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2	CLUE Working Group                                             R. Presta
3	Internet-Draft                                                 S. Romano
4	Intended status: Standards Track                    University of Napoli
5	Expires: May 5, 2017                                    November 1, 2016

7	                             CLUE protocol
8	                      draft-ietf-clue-protocol-10

10	Abstract

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

23	Status of This Memo

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

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

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

38	   This Internet-Draft will expire on May 5, 2017.

40	Copyright Notice

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

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

55	Table of Contents

57	   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
58	   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
59	   3.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  5
60	   4.  Overview of the CLUE protocol  . . . . . . . . . . . . . . . .  5
61	   5.  Protocol messages  . . . . . . . . . . . . . . . . . . . . . .  7
62	     5.1.  OPTIONS  . . . . . . . . . . . . . . . . . . . . . . . . .  9
63	     5.2.  OPTIONS RESPONSE . . . . . . . . . . . . . . . . . . . . . 11
64	     5.3.  ADVERTISEMENT  . . . . . . . . . . . . . . . . . . . . . . 12
65	     5.4.  ADVERTISEMENT ACKNOWLEDGEMENT  . . . . . . . . . . . . . . 13
66	     5.5.  CONFIGURE  . . . . . . . . . . . . . . . . . . . . . . . . 14
67	     5.6.  CONFIGURE RESPONSE . . . . . . . . . . . . . . . . . . . . 14
68	     5.7.  Response codes and reason strings  . . . . . . . . . . . . 15
69	   6.  Protocol state machines  . . . . . . . . . . . . . . . . . . . 17
70	     6.1.  Media Provider's state machine . . . . . . . . . . . . . . 19
71	     6.2.  Media Consumer's state machine . . . . . . . . . . . . . . 22
72	   7.  Versioning . . . . . . . . . . . . . . . . . . . . . . . . . . 25
73	   8.  Extensions and options . . . . . . . . . . . . . . . . . . . . 25
74	   9.  XML Schema . . . . . . . . . . . . . . . . . . . . . . . . . . 27
75	   10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
76	     10.1. Simple ADV . . . . . . . . . . . . . . . . . . . . . . . . 31
77	     10.2. ADV with MCCs  . . . . . . . . . . . . . . . . . . . . . . 37
78	   11. Security Considerations  . . . . . . . . . . . . . . . . . . . 44
79	   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 46
80	     12.1. URN Sub-Namespace Registration . . . . . . . . . . . . . . 46
81	     12.2. XML Schema registration  . . . . . . . . . . . . . . . . . 47
82	     12.3. MIME Media Type Registration for 'application/clue+xml'  . 47
83	     12.4. CLUE Protocol Registry . . . . . . . . . . . . . . . . . . 48
84	       12.4.1.  CLUE Message Types  . . . . . . . . . . . . . . . . . 48
85	       12.4.2.  CLUE Response Codes . . . . . . . . . . . . . . . . . 50
86	   13. Diff with draft-ietf-clue-protocol-06  . . . . . . . . . . . . 51
87	   14. Diff with draft-ietf-clue-protocol-05  . . . . . . . . . . . . 51
88	   15. Diff with draft-ietf-clue-protocol-04  . . . . . . . . . . . . 51
89	   16. Diff with draft-ietf-clue-protocol-03  . . . . . . . . . . . . 51
90	   17. Diff with draft-ietf-clue-protocol-02  . . . . . . . . . . . . 51
91	   18. Diff with draft-ietf-clue-protocol-01  . . . . . . . . . . . . 52
92	   19. Diff with draft-ietf-clue-protocol-00  . . . . . . . . . . . . 52
93	   20. Diff with draft-presta-clue-protocol-04  . . . . . . . . . . . 53
94	   21. Diff with draft-presta-clue-protocol-03  . . . . . . . . . . . 53
95	   22. Diff with draft-presta-clue-protocol-02  . . . . . . . . . . . 53
96	   23. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 53
97	   24. References . . . . . . . . . . . . . . . . . . . . . . . . . . 53
98	     24.1. Normative References . . . . . . . . . . . . . . . . . . . 53
99	     24.2. Informative References . . . . . . . . . . . . . . . . . . 55

101	1.  Introduction

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

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

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

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

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

130	2.  Terminology

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

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

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

146	   Endpoint:  The logical point of final termination through receiving,
147	      decoding and rendering, and/or initiation through capturing,
148	      encoding, and sending of media streams.  An endpoint consists of
149	      one or more physical devices which source and sink media streams,
150	      and exactly one [RFC4353] Participant (which, in turn, includes
151	      exactly one SIP User Agent).  Endpoints can be anything from
152	      multiscreen/multicamera room controllers to handheld devices.

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

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

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

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

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

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

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

176	3.  Conventions

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

183	4.  Overview of the CLUE protocol

185	   The CLUE protocol is conceived to enable CLUE telepresence sessions.
186	   It is designed in order to address SDP limitations in terms of the
187	   description of some information about the multimedia streams that are
188	   involved in a real-time multimedia conference.  Indeed, by simply
189	   using SDP we are not able to convey information about the features of
190	   the flowing multimedia streams that are needed to enable a "being
191	   there" rendering experience.  Such information is designed in the
192	   CLUE framework document and formally defined and described in the
193	   CLUE data model document.  The CLUE protocol represents the mechanism
194	   for the exchange of CLUE information between CLUE Participants.  It
195	   mainly provides the messages to enable a Media Provider to advertise
196	   its telepresence capabilities and to enable a Media Consumer to
197	   select the desired telepresence options.

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

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

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

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

224	   As soon as the channel is ready, the CLUE Participants must agree on
225	   the protocol version and extensions to be used within the
226	   telepresence session.  CLUE protocol version numbers are
227	   characterized by a major version number (single digit) and a minor
228	   version number (single digit), both unsigned integers, separated by a
229	   dot.  While minor version numbers denote backward compatible changes
230	   in the context of a given major version, different major version
231	   numbers generally indicate a lack of interoperability between the
232	   protocol implementations.  In order to correctly establish a CLUE
233	   dialogue, the involved CPs MUST have in common a major version number
234	   (see Section 7 for further details).  The subset of the protocol
235	   options and extensions that are allowed within the CLUE session is
236	   also determined in the initiation phase, such subset being the one
237	   including only the options that are supported by both parties.  A
238	   mechanism for the negotiation of the CLUE protocol version and
239	   extensions is is part of the initial phase.  According to such a
240	   solution, the CP which is the CLUE Channel initiator (CI) issues a
241	   proper CLUE message (OPTIONS) to the CP which is the Channel Receiver
242	   (CR) specifying the supported version and extensions.  The CR then
243	   answers by selecting the subset of the CI extensions that it is able
244	   to support and determines the protocol version to be used.

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

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

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

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

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

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

279	   Besides ADVERTISEMENT and CONFIGURE, other messages have been
280	   conceived in order to provide all the needed mechanisms and
281	   operations.  Such messages will be detailed in the following
282	   sections.

284	5.  Protocol messages

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

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

297	   The CLUE protocol messages are the following:

299	   o  OPTIONS

301	   o  OPTIONS RESPONSE

303	   o  ADVERTISEMENT (ADV)

305	   o  ADVERTISEMENT ACKNOWLEDGEMENT (ACK)

307	   o  CONFIGURE (CONF)

309	   o  CONFIGURE RESPONSE (CONF RESPONSE)

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

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

318	   <!-- CLUE MESSAGE TYPE -->
319	   <xs:complexType name="clueMessageType" abstract="true">
320	   <xs:sequence>
321	   <xs:element name="clueId" type="xs:string"/>
322	   <xs:element name="sequenceNr" type="xs:positiveInteger"/>
323	   </xs:sequence>
324	   <xs:attribute name="protocol" type="xs:string" fixed="CLUE"
325	           use="required"/>
326	   <xs:attribute name="v" type="versionType" use="required"/>
327	   </xs:complexType>

329	   <!-- VERSION TYPE -->
330	   <xs:simpleType name="versionType">
331	   <xs:restriction base="xs:string">
332	   <xs:pattern value="[0-9]\.[0-9]"></xs:pattern>
333	   </xs:restriction>
334	   </xs:simpleType>
335	   The basic structure determines the mandatory information that is
336	   carried within each CLUE message.  Such an information is made by:

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

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

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

351	   o  v: a mandatory attribute carrying the version of the protocol.
352	      The content of the "v" attribute is composed by the major version
353	      number followed by a dot and then by the minor version number of
354	      the CLUE protocol in use.  Allowed values are of this kind: "1.3",
355	      "2.4", etc.

357	   Each CP MUST be able to manage up to three (independent) streams of
358	   sequence numbers: (i) one for the messages exchanged in the
359	   initiation phase, (ii) one for the messages exchanged as MP, and
360	   (iii) one for the messages exchanged as MC.

362	5.1.  OPTIONS

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

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

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

374	   o  supportedVersions: the list of the supported versions

376	   o  supportedOptions: the list of the supported options

378	   The XML Schema of such a message is reported below:

380	   <!-- CLUE OPTIONS -->
381	   <xs:complexType name="optionsMessageType">
382	   <xs:complexContent>
383	   <xs:extension base="clueMessageType">
384	   <xs:sequence>
385	   <xs:element name="mediaProvider" type="xs:boolean"/>
386	   <xs:element name="mediaConsumer" type="xs:boolean"/>
387	   <xs:element name="supportedVersions" type="versionsListType"
388	    minOccurs="0"/>
389	   <xs:element name="supportedOptions" type="optionsListType"
390	    minOccurs="0"/>
391	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
392	   </xs:sequence>
393	   <xs:anyAttribute namespace="##other" processContents="lax"/>
394	   </xs:extension>
395	   </xs:complexContent>
396	   </xs:complexType>

398	   <!-- VERSIONS LIST TYPE -->
399	   <xs:complexType name="versionsListType">
400	   <xs:sequence>
401	   <xs:element name="version" type="versionType" minOccurs="1"
402	    maxOccurs="unbounded"/>
403	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
404	   </xs:sequence>
405	   <xs:anyAttribute namespace="##other" processContents="lax"/>
406	   </xs:complexType>

408	   <!-- OPTIONS LIST TYPE -->
409	   <xs:complexType name="optionsListType">
410	   <xs:sequence>
411	   <xs:element name="option" type="optionType" minOccurs="1"
412	    maxOccurs="unbounded"/>
413	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
414	   </xs:sequence>
415	   <xs:anyAttribute namespace="##other" processContents="lax"/>
416	   </xs:complexType>

418	   <!-- OPTION TYPE -->
419	   <xs:complexType name="optionType">
420	   <xs:sequence>
421	   <xs:element name="name" type="xs:string" />
422	   <xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
423	   <xs:element name="version" type="versionType" minOccurs="0"/>
424	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
425	   </xs:sequence>
426	   <xs:anyAttribute namespace="##other" processContents="lax"/>
427	   </xs:complexType>
428	   <supportedVersions> contains the list of the versions that are
429	   supported by the CI, each one represented in a child <version>
430	   element.  The content of each <version> element is a string made by
431	   the major version number followed by a dot and then by the minor
432	   version number (e.g., 1.3 or 2.4).  Exactly one <version> element
433	   MUST be provided for each major version supported, containing the
434	   maximum minor version number of such a version, since all minor
435	   versions are backward compatible.  If no <supportedVersions> is
436	   carried within the OPTIONS message, the CI supports only the version
437	   declared in the "v" attribute and all the versions having the same
438	   major version number and lower minor version number.  For example, if
439	   the "v" attribute has a value of "3.4" and there is no
440	   <supportedVersions> tag in the OPTIONS message, it means the CI
441	   supports only major version 3 with all the minor versions comprised
442	   between 3.0 and 3.4, with version 3.4 included.  If a
443	   <supportedVersion> is provided, at least one <version> tag MUST be
444	   included.

446	   The <supportedOptions> element specifies the list of options
447	   supported by the CI.  If there is no <supportedOptions> in the
448	   OPTIONS message, the CI does not support anything other than what is
449	   envisioned in the versions it supports.  For each option, an <option>
450	   element is provided.  An option is characterized by a name, an XML
451	   schema of reference where the option is defined, and the version of
452	   the protocol which the option refers to.

