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

CLUE Working Group                                             R. Presta
Internet-Draft                                               S P. Romano
Intended status: Informational                      University of Napoli
Expires: March 21, 2014                               September 17, 2013


                             CLUE protocol
                     draft-presta-clue-protocol-01

Abstract

   ToDo.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 21, 2014.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.







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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Overview of the CLUE protocol messages . . . . . . . . . . . .  3
     3.1.  ADVERTISEMENT  . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  CONFIGURE  . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.3.  RESPONSE . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.4.  RE-ADV . . . . . . . . . . . . . . . . . . . . . . . . . .  8
   4.  Protocol state machines  . . . . . . . . . . . . . . . . . . .  9
   5.  Media Consumer's state machine . . . . . . . . . . . . . . . . 10
   6.  Media Provider's state machine . . . . . . . . . . . . . . . . 12
   7.  About CLUE protocol XML schema extensibility and versioning  . 14
     7.1.  Aspect 1 - new information within existing messages  . . . 15
     7.2.  Aspect 2 - new messages  . . . . . . . . . . . . . . . . . 16
   8.  Diff with -00 version  . . . . . . . . . . . . . . . . . . . . 16
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 16


































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1.  Introduction

   The CLUE protocol is an application protocol used by a Media Provider
   (MP) and a Media Consumer (MC) in order to establish a multimedia
   telepresence session.  CLUE protocol messages flow upon a DTLS/SCTP
   channel established as depicted in [I-D.kyzivat-clue-signaling].
   While [I-D.kyzivat-clue-signaling] focuses onto signaling details
   about the protocol and its interaction with the SIP/SDP session
   establishment, we herein concentrate only on the protocol in action
   (?) and try to define the behavior of both the MP and the MC at the
   CLUE application level.  In other words, we assume the DTLS/SCTP
   channel is established and discuss how the CLUE dialogue between the
   MP and the MC can be exploited to successfully setup the telepresence
   session according to the principles and concepts pointed out in in
   [I-D.kyzivat-clue-signaling] and in [I-D.ietf-clue-framework].

   In Section 3 we provide the list of the CLUE messages and an overview
   of their features and functionality.  MC's and MP's state machines
   are introduced in Section 4 and further described in Section 5 and
   Section 6 respectively.

2.  Terminology

   This document refers to the same terminology used in
   [I-D.ietf-clue-framework] and in [I-D.kyzivat-clue-signaling].

3.  Overview of the CLUE protocol messages

   This section contains a bird's-eye view of the CLUE protocol
   messages.  For each message it is indicated who sends it, who
   receives it, a brief description of the information it carries, and
   how/when it is used.  Besides the well-known ADVERTISEMENT and
   CONFIGURE ones, new messages have been conceived in order to fulfill
   the mechanisms and operations pointed out in
   [I-D.kyzivat-clue-signaling].

   o  ADVERTISEMENT (ADV)

   o  CONFIGURE (CONF)

   o  RESPONSE

   o  RE-ADV








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3.1.  ADVERTISEMENT



  +---------- ---+-----------------------------------------------------+
  |              |                                                     |
  | FROM         |                        MP                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TO           |                        MC                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TYPE         |                   Notification                      |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | DESCRIPTION  |   This message is used by the MP to advertise the   |
  |              |   available media captures and related information  |
  |              |   to the MC.                                        |
  |              |   The ADV contains elements compliant with the      |
  |              |   CLUE data model and other information like the    |
  |              |   CLUE protocol version and a sequence number.      |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | USAGE        |   The MP sends this message as soon as the CLUE     |
  |              |   CLUE channel is ready. The MP sends an ADV to the |
  |              |   MC each time there is a modification of the MP's  |
  |              |   telepresence capabilities.                        |
  |              |   The ADV message is also sent back to the MC       |
  |              |   when the MP receives a RE-ADV request.            |
  +--------------+-----------------------------------------------------+


