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Versions: 00 01 02 03 04 draft-ietf-clue-protocol

CLUE Working Group                                             R. Presta
Internet-Draft                                                 S. Romano
Intended status: Standards Track                    University of Napoli
Expires: November 10, 2014                                   May 9, 2014


                             CLUE protocol
                     draft-presta-clue-protocol-04

Abstract

   The CLUE protocol is an application protocol conceived for the
   description and negotiation of a CLUE telepresence session.  The
   design of the CLUE protocol takes into account the requirements and
   the framework defined, respectively, in [I-D.ietf-clue-framework] and
   [I-D.ietf-clue-telepresence-requirements].  The companion document
   [I-D.kyzivat-clue-signaling] delves into CLUE signaling details, as
   well as on the SIP/SDP session establishment phase.  CLUE messages
   flow upon the CLUE data channel, based on reliable and ordered SCTP
   over DTLS transport, as described in [I-D.ietf-clue-datachannel].
   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 November 10, 2014.

Copyright Notice

   Copyright (c) 2014 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



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

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of the CLUE protocol  . . . . . . . . . . . . . . . .  4
   4.  Protocol messages  . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  OPTIONS  . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  OPTIONS RESPONSE . . . . . . . . . . . . . . . . . . . . . 10
     4.3.  ADVERTISEMENT  . . . . . . . . . . . . . . . . . . . . . . 11
     4.4.  ADVERTISEMENT ACKNOWLEDGEMENT  . . . . . . . . . . . . . . 12
     4.5.  CONFIGURE  . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.6.  CONFIGURE RESPONSE . . . . . . . . . . . . . . . . . . . . 14
     4.7.  READV  . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     4.8.  READV RESPONSE . . . . . . . . . . . . . . . . . . . . . . 15
     4.9.  Response codes and reason strings  . . . . . . . . . . . . 16
   5.  Protocol state machines  . . . . . . . . . . . . . . . . . . . 18
   6.  CLUE Participant's state machine . . . . . . . . . . . . . . . 18
     6.1.  Media Consumer's state machine . . . . . . . . . . . . . . 21
     6.2.  Media Provider's state machine . . . . . . . . . . . . . . 23
   7.  Versioning . . . . . . . . . . . . . . . . . . . . . . . . . . 25
   8.  Extensions and options . . . . . . . . . . . . . . . . . . . . 26
   9.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 28
   10. Diff with the -03 version  . . . . . . . . . . . . . . . . . . 33
   11. Diff with the -02 version  . . . . . . . . . . . . . . . . . . 34
   12. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 34
   13. Informative References . . . . . . . . . . . . . . . . . . . . 34

















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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 MP to fully announce its current telepresence
       capabilities to a MC in terms of available media captures, groups
       of encodings, simultaneity constraints and other information
       envisioned in [I-D.ietf-clue-framework];

   2.  enabling a MC to request the desired multimedia streams to 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
   depicted respectively in [I-D.kyzivat-clue-signaling] and
   [I-D.kyzivat-clue-signaling].  CLUE protocol messages flowing upon
   such channel are detailed in the following, both syntactically and
   semantically.

   In Section 3 we provide a general overview of the CLUE protocol.
   CLUE protocol messages are detailed in Section 4 The CLUE Participant
   state machine is introduced in Section 5.  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
   [I-D.ietf-clue-telepresence-requirements].  We briefly recall herein
   some of the main terms exploited in the document.  We further
   introduce the definition of CLUE Participant.

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

   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 [RFC4353] Participant (which, in turn, includes
      exactly one SIP User Agent).  Endpoints can be anything from
      multiscreen/multicamera room controllers to handheld devices.





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   MCU  Multipoint Control Unit (MCU) - a device that connects two or
      more endpoints together into one single multimedia conference
      [RFC5117].  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.

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

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

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

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

3.  Overview of the CLUE protocol

   The CLUE protocol has been conceived to enable CLUE telepresence
   session.  It is designed in order to address SDP limitations in terms
   of the description of several information about the multimedia
   streams that are involved in a real-time multimedia conference.
   Indeed, by simply using SDP we are not able to convey the information
   about the features of the flowing multimedia streams that is needed
   to enable a "being there" rendering.  Such information is designed in
   the CLUE framework document and formally defined and described in the
   CLUE data model document.  The CLUE protocol represents the mechanism
   that enables 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 realiable and ordered SCTP over DTLS transport
   channel connecting two CLUE Participants.  Messages carries
   information taken from the XML-based CLUE data model
   ([I-D.ietf-clue-data-model-schema]).  Three main communication layers
   can be identified:

   1.  Establishment of the CLUE data channel: in this phase, the CLUE
       data channel setup takes place.  If it ends up successfully, the



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       CPs are able to communicate and start the initiation phase.