454	5.2.  OPTIONS RESPONSE

456	   The OPTIONS RESPONSE is sent by a CR to a CI as a reply to the
457	   OPTIONS message.  As depicted in the figure below, the OPTIONS
458	   RESPONSE contains mandatorily a response code and a reason string
459	   indicating the processing result of the OPTIONS message.  If the
460	   responseCode is of the type 2xx the response MUST also include
461	   <mediaProvider>, <mediaConsumer>, <version> and <commonOptions>
462	   elements; it MAY include them for any other response code.
463	   <mediaProvider> and <mediaConsumer> elements are associated with the
464	   supported roles (in terms of, respectively MP and MC), similarly to
465	   what the CI does in the OPTIONS message.  The <version> field
466	   indicates the highest commonly supported version number.  The content
467	   of the <version> element MUST be a string made of the major version
468	   number followed by a dot and then by the minor version number (e.g.,
469	   1.3 or 2.4).  Finally, the commonly supported options are copied in
470	   the the <commonOptions> field.

472	 <!-- CLUE OPTIONS RESPONSE -->
473	 <xs:complexType name="optionsResponseMessageType">
474	 <xs:complexContent>
475	 <xs:extension base="clueMessageType">
476	 <xs:sequence>
477	 <xs:element name="responseCode" type="xs:short"/>
478	 <xs:element name="reasonString" type="xs:string"/>
479	 <xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
480	 <xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
481	 <xs:element name="version" type="versionType" minOccurs="0"/>
482	 <xs:element name="commonOptions" type="optionsListType" minOccurs="0"/>
483	 <xs:any namespace="##other"
484	 processContents="lax" minOccurs="0"/>
485	 </xs:sequence>
486	 <xs:anyAttribute namespace="##other" processContents="lax"/>
487	 </xs:extension>
488	 </xs:complexContent>
489	 </xs:complexType>

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

498	5.3.  ADVERTISEMENT

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

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

520	   <!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
521	   <xs:complexType name="advertisementMessageType">
522	   <xs:complexContent>
523	   <xs:extension base="clueMessageType">
524	   <xs:sequence>
525	   <!-- mandatory -->
526	   <xs:element name="mediaCaptures" type="dm:mediaCapturesType"/>
527	   <xs:element name="encodingGroups" type="dm:encodingGroupsType"/>
528	   <xs:element name="captureScenes" type="dm:captureScenesType"/>
529	   <!-- optional -->
530	   <xs:element name="simultaneousSets" type="dm:simultaneousSetsType"
531	    minOccurs="0"/>
532	   <xs:element name="globalViews" type="dm:globalViewsType"
533	    minOccurs="0"/>
534	   <xs:element name="people" type="dm:peopleType" minOccurs="0"/>
535	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
536	   </xs:sequence>
537	   <xs:anyAttribute namespace="##other" processContents="lax"/>
538	   </xs:extension>
539	   </xs:complexContent>
540	   </xs:complexType>

542	5.4.  ADVERTISEMENT ACKNOWLEDGEMENT

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

551	   <!-- ADV ACK MESSAGE TYPE -->
552	   <xs:complexType name="advAcknowledgementMessageType">
553	   <xs:complexContent>
554	   <xs:extension base="clueMessageType">
555	   <xs:sequence>
556	   <xs:element name="responseCode" type="xs:short"/>
557	   <xs:element name="reasonString" type="xs:string"/>
558	   <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
559	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
560	   </xs:sequence>
561	   <xs:anyAttribute namespace="##other" processContents="lax"/>
562	   </xs:extension>
563	   </xs:complexContent>
564	   </xs:complexType>

566	5.5.  CONFIGURE

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

574	    <!-- CLUE CONFIGURE MESSAGE TYPE -->
575	   <xs:complexType name="configureMessageType">
576	   <xs:complexContent>
577	   <xs:extension base="clueMessageType">
578	   <xs:sequence>
579	   <!-- mandatory fields -->
580	   <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
581	   <xs:element name="ack" type="xs:boolean" minOccurs="0" fixed="true"/>
582	   <xs:element name="captureEncodings" type="dm:captureEncodingsType"
583	    minOccurs="0"/>
584	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
585	   </xs:sequence>
586	   <xs:anyAttribute namespace="##other" processContents="lax"/>
587	   </xs:extension>
588	   </xs:complexContent>
589	   </xs:complexType>

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

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

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

606	5.6.  CONFIGURE RESPONSE
607	   <!-- CONFIGURE RESPONSE MESSAGE TYPE -->
608	   <xs:complexType name="configureResponseMessageType">
609	   <xs:complexContent>
610	   <xs:extension base="clueMessageType">
611	   <xs:sequence>
612	   <xs:element name="responseCode" type="xs:short"/>
613	   <xs:element name="reasonString" type="xs:string"/>
614	   <xs:element name="confSequenceNr" type="xs:positiveInteger"/>
615	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
616	   </xs:sequence>
617	   <xs:anyAttribute namespace="##other" processContents="lax"/>
618	   </xs:extension>
619	   </xs:complexContent>
620	   </xs:complexType>

622	   The CONFIGURE RESPONSE message (CONF RESPONSE) is sent from the MP to
623	   the MC to communicate the processing result of requests carried in
624	   the previously received CONF message.  It contains a response code
625	   with a reason string indicating either the success or the failure
626	   (along with failure details) of a CONF request processing.
627	   Following, the <confSequenceNr> field contains the sequence number of
628	   the CONF message the response refers to.

630	5.7.  Response codes and reason strings

632	   Response codes are defined as a sequence of three digits.  A well-
633	   defined meaning is associated with the first digit.  Response codes
634	   beginning with "2" are associated with successful responses.
635	   Response codes beginning with "1" will represent a delayed or
636	   incomplete response.  Response codes that do not begin with either
637	   "2" or "1" indicate an error response, i.e., that an error occurred
638	   while processing a CLUE request.  In particular, response codes
639	   beginning with "3" indicate problems with the XML content of the
640	   message (""Bad syntax", "Invalid value", etc.), while response codes
641	   beginning with "4" refer to problems related to CLUE protocol
642	   semantics ("Invalid sequencing", "Version not supported", etc.). 100,
643	   200, 300 and 400 codes are considered catch-alls.  Further response
644	   codes can be designed in future versions of the protocol, provided
645	   they do not overwrite the ones here defined and they respect the
646	   semantics of the first code digit.

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

651	   +-----------------+----------------------+--------------------------+
652	   |                 |                      |                          |
653	   |  Response code  |  Reason string       |       Description        |
654	   |                 |                      |                          |
655	   +-----------------+----------------------+--------------------------+
656	   |                 |                      |                          |
657	   |   200           |  Success             |  The request has been    |
658	   |                 |                      |  successfully processed. |
659	   |                 |                      |                          |
660	   +-----------------+----------------------+--------------------------+
661	   |                 |                      |                          |
662	   |   300           |  Syntax errors or    |  The XML syntax of the   |
663	   |                 |  inconsistencies     |  message is not correct  |
664	   |                 |                      |  or there are invalid    |
665	   |                 |                      |  values.                 |
666	   +-----------------+----------------------+--------------------------+
667	   |                 |                      |                          |
668	   |   301           |  Bad syntax          |  The XML syntax of the   |
669	   |                 |                      |  message is not correct. |
670	   +-----------------+----------------------+--------------------------+
671	   |                 |                      |                          |
672	   |   302           |  Invalid value       |  The message             |
673	   |                 |                      |  contains an invalid     |
674	   |                 |                      |  parameter value.        |
675	   +-----------------+----------------------+--------------------------+
676	   |                 |                      |                          |
677	   |   302           |  Conflicting values  |  The message             |
678	   |                 |                      |  contains values that    |
679	   |                 |                      |  cannot be used together.|
680	   +-----------------+----------------------+--------------------------+
681	   |                 |                      |                          |
682	   |   400           | Semantic errors      |  Semantic errors in the  |
683	   |                 |                      |  received CLUE protocol  |
684	   |                 |                      |  message.                |
685	   |                 |                      |                          |
686	   +-----------------+----------------------+--------------------------+
687	   |                 |                      |                          |
688	   |   401           | Version not supported|  The protocol version    |
689	   |                 |                      |  used in the message     |
690	   |                 |                      |  is not supported.       |
691	   |                 |                      |                          |
692	   +-----------------+----------------------+--------------------------+
693	   |                 |                      |                          |
694	   |   402           |  Invalid sequencing  |  The sequence number of  |
695	   |                 |                      |  the message is out      |
696	   |                 |                      |  of date.                |
697	   +-----------------+----------------------+--------------------------+
698	   |                 |                      |                          |
699	   |   403           |  Invalid identifier  |  The identifier used in  |
700	   |                 |                      |  the message is          |
701	   |                 |                      |  not valid or unknown.   |
702	   +-----------------+----------------------+--------------------------+
703	   |                 |                      |                          |
704	   |   404           |  ADV Expired         |  The number of the ADV   |
705	   |                 |                      |  the CONF refers to is   |
706	   |                 |                      |  out of date.            |
707	   +-----------------+----------------------+--------------------------+
708	   |                 |                      |                          |
709	   |   405           |  Subset choice not   |  The subset choice is not|
710	   |                 |  allowed             | allowed for the specified|
711	   |                 |                      |  MCC                     |
712	   +-----------------+----------------------+--------------------------+

714	6.  Protocol state machines

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

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

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

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

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

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

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

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

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

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

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

784	                                  +----+
785	          +---------------------->|IDLE|<----------------------------+
786	          |                       +-+--+                             |
787	          |                         |                                |
788	          |                         |  start                         |
789	          |                         |  channel                       |
790	          |                         v                                |
791	          |  channel error/      +--------+                          |
792	          |  session ends        | CHANNEL|                          |
793	          +----------------------+ SETUP  |                          |
794	          |                      +--+-----+                          |
795	          |                         |                                |
796	          |                         |  channel                       |
797	          |                         |  established                   |
798	          |  channel error/         v                 OPTIONS phase  |
799	          |  session ends         +-------+           failure        |
800	          +-----------------------+OPTIONS+--------------------------+
801	          |                       +-+-----+                          |
802	          |                         |                                |
803	          |                         |  OPTIONS phase                 |
804	          |                         |  success                       |
805	          |                         v                                |
806	          |   channel error/     +---------+                         |
807	          |   session ends       | ACTIVE  |                         |
808	          +----------------------+         |                         |
809	                                 | +----+  +------------------+      |
810	                                 | | MP |  |    send/receive  |      |
811	                                 | +----+  |    CLUE messages |      |
812	                                 |         |<-----------------+      |
813	                                 | +----+  |                         |
814	                                 | | MC |  |both sub state machines  |
815	                                 | +----+  |terminated               |
816	                                 |         |                         |
817	                                 +---------+-------------------------+

819	6.1.  Media Provider's state machine

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

825	   After the ADV has been sent ("ADV sent"), the MP moves from the ADV
826	   state to the WAIT FOR ACK state.  If an ACK message with a successful
827	   response code arrives ("ACK received"), the MP moves to the WAIT FOR
828	   CONF state.  If a NACK arrives (i.e., an ACK message with an error
829	   response code), and the number of NACKs for the issued ADV is under
830	   the retry threshold ("NACK received && retry not expired"), the MP
831	   moves back to the ADV state for preparing a new ADV.  If a NACK
832	   arrives and the number of received NACKs for that ADV overcomes the
833	   threshold ("NACK received and && retry expired"), the MP goes to the
834	   MP-TERMINATED state.  The same happens if the waiting time for the
835	   ACK is fired a number of times under the retry threshold ("timeout &&
836	   retry not expired"): also in this case, the MP goes back to the ADV
837	   state to send a new copy of the ADV.  If the number of retries
838	   overcomes the threshold ("timeout && retry expired"), the MP moves
839	   from the WAIT FOR ACK state to the MP-TERMINATED state.  When in the
840	   WAIT FOR ACK state, if a CONFIGURE message with the <ack> element set
841	   to TRUE arrives ("CONF+ACK received"), the MP goes directly to the
842	   CONF RESPONSE state.  CONF+ACK messages referring to out-of-date
843	   (i.e., having a sequence number equal to or less than the highest
844	   seen so far) ADVs MUST be ignored, i.e., they do not trigger any
845	   state transition.  If the telepresence settings of the MP change
846	   while in the WAIT FOR ACK state ("changed telepresence settings"),
847	   the MP switches from the WAIT FOR ACK state to the ADV state to
848	   create a new ADV.

