Network Working Group                                       T. Melanchuk
Internet-Draft                                         November 12, 2005
Expires: May 16, 2006


                 Media Sessions Markup Language (MSML)
                    draft-melanchuk-sipping-msml-07

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   This Internet-Draft will expire on May 16, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   The Media Sessions Markup Language (MSML) is used to control and
   invoke many different types of services on IP media servers.  Clients
   can use it define how multimedia sessions interact on a media server
   and to apply services to individual or groups of users.  MSML can be
   used, for example, to control media server conferencing features such
   as video layout and audio mixing, create sidebar conferences or
   personal mixes, and set the properties of media streams.  As well,
   clients can use MSML with other languages such as VoiceXML to
   interact with individual users or with groups of conference



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   participants.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  MSML SIP Usage . . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Language Structure . . . . . . . . . . . . . . . . . . . . . .  8
     5.1.  Execution Flow . . . . . . . . . . . . . . . . . . . . . .  8
     5.2.  MSML Root Element  . . . . . . . . . . . . . . . . . . . .  9
     5.3.  Sending Events to a Media Server . . . . . . . . . . . . . 10
       5.3.1.  <send> . . . . . . . . . . . . . . . . . . . . . . . . 10
     5.4.  Transaction Results and Notifications  . . . . . . . . . . 10
       5.4.1.  <result> . . . . . . . . . . . . . . . . . . . . . . . 10
       5.4.2.  <event>  . . . . . . . . . . . . . . . . . . . . . . . 11
   6.  Media Server Object Model  . . . . . . . . . . . . . . . . . . 11
     6.1.  Objects  . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 13
   7.  Media Streams  . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.1.  <join> . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     7.2.  <modifystream> . . . . . . . . . . . . . . . . . . . . . . 19
     7.3.  <unjoin> . . . . . . . . . . . . . . . . . . . . . . . . . 20
     7.4.  <stream> Elements  . . . . . . . . . . . . . . . . . . . . 21
       7.4.1.  Audio Stream Properties  . . . . . . . . . . . . . . . 22
       7.4.2.  Video Stream Properties  . . . . . . . . . . . . . . . 23
     7.5.  <monitor>  . . . . . . . . . . . . . . . . . . . . . . . . 24
   8.  Conferences  . . . . . . . . . . . . . . . . . . . . . . . . . 24
     8.1.  <createconference> . . . . . . . . . . . . . . . . . . . . 25
     8.2.  <modifyconference> . . . . . . . . . . . . . . . . . . . . 27
     8.3.  <destroyconference>  . . . . . . . . . . . . . . . . . . . 28
     8.4.  Audio Mix  . . . . . . . . . . . . . . . . . . . . . . . . 29
       8.4.1.  N-Loudest  . . . . . . . . . . . . . . . . . . . . . . 29
       8.4.2.  Active Speaker Notification  . . . . . . . . . . . . . 29
     8.5.  Video Layout . . . . . . . . . . . . . . . . . . . . . . . 30
       8.5.1.  Root Window  . . . . . . . . . . . . . . . . . . . . . 30
       8.5.2.  Regions  . . . . . . . . . . . . . . . . . . . . . . . 31
       8.5.3.  Stream Selection . . . . . . . . . . . . . . . . . . . 34
     8.6.  Reserving Conference Resources . . . . . . . . . . . . . . 37
   9.  Dialogs  . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
     9.1.  <dialogstart>  . . . . . . . . . . . . . . . . . . . . . . 38
     9.2.  <dialogend>  . . . . . . . . . . . . . . . . . . . . . . . 39
   10. Response Codes . . . . . . . . . . . . . . . . . . . . . . . . 40
   11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
     11.1. Establishing a Dial-In Conference  . . . . . . . . . . . . 42
     11.2. Example of a Sidebar Audio Conference  . . . . . . . . . . 45
     11.3. Example of Removing Conference . . . . . . . . . . . . . . 47



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     11.4. Example of Modifying a Video Layout  . . . . . . . . . . . 47
   12. Change Summary . . . . . . . . . . . . . . . . . . . . . . . . 48
   13. Future Work  . . . . . . . . . . . . . . . . . . . . . . . . . 50
   14. XML Schemas  . . . . . . . . . . . . . . . . . . . . . . . . . 50
   15. Security Considerations  . . . . . . . . . . . . . . . . . . . 61
   16. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 61
   17. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 61
   18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 62
     18.1. Normative References . . . . . . . . . . . . . . . . . . . 62
     18.2. Informative References . . . . . . . . . . . . . . . . . . 62
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 64
   Intellectual Property and Copyright Statements . . . . . . . . . . 65







































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1.  Introduction

   Media servers contain dynamic pools of media resources.  Application
   servers and other users of media servers (called media server
   clients) can define and create many different services based on how
   they configure and use those resources.  Often, that configuration
   and the ways in which those resources interact will be changed
   dynamically over the course of a call, to reflect changes in the way
   that an application interacts with a user.

   For example, a call may undergo an initial IVR dialog before being
   placed into a conference.  Calls may be moved from a main conference
   to a sidebar conference and then back again.  Individual calls may be
   directly bridged to create small n-way calls or simple sidebars.
   None of these change the SIP [1] dialog or RTP [10] session.  Yet
   these do affect the media flow internal to the media server.

   The Media Sessions Markup Language (MSML) is an XML [2] language used
   to change the flow of and services on media streams within a media
   server.  It is used to invoke many different types of services on
   individual sessions, groups of sessions, and conferences.  MSML
   allows the creation of conferences, bridging different sessions
   together, and bridging sessions into conferences.

   MSML can be used to apply IVR operations and dialogs to sessions or
   conferences, and to modify the media flowing on a session.  Dialogs
   may be specified in different languages depending on application
   requirements.  VoiceXML [11] is a W3C standard that allows complete
   single-party application interfaces to be executed by a media server.
   Media servers that support MSML MUST support VoiceXML.

   A network connection is established with the media server using SIP.
   Media received and transmitted on that connection will flow through
   different media resources on the media server depending on the
   requested service.  Basic Network Media Services with SIP [13]
   defines conventions for associating a basic service with a SIP
   Request-URI.  MSML allows services to be dynamically applied and
   changed by an application server during the lifetime of the SIP
   dialog.


2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [7].





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3.  Glossary

   Media Server: a general-purpose platform for executing real-time
   media processing tasks.  It may be a single physical device or a
   logical function within a physical device.

   Media Server Client: an application residing on an external server
   which originates MSML requests to a media server.

   Object: the generic term for a media server entity that terminates,
   originates, or processes media.  This specification defines four
   classes of objects and specifies mechanisms to create them, join them
   together, and destroy them.

   Participant Object: an object in a media server that sources original
   media in a call or that receives and terminates media in a call.

   Intermediary Object: an object in a media server that acts on media
   within a call for the benefit of the participants.

   Independent Object: an object that can exist on a media server
   independent of other objects.

   Network Connection: a participant object class that represents the
   termination on a media server of one or more RTP [10] sessions (for
   example audio and video) associated with a call.  Network connections
   are established and removed using a session establishment protocol
   such as SIP.  An instance of a network connection is an independent
   object.

   Dialog: an automated participant object class.  Examples of dialogs
   may be announcement players, IVR interfaces, or voice recorders.
   Specific types of dialogs are not defined within MSML.  Dialogs may
   be defined in VoiceXML [11], or other similar languages.

   Conference: an intermediary object class that provides multimedia
   mixing and other advanced conferencing services.  This specification
   currently considers conferences with audio and/or video media types,
   but is extensible to other media types.  An instance of a conference
   is an independent object.

   Identifier: a name that is used to refer to a specific instance of an
   object on the media server.  Identifiers are composed of one or more
   terms where each term identifies an object class and instance.

   Media Stream: a single media flow between two objects.  A media
   stream has a media type and may be uni-directional or bi-directional.




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   Media Stream Collection: a set of associated media streams between
   two objects that are treated as a single logical unit.  An example of
   a media stream collection would be the audio and video streams
   between a network connection and a multimedia conference.


4.  MSML SIP Usage

   SIP is used to create and modify media sessions with a media server
   according to the procedures defined in RFC 3261 [1].  Often, SIP
   third [12] party call control will be used to create sessions to a
   media server on behalf of end users.  MSML is used to define and
   change the service which a user connected to a media server will
   receive.  As such, MSML clients are expected to be application
   servers, which MUST have an authorized security relationship with the
   media server.  MSML itself does not define authorization mechanisms.

   MSML transactions are originated based upon events that occur in the
   application domain.  These events may be independent from any media
   or user interaction.  For example, an application may wish to play an
   announcement to a conference warning that its scheduled completion
   time is approaching.  Applications themselves are structured in many
   different ways.  Their structure and requirements contribute to their
   selection of protocols and languages.  To accommodate differing
   application needs, MSML has been designed to be neutral to other
   languages and independent of the transport used to carry it.

   Many alternatives exist for a transport mechanism for MSML.  There
   may be one or many transport channels used to carry MSML based upon
   the requirements and structure of applications.  SIP INVITE and INFO
   [5] requests and responses have been chosen to carry MSML in this
   release of the specification.  INFO requests allow asynchronous mid-
   call messages within SIP with few additional semantics.  In addition,
   there are existing widely deployed implementations of that method, it
   aids in initial developments which are closely coupled with SIP
   session establishment, and it allows MSML to be directly associated
   with user dialogs when third party call control is used.

   Although INFO is generally not considered to be a suitable general-
   purpose transport mechanism for messages within SIP, there have been
   proposals to make it more acceptable.  MSML is expected to evolve to
   include other SIP usage and/or to work with other protocols or as a
   stand-alone protocol established through SIP, in future releases of
   this document.

   MSML supports several models for client interaction.  When clients
   use 3PCC to establish media sessions on behalf of end users, clients
   will have a SIP dialog for each media session.  MSML MAY be sent on



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   these dialogs.  However the targets of MSML actions are not inferred
   from the session associated with the SIP dialog.  The targets of MSML
   actions are always explicitly specified using identifiers as
   previously defined.

   An application, after interacting with a user, may want to affect
   multiple objects within a media server.  For example, tones or
   messages are often played to a conference when connections are added
   or removed.  A separate message may also be played to a participant
   as they are joined, or to moderators.  Explicit identifiers not
   inferred from a transport mechanism allow these multiple actions to
   be easily grouped into a single transaction sent on any SIP dialog.

   MSML also supports a model of dedicated control associations.  This
   supports decoupled application architectures where a client can
   control media server services without also establishing all of the
   media sessions itself.  Control associations are created using SIP
   but they do not have any associated media session.  Although
   initially INFO messages will be sent on this SIP dialog, just as with
   dialogs associated with media sessions, it is expected that in the
   future, the SIP dialog will be used to establish a separate control
   session (defined in SDP [4]) that does not use SIP as the transport
   for MSML messages.

   A media server using MSML also sends asynchronous events to a client
   using SIP INFO.  Events are sent based on previous MSML requests and
   are sent within the SIP dialog on which the MSML request that caused
   the event to be generated was received.  If the dialog no longer
   exists when the event is generated, the event is discarded.

   Events may be generated during the execution of a dialog created by a
   "<dialogstart>" element when the dialog language supports events.
   VoiceXML dialogs however, generally interact with other servers
   outside of MSML using HTTP.

   An event is also generated when the execution of a dialog terminates,
   either because of completion or failure.  The exact information
   returned is dependent on the dialog language, the capabilities of the
   dialog execution environment, and what was specified by the dialog.
   VoiceXML [11] allows information to be returned when the VoiceXML
   completes.  Events may be sent in a SIP INFO or a SIP BYE.  BYE is
   used when the dialog itself specifies that the connection should be
   disconnected such as through the use of the VoiceXML <disconnect>
   element.

   Conferences may also generate events based upon their configuration.
   An example of this is the notification of the set of active speakers.




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5.  Language Structure

5.1.  Execution Flow

   MSML assumes a model where there is a single control context within a
   media server for MSML processing.  That context may have one or many
   SIP [1] dialogs associated with it.  It is assumed that any SIP
   dialogs associated with the MSML control context have been authorized
   by mechanisms outside the scope of MSML.

   A media server control context maintains information about the state
   of all media objects and media streams within a media server.  It
   receives and processes all MSML requests from authorized SIP dialogs
   and receives all events generated internally by media objects and
   sends them on the appropriate SIP dialog.  An MSML request is able to
   create new media objects and streams, and to modify or destroy any
   existing media objects and streams.

