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CLUE WG                                               M. Duckworth, Ed.
Internet Draft                                                  Polycom
Intended status: Standards Track                           A. Pepperell
Expires: July 8, 2016                                             Acano
                                                              S. Wenger
                                                                  Vidyo
                                                        January 8, 2016



                Framework for Telepresence Multi-Streams
                    draft-ietf-clue-framework-25.txt


Abstract

   This document defines a framework for a protocol to enable devices
   in a telepresence conference to interoperate.  The protocol enables
   communication of information about multiple media streams so a
   sending system and receiving system can make reasonable decisions
   about transmitting, selecting and rendering the media streams.
   This protocol is used in addition to SIP signaling and SDP
   negotiation for setting up a telepresence session.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current
   Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
   documents at any time.  It is inappropriate to use Internet-Drafts
   as reference material or to cite them other than as "work in
   progress."

   This Internet-Draft will expire on July 8, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with
   respect to this document.  Code Components extracted from this
   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
   warranty as described in the Simplified BSD License.

Table of Contents




   1. Introduction...................................................3
   2. Terminology....................................................4
   3. Definitions....................................................4
   4. Overview and Motivation........................................7
   5. Description of the Framework/Model............................10
   6. Spatial Relationships.........................................15
   7. Media Captures and Capture Scenes.............................17
      7.1. Media Captures...........................................17
         7.1.1. Media Capture Attributes............................18
      7.2. Multiple Content Capture.................................24
         7.2.1. MCC Attributes......................................25
      7.3. Capture Scene............................................30
         7.3.1. Capture Scene attributes............................33
         7.3.2. Capture Scene View attributes.......................33
      7.4. Global View List.........................................34
   8. Simultaneous Transmission Set Constraints.....................35
   9. Encodings.....................................................37
      9.1. Individual Encodings.....................................37
      9.2. Encoding Group...........................................38
      9.3. Associating Captures with Encoding Groups................39
   10. Consumer's Choice of Streams to Receive from the Provider....40
      10.1. Local preference........................................43
      10.2. Physical simultaneity restrictions......................43
      10.3. Encoding and encoding group limits......................43
   11. Extensibility................................................44
   12. Examples - Using the Framework (Informative).................44
      12.1. Provider Behavior.......................................44
         12.1.1. Three screen Endpoint Provider.....................44
         12.1.2. Encoding Group Example.............................51
         12.1.3. The MCU Case.......................................52


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      12.2. Media Consumer Behavior.................................53
         12.2.1. One screen Media Consumer..........................53
         12.2.2. Two screen Media Consumer configuring the example..54
         12.2.3. Three screen Media Consumer configuring the example55
      12.3. Multipoint Conference utilizing Multiple Content Captures55
         12.3.1. Single Media Captures and MCC in the same
         Advertisement..............................................55
         12.3.2. Several MCCs in the same Advertisement.............59
         12.3.3. Heterogeneous conference with switching and
         composition................................................60
         12.3.4. Heterogeneous conference with voice activated
         switching..................................................67
   13. Acknowledgements.............................................70
   14. IANA Considerations..........................................70
   15. Security Considerations......................................70
   16. Changes Since Last Version...................................73
   17. Normative References.........................................81
   18. Informative References.......................................82
   19. Authors' Addresses...........................................83



1. Introduction

   Current telepresence systems, though based on open standards such
   as RTP [RFC3550] and SIP [RFC3261], cannot easily interoperate with
   each other.  A major factor limiting the interoperability of
   telepresence systems is the lack of a standardized way to describe
   and negotiate the use of multiple audio and video streams
   comprising the media flows.  This document provides a framework for
   protocols to enable interoperability by handling multiple streams
   in a standardized way.  The framework is intended to support the
   use cases described in Use Cases for Telepresence Multistreams
   [RFC7205] and to meet the requirements in Requirements for
   Telepresence Multistreams [RFC7262]. This includes cases using
   multiple media streams that are not necessarily telepresence.

   This document occasionally refers to the term "CLUE", in capital
   letters.  CLUE is an acronym for "ControLling mUltiple streams for
   tElepresence", which is the name of the IETF working group in which
   this document and certain companion documents have been developed.
   Often, CLUE-something refers to something that has been designed by
   the CLUE working group; for example, this document may be called
   the CLUE-framework.



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   The basic session setup for the use cases is based on SIP [RFC3261]
   and SDP offer/answer [RFC3264].  In addition to basic SIP & SDP
   offer/answer, CLUE specific signaling is required to exchange the
   information describing the multiple media streams.  The motivation
   for this framework, an overview of the signaling, and information
   required to be exchanged is described in subsequent sections of
   this document.  Companion documents describe the signaling details
   [I-D.ietf-clue-signaling] and the data model [I-D.ietf-clue-data-
   model-schema] and protocol [I-D.ietf-clue-protocol].





2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
   this document are to be interpreted as described in RFC 2119
   [RFC2119].

3. Definitions

   The terms defined below are used throughout this document and
   companion documents.  In order to easily identify the use of a
   defined term, those terms are capitalized.

   Advertisement: a CLUE message a Media Provider sends to a Media
   Consumer describing specific aspects of the content of the media,
   and any restrictions it has in terms of being able to provide
   certain Streams simultaneously.

   Audio Capture: Media Capture for audio.  Denoted as ACn in the
   examples in this document.

   Capture: Same as Media Capture.

   Capture Device: A device that converts physical input, such as
   audio, video or text, into an electrical signal, in most cases to
   be fed into a media encoder.

   Capture Encoding: A specific encoding of a Media Capture, to be
   sent by a Media Provider to a Media Consumer via RTP.




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   Capture Scene: a structure representing a spatial region captured
   by one or more Capture Devices, each capturing media representing a
   portion of the region. The spatial region represented by a Capture
   Scene may correspond to a real region in physical space, such as a
   room.  A Capture Scene includes attributes and one or more Capture
   Scene Views, with each view including one or more Media Captures.

   Capture Scene View (CSV): a list of Media Captures of the same
   media type that together form one way to represent the entire
   Capture Scene.

   CLUE-capable device: A device that supports the CLUE data channel
   [I-D.ietf-clue-datachannel], the CLUE protocol [I-D.ietf-clue-
   protocol] and the principles of CLUE negotiation, and seeks CLUE-
   enabled calls.

   CLUE-enabled call: A call in which two CLUE-capable devices have
   successfully negotiated support for a CLUE data channel in SDP
   [RFC4566]. A CLUE-enabled call is not necessarily immediately able
   to send CLUE-controlled media; negotiation of the data channel and
   of the CLUE protocol must complete first. Calls between two CLUE-
   capable devices which have not yet successfully completed
   negotiation of support for the CLUE data channel in SDP are not
   considered CLUE- enabled.

   Conference: used as defined in [RFC4353], A Framework for
   Conferencing within the Session Initiation Protocol (SIP).

   Configure Message: A CLUE message a Media Consumer sends to a Media
   Provider specifying which content and Media Streams it wants to
   receive, based on the information in a corresponding Advertisement
   message.

   Consumer: short for Media Consumer.

   Encoding: short for Individual Encoding.

   Encoding Group: A set of encoding parameters representing a total
   media encoding capability to be sub-divided across potentially
   multiple Individual Encodings.

   Endpoint: A CLUE-capable device which is the logical point of final
   termination through receiving, decoding and rendering, and/or
   initiation through capturing, encoding, and sending of media
   streams.  An endpoint consists of one or more physical devices


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   which source and sink media streams, and exactly one [RFC4353]
   Participant (which, in turn, includes exactly one SIP User Agent).
   Endpoints can be anything from multiscreen/multicamera rooms to
   handheld devices.

   Global View: A set of references to one or more Capture Scene Views
   of the same media type that are defined within Scenes of the same
   advertisement.  A Global View is a suggestion from the Provider to
   the Consumer for one set of CSVs that provide a useful
   representation of all the scenes in the advertisement.

   Global View List: A list of Global Views included in an
   Advertisement.  A Global View List may include Global Views of
   different media types.

   Individual Encoding: a set of parameters representing a way to
   encode a Media Capture to become a Capture Encoding.

   Multipoint Control Unit (MCU): a CLUE-capable device that connects
   two or more endpoints together into one single multimedia
   conference [RFC5117].  An MCU includes an [RFC4353]-like Mixer,
   without the [RFC4353] requirement to send media to each
   participant.

   Media: Any data that, after suitable encoding, can be conveyed over
   RTP, including audio, video or timed text.

   Media Capture: a source of Media, such as from one or more Capture
   Devices or constructed from other Media streams.

   Media Consumer: a CLUE-capable device that intends to receive
   Capture Encodings.

   Media Provider: a CLUE-capable device that intends to send Capture
   Encodings.

   Multiple Content Capture (MCC): A Capture that mixes and/or
   switches other Captures of a single type. (E.g. all audio or all
   video.) Particular Media Captures may or may not be present in the
   resultant Capture Encoding depending on time or space.  Denoted as
   MCCn in the example cases in this document.

   Plane of Interest: The spatial plane within a scene containing the
   most relevant subject matter.



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   Provider: Same as Media Provider.

   Render: the process of generating a representation from media, such
   as displayed motion video or sound emitted from loudspeakers.

   Scene: Same as Capture Scene

   Simultaneous Transmission Set: a set of Media Captures that can be
   transmitted simultaneously from a Media Provider.

   Single Media Capture: A capture which contains media from a single
   source capture device, e.g. an audio capture from a single
   microphone, a video capture from a single camera.

   Spatial Relation: The arrangement in space of two objects, in
   contrast to relation in time or other relationships.

   Stream: a Capture Encoding sent from a Media Provider to a Media
   Consumer via RTP [RFC3550].

   Stream Characteristics: the media stream attributes commonly used
   in non-CLUE SIP/SDP environments (such as: media codec, bit rate,
   resolution, profile/level etc.) as well as CLUE specific
   attributes, such as the Capture ID or a spatial location.

   Video Capture: Media Capture for video.  Denoted as VCn in the
   example cases in this document.

   Video Composite: A single image that is formed, normally by an RTP
   mixer inside an MCU, by combining visual elements from separate
   sources.

4. Overview and Motivation

   This section provides an overview of the functional elements
   defined in this document to represent a telepresence or
   multistream system.  The motivations for the framework described
   in this document are also provided.

   Two key concepts introduced in this document are the terms "Media
   Provider" and "Media Consumer". A Media Provider represents the
   entity that sends the media and a Media Consumer represents the
   entity that receives the media. A Media Provider provides Media in
   the form of RTP packets, a Media Consumer consumes those RTP
   packets.  Media Providers and Media Consumers can reside in


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   Endpoints or in Multipoint Control Units (MCUs).  A Media Provider
   in an Endpoint is usually associated with the generation of media
   for Media Captures; these Media Captures are typically sourced
   from cameras, microphones, and the like.  Similarly, the Media
   Consumer in an Endpoint is usually associated with renderers, such
   as screens and loudspeakers.  In MCUs, Media Providers and
   Consumers can have the form of outputs and inputs, respectively,
   of RTP mixers, RTP translators, and similar devices.  Typically,
   telepresence devices such as Endpoints and MCUs would perform as
   both Media Providers and Media Consumers, the former being
   concerned with those devices' transmitted media and the latter
   with those devices' received media.  In a few circumstances, a
   CLUE-capable device includes only Consumer or Provider
   functionality, such as recorder-type Consumers or webcam-type
   Providers.

   The motivations for the framework outlined in this document
   include the following:

   (1) Endpoints in telepresence systems typically have multiple Media
   Capture and Media Render devices, e.g., multiple cameras and
   screens. While previous system designs were able to set up calls
   that would capture media using all cameras and display media on all
   screens, for example, there was no mechanism that could associate
   these Media Captures with each other in space and time, in a cross-
   vendor interoperable way.

   (2) The mere fact that there are multiple capturing and rendering
   devices, each of which may be configurable in aspects such as zoom,
   leads to the difficulty that a variable number of such devices can
   be used to capture different aspects of a region.  The Capture
   Scene concept allows for the description of multiple setups for
   those multiple capture devices that could represent sensible
   operation points of the physical capture devices in a room, chosen
   by the operator.  A Consumer can pick and choose from those
   configurations based on its rendering abilities and inform the
   Provider about its choices.  Details are provided in section 7.

   (3) In some cases, physical limitations or other reasons disallow
   the concurrent use of a device in more than one setup.  For
   example, the center camera in a typical three-camera conference
   room can set its zoom objective either to capture only the middle
   few seats, or all seats of a room, but not both concurrently.  The
   Simultaneous Transmission Set concept allows a Provider to signal



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   such limitations.  Simultaneous Transmission Sets are part of the
   Capture Scene description, and are discussed in section 8.

   (4) Often, the devices in a room do not have the computational
   complexity or connectivity to deal with multiple encoding options
   simultaneously, even if each of these options is sensible in
   certain scenarios, and even if the simultaneous transmission is
   also sensible (i.e. in case of multicast media distribution to
   multiple endpoints).   Such constraints can be expressed by the
   Provider using the Encoding Group concept, described in section 9.

   (5) Due to the potentially large number of RTP streams required for
   a Multimedia Conference involving potentially many Endpoints, each
   of which can have many Media Captures and media renderers, it has
   become common to multiplex multiple RTP streams onto the same
   transport address, so to avoid using the port number as a
   multiplexing point and the associated shortcomings such as
   NAT/firewall traversal.  The large number of possible permutations
   of sensible options a Media Provider can make available to a Media
   Consumer makes a mechanism desirable that allows it to narrow down
   the number of possible options that a SIP offer/answer exchange has
   to consider.  Such information is made available using protocol
   mechanisms specified in this document and companion documents. The
   Media Provider and Media Consumer may use information in CLUE
   messages to reduce the complexity of SIP offer/answer messages.
   Also, there are aspects of the control of both Endpoints and MCUs
   that dynamically change during the progress of a call, such as
   audio-level based screen switching, layout changes, and so on,
   which need to be conveyed.  Note that these control aspects are
   complementary to those specified in traditional SIP based
   conference management such as BFCP.  An exemplary call flow can be
   found in section 5.

   Finally, all this information needs to be conveyed, and the notion
   of support for it needs to be established.  This is done by the
   negotiation of a "CLUE channel", a data channel negotiated early
   during the initiation of a call.  An Endpoint or MCU that rejects
   the establishment of this data channel, by definition, does not
   support CLUE based mechanisms, whereas an Endpoint or MCU that
   accepts it is indicating support for CLUE as specified in this
   document and its companion documents.






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5. Description of the Framework/Model

   The CLUE framework specifies how multiple media streams are to be
   handled in a telepresence conference.

   A Media Provider (transmitting Endpoint or MCU) describes specific
   aspects of the content of the media and the media stream encodings
   it can send in an Advertisement; and the Media Consumer responds to
   the Media Provider by specifying which content and media streams it
   wants to receive in a Configure message.  The Provider then
   transmits the asked-for content in the specified streams.

   This Advertisement and Configure typically occur during call
   initiation, after CLUE has been enabled in a call, but MAY also
   happen at any time throughout the call, whenever there is a change
   in what the Consumer wants to receive or (perhaps less common) the
   Provider can send.

   An Endpoint or MCU typically act as both Provider and Consumer at
   the same time, sending Advertisements and sending Configurations in
   response to receiving Advertisements.  (It is possible to be just
   one or the other.)

   The data model [I-D.ietf-clue-data-model-schema]is based around two
   main concepts: a Capture and an Encoding.  A Media Capture (MC),
   such as of type audio or video, has attributes to describe the
   content a Provider can send.  Media Captures are described in terms
   of CLUE-defined attributes, such as spatial relationships and
   purpose of the capture.  Providers tell Consumers which Media
   Captures they can provide, described in terms of the Media Capture
   attributes.

   A Provider organizes its Media Captures into one or more Capture
   Scenes, each representing a spatial region, such as a room.  A
   Consumer chooses which Media Captures it wants to receive from the
   Capture Scenes.

   In addition, the Provider can send the Consumer a description of
   the Individual Encodings it can send in terms of identifiers which
   relate to items in SDP [RFC4566].

   The Provider can also specify constraints on its ability to provide
   Media, and a sensible design choice for a Consumer is to take these
   into account when choosing the content and Capture Encodings it
   requests in the later offer/answer exchange.  Some constraints are


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   due to the physical limitations of devices--for example, a camera
   may not be able to provide zoom and non-zoom views simultaneously.
   Other constraints are system based, such as maximum bandwidth.

