RFC 8846 An XML Schema for the CLUE Data Model January 2021
Presta & Romano Standards Track [Page]
Stream:
Internet Engineering Task Force (IETF)
RFC:
8846
Category:
Standards Track
Published:
ISSN:
2070-1721
Authors:
R. Presta
University of Napoli
S P. Romano
University of Napoli

RFC 8846

An XML Schema for the Controlling Multiple Streams for Telepresence (CLUE) Data Model

Abstract

This document provides an XML schema file for the definition of CLUE data model types. The term "CLUE" stands for "Controlling Multiple Streams for Telepresence" and is the name of the IETF working group in which this document, as well as other companion documents, has been developed. The document defines a coherent structure for information associated with the description of a telepresence scenario.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8846.

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Table of Contents

1. Introduction

This document provides an XML schema file for the definition of CLUE data model types. For the benefit of the reader, the term "CLUE" stands for "Controlling Multiple Streams for Telepresence" and is the name of the IETF working group in which this document, as well as other companion documents, has been developed. A thorough definition of the CLUE framework can be found in [RFC8845].

The schema is based on information contained in [RFC8845]. It encodes information and constraints defined in the aforementioned document in order to provide a formal representation of the concepts therein presented.

The document specifies the definition of a coherent structure for information associated with the description of a telepresence scenario. Such information is used within the CLUE protocol messages [RFC8847], enabling the dialogue between a Media Provider and a Media Consumer. CLUE protocol messages, indeed, are XML messages allowing (i) a Media Provider to advertise its telepresence capabilities in terms of media captures, capture scenes, and other features envisioned in the CLUE framework, according to the format herein defined and (ii) a Media Consumer to request the desired telepresence options in the form of capture encodings, represented as described in this document.

2. Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Definitions

This document refers to the same definitions used in [RFC8845], except for the "CLUE Participant" definition. We briefly recall herein some of the main terms used in the document.

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.
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 Participant:
This term is imported from the CLUE protocol document [RFC8847].
Consumer:
Short for Media Consumer.
Encoding or Individual Encoding:
A set of parameters representing a way to encode a Media Capture to become a Capture Encoding.
Encoding Group:
A set of encoding parameters representing a total media encoding capability to be subdivided across potentially multiple Individual Encodings.
Endpoint:
A CLUE-capable device that 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 that source and sink media streams, and exactly one participant [RFC4353] (which, in turn, includes exactly one SIP User Agent). Endpoints can be anything from multiscreen/multicamera rooms to handheld devices.
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 (for example, 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.
Multipoint Control Unit (MCU):
A CLUE-capable device that connects two or more endpoints together into one single multimedia conference [RFC7667]. An MCU includes a Mixer, similar to those in [RFC4353], but without the requirement to send media to each participant.
Plane of Interest:
The spatial plane within a scene containing the most-relevant subject matter.
Provider:
Same as a Media Provider.
Render:
The process of generating a representation from Media, such as displayed motion video or sound emitted from loudspeakers.
Scene:
Same as a Capture Scene.
Simultaneous Transmission Set:
A set of Media Captures that can be transmitted simultaneously from a Media Provider.
Single Media Capture:
A capture that contains media from a single source capture device, e.g., an audio capture from a single microphone or a video capture from a single camera.
Spatial Relation:
The arrangement of two objects in space, 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, bitrate, resolution, profile/level, etc.) as well as CLUE-specific attributes, such as the Capture ID or a spatial location.
Video Capture:
A Media Capture for video.

4. XML Schema

This section contains the XML schema for the CLUE data model definition.

The element and attribute definitions are formal representations of the concepts needed to describe the capabilities of a Media Provider and the streams that are requested by a Media Consumer given the Media Provider's ADVERTISEMENT [RFC8847].

The main groups of information are:

All of the above refer to concepts that have been introduced in [RFC8845] and further detailed in this document.

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema
   targetNamespace="urn:ietf:params:xml:ns:clue-info"
   xmlns:tns="urn:ietf:params:xml:ns:clue-info"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:clue-info"
   xmlns:xcard="urn:ietf:params:xml:ns:vcard-4.0"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified"
   version="1.0">

<!-- Import xCard XML schema -->
<xs:import namespace="urn:ietf:params:xml:ns:vcard-4.0"
schemaLocation=
  "https://www.iana.org/assignments/xml-registry/schema/
   vcard-4.0.xsd"/>

<!-- ELEMENT DEFINITIONS -->
<xs:element name="mediaCaptures" type="mediaCapturesType"/>
<xs:element name="encodingGroups" type="encodingGroupsType"/>
<xs:element name="captureScenes" type="captureScenesType"/>
<xs:element name="simultaneousSets" type="simultaneousSetsType"/>
<xs:element name="globalViews" type="globalViewsType"/>
<xs:element name="people" type="peopleType"/>

<xs:element name="captureEncodings" type="captureEncodingsType"/>


<!-- MEDIA CAPTURES TYPE -->
<!-- envelope of media captures -->
<xs:complexType name="mediaCapturesType">
 <xs:sequence>
   <xs:element name="mediaCapture" type="mediaCaptureType"
   maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>


<!-- DESCRIPTION element -->
<xs:element name="description">
 <xs:complexType>
  <xs:simpleContent>
   <xs:extension base="xs:string">
     <xs:attribute name="lang" type="xs:language"/>
   </xs:extension>
  </xs:simpleContent>
 </xs:complexType>
</xs:element>

<!-- MEDIA CAPTURE TYPE -->
<xs:complexType name="mediaCaptureType" abstract="true">
  <xs:sequence>
    <!-- mandatory fields -->
    <xs:element name="captureSceneIDREF" type="xs:IDREF"/>
    <xs:choice>
      <xs:sequence>
        <xs:element name="spatialInformation"
                    type="tns:spatialInformationType"/>
      </xs:sequence>
      <xs:element name="nonSpatiallyDefinable" type="xs:boolean"
      fixed="true"/>
    </xs:choice>
    <!-- for handling multicontent captures: -->
    <xs:choice>
      <xs:sequence>
        <xs:element name="synchronizationID" type="xs:ID"
         minOccurs="0"/>
        <xs:element name="content" type="contentType" minOccurs="0"/>
        <xs:element name="policy" type="policyType" minOccurs="0"/>
        <xs:element name="maxCaptures" type="maxCapturesType"
         minOccurs="0"/>
        <xs:element name="allowSubsetChoice" type="xs:boolean"
         minOccurs="0"/>
      </xs:sequence>
      <xs:element name="individual" type="xs:boolean" fixed="true"/>
    </xs:choice>
    <!-- optional fields -->
    <xs:element name="encGroupIDREF" type="xs:IDREF" minOccurs="0"/>
    <xs:element ref="description" minOccurs="0"
     maxOccurs="unbounded"/>
    <xs:element name="priority" type="xs:unsignedInt" minOccurs="0"/>
    <xs:element name="lang" type="xs:language" minOccurs="0"
     maxOccurs="unbounded"/>
        <xs:element name="mobility" type="mobilityType"
         minOccurs="0" />
    <xs:element ref="presentation" minOccurs="0" />
    <xs:element ref="embeddedText" minOccurs="0" />
    <xs:element ref="view" minOccurs="0" />
    <xs:element name="capturedPeople" type="capturedPeopleType"
     minOccurs="0"/>
    <xs:element name="relatedTo" type="xs:IDREF" minOccurs="0"/>
  </xs:sequence>
  <xs:attribute name="captureID" type="xs:ID" use="required"/>
  <xs:attribute name="mediaType" type="xs:string" use="required"/>

</xs:complexType>

<!-- POLICY TYPE -->
<xs:simpleType name="policyType">
 <xs:restriction base="xs:string">
      <xs:pattern value="([a-zA-Z0-9])+[:]([0-9])+"/>
    </xs:restriction>
</xs:simpleType>

<!-- CONTENT TYPE -->
<xs:complexType name="contentType">
 <xs:sequence>
   <xs:element name="mediaCaptureIDREF" type="xs:string"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="sceneViewIDREF" type="xs:string"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- MAX CAPTURES TYPE -->
<xs:simpleType name="positiveShort">
        <xs:restriction base="xs:unsignedShort">
                <xs:minInclusive value="1">
                </xs:minInclusive>
        </xs:restriction>
</xs:simpleType>

<xs:complexType name="maxCapturesType">
        <xs:simpleContent>
                <xs:extension base="positiveShort">
                        <xs:attribute name="exactNumber"
                                type="xs:boolean"/>
                </xs:extension>
        </xs:simpleContent>
</xs:complexType>

<!-- CAPTURED PEOPLE TYPE -->
<xs:complexType name="capturedPeopleType">
 <xs:sequence>
  <xs:element name="personIDREF" type="xs:IDREF"
   maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- PEOPLE TYPE -->
<xs:complexType name="peopleType">
 <xs:sequence>
  <xs:element name="person" type="personType" maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- PERSON TYPE -->
<xs:complexType name="personType">
  <xs:sequence>
     <xs:element name="personInfo" type="xcard:vcardType"
      maxOccurs="1" minOccurs="0"/>
     <xs:element ref="personType" minOccurs="0"
      maxOccurs="unbounded" />
     <xs:any namespace="##other" processContents="lax" minOccurs="0"
      maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:attribute name="personID" type="xs:ID" use="required"/>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- PERSON TYPE ELEMENT -->
<xs:element name="personType" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;personType&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

