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Versions: (draft-presta-clue-protocol) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 Draft is active
In: AD_Evaluation
CLUE Working Group                                             R. Presta
Internet-Draft                                                 S. Romano
Intended status: Standards Track                    University of Napoli
Expires: August 27, 2017                               February 23, 2017


                             CLUE protocol
                      draft-ietf-clue-protocol-13

Abstract

   The CLUE protocol is an application protocol conceived for the
   description and negotiation of a telepresence session.  The design of
   the CLUE protocol takes into account the requirements and the
   framework defined within the IETF CLUE working group.  A companion
   document delves into CLUE signaling details, as well as on the SIP/
   SDP session establishment phase.  CLUE messages flow over the CLUE
   data channel, based on reliable and ordered SCTP over DTLS transport.
   Message details, together with the behavior of CLUE Participants
   acting as Media Providers and/or Media Consumers, are herein
   discussed.

Status of This Memo

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

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

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

   This Internet-Draft will expire on August 27, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Overview of the CLUE protocol . . . . . . . . . . . . . . . .   4
   5.  Protocol messages . . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . .   9
     5.2.  OPTIONS RESPONSE  . . . . . . . . . . . . . . . . . . . .  11
     5.3.  ADVERTISEMENT . . . . . . . . . . . . . . . . . . . . . .  12
     5.4.  ADVERTISEMENT ACKNOWLEDGEMENT . . . . . . . . . . . . . .  13
     5.5.  CONFIGURE . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.6.  CONFIGURE RESPONSE  . . . . . . . . . . . . . . . . . . .  14
     5.7.  Response codes and reason strings . . . . . . . . . . . .  15
   6.  Protocol state machines . . . . . . . . . . . . . . . . . . .  17
     6.1.  Media Provider's state machine  . . . . . . . . . . . . .  19
     6.2.  Media Consumer's state machine  . . . . . . . . . . . . .  23
   7.  Versioning  . . . . . . . . . . . . . . . . . . . . . . . . .  26
   8.  Extensions  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     8.1.  Extension example . . . . . . . . . . . . . . . . . . . .  28
   9.  XML Schema  . . . . . . . . . . . . . . . . . . . . . . . . .  30
   10. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  34
     10.1.  Simple ADV . . . . . . . . . . . . . . . . . . . . . . .  35
     10.2.  ADV with MCCs  . . . . . . . . . . . . . . . . . . . . .  42
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  52
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  54
     12.1.  URN Sub-Namespace Registration . . . . . . . . . . . . .  54
     12.2.  XML Schema registration  . . . . . . . . . . . . . . . .  54
     12.3.  MIME Media Type Registration for 'application/clue+xml'   55
     12.4.  CLUE Protocol Registry . . . . . . . . . . . . . . . . .  56
       12.4.1.  CLUE Message Types . . . . . . . . . . . . . . . . .  56
       12.4.2.  CLUE Response Codes  . . . . . . . . . . . . . . . .  57
   13. Diff with draft-ietf-clue-protocol-12 . . . . . . . . . . . .  59
   14. Diff with draft-ietf-clue-protocol-06 . . . . . . . . . . . .  59
   15. Diff with draft-ietf-clue-protocol-05 . . . . . . . . . . . .  59
   16. Diff with draft-ietf-clue-protocol-04 . . . . . . . . . . . .  59
   17. Diff with draft-ietf-clue-protocol-03 . . . . . . . . . . . .  59
   18. Diff with draft-ietf-clue-protocol-02 . . . . . . . . . . . .  59
   19. Diff with draft-ietf-clue-protocol-01 . . . . . . . . . . . .  60
   20. Diff with draft-ietf-clue-protocol-00 . . . . . . . . . . . .  60
   21. Diff with draft-presta-clue-protocol-04 . . . . . . . . . . .  60
   22. Diff with draft-presta-clue-protocol-03 . . . . . . . . . . .  61



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   23. Diff with draft-presta-clue-protocol-02 . . . . . . . . . . .  61
   24. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  61
   25. References  . . . . . . . . . . . . . . . . . . . . . . . . .  61
     25.1.  Normative References . . . . . . . . . . . . . . . . . .  61
     25.2.  Informative References . . . . . . . . . . . . . . . . .  62
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  63

1.  Introduction

   The CLUE protocol is an application protocol used by two CLUE
   Participants to enhance the experience of a multimedia telepresence
   session.  The main goals of the CLUE protocol are:

   1.  enabling a Media Provider (MP) to properly announce its current
       telepresence capabilities to a Media Consumer (MC) in terms of
       available media captures, groups of encodings, simultaneity
       constraints and other information defined in
       [I-D.ietf-clue-framework];

   2.  enabling an MC to request the desired multimedia streams from the
       offering MP.

   CLUE-capable endpoints are connected by means of the CLUE data
   channel, an SCTP over DTLS channel which is opened and established as
   described in [I-D.ietf-clue-signaling] and
   [I-D.ietf-clue-datachannel].  CLUE protocol messages flowing over
   such a channel are detailed in this document, both syntactically and
   semantically.

   In Section 4 we provide a general overview of the CLUE protocol.
   CLUE protocol messages are detailed in Section 5.  The CLUE Protocol
   state machines are introduced in Section 6.  Versioning and
   extensions are discussed in Section 7 and Section 8, respectively.
   The XML schema defining the CLUE messages is reported in Section 9.

2.  Terminology

   This document refers to the same terminology used in
   [I-D.ietf-clue-framework] and in [RFC7262].  We briefly recall herein
   some of the main terms used in the document.  The definition of "CLUE
   Participant" herein proposed is not imported from any of the above
   documents.

   CLUE Participant (CP):  An entity able to use the CLUE protocol
      within a telepresence session.  It can be an endpoint or an MCU
      able to use the CLUE protocol.





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

   Endpoint:  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 which source and sink media streams,
      and exactly one Participant (e.g., a [RFC4353] participant).
      Endpoints can be anything from multiscreen/multicamera room
      controllers to handheld devices.

   MCU:  Multipoint Control Unit (MCU) - a device that connects two or
      more endpoints together into one single multimedia conference
      [RFC7667].  An MCU may include a Mixer [RFC4353].

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

   Media Capture:  A "Media Capture", or simply "Capture", is a source
      of Media.

   Media Consumer (MC):  A CLUE Participant (i.e., an Endpoint or an
      MCU) able to receive Media Streams.

   Capture Encoding:  A specific encoding of a Media Capture, to be sent
      via RTP [RFC3550].

   Media Provider (MP):  A CLUE Participant (i.e., an Endpoint or an
      MCU) able to send Media Streams.

   Media Stream:  The term "Media Stream", or simply "Stream", is used
      as a synonym of Capture Encoding.

3.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in BCP 14, RFC 2119
   [RFC2119].

4.  Overview of the CLUE protocol

   The CLUE protocol is conceived to enable CLUE telepresence sessions.
   It is designed in order to address SDP limitations in terms of the
   description of some information about the multimedia streams that are
   involved in a real-time multimedia conference.  Indeed, by simply
   using SDP it is not possible to convey information about the features



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   of the flowing multimedia streams that are needed to enable a "being
   there" rendering experience.  Such information is contained in the
   CLUE framework document and formally defined and described in the
   CLUE data model document.  The CLUE protocol represents the mechanism
   for the exchange of CLUE information between CLUE Participants.  It
   mainly provides the messages to enable a Media Provider to advertise
   its telepresence capabilities and to enable a Media Consumer to
   select the desired telepresence options.

   The CLUE protocol, as defined in the following, is a stateful,
   client-server, XML-based application protocol.  CLUE protocol
   messages flow on a reliable and ordered SCTP over DTLS transport
   channel connecting two CLUE Participants.  Messages carry information
   taken from the XML-based CLUE data model
   ([I-D.ietf-clue-data-model-schema]).  Three main communication phases
   can be identified:

   1.  Establishment of the CLUE data channel: in this phase, the CLUE
       data channel setup takes place.  If it completes successfully,
       the CPs are able to communicate and start the initiation phase.

   2.  Negotiation of the CLUE protocol version and extensions
       (initiation phase): the CPs connected via the CLUE data channel
       agree on the version and on the extensions to be used during the
       telepresence session.  Special CLUE messages are used for such a
       task (OPTIONS and OPTIONS RESPONSE).  The version and extensions
       negotiation can be performed once during the CLUE session and
       only at this stage.  At the end of that basic negotiation, each
       CP starts its activity as a CLUE MP and/or CLUE MC.

   3.  CLUE telepresence capabilities description and negotiation: in
       this phase, the MP-MC dialogues take place on the data channel by
       means of the CLUE protocol messages.