   The following diagram illustrates the information contained in an
   Advertisement.









































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   ...................................................................
   .  Provider Advertisement             +--------------------+      .
   .                                     | Simultaneous Sets  |      .
   .        +------------------------+   +--------------------+      .
   .        |       Capture Scene N  |   +--------------------+      .
   .      +-+----------------------+ |   | Global View List   |      .
   .      |       Capture Scene 2  | |   +--------------------+      .
   .    +-+----------------------+ | |      +----------------------+ .
   .    |  Capture Scene 1       | | |      |  Encoding Group N    | .
   .    |    +---------------+   | | |    +-+--------------------+ | .
   .    |    | Attributes    |   | | |    |   Encoding Group 2   | | .
   .    |    +---------------+   | | |  +-+--------------------+ | | .
   .    |                        | | |  |   Encoding Group 1   | | | .
   .    |    +----------------+  | | |  |     parameters       | | | .
   .    |    |  V i e w s     |  | | |  |      bandwidth       | | | .
   .    |    |  +---------+   |  | | |  | +-------------------+| | | .
   .    |    |  |Attribute|   |  | | |  | | V i d e o         || | | .
   .    |    |  +---------+   |  | | |  | | E n c o d i n g s || | | .
   .    |    |                |  | | |  | | Encoding 1        || | | .
   .    |    | View 1         |  | | |  | |                   || | | .
   .    |    |  (list of MCs) |  | |-+  | +-------------------+| | | .
   .    |    +----|-|--|------+  |-+    |                      | | | .
   .    +---------|-|--|---------+      | +-------------------+| | | .
   .              | |  |                | | A u d i o         || | | .
   .              | |  |                | | E n c o d i n g s || | | .
   .              v |  |                | | Encoding 1        || | | .
   .      +---------|--|--------+       | |                   || | | .
   .      | Media Capture N     |------>| +-------------------+| | | .
   .    +-+---------v--|------+ |       |                      | | | .
   .    | Media Capture 2     | |       |                      | |-+ .
   .  +-+--------------v----+ |-------->|                      | |   .
   .  | Media Capture  1    | | |       |                      |-+   .
   .  |  +----------------+ |---------->|                      |     .
   .  |  | Attributes     | | |_+       +----------------------+     .
   .  |  +----------------+ |_+                                      .
   .  +---------------------+                                        .
   .                                                                 .
   ...................................................................

                   Figure 1:   Advertisement Structure

   A very brief outline of the call flow used by a simple system (two
   Endpoints) in compliance with this document can be described as
   follows, and as shown in the following figure.



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         +-----------+                     +-----------+
         | Endpoint1 |                     | Endpoint2 |
         +----+------+                     +-----+-----+
              | INVITE (BASIC SDP+CLUECHANNEL)   |
              |--------------------------------->|
              |    200 0K (BASIC SDP+CLUECHANNEL)|
              |<---------------------------------|
              | ACK                              |
              |--------------------------------->|
              |                                  |
              |<################################>|
              |       BASIC MEDIA SESSION        |
              |<################################>|
              |                                  |
              |    CONNECT (CLUE CTRL CHANNEL)   |
              |=================================>|
              |            ...                   |
              |<================================>|
              |   CLUE CTRL CHANNEL ESTABLISHED  |
              |<================================>|
              |                                  |
              | ADVERTISEMENT 1                  |
              |*********************************>|
              |                  ADVERTISEMENT 2 |
              |<*********************************|
              |                                  |
              |                      CONFIGURE 1 |
              |<*********************************|
              | CONFIGURE 2                      |
              |*********************************>|
              |                                  |
              | REINVITE (UPDATED SDP)           |
              |--------------------------------->|
              |              200 0K (UPDATED SDP)|
              |<---------------------------------|
              | ACK                              |
              |--------------------------------->|
              |                                  |
              |<################################>|
              |     UPDATED MEDIA SESSION        |
              |<################################>|
              |                                  |
              v                                  v

                   Figure 2:   Basic Information Flow


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   An initial offer/answer exchange establishes a basic media session,
   for example audio-only, and a CLUE channel between two Endpoints.
   With the establishment of that channel, the endpoints have
   consented to use the CLUE protocol mechanisms and, therefore, MUST
   adhere to the CLUE protocol suite as outlined herein.

   Over this CLUE channel, the Provider in each Endpoint conveys its
   characteristics and capabilities by sending an Advertisement as
   specified herein.  The Advertisement is typically not sufficient to
   set up all media.  The Consumer in the Endpoint receives the
   information provided by the Provider, and can use it for several
   purposes.  It uses it, along with information from an offer/answer
   exchange, to construct a CLUE Configure message to tell the
   Provider what the Consumer wishes to receive.  Also, the Consumer
   may use the information provided to tailor the SDP it is going to
   send during any following SIP offer/answer exchange, and its
   reaction to SDP it receives in that step.  It is often a sensible
   implementation choice to do so.  Spatial relationships associated
   with the Media can be included in the Advertisement, and it is
   often sensible for the Media Consumer to take those spatial
   relationships into account when tailoring the SDP.  The Consumer
   can also limit the number of encodings it must set up resources to
   receive, and not waste resources on unwanted encodings, because it
   has the Provider's Advertisement information ahead of time to
   determine what it really wants to receive.  The Consumer can also
   use the Advertisement information for local rendering decisions.

   This initial CLUE exchange is followed by an SDP offer/answer
   exchange that not only establishes those aspects of the media that
   have not been "negotiated" over CLUE, but has also the effect of
   setting up the media transmission itself, involving potentially
   security exchanges, ICE, and whatnot.  This step is plain vanilla
   SIP.

   During the lifetime of a call, further exchanges MAY occur over the
   CLUE channel.  In some cases, those further exchanges lead to a
   modified system behavior of Provider or Consumer (or both) without
   any other protocol activity such as further offer/answer exchanges.
   For example, a Configure Message requesting the Provider to place a
   different Capture source into a Capture Encoding, signaled over the
   CLUE channel, ought not to lead to heavy-handed mechanisms like SIP
   re-invites.  However, in other cases, after the CLUE negotiation an
   additional offer/answer exchange becomes necessary.  For example,


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   if both sides decide to upgrade the call from a single screen to a
   multi-screen call and more bandwidth is required for the additional
   video channels compared to what was previously negotiated using
   offer/answer, a new O/A exchange is required.

   One aspect of the protocol outlined herein and specified in more
   detail in companion documents is that it makes available, to the
   Consumer, information regarding the Provider's capabilities to
   deliver Media, and attributes related to that Media such as their
   spatial relationship.  The operation of the renderer inside the
   Consumer is unspecified in that it can choose to ignore some
   information provided by the Provider, and/or not render media
   streams available from the Provider (although the Consumer follows
   the CLUE protocol and, therefore, gracefully receives and responds
   to the Provider's information using a Configure operation).

   A CLUE-capable device interoperates with a device that does not
   support CLUE.  The CLUE-capable device can determine, by the result
   of the initial offer/answer exchange, if the other device supports
   and wishes to use CLUE. The specific mechanism for this is
   described in [I-D.ietf-clue-signaling].  If the other device does
   not use CLUE, then the CLUE-capable device falls back to behavior
   that does not require CLUE.

   As for the media, Provider and Consumer have an end-to-end
   communication relationship with respect to (RTP transported) media;
   and the mechanisms described herein and in companion documents do
   not change the aspects of setting up those RTP flows and sessions.
   In other words, the RTP media sessions conform to the negotiated
   SDP whether or not CLUE is used.

6. Spatial Relationships

   In order for a Consumer to perform a proper rendering, it is often
   necessary or at least helpful for the Consumer to have received
   spatial information about the streams it is receiving.  CLUE
   defines a coordinate system that allows Media Providers to describe
   the spatial relationships of their Media Captures to enable proper
   scaling and spatially sensible rendering of their streams.  The
   coordinate system is based on a few principles:

   o  Each Capture Scene has a distinct coordinate system, unrelated
      to the coordinate systems of other scenes.




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   o  Simple systems which do not have multiple Media Captures to
      associate spatially need not use the coordinate model, although
      it can still be useful to provide an Area of Capture.

   o  Coordinates can be either in real, physical units (millimeters),
      have an unknown scale or have no physical scale.  Systems which
      know their physical dimensions (for example professionally
      installed Telepresence room systems) MUST provide those real-
      world measurements to enable the best user experience for
      advanced receiving systems that can utilize this information.
      Systems which don't know specific physical dimensions but still
      know relative distances MUST use 'unknown scale'.  'No scale' is
      intended to be used only where Media Captures from different
      devices (with potentially different scales) will be forwarded
      alongside one another (e.g. in the case of an MCU).

      *  "Millimeters" means the scale is in millimeters.

      *  "Unknown" means the scale is not necessarily millimeters, but
         the scale is the same for every Capture in the Capture Scene.

      *  "No Scale" means the scale could be different for each
         capture- an MCU Provider that advertises two adjacent
         captures and picks sources (which can change quickly) from
         different endpoints might use this value; the scale could be
         different and changing for each capture.  But the areas of
         capture still represent a spatial relation between captures.

   o  The coordinate system is right-handed Cartesian X, Y, Z with the
      origin at a spatial location of the Provider's choosing.  The
      Provider MUST use the same coordinate system with the same scale
      and origin for all coordinates within the same Capture Scene.

   The direction of increasing coordinate values is:
   X increases from left to right, from the point of view of an
   observer at the front of the room looking toward the back
   Y increases from the front of the room to the back of the room
   Z increases from low to high (i.e. floor to ceiling)

   Cameras in a scene typically point in the direction of increasing
   Y, from front to back.  But there could be multiple cameras
   pointing in different directions.  If the physical space does not
   have a well-defined front and back, the provider chooses any
   direction for X and Y and Z consistent with right-handed
   coordinates.


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7. Media Captures and Capture Scenes

   This section describes how Providers can describe the content of
   media to Consumers.

7.1. Media Captures

   Media Captures are the fundamental representations of streams that
   a device can transmit.  What a Media Capture actually represents is
   flexible:

   o  It can represent the immediate output of a physical source (e.g.
      camera, microphone) or 'synthetic' source (e.g. laptop computer,
      DVD player)

   o  It can represent the output of an audio mixer or video composer

   o  It can represent a concept such as 'the loudest speaker'

   o  It can represent a conceptual position such as 'the leftmost
      stream'

   To identify and distinguish between multiple Capture instances
   Captures have a unique identity.  For instance: VC1, VC2 and AC1,
   AC2, where VC1 and VC2 refer to two different video captures and
   AC1 and AC2 refer to two different audio captures.

   Some key points about Media Captures:

     . A Media Capture is of a single media type (e.g. audio or
        video)
     . A Media Capture is defined in a Capture Scene and is given an
        Advertisement unique identity.  The identity may be referenced
        outside the Capture Scene that defines it through a Multiple
        Content Capture (MCC)
     . A Media Capture may be associated with one or more Capture
        Scene Views
     . A Media Capture has exactly one set of spatial information
     . A Media Capture can be the source of at most one Capture
        Encoding

   Each Media Capture can be associated with attributes to describe
   what it represents.




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7.1.1. Media Capture Attributes

   Media Capture Attributes describe information about the Captures.
   A Provider can use the Media Capture Attributes to describe the
   Captures for the benefit of the Consumer of the Advertisement
   message.  All these attributes are optional.  Media Capture
   Attributes include:

     . Spatial information, such as point of capture, point on line
        of capture, and area of capture, all of which, in combination
        define the capture field of, for example, a camera
     . Other descriptive information to help the Consumer choose
        between captures (e.g. description, presentation, view,
        priority, language, person information and type)

   The sub-sections below define the Capture attributes.

7.1.1.1. Point of Capture

   The Point of Capture attribute is a field with a single Cartesian
   (X, Y, Z) point value which describes the spatial location of the
   capturing device (such as camera).  For an Audio Capture with
   multiple microphones, the Point of Capture defines the nominal mid-
   point of the microphones.

7.1.1.2. Point on Line of Capture

   The Point on Line of Capture attribute is a field with a single
   Cartesian (X, Y, Z) point value which describes a position in space
   of a second point on the axis of the capturing device, toward the
   direction it is pointing; the first point being the Point of
   Capture (see above).

   Together, the Point of Capture and Point on Line of Capture define
   the direction and axis of the capturing device, for example the
   optical axis of a camera or the axis of a microphone.  The Media
   Consumer can use this information to adjust how it renders the
   received media if it so chooses.

   For an Audio Capture, the Media Consumer can use this information
   along with the Audio Capture Sensitivity Pattern to define a 3-
   dimensional volume of capture where sounds can be expected to be
   picked up by the microphone providing this specific audio capture.
   If the Consumer wants to associate an Audio Capture with a Video
   Capture, it can compare this volume with the area of capture for


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   video media to provide a check on whether the audio capture is
   indeed spatially associated with the video capture. For example, a
   video area of capture that fails to intersect at all with the audio
   volume of capture, or is at such a long radial distance from the
   microphone point of capture that the audio level would be very low,
   would be inappropriate.

7.1.1.3. Area of Capture

   The Area of Capture is a field with a set of four (X, Y, Z) points
   as a value which describes the spatial location of what is being
   "captured".  This attribute applies only to video captures, not
   other types of media. By comparing the Area of Capture for
   different Video Captures within the same Capture Scene a Consumer
   can determine the spatial relationships between them and render
   them correctly.

   The four points MUST be co-planar, forming a quadrilateral, which
   defines the Plane of Interest for the particular Media Capture.

   If the Area of Capture is not specified, it means the Video Capture
   might be spatially related to other Captures in the same Scene, but
   there is no detailed information on the relationship.For a switched
   Capture that switches between different sections within a larger
   area, the area of capture MUST use coordinates for the larger
   potential area.

7.1.1.4. Mobility of Capture

   The Mobility of Capture attribute indicates whether or not the
   point of capture, line on point of capture, and area of capture
   values stay the same over time, or are expected to change
   (potentially frequently).  Possible values are static, dynamic, and
   highly dynamic.

   An example for "dynamic" is a camera mounted on a stand which is
   occasionally hand-carried and placed at different positions in
   order to provide the best angle to capture a work task.  A camera
   worn by a person who moves around the room is an example for
   "highly dynamic". In either case, the effect is that the capture
   point, capture axis and area of capture change with time.

   The capture point of a static Capture MUST NOT move for the life of
   the CLUE session. The capture point of dynamic Captures is
   categorized by a change in position followed by a reasonable period


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   of stability--in the order of magnitude of minutes. Highly dynamic
   captures are categorized by a capture point that is constantly
   moving.  If the "area of capture", "capture point" and "line of
   capture" attributes are included with dynamic or highly dynamic
   Captures they indicate spatial information at the time of the
   Advertisement.

7.1.1.5. Audio Capture Sensitivity Pattern

   The Audio Capture Sensitivity Pattern attribute applies only to
   audio captures.  This attribute gives information about the nominal
   sensitivity pattern of the microphone which is the source of the
   Capture.  Possible values include patterns such as omni, shotgun,
   cardioid, hyper-cardioid.

7.1.1.6. Description

   The Description attribute is a human-readable description (which
   could be in multiple languages) of the Capture.

7.1.1.7. Presentation

   The Presentation attribute indicates that the capture originates
   from a presentation device, that is one that provides supplementary
   information to a conference through slides, video, still images,
   data etc.  Where more information is known about the capture it MAY
   be expanded hierarchically to indicate the different types of
   presentation media, e.g. presentation.slides, presentation.image
   etc.

   Note: It is expected that a number of keywords will be defined that
   provide more detail on the type of presentation. Refer to [I-
   D.ietf-clue-data-model-schema] for how to extend the model.

7.1.1.8. View

   The View attribute is a field with enumerated values, indicating
   what type of view the Capture relates to.  The Consumer can use
   this information to help choose which Media Captures it wishes to
   receive.  Possible values are:

   Room - Captures the entire scene

   Table - Captures the conference table with seated people



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   Individual - Captures an individual person

   Lectern - Captures the region of the lectern including the
   presenter, for example in a classroom style conference room

   Audience - Captures a region showing the audience in a classroom
   style conference room

7.1.1.9. Language

   The Language attribute indicates one or more languages used in the
   content of the Media Capture.  Captures MAY be offered in different
   languages in case of multilingual and/or accessible conferences.  A
   Consumer can use this attribute to differentiate between them and
   pick the appropriate one.

   Note that the Language attribute is defined and meaningful both for
   audio and video captures.  In case of audio captures, the meaning
   is obvious.  For a video capture, "Language" could, for example, be
   sign interpretation or text.

   The Language attribute is coded per [RFC5646].

