for Audio 2072 Capture Scenes: 2074 The following table represents the capture scenes for this 2075 provider. Recall that a capture scene is composed of alternative 2076 capture scene views covering the same spatial region. Capture 2077 Scene #1 is for the main people captures, and Capture Scene #2 is 2078 for presentation. 2080 Each row in the table is a separate Capture Scene View 2082 +------------------+ 2083 | Capture Scene #1 | 2084 +------------------+ 2085 | VC0, VC1, VC2 | 2086 | MCC3 | 2087 | MCC4 | 2088 | VC5 | 2089 | AC0, AC1, AC2 | 2090 | AC3 | 2091 +------------------+ 2093 +------------------+ 2094 | Capture Scene #2 | 2095 +------------------+ 2096 | VC6 | 2097 | AC4 | 2098 +------------------+ 2100 Table 7: Example Capture Scene Views 2102 Different capture scenes are unique to each other, non- 2103 overlapping. A consumer can choose a view from each capture scene. 2104 In this case the three captures VC0, VC1, and VC2 are one way of 2105 representing the video from the endpoint. These three captures 2106 should appear adjacent next to each other. Alternatively, another 2107 way of representing the Capture Scene is with the capture MCC3, 2108 which automatically shows the person who is talking. Similarly 2109 for the MCC4 and VC5 alternatives. 2111 As in the video case, the different views of audio in Capture 2112 Scene #1 represent the "same thing", in that one way to receive 2113 the audio is with the 3 audio captures (AC0, AC1, AC2), and 2114 another way is with the mixed AC3. The Media Consumer can choose 2115 an audio CSV it is capable of receiving. 2117 The spatial ordering is understood by the media capture attributes 2118 Area of Capture and Point of Capture and Point on Line of Capture. 2120 A Media Consumer would likely want to choose a capture scene view 2121 to receive based in part on how many streams it can simultaneously 2122 receive. A consumer that can receive three people streams would 2123 probably prefer to receive the first view of Capture Scene #1 2124 (VC0, VC1, VC2) and not receive the other views. A consumer that 2125 can receive only one people stream would probably choose one of 2126 the other views. 2128 If the consumer can receive a presentation stream too, it would 2129 also choose to receive the only view from Capture Scene #2 (VC6). 2131 12.1.2. Encoding Group Example 2133 This is an example of an encoding group to illustrate how it can 2134 express dependencies between encodings. 2136 encodeGroupID=EG0 maxGroupBandwidth=6000000 2137 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2138 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2139 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2140 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2141 encodeID=AUDENC0, maxBandwidth=96000 2142 encodeID=AUDENC1, maxBandwidth=96000 2143 encodeID=AUDENC2, maxBandwidth=96000 2145 Here, the encoding group is EG0. Although the encoding group is 2146 capable of transmitting up to 6Mbit/s, no individual video 2147 encoding can exceed 4Mbit/s. 2149 This encoding group also allows up to 3 audio encodings, AUDENC<0- 2150 2>. It is not required that audio and video encodings reside 2151 within the same encoding group, but if so then the group's overall 2152 maxBandwidth value is a limit on the sum of all audio and video 2153 encodings configured by the consumer. A system that does not wish 2154 or need to combine bandwidth limitations in this way should 2155 instead use separate encoding groups for audio and video in order 2156 for the bandwidth limitations on audio and video to not interact. 2158 Audio and video can be expressed in separate encoding groups, as 2159 in this illustration. 2161 encodeGroupID=EG0 maxGroupBandwidth=6000000 2162 encodeID=VIDENC0, maxWidth=1920, maxHeight=1088, 2163 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2164 encodeID=VIDENC1, maxWidth=1920, maxHeight=1088, 2165 maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000 2166 encodeGroupID=EG1 maxGroupBandwidth=500000 2167 encodeID=AUDENC0, maxBandwidth=96000 2168 encodeID=AUDENC1, maxBandwidth=96000 2169 encodeID=AUDENC2, maxBandwidth=96000 2171 12.1.3. The MCU Case 2173 This section shows how an MCU might express its Capture Scenes, 2174 intending to offer different choices for consumers that can handle 2175 different numbers of streams. A single audio capture stream is 2176 provided for all single and multi-screen configurations that can 2177 be associated (e.g. lip-synced) with any combination of video 2178 captures at the consumer. 2180 +-----------------------+---------------------------------+ 2181 | Capture Scene #1 | | 2182 +-----------------------|---------------------------------+ 2183 | VC0 | VC for a single screen consumer | 2184 | VC1, VC2 | VCs for a two screen consumer | 2185 | VC3, VC4, VC5 | VCs for a three screen consumer | 2186 | VC6, VC7, VC8, VC9 | VCs for a four screen consumer | 2187 | AC0 | AC representing all participants| 2188 | CSV(VC0) | | 2189 | CSV(VC1,VC2) | | 2190 | CSV(VC3,VC4,VC5) | | 2191 | CSV(VC6,VC7,VC8,VC9) | | 2192 | CSV(AC0) | | 2193 +-----------------------+---------------------------------+ 2195 Table 8: MCU main Capture Scenes 2197 If / when a presentation stream becomes active within the 2198 conference the MCU might re-advertise the available media as: 2200 +------------------+--------------------------------------+ 2201 | Capture Scene #2 | note | 2202 +------------------+--------------------------------------+ 2203 | VC10 | video capture for presentation | 2204 | AC1 | presentation audio to accompany VC10 | 2205 | CSV(VC10) | | 2206 | CSV(AC1) | | 2207 +------------------+--------------------------------------+ 2209 Table 9: MCU presentation Capture Scene 2211 12.2. Media Consumer Behavior 2213 This section gives an example of how a Media Consumer might behave 2214 when deciding how to request streams from the three screen 2215 endpoint described in the previous section. 2217 The receive side of a call needs to balance its requirements, 2218 based on number of screens and speakers, its decoding capabilities 2219 and available bandwidth, and the provider's capabilities in order 2220 to optimally configure the provider's streams. Typically it would 2221 want to receive and decode media from each Capture Scene 2222 advertised by the Provider. 2224 A sane, basic, algorithm might be for the consumer to go through 2225 each Capture Scene View in turn and find the collection of Video 2226 Captures that best matches the number of screens it has (this 2227 might include consideration of screens dedicated to presentation 2228 video display rather than "people" video) and then decide between 2229 alternative views in the video Capture Scenes based either on 2230 hard-coded preferences or user choice. Once this choice has been 2231 made, the consumer would then decide how to configure the 2232 provider's encoding groups in order to make best use of the 2233 available network bandwidth and its own decoding capabilities. 