   As soon as the channel is ready, the CLUE Participants must agree on
   the protocol version and extensions to be used within the
   telepresence session.  CLUE protocol version numbers are
   characterized by a major version number (single digit) and a minor
   version number (single digit), both unsigned integers, separated by a
   dot.  While minor version numbers denote backward compatible changes
   in the context of a given major version, different major version
   numbers generally indicate a lack of interoperability between the
   protocol implementations.  In order to correctly establish a CLUE
   dialogue, the involved CPs MUST have in common a major version number
   (see Section 7 for further details).  The subset of the extensions
   that are allowed within the CLUE session is also determined in the
   initiation phase, such subset being the one including only the
   extensions that are supported by both parties.  A mechanism for the



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   negotiation of the CLUE protocol version and extensions is part of
   the initial phase.  According to such a solution, the CP which is the
   CLUE Channel initiator (CI) issues a proper CLUE message (OPTIONS) to
   the CP which is the Channel Receiver (CR) specifying the supported
   version and extensions.  The CR then answers by selecting the subset
   of the CI extensions that it is able to support and determines the
   protocol version to be used.

   After the negotiation phase is completed, CLUE Participants describe
   and agree on the media flows to be exchanged.  In many cases CPs will
   seek to both transmit and receive media.  Hence in a call between two
   CPs, A and B, there would be two separate dialogs, as follows:

   1.  the one needed to describe and set up the media streams sent from
       A to B, i.e., the dialogue between A's Media Provider side and
       B's Media Consumer side

   2.  the one needed to describe and set up the media streams sent from
       B to A, i.e., the dialogue between B's Media Provider side and
       A's Media Consumer side

   CLUE messages for the media session description and negotiation are
   designed by considering the MP side as the server side of the
   protocol, since it produces and provides media streams, and the MC
   side as the client side of the protocol, since it requests and
   receives media streams.  The messages that are exchanged to set up
   the telepresence media session are described by focusing on a single
   MP-MC dialogue.

   The MP first advertises its available media captures and encoding
   capabilities to the MC, as well as its simultaneity constraints,
   according to the information model defined in
   [I-D.ietf-clue-framework].  The CLUE message conveying the MP's
   multimedia offer is the ADVERTISEMENT message.  Such message
   leverages the XML data model definitions provided in
   [I-D.ietf-clue-data-model-schema].

   The MC selects the desired streams of the MP by using the CONFIGURE
   message, which makes reference to the information carried in the
   previously received ADVERTISEMENT.

   Besides ADVERTISEMENT and CONFIGURE, other messages have been
   conceived in order to provide all the needed mechanisms and
   operations.  Such messages are detailed in the following sections.







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5.  Protocol messages

   CLUE protocol messages are textual, XML-based messages that enable
   the configuration of the telepresence session.  The formal definition
   of such messages is provided in the XML Schema provided at the end of
   this document (Section 9).

   The XML definitions of the CLUE information provided in
   [I-D.ietf-clue-data-model-schema] are included within some CLUE
   protocol messages (namely the ADVERTISEMENT and the CONFIGURE
   messages), in order to use the concepts defined in
   [I-D.ietf-clue-framework].

   The CLUE protocol messages are the following:

   o  OPTIONS

   o  OPTIONS RESPONSE

   o  ADVERTISEMENT (ADV)

   o  ADVERTISEMENT ACKNOWLEDGEMENT (ACK)

   o  CONFIGURE (CONF)

   o  CONFIGURE RESPONSE (CONF RESPONSE)

   While the OPTIONS and OPTIONS RESPONSE messages are exchanged in the
   initiation phase between the CPs, the other messages are involved in
   MP-MC dialogues.

   Each CLUE message inherits a basic structure depicted in the
   following excerpt:


















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   <!-- CLUE MESSAGE TYPE -->
   <xs:complexType name="clueMessageType" abstract="true">
   <xs:sequence>
   <xs:element name="clueId" type="xs:string" minOccurs="0"/>
   <xs:element name="sequenceNr" type="xs:positiveInteger"/>
   </xs:sequence>
   <xs:attribute name="protocol" type="xs:string" fixed="CLUE"
           use="required"/>
   <xs:attribute name="v" type="versionType" use="required"/>
   </xs:complexType>

   <!-- VERSION TYPE -->
   <xs:simpleType name="versionType">
   <xs:restriction base="xs:string">
   <xs:pattern value="[0-9]\.[0-9]"></xs:pattern>
   </xs:restriction>
   </xs:simpleType>


   The information contained in each CLUE message is:

   o  clueId: an optional XML element containing the identifier (in the
      form of a generic string) of the CP within the telepresence
      system;

   o  sequenceNr: an XML element containing the local message sequence
      number.  The sender must increment the sequence numbers by one for
      each new message sent, the receiver must remember the most recent
      sequence number received and send back a 402 error if it receives
      a message with an unexpected sequence number.  The initial
      sequence number can be chosen randomly by each party;

   o  protocol: a mandatory attribute set to "CLUE", identifying the
      procotol the messages refer to;

   o  v: a mandatory attribute carrying the version of the protocol.
      The content of the "v" attribute is composed by the major version
      number followed by a dot and then by the minor version number of
      the CLUE protocol in use.  Allowed values are of this kind are,
      e.g., "1.3", "2.4" etc.

   Each CP is responsible for creating and updating up to three
   independent streams of sequence numbers in messages it sends: (i) one
   for the messages sent in the initiation phase, (ii) one for the
   messages sent as MP (if it is acting as a MP), and (iii) one for the
   messages sent as MC (if it is acting as a MC).





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5.1.  OPTIONS

   The OPTIONS message is sent by the CP which is the CI to the CP which
   is the CR as soon as the CLUE data channel is ready.  Besides the
   information envisioned in the basic structure, it specifies:

   o  mediaProvider: a mandatory boolean field set to "true" if the CP
      is able to act as a MP

   o  mediaConsumer: a mandatory boolean field set to "true" if the CP
      is able to act as a MC

   o  supportedVersions: the list of the supported versions

   o  supportedExtensions: the list of the supported extensions

   The XML Schema of such a message is reported below:


   <!-- CLUE OPTIONS -->
   <xs:complexType name="optionsMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <xs:element name="mediaProvider" type="xs:boolean"/>
   <xs:element name="mediaConsumer" type="xs:boolean"/>
   <xs:element name="supportedVersions" type="versionsListType"
    minOccurs="0"/>
   <xs:element name="supportedExtensions" type="extensionsListType"
    minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>

   <!-- VERSIONS LIST TYPE -->
   <xs:complexType name="versionsListType">
   <xs:sequence>
   <xs:element name="version" type="versionType" minOccurs="1"
    maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:complexType>

   <!-- EXTENSIONS LIST TYPE -->



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   <xs:complexType name="extensionsListType">
   <xs:sequence>
   <xs:element name="extension" type="extensionType" minOccurs="1"
    maxOccurs="unbounded"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:complexType>

   <!-- EXTENSION TYPE -->
   <xs:complexType name="extensionType">
   <xs:sequence>
   <xs:element name="name" type="xs:string" />
   <xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
   <xs:element name="version" type="versionType" minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:complexType>


   <supportedVersions> contains the list of the versions that are
   supported by the CI, each one represented in a child <version>
   element.  The content of each <version> element is a string made by
   the major version number followed by a dot and then by the minor
   version number (e.g., 1.3 or 2.4).  Exactly one <version> element
   MUST be provided for each major version supported, containing the
   maximum minor version number of such a version, since all minor
   versions are backward compatible.  If no <supportedVersions> is
   carried within the OPTIONS message, the CI supports only the version
   declared in the "v" attribute and all the versions having the same
   major version number and lower minor version number.  For example, if
   the "v" attribute has a value of "3.4" and there is no
   <supportedVersions> tag in the OPTIONS message, it means the CI
   supports only major version 3 with all the minor versions comprised
   between 3.0 and 3.4, with version 3.4 included.  If a
   <supportedVersion> is provided, at least one <version> tag MUST be
   included.

   The <supportedExtensions> element specifies the list of extensions
   supported by the CI.  If there is no <supportedExtensions> in the
   OPTIONS message, the CI does not support anything other than what is
   envisioned in the versions it supports.  For each extension, an
   <extension> element is provided.  An extension is characterized by a
   name, an XML schema of reference where the extension is defined, and
   the version of the protocol which the extension refers to.





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5.2.  OPTIONS RESPONSE

   The OPTIONS RESPONSE is sent by a CR to a CI as a reply to the
   OPTIONS message.  As depicted in the figure below, the OPTIONS
   RESPONSE contains a mandatory response code and a reason string
   indicating the processing result of the OPTIONS message.  If the
   responseCode is of the type 2xx the response MUST also include
   <mediaProvider>, <mediaConsumer>, <version> and <commonExtensions>
   elements; it MAY include them for any other response code.
   <mediaProvider> and <mediaConsumer> elements are associated with the
   supported roles (in terms of, respectively MP and MC), similarly to
   what the CI does in the OPTIONS message.  The <version> field
   indicates the highest commonly supported version number.  The content
   of the <version> element MUST be a string made of the major version
   number followed by a dot and then by the minor version number (e.g.,
   1.3 or 2.4).  Finally, the commonly supported extensions are copied
   in the <commonExtensions> field.


<!-- CLUE OPTIONS RESPONSE -->
<xs:complexType name="optionsResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="responseCodeType"/>
<xs:element name="reasonString" type="xs:string" minOccurs="0"/>
<xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
<xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
<xs:element name="version" type="versionType" minOccurs="0"/>
<xs:element name="commonExtensions" type="extensionsListType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>


   Upon reception of the OPTIONS RESPONSE the version to be used is
   provided in the <version> tag of the message.  The following CLUE
   messages MUST use such a version number in the "v" attribute.  The
   allowed extensions in the CLUE dialogue are those indicated in the
   <commonExtensions> of the OPTIONS RESPONSE message.