7.1.1.10. Person Information

   The Person Information attribute allows a Provider to provide
   specific information regarding the people in a Capture (regardless
   of whether or not the capture has a Presentation attribute). The
   Provider may gather the information automatically or manually from
   a variety of sources however the xCard [RFC6351] format is used to
   convey the information. This allows various information such as
   Identification information (section 6.2/[RFC6350]), Communication
   Information (section 6.4/[RFC6350]) and Organizational information
   (section 6.6/[RFC6350]) to be communicated. A Consumer may then
   automatically (i.e. via a policy) or manually select Captures
   based on information about who is in a Capture. It also allows a
   Consumer to render information regarding the people participating
   in the conference or to use it for further processing.

   The Provider may supply a minimal set of information or a larger
   set of information. However it MUST be compliant to [RFC6350] and
   supply a "VERSION" and "FN" property. A Provider may supply
   multiple xCards per Capture of any KIND (section 6.1.4/[RFC6350]).




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   In order to keep CLUE messages compact the Provider SHOULD use a
   URI to point to any LOGO, PHOTO or SOUND contained in the xCARD
   rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE
   message.

7.1.1.11. Person Type

   The Person Type attribute indicates the type of people contained in
   the capture with respect to the meeting agenda (regardless of
   whether or not the capture has a Presentation attribute). As a
   capture may include multiple people the attribute may contain
   multiple values. However values MUST NOT be repeated within the
   attribute.

   An Advertiser associates the person type with an individual capture
   when it knows that a particular type is in the capture. If an
   Advertiser cannot link a particular type with some certainty to a
   capture then it is not included. A Consumer on reception of a
   capture with a person type attribute knows with some certainly that
   the capture contains that person type. The capture may contain
   other person types but the Advertiser has not been able to
   determine that this is the case.

   The types of Captured people include:

     . Chair - the person responsible for running the meeting
        according to the agenda.
     . Vice-Chair - the person responsible for assisting the chair in
        running the meeting.
     . Minute Taker - the person responsible for recording the
        minutes of the meeting.
     . Attendee - the person has no particular responsibilities with
        respect to running the meeting.
     . Observer - an Attendee without the right to influence the
        discussion.
     . Presenter - the person is scheduled on the agenda to make a
        presentation in the meeting. Note: This is not related to any
        "active speaker" functionality.
     . Translator - the person is providing some form of translation
        or commentary in the meeting.
     . Timekeeper - the person is responsible for maintaining the
        meeting schedule.





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   Furthermore the person type attribute may contain one or more
   strings allowing the Provider to indicate custom meeting specific
   types.

7.1.1.12. Priority

   The Priority attribute indicates a relative priority between
   different Media Captures.  The Provider sets this priority, and the
   Consumer MAY use the priority to help decide which Captures it
   wishes to receive.

   The "priority" attribute is an integer which indicates a relative
   priority between Captures. For example it is possible to assign a
   priority between two presentation Captures that would allow a
   remote Endpoint to determine which presentation is more important.
   Priority is assigned at the individual Capture level. It represents
   the Provider's view of the relative priority between Captures with
   a priority. The same priority number MAY be used across multiple
   Captures. It indicates they are equally important. If no priority
   is assigned no assumptions regarding relative importance of the
   Capture can be assumed.

7.1.1.13. Embedded Text

   The Embedded Text attribute indicates that a Capture provides
   embedded textual information. For example the video Capture may
   contain speech to text information composed with the video image.

7.1.1.14. Related To

   The Related To attribute indicates the Capture contains additional
   complementary information related to another Capture.  The value
   indicates the identity of the other Capture to which this Capture
   is providing additional information.

   For example, a conference can utilize translators or facilitators
   that provide an additional audio stream (i.e. a translation or
   description or commentary of the conference).  Where multiple
   captures are available, it may be advantageous for a Consumer to
   select a complementary Capture instead of or in addition to a
   Capture it relates to.






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7.2. Multiple Content Capture

   The MCC indicates that one or more Single Media Captures are
   multiplexed (temporally and/or spatially) or mixed in one Media
   Capture.  Only one Capture type (i.e. audio, video, etc.) is
   allowed in each MCC instance.  The MCC may contain a reference to
   the Single Media Captures (which may have their own attributes) as
   well as attributes associated with the MCC itself.  A MCC may also
   contain other MCCs.  The MCC MAY reference Captures from within the
   Capture Scene that defines it or from other Capture Scenes.  No
   ordering is implied by the order that Captures appear within a MCC.
   A MCC MAY contain no references to other Captures to indicate that
   the MCC contains content from multiple sources but no information
   regarding those sources is given. MCCs either contain the
   referenced Captures and no others, or have no referenced captures
   and therefore may contain any Capture.

   One or more MCCs may also be specified in a CSV.  This allows an
   Advertiser to indicate that several MCC captures are used to
   represent a capture scene.  Table 14 provides an example of this
   case.

   As outlined in section 7.1. each instance of the MCC has its own
   Capture identity i.e. MCC1. It allows all the individual captures
   contained in the MCC to be referenced by a single MCC identity.

   The example below shows the use of a Multiple Content Capture:

        +-----------------------+---------------------------------+
        | Capture Scene #1      |                                 |
        +-----------------------|---------------------------------+
        | VC1                   | {MC attributes}                 |
        | VC2                   | {MC attributes}                 |
        | VC3                   | {MC attributes}                 |
        | MCC1(VC1,VC2,VC3)     | {MC and MCC attributes}         |
        | CSV(MCC1)             |                                 |
        +---------------------------------------------------------+

                Table 1: Multiple Content Capture concept

   This indicates that MCC1 is a single capture that contains the
   Captures VC1, VC2 and VC3 according to any MCC1 attributes.





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7.2.1. MCC Attributes

   Media Capture Attributes may be associated with the MCC instance
   and the Single Media Captures that the MCC references.  A Provider
   should avoid providing conflicting attribute values between the MCC
   and Single Media Captures. Where there is conflict the attributes
   of the MCC override any that may be present in the individual
   Captures.

   A Provider MAY include as much or as little of the original source
   Capture information as it requires.

   There are MCC specific attributes that MUST only be used with
   Multiple Content Captures. These are described in the sections
   below. The attributes described in section 7.1.1. MAY also be used
   with MCCs.

   The spatial related attributes of an MCC indicate its area of
   capture and point of capture within the scene, just like any other
   media capture.  The spatial information does not imply anything
   about how other captures are composed within an MCC.

   For example:  A virtual scene could be constructed for the MCC
   capture with two Video Captures with a "MaxCaptures" attribute set
   to 2 and an "Area of Capture" attribute provided with an overall
   area.  Each of the individual Captures could then also include an
   "Area of Capture" attribute with a sub-set of the overall area.
   The Consumer would then know how each capture is related to others
   within the scene, but not the relative position of the individual
   captures within the composed capture.

        +-----------------------+---------------------------------+
        | Capture Scene #1      |                                 |
        +-----------------------|---------------------------------+
        | VC1                   | AreaofCapture=(0,0,0)(9,0,0)    |
        |                       |               (0,0,9)(9,0,9)    |
        | VC2                   | AreaofCapture=(10,0,0)(19,0,0)  |
        |                       |               (10,0,9)(19,0,9)  |
        | MCC1(VC1,VC2)         | MaxCaptures=2                   |
        |                       | AreaofCapture=(0,0,0)(19,0,0)   |
        |                       |               (0,0,9)(19,0,9)   |
        | CSV(MCC1)             |                                 |
        +---------------------------------------------------------+

        Table 2: Example of MCC and Single Media Capture attributes


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   The sub-sections below describe the MCC only attributes.

7.2.1.1. Maximum Number of Captures within a MCC

   The Maximum Number of Captures MCC attribute indicates the maximum
   number of individual Captures that may appear in a Capture Encoding
   at a time.  The actual number at any given time can be less than or
   equal to this maximum.  It may be used to derive how the Single
   Media Captures within the MCC are composed / switched with regards
   to space and time.

   A Provider can indicate that the number of Captures in a MCC
   Capture Encoding is equal "=" to the MaxCaptures value or that
   there may be any number of Captures up to and including "<=" the
   MaxCaptures value. This allows a Provider to distinguish between a
   MCC that purely represents a composition of sources versus a MCC
   that represents switched or switched and composed sources.

   MaxCaptures may be set to one so that only content related to one
   of the sources are shown in the MCC Capture Encoding at a time or
   it may be set to any value up to the total number of Source Media
   Captures in the MCC.

   The bullets below describe how the setting of MaxCapture versus the
   number of Captures in the MCC affects how sources appear in a
   Capture Encoding:

     . When MaxCaptures is set to <= 1 and the number of Captures in
        the MCC is greater than 1 (or not specified) in the MCC this
        is a switched case. Zero or 1 Captures may be switched into
        the Capture Encoding. Note: zero is allowed because of the
        "<=".
     . When MaxCaptures is set to = 1 and the number of Captures in
        the MCC is greater than 1 (or not specified) in the MCC this
        is a switched case. Only one Capture source is contained in a
        Capture Encoding at a time.
     . When MaxCaptures is set to <= N (with N > 1) and the number of
        Captures in the MCC is greater than N (or not specified) this
        is a switched and composed case. The Capture Encoding may
        contain purely switched sources (i.e. <=2 allows for 1 source
        on its own), or may contain composed and switched sources
        (i.e. a composition of 2 sources switched between the
        sources).
     . When MaxCaptures is set to = N (with N > 1) and the number of
        Captures in the MCC is greater than N (or not specified) this


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        is a switched and composed case. The Capture Encoding contains
        composed and switched sources (i.e. a composition of N sources
        switched between the sources). It is not possible to have a
        single source.
     . When MaxCaptures is set to <= to the number of Captures in the
        MCC this is a switched and composed case. The Capture Encoding
        may contain media switched between any number (up to the
        MaxCaptures) of composed sources.
     . When MaxCaptures is set to = to the number of Captures in the
        MCC this is a composed case. All the sources are composed into
        a single Capture Encoding.

   If this attribute is not set then as default it is assumed that all
   source media capture content can appear concurrently in the Capture
   Encoding associated with the MCC.

   For example: The use of MaxCaptures equal to 1 on a MCC with three
   Video Captures VC1, VC2 and VC3 would indicate that the Advertiser
   in the Capture Encoding would switch between VC1, VC2 or VC3 as
   there may be only a maximum of one Capture at a time.

7.2.1.2. Policy

   The Policy MCC Attribute indicates the criteria that the Provider
   uses to determine when and/or where media content appears in the
   Capture Encoding related to the MCC.

   The attribute is in the form of a token that indicates the policy
   and an index representing an instance of the policy.  The same
   index value can be used for multiple MCCs.

   The tokens are:

   SoundLevel - This indicates that the content of the MCC is
   determined by a sound level detection algorithm. The loudest
   (active) speaker (or a previous speaker, depending on the index
   value) is contained in the MCC.

   RoundRobin - This indicates that the content of the MCC is
   determined by a time based algorithm. For example: the Provider
   provides content from a particular source for a period of time and
   then provides content from another source and so on.

   An index is used to represent an instance in the policy setting. An
   index of 0 represents the most current instance of the policy, i.e.


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   the active speaker, 1 represents the previous instance, i.e. the
   previous active speaker and so on.

   The following example shows a case where the Provider provides two
   media streams, one showing the active speaker and a second stream
   showing the previous speaker.

        +-----------------------+---------------------------------+
        | Capture Scene #1      |                                 |
        +-----------------------|---------------------------------+
        | VC1                   |                                 |
        | VC2                   |                                 |
        | MCC1(VC1,VC2)         | Policy=SoundLevel:0             |
        |                       | MaxCaptures=1                   |
        | MCC2(VC1,VC2)         | Policy=SoundLevel:1             |
        |                       | MaxCaptures=1                   |
        | CSV(MCC1,MCC2)        |                                 |
        +---------------------------------------------------------+

                Table 3: Example Policy MCC attribute usage

7.2.1.3. Synchronisation Identity

   The Synchronisation Identity MCC attribute indicates how the
   individual Captures in multiple MCC Captures are synchronised.  To
   indicate that the Capture Encodings associated with MCCs contain
   Captures from the same source at the same time a Provider should
   set the same Synchronisation Identity on each of the concerned
   MCCs.  It is the Provider that determines what the source for the
   Captures is, so a Provider can choose how to group together Single
   Media Captures into a combined "source" for the purpose of
   switching them together to keep them synchronized according to the
   SynchronisationID attribute.  For example when the Provider is in
   an MCU it may determine that each separate CLUE Endpoint is a
   remote source of media. The Synchronisation Identity may be used
   across media types, i.e. to synchronize audio and video related
   MCCs.

   Without this attribute it is assumed that multiple MCCs may provide
   content from different sources at any particular point in time.

   For example:





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        +=======================+=================================+
        | Capture Scene #1      |                                 |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Left                |
        | VC2                   | Description=Centre              |
        | VC3                   | Description=Right               |
        | AC1                   | Description=Room                |
        | CSV(VC1,VC2,VC3)      |                                 |
        | CSV(AC1)              |                                 |
        +=======================+=================================+
        | Capture Scene #2      |                                 |
        +-----------------------|---------------------------------+
        | VC4                   | Description=Left                |
        | VC5                   | Description=Centre              |
        | VC6                   | Description=Right               |
        | AC2                   | Description=Room                |
        | CSV(VC4,VC5,VC6)      |                                 |
        | CSV(AC2)              |                                 |
        +=======================+=================================+
        | Capture Scene #3      |                                 |
        +-----------------------|---------------------------------+
        | VC7                   |                                 |
        | AC3                   |                                 |
        +=======================+=================================+
        | Capture Scene #4      |                                 |
        +-----------------------|---------------------------------+
        | VC8                   |                                 |
        | AC4                   |                                 |
        +=======================+=================================+
        | Capture Scene #5      |                                 |
        +-----------------------|---------------------------------+
        | MCC1(VC1,VC4,VC7)     | SynchronisationID=1             |
        |                       | MaxCaptures=1                   |
        | MCC2(VC2,VC5,VC8)     | SynchronisationID=1             |
        |                       | MaxCaptures=1                   |
        | MCC3(VC3,VC6)         | MaxCaptures=1                   |
        | MCC4(AC1,AC2,AC3,AC4) | SynchronisationID=1             |
        |                       | MaxCaptures=1                   |
        | CSV(MCC1,MCC2,MCC3)   |                                 |
        | CSV(MCC4)             |                                 |
        +=======================+=================================+

       Table 4: Example Synchronisation Identity MCC attribute usage




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   The above Advertisement would indicate that MCC1, MCC2, MCC3 and
   MCC4 make up a Capture Scene.  There would be four Capture
   Encodings (one for each MCC).  Because MCC1 and MCC2 have the same
   SynchronisationID, each Encoding from MCC1 and MCC2 respectively
   would together have content from only Capture Scene 1 or only
   Capture Scene 2 or the combination of VC7 and VC8 at a particular
   point in time.  In this case the Provider has decided the sources
   to be synchronized are Scene #1, Scene #2, and Scene #3 and #4
   together. The Encoding from MCC3 would not be synchronised with
   MCC1 or MCC2. As MCC4 also has the same Synchronisation Identity
   as MCC1 and MCC2 the content of the audio Encoding will be
   synchronised with the video content.

7.2.1.4. Allow Subset Choice

   The Allow Subset Choice MCC attribute is a boolean value,
   indicating whether or not the Provider allows the Consumer to
   choose a specific subset of the Captures referenced by the MCC.
   If this attribute is true, and the MCC references other Captures,
   then the Consumer MAY select (in a Configure message) a specific
   subset of those Captures to be included in the MCC, and the
   Provider MUST then include only that subset.  If this attribute is
   false, or the MCC does not reference other Captures, then the
   Consumer MUST NOT select a subset.

7.3. Capture Scene

   In order for a Provider's individual Captures to be used
   effectively by a Consumer, the Provider organizes the Captures into
   one or more Capture Scenes, with the structure and contents of
   these Capture Scenes being sent from the Provider to the Consumer
   in the Advertisement.

   A Capture Scene is a structure representing a spatial region
   containing one or more Capture Devices, each capturing media
   representing a portion of the region.  A Capture Scene includes one
   or more Capture Scene Views (CSV), with each CSV including one or
   more Media Captures of the same media type.  There can also be
   Media Captures that are not included in a Capture Scene View. A
   Capture Scene represents, for example, the video image of a group
   of people seated next to each other, along with the sound of their
   voices, which could be represented by some number of VCs and ACs in
   the Capture Scene Views.  An MCU can also describe in Capture
   Scenes what it constructs from media Streams it receives.



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   A Provider MAY advertise one or more Capture Scenes.  What
   constitutes an entire Capture Scene is up to the Provider.  A
   simple Provider might typically use one Capture Scene for
   participant media (live video from the room cameras) and another
   Capture Scene for a computer generated presentation.  In more
   complex systems, the use of additional Capture Scenes is also
   sensible.  For example, a classroom may advertise two Capture
   Scenes involving live video, one including only the camera
   capturing the instructor (and associated audio), the other
   including camera(s) capturing students (and associated audio).