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

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

875	   The MP in the ESTABLISHED state has successfully negotiated the media
876	   streams with the MC by means of the CLUE messages.  If there are
877	   changes in the MP's telepresence settings ("changed telepresence
878	   settings"), the MP moves back to the ADV state.  In the ESTABLISHED
879	   state, the CLUE-controlled media streams of the session are those
880	   described in the last successfully processed CONF message.

882	+------------------------->+-----+<---------------------------+
883	|            +------------>| ADV |<-------------------+       |
884	|            |             +-+---+                    |       |timeout
885	|            |               |       NACK received    |       |&&
886	|            |       ADV sent|             &&         |       |retry
887	|            |               v       retry not expired|       |not
888	|     changed|             +--------+                 |       |expired
889	|telepresence+-------------+WAIT FOR+-----------------+       |
890	|    settings|   +---------+  ACK   +-------------------------+
891	|            |   |CONF+ACK +-+------+----------------------------------+
892	|            |   |received   |                        NACK received && |
893	|            |   |           |ACK received               retry expired,|
894	|            |   |           v                 timeout && retry expired|
895	+------------|-------------+--------+                                  |
896	timeout      +-------------+WAIT FOR| timeout && retry expired         |
897	&&           |   |         |  CONF  +----------------------------------+
898	retry        |   |         +-+------+<-----------------------------+   |
899	not expired  |   |           |                                     |   |
900	             |   |           |CONF received                        |   |
901	             |   |           v             error CONF RESPONSE sent|   |
902	             |   +-------->+---------+      && retry not expired   |   |
903	             +-------------+CONF     |-----------------------------+   |
904	    +--------------------->|RESPONSE +---------------------------------+
905	    |        |             +-+-------+         error CONF RESPONSE sent|
906	    |        |               |                         && retry expired|
907	    |        |               |  success                                |
908	    |        |               |  CONF RESPONSE                          |
909	    |        |               |  sent                                   |
910	    |        |               |                                         |
911	    |        |               |                                         |
912	    |CONF    |               |                                         |
913	    |received|               v                                         |
914	    |        |             +------------+                              |
915	    |        +-------------+ESTABLISHED |                              |
916	    +----------------------+------------+                              |
917	                                                                       |
918	                                                                       |
919	                                                                       |
920	                           +-----------+                               |
921	                           !    MP     |                               |
922	                           |TERMINATED |                               |
923	                           +-----------+<------------------------------+

925	6.2.  Media Consumer's state machine

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

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

941	   If the ADV elaboration is unsuccessful (bad syntax, missing XML
942	   elements, etc.), and the number of times this has happened is under
943	   the retry treshold, the MC sends a NACK message (i.e., an ACK with an
944	   error response code) to the MP describing the problem via a proper
945	   reason phrase.  By this way ("NACK sent && retry not expired"), the
946	   MC switches back to the WAIT FOR ADV state, waiting for a new ADV.
947	   If the NACK retry expires ("NACK sent && retry expired"), the MC
948	   moves to the MC TERMINATED state.

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

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

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

986	                           +----------+
987	                           | WAIT FOR |
988	                           |   ADV    |
989	                           +----+-----+<--------+
990	                                |               |
991	                        ADV     |      NACK sent|
992	                        received|      && retry |
993	                                v    not expired|    NACK sent &&
994	                           +-----------+--------+    retry expired
995	                           |  ADV      +---------------------------+
996	                           | PROCESSING|<-----------------------+  |
997	                           +-+-----+---+                        |  |
998	                             |     |                            |  |
999	                   CONF+ACK  |     |  ACK                       |  |
1000	                     sent    |     |  sent                      |  |
1001	                             |     v                            |  |
1002	                             |  +-----+                         |  |
1003	                             |  |CONF |            ADV received |  |
1004	       +----------------------->|     +-------------------------+  |
1005	       |                     |  +--+--+                         |  |
1006	       |error CONF RESPONSE  |     |        error CONF RESPONSE |  |
1007	       |received &&          |     | CONF   received &&         |  |
1008	       |retry not expired,   |     | sent   retry expired       |  |
1009	       |timeout &&           |     |      +------------------------+
1010	       |retry not expired    v     v      |                     |  |
1011	       +------------------+---------------+        ADV received |  |
1012	               +--------->|   WAIT FOR    +---------------------+  |
1013	               |          |  CONF RESPONSE+------------------------+
1014	               |          +-------+-------+       timeout&&     |  |
1015	               |                  |             retry expired   |  |
1016	               |                  |                             |  |
1017	               |                  |successful                   |  |
1018	               |                  |CONF RESPONSE                |  |
1019	               |                  |received                     |  |
1020	               |                  v                             |  |
1021	               |CONF sent   +-----------+           ADV received|  |
1022	               +------------+ESTABLISHED+-----------------------+  |
1023	                            +-----------+                          |
1024	                                                                   |
1025	                                                                   |
1026	                                                                   |
1027	                             +-----------+                         |
1028	                             |   MC      |<------------------------+
1029	                             |TERMINATED |
1030	                             +-----------+

1032	7.  Versioning

1034	   CLUE protocol messages are XML messages compliant to the CLUE
1035	   protocol XML schema [I-D.ietf-clue-data-model-schema].  The version
1036	   of the protocol corresponds to the version of the schema.  Both
1037	   client and server have to test the compliance of the received
1038	   messages with the XML schema of the CLUE protocol.  If the compliance
1039	   is not verified, the message cannot be processed further.

1041	   Obviously, client and server cannot communicate if they do not share
1042	   exactly the same XML schema.  Such a schema associated with the CLUE
1043	   URN "urn:ietf:params:xml:ns:clue-protocol".  If all CLUE-enabled
1044	   devices use that schema there will be no interoperability problems
1045	   due to schema issues.

1047	   The version of the XML schema contained in the standard document
1048	   deriving from this draft will be 1.0.  The version usage is similar
1049	   in philosophy to XMPP ([RFC6120]).  A version number has major and
1050	   minor components, each a non-negative integer.  Major version changes
1051	   denote non-interoperable changes.  Minor version changes denote
1052	   schema changes that are backward compatible by ignoring unknown XML
1053	   elements, or other backward compatible changes.

1055	   The minor versions of the XML schema MUST be backward compatible, not
1056	   only in terms of schema but also semantically and procedurally as
1057	   well.  This means that they should define further features and
1058	   functionality besides those defined in the previous versions, in an
1059	   incremental way, without impacting the basic rules defined in the
1060	   previous version of the schema.  In this way, if a MP is able to
1061	   speak, e.g., version 1.5 of the protocol while the MC only
1062	   understands version 1.4, the MP should have no problem in reverting
1063	   the dialogue back to version 1.4 without exploiting 1.5 features and
1064	   functionality.  Version 1.4 is the one to be spoken and has to appear
1065	   in the "v" attribute of the subsequent CLUE messages.  In other
1066	   words, in this example, the MP MUST use version 1.4 and downgrade to
1067	   the lower version.  This said, and coherently with the general IETF
1068	   "protocol robustness principle" stating that "an implementation must
1069	   be conservative in its sending behavior, and liberal in its receiving
1070	   behavior" [RFC1122], Clue Participants MUST ignore unknown elements
1071	   or attributes that are not envisioned in the negotiated protocol
1072	   version and related options.

1074	8.  Extensions and options

1076	   Although the standard version of the CLUE protocol XML schema is
1077	   designed to thoroughly cope with the requirements emerging from the
1078	   application domain, new needs might arise and extensions can be
1079	   designed.  Extensions specify information and behaviors that are not
1080	   described in a certain version of the protocol.  They can relate to:

1082	   1.  new information, to be carried in the existing messages.  For
1083	       example, we may want to add more fields within an existing
1084	       message;

1086	   2.  new messages.  This is the case if there is no proper message for
1087	       a certain task, so a brand new CLUE message needs to be defined.

1089	   As to the first type of extensions, it is possible to distinguish
1090	   between protocol-specific and data model information.  Indeed, CLUE
1091	   messages are envelopes carrying both:

1093	   o  (i) XML elements defined within the CLUE protocol XML schema
1094	      itself (protocol-specific information)

1096	   o  (ii) other XML elements compliant to the CLUE data model schema
1097	      (data model information)

1099	   When new protocol-specific information is needed somewhere in the
1100	   protocol messages, it can be added in place of the <any> elements and
1101	   <anyAttribute> elements envisioned by the protocol schema.  The
1102	   policy currently defined in the protocol schema for handling <any>
1103	   and <anyAttribute> elements is:

1105	   o  elementFormDefault="qualified"

1107	   o  attributeFormDefault="unqualified"

1109	   In that case, the new information must be qualified by namespaces
1110	   other than "urn:ietf:params:xml:ns:clue-protocol" (the protocol URN)
1111	   and "urn:ietf:params:xml:ns:clue-info" (the data model URN).
1112	   Elements or attributes from unknown namespaces MUST be ignored.

1114	   The other matter concerns data model information.  Data model
1115	   information is defined by the XML schema associated with the URN
1116	   "urn:ietf:params:xml:ns:clue-info".  Also for the XML elements
1117	   defined in such a schema there are extensibility issues.  Those
1118	   issues are overcome by using <any> and <anyAttribute> placeholders.
1119	   Similarly to what said before, new information within data model
1120	   elements can be added in place of <any> and <anyAttribute> schema
1121	   elements, as long as they are properly namespace qualified.

1123	   On the other hand (second type of extensions), "extra" CLUE protocol
1124	   messages, i.e., messages not envisioned in the latest standard
1125	   version of the schema, can be needed.  In that case, the messages and
1126	   the associated behavior should be defined in external documents that
1127	   both communication parties must be aware of.

1129	   Both types of extensions, i.e., new information and new messages, can
1130	   be characterized by:

1132	   o  a name;

1134	   o  an external XML Schema defining the XML information and/or the XML
1135	      messages representing the extension;

1137	   o  the standard version of the protocol the extension refers to.

1139	   For that reason, the extensions can be represented by means of the
1140	   <option> element as defined below, which is carried within the
1141	   OPTIONS and OPTIONS RESPONSE messages to represent the extensions
1142	   supported by the CI and by the CR.