<!-- VIEW ELEMENT -->
<xs:element name="view" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;view&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

<!-- PRESENTATION ELEMENT -->
<xs:element name="presentation" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;presentation&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

<!-- SPATIAL INFORMATION TYPE -->
<xs:complexType name="spatialInformationType">
 <xs:sequence>
  <xs:element name="captureOrigin" type="captureOriginType"
   minOccurs="0"/>
  <xs:element name="captureArea" type="captureAreaType"
   minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>


<!-- POINT TYPE -->
<xs:complexType name="pointType">
 <xs:sequence>
  <xs:element name="x" type="xs:decimal"/>
  <xs:element name="y" type="xs:decimal"/>
  <xs:element name="z" type="xs:decimal"/>
 </xs:sequence>
</xs:complexType>

<!-- CAPTURE ORIGIN TYPE -->
<xs:complexType name="captureOriginType">
  <xs:sequence>
       <xs:element name="capturePoint" type="pointType"></xs:element>
       <xs:element name="lineOfCapturePoint" type="pointType"
        minOccurs="0">
       </xs:element>
  </xs:sequence>
  <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>


<!-- CAPTURE AREA TYPE -->
<xs:complexType name="captureAreaType">
 <xs:sequence>
  <xs:element name="bottomLeft" type="pointType"/>
  <xs:element name="bottomRight" type="pointType"/>
  <xs:element name="topLeft" type="pointType"/>
  <xs:element name="topRight" type="pointType"/>
 </xs:sequence>
</xs:complexType>


<!-- MOBILITY TYPE -->
<xs:simpleType name="mobilityType">
 <xs:restriction base="xs:string">
  <xs:enumeration value="static" />
  <xs:enumeration value="dynamic" />
  <xs:enumeration value="highly-dynamic" />
 </xs:restriction>
</xs:simpleType>

<!-- TEXT CAPTURE TYPE -->
<xs:complexType name="textCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
  <xs:sequence>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>


<!-- OTHER CAPTURE TYPE -->
<xs:complexType name="otherCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
  <xs:sequence>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

<!-- AUDIO CAPTURE TYPE -->
<xs:complexType name="audioCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
   <xs:sequence>
        <xs:element ref="sensitivityPattern" minOccurs="0" />
    <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>


<!-- SENSITIVITY PATTERN ELEMENT -->
<xs:element name="sensitivityPattern" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed by
   IANA in the "CLUE Schema &lt;sensitivityPattern&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>


<!-- VIDEO CAPTURE TYPE -->
<xs:complexType name="videoCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
   <xs:sequence>
    <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

<!-- EMBEDDED TEXT ELEMENT -->
<xs:element name="embeddedText">
 <xs:complexType>
  <xs:simpleContent>
   <xs:extension base="xs:boolean">
    <xs:attribute name="lang" type="xs:language"/>
   </xs:extension>
  </xs:simpleContent>
 </xs:complexType>
</xs:element>

<!-- CAPTURE SCENES TYPE -->
<!-- envelope of capture scenes -->
<xs:complexType name="captureScenesType">
 <xs:sequence>
  <xs:element name="captureScene" type="captureSceneType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- CAPTURE SCENE TYPE -->
<xs:complexType name="captureSceneType">
 <xs:sequence>
  <xs:element ref="description" minOccurs="0" maxOccurs="unbounded"/>
  <xs:element name="sceneInformation" type="xcard:vcardType"
   minOccurs="0"/>
  <xs:element name="sceneViews" type="sceneViewsType" minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
  maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="sceneID" type="xs:ID" use="required"/>
 <xs:attribute name="scale" type="scaleType" use="required"/>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- SCALE TYPE -->
<xs:simpleType name="scaleType">
 <xs:restriction base="xs:string">
  <xs:enumeration value="mm"/>
  <xs:enumeration value="unknown"/>
  <xs:enumeration value="noscale"/>
 </xs:restriction>
</xs:simpleType>

<!-- SCENE VIEWS TYPE -->
<!-- envelope of scene views of a capture scene -->
<xs:complexType name="sceneViewsType">
 <xs:sequence>
  <xs:element name="sceneView" type="sceneViewType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- SCENE VIEW TYPE -->
<xs:complexType name="sceneViewType">
 <xs:sequence>
  <xs:element ref="description" minOccurs="0" maxOccurs="unbounded"/>
  <xs:element name="mediaCaptureIDs" type="captureIDListType"/>
 </xs:sequence>
 <xs:attribute name="sceneViewID" type="xs:ID" use="required"/>
</xs:complexType>


<!-- CAPTURE ID LIST TYPE -->
<xs:complexType name="captureIDListType">
 <xs:sequence>
  <xs:element name="mediaCaptureIDREF" type="xs:IDREF"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- ENCODING GROUPS TYPE -->
<xs:complexType name="encodingGroupsType">
 <xs:sequence>
  <xs:element name="encodingGroup" type="tns:encodingGroupType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- ENCODING GROUP TYPE -->
<xs:complexType name="encodingGroupType">
 <xs:sequence>
  <xs:element name="maxGroupBandwidth" type="xs:unsignedLong"/>
  <xs:element name="encodingIDList" type="encodingIDListType"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
  maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="encodingGroupID" type="xs:ID" use="required"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<!-- ENCODING ID LIST TYPE -->
<xs:complexType name="encodingIDListType">
 <xs:sequence>
  <xs:element name="encodingID" type="xs:string"
   maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- SIMULTANEOUS SETS TYPE -->
<xs:complexType name="simultaneousSetsType">
 <xs:sequence>
  <xs:element name="simultaneousSet" type="simultaneousSetType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- SIMULTANEOUS SET TYPE -->
<xs:complexType name="simultaneousSetType">
 <xs:sequence>
   <xs:element name="mediaCaptureIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="sceneViewIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="captureSceneIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="setID" type="xs:ID" use="required"/>
 <xs:attribute name="mediaType" type="xs:string"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<!-- GLOBAL VIEWS TYPE -->
<xs:complexType name="globalViewsType">
 <xs:sequence>
  <xs:element name="globalView" type="globalViewType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- GLOBAL VIEW TYPE -->
<xs:complexType name="globalViewType">
 <xs:sequence>
   <xs:element name="sceneViewIDREF" type="xs:IDREF"
    maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="globalViewID" type="xs:ID"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<!-- CAPTURE ENCODINGS TYPE -->
<xs:complexType name="captureEncodingsType">
 <xs:sequence>
  <xs:element name="captureEncoding" type="captureEncodingType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

<!-- CAPTURE ENCODING TYPE -->
<xs:complexType name="captureEncodingType">
 <xs:sequence>
  <xs:element name="captureID" type="xs:string"/>
  <xs:element name="encodingID" type="xs:string"/>
  <xs:element name="configuredContent" type="contentType"
   minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="ID" type="xs:ID" use="required"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<!-- CLUE INFO ELEMENT -->
<xs:element name="clueInfo" type="clueInfoType"/>

<!-- CLUE INFO TYPE -->
<xs:complexType name="clueInfoType">
  <xs:sequence>
   <xs:element ref="mediaCaptures"/>
   <xs:element ref="encodingGroups"/>
   <xs:element ref="captureScenes"/>
   <xs:element ref="simultaneousSets" minOccurs="0"/>
   <xs:element ref="globalViews" minOccurs="0"/>
   <xs:element ref="people" minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:attribute name="clueInfoID" type="xs:ID" use="required"/>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>
</xs:schema>

The following sections describe the XML schema in more detail. As a general remark, please notice that optional elements that don't define what their absence means are intended to be associated with undefined properties.

5. <mediaCaptures>

<mediaCaptures> represents the list of one or more media captures available at the Media Provider's side. Each media capture is represented by a <mediaCapture> element (Section 11).

6. <encodingGroups>

<encodingGroups> represents the list of the encoding groups organized on the Media Provider's side. Each encoding group is represented by an <encodingGroup> element (Section 18).

7. <captureScenes>

<captureScenes> represents the list of the capture scenes organized on the Media Provider's side. Each capture scene is represented by a <captureScene> element (Section 16).

8. <simultaneousSets>

<simultaneousSets> contains the simultaneous sets indicated by the Media Provider. Each simultaneous set is represented by a <simultaneousSet> element (Section 19).

9. <globalViews>

<globalViews> contains a set of alternative representations of all the scenes that are offered by a Media Provider to a Media Consumer. Each alternative is named "global view", and it is represented by a <globalView> element (Section 20).

10. <captureEncodings>

<captureEncodings> is a list of capture encodings. It can represent the list of the desired capture encodings indicated by the Media Consumer or the list of instantiated captures on the provider's side. Each capture encoding is represented by a <captureEncoding> element (Section 22).

11. <mediaCapture>

A media capture is the fundamental representation of a media flow that is available on the provider's side. Media captures are characterized by (i) a set of features that are independent from the specific type of medium and (ii) a set of features that are media specific. The features that are common to all media types appear within the media capture type, which has been designed as an abstract complex type. Media-specific captures, such as video captures, audio captures, and others, are specializations of that abstract media capture type, as in a typical generalization-specialization hierarchy.