   An MSML request may simply specify a single action for a media server
   to undertake.  In this case, the document is very similar to a simple
   command request.  Often, though, it may be more natural for a client
   to request multiple actions at one time, or the client would like
   several actions to be closely coordinated by the media server.
   Multiple MSML elements received in a single request MUST be processed
   sequentially in document order.

   An example of the first scenario would be to create a conference and
   join it with an initial participant.  An example of the second case
   would be to unjoin one or more participants from a main conference
   and join them to a sidebar conference.  In the first scenario,
   network latencies may not be an issue, but it is simpler for the
   client to combine the requests.  In the second case, the added
   network latency between separate requests could mean perceptible
   audio loss to the participant.

   Each MSML request is processed as a single transaction.  A media
   server MUST ensure that it has the necessary resources available to
   carry out the complete transaction before executing any elements of
   the request.  If it does not have sufficient resources, it MUST
   return a 520 response and MUST NOT execute the transaction.

   The MSML request MUST be checked for well-formedness and validated
   against the schema prior to executing any elements.  This allows XML
   [2] errors to reported immediately and minimizes failures within a
   transaction and the corresponding execution of only part of the
   transaction.

   Each element is expected to execute immediately.  Elements such as



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   "<dialogstart>", which take time, are "forked" and executed in a
   separate thread.  Once successfully forked, execution continues with
   the element following the dialog.  As such, MSML does not provide
   mechanisms to sequence or coordinate other operations with dialog
   elements.

   Processing within a transaction MUST stop if any errors occur.
   Elements that were executed prior to the error are not rolled back.
   It is the responsibility of the client to determine appropriate
   actions based upon the results indicated in the response.  Most
   elements MAY contain an optional "mark" attribute.  The value of that
   attribute from the last successfully executed element MUST be
   returned in an error response.  Note that errors that occur during
   the execution of a dialog occur outside the context of an MSML
   transaction.  These errors will be indicated in an asynchronous
   event.

   Transaction results are returned as part of the SIP request response.
   The transaction results indicate the success or failure of the
   transaction.  The result MUST also include identifiers for any
   objects created by a media server for which the client did not
   provide an instance name.  Additionally, if the transaction fails,
   the reason for the failure MUST be returned, and an indication of how
   much of the transaction was executed before the failure occurred
   SHOULD be returned.

5.2.  MSML Root Element

   "<msml>" is the root element.  When received by a media server, it
   defines the set of operations that form a single MSML transaction.
   Operations are requested by the contents of the element.  Each
   operation MAY appear zero or more times as children of "<msml>".
   Specific operations are defined in sections 7 through 9.

   The results of a request or the contents of events sent by a media
   server are also enclosed within the "<msml>"element.  The results of
   the transaction are included as a body in the response to the SIP
   request that contained the transaction.  This response will contain
   any identifiers that the media server assigned to newly created
   objects.  All messages that a media server generates are correlated
   to an object identifier.  Objects and identifiers are discussed in
   section 6.

   Attributes:

   version: "1.0" Mandatory





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5.3.  Sending Events to a Media Server

5.3.1.  <send>

   Events are used to affect the behavior of different objects within a
   media server.  The <send> element is used to send an event to the
   specified recipient.

   attributes:

   event: the name of an event.  Mandatory.

   target: an object identifier.  Mandatory.

   valuelist: a list of zero or more parameters that are included with
   the event.

   mark: a token that can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   should be unique.

5.4.  Transaction Results and Notifications

5.4.1.  <result>

   The <result> element is used to report the results of an MSML
   transaction.  It is included as a body in the final response to the
   SIP request which initiated the transaction.  An optional child
   element <description> may include text which expands on the meaning
   of error responses.  Response codes are defined in section 10.

   attributes:

   response: a numeric code indicating the overall success or failure of
   the transaction, and in the case of failure, an indication of the
   reason.  Mandatory.

   mark: in the case of an error, the value of the mark attribute from
   the last successfully executed element that included the mark
   attribute.

   In the case of failure, a description of the reason SHOULD be
   provided using the child element <description>.

   Two optional child elements allow the response to include identifiers
   for objects created by a request that did not have instance names



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   specified by the client.  Those elements are <confid> and <dialogid>
   for objects created though a <createconference> and <dialogstart>
   respectively.

5.4.2.  <event>

   The <event> element is used to notify an event to a media server
   client.  Two types of events are defined by MSML: "msml.dialog.exit",
   "msml.conf.nomedia", and "msml.conf.asn".  These correspond to the
   termination of an executing dialog, a conference being automatically
   deleted when the last participant has left, and the notification of
   the current set of active speakers for a conference, respectively.
   Events may also be generated by an executing dialog.  In this case
   the event type is specified by the dialog.

   attributes:

   name: the type of event.  Mandatory.

   id: the identifier of the conference or dialog that generated the
   event or caused the event to be generated.  Mandatory.

   <event> has two children, <name> and <value>, which contain the name
   and value respectively of each namelist item associated with the
   event.


6.  Media Server Object Model

   Media servers are general-purpose platforms for executing real-time
   media processing tasks.  These tasks range in complexity from simple
   ones such as serving announcements, to complex ones, such as speech
   interfaces, centralized multimedia conferencing, and sophisticated
   gaming applications.

   Calls are established to a media server using SIP.  Clients will
   often use SIP third party call control (3PCC) [12] to establish calls
   to a media server on behalf of end users.  However MSML does not
   require that 3PCC be used; only that the client and the media server
   share a common identifier for the call and its associated RTP [10]
   sessions.

   Objects represent entities which source, sink, or modify media
   streams.  A media streams is a bi-directional or uni-directional
   media flow between objects on a media server.  Media streams and
   operations on them are discussed in depth in section 7.  The
   following subsections define the classes of objects that exist on a
   media server and the way these are identified in MSML.



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6.1.  Objects

   A media object is an endpoint of one or more media streams.  It may
   be a connection that terminates RTP sessions from the network or a
   resource that transforms or manipulates media.  MSML defines three
   classes of media objects.  Each class defines the basic properties of
   how object instances are used within a media server.

   The following classes of media processing objects are defined.  The
   class names are given in parentheses:

   o  network connection (conn)
   o  conference (conf)
   o  dialog (dialog)

   Network connection is an abstraction for the media processing
   resources involved in terminating the RTP session(s) of a call.  For
   audio services a connection instance presents a full-duplex audio
   stream interface within a media server.  Multimedia connections have
   multiple media streams of different media types, each corresponding
   to an RTP session.  Network connections get instantiated through SIP
   [1].

   A conference represents the media resources and state information
   required for a single logical mix of each media type in the
   conference (e.g. audio and video).  MSML models multiple mixes/views
   of the same media type as separate conferences.  Each conference has
   multiple inputs.  Inputs may be divided into classes that allow an
   application to request different media treatment for different
   participants.  For example, the video streams for some participants
   may be assigned to fixed regions of the screen while those for other
   participants may only be shown when they are speaking.

   A conference has a single logical output per media type.  For each
   participant, it consists of the audio conference mix, less any
   contributed audio of the participant, and the video mix shared by all
   conference participants.  Some video conferences may have an optional
   ability to show the previous speaker to the current speaker when
   voice activated switching is used to select the video stream to
   display.

   Conferences are instantiated using the "<createconference>" element.
   The content of the "<createconference>" element specifies the
   parameters of the audio and/or video mixes.  Conferences are
   discussed in depth in section 8.

   Dialogs are a class of objects that represent automated participants.
   They are similar to network connections from a media flow perspective



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   and may have one or more media streams as the abstraction for their
   interface within a media server.  Unlike connections however, dialogs
   are created and destroyed through MSML, and the media server itself
   implements the dialog participant.

   The function that an instance of a dialog fulfills is defined by a
   client using a language such as VoiceXML.  As such, "dialog" is a
   generic reference to the set of resources, both media and control,
   that are used to create either a simple action, such as an atomic
   play or record operation, or more complex application interface
   components, such as a VoiceXML interpreter.  Dialogs are instantiated
   through the "<dialogstart>" element.  Dialogs operations are
   presented in section 9.

   The relationships between the different object classes is shown in
   the figure below.

                   +--------------------------------------+
                   |           Media Server               |
                   |                                      |
                   |------+                      ,---.    |
                   |      |                     /     \   |
        <== RTP ==>| conn |<------------------>( conf  )  |
                   |      |                     \     /   |
                   |------+                      `---'    |
                   |   ^                           ^      |
                   |   |                           |      |
                   |   |   +------+    +------+    |      |
                   |   |   |      |    |      |    |      |
                   |   +-->|dialog|    |dialog|<---+      |
                   |       |      |    |      |           |
                   |       +------+    +------+           |
                   +--------------------------------------+

   A single, full-duplex instance of each object class is shown together
   with common relationships between them.  The figure is not meant to
   imply only one to one relationships.  Conferences will often have
   hundreds of participants, and either connections or conferences may
   be interacting with more than one dialog.  For example, one dialog
   may be recording a conference while other dialogs announce
   participants joining or leaving the conference.

6.2.  Identifiers

   Objects are referenced using identifiers that are composed of one or
   more terms.  Each term specifies an object class and names a specific
   instance within that class.  The object class and instance are
   separated by a colon ":" in an identifier term.



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   Identifiers are assigned to objects when they are first created.  In
   general, either the MSML client or a media server may specify the
   instance name for an object.  Objects for which a client does not
   assign an instance name will be assigned one by a media server.
   Media server assigned instance names are returned to the client as a
   complete object identifier in the response to the request that
   created the object.

   It is meaningful for some classes of objects to exist independently
   on a media server.  Network connections may be created through SIP at
   any time.  MSML can then be used to associate their media with other
   objects as required to create services.  Conferences may be created
   and have specific resources reserved waiting for participant
   connections.

   Objects from these two classes, connections and conferences, are
   considered independent objects since they can exist on a standalone
   basis.  Identifiers for independent objects consist of single term as
   defined above.  For example, identifiers for a conference and
   connection could be "conf:abc" or "conn:1234" respectively.  Clients
   which choose to assign instance names to independent objects must use
   globally unique instance names.  One way to create globally unique
   names is to include the domain name of the client as part of the
   name.

   Dialogs are only created to provide a service to independent objects.
   Dialogs may act as a participant in a conference or interact with a
   connection similar to a two participant call.  As such, dialogs
   depend upon the existence of independent objects and this is
   reflected in the composition of their identifiers.

   Identifiers for dialogs are composed of a structured list of slash
   ('/') separated terms.  The left-most term of the identifier must
   specify a conference or connection.  This serves as the root for the
   identifier.  An example of an identifier for a dialog acting as a
   conference participant could be:

      conf:abc/dialog:recorder

   All objects except connections are created using MSML.  Connections
   are created when media sessions get established through SIP.  There
   are several options clients and media servers can use to establish a
   shared instance name for a connection and its media streams.

   When media servers support multiple media types, it is RECOMMENDED
   that the instance name be a call identifier that can be used to
   identify the collection of RTP sessions associated with a call.  When
   MSML is used in conjunction with SIP and third party call control,



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   the call identifier MUST be the same as the local tag assigned by the
   media server to identify the SIP dialog.  This will be the tag the
   media server adds to the "To" header in its response to an initial
   invite transaction.  RFC 3261 requires the tag values to be globally
   unique.

   An example of a connection identifier is: conn:74jgd63956ts.

   With third party call control, the MSML client acts as a back to back
   user agent (B2BUA) to establish the media sessions.  SIP dialogs are
   established between the client and the media server allowing the use
   of the media server local tag as a connection identifier.  If this is
   not the case, a SIP event package could be defined and used to allow
   a media server to notify new sessions to a client that has subscribed
   to this information.

   Identifiers as described above allow every object in a media server
   to be uniquely addressed.  They can also be used to refer to multiple
   objects.  There are two ways in which this can currently be done:

   o  wildcards
   o  common instance names

   An identifier can reference multiple objects when a wildcard is used
   as an instance name.  MSML reserves the instance name comprised of a
   single asterisk ('*') to mean all objects that have the same
   identifier root and class.  Instance names containing an asterisk
   cannot be created.  Wildcards MUST only be used as the right most
   term of an identifier and MUST NOT be used as part of the root for
   dialog identifiers.  Wildcards are only allowed where explicitly
   indicated below.

