One document matched: draft-presta-clue-protocol-02.xml
<?xml version="1.0" encoding="us-ascii"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes" ?>
<?rfc compact="yes" ?>
<?rfc subcompact="no"?>
<?rfc sortrefs="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc rfcedstyle="yes" ?>
<rfc docTitle="draft-presta-clue-protocol-02" submissionType="IETF" consensus="yes"
category="info" ipr="trust200902">
<front>
<title abbrev="draft-presta-clue-protocol-02">
CLUE protocol
</title>
<author initials="R." surname="Presta" fullname="Roberta Presta">
<organization>University of Napoli</organization>
<address>
<postal>
<street>Via Claudio 21</street>
<code>80125</code>
<city>Napoli</city>
<country>Italy</country>
</postal>
<email>roberta.presta@unina.it</email>
</address>
</author>
<author initials="S P" surname="Romano" fullname="Simon Pietro Romano">
<organization>University of Napoli</organization>
<address>
<postal>
<street>Via Claudio 21</street>
<code>80125</code>
<city>Napoli</city>
<country>Italy</country>
</postal>
<email>spromano@unina.it</email>
</address>
</author>
<date month="October" year="2013"/>
<area>RAI</area>
<workgroup>CLUE Working Group</workgroup>
<!-- [rfced] Please insert any keywords (beyond those that appear in
the title) for use on http://www.rfc-editor.org/rfcsearch.html. -->
<keyword>CLUE</keyword>
<keyword>Telepresence</keyword>
<keyword>Protocol</keyword>
<keyword>Framework</keyword>
<abstract>
<t>
The CLUE protocol is an application protocol conceived for the description and negotiation
of a CLUE telepresence session.
The design of the CLUE protocol takes into account the
requirements and the framework defined, respectively, in
<xref target="I-D.ietf-clue-framework"/> and
<xref target="I-D.ietf-clue-telepresence-requirements"/>.
The companion document <xref target="I-D.kyzivat-clue-signaling"/> delves into
CLUE signaling details, as well as on the SIP/SDP session establishment phase.
We herein focus on the application level perspective.
Message details, together with the behavior of both the Media Provider
and the Media Consumer are discussed.
</t>
</abstract>
</front>
<middle>
<!-- Introduction -->
<section title="Introduction" anchor="sec-intro">
<t>
The CLUE protocol is an application protocol used by a
Media Provider (MP) and a Media Consumer (MC) to
establish a CLUE multimedia telepresence session.
The main goals of the CLUE protocol are:
<list style="numbers">
<t>enabling a MP to
fully announce its current telepresence capabilities to the MC
in terms of available media captures, encodings, and simultaneity constraints;</t>
<t>enabling a MC to request the desired multimedia streams from
the offering MP.</t>
</list>
</t>
<t>
CLUE protocol messages flow upon a DTLS/SCTP/UDP channel established
as depicted in <xref target="I-D.kyzivat-clue-signaling"/>.
While <xref target="I-D.kyzivat-clue-signaling"/> focuses on
protocol signaling details and on its interaction with
the SIP/SDP session establishment phase, we herein investigate the
protocol in action and try to define the behavior of both the MP
and the MC at the CLUE application level.
We assume the DTLS/SCTP/UDP 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 <xref target="I-D.ietf-clue-framework"/>.
</t>
<t>
In <xref target="sec-messages"/> we provide an overview of the CLUE
protocol and describe CLUE messages along with their features and functionality.
MC's and MP's state machines are introduced in <xref target="sec-sm"/>
and further described in
<xref target="sec-mc"/> and
<xref target="sec-mp"/> respectively.
Versioning, extensions and options management mechanisms are discussed in <xref target="sec-vers"/>,
<xref target="sec-ext"/> and <xref target="sec-opt"/>, respectively.
The XML schema defining the CLUE messages is reported in <xref target="sec-schema"/>.
</t>
</section>
<!-- Terminology -->
<section title="Terminology" anchor="sec-teminology">
<t> This document refers to the same terminology used in
<xref target="I-D.ietf-clue-framework"/> and in
<xref target="I-D.kyzivat-clue-signaling"/>.</t>
</section>
<!-- Overview of the protocol messages -->
<section title="Overview of the CLUE protocol messages" anchor="sec-messages">
<t>
The CLUE protocol, as defined in the following, is a stateful, client-server,
XML-based application protocol.