1144	   <!-- OPTION TYPE -->
1145	   <xs:complexType name="optionType">
1146	   <xs:sequence>
1147	   <xs:element name="name" type="xs:string" />
1148	   <xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
1149	   <xs:element name="version" type="versionType" minOccurs="0"/>
1150	   <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1151	   </xs:sequence>
1152	   <xs:anyAttribute namespace="##other" processContents="lax"/>
1153	   </xs:complexType>

1155	9.  XML Schema

1157	   In this section, the XML schema defining the CLUE messages is
1158	   provided.

1160	 <?xml version="1.0" encoding="UTF-8" ?>
1161	 <xs:schema
1162	 version="1.0"
1163	 targetNamespace="urn:ietf:params:xml:ns:clue-protocol"
1164	 xmlns:tns="urn:ietf:params:xml:ns:clue-protocol"
1165	 xmlns:xs="http://www.w3.org/2001/XMLSchema"
1166	 xmlns:dm="urn:ietf:params:xml:ns:clue-info"
1167	 xmlns="urn:ietf:params:xml:ns:clue-protocol"
1168	 elementFormDefault="qualified"
1169	 attributeFormDefault="unqualified">

1171	 <!-- Import data model schema -->
1172	 <xs:import namespace="urn:ietf:params:xml:ns:clue-info"
1173	 schemaLocation="data-model-schema-12.xsd"/>

1175	 <!-- ELEMENT DEFINITIONS -->
1176	 <xs:element name="options" type="optionsMessageType"/>
1177	 <xs:element name="optionsResponse" type="optionsResponseMessageType"/>
1178	 <xs:element name="advertisement" type="advertisementMessageType"/>
1179	 <xs:element name="ack" type="advAcknowledgementMessageType"/>
1180	 <xs:element name="configure" type="configureMessageType"/>
1181	 <xs:element name="configureResponse"
1182	  type="configureResponseMessageType"/>

1184	 <!-- CLUE MESSAGE TYPE -->
1185	 <xs:complexType name="clueMessageType" abstract="true">
1186	 <xs:sequence>
1187	 <xs:element name="clueId" type="xs:string"/>
1188	 <xs:element name="sequenceNr" type="xs:positiveInteger"/>
1189	 </xs:sequence>
1190	 <xs:attribute name="protocol" type="xs:string" fixed="CLUE"
1191	  use="required"/>
1192	 <xs:attribute name="v" type="versionType" use="required"/>
1193	 </xs:complexType>

1195	 <!-- VERSION TYPE -->
1196	 <xs:simpleType name="versionType">
1197	 <xs:restriction base="xs:string">
1198	 <xs:pattern value="[0-9]\.[0-9]"></xs:pattern>
1199	 </xs:restriction>
1200	 </xs:simpleType>

1202	 <!-- RESPONSE CODE TYPE -->
1203	 <xs:simpleType name="responseCodeType">
1204	   <xs:restriction base="xs:integer">
1205	    <xs:pattern value="[1-9][0-9][0-9]"/>
1206	   </xs:restriction>
1207	 </xs:simpleType>

1209	 <!-- CLUE OPTIONS -->
1210	 <xs:complexType name="optionsMessageType">
1211	 <xs:complexContent>
1212	 <xs:extension base="clueMessageType">
1213	 <xs:sequence>
1214	 <xs:element name="mediaProvider" type="xs:boolean"/>
1215	 <xs:element name="mediaConsumer" type="xs:boolean"/>
1216	 <xs:element name="supportedVersions" type="versionsListType"
1217	  minOccurs="0"/>

1219	 <xs:element name="supportedOptions" type="optionsListType"
1220	  minOccurs="0"/>
1221	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1222	 </xs:sequence>
1223	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1224	 </xs:extension>
1225	 </xs:complexContent>
1226	 </xs:complexType>

1228	 <!-- VERSIONS LIST TYPE -->
1229	 <xs:complexType name="versionsListType">
1230	 <xs:sequence>
1231	 <xs:element name="version" type="versionType" minOccurs="1"
1232	  maxOccurs="unbounded"/>
1233	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1234	 </xs:sequence>
1235	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1236	 </xs:complexType>

1238	 <!-- OPTIONS LIST TYPE -->
1239	 <xs:complexType name="optionsListType">
1240	 <xs:sequence>
1241	 <xs:element name="option" type="optionType" minOccurs="1"
1242	  maxOccurs="unbounded"/>
1243	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1244	 </xs:sequence>
1245	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1246	 </xs:complexType>

1248	 <!-- OPTION TYPE -->
1249	 <xs:complexType name="optionType">
1250	 <xs:sequence>
1251	 <xs:element name="name" type="xs:string" />
1252	 <xs:element name="schemaRef" type="xs:anyURI" minOccurs="0"/>
1253	 <xs:element name="version" type="versionType" minOccurs="0"/>
1254	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1255	 </xs:sequence>
1256	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1257	 </xs:complexType>

1259	 <!-- CLUE OPTIONS RESPONSE -->
1260	 <xs:complexType name="optionsResponseMessageType">
1261	 <xs:complexContent>
1262	 <xs:extension base="clueMessageType">
1263	 <xs:sequence>
1264	 <xs:element name="responseCode" type="responseCodeType"/>
1265	 <xs:element name="reasonString" type="xs:string"/>
1266	 <xs:element name="mediaProvider" type="xs:boolean" minOccurs="0"/>
1267	 <xs:element name="mediaConsumer" type="xs:boolean" minOccurs="0"/>
1268	 <xs:element name="version" type="versionType" minOccurs="0"/>
1269	 <xs:element name="commonOptions" type="optionsListType" minOccurs="0"/>
1270	 <xs:any namespace="##other"
1271	 processContents="lax" minOccurs="0"/>
1272	 </xs:sequence>
1273	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1274	 </xs:extension>
1275	 </xs:complexContent>
1276	 </xs:complexType>

1278	 <!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
1279	 <xs:complexType name="advertisementMessageType">
1280	 <xs:complexContent>
1281	 <xs:extension base="clueMessageType">
1282	 <xs:sequence>
1283	 <!-- mandatory -->
1284	 <xs:element name="mediaCaptures" type="dm:mediaCapturesType"/>
1285	 <xs:element name="encodingGroups" type="dm:encodingGroupsType"/>
1286	 <xs:element name="captureScenes" type="dm:captureScenesType"/>
1287	 <!-- optional -->
1288	 <xs:element name="simultaneousSets" type="dm:simultaneousSetsType"
1289	  minOccurs="0"/>
1290	 <xs:element name="globalViews" type="dm:globalViewsType"
1291	  minOccurs="0"/>
1292	 <xs:element name="people" type="dm:peopleType" minOccurs="0"/>
1293	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1294	 </xs:sequence>
1295	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1296	 </xs:extension>
1297	 </xs:complexContent>
1298	 </xs:complexType>

1300	 <!-- ACK MESSAGE TYPE -->
1301	 <xs:complexType name="advAcknowledgementMessageType">
1302	 <xs:complexContent>
1303	 <xs:extension base="clueMessageType">
1304	 <xs:sequence>
1305	 <xs:element name="responseCode" type="responseCodeType"/>
1306	 <xs:element name="reasonString" type="xs:string"/>
1307	 <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
1308	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1309	 </xs:sequence>
1310	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1311	 </xs:extension>
1312	 </xs:complexContent>
1313	 </xs:complexType>
1314	 <!-- CLUE CONFIGURE MESSAGE TYPE -->
1315	 <xs:complexType name="configureMessageType">
1316	 <xs:complexContent>
1317	 <xs:extension base="clueMessageType">
1318	 <xs:sequence>
1319	 <xs:element name="advSequenceNr" type="xs:positiveInteger"/>
1320	 <xs:element name="ack" type="xs:boolean"
1321	  minOccurs="0" fixed="true"/>
1322	 <xs:element name="captureEncodings" type="dm:captureEncodingsType"
1323	  minOccurs="0"/>
1324	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1325	 </xs:sequence>
1326	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1327	 </xs:extension>
1328	 </xs:complexContent>
1329	 </xs:complexType>

1331	 <!-- CONFIGURE RESPONSE MESSAGE TYPE -->
1332	 <xs:complexType name="configureResponseMessageType">
1333	 <xs:complexContent>
1334	 <xs:extension base="clueMessageType">
1335	 <xs:sequence>
1336	 <xs:element name="responseCode" type="responseCodeType"/>
1337	 <xs:element name="reasonString" type="xs:string"/>
1338	 <xs:element name="confSequenceNr" type="xs:positiveInteger"/>
1339	 <xs:any namespace="##other" processContents="lax" minOccurs="0"/>
1340	 </xs:sequence>
1341	 <xs:anyAttribute namespace="##other" processContents="lax"/>
1342	 </xs:extension>
1343	 </xs:complexContent>
1344	 </xs:complexType>

1346	 </xs:schema>

1348	10.  Examples

1350	   In the following we provide an example of ADVERTISEMENT representing
1351	   the telepresence environment described in
1352	   [I-D.ietf-clue-data-model-schema], Section "Sample XML file" and
1353	   Section "MCC example" respectively.

1355	10.1.  Simple ADV

1357	   The associated Media Provider's telepresence capabilities are
1358	   described in [I-D.ietf-clue-data-model-schema], Section "Sample XML
1359	   file".

1361	 <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
1362	 <advertisement xmlns="urn:ietf:params:xml:ns:clue-protocol"
1363	                xmlns:ns2="urn:ietf:params:xml:ns:clue-info"
1364	                xmlns:ns3="urn:ietf:params:xml:ns:vcard-4.0"
1365	                protocol="CLUE" v="0.4">
1366	     <clueId>Napoli</clueId>
1367	     <sequenceNr>45</sequenceNr>
1368	     <mediaCaptures>
1369	         <ns2:mediaCapture
1370	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1371	          xsi:type="ns2:videoCaptureType"
1372	          captureID="AC0" mediaType="video">
1373	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1374	             <ns2:encGroupIDREF>EG1</ns2:encGroupIDREF>
1375	             <ns2:spatialInformation>
1376	                 <ns2:capturePoint>
1377	                     <ns2:x>0.5</ns2:x>
1378	                     <ns2:y>1.0</ns2:y>
1379	                     <ns2:z>0.5</ns2:z>
1380	                     <ns2:lineOfCapturePoint>
1381	                         <ns2:x>0.5</ns2:x>
1382	                         <ns2:y>0.0</ns2:y>
1383	                         <ns2:z>0.5</ns2:z>
1384	                     </ns2:lineOfCapturePoint>
1385	                 </ns2:capturePoint>
1386	             </ns2:spatialInformation>
1387	             <ns2:individual>true</ns2:individual>
1388	             <ns2:description lang="en">
1389	              main audio from the room</ns2:description>
1390	             <ns2:priority>1</ns2:priority>
1391	             <ns2:lang>it</ns2:lang>
1392	             <ns2:mobility>static</ns2:mobility>
1393	             <ns2:view>room</ns2:view>
1394	             <ns2:capturedPeople>
1395	                 <ns2:personIDREF>alice</ns2:personIDREF>
1396	                 <ns2:personIDREF>bob</ns2:personIDREF>
1397	                 <ns2:personIDREF>ciccio</ns2:personIDREF>
1398	             </ns2:capturedPeople>
1399	         </ns2:mediaCapture>
1400	         <ns2:mediaCapture
1401	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1402	          xsi:type="ns2:videoCaptureType"
1403	          mediaType="video" captureID="VC0">
1404	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1405	             <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1406	             <ns2:spatialInformation>
1407	                 <ns2:capturePoint>
1408	                     <ns2:x>0.5</ns2:x>
1409	                     <ns2:y>1.0</ns2:y>
1410	                     <ns2:z>0.5</ns2:z>
1411	                     <ns2:lineOfCapturePoint>
1412	                         <ns2:x>0.5</ns2:x>
1413	                         <ns2:y>0.0</ns2:y>
1414	                         <ns2:z>0.5</ns2:z>
1415	                     </ns2:lineOfCapturePoint>
1416	                 </ns2:capturePoint>
1417	             </ns2:spatialInformation>
1418	             <ns2:individual>true</ns2:individual>
1419	             <ns2:description lang="en">left camera video capture
1420	             </ns2:description>
1421	             <ns2:priority>1</ns2:priority>
1422	             <ns2:lang>it</ns2:lang>
1423	             <ns2:mobility>static</ns2:mobility>
1424	             <ns2:view>individual</ns2:view>
1425	             <ns2:capturedPeople>
1426	                 <ns2:personIDREF>ciccio</ns2:personIDREF>
1427	             </ns2:capturedPeople>
1428	         </ns2:mediaCapture>
1429	         <ns2:mediaCapture
1430	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1431	          xsi:type="ns2:videoCaptureType"
1432	          mediaType="video" captureID="VC1">
1433	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1434	             <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1435	             <ns2:spatialInformation>
1436	                 <ns2:capturePoint>
1437	                     <ns2:x>0.5</ns2:x>
1438	                     <ns2:y>1.0</ns2:y>
1439	                     <ns2:z>0.5</ns2:z>
1440	                     <ns2:lineOfCapturePoint>
1441	                         <ns2:x>0.5</ns2:x>
1442	                         <ns2:y>0.0</ns2:y>
1443	                         <ns2:z>0.5</ns2:z>
1444	                     </ns2:lineOfCapturePoint>
1445	                 </ns2:capturePoint>
1446	             </ns2:spatialInformation>
1447	             <ns2:individual>true</ns2:individual>
1448	             <ns2:description lang="en">central camera video capture
1449	             </ns2:description>
1450	             <ns2:priority>1</ns2:priority>
1451	             <ns2:lang>it</ns2:lang>
1452	             <ns2:mobility>static</ns2:mobility>
1453	             <ns2:view>individual</ns2:view>
1454	             <ns2:capturedPeople>
1455	                 <ns2:personIDREF>alice</ns2:personIDREF>
1456	             </ns2:capturedPeople>