The following is the XML schema definition of the media capture type:

<!-- MEDIA CAPTURE TYPE -->
<xs:complexType name="mediaCaptureType" abstract="true">
  <xs:sequence>
    <!-- mandatory fields -->
    <xs:element name="captureSceneIDREF" type="xs:IDREF"/>
    <xs:choice>
      <xs:sequence>
        <xs:element name="spatialInformation"
                    type="tns:spatialInformationType"/>
      </xs:sequence>
      <xs:element name="nonSpatiallyDefinable" type="xs:boolean"
      fixed="true"/>
    </xs:choice>
    <!-- for handling multicontent captures: -->
    <xs:choice>
      <xs:sequence>
        <xs:element name="synchronizationID" type="xs:ID"
         minOccurs="0"/>
        <xs:element name="content" type="contentType" minOccurs="0"/>
        <xs:element name="policy" type="policyType" minOccurs="0"/>
        <xs:element name="maxCaptures" type="maxCapturesType"
         minOccurs="0"/>
        <xs:element name="allowSubsetChoice" type="xs:boolean"
         minOccurs="0"/>
      </xs:sequence>
      <xs:element name="individual" type="xs:boolean" fixed="true"/>
    </xs:choice>
    <!-- optional fields -->
    <xs:element name="encGroupIDREF" type="xs:IDREF" minOccurs="0"/>
    <xs:element ref="description" minOccurs="0"
     maxOccurs="unbounded"/>
    <xs:element name="priority" type="xs:unsignedInt" minOccurs="0"/>
    <xs:element name="lang" type="xs:language" minOccurs="0"
     maxOccurs="unbounded"/>
    <xs:element name="mobility" type="mobilityType" minOccurs="0" />
    <xs:element ref="presentation" minOccurs="0" />
    <xs:element ref="embeddedText" minOccurs="0" />
    <xs:element ref="view" minOccurs="0" />
    <xs:element name="capturedPeople" type="capturedPeopleType"
     minOccurs="0"/>
    <xs:element name="relatedTo" type="xs:IDREF" minOccurs="0"/>
  </xs:sequence>
  <xs:attribute name="captureID" type="xs:ID" use="required"/>
  <xs:attribute name="mediaType" type="xs:string" use="required"/>
</xs:complexType>

11.1. captureID Attribute

The "captureID" attribute is a mandatory field containing the identifier of the media capture. Such an identifier serves as the way the capture is referenced from other data model elements (e.g., simultaneous sets, capture encodings, and others via <mediaCaptureIDREF>).

11.2. mediaType Attribute

The "mediaType" attribute is a mandatory attribute specifying the media type of the capture. Common standard values are "audio", "video", and "text", as defined in [RFC6838]. Other values can be provided. It is assumed that implementations agree on the interpretation of those other values. The "mediaType" attribute is as generic as possible. Here is why: (i) the basic media capture type is an abstract one; (ii) "concrete" definitions for the standard audio, video, and text capture types [RFC6838] have been specified; (iii) a generic "otherCaptureType" type has been defined; and (iv) the "mediaType" attribute has been generically defined as a string, with no particular template. From the considerations above, it is clear that if one chooses to rely on a brand new media type and wants to interoperate with others, an application-level agreement is needed on how to interpret such information.

11.3. <captureSceneIDREF>

<captureSceneIDREF> is a mandatory field containing the value of the identifier of the capture scene the media capture is defined in, i.e., the value of the sceneID attribute (Section 16.3) of that capture scene. Indeed, each media capture MUST be defined within one and only one capture scene. When a media capture is spatially definable, some spatial information is provided along with it in the form of point coordinates (see Section 11.5). Such coordinates refer to the space of coordinates defined for the capture scene containing the capture.

11.4. <encGroupIDREF>

<encGroupIDREF> is an optional field containing the identifier of the encoding group the media capture is associated with, i.e., the value of the encodingGroupID attribute (Section 18.3) of that encoding group. Media captures that are not associated with any encoding group cannot be instantiated as media streams.

11.5. <spatialInformation>

Media captures are divided into two categories: (i) non spatially definable captures and (ii) spatially definable captures.

Captures are spatially definable when at least it is possible to provide (i) the coordinates of the device position within the telepresence room of origin (capture point) together with its capturing direction specified by a second point (point on line of capture) or (ii) the represented area within the telepresence room, by listing the coordinates of the four coplanar points identifying the plane of interest (area of capture). The coordinates of the above mentioned points MUST be expressed according to the coordinate space of the capture scene the media captures belong to.

Non spatially definable captures cannot be characterized within the physical space of the telepresence room of origin. Captures of this kind are, for example, those related to recordings, text captures, DVDs, registered presentations, or external streams that are played in the telepresence room and transmitted to remote sites.

Spatially definable captures represent a part of the telepresence room. The captured part of the telepresence room is described by means of the <spatialInformation> element. By comparing the <spatialInformation> element of different media captures within the same capture scene, a consumer can better determine the spatial relationships between them and render them correctly. Non spatially definable captures do not embed such elements in their XML description: they are instead characterized by having the <nonSpatiallyDefinable> tag set to "true" (see Section 11.6).

The definition of the spatial information type is the following:

<!-- SPATIAL INFORMATION TYPE -->
<xs:complexType name="spatialInformationType">
 <xs:sequence>
  <xs:element name="captureOrigin" type="captureOriginType"
   minOccurs="0"/>
  <xs:element name="captureArea" type="captureAreaType"
   minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

The <captureOrigin> contains the coordinates of the capture device that is taking the capture (i.e., the capture point) as well as, optionally, the pointing direction (i.e., the point on line of capture); see Section 11.5.1.

The <captureArea> is an optional field containing four points defining the captured area covered by the capture (see Section 11.5.2).

The scale of the points coordinates is specified in the scale attribute (Section 16.4) of the capture scene the media capture belongs to. Indeed, all the spatially definable media captures referring to the same capture scene share the same coordinate system and express their spatial information according to the same scale.

11.5.1. <captureOrigin>

The <captureOrigin> element is used to represent the position and optionally the line of capture of a capture device. <captureOrigin> MUST be included in spatially definable audio captures, while it is optional for spatially definable video captures.

The XML schema definition of the <captureOrigin> element type is the following:

<!-- CAPTURE ORIGIN TYPE -->
<xs:complexType name="captureOriginType">
  <xs:sequence>
        <xs:element name="capturePoint" type="pointType"/>
        <xs:element name="lineOfCapturePoint" type="pointType"
         minOccurs="0"/>
  </xs:sequence>
  <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

<!-- POINT TYPE -->
<xs:complexType name="pointType">
 <xs:sequence>
  <xs:element name="x" type="xs:decimal"/>
  <xs:element name="y" type="xs:decimal"/>
  <xs:element name="z" type="xs:decimal"/>
 </xs:sequence>
</xs:complexType>

The point type contains three spatial coordinates (x,y,z) representing a point in the space associated with a certain capture scene.

The <captureOrigin> element includes a mandatory <capturePoint> element and an optional <lineOfCapturePoint> element, both of the type "pointType". <capturePoint> specifies the three coordinates identifying the position of the capture device. <lineOfCapturePoint> is another pointType element representing the "point on line of capture", which gives the pointing direction of the capture device.

The coordinates of the point on line of capture MUST NOT be identical to the capture point coordinates. For a spatially definable video capture, if the point on line of capture is provided, it MUST belong to the region between the point of capture and the capture area. For a spatially definable audio capture, if the point on line of capture is not provided, the sensitivity pattern should be considered omnidirectional.

11.5.2. <captureArea>

<captureArea> is an optional element that can be contained within the spatial information associated with a media capture. It represents the spatial area captured by the media capture. <captureArea> MUST be included in the spatial information of spatially definable video captures, while it MUST NOT be associated with audio captures.

The XML representation of that area is provided through a set of four point-type elements, <bottomLeft>, <bottomRight>, <topLeft>, and <topRight>, that MUST be coplanar. The four coplanar points are identified from the perspective of the capture device. The XML schema definition is the following:

<!-- CAPTURE AREA TYPE -->
<xs:complexType name="captureAreaType">
 <xs:sequence>
  <xs:element name="bottomLeft" type="pointType"/>
  <xs:element name="bottomRight" type="pointType"/>
  <xs:element name="topLeft" type="pointType"/>
  <xs:element name="topRight" type="pointType"/>
 </xs:sequence>
</xs:complexType>

11.6. <nonSpatiallyDefinable>

When media captures are non spatially definable, they MUST be marked with the boolean <nonSpatiallyDefinable> element set to "true", and no <spatialInformation> MUST be provided. Indeed, <nonSpatiallyDefinable> and <spatialInformation> are mutually exclusive tags, according to the <choice> section within the XML schema definition of the media capture type.

11.7. <content>

A media capture can be (i) an individual media capture or (ii) an MCC. An MCC is made by different captures that can be arranged spatially (by a composition operation), or temporally (by a switching operation), or that can result from the orchestration of both the techniques. If a media capture is an MCC, then it MAY show in its XML data model representation the <content> element. It is composed by a list of media capture identifiers ("mediaCaptureIDREF") and capture scene view identifiers ("sceneViewIDREF"), where the latter ones are used as shortcuts to refer to multiple capture identifiers. The referenced captures are used to create the MCC according to a certain strategy. If the <content> element does not appear in an MCC, or it has no child elements, then the MCC is assumed to be made of multiple sources, but no information regarding those sources is provided.