The server side of the protocol is represented by a Media Provider, which produces
media streams, while the client side is represented by the Media Consumer, which requests
media streams.
</t>
<t>
The MP first advertises the media captures and associated encodings to the MC, as well as
possible simultaneity constraints. The description of such telepresence features is made
according to the information defined in the CLUE framework and data model
(<xref target="I-D.ietf-clue-framework"/> and <xref target="I-D.ietf-clue-data-model-schema"/>).
The CLUE message conveing the MP's multimedia offer is the ADVERTISEMENT
message. Such message leverages the XML definitions provided in
<xref target="I-D.ietf-clue-data-model-schema"/> for the description of
media captures, encodings, and simultaneity constraints features.
</t>
<t>
The MC selects the desired streams coming from the MP by using the CONFIGURE message,
which makes reference to the information carried in the ADVERTISEMENT previously received by the
MP.
</t>
<t>
In the following, a bird's-eye view of the CLUE protocol messages is provided.
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 ADVERTISEMENT
and CONFIGURE, new messages have been conceived in order to provide all the mechanisms
and operations envisaged
in <xref target="I-D.kyzivat-clue-signaling"/>.
</t>
<t>
<list style="symbols">
<t>ADVERTISEMENT (ADV)</t>
<t>CONFIGURE (CONF)</t>
<t>RESPONSE </t>
<t>RE-ADV</t>
<t>OPTIONS</t>
</list>
</t>
<section title="ADVERTISEMENT" label="subsec-adv">
<t>
<figure>
<artwork>
<![CDATA[
+---------- ---+-----------------------------------------------------+
| | |
| 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 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. |
+--------------+-----------------------------------------------------+
]]>
</artwork>
</figure>
</t>
<t>
The ADV message is considered a notification since, during the session,
it can be sent from the MP also on a per-event basis,
i.e. when the CLUE capabilities of the MP change with respect to the last
issued ADV.
It is still to be discussed if a "delta" mechanism for advertising only the changes
with respect to the previous notification should be adopted.
Similar approaches have been proposed for partial notifications in centralized conferencing
frameworks (<xref target="RFC6502"/>),
leveraging the XML diff codification mechanism defined in <xref target="RFC5261"/>.
</t>
</section>
<section title="CONFIGURE" label="sec-conf">
<t>
<figure>
<artwork>
<![CDATA[
+--------------+-----------------------------------------------------+
| | |
| FROM | MC |
| | |
+--------------+-----------------------------------------------------+
| | |
| TO | MP |
| | |
+--------------+-----------------------------------------------------+
| | |
| TYPE | Request |
| | |
+--------------+-----------------------------------------------------+
| | |
| DESCRIPTION | This message allows a MC to ask 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 from the MP. |
+--------------+-----------------------------------------------------+ ]]>
</artwork>
</figure>
</t>
</section>
<section title="RESPONSE" label="sec-resp">
<t>
<figure>
<artwork>
<![CDATA[
+--------------+-----------------------------------------------------+
| | |
| 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 either the success |
| | or the failure (along with failure details) of |
| | a CONF request elaboration. Example response |
| | codes and strings are provided in the following |
| | table. |
| | |
+--------------+-----------------------------------------------------+
| | |
| USAGE | The MP sends this message in response to a CONF |
| | message. |
+--------------+-----------------------------------------------------+
]]>
</artwork>
</figure>
</t>
<t>
Response codes can be designed by adhering to the HTTP semantics, as shown below.