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5.3.  ADVERTISEMENT

   The ADVERTISEMENT message (ADV) is used by the MP to advertise the
   available media captures and related information to the MC.  The MP
   sends an ADV to the MC as soon as it is ready after the successful
   completion of the initiation phase, i.e., as soon as the version and
   the extensions of the CLUE protocol are agreed between the CPs.
   During a single CLUE session, an MP may send new ADV messages to
   replace the previous advertisement, if, for instance, its CLUE
   telepresence media capabilities change mid-call.  A new ADV
   completely replaces the previous ADV.

   The ADV structure is defined in the schema excerpt below.  The ADV
   contains elements compliant with the CLUE data model that
   characterize the MP's telepresence offer.  Namely, such elements are:
   the list of the media captures (<mediaCaptures>), of the encoding
   groups (<encodingGroups>), of the capture scenes (<captureScenes>),
   of the simultaneous sets (<simultaneousSets>), of the global views
   (<globalViews>), and of the represented participants (<people>).
   Each of them is fully described in the CLUE framework document and
   formally defined in the CLUE data model document.


   <!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
   <xs:complexType name="advertisementMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <!-- mandatory -->
   <xs:element name="mediaCaptures" type="dm:mediaCapturesType"/>
   <xs:element name="encodingGroups" type="dm:encodingGroupsType"/>
   <xs:element name="captureScenes" type="dm:captureScenesType"/>
   <!-- optional -->
   <xs:element name="simultaneousSets" type="dm:simultaneousSetsType"
    minOccurs="0"/>
   <xs:element name="globalViews" type="dm:globalViewsType"
    minOccurs="0"/>
   <xs:element name="people" type="dm:peopleType" minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>







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5.4.  ADVERTISEMENT ACKNOWLEDGEMENT

   The ADVERTISEMENT ACKNOWLEDGEMENT message (ACK) is sent by a MC to a
   MP to acknowledge an ADV message.  As it can be seen from the message
   schema provided in the following, the ACK contains a response code
   and a reason string for describing the processing result of the ADV.
   The <advSequenceNr> carries the sequence number of the ADV the ACK
   refers to.


   <!-- ADV ACK MESSAGE TYPE -->
   <xs:complexType name="advAcknowledgementMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <xs:element name="responseCode" type="responseCodeType"/>
   <xs:element name="reasonString" type="xs:string" minOccurs="0"/>
   <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>


5.5.  CONFIGURE

   The CONFIGURE message (CONF) is sent from a MC to a MP to list the
   advertised captures the MC wants to receive.  The MC can send a CONF
   after the reception of an ADV or each time it wants to request other
   captures that have been previously advertised by the MP.  The content
   of the CONF message is shown below.


















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    <!-- CLUE CONFIGURE MESSAGE TYPE -->
   <xs:complexType name="configureMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <!-- mandatory fields -->
   <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
   <xs:element name="ack" type="xs:boolean" minOccurs="0" fixed="true"/>
   <xs:element name="captureEncodings" type="dm:captureEncodingsType"
    minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>


   The <advSequenceNr> element contains the sequence number of the ADV
   message the CONF refers to.

   The optional boolean <ack> element, set to "true" when present,
   indicates that the CONF message also acknowledges with success the
   referred advertisement (CONF + ACK message), by applying in that way
   a piggybacking mechanism for simultaneously acknowledging and
   replying to the ADV message.  The <ack> element MUST NOT be present
   if an ACK message has been already sent back to the MP.

   The most important content of the CONFIGURE message is the list of
   the capture encodings provided in the <captureEncodings> element.
   Such an element contains a sequence of capture encodings,
   representing the streams to be instantiated.

5.6.  CONFIGURE RESPONSE

















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   <!-- CONFIGURE RESPONSE MESSAGE TYPE -->
   <xs:complexType name="configureResponseMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <xs:element name="responseCode" type="responseCodeType"/>
   <xs:element name="reasonString" type="xs:string" minOccurs="0"/>
   <xs:element name="confSequenceNr" type="xs:positiveInteger"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>


   The CONFIGURE RESPONSE message (CONF RESPONSE) is sent from the MP to
   the MC to communicate the processing result of requests carried in
   the previously received CONF message.  It contains a response code
   with a reason string indicating either the success or the failure
   (along with failure details) of a CONF request processing.
   Following, the <confSequenceNr> field contains the sequence number of
   the CONF message the response refers to.  There is no partial
   execution of commands.  As an example, if a MP is able to understand
   all the selected capture encodings except one, then the whole command
   fails and nothing is instantiated.

5.7.  Response codes and reason strings

   Response codes are defined as a sequence of three digits.  A well-
   defined meaning is associated with the first digit.  Response codes
   beginning with "2" are associated with successful responses.
   Response codes beginning with "1" will represent a delayed or
   incomplete response.  Response codes that do not begin with either
   "2" or "1" indicate an error response, i.e., that an error occurred
   while processing a CLUE request.  In particular, response codes
   beginning with "3" indicate problems with the XML content of the
   message (""Bad syntax", "Invalid value", etc.), while response codes
   beginning with "4" refer to problems related to CLUE protocol
   semantics ("Invalid sequencing", "Version not supported", etc.).
   100, 200, 300 and 400 codes are considered catch-alls.  Further
   response codes can be either defined in future versions of the
   protocol (by adding them to the related IANA registry), or defined by
   leveraging the extension mechanism.  In both cases, the new response
   codes MUST be registered with IANA.  Such new response codes MUST NOT
   overwrite the ones here defined and they MUST respect the semantics
   of the first code digit.




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   The response codes and strings defined for use with CLUE are as
   follows:



   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |  Response code  |  Reason string       |       Description        |
   |                 |                      |                          |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   200           |  Success             |  The request has been    |
   |                 |                      |  successfully processed. |
   |                 |                      |                          |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   300           |  Syntax errors or    |  The XML syntax of the   |
   |                 |  inconsistencies     |  message is not correct  |
   |                 |                      |  or there are invalid    |
   |                 |                      |  values.                 |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   301           |  Bad syntax          |  The XML syntax of the   |
   |                 |                      |  message is not correct. |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   302           |  Invalid value       |  The message             |
   |                 |                      |  contains an invalid     |
   |                 |                      |  parameter value.        |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   303           |  Conflicting values  |  The message             |
   |                 |                      |  contains values that    |
   |                 |                      |  cannot be used together.|
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   400           | Semantic errors      |  Semantic errors in the  |
   |                 |                      |  received CLUE protocol  |
   |                 |                      |  message.                |
   |                 |                      |                          |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   401           | Version not supported|  The protocol version    |
   |                 |                      |  used in the message     |
   |                 |                      |  is not supported.       |
   |                 |                      |                          |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |



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   |   402           |  Invalid sequencing  |  The sequence number of  |
   |                 |                      |  the message is out      |
   |                 |                      |  of date.                |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   403           |  Invalid identifier  |  The identifier used in  |
   |                 |                      |  the message is          |
   |                 |                      |  not valid or unknown.   |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   404           |  ADV Expired         |  The number of the ADV   |
   |                 |                      |  the CONF refers to is   |
   |                 |                      |  out of date.            |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   405           |  Subset choice not   |  The subset choice is not|
   |                 |  allowed             | allowed for the specified|
   |                 |                      |  MCC                     |
   +-----------------+----------------------+--------------------------+



6.  Protocol state machines

   The CLUE protocol is an application protocol used between two CPs in
   order to properly configure a multimedia telepresence session.  CLUE
   protocol messages flow over the CLUE Data Channel, a DTLS/SCTP
   channel established as depicted in [I-D.ietf-clue-datachannel].  We
   herein discuss the state machines associated, respectively, with the
   CLUE Participant, with the MC process and with the MP process.
   Endpoints often wish to both send and receive media, i.e., act as
   both MP and MC.  As such there will often be two sets of messages
   flowing in opposite directions; the state machines of these two flows
   do not interact with each other.  Only the CLUE application logic is
   considered.  The interaction of CLUE protocol and SDP negotiations
   for the media streams exchanged is treated in
   [I-D.ietf-clue-signaling].

   The main state machines focus on the behavior of the CLUE Participant
   (CP) acting as a CLUE channel initiator/receiver (CI/CR).

   The initial state is the IDLE one.  When in the IDLE state, the CLUE
   data channel is not established and no CLUE-controlled media are
   exchanged between the two considered CLUE-capable devices (if there
   is an ongoing exchange of media streams, such media streams are not
   currently CLUE-controlled).





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   When the CLUE data channel set up starts ("start channel"), the CP
   moves from the IDLE state to the CHANNEL SETUP state.

   If the CLUE data channel is successfully set up ("channel
   established"), the CP moves from the CHANNEL SETUP state to the
   OPTIONS state.  Otherwise if "channel error", it moves back to the
   IDLE state.  The same transition happens if the CLUE-enabled
   telepresence session ends ("session ends"), i.e., when an SDP
   negotiation for removing the CLUE channel is performed.