3.2.  CONFIGURE














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  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | FROM         |                        MC                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TO           |                        MP                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TYPE         |                   Request                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | DESCRIPTION  |   This message allows a MC to request for the       |
  |              |   desired advertised capture. It contains capture   |
  |              |   encodings and other information like the CLUE     |
  |              |   protocol version and a sequence number.           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | USAGE        |   The MC can send a CONF after the reception of     |
  |              |   an ADV or each time it wants to request other     |
  |              |   advertised captures to the MP.                    |
  +--------------+-----------------------------------------------------+

3.3.  RESPONSE
























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  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | FROM         |                        MP                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TO           |                        MC                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TYPE         |                      Response                       |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | DESCRIPTION  |   This message allows a MP to answer to a CONF      |
  |              |   message. Besides the protocol version and a       |
  |              |   sequence number, it contains a response code with |
  |              |   a response string indicating the success or the   |
  |              |   failure (along with failure details) of the CONF  |
  |              |   request elaboration. Example of response codes    |
  |              |   and strings are provided in a following table.    |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | USAGE        |   The MP sends this message in response to CONF     |
  |              |   messages.                                         |
  +--------------+-----------------------------------------------------+


   Response code can be designed by following the HTTP semantics as
   below.




















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



   ...  TBC.





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


3.4.  RE-ADV























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  +---------- ---+-----------------------------------------------------+
  |              |                                                     |
  | FROM         |                        MC                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TO           |                        MP                           |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | TYPE         |                      Request                        |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | DESCRIPTION  |   This message allows a MC to request for the MP    |
  |              |   issuing a new copy of the ADV. This message can   |
  |              |   contain a reason string indicating the motivation |
  |              |   for the request (e.g., refresh, missing elements  |
  |              |   in the received ADV, wrong syntax in the received |
  |              |   ADV, invalid capture area, invalid line of        |
  |              |   capture point, etc).                              |
  |              |                                                     |
  +--------------+-----------------------------------------------------+
  |              |                                                     |
  | USAGE        |   The MC sends this message to the MP when the      |
  |              |   timeout for the ADV is fired, or when the ADV is  |
  |              |   not compliant with the CLUE specifications (this  |
  |              |   can be useful for interoperability testing        |
  |              |   purposes)                                         |
  |              |                                                     |
  +--------------+-----------------------------------------------------+

4.  Protocol state machines

   The CLUE protocol is an application protocol used between a Media
   Provider (MP) and a Media Consumer (MC) in order to establish a
   multimedia telepresence session.  CLUE protocol messages flow upon a
   DTLS/SCTP channel established as depicted in
   [I-D.kyzivat-clue-signaling].  Over such a channel there are
   typically two CLUE streams between the channel terminations flowing
   in opposite directions.  In other words, typically, both channel
   terminations act simultaneously as a MP and as a MC.  We herein
   discuss the state machines associated with the MP process and with
   the MC process.







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5.  Media Consumer's state machine

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

   In the TIMEOUT state, if the number of trials is under the retry
   threshold, the MC issues a RE-ADV/refresh message to the MP ("send
   RE-ADV"), coming back to the IDLE state.  Otherwise, the MC moves to
   the TERMINATED state.

   When the ADV has been received ("receive ADV"), the MC goes into the
   ADV RECEIVED state.  The ADV is then parsed.  If something goes wrong
   with the ADV (bad syntax, missing XML elements, etc.), the MC sends a
   RE-ADV message to the MP specifying the encountered problem via a
   proper reason phrase.  By this way, the MC comes back to the IDLE
   state, waiting for a new copy of the ADV.  If the ADV is successfully
   processed, the MC issues a CONF message to the MP ("send CONF") and
   switches to the TRYING state.