<!-- CONTENT TYPE -->
<xs:complexType name="contentType">
 <xs:sequence>
   <xs:element name="mediaCaptureIDREF" type="xs:string"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="sceneViewIDREF" type="xs:string"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

11.8. <synchronizationID>

<synchronizationID> is an optional element for multiple content captures that contains a numeric identifier. Multiple content captures marked with the same identifier in the <synchronizationID> contain at all times captures coming from the same sources. It is the Media Provider that determines what the source is for the captures. In this way, the Media Provider can choose how to group together single captures for the purpose of keeping them synchronized according to the <synchronizationID> element.

11.9. <allowSubsetChoice>

<allowSubsetChoice> is an optional boolean element for multiple content captures. It indicates 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 specify 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. If <allowSubsetChoice> is not shown in the XML description of the MCC, its value is to be considered "false".

11.10. <policy>

<policy> is an optional element that can be used only for multiple content captures. It indicates the criteria applied to build the multiple content capture using the media captures referenced in the <mediaCaptureIDREF> list. The <policy> value is in the form of a token that indicates the policy and an index representing an instance of the policy, separated by a ":" (e.g., SoundLevel:2, RoundRobin:0, etc.). The XML schema defining the type of the <policy> element is the following:

<!-- POLICY TYPE -->
<xs:simpleType name="policyType">
 <xs:restriction base="xs:string">
      <xs:pattern value="([a-zA-Z0-9])+[:]([0-9])+"/>
    </xs:restriction>
</xs:simpleType>

At the time of writing, only two switching policies are defined; they are in [RFC8845] as follows:

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.

Other values for the <policy> element can be used. In this case, it is assumed that implementations agree on the meaning of those other values and/or those new switching policies are defined in later documents.

11.11. <maxCaptures>

<maxCaptures> is an optional element that can be used only for MCCs. It provides information about the number of media captures that can be represented in the multiple content capture at a time. If <maxCaptures> is not provided, all the media captures listed in the <content> element can appear at a time in the capture encoding. The type definition is provided below.

<!-- MAX CAPTURES TYPE -->
<xs:simpleType name="positiveShort">
        <xs:restriction base="xs:unsignedShort">
                <xs:minInclusive value="1">
                </xs:minInclusive>
        </xs:restriction>
</xs:simpleType>

<xs:complexType name="maxCapturesType">
        <xs:simpleContent>
                <xs:extension base="positiveShort">
                        <xs:attribute name="exactNumber"
                                type="xs:boolean"/>
                </xs:extension>
        </xs:simpleContent>
</xs:complexType>

When the "exactNumber" attribute is set to "true", it means the <maxCaptures> element carries the exact number of the media captures appearing at a time. Otherwise, the number of the represented media captures MUST be considered "<=" the <maxCaptures> value.

For instance, an audio MCC having the <maxCaptures> value set to 1 means that a media stream from the MCC will only contain audio from a single one of its constituent captures at a time. On the other hand, if the <maxCaptures> value is set to 4 and the exactNumber attribute is set to "true", it would mean that the media stream received from the MCC will always contain a mix of audio from exactly four of its constituent captures.

11.12. <individual>

<individual> is a boolean element that MUST be used for single-content captures. Its value is fixed and set to "true". Such element indicates the capture that is being described is not an MCC. Indeed, <individual> and the aforementioned tags related to MCC attributes (from Sections 11.7 to 11.11) are mutually exclusive, according to the <choice> section within the XML schema definition of the media capture type.

11.13. <description>

<description> is used to provide human-readable textual information. This element is included in the XML definition of media captures, capture scenes, and capture scene views to provide human-readable descriptions of, respectively, media captures, capture scenes, and capture scene views. According to the data model definition of a media capture (Section 11)), zero or more <description> elements can be used, each providing information in a different language. The <description> element definition is the following:

<!-- DESCRIPTION element -->
<xs:element name="description">
 <xs:complexType>
  <xs:simpleContent>
   <xs:extension base="xs:string">
     <xs:attribute name="lang" type="xs:language"/>
   </xs:extension>
  </xs:simpleContent>
 </xs:complexType>
</xs:element>

As can be seen, <description> is a string element with an attribute ("lang") indicating the language used in the textual description. Such an attribute is compliant with the Language-Tag ABNF production from [RFC5646].

11.14. <priority>

<priority> is an optional unsigned integer field indicating the importance of a media capture according to the Media Provider's perspective. It can be used on the receiver's side to automatically identify the most relevant contribution from the Media Provider. The higher the importance, the lower the contained value. If no priority is assigned, no assumptions regarding relative importance of the media capture can be assumed.

11.15. <lang>

<lang> is an optional element containing the language used in the capture. Zero or more <lang> elements can appear in the XML description of a media capture. Each such element has to be compliant with the Language-Tag ABNF production from [RFC5646].

11.16. <mobility>

<mobility> is an optional element indicating whether or not the capture device originating the capture may move during the telepresence session. That optional element can assume one of the three following values:

  • static:
    SHOULD NOT change for the duration of the CLUE session, across multiple ADVERTISEMENT messages.
    dynamic:
    MAY change in each new ADVERTISEMENT message. Can be assumed to remain unchanged until there is a new ADVERTISEMENT message.
    highly-dynamic:
    MAY change dynamically, even between consecutive ADVERTISEMENT messages. The spatial information provided in an ADVERTISEMENT message is simply a snapshot of the current values at the time when the message is sent.

11.17. <relatedTo>

The optional <relatedTo> element contains the value of the captureID attribute (Section 11.1) of the media capture to which the considered media capture refers. The media capture marked with a <relatedTo> element can be, for example, the translation of the referred media capture in a different language.

11.18. <view>

The <view> element is an optional tag describing what is represented in the spatial area covered by a media capture. It has been specified as a simple string with an annotation pointing to an IANA registry that is defined ad hoc:

<!-- VIEW ELEMENT -->
<xs:element name="view" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;view&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

The current possible values, as per the CLUE framework document [RFC8845], are: "room", "table", "lectern", "individual", and "audience".

11.19. <presentation>

The <presentation> element is an optional tag used for media captures conveying information about presentations within the telepresence session. It has been specified as a simple string with an annotation pointing to an IANA registry that is defined ad hoc:

<!-- PRESENTATION ELEMENT -->
<xs:element name="presentation" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;presentation&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

The current possible values, as per the CLUE framework document [RFC8845], are "slides" and "images".

11.20. <embeddedText>

The <embeddedText> element is a boolean element indicating that there is text embedded in the media capture (e.g., in a video capture). The language used in such an embedded textual description is reported in the <embeddedText> "lang" attribute.

The XML schema definition of the <embeddedText> element is:

<!-- EMBEDDED TEXT ELEMENT -->
<xs:element name="embeddedText">
 <xs:complexType>
  <xs:simpleContent>
   <xs:extension base="xs:boolean">
    <xs:attribute name="lang" type="xs:language"/>
   </xs:extension>
  </xs:simpleContent>
 </xs:complexType>
</xs:element>

11.21. <capturedPeople>

This optional element is used to indicate which telepresence session participants are represented in within the media captures. For each participant, a <personIDREF> element is provided.

11.21.1. <personIDREF>

<personIDREF> contains the identifier of the represented person, i.e., the value of the related personID attribute (Section 21.1.1). Metadata about the represented participant can be retrieved by accessing the <people> list (Section 21).

12. Audio Captures

Audio captures inherit all the features of a generic media capture and present further audio-specific characteristics. The XML schema definition of the audio capture type is reported below:

<!-- AUDIO CAPTURE TYPE -->
<xs:complexType name="audioCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
   <xs:sequence>
        <xs:element ref="sensitivityPattern" minOccurs="0" />
    <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

An example of audio-specific information that can be included is represented by the <sensitivityPattern> element (Section 12.1).

12.1. <sensitivityPattern>

The <sensitivityPattern> element is an optional field describing the characteristics of the nominal sensitivity pattern of the microphone capturing the audio signal. It has been specified as a simple string with an annotation pointing to an IANA registry that is defined ad hoc:

<!-- SENSITIVITY PATTERN ELEMENT -->
<xs:element name="sensitivityPattern" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed by
   IANA in the "CLUE Schema &lt;sensitivityPattern&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

The current possible values, as per the CLUE framework document [RFC8845], are "uni", "shotgun", "omni", "figure8", "cardioid", and "hyper-cardioid".

13. Video Captures

Video captures, similarly to audio captures, extend the information of a generic media capture with video-specific features.

The XML schema representation of the video capture type is provided in the following:

<!-- VIDEO CAPTURE TYPE -->
<xs:complexType name="videoCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
   <xs:sequence>
    <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

14. Text Captures

Similar to audio captures and video captures, text captures can be described by extending the generic media capture information.

There are no known properties of a text-based media that aren't already covered by the generic mediaCaptureType. Text captures are hence defined as follows:

<!-- TEXT CAPTURE TYPE -->
<xs:complexType name="textCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
  <xs:sequence>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

Text captures MUST be marked as non spatially definable (i.e., they MUST present in their XML description the <nonSpatiallyDefinable> (Section 11.6) element set to "true").

15. Other Capture Types

Other media capture types can be described by using the CLUE data model. They can be represented by exploiting the "otherCaptureType" type. This media capture type is conceived to be filled in with elements defined within extensions of the current schema, i.e., with elements defined in other XML schemas (see Section 24 for an example). The otherCaptureType inherits all the features envisioned for the abstract mediaCaptureType.