   When in the OPTIONS state, the CP addresses the initiation phase
   where both parts agree on the version and on the extensions to be
   used in the subsequent CLUE messages exchange phase.  If the CP is
   the Channel Initiator (CI), it sends an OPTIONS message and waits for
   the OPTIONS RESPONSE message.  If the CP is the Channel Receiver
   (CR), it waits for the OPTIONS message and, as soon as it arrives,
   replies with the OPTIONS RESPONSE message.  If the negotiation is
   successfully completed ("OPTIONS phase success"), the CP moves from
   the OPTIONS state to the ACTIVE state.  If the initiation phase fails
   ("OPTIONS phase failure"), the CP moves from the OPTIONS state to the
   IDLE state.  The initiation phase might fail because of one of the
   following reasons:

   1.  the CI receives an OPTIONS RESPONSE with an error response code

   2.  the CI does not receive any OPTIONS RESPONSE and a timeout error
       is raised

   3.  the CR does not receive any OPTIONS and a timeout error is raised

   When in the ACTIVE state, the CP starts the envisioned sub-state
   machines (i.e., the MP state machine and the MC state machine)
   according to the roles it plays in the telepresence sessions.  Such
   roles have been previously declared in the OPTIONS and OPTIONS
   RESPONSE messages involved in the initiation phase (see OPTIONS
   sections Section 5.1 and Section 5.2 for the details).  When in the
   ACTIVE state, the CP delegates the sending and the processing of the
   CLUE messages to the appropriate MP/MC sub-state machines.  If the CP
   receives a further OPTIONS/OPTIONS RESPONSE message, it MUST ignore
   the message and stay in the ACTIVE state.

   The CP moves from the ACTIVE state to the IDLE one when the sub-state
   machines that have been activated are (both) in the relative
   TERMINATED state (see sections Section 6.1 and Section 6.2).







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                                  +----+
          +---------------------->|IDLE|<----------------------------+
          |                       +-+--+                             |
          |                         |                                |
          |                         |  start                         |
          |                         |  channel                       |
          |                         v                                |
          |  channel error/      +--------+                          |
          |  session ends        | CHANNEL|                          |
          +----------------------+ SETUP  |                          |
          |                      +--+-----+                          |
          |                         |                                |
          |                         |  channel                       |
          |                         |  established                   |
          |  channel error/         v                 OPTIONS phase  |
          |  session ends         +-------+           failure        |
          +-----------------------+OPTIONS+--------------------------+
          |                       +-+-----+                          |
          |                         |                                |
          |                         |  OPTIONS phase                 |
          |                         |  success                       |
          |                         v                                |
          |   channel error/     +---------+                         |
          |   session ends       | ACTIVE  |                         |
          +----------------------+         |                         |
                                 | +----+  +------------------+      |
                                 | | MP |  |    send/receive  |      |
                                 | +----+  |    CLUE messages |      |
                                 |         |<-----------------+      |
                                 | +----+  |                         |
                                 | | MC |  |both sub state machines  |
                                 | +----+  |terminated               |
                                 |         |                         |
                                 +---------+-------------------------+




6.1.  Media Provider's state machine

   As soon as the sub-state machine of the MP is activated, it is in the
   ADV state.  In the ADV state, the MP prepares the ADV message
   reflecting its actual telepresence capabilities.

   After the ADV has been sent ("ADV sent"), the MP moves from the ADV
   state to the WAIT FOR ACK state.  If an ACK message with a successful
   response code arrives ("ACK received"), the MP moves to the WAIT FOR
   CONF state.  If a NACK arrives (i.e., an ACK message with an error



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   response code), and the number of NACKs for the issued ADV is under
   the retry threshold ("NACK received && retry not expired"), the MP
   moves back to the ADV state for preparing a new ADV.  If a NACK
   arrives and the number of received NACKs for that ADV overcomes the
   threshold ("NACK received && retry expired"), the MP goes to the MP-
   TERMINATED state.  The same happens if the waiting time for the ACK
   is fired a number of times under the retry threshold ("timeout &&
   retry not expired"): also in this case, the MP goes back to the ADV
   state to send a new copy of the ADV.  If the number of retries
   overcomes the threshold ("timeout && retry expired"), the MP moves
   from the WAIT FOR ACK state to the MP-TERMINATED state.  When in the
   WAIT FOR ACK state, if a CONFIGURE message with the <ack> element set
   to TRUE arrives ("CONF+ACK received"), the MP goes directly to the
   CONF RESPONSE state.  CONF+ACK messages referring to out-of-date
   (i.e., having a sequence number equal to or less than the highest
   seen so far) ADVs MUST be ignored, i.e., they do not trigger any
   state transition.  If the telepresence settings of the MP change
   while in the WAIT FOR ACK state ("changed telepresence settings"),
   the MP switches from the WAIT FOR ACK state to the ADV state to
   create a new ADV.

   When in the WAIT FOR CONF state, the MP listens to the channel for a
   CONF request coming from the MC.  If a CONF arrives ("CONF
   received"), the MP switches to the CONF RESPONSE state.  If the CONF
   does not arrive within the timeout interval and the retry threshold
   has not been overcome ("timeout && retry not expired"), the MP moves
   back to the ADV state.  When the retry expires ("timeout && retry
   expired") the MP moves to the MP TERMINATED state.  If the
   telepresence settings change in the meanwhile ("changed telepresence
   settings"), the MP moves from the WAIT FOR CONF back to the ADV state
   to create the new ADV to be sent to the MC.

   The MP in the CONF RESPONSE state processes the received CONF in
   order to produce a CONF RESPONSE message.  If the MP successfully
   processes the MC's configuration, then it sends a 200 CONF RESPONSE
   ("success CONF RESPONSE sent") and moves to the ESTABLISHED state.
   If there are errors in the CONF processing, then the MP issues a CONF
   RESPONSE carrying an error response code and, if under the retry
   treshold ("error CONF RESPONSE sent && retry not expired"), it goes
   back to the WAIT FOR CONF state to wait for a new configuration
   request.  If the number of trials exceeds the retry threshold ("error
   CONF RESPONSE sent && retry expired"), the state MP TERMINATED is
   reached.  Finally, if there are changes in the MP's telepresence
   settings ("changed telepresence settings"), the MP switches to the
   ADV state.

   The MP in the ESTABLISHED state has successfully negotiated the media
   streams with the MC by means of the CLUE messages.  If there are



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   changes in the MP's telepresence settings ("changed telepresence
   settings"), the MP moves back to the ADV state.  In the ESTABLISHED
   state, the CLUE-controlled media streams of the session are those
   described in the last successfully processed CONF message.















































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+------------------------->+-----+<---------------------------+
|            +------------>| ADV |<-------------------+       |
|            |             +-+---+                    |       |timeout
|            |               |       NACK received    |       |&&
|            |       ADV sent|             &&         |       |retry
|            |               v       retry not expired|       |not
|     changed|             +--------+                 |       |expired
|telepresence+-------------+WAIT FOR+-----------------+       |
|    settings|   +---------+  ACK   +-------------------------+
|            |   |CONF+ACK +-+------+----------------------------------+
|            |   |received   |                        NACK received && |
|            |   |           |ACK received               retry expired,|
|            |   |           v                 timeout && retry expired|
+------------|-------------+--------+                                  |
timeout      +-------------+WAIT FOR| timeout && retry expired         |
&&           |   |         |  CONF  +----------------------------------+
retry        |   |         +-+------+<-----------------------------+   |
not expired  |   |           |                                     |   |
             |   |           |CONF received                        |   |
             |   |           v             error CONF RESPONSE sent|   |
             |   +-------->+---------+      && retry not expired   |   |
             +-------------+CONF     |-----------------------------+   |
    +--------------------->|RESPONSE +---------------------------------+
    |        |             +-+-------+         error CONF RESPONSE sent|
    |        |               |                         && retry expired|
    |        |               |  success                                |
    |        |               |  CONF RESPONSE                          |
    |        |               |  sent                                   |
    |        |               |                                         |
    |        |               |                                         |
    |CONF    |               |                                         |
    |received|               v                                         |
    |        |             +------------+                              |
    |        +-------------+ESTABLISHED |                              |
    +----------------------+------------+                              |
                                                                       |
                                                                       |
                                                                       |
                           +-----------+                               |
                           !    MP     |                               |
                           |TERMINATED |                               |
                           +-----------+<------------------------------+









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6.2.  Media Consumer's state machine

   As soon as the sub-state machine of the MC is activated, it is in the
   WAIT FOR ADV state.  An MC in the WAIT FOR ADV state is waiting for
   an ADV coming from the MP.  If the ADV arrives ("ADV received"), the
   MC reaches the ADV PROCESSING state.  Otherwise, the MC stays in the
   WAIT FOR ADV state.

   In the ADV PROCESSING state, the ADV is parsed by the MC.  If the ADV
   is successfully processed, there are two possibilities.  According to
   the first one, the MC issues a successful ACK message to the MP ("ACK
   sent") and moves to the CONF state.  In the second one, the MC
   prepares and sends a CONF message with the <ack> field set to "true"
   ("CONF+ACK sent") and goes directly to the WAIT FOR CONF RESPONSE
   state.