   The following are examples of valid wildcards:

      conf:abc/dialog:*
      conn:*

   Examples of illegal wildcard usage are:

      conf:*/dialog:73849

   Although identifiers share a common syntax, MSML elements restrict
   the class of objects which are valid in a given context.  As an
   example, although it is valid to join two connections together, it is
   not valid to join two IVR dialogs.






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7.  Media Streams

   Objects have at least one media input and output for each type of
   media that they support.  Each object class defines the number of
   inputs and outputs objects of that class support.  Media streams are
   created when objects are joined, either explicitly using "<join>", or
   implicitly when dialogs are created using "<startdialog>".  Dialog
   creation has two stages, allocating and configuring the resources
   required for the dialog instance, and implicitly joining those
   resources to the dialog target during the dialog execution.

   A join operation by default creates a bi-directional audio stream
   between two objects.  Video and uni-directional streams may also be
   created.  A media stream is created by connecting the output from one
   object to the input of another object and vice versa (assuming a bi-
   directional or full-duplex join).

   Many objects may only support a single input for each type of media.
   Within this specification, only the conference object class supports
   an arbitrary number of inputs.  When a stream is requested to be
   created to an object that already has a stream of the same type
   connected to its single input, the result of the request depends upon
   the type of the media stream.

   Audio mixing is done by summing audio signals.  Automatically mixing
   audio streams has common and straight forward applications.  For
   example, the ability to bridge two streams allows for the easy
   creation of simple three-way calls or to bridge private announcements
   with a [whispered] conference mix for an individual participant.  In
   the case of general conferences however, an MSML client SHOULD create
   an audio conference and then join participants to the conference.
   Conference mixers MUST subtract the audio of each participant from
   the mix so that they do not hear themselves.

   A media server that receives a request that requires joining an audio
   stream to the single audio input of an object that already has an
   audio stream connected, SHOULD automatically bridge the new stream
   with the existing stream, creating a mix of the two audio streams.
   The maximum number of streams that may be bridged in this manner is
   implementation-specific.  It is RECOMMENDED that a media server
   support bridging at least two streams.  A media server that cannot
   bridge a new stream with any existing streams MUST fail the operation
   requesting the join.

   Unlike audio mixing, there are many different ways that two video
   streams may be combined and presented.  For example, they may be
   presented side by side in separate panes, picture in picture, or in a
   single pane which displays only a single stream at a time based on a



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   heuristic such as active speaker.  Each of these options creates a
   very different presentation and require significantly different media
   resources.

   A join operation does not describe how a new stream can be combined
   with an existing stream.  Therefore automatic bridging of video is
   not supported.  A media server MUST fail requests to join a new video
   stream to an object that only supports a single video input and
   already has a video stream connected to that input.  For an object to
   have multiple video streams joined to it, the object itself must be
   capable of supporting multiple video streams.  Conference objects can
   support multiple video streams and provide a way to specify the
   mixing presentation for the video streams.

   A media server MUST NOT establish any streams unless the media server
   is able to create all the streams requested by an operation.  Streams
   are only able to be created if both objects support a media type and
   at least one of the following conditions is true:

   1.  each object that is to receive media is not already receiving a
       stream of that type.
   2.  any object that is to receive media and is already receiving a
       stream of that type supports receiving an additional stream of
       that type.  The only class of objects defined in this
       specification that directly support receiving multiple streams of
       the same type are conferences.
   3.  the media server is able to automatically bridge media streams
       for an object that is to receive media and that is already
       receiving a stream of the requested type.  The only type of media
       defined in this specification that MAY be automatically bridged
       is audio.

   The directionality of media streams associated with a connection are
   modeled independently from what SDP [4] allows for the corresponding
   RTP [10] sessions.  Media servers MUST respect the SDP in what they
   actually transmit but MUST NOT allow the SDP to affect the
   directionality when joining streams internal to the media server.

   The following three sub-sections describe the elements that
   establish, modify, and remove streams.  These are followed by sub-
   sections describing stream properties and specialized methods for
   establishing a stream.

7.1.  <join>

   "<join>" is used to create one or more streams between two
   independent objects.  Streams may be audio or video and may be bi-
   directional or uni-directional.  A bi-directional stream is



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   implicitly composed of two uni-directional streams that can be
   manipulated independently.  The streams to be established are
   specified by "<stream>" elements (section 7.4) as the content of
   "<join>".

   Without any content, "<join>" by default establishes a bi-directional
   audio stream.  When only a stream of a single type has previously
   been created between two objects, or when only a uni-directional
   stream exists, "<join>" can be used to add a stream of another media
   type or make the stream bi-directional by including the necessary
   "<stream>" elements.  Bi-directional streams are made uni-directional
   by using "<unjoin>" (section 7.3) to remove the uni-directional
   stream for the direction that is no longer required.

   In addition to defining the media type and direction of streams,
   "<stream>" elements are also used to establish the properties of
   streams, such as gain, voice masking, or tone clamping of audio
   streams, or labels and other visual characteristics of video streams.
   Properties are often defined asymmetrically for a single direction of
   a stream.  Creating a bi-directional stream requires two "<stream>"
   elements within the "<join>", one for each direction, if one
   direction is to have different properties from the other direction.

   If a media server can provide services using both compressed or
   uncompressed media, the MSML client may need to distinguish within
   requests which format is to be used.  When compressed streams are
   created, both objects must use the same media format or an error
   response (450) is generated.

   attributes:

   id1: an identifier of either a connection or conference.  Wildcards
   MUST NOT be used.  Any other object class results in a 440 error.

   id2: an identifier of either a connection or conference.  Wildcards
   MUST NOT be used.  Any other object class results in a 440 error.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   SHOULD be unique.

   For example, consider a call center coaching scenario where a
   supervisor can listen to the conversation between an agent and a
   customer, and provide hints to the agent, which are not heard by the
   customer.  One join establishes a stream between the agent and the
   customer and another join establishes a stream between the agent and



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   the supervisor.  A third join is used to establish a half-duplex
   stream from the customer to the supervisor.  The media server
   automatically bridges the media streams from the customer and the
   supervisor for the agent, and from the customer and the agent for the
   supervisor.

   Assuming the following connections with mneumonics as the instance
   identifiers, each with a single audio stream:

   o  conn:supervisor
   o  conn:agent
   o  conn:customer

   The following would create the media flows previously described:

      <?xml version="1.0" encoding="UTF-8"?>
      <msml version="1.0">
         <join id1="conn:supervisor" id2="conn:agent"/>
         <join id1="conn:agent" id2="conn:customer"/>
         <join id1="conn:supervisor" id2="conn:customer">
            <stream media="audio" dir="to-id1"/>
         </join>
      </msml>

   The following example, shows joining a participant to a multimedia
   conference.  It assumes that the conference has a video presentation
   region named "topright".  The "display" attribute is explained in
   section 7.4.2.

      <?xml version="1.0" encoding="UTF-8"?>
      <msml version="1.0">
         <join id1="conn:hd83t5hf7g3" id2="conf:example">
            <stream type="audio"/>
            <stream type="video" dir="from-id1" display="topright"/>
            <stream type="video" dir="to-id1"/>
      </msml>

7.2.  <modifystream>

   Media streams can have different properties such as the gain for an
   audio stream or a visual label for a video stream.  These properties
   are specified as the content of "<stream>" elements (see section
   7.4). "<modifystream>" is used to change the properties of a stream
   by including one or more "<stream>" elements that are to have their
   properties changed.

   A media server MUST set the properties of streams that are included
   within "<modifystream>" to that stated by the child elements of the



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   "<stream>" elements.  Any properties not included within a "<stream>"
   element MUST NOT be changed.  Setting a property for only one
   direction of a bi-directional stream MUST NOT affect the other
   direction.  The directionality of streams are changed using
   "<unjoin>" and "<join>".  Any streams that exist between the two
   objects that are not included within "<modifystream>" MUST NOT be
   affected.

   attributes:

   id1: an identifier of either a conference or a connection.  The
   instance name MUST NOT contain a wildcard if "id2" contains a
   wildcard.  Mandatory.

   id2: an identifier of either a conference or a connection.  The
   instance name MUST NOT contain a wildcard if "id1" contains a
   wildcard.  Mandatory.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   SHOULD be unique.

7.3.  <unjoin>

   Unjoin removes one or more media streams between two objects.
   Without any "<stream>" elements as content, a media server MUST
   remove all of the streams between the objects.  Individual streams
   are removed by specifying them using "<stream>" elements.  When
   "<stream>" elements are included, a media server MUST NOT remove any
   streams that are not defined by "<stream>" elements. "<stream>"
   elements that are used to identify streams within "<unjoin>" MUST NOT
   specify any properties.  A media server MUST ignore any property
   elements that are included.

   A bi-directional stream is changed to a uni-directional stream by
   using "<unjoin>" to remove the direction that is no longer required.
   "<unjoin>" and "<join>" may be used together to move a media stream,
   such as from a main conference to a sidebar conference.

   attributes:

   id1: an identifier of either a conference or a connection.  The
   instance name MUST NOT contain a wildcard if "id2" contains a
   wildcard.  Mandatory.

   id2: an identifier of either a conference or a connection.  The



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   instance name MUST NOT contain a wildcard if "id1" contains a
   wildcard.  Mandatory.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   SHOULD be unique.

   The following removes a participant from a conference and plays a
   leave tone for the remaining participants in the conference.

            <?xml version="1.0" encoding="UTF-8"?>
            <msml version="1.0">
               <unjoin id1="conn:jd73ht89sf489f" id2="conf:1"/>
               <dialogstart target="conf:1" type="application/voicexml+xml">
                   ...
               </dialogstart>
            </msml>

7.4.  <stream> Elements

   Individual streams are specified using the "<stream>" element.  They
   MAY be included as a child in any of the stream manipulation elements
   "<join>", "<modifystream>", or "<unjoin>".

   The type of the stream is specified using a "media" attribute that
   uses values corresponding to the top-level MIME media types as
   defined in RFC 2046 [6].  This specification only addresses audio and
   video media.  Other specifications may define procedures for
   additional types.

   A bi-directional stream is identified when no direction attribute
   "dir" is present.  A uni-directional stream is identified when a
   direction attribute is present.  The "dir" attribute MUST have a
   value of "from-id1" or "to-id1" depending on the required direction.
   These values are relative to the identifier attributes of the parent
   element.

   The compressed attribute is used to distinguish the compressed nature
   of the stream when necessary.  It is implementation specific what is
   used when the attribute is not present.  Joining compressed streams
   acts much like an RTP [10] relay.

   The properties of the media streams are specified as the content of
   "<stream>" elements when the element is used as a child of "<join>"
   or "<modifystream>".  Stream elements MUST NOT have any content when
   they are used as a child of "<unjoin>" to identify specific streams



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   to remove.

   Properties are defined within MSML as additional attributes or child
   elements of "<stream>" and are media type specific.  Those for audio
   streams and video streams are defined in the following two sub-
   sections.

   attributes:

   media: "audio" or video".  Mandatory.

   dir: "from-id1" or "to-id1".

   compressed: "true" or "false".  Specifies whether the stream uses
   compressed media.  Default is implementation specific.

7.4.1.  Audio Stream Properties

   Audio mixes can be specified to only mix the N-loudest participants.
   However there may be some "preferred" participants that are always
   able to contribute.  When audio streams are joined to a conference
   that uses N-loudest audio mixing, preferred streams need to be
   identified.

   A preferred audio stream is identified using the "preferred"
   attribute.  The "preferred" attribute MAY be used for an audio stream
   that is input to a conference and MUST NOT be used for streams not
   joined to a conference.

   Additional attributes of the "<stream>" element for audio streams
   are:

   preferred: a boolean value that defines whether the stream does not
   contend for N-loudest mixing.  A media server MUST include streams
   with a preferred value of "true" in the conference audio mix.
   Streams with a value of "false" MAY contend to be included when
   N-loudest mixing is enabled for the conference.  Default "false".

   There are two elements that can be used to change the characteristics
   of an audio stream as defined below.

7.4.1.1.  Gain

   The "<gain>" element is used to adjust the volume of an audio media
   stream.  It may be set to a specific gain amount, to automatically
   adjust the gain to a desired target level, or to mute the stream.