2235 12.2.1. One screen Media Consumer 2237 MCC3, MCC4 and VC5 are all different views by themselves, not 2238 grouped together in a single view, so the receiving device should 2239 choose between one of those. The choice would come down to 2240 whether to see the greatest number of participants simultaneously 2241 at roughly equal precedence (VC5), a switched view of just the 2242 loudest region (MCC3) or a switched view with PiPs (MCC4). An 2243 endpoint device with a small amount of knowledge of these 2244 differences could offer a dynamic choice of these options, in- 2245 call, to the user. 2247 12.2.2. Two screen Media Consumer configuring the example 2249 Mixing systems with an even number of screens, "2n", and those 2250 with "2n+1" cameras (and vice versa) is always likely to be the 2251 problematic case. In this instance, the behavior is likely to be 2252 determined by whether a "2 screen" system is really a "2 decoder" 2253 system, i.e., whether only one received stream can be displayed 2254 per screen or whether more than 2 streams can be received and 2255 spread across the available screen area. To enumerate 3 possible 2256 behaviors here for the 2 screen system when it learns that the far 2257 end is "ideally" expressed via 3 capture streams: 2259 1. Fall back to receiving just a single stream (MCC3, MCC4 or VC5 2260 as per the 1 screen consumer case above) and either leave one 2261 screen blank or use it for presentation if / when a 2262 presentation becomes active. 2264 2. Receive 3 streams (VC0, VC1 and VC2) and display across 2 2265 screens (either with each capture being scaled to 2/3 of a 2266 screen and the center capture being split across 2 screens) or, 2267 as would be necessary if there were large bezels on the 2268 screens, with each stream being scaled to 1/2 the screen width 2269 and height and there being a 4th "blank" panel. This 4th panel 2270 could potentially be used for any presentation that became 2271 active during the call. 2273 3. Receive 3 streams, decode all 3, and use control information 2274 indicating which was the most active to switch between showing 2275 the left and center streams (one per screen) and the center and 2276 right streams. 2278 For an endpoint capable of all 3 methods of working described 2279 above, again it might be appropriate to offer the user the choice 2280 of display mode. 2282 12.2.3. Three screen Media Consumer configuring the example 2284 This is the most straightforward case - the Media Consumer would 2285 look to identify a set of streams to receive that best matched its 2286 available screens and so the VC0 plus VC1 plus VC2 should match 2287 optimally. The spatial ordering would give sufficient information 2288 for the correct video capture to be shown on the correct screen, 2289 and the consumer would either need to divide a single encoding 2290 group's capability by 3 to determine what resolution and frame 2291 rate to configure the provider with or to configure the individual 2292 video captures' encoding groups with what makes most sense (taking 2293 into account the receive side decode capabilities, overall call 2294 bandwidth, the resolution of the screens plus any user preferences 2295 such as motion vs sharpness). 2297 12.3. Multipoint Conference utilizing Multiple Content Captures 2299 The use of MCCs allows the MCU to construct outgoing Advertisements 2300 describing complex and media switching and composition scenarios. 2301 The following sections provide several examples. 2303 Note: In the examples the identities of the CLUE elements (e.g. 2304 Captures, Capture Scene) in the incoming Advertisements overlap. 2305 This is because there is no co-ordination between the endpoints. 2306 The MCU is responsible for making these unique in the outgoing 2307 advertisement. 2309 12.3.1. Single Media Captures and MCC in the same Advertisement 2311 Four endpoints are involved in a Conference where CLUE is used. An 2312 MCU acts as a middlebox between the endpoints with a CLUE channel 2313 between each endpoint and the MCU. The MCU receives the following 2314 Advertisements. 2316 +-----------------------+---------------------------------+ 2317 | Capture Scene #1 | Description=AustralianConfRoom | 2318 +-----------------------|---------------------------------+ 2319 | VC1 | Description=Audience | 2320 | | EncodeGroupID=1 | 2321 | CSV(VC1) | | 2322 +---------------------------------------------------------+ 2323 Table 10: Advertisement received from Endpoint A 2325 +-----------------------+---------------------------------+ 2326 | Capture Scene #1 | Description=ChinaConfRoom | 2327 +-----------------------|---------------------------------+ 2328 | VC1 | Description=Speaker | 2329 | | EncodeGroupID=1 | 2330 | VC2 | Description=Audience | 2331 | | EncodeGroupID=1 | 2332 | CSV(VC1, VC2) | | 2333 +---------------------------------------------------------+ 2335 Table 11: Advertisement received from Endpoint B 2337 +-----------------------+---------------------------------+ 2338 | Capture Scene #1 | Description=USAConfRoom | 2339 +-----------------------|---------------------------------+ 2340 | VC1 | Description=Audience | 2341 | | EncodeGroupID=1 | 2342 | CSV(VC1) | | 2343 +---------------------------------------------------------+ 2345 Table 12: Advertisement received from Endpoint C 2347 Note: Endpoint B above indicates that it sends two streams. 2349 If the MCU wanted to provide a Multiple Content Capture containing 2350 a round robin switched view of the audience from the 3 endpoints 2351 and the speaker it could construct the following advertisement: 2353 Advertisement sent to Endpoint F 2355 +=======================+=================================+ 2356 | Capture Scene #1 | Description=AustralianConfRoom | 2357 +-----------------------|---------------------------------+ 2358 | VC1 | Description=Audience | 2359 | CSV(VC1) | | 2360 +=======================+=================================+ 2361 | Capture Scene #2 | Description=ChinaConfRoom | 2362 +-----------------------|---------------------------------+ 2363 | VC2 | Description=Speaker | 2364 | VC3 | Description=Audience | 2365 | CSV(VC2, VC3) | | 2366 +=======================+=================================+ 2367 | Capture Scene #3 | Description=USAConfRoom | 2368 +-----------------------|---------------------------------+ 2369 | VC4 | Description=Audience | 2370 | CSV(VC4) | | 2371 +=======================+=================================+ 2372 | Capture Scene #4 | | 2373 +-----------------------|---------------------------------+ 2374 | MCC1(VC1,VC2,VC3,VC4) | Policy=RoundRobin:1 | 2375 | | MaxCaptures=1 | 2376 | | EncodingGroup=1 | 2377 | CSV(MCC1) | | 2378 +=======================+=================================+ 2380 Table 13: Advertisement sent to Endpoint F - One Encoding 2382 Alternatively if the MCU wanted to provide the speaker as one media 2383 stream and the audiences as another it could assign an encoding 2384 group to VC2 in Capture Scene 2 and provide a CSV in Capture Scene 2385 #4 as per the example below. 