The XML schema representation of the otherCaptureType is the following:

<!-- OTHER CAPTURE TYPE -->
<xs:complexType name="otherCaptureType">
 <xs:complexContent>
  <xs:extension base="tns:mediaCaptureType">
  <xs:sequence>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
    maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

When defining new media capture types that are going to be described by means of the <otherMediaCapture> element, spatial properties of such new media capture types SHOULD be defined (e.g., whether or not they are spatially definable and whether or not they should be associated with an area of capture or other properties that may be defined).

16. <captureScene>

A Media Provider organizes the available captures in capture scenes in order to help the receiver in both the rendering and the selection of the group of captures. Capture scenes are made of media captures and capture scene views, which are sets of media captures of the same media type. Each capture scene view is an alternative to completely represent a capture scene for a fixed media type.

The XML schema representation of a <captureScene> element is the following:

<!-- CAPTURE SCENE TYPE -->
<xs:complexType name="captureSceneType">
 <xs:sequence>
  <xs:element ref="description" minOccurs="0" maxOccurs="unbounded"/>
  <xs:element name="sceneInformation" type="xcard:vcardType"
   minOccurs="0"/>
  <xs:element name="sceneViews" type="sceneViewsType" minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
  maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="sceneID" type="xs:ID" use="required"/>
 <xs:attribute name="scale" type="scaleType" use="required"/>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

Each capture scene is identified by a "sceneID" attribute. The <captureScene> element can contain zero or more textual <description> elements, as defined in Section 11.13. Besides <description>, there is the optional <sceneInformation> element (Section 16.1), which contains structured information about the scene in the vCard format, and the optional <sceneViews> element (Section 16.2), which is the list of the capture scene views. When no <sceneViews> is provided, the capture scene is assumed to be made of all the media captures that contain the value of its sceneID attribute in their mandatory captureSceneIDREF attribute.

16.1. <sceneInformation>

The <sceneInformation> element contains optional information about the capture scene according to the vCard format, as specified in the xCard specification [RFC6351].

16.2. <sceneViews>

The <sceneViews> element is a mandatory field of a capture scene containing the list of scene views. Each scene view is represented by a <sceneView> element (Section 17).

<!-- SCENE VIEWS TYPE -->
<!-- envelope of scene views of a capture scene -->
<xs:complexType name="sceneViewsType">
 <xs:sequence>
  <xs:element name="sceneView" type="sceneViewType"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

16.3. sceneID Attribute

The sceneID attribute is a mandatory attribute containing the identifier of the capture scene.

16.4. scale Attribute

The scale attribute is a mandatory attribute that specifies the scale of the coordinates provided in the spatial information of the media capture belonging to the considered capture scene. The scale attribute can assume three different values:

  • "mm":
    the scale is in millimeters. Systems that know their physical dimensions (for example, professionally installed telepresence room systems) should always provide such real-world measurements.
    "unknown":
    the scale is the same for every media capture in the capture scene, but the unity of measure is undefined. Systems that are not aware of specific physical dimensions yet still know relative distances should select "unknown" in the scale attribute of the capture scene to be described.
    "noscale":
    there is no common physical scale among the media captures of the capture scene. That means the scale could be different for each media capture. 
<!-- SCALE TYPE -->
<xs:simpleType name="scaleType">
 <xs:restriction base="xs:string">
  <xs:enumeration value="mm"/>
  <xs:enumeration value="unknown"/>
  <xs:enumeration value="noscale"/>
 </xs:restriction>
</xs:simpleType>

17. <sceneView>

A <sceneView> element represents a capture scene view, which contains a set of media captures of the same media type describing a capture scene.

A <sceneView> element is characterized as follows.

<!-- SCENE VIEW TYPE -->
<xs:complexType name="sceneViewType">
 <xs:sequence>
  <xs:element ref="description" minOccurs="0" maxOccurs="unbounded"/>
  <xs:element name="mediaCaptureIDs" type="captureIDListType"/>
 </xs:sequence>
 <xs:attribute name="sceneViewID" type="xs:ID" use="required"/>
</xs:complexType>

One or more optional <description> elements provide human-readable information about what the scene view contains. <description> is defined in Section 11.13.

The remaining child elements are described in the following subsections.

17.1. <mediaCaptureIDs>

<mediaCaptureIDs> is the list of the identifiers of the media captures included in the scene view. It is an element of the captureIDListType type, which is defined as a sequence of <mediaCaptureIDREF>, each containing the identifier of a media capture listed within the <mediaCaptures> element:

<!-- CAPTURE ID LIST TYPE -->
<xs:complexType name="captureIDListType">
 <xs:sequence>
  <xs:element name="mediaCaptureIDREF" type="xs:IDREF"
  maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

17.2. sceneViewID Attribute

The sceneViewID attribute is a mandatory attribute containing the identifier of the capture scene view represented by the <sceneView> element.

18. <encodingGroup>

The <encodingGroup> element represents an encoding group, which is made by a set of one or more individual encodings and some parameters that apply to the group as a whole. Encoding groups contain references to individual encodings that can be applied to media captures. The definition of the <encodingGroup> element is the following:

<!-- ENCODING GROUP TYPE -->
<xs:complexType name="encodingGroupType">
 <xs:sequence>
  <xs:element name="maxGroupBandwidth" type="xs:unsignedLong"/>
  <xs:element name="encodingIDList" type="encodingIDListType"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
  maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="encodingGroupID" type="xs:ID" use="required"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

In the following subsections, the contained elements are further described.

18.1. <maxGroupBandwidth>

<maxGroupBandwidth> is an optional field containing the maximum bitrate expressed in bits per second that can be shared by the individual encodings included in the encoding group.

18.2. <encodingIDList>

<encodingIDList> is the list of the individual encodings grouped together in the encoding group. Each individual encoding is represented through its identifier contained within an <encodingID> element.

<!-- ENCODING ID LIST TYPE -->
<xs:complexType name="encodingIDListType">
 <xs:sequence>
  <xs:element name="encodingID" type="xs:string"
   maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

18.3. encodingGroupID Attribute

The encodingGroupID attribute contains the identifier of the encoding group.

19. <simultaneousSet>

<simultaneousSet> represents a simultaneous transmission set, i.e., a list of captures of the same media type that can be transmitted at the same time by a Media Provider. There are different simultaneous transmission sets for each media type.

<!-- SIMULTANEOUS SET TYPE -->
<xs:complexType name="simultaneousSetType">
 <xs:sequence>
   <xs:element name="mediaCaptureIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="sceneViewIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:element name="captureSceneIDREF" type="xs:IDREF"
   minOccurs="0" maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="setID" type="xs:ID" use="required"/>
 <xs:attribute name="mediaType" type="xs:string"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

Besides the identifiers of the captures (<mediaCaptureIDREF> elements), the identifiers of capture scene views and capture scenes can also be exploited as shortcuts (<sceneViewIDREF> and <captureSceneIDREF> elements). As an example, let's consider the situation where there are two capture scene views (S1 and S7). S1 contains captures AC11, AC12, and AC13. S7 contains captures AC71 and AC72. Provided that AC11, AC12, AC13, AC71, and AC72 can be simultaneously sent to the Media Consumer, instead of having 5 <mediaCaptureIDREF> elements listed in the simultaneous set (i.e., one <mediaCaptureIDREF> for AC11, one for AC12, and so on), there can be just two <sceneViewIDREF> elements (one for S1 and one for S7).

19.1. setID Attribute

The "setID" attribute is a mandatory field containing the identifier of the simultaneous set.

19.2. mediaType Attribute

The "mediaType" attribute is an optional attribute containing the media type of the captures referenced by the simultaneous set.

When only capture scene identifiers are listed within a simultaneous set, the media type attribute MUST appear in the XML description in order to determine which media captures can be simultaneously sent together.

19.3. <mediaCaptureIDREF>

<mediaCaptureIDREF> contains the identifier of the media capture that belongs to the simultaneous set.

19.4. <sceneViewIDREF>

<sceneViewIDREF> contains the identifier of the scene view containing a group of captures that are able to be sent simultaneously with the other captures of the simultaneous set.

19.5. <captureSceneIDREF>

<captureSceneIDREF> contains the identifier of the capture scene where all the included captures of a certain media type are able to be sent together with the other captures of the simultaneous set.

20. <globalView>

<globalView> is a set of captures of the same media type representing a summary of the complete Media Provider's offer. The content of a global view is expressed by leveraging only scene view identifiers, put within <sceneViewIDREF> elements. Each global view is identified by a unique identifier within the "globalViewID" attribute.

<!-- GLOBAL VIEW TYPE -->
<xs:complexType name="globalViewType">
 <xs:sequence>
   <xs:element name="sceneViewIDREF" type="xs:IDREF"
    maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="globalViewID" type="xs:ID"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

21. <people>

Information about the participants that are represented in the media captures is conveyed via the <people> element. As it can be seen from the XML schema depicted below, for each participant, a <person> element is provided.

<!-- PEOPLE TYPE -->
<xs:complexType name="peopleType">
 <xs:sequence>
  <xs:element name="person" type="personType" maxOccurs="unbounded"/>
 </xs:sequence>
</xs:complexType>

21.1. <person>

<person> includes all the metadata related to a person represented within one or more media captures. Such element provides the vCard of the subject (via the <personInfo> element; see Section 21.1.2) and its conference role(s) (via one or more <personType> elements; see Section 21.1.3). Furthermore, it has a mandatory "personID" attribute (Section 21.1.1).