</t>
<t>
<figure>
<artwork>
<![CDATA[
+-----------------+----------------------+--------------------------+
| | | |
| 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. |
+-----------------+----------------------+--------------------------+
]]>
</artwork>
</figure>
</t>
<t>... TBC.</t>
<t>
<figure>
<artwork>
<![CDATA[
+---------------+------------------------+
| | |
| Response code | Rescription |
| family | |
+---------------+------------------------+
| | |
| 1XX | Temporary info |
| | |
+---------------+------------------------+
| | |
| 2XX | Success |
| | |
+---------------+------------------------+
| | |
| 3XX | Redirection |
| | |
+---------------+------------------------+
| | |
| 4XX | Client error |
| | |
+---------------+------------------------+
| | |
| 5XX | Server error |
| | |
+---------------+------------------------+
]]>
</artwork>
</figure>
</t>
</section>
<section title="RE-ADV" label="sec-readv">
<t>
<figure>
<artwork>
<![CDATA[
+---------- ---+-----------------------------------------------------+
| | |
| FROM | MC |
| | |
+--------------+-----------------------------------------------------+
| | |
| TO | MP |
| | |
+--------------+-----------------------------------------------------+
| | |
| TYPE | Request |
| | |
+--------------+-----------------------------------------------------+
| | |
| DESCRIPTION | This message allows a MC to request a MP to |
| | issue 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) |
| | |
+--------------+-----------------------------------------------------+ ]]>
</artwork>
</figure>
</t>
</section>
<section title="OPTIONS" label="sec-opt-msg">
<t>
ToDo. See <xref target="sec-opt"/>.
</t>
</section>
</section>
<section title="Protocol state machines" anchor="sec-sm">
<t> 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 <xref target="I-D.kyzivat-clue-signaling"/>.
Over such a channel there are typically two CLUE streams between the
channel terminations flowing in opposite directions.
In other words, typically, both channel terminations act simultaneously
as a MP and as a MC.
We herein discuss the state machines associated, respectively, with the MC process and
with the MP process.
</t>
</section>
<section title="Media Consumer's state machine" anchor="sec-mc">
<t>
An MC in the IDLE state is waiting for an ADV coming from the MP.
If the timeout expires ("timeout"), the MC switches to the TIMEOUT state.</t>
<t>
In the TIMEOUT state, if the number of trials is below the retry threshold,
the MC sends a RE-ADV/refresh message to the MP ("send RE-ADV"), switching back
to the IDLE state. Otherwise, the MC moves to the TERMINATED state.
</t>
<t>
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. In this way, the MC
switches 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 towards the MP
("send CONF") and switches to the TRYING state.
</t>
<t>
While in the TRYING state, the MC is waiting for a RESPONSE message (to the issued CONF)
from the MP. 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 moves 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 into the IN CALL
state.
If a new ADV arrives in the meanwhile, it is ignored. Indeed, as soon as the timeout
expires, the MC switches to the TIMEOUT state and then sends a RE-ADV to the MP.
</t>
<t>
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 the MP and the MC have agreed on (and are aware of) the media streams
to be exchanged within the call.
If the MC decides to change something in the call settings,
it issues a new CONF ("send CONF") and moves back to the TRYING state.
If a new ADV arrives from the MP ("receive ADV"), it means that something has
changed on the MP's side. The MC then moves to the ADV-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.
</t>
<t>
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.
</t>
<t>
<figure>
<artwork>
<![CDATA[
+-----+
+--------+-------------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 +------+ |
| +--+---+ |
| | |
| | |
| | |
| | |
| connection |
| closed |
| | |
| | |
| | |
| | |
| | |
| v |
| +----------+<---------------------------------+
+----------->+TERMINATED|
+----------+
]]>
</artwork>
</figure>
</t>
</section>
<section title="Media Provider's state machine" anchor="sec-mp">
<t>
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.
</t>
<t>
When in the WAIT FOR CONF state, the MP is listening to the channel for a CONF
coming from the MC.
If a RE-ADV is received, the MP goes back to the IDLE state and issues an ADV
again.
If telepresence settings change in the meanwhile,
it moves back to the IDLE state too, and prepares a new ADV to be sent
to the MC.
If a CONF arrives, the MP switches to the CONF RECEIVED state.
If nothing happens and the timeout expires, than the MC falls into
the TIMEOUT state.
</t>
<t>
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.
</t>
<t>
The MP in the CONF RECEIVED state is processing the received CONF in order to
produce a RESPONSE message.
If the MP is fine with the MC's configuration, then it sends back a 200 OK
successful RESPONSE and moves to the IN CALL state.