   A Capture Scene MAY (and typically will) include more than one type
   of media.  For example, a Capture Scene can include several Capture
   Scene Views for Video Captures, and several Capture Scene Views for
   Audio Captures.  A particular Capture MAY be included in more than
   one Capture Scene View.

   A Provider MAY express spatial relationships between Captures that
   are included in the same Capture Scene.  However, there is no
   spatial relationship between Media Captures from different Capture
   Scenes.  In other words, Capture Scenes each use their own spatial
   measurement system as outlined above in section 6.

   A Provider arranges Captures in a Capture Scene to help the
   Consumer choose which captures it wants to render.  The Capture
   Scene Views in a Capture Scene are different alternatives the
   Provider is suggesting for representing the Capture Scene.  Each
   Capture Scene View is given an advertisement unique identity.  The
   order of Capture Scene Views within a Capture Scene has no
   significance.  The Media Consumer can choose to receive all Media
   Captures from one Capture Scene View for each media type (e.g.
   audio and video), or it can pick and choose Media Captures
   regardless of how the Provider arranges them in Capture Scene
   Views.  Different Capture Scene Views of the same media type are
   not necessarily mutually exclusive alternatives.  Also note that
   the presence of multiple Capture Scene Views (with potentially
   multiple encoding options in each view) in a given Capture Scene
   does not necessarily imply that a Provider is able to serve all the
   associated media simultaneously (although the construction of such
   an over-rich Capture Scene is probably not sensible in many cases).
   What a Provider can send simultaneously is determined through the
   Simultaneous Transmission Set mechanism, described in section 8.

   Captures within the same Capture Scene View MUST be of the same
   media type - it is not possible to mix audio and video captures in


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   the same Capture Scene View, for instance.  The Provider MUST be
   capable of encoding and sending all Captures (that have an encoding
   group) in a single Capture Scene View simultaneously.  The order of
   Captures within a Capture Scene View has no significance.  A
   Consumer can decide to receive all the Captures in a single Capture
   Scene View, but a Consumer could also decide to receive just a
   subset of those captures.  A Consumer can also decide to receive
   Captures from different Capture Scene Views, all subject to the
   constraints set by Simultaneous Transmission Sets, as discussed in
   section 8.

   When a Provider advertises a Capture Scene with multiple CSVs, it
   is essentially signaling that there are multiple representations of
   the same Capture Scene available.  In some cases, these multiple
   views would be used simultaneously (for instance a "video view" and
   an "audio view").  In some cases the views would conceptually be
   alternatives (for instance a view consisting of three Video
   Captures covering the whole room versus a view consisting of just a
   single Video Capture covering only the center of a room).  In this
   latter example, one sensible choice for a Consumer would be to
   indicate (through its Configure and possibly through an additional
   offer/answer exchange) the Captures of that Capture Scene View that
   most closely matched the Consumer's number of display devices or
   screen layout.

   The following is an example of 4 potential Capture Scene Views for
   an endpoint-style Provider:

   1.  (VC0, VC1, VC2) - left, center and right camera Video Captures

   2.  (MCC3) - Video Capture associated with loudest room segment

   3.  (VC4) - Video Capture zoomed out view of all people in the room

   4.  (AC0) - main audio

   The first view in this Capture Scene example is a list of Video
   Captures which have a spatial relationship to each other.
   Determination of the order of these captures (VC0, VC1 and VC2) for
   rendering purposes is accomplished through use of their Area of
   Capture attributes.  The second view (MCC3) and the third view
   (VC4) are alternative representations of the same room's video,
   which might be better suited to some Consumers' rendering
   capabilities.  The inclusion of the Audio Capture in the same
   Capture Scene indicates that AC0 is associated with all of those


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   Video Captures, meaning it comes from the same spatial region.
   Therefore, if audio were to be rendered at all, this audio would be
   the correct choice irrespective of which Video Captures were
   chosen.

7.3.1. Capture Scene attributes

   Capture Scene Attributes can be applied to Capture Scenes as well
   as to individual media captures.  Attributes specified at this
   level apply to all constituent Captures.  Capture Scene attributes
   include

     . Human-readable description of the Capture Scene, which could
        be in multiple languages;
     . xCard scene information
     . Scale information (millimeters, unknown, no scale), as
        described in Section 6.

7.3.1.1. Scene Information

   The Scene information attribute provides information regarding the
   Capture Scene rather than individual participants. The Provider
   may gather the information automatically or manually from a
   variety of sources. The scene information attribute allows a
   Provider to indicate information such as: organizational or
   geographic information allowing a Consumer to determine which
   Capture Scenes are of interest in order to then perform Capture
   selection. It also allows a Consumer to render information
   regarding the Scene or to use it for further processing.

   As per 7.1.1.10. the xCard format is used to convey this
   information and the Provider may supply a minimal set of
   information or a larger set of information.

   In order to keep CLUE messages compact the Provider SHOULD use a
   URI to point to any LOGO, PHOTO or SOUND contained in the xCARD
   rather than transmitting the LOGO, PHOTO or SOUND data in a CLUE
   message.

7.3.2. Capture Scene View attributes

   A Capture Scene can include one or more Capture Scene Views in
   addition to the Capture Scene wide attributes described above.
   Capture Scene View attributes apply to the Capture Scene View as a



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   whole, i.e. to all Captures that are part of the Capture Scene
   View.

   Capture Scene View attributes include:

     . Human-readable description (which could be in multiple
        languages) of the Capture Scene View

7.4. Global View List

   An Advertisement can include an optional Global View list.  Each
   item in this list is a Global View.  The Provider can include
   multiple Global Views, to allow a Consumer to choose sets of
   captures appropriate to its capabilities or application.  The
   choice of how to make these suggestions in the Global View list
   for what represents all the scenes for which the Provider can send
   media is up to the Provider.  This is very similar to how each CSV
   represents a particular scene.

   As an example, suppose an advertisement has three scenes, and each
   scene has three CSVs, ranging from one to three video captures in
   each CSV.  The Provider is advertising a total of nine video
   Captures across three scenes.  The Provider can use the Global
   View list to suggest alternatives for Consumers that can't receive
   all nine video Captures as separate media streams.  For
   accommodating a Consumer that wants to receive three video
   Captures, a Provider might suggest a Global View containing just a
   single CSV with three Captures and nothing from the other two
   scenes.  Or a Provider might suggest a Global View containing
   three different CSVs, one from each scene, with a single video
   Capture in each.

   Some additional rules:

     . The ordering of Global Views in the Global View list is
        insignificant.
     . The ordering of CSVs within each Global View is
        insignificant.
     . A particular CSV may be used in multiple Global Views.
     . The Provider must be capable of encoding and sending all
        Captures within the CSVs of a given Global View
        simultaneously.

   The following figure shows an example of the structure of Global
   Views in a Global View List.


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      ........................................................
      . Advertisement                                        .
      .                                                      .
      . +--------------+         +-------------------------+ .
      . |Scene 1       |         |Global View List         | .
      . |              |         |                         | .
      . | CSV1 (v)<----------------- Global View (CSV 1)   | .
      . |         <-------.      |                         | .
      . |              |  *--------- Global View (CSV 1,5) | .
      . | CSV2 (v)     |  |      |                         | .
      . |              |  |      |                         | .
      . | CSV3 (v)<---------*------- Global View (CSV 3,5) | .
      . |              |  | |    |                         | .
      . | CSV4 (a)<----------------- Global View (CSV 4)   | .
      . |         <-----------.  |                         | .
      . +--------------+  | | *----- Global View (CSV 4,6) | .
      .                   | | |  |                         | .
      . +--------------+  | | |  +-------------------------+ .
      . |Scene 2       |  | | |                              .
      . |              |  | | |                              .
      . | CSV5 (v)<-------' | |                              .
      . |         <---------' |                              .
      . |              |      |        (v) = video           .
      . | CSV6 (a)<-----------'        (a) = audio           .
      . |              |                                     .
      . +--------------+                                     .
      `......................................................'

                 Figure 3:   Global View List Structure

8. Simultaneous Transmission Set Constraints

   In many practical cases, a Provider has constraints or limitations
   on its ability to send Captures simultaneously.  One type of
   limitation is caused by the physical limitations of capture
   mechanisms; these constraints are represented by a Simultaneous
   Transmission Set.  The second type of limitation reflects the
   encoding resources available, such as bandwidth or video encoding
   throughput (macroblocks/second).  This type of constraint is
   captured by Individual Encodings and Encoding Groups, discussed
   below.

   Some Endpoints or MCUs can send multiple Captures simultaneously;
   however sometimes there are constraints that limit which Captures
   can be sent simultaneously with other Captures.  A device may not


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   be able to be used in different ways at the same time.  Provider
   Advertisements are made so that the Consumer can choose one of
   several possible mutually exclusive usages of the device.  This
   type of constraint is expressed in a Simultaneous Transmission Set,
   which lists all the Captures of a particular media type (e.g.
   audio, video, text) that can be sent at the same time.  There are
   different Simultaneous Transmission Sets for each media type in the
   Advertisement.  This is easier to show in an example.

   Consider the example of a room system where there are three cameras
   each of which can send a separate Capture covering two persons
   each- VC0, VC1, VC2.  The middle camera can also zoom out (using an
   optical zoom lens) and show all six persons, VC3.  But the middle
   camera cannot be used in both modes at the same time - it has to
   either show the space where two participants sit or the whole six
   seats, but not both at the same time.  As a result, VC1 and VC3
   cannot be sent simultaneously.

   Simultaneous Transmission Sets are expressed as sets of the Media
   Captures that the Provider could transmit at the same time (though,
   in some cases, it is not intuitive to do so).  If a Multiple
   Content Capture is included in a Simultaneous Transmission Set it
   indicates that the Capture Encoding associated with it could be
   transmitted as the same time as the other Captures within the
   Simultaneous Transmission Set. It does not imply that the Single
   Media Captures contained in the Multiple Content Capture could all
   be transmitted at the same time.

   In this example the two Simultaneous Transmission Sets are shown in
   Table 5.  If a Provider advertises one or more mutually exclusive
   Simultaneous Transmission Sets, then for each media type the
   Consumer MUST ensure that it chooses Media Captures that lie wholly
   within one of those Simultaneous Transmission Sets.

                           +-------------------+
                           | Simultaneous Sets |
                           +-------------------+
                           | {VC0, VC1, VC2}   |
                           | {VC0, VC3, VC2}   |
                           +-------------------+

                Table 5: Two Simultaneous Transmission Sets

   A Provider OPTIONALLY can include the Simultaneous Transmission
   Sets in its Advertisement.  These constraints apply across all the


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   Capture Scenes in the Advertisement.  It is a syntax conformance
   requirement that the Simultaneous Transmission Sets MUST allow all
   the media Captures in any particular Capture Scene View to be used
   simultaneously.  Similarly, the Simultaneous Transmission Sets MUST
   reflect the simultaneity expressed by any Global View.

   For shorthand convenience, a Provider MAY describe a Simultaneous
   Transmission Set in terms of Capture Scene Views and Capture
   Scenes.  If a Capture Scene View is included in a Simultaneous
   Transmission Set, then all Media Captures in the Capture Scene View
   are included in the Simultaneous Transmission Set.  If a Capture
   Scene is included in a Simultaneous Transmission Set, then all its
   Capture Scene Views (of the corresponding media type) are included
   in the Simultaneous Transmission Set.  The end result reduces to a
   set of Media Captures, of a particular media type, in either case.

   If an Advertisement does not include Simultaneous Transmission
   Sets, then the Provider MUST be able to simultaneously provide all
   the Captures from any one CSV of each media type from each Capture
   Scene.  Likewise, if there are no Simultaneous Transmission Sets
   and there is a Global View list, then the Provider MUST be able to
   simultaneously provide all the Captures from any particular Global
   View (of each media type) from the Global View list.

   If an Advertisement includes multiple Capture Scene Views in a
   Capture Scene then the Consumer MAY choose one Capture Scene View
   for each media type, or MAY choose individual Captures based on the
   Simultaneous Transmission Sets.

9. Encodings

   Individual encodings and encoding groups are CLUE's mechanisms
   allowing a Provider to signal its limitations for sending Captures,
   or combinations of Captures, to a Consumer.  Consumers can map the
   Captures they want to receive onto the Encodings, with the encoding
   parameters they want.  As for the relationship between the CLUE-
   specified mechanisms based on Encodings and the SIP offer/answer
   exchange, please refer to section 5.

9.1. Individual Encodings

   An Individual Encoding represents a way to encode a Media Capture
   as a Capture Encoding, to be sent as an encoded media stream from
   the Provider to the Consumer.  An Individual Encoding has a set of
   parameters characterizing how the media is encoded.


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   Different media types have different parameters, and different
   encoding algorithms may have different parameters.  An Individual
   Encoding can be assigned to at most one Capture Encoding at any
   given time.

   Individual Encoding parameters are represented in SDP [RFC4566],
   not in CLUE messages.  For example, for a video encoding using
   H.26x compression technologies, this can include parameters such
   as:

     . Maximum bandwidth;
     . Maximum picture size in pixels;
     . Maximum number of pixels to be processed per second;

   The bandwidth parameter is the only one that specifically relates
   to a CLUE Advertisement, as it can be further constrained by the
   maximum group bandwidth in an Encoding Group.

9.2. Encoding Group

   An Encoding Group includes a set of one or more Individual
   Encodings, and parameters that apply to the group as a whole.  By
   grouping multiple individual Encodings together, an Encoding Group
   describes additional constraints on bandwidth for the group. A
   single Encoding Group MAY refer to Encodings for different media
   types.

   The Encoding Group data structure contains:

     . Maximum bitrate for all encodings in the group combined;
     . A list of identifiers for the Individual Encodings belonging
        to the group.

   When the Individual Encodings in a group are instantiated into
   Capture Encodings, each Capture Encoding has a bitrate that MUST be
   less than or equal to the max bitrate for the particular Individual
   Encoding.  The "maximum bitrate for all encodings in the group"
   parameter gives the additional restriction that the sum of all the
   individual Capture Encoding bitrates MUST be less than or equal to
   this group value.

   The following diagram illustrates one example of the structure of a
   media Provider's Encoding Groups and their contents.




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   ,-------------------------------------------------.
   |             Media Provider                      |
   |                                                 |
   |  ,--------------------------------------.       |
   |  | ,--------------------------------------.     |
   |  | | ,--------------------------------------.   |
   |  | | |          Encoding Group              |   |
   |  | | | ,-----------.                        |   |
   |  | | | |           | ,---------.            |   |
   |  | | | |           | |         | ,---------.|   |
   |  | | | | Encoding1 | |Encoding2| |Encoding3||   |
   |  `.| | |           | |         | `---------'|   |
   |    `.| `-----------' `---------'            |   |
   |      `--------------------------------------'   |
   `-------------------------------------------------'

                  Figure 4:   Encoding Group Structure

   A Provider advertises one or more Encoding Groups.  Each Encoding
   Group includes one or more Individual Encodings.  Each Individual
   Encoding can represent a different way of encoding media.  For
   example one Individual Encoding may be 1080p60 video, another could
   be 720p30, with a third being CIF, all in, for example, H.264
   format.
   While a typical three codec/display system might have one Encoding
   Group per "codec box" (physical codec, connected to one camera and
   one screen), there are many possibilities for the number of
   Encoding Groups a Provider may be able to offer and for the
   encoding values in each Encoding Group.

   There is no requirement for all Encodings within an Encoding Group
   to be instantiated at the same time.

9.3. Associating Captures with Encoding Groups

   Each Media Capture, including MCCs, MAY be associated with one
   Encoding Group. To be eligible for configuration, a Media Capture
   MUST be associated with one Encoding Group, which is used to
   instantiate that Capture into a Capture Encoding. When an MCC is
   configured all the Media Captures referenced by the MCC will appear
   in the Capture Encoding according to the attributes of the chosen
   encoding of the MCC. This allows an Advertiser to specify encoding
   attributes associated with the Media Captures without the need to
   provide an individual Capture Encoding for each of the inputs.



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   If an Encoding Group is assigned to a Media Capture referenced by
   the MCC it indicates that this Capture may also have an individual
   Capture Encoding.

   For example:

        +--------------------+------------------------------------+
        | Capture Scene #1   |                                    |
        +--------------------+------------------------------------+
        | VC1                | EncodeGroupID=1                    |
        | VC2                |                                    |
        | MCC1(VC1,VC2)      | EncodeGroupID=2                    |
        | CSV(VC1)           |                                    |
        | CSV(MCC1)          |                                    |
        +--------------------+------------------------------------+

     Table 6: Example usage of Encoding with MCC and source Captures

   This would indicate that VC1 may be sent as its own Capture
   Encoding from EncodeGroupID=1 or that it may be sent as part of a
   Capture Encoding from EncodeGroupID=2 along with VC2.