   2.  Negotiation of the CLUE protocol version and options (initiation
       phase): the CPs connected via the CLUE data channel agree on the
       version and on the options to be used during the telepresence
       session.  Special CLUE messages are used for such a task.  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 offer-answer 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 and a minor version number,
   both unsigned integer, separated by a dot.  While minor version
   numbers denote backword 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 protocol options and extensions that are
   allowed within the CLUE session is also determined in the initiation
   phase, such subset being the one including only the options that are
   supported by both parties.  A mechanism for the negotiation of the
   CLUE protocol version and extensions is envisioned in the initiation
   phase.  According to such 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 that negotiation phase is completed, CLUE Participants describe
   and agree on the media flows to be exchanged.  Indeed, being CPs A
   and B both transmitting and receiving, it is possible to distinguish
   between two dialogues:

   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




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   CLUE messages for the media session description and negotiation is
   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 conveing 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 and will be detailed in the following sections.

4.  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, the CONFIGURE, and the
   READV RESPONSE messages), in order to use the concept defined in
   [I-D.ietf-clue-framework].

   The CLUE protocol messages that have been defined up to now are the
   following:

   o  OPTIONS

   o  OPTIONS RESPONSE

   o  ADVERTISEMENT (ADV)

   o  ADVERTISEMENT ACKNOWLEDGE (ACK)




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   o  CONFIGURE (CONF)

   o  CONFIGURE RESPONSE

   o  READV

   o  READV 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 figure:



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


   The basic structure determines the mandatory information that is
   carried within each CLUE message.  Such an information is made by:

   o  clueId: an XML element containing the identifier of the CP within
      the telepresence system;

   o  sequenceNr: an XML element containing the local message sequence
      number;

   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

   Each CP should manage uo to three streams of sequence numbers: (i)
   one for the messages exchanged in the initiation phase, (ii) one for
   the messages exchanged as MP, and (iii) one for the messages
   exchanged as MC.





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4.1.  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  supportedOptions: the list of the supported options

   The XML Schema of such a message is reported below:


































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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="supportedOptions" type="optionsListType" 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="xs:string" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

<!-- OPTIONS LIST TYPE -->
<xs:complexType name="optionsListType">
<xs:sequence>
<xs:element name="option" type="optionType" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

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





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   <supportedVersions> contains the list of the versions that are
   supported by the CI.  Only one <version> element SHOULD 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 whithin
   the OPTIONS message, the CI supports only the version declared in the
   "v" attribute.  For example, if the "v" attribute has a value of
   "3.4" and there is not a <supportedVersions> tag in the OPTIONS
   message, it means the CI supports only major version 3 with all the
   minor versions comprised between 3.0 the 3.4 included.  If a
   <supportedVersion> is provided, at least one <version> tag MUST be
   included.

   The <supportedOptions> element specifies the list of the options
   supported by the CI.  If there is no <supportedOptions> in the
   OPTIONS message, the CI does not support anything more than what is
   envisioned in the versions it supports.  For each option, an <option>
   element is provided.  An option is characterized by a name, an XML
   schema of reference where the option is defined, and the version of
   the protocol which the option refers to. [to be discussed: difference
   between options and extensions]

4.2.  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 mandatorily a response code and a response string
   indicating the processing result of the OPTIONS message.  Following,
   the CR attaches two boolean tags, <mediaProvider> and
   <mediaConsumer>, expressing the supported roles in terms of
   respectively MP and MC, similarly to what the CI does in the OPTIONS
   message.  Finally, the highest commonly supported version number is
   expressed in the <version> field and just the commonly supported
   options in the <commonOptions> field.

















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 <!-- CLUE OPTIONS RESPONSE (2 WAY) -->
 <xs:complexType name="optionsResponseMessageType">
 <xs:complexContent>
 <xs:extension base="clueMessageType">
 <xs:sequence>
 <xs:element name="responseCode" type="xs:string"/>
 <xs:element name="reasonString" type="xs:string"/>
 <xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
 <xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
 <xs:element name="version" type="xs:string" minOccurs="0"/>
 <xs:element name="commonOptions" type="optionsListType" minOccurs="0"/>
 <xs:any namespace="##other"
 processContents="lax" minOccurs="0"/>
 </xs:sequence>
 <xs:anyAttribute namespace="##other" processContents="lax"/>
 </xs:extension>
 </xs:complexContent>
 </xs:complexType>


   After the reception of such message, the version to be used is
   determined by each part of the conversation.  Indeed, it is the one
   provided in the <version> tag of the OPTIONS RESPONSE message.  The
   following CLUE messages will use such a version number in the "v"
   attribute.  The allowed options in the CLUE dialogue will be those
   indicated in the <commonOptions> of the OPTIONS RESPONSE message.