If there are errors duting CONF processing, 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.
</t>
<t>
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 request.
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.
</t>
<t>
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.
</t>
<t>
<figure>
<artwork>
<![CDATA[
+------------------->+-----+-+<----------------------------+
| +--------------->| 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 |
| | |
| | |
| | |
| | |
connection | |
closed | |
| | |
| | |
v | |
+------------+<-----+-----------------------------+
| TERMINATED | |
+------------+<-----+
]]>
</artwork>
</figure>
</t>
</section>
<section title="About CLUE protocol XML schema versioning"
anchor="sec-vers">
<t>
CLUE protocol messages are XML messages compliant to the CLUE protocol XML schema.
The version of the protocol corresponds to the version of the schema.
Both client and server have to test the compliance of the received messages with
the XML schema of the CLUE protocol.
If the compliance is not verified, the message cannot be processed.
</t>
<t>
Obviously, client and server can not communicate if they do not share exactly the same XML schema.
Such a schema is the one included in the yet to come RFC,
and associated with the CLUE URN "urn:ietf:params:xml:ns:clue-message".
If all CLUE-enabled devices use that schema
there will be no interoperability problems due to schema issues.
</t>
<t>The version of the XML schema contained in the standard document deriving
from this draft will be 1.0.
The subsequet versions of the XML schema should be backward compatible.
This means that they should define further features and functionality besides those
defined in the previous versions, in an incremental way, without impacting the
basic rules defined in the previous version of the schema.
In this way, if a MP is able to speak, e.g., version 5.0 of the protocol while the
MC only understands version 4.0, the MP should have no problem in reverting the dialogue to version 4.0
without exploiting 5.0 features and functionality.
</t>
<t>
It is expected that, before the CLUE protocol XML schema reaches a steady state,
prototypes developed by different organizations will conduct interoperability testing.
In that case, in order to interoperate, they have to be compliant to the
current version of the XML schema, i.e., the one copied in the most up-to-date
version of the draft defining the CLUE protocol.
The versions of the non-standard XML schema will be numbered as 0.01, 0.02, and so on.
During the standard development phase, the versions of the XML schema will probably not be
backward compatible so it is left to prototype implementers the responsibility of keeping their products
up to date.
</t>
<t>
Even though strongly discouraged, if a future version of the protocol
is designed which breaks the backward compatibility constraint, this ascpect MUST
be explicitely advertised in the corresponding new RFC document. In such a case, it would
up to developers to update their systems accordingly.
</t>
</section>
<section title="Extensibility issues"
anchor="sec-ext">
<t>
Although the standard version of the CLUE protocol XML schema will be designed
to thoroughly cope with the requirements emerging from the application domain,
new needs might arise in the future. Such needs may relate to two main aspects of the protocol:
</t>
<t>
<list>
<t>
the information carried in the existing messages
(for example, we may want to add more fields within an existing message);
</t>
<t>
the meaning of the messages.
This is the case if there is no proper message for a certain task,
so a brand new CLUE message needs to be defined.
</t>
</list>
</t>
<section title="Aspect 1 - new information within existing messages">
<t>
CLUE messages are envelopes carrying two types of information:
</t>
<t>
<list>
<t> XML elements defined within the CLUE protocol XML schema itself
(protocol-specific information)</t>
<t> other XML elements compliant to the CLUE data model schema
(data model information)</t>
</list>
</t>
<t>
When new protocol-specific information is needed somewhere in the protocol
messages, it can be added in place of the <any> elements and
<anyAttribute> elements envisioned by the protocol schema.
The policy currently defined in the protocol schema for handling
<any> and <anyAttribute> elements is:
</t>
<t>
<list>
<t> elementFormDefault="qualified"</t>
<t> attributeFormDefault="unqualified"</t>
</list>
</t>
<t>
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.
</t>
<t>
The other matter concerns data model information.
Data model information is defined by the XML schema associated
with the URN "urn:ietf:params:xml:ns:clue-info".
Also for the XML elements defined in such a schema there are extensibility issues.
Those issues are overcome by using <any> and <anyAttribute>
placeholders.