   If the ADV processing is unsuccessful (bad syntax, missing XML
   elements, etc.), and the number of times this has happened is under
   the retry threshold, the MC sends a NACK message (i.e., an ACK with
   an error response code) to the MP and optionally further describes
   the problem via a proper reason phrase.  In this way ("NACK sent &&
   retry not expired"), the MC switches back to the WAIT FOR ADV state,
   waiting for a new ADV.  If the NACK retry expires ("NACK sent &&
   retry expired"), the MC moves to the MC TERMINATED state.

   When in the CONF state, the MC prepares the CONF request to be issued
   to the MP on the basis of the previously ACK-ed ADV.  When the CONF
   has been sent ("CONF sent"), the MC moves to the WAIT FOR CONF
   RESPONSE state.  If a new ADV arrives in the meanwhile ("ADV
   received"), the MC goes back to the ADV PROCESSING state.

   In the WAIT FOR CONF RESPONSE state, the MC waits for the MP's
   response to the issued CONF or CONF+ACK.  If a 200 CONF RESPONSE
   message is received ("successful CONF RESPONSE received"), it means
   that the MP and the MC have successfully agreed on the media streams
   to be shared.  Then, the MC can move to the ESTABLISHED state.  On
   the other hand, if an error response is received and the associated
   retry counter does not overcome the threshold ("error CONF RESPONSE
   received && retry not expired"), the MC moves back to the CONF state
   to prepare a new CONF request.  In case of "error CONF RESPONSE
   received && retry expired", the MC moves to the MC TERMINATED state.
   If no CONF RESPONSE arrives and the number of timeouts is under the
   threshold ("timeout && retry not expired"), the MC moves to the CONF
   state and sends again the CONF message.  If no CONF RESPONSE arrives
   and the number of timeouts is over the threshold ("timeout && retry
   expired"), the MC moves to the MC TERMINATED state.  If a new ADV is
   received in the WAIT FOR CONF RESPONSE state, the MC switches to the
   ADV PROCESSING state.



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   When the MC is in the ESTABLISHED state, the telepresence session
   configuration has been set up at the CLUE application level according
   to the MC's preferences.  Both the MP and the MC have agreed on (and
   are aware of) the CLUE-controlled media streams to be exchanged
   within the call.  While in the ESTABLISHED state, it might happen
   that the MC decides to change something in the call settings.  The MC
   then issues a new CONF ("CONF sent") and goes to wait for the new
   CONF RESPONSE in the WAIT FOR CONF RESPONSE state.  On the other
   hand, in the ESTABLISHED state, if a new ADV arrives from the MP
   ("ADV received"), it means that something has changed on the MP's
   side.  The MC then moves to the ADV PROCESSING state.








































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                           +----------+
                           | WAIT FOR |
                           |   ADV    |
                           +----+-----+<--------+
                                |               |
                        ADV     |      NACK sent|
                        received|      && retry |
                                v    not expired|    NACK sent &&
                           +-----------+--------+    retry expired
                           |  ADV      +---------------------------+
                           | PROCESSING|<-----------------------+  |
                           +-+-----+---+                        |  |
                             |     |                            |  |
                   CONF+ACK  |     |  ACK                       |  |
                     sent    |     |  sent                      |  |
                             |     v                            |  |
                             |  +-----+                         |  |
                             |  |CONF |            ADV received |  |
       +----------------------->|     +-------------------------+  |
       |                     |  +--+--+                         |  |
       |error CONF RESPONSE  |     |        error CONF RESPONSE |  |
       |received &&          |     | CONF   received &&         |  |
       |retry not expired,   |     | sent   retry expired       |  |
       |timeout &&           |     |      +------------------------+
       |retry not expired    v     v      |                     |  |
       +------------------+---------------+        ADV received |  |
               +--------->|   WAIT FOR    +---------------------+  |
               |          |  CONF RESPONSE+------------------------+
               |          +-------+-------+       timeout&&     |  |
               |                  |             retry expired   |  |
               |                  |                             |  |
               |                  |successful                   |  |
               |                  |CONF RESPONSE                |  |
               |                  |received                     |  |
               |                  v                             |  |
               |CONF sent   +-----------+           ADV received|  |
               +------------+ESTABLISHED+-----------------------+  |
                            +-----------+                          |
                                                                   |
                                                                   |
                                                                   |
                             +-----------+                         |
                             |   MC      |<------------------------+
                             |TERMINATED |
                             +-----------+






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7.  Versioning

   CLUE protocol messages are XML messages compliant to the CLUE
   protocol XML schema [I-D.ietf-clue-data-model-schema].  The version
   of the protocol corresponds to the version of the schema.  Both
   client and server have to test the compliance of the received
   messages with the XML schema of the CLUE protocol.  If the compliance
   is not verified, the message cannot be processed further.

   Obviously, client and server cannot communicate if they do not share
   exactly the same XML schema.  Such a schema associated with the CLUE
   URN "urn:ietf:params:xml:ns:clue-protocol".  If all CLUE-enabled
   devices use that schema there will be no interoperability problems
   due to schema issues.

   This document defines XML schema version 1.0.  The version usage is
   similar in philosophy to XMPP ([RFC6120]).  A version number has
   major and minor components, each a non-negative integer.  Major
   version changes denote non-interoperable changes.  Minor version
   changes denote schema changes that are backward compatible by
   ignoring unknown XML elements, or other backward compatible changes.

   The minor versions of the XML schema MUST be backward compatible, not
   only in terms of schema but also semantically and procedurally as
   well.  This means that they should define further features and
   functionality besides those defined in the previous versions, in an
   incremental way, without impacting the basic rules defined in the
   previous version of the schema.  In this way, if a MP is able to
   speak, e.g., version 1.5 of the protocol while the MC only
   understands version 1.4, the MP should have no problem in reverting
   the dialogue back to version 1.4 without exploiting 1.5 features and
   functionality.  Version 1.4 is the one to be spoken and has to appear
   in the "v" attribute of the subsequent CLUE messages.  In other
   words, in this example, the MP MUST use version 1.4 and downgrade to
   the lower version.  This said, and coherently with the general IETF
   "protocol robustness principle" stating that "an implementation must
   be conservative in its sending behavior, and liberal in its receiving
   behavior" [RFC1122], Clue Participants MUST ignore unknown elements
   or attributes that are not envisioned in the negotiated protocol
   version and related extensions.

8.  Extensions

   Although the standard version of the CLUE protocol XML schema is
   designed to thoroughly cope with the requirements emerging from the
   application domain, new needs might arise and extensions can be
   designed.  Extensions specify information and behaviors that are not
   described in a certain version of the protocol and specified in the



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   related RFC document.  Such information and behaviors can be
   optionally used in a CLUE dialogue and MUST be negotiated in the CLUE
   initiation phase.  They can relate to:

   1.  new information, to be carried in the existing messages.  For
       example, more fields may be added within an existing message;

   2.  new messages.  This is the case if there is no proper message for
       a certain task, so a brand new CLUE message needs to be defined.

   As to the first type of extensions, it is possible to distinguish
   between protocol-specific and data model information.  Indeed, CLUE
   messages are envelopes carrying both:

   o  (i) XML elements defined within the CLUE protocol XML schema
      itself (protocol-specific information)

   o  (ii) other XML elements compliant to the CLUE data model schema
      (data model information)

   When new protocol-specific information is needed somewhere in the
   protocol messages, it can be added in place of the <any> elements and
   <anyAttribute> elements envisioned by the protocol schema.  The
   policy currently defined in the protocol schema for handling <any>
   and <anyAttribute> elements is:

   o  elementFormDefault="qualified"

   o  attributeFormDefault="unqualified"

   In that case, the new information must be qualified by namespaces
   other than "urn:ietf:params:xml:ns:clue-protocol" (the protocol URN)
   and "urn:ietf:params:xml:ns:clue-info" (the data model URN).
   Elements or attributes from unknown namespaces MUST be ignored.

   The other matter concerns data model information.  Data model
   information is defined by the XML schema associated with the URN
   "urn:ietf:params:xml:ns:clue-info".  Also for the XML elements
   defined in such a schema there are extensibility issues.  Those
   issues are overcome by using <any> and <anyAttribute> placeholders.
   Similarly to what said before, new information within data model
   elements can be added in place of <any> and <anyAttribute> schema
   elements, as long as they are properly namespace qualified.

   On the other hand (second type of extensions), "extra" CLUE protocol
   messages, i.e., messages not envisioned in the latest standard
   version of the schema, can be needed.  In that case, the messages and




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   the associated behavior should be defined in external documents that
   both communication parties must be aware of.

   Both types of extensions, i.e., new information and new messages, can
   be characterized by:

   o  a name;

   o  an external XML Schema defining the XML information and/or the XML
      messages representing the extension;

   o  the standard version of the protocol the extension refers to.

   For that reason, the extensions are represented by means of the
   <extension> element as defined below, which is carried within the
   OPTIONS and OPTIONS RESPONSE messages to represent the extensions
   supported by the CI and by the CR.