2387 Advertisement sent to Endpoint F 2389 +=======================+=================================+ 2390 | Capture Scene #1 | Description=AustralianConfRoom | 2391 +-----------------------|---------------------------------+ 2392 | VC1 | Description=Audience | 2393 | CSV(VC1) | | 2394 +=======================+=================================+ 2395 | Capture Scene #2 | Description=ChinaConfRoom | 2396 +-----------------------|---------------------------------+ 2397 | VC2 | Description=Speaker | 2398 | | EncodingGroup=1 | 2399 | VC3 | Description=Audience | 2400 | CSV(VC2, VC3) | | 2401 +=======================+=================================+ 2402 | Capture Scene #3 | Description=USAConfRoom | 2403 +-----------------------|---------------------------------+ 2404 | VC4 | Description=Audience | 2405 | CSV(VC4) | | 2406 +=======================+=================================+ 2407 | Capture Scene #4 | | 2408 +-----------------------|---------------------------------+ 2409 | MCC1(VC1,VC3,VC4) | Policy=RoundRobin:1 | 2410 | | MaxCaptures=1 | 2411 | | EncodingGroup=1 | 2412 | MCC2(VC2) | MaxCaptures=1 | 2413 | | EncodingGroup=1 | 2414 | CSV2(MCC1,MCC2) | | 2415 +=======================+=================================+ 2417 Table 14: Advertisement sent to Endpoint F - Two Encodings 2419 Therefore a Consumer could choose whether or not to have a separate 2420 speaker related stream and could choose which endpoints to see. If 2421 it wanted the second stream but not the Australian conference room 2422 it could indicate the following captures in the Configure message: 2424 +-----------------------+---------------------------------+ 2425 | MCC1(VC3,VC4) | Encoding | 2426 | VC2 | Encoding | 2427 +-----------------------|---------------------------------+ 2428 Table 15: MCU case: Consumer Response 2430 12.3.2. Several MCCs in the same Advertisement 2432 Multiple MCCs can be used where multiple streams are used to carry 2433 media from multiple endpoints. For example: 2435 A conference has three endpoints D, E and F. Each end point has 2436 three video captures covering the left, middle and right regions of 2437 each conference room. The MCU receives the following 2438 advertisements from D and E. 2440 +-----------------------+---------------------------------+ 2441 | Capture Scene #1 | Description=AustralianConfRoom | 2442 +-----------------------|---------------------------------+ 2443 | VC1 | CaptureArea=Left | 2444 | | EncodingGroup=1 | 2445 | VC2 | CaptureArea=Centre | 2446 | | EncodingGroup=1 | 2447 | VC3 | CaptureArea=Right | 2448 | | EncodingGroup=1 | 2449 | CSV(VC1,VC2,VC3) | | 2450 +---------------------------------------------------------+ 2452 Table 16: Advertisement received from Endpoint D 2454 +-----------------------+---------------------------------+ 2455 | Capture Scene #1 | Description=ChinaConfRoom | 2456 +-----------------------|---------------------------------+ 2457 | VC1 | CaptureArea=Left | 2458 | | EncodingGroup=1 | 2459 | VC2 | CaptureArea=Centre | 2460 | | EncodingGroup=1 | 2461 | VC3 | CaptureArea=Right | 2462 | | EncodingGroup=1 | 2463 | CSV(VC1,VC2,VC3) | | 2464 +---------------------------------------------------------+ 2466 Table 17: Advertisement received from Endpoint E 2468 The MCU wants to offer Endpoint F three Capture Encodings. Each 2469 Capture Encoding would contain all the Captures from either 2470 Endpoint D or Endpoint E depending based on the active speaker. 2471 The MCU sends the following Advertisement: 2473 +=======================+=================================+ 2474 | Capture Scene #1 | Description=AustralianConfRoom | 2475 +-----------------------|---------------------------------+ 2476 | VC1 | | 2477 | VC2 | | 2478 | VC3 | | 2479 | CSV(VC1,VC2,VC3) | | 2480 +=======================+=================================+ 2481 | Capture Scene #2 | Description=ChinaConfRoom | 2482 +-----------------------|---------------------------------+ 2483 | VC4 | | 2484 | VC5 | | 2485 | VC6 | | 2486 | CSV(VC4,VC5,VC6) | | 2487 +=======================+=================================+ 2488 | Capture Scene #3 | | 2489 +-----------------------|---------------------------------+ 2490 | MCC1(VC1,VC4) | CaptureArea=Left | 2491 | | MaxCaptures=1 | 2492 | | SynchronisationID=1 | 2493 | | EncodingGroup=1 | 2494 | MCC2(VC2,VC5) | CaptureArea=Centre | 2495 | | MaxCaptures=1 | 2496 | | SynchronisationID=1 | 2497 | | EncodingGroup=1 | 2498 | MCC3(VC3,VC6) | CaptureArea=Right | 2499 | | MaxCaptures=1 | 2500 | | SynchronisationID=1 | 2501 | | EncodingGroup=1 | 2502 | CSV(MCC1,MCC2,MCC3) | | 2503 +=======================+=================================+ 2505 Table 17: Advertisement received from Endpoint E 2507 12.3.3. Heterogeneous conference with switching and composition 2509 Consider a conference between endpoints with the following 2510 characteristics: 2512 Endpoint A - 4 screens, 3 cameras 2514 Endpoint B - 3 screens, 3 cameras 2516 Endpoint C - 3 screens, 3 cameras 2518 Endpoint D - 3 screens, 3 cameras 2520 Endpoint E - 1 screen, 1 camera 2522 Endpoint F - 2 screens, 1 camera 2524 Endpoint G - 1 screen, 1 camera 2526 This example focuses on what the user in one of the 3-camera multi- 2527 screen endpoints sees. Call this person User A, at Endpoint A. 2528 There are 4 large display screens at Endpoint A. Whenever somebody 2529 at another site is speaking, all the video captures from that 2530 endpoint are shown on the large screens. If the talker is at a 3- 2531 camera site, then the video from those 3 cameras fills 3 of the 2532 screens. If the talker is at a single-camera site, then video from 2533 that camera fills one of the screens, while the other screens show 2534 video from other single-camera endpoints. 2536 User A hears audio from the 4 loudest talkers. 2538 User A can also see video from other endpoints, in addition to the 2539 current talker, although much smaller in size. Endpoint A has 4 2540 screens, so one of those screens shows up to 9 other Media Captures 2541 in a tiled fashion. When video from a 3 camera endpoint appears in 2542 the tiled area, video from all 3 cameras appears together across 2543 the screen with correct spatial relationship among those 3 images. 