4.3.  ADVERTISEMENT

   This message is used by the MP to advertise the available media
   captures and related information to the MC.  The MP sends to the MC
   an ADV as soon as it is ready after the successful completion of the
   initiation phase.  During the telepresence session, the ADV can be
   sent from the MP both periodically and on a per-event basis, i.e.,
   each time there are changes in the MP's CLUE telepresence
   capabilities.

   The ADV structure is defined in the picture 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>) and of
   the global capture entries (>globalCaptureEntries>), and the list of
   the represented participants (>participants>).  Each of them is fully
   described in the CLUE framework document and formally defined in the
   CLUE data model document.





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


   [to be discussed: a "delta" mechanism for advertising only the
   changes with respect to the previous notification should be adopted.
   Similar approaches have been proposed for partial notifications in
   centralized conferencing frameworks ([RFC6502]), leveraging the XML
   diff codification mechanism defined in [RFC5261]].

4.4.  ADVERTISEMENT ACKNOWLEDGEMENT

   The ACK message 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.
















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


4.5.  CONFIGURE

   The CLUE CONFIGURE message 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.



    <!-- CLUE CONFIGURE MESSAGE TYPE -->
   <xs:complexType name="configureMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <!-- mandatory fields -->
   <xs:element name="advSequenceNr" type="xs:unsignedInt"/>
   <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>


   In the >advSequenceNr< element is contained the sequence number of
   the ADVERTISEMENT or of the READV RESPONSE message the CONFIGURE
   refers to.




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   The optional boolean <ack> element, set to "true", if present,
   indicates that the CONF message also acknowledge the referred
   advertisement, by applying in that way a piggibacking mechanism for
   simultaneously acknowledging and replying to the ADV message.  The
   <ack> element SHOULD not be present at all if an ADV ACK message has
   been already sent back to the MP and if the CONFIGURE refers to a
   READV RESPONSE message.

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

4.6.  CONFIGURE RESPONSE




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


   The CONF RESPONSE message 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 number of the CONF message the
   response refers to.

4.7.  READV

   The READV message is a request the MC issues to the MP to retrieve an
   updated version of the MP's telepresence offer.  The content of the
   READV message is specified in the following.



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   <!-- CLUE READV MESSAGE TYPE -->
   <xs:complexType name="readvMessageType">
   <xs:complexContent>
   <xs:extension base="clueMessageType">
   <xs:sequence>
   <xs:element name="lastReceivedAdv" type="xs:short"/>
   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
   </xs:sequence>
   <xs:anyAttribute namespace="##other" processContents="lax"/>
   </xs:extension>
   </xs:complexContent>
   </xs:complexType>



   The <lastReceivedAdv> element specifies the sequence number of the
   last ADVERTISEMENT or READV RESPONSE correctly received by the MC.

4.8.  READV RESPONSE

   The READV RESPONSE is sent by the MP to the MC to reply to a READV
   message.  As shown in the schema below, it contains, besides a
   response code and a reason string, all the information carried within
   an ADVERTISEMENT message (media captures, encoding groups, and so
   on).  If there are no updates with respect to the last telepresence
   offer successfully delivered to the MC (i.e, that having the sequence
   number specified in the <lastReceiveAdv> field of the READV message),
   the READV RESPONSE SHOULD carry only the response code with the
   reason string.






















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<!-- CLUE READV RESPONSE MESSAGE TYPE -->
<xs:complexType name="readvResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="xs:short"/>
<xs:element name="reasonString" type="xs:string"/>
<xs:element name="readvSequenceNr" type="xs:string" minOccurs="0"/>
<xs:element name="mediaCaptures" type="dm:mediaCapturesType" minOccurs="0"/>
<xs:element name="encodingGroups" type="dm:encodingGroupsType" minOccurs="0"/>
<xs:element name="captureScenes" type="dm:captureScenesType" minOccurs="0"/>
<xs:element name="simultaneousSets" type="dm:simultaneousSetsType" minOccurs="0"/>
<xs:element name="globalCaptureEntries" type="dm:globalCaptureEntriesType" minOccurs="0"/>
<xs:element name="participants" type="dm:participantsType" minOccurs="0"/>
<xs:any namespace="##other"
 processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>


4.9.  Response codes and reason strings

   Examples of response codes and strings are provided in the following
   table.  Response codes can be designed by adhering to the HTTP
   semantics, as shown below.
