   Attributes of the "<gain>" element are:



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   amt: a specific gain to apply specified in dB or the string "mute"
   indicating that the stream should be muted.  This attribute MUST NOT
   be used if "agc" is present.

   agc: boolean indicating whether automatic gain control is to be used.
   This attribute MUST NOT be used if "amt" is present.

   tgtlvl: the desired target level for AGC specified in dBm0.  This
   attribute MUST be specified if "agc" is present with a value of
   "true".

   maxgain: the maximum gain that AGC will apply specified in dB.  This
   attribute MAY be used if "agc" is present and MUST NOT be used
   otherwise.

7.4.1.2.  Tone Removal

   The "<clamp>" element is used to filter tones and/or audio-band dtmf
   from a media stream.

   Attributes of the "<clamp>" element are:

   dtmf: boolean indicating whether DTMF tones should be removed.

   tone: boolean indicating whether other tones should be removed.

7.4.2.  Video Stream Properties

   Video mixes define a presentation that may have multiple regions,
   such as a quad-split.  Each region displays the video from one or
   more participants.  When video streams are joined to such a
   conference, the region that will display the video needs to be
   specified as part of the join operation.

   The region that will display the video is specified using the
   "display" attribute.  The "display" attribute MUST be used for a
   video stream that is input to a conference and MUST NOT be used for
   other streams.  The value of the attribute MUST identify a "<region>"
   (section 8.5.2) or a "<selector>" (section 8.5.3) that is defined for
   the conference.  A stream MUST NOT be directly joined to a region
   that is defined within a selector.  Changing the value of the
   "display" attribute, using "<modifystream>", will change the region
   of a video presentation layout in which a video stream is displayed.

   Additional attributes of the "<stream>" element for video streams
   are:

   display: the identifier of a video layout region or selector that is



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   to be used to display the video stream.

7.4.2.1.  Visual Characteristics

   Some regions of video conferences may display different streams
   automatically, such as when voice activated switching is used.
   Connections MAY also be joined directly without the use of video
   mixing.  In these cases, the "<visual>" element may be used to define
   visual display properties for a stream.

   The "<visual>" element MAY use any of the visual attributes defined
   for regions (see section 8.5.2).  This allows the visual aspects of
   regions within a "<selector>" to be tailored to the selected video
   stream, or for streams that are directly joined to display a name or
   logo.

7.5.  <monitor>

   Monitor is a specialized uni-directional join that copies the media
   that is destined for a connection object.  One example of the use for
   <monitor> may be quality monitoring within a conference.  The media
   stream may be removed using the <unjoin> element described in section
   7.3.

   attributes:

   id1: an identifier of the connection to be monitored.  Any other
   object class results in a 440 error.  Wildcards MUST NOT be used.

   id2: an identifier of the object which is to receive the copy of the
   media destined to id1. id2 may be a connection or a conference.  Any
   other object class results in a 440 error.  Wildcards MUST NOT be
   used.

   compressed: "true" or "false".  Specifies whether the join should
   occur before or after compression.  When "true", id2 must be a
   connection using the same media format as id1 or an error response
   (450) is generated.  Default is "false.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   SHOULD be unique.


8.  Conferences




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   A conference has a mixer for each type of media that the conference
   supports.  Each mix has a corresponding description that defines how
   the media from participants contributes to that mix.  A mixer has
   multiple inputs that are combined in a media specific way to create a
   single logical output.

   The elements that describe the mix for each media type are called
   mixer description elements.  They are:

   o  "<audiomix>" defines the parameters for mixing audio media.
   o  "<videolayout>" defines the composition of a video window.

   These elements, defined in sections 8.4 and 8.5 respectively, are
   used as content of the "<createconference>" element to establish the
   initial properties of a conference.  The elements are used within the
   "<modifyconference>" element to change the properties of a conference
   once it has been created, or within the "<destroyconference>" element
   to remove individual mixes from the conference.

   Conferences can be terminated by an MSML client using the
   "<destroyconference>" element to remove the entire conference or by
   removing the last mixer(s) associated with the conference.
   Conferences can also be terminated automatically by a media server
   based on criteria specified when the conference is created.  When the
   conference is deleted, any remaining participants will have their
   associated SIP dialogs left unchanged or deleted based on the value
   of the "term" attribute specified when the conference was created.

   The following three sub-sections describe the elements that create,
   modify, and delete conferences.  These are followed by sub-sections
   describing the properties for the mixers of each media type.

8.1.  <createconference>

   "<createconference>" is used to allocate and configure the media
   mixing resources for conferences.  A description of the properties
   for each type of media mix required for the conference is defined
   within the content of the "<createconference>" element.  Mixer
   descriptions are described in sections 8.4 and 8.5.  At least one
   mixer description element SHOULD be included.  When no mixer
   descriptions are included, a media server MUST behave as if a single
   "<audiomix>" element with no content was present.

   Clients can request that a media server automatically delete a
   conference when a specified condition occurs by using the
   "deletewhen" attribute.  A media server MUST delete a conference when
   all mixes have no streams if the "deletewhen" attribute has a value
   of "nomedia".  When this occurs, a media server MUST send an



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   "msml.conf.nomedia" event to the MSML client.  A media server MUST
   delete a conference when the SIP [1] dialog that carries the
   "<createconference>" element is terminated if the "deletewhen"
   attribute has value of "nocontrol".  A value of "never" leaves
   conference deletion under the control of the MSML client.

   attributes:

   name: the instance name of the conference.  If the attribute is not
   present, the media server MUST assign a globally unique name for the
   conference.  If the attribute is present but the name is already in
   use, an error (432) will result and MSML document execution MUST
   stop.  Events which the conference generates use this name as the
   value of their "id" attribute (see section 5.4.2).

   deletewhen: defines whether a media server should automatically
   delete the conference.  Possible values are "nomedia", "nocontrol",
   and "never".  Default is "nomedia".

   term: when true, the media server MUST send a BYE request on all SIP
   dialogs still associated with the conference when the conference is
   deleted.  Setting term equal to false allows clients to start dialogs
   on connections once the conference has completed.  Default true.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all mark attributes within an MSML document
   should be unique.

   An example of creating an audio conference is shown below.  This
   conference allows at most two participants to contend to be heard and
   reports the set of active speakers no more frequently than every ten
   seconds.

            <?xml version="1.0" encoding="UTF-8"?>
            <msml version="1.0">
               <createconference name="example">
                  <audiomix>
                     <n-loudest n="3"/>
                     <asn ri="10s"/>
                  </audiomix>
               </createconference>
            </msml>







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8.2.  <modifyconference>

   All of the properties of an audio mix or the presentation of a video
   mix can be changed during the life of a conference using the
   "<modifyconference>" element.  Changes to an audio mix are requested
   by including an "<audiomix>" element (see section 8.4) as a child of
   "<modifyconference>".  This can be used to add an audio mixer to the
   conference if none was previously allocated.  Changes to a video
   presentation are requested by including a "<videolayout>" element
   (see section 8.5) as a child of "<modifyconference>".  Similar to an
   audio mixer, this can be used to add a video mixer if none was
   previously allocated.

   Mixers are removed by including a mixer description element within
   "<destroyconference/>".

   Features and presentation aspects are enabled/added or modified by
   including the element(s) that define the feature or presentation
   aspect within a mixer description.  The complete specification of the
   feature or presentation element must be included just as it would be
   included when the conference is created.  The new definition
   completely replaces any previous definition that existed.  Only
   things that are defined by elements included in the mixer
   descriptions are affected.  A media server MUST maintain the current
   configuration of features and presentation aspects that are not
   included within the mixer descriptions present in the
   "<modifyconference>" element.  Any mixers that are not included in
   "<modifyconference>" MUST NOT be affected.

   For example, if an MSML client wanted to change the minimum reporting
   interval for active speaker notification from that shown in the
   example in section 8.1 it would send the following to the media
   server:

            <?xml version="1.0" encoding="UTF-8"?>
            <msml version="1.0">
               <modifyconference id1="conf:example">
                  <audiomix>
                     <asn ri="4">
                  </audiomix>
               </modifyconference>
            </msml>

   This would also enable active speaker notification if it had not
   previously been enabled.  The N-loudest mixing is unaffected.

   Multiple elements MAY be included in the mixer descriptions similar
   to when conferences are created.  For example, in a video conference,



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   the video mix description ("<videolayout>") could specify that the
   layout of the video being displayed should change such that the
   regions currently displaying participants get smaller and new
   region(s) are created to support additional participants.  A media
   server MUST make all of the requested changes or none of the
   requested changes.

   Additional examples of modifying conferences are presented in section
   11.

   attributes:

   id: the identifier for a conference.  Wildcards MUST NOT be used.
   Mandatory.

8.3.  <destroyconference>

   Destroy conference is used to delete mixers or to delete the entire
   conference and all state and shared resources.  When a mixer is
   removed, all of the streams joined to that mixer are unjoined.  When
   a conference is destroyed, SIP dialogs for any remaining participants
   MUST be maintained or removed based on the value specified for the
   "term" attribute when the conference was created.

   When there is no element content, "<destroyconference/>" deletes the
   entire conference.  Individual mixers are removed by including a
   mixer description element for each of the mix(es) that is to be
   removed. "<audiomix/>" is used remove audio mixers and
   "<videolayout/>" is used remove video mixers.  When one or more mixer
   descriptions are specified, then Media Server MUST only delete mixers
   that correspond to the specified description(s) and MUST NOT affect
   any other mixers.  Elements that define features and presentation
   aspects of a mix MUST NOT be included when "<audiomix/>" and
   "<videolayout/>" are used to identify individual mixes to be removed.
   A media server MUST ignore any such elements that are present.  When
   the last mixer is removed from a conference, a media server removes
   all conference state, leaving or removing any remaining SIP dialogs
   as described above.

   attributes:

   id: the identifier for a conference.  Mandatory.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all "mark" attributes within an MSML document
   SHOULD be unique.



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8.4.  Audio Mix

   The properties of the overall audio mix are specified using the
   "<audiomix>" element.

   Attributes:

   id: an optional identifier for the audio mix.

   An example of the description for an audio mix is:

      <audiomix id="mix1">
         <asn ri="10s"/>
         <n-loudest n="3">
      </audiomix>

8.4.1.  N-Loudest

   The "<n-loudest>" element defines that participants contend to be
   included in the conference mix based upon their audio energy.  When
   "N-Loudest" has not been specified, all participants are mixed.  Once
   enabled, N-loudest mixing is disabled by setting the value of "n" to
   be equal to the maximum or default mixing capability of the media
   server.

   Attributes:

   n: the number of participants that will be included in the audio mix
   based upon having the greatest audio energy.

8.4.2.  Active Speaker Notification

   The "<asn>" element enables notification of active speakers.  Active
   speakers are notified using the "<event>" element (section 5.4.2)
   with an event name of "msml.conf.asn".  The namelist of the event
   consists of the set of active speakers.  The name of each item is the
   string "speaker" with a value of the connection identifier for the
   connection.

   Attributes:

   ri: the minimum reporting interval defines the minimum duration of
   time which must pass before changes to active speakers will be
   reported.  A value of zero disables active speaker notification.







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   An example of an active speaker notification is:

      <event name="msml.conf.asn" id="conf:example">
         <name>speaker</name>
         <value>conn:hd93tg5hdf</value>
         <name>speaker</name>
         <value>conn:w8cn59vei7</value>
         <name>speaker</name>
         <value>conn:p78fnh6sek47fg</value>
      </event>

8.5.  Video Layout

   A video layout is specified using the "<videolayout>" element.  It is
   used as a container to hold elements that describe all of the
   properties of a video mix.  The parameters of the window that
   displays the video mix are defined by the "<root>" element.  When the
   video mix is composed of multiple panes, the location and
   characteristics of the panes are defined by one or more "<region>"
   elements.  A "<region>" element is not required when only a single
   video stream is displayed at one time and none of the visual
   attributes of regions are required.

   Some regions may be used to display a video stream based on a
   selection criteria rather than having a video stream of a single
   participant continuously presented in the region.  One such example
   is a distance learning lecture where the instructor sees each of the
   students periodically displayed in a region.  When a region is used
   to display one of a number of streams, it is placed as a child of a
   "<selector>" element.

   Attributes:

   type: specifies the language used to define the layout.  Layouts
   defined using MSML use the value "text/msml-basic-layout".  This is
   the same convention as defined for the layout module from the W3C
   SMIL 2.0 specification [16].  The default when omitted is "text/
   msml-basic-layout".

   id: an optional identifier for the video layout.

