Network Working Group A. Saleem
Internet-Draft G. Sharratt
Expires: April 24, 2006 Convedia
October 21, 2005
Media Sessions Markup Language (MSML)
draft-melanchuk-sipping-msml-06
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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 the Media Objects
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Markup Language (MOML) or VoiceXML to interact with individual users
or with groups of conference participants.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions used in this document . . . . . . . . . . . . . . 5
3. Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. MSML SIP Usage . . . . . . . . . . . . . . . . . . . . . . . . 8
5. Language Structure . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Package Scheme . . . . . . . . . . . . . . . . . . . . . . 10
5.2. Profile Scheme . . . . . . . . . . . . . . . . . . . . . . 10
5.3. Execution Flow . . . . . . . . . . . . . . . . . . . . . . 11
5.4. MSML Root Element . . . . . . . . . . . . . . . . . . . . 12
5.5. Sending Events to a Media Server . . . . . . . . . . . . . 13
5.5.1. <send> . . . . . . . . . . . . . . . . . . . . . . . . 13
5.6. Transaction Results and Notifications . . . . . . . . . . 13
5.6.1. <result> . . . . . . . . . . . . . . . . . . . . . . . 13
5.6.2. <event> . . . . . . . . . . . . . . . . . . . . . . . 14
6. Media Server Object Model . . . . . . . . . . . . . . . . . . 15
6.1. Objects . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 18
7. Media Streams . . . . . . . . . . . . . . . . . . . . . . . . 21
7.1. <join> . . . . . . . . . . . . . . . . . . . . . . . . . . 22
7.2. <modifystream> . . . . . . . . . . . . . . . . . . . . . . 24
7.3. <unjoin> . . . . . . . . . . . . . . . . . . . . . . . . . 25
7.4. <stream> Elements . . . . . . . . . . . . . . . . . . . . 26
7.4.1. Audio Stream Properties . . . . . . . . . . . . . . . 27
7.4.2. Video Stream Properties . . . . . . . . . . . . . . . 28
7.5. <monitor> . . . . . . . . . . . . . . . . . . . . . . . . 29
8. Conferences . . . . . . . . . . . . . . . . . . . . . . . . . 30
8.1. <createconference> . . . . . . . . . . . . . . . . . . . . 30
8.2. <modifyconference> . . . . . . . . . . . . . . . . . . . . 32
8.3. <destroyconference> . . . . . . . . . . . . . . . . . . . 33
8.4. Audio Mix . . . . . . . . . . . . . . . . . . . . . . . . 34
8.4.1. N-Loudest . . . . . . . . . . . . . . . . . . . . . . 34
8.4.2. Active Speaker Notification . . . . . . . . . . . . . 34
8.5. Video Layout . . . . . . . . . . . . . . . . . . . . . . . 35
8.5.1. Root Layout . . . . . . . . . . . . . . . . . . . . . 35
8.5.2. Regions . . . . . . . . . . . . . . . . . . . . . . . 36
8.5.3. Stream Selection . . . . . . . . . . . . . . . . . . . 40
8.6. Reserving Conference Resources . . . . . . . . . . . . . . 42
9. Dialogs . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
9.1. <dialogstart> . . . . . . . . . . . . . . . . . . . . . . 43
9.2. <dialogend> . . . . . . . . . . . . . . . . . . . . . . . 44
10. Response Codes . . . . . . . . . . . . . . . . . . . . . . . . 46
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
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11.1. Establishing a Dial-In Conference . . . . . . . . . . . . 48
11.2. Example of a Sidebar Audio Conference . . . . . . . . . . 52
11.3. Example of Removing Conference . . . . . . . . . . . . . . 53
11.4. Example of Modifying a Video Layout . . . . . . . . . . . 54
12. Change Summary . . . . . . . . . . . . . . . . . . . . . . . . 56
13. XML Schemas . . . . . . . . . . . . . . . . . . . . . . . . . 59
14. Security Considerations . . . . . . . . . . . . . . . . . . . 70
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 71
16. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 72
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 73
17.1. Normative References . . . . . . . . . . . . . . . . . . . 73
17.2. Informative References . . . . . . . . . . . . . . . . . . 73
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 75
Intellectual Property and Copyright Statements . . . . . . . . . . 76
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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] allows complete single-party application
interfaces to be executed by a media server. Media Objects Markup
Language (MOML) [12] can be used to specify individual user dialog or
media control commands.