   More than one Capture MAY use the same Encoding Group.

   The maximum number of Capture Encodings that can result from a
   particular Encoding Group constraint is equal to the number of
   individual Encodings in the group.  The actual number of Capture
   Encodings used at any time MAY be less than this maximum.  Any of
   the Captures that use a particular Encoding Group can be encoded
   according to any of the Individual Encodings in the group.

   It is a protocol conformance requirement that the Encoding Groups
   MUST allow all the Captures in a particular Capture Scene View to
   be used simultaneously.

10. Consumer's Choice of Streams to Receive from the Provider

   After receiving the Provider's Advertisement message (that includes
   media captures and associated constraints), the Consumer composes
   its reply to the Provider in the form of a Configure message.  The
   Consumer is free to use the information in the Advertisement as it
   chooses, but there are a few obviously sensible design choices,
   which are outlined below.




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   If multiple Providers connect to the same Consumer (i.e. in an MCU-
   less multiparty call), it is the responsibility of the Consumer to
   compose Configures for each Provider that both fulfill each
   Provider's constraints as expressed in the Advertisement, as well
   as its own capabilities.

   In an MCU-based multiparty call, the MCU can logically terminate
   the Advertisement/Configure negotiation in that it can hide the
   characteristics of the receiving endpoint and rely on its own
   capabilities (transcoding/transrating/...) to create Media Streams
   that can be decoded at the Endpoint Consumers.  The timing of an
   MCU's sending of Advertisements (for its outgoing ports) and
   Configures (for its incoming ports, in response to Advertisements
   received there) is up to the MCU and implementation dependent.

   As a general outline, a Consumer can choose, based on the
   Advertisement it has received, which Captures it wishes to receive,
   and which Individual Encodings it wants the Provider to use to
   encode the Captures.

   On receipt of an Advertisement with an MCC the Consumer treats the
   MCC as per other non-MCC Captures with the following differences:

   - The Consumer would understand that the MCC is a Capture that
   includes the referenced individual Captures (or any Captures, if
   none are referenced) and that these individual Captures are
   delivered as part of the MCC's Capture Encoding.

   - The Consumer may utilise any of the attributes associated with
   the referenced individual Captures and any Capture Scene attributes
   from where the individual Captures were defined to choose Captures
   and for rendering decisions.

   - If the MCC attribute Allow Subset Choice is true, then the
   Consumer may or may not choose to receive all the indicated
   Captures.  It can choose to receive a sub-set of Captures indicated
   by the MCC.

   For example if the Consumer receives:

           MCC1(VC1,VC2,VC3){attributes}

   A Consumer could choose all the Captures within a MCC however if
   the Consumer determines that it doesn't want VC3 it can return
   MCC1(VC1,VC2).  If it wants all the individual Captures then it


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   returns only the MCC identity (i.e. MCC1).  If the MCC in the
   advertisement does not reference any individual captures, or the
   Allow Subset Choice attribute is false, then the Consumer cannot
   choose what is included in the MCC, it is up to the Provider to
   decide.

   A Configure Message includes a list of Capture Encodings.  These
   are the Capture Encodings the Consumer wishes to receive from the
   Provider.  Each Capture Encoding refers to one Media Capture and
   one Individual Encoding.

   For each Capture the Consumer wants to receive, it configures one
   of the Encodings in that Capture's Encoding Group.  The Consumer
   does this by telling the Provider, in its Configure Message, which
   Encoding to use for each chosen Capture.  Upon receipt of this
   Configure from the Consumer, common knowledge is established
   between Provider and Consumer regarding sensible choices for the
   media streams.  The setup of the actual media channels, at least in
   the simplest case, is left to a following offer/answer exchange.
   Optimized implementations may speed up the reaction to the
   offer/answer exchange by reserving the resources at the time of
   finalization of the CLUE handshake.

   CLUE advertisements and configure messages don't necessarily
   require a new SDP offer/answer for every CLUE message
   exchange.  But the resulting encodings sent via RTP must conform to
   the most recent SDP offer/answer result.

   In order to meaningfully create and send an initial Configure, the
   Consumer needs to have received at least one Advertisement, and an
   SDP offer defining the Individual Encodings, from the Provider.

   In addition, the Consumer can send a Configure at any time during
   the call.  The Configure MUST be valid according to the most
   recently received Advertisement.  The Consumer can send a Configure
   either in response to a new Advertisement from the Provider or on
   its own, for example because of a local change in conditions
   (people leaving the room, connectivity changes, multipoint related
   considerations).

   When choosing which Media Streams to receive from the Provider, and
   the encoding characteristics of those Media Streams, the Consumer
   advantageously takes several things into account: its local
   preference, simultaneity restrictions, and encoding limits.



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10.1. Local preference

   A variety of local factors influence the Consumer's choice of
   Media Streams to be received from the Provider:

   o  if the Consumer is an Endpoint, it is likely that it would
      choose, where possible, to receive video and audio Captures that
      match the number of display devices and audio system it has

   o  if the Consumer is an MCU, it may choose to receive loudest
      speaker streams (in order to perform its own media composition)
      and avoid pre-composed video Captures

   o  user choice (for instance, selection of a new layout) may result
      in a different set of Captures, or different encoding
      characteristics, being required by the Consumer

10.2. Physical simultaneity restrictions

   Often there are physical simultaneity constraints of the Provider
   that affect the Provider's ability to simultaneously send all of
   the captures the Consumer would wish to receive.  For instance, an
   MCU, when connected to a multi-camera room system, might prefer to
   receive both individual video streams of the people present in the
   room and an overall view of the room from a single camera.  Some
   Endpoint systems might be able to provide both of these sets of
   streams simultaneously, whereas others might not (if the overall
   room view were produced by changing the optical zoom level on the
   center camera, for instance).

10.3. Encoding and encoding group limits

   Each of the Provider's encoding groups has limits on bandwidth,
   and the constituent potential encodings have limits on the
   bandwidth, computational complexity, video frame rate, and
   resolution that can be provided.  When choosing the Captures to be
   received from a Provider, a Consumer device MUST ensure that the
   encoding characteristics requested for each individual Capture
   fits within the capability of the encoding it is being configured
   to use, as well as ensuring that the combined encoding
   characteristics for Captures fit within the capabilities of their
   associated encoding groups.  In some cases, this could cause an
   otherwise "preferred" choice of capture encodings to be passed
   over in favor of different Capture Encodings--for instance, if a
   set of three Captures could only be provided at a low resolution


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   then a three screen device could switch to favoring a single,
   higher quality, Capture Encoding.

11. Extensibility

   One important characteristics of the Framework is its
   extensibility.  The standard for interoperability and handling
   multiple streams must be future-proof. The framework itself is
   inherently extensible through expanding the data model types.  For
   example:

   o  Adding more types of media, such as telemetry, can done by
      defining additional types of Captures in addition to audio and
      video.

   o  Adding new functionalities, such as 3-D video Captures, say, may
      require additional attributes describing the Captures.

   The infrastructure is designed to be extended rather than
   requiring new infrastructure elements.  Extension comes through
   adding to defined types.

12. Examples - Using the Framework (Informative)

   This section gives some examples, first from the point of view of
   the Provider, then the Consumer, then some multipoint scenarios

12.1. Provider Behavior

   This section shows some examples in more detail of how a Provider
   can use the framework to represent a typical case for telepresence
   rooms.  First an endpoint is illustrated, then an MCU case is
   shown.

12.1.1. Three screen Endpoint Provider

   Consider an Endpoint with the following description:

   3 cameras, 3 displays, a 6 person table

   o  Each camera can provide one Capture for each 1/3 section of the
      table





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   o  A single Capture representing the active speaker can be provided
      (voice activity based camera selection to a given encoder input
      port implemented locally in the Endpoint)

   o  A single Capture representing the active speaker with the other
      2 Captures shown picture in picture (PiP) within the stream can
      be provided (again, implemented inside the endpoint)

   o  A Capture showing a zoomed out view of all 6 seats in the room
      can be provided

   The video and audio Captures for this Endpoint can be described as
   follows.

   Video Captures:

   o  VC0- (the left camera stream), encoding group=EG0, view=table

   o  VC1- (the center camera stream), encoding group=EG1, view=table

   o  VC2- (the right camera stream), encoding group=EG2, view=table

   o  MCC3- (the loudest panel stream), encoding group=EG1,
      view=table, MaxCaptures=1, policy=SoundLevel

   o  MCC4- (the loudest panel stream with PiPs), encoding group=EG1,
      view=room, MaxCaptures=3, policy=SoundLevel

   o  VC5- (the zoomed out view of all people in the room), encoding
      group=EG1, view=room

   o  VC6- (presentation stream), encoding group=EG1, presentation

   The following diagram is a top view of the room with 3 cameras, 3
   displays, and 6 seats.  Each camera captures 2 people.  The six
   seats are not all in a straight line.











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      ,-. d
     (   )`--.__        +---+
      `-' /     `--.__  |   |
    ,-.  |            `-.._ |_-+Camera 2 (VC2)
   (   ).'     <--(AC1)-+-''`+-+
    `-' |_...---''      |   |
    ,-.c+-..__          +---+
   (   )|     ``--..__  |   |
    `-' |             ``+-..|_-+Camera 1 (VC1)
    ,-. |      <--(AC2)..--'|+-+                          ^
   (   )|     __..--'   |   |                             |
    `-'b|..--'          +---+                             |X
    ,-. |``---..___     |   |                             |
   (   )\          ```--..._|_-+Camera 0 (VC0)            |
    `-'  \     <--(AC0) ..-''`-+                          |
     ,-. \      __.--'' |   |                  <----------+
    (   ) |..-''        +---+                     Y
     `-' a                          (0,0,0) origin is under Camera 1


                    Figure 5:   Room Layout Top View


























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   The two points labeled b and c are intended to be at the midpoint
   between the seating positions, and where the fields of view of the
   cameras intersect.

   The plane of interest for VC0 is a vertical plane that intersects
   points 'a' and 'b'.

   The plane of interest for VC1 intersects points 'b' and 'c'. The
   plane of interest for VC2 intersects points 'c' and 'd'.

   This example uses an area scale of millimeters.

   Areas of capture:

       bottom left    bottom right  top left         top right
   VC0 (-2011,2850,0) (-673,3000,0) (-2011,2850,757) (-673,3000,757)
   VC1 ( -673,3000,0) ( 673,3000,0) ( -673,3000,757) ( 673,3000,757)
   VC2 (  673,3000,0) (2011,2850,0) (  673,3000,757) (2011,3000,757)
   MCC3(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
   MCC4(-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
   VC5 (-2011,2850,0) (2011,2850,0) (-2011,2850,757) (2011,3000,757)
   VC6 none

   Points of capture:
   VC0 (-1678,0,800)
   VC1 (0,0,800)
   VC2 (1678,0,800)
   MCC3 none
   MCC4 none
   VC5 (0,0,800)
   VC6 none

   In this example, the right edge of the VC0 area lines up with the
   left edge of the VC1 area.  It doesn't have to be this way.  There
   could be a gap or an overlap.  One additional thing to note for
   this example is the distance from a to b is equal to the distance
   from b to c and the distance from c to d.  All these distances are
   1346 mm. This is the planar width of each area of capture for VC0,
   VC1, and VC2.

   Note the text in parentheses (e.g. "the left camera stream") is
   not explicitly part of the model, it is just explanatory text for
   this example, and is not included in the model with the media


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   captures and attributes.  Also, MCC4 doesn't say anything about
   how a capture is composed, so the media consumer can't tell based
   on this capture that MCC4 is composed of a "loudest panel with
   PiPs".

   Audio Captures:

   Three ceiling microphones are located between the cameras and the
   table, at the same height as the cameras.  The microphones point
   down at an angle toward the seating positions.

   o  AC0 (left), encoding group=EG3

   o  AC1 (right), encoding group=EG3

   o  AC2 (center) encoding group=EG3

   o  AC3 being a simple pre-mixed audio stream from the room (mono),
      encoding group=EG3

   o  AC4 audio stream associated with the presentation video (mono)
      encoding group=EG3, presentation

       Point of capture:      Point on Line of Capture:

   AC0 (-1342,2000,800)       (-1342,2925,379)
   AC1 ( 1342,2000,800)       ( 1342,2925,379)
   AC2 (    0,2000,800)       (    0,3000,379)
   AC3 (    0,2000,800)       (    0,3000,379)
   AC4 none

   The physical simultaneity information is:

      Simultaneous transmission set #1 {VC0, VC1, VC2, MCC3, MCC4,
   VC6}

      Simultaneous transmission set #2 {VC0, VC2, VC5, VC6}

   This constraint indicates it is not possible to use all the VCs at
   the same time.  VC5 cannot be used at the same time as VC1 or MCC3
   or MCC4.  Also, using every member in the set simultaneously may
   not make sense - for example MCC3(loudest) and MCC4 (loudest with
   PiP).  In addition, there are encoding constraints that make
   choosing all of the VCs in a set impossible.  VC1, MCC3, MCC4,
   VC5, VC6 all use EG1 and EG1 has only 3 ENCs.  This constraint


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   shows up in the encoding groups, not in the simultaneous
   transmission sets.

   In this example there are no restrictions on which Audio Captures
   can be sent simultaneously.

   Encoding Groups:

   This example has three encoding groups associated with the video
   captures.  Each group can have 3 encodings, but with each
   potential encoding having a progressively lower specification.  In
   this example, 1080p60 transmission is possible (as ENC0 has a
   maxPps value compatible with that).  Significantly, as up to 3
   encodings are available per group, it is possible to transmit some
   video Captures simultaneously that are not in the same view in the
   Capture Scene.  For example VC1 and MCC3 at the same time.  The
   information below about Encodings is a summary of what would be
   conveyed in SDP, not directly in the CLUE Advertisement.

   encodeGroupID=EG0, maxGroupBandwidth=6000000
       encodeID=ENC0, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
                      maxPps=124416000, maxBandwidth=4000000
       encodeID=ENC1, maxWidth=1280, maxHeight=720, maxFrameRate=30,
                      maxPps=27648000, maxBandwidth=4000000
       encodeID=ENC2, maxWidth=960, maxHeight=544, maxFrameRate=30,
                      maxPps=15552000, maxBandwidth=4000000
   encodeGroupID=EG1  maxGroupBandwidth=6000000
       encodeID=ENC3, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
                      maxPps=124416000, maxBandwidth=4000000
       encodeID=ENC4, maxWidth=1280, maxHeight=720, maxFrameRate=30,
                      maxPps=27648000, maxBandwidth=4000000
       encodeID=ENC5, maxWidth=960, maxHeight=544, maxFrameRate=30,
                      maxPps=15552000, maxBandwidth=4000000
   encodeGroupID=EG2  maxGroupBandwidth=6000000
       encodeID=ENC6, maxWidth=1920, maxHeight=1088, maxFrameRate=60,
                      maxPps=124416000, maxBandwidth=4000000
       encodeID=ENC7, maxWidth=1280, maxHeight=720, maxFrameRate=30,
                      maxPps=27648000, maxBandwidth=4000000
       encodeID=ENC8, maxWidth=960, maxHeight=544, maxFrameRate=30,
                      maxPps=15552000, maxBandwidth=4000000

              Figure 6:   Example Encoding Groups for Video

   For audio, there are five potential encodings available, so all
   five Audio Captures can be encoded at the same time.


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   encodeGroupID=EG3, maxGroupBandwidth=320000
       encodeID=ENC9, maxBandwidth=64000
       encodeID=ENC10, maxBandwidth=64000
       encodeID=ENC11, maxBandwidth=64000
       encodeID=ENC12, maxBandwidth=64000
       encodeID=ENC13, maxBandwidth=64000

              Figure 7:   Example Encoding Group for Audio

   Capture Scenes:

   The following table represents the Capture Scenes for this
   Provider. Recall that a Capture Scene is composed of alternative
   Capture Scene Views covering the same spatial region.  Capture
   Scene #1 is for the main people captures, and Capture Scene #2 is
   for presentation.