8.5.1.  Root Window

   The "<root>" element describes the root window or virtual screen in
   which the conference video mix will be displayed.  Simple conferences
   can display participant video directly within the root window but
   more complex conferences will use regions for this purpose.  Areas of
   the window which are not used to display video will show the root



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   window background.

   All video presentations require a root window.  The "<root>" element
   MUST be present when a video mix is created.  The root window cannot
   be disabled but its attributes MAY be changed using
   "<modifyconference>".

   Attributes:

   size: the size of the root window specified as one of the five
   standard common intermediate formats (e.g.  CIF, QCIF, etc.).

   backgroundcolor: the color for the root window background defined
   using the values for the "background-color" property of the CSS2
   specification [8].

   backgroundimage: the URI for an image to be displayed as the root
   window background.  Transparent portions of the image allow the
   background color to show through.

8.5.2.  Regions

   "<region>" elements define video panes that are used to display
   participant video streams.  Regions are rendered on top of the root
   window.

   The size of a region is specified relative to the size of the root
   window using the "relativesize" attribute.  Relative sizes are
   expressed as fractions (e.g. 1/4, 1/3) that preserve the aspect ratio
   of the original video stream while allowing for efficient scaling
   implementations.

   Regions are located on the root window based on the value of the
   position attributes "top" and "left".  These attributes define the
   position of the top left corner of the region as an offset from the
   top left corner of the root window.  Their values may be expressed
   either as a number of pixels or as a percent of the vertical or
   horizontal dimension of the root window.  Percent values are appended
   with a percent ('%') character.  Percent values of "33%" and "67%"
   SHOULD be interpreted as "1/3" and "2/3" to allow easy alignment of
   regions whose size is expressed relative to the size of the root
   window.









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   An example of a video layout with six regions is:

   +-------+---+
   |       | 2 |
   |   1   +---+
   |       | 3 |
   +---+---+---+
   | 6 | 5 | 4 |
   +---+---+---+

      <videolayout type="text/msml-basic-layout">
         <root size="CIF"/>
         <region id="1" left="0" top="0" size="2/3"/>
         <region id="2" left="67%" top="0" size="1/3"/>
         <region id="3" left="67%" top="33%" size="1/3">
         <region id="4" left="67%" top="67%" size="1/3"/>
         <region id="5" left="33%" top="67%" size="1/3"/>
         <region id="6" left="0" top="67%" size="1/3"/>
      </videolayout>

   The area of the root window covered by a region is a function of the
   region's position and its size.  When areas of different regions
   overlap, they are layered in order of their "priority" attribute.
   The region with the highest value for the "priority" attribute is
   below all other regions and will be hidden by overlapping regions.
   The region with the lowest non-zero value for the "priority"
   attribute is on top of all other regions and will not be hidden by
   overlapping regions.  The priority attribute may be assigned values
   between 0 and 1.  A value of zero disables the region, freeing any
   resources associated with the region, and unjoining any video stream
   displayed in the region.

   Regions that do not specify a priority will be assigned a priority by
   a media server when a conference is created.  The first region within
   the "<videolayout>" element that does not specify a priority will be
   assigned a priority of one, the second a priority of two, etc.  In
   this way, all regions that do not explicitly specify a priority will
   be underneath all regions that do specify a priority.  As well,
   within those regions that do not specify a priority, they will be
   layered from top to bottom, in the order they appear within the
   "<videolayout>" element.










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   For example, if a layout was specified as follows:

      <videolayout>
         <root size="CIF"/>
         <region id="a" ... priority=".3" .../>
         <region id="b" ... />
         <region id="c" ... priority=".2" ...>
         <region id="d" ... />
      </videolayout>

   Then the regions would be layered, from top to bottom, c,a,b,d.

   Portions of regions that extend beyond the root window will be
   cropped.  For example, a layout specified as:

      <videolayout>
         <root size="CIF"/>
         <region id="foo" left="50%" top="50%" size="2/3"/>
      </videolayout>

   would appear similar to:

   +-----------+
   |   root    |
   |background |
   |     +-----+--
   |     |     |//
   |     | foo |//
   +-----+-----+//
         |////////

   Visual attributes are used to define aspects of the visual appearance
   of individual regions.  A border may be defined together with a title
   and/or logo.  Text and logos are displayed as images on top of the
   region's video, below all regions with a lower priority.  The visual
   attributes are "title", "titletextcolor", "titlebackgroundcolor",
   "bordercolor", "borderwidth", and "logo".

   Visual attributes can also be defined for individual streams (section
   7.4.2.  When visual attributes are specified as part of both a region
   and a stream, those associated with the stream MUST take precedence.
   This allows streams that are chosen for display automatically (see
   8.5.3 to have proper text and logos displayed.  The region visual
   attributes are displayed when no stream is associated with the
   region.

   Two other attributes associated with a region, "blank" and "freeze",
   define the state of the video displayed in the region.  When the



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   "blank" attribute has a value of "true", then a media server MUST
   display the region as if there was no input stream.  When the
   "freeze" attribute has a value of "true", then a media server MUST
   display the last video frame received prior to the freeze.

   Attributes associated with each region are:

   id: a name that can be used to refer to the region.

   left: the position of the region from the left side of the root
   window.

   top: the position of the region from the top of the root window.

   relativesize: the size of the region expressed as a fraction of the
   root window size.

   priority: a number between 0 and 1 that is used to define the
   precedence when rendering overlapping regions.  A value of zero
   disables the region.

   title: text to be displayed as the title for the region

   titletextcolor: the color of the text

   titlebackgroundcolor: the color of the text background

   bordercolor: the color of the region border

   borderwidth: the width of the region border

   logo: the URI of an image file to be displayed

   freeze: a boolean value that defines whether the video image should
   be frozen at the currently displayed frame.  Default is false.

   blank: a boolean value that defines whether the region should display
   black instead of the associated video stream.  Default is false.

8.5.3.  Stream Selection

   It is often desired that one of several video streams be
   automatically selected to be displayed.  The "<selector>" element is
   used to define the selection criteria and its associated parameters.
   The selection algorithm is specified by the "method" attribute.
   Currently defined selection methods allow for voice activated
   switching and to iterate sequentially through the set of associated
   video streams.



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   The regions that will display the selected video stream are placed as
   child elements of the "<selector>" element.  Including regions within
   a "<selector>" element does not affect their layout with respect to
   regions not subject to the selection.  For simple video conferences
   that display the video directly in the root window, the "<root>"
   element can be placed as a child of "<selector>".  Region elements
   MUST NOT be used in this case.

   For example, below is a common video layout that allows the video
   stream from the currently active speaker to be displayed in the large
   region ("1") at the top left of the layout while the streams from
   five other participants are displayed in regions located at the
   layout periphery.

   +-------+---+
   |       | 2 |
   |   1   +---+
   |       | 3 |
   +---+---+---+
   | 6 | 5 | 4 |
   +---+---+---+

      <videolayout type="text/msml-basic-layout">
         <root size="CIF"/>
         <selector id="switch" method="vas">
            <region id="1" left="0" top="0" size="2/3"/>
         </selector>
         <region id="2" left="67%" top="0" size="1/3"/>
         <region id="3" left="67%" top="33%" size="1/3">
         <region id="4" left="67%" top="67%" size="1/3"/>
         <region id="5" left="33%" top="67%" size="1/3"/>
         <region id="6" left="0" top="67%" size="1/3"/>
      </videolayout>

   Selector methods defined in other specifications MUST be defined so
   that they work if only a single region is a child of the selector.
   Selector methods that support more than one child region MUST specify
   how the method works across multiple regions.  Media server
   implementations MAY support only a single region for methods that are
   defined to allow multiple regions.

   The selector or region in which a participant's video stream is to be
   displayed is specified during a join operation using the "display"
   attribute of "<stream>".  Specifying a selector allows a media server
   to select the stream to be displayed based upon the criteria defined
   by the selector method.  Specifying a region allows continuous
   presence display of the participant's video.  Some streams may be
   joined with both a selector and a region.  In this case, the value of



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   the "blankothers" attribute defines whether the streams associated
   with a continuous presence region should be blanked when the stream
   is selected for display in one of the selector regions.

   Attributes common to all selector methods are:

   id: a name that can be used to refer to the selector.

   method: the name of the method used to select the video stream.

   status: specifies whether the selector is "active" or "disabled".

   blankothers: when "true", video streams that are also displayed in
   continuous presence regions will have the continuous presence regions
   blanked when the stream is displayed in a selection region.

8.5.3.1.  Voice Activated Switching

   Voice activated switching (VAS) is used to display the video stream
   that correlates with the participant who is currently speaking.  It
   is specified using a selector method value of "vas".

   If the video stream associated with the active speaker is not
   currently displayed in a selection region, then it replaces the video
   in the region that is displaying the video of the speaker that was
   least recently active.  If the video of the active speaker is
   currently displayed in a selection region, then there is no change to
   any region.  When VAS is applied to a single region, this has the
   effect that the current speaker is displayed in that region.

   Attributes associated with voice activated switching are:

   si: switching interval is the minimum period of time that must elapse
   before allowing the video to switch to the active speaker.

   speakersees: defines whether the active speaker sees the "current"
   speaker (themselves) or the "previous" speaker.

      Open Issue: the ability to display the previous speaker is likely
      constrained by media server resources to limited use cases such as
      a simple voice activated switch conference.  Because of this,
      should this attribute be include as part of a VAS selector or
      should there be a mechanism specific to that specific use case?

8.5.3.2.  Sequencing Video Streams

   to be completed later.




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8.6.  Reserving Conference Resources

   Conference resources may be reserved by including the "<reserve>"
   element as a child of "<createconference>". "<reserve>" allows the
   specification of a set of resources which a media server will reserve
   for the conference.  Any requests for resources beyond those that
   have been reserved should be honored on a best-effort basis by a
   media server.

   attributes:

   required: boolean that specifies whether <createconference> should
   fail if the requested resources are not available.  When set to
   false, the conference will be created, with no reserved resources, if
   the complete reservation cannot be honored.  Default true.

   The resources to be reserved are defined using "<resource>" The
   contents of these elements describe a resource that is to be
   reserved.  Descriptions are implementation- dependent.  Each resource
   element may use the attribute "n" to define the quantity of the
   resource to reserve.

   For example, the following creates a conference and reserves two
   types of resources.  One resource element may represent resources
   that are shared by all participants of the conference with the other
   may represent resources that are reserved for each of the expected
   participants.

      <createconference>
         <reserve>
            <resource n="20">
               <!-- description of resources used by each participant -->
            </individual>
            <resource n="2">
               <!-- description of the shared conference resources -->
            </shared>
         </reserve>
      </createconference>


9.  Dialogs

   Dialogs are used for interaction with a user.  A dialog may consist
   of a simple atomic command such as playing an announcement, or it may
   be an entire sequence of interactions.  Dialogs may be speech or IVR
   dialogs with human participants, of fax dialogs with a machine.  A
   media server MUST support VoiceXML as the standard IVR language and
   MAY support other languages.  For example, MSCML [14] defines prompt,



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   collect, record and fax commands that would be suitable as a
   lightweight dialog language.

   The control resources associated with dialogs are separate from the
   MSML thread of execution.  When a dialog is started, MSML allocates
   the dialog control resources, and if successful, starts those
   resources executing.  MSML execution then continues without waiting
   for the dialog to complete.

   Media streams are created between the dialog target and other
   internal media server resources as part of dialog execution.  Stream
   creation is subject to the requirements defined in section 7.

9.1.  <dialogstart>

   "<dialogstart>" is used to instantiate media dialog on connections or
   conferences.  The dialog is specified either inline or by a URI [3].
   The dialog description MUST NOT be inline if the src attribute is
   present.

   The originator of the dialog is notified using a "msml.dialog.exit"
   event when the dialog completes.  Any results returned by the dialog
   when it exits are sent as a namelist to the event.