Similarly to what said before, new information within data model elements can be added in place
of <any> and <anyAttribute> schema elements, as long as they are properly namespace qualified.
If brand new data model elements are needed, then there are three options:
</t>
<t>
<list style="numbers">
<t> writing 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.</t>
<t> putting 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.</t>
<t> designing a wildcard envelope for future data model elements.</t>
</list>
</t>
</section>
<section title="Aspect 2 - new messages">
<t>New CLUE protocol messages, not envisioned in the standard version of the schema, are needed.
Also in that case we have three chances:
</t>
<t>
<list>
<t>
writing 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.
</t>
<t>
putting 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.
[Editors' note: we strongly dislike this option!!]
</t>
<t>
designing a wildcard envelope for future messages.
This is an approach used also within the CCMP protocol
(Centralized Conferencing Manipulation Protocol, <xref target="RFC6503"/>). In that case, a mechanism for the extension negotiation is also envisioned.
</t>
</list>
</t>
</section>
</section>
<section title="Managing protocol version negotiation and extensions: the OPTIONS request" anchor="sec-opt">
<t>In this section we provide a mechanism for handling protocol extension matters
as those pointed out in the previous section, as well as version negotiation issues.
</t>
<t>We propose a new request message issued by the MC to the MP as soon as the
CLUE channel is instatiated: the OPTIONS request. This message carries:</t>
<t>
<list>
<t>the CLUE protocol version spoken by the MC</t>
<t>the data model extensions supported by the MC</t>
<t>the protocol extensions supported by the MC</t>
</list>
</t>
<t>
When the MP receives the OPTIONS message, it reads the CLUE protocol version of the MC
(the highest protocol version of the MC).
If the MC's version is higher than the MP's one, then the MP responds to the MC
by using in the RESPONSE message its version. The MC has to downgrade the CLUE dialogue
to the version specified by the MP in the subsequent CLUE messages.
If the MC's version is equal to (case i) or lower than (case ii) the MP version, then the MP will
use in the RESPONSE message the same version as the one in hthe OPTIONS message and all
subsequent CLUE messages must carry that version number. In the (ii) case,
it is the MP who has to to downgrade the CLUE dialogue in order to be understood by the MC.
</t>
<t>
A data model extension is a set of XML definitions related to the description of
telepresence capabilities that is contained in an XML schema and which
is different from the normative CLUE data model schema.
Such XML definitions can represent further entities not envisioned in the CLUE
framework at the time of writing of the data model draft.
The entities defined in a data model extension can appear in place of the
<any> and <anyAttribute> elements included in the data model document.
A data model extension is then represented by a reference to the defining XML schema.
The schema reference is represented by a URI defining the schema location. [TBC]
If a data model extension is supported by both a MP and a MC, it means that
both are aware of the associated XML schema and of the meanings of the
elements defined within it.
</t>
<t>
A protocol extension is a set of XML definitions related to the CLUE protocol
that is contained in an XML schema which
is different from the normative CLUE protocol schema.
Such definitions can represent: (i) information to be carried within the
existing messages in place of <any> and <anyAttribute> elements;
(ii) new messages designed for the CLUE telepresence control.
Such XML definitions refer to information not envisioned during the CLUE protocol
design phase.
A protocol extension is then represented by a reference to the defining XML schema.
If a protocol extension is supported by both a MP and a MC, it means that
both are aware of the associated XML schema and of the meanings of the
elements defined within it.
</t>
<t>
When the MP receives the MC's OPTIONS message, it selects the data model extensions
and the protocol extensions that it is able to support, and then provides them into
the RESPONSE message back to the MC.
Only the extensions included in the RESPONSE message can be used during the
telepresence session.
