CLUE protocol
draft-presta-clue-protocol-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Authors | Roberta Presta , Simon Pietro Romano | ||
| Last updated | 2013-10-08 | ||
| Replaced by | draft-ietf-clue-protocol, draft-ietf-clue-protocol, RFC 8847 | ||
| RFC stream | (None) | ||
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| Additional resources | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-presta-clue-protocol-02
CLUE Working Group R. Presta
Internet-Draft S P. Romano
Intended status: Informational University of Napoli
Expires: April 11, 2014 October 8, 2013
CLUE protocol
draft-presta-clue-protocol-02
Abstract
The CLUE protocol is an application protocol conceived for the
description and negotiation of a CLUE telepresence session. The
design of the CLUE protocol takes into account the requirements and
the framework defined, respectively, in [I-D.ietf-clue-framework] and
[I-D.ietf-clue-telepresence-requirements]. The companion document
[I-D.kyzivat-clue-signaling] delves into CLUE signaling details, as
well as on the SIP/SDP session establishment phase. 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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 11, 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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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of the CLUE protocol messages . . . . . . . . . . . . 3
3.1. ADVERTISEMENT . . . . . . . . . . . . . . . . . . . . . . 4
3.2. CONFIGURE . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. RESPONSE . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. RE-ADV . . . . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. OPTIONS . . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Protocol state machines . . . . . . . . . . . . . . . . . . . 10
5. Media Consumer's state machine . . . . . . . . . . . . . . . . 11
6. Media Provider's state machine . . . . . . . . . . . . . . . . 13
7. About CLUE protocol XML schema versioning . . . . . . . . . . 15
8. Extensibility issues . . . . . . . . . . . . . . . . . . . . . 16
8.1. Aspect 1 - new information within existing messages . . . 16
8.2. Aspect 2 - new messages . . . . . . . . . . . . . . . . . 17
9. Managing protocol version negotiation and extensions: the
OPTIONS request . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. An example using OPTIONS . . . . . . . . . . . . . . . . . 19
10. XML Schema of CLUE protocol messages . . . . . . . . . . . . . 20
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
12. Handling channel errors . . . . . . . . . . . . . . . . . . . 24
13. Diff with the -01 version . . . . . . . . . . . . . . . . . . 24
14. Diff with -00 version . . . . . . . . . . . . . . . . . . . . 25
15. Informative References . . . . . . . . . . . . . . . . . . . . 25
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1. Introduction
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:
1. enabling a MP to fully announce its current telepresence
capabilities to the MC in terms of available media captures,
encodings, and simultaneity constraints;
2. enabling a MC to request the desired multimedia streams from the
offering MP.
CLUE protocol messages flow upon a DTLS/SCTP/UDP channel established
as depicted in [I-D.kyzivat-clue-signaling]. While
[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 [I-D.ietf-clue-framework].
In Section 3 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 Section 4 and further described
in Section 5 and Section 6 respectively. Versioning, extensions and
options management mechanisms are discussed in Section 7, Section 8
and Section 9, respectively. The XML schema defining the CLUE
messages is reported in Section 10.
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
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.
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
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information defined in the CLUE framework and data model
([I-D.ietf-clue-framework] and [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 [I-D.ietf-clue-data-model-schema] for the description of
media captures, encodings, and simultaneity constraints features.
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.
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 [I-D.kyzivat-clue-signaling].
o ADVERTISEMENT (ADV)
o CONFIGURE (CONF)
o RESPONSE
o RE-ADV
o OPTIONS
3.1. ADVERTISEMENT
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+---------- ---+-----------------------------------------------------+
| | |
| 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. |
+--------------+-----------------------------------------------------+
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 ([RFC6502]), leveraging the XML diff codification
mechanism defined in [RFC5261].
3.2. CONFIGURE
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+--------------+-----------------------------------------------------+
| | |
| 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. |
+--------------+-----------------------------------------------------+
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 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. |
+--------------+-----------------------------------------------------+
Response codes can be designed by adhering to the HTTP semantics, as
shown below.
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+-----------------+----------------------+--------------------------+
| | | |
| Response code | Response string | Description |
| | | |
+-----------------+----------------------+--------------------------+
| | | |
| 410 | Bad syntax | The XML syntax of the |
| | | CONF message is not |
| | | correct. |
+-----------------+----------------------+--------------------------+
| | | |
| 411 | Invalid value | The CONF message |
| | | contains an invalid |
| | | parameter value. |
+-----------------+----------------------+--------------------------+
| | | |
| 412 | Invalid identifier | The identifier used for |
| | | requesting a capture is |
| | | not valid or unknown. |
+-----------------+----------------------+--------------------------+
| | | |
| 413 | Conflicting values | The CONF message |
| | | contains values that |
| | | cannot be used together.|
+-----------------+----------------------+--------------------------+
| | | |
| 420 | Invalid sequencing | The sequence number of |
| | | the CONF message is out |
| | | of date or corresponds |
| | | to an obsoleted ADV. |
+-----------------+----------------------+--------------------------+
| | | |
| 510 | Version not supported| The CLUE protocol |
| | | version of the CONF |
| | | message is not supported|
| | | by the MP. |
+-----------------+----------------------+--------------------------+
| | | |
| 511 | Option not supported | The option requested in |
| | | the CONF message is not |
| | | supported by the MP. |
+-----------------+----------------------+--------------------------+
... TBC.