   The "msml.dialog.exit" event is also used when dialogs fail due to
   errors encountered fetching external documents or errors that occur
   within the dialog execution thread.  In this case, a namelist
   containing the items "dialog.exit.status" and
   "dialog.exit.description" is returned with the event to inform the
   client of the failure and the failure reason.  The values of these
   items are defined in section 9.  Information from the failed dialog
   may be returned as additional namelist items.

   attributes:

   target: an identifier of a connection or a conference which will
   interact with the dialog.  The identifier must not contain wildcards.
   Mandatory.

   src: the URL of the dialog description.  MUST NOT be used if the
   dialog description is inline.  Otherwise an error (422) will result
   and MSML document execution will stop.

   type: a MIME type which identifies the type of language used to
   describe the dialog. application/vxml+xml is used to identify
   VoiceXML [11].

   name: an instance name for the dialog.  If the attribute is not



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   present, the media server will assign an identifier to the dialog.
   If the attribute is present but the name is already associated with
   the target, an error (431) will result and MSML document execution
   will stop.  Any results that a dialog generates will be correlated to
   its identifier.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all "mark" attributes within an MSML document
   should be unique.

   The following example starts a VoiceXML dialog on a connection.

            <?xml version="1.0" encoding="UTF-8"?>
            <msml version="1.0">
               <dialogstart target="conn:abcd1234"
                   type="application/vxml+xml"
                   name="sample"
                   src="http://server.example.com/scripts/foo.vxml"/>
            </msml>

   If this dialog failed once its execution thread had begun, for
   example the fetch of the VoiceXML document failed, an example of the
   event which would be returned would be:

            <?xml version="1.0" encoding="UTF-8"?>
            <event name="msml.dialog.exit"
                   id="conn:abcd1234/dialog:sample">
               <name>dialog.exit.status</name>
               <value>423</value>
               <name>dialog.exit.description</name>
               <value>External document fetch error</value>
            </event>

9.2.  <dialogend>

   Dialog end is used to terminate a dialog created through
   <dialogstart> before it completes of its own accord.  The operation
   of <dialogend> depends on the dialog language being used by the
   executing context.  When that context is VoiceXML, a
   "connection.disconnected" event will be thrown to the VoiceXML
   application.

   <dialogend> allows the executing dialog the opportunity to gracefully
   complete before generating a "msml.dialog.exit" event.  Dialog
   results may be returned and will be contained as a namelist to that
   event.



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   attributes:

   id: the identifier of a dialog.  Mandatory.

   mark: a token which can be used to identify execution progress in the
   case of errors.  The value of the mark attribute from the last
   successfully executed MSML element is returned in an error response.
   Therefore the value of all "mark" attributes within an MSML document
   should be unique.

   For example, if the dialog from the previous example was still
   executing, the following would terminate the dialog and generate a
   "msml.dialog.exit" event.

            <?xml version="1.0" encoding="UTF-8"?>
            <msml version="1.0">
               <dialogend id="conn:abcd1234/dialog:sample"/>
            </msml>


10.  Response Codes

   The response codes defined in this section are returned as the value
   of the response attribute to the <result> element.  Some values may
   also be returned as part of a namelist to an "msml.dialog.exit" event
   generated when an executing dialog fails.

   Informational (1xx)

   Reserved for future use

   Success

      200 Ok

   Client Error (4xx)

      400 Bad Request
      401 Unknown Element
      402 Unsupported Element
      403 Missing mandatory element content
      404 Forbidden element content
      405 Invalid element content
      406 Unknown attribute







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      407 Attribute not supported
      408 Missing mandatory attribute
      409 Forbidden attribute is present
      410 Invalid attribute value

      420 Unsupported media description language
      421 Unknown media description language
      422 Ambiguous request (both URI and inline description)
      423 External document fetch error
      424 Syntax error in foreign language
      425 Semantic error in foreign language
      426 Unknown error executing foreign language

      430 Object does not exist
      431 Object instance name already used
      432 Conference name already in use
      433 reserved
      434 External document fetch error

      440 Cannot join objects of the specified class
      441 Objects have incompatible media types
      442 reserved
      443 reserved
      444 Number of media inputs exceeded

      450 Objects have incompatible media formats
      451 Incompatible media stream format

   Server Error (5xx)

      500 Internal media server error
      510 Not in service
      511 Service Unavailable
      520 No resource to fulfill request
      521 Internal limit exceeded


11.  Examples

   These examples focus on the MSML used by an Application Server (AS)
   to control services on a Media Server (MS).  They show the
   relationship between SIP signalling to establish media sessions and
   MSML service control commands.  For brevity, only the content of MSML
   messages is shown.  The examples assumes that the AS and MS use the
   IPv4 address and UDP port number of the audio stream (on the MS) to
   identify the MSML connection.

11.1.  Establishing a Dial-In Conference



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           UA                 Application Server        Media Server
           |                         |                           |
           |                         |        INVITE F1          |
           |                         |-------------------------->|
           |                         |           200 F2          |
           |                         |<--------------------------|
           |                         |           ACK F3          |
           |                         |-------------------------->|
           |                         |                           |
           |                         |     createconference> F4  |
           |                         |-------------------------->|
           |                         |           200 F5          |
           |                         |<--------------------------|
           |    INVITE (SDP UA) F6   |                           |
           |------------------------>|                           |
           |                         |      INVITE (SDP UA) F7   |
           |                         |-------------------------->|
           |                         |        200 (SDP MS) F8    |
           |                         |<--------------------------|
           |                         |           ACK F9          |
           |                         |-------------------------->|
           |     200 (SDP MS) F10    |                           |
           |<------------------------|                           |
           |        ACK F11          |                           |
           |------------------------>|                           |
           |                         |     <startdialog> F12     |
           |                         |-------------------------->|
           |                         |           200 F13         |
           |                         |<--------------------------|
           |                         |    HTTP interactions F14  |
           |                         |<------------------------->|
           |                         |  <event>(dialog.exit) F15 |
           |                         |<--------------------------|
           |                         |         <join> F16        |
           |                         |-------------------------->|
           |                         |           200 F17         |
           |                         |<--------------------------|
           |         ...             |            ...            |
           |                         |                           |
           |                         |     <startdialog> F18     |
           |                         |-------------------------->|
           |                         |           200 F19         |
           |                         |-------------------------->|
           |                         |    HTTP interactions F20  |
           |                         |<--------------------------|
           |                         |  <event>(dialog.exit) F21 |
           |                         |-------------------------->|
           |         ...             |            ...            |



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           |                         |                           |

   Steps 1-3: establish an MSML control channel for the conference.
   Alternatively, a control channel could already have been established
   which was used for all AS/MS interactions.  A control channel per
   conference is only one possible model.  Currently MSML uses SIP INFO
   requests and responses on this SIP dialog.  There is a proposal to
   use this message exchange to establish a TCP channel for MSML similar
   to the approach used for MRCPv2.  This approach would require that a
   request identifier be added to the <msml> element to correlate
   requests and responses.  This currently relies on the SIP INFO
   request and response for this property.  MSML messages are shown
   without specifying the transport in this example but it assumes a
   request/response correlation based on transport messages.

   Step 4: create a conference that will mix the loudest two speakers
   and report those speakers to the application server every ten
   seconds.  The media server will automatically terminate remaining
   media sessions and delete the conference and associated resources and
   when the control channel is terminated.

      <msml version="1.0">
         <createconference name="exampleConf" deletewhen="nocontrol"/>
             <audiomix>
                <n-loudest n="3"/>
                <asn ri="10s"/>
             </audiomix>
         </createconference>
      </msml>

   Step 5: conference created successfully

      <msml version="1.0">
         <result response="200"/>
      </msml>

   Steps 6-11: standard 3PCC establishment of a user initiated media
   session to a media server.  This is the equivalent of a dial-in
   conference participant.  The "To:" header returned by the MS in the
   200 response of Step F8 was:

   To: <sip:msml@ms.example.com>;tag=jd87dfg4h

   Step 12: request an initial dialog with the participant to prompt for
   their name, desired conference, etc.  The dialog completes by
   informing the participant they are joining the conference.  If this
   was not the first participant, the dialog could also announce the
   other participants.



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      <msml version="1.0">
         <dialogstart target="conn:jd87dfg4h"
             type="application/vxml+xml"
             src="http://server.example.com/scripts/initial.vxml"/>
      </msml>

   Step 13: dialog started successfully.  The dialog identifier is
   returned.

      <msml version="1.0">
         <result response="200"/>
         <dialogid>conn:jd87dfg4h/dialog:12v5tq9</dialogid>
      </msml>

   Step 14: sequence of HTTP VoiceXML dialog interactions.

   Step 15: the VoiceXML browser exits (but does not disconnect).  If a
   namelist had been specified within the VoiceXML <exit> element, it
   would have been included in the <event> sent to the AS.

      <msml version="1.0">
         <event name="msml.dialog.exit"
                id="conn:jd87dfg4h/dialog:12v5tq9"/>
      </msml>

   Step 16: join the participant to the conference and have the volume
   of their contributing audio automatically adjusted to a target level
   of -20 dBm0.

      <msml version="1.0">
         <join id1="conn:jd87dfg4h" id2="conf:exampleConf">
            <stream media="audio" dir="from-id1">
                <gain agc="true" tgtlvl="-20"/>
            </stream>
            <stream media="audio" dir="to-id1"/>
      </msml>

   Step 17: successfully joined to conference

      <msml version="1.0">
         <result response="200"/>
      </msml>

   Steps 6 through 17 are repeated for the second participant.







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   Step 18: play a join tone or message announcing the new participant
   to the conference.

      <msml version="1.0">
         <dialogstart target="conf:exampleConf"
             type="application/vxml+xml"
             src="http://server.example.com/scripts/joinmsg.vxml"/>
      </msml>

   Step 19: dialog started successfully.  The dialog identifier is
   returned.

      <msml version="1.0">
         <result response="200"/>
         <dialogid>conf:ExampleConf/dialog:j6fs8745</dialogid>
      </msml>

   Step 20: HTTP VoiceXML dialog interaction(s).

   Step 21: the VoiceXML browser exits.

      <msml version="1.0">
         <event name="msml.dialog.exit"
                id="conf:ExampleConf/dialog:j6fs8745"/>
      </msml>

   Steps 6 through 21 are repeated for the third and subsequent
   participants.

11.2.  Example of a Sidebar Audio Conference

   This example assumes that a conference has already been established
   as in the previous example.  It creates a sidebar conference that
   hears the main conference as a whisper.  Three participants are moved
   to the side bar.  After some period of time, the sidebar participants
   are returned to the main conference and the sidebar is deleted.















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   Step1: the sidebar conference is created.  It is joined half-duplex
   to the main conference and a manual gain object is inserted in the
   media stream.  Three participants are then moved from the main
   conference to the sidebar.  Although not shown, an AS could include
   the "mark" attribute in each element to allow recovery in the event
   of a mid- transaction error.

      <msml version="1.0">
         <createconference name="sidebarConf"
                           deletewhen="nomedia">
             <audiomix/>
         </createconference>
         <join id1="conf:sidebarConf" id2="conf:exampleConf">
             <stream media="audio" dir="to-id1">
                 <gain amt="-20"/>
             </stream>
         </join>
         <unjoin id1="conn:gs5s4-1" id2="conf:exampleConf"/>
         <join id1="conn:gs5s4-1" id2="conf:sidebarConf"/>
         <unjoin id1="conn:hd764gr9-2" id2="conf:exampleConf"/>
         <join id1="conn:hd764gr9-2" id2="conf:sidebarConf"/>
         <unjoin id1="conn:h37frdvgs65-3" id2="conf:exampleConf"/>
         <join id1="conn:h37frdvgs65-3" id2="conf:sidebarConf"/>
      </msml>

   Step 2: sidebar conference created successfully and participants
   joined.

      <msml version="1.0">
         <result response="200"/>
      </msml>

   Step 3: once the sidebar conference has completed, the participants
   are rejoined to the main conference.  The sidebar is destroyed
   automatically by the MS when the last media stream is removed as
   specified when the sidebar conference was created.

      <msml version="1.0">
         <unjoin id1="conn:gs5s4-1" id2="conf:sidebarConf"/>
         <join id1="conn:gs5s4-1" id2="conf:exampleConf"/>
         <unjoin id1="conn:hd764gr9-2" id2="conf:sidebarConf"/>
         <join id1="conn:hd764gr9-2" id2="conf:exampleConf"/>
         <unjoin id1="conn:h37frdvgs65-3" id2="conf:sidebarConf"/>
         <join id1="conn:h37frdvgs65-3" id2="conf:exampleConf"/>
      </msml>






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   Step 4: participants successfully moved to main conference and
   sidebar destroyed.