2545 +---+---+---+ +-------------+ +-------------+ +-------------+ 2546 | | | | | | | | | | 2547 +---+---+---+ | | | | | | 2548 | | | | | | | | | | 2549 +---+---+---+ | | | | | | 2550 | | | | | | | | | | 2551 +---+---+---+ +-------------+ +-------------+ +-------------+ 2552 Figure 7: Endpoint A - 4 Screen Display 2554 User B at Endpoint B sees a similar arrangement, except there are 2555 only 3 screens, so the 9 other Media Captures are spread out across 2556 the bottom of the 3 displays, in a picture-in-picture (PIP) format. 2557 When video from a 3 camera endpoint appears in the PIP area, video 2558 from all 3 cameras appears together across a single screen with 2559 correct spatial relationship. 2561 +-------------+ +-------------+ +-------------+ 2562 | | | | | | 2563 | | | | | | 2564 | | | | | | 2565 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2566 | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ | 2567 +-------------+ +-------------+ +-------------+ 2568 Figure 8: Endpoint B - 3 Screen Display with PiPs 2570 When somebody at a different endpoint becomes the current talker, 2571 then User A and User B both see the video from the new talker 2572 appear on their large screen area, while the previous talker takes 2573 one of the smaller tiled or PIP areas. The person who is the 2574 current talker doesn't see themselves; they see the previous talker 2575 in their large screen area. 2577 One of the points of this example is that endpoints A and B each 2578 want to receive 3 capture encodings for their large display areas, 2579 and 9 encodings for their smaller areas. A and B are be able to 2580 each send the same Configure message to the MCU, and each receive 2581 the same conceptual Media Captures from the MCU. The differences 2582 are in how they are rendered and are purely a local matter at A and 2583 B. 2585 The Advertisements for such a scenario are described below. 2587 +-----------------------+---------------------------------+ 2588 | Capture Scene #1 | Description=Endpoint x | 2589 +-----------------------|---------------------------------+ 2590 | VC1 | EncodingGroup=1 | 2591 | VC2 | EncodingGroup=1 | 2592 | VC3 | EncodingGroup=1 | 2593 | AC1 | EncodingGroup=2 | 2594 | CSV1(VC1, VC2, VC3) | | 2595 | CSV2(AC1) | | 2596 +---------------------------------------------------------+ 2598 Table 19: Advertisement received at the MCU from Endpoints A to D 2600 +-----------------------+---------------------------------+ 2601 | Capture Scene #1 | Description=Endpoint y | 2602 +-----------------------|---------------------------------+ 2603 | VC1 | EncodingGroup=1 | 2604 | AC1 | EncodingGroup=2 | 2605 | CSV1(VC1) | | 2606 | CSV2(AC1) | | 2607 +---------------------------------------------------------+ 2609 Table 20: Advertisement received at the MCU from Endpoints E to F 2611 Rather than considering what is displayed CLUE concentrates more 2612 on what the MCU sends. The MCU doesn't know anything about the 2613 number of screens an endpoint has. 2615 As Endpoints A to D each advertise that three Captures make up a 2616 Capture Scene, the MCU offers these in a "site" switching mode. 2617 That is that there are three Multiple Content Captures (and 2618 Capture Encodings) each switching between Endpoints. The MCU 2619 switches in the applicable media into the stream based on voice 2620 activity. Endpoint A will not see a capture from itself. 2622 Using the MCC concept the MCU would send the following 2623 Advertisement to endpoint A: 2625 +=======================+=================================+ 2626 | Capture Scene #1 | Description=Endpoint B | 2627 +-----------------------|---------------------------------+ 2628 | VC4 | Left | 2629 | VC5 | Center | 2630 | VC6 | Right | 2631 | AC1 | | 2632 | CSV(VC4,VC5,VC6) | | 2633 | CSV(AC1) | | 2634 +=======================+=================================+ 2635 | Capture Scene #2 | Description=Endpoint C | 2636 +-----------------------|---------------------------------+ 2637 | VC7 | Left | 2638 | VC8 | Center | 2639 | VC9 | Right | 2640 | AC2 | | 2641 | CSV(VC7,VC8,VC9) | | 2642 | CSV(AC2) | | 2643 +=======================+=================================+ 2644 | Capture Scene #3 | Description=Endpoint D | 2645 +-----------------------|---------------------------------+ 2646 | VC10 | Left | 2647 | VC11 | Center | 2648 | VC12 | Right | 2649 | AC3 | | 2650 | CSV(VC10,VC11,VC12) | | 2651 | CSV(AC3) | | 2652 +=======================+=================================+ 2653 | Capture Scene #4 | Description=Endpoint E | 2654 +-----------------------|---------------------------------+ 2655 | VC13 | | 2656 | AC4 | | 2657 | CSV(VC13) | | 2658 | CSV(AC4) | | 2659 +=======================+=================================+ 2660 | Capture Scene #5 | Description=Endpoint F | 2661 +-----------------------|---------------------------------+ 2662 | VC14 | | 2663 | AC5 | | 2664 | CSV(VC14) | | 2665 | CSV(AC5) | | 2666 +=======================+=================================+ 2667 | Capture Scene #6 | Description=Endpoint G | 2668 +-----------------------|---------------------------------+ 2669 | VC15 | | 2670 | AC6 | | 2671 | CSV(VC15) | | 2672 | CSV(AC6) | | 2673 +=======================+=================================+ 2675 Table 21: Advertisement sent to endpoint A - Source Part 2677 The above part of the Advertisement presents information about the 2678 sources to the MCC. The information is effectively the same as the 2679 received Advertisements except that there are no Capture Encodings 2680 associated with them and the identities have been re-numbered. 2682 In addition to the source Capture information the MCU advertises 2683 "site" switching of Endpoints B to G in three streams. 