</t>
<t>The XML schema definition of the OPTIONS message is provided in the
following.</t>
<t>
<figure>
<artwork>
<![CDATA[
<!-- CLUE OPTIONS REQUEST -->
<xs:complexType name="optionsMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- optional fields -->
<xs:element ref="options" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE OPTIONS -->
<xs:element name="options" type="optionsType"/>
<xs:complexType name="optionsType">
<xs:sequence>
<xs:element name="dm-exts" type="schemaRefList" minOccurs="0" maxOccurs="1"/>
<xs:element name="protocol-exts" type="schemaRefList" minOccurs="0"
maxOccurs="1"/>
</xs:sequence>
</xs:complexType>
<!-- SCHEMA REF LIST TYPE -->
<xs:complexType name="schemaRefList">
<sequence>
<element name="schemaRef" type="xs:anyURI" maxOccurs="unbounded"/>
</sequence>
</xs:complexType>
]]>
</artwork>
</figure>
</t>
<section title="An example using OPTIONS">
<t>An example of OPTIONS dialogue is provided in the following.</t>
<t>
<figure>
<artwork>
<![CDATA[
+------+ +------+
| MP | | MC |
| | | |
+--+---+ +--+---+
| |
| OPTIONS 3.0 |
| dm-ext: s1, s2, s3 |
| pr-ext: s4, s5 |
|<--------------------+|
| |
| RESPONSE 1.0 |
| dm-ext: s1 |
| pr-ext: - |
|+-------------------->|
| |
| |
| ADV 1.0 |
|+-------------------->|
| |
| CONFIGURE 1.0 |
|<--------------------+|
| |
| |
v v
]]>
</artwork>
</figure>
</t>
<t>When the CLUE channel is ready, the MC issues an OPTIONS request to
the MP. The MC uses the 3.0 version of the CLUE protocol, and supports
schemas s1, s2, s3 as data model extensions and schemas s4, s5 as protocol
extensions.</t>
<t>The MP speaks the 1.0 version of the CLUE protocol and supports only the first
data model extension among those indicated by the MC. It then issues
a v. 1.0 RESPONSE to the MC copying only the supported option. The MC
is able to understand that it can use only the 1.0 version of the protocol and
the s1 extension.</t>
</section>
</section>
<section title="XML Schema of CLUE protocol messages" anchor="sec-schema">
<t>
In this section we paste the XML schema defining the ADVERTISEMENT, CONFIGURE
and RESPONSE messages contained in <xref target="I-D.kyzivat-clue-signaling"/>.
At the time of writing, it assumes that encodings are described
in SDP as m-lines with a text identifier, and that the identifier has
the same value as the encodingIDs embedded in the <encodingGroups>.
However, that assumption is still under discussion in the context of
the CLUE-SDP coupling issues.
</t>
<t>
<figure>
<artwork>
<![CDATA[
<?xml version="1.0" encoding="UTF-8" ?>
<xs:schema
version="0.02"
targetNamespace="urn:ietf:params:xml:ns:clue-message"
xmlns:tns="urn:ietf:params:xml:ns:clue-message"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
xmlns:dm="urn:ietf:params:xml:ns:clue-info"
xmlns="urn:ietf:params:xml:ns:clue-message"
elementFormDefault="qualified"
attributeFormDefault="unqualified">
<!-- Import data model schema -->
<xs:import namespace="urn:ietf:params:xml:ns:clue-info"
schemaLocation="clue-data-model-01.xsd"/>
<!-- ELEMENT DEFINITIONS -->
<xs:element name="response" type="responseMessageType"/>
<xs:element name="advertisement" type="advertisementMessageType"/>
<xs:element name="configure" type="configureMessageType"/>
<xs:element name="readv" type="readvMessageType"/>
<xs:element name="options" type="optionsMessageType"/>
<!-- CLUE MESSAGE TYPE -->
<xs:complexType name="clueMessageType" abstract="true">
<xs:sequence>
<!-- mandatory fields -->
<!-- TBS: version info -->
</xs:sequence>
</xs:complexType>
<!-- CLUE REQUEST MESSAGE TYPE -->
<xs:complexType name="clueRequestMessageType" abstract="true">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="requestNumber" type="xs:integer"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE OPTIONS REQUEST -->
<xs:complexType name="optionsMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- optional fields -->
<xs:element ref="options" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE OPTIONS -->
<xs:element name="options" type="optionsType"/>