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 [14]
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.
MSML and MOML have been designed to work closely together: MOML
addresses the control and manipulation of media processing operations
(e.g., announcement, IVR, play and record, ASR/TTS, fax, video),
while MSML addresses the relationships of media streams (e.g., simple
and advanced conferencing). Together, MSML and MOML create a
general-purpose media server control architecture. MSML can
additionally be used to invoke other IVR languages such as VoiceXML.
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2. Conventions used in this document
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.
Operator: an intermediary object class that modifies or transforms a
media stream. Examples of operators may be audio gain controls,
video scaling, or voice masking. Specific types of operators are not
defined within MSML. Operators may be defined in MOML [12] or other
similar languages.
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], MOML, 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
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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 unidirectional or bidirectional.
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.
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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 [13] 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
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
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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. For example, dialogs defined in MOML can
send events based on user input. VoiceXML dialogs on the other hand,
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.
Both MOML [12] and VoiceXML [11] allow information to be returned
when they exit. These 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 <disconnect>.
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. Package Scheme
The primary mechanism for extending MSML is the "package". A package
is an integrated set of one or more XML schemas that define
additional features and functions via new or extended use of elements
and attributes. Each package is defined in a separate standards
document, e.g., an Internet Draft or an RFC. All packages, extending
the base MSML functionality, MUST include references to the MSML base
set of schemas provided in the Internet drafts.
A schema in a package MUST extend MSML or MOML, i.e., may not mix
MSML and MOML. A package MAY contain any combination of schemas
extending MSML and schemas extending MOML.
A particular MSML or MOML script will include references to all the
schemas defining the packages whose elements and attributes it makes
use of. A particular script MUST reference either MSML base and
optionally package(s) or MOML base and optionally package(s). See
IANA Considerations section 15.
Each package MUST have its own namespace so that elements or
attributes with the same name in different packages do not conflict.
A script using a particular element or attribute MUST prefix the
namespace name on that element or attribute's name if it is defined
in a package (as opposed to being defined in the base).
5.2. Profile Scheme
Not all devices and applications using MSML/MOML will need to support
the entire MSML/MOML base schema. For example, a media processing
device might support only audio announcements, only audio simple
conferencing, or only multimedia IVR. It is high desirable to have a
system for describing what portion of the MSML/MOML base a particular
media processing device or application server supports.
Since packages are the scheme used for describing chunks of MSML/MOML
functionality beyond the MSML/MOML base, one possibility might be to
break the MSML/MOML base into a number of packages. MSML/MOML,
however, is an XML-based language with sophisticated capabilities,
and audio and video capabilities, for example, are intertwined in the
schema. So it would not be technically feasible to break the MSML
base and the MOML base into individual packages.
A much better solution is to create profiles of the MSML/MOML for the
different uses. Each profile would identify a subset of the MOML/
MOML base element and attributes, and each profile would be
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accompanied by one or two corresponding schemas that are a subset of
the MSML base and/or the MOML base. To use the examples above, there
could be an audio announcements profile, an audio simple conferencing
profile, and a multimedia IVR profile.
These profiles would be published separately from the MSML/MOML base
documents, in one or more standards documents (e.g., Internet Drafts
or RFCs) dedicated to profiles. Profiles would not be registered
with IANA and any organization would additionally be free to create
its own profile(s) if required.
5.3. 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
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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
"<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, as well as an indication
of how much of the transaction was executed before the failure
occurred SHOULD be returned.
5.4. 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
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objects. All messages that a media server generates are correlated
to an object identifier. Objects and identifiers are discussed in
section 6.
Attributes:
version: "1.1" Mandatory
5.5. Sending Events to a Media Server
5.5.1. <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. When the identifier is for a dialog,
it may optionally be appended with a slash "/" followed by the target
to be included in a MOML <send>. 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.
5.6. Transaction Results and Notifications
5.6.1. <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.
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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>.
Three other child elements allow the response to include identifiers
for objects created by the request but which did not have instance
names specified by the client. Those elements are <confid> and
<dialogid>, for objects created though a <createconference> and
<dialogstart> respectively.
5.6.2. <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.
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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) [13] 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 bidirectional or unidirectional 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.