   When in the TRYING state, the MC is waiting for a RESPONSE message
   from the MP to the issued CONF.  If the timeout expires ("timeout"),
   the MC moves to the TIMEOUT state and sends a RE-ADV in order to
   solicit a new ADV from the MP.  If a RESPONSE with an error code is
   received ("receive 4xx, 5xx not supported"), then the MC comes back
   to the ADV-RCVD state and produces a new CONF message to be sent to
   the MP.  If a successful RESPONSE arrives ("receive 200 OK"), the MC
   gets the IN CALL state.  If a new ADV arrives in the while, it is
   ignored.  Indeed, after the timeout is exceeded, the MC goes to the
   TIMEOUT state and then sends a RE-ADV to the MP.

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

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

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



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




                                                                      +-----+
                            +--------+-------------timeout------>+----+--+  |
                            |  IDLE  +<----+                     |TIMEOUT|  |
                            +---+----+<----+--------send---------+-------+  |
                                |          |     RE-ADV(refresh)      ^     |
                                |          |                          |     |
                                |          |                          |     |
                             receive     send                         |     |
                               ADV       RE-ADV                       |     |
           +---receive-------+  |       (missing elements,            |     |
           |   error RESP    |  |        invalid area,...)            |     |
           |                 v  v          |                          |     |
           +---------------++---------+    |                          |     |
          +---------------->+  ADV    +----+                      timeout   |
          |          +----->| RECEIVED|<-----+                        |     |
          |          |      +---+-----+      |                        |     |
      receive        |          |            |                        |     |
        ADV          |          |            |                        |     |
          |          |          |            |                        |     |
          |        receive     send      receive                      |     |
          |        ADV         CONF      error RESP,                  |     |
          |          |          |        retry not expired            |     |
          |          |          v            |                        |     |
          +-----------------+--------+-------+------------------------+     |
                 +---+------+ TRYING +-------+                              |
                 |   |      +---+----+<----+                                |
                 |   |          |          |                                |
                 |   |          |          |                                |
          receive|   |         receive    send                          retry
          error RESP,|          200 OK    CONF                        expires
          retry  |   |          |          |                                |
          expired|   |          |          |                                |
                 |   |          |          |                                |
                 |   |          v          |                                |
                 |   |       +------+      |                                |
                 |   +-------+  IN  |      |                                |
                 |           | CALL +------+                                |
                 |           +--+---+                                       |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |



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                 |            connection                                    |
                 |             closed                                       |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              |                                           |
                 |              v                                           |
                 |            +----------+<---------------------------------+
                 +----------->+TERMINATED|
                              +----------+


6.  Media Provider's state machine

   In the IDLE state, the MP is preparing the ADV message reflecting the
   actual telepresence capabilities.  After the ADV has been sent, the
   MP moves to the WAIT FOR CONF state.

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

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

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

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

   The TERMINATED state is reachable from each of the aforementioned



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






 +------------------->+-----+-+<----------------------------+
 |   +--------------->| IDLE  |<-------------retry----------+---------+
 |   |       +------->+---+---+<----+         not           |         |
 |   |       |            |         |        expired        |         |
 |   |       |            |         |                       |         |
 |   |  change          send       receive                  |        ++------+
 |   |  telepresence     ADV       RE-ADV                   |        |TIMEOUT|
 |   |  settings          |         |                       |        ++--+---+
 |   |       |            |         |                       |         ^  |
 |   |       |            v         |                       |         |  |
 |   |       |    +-------------+---+                       |         |  |
 |   |       +----+  WAIT FOR   +------------timeout--------+---------+  |
 |   |            |    CONF     |                           |            |
 change           +-------+-----+<--+                       |            |
 telepresence             |         |                       |            |
 settings                 |         |                       |            |
 |   |                  receive     CONF error,             |            |
 |   |                   CONF       retry not expired,      |            |
 |   |                    |         send error RESP         |            |
 |   |                    |         |                       |            |
 |   |                    |         |                       |            |
 |   |                    v         |                       |            |
 |   |              +-----------+---+                       |            |
 +---+-------------+|   CONF    |                           |            |
     |       +----->| RECEIVED  |----CONF error,            |            |
     |       |      +-----+-----+    retry expired          |            |
     |       |            |                |                |            |
     |       |            |                |                |            |
     |       |            |                |                |            |
 receive   receive      send               |                |            |
 RE-ADV     CONF       200 OK              |                |       retry|
     |       |            |                |                |      expired
     |       |            |                |                |            |
     |       |            |                |                |            |
     |       |            v                |                |            |
     |       |       +----------+        change             |            |
     |       +-------+  IN CALL +--------telepresence-------+            |
     +---------------+----+-----+        settings                        |
                          |                |                             |