<!-- PERSON TYPE -->
<xs:complexType name="personType">
 <xs:sequence>
  <xs:element name="personInfo" type="xcard:vcardType" maxOccurs="1"
   minOccurs="0"/>
  <xs:element ref="personType" minOccurs="0" maxOccurs="unbounded" />
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="personID" type="xs:ID" use="required"/>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

21.1.1. personID Attribute

The "personID" attribute carries the identifier of a represented person. Such an identifier can be used to refer to the participant, as in the <capturedPeople> element in the media captures representation (Section 11.21).

21.1.2. <personInfo>

The <personInfo> element is the XML representation of all the fields composing a vCard as specified in the xCard document [RFC6351]. The vcardType is imported by the xCard XML schema provided in Appendix A of [RFC7852]. As such schema specifies, the <fn> element within <vcard> is mandatory.

21.1.3. <personType>

The value of the <personType> element determines the role of the represented participant within the telepresence session organization. It has been specified as a simple string with an annotation pointing to an IANA registry that is defined ad hoc:

<!-- PERSON TYPE ELEMENT -->
<xs:element name="personType" type="xs:string">
 <xs:annotation>
  <xs:documentation>
   Acceptable values (enumerations) for this type are managed
   by IANA in the "CLUE Schema &lt;personType&gt;" registry,
   accessible at https://www.iana.org/assignments/clue.
  </xs:documentation>
 </xs:annotation>
</xs:element>

The current possible values, as per the CLUE framework document [RFC8845], are: "presenter", "timekeeper", "attendee", "minute taker", "translator", "chairman", "vice-chairman", and "observer".

A participant can play more than one conference role. In that case, more than one <personType> element will appear in its description.

22. <captureEncoding>

A capture encoding is given from the association of a media capture with an individual encoding, to form a capture stream as defined in [RFC8845]. Capture encodings are used within CONFIGURE messages from a Media Consumer to a Media Provider for representing the streams desired by the Media Consumer. For each desired stream, the Media Consumer needs to be allowed to specify: (i) the capture identifier of the desired capture that has been advertised by the Media Provider; (ii) the encoding identifier of the encoding to use, among those advertised by the Media Provider; and (iii) optionally, in case of multicontent captures, the list of the capture identifiers of the desired captures. All the mentioned identifiers are intended to be included in the ADVERTISEMENT message that the CONFIGURE message refers to. The XML model of <captureEncoding> is provided in the following.

<!-- CAPTURE ENCODING TYPE -->
<xs:complexType name="captureEncodingType">
 <xs:sequence>
  <xs:element name="captureID" type="xs:string"/>
  <xs:element name="encodingID" type="xs:string"/>
  <xs:element name="configuredContent" type="contentType"
   minOccurs="0"/>
  <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="ID" type="xs:ID" use="required"/>
 <xs:anyAttribute namespace="##any" processContents="lax"/>
</xs:complexType>

22.1. <captureID>

<captureID> is the mandatory element containing the identifier of the media capture that has been encoded to form the capture encoding.

22.2. <encodingID>

<encodingID> is the mandatory element containing the identifier of the applied individual encoding.

22.3. <configuredContent>

<configuredContent> is an optional element to be used in case of the configuration of MCC. It contains the list of capture identifiers and capture scene view identifiers the Media Consumer wants within the MCC. That element is structured as the <content> element used to describe the content of an MCC. The total number of media captures listed in the <configuredContent> MUST be lower than or equal to the value carried within the <maxCaptures> attribute of the MCC.

23. <clueInfo>

The <clueInfo> element includes all the information needed to represent the Media Provider's description of its telepresence capabilities according to the CLUE framework. Indeed, it is made by:

It has been conceived only for data model testing purposes, and though it resembles the body of an ADVERTISEMENT message, it is not actually used in the CLUE protocol message definitions. The telepresence capabilities descriptions compliant to this data model specification that can be found in Sections 27 and 28 are provided by using the <clueInfo> element.

<!-- CLUE INFO TYPE -->
<xs:complexType name="clueInfoType">
  <xs:sequence>
   <xs:element ref="mediaCaptures"/>
   <xs:element ref="encodingGroups"/>
   <xs:element ref="captureScenes"/>
   <xs:element ref="simultaneousSets" minOccurs="0"/>
   <xs:element ref="globalViews" minOccurs="0"/>
   <xs:element ref="people" minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"
   maxOccurs="unbounded"/>
  </xs:sequence>
  <xs:attribute name="clueInfoID" type="xs:ID" use="required"/>
  <xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

24. XML Schema Extensibility

The telepresence data model defined in this document is meant to be extensible. Extensions are accomplished by defining elements or attributes qualified by namespaces other than "urn:ietf:params:xml:ns:clue-info" and "urn:ietf:params:xml:ns:vcard-4.0" for use wherever the schema allows such extensions (i.e., where the XML schema definition specifies "anyAttribute" or "anyElement"). Elements or attributes from unknown namespaces MUST be ignored. Extensibility was purposefully favored as much as possible based on expectations about custom implementations. Hence, the schema offers people enough flexibility as to define custom extensions, without losing compliance with the standard. This is achieved by leveraging <xs:any> elements and <xs:anyAttribute> attributes, which is a common approach with schemas, while still matching the Unique Particle Attribution (UPA) constraint.

24.1. Example of Extension

When extending the CLUE data model, a new schema with a new namespace associated with it needs to be specified.

In the following, an example of extension is provided. The extension defines a new audio capture attribute ("newAudioFeature") and an attribute for characterizing the captures belonging to an "otherCaptureType" defined by the user. An XML document compliant with the extension is also included. The XML file results are validated against the current XML schema for the CLUE data model.

<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema
   targetNamespace="urn:ietf:params:xml:ns:clue-info-ext"
   xmlns:tns="urn:ietf:params:xml:ns:clue-info-ext"
   xmlns:clue-ext="urn:ietf:params:xml:ns:clue-info-ext"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns="urn:ietf:params:xml:ns:clue-info-ext"
   xmlns:xcard="urn:ietf:params:xml:ns:vcard-4.0"
   xmlns:info="urn:ietf:params:xml:ns:clue-info"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified">

<!-- Import xCard XML schema -->
<xs:import namespace="urn:ietf:params:xml:ns:vcard-4.0"
schemaLocation=
  "https://www.iana.org/assignments/xml-registry/schema/
   vcard-4.0.xsd"/>

<!-- Import CLUE XML schema -->
<xs:import namespace="urn:ietf:params:xml:ns:clue-info"
schemaLocation="clue-data-model-schema.xsd"/>

<!-- ELEMENT DEFINITIONS -->
<xs:element name="newAudioFeature" type="xs:string"/>
<xs:element name="otherMediaCaptureTypeFeature" type="xs:string"/>

</xs:schema>

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<clueInfo xmlns="urn:ietf:params:xml:ns:clue-info"
xmlns:ns2="urn:ietf:params:xml:ns:vcard-4.0"
xmlns:ns3="urn:ietf:params:xml:ns:clue-info-ext"
clueInfoID="NapoliRoom">
    <mediaCaptures>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="audioCaptureType"
        captureID="AC0"
        mediaType="audio">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <nonSpatiallyDefinable>true</nonSpatiallyDefinable>
            <individual>true</individual>
            <encGroupIDREF>EG1</encGroupIDREF>
            <ns3:newAudioFeature>newAudioFeatureValue
            </ns3:newAudioFeature>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="otherCaptureType"
        captureID="OMC0"
        mediaType="other media type">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <nonSpatiallyDefinable>true</nonSpatiallyDefinable>
            <encGroupIDREF>EG1</encGroupIDREF>
            <ns3:otherMediaCaptureTypeFeature>OtherValue
            </ns3:otherMediaCaptureTypeFeature>
        </mediaCapture>
    </mediaCaptures>
    <encodingGroups>
        <encodingGroup encodingGroupID="EG1">
            <maxGroupBandwidth>300000</maxGroupBandwidth>
            <encodingIDList>
                <encodingID>ENC4</encodingID>
                <encodingID>ENC5</encodingID>
            </encodingIDList>
        </encodingGroup>
    </encodingGroups>
    <captureScenes>
        <captureScene scale="unknown" sceneID="CS1"/>
    </captureScenes>
</clueInfo>

25. Security Considerations

This document defines, through an XML schema, a data model for telepresence scenarios. The modeled information is identified in the CLUE framework as necessary in order to enable a full-fledged media stream negotiation and rendering. Indeed, the XML elements herein defined are used within CLUE protocol messages to describe both the media streams representing the Media Provider's telepresence offer and the desired selection requested by the Media Consumer. Security concerns described in [RFC8845], Section 15 apply to this document.

Data model information carried within CLUE messages SHOULD be accessed only by authenticated endpoints. Indeed, authenticated access is strongly advisable, especially if you convey information about individuals (<personalInfo>) and/or scenes (<sceneInformation>). There might be more exceptions, depending on the level of criticality that is associated with the setup and configuration of a specific session. In principle, one might even decide that no protection at all is needed for a particular session; here is why authentication has not been identified as a mandatory requirement.

Going deeper into details, some information published by the Media Provider might reveal sensitive data about who and what is represented in the transmitted streams. The vCard included in the <personInfo> elements (Section 21.1) mandatorily contains the identity of the represented person. Optionally, vCards can also carry the person's contact addresses, together with their photo and other personal data. Similar privacy-critical information can be conveyed by means of <sceneInformation> elements (Section 16.1) describing the capture scenes. The <description> elements (Section 11.13) also can specify details about the content of media captures, capture scenes, and scene views that should be protected.