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   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |  Response code  |  Response string     |       Description        |
   |                 |                      |                          |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   410           |  Bad syntax          |  The XML syntax of the   |
   |                 |                      |  CONF message is not     |
   |                 |                      |  correct.                |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   411           |  Invalid value       |  The CONF message        |
   |                 |                      |  contains an invalid     |
   |                 |                      |  parameter value.        |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   412           |  Invalid identifier  |  The identifier used for |
   |                 |                      |  requesting a capture is |
   |                 |                      |  not valid or unknown.   |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   413           |  Conflicting values  |  The CONF message        |
   |                 |                      |  contains values that    |
   |                 |                      |  cannot be used together.|
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   420           |  Invalid sequencing  |  The sequence number of  |
   |                 |                      |  the CONF message is out |
   |                 |                      |  of date or corresponds  |
   |                 |                      |  to an obsoleted ADV.    |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   510           | Version not supported|  The CLUE protocol       |
   |                 |                      |  version of the CONF     |
   |                 |                      |  message is not supported|
   |                 |                      |  by the MP.              |
   +-----------------+----------------------+--------------------------+
   |                 |                      |                          |
   |   511           | Option not supported |  The option requested in |
   |                 |                      |  the CONF message is not |
   |                 |                      |  supported by the MP.    |
   +-----------------+----------------------+--------------------------+



   ...  TBC.





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   +---------------+------------------------+
   |               |                        |
   | Response code | Description            |
   | family        |                        |
   +---------------+------------------------+
   |               |                        |
   |     1XX       | Temporary info         |
   |               |                        |
   +---------------+------------------------+
   |               |                        |
   |     2XX       | Success                |
   |               |                        |
   +---------------+------------------------+
   |               |                        |
   |     3XX       | Redirection            |
   |               |                        |
   +---------------+------------------------+
   |               |                        |
   |     4XX       | Client error           |
   |               |                        |
   +---------------+------------------------+
   |               |                        |
   |     5XX       | Server error           |
   |               |                        |
   +---------------+------------------------+


5.  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 upon the CLUE Data Channel, a DTLS/SCTP
   channel established as depicted in [I-D.kyzivat-clue-signaling].
   Over such a channel there are typically two CLUE streams between the
   channel terminations flowing in opposite directions.  In other words,
   typically, both channel terminations act simultaneously as a MP and
   as a MC.  We herein discuss the state machines associated,
   respectively, with the CLUE Participant, with MC process and with the
   MP process.

6.  CLUE Participant's state machine

   The main state machines focus on describing the states of CLUE
   channel from a CLUE channel initiator/receiver.  In the IDLE state,
   when the CP has established a CLUE channel, the main state moves to
   the ESTABLISHED state.  When in the ESTABLISHED state, if the CP is
   the Channel Initiator (CI), it prepares sending an OPTIONS message
   for version negotiation; otherwise, if the is the Channel Receiver



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   (CR), it listens to the channel for an OPTIONS message for version
   negotiation.  If an OPTIONS message is sent or is received, the CP
   moves to the NEGOTIATING state.  If the CP checks some error in the
   request message received, the main state goes back to the IDLE state.
   [TODO: check this] When in the NEGOTIATING state, the CR prepares an
   OPTIONS RESPONSE message while the CI listens to the channel for an
   OPTIONS RESPONSE.  If an OPTIONS RESPONSE message for version
   negotiation is sent or is received, the main state moves to the
   ACTIVE state.  If the CI checks some error in the OPTIONS RESPONSE
   message received or receives an OPTIONS RESPONSE indicating an error,
   it goes back to the IDLE state.  When the CP enters in the ACTIVE
   state, it creates two sub state machines which are the MC state
   machine and the MP state machine, accordingly to the supported roles.
   When in the ACTIVE state, if the CP receives a further OPTIONS
   message for version negotiation or a further OPTIONS RESPONSE
   messages for version negotiation, it MUST ignore the messages and
   keep in the ACTIVE state.  When in the ACTIVE state, the CP delegates
   the sending and the processing of the CLUE messages the appropriate
   MP/MC sub-state machines.  The TERMINATED state is reachable from
   each of the aforementioned states whenever the session is canceled or
   released.  The IDLE state is reachable from each of the
   aforementioned states whenever the underlying channel is closed due
   to connection error.  [TODO: CLUE messages to cancel/release the
   session] [TODO: check the diagram]



