1458	         </ns2:mediaCapture>
1459	         <ns2:mediaCapture
1460	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1461	          xsi:type="ns2:videoCaptureType"
1462	          mediaType="video" captureID="VC2">
1463	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1464	             <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1465	             <ns2:spatialInformation>
1466	                 <ns2:capturePoint>
1467	                     <ns2:x>0.5</ns2:x>
1468	                     <ns2:y>1.0</ns2:y>
1469	                     <ns2:z>0.5</ns2:z>
1470	                     <ns2:lineOfCapturePoint>
1471	                         <ns2:x>0.5</ns2:x>
1472	                         <ns2:y>0.0</ns2:y>
1473	                         <ns2:z>0.5</ns2:z>
1474	                     </ns2:lineOfCapturePoint>
1475	                 </ns2:capturePoint>
1476	             </ns2:spatialInformation>
1477	             <ns2:individual>true</ns2:individual>
1478	             <ns2:description lang="en">right camera video capture
1479	             </ns2:description>
1480	             <ns2:priority>1</ns2:priority>
1481	             <ns2:lang>it</ns2:lang>
1482	             <ns2:mobility>static</ns2:mobility>
1483	             <ns2:view>individual</ns2:view>
1484	             <ns2:capturedPeople>
1485	                 <ns2:personIDREF>bob</ns2:personIDREF>
1486	             </ns2:capturedPeople>
1487	         </ns2:mediaCapture>
1488	         <ns2:mediaCapture
1489	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1490	          xsi:type="ns2:videoCaptureType"
1491	          mediaType="video" captureID="VC3">
1492	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1493	             <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1494	             <ns2:nonSpatiallyDefinable>true</ns2:nonSpatiallyDefinable>
1495	             <ns2:composed>false</ns2:composed>
1496	             <ns2:switched>true</ns2:switched>
1497	             <ns2:policy>Soundlevel:0</ns2:policy>
1498	             <ns2:maxCaptures>1</ns2:maxCaptures>
1499	             <ns2:description lang="en">
1500	              loudest room segment</ns2:description>
1501	             <ns2:priority>1</ns2:priority>
1502	             <ns2:lang>it</ns2:lang>
1503	             <ns2:mobility>static</ns2:mobility>
1504	             <ns2:view>individual</ns2:view>
1505	         </ns2:mediaCapture>
1506	         <ns2:mediaCapture
1507	          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1508	          xsi:type="ns2:videoCaptureType"
1509	          mediaType="video" captureID="VC4">
1510	             <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1511	             <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1512	             <ns2:spatialInformation>
1513	                 <ns2:capturePoint>
1514	                     <ns2:x>0.5</ns2:x>
1515	                     <ns2:y>1.0</ns2:y>
1516	                     <ns2:z>0.5</ns2:z>
1517	                     <ns2:lineOfCapturePoint>
1518	                         <ns2:x>0.5</ns2:x>
1519	                         <ns2:y>0.0</ns2:y>
1520	                         <ns2:z>0.5</ns2:z>
1521	                     </ns2:lineOfCapturePoint>
1522	                 </ns2:capturePoint>
1523	             </ns2:spatialInformation>
1524	             <ns2:individual>true</ns2:individual>
1525	             <ns2:description lang="en">zoomed out view of all people in
1526	             the room
1527	             </ns2:description>
1528	             <ns2:priority>1</ns2:priority>
1529	             <ns2:lang>it</ns2:lang>
1530	             <ns2:mobility>static</ns2:mobility>
1531	             <ns2:view>room</ns2:view>
1532	             <ns2:capturedPeople>
1533	                 <ns2:personIDREF>alice</ns2:personIDREF>
1534	                 <ns2:personIDREF>bob</ns2:personIDREF>
1535	                 <ns2:personIDREF>ciccio</ns2:personIDREF>
1536	             </ns2:capturedPeople>
1537	         </ns2:mediaCapture>
1538	     </mediaCaptures>
1539	     <encodingGroups>
1540	         <ns2:encodingGroup encodingGroupID="EG0">
1541	             <ns2:maxGroupBandwidth>600000</ns2:maxGroupBandwidth>
1542	             <ns2:encodingIDList>
1543	                 <ns2:encID>ENC1</ns2:encID>
1544	                 <ns2:encID>ENC2</ns2:encID>
1545	                 <ns2:encID>ENC3</ns2:encID>
1546	             </ns2:encodingIDList>
1547	         </ns2:encodingGroup>
1548	         <ns2:encodingGroup encodingGroupID="EG1">
1549	             <ns2:maxGroupBandwidth>300000</ns2:maxGroupBandwidth>
1550	             <ns2:encodingIDList>
1551	                 <ns2:encID>ENC4</ns2:encID>
1552	                 <ns2:encID>ENC5</ns2:encID>
1553	             </ns2:encodingIDList>

1555	         </ns2:encodingGroup>
1556	     </encodingGroups>
1557	     <captureScenes>
1558	         <ns2:captureScene scale="unknown" sceneID="CS1">
1559	             <ns2:sceneViews>
1560	                 <ns2:sceneView sceneViewID="SE1">
1561	                     <ns2:mediaCaptureIDs>
1562	                         <ns2:captureIDREF>VC0</ns2:captureIDREF>
1563	                         <ns2:captureIDREF>VC1</ns2:captureIDREF>
1564	                         <ns2:captureIDREF>VC2</ns2:captureIDREF>
1565	                     </ns2:mediaCaptureIDs>
1566	                 </ns2:sceneView>
1567	                 <ns2:sceneView sceneViewID="SE2">
1568	                     <ns2:mediaCaptureIDs>
1569	                         <ns2:captureIDREF>VC3</ns2:captureIDREF>
1570	                     </ns2:mediaCaptureIDs>
1571	                 </ns2:sceneView>
1572	                 <ns2:sceneView sceneViewID="SE3">
1573	                     <ns2:mediaCaptureIDs>
1574	                         <ns2:captureIDREF>VC4</ns2:captureIDREF>
1575	                     </ns2:mediaCaptureIDs>
1576	                 </ns2:sceneView>
1577	                 <ns2:sceneView sceneViewID="SE4">
1578	                     <ns2:mediaCaptureIDs>
1579	                         <ns2:captureIDREF>VC4</ns2:captureIDREF>
1580	                     </ns2:mediaCaptureIDs>
1581	                 </ns2:sceneView>
1582	             </ns2:sceneViews>
1583	         </ns2:captureScene>
1584	     </captureScenes>
1585	     <simultaneousSets>
1586	         <ns2:simultaneousSet setID="SS1">
1587	             <ns2:mediaCaptureIDREF>VC3</ns2:mediaCaptureIDREF>
1588	             <ns2:sceneViewIDREF>SE1</ns2:sceneViewIDREF>
1589	         </ns2:simultaneousSet>
1590	         <ns2:simultaneousSet setID="SS2">
1591	             <ns2:mediaCaptureIDREF>VC0</ns2:mediaCaptureIDREF>
1592	             <ns2:mediaCaptureIDREF>VC2</ns2:mediaCaptureIDREF>
1593	             <ns2:mediaCaptureIDREF>VC4</ns2:mediaCaptureIDREF>
1594	             <ns2:mediaCaptureIDREF>VC3</ns2:mediaCaptureIDREF>
1595	         </ns2:simultaneousSet>
1596	     </simultaneousSets>
1597	     <people>
1598	         <ns2:person personID="bob">
1599	             <ns2:personInfo>
1600	                 <ns3:fn>
1601	                     <ns3:text>Bob</ns3:text>
1602	                 </ns3:fn>

1604	             </ns2:personInfo>
1605	             <ns2:personType>minute taker</ns2:personType>
1606	         </ns2:person>
1607	         <ns2:person personID="alice">
1608	             <ns2:personInfo>
1609	                 <ns3:fn>
1610	                     <ns3:text>Alice</ns3:text>
1611	                 </ns3:fn>
1612	             </ns2:personInfo>
1613	             <ns2:personType>presenter</ns2:personType>
1614	         </ns2:person>
1615	         <ns2:person personID="ciccio">
1616	             <ns2:personInfo>
1617	                 <ns3:fn>
1618	                     <ns3:text>Ciccio</ns3:text>
1619	                 </ns3:fn>
1620	             </ns2:personInfo>
1621	             <ns2:personType>chairman</ns2:personType>
1622	             <ns2:personType>timekeeper</ns2:personType>
1623	         </ns2:person>
1624	     </people>
1625	 </advertisement>

1627	10.2.  ADV with MCCs

1629	   The associated Media Provider's telepresence capabilities are
1630	   described in [I-D.ietf-clue-data-model-schema], Section "MCC
1631	   example".

1633	<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
1634	<advertisement xmlns="urn:ietf:params:xml:ns:clue-protocol"
1635	 xmlns:ns2="urn:ietf:params:xml:ns:clue-info"
1636	 xmlns:ns3="urn:ietf:params:xml:ns:vcard-4.0" protocol="CLUE" v="0.4">
1637	    <clueId>Napoli CLUE Endpoint</clueId>
1638	    <sequenceNr>34</sequenceNr>
1639	    <mediaCaptures>
1640	        <ns2:mediaCapture
1641	         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1642	         xsi:type="ns2:videoCaptureType" mediaType="video"
1643	         captureID="AC0">
1644	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1645	            <ns2:encGroupIDREF>EG1</ns2:encGroupIDREF>
1646	            <ns2:spatialInformation>
1647	                <ns2:capturePoint>
1648	                    <ns2:x>0.5</ns2:x>
1649	                    <ns2:y>1.0</ns2:y>
1650	                    <ns2:z>0.5</ns2:z>
1651	                    <ns2:lineOfCapturePoint>
1652	                        <ns2:x>0.5</ns2:x>
1653	                        <ns2:y>0.0</ns2:y>
1654	                        <ns2:z>0.5</ns2:z>
1655	                    </ns2:lineOfCapturePoint>
1656	                </ns2:capturePoint>
1657	            </ns2:spatialInformation>
1658	            <ns2:individual>true</ns2:individual>
1659	            <ns2:description lang="en">
1660	             main audio from the room</ns2:description>
1661	            <ns2:priority>1</ns2:priority>
1662	            <ns2:lang>it</ns2:lang>
1663	            <ns2:mobility>static</ns2:mobility>
1664	            <ns2:view>room</ns2:view>
1665	            <ns2:capturedPeople>
1666	                <ns2:personIDREF>alice</ns2:personIDREF>
1667	                <ns2:personIDREF>bob</ns2:personIDREF>
1668	                <ns2:personIDREF>ciccio</ns2:personIDREF>
1669	            </ns2:capturedPeople>
1670	        </ns2:mediaCapture>
1671	        <ns2:mediaCapture
1672	         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1673	         xsi:type="ns2:videoCaptureType"
1674	         captureID="VC0" mediaType="video" >
1675	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1676	            <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1677	            <ns2:spatialInformation>
1678	                <ns2:capturePoint>
1679	                    <ns2:x>0.5</ns2:x>
1680	                    <ns2:y>1.0</ns2:y>
1681	                    <ns2:z>0.5</ns2:z>
1682	                    <ns2:lineOfCapturePoint>
1683	                        <ns2:x>0.5</ns2:x>
1684	                        <ns2:y>0.0</ns2:y>
1685	                        <ns2:z>0.5</ns2:z>
1686	                    </ns2:lineOfCapturePoint>
1687	                </ns2:capturePoint>
1688	            </ns2:spatialInformation>
1689	            <ns2:individual>true</ns2:individual>
1690	            <ns2:description lang="en">
1691	            left camera video capture</ns2:description>
1692	            <ns2:priority>1</ns2:priority>
1693	            <ns2:lang>it</ns2:lang>
1694	            <ns2:mobility>static</ns2:mobility>
1695	            <ns2:view>individual</ns2:view>
1696	            <ns2:capturedPeople>
1697	                <ns2:personIDREF>ciccio</ns2:personIDREF>
1698	            </ns2:capturedPeople>
1699	        </ns2:mediaCapture>
1700	        <ns2:mediaCapture
1701	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1702	        xsi:type="ns2:videoCaptureType"
1703	        captureID="VC1" mediaType="video">
1704	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1705	            <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1706	            <ns2:spatialInformation>
1707	                <ns2:capturePoint>
1708	                    <ns2:x>0.5</ns2:x>
1709	                    <ns2:y>1.0</ns2:y>
1710	                    <ns2:z>0.5</ns2:z>
1711	                    <ns2:lineOfCapturePoint>
1712	                        <ns2:x>0.5</ns2:x>
1713	                        <ns2:y>0.0</ns2:y>
1714	                        <ns2:z>0.5</ns2:z>
1715	                    </ns2:lineOfCapturePoint>
1716	                </ns2:capturePoint>
1717	            </ns2:spatialInformation>
1718	            <ns2:individual>true</ns2:individual>
1719	            <ns2:description lang="en">central camera video capture
1720	            </ns2:description>
1721	            <ns2:priority>1</ns2:priority>
1722	            <ns2:lang>it</ns2:lang>
1723	            <ns2:mobility>static</ns2:mobility>
1724	            <ns2:view>individual</ns2:view>
1725	            <ns2:capturedPeople>
1726	                <ns2:personIDREF>alice</ns2:personIDREF>
1727	            </ns2:capturedPeople>
1728	        </ns2:mediaCapture>
1729	        <ns2:mediaCapture
1730	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1731	        xsi:type="ns2:videoCaptureType"
1732	        captureID="VC2" mediaType="video" >
1733	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1734	            <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1735	            <ns2:spatialInformation>
1736	                <ns2:capturePoint>
1737	                    <ns2:x>0.5</ns2:x>
1738	                    <ns2:y>1.0</ns2:y>
1739	                    <ns2:z>0.5</ns2:z>
1740	                    <ns2:lineOfCapturePoint>
1741	                        <ns2:x>0.5</ns2:x>
1742	                        <ns2:y>0.0</ns2:y>
1743	                        <ns2:z>0.5</ns2:z>