      <msml version="1.0">
         <result response="200"/>
      </msml>

11.3.  Example of Removing Conference

   This example assumes a conference created similar to the first
   example where there is an MSML control channel specific to the
   conference and the conference has been configured to be deleted when
   that channel is removed (using SIP).

   Steps 1-2: the AS signals BYE for the dialog used to establish the
   conference control channel.

   Steps 3-6: the MS initiates terminating the media sessions for each
   participant remaining in the conference.

   The MS deletes the conference and removes all resources when the last
   participant has been removed.

11.4.  Example of Modifying a Video Layout

   Assume that a conference named "example" is created using the
   following mixer descriptions.

       +---+---+
       | 1 | 2 |
       +---+---+
       | 3 | 4 |
       +---+---+

   <createconference name="quad-split">
      <audiomix>
         <n-loudest n="3"/>
         <asn ri="10s"/>
      </audiomix>
      <videolayout>
         <root size="CIF" background="white" />
         <selector id="default" method="vas" si="500ms">
            <region id="1" left="0" top="0" size="1/4"/>
         </selector>
         <region id="2" left="50%" top="0" size="1/4"/>
         <region id="3" left="0%" top="50%" size="1/4">
         <region id="4" left="50%" top="50%" size="1/4"/>
      </videolayout>



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   </createconference>

   The following would change the size of the video window to QCIF and
   the background color to the default "black".

   <modifyconference id1="conf:example">
      <videolayout>
         <root size="4CIF"/>
      </videolayout>
   </modifyconference>

   The relative location of the regions does not change.  However the
   sizes of the regions do change because they are relative to the size
   of the root window.  The result is a layout that looks identical but
   half the size.

   The following would freeze the video displayed in in region "2"
   without affecting any other attributes of that region.

   <modifyconference id1="conf:example">
      <videolayout>
         <region id="2" left="50%" top="0" size="1/4" freeze="true"/>
      </videolayout>
   </modifyconference>


12.  Change Summary

   The following are the primary changes between the -07 version of the
   draft and the -06 version:

   o  formatted the document according to the conventions defined in RFC
      2119.
   o  added a security considerations section.
   o  made VoiceXML the normative refernce for the IVR dialog language
      and removed references to proprietary languages.
   o  removed remaining references to "operators".

   The -06 version of the draft should not have been submitted.  Text
   specific to that draft was removed in -07.

   The following are the primary changes between the -05 version of the
   draft and the -04 version:

   o  none.

   The following are the primary changes between the -04 version of the
   draft and the -03 version:



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   o  none.

   The following are the primary changes between the -03 version of the
   draft and the -02 version:

   o  added framework for multimedia streams and defined video streams.
   o  added descriptions for audio mixes and video presentation layouts.
      The audio mix description replaces the "<createconference>"
      attributes "n", "asn" and, "ri".
   o  added the "<stream>" element to define a stream and several child
      elements that define properties of a stream.  Made the "<insert>"
      element a child of "<stream>".
   o  added the elements "<modifystream>" and "<modifyconference>" to
      modify streams and conferences respectively.
   o  moved the "term" attribute from "<destroyconference>" to
      "<createconference>" so that it can affect the behaviour when
      conferences are automatically deleted.
   o  deprecated the "<remove>" and "<cjoin>" elements.  Removing
      operators is now accomplished as part of "<modifystream>".
      Compressed join is no longer necessary because "<stream>" elements
      allow compressed media to be identified and a compressed join can
      be accomplished using the standard "<join>" element.

   The following are the primary changes between the -02 version of the
   draft and the -01 version:

   o  added the specialized join operations <cjoin> and <monitor>
   o  added "deletewhen" attribute to <createconference> to allow a
      media server to automatically delete conferences when the
      specified condition occurs
   o  clarified that <join> is used to change the duplexity of a media
      stream

   The following are the primary changes between the -01 version of the
   draft and the -00 version.

   o  added a glossary
   o  rewrote the description of objects to precisely distinguish
      between classes and instances.  All classes are now defined in
      MSML.  The "oper" class replaces "application defined classes".
   o  rewrote the description of identifiers.  All terms must use
      "class:instance" where the instance may be assigned by the client
      or media server. "/" replaces ";" as the term separator for
      identifiers.
   o  clarified the definition of connection identifiers and require
      that "conn" be the class for all forms of the identifier.





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   o  '*' wildcard allowed for an instance name in limited situations.
   o  alias only names a single connection.
   o  clarified SIP usage and transport neutrality.  All actions use
      mandatory explicit identifiers rather than inferring targets from
      a SIP dialog.
   o  changed the attribute name from "id" to "name" for client assigned
      instance names.
   o  fixed <destroy> so that MOML target is appended to the MSML target
      rather than the MSML event.
   o  changed xml+moml to moml+xml and xml+vxml to vxml+xml.
   o  changed "namelist" to "valuelist" in send.
   o  removed explicit "lhs" / "rhs" labeling of full duplex objects.
   o  added specification of result codes and when they are returned.


13.  Future Work

   The following work is planned:

   o  define extensibility for MSML.  Because not all media servers
      support video capabilities, those capabilities will be moved to
      separate video draft(s) that extend the base MSML audio
      capabilities.  Video may be defined in terms of two drafts; one
      which defines base IVR and video switched conferences and another
      which defines layout capabilities for continuous presence
      conferences.
   o  define MSML operation using the framework presented in [15]


14.  XML Schemas

   The MSML schema uses one core schema which includes another schema
   that defines the MSML datatypes.

   Note: the schema contains several XML errors and inconsistencies with
   the text.  These will be corrected as part of the extensibility
   support planned for the next version of this draft.

   The core schema is:

   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
     elementFormDefault="qualified"
     attributeFormDefault="unqualified">
     <xs:include schemaLocation="moml.xsd"/>
     <xs:include schemaLocation="msml-datatypes.xsd"/>
     <xs:element name="msml">
       <xs:complexType>



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         <xs:choice>
           <xs:group ref="msmlRequest" maxOccurs="unbounded"/>
           <xs:element name="event">
             <xs:complexType>
               <xs:choice maxOccurs="unbounded">
                 <xs:sequence>
                   <xs:element name="name"
                     type="msmlEventNameValue.datatype"/>
                   <xs:element name="value">
                     <xs:simpleType>
                       <xs:restriction base="xs:string">
                         <xs:pattern value="[a-zA-Z0-9.]+"/>
                       </xs:restriction>
                     </xs:simpleType>
                   </xs:element>
                 </xs:sequence>
               </xs:choice>
               <xs:attribute name="name"
                 type="msmlEventName.datatype" use="required"/>
               <xs:attribute name="id"
                 type="msmlEventSource.datatype" use="required"/>
             </xs:complexType>
           </xs:element>
           <xs:element name="result">
             <xs:complexType>
               <xs:sequence>
                 <xs:element name="description" minOccurs="0">
                   <xs:simpleType>
                     <xs:restriction base="xs:string">
                       <xs:pattern value="[a-zA-Z0-9.-_]+"/>
                     </xs:restriction>
                   </xs:simpleType>
                 </xs:element>
                 <xs:choice minOccurs="0" maxOccurs="unbounded">
                   <xs:element name="confid" type="confID.datatype"/>
                   <xs:element name="dialogid"
                     type="dialogID.datatype"/>
                 </xs:choice>
               </xs:sequence>
               <xs:attribute name="response">
                 <xs:simpleType>
                   <xs:restriction base="xs:string">
                     <xs:pattern value="\d{3}"/>
                   </xs:restriction>
                 </xs:simpleType>
               </xs:attribute>
             </xs:complexType>
           </xs:element>



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         </xs:choice>
         <xs:attribute name="version" type="xs:string"
           use="required" fixed="1.0"/>
       </xs:complexType>
     </xs:element>
     <xs:group name="msmlRequest">
       <xs:choice>
         <xs:element name="createconference">
           <xs:complexType>
             <xs:all>
               <xs:element name="audioMix" type="audioMixType"/>
               <xs:element name="videoLayout"
                 type="videoLayoutType"/>
               <xs:element name="reserve">
                 <xs:complexType>
                   <xs:sequence>
                     <xs:element name="resource" maxOccurs="unbounded">
                       <xs:complexType>
                         <xs:sequence>
                           <xs:any namespace="##other"
                             processContents="lax" minOccurs="0"
                             maxOccurs="unbounded"/>
                         </xs:sequence>
                         <xs:attribute name="n"
                           type="xs:positiveInteger" default="1"/>
                         <xs:anyAttribute namespace="##any"/>
                       </xs:complexType>
                     </xs:element>
                   </xs:sequence>
                   <xs:attribute name="required"
                     type="boolean.datatype" default="true"/>
                 </xs:complexType>
               </xs:element>
             </xs:all>
             <xs:attribute name="name" type="msmlInstanceID.datatype"/>
             <xs:attribute name="deletewhen" default="never">
               <xs:simpleType>
                 <xs:restriction base="xs:string">
                   <xs:enumeration value="nomedia"/>
                   <xs:enumeration value="nocontrol"/>
                   <xs:enumeration value="never"/>
                 </xs:restriction>
               </xs:simpleType>
             </xs:attribute>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="modifyconference">



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           <xs:complexType>
             <xs:all>
               <xs:element name="audioMix" type="audioMixType"/>
               <xs:element name="videoLayout" type="videoLayoutType"/>
             </xs:all>
           </xs:complexType>
         </xs:element>
         <xs:element name="destroyconference">
           <xs:complexType>
             <xs:attribute name="id" type="confID.datatype"
               use="required"/>
             <xs:attribute name="term" type="boolean.datatype"
               default="true"/>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="dialogstart">
           <xs:complexType>
             <xs:sequence>
               <xs:group ref="momlRequest"/>
               <xs:group ref="sendType" minOccurs="0"/>
             </xs:sequence>
             <xs:attribute name="target"
               type="independentID.datatype" use="required"/>
             <xs:attribute name="type" type="dialogLanguage.datatype"
               use="required"/>
             <xs:attribute name="name"
               type="msmlInstanceID.datatype"/>
             <xs:attribute name="src" type="xs:anyURI"
               use="optional"/>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="dialogend">
           <xs:complexType>
             <xs:attribute name="id" type="dialogID.datatype"
               use="required"/>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="join">
           <xs:complexType>
             <xs:sequence>
               <xs:element name="stream" type="streamType"
                 minOccurs="0" maxOccurs="4"/>
             </xs:sequence>
             <xs:attribute name="id1"
               type="independentID.datatype" use="required"/>



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             <xs:attribute name="id2"
               type="independentID.datatype" use="required"/>
             <xs:attribute ref="mark" type="mark.datatype"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="modifystream">
           <xs:complexType>
             <xs:sequence>
               <xs:element name="stream" type="streamType"
                 maxOccurs="4"/>
             </xs:sequence>
           </xs:complexType>
         </xs:element>
         <xs:element name="unjoin">
           <xs:complexType>
             <xs:sequence>
               <xs:element name="stream" type="streamType"
                 minOccurs="0" maxOccurs="4"/>
             </xs:sequence>
             <xs:attribute name="id1"
               type="independentID.datatype" use="required"/>
             <xs:attribute name="id2"
               type="independentID.datatype" use="required"/>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="monitor">
           <xs:complexType>
             <xs:attribute name="id1"
               type="connID.datatype" use="required"/>
             <xs:attribute name="id2"
               type="independentID.datatype" use="required"/>
             <xs:attribute name="compressed"
               type="boolean.datatype" default="false"/>
             <xs:attribute ref="mark" type="mark.datatype"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="send">
           <xs:complexType>
             <xs:attribute name="event"
               type="msmlEvent.datatype" use="required"/>
             <xs:attribute name="target"
               type="msmlTarget.datatype" use="required"/>
             <xs:attribute name="valuelist" type="xs:string"/>
             <xs:attribute ref="mark"/>
           </xs:complexType>
         </xs:element>
       </xs:choice>