Integrity attacks to the data model information encapsulated in CLUE messages can invalidate the success of the telepresence session's setup by misleading the Media Consumer's and Media Provider's interpretation of the offered and desired media streams.

The assurance of the authenticated access and of the integrity of the data model information is up to the involved transport mechanisms, namely the CLUE protocol [RFC8847] and the CLUE data channel [RFC8850].

XML parsers need to be robust with respect to malformed documents. Reading malformed documents from unknown or untrusted sources could result in an attacker gaining privileges of the user running the XML parser. In an extreme situation, the entire machine could be compromised.

26. IANA Considerations

This document registers a new XML namespace, a new XML schema, the media type for the schema, and four new registries associated, respectively, with acceptable <view>, <presentation>, <sensitivityPattern>, and <personType> values.

26.1. XML Namespace Registration

URI:
urn:ietf:params:xml:ns:clue-info
Registrant Contact:
IETF CLUE Working Group <clue@ietf.org>, Roberta Presta <roberta.presta@unina.it>
XML:
<CODE BEGINS>
<?xml version="1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML Basic 1.0//EN"
 "http://www.w3.org/TR/xhtml-basic/xhtml-basic10.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
 <head>
  <meta http-equiv="content-type"
        content="text/html;charset=iso-8859-1"/>
  <title>CLUE Data Model Namespace</title>
 </head>
 <body>
  <h1>Namespace for CLUE Data Model</h1>
  <h2>urn:ietf:params:xml:ns:clue-info</h2>
  <p>See
   <a href="https://www.rfc-editor.org/rfc/rfc8846.txt">RFC 8846</a>.
  </p>
 </body>
</html>

<CODE ENDS>

26.2. XML Schema Registration

This section registers an XML schema per the guidelines in [RFC3688].

URI:
urn:ietf:params:xml:schema:clue-info
Registrant Contact:
CLUE Working Group (clue@ietf.org), Roberta Presta (roberta.presta@unina.it).
Schema:
The XML for this schema can be found in its entirety in Section 4 of this document.

26.3. Media Type Registration for "application/clue_info+xml"

This section registers the "application/clue_info+xml" media type.

To:
ietf-types@iana.org
Subject:
Registration of media type application/clue_info+xml
Type name:
application
Subtype name:
clue_info+xml
Required parameters:
(none)
Optional parameters:
charset Same as the charset parameter of "application/xml" as specified in [RFC7303], Section 3.2.
Encoding considerations:
Same as the encoding considerations of "application/xml" as specified in [RFC7303], Section 3.2.
Security considerations:
This content type is designed to carry data related to telepresence information. Some of the data could be considered private. This media type does not provide any protection and thus other mechanisms such as those described in Section 25 are required to protect the data. This media type does not contain executable content.
Interoperability considerations:
None.
Published specification:
RFC 8846
Applications that use this media type:
CLUE-capable telepresence systems.
Additional Information:


Magic Number(s):
none
File extension(s):
.clue
Macintosh File Type Code(s):
TEXT
Person & email address to contact for further information:
Roberta Presta (roberta.presta@unina.it).
Intended usage:
LIMITED USE
Author/Change controller:
The IETF
Other information:
This media type is a specialization of "application/xml" [RFC7303], and many of the considerations described there also apply to "application/clue_info+xml".

26.4. Registry for Acceptable <view> Values

IANA has created a registry of acceptable values for the <view> tag as defined in Section 11.18. The initial values for this registry are "room", "table", "lectern", "individual", and "audience".

New values are assigned by Expert Review per [RFC8126]. This reviewer will ensure that the requested registry entry conforms to the prescribed formatting.

26.5. Registry for Acceptable <presentation> Values

IANA has created a registry of acceptable values for the <presentation> tag as defined in Section 11.19. The initial values for this registry are "slides" and "images".

New values are assigned by Expert Review per [RFC8126]. This reviewer will ensure that the requested registry entry conforms to the prescribed formatting.

26.6. Registry for Acceptable <sensitivityPattern> Values

IANA has created a registry of acceptable values for the <sensitivityPattern> tag as defined in Section 12.1. The initial values for this registry are "uni", "shotgun", "omni", "figure8", "cardioid", and "hyper-cardioid".

New values are assigned by Expert Review per [RFC8126]. This reviewer will ensure that the requested registry entry conforms to the prescribed formatting.

26.7. Registry for Acceptable <personType> Values

IANA has created a registry of acceptable values for the <personType> tag as defined in Section 21.1.3. The initial values for this registry are "presenter", "timekeeper", "attendee", "minute taker", "translator", "chairman", "vice-chairman", and "observer".

New values are assigned by Expert Review per [RFC8126]. This reviewer will ensure that the requested registry entry conforms to the prescribed formatting.

27. Sample XML File

The following XML document represents a schema-compliant example of a CLUE telepresence scenario. Taking inspiration from the examples described in the framework specification [RFC8845], the XML representation of an endpoint-style Media Provider's ADVERTISEMENT is provided.

There are three cameras, where the central one is also capable of capturing a zoomed-out view of the overall telepresence room. Besides the three video captures coming from the cameras, the Media Provider makes available a further multicontent capture of the loudest segment of the room, obtained by switching the video source across the three cameras. For the sake of simplicity, only one audio capture is advertised for the audio of the whole room.

The three cameras are placed in front of three participants (Alice, Bob, and Ciccio), whose vCard and conference role details are also provided.

Media captures are arranged into four capture scene views:

  1. (VC0, VC1, VC2) - left, center, and right camera video captures
  2. (VC3) - video capture associated with loudest room segment
  3. (VC4) - video capture zoomed-out view of all people in the room
  4. (AC0) - main audio

There are two encoding groups: (i) EG0, for video encodings, and (ii) EG1, for audio encodings.

As to the simultaneous sets, VC1 and VC4 cannot be transmitted simultaneously since they are captured by the same device, i.e., the central camera (VC4 is a zoomed-out view while VC1 is a focused view of the front participant). On the other hand, VC3 and VC4 cannot be simultaneous either, since VC3, the loudest segment of the room, might be at a certain point in time focusing on the central part of the room, i.e., the same as VC1. The simultaneous sets would then be the following:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<clueInfo xmlns="urn:ietf:params:xml:ns:clue-info"
          xmlns:ns2="urn:ietf:params:xml:ns:vcard-4.0"
          clueInfoID="NapoliRoom">
    <mediaCaptures>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="audioCaptureType" captureID="AC0"
              mediaType="audio">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                    <lineOfCapturePoint>
                        <x>0.0</x>
                        <y>1.0</y>
                        <z>10.0</z>
                    </lineOfCapturePoint>
                </captureOrigin>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG1</encGroupIDREF>
            <description lang="en">main audio from the room
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>room</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
                <personIDREF>bob</personIDREF>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="videoCaptureType" captureID="VC0"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>-2.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">left camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC1"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">central camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC2"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>2.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">right camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>bob</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC3"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <content>
                <sceneViewIDREF>SE1</sceneViewIDREF>
            </content>
            <policy>SoundLevel:0</policy>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">loudest room segment</description>
            <priority>2</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC4"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>7.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>7.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>13.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>13.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">zoomed-out view of all people
            in the room</description>
            <priority>2</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>room</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
                <personIDREF>bob</personIDREF>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
    </mediaCaptures>
    <encodingGroups>
        <encodingGroup encodingGroupID="EG0">
            <maxGroupBandwidth>600000</maxGroupBandwidth>
            <encodingIDList>
                <encodingID>ENC1</encodingID>
                <encodingID>ENC2</encodingID>
                <encodingID>ENC3</encodingID>
            </encodingIDList>
        </encodingGroup>
        <encodingGroup encodingGroupID="EG1">
            <maxGroupBandwidth>300000</maxGroupBandwidth>
            <encodingIDList>
                <encodingID>ENC4</encodingID>
                <encodingID>ENC5</encodingID>
            </encodingIDList>
        </encodingGroup>
    </encodingGroups>
    <captureScenes>
        <captureScene scale="unknown" sceneID="CS1">
            <sceneViews>
                <sceneView sceneViewID="SE1">
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC0</mediaCaptureIDREF>
                        <mediaCaptureIDREF>VC1</mediaCaptureIDREF>
                        <mediaCaptureIDREF>VC2</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE2">
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC3</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE3">
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC4</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE4">
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>AC0</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
            </sceneViews>
        </captureScene>
    </captureScenes>
    <simultaneousSets>
        <simultaneousSet setID="SS1">
            <mediaCaptureIDREF>VC3</mediaCaptureIDREF>
            <sceneViewIDREF>SE1</sceneViewIDREF>
        </simultaneousSet>
        <simultaneousSet setID="SS2">
            <mediaCaptureIDREF>VC0</mediaCaptureIDREF>
            <mediaCaptureIDREF>VC2</mediaCaptureIDREF>
            <mediaCaptureIDREF>VC4</mediaCaptureIDREF>
        </simultaneousSet>
    </simultaneousSets>
    <people>
        <person personID="bob">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Bob</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>minute taker</personType>
        </person>
        <person personID="alice">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Alice</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>presenter</personType>
        </person>
        <person personID="ciccio">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Ciccio</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>chairman</personType>
            <personType>timekeeper</personType>
        </person>
    </people>
</clueInfo>

28. MCC Example

Enhancing the scenario presented in the previous example, the Media Provider is able to advertise a composed capture VC7 made by a big picture representing the current speaker (VC3) and two picture-in-picture boxes representing the previous speakers (the previous one, VC5, and the oldest one, VC6). The provider does not want to instantiate and send VC5 and VC6, so it does not associate any encoding group with them. Their XML representations are provided for enabling the description of VC7.