1745	                    </ns2:lineOfCapturePoint>
1746	                </ns2:capturePoint>
1747	            </ns2:spatialInformation>
1748	            <ns2:individual>true</ns2:individual>
1749	            <ns2:description lang="en">right camera video capture
1750	            </ns2:description>
1751	            <ns2:priority>1</ns2:priority>
1752	            <ns2:lang>it</ns2:lang>
1753	            <ns2:mobility>static</ns2:mobility>
1754	            <ns2:view>individual</ns2:view>
1755	            <ns2:capturedPeople>
1756	                <ns2:personIDREF>bob</ns2:personIDREF>
1757	            </ns2:capturedPeople>
1758	        </ns2:mediaCapture>
1759	        <ns2:mediaCapture
1760	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1761	        xsi:type="ns2:videoCaptureType"
1762	        captureID="VC3" mediaType="video" >
1763	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1764	            <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1765	            <ns2:nonSpatiallyDefinable>true</ns2:nonSpatiallyDefinable>
1766	            <ns2:content>
1767	                <ns2:sceneViewIDREF>SE1</ns2:sceneViewIDREF>
1768	            </ns2:content>
1769	            <ns2:policy>Soundlevel:0</ns2:policy>
1770	            <ns2:maxCaptures>1</ns2:maxCaptures>
1771	            <ns2:allowSubsetChoice>false</ns2:allowSubsetChoice>
1772	            <ns2:description lang="en">
1773	            loudest room segment</ns2:description>
1774	            <ns2:priority>1</ns2:priority>
1775	            <ns2:lang>it</ns2:lang>
1776	            <ns2:mobility>static</ns2:mobility>
1777	            <ns2:view>individual</ns2:view>
1778	        </ns2:mediaCapture>
1779	        <ns2:mediaCapture
1780	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1781	        xsi:type="ns2:videoCaptureType"
1782	        captureID="VC4" mediaType="video">
1783	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1784	            <ns2:encGroupIDREF>EG0</ns2:encGroupIDREF>
1785	            <ns2:spatialInformation>
1786	                <ns2:capturePoint>
1787	                    <ns2:x>0.5</ns2:x>
1788	                    <ns2:y>1.0</ns2:y>
1789	                    <ns2:z>0.5</ns2:z>
1790	                    <ns2:lineOfCapturePoint>
1791	                        <ns2:x>0.5</ns2:x>
1792	                        <ns2:y>0.0</ns2:y>
1793	                        <ns2:z>0.5</ns2:z>
1794	                    </ns2:lineOfCapturePoint>
1795	                </ns2:capturePoint>
1796	            </ns2:spatialInformation>
1797	            <ns2:individual>true</ns2:individual>
1798	            <ns2:description lang="en">
1799	            zoomed out view of all people in the room
1800	            </ns2:description>
1801	            <ns2:priority>1</ns2:priority>
1802	            <ns2:lang>it</ns2:lang>
1803	            <ns2:mobility>static</ns2:mobility>
1804	            <ns2:view>room</ns2:view>
1805	            <ns2:capturedPeople>
1806	                <ns2:personIDREF>alice</ns2:personIDREF>
1807	                <ns2:personIDREF>bob</ns2:personIDREF>
1808	                <ns2:personIDREF>ciccio</ns2:personIDREF>
1809	            </ns2:capturedPeople>
1810	        </ns2:mediaCapture>
1811	        <ns2:mediaCapture
1812	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1813	        xsi:type="ns2:videoCaptureType"
1814	        captureID="VC5" mediaType="video">
1815	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1816	            <ns2:nonSpatiallyDefinable>true</ns2:nonSpatiallyDefinable>
1817	            <ns2:content>
1818	                <ns2:sceneViewIDREF>SE1</ns2:sceneViewIDREF>
1819	            </ns2:content>
1820	            <ns2:policy>Soundlevel:1</ns2:policy>
1821	            <ns2:maxCaptures>1</ns2:maxCaptures>
1822	            <ns2:allowSubsetChoice>false</ns2:allowSubsetChoice>
1823	            <ns2:description lang="en">penultimate loudest room segment
1824	            </ns2:description>
1825	            <ns2:priority>1</ns2:priority>
1826	            <ns2:lang>it</ns2:lang>
1827	            <ns2:mobility>static</ns2:mobility>
1828	            <ns2:view>individual</ns2:view>
1829	        </ns2:mediaCapture>
1830	        <ns2:mediaCapture
1831	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1832	        xsi:type="ns2:videoCaptureType"
1833	        captureID="VC6" mediaType="video">
1834	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1835	            <ns2:nonSpatiallyDefinable>true</ns2:nonSpatiallyDefinable>
1836	            <ns2:content>
1837	                <ns2:sceneViewIDREF>SE1</ns2:sceneViewIDREF>
1838	            </ns2:content>
1839	            <ns2:composed>false</ns2:composed>
1840	            <ns2:switched>true</ns2:switched>
1841	            <ns2:policy>Soundlevel:2</ns2:policy>
1842	            <ns2:maxCaptures>1</ns2:maxCaptures>
1843	            <ns2:allowSubsetChoice>false</ns2:allowSubsetChoice>
1844	            <ns2:description lang="en">last but two loudest room segment
1845	            </ns2:description>
1846	            <ns2:priority>1</ns2:priority>
1847	            <ns2:lang>it</ns2:lang>
1848	            <ns2:mobility>static</ns2:mobility>
1849	            <ns2:view>individual</ns2:view>
1850	        </ns2:mediaCapture>
1851	        <ns2:mediaCapture
1852	        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
1853	        xsi:type="ns2:videoCaptureType"
1854	        captureID="VC7" mediaType="video">
1855	            <ns2:captureSceneIDREF>CS1</ns2:captureSceneIDREF>
1856	            <ns2:nonSpatiallyDefinable>true</ns2:nonSpatiallyDefinable>
1857	            <ns2:content>
1858	                <ns2:captureIDREF>VC3</ns2:captureIDREF>
1859	                <ns2:captureIDREF>VC5</ns2:captureIDREF>
1860	                <ns2:captureIDREF>VC6</ns2:captureIDREF>
1861	            </ns2:content>
1862	            <ns2:composed>true</ns2:composed>
1863	            <ns2:switched>true</ns2:switched>
1864	            <ns2:maxCaptures>1</ns2:maxCaptures>
1865	            <ns2:allowSubsetChoice>false</ns2:allowSubsetChoice>
1866	            <ns2:description lang="en">
1867	            big picture of the current speaker +
1868	            pips about previous speakers</ns2:description>
1869	            <ns2:priority>1</ns2:priority>
1870	            <ns2:lang>it</ns2:lang>
1871	            <ns2:mobility>static</ns2:mobility>
1872	            <ns2:view>individual</ns2:view>
1873	        </ns2:mediaCapture>
1874	    </mediaCaptures>
1875	    <encodingGroups>
1876	        <ns2:encodingGroup encodingGroupID="EG0">
1877	            <ns2:maxGroupBandwidth>600000</ns2:maxGroupBandwidth>
1878	            <ns2:encodingIDList>
1879	                <ns2:encID>ENC1</ns2:encID>
1880	                <ns2:encID>ENC2</ns2:encID>
1881	                <ns2:encID>ENC3</ns2:encID>
1882	            </ns2:encodingIDList>
1883	        </ns2:encodingGroup>
1884	        <ns2:encodingGroup encodingGroupID="EG1">
1885	            <ns2:maxGroupBandwidth>300000</ns2:maxGroupBandwidth>
1886	            <ns2:encodingIDList>
1887	                <ns2:encID>ENC4</ns2:encID>
1888	                <ns2:encID>ENC5</ns2:encID>

1890	            </ns2:encodingIDList>
1891	        </ns2:encodingGroup>
1892	    </encodingGroups>
1893	    <captureScenes>
1894	        <ns2:captureScene scale="unknown" sceneID="CS1">
1895	            <ns2:sceneViews>
1896	                <ns2:sceneView sceneViewID="SE1">
1897	                    <ns2:description lang="en">
1898	                    participants' individual videos
1899	                    </ns2:description>
1900	                    <ns2:mediaCaptureIDs>
1901	                        <ns2:captureIDREF>VC0</ns2:captureIDREF>
1902	                        <ns2:captureIDREF>VC1</ns2:captureIDREF>
1903	                        <ns2:captureIDREF>VC2</ns2:captureIDREF>
1904	                    </ns2:mediaCaptureIDs>
1905	                </ns2:sceneView>
1906	                <ns2:sceneView sceneViewID="SE2">
1907	                    <ns2:description lang="en">
1908	                    loudest segment of the room
1909	                    </ns2:description>
1910	                    <ns2:mediaCaptureIDs>
1911	                        <ns2:captureIDREF>VC3</ns2:captureIDREF>
1912	                    </ns2:mediaCaptureIDs>
1913	                </ns2:sceneView>
1914	                <ns2:sceneView sceneViewID="SE5">
1915	                    <ns2:description lang="en">loudest segment
1916	                    of the room + pips</ns2:description>
1917	                    <ns2:mediaCaptureIDs>
1918	                        <ns2:captureIDREF>VC7</ns2:captureIDREF>
1919	                    </ns2:mediaCaptureIDs>
1920	                </ns2:sceneView>
1921	                <ns2:sceneView sceneViewID="SE4">
1922	                    <ns2:description lang="en">
1923	                    room audio</ns2:description>
1924	                    <ns2:mediaCaptureIDs>
1925	                        <ns2:captureIDREF>AC0</ns2:captureIDREF>
1926	                    </ns2:mediaCaptureIDs>
1927	                </ns2:sceneView>
1928	                <ns2:sceneView sceneViewID="SE3">
1929	                    <ns2:description lang="en">
1930	                    room video</ns2:description>
1931	                    <ns2:mediaCaptureIDs>
1932	                        <ns2:captureIDREF>VC4</ns2:captureIDREF>
1933	                    </ns2:mediaCaptureIDs>
1934	                </ns2:sceneView>
1935	            </ns2:sceneViews>
1936	        </ns2:captureScene>
1937	    </captureScenes>
1938	    <simultaneousSets>
1939	        <ns2:simultaneousSet setID="SS1">
1940	            <ns2:mediaCaptureIDREF>VC7</ns2:mediaCaptureIDREF>
1941	            <ns2:sceneViewIDREF>SE1</ns2:sceneViewIDREF>
1942	        </ns2:simultaneousSet>
1943	        <ns2:simultaneousSet setID="SS2">
1944	            <ns2:mediaCaptureIDREF>VC0</ns2:mediaCaptureIDREF>
1945	            <ns2:mediaCaptureIDREF>VC2</ns2:mediaCaptureIDREF>
1946	            <ns2:mediaCaptureIDREF>VC4</ns2:mediaCaptureIDREF>
1947	            <ns2:mediaCaptureIDREF>VC7</ns2:mediaCaptureIDREF>
1948	        </ns2:simultaneousSet>
1949	    </simultaneousSets>
1950	    <people>
1951	        <ns2:person personID="bob">
1952	            <ns2:personInfo>
1953	                <ns3:fn>
1954	                    <ns3:text>Bob</ns3:text>
1955	                </ns3:fn>
1956	            </ns2:personInfo>
1957	            <ns2:personType>minute taker</ns2:personType>
1958	        </ns2:person>
1959	        <ns2:person personID="alice">
1960	            <ns2:personInfo>
1961	                <ns3:fn>
1962	                    <ns3:text>Alice</ns3:text>
1963	                </ns3:fn>
1964	            </ns2:personInfo>
1965	            <ns2:personType>presenter</ns2:personType>
1966	        </ns2:person>
1967	        <ns2:person personID="ciccio">
1968	            <ns2:personInfo>
1969	                <ns3:fn>
1970	                    <ns3:text>Ciccio</ns3:text>
1971	                </ns3:fn>
1972	            </ns2:personInfo>
1973	            <ns2:personType>chairman</ns2:personType>
1974	            <ns2:personType>timekeeper</ns2:personType>
1975	        </ns2:person>
1976	    </people>
1977	</advertisement>