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                          |                |                             |
                          |                |                             |
                          |                |                             |
                       connection          |                             |
                        closed             |                             |
                          |                |                             |
                          |                |                             |
                          v                |                             |
                       +------------+<-----+-----------------------------+
                       | TERMINATED |      |
                       +------------+<-----+


7.  About CLUE protocol XML schema extensibility and versioning

   CLUE protocol messages are XML messages compliant to the CLUE
   protocol XML schema.  Both client and server have to test the
   compliance of the received messages with the XML schema of the CLUE
   protocol.  If the compliance is not verified, the message cannot be
   processed.

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

   It is hoped that, before the CLUE protocol XML schema reaches a
   steady state, prototypes developed by different organizations would
   perform some tests.  In that case, in order to interoperate, they
   have to be compliant to the current version of the XML schema, i.e.,
   the one copied in the most up-to-date version of the draft defining
   the CLUE protocol.  It is up to prototype implementors to keep up to
   date their products.

   Although the standard version of the CLUE protocol XML schema will be
   designed to thoroughly cope with the requirements emerging from the
   application domain, new needs can arise in the future.  A mechanism
   assuring forward compatibility must be envisioned.  New needs can
   interest two main aspects of the protocol:

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

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



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7.1.  Aspect 1 - new information within existing messages

   CLUE messages are envelopes carrying two types of information:

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

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

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

      elementFormDefault="qualified"

      attributeFormDefault="unqualified"

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

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

      write down a new version of the data model schema, with the new
      elements added after the existing ones.  This is a possible
      solution.  However, we must state that telepresence applications
      are forced to check the version attribute of the schema they use.
      [To be discussed]

      put all the new elements inside a brand new schema to be linked to
      a new URN that the most up to date telepresence system must be
      aware of.  [To be discussed]

      design a wildcard envelope for future data model elements.  [To be
      discussed]




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7.2.  Aspect 2 - new messages

   New CLUE protocol messages, not envisioned in the standard version of
   the schema, are needed.  Also in that case we have three chances:

      write down a new version of the protocol schema, with the new
      messages added after the existing ones.  The same considerations
      of the first option above hold here.  [To be discussed]

      put all the new messages inside a brand new schema to be linked to
      a new URN that the most up to date telepresence system must be
      aware of. :( [To be discussed]

      design a wildcard envelope for future messages.  This is an
      approach used also within the CCMP protocol (Centralized
      Conferencing Manipulation Protocol, [RFC6503]).  In that case, a
      mechanism for the extension negotiation is also envisioned.  [To
      be discussed]

8.  Diff with -00 version

      MC and MP state diagrams have been updated for discussion in
      http://www.ietf.org/mail-archive/web/clue/current/msg02650.html

      Consideration about protocol extension and versioning have been
      added to foster discussion.

9.  Informative References

   [I-D.ietf-clue-framework]     Duckworth, M., Pepperell, A., and S.
                                 Wenger, "Framework for Telepresence
                                 Multi-Streams",
                                 draft-ietf-clue-framework-11 (work in
                                 progress), July 2013.

   [I-D.kyzivat-clue-signaling]  Kyzivat, P., Xiao, L., Groves, C., and
                                 R. Hansen, "CLUE Signaling",
                                 draft-kyzivat-clue-signaling-05 (work
                                 in progress), September 2013.

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







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Authors' Addresses

   Roberta Presta
   University of Napoli
   Via Claudio 21
   Napoli  80125
   Italy

   EMail: roberta.presta@unina.it


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

   EMail: spromano@unina.it

































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