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 four
classes of media objects. Each class defines the basic properties of
how object instances are used within a media server. However most
classes require that the function of specific instances be defined by
the client, using MSML or other languages such as VoiceXML, or the
Media Objects Markup Language (MOML).
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)
o operator (oper)
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
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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
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 or MOML. 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. Dialog operations
are presented in section 9.
Operators are functions that are used to filter or transform a media
stream. The function that an instance of an operator fulfills is
defined as a property of the media stream. Operators may be
unidirectional or bidirectional and have a media type.
Unidirectional operators reflect simple atomic functions such as
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automatic gain control, filtering tones from conferences, or applying
specific gain values to a stream. Unidirectional operators have a
single media input, which is connected to the media stream from one
object, and a single media output, which is connected to the media
stream of a different object.
Bidirectional operators have two media inputs and two media outputs.
One media input and output is associated with the stream to one
object and the other input and output is associated with a stream to
a different object. Bidirectional objects may treat the media
differently in each direction. For example, an operator could be
defined which changed the media sent to a connection based upon
recognized speech or DTMF received from the connection. Operators
get instantiated when streams are created or modified using the
elements "<join>" element and elements "<modifystream>" respectively.
The relationships between the different object classes is shown in
the figure below.
+--------------------------------------+
| Media Server |
| |
|------+ ,---. |
| | +------+ / \ |
<== RTP ==>| conn |<---->| oper |<---->( conf ) |
| | +------+ \ / |
|------+ `---' |
| ^ ^ |
| | | |
| | +------+ +------+ | |
| | | | | | | |
| +-->|dialog| |dialog|<---+ |
| | | | | |
| +------+ +------+ |
+--------------------------------------+
A single, full-duplex instance of each object class is shown together
with common relationships between them. An operator (such as gain)
is shown between a connection and a conference and dialogs are shown
participating both with an individual connection and with a
conference. 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.
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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.
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. Dialogs depend upon
the existence of independent objects and this is reflected in the
composition of their identifiers. Operators modify the media flow
between other objects, such as application of gain between a
connection and a conference. As operators are merely media transform
primitives defined as properties of the media stream, they are not
represented by 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:
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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, the instance name
SHOULD 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, 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 MAY be 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:
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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 bidirectional audio stream
between two objects. Video and unidirectional 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
bidirectional 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 SHOULD 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 in 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
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independent objects. Streams may be audio or video and may be
bidirectional or unidirectional. A bidirectional stream is
implicitly composed of two unidirectional 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 bidirectional
audio stream. When only a stream of a single type has previously
been created between two objects, or when only a unidirectional
stream exists, "<join>" can be used to add a stream of another media
type or make the stream bidirectional by including the necessary
"<stream>" elements. Bidirectional streams are made unidirectional
by using "<unjoin>" (section 7.3) to remove the unidirectional 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 bidirectional 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
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customer. One join establishes a stream between the agent and the
customer and another join establishes a stream between the agent and
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, 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="1.1">
<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="1.1">
<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.
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Stream properties MUST be set as specified by the element "<stream>"
as a child element of "<modifystream>" element. Any properties not
included in the "<stream>" element when modifying a stream MUST
remain unchanged. Setting a property for only one direction of a
bidirectional stream MUST NOT affect the other direction. The
directionality of streams can be changed using issuing an "<unjoin>"
followed by a "<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
are RECOMMENDED to be unique.
7.3. <unjoin>
Unjoin removes one or more media streams between two objects. In the
absence of any content in "<stream>" element, all media streams
between the objects MUST be removed. Individual streams may be
removed by specifying them using "<stream>" elements, while the
unspecified streams MUST NOT be removed. A bidirectional stream is
changed to a unidirectional stream by unjoining the direction that is
no longer required, using the "<unjoin>" element. Operator elements
MUST NOT be specified within "<stream>" elements when streams are
being unjoined using the "<unjoin>" element. Any specified stream
operators MUST be ignored.
"<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.
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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.
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="1.1">
<unjoin id1="conn:jd73ht89sf489f" id2="conf:1"/>
<dialogstart target="conf:1" type="application/moml+xml">
<play>
<audio uri="file://leave_tone.wav"/>
</play>
</dialogstart>
</msml>
7.4. <stream> Elements
Individual streams are specified using the "<stream>" element. They
MAY be included as a child element 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 bidirectional stream is identified when no direction attribute
"dir" is present. A unidirectional 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
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"<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
to remove.