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                      +-------------+<------------------------------+---------+
         +----------->+     IDLE    +<--------------------------+   + TIMEOUT +
         |            +------+------+<-----------+              |   +------+--+
         |                   |                   |              |          |
         |                   |                   |              |          |
     Connection            CLUE                  |              |          |
       error              channel                |              |          |
         |           has been established        |              |          |
         |                   |                   |              |          |
         |                   V               Receive error      |          |
         +------------+-------------+     (version mismatch,    |          |
   +------------------+ ESTABLISHED +      missing elements,...)  |       time out
   |                  +------+------+            |              |          |
   |                         |                   |          Connection     |
   |                         |                   |             error       |
   |                  Send/Receive OPTIONS       |              |          |
   |                         |                   |              |          |
   |                         V                   |              |          |
   |                  +-------------+------------+              |          |
   |     +------------+ NEGOTIATING +---------------------------+          |
   |     |            +------+------+---------------------------|----------+
   |     |                   |                                  |
   |     |                   |                                  |
   |     |             Receive/Send                        Connection
   |     |            OPTIONS RESPONSE                       error
Session  |                   |                                  |
  ends   |                   V                                  |
   |     |            +-------------+---------------------------+
   |     |            |   ACTIVE    +<-------------------+
   |     |            |  +-------+  |           Receive OPTIONS/
   |     |            |  |SUBIDLE|  |             OPTIONS RESPONSE
   |   Session        |  |MC     |  +--------------------+
   |    ends          |  +-------+  |
   |     |            |  +-------+  +<-------------------+
   |     |            |  |SUBIDLE|  |       Send/Receive other CLUE messages
   |     |            |  |MP     |  |                    |
   |     |            |  +-------+  |                    |
   |     |            +------+------+--------------------+
   |     |                   |
   |     |                   |
   |     |                Session
   |     |                  ends
   |     |                   |
   |     |                   V
   |     |            +-------------+
   |     +----------->+ TERMINATED  +
   +----------------->+-------------+




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6.1.  Media Consumer's state machine

   An MC in the WAIT FOR ADV state is waiting for an ADV coming from the
   MP.  If the timeout expires ("timeout"), the MC switches to the
   TIMEOUT state.

   In the TIMEOUT state, if the number of trials is below the retry
   threshold, the MC sends a READV message to the MP ("send RE-ADV"),
   switching back to the WAIT FOR ADV.  Otherwise, the MC moves to the
   TERMINATED state.

   When the ADV has been received ("receive ADV"), the MC goes into the
   ADV RECEIVED state.  The ADV is then parsed.  If something goes wrong
   with the ADV (bad syntax, missing XML elements, etc.), the MC sends a
   NACK message (an ACK with an error response code) to the MP
   specifying the encountered problem via a proper reason phrase.  In
   this way, the MC switches back to the WAIT FOR ADV state, waiting for
   a new copy of the ADV.  If the ADV is successfully processed, the MC
   issues a successful ACK message to the MP and moves to the ADV ACKED
   state.  When the SDP information arrives, from the ADV RECEIVED or
   the ADV ACKED state the MC switches to the READY TO CONF state.  When
   the CONF request is ready, the MC sends it and moves to the TRYING
   state.  If the ADV has not been already sent, the MC can piggyback
   the ACK message within the CONF request.

   While in the TRYING state, the MC is waiting for a CONF RESPONSE
   message (to the issued CONF) from the MP.  If the timeout expires
   ("timeout"), the MC moves to the TIMEOUT state and sends a READV in
   order to solicit a new ADV from the MP.  If a CONF RESPONSE with an
   error code is received ("receive 4xx, 5xx not supported"), then the
   MC moves back to the ADV RECEIVED state and produces a new CONF
   message to be sent to the MP.  If a successful CONF RESPONSE arrives
   ("receive 200 OK"), the MC gets into the CONF COMPLETED state. state.

   When the MC is in the CONF COMPLETED state, it means that the
   telepresence session configuration has been set up according to the
   MC's preferences.  Both the MP and the MC have agreed on (and are
   aware of) the media streams to be exchanged within the call.  If the
   MC decides to change something in the call settings, it issues a new
   CONF ("send CONF") and moves back to the TRYING state.  If a new ADV
   arrives from the MP ("receive ADV"), it means that something has
   changed on the MP's side.  The MC then moves to the ADV RECEIVED
   state and prepares a new CONF taking into account the received
   updates.  When the underlying channel is closed, the MC moves into
   the TERMINATED state.

   The TERMINATED state is reachable from each of the aforementioned
   states whenever the underlying channel is closed.  The corresponding



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   transitions have not been reported for the sake of simplicity.  This
   termination condition is a temporary solution.