   Each row in the table is a separate Capture Scene View

                           +------------------+
                           | Capture Scene #1 |
                           +------------------+
                           | VC0, VC1, VC2    |
                           | MCC3             |
                           | MCC4             |
                           | VC5              |
                           | AC0, AC1, AC2    |
                           | AC3              |
                           +------------------+

                           +------------------+
                           | Capture Scene #2 |
                           +------------------+
                           | VC6              |
                           | AC4              |
                           +------------------+

                Table 7: Example Capture Scene Views

   Different Capture Scenes are distinct from each other, and are
   non-overlapping. A Consumer can choose a view from each Capture
   Scene.  In this case the three Captures VC0, VC1, and VC2 are one
   way of representing the video from the Endpoint.  These three
   Captures should appear adjacent next to each other.
   Alternatively, another way of representing the Capture Scene is


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   with the capture MCC3, which automatically shows the person who is
   talking.  Similarly for the MCC4 and VC5 alternatives.

   As in the video case, the different views of audio in Capture
   Scene #1 represent the "same thing", in that one way to receive
   the audio is with the 3 Audio Captures (AC0, AC1, AC2), and
   another way is with the mixed AC3.  The Media Consumer can choose
   an audio CSV it is capable of receiving.

   The spatial ordering is understood by the Media Capture attributes
   Area of Capture, Point of Capture and Point on Line of Capture.

   A Media Consumer would likely want to choose a Capture Scene View
   to receive based in part on how many streams it can simultaneously
   receive.  A consumer that can receive three video streams would
   probably prefer to receive the first view of Capture Scene #1
   (VC0, VC1, VC2) and not receive the other views.  A consumer that
   can receive only one video stream would probably choose one of the
   other views.

   If the consumer can receive a presentation stream too, it would
   also choose to receive the only view from Capture Scene #2 (VC6).

12.1.2. Encoding Group Example

   This is an example of an Encoding Group to illustrate how it can
   express dependencies between Encodings.  The information below
   about Encodings is a summary of what would be conveyed in SDP, not
   directly in the CLUE Advertisement.

   encodeGroupID=EG0 maxGroupBandwidth=6000000
       encodeID=VIDENC0, maxWidth=1920, maxHeight=1088,
         maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
       encodeID=VIDENC1, maxWidth=1920, maxHeight=1088,
         maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
       encodeID=AUDENC0, maxBandwidth=96000
       encodeID=AUDENC1, maxBandwidth=96000
       encodeID=AUDENC2, maxBandwidth=96000

   Here, the Encoding Group is EG0.  Although the Encoding Group is
   capable of transmitting up to 6Mbit/s, no individual video
   Encoding can exceed 4Mbit/s.

   This encoding group also allows up to 3 audio encodings, AUDENC<0-
   2>. It is not required that audio and video encodings reside


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   within the same encoding group, but if so then the group's overall
   maxBandwidth value is a limit on the sum of all audio and video
   encodings configured by the consumer.  A system that does not wish
   or need to combine bandwidth limitations in this way should
   instead use separate encoding groups for audio and video in order
   for the bandwidth limitations on audio and video to not interact.

   Audio and video can be expressed in separate encoding groups, as
   in this illustration.

   encodeGroupID=EG0 maxGroupBandwidth=6000000
       encodeID=VIDENC0, maxWidth=1920, maxHeight=1088,
         maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
       encodeID=VIDENC1, maxWidth=1920, maxHeight=1088,
         maxFrameRate=60, maxPps=62208000, maxBandwidth=4000000
   encodeGroupID=EG1 maxGroupBandwidth=500000
       encodeID=AUDENC0, maxBandwidth=96000
       encodeID=AUDENC1, maxBandwidth=96000
       encodeID=AUDENC2, maxBandwidth=96000

12.1.3. The MCU Case

   This section shows how an MCU might express its Capture Scenes,
   intending to offer different choices for consumers that can handle
   different numbers of streams. Each MCC is for video. A single
   Audio Capture is provided for all single and multi-screen
   configurations that can be associated (e.g. lip-synced) with any
   combination of Video Captures (the MCCs) at the consumer.

        +-----------------------+---------------------------------+
        | Capture Scene #1      |                                 |
        +-----------------------|---------------------------------+
        | MCC                   | for a single screen consumer    |
        | MCC1, MCC2            | for a two screen consumer       |
        | MCC3, MCC4, MCC5      | for a three screen consumer     |
        | MCC6, MCC7, MCC8, MCC9| for a four screen consumer      |
        | AC0                   | AC representing all participants|
        | CSV(MCC0)             |                                 |
        | CSV(MCC1,MCC2)        |                                 |
        | CSV(MCC3,MCC4,MCC5)   |                                 |
        | CSV(MCC6,MCC7,        |                                 |
        |     MCC8,MCC9)        |                                 |
        | CSV(AC0)              |                                 |
        +-----------------------+---------------------------------+



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                Table 8: MCU main Capture Scenes

   If / when a presentation stream becomes active within the
   conference the MCU might re-advertise the available media as:

        +------------------+--------------------------------------+
        | Capture Scene #2 | note                                 |
        +------------------+--------------------------------------+
        | VC10             | video capture for presentation       |
        | AC1              | presentation audio to accompany VC10 |
        | CSV(VC10)        |                                      |
        | CSV(AC1)         |                                      |
        +------------------+--------------------------------------+

                Table 9: MCU presentation Capture Scene

12.2. Media Consumer Behavior

   This section gives an example of how a Media Consumer might behave
   when deciding how to request streams from the three screen
   endpoint described in the previous section.

   The receive side of a call needs to balance its requirements,
   based on number of screens and speakers, its decoding capabilities
   and available bandwidth, and the provider's capabilities in order
   to optimally configure the provider's streams.  Typically it would
   want to receive and decode media from each Capture Scene
   advertised by the Provider.

   A sane, basic, algorithm might be for the consumer to go through
   each Capture Scene View in turn and find the collection of Video
   Captures that best matches the number of screens it has (this
   might include consideration of screens dedicated to presentation
   video display rather than "people" video) and then decide between
   alternative views in the video Capture Scenes based either on
   hard-coded preferences or user choice.  Once this choice has been
   made, the consumer would then decide how to configure the
   provider's encoding groups in order to make best use of the
   available network bandwidth and its own decoding capabilities.

12.2.1. One screen Media Consumer

   MCC3, MCC4 and VC5 are all different views by themselves, not
   grouped together in a single view, so the receiving device should
   choose between one of those.  The choice would come down to


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   whether to see the greatest number of participants simultaneously
   at roughly equal precedence (VC5), a switched view of just the
   loudest region (MCC3) or a switched view with PiPs (MCC4).  An
   endpoint device with a small amount of knowledge of these
   differences could offer a dynamic choice of these options, in-
   call, to the user.

12.2.2. Two screen Media Consumer configuring the example

   Mixing systems with an even number of screens, "2n", and those
   with "2n+1" cameras (and vice versa) is always likely to be the
   problematic case.  In this instance, the behavior is likely to be
   determined by whether a "2 screen" system is really a "2 decoder"
   system, i.e., whether only one received stream can be displayed
   per screen or whether more than 2 streams can be received and
   spread across the available screen area.  To enumerate 3 possible
   behaviors here for the 2 screen system when it learns that the far
   end is "ideally" expressed via 3 capture streams:

   1. Fall back to receiving just a single stream (MCC3, MCC4 or VC5
      as per the 1 screen consumer case above) and either leave one
      screen blank or use it for presentation if / when a
      presentation becomes active.

   2. Receive 3 streams (VC0, VC1 and VC2) and display across 2
      screens (either with each capture being scaled to 2/3 of a
      screen and the center capture being split across 2 screens) or,
      as would be necessary if there were large bezels on the
      screens, with each stream being scaled to 1/2 the screen width
      and height and there being a 4th "blank" panel.  This 4th panel
      could potentially be used for any presentation that became
      active during the call.

   3. Receive 3 streams, decode all 3, and use control information
      indicating which was the most active to switch between showing
      the left and center streams (one per screen) and the center and
      right streams.

   For an endpoint capable of all 3 methods of working described
   above, again it might be appropriate to offer the user the choice
   of display mode.






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12.2.3. Three screen Media Consumer configuring the example

   This is the most straightforward case - the Media Consumer would
   look to identify a set of streams to receive that best matched its
   available screens and so the VC0 plus VC1 plus VC2 should match
   optimally.  The spatial ordering would give sufficient information
   for the correct Video Capture to be shown on the correct screen,
   and the consumer would either need to divide a single encoding
   group's capability by 3 to determine what resolution and frame
   rate to configure the provider with or to configure the individual
   Video Captures' Encoding Groups with what makes most sense (taking
   into account the receive side decode capabilities, overall call
   bandwidth, the resolution of the screens plus any user preferences
   such as motion vs. sharpness).

12.3. Multipoint Conference utilizing Multiple Content Captures

   The use of MCCs allows the MCU to construct outgoing Advertisements
   describing complex media switching and composition scenarios.  The
   following sections provide several examples.

   Note: In the examples the identities of the CLUE elements (e.g.
   Captures, Capture Scene) in the incoming Advertisements overlap.
   This is because there is no co-ordination between the endpoints.
   The MCU is responsible for making these unique in the outgoing
   advertisement.

12.3.1. Single Media Captures and MCC in the same Advertisement

   Four endpoints are involved in a Conference where CLUE is used. An
   MCU acts as a middlebox between the endpoints with a CLUE channel
   between each endpoint and the MCU. The MCU receives the following
   Advertisements.

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=AustralianConfRoom  |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Audience            |
        |                       | EncodeGroupID=1                 |
        | CSV(VC1)              |                                 |
        +---------------------------------------------------------+

            Table 10: Advertisement received from Endpoint A




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        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=ChinaConfRoom       |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Speaker             |
        |                       | EncodeGroupID=1                 |
        | VC2                   | Description=Audience            |
        |                       | EncodeGroupID=1                 |
        | CSV(VC1, VC2)         |                                 |
        +---------------------------------------------------------+

            Table 11: Advertisement received from Endpoint B

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=USAConfRoom         |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Audience            |
        |                       | EncodeGroupID=1                 |
        | CSV(VC1)              |                                 |
        +---------------------------------------------------------+

            Table 12: Advertisement received from Endpoint C

   Note: Endpoint B above indicates that it sends two streams.

   If the MCU wanted to provide a Multiple Content Capture containing
   a round robin switched view of the audience from the 3 endpoints
   and the speaker it could construct the following advertisement:

   Advertisement sent to Endpoint F


















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        +=======================+=================================+
        | Capture Scene #1      | Description=AustralianConfRoom  |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Audience            |
        | CSV(VC1)              |                                 |
        +=======================+=================================+
        | Capture Scene #2      | Description=ChinaConfRoom       |
        +-----------------------|---------------------------------+
        | VC2                   | Description=Speaker             |
        | VC3                   | Description=Audience            |
        | CSV(VC2, VC3)         |                                 |
        +=======================+=================================+
        | Capture Scene #3      | Description=USAConfRoom         |
        +-----------------------|---------------------------------+
        | VC4                   | Description=Audience            |
        | CSV(VC4)              |                                 |
        +=======================+=================================+
        | Capture Scene #4      |                                 |
        +-----------------------|---------------------------------+
        | MCC1(VC1,VC2,VC3,VC4) | Policy=RoundRobin:1             |
        |                       | MaxCaptures=1                   |
        |                       | EncodingGroup=1                 |
        | CSV(MCC1)             |                                 |
        +=======================+=================================+

         Table 13: Advertisement sent to Endpoint F - One Encoding

   Alternatively if the MCU wanted to provide the speaker as one media
   stream and the audiences as another it could assign an encoding
   group to VC2 in Capture Scene 2 and provide a CSV in Capture Scene
   #4 as per the example below.

   Advertisement sent to Endpoint F














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        +=======================+=================================+
        | Capture Scene #1      | Description=AustralianConfRoom  |
        +-----------------------|---------------------------------+
        | VC1                   | Description=Audience            |
        | CSV(VC1)              |                                 |
        +=======================+=================================+
        | Capture Scene #2      | Description=ChinaConfRoom       |
        +-----------------------|---------------------------------+
        | VC2                   | Description=Speaker             |
        |                       | EncodingGroup=1                 |
        | VC3                   | Description=Audience            |
        | CSV(VC2, VC3)         |                                 |
        +=======================+=================================+
        | Capture Scene #3      | Description=USAConfRoom         |
        +-----------------------|---------------------------------+
        | VC4                   | Description=Audience            |
        | CSV(VC4)              |                                 |
        +=======================+=================================+
        | Capture Scene #4      |                                 |
        +-----------------------|---------------------------------+
        | MCC1(VC1,VC3,VC4)     | Policy=RoundRobin:1             |
        |                       | MaxCaptures=1                   |
        |                       | EncodingGroup=1                 |
        |                       | AllowSubset=True                |
        | MCC2(VC2)             | MaxCaptures=1                   |
        |                       | EncodingGroup=1                 |
        | CSV2(MCC1,MCC2)       |                                 |
        +=======================+=================================+

        Table 14: Advertisement sent to Endpoint F - Two Encodings

   Therefore a Consumer could choose whether or not to have a separate
   speaker related stream and could choose which endpoints to see.  If
   it wanted the second stream but not the Australian conference room
   it could indicate the following captures in the Configure message:

        +-----------------------+---------------------------------+
        | MCC1(VC3,VC4)         | Encoding                        |
        | VC2                   | Encoding                        |
        +-----------------------|---------------------------------+
                      Table 15: MCU case: Consumer Response






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12.3.2. Several MCCs in the same Advertisement

   Multiple MCCs can be used where multiple streams are used to carry
   media from multiple endpoints.  For example:

   A conference has three endpoints D, E and F. Each end point has
   three video captures covering the left, middle and right regions of
   each conference room.  The MCU receives the following
   advertisements from D and E.

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=AustralianConfRoom  |
        +-----------------------|---------------------------------+
        | VC1                   | CaptureArea=Left                |
        |                       | EncodingGroup=1                 |
        | VC2                   | CaptureArea=Centre              |
        |                       | EncodingGroup=1                 |
        | VC3                   | CaptureArea=Right               |
        |                       | EncodingGroup=1                 |
        | CSV(VC1,VC2,VC3)      |                                 |
        +---------------------------------------------------------+

            Table 16: Advertisement received from Endpoint D

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=ChinaConfRoom       |
        +-----------------------|---------------------------------+
        | VC1                   | CaptureArea=Left                |
        |                       | EncodingGroup=1                 |
        | VC2                   | CaptureArea=Centre              |
        |                       | EncodingGroup=1                 |
        | VC3                   | CaptureArea=Right               |
        |                       | EncodingGroup=1                 |
        | CSV(VC1,VC2,VC3)      |                                 |
        +---------------------------------------------------------+

            Table 17: Advertisement received from Endpoint E

   The MCU wants to offer Endpoint F three Capture Encodings.  Each
   Capture Encoding would contain all the Captures from either
   Endpoint D or Endpoint E depending based on the active speaker.
   The MCU sends the following Advertisement:





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        +=======================+=================================+
        | Capture Scene #1      | Description=AustralianConfRoom  |
        +-----------------------|---------------------------------+
        | VC1                   |                                 |
        | VC2                   |                                 |
        | VC3                   |                                 |
        | CSV(VC1,VC2,VC3)      |                                 |
        +=======================+=================================+
        | Capture Scene #2      | Description=ChinaConfRoom       |
        +-----------------------|---------------------------------+
        | VC4                   |                                 |
        | VC5                   |                                 |
        | VC6                   |                                 |
        | CSV(VC4,VC5,VC6)      |                                 |
        +=======================+=================================+
        | Capture Scene #3      |                                 |
        +-----------------------|---------------------------------+
        | MCC1(VC1,VC4)         | CaptureArea=Left                |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | EncodingGroup=1                 |
        | MCC2(VC2,VC5)         | CaptureArea=Centre              |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | EncodingGroup=1                 |
        | MCC3(VC3,VC6)         | CaptureArea=Right               |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | EncodingGroup=1                 |
        | CSV(MCC1,MCC2,MCC3)   |                                 |
        +=======================+=================================+

            Table 18: Advertisement sent to Endpoint F

12.3.3. Heterogeneous conference with switching and composition

   Consider a conference between endpoints with the following
   characteristics:

      Endpoint A - 4 screens, 3 cameras

      Endpoint B - 3 screens, 3 cameras

      Endpoint C - 3 screens, 3 cameras



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      Endpoint D - 3 screens, 3 cameras

      Endpoint E - 1 screen, 1 camera

      Endpoint F - 2 screens, 1 camera

      Endpoint G - 1 screen, 1 camera

   This example focuses on what the user in one of the 3-camera multi-
   screen endpoints sees.  Call this person User A, at Endpoint A.
   There are 4 large display screens at Endpoint A. Whenever somebody
   at another site is speaking, all the video captures from that
   endpoint are shown on the large screens.  If the talker is at a 3-
   camera site, then the video from those 3 cameras fills 3 of the
   screens.  If the talker is at a single-camera site, then video from
   that camera fills one of the screens, while the other screens show
   video from other single-camera endpoints.