A possible description for that scenario could be the following:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<clueInfo xmlns="urn:ietf:params:xml:ns:clue-info"
xmlns:ns2="urn:ietf:params:xml:ns:vcard-4.0" clueInfoID="NapoliRoom">
    <mediaCaptures>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="audioCaptureType" captureID="AC0"
              mediaType="audio">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                    <lineOfCapturePoint>
                        <x>0.0</x>
                        <y>1.0</y>
                        <z>10.0</z>
                    </lineOfCapturePoint>
                </captureOrigin>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG1</encGroupIDREF>
            <description lang="en">main audio from the room
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>room</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
                <personIDREF>bob</personIDREF>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC0"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.5</x>
                        <y>1.0</y>
                        <z>0.5</z>
                    </capturePoint>
                    <lineOfCapturePoint>
                        <x>0.5</x>
                        <y>0.0</y>
                        <z>0.5</z>
                    </lineOfCapturePoint>
                </captureOrigin>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">left camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC1"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">central camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC2"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>2.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>1.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">right camera video capture
            </description>
            <priority>1</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
            <capturedPeople>
                <personIDREF>bob</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
        xsi:type="videoCaptureType" captureID="VC3"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <content>
                <sceneViewIDREF>SE1</sceneViewIDREF>
            </content>
            <policy>SoundLevel:0</policy>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">loudest room segment</description>
            <priority>2</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="videoCaptureType" captureID="VC4"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureOrigin>
                        <capturePoint>
                        <x>0.0</x>
                        <y>0.0</y>
                        <z>10.0</z>
                    </capturePoint>
                </captureOrigin>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>7.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>7.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>13.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>13.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <individual>true</individual>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">
              zoomed-out view of all people in the room
            </description>
            <priority>2</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>room</view>
            <capturedPeople>
                <personIDREF>alice</personIDREF>
                <personIDREF>bob</personIDREF>
                <personIDREF>ciccio</personIDREF>
            </capturedPeople>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="videoCaptureType" captureID="VC5"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <content>
                <sceneViewIDREF>SE1</sceneViewIDREF>
            </content>
            <policy>SoundLevel:1</policy>
            <description lang="en">previous loudest room segment
            per the most recent iteration of the sound level
            detection algorithm
            </description>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="videoCaptureType" captureID="VC6"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <content>
                <sceneViewIDREF>SE1</sceneViewIDREF>
            </content>
            <policy>SoundLevel:2</policy>
            <description lang="en">previous loudest room segment
            per the second most recent iteration of the sound
            level detection algorithm
            </description>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
        </mediaCapture>
        <mediaCapture
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:type="videoCaptureType" captureID="VC7"
              mediaType="video">
            <captureSceneIDREF>CS1</captureSceneIDREF>
            <spatialInformation>
                <captureArea>
                        <bottomLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomLeft>
                        <bottomRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>9.0</z>
                        </bottomRight>
                        <topLeft>
                                <x>-3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topLeft>
                        <topRight>
                                <x>3.0</x>
                        <y>20.0</y>
                        <z>11.0</z>
                        </topRight>
                </captureArea>
            </spatialInformation>
            <content>
                <mediaCaptureIDREF>VC3</mediaCaptureIDREF>
                <mediaCaptureIDREF>VC5</mediaCaptureIDREF>
                <mediaCaptureIDREF>VC6</mediaCaptureIDREF>
            </content>
            <maxCaptures exactNumber="true">3</maxCaptures>
            <encGroupIDREF>EG0</encGroupIDREF>
            <description lang="en">big picture of the current
            speaker + pips about previous speakers</description>
            <priority>3</priority>
            <lang>it</lang>
            <mobility>static</mobility>
            <view>individual</view>
        </mediaCapture>
    </mediaCaptures>
    <encodingGroups>
        <encodingGroup encodingGroupID="EG0">
            <maxGroupBandwidth>600000</maxGroupBandwidth>
            <encodingIDList>
                <encodingID>ENC1</encodingID>
                <encodingID>ENC2</encodingID>
                <encodingID>ENC3</encodingID>
            </encodingIDList>
        </encodingGroup>
        <encodingGroup encodingGroupID="EG1">
            <maxGroupBandwidth>300000</maxGroupBandwidth>
            <encodingIDList>
                <encodingID>ENC4</encodingID>
                <encodingID>ENC5</encodingID>
            </encodingIDList>
        </encodingGroup>
    </encodingGroups>
    <captureScenes>
        <captureScene scale="unknown" sceneID="CS1">
            <sceneViews>
                <sceneView sceneViewID="SE1">
                    <description lang="en">participants' individual
                    videos</description>
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC0</mediaCaptureIDREF>
                        <mediaCaptureIDREF>VC1</mediaCaptureIDREF>
                        <mediaCaptureIDREF>VC2</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE2">
                    <description lang="en">loudest segment of the
                    room</description>
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC3</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE5">
                    <description lang="en">loudest segment of the
                    room + pips</description>
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC7</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE4">
                    <description lang="en">room audio</description>
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>AC0</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
                <sceneView sceneViewID="SE3">
                    <description lang="en">room video</description>
                    <mediaCaptureIDs>
                        <mediaCaptureIDREF>VC4</mediaCaptureIDREF>
                    </mediaCaptureIDs>
                </sceneView>
            </sceneViews>
        </captureScene>
    </captureScenes>
    <simultaneousSets>
        <simultaneousSet setID="SS1">
            <mediaCaptureIDREF>VC3</mediaCaptureIDREF>
            <mediaCaptureIDREF>VC7</mediaCaptureIDREF>
            <sceneViewIDREF>SE1</sceneViewIDREF>
        </simultaneousSet>
        <simultaneousSet setID="SS2">
            <mediaCaptureIDREF>VC0</mediaCaptureIDREF>
            <mediaCaptureIDREF>VC2</mediaCaptureIDREF>
            <mediaCaptureIDREF>VC4</mediaCaptureIDREF>
        </simultaneousSet>
    </simultaneousSets>
    <people>
        <person personID="bob">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Bob</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>minute taker</personType>
        </person>
        <person personID="alice">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Alice</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>presenter</personType>
        </person>
        <person personID="ciccio">
            <personInfo>
                <ns2:fn>
                    <ns2:text>Ciccio</ns2:text>
                </ns2:fn>
            </personInfo>
            <personType>chairman</personType>
            <personType>timekeeper</personType>
        </person>
    </people>
</clueInfo>

29. References

29.1. Normative References

[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC5646]
Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, , <https://www.rfc-editor.org/info/rfc5646>.
[RFC6351]
Perreault, S., "xCard: vCard XML Representation", RFC 6351, DOI 10.17487/RFC6351, , <https://www.rfc-editor.org/info/rfc6351>.
[RFC7303]
Thompson, H. and C. Lilley, "XML Media Types", RFC 7303, DOI 10.17487/RFC7303, , <https://www.rfc-editor.org/info/rfc7303>.
[RFC7852]
Gellens, R., Rosen, B., Tschofenig, H., Marshall, R., and J. Winterbottom, "Additional Data Related to an Emergency Call", RFC 7852, DOI 10.17487/RFC7852, , <https://www.rfc-editor.org/info/rfc7852>.
[RFC8126]
Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, , <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8845]
Duckworth, M., Ed., Pepperell, A., and S. Wenger, "Framework for Telepresence Multi-Streams", RFC 8845, DOI 10.17487/RFC8845, , <https://www.rfc-editor.org/info/rfc8845>.
[RFC8847]
Presta, R. and S P. Romano, "Protocol for Controlling Multiple Streams for Telepresence (CLUE)", RFC 8847, DOI 10.17487/RFC8847, , <https://www.rfc-editor.org/info/rfc8847>.
[RFC8850]
Holmberg, C., "Controlling Multiple Streams for Telepresence (CLUE) Protocol Data Channel", RFC 8850, DOI 10.17487/RFC8850, , <https://www.rfc-editor.org/info/rfc8850>.

29.2. Informative References

[RFC3550]
Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, , <https://www.rfc-editor.org/info/rfc3550>.
[RFC3688]
Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/info/rfc3688>.
[RFC4353]
Rosenberg, J., "A Framework for Conferencing with the Session Initiation Protocol (SIP)", RFC 4353, DOI 10.17487/RFC4353, , <https://www.rfc-editor.org/info/rfc4353>.
[RFC6838]
Freed, N., Klensin, J., and T. Hansen, "Media Type Specifications and Registration Procedures", BCP 13, RFC 6838, DOI 10.17487/RFC6838, , <https://www.rfc-editor.org/info/rfc6838>.
[RFC7667]
Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667, DOI 10.17487/RFC7667, , <https://www.rfc-editor.org/info/rfc7667>.

Acknowledgements

The authors thank all the CLUE contributors for their valuable feedback and support. Thanks also to Alissa Cooper, whose AD review helped us improve the quality of the document.

Authors' Addresses

Roberta Presta
University of Napoli
Via Claudio 21
80125 Napoli
Italy
Simon Pietro Romano
University of Napoli
Via Claudio 21
80125 Napoli
Italy