   <!-- EXTENSION TYPE -->
   <xs:complexType name="extensionType">
   <xs:sequence>
   <xs:element name="name" type="xs:string" />
   <xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
   <xs:element name="version" type="versionType" minOccurs="0"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:complexType>


8.1.  Extension example

   An example of extension might be a "new" capture attribute (i.e., a
   capture attribute which is not envisioned in the current standard
   defining the CLUE data model in [I-D.ietf-clue-data-model-schema])
   needed to further describe a video capture.  Such a new attribute
   MUST be defined in a separated XML schema file and SHOULD be provided
   with a companion document describing its semantics and use.

   The CLUE data model document ([I-D.ietf-clue-data-model-schema])
   envisions the possibility of adding this kind of "extra" information
   in the description of a video capture by keeping the compatibility
   with the CLUE data model schema.  This is made possible thanks to the
   presence of the <any> element in the XML definition of the video
   capture, allowing for the introduction of a new XML field in the XML
   description.  For the sake of convenience, the XML definition of a




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   video capture taken from [I-D.ietf-clue-data-model-schema] is
   reported below.



  <!-- 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>


   According to such a definition, a video capture might have, after the
   set of the generic media capture attributes, a set of new attributes
   defined elsewhere, i.e., in an XML schema defining an extension.  The
   XML schema defining the extension might look like the following:




























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   <?xml version="1.0" encoding="UTF-8" ?>
   <xs:schema
   version="1.0"
   targetNamespace="clue-info-extension-myVideoExtensions"
   xmlns:xs="http://www.w3.org/2001/XMLSchema"
   xmlns="clue-info-extension-myVideoExtensions"
   elementFormDefault="qualified"
   attributeFormDefault="unqualified">

   <!-- this is the new element to be put in place of the <any>
   element in the video capture definition
   of the CLUE data model schema -->

   <xs:element name="myVideoExtension">
    <xs:complexType>
     <xs:sequence>
      <xs:element ref="newVideoAttribute1"/>
      <xs:element ref="newVideoAttribute2"/>
     </xs:sequence>
    </xs:complexType>
   </xs:element>

   <xs:element name="newVideoAttribute1" type = "xs:string">
   </xs:element>

   <xs:element name = "newVideoAttribute2" type = "xs:boolean">
   </xs:element>

   </xs:schema>



   By using the extension above, a video capture can be further
   described in the advertisement using the <myVideoExtension> element
   containing two extra information (<newVideoAttribute1> and
   <newVideoAttribute2>) besides using the attributes envisioned for a
   generic media capture.  As stated in this document, both participants
   MUST be aware of the extension schema and related semantics to use
   such an extension and MUST negotiate it via the OPTIONS and OPTIONS
   RESPONSE mechanism.

9.  XML Schema

   In this section, the XML schema defining the CLUE messages is
   provided.


<?xml version="1.0" encoding="UTF-8" ?>



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<xs:schema
version="1.0"
targetNamespace="urn:ietf:params:xml:ns:clue-protocol"
xmlns:tns="urn:ietf:params:xml:ns:clue-protocol"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dm="urn:ietf:params:xml:ns:clue-info"
xmlns="urn:ietf:params:xml:ns:clue-protocol"
elementFormDefault="qualified"
attributeFormDefault="unqualified">

<!-- Import data model schema -->
<xs:import namespace="urn:ietf:params:xml:ns:clue-info"
schemaLocation="data-model-schema-17.xsd"/>

<!-- ELEMENT DEFINITIONS -->
<xs:element name="options" type="optionsMessageType"/>
<xs:element name="optionsResponse" type="optionsResponseMessageType"/>
<xs:element name="advertisement" type="advertisementMessageType"/>
<xs:element name="ack" type="advAcknowledgementMessageType"/>
<xs:element name="configure" type="configureMessageType"/>
<xs:element name="configureResponse"
 type="configureResponseMessageType"/>

<!-- CLUE MESSAGE TYPE -->
<xs:complexType name="clueMessageType" abstract="true">
<xs:sequence>
<xs:element name="clueId" type="xs:string" minOccurs="0"/>
<xs:element name="sequenceNr" type="xs:positiveInteger"/>
</xs:sequence>
<xs:attribute name="protocol" type="xs:string" fixed="CLUE"
 use="required"/>
<xs:attribute name="v" type="versionType" use="required"/>
</xs:complexType>

<!-- VERSION TYPE -->
<xs:simpleType name="versionType">
<xs:restriction base="xs:string">
<xs:pattern value="[0-9]\.[0-9]"></xs:pattern>
</xs:restriction>
</xs:simpleType>


<!-- RESPONSE CODE TYPE -->
<xs:simpleType name="responseCodeType">
  <xs:restriction base="xs:integer">
   <xs:pattern value="[1-9][0-9][0-9]"/>
  </xs:restriction>
</xs:simpleType>



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<!-- CLUE OPTIONS -->
<xs:complexType name="optionsMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="mediaProvider" type="xs:boolean"/>
<xs:element name="mediaConsumer" type="xs:boolean"/>
<xs:element name="supportedVersions" type="versionsListType"
 minOccurs="0"/>
<xs:element name="supportedExtensions" type="extensionsListType"
 minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- VERSIONS LIST TYPE -->
<xs:complexType name="versionsListType">
<xs:sequence>
<xs:element name="version" type="versionType" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- EXTENSIONS LIST TYPE -->
<xs:complexType name="extensionsListType">
<xs:sequence>
<xs:element name="extension" type="extensionType" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- EXTENSION TYPE -->
<xs:complexType name="extensionType">
<xs:sequence>
<xs:element name="name" type="xs:string" />
<xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
<xs:element name="version" type="versionType" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>



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<!-- CLUE OPTIONS RESPONSE -->
<xs:complexType name="optionsResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="responseCodeType"/>
<xs:element name="reasonString" type="xs:string" minOccurs="0"/>
<xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
<xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
<xs:element name="version" type="versionType" minOccurs="0"/>
<xs:element name="commonExtensions" type="extensionsListType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
<xs:complexType name="advertisementMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory -->
<xs:element name="mediaCaptures" type="dm:mediaCapturesType"/>
<xs:element name="encodingGroups" type="dm:encodingGroupsType"/>
<xs:element name="captureScenes" type="dm:captureScenesType"/>
<!-- optional -->
<xs:element name="simultaneousSets" type="dm:simultaneousSetsType"
 minOccurs="0"/>
<xs:element name="globalViews" type="dm:globalViewsType"
 minOccurs="0"/>
<xs:element name="people" type="dm:peopleType" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- ACK MESSAGE TYPE -->
<xs:complexType name="advAcknowledgementMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="responseCodeType"/>
<xs:element name="reasonString" type="xs:string" minOccurs="0"/>



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<xs:element name="advSequenceNr" type="xs:positiveInteger"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- CLUE CONFIGURE MESSAGE TYPE -->
<xs:complexType name="configureMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="advSequenceNr" type="xs:positiveInteger"/>
<xs:element name="ack" type="xs:boolean"
 minOccurs="0" fixed="true"/>
<xs:element name="captureEncodings" type="dm:captureEncodingsType"
 minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- CONFIGURE RESPONSE MESSAGE TYPE -->
<xs:complexType name="configureResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="responseCodeType"/>
<xs:element name="reasonString" type="xs:string" minOccurs="0"/>
<xs:element name="confSequenceNr" type="xs:positiveInteger"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

</xs:schema>


10.  Examples

   In the following we provide an example of ADVERTISEMENT representing
   the telepresence environment described in




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   [I-D.ietf-clue-data-model-schema], Section "Sample XML file" and
   Section "MCC example" respectively.

10.1.  Simple ADV

   The associated Media Provider's telepresence capabilities are
   described in [I-D.ietf-clue-data-model-schema], Section "Sample XML
   file".


<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:advertisement xmlns="urn:ietf:params:xml:ns:clue-info"
 xmlns:ns2="urn:ietf:params:xml:ns:clue-protocol"
 xmlns:ns3="urn:ietf:params:xml:ns:vcard-4.0" protocol="CLUE" v="1.0">
    <ns2:clueId>Napoli CLUE Endpoint</ns2:clueId>
    <ns2:sequenceNr>34</ns2:sequenceNr>
        <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>



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         </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>



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         <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



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          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"



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          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>



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                 </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>



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         <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>



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         <person personID="bob">
             <personInfo>
                 <ns2:fn>
                     <ns2:text>Bob</ns2:text>
                 </ns2:fn>
             </personInfo>
             <personType>minute taker</personType>
         </person>
         <person personID="alice">
             <personInfo>
                 <ns3:fn>
                     <ns3:text>Alice</ns3:text>
                 </ns3:fn>
             </personInfo>
             <personType>presenter</personType>
         </person>
         <person personID="ciccio">
             <personInfo>
                 <ns3:fn>
                     <ns3:text>Ciccio</ns3:text>
                 </ns3:fn>
             </personInfo>
             <personType>chairman</personType>
             <personType>timekeeper</personType>
         </person>
     </people>
</ns2:advertisement>


10.2.  ADV with MCCs

   The associated Media Provider's telepresence capabilities are
   described in [I-D.ietf-clue-data-model-schema], Section "MCC
   example".