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     </xs:group>
     <xs:complexType name="streamType">
       <xs:choice minOccurs="0" maxOccurs="unbounded">
         <xs:element name="gain">
           <xs:complexType>
             <xs:attribute name="amt" use="optional">
               <xs:simpleType>
                 <xs:restriction base="xs:integer">
                   <xs:minInclusive value="-96"/>
                   <xs:maxInclusive value="96"/>
                 </xs:restriction>
               </xs:simpleType>
             </xs:attribute>
             <xs:attribute name="agc" type="boolean.datatype"/>
             <xs:attribute name="tgtlvl" use="optional">
               <xs:simpleType>
                 <xs:restriction base="xs:nonPositiveInteger">
                   <xs:minInclusive value="-40"/>
                   <xs:maxInclusive value="0"/>
                 </xs:restriction>
               </xs:simpleType>
             </xs:attribute>
             <xs:attribute name="maxgain" default="10">
               <xs:simpleType>
                 <xs:restriction base="xs:nonNegativeInteger">
                   <xs:minInclusive value="0"/>
                   <xs:maxInclusive value="40"/>
                 </xs:restriction>
               </xs:simpleType>
             </xs:attribute>
           </xs:complexType>
         </xs:element>
         <xs:element name="clamp">
           <xs:complexType>
             <xs:attribute name="dtmf" type="boolean.datatype"/>
             <xs:attribute name="tones" type="boolean.datatype"/>
           </xs:complexType>
         </xs:element>
         <xs:element name="visual"/>
         <xs:element name="insert">
           <xs:complexType>
             <xs:group ref="momlRequest"/>
             <xs:attribute name="type"
               type="xs:string" use="required"
               fixed="application/moml+xml"/>
             <xs:attribute name="name"
               type="msmlInstanceID.datatype"/>
           </xs:complexType>



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         </xs:element>
       </xs:choice>
       <xs:attribute name="dir">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="to-id1"/>
             <xs:enumeration value="from-id1"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="media">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="audio"/>
             <xs:enumeration value="video"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="preferred" type="boolean.datatype"/>
       <xs:attribute name="display" type="xs:string"/>
     </xs:complexType>
     <xs:complexType name="audioMixType">
       <xs:all>
         <xs:element name="asn" minOccurs="0">
           <xs:complexType>
             <xs:attribute name="ri" type="posDuration.datatype"/>
           </xs:complexType>
         </xs:element>
       </xs:all>
       <xs:attribute name="contrib">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="n-loudest"/>
             <xs:enumeration value="all"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="n" type="xs:unsignedInt"/>
     </xs:complexType>
     <xs:complexType name="videoLayoutType">
       <xs:choice>
         <xs:element name="selector">
           <xs:complexType>
             <xs:complexContent>
               <xs:extension base="selectorType">
                 <xs:sequence>
                   <xs:element name="root" type="rootType"/>
                 </xs:sequence>



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               </xs:extension>
             </xs:complexContent>
           </xs:complexType>
         </xs:element>
         <xs:sequence>
           <xs:element name="root" type="rootType"/>
           <xs:choice maxOccurs="unbounded">
             <xs:element name="selector" minOccurs="0"
               maxOccurs="unbounded">
               <xs:complexType>
                 <xs:complexContent>
                   <xs:extension base="selectorType">
                     <xs:sequence>
                       <xs:element name="region"/>
                     </xs:sequence>
                   </xs:extension>
                 </xs:complexContent>
               </xs:complexType>
             </xs:element>
             <xs:element name="region" minOccurs="0"
               maxOccurs="unbounded">
               <xs:complexType>
                 <xs:complexContent>
                   <xs:extension base="regionType"/>
                 </xs:complexContent>
               </xs:complexType>
             </xs:element>
           </xs:choice>
         </xs:sequence>
       </xs:choice>
       <xs:attribute name="type" type="xs:string"
         use="required" fixed="text/msml-basic-layout"/>
     </xs:complexType>
     <xs:complexType name="regionType">
       <xs:attribute name="id" type="xs:string" use="required"/>
       <xs:attribute name="left" type="xs:positiveInteger"/>
       <xs:attribute name="top" type="xs:positiveInteger"/>
       <xs:attribute name="relativeSize">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="1/4"/>
             <xs:enumeration value="1/3"/>
             <xs:enumeration value="2/3"/>
             <xs:enumeration value="3/4"/>
             <xs:enumeration value="1"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>



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       <xs:attribute name="priority">
         <xs:simpleType>
           <xs:restriction base="xs:float">
             <xs:minInclusive value="0"/>
             <xs:maxExclusive value="1"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="title" type="xs:string"/>
       <xs:attribute name="titleTextColor" type="xs:string"/>
       <xs:attribute name="titleBackgroundColor" type="xs:string"/>
       <xs:attribute name="borderColor" type="xs:string"/>
       <xs:attribute name="borderWidth" type="xs:positiveInteger"/>
       <xs:attribute name="logo" type="xs:anyURI"/>
     </xs:complexType>
     <xs:complexType name="selectorType">
       <xs:attribute name="id" type="xs:string" use="required"/>
       <xs:attribute name="method" use="required">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="vas"/>
             <xs:enumeration value="sequence"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="status" default="active">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="active"/>
             <xs:enumeration value="disabled"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="si" type="posDuration.datatype"
         default="1s"/>
       <xs:attribute name="blankothers" type="xs:boolean"
         default="false"/>
       <xs:attribute name="speakersees" default="current">
         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="current"/>
             <xs:enumeration value="previous"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
     </xs:complexType>
     <xs:complexType name="rootType">
       <xs:attribute name="size" default="CIF">



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         <xs:simpleType>
           <xs:restriction base="xs:string">
             <xs:enumeration value="16CIF"/>
             <xs:enumeration value="4CIF"/>
             <xs:enumeration value="CIF"/>
             <xs:enumeration value="QCIF"/>
           </xs:restriction>
         </xs:simpleType>
       </xs:attribute>
       <xs:attribute name="backgroundcolor" type="xs:string"
         default="black"/>
       <xs:attribute name="backgroundimage" type="xs:anyURI"/>
     </xs:complexType>
     <xs:attribute name="mark" type="mark.datatype"/>
   </xs:schema>

   Following is the schema which defines the basic datatypes used by the
   other schema.  Note that several regular expressions required them to
   be split across two lines for formatting reasons.


   <?xml version="1.0" encoding="UTF-8"?>
   <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
      elementFormDefault="qualified"
         attributeFormDefault="unqualified">
      <xs:simpleType name="conferenceType.datatype">
         <xs:restriction base="xs:string">
            <xs:enumeration value="audio.basic"/>
            <xs:enumeration value="audio.advanced"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="msmlInstanceID.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="connID.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="conn:[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="confID.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="conf:[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="dialogID.datatype">
         <xs:restriction base="xs:string">



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            <xs:pattern
            value="conf:[a-zA-Z0-9.:-_]+/dialog:[a-zA-Z0-9.:-_]+"/>
            <xs:pattern
            value="conn:[a-zA-Z0-9.:-_]+/dialog:[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="independentID.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="conf:[a-zA-Z0-9.:-_]+"/>
            <xs:pattern value="conn:[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="duplex.datatype">
         <xs:restriction base="xs:string">
            <xs:enumeration value="half"/>
            <xs:enumeration value="full"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="confclass.datatype">
         <xs:restriction base="xs:string">
            <xs:enumeration value="standard"/>
            <xs:enumeration value="preferred"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="dialogLanguage.datatype">
         <xs:restriction base="xs:string">
            <xs:enumeration value="application/moml+xml"/>
            <xs:enumeration value="application/voicexml+xml"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="msmlEvent.datatype">
         <xs:restriction base="xs:string"/>
      </xs:simpleType>
      <xs:simpleType name="msmlEventName.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="msml.dialog.exit"/>
            <xs:pattern value="msml.conf.asn"/>
            <xs:pattern value="msml.dialog.exit"/>
            <xs:pattern value="[a-zA-Z0-9.:_-]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="msmlTarget.datatype">
         <xs:restriction base="xs:string">
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="msmlEventSource.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="conf:[a-zA-Z0-9.:_-]+"/>



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            <xs:pattern
            value="(conf:[a-zA-Z0-9.:_-]+| \
            conn:[a-zA-Z0-9.:_-]+)/dialog:[a-zA-Z0-9.:_-]+"/>
         </xs:restriction>
      </xs:simpleType>
      <xs:simpleType name="msmlEventNameValue.datatype">
         <xs:restriction base="xs:string"/>
      </xs:simpleType>
      <xs:simpleType name="mark.datatype">
         <xs:restriction base="xs:string">
            <xs:pattern value="[a-zA-Z0-9.:-_]+"/>
         </xs:restriction>
      </xs:simpleType>
   </xs:schema>



15.  Security Considerations

   MSML is invoked through other languages and protocols and as such
   security considerations depend on those environments.  Because MSML
   is capable of intercepting and modifying end user media, MSML clients
   MUST be authenticated and MSML transport channels MUST permit the use
   of both confidentialty and integrity mechanisms.  MSML servers MUST
   support the use of SRTP for media sessions.

   MSML being an XML based language, security considerations as defined
   by RFC 3023 [9]. are applicable.


16.  IANA Considerations

   IANA registration for the 'application/msml+xml' and 'text/
   msml-basic-layout' media types are planned.


17.  Acknowledgements

   Adnan Saleem and Yong Xin have provided key insights, both theoretic
   and through development experience.  Chris Boulton, Michael Rice, and
   Eric Burger helped clarify several issues.  Peter Danielsen has
   contributed thoughtful and detailed reviews for several versions of
   the draft.  Discussions with Garland Sharratt helped shape the
   initial requirements and provided motivation for this work.


18.  References




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18.1.  Normative References

   [1]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
        Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
        Session Initiation Protocol", RFC 3261, June 2002.

   [2]  Bray, T., Paoli, J., Sperberg-McQueen, C., and E. Maler,
        "Extensible Markup Language (XML) 1.0 (Second Edition)", W3C
        FirstEdition REC-xml-20001006, October 2000.

   [3]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
        Resource Identifiers (URI): Generic Syntax", RFC 2396,
        August 1998.

   [4]  Handley, M. and V. Jacobson, "SDP: Session Description
        Protocol", RFC 2327, April 1998.

   [5]  Donovan, S., "The SIP INFO Method", RFC 2976, October 2000.

   [6]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
        Extensions (MIME) Part Two: Media Types", RFC 2046,
        November 1996.

   [7]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", RFC 2119, March 1997.

   [8]  Bos, B., Lie, H., Lilley, C., and I. Jacobs, "Cascading Style
        Sheets, level 2 (CSS2) Specification", W3C REC REC-CSS2-
        19980512, May 1998.

   [9]  Murata, M., St.Laurent, S., and D. Kohn, "XML Media Types",
        RFC 3023, January 2001.

18.2.  Informative References

   [10]  Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
         "RTP Profile for Audio and Video Conferences with Minimal
         Control", RFC 3550, July 2003.

   [11]  Ferrans, J., Hunt, A., Lucas, B., Porter, B., Rehor, K.,
         Tryphonas, S., McGlashan, S., Burnett, D., Carter, J., and P.
         Danielsen, "Voice Extensible Markup Language (VoiceXML) Version
         2.0", W3C REC REC-voicexml20-20040316, March 2004.

   [12]  Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo,
         "Best Current Practices for Third Party Call Control (3pcc) in
         the Session Initiation Protocol (SIP)", RFC 3725, April 2004.




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   [13]  Van Dyke, J., Burger, E., and A. Spitzer, "Basic Network Media
         Services with SIP", draft-burger-sipping-netann-11 (work in
         progress), February 2005.

   [14]  Van Dyke, J., Burger, E., and A. Spitzer, "Media Server Control
         Markup Language (MSCML) and Protocol", draft-vandyke-mscml-06
         (work in progress), December 2004.

   [15]  Boulton, C. and T. Melanchuk, "Media Server Request Protocol",
         draft-boulton-media-server-control-00 (work in progress),
         July 2005.

   [16]  Ossenbruggen, J., Rutledge, L., Saccocio, B., Schmitz, P.,
         Kate, W., Ayars, J., Bulterman, D., Cohen, A., Day, K., Hodge,
         E., Hoschka, P., Hyche, E., Jourdan, M., Kubota, K., Lanphier,
         R., Layaida, N., Michel, T., and D. Newman, "Synchronized
         Multimedia Integration Language (SMIL 2.0) Specification", W3C
         REC REC-smil20-20010807, August 2001.

   [17]  Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
         Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
         HTTP/1.1", RFC 2616, June 1999.





























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Author's Address

   Tim Melanchuk

   Phone: +1 604 837 7867
   Email: tim.melanchuk@gmail.com













































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