1979	11.  Security Considerations

1981	   As a general consideration, we remark that the CLUE framework (and
1982	   related protocol) has been conceived at the outset by embracing the
1983	   security-by-design paradigm.  This entails that a number of
1984	   requirements have been identified and properly standardized as
1985	   mandatory within the entire set of documents associated with the CLUE
1986	   architecture.  Requirements include: (i) the use of cryptography and
1987	   authentication; (ii) protection of all sensitive fields; (iii) mutual
1988	   authentication between CLUE endpoints; (iv) the presence of
1989	   authorization mechanisms; (v) the presence of native defence
1990	   mechanisms against malicious activities such as eavesdropping,
1991	   selective modification, deletion, replay (and related combinations
1992	   thereof).  Hence, security of the single components of the CLUE
1993	   solution cannot be evaluated independently of the integrated view of
1994	   the final architecture.

1996	   The CLUE protocol is an application-level protocol allowing a Media
1997	   Producer and a Media Consumer to negotiate a variegated set of
1998	   parameters associated with the establishment of a telepresence
1999	   session.  This unavoidably exposes a CLUE-enabled telepresence system
2000	   to a number of potential threats, most of which are extensively
2001	   discussed in the framework document [I-D.ietf-clue-framework].  The
2002	   security considerations section of the mentioned document actually
2003	   discusses issues associated with the setup and management of a
2004	   telepresence session both in the basic case involving two CLUE
2005	   endpoints acting, respectively, as MP and MC, and in the more
2006	   advanced scenario envisaging the presence of an MCU.

2008	   The framework document also mentions that the information carried
2009	   within CLUE protocol messages might contain sensitive data, which
2010	   SHOULD hence be accessed only by authenticated endpoints.  Security
2011	   issues associated with the CLUE data model schema are discussed in
2012	   [I-D.ietf-clue-data-model-schema].

2014	   There is extra information carried by the CLUE protocol which is not
2015	   associated with the CLUE data model schema and which exposes
2016	   information that might be of concern.  This information is primarily
2017	   exchanged during the options negotiation phase.  In the Clue
2018	   Participant state machine OPTIONS state, both parties agree on the
2019	   version and on the options to be used in the subsequent CLUE messages
2020	   exchange phase.  A malicious participant might either try to retrieve
2021	   a detailed footprint of a specific CLUE protocol implementation
2022	   during this initial setup phase, or force the communicating party to
2023	   use a non-up-to-date version of the protocol which they know how to
2024	   break.  Indeed, exposing all of the supported versions and options
2025	   could conceivably leak information about the specific implementation
2026	   of the protocol.  In theory an implementation could choose not to
2027	   announce all of the versions it supports if it wants to avoid such
2028	   leakage, though at the expenses of interoperability.  With respect to
2029	   the above considerations, it is noted that the OPTIONS state is only
2030	   reached after the CLUE data channel has been successfully set up.
2031	   This ensures that only authenticated parties can exchange OPTIONS and
2032	   related OPTIONS RESPONSE messages and hence drastically reduces the
2033	   attack surface which is exposed to malicious parties.

2035	   The CLUE framework clearly states the requirement to protect CLUE
2036	   protocol messages against threats deriving from the presence of a
2037	   malicious agent capable to gain access to the CLUE data channel.
2038	   Such a requirement is met by the CLUE data channel solution described
2039	   in [I-D.ietf-clue-datachannel], which ensures protection from both
2040	   message recovery and message tampering.  With respect to this last
2041	   point, any implementation of the CLUE protocol compliant with the
2042	   CLUE specification MUST rely on the exchange of messages which flow
2043	   on top of a reliable and ordered SCTP over DTLS transport channel
2044	   connecting two CLUE Participants.

2046	12.  IANA Considerations

2048	   This document registers a new XML namespace, a new XML schema and the
2049	   MIME type for the schema.  This document also registers the "CLUE"
2050	   Application Service tag and the "CLUE" Application Protocol tag and
2051	   defines registries for the CLUE messages and response codes.

2053	12.1.  URN Sub-Namespace Registration

2055	   This section registers a new XML namespace,
2056	   ""urn:ietf:params:xml:ns:clue-protocol"".

2058	   URI: urn:ietf:params:xml:ns:clue-protocol

2060	   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
2061	   Pietro Romano (spromano@unina.it).

2063	   XML:

2065	   BEGIN
2066	    <?xml version="1.0"?>
2067	    <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
2068	      "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
2069	    <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
2070	      <head>
2071	        <title>CLUE Messages</title>
2072	      </head>
2073	      <body>
2074	        <h1>Namespace for CLUE Messages</h1>
2075	        <h2>urn:ietf:params:xml:ns:clue-protocol</h2>
2076	   [[NOTE TO IANA/RFC-EDITOR: Please update RFC URL and replace XXXX
2077	       with the RFC number for this specification.]]
2078	        <p>See <a href="[[RFC URL]]">
2079	           RFCXXXX</a>.</p>
2080	      </body>
2081	    </html>
2082	   END

2084	12.2.  XML Schema registration

2086	   This section registers an XML schema per the guidelines in [RFC3688].

2088	   URI: urn:ietf:params:xml:schema:clue-protocol

2090	   Registrant Contact: CLUE working group (clue@ietf.org), Simon Pietro
2091	   Romano (spromano@unina.it).

2093	   Schema: The XML for this schema can be found as the entirety of
2094	   Section 9 of this document.

2096	12.3.  MIME Media Type Registration for 'application/clue+xml'

2098	   This section registers the " "application/clue+xml"" MIME type.

2100	   To: ietf-types@iana.org

2102	   Subject: Registration of MIME media type application/clue+xml

2104	   MIME media type name: application

2106	   MIME subtype name: clue+xml

2108	   Required parameters: (none)

2110	   Optional parameters: charset
2111	   Same as the charset parameter of "application/xml" as specified in

2113	   [RFC7303], Section 3.2.

2115	   Encoding considerations: Same as the encoding considerations of
2116	   "application/xml" as specified in [RFC7303], Section 3.2.

2118	   Security considerations: This content type is designed to carry
2119	   protocol data related to telepresence session control.  Some of the
2120	   data could be considered private.  This media type does not provide
2121	   any protection and thus other mechanisms such as those described in
2122	   Section Security are required to protect the data.  This media type
2123	   does not contain executable content.

2125	   Interoperability considerations: None.

2127	   Published specification: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please
2128	   replace XXXX with the RFC number for this specification.]]

2130	   Applications that use this media type: CLUE participants.

2132	   Additional Information: Magic Number(s): (none),
2133	   File extension(s): .xml,
2134	   Macintosh File Type Code(s): TEXT.

2136	   Person & email address to contact for further information: Simon
2137	   Pietro Romano (spromano@unina.it).

2139	   Intended usage: LIMITED USE

2141	   Author/Change controller: The IETF

2143	   Other information: This media type is a specialization of
2144	   application/xml [RFC7303], and many of the considerations described
2145	   there also apply to application/clue+xml.

2147	12.4.  CLUE Protocol Registry

2149	   The document requests that the IANA creates new registries for CLUE
2150	   messages and response codes.

2152	12.4.1.  CLUE Message Types

2154	   The following summarizes the registry for CLUE messages:

2156	   Related Registry: CLUE Message Types Registry

2158	   Defining RFC: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please replace XXXX
2159	   with the RFC number for this specification.]]
2160	   Registration/Assignment Procedures: Following the policies outlined
2161	   in [RFC5226], the IANA policy for assigning new values for the CLUE
2162	   message types for the CLUE protocol is Specification Required.

2164	   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
2165	   Pietro Romano (spromano@unina.it).

2167	   The initial Message table is populated using the CLUE messages
2168	   described in Section 5 and defined in the XML schema in Section 9.

2170	   +-------------------+-----------------------------------+-----------+
2171	   | Message           | Description                       | Reference |
2172	   +-------------------+-----------------------------------+-----------+
2173	   | options           | "OPTIONS" in this document.  Sent | RFCXXXX   |
2174	   |                   | by the CI to the CR in the        |           |
2175	   |                   | initiation phase to specify the   |           |
2176	   |                   | roles played by the CI, the       |           |
2177	   |                   | supported versions and the        |           |
2178	   |                   | supported protocol options.       |           |
2179	   | optionsResponse   | "OPTIONS RESPONSE" in this        | RFCXXXX   |
2180	   |                   | document.  Sent by the CI to the  |           |
2181	   |                   | CR in reply to an OPTIONS message |           |
2182	   |                   | to finally estabilsh the version  |           |
2183	   |                   | and the options to be used in the |           |
2184	   |                   | following CLUE messages exchange. |           |
2185	   | advertisement     | "ADVERTISEMENT" or "ADV" in this  | RFCXXXX   |
2186	   |                   | document.  Sent by the MP to the  |           |
2187	   |                   | MC to specify the telepresence    |           |
2188	   |                   | capabilities of the MP expressed  |           |
2189	   |                   | according to the CLUE framework.  |           |
2190	   | ack               | "ACK" in this document.  Sent by  | RFCXXXX   |
2191	   |                   | the MC to the MP to acknowledge   |           |
2192	   |                   | the reception of an ADVERTISEMENT |           |
2193	   |                   | message.                          |           |
2194	   | configure         | "CONFIGURE" or "CONF" in this     | RFCXXXX   |
2195	   |                   | document.  Sent by the MC to the  |           |
2196	   |                   | MP to specify the desired media   |           |
2197	   |                   | captures among those specified in |           |
2198	   |                   | the ADVERTISEMENT.                |           |
2199	   | configureResponse | "CONFIGURE RESPONSE" or "CONF     | RFCXXXX   |
2200	   |                   | RESPONSE" in this document.  Sent |           |
2201	   |                   | by the MP to the MC in reply to a |           |
2202	   |                   | CONFIGURE message to communicate  |           |
2203	   |                   | if the configuration request has  |           |
2204	   |                   | been successfully processed or    |           |
2205	   |                   | not.                              |           |
2206	   +-------------------+-----------------------------------+-----------+
2207	                                 IANA-CLUE

2209	12.4.2.  CLUE Response Codes

2211	   The following summarizes the requested registry for CLUE response
2212	   codes:

2214	   Related Registry: CLUE Response Code Registry

2216	   Defining RFC: RFC XXXX [[NOTE TO IANA/RFC-EDITOR: Please replace XXXX
2217	   with the RFC number for this specification.]]