2685 +=======================+=================================+ 2686 | Capture Scene #7 | Description=Output3streammix | 2687 +-----------------------|---------------------------------+ 2688 | MCC1(VC4,VC7,VC10, | CaptureArea=Left | 2689 | VC13) | MaxCaptures=1 | 2690 | | SynchronisationID=1 | 2691 | | Policy=SoundLevel:0 | 2692 | | EncodingGroup=1 | 2693 | | | 2694 | MCC2(VC5,VC8,VC11, | CaptureArea=Center | 2695 | VC14) | MaxCaptures=1 | 2696 | | SynchronisationID=1 | 2697 | | Policy=SoundLevel:0 | 2698 | | EncodingGroup=1 | 2699 | | | 2700 | MCC3(VC6,VC9,VC12, | CaptureArea=Right | 2701 | VC15) | MaxCaptures=1 | 2702 | | SynchronisationID=1 | 2703 | | Policy=SoundLevel:0 | 2704 | | EncodingGroup=1 | 2705 | | | 2706 | MCC4() (for audio) | CaptureArea=whole scene | 2707 | | MaxCaptures=1 | 2708 | | Policy=SoundLevel:0 | 2709 | | EncodingGroup=2 | 2710 | | | 2711 | MCC5() (for audio) | CaptureArea=whole scene | 2712 | | MaxCaptures=1 | 2713 | | Policy=SoundLevel:1 | 2714 | | EncodingGroup=2 | 2715 | | | 2716 | MCC6() (for audio) | CaptureArea=whole scene | 2717 | | MaxCaptures=1 | 2718 | | Policy=SoundLevel:2 | 2719 | | EncodingGroup=2 | 2720 | | | 2721 | MCC7() (for audio) | CaptureArea=whole scene | 2722 | | MaxCaptures=1 | 2723 | | Policy=SoundLevel:3 | 2724 | | EncodingGroup=2 | 2725 | | | 2726 | CSV(MCC1,MCC2,MCC3) | | 2727 | CSV(MCC4,MCC5,MCC6, | | 2728 | MCC7) | | 2729 +=======================+=================================+ 2731 Table 22: Advertisement send to endpoint A - switching part 2733 The above part describes the switched 3 main streams that relate to 2734 site switching. MaxCaptures=1 indicates that only one Capture from 2735 the MCC is sent at a particular time. SynchronisationID=1 indicates 2736 that the source sending is synchronised. The provider can choose to 2737 group together VC13, VC14, and VC15 for the purpose of switching 2738 according to the SynchronisationID. Therefore when the provider 2739 switches one of them into an MCC, it can also switch the others 2740 even though they are not part of the same Capture Scene. 2742 All the audio for the conference is included in this Scene #7. 2743 There isn't necessarily a one to one relation between any audio 2744 capture and video capture in this scene. Typically a change in 2745 loudest talker will cause the MCU to switch the audio streams more 2746 quickly than switching video streams. 2748 The MCU can also supply nine media streams showing the active and 2749 previous eight speakers. It includes the following in the 2750 Advertisement: 2752 +=======================+=================================+ 2753 | Capture Scene #8 | Description=Output9stream | 2754 +-----------------------|---------------------------------+ 2755 | MCC8(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2756 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:0 | 2757 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2758 | | | 2759 | MCC9(VC4,VC5,VC6,VC7, | MaxCaptures=1 | 2760 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:1 | 2761 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2762 | | | 2763 to to | 2764 | | | 2765 | MCC16(VC4,VC5,VC6,VC7,| MaxCaptures=1 | 2766 | VC8,VC9,VC10,VC11, | Policy=SoundLevel:8 | 2767 | VC12,VC13,VC14,VC15)| EncodingGroup=1 | 2768 | | | 2769 | CSV(MCC8,MCC9,MCC10, | | 2770 | MCC11,MCC12,MCC13,| | 2771 | MCC14,MCC15,MCC16)| | 2772 +=======================+=================================+ 2774 Table 23: Advertisement sent to endpoint A - 9 switched part 2776 The above part indicates that there are 9 capture encodings. Each 2777 of the Capture Encodings may contain any captures from any source 2778 site with a maximum of one Capture at a time. Which Capture is 2779 present is determined by the policy. The MCCs in this scene do not 2780 have any spatial attributes. 2782 Note: The Provider alternatively could provide each of the MCCs 2783 above in its own Capture Scene. 2785 If the MCU wanted to provide a composed Capture Encoding containing 2786 all of the 9 captures it could Advertise in addition: 2788 +=======================+=================================+ 2789 | Capture Scene #9 | Description=NineTiles | 2790 +-----------------------|---------------------------------+ 2791 | MCC13(MCC8,MCC9,MCC10,| MaxCaptures=9 | 2792 | MCC11,MCC12,MCC13,| EncodingGroup=1 | 2793 | MCC14,MCC15,MCC16)| | 2794 | | | 2795 | CSV(MCC13) | | 2796 +=======================+=================================+ 2798 Table 24: Advertisement sent to endpoint A - 9 composed part 2800 As MaxCaptures is 9 it indicates that the capture encoding contains 2801 information from 9 sources at a time. 2803 The Advertisement to Endpoint B is identical to the above other 2804 than the captures from Endpoint A would be added and the captures 2805 from Endpoint B would be removed. Whether the Captures are rendered 2806 on a four screen display or a three screen display is up to the 2807 Consumer to determine. The Consumer wants to place video captures 2808 from the same original source endpoint together, in the correct 2809 spatial order, but the MCCs do not have spatial attributes. So the 2810 Consumer needs to associate incoming media packets with the 2811 original individual captures in the advertisement (such as VC4, 2812 VC5, and VC6) in order to know the spatial information it needs for 2813 correct placement on the screens. 2815 Editor's note: this is an open issue, about how to associate 2816 incoming packets with the original capture that is a constituent of 2817 an MCC. This document probably should mention it in an earlier 2818 section, after the solution is worked out in the other CLUE 2819 documents. 2821 12.3.4. Heterogeneous conference with voice activated switching 2823 This example illustrates how multipoint "voice activated switching" 2824 behavior can be realized, with an endpoint making its own decision 2825 about which of its outgoing video streams is considered the "active 2826 talker" from that endpoint. Then an MCU can decide which is the 2827 active talker among the whole conference. 2829 Consider a conference between endpoints with the following 2830 characteristics: 2832 Endpoint A - 3 screens, 3 cameras 2834 Endpoint B - 3 screens, 3 cameras 2836 Endpoint C - 1 screen, 1 camera 2838 This example focuses on what the user at endpoint C sees. The 2839 user would like to see the video capture of the current talker, 2840 without composing it with any other video capture. In this 2841 example endpoint C is capable of receiving only a single video 2842 stream. The following tables describe advertisements from A and B 2843 to the MCU, and from the MCU to C, that can be used to accomplish 2844 this. 2846 +-----------------------+---------------------------------+ 2847 | Capture Scene #1 | Description=Endpoint x | 2848 +-----------------------|---------------------------------+ 2849 | VC1 | CaptureArea=Left | 2850 | | EncodingGroup=1 | 2851 | VC2 | CaptureArea=Center | 2852 | | EncodingGroup=1 | 2853 | VC3 | CaptureArea=Right | 2854 | | EncodingGroup=1 | 2855 | MCC1(VC1,VC2,VC3) | MaxCaptures=1 | 2856 | | CaptureArea=whole scene | 2857 | | Policy=SoundLevel:0 | 2858 | | EncodingGroup=1 | 2859 | AC1 | CaptureArea=whole scene | 2860 | | EncodingGroup=2 | 2861 | CSV1(VC1, VC2, VC3) | | 2862 | CSV2(MCC1) | | 2863 | CSV3(AC1) | | 2864 +---------------------------------------------------------+ 2866 Table 25: Advertisement received at the MCU from Endpoints A and B 2868 Endpoints A and B are advertising each individual video capture, 2869 and also a switched capture MCC1 which switches between the other 2870 three based on who is the active talker. These endpoints do not 2871 advertise distinct audio captures associated with each individual 2872 video capture, so it would be impossible for the MCU (as a media 2873 consumer) to make its own determination of which video capture is 2874 the active talker based just on information in the audio streams. 