   User A hears audio from the 4 loudest talkers.

   User A can also see video from other endpoints, in addition to the
   current talker, although much smaller in size.  Endpoint A has 4
   screens, so one of those screens shows up to 9 other Media Captures
   in a tiled fashion.  When video from a 3 camera endpoint appears in
   the tiled area, video from all 3 cameras appears together across
   the screen with correct spatial relationship among those 3 images.

      +---+---+---+ +-------------+ +-------------+ +-------------+
      |   |   |   | |             | |             | |             |
      +---+---+---+ |             | |             | |             |
      |   |   |   | |             | |             | |             |
      +---+---+---+ |             | |             | |             |
      |   |   |   | |             | |             | |             |
      +---+---+---+ +-------------+ +-------------+ +-------------+
                Figure 8:   Endpoint A - 4 Screen Display

   User B at Endpoint B sees a similar arrangement, except there are
   only 3 screens, so the 9 other Media Captures are spread out across
   the bottom of the 3 displays, in a picture-in-picture (PiP) format.
   When video from a 3 camera endpoint appears in the PiP area, video
   from all 3 cameras appears together across a single screen with
   correct spatial relationship.





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              +-------------+ +-------------+ +-------------+
              |             | |             | |             |
              |             | |             | |             |
              |             | |             | |             |
              | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ |
              | +-+ +-+ +-+ | | +-+ +-+ +-+ | | +-+ +-+ +-+ |
              +-------------+ +-------------+ +-------------+
           Figure 9:   Endpoint B - 3 Screen Display with PiPs

   When somebody at a different endpoint becomes the current talker,
   then User A and User B both see the video from the new talker
   appear on their large screen area, while the previous talker takes
   one of the smaller tiled or PiP areas.  The person who is the
   current talker doesn't see themselves; they see the previous talker
   in their large screen area.

   One of the points of this example is that endpoints A and B each
   want to receive 3 capture encodings for their large display areas,
   and 9 encodings for their smaller areas.  A and B are be able to
   each send the same Configure message to the MCU, and each receive
   the same conceptual Media Captures from the MCU.  The differences
   are in how they are rendered and are purely a local matter at A and
   B.

   The Advertisements for such a scenario are described below.

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=Endpoint x          |
        +-----------------------|---------------------------------+
        | VC1                   | EncodingGroup=1                 |
        | VC2                   | EncodingGroup=1                 |
        | VC3                   | EncodingGroup=1                 |
        | AC1                   | EncodingGroup=2                 |
        | CSV1(VC1, VC2, VC3)   |                                 |
        | CSV2(AC1)             |                                 |
        +---------------------------------------------------------+

   Table 19: Advertisement received at the MCU from Endpoints A to D









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        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=Endpoint y          |
        +-----------------------|---------------------------------+
        | VC1                   | EncodingGroup=1                 |
        | AC1                   | EncodingGroup=2                 |
        | CSV1(VC1)             |                                 |
        | CSV2(AC1)             |                                 |
        +---------------------------------------------------------+

   Table 20: Advertisement received at the MCU from Endpoints E to G

   Rather than considering what is displayed CLUE concentrates more
   on what the MCU sends. The MCU doesn't know anything about the
   number of screens an endpoint has.

   As Endpoints A to D each advertise that three Captures make up a
   Capture Scene, the MCU offers these in a "site" switching mode.
   That is that there are three Multiple Content Captures (and
   Capture Encodings) each switching between Endpoints. The MCU
   switches in the applicable media into the stream based on voice
   activity. Endpoint A will not see a capture from itself.

   Using the MCC concept the MCU would send the following
   Advertisement to endpoint A:

        +=======================+=================================+
        | Capture Scene #1      | Description=Endpoint B          |
        +-----------------------|---------------------------------+
        | VC4                   | CaptureArea=Left                |
        | VC5                   | CaptureArea=Center              |
        | VC6                   | CaptureArea=Right               |
        | AC1                   |                                 |
        | CSV(VC4,VC5,VC6)      |                                 |
        | CSV(AC1)              |                                 |
        +=======================+=================================+
        | Capture Scene #2      | Description=Endpoint C          |
        +-----------------------|---------------------------------+
        | VC7                   | CaptureArea=Left                |
        | VC8                   | CaptureArea=Center              |
        | VC9                   | CaptureArea=Right               |
        | AC2                   |                                 |
        | CSV(VC7,VC8,VC9)      |                                 |
        | CSV(AC2)              |                                 |
        +=======================+=================================+
        | Capture Scene #3      | Description=Endpoint D          |


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        +-----------------------|---------------------------------+
        | VC10                  | CaptureArea=Left                |
        | VC11                  | CaptureArea=Center              |
        | VC12                  | CaptureArea=Right               |
        | AC3                   |                                 |
        | CSV(VC10,VC11,VC12)   |                                 |
        | CSV(AC3)              |                                 |
        +=======================+=================================+
        | Capture Scene #4      | Description=Endpoint E          |
        +-----------------------|---------------------------------+
        | VC13                  |                                 |
        | AC4                   |                                 |
        | CSV(VC13)             |                                 |
        | CSV(AC4)              |                                 |
        +=======================+=================================+
        | Capture Scene #5      | Description=Endpoint F          |
        +-----------------------|---------------------------------+
        | VC14                  |                                 |
        | AC5                   |                                 |
        | CSV(VC14)             |                                 |
        | CSV(AC5)              |                                 |
        +=======================+=================================+
        | Capture Scene #6      | Description=Endpoint G          |
        +-----------------------|---------------------------------+
        | VC15                  |                                 |
        | AC6                   |                                 |
        | CSV(VC15)             |                                 |
        | CSV(AC6)              |                                 |
        +=======================+=================================+

         Table 21: Advertisement sent to endpoint A - Source Part

   The above part of the Advertisement presents information about the
   sources to the MCC. The information is effectively the same as the
   received Advertisements except that there are no Capture Encodings
   associated with them and the identities have been re-numbered.

   In addition to the source Capture information the MCU advertises
   "site" switching of Endpoints B to G in three streams.

        +=======================+=================================+
        | Capture Scene #7      | Description=Output3streammix    |
        +-----------------------|---------------------------------+
        | MCC1(VC4,VC7,VC10,    | CaptureArea=Left                |
        |      VC13)            | MaxCaptures=1                   |


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        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC2(VC5,VC8,VC11,    | CaptureArea=Center              |
        |      VC14)            | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC3(VC6,VC9,VC12,    | CaptureArea=Right               |
        |      VC15)            | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC4() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=2                 |
        |                       |                                 |
        | MCC5() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:1             |
        |                       | EncodingGroup=2                 |
        |                       |                                 |
        | MCC6() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:2             |
        |                       | EncodingGroup=2                 |
        |                       |                                 |
        | MCC7() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:3             |
        |                       | EncodingGroup=2                 |
        |                       |                                 |
        | CSV(MCC1,MCC2,MCC3)   |                                 |
        | CSV(MCC4,MCC5,MCC6,   |                                 |
        |     MCC7)             |                                 |
        +=======================+=================================+

       Table 22: Advertisement send to endpoint A - switching part

   The above part describes the switched 3 main streams that relate to
   site switching. MaxCaptures=1 indicates that only one Capture from


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   the MCC is sent at a particular time. SynchronisationID=1 indicates
   that the source sending is synchronised. The provider can choose to
   group together VC13, VC14, and VC15 for the purpose of switching
   according to the SynchronisationID.  Therefore when the provider
   switches one of them into an MCC, it can also switch the others
   even though they are not part of the same Capture Scene.

   All the audio for the conference is included in this Scene #7.
   There isn't necessarily a one to one relation between any audio
   capture and video capture in this scene.  Typically a change in
   loudest talker will cause the MCU to switch the audio streams more
   quickly than switching video streams.

   The MCU can also supply nine media streams showing the active and
   previous eight speakers. It includes the following in the
   Advertisement:

        +=======================+=================================+
        | Capture Scene #8      | Description=Output9stream       |
        +-----------------------|---------------------------------+
        | MCC8(VC4,VC5,VC6,VC7, | MaxCaptures=1                   |
        |   VC8,VC9,VC10,VC11,  | Policy=SoundLevel:0             |
        |   VC12,VC13,VC14,VC15)| EncodingGroup=1                 |
        |                       |                                 |
        | MCC9(VC4,VC5,VC6,VC7, | MaxCaptures=1                   |
        |   VC8,VC9,VC10,VC11,  | Policy=SoundLevel:1             |
        |   VC12,VC13,VC14,VC15)| EncodingGroup=1                 |
        |                       |                                 |
                    to                           to               |
        |                       |                                 |
        | MCC16(VC4,VC5,VC6,VC7,| MaxCaptures=1                   |
        |   VC8,VC9,VC10,VC11,  | Policy=SoundLevel:8             |
        |   VC12,VC13,VC14,VC15)| EncodingGroup=1                 |
        |                       |                                 |
        | CSV(MCC8,MCC9,MCC10,  |                                 |
        |     MCC11,MCC12,MCC13,|                                 |
        |     MCC14,MCC15,MCC16)|                                 |
        +=======================+=================================+

       Table 23: Advertisement sent to endpoint A - 9 switched part

   The above part indicates that there are 9 capture encodings. Each
   of the Capture Encodings may contain any captures from any source
   site with a maximum of one Capture at a time. Which Capture is



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   present is determined by the policy.  The MCCs in this scene do not
   have any spatial attributes.

   Note: The Provider alternatively could provide each of the MCCs
   above in its own Capture Scene.

   If the MCU wanted to provide a composed Capture Encoding containing
   all of the 9 captures it could advertise in addition:

        +=======================+=================================+
        | Capture Scene #9      | Description=NineTiles           |
        +-----------------------|---------------------------------+
        | MCC13(MCC8,MCC9,MCC10,| MaxCaptures=9                   |
        |     MCC11,MCC12,MCC13,| EncodingGroup=1                 |
        |     MCC14,MCC15,MCC16)|                                 |
        |                       |                                 |
        | CSV(MCC13)            |                                 |
        +=======================+=================================+

      Table 24: Advertisement sent to endpoint A - 9 composed part

   As MaxCaptures is 9 it indicates that the capture encoding contains
   information from 9 sources at a time.

   The Advertisement to Endpoint B is identical to the above other
   than the captures from Endpoint A would be added and the captures
   from Endpoint B would be removed. Whether the Captures are rendered
   on a four screen display or a three screen display is up to the
   Consumer to determine.  The Consumer wants to place video captures
   from the same original source endpoint together, in the correct
   spatial order, but the MCCs do not have spatial attributes.  So the
   Consumer needs to associate incoming media packets with the
   original individual captures in the advertisement (such as VC4,
   VC5, and VC6) in order to know the spatial information it needs for
   correct placement on the screens.  The Provider can use the RTCP
   CaptureId SDES item and associated RTP header extension, as
   described in [I-D.ietf-clue-rtp-mapping], to convey this
   information to the Consumer.

12.3.4. Heterogeneous conference with voice activated switching

   This example illustrates how multipoint "voice activated switching"
   behavior can be realized, with an endpoint making its own decision
   about which of its outgoing video streams is considered the "active



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   talker" from that endpoint.  Then an MCU can decide which is the
   active talker among the whole conference.

   Consider a conference between endpoints with the following
   characteristics:

      Endpoint A - 3 screens, 3 cameras

      Endpoint B - 3 screens, 3 cameras

      Endpoint C - 1 screen, 1 camera

   This example focuses on what the user at endpoint C sees.  The
   user would like to see the video capture of the current talker,
   without composing it with any other video capture.  In this
   example endpoint C is capable of receiving only a single video
   stream.  The following tables describe advertisements from A and B
   to the MCU, and from the MCU to C, that can be used to accomplish
   this.

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=Endpoint x          |
        +-----------------------|---------------------------------+
        | VC1                   | CaptureArea=Left                |
        |                       | EncodingGroup=1                 |
        | VC2                   | CaptureArea=Center              |
        |                       | EncodingGroup=1                 |
        | VC3                   | CaptureArea=Right               |
        |                       | EncodingGroup=1                 |
        | MCC1(VC1,VC2,VC3)     | MaxCaptures=1                   |
        |                       | CaptureArea=whole scene         |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        | AC1                   | CaptureArea=whole scene         |
        |                       | EncodingGroup=2                 |
        | CSV1(VC1, VC2, VC3)   |                                 |
        | CSV2(MCC1)            |                                 |
        | CSV3(AC1)             |                                 |
        +---------------------------------------------------------+

   Table 25: Advertisement received at the MCU from Endpoints A and B

   Endpoints A and B are advertising each individual video capture,
   and also a switched capture MCC1 which switches between the other
   three based on who is the active talker.  These endpoints do not


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   advertise distinct audio captures associated with each individual
   video capture, so it would be impossible for the MCU (as a media
   consumer) to make its own determination of which video capture is
   the active talker based just on information in the audio streams.

        +-----------------------+---------------------------------+
        | Capture Scene #1      | Description=conference          |
        +-----------------------|---------------------------------+
        | MCC1()                | CaptureArea=Left                |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC2()                | CaptureArea=Center              |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC3()                | CaptureArea=Right               |
        |                       | MaxCaptures=1                   |
        |                       | SynchronisationID=1             |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC4()                | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=1                 |
        |                       |                                 |
        | MCC5() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:0             |
        |                       | EncodingGroup=2                 |
        |                       |                                 |
        | MCC6() (for audio)    | CaptureArea=whole scene         |
        |                       | MaxCaptures=1                   |
        |                       | Policy=SoundLevel:1             |
        |                       | EncodingGroup=2                 |
        | CSV1(MCC1,MCC2,MCC3   |                                 |
        | CSV2(MCC4)            |                                 |
        | CSV3(MCC5,MCC6)       |                                 |
        +---------------------------------------------------------+



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            Table 26: Advertisement sent from the MCU to C

   The MCU advertises one scene, with four video MCCs.  Three of them
   in CSV1 give a left, center, right view of the conference, with
   "site switching". MCC4 provides a single video capture
   representing a view of the whole conference.  The MCU intends for
   MCC4 to be switched between all the other original source
   captures.  In this example advertisement the MCU is not giving all
   the information about all the other endpoints' scenes and which of
   those captures is included in the MCCs.  The MCU could include all
   that information if it wants to give the consumers more
   information, but it is not necessary for this example scenario.

   The Provider advertises MCC5 and MCC6 for audio.  Both are
   switched captures, with different SoundLevel policies indicating
   they are the top two dominant talkers.  The Provider advertises
   CSV3 with both MCCs, suggesting the Consumer should use both if it
   can.

   Endpoint C, in its configure message to the MCU, requests to
   receive MCC4 for video, and MCC5 and MCC6 for audio.  In order for
   the MCU to get the information it needs to construct MCC4, it has
   to send configure messages to A and B asking to receive MCC1 from
   each of them, along with their AC1 audio.  Now the MCU can use
   audio energy information from the two incoming audio streams from
   A and B to determine which of those alternatives is the current
   talker.  Based on that, the MCU uses either MCC1 from A or MCC1
   from B as the source of MCC4 to send to C.

13. Acknowledgements

   Allyn Romanow and Brian Baldino were authors of early versions.
   Mark Gorzynski also contributed much to the initial approach.
   Many others also contributed, including Christian Groves, Jonathan
   Lennox, Paul Kyzivat, Rob Hansen, Roni Even, Christer Holmberg,
   Stephen Botzko, Mary Barnes, John Leslie, Paul Coverdale.

14. IANA Considerations

   None.

15. Security Considerations

   There are several potential attacks related to telepresence, and
   specifically the protocols used by CLUE, in the case of


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   conferencing sessions, due to the natural involvement of multiple
   endpoints and the many, often user-invoked, capabilities provided
   by the systems.

   An MCU involved in a CLUE session can experience many of the same
   attacks as that of a conferencing system such as that enabled by
   the XCON framework [RFC5239]. Examples of attacks include the
   following: an endpoint attempting to listen to sessions in which
   it is not authorized to participate, an endpoint attempting to
   disconnect or mute other users, and theft of service by an
   endpoint in attempting to create telepresence sessions it is not
   allowed to create. Thus, it is RECOMMENDED that an MCU
   implementing the protocols necessary to support CLUE, follow the
   security recommendations specified in the conference control
   protocol documents.  In the case of CLUE, SIP is the conferencing
   protocol, thus the security considerations in [RFC4579] MUST be
   followed. Other security issues related to MCUs are discussed in
   the XCON framework [RFC5239]. The use of xCard with potentially
   sensitive information provides another reason to implement
   recommendations of section 11/[RFC5239].