                                                                      +-----+
                     +---------------+-------------timeout------>+----+--+  |
                     | WAIT FOR ADV  |<----+                     |TIMEOUT|  |
                     +---------------+<----+--------send---------+-------+  |
                                |          |     RE-ADV(refresh)      ^     |
                                |          |                          |     |
                                |          |                          |     |
                             receive     send                         |     |
                               ADV       NACK                         |     |
           +---receive-------+  |       (missing elements,            |     |
           |   error RESP    |  |        invalid area,...)            |     |
           |                 v  v          |                          |     |
           +----------------+---------+----+      +--------+          |     |
          +---------------->|  ADV    |---send--->|  ADV   |      timeout   |
          |                 | RECEIVED|   ACK     | ACKED  |          |     |
          |     +---------->|         |           |        |          |     |
          |    recv  +----->+-----+---+<--recv----+----+---+          |     |
          |   error  |            |       ADV          |              |     |
          |    CONF  |            |                    |              |     |
          |     |    |         SDP info            SDP info           |     |
          |     |    |         received             received          |     |
          |     |    |            |     +--------+     |              |     +
          +     |    +            +---->|READY TO|<----+              +     |
          |     |    |                  | CONF   |                    |     |
          |     +    |            +-----+--------+-----+              +     |
          |     |    |            |                    +              +     |
          |     |    +            |                    |              +     +
          +     +    |            +                    |              |     |
      receive   |    |           send              send|              |     |
        ADV     |    |         CONF+ACK            CONF|              |     |
          |     |    |            |                    |              |     |
          |     |  receive        v                    |              |     |
          |     |  ADV         +-----------+<----------+              |     |
          |     |    |         |           |+-------------------------+     |
          |     +----|--------+|  TRYING   |                                |
          +----------|---------|           |                                |
                 +---|---------+-----------+                                |
                 |   |          |          ^                                |
                 |   |          |          |                                |
                 |   |          |          |                                |
          receive|   |         receive    send                          retry
          error RESP,|          200 OK    CONF                        expires



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          retry  |   |          |          |                                |
          expired|   |          |          |                                |
                 |   |          |          |                                |
                 |   |          v          |                                |
                 |   |       +---------+   |                                |
                 |   +-------| CONF    |   |                                |
                 |           |COMPLETED|---+                                |
                 |           +---------+                                    |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |            connection                                    |
                 |             closed                                       |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              v                                           |
                 |            +----------+<---------------------------------+
                 +----------->+TERMINATED|
                              +----------+

6.2.  Media Provider's state machine

   In the PREPARING ADV state, the MP is preparing the ADV message
   reflecting the actual telepresence capabilities.  After the ADV has
   been sent, the MP moves to the WAIT FOR ACK state.  If the ACK
   arrives, the MP moves to the WAIT FOR CONF state.  If a NACK arrives,
   it goes back to the PREPARING ADV state.

   When in the WAIT FOR ACK state, if a CONF or a CONF+ACK arrives, the
   MP switch to the CONF RECEIVED state directly.

   When in the WAIT FOR CONF state, the MP is listening to the channel
   for a CONF coming from the MC.  If a RE-ADV is received, the MP goes
   back to the IDLE state and issues an ADV again.  If telepresence
   settings change in the meanwhile, it moves back to the PREPARING ADV
   state and prepares a new ADV to be sent to the MC.  If a CONF
   arrives, the MP switches to the CONF RECEIVED state.  If nothing
   happens and the timeout expires, than the MC falls into the TIMEOUT
   state.

   In the TIMEOUT state, if the number of trials does not exceed the
   retry threshold, the MC comes back to the PREPARING ADV state for
   sending a new ADV.  Otherwise, it goes to the TERMINATED state.




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   The MP in the CONF RECEIVED state is processing the received CONF in
   order to produce a CONF RESPONSE message.  If the MP is fine with the
   MC's configuration, then it sends back a 200 OK successful CONF
   RESPONSE and moves to the IN CALL state.  If there are errors duting
   CONF processing, then the MC returns a CONF RESPONSE carrying an
   error response code.  Finally, if there are changes in the
   telepresence settings, it goes back to the PREPARING ADV state to
   issue an updated ADV.

   When in the CONF COMPLETED state, the MP has successfully configured
   the telepresence session according to the MC's specifications.  If a
   new CONF arrives, it switches to the CONF RECEIVED state to analyze
   the new request.  If a RE-ADV arrives, or some modifications are
   applied to the telepresence options, then it moves to the PREPARE-ADV
   state to issue the ADV.  When the channel is terminated, the MP falls
   into the TERMINATED state.

   The TERMINATED state is reachable from each of the aforementioned
   states whenever the underlying channel is closed.  The corresponding
   transitions have not been reported for the sake of simplicity.  This
   termination condition is a temporary solution.





                    +-----------+
                    |           |
                    | PREPARING |
 +----------------->|   ADV     |<--------------------------+
 |   +------------->|           |<-----------retry----------+---------+
 |   |       +----->|           |<--+         not           |         |
 |   |       |      +-----------+   |        expired        |         |
 |   |       |            |         |                       |         |
 |   |  change          send       receive                  |        ++------+
 |   |  telepresence     ADV        NACK                    |        |TIMEOUT|
 |   |  settings          |         |                       |        ++--+---+
 |   |       |            |         |                       |         ^  |
 |   |       |            v         |                       |         |  |
 |   |       |    +-------------+---+                       |         |  |
 |   |       +----+  WAIT FOR   +------------timeout--------+---------+  |
 |   |         +--+     ACK     |                           |            |
 change        |  +-------+-----+                           |            |
 telepresence  |          |                                 |            |
 settings      |        recv                                |            +
 +   +         |        ACK                                 +            |
 |   |         |          |                                 |            |
 |   |         |          v                                 |            |