<xs:complexType name="optionsType">
<xs:sequence>
<xs:element name="dm-exts" type="schemaRefList" minOccurs="0" maxOccurs="1"/>
<xs:element name="protocol-exts" type="schemaRefList" minOccurs="0"
maxOccurs="1"/>
</xs:sequence>
</xs:complexType>
<!-- SCHEMA REF LIST TYPE -->
<xs:complexType name="schemaRefList">
<sequence>
<element name="schemaRef" type="xs:anyURI" maxOccurs="unbounded"/>
</sequence>
</xs:complexType>
<!-- CLUE NOTIFICATION MESSAGE TYPE -->
<xs:complexType name="clueNotificationMessageType" abstract="true">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory fields -->
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE RESPONSE MESSAGE TYPE -->
<xs:complexType name="clueResponseMessageType">
<xs:complexContent>
<xs:extension base="clueMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="requestNumber" type="xs:integer"/>
<xs:element name="reason" type="reasonType" minOccurs="1"/>
<!-- optional fields -->
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- RESPONSE MESSAGE TYPE -->
<xs:complexType name="responseMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- mandatory fields -->
<!-- TBD. -->
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE ADVERTISEMENT MESSAGE TYPE -->
<xs:complexType name="advertisementMessageType">
<xs:complexContent>
<xs:extension base="clueNotificationMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="advNumber" type="xs:unsignedInt"/>
<xs:element name="mediaCaptures"
type="dm:mediaCapturesType"/>
<xs:element name="encodingGroups"
type="dm:encodingGroupsType"/>
<!-- The encodings are defined via identifiers in the SDP,
referenced in encodingGroups -->
<xs:element name="captureScenes"
type="dm:captureScenesType"/>
<!-- optional fields -->
<xs:element name="simultaneousSets"
type="dm:simultaneousSetsType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- CLUE CONFIGURE MESSAGE TYPE -->
<xs:complexType name="configureMessageType">
<xs:complexContent>
<xs:extension base="clueRequestMessageType">
<xs:sequence>
<!-- mandatory fields -->
<xs:element name="advNumber" type="xs:unsignedInt"/>
<!-- optional fields -->
<xs:element name="captureEncodings"
type="dm:captureEncodingsType" minOccurs="0"/>
<xs:any namespace="##other"
processContents="lax" minOccurs="0"/>
</xs:sequence>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<!-- REASON TYPE -->
<xs:complexType name="reasonType">
<xs:simpleContent>
<xs:extension base="xs:string">
<xs:attribute type="xs:short" name="code" use="required"/>
</xs:extension>
</xs:simpleContent>
</xs:complexType>
</xs:schema>
]]>
</artwork>
</figure>
</t>
</section>
<section title="Examples"><t>TBD</t></section>
<section title="Handling channel errors"><t>TBD</t></section>
<section title="Diff with the -01 version">
<t>
<list>
<t>XML Schema moved here from <xref target="I-D.kyzivat-clue-signaling"/></t>
<t>advNumber introduced to couple a configure with an advertisement message</t>
<t>added introductory text</t>
<t>added a version and extension negotiation proposal</t>
</list>
</t>
</section>
<section title="Diff with -00 version">
<t>
<list>
<t>
MC and MP state diagrams have been updated for discussion in
http://www.ietf.org/mail-archive/web/clue/current/msg02650.html
</t>
<t>
Consideration about protocol extension and versioning have been added to foster
discussion.
</t>
</list>
</t>
</section>
</middle>
<back>
<references title="Informative References">
<!-- clue framework -->
<?rfc include="reference.I-D.ietf-clue-framework"?>
<!-- clue signaling -->
<?rfc include="reference.I-D.kyzivat-clue-signaling"?>
<!-- clue requirements -->
<?rfc include="reference.I-D.ietf-clue-telepresence-requirements"?>
<!-- clue data model -->
<?rfc include="reference.I-D.ietf-clue-data-model-schema"?>
<!-- RFC6503 -->
<?rfc include="reference.RFC.6503"?>
<!-- RFC6502 -->
<?rfc include="reference.RFC.6502"?>
<!-- RFC5261 -->
<?rfc include="reference.RFC.5261"?>
</references>
</back>
</rfc>| PAFTECH AB 2003-2026 | 2026-04-24 04:07:25 |