<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<ns2:advertisement xmlns="urn:ietf:params:xml:ns:clue-info"
 xmlns:ns2="urn:ietf:params:xml:ns:clue-protocol"
 xmlns:ns3="urn:ietf:params:xml:ns:vcard-4.0" protocol="CLUE" v="1.0">
    <ns2:clueId>Napoli CLUE Endpoint</ns2:clueId>
    <ns2:sequenceNr>34</ns2:sequenceNr>
     <mediaCaptures>
         <mediaCapture
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:type="audioCaptureType" captureID="AC0" mediaType="audio">
             <captureSceneIDREF>CS1</captureSceneIDREF>
             <spatialInformation>



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                 <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



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             </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>



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             <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>



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             <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"



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          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>



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         <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">penultimate loudest room segment
             </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>



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                         </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">last but two loudest room segment
             </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>



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                         </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>



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                         <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>



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                 <ns3:fn>
                     <ns3:text>Bob</ns2:text>
                 </ns3:fn>
             </personInfo>
             <personType>minute taker</personType>
         </person>
         <person personID="alice">
             <personInfo>
                 <ns3:fn>
                     <ns3:text>Alice</ns2:text>
                 </ns3:fn>
             </personInfo>
             <personType>presenter</personType>
         </person>
         <person personID="ciccio">
             <personInfo>
                 <ns3:fn>
                     <ns3:text>Ciccio</ns2:text>
                 </ns3:fn>
             </personInfo>
             <personType>chairman</personType>
             <personType>timekeeper</personType>
         </person>
     </people>
</ns2:advertisement>


11.  Security Considerations

   As a general consideration, we remark that the CLUE framework (and
   related protocol) has been conceived at the outset by embracing the
   security-by-design paradigm.  This entails that a number of
   requirements have been identified and properly standardized as
   mandatory within the entire set of documents associated with the CLUE
   architecture.  Requirements include: (i) the use of cryptography and
   authentication; (ii) protection of all sensitive fields; (iii) mutual
   authentication between CLUE endpoints; (iv) the presence of
   authorization mechanisms; (v) the presence of native defence
   mechanisms against malicious activities such as eavesdropping,
   selective modification, deletion, replay (and related combinations
   thereof).  Hence, security of the single components of the CLUE
   solution cannot be evaluated independently of the integrated view of
   the final architecture.

   The CLUE protocol is an application-level protocol allowing a Media
   Producer and a Media Consumer to negotiate a variegated set of
   parameters associated with the establishment of a telepresence
   session.  This unavoidably exposes a CLUE-enabled telepresence system



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   to a number of potential threats, most of which are extensively
   discussed in the framework document [I-D.ietf-clue-framework].  The
   security considerations section of the mentioned document actually
   discusses issues associated with the setup and management of a
   telepresence session both in the basic case involving two CLUE
   endpoints acting, respectively, as MP and MC, and in the more
   advanced scenario envisaging the presence of an MCU.

   The framework document also mentions that the information carried
   within CLUE protocol messages might contain sensitive data, which
   SHOULD hence be accessed only by authenticated endpoints.  Security
   issues associated with the CLUE data model schema are discussed in
   [I-D.ietf-clue-data-model-schema].

   There is extra information carried by the CLUE protocol which is not
   associated with the CLUE data model schema and which exposes
   information that might be of concern.  This information is primarily
   exchanged during the negotiation phase via the OPTIONS and OPTIONS
   RESPONSE messages.  In the Clue Participant state machine OPTIONS
   state, both parties agree on the version and on the extensions to be
   used in the subsequent CLUE messages exchange phase.  A malicious
   participant might either try to retrieve a detailed footprint of a
   specific CLUE protocol implementation during this initial setup
   phase, or force the communicating party to use a non-up-to-date
   version of the protocol which they know how to break.  Indeed,
   exposing all of the supported versions and extensions could
   conceivably leak information about the specific implementation of the
   protocol.  In theory an implementation could choose not to announce
   all of the versions it supports if it wants to avoid such leakage,
   though at the expenses of interoperability.  With respect to the
   above considerations, it is noted that the OPTIONS state is only
   reached after the CLUE data channel has been successfully set up.
   This ensures that only authenticated parties can exchange OPTIONS and
   related OPTIONS RESPONSE messages and hence drastically reduces the
   attack surface which is exposed to malicious parties.

   The CLUE framework clearly states the requirement to protect CLUE
   protocol messages against threats deriving from the presence of a
   malicious agent capable to gain access to the CLUE data channel.
   Such a requirement is met by the CLUE data channel solution described
   in [I-D.ietf-clue-datachannel], which ensures protection from both
   message recovery and message tampering.  With respect to this last
   point, any implementation of the CLUE protocol compliant with the
   CLUE specification MUST rely on the exchange of messages which flow
   on top of a reliable and ordered SCTP over DTLS transport channel
   connecting two CLUE Participants.





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12.  IANA Considerations

   This document registers a new XML namespace, a new XML schema and the
   MIME type for the schema.  This document also registers the "CLUE"
   Application Service tag and the "CLUE" Application Protocol tag and
   defines registries for the CLUE messages and response codes.

12.1.  URN Sub-Namespace Registration

   This section registers a new XML namespace,
   ""urn:ietf:params:xml:ns:clue-protocol"".

   URI: urn:ietf:params:xml:ns:clue-protocol

   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
   Pietro Romano (spromano@unina.it).

   XML:


   BEGIN
    <?xml version="1.0"?>
    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
      "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
      <head>
        <title>CLUE Messages</title>
      </head>
      <body>
        <h1>Namespace for CLUE Messages</h1>
        <h2>urn:ietf:params:xml:ns:clue-protocol</h2>
   [[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX
       with the RFC number for this specification.]]
        <p>See <a href="[[RFC URL]]">
           RFCXXXX</a>.</p>
      </body>
    </html>
   END


12.2.  XML Schema registration

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

   URI: urn:ietf:params:xml:schema:clue-protocol

   Registrant Contact: CLUE working group (clue@ietf.org), Simon Pietro
   Romano (spromano@unina.it).



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   Schema: The XML for this schema can be found as the entirety of
   Section 9 of this document.

12.3.  MIME Media Type Registration for 'application/clue+xml'

   This section registers the ""application/clue+xml"" MIME type.

   To: ietf-types@iana.org

   Subject: Registration of MIME media type application/clue+xml

   MIME media type name: application

   MIME subtype name: clue+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
   protocol data related to telepresence session control.  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 Security are required to protect the data.  This media type
   does not contain executable content.

   Interoperability considerations: None.

   Published specification: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please
   replace XXXX with the RFC number for this specification.]]

   Applications that use this media type: CLUE participants.

   Additional Information: Magic Number(s): (none),
   File extension(s): .xml,
   Macintosh File Type Code(s): TEXT.

   Person & email address to contact for further information: Simon
   Pietro Romano (spromano@unina.it).

   Intended usage: LIMITED USE

   Author/Change controller: The IETF



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   Other information: This media type is a specialization of
   application/xml [RFC7303], and many of the considerations described
   there also apply to application/clue+xml.

12.4.  CLUE Protocol Registry

   The document requests that the IANA creates new registries for CLUE
   messages and response codes.

12.4.1.  CLUE Message Types

   The following summarizes the registry for CLUE messages:

   Related Registry: CLUE Message Types Registry

   Defining RFC: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please replace XXXX
   with the RFC number for this specification.]]

   Registration/Assignment Procedures: Following the policies outlined
   in [RFC5226], the IANA policy for assigning new values for the CLUE
   message types for the CLUE protocol is Specification Required.

   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
   Pietro Romano (spromano@unina.it).

   The initial Message table is populated using the CLUE messages
   described in Section 5 and defined in the XML schema in Section 9.
























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   +-------------------+-----------------------------------+-----------+
   | Message           | Description                       | Reference |
   +-------------------+-----------------------------------+-----------+
   | options           | "OPTIONS" in this document. Sent  | RFCXXXX   |
   |                   | by the CI to the CR  in the       |           |
   |                   | initiation phase to specify the   |           |
   |                   | roles played by the CI, the       |           |
   |                   | supported versions and the        |           |
   |                   | supported extensions.             |           |
   | optionsResponse   | "OPTIONS RESPONSE" in this        | RFCXXXX   |
   |                   | document. Sent by the CI to the   |           |
   |                   | CR in reply to an OPTIONS message |           |
   |                   | to finally estabilsh the version  |           |
   |                   | and the extensions to be used in  |           |
   |                   | the following CLUE messages       |           |
   |                   | exchange.                         |           |
   | advertisement     | "ADVERTISEMENT" or "ADV" in this  | RFCXXXX   |
   |                   | document. Sent by the MP to the   |           |
   |                   | MC to specify the telepresence    |           |
   |                   | capabilities of the MP expressed  |           |
   |                   | according to the CLUE framework.  |           |
   | ack               | "ACK" in this document. Sent by   | RFCXXXX   |
   |                   | the MC to the MP to acknowledge   |           |
   |                   | the reception of an ADVERTISEMENT |           |
   |                   | message.                          |           |
   | configure         | "CONFIGURE" or "CONF" in this     | RFCXXXX   |
   |                   | document. Sent by the MC to the   |           |
   |                   | MP to specify the desired media   |           |
   |                   | captures among those specified in |           |
   |                   | the ADVERTISEMENT.                |           |
   | configureResponse | "CONFIGURE RESPONSE" or "CONF     | RFCXXXX   |
   |                   | RESPONSE" in this document. Sent  |           |
   |                   | by the MP to the MC in reply to a |           |
   |                   | CONFIGURE message to communicate  |           |
   |                   | if the configuration request has  |           |
   |                   | been successfully processed or    |           |
   |                   | not.                              |           |
   +-------------------+-----------------------------------+-----------+

                                 IANA-CLUE

12.4.2.  CLUE Response Codes

   The following summarizes the requested registry for CLUE response
   codes:

   Related Registry: CLUE Response Code Registry




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   Defining RFC: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please replace XXXX
   with the RFC number for this specification.]]