Some properties are defined within MSML as additional attributes or
child elements of "<stream>" that are media type specific. Ones for
audio streams and video streams are defined in the following two sub-
sections. Operators, viewed as properties of the media stream, MAY
be specified as child elements of the "<stream>" element.
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 other streams.
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 value of "true" means that the
stream MUST always be mixed while a value of "false" means that the
stream MAY contend for mixing into a conference when N-loudest mixing
is enabled. 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 may be used to adjust the volume of an audio
media stream. It may be set to a specific gain amount, to
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automatically adjust the gain to a desired target level, or to mute
the stream.
Attributes of the "<gain>" element are:
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 set to "true". This
attribute MUST NOT be specified if "agc" is not present.
maxgain: the maximum gain that AGC may apply. Maxgain is specified
in dB. This attribute MUST be used if "agc" is present and MUST NOT
be used when "agc" is not present.
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 can be used to change where in a video
presentation layout a video stream is displayed.
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Additional attributes of the "<stream>" element for video streams
are:
display: the identifier of a video layout region or selector that is
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 unidirectional 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.
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8. Conferences
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 may 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. When no mixer
descriptions are specified, the default behavior MUST be equivalent
to inclusion of a single "<audiomix>".
Clients can request that a media server automatically delete a
conference when a specified condition occurs by using the
"deletewhen" attribute. A value of "nomedia" indicates that the
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conference MUST be deleted when no mixes remain into the conference.
When this occurs, an "msml.conf.nomedia" event MUST be notified to
the MSML client. A value of "nocontrol" indicates the conference
MUST be deleted when the SIP [1] dialog that carries the
"<createconference>" element is terminated. When this occurs, a
media server MUST terminate all participant dialogs by sending a BYE
for their associated SIP dialog. A value of "never" MUST leave the
ability to delete a conference 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 5.6.2).
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 MAY 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="1.1">
<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 may 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 may also 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 may 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
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. Any
existing configuration aspects of a conference, which are not
specified within the "<modifyconference/>" element, MUST maintain
their current state in the Media Server.
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="1.1">
<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,
the video mix description ("<videolayout>") could specify that the
layout of the video being displayed should change such that the
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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 of the "term"
attribute when the conference was created..
When there is no element content, "<destroyconference/>" deletes the
entire conference. Individual mixer(s) are removed by including a
mixer description element identifying the mix(es) to be removed as
content to "<destroyconference/>". "<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 the specified mixer and MUST NOT affect any other existing
mixers. When "<audiomix/>" or "<videolayout/>" are identified for
individual removal, other feature aspects of the mix MUST NOT be
included. If specified, the Media Server MUST ignore any such
elements. When the last mixer is removed from a conference, a media
server MUST remove 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
the element is not present, all participants are mixed.
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 MUST be notified using the "<event>" element (section 5.6.2)
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 in 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 an
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 MUST 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 [15]. The default when omitted is "text/
msml-basic-layout".
id: an optional identifier for the video layout.
8.5.1. Root Layout
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. It MUST be present
when a video mix is created and it cannot be deleted, however its
attributes MAY be changed using the "<modifyconference>" element.
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 or freeze attribute is assigned the value "true", then the
Media Server MUST display the region either as a blank region, or the
video image frozen at the last received frame.
Open Issue: these attributes are specified for a region and not
allowed for streams because that appears to be the common use
case. Applying them to streams would allow only that stream to be
affected within a selector while other streams continue to display
normally. Except for personal mixing scenarios, the same effect
can be achieved by having the participant mute their own
transmission to the media server.
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, with a default of false, that defines
whether the video image should be frozen at the currently displayed
frame
blank: a boolean value, with a default of false, that defines whether
the region should display black instead of the associated video
stream
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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.
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>
All selector methods 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
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only a single region for methods that are defined to allow multiple
regions.
The selector or region for a participant's video is defined using the
"display" attribute of "<stream>" during a join operation.
Specifying a selector allows the stream to be displayed according to
the criteria defined by the selector method. Specifying a region
supports continuous presence display of participants. Some streams
may be joined with both a selector and a region. In this case, the
value of "<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.
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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. Media servers
that support MOML may use the elements from that language as the
basis for resource descriptions. 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>
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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 MOML [12] to allow command driven and fax
interactions, and SHOULD support VoiceXML to allow execution of
complex user interfaces. Other dialog languages MAY also be
supported.