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+---------------+------------------------+
| | |
| Response code | 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 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) |
| | |
+--------------+-----------------------------------------------------+
3.5. OPTIONS
ToDo. See Section 9.
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, respectively, with the MC
process and with the MP 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 switches to the TIMEOUT
state.
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.
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.
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.
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.
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.
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+-----+
+--------+-------------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 |
| | |
| | |
| | |
| | |
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| | |
| 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 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.
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 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.
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.
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.
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+------------------->+-----+-+<----------------------------+
| +--------------->| 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 | |
+------------+<-----+-----------------------------+
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| TERMINATED | |
+------------+<-----+
7. About CLUE protocol XML schema versioning
CLUE protocol messages are XML messages compliant to the CLUE
protocol XML schema. The version of the protocol corresponds to the
version of the schema. Both client and server have to test the
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 a schema is the one included in
the yet to come RFC, and associated with the CLUE URN
"urn:ietf:params:xml:ns:clue-message". If all CLUE-enabled devices
use that schema there will be no interoperability problems due to
schema issues.
The version of the XML schema contained in the standard document
deriving from this draft will be 1.0. The 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.
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.
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.
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8. Extensibility issues
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:
the information carried in the existing messages (for example, we
may want to add more fields within an existing message);
the meaning of the messages. This is the case if there is no
proper message for a certain task, so a brand new CLUE message
needs to be defined.
8.1. 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 is needed somewhere in the
protocol messages, it can be added in place of the <any> elements and
<anyAttribute> elements envisioned by the protocol schema. The
policy currently defined in the protocol schema for handling <any>
and <anyAttribute> elements is:
elementFormDefault="qualified"
attributeFormDefault="unqualified"
In that case, the new information must be qualified by namespaces
other than "urn:ietf:params:xml:ns:clue-message" (the protocol URN)
and "urn:ietf:params:xml:ns:clue-info" (the data model URN).
Elements or attributes from unknown namespaces MUST be ignored.
The other matter concerns data model information. Data model
information is defined by the XML schema associated with the URN
"urn:ietf:params:xml:ns:clue-info". Also for the XML elements
defined in such a schema there are extensibility issues. Those
issues are overcome by using <any> and <anyAttribute> placeholders.
Similarly to what said before, new information within data model
elements can be added in place of <any> and <anyAttribute> schema
elements, as long as they are properly namespace qualified. If brand
new data model elements are needed, then there are three options:
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1. 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.
2. 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.
3. designing a wildcard envelope for future data model elements.
8.2. 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:
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.
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!!]
designing 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.
9. Managing protocol version negotiation and extensions: the OPTIONS
request
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.
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:
the CLUE protocol version spoken by the MC
the data model extensions supported by the MC
the protocol extensions supported by the MC
When the MP receives the OPTIONS message, it reads the CLUE protocol
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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.
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.
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.
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.
The XML schema definition of the OPTIONS message is provided in the
following.
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<!-- 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>
9.1. An example using OPTIONS
An example of OPTIONS dialogue is provided in the following.
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+------+ +------+
| 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
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.
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.
10. XML Schema of CLUE protocol messages
In this section we paste the XML schema defining the ADVERTISEMENT,
CONFIGURE and RESPONSE messages contained in
[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.
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<?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 -->
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<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"
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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>
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<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>
11. Examples
TBD
12. Handling channel errors
TBD
13. Diff with the -01 version
XML Schema moved here from [I-D.kyzivat-clue-signaling]
advNumber introduced to couple a configure with an advertisement
message
added introductory text
added a version and extension negotiation proposal
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14. 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.
15. Informative References
[I-D.ietf-clue-data-model-schema] Presta, R. and S. Romano,
"An XML Schema for the
CLUE data model", draft-
ietf-clue-data-model-
schema-00 (work in
progress), July 2013.
[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.ietf-clue-telepresence-requirements] Romanow, A., Botzko, S.,
and M. Barnes,
"Requirements for
Telepresence Multi-
Streams", draft-ietf-clue-
telepresence-requirements-
05 (work in progress),
August 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.
[RFC5261] Urpalainen, J., "An
Extensible Markup Language
(XML) Patch Operations
Framework Utilizing XML
Path Language (XPath)
Selectors", RFC 5261,
September 2008.
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[RFC6502] Camarillo, G., Srinivasan,
S., Even, R., and J.
Urpalainen, "Conference
Event Package Data Format
Extension for Centralized
Conferencing (XCON)",
RFC 6502, March 2012.
[RFC6503] Barnes, M., Boulton, C.,
Romano, S., and H.
Schulzrinne, "Centralized
Conferencing Manipulation
Protocol", RFC 6503,
March 2012.
Authors' Addresses
Roberta Presta
University of Napoli
Via Claudio 21
Napoli 80125
Italy
EMail: roberta.presta@unina.it
Simon Pietro Romano
University of Napoli
Via Claudio 21
Napoli 80125
Italy
EMail: spromano@unina.it
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