2876 +-----------------------+---------------------------------+ 2877 | Capture Scene #1 | Description=conference | 2878 +-----------------------|---------------------------------+ 2879 | MCC1() | CaptureArea=Left | 2880 | | MaxCaptures=1 | 2881 | | SynchronisationID=1 | 2882 | | Policy=SoundLevel:0 | 2883 | | EncodingGroup=1 | 2884 | | | 2885 | MCC2() | CaptureArea=Center | 2886 | | MaxCaptures=1 | 2887 | | SynchronisationID=1 | 2888 | | Policy=SoundLevel:0 | 2889 | | EncodingGroup=1 | 2890 | | | 2891 | MCC3() | CaptureArea=Right | 2892 | | MaxCaptures=1 | 2893 | | SynchronisationID=1 | 2894 | | Policy=SoundLevel:0 | 2895 | | EncodingGroup=1 | 2896 | | | 2897 | MCC4() | CaptureArea=whole scene | 2898 | | MaxCaptures=1 | 2899 | | Policy=SoundLevel:0 | 2900 | | EncodingGroup=1 | 2901 | | | 2902 | MCC5() (for audio) | CaptureArea=whole scene | 2903 | | MaxCaptures=1 | 2904 | | Policy=SoundLevel:0 | 2905 | | EncodingGroup=2 | 2906 | | | 2907 | MCC6() (for audio) | CaptureArea=whole scene | 2908 | | MaxCaptures=1 | 2909 | | Policy=SoundLevel:1 | 2910 | | EncodingGroup=2 | 2911 | CSV1(MCC1,MCC2,MCC3 | | 2912 | CSV2(MCC4) | | 2913 | CSV3(MCC5,MCC6) | | 2914 +---------------------------------------------------------+ 2916 Table 26: Advertisement sent from the MCU to C 2918 The MCU advertises one scene, with four video MCCs. Three of them 2919 in CSV1 give a left, center, right view of the conference, with 2920 "site switching". MCC4 provides a single video capture 2921 representing a view of the whole conference. The MCU intends for 2922 MCC4 to be switched between all the other original source 2923 captures. In this example advertisement the MCU is not giving all 2924 the information about all the other endpoints' scenes and which of 2925 those captures is included in the MCCs. The MCU could include all 2926 that information if it wants to give the consumers more 2927 information, but it is not necessary for this example scenario. 2929 The Provider advertises MCC5 and MCC6 for audio. Both are 2930 switched captures, with different SoundLevel policies indicating 2931 they are the top two dominant talkers. The Provider advertises 2932 CSV3 with both MCCs, suggesting the Consumer should use both if it 2933 can. 2935 Endpoint C, in its configure message to the MCU, requests to 2936 receive MCC4 for video, and MCC5 and MCC6 for audio. In order for 2937 the MCU to get the information it needs to construct MCC4, it has 2938 to send configure messages to A and B asking to receive MCC1 from 2939 each of them, along with their AC1 audio. Now the MCU can use 2940 audio energy information from the two incoming audio streams from 2941 A and B to determine which of those alternatives is the current 2942 talker. Based on that, the MCU uses either MCC1 from A or MCC1 2943 from B as the source of MCC4 to send to C. 2945 13. Acknowledgements 2947 Allyn Romanow and Brian Baldino were authors of early versions. 2948 Mark Gorzynski also contributed much to the initial approach. 2949 Many others also contributed, including Christian Groves, Jonathan 2950 Lennox, Paul Kyzivat, Rob Hansen, Roni Even, Christer Holmberg, 2951 Stephen Botzko, Mary Barnes, John Leslie, Paul Coverdale. 2953 14. IANA Considerations 2955 None. 2957 15. Security Considerations 2959 There are several potential attacks related to telepresence, and 2960 specifically the protocols used by CLUE, in the case of 2961 conferencing sessions, due to the natural involvement of multiple 2962 endpoints and the many, often user-invoked, capabilities provided 2963 by the systems. 2965 An MCU involved in a CLUE session can experience many of the same 2966 attacks as that of a conferencing system such as that enabled by 2967 the XCON framework [RFC 6503]. Examples of attacks include the 2968 following: an endpoint attempting to listen to sessions in which 2969 it is not authorized to participate, an endpoint attempting to 2970 disconnect or mute other users, and theft of service by an 2971 endpoint in attempting to create telepresence sessions it is not 2972 allowed to create. Thus, it is RECOMMENDED that an MCU 2973 implementing the protocols necessary to support CLUE, follow the 2974 security recommendations specified in the conference control 2975 protocol documents. In the case of CLUE, SIP is the default 2976 conferencing protocol, thus the security considerations in RFC 2977 4579 MUST be followed. 2979 One primary security concern, surrounding the CLUE framework 2980 introduced in this document, involves securing the actual 2981 protocols and the associated authorization mechanisms. These 2982 concerns apply to endpoint to endpoint sessions, as well as 2983 sessions involving multiple endpoints and MCUs. Figure 2 in 2984 section 5 provides a basic flow of information exchange for CLUE 2985 and the protocols involved. 2987 As described in section 5, CLUE uses SIP/SDP to establish the 2988 session prior to exchanging any CLUE specific information. Thus 2989 the security mechanisms recommended for SIP [RFC 3261], including 2990 user authentication and authorization, SHOULD be followed. In 2991 addition, the media is based on RTP and thus existing RTP security 2992 mechanisms, such as DTLS/SRTP, MUST be supported. 2994 A separate data channel is established to transport the CLUE 2995 protocol messages. The contents of the CLUE protocol messages are 2996 based on information introduced in this document, which is 2997 represented by an XML schema for this information defined in the 2998 CLUE data model [ref]. Some of the information which could 2999 possibly introduce privacy concerns is the xCard information as 3000 described in section 7.1.1.11. In addition, the (text) 3001 description field in the Media Capture attribute (section 7.1.1.7) 3002 could possibly reveal sensitive information or specific 3003 identities. The same would be true for the descriptions in the 3004 Capture Scene (section 7.3.1) and Capture Scene View (7.3.2) 3005 attributes. One other important consideration for the 3006 information in the xCard as well as the description field in the 3007 Media Capture and Capture Scene View attributes is that while the 3008 endpoints involved in the session have been authenticated, there 3009 is no assurance that the information in the xCard or description 3010 fields is authentic. Thus, this information SHOULD not be used to 3011 make any authorization decisions and the participants in the 3012 sessions SHOULD be made aware of this. 3014 While other information in the CLUE protocol messages does not 3015 reveal specific identities, it can reveal characteristics and 3016 capabilities of the endpoints. That information could possibly 3017 uniquely identify specific endpoints. It might also be possible 3018 for an attacker to manipulate the information and disrupt the CLUE 3019 sessions. It would also be possible to mount a DoS attack on the 3020 CLUE endpoints if a malicious agent has access to the data 3021 channel. Thus, It MUST be possible for the endpoints to establish 3022 a channel which is secure against both message recovery and 3023 message modification. Further details on this are provided in the 3024 CLUE data channel solution document. 