   One primary security concern, surrounding the CLUE framework
   introduced in this document, involves securing the actual
   protocols and the associated authorization mechanisms.  These
   concerns apply to endpoint to endpoint sessions, as well as
   sessions involving multiple endpoints and MCUs. Figure 2 in
   section 5 provides a basic flow of information exchange for CLUE
   and the protocols involved.

   As described in section 5, CLUE uses SIP/SDP to establish the
   session prior to exchanging any CLUE specific information. Thus
   the security mechanisms recommended for SIP [RFC3261], including
   user authentication and authorization, MUST be supported. In
   addition, the media MUST be secured. DTLS/SRTP MUST be supported
   and SHOULD be used unless the media, which is based on RTP, is
   secured by other means (see [RFC7201] [RFC7202]).  Media security
   is also discussed in [I-D.ietf-clue-signaling] and [I-D.ietf-clue-
   rtp-mapping]. Note that SIP call setup is done before any CLUE
   specific information is available so the authentication and
   authorization are based on the SIP mechanisms. The entity that
   will be authenticated may use the Endpoint identity or the
   endpoint user identity; this is an application issue and not a
   CLUE specific issue.




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   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.  The CLUE data
   model [I-D.ietf-clue-data-model-schema] defines through an XML
   schema the syntax to be used. Some of the information which could
   possibly introduce privacy concerns is the xCard information as
   described in section 7.1.1.10. The decision about which xCard
   information to send in the CLUE channel is an application policy
   for point to point and multipoint calls based on the authenticated
   identity that can be the endpoint identity or the user of the
   endpoint. For example the telepresence multipoint application can
   authenticate a user before starting a CLUE exchange with the
   telepresence system and have a policy per user.

   In addition, the (text) description field in the Media Capture
   attribute (section 7.1.1.6) 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. An implementation SHOULD give users
   control over what sensitive information is sent in an
   Advertisement. 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 MUST NOT be used to
   make any authorization decisions.

   While other information in the CLUE protocol messages does not
   reveal specific identities, it can reveal characteristics and
   capabilities of the endpoints.  That information could possibly
   uniquely identify specific endpoints.  It might also be possible
   for an attacker to manipulate the information and disrupt the CLUE
   sessions.  It would also be possible to mount a DoS attack on the
   CLUE endpoints if a malicious agent has access to the data
   channel.  Thus, it MUST be possible for the endpoints to establish
   a channel which is secure against both message recovery and
   message modification. Further details on this are provided in the
   CLUE data channel solution document [I-D.ietf-clue-datachannel].

   There are also security issues associated with the authorization
   to perform actions at the CLUE endpoints to invoke specific
   capabilities (e.g., re-arranging screens, sharing content, etc.).
   However, the policies and security associated with these actions



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   are outside the scope of this document and the overall CLUE
   solution.

16. Changes Since Last Version

   NOTE TO THE RFC-Editor: Please remove this section prior to
   publication as an RFC.

   Changes from 24 to 25:

   Updates from IESG review.

     1. A few clarifications in various places.
     2. Change references to RFC5239 and RFC5646 from informative to
        normative.
   Changes from 23 to 24:

     1. Updates to Security Considerations section.
     2. Update version number of references to other CLUE documents
        in progress.
   Changes from 22 to 23:

     1. Updates to Security Considerations section.
     2. Update version number of references to other CLUE documents
        in progress.
     3. Change some "MAY" to "may".
     4. Fix a few grammatical errors.

   Changes from 21 to 22:

     1. Add missing references.
     2. Update version number of referenced working group drafts.
     3. Minor updates for idnits issues.

   Changes from 20 to 21:

     1. Clarify CLUE can be useful for multi-stream non-telepresence
        cases.
     2. Remove unnecessary ambiguous sentence about optional use of
        CLUE protocol.


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     3. Clarify meaning if Area of Capture is not specified.
     4. Remove use of "conference" where it didn't fit according to
        the definition.  Use "CLUE session" or "meeting" instead.
     5. Embedded Text Attribute: Remove restriction it is for video
        only.
     6. Minor cleanup in section 12 examples.
     7. Minor editorial corrections suggested by Christian Groves.

   Changes from 19 to 20:

     1. Define term "CLUE" in introduction.
     2. Add MCC attribute Allow Subset Choice.
     3. Remove phrase about reducing SDP size, replace with
        potentially saving consumer resources.
     4. Change example of a CLUE exchange that does not require SDP
        exchange.
     5. Language attribute uses RFC5646.
     6. Change Member person type to Attendee.  Add Observer type.
     7. Clarify DTLS/SRTP MUST be supported.
     8. Change SHOULD NOT to MUST NOT regarding using xCard or
        description information for authorization decisions.
     9. Clarify definition of Global View.
     10. Refer to signaling doc regarding interoperating with a
        device that does not support CLUE.
     11. Various minor editorial changes from working group last call
        feedback.
     12. Capitalize defined terms.

   Changes from 18 to 19:

     1. Remove the Max Capture Encodings media capture attribute.
     2. Refer to RTP mapping document in the MCC example section.
     3. Update references to current versions of drafts in progress.

   Changes from 17 to 18:



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     1. Add separate definition of Global View List.
     2. Add diagram for Global View List structure.
     3. Tweak definitions of Media Consumer and Provider.

   Changes from 16 to 17:

     1. Ticket #59 - rename Capture Scene Entry (CSE) to Capture
        Scene View (CSV)

     2. Ticket #60 - rename Global CSE List to Global View List

     3. Ticket #61 - Proposal for describing the coordinate system.
        Describe it better, without conflicts if cameras point in
        different directions.

     4. Minor clarifications and improved wording for Synchronisation
        Identity, MCC, Simultaneous Transmission Set.

     5. Add definitions for CLUE-capable device and CLUE-enabled
        call, taken from the signaling draft.

     6. Update definitions of Capture Device, Media Consumer, Media
        Provider, Endpoint, MCU, MCC.

     7. Replace "middle box" with "MCU".

     8. Explicitly state there can also be Media Captures that are
        not included in a Capture Scene View.

     9. Explicitly state "A single Encoding Group MAY refer to
        encodings for different media types."

     10. In example 12.1.1 add axes and audio captures to the
        diagram, and describe placement of microphones.

     11. Add references to data model and signaling drafts.

     12. Split references into Normative and Informative sections.
        Add heading number for references section.

   Changes from 15 to 16:

     1. Remove Audio Channel Format attribute



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     2. Add Audio Capture Sensitivity Pattern attribute

     3. Clarify audio spatial information regarding point of capture
        and point on line of capture.  Area of capture does not apply
        to audio.

     4. Update section 12 example for new treatment of audio spatial
        information.

     5. Clean up wording of some definitions, and various places in
        sections 5 and 10.

     6. Remove individual encoding parameter paragraph from section
        9.

     7. Update Advertisement diagram.

     8. Update Acknowledgements.

     9. References to use cases and requirements now refer to RFCs.

     10. Minor editorial changes.

   Changes from 14 to 15:

     1. Add "=" and "<=" qualifiers to MaxCaptures attribute, and
        clarify the meaning regarding switched and composed MCC.

     2. Add section 7.3.3 Global Capture Scene Entry List, and a few
        other sentences elsewhere that refer to global CSE sets.

     3. Clarify: The Provider MUST be capable of encoding and sending
        all Captures (*that have an encoding group*) in a single
        Capture Scene Entry simultaneously.

     4. Add voice activated switching example in section 12.

     5. Change name of attributes Participant Info/Type to Person
        Info/Type.

     6. Clarify the Person Info/Type attributes have the same meaning
        regardless of whether or not the capture has a Presentation
        attribute.




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     7. Update example section 12.1 to be consistent with the rest of
        the document, regarding MCC and capture attributes.

     8. State explicitly each CSE has a unique ID.

   Changes from 13 to 14:

     1. Fill in section for Security Considerations.

     2. Replace Role placeholder with Participant Information,
        Participant Type, and Scene Information attributes.

     3. Spatial information implies nothing about how constituent
        media captures are combined into a composed MCC.

     4. Clean up MCC example in Section 12.3.3.  Clarify behavior of
        tiled and PIP display windows.  Add audio.  Add new open
        issue about associating incoming packets to original source
        capture.

     5. Remove editor's note and associated statement about RTP
        multiplexing at end of section 5.

     6. Remove editor's note and associated paragraph about
        overloading media channel with both CLUE and non-CLUE usage,
        in section 5.

     7. In section 10, clarify intent of media encodings conforming
        to SDP, even with multiple CLUE message exchanges.  Remove
        associated editor's note.

   Changes from 12 to 13:

     1. Added the MCC concept including updates to existing sections
        to incorporate the MCC concept. New MCC attributes:
        MaxCaptures, SynchronisationID and Policy.

     2. Removed the "composed" and "switched" Capture attributes due
        to overlap with the MCC concept.

     3. Removed the "Scene-switch-policy" CSE attribute, replaced by
        MCC and SynchronisationID.

     4. Editorial enhancements including numbering of the Capture
        attribute sections, tables, figures etc.


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   Changes from 11 to 12:

     1. Ticket #44. Remove note questioning about requiring a
        Consumer to send a Configure after receiving Advertisement.

     2. Ticket #43. Remove ability for consumer to choose value of
        attribute for scene-switch-policy.

     3. Ticket #36. Remove computational complexity parameter,
        MaxGroupPps, from Encoding Groups.

     4. Reword the Abstract and parts of sections 1 and 4 (now 5)
        based on Mary's suggestions as discussed on the list.  Move
        part of the Introduction into a new section Overview &
        Motivation.

     5. Add diagram of an Advertisement, in the Overview of the
        Framework/Model section.

     6. Change Intended Status to Standards Track.

     7. Clean up RFC2119 keyword language.

   Changes from 10 to 11:

     1. Add description attribute to Media Capture and Capture Scene
        Entry.

     2. Remove contradiction and change the note about open issue
        regarding always responding to Advertisement with a Configure
        message.

     3. Update example section, to cleanup formatting and make the
        media capture attributes and encoding parameters consistent
        with the rest of the document.

   Changes from 09 to 10:

     1. Several minor clarifications such as about SDP usage, Media
        Captures, Configure message.

     2. Simultaneous Set can be expressed in terms of Capture Scene
        and Capture Scene Entry.

     3. Removed Area of Scene attribute.


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     4. Add attributes from draft-groves-clue-capture-attr-01.

     5. Move some of the Media Capture attribute descriptions back
        into this document, but try to leave detailed syntax to the
        data model.  Remove the OUTSOURCE sections, which are already
        incorporated into the data model document.



   Changes from 08 to 09:

     1. Use "document" instead of "memo".

     2. Add basic call flow sequence diagram to introduction.

     3. Add definitions for Advertisement and Configure messages.

     4. Add definitions for Capture and Provider.

     5. Update definition of Capture Scene.

     6. Update definition of Individual Encoding.

     7. Shorten definition of Media Capture and add key points in the
        Media Captures section.

     8. Reword a bit about capture scenes in overview.

     9. Reword about labeling Media Captures.

     10. Remove the Consumer Capability message.

     11. New example section heading for media provider behavior

     12. Clarifications in the Capture Scene section.

     13. Clarifications in the Simultaneous Transmission Set section.

     14. Capitalize defined terms.

     15. Move call flow example from introduction to overview section

     16. General editorial cleanup

     17. Add some editors' notes requesting input on issues


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     18. Summarize some sections, and propose details be outsourced
        to other documents.

   Changes from 06 to 07:

     1. Ticket #9.  Rename Axis of Capture Point attribute to Point
        on Line of Capture.  Clarify the description of this
        attribute.

     2. Ticket #17.  Add "capture encoding" definition.  Use this new
        term throughout document as appropriate, replacing some usage
        of the terms "stream" and "encoding".

     3. Ticket #18.  Add Max Capture Encodings media capture
        attribute.

     4. Add clarification that different capture scene entries are
        not necessarily mutually exclusive.

   Changes from 05 to 06:

   1. Capture scene description attribute is a list of text strings,
      each in a different language, rather than just a single string.

   2. Add new Axis of Capture Point attribute.

   3. Remove appendices A.1 through A.6.

   4. Clarify that the provider must use the same coordinate system
      with same scale and origin for all coordinates within the same
      capture scene.

   Changes from 04 to 05:

   1. Clarify limitations of "composed" attribute.

   2. Add new section "capture scene entry attributes" and add the
      attribute "scene-switch-policy".

   3. Add capture scene description attribute and description
      language attribute.

   4. Editorial changes to examples section for consistency with the
      rest of the document.



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   Changes from 03 to 04:

   1. Remove sentence from overview - "This constitutes a significant
      change ..."

   2. Clarify a consumer can choose a subset of captures from a
      capture scene entry or a simultaneous set (in section "capture
      scene" and "consumer's choice...").

   3. Reword first paragraph of Media Capture Attributes section.

   4. Clarify a stereo audio capture is different from two mono audio
      captures (description of audio channel format attribute).

   5. Clarify what it means when coordinate information is not
      specified for area of capture, point of capture, area of scene.

   6. Change the term "producer" to "provider" to be consistent (it
      was just in two places).

   7. Change name of "purpose" attribute to "content" and refer to
      RFC4796 for values.

   8. Clarify simultaneous sets are part of a provider advertisement,
      and apply across all capture scenes in the advertisement.

   9. Remove sentence about lip-sync between all media captures in a
      capture scene.

   10.   Combine the concepts of "capture scene" and "capture set"
      into a single concept, using the term "capture scene" to
      replace the previous term "capture set", and eliminating the
      original separate capture scene concept.

17. Normative References

   [I-D.ietf-clue-datachannel]
              Holmberg, C., "CLUE Protocol Data Channel", draft-
              ietf-clue-datachannel-11 (work in progress), November
              2015.

   [I-D.ietf-clue-data-model-schema]
              Presta, R., Romano, S P., "An XML Schema for the CLUE
              data model", draft-ietf-clue-data-model-schema-11 (work
              in progress), October 2015.


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   [I-D.ietf-clue-protocol]
              Presta, R. and S. Romano, "CLUE protocol", draft-
              ietf-clue-protocol-06 (work in progress), October 2015.

   [I-D.ietf-clue-signaling]
              Kyzivat, P., Xiao, L., Groves, C., Hansen, R., "CLUE
              Signaling", draft-ietf-clue-signaling-06 (work in
              progress), August 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G.,
              Johnston, A., Peterson, J., Sparks, R., Handley, M.,
              and E. Schooler, "SIP: Session Initiation Protocol",
              RFC 3261, June 2002.

   [RFC3264]  Rosenberg, J., Schulzrinne, H., "An Offer/Answer Model
              with the Session Description Protocol (SDP)", RFC 3264,
              June 2002.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC4566]  Handley, M., Jacobsen, V., Perkins, C., "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC4579]  Johnston, A., Levin, O., "SIP Call Control -
              Conferencing for User Agents", RFC 4579, August 2006

   [RFC5239]  Barnes, M., Boulton, C., Levin, O., "A Framework
              for Centralized Conferencing", RFC 5239, June 2008.

   [RFC5646]  Phillips, A., Davis, M., "Tags for Identifying
              Languages", RFC 5646, September 2009.

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              August 2011.

   [RFC6351]  Perreault, S., "xCard: vCard XML Representation",
              RFC 6351, August 2011.





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18. Informative References

   [I-D.ietf-clue-rtp-mapping]
              Even, R., Lennox, J., "Mapping RP streams to CLUE media
              captures", draft-ietf-clue-rtp-mapping-05 (work in
              progress), October 2015.

   [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
              Session Initiation Protocol (SIP)", RFC 4353,
              February 2006.

   [RFC5117]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC
              5117, January 2008.

   [RFC7201]  Westerlund, M., Perkins, C., "Options for Securing RTP
              Sessions", RFC 7201, April 2014.

   [RFC7202]  Perkins, C., Westerlund, M., "Why RTP Does Not Mandate
              a Single Media Security Solution ", RFC 7202, April
              2014.

   [RFC7205]  Romanow, A., Botzko, S., Duckworth, M., Even, R.,
              "Use Cases for Telepresence Multistreams", RFC 7205,
              April 2014.

   [RFC7262]  Romanow, A., Botzko, S., Barnes, M., "Requirements
              for Telepresence Multistreams", RFC 7262, June 2014.



19. Authors' Addresses

   Mark Duckworth (editor)
   Polycom
   Andover, MA  01810
   USA

   Email: mark.duckworth@polycom.com



   Andrew Pepperell
   Acano
   Uxbridge, England
   UK


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   Email: apeppere@gmail.com



   Stephan Wenger
   Vidyo, Inc.
   433 Hackensack Ave.
   Hackensack, N.J. 07601
   USA

   Email: stewe@stewe.org




































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