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 |   |         |     +-----------+                          |            |
 |   |      recv     | WAIT FOR  |                          |            |
 |   |         |     |   CONF    |<-+                       |            |
 |   |    CONF+ACK   +----+------+  |                       |            |
 |   |         |          |         +                       |            |
 +   |         |        receive     CONF error,             +            |
 |   +         |         CONF       retry not expired,      |            +
 |   |         |          |         send error RESP         |            |
 |   |         |          |         |                       |            |
 |   |         |          |         |                       |            |
 |   |         |          v         |                       |            |
 |   |         +--->+-----------+---+                       |            |
 +---+-------------+|   CONF    |                           |            |
     |       +----->| RECEIVED  |----CONF error,            |            |
     |       |      +-----+-----+    retry expired          |            |
     |       |            |          +                      |            |
     |       |            |          |                      |            |
     |       |            |          |                      |            |
 receive   receive      send         |                      |            |
 RE-ADV     CONF       200 OK        |                      |       retry|
     |       |            |          |                      |      expired
     |       |            |          |                      |            |
     |       |            |          |                      |            |
     |       |            v          |                      |            |
     |       |       +----------+    |   change             |            |
     |       +-------|  CONF    |----|---telepresence-------+            |
     +---------------| COMPLETED|    |   settings                        |
                     +----------+    |                                   |
                          |          |                                   |
                          |          |                                   |
                          |          |                                   |
                       connection    |                                   |
                        closed       |                                   |
                          |          |                                   |
                          |          |                                   |
                          v          |                                   +
                 +----------------+<-+                                   |
                 |   TERMINATED   |<-------------------------------------+
                 |                |
                 +----------------+



7.  Versioning

   CLUE protocol messages are XML messages compliant to the CLUE
   protocol XML schema.  The version of the protocol corresponds to the
   version of the schema.  Both client and server have to test the



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   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 can not communicate if they do not share
   exactly the same XML schema.  Such a schema is the one included in
   the yet to come RFC, and associated with the CLUE URN
   "urn:ietf:params:xml:ns:clue-message".  If all CLUE-enabled devices
   use that schema there will be no interoperability problems due to
   schema issues.

   The version of the XML schema contained in the standard document
   deriving from this draft will be 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 to version 1.4 without exploiting 1.5 features and
   functionality.

   It is expected that, before the CLUE protocol XML schema reaches a
   steady state, prototypes developed by different organizations will
   conduct interoperability testing.  In that case, in order to
   interoperate, they have to be compliant to the current version of the
   XML schema, i.e., the one copied in the most up-to-date version of
   the draft defining the CLUE protocol.  The versions of the non-
   standard XML schema will be numbered as 0.01, 0.02, and so on.
   During the standard development phase, the versions of the XML schema
   will probably not be backward compatible so it is left to prototype
   implementers the responsibility of keeping their products up to date.

8.  Extensions and options

   Although the standard version of the CLUE protocol XML schema will be
   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.  They can relate to:



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      the information carried in the existing messages (for example, we
      may want to add more fields within an existing message);

      the meaning of the 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:

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

      (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:

      elementFormDefault="qualified"

      attributeFormDefault="unqualified"

   In that case, the new information must be qualified by namespaces
   other than "urn:ietf:params:xml:ns:clue-message" (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 last standard version
   of the schema, can be needed.  In that case, the messages and the
   associated behavior should be defined in external documents that both
   the communication parties must be aware of.

   Both the types of extensions, i.e., the information and the protocol



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   extensions, can be characterized by:

      a name;

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

      the standard version of the protocol the extension refers to.

   For that reason, the extensions can be represented by means of the
   <option> 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.



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


9.  XML Schema

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



<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema
version="0.02"
targetNamespace="urn:ietf:params:xml:ns:clue-message"
xmlns:tns="urn:ietf:params:xml:ns:clue-message"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dm="urn:ietf:params:xml:ns:clue-info"
xmlns="urn:ietf:params:xml:ns:clue-message"
elementFormDefault="qualified"
attributeFormDefault="unqualified">

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



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schemaLocation="data-model-schema-05.xsd"/>

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

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

<!-- 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="supportedOptions" type="optionsListType" 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="xs:string" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>



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<!-- OPTIONS LIST TYPE -->
<xs:complexType name="optionsListType">
<xs:sequence>
<xs:element name="option" type="optionType" minOccurs="1"
 maxOccurs="unbounded"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:complexType>