2219	   Registration/Assignment Procedures: Following the policies outlined
2220	   in [RFC5226], the IANA policy for assigning new values for the
2221	   Response codes for CLUE shall be Specification Required.

2223	   Registrant Contact: IETF CLUE working group (clue@ietf.org), Simon
2224	   Pietro Romano (spromano@unina.it).

2226	   The initial Response-code table is populated using the Response codes
2227	   defined in Section 5.7 as follows:

2229	   +--------+-----------------+----------------------------+-----------+
2230	   | Number | Default         | Description                | Reference |
2231	   |        | Response String |                            |           |
2232	   +--------+-----------------+----------------------------+-----------+
2233	   | 200    | Success         | The request has been       | RFCXXXX   |
2234	   |        |                 | successfully processed.    |           |
2235	   | 300    | Syntax errors   | The XML syntax of the      | RFCXXXX   |
2236	   |        | and             | message is not correct or  |           |
2237	   |        | inconsistencies | there are invalid values.  |           |
2238	   | 301    | Bad syntax      | The XML syntax of the      | RFCXXXX   |
2239	   |        |                 | message is not correct.    |           |
2240	   | 302    | Invalid value   | The message contains an    | RFCXXXX   |
2241	   |        |                 | invalid parameter value.   |           |
2242	   | 303    | Conficting      | The message contains       | RFCXXXX   |
2243	   |        | values          | values that cannot be used |           |
2244	   |        |                 | together.                  |           |
2245	   | 400    | Semantic errors | Semantic errors in the     | RFCXXXX   |
2246	   |        |                 | received CLUE protocol     |           |
2247	   |        |                 | message.                   |           |
2248	   | 401    | Version not     | The protocol version used  | RFCXXXX   |
2249	   |        | supported       | in the message is not      |           |
2250	   |        |                 | supported.                 |           |
2251	   | 402    | Invalid         | The sequence number of the | RFCXXXX   |
2252	   |        | sequencing      | message is out of date.    |           |
2253	   | 403    | Invalid         | The identifier used in the | RFCXXXX   |
2254	   |        | identifier      | message is no valid or     |           |
2255	   |        |                 | unknown.                   |           |
2256	   | 404    | ADV Expired     | The number of the ADV the  | RFCXXXX   |
2257	   |        |                 | CONF refers to is out of   |           |
2258	   |        |                 | date.                      |           |
2259	   | 405    | Subset choice   | The subset choice is not   | RFCXXXX   |
2260	   |        | not allowed     | allowed for the specified  |           |
2261	   |        |                 | MCC.                       |           |
2262	   +--------+-----------------+----------------------------+-----------+

2264	13.  Diff with draft-ietf-clue-protocol-06

2266	   o  XML schema definition of <version> has been changed to match
2267	      pattern "X.Y", where X and Y are single digits.

2269	   o  100, 200, 300, 400 defined as catch-all response codes.

2271	   o  Updates in IANA section.

2273	14.  Diff with draft-ietf-clue-protocol-05

2275	   o  This document corrects some versioning errors of
2276	      draft-ietf-clue-protocol-05.

2278	15.  Diff with draft-ietf-clue-protocol-04

2280	   o  The document has been revised based on feedback recevied on the
2281	      ML.  No major modification is included in this version.

2283	16.  Diff with draft-ietf-clue-protocol-03

2285	   o  Response codes section updated.

2287	   o  maxCaptureEncodings removed from examples, allowSubsetChoice
2288	      added.

2290	   o  State machines descriptions aligned with pictures.

2292	   o  Applied recommended updates indicated in Christian's review (2015-
2293	      03-19).

2295	17.  Diff with draft-ietf-clue-protocol-02

2297	   o  CLUE Participant state machine: TERMINATED state replaced with
2298	      IDLE.

2300	   o  MP and MC state machines: SDP O/A state removed.

2302	   o  Diff mechanism (and related example) removed.

2304	   o  Schema updates: versionType used as the data type for all versions
2305	      fields, xs:unsignedInt used as the data type for all sequence
2306	      number fields, diff support removed from the ADV definition.

2308	18.  Diff with draft-ietf-clue-protocol-01

2310	   o  The diff mechanism for the ADV message has been introduced.

2312	   o  READV and READV RESPONSE message have been both removed.

2314	   o  The state machines have been deeply reviewed and changed.

2316	   o  References: references have been updated and splitted into
2317	      Informative references and Normative references as in framework
2318	      v17.

2320	   o  Schema: <globalSceneEntries> changed in <globalViews>,
2321	      <participants> in <people>

2323	   o  Terminology: many definitions added.

2325	   o  Response codes updated.

2327	19.  Diff with draft-ietf-clue-protocol-00

2329	   1.  The XML schema of the ADVERTISEMENT and of the READV have been
2330	       aligned with the current definitions in
2331	       [I-D.ietf-clue-data-model-schema] (example of updates:
2332	       <participants> --> <people>, <globalCaptureEntries> -->
2333	       <globalSceneEntries>)

2335	   2.  Text has been added to clarify that, in the OPTIONS RESPONSE,
2336	       when the response code is not an error response code, both
2337	       <mediaProvider> and <mediaConsumer> are mandatory.

2339	   3.  The content of the "v" attribute and of the <version> elements
2340	       carried in the OPTIONS and OPTIONS RESPONSE messages has been
2341	       described more precisely.

2343	   4.  Advertisement examples have been added.

2345	20.  Diff with draft-presta-clue-protocol-04

2347	   1.  The response code type error in the OPTIONS response (and in
2348	       other parts) has been corrected.

2350	21.  Diff with draft-presta-clue-protocol-03

2352	   1.  The XML Schema has been deeply revised and completed.

2354	   2.  The descriptions of the CLUE messages have been added.

2356	   3.  The distinction between major version numbers and minor version
2357	       numbers has been cut and pasted from [I-D.ietf-clue-signaling].

2359	   4.  Besides the two way one, a three way mechanism for the options
2360	       negotiation has been proposed and provided to foster discussion.

2362	22.  Diff with draft-presta-clue-protocol-02

2364	   1.  "Terminology" section added.

2366	   2.  Introduced the concept of "CLUE Participant" - an Endpoint or a
2367	       MCU able to use the CLUE protocol within a telepresence session.
2368	       A CLUE Participant can act as a Media Provider and/or as a Media
2369	       Consumer.

2371	   3.  Introduced the ACK/NACK mechanism for the ADVERTISEMENT.

2373	   4.  MP and MC state machines have been updated.  The CP state machine
2374	       has been added.

2376	23.  Acknowledgments

2378	   The authors thank all the CLUErs for their precious feedbacks and
2379	   support, in particular Paul Kyzivat, Christian Groves and Scarlett
2380	   Liuyan.

2382	24.  References

2384	24.1.  Normative References

2386	   [I-D.ietf-clue-data-model-schema]  Presta, R. and S. Romano, "An XML
2387	                                      Schema for the CLUE data model", d
2388	                                      raft-ietf-clue-data-model-schema-
2389	                                      17 (work in progress),
2390	                                      August 2016.

2392	   [I-D.ietf-clue-datachannel]        Holmberg, C., "CLUE Protocol data
2393	                                      channel",
2394	                                      draft-ietf-clue-datachannel-14
2395	                                      (work in progress), August 2016.

2397	   [I-D.ietf-clue-framework]          Duckworth, M., Pepperell, A., and
2398	                                      S. Wenger, "Framework for
2399	                                      Telepresence Multi-Streams",
2400	                                      draft-ietf-clue-framework-25 (work
2401	                                      in progress), January 2016.

2403	   [I-D.ietf-clue-signaling]          Kyzivat, P., Xiao, L., Groves, C.,
2404	                                      and R. Hansen, "CLUE Signaling",
2405	                                      draft-ietf-clue-signaling-09 (work
2406	                                      in progress), March 2016.

2408	   [RFC2119]                          Bradner, S., "Key words for use in
2409	                                      RFCs to Indicate Requirement
2410	                                      Levels", BCP 14, RFC 2119,
2411	                                      DOI 10.17487/RFC2119, March 1997,
2412	                                      <http://www.rfc-editor.org/info/
2413	                                      rfc2119>.

2415	   [RFC3550]                          Schulzrinne, H., Casner, S.,
2416	                                      Frederick, R., and V. Jacobson,
2417	                                      "RTP: A Transport Protocol for
2418	                                      Real-Time Applications", STD 64,
2419	                                      RFC 3550, DOI 10.17487/RFC3550,
2420	                                      July 2003, <http://
2421	                                      www.rfc-editor.org/info/rfc3550>.

2423	   [RFC3688]                          Mealling, M., "The IETF XML
2424	                                      Registry", BCP 81, RFC 3688,
2425	                                      DOI 10.17487/RFC3688,
2426	                                      January 2004, <http://
2427	                                      www.rfc-editor.org/info/rfc3688>.

2429	   [RFC3958]                          Daigle, L. and A. Newton, "Domain-
2430	                                      Based Application Service Location
2431	                                      Using SRV RRs and the Dynamic
2432	                                      Delegation Discovery Service
2433	                                      (DDDS)", RFC 3958, DOI 10.17487/
2434	                                      RFC3958, January 2005, <http://
2435	                                      www.rfc-editor.org/info/rfc3958>.

2437	   [RFC5226]                          Narten, T. and H. Alvestrand,
2438	                                      "Guidelines for Writing an IANA
2439	                                      Considerations Section in RFCs",
2440	                                      BCP 26, RFC 5226, DOI 10.17487/
2441	                                      RFC5226, May 2008, <http://
2442	                                      www.rfc-editor.org/info/rfc5226>.

2444	   [RFC7303]                          Thompson, H. and C. Lilley, "XML
2445	                                      Media Types", RFC 7303,
2446	                                      DOI 10.17487/RFC7303, July 2014, <
2447	                                      http://www.rfc-editor.org/info/
2448	                                      rfc7303>.

2450	24.2.  Informative References

2452	   [RFC1122]                          Braden, R., Ed., "Requirements for
2453	                                      Internet Hosts - Communication
2454	                                      Layers", STD 3, RFC 1122,
2455	                                      DOI 10.17487/RFC1122,
2456	                                      October 1989, <http://
2457	                                      www.rfc-editor.org/info/rfc1122>.

2459	   [RFC4353]                          Rosenberg, J., "A Framework for
2460	                                      Conferencing with the Session
2461	                                      Initiation Protocol (SIP)",
2462	                                      RFC 4353, DOI 10.17487/RFC4353,
2463	                                      February 2006, <http://
2464	                                      www.rfc-editor.org/info/rfc4353>.

2466	   [RFC6120]                          Saint-Andre, P., "Extensible
2467	                                      Messaging and Presence Protocol
2468	                                      (XMPP): Core", RFC 6120,
2469	                                      DOI 10.17487/RFC6120, March 2011,
2470	                                      <http://www.rfc-editor.org/info/
2471	                                      rfc6120>.

2473	   [RFC7262]                          Romanow, A., Botzko, S., and M.
2474	                                      Barnes, "Requirements for
2475	                                      Telepresence Multistreams",
2476	                                      RFC 7262, DOI 10.17487/RFC7262,
2477	                                      June 2014, <http://
2478	                                      www.rfc-editor.org/info/rfc7262>.

2480	   [RFC7667]                          Westerlund, M. and S. Wenger, "RTP
2481	                                      Topologies", RFC 7667,
2482	                                      DOI 10.17487/RFC7667,
2483	                                      November 2015, <http://
2484	                                      www.rfc-editor.org/info/rfc7667>.

2486	Authors' Addresses

2488	   Roberta Presta
2489	   University of Napoli
2490	   Via Claudio 21
2491	   Napoli  80125
2492	   Italy

2494	   EMail: roberta.presta@unina.it

2496	   Simon Pietro Romano
2497	   University of Napoli
2498	   Via Claudio 21
2499	   Napoli  80125
2500	   Italy

2502	   EMail: spromano@unina.it