3026 There are also security issues associated with the authorization 3027 to perform actions at the CLUE endpoints to invoke specific 3028 capabilities (e.g., re-arranging screens, sharing content, etc.). 3029 However, the policies and security associated with these actions 3030 are outside the scope of this document and the overall CLUE 3031 solution. 3033 16. Changes Since Last Version 3035 NOTE TO THE RFC-Editor: Please remove this section prior to 3036 publication as an RFC. 3038 Changes from 16 to 17: 3040 1. Ticket #59 - rename Capture Scene Entry (CSE) to Capture 3041 Scene View (CSV) 3043 2. Ticket #60 - rename Global CSE List to Global View List 3045 3. Ticket #61 - Proposal for describing the coordinate system. 3046 Describe it better, without conflicts if cameras point in 3047 different directions. 3049 4. Minor clarifications and improved wording for Synchronisation 3050 Identity, MCC, Simultaneous Transmission Set. 3052 5. Add definitions for CLUE-capable device and CLUE-enabled 3053 call, taken from the signaling draft. 3055 6. Update definitions of Capture Device, Media Consumer, Media 3056 Provider, Endpoint, MCU, MCC. 3058 7. Replace "middle box" with "MCU". 3060 8. Explicitly state there can also be Media Captures that are 3061 not included in a Capture Scene View. 3063 9. Explicitly state "A single Encoding Group MAY refer to 3064 encodings for different media types." 3066 10. In example 12.1.1 add axes and audio captures to the 3067 diagram, and describe placement of microphones. 3069 11. Add references to data model and signaling drafts. 3071 12. Split references into Normative and Informative sections. 3072 Add heading number for references section. 3074 Changes from 15 to 16: 3076 1. Remove Audio Channel Format attribute 3078 2. Add Audio Capture Sensitivity Pattern attribute 3080 3. Clarify audio spatial information regarding point of capture 3081 and point on line of capture. Area of capture does not apply 3082 to audio. 3084 4. Update section 12 example for new treatment of audio spatial 3085 information. 3087 5. Clean up wording of some definitions, and various places in 3088 sections 5 and 10. 3090 6. Remove individual encoding parameter paragraph from section 3091 9. 3093 7. Update Advertisement diagram. 3095 8. Update Acknowledgements. 3097 9. References to use cases and requirements now refer to RFCs. 3099 10. Minor editorial changes. 3101 Changes from 14 to 15: 3103 1. Add "=" and "<=" qualifiers to MaxCaptures attribute, and 3104 clarify the meaning regarding switched and composed MCC. 3106 2. Add section 7.3.3 Global Capture Scene Entry List, and a few 3107 other sentences elsewhere that refer to global CSE sets. 3109 3. Clarify: The Provider MUST be capable of encoding and sending 3110 all Captures (*that have an encoding group*) in a single 3111 Capture Scene Entry simultaneously. 3113 4. Add voice activated switching example in section 12. 3115 5. Change name of attributes Participant Info/Type to Person 3116 Info/Type. 3118 6. Clarify the Person Info/Type attributes have the same meaning 3119 regardless of whether or not the capture has a Presentation 3120 attribute. 3122 7. Update example section 12.1 to be consistent with the rest of 3123 the document, regarding MCC and capture attributes. 3125 8. State explicitly each CSE has a unique ID. 3127 Changes from 13 to 14: 3129 1. Fill in section for Security Considerations. 3131 2. Replace Role placeholder with Participant Information, 3132 Participant Type, and Scene Information attributes. 3134 3. Spatial information implies nothing about how constituent 3135 media captures are combined into a composed MCC. 3137 4. Clean up MCC example in Section 12.3.3. Clarify behavior of 3138 tiled and PIP display windows. Add audio. Add new open 3139 issue about associating incoming packets to original source 3140 capture. 3142 5. Remove editor's note and associated statement about RTP 3143 multiplexing at end of section 5. 3145 6. Remove editor's note and associated paragraph about 3146 overloading media channel with both CLUE and non-CLUE usage, 3147 in section 5. 3149 7. In section 10, clarify intent of media encodings conforming 3150 to SDP, even with multiple CLUE message exchanges. Remove 3151 associated editor's note. 3153 Changes from 12 to 13: 3155 1. Added the MCC concept including updates to existing sections 3156 to incorporate the MCC concept. New MCC attributes: 3157 MaxCaptures, SynchronisationID and Policy. 3159 2. Removed the "composed" and "switched" Capture attributes due 3160 to overlap with the MCC concept. 3162 3. Removed the "Scene-switch-policy" CSE attribute, replaced by 3163 MCC and SynchronisationID. 3165 4. Editorial enhancements including numbering of the Capture 3166 attribute sections, tables, figures etc. 3168 Changes from 11 to 12: 3170 1. Ticket #44. Remove note questioning about requiring a 3171 Consumer to send a Configure after receiving Advertisement. 3173 2. Ticket #43. Remove ability for consumer to choose value of 3174 attribute for scene-switch-policy. 3176 3. Ticket #36. Remove computational complexity parameter, 3177 MaxGroupPps, from Encoding Groups. 3179 4. Reword the Abstract and parts of sections 1 and 4 (now 5) 3180 based on Mary's suggestions as discussed on the list. Move 3181 part of the Introduction into a new section Overview & 3182 Motivation. 3184 5. Add diagram of an Advertisement, in the Overview of the 3185 Framework/Model section. 3187 6. Change Intended Status to Standards Track. 3189 7. Clean up RFC2119 keyword language. 3191 Changes from 10 to 11: 3193 1. Add description attribute to Media Capture and Capture Scene 3194 Entry. 3196 2. Remove contradiction and change the note about open issue 3197 regarding always responding to Advertisement with a Configure 3198 message. 