   Registration/Assignment Procedures: Following the policies outlined
   in [RFC5226], the IANA policy for assigning new values for the
   Response codes for CLUE shall be Specification Required.

   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
   Pietro Romano (spromano@unina.it).

   The initial Response-code table is populated using the Response codes
   defined in Section 5.7 as follows:

   +--------+-----------------+----------------------------+-----------+
   | Number | Default         | Description                | Reference |
   |        | Response String |                            |           |
   +--------+-----------------+----------------------------+-----------+
   | 200    | Success         | The request has been       | RFCXXXX   |
   |        |                 | successfully processed.    |           |
   | 300    | Syntax errors   | The XML syntax of the      | RFCXXXX   |
   |        | and             | message is not correct or  |           |
   |        | inconsistencies | there are invalid values.  |           |
   | 301    | Bad syntax      | The XML syntax of the      | RFCXXXX   |
   |        |                 | message is not correct.    |           |
   | 302    | Invalid value   | The message contains an    | RFCXXXX   |
   |        |                 | invalid parameter value.   |           |
   | 303    | Conficting      | The message contains       | RFCXXXX   |
   |        | values          | values that cannot be used |           |
   |        |                 | together.                  |           |
   | 400    | Semantic errors | Semantic errors in the     | RFCXXXX   |
   |        |                 | received CLUE protocol     |           |
   |        |                 | message.                   |           |
   | 401    | Version not     | The protocol version used  | RFCXXXX   |
   |        | supported       | in the message is not      |           |
   |        |                 | supported.                 |           |
   | 402    | Invalid         | The sequence number of the | RFCXXXX   |
   |        | sequencing      | message is out of date.    |           |
   | 403    | Invalid         | The identifier used in the | RFCXXXX   |
   |        | identifier      | message is no valid or     |           |
   |        |                 | unknown.                   |           |
   | 404    | ADV Expired     | The number of the ADV the  | RFCXXXX   |
   |        |                 | CONF refers to is out of   |           |
   |        |                 | date.                      |           |
   | 405    | Subset choice   | The subset choice is not   | RFCXXXX   |
   |        | not allowed     | allowed for the specified  |           |
   |        |                 | MCC.                       |           |
   +--------+-----------------+----------------------------+-----------+




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13.  Diff with draft-ietf-clue-protocol-12

   o  Section 6: brackets removed from "Otherwise if ("channel error"),"

   o  Section 5.7: new response codes MUST always be registered with
      IANA (i.e., in case of both new versions and extensions).

   o  Section 5: clueId has been made optional.

14.  Diff with draft-ietf-clue-protocol-06

   o  XML schema definition of <version> has been changed to match
      pattern "X.Y", where X and Y are single digits.

   o  100, 200, 300, 400 defined as catch-all response codes.

   o  Updates in IANA section.

15.  Diff with draft-ietf-clue-protocol-05

   o  This document corrects some versioning errors of draft-ietf-clue-
      protocol-05.

16.  Diff with draft-ietf-clue-protocol-04

   o  The document has been revised based on feedback recevied on the
      ML.  No major modification is included in this version.

17.  Diff with draft-ietf-clue-protocol-03

   o  Response codes section updated.

   o  maxCaptureEncodings removed from examples, allowSubsetChoice
      added.

   o  State machines descriptions aligned with pictures.

   o  Applied recommended updates indicated in Christian's review
      (2015-03-19).

18.  Diff with draft-ietf-clue-protocol-02

   o  CLUE Participant state machine: TERMINATED state replaced with
      IDLE.

   o  MP and MC state machines: SDP O/A state removed.

   o  Diff mechanism (and related example) removed.



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   o  Schema updates: versionType used as the data type for all versions
      fields, xs:unsignedInt used as the data type for all sequence
      number fields, diff support removed from the ADV definition.

19.  Diff with draft-ietf-clue-protocol-01

   o  The diff mechanism for the ADV message has been introduced.

   o  READV and READV RESPONSE message have been both removed.

   o  The state machines have been deeply reviewed and changed.

   o  References: references have been updated and splitted into
      Informative references and Normative references as in framework
      v17.

   o  Schema: <globalSceneEntries> changed in <globalViews>,
      <participants> in <people>

   o  Terminology: many definitions added.

   o  Response codes updated.

20.  Diff with draft-ietf-clue-protocol-00

   1.  The XML schema of the ADVERTISEMENT and of the READV have been
       aligned with the current definitions in
       [I-D.ietf-clue-data-model-schema] (example of updates:
       <participants> --> <people>, <globalCaptureEntries> -->
       <globalSceneEntries>)

   2.  Text has been added to clarify that, in the OPTIONS RESPONSE,
       when the response code is not an error response code, both
       <mediaProvider> and <mediaConsumer> are mandatory.

   3.  The content of the "v" attribute and of the <version> elements
       carried in the OPTIONS and OPTIONS RESPONSE messages has been
       described more precisely.

   4.  Advertisement examples have been added.

21.  Diff with draft-presta-clue-protocol-04

   1.  The response code type error in the OPTIONS response (and in
       other parts) has been corrected.






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22.  Diff with draft-presta-clue-protocol-03

   1.  The XML Schema has been deeply revised and completed.

   2.  The descriptions of the CLUE messages have been added.

   3.  The distinction between major version numbers and minor version
       numbers has been cut and pasted from [I-D.ietf-clue-signaling].

   4.  Besides the two way one, a three way mechanism for the options
       negotiation has been proposed and provided to foster discussion.

23.  Diff with draft-presta-clue-protocol-02

   1.  "Terminology" section added.

   2.  Introduced the concept of "CLUE Participant" - an Endpoint or a
       MCU able to use the CLUE protocol within a telepresence session.
       A CLUE Participant can act as a Media Provider and/or as a Media
       Consumer.

   3.  Introduced the ACK/NACK mechanism for the ADVERTISEMENT.

   4.  MP and MC state machines have been updated.  The CP state machine
       has been added.

24.  Acknowledgments

   The authors thank all the CLUErs for their precious feedbacks and
   support, in particular Paul Kyzivat, Christian Groves and Scarlett
   Liuyan.

25.  References

25.1.  Normative References

   [I-D.ietf-clue-data-model-schema]
              Presta, R. and S. Romano, "An XML Schema for the CLUE data
              model", draft-ietf-clue-data-model-schema-17 (work in
              progress), August 2016.

   [I-D.ietf-clue-datachannel]
              Holmberg, C., "CLUE Protocol data channel", draft-ietf-
              clue-datachannel-14 (work in progress), August 2016.







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   [I-D.ietf-clue-framework]
              Duckworth, M., Pepperell, A., and S. Wenger, "Framework
              for Telepresence Multi-Streams", draft-ietf-clue-
              framework-25 (work in progress), January 2016.

   [I-D.ietf-clue-signaling]
              Kyzivat, P., Xiao, L., Groves, C., and R. Hansen, "CLUE
              Signaling", draft-ietf-clue-signaling-10 (work in
              progress), January 2017.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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,
              July 2003, <http://www.rfc-editor.org/info/rfc3550>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <http://www.rfc-editor.org/info/rfc5226>.

   [RFC7303]  Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
              DOI 10.17487/RFC7303, July 2014,
              <http://www.rfc-editor.org/info/rfc7303>.

25.2.  Informative References

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122,
              DOI 10.17487/RFC1122, October 1989,
              <http://www.rfc-editor.org/info/rfc1122>.

   [RFC4353]  Rosenberg, J., "A Framework for Conferencing with the
              Session Initiation Protocol (SIP)", RFC 4353,
              DOI 10.17487/RFC4353, February 2006,
              <http://www.rfc-editor.org/info/rfc4353>.

   [RFC6120]  Saint-Andre, P., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 6120, DOI 10.17487/RFC6120,
              March 2011, <http://www.rfc-editor.org/info/rfc6120>.



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   [RFC7262]  Romanow, A., Botzko, S., and M. Barnes, "Requirements for
              Telepresence Multistreams", RFC 7262,
              DOI 10.17487/RFC7262, June 2014,
              <http://www.rfc-editor.org/info/rfc7262>.

   [RFC7667]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
              DOI 10.17487/RFC7667, November 2015,
              <http://www.rfc-editor.org/info/rfc7667>.

Authors' Addresses

   Roberta Presta
   University of Napoli
   Via Claudio 21
   Napoli  80125
   Italy

   EMail: roberta.presta@unina.it


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

   EMail: spromano@unina.it
























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