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 working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 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 Presta & Romano Expires April 11, 2014 [Page 1] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 Presta & Romano Expires April 11, 2014 [Page 2] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 Presta & Romano Expires April 11, 2014 [Page 3] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 Presta & Romano Expires April 11, 2014 [Page 4] Internet-Draft draft-presta-clue-protocol-02 October 2013 +---------- ---+-----------------------------------------------------+ | | | | 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 Presta & Romano Expires April 11, 2014 [Page 5] Internet-Draft draft-presta-clue-protocol-02 October 2013 +--------------+-----------------------------------------------------+ | | | | 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 Presta & Romano Expires April 11, 2014 [Page 6] Internet-Draft draft-presta-clue-protocol-02 October 2013 +--------------+-----------------------------------------------------+ | | | | 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. Presta & Romano Expires April 11, 2014 [Page 7] Internet-Draft draft-presta-clue-protocol-02 October 2013 +-----------------+----------------------+--------------------------+ | | | | | 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. Presta & Romano Expires April 11, 2014 [Page 8] Internet-Draft draft-presta-clue-protocol-02 October 2013 +---------------+------------------------+ | | | | Response code | Rescription | | family | | +---------------+------------------------+ | | | | 1XX | Temporary info | | | | +---------------+------------------------+ | | | | 2XX | Success | | | | +---------------+------------------------+ | | | | 3XX | Redirection | | | | +---------------+------------------------+ | | | | 4XX | Client error | | | | +---------------+------------------------+ | | | | 5XX | Server error | | | | +---------------+------------------------+ 3.4. RE-ADV Presta & Romano Expires April 11, 2014 [Page 9] Internet-Draft draft-presta-clue-protocol-02 October 2013 +---------- ---+-----------------------------------------------------+ | | | | 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. Presta & Romano Expires April 11, 2014 [Page 10] Internet-Draft draft-presta-clue-protocol-02 October 2013 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. Presta & Romano Expires April 11, 2014 [Page 11] Internet-Draft draft-presta-clue-protocol-02 October 2013 +-----+ +--------+-------------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 | | | | | | | | | | | | | Presta & Romano Expires April 11, 2014 [Page 12] Internet-Draft draft-presta-clue-protocol-02 October 2013 | | | | 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. Presta & Romano Expires April 11, 2014 [Page 13] Internet-Draft draft-presta-clue-protocol-02 October 2013 +------------------->+-----+-+<----------------------------+ | +--------------->| 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 | | +------------+<-----+-----------------------------+ Presta & Romano Expires April 11, 2014 [Page 14] Internet-Draft draft-presta-clue-protocol-02 October 2013 | 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. Presta & Romano Expires April 11, 2014 [Page 15] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 elements and elements envisioned by the protocol schema. The policy currently defined in the protocol schema for handling and 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 and placeholders. Similarly to what said before, new information within data model elements can be added in place of and schema elements, as long as they are properly namespace qualified. If brand new data model elements are needed, then there are three options: Presta & Romano Expires April 11, 2014 [Page 16] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 Presta & Romano Expires April 11, 2014 [Page 17] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 and 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 and 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. Presta & Romano Expires April 11, 2014 [Page 18] Internet-Draft draft-presta-clue-protocol-02 October 2013 9.1. An example using OPTIONS An example of OPTIONS dialogue is provided in the following. Presta & Romano Expires April 11, 2014 [Page 19] Internet-Draft draft-presta-clue-protocol-02 October 2013 +------+ +------+ | 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 . However, that assumption is still under discussion in the context of the CLUE-SDP coupling issues. Presta & Romano Expires April 11, 2014 [Page 20] Internet-Draft draft-presta-clue-protocol-02 October 2013 Presta & Romano Expires April 11, 2014 [Page 21] Internet-Draft draft-presta-clue-protocol-02 October 2013 Presta & Romano Expires April 11, 2014 [Page 23] Internet-Draft draft-presta-clue-protocol-02 October 2013 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 Presta & Romano Expires April 11, 2014 [Page 24] Internet-Draft draft-presta-clue-protocol-02 October 2013 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. Presta & Romano Expires April 11, 2014 [Page 25] Internet-Draft draft-presta-clue-protocol-02 October 2013 [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 Presta & Romano Expires April 11, 2014 [Page 26]