3200 3. Update example section, to cleanup formatting and make the 3201 media capture attributes and encoding parameters consistent 3202 with the rest of the document. 3204 Changes from 09 to 10: 3206 1. Several minor clarifications such as about SDP usage, Media 3207 Captures, Configure message. 3209 2. Simultaneous Set can be expressed in terms of Capture Scene 3210 and Capture Scene Entry. 3212 3. Removed Area of Scene attribute. 3214 4. Add attributes from draft-groves-clue-capture-attr-01. 3216 5. Move some of the Media Capture attribute descriptions back 3217 into this document, but try to leave detailed syntax to the 3218 data model. Remove the OUTSOURCE sections, which are already 3219 incorporated into the data model document. 3221 Changes from 08 to 09: 3223 1. Use "document" instead of "memo". 3225 2. Add basic call flow sequence diagram to introduction. 3227 3. Add definitions for Advertisement and Configure messages. 3229 4. Add definitions for Capture and Provider. 3231 5. Update definition of Capture Scene. 3233 6. Update definition of Individual Encoding. 3235 7. Shorten definition of Media Capture and add key points in the 3236 Media Captures section. 3238 8. Reword a bit about capture scenes in overview. 3240 9. Reword about labeling Media Captures. 3242 10. Remove the Consumer Capability message. 3244 11. New example section heading for media provider behavior 3246 12. Clarifications in the Capture Scene section. 3248 13. Clarifications in the Simultaneous Transmission Set section. 3250 14. Capitalize defined terms. 3252 15. Move call flow example from introduction to overview section 3254 16. General editorial cleanup 3256 17. Add some editors' notes requesting input on issues 3257 18. Summarize some sections, and propose details be outsourced 3258 to other documents. 3260 Changes from 06 to 07: 3262 1. Ticket #9. Rename Axis of Capture Point attribute to Point 3263 on Line of Capture. Clarify the description of this 3264 attribute. 3266 2. Ticket #17. Add "capture encoding" definition. Use this new 3267 term throughout document as appropriate, replacing some usage 3268 of the terms "stream" and "encoding". 3270 3. Ticket #18. Add Max Capture Encodings media capture 3271 attribute. 3273 4. Add clarification that different capture scene entries are 3274 not necessarily mutually exclusive. 3276 Changes from 05 to 06: 3278 1. Capture scene description attribute is a list of text strings, 3279 each in a different language, rather than just a single string. 3281 2. Add new Axis of Capture Point attribute. 3283 3. Remove appendices A.1 through A.6. 3285 4. Clarify that the provider must use the same coordinate system 3286 with same scale and origin for all coordinates within the same 3287 capture scene. 3289 Changes from 04 to 05: 3291 1. Clarify limitations of "composed" attribute. 3293 2. Add new section "capture scene entry attributes" and add the 3294 attribute "scene-switch-policy". 3296 3. Add capture scene description attribute and description 3297 language attribute. 3299 4. Editorial changes to examples section for consistency with the 3300 rest of the document. 3302 Changes from 03 to 04: 3304 1. Remove sentence from overview - "This constitutes a significant 3305 change ..." 3307 2. Clarify a consumer can choose a subset of captures from a 3308 capture scene entry or a simultaneous set (in section "capture 3309 scene" and "consumer's choice..."). 3311 3. Reword first paragraph of Media Capture Attributes section. 3313 4. Clarify a stereo audio capture is different from two mono audio 3314 captures (description of audio channel format attribute). 3316 5. Clarify what it means when coordinate information is not 3317 specified for area of capture, point of capture, area of scene. 3319 6. Change the term "producer" to "provider" to be consistent (it 3320 was just in two places). 3322 7. Change name of "purpose" attribute to "content" and refer to 3323 RFC4796 for values. 3325 8. Clarify simultaneous sets are part of a provider advertisement, 3326 and apply across all capture scenes in the advertisement. 3328 9. Remove sentence about lip-sync between all media captures in a 3329 capture scene. 3331 10. Combine the concepts of "capture scene" and "capture set" 3332 into a single concept, using the term "capture scene" to 3333 replace the previous term "capture set", and eliminating the 3334 original separate capture scene concept. 3336 17. Normative References 3338 [I-D.ietf-clue-datachannel] 3339 Holmberg, C., "CLUE Protocol Data Channel", draft- 3340 ietf-clue-datachannel-00 (work in progress), March 3341 2014. 3343 [I-D.ietf-clue-data-model-schema] 3344 Presta, R., Romano, S P., "An XML Schema for the CLUE 3345 data model", draft-ietf-clue-data-model-schema-06 (work 3346 in progress), June 2014. 3348 [I-D.presta-clue-protocol] 3349 Presta, R. and S. Romano, "CLUE protocol", draft- 3350 prestaclue-protocol-04 (work in progress), May 2014. 3352 [I-D.ietf-clue-signaling] 3353 Kyzivat, P., Xiao, L., Groves, C., Hansen, R., "CLUE 3354 Signaling", draft-ietf-clue-signaling-03 (work in 3355 progress), August 2014. 3357 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3358 Requirement Levels", BCP 14, RFC 2119, March 1997. 3360 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., 3361 Johnston, 3362 A., Peterson, J., Sparks, R., Handley, M., and E. 3363 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 3364 June 2002. 3366 [RFC3264] Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model 3367 with the Session Description Protocol (SDP)", RFC 3264, 3368 June 2002. 3370 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 3371 Jacobson, "RTP: A Transport Protocol for Real-Time 3372 Applications", STD 64, RFC 3550, July 2003. 3374 [RFC4579] Johnston, A., Levin, O., "SIP Call Control - 3375 Conferencing for User Agents", RFC 4579, August 2006 3377 18. Informative References 3379 [RFC4353] Rosenberg, J., "A Framework for Conferencing with the 3380 Session Initiation Protocol (SIP)", RFC 4353, 3381 February 2006. 3383 [RFC5117] Westerlund, M. and S. Wenger, "RTP Topologies", RFC 3384 5117, January 2008. 3386 [RFC7205] Romanow, A., Botzko, S., Duckworth, M., Even, R., 3387 "Use Cases for Telepresence Multistreams", RFC 7205, 3388 April 2014. 3390 [RFC7262] Romanow, A., Botzko, S., Barnes, M., "Requirements 3391 for Telepresence Multistreams", RFC 7262, June 2014. 3393 19. Authors' Addresses 3395 Mark Duckworth (editor) 3396 Polycom 3397 Andover, MA 01810 3398 USA 3400 Email: mark.duckworth@polycom.com 3402 Andrew Pepperell 3403 Acano 3404 Uxbridge, England 3405 UK 3407 Email: apeppere@gmail.com 3409 Stephan Wenger 3410 Vidyo, Inc. 3411 433 Hackensack Ave. 3412 Hackensack, N.J. 07601 3413 USA 3415 Email: stewe@stewe.org