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

<!-- CLUE OPTIONS RESPONSE (2 WAY) -->
<xs:complexType name="optionsResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="xs:string"/>
<xs:element name="reasonString" type="xs:string"/>
<xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
<xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
<xs:element name="version" type="xs:string" minOccurs="0"/>
<xs:element name="commonOptions" type="optionsListType" 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 OPTIONS RESPONSE (3 WAYS) -->
<!-- <xs:complexType name="optionsResponseMessageType">
<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"



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 minOccurs="0"/>
<xs:element name="supportedOptions" type="optionsListType" 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 OPTIONS ACK (3 WAYS)-->
<!--
<xs:complexType name="optionsAckMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="xs:string"/>
<xs:element name="reasonString" type="xs:string"/>
<xs:element name="version" type="xs:string" minOccurs="0"
 maxOccurs="1"/>
<xs:element name="commonOptions" type="supportedOptionsType" 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 fields -->
<xs:element name="mediaCaptures" type="dm:mediaCapturesType"/>
<xs:element name="encodingGroups" type="dm:encodingGroupsType"/>
<xs:element name="captureScenes" type="dm:captureScenesType"/>
<xs:element name="simultaneousSets" type="dm:simultaneousSetsType"
 minOccurs="0"/>
<xs:element name="globalCaptureEntries" type="dm:globalCaptureEntriesType"
 minOccurs="0"/>
<xs:element name="participants" type="dm:participantsType" minOccurs="0"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>



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</xs:extension>
</xs:complexContent>
</xs:complexType>

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



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</xs:complexContent>
</xs:complexType>

<!-- CLUE READV MESSAGE TYPE -->
<xs:complexType name="readvMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="lastReceivedAdv" type="xs:short"/>
<xs:any namespace="##other" processContents="lax" minOccurs="0"/>
</xs:sequence>
<xs:anyAttribute namespace="##other" processContents="lax"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>

<!-- CLUE READV RESPONSE MESSAGE TYPE -->
<xs:complexType name="readvResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<xs:element name="responseCode" type="xs:short"/>
<xs:element name="reasonString" type="xs:string"/>
<xs:element name="readvSequenceNr" type="xs:string" minOccurs="0"/>
<xs:element name="mediaCaptures" type="dm:mediaCapturesType" minOccurs="0"/>
<xs:element name="encodingGroups" type="dm:encodingGroupsType" minOccurs="0"/>
<xs:element name="captureScenes" type="dm:captureScenesType" minOccurs="0"/>
<xs:element name="simultaneousSets" type="dm:simultaneousSetsType" minOccurs="0"/>
<xs:element name="globalCaptureEntries" type="dm:globalCaptureEntriesType" minOccurs="0"/>
<xs:element name="participants" type="dm:participantsType" minOccurs="0"/>
<xs:any namespace="##other"
 processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>

</xs:schema>


10.  Diff with the -03 version

   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



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       [I-D.kyzivat-clue-signaling].

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

11.  Diff with the -02 version

   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.

12.  Acknowledgments

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

13.  Informative 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-04 (work in
                                              progress), March 2014.

   [I-D.ietf-clue-datachannel]                Holmberg, C., "CLUE
                                              Protocol Data Channel", dr
                                              aft-ietf-clue-datachannel-
                                              00 (work in progress),
                                              March 2014.

   [I-D.ietf-clue-framework]                  Duckworth, M., Pepperell,
                                              A., and S. Wenger,
                                              "Framework for
                                              Telepresence Multi-
                                              Streams", draft-ietf-clue-
                                              framework-14 (work in
                                              progress), February 2014.




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   [I-D.ietf-clue-telepresence-requirements]  Romanow, A., Botzko, S.,
                                              and M. Barnes,
                                              "Requirements for
                                              Telepresence Multi-
                                              Streams", draft-ietf-clue-
                                              telepresence-requirements-
                                              07 (work in progress),
                                              December 2013.

   [I-D.kyzivat-clue-signaling]               Kyzivat, P., Xiao, L.,
                                              Groves, C., and R. Hansen,
                                              "CLUE Signaling", draft-
                                              kyzivat-clue-signaling-08
                                              (work in progress),
                                              April 2014.

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

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

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

   [RFC5261]                                  Urpalainen, J., "An
                                              Extensible Markup Language
                                              (XML) Patch Operations
                                              Framework Utilizing XML
                                              Path Language (XPath)
                                              Selectors", RFC 5261,
                                              September 2008.

   [RFC6502]                                  Camarillo, G., Srinivasan,
                                              S., Even, R., and J.
                                              Urpalainen, "Conference
                                              Event Package Data Format
                                              Extension for Centralized



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                                              Conferencing (XCON)",
                                              RFC 6502, March 2012.

   [RFC6503]                                  Barnes, M., Boulton, C.,
                                              Romano, S., and H.
                                              Schulzrinne, "Centralized
                                              Conferencing Manipulation
                                              Protocol", RFC 6503,
                                              March 2012.

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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