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
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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/moml+xml and application/vxml+xml
are used to identify MOML and VoiceXML [11] respectively.
name: an instance name for the dialog. If the attribute is not
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="1.1">
<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
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executing context. When that context is VoiceXML, a
"connection.disconnected" event will be thrown to the VoiceXML
application. When that context is MOML, a "terminate" event will be
sent to the MOML context.
<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.
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="1.1">
<dialogend id="conn:abcd1234/dialog:sample"/>
</msml>
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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
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)
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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
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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 signaling 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
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 |
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| |-------------------------->|
| | 200 F17 |
| |<--------------------------|
| ... | ... |
| | |
| | <startdialog> F18 |
| |-------------------------->|
| | 200 F19 |
| |-------------------------->|
| | HTTP interactions F20 |
| |<--------------------------|
| | <event>(dialog.exit) F21 |
| |-------------------------->|
| ... | ... |
| | |
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="1.1">
<createconference name="exampleConf" deletewhen="nocontrol"/>
<audiomix>
<n-loudest n="3"/>
<asn ri="10s"/>
</audiomix>
</createconference>
</msml>
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Step 5: conference created successfully
<msml version="1.1">
<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.
<msml version="1.1">
<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="1.1">
<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="1.1">
<event name="msml.dialog.exit"
id="conn:jd87dfg4h/dialog:12v5tq9"/>
</msml>
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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="1.1">
<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="1.1">
<result response="200"/>
</msml>
Steps 6 through 17 are repeated for the second participant.
Step 18: play a join tone or message announcing the new participant
to the conference.
<msml version="1.1">
<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="1.1">
<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="1.1">
<event name="msml.dialog.exit"
id="conf:ExampleConf/dialog:j6fs8745"/>
</msml>
Steps 6 through 21 are repeated for the third and subsequent
participants.
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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.
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="1.1">
<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="1.1">
<result response="200"/>
</msml>
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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="1.1">
<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>
Step 4: participants successfully moved to main conference and
sidebar destroyed.
<msml version="1.1">
<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.
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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>
</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 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>
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</modifyconference>
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12. Change Summary
The following is a summary of changes between the -06 version of the
draft and the -05 version:
o This version is derived from earlier versions co-authored by Tim
Melanchuk and Garland Sharratt.
o Reformatting of document according to conventions stated in RFC
2119.
o Restated the description of operators to indicate that they are
not MOML objects. Rather, operators are media transform functions
operating on or defined as properties of media streams. Operators
are defined as primitive MSML elements, such as gain.
o Removed references to "<insert>" element, which is not required
since operators defined as MOML objects are no longer inserted.
o Clarifications added in several places indicating expected
behavior when elements or attributes are omitted.
o Changed MSML version number from 1.0 to 1.1
The following is a summary of changes between the -05 version of the
draft and the -04 version:
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 behavior when
conferences are automatically deleted.
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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.
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.
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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.
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13. XML Schemas
The MSML schema uses one core schema which includes two other
schemas; one defines the MSML datatypes, the other is for MOML which
is optionally used for dialogs.
The core schema is:
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema elementFormDefault="qualified"
attributeFormDefault="unqualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:include schemaLocation="moml.xsd"/>
<xs:include schemaLocation="msml-datatypes.xsd"/>
<xs:element name="msml">
<xs:complexType>
<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>
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<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:attribute name="mark" type="mark.datatype"/>
</xs:complexType>
</xs:element>
</xs:choice>
<xs:attribute name="version" type="xs:string"
use="required" fixed="1.1"/>
</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">
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<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 name="term" type="boolean.datatype" default="true"/>
<xs:attribute ref="mark"/>
</xs:complexType>
</xs:element>
<xs:element name="modifyconference">
<xs:complexType>
<xs:all>
<xs:element name="audioMix" type="audioMixType" minOccurs="0"/>
<xs:element name="videoLayout" type="videoLayoutType" minOccurs="0"/>
</xs:all>
<xs:attribute name="id" type="confID.datatype" use="required"/>
<xs:attribute ref="mark"/>
</xs:complexType>
</xs:element>
<xs:element name="destroyconference">
<xs:complexType>
<xs:all>
<xs:element name="audioMix" type="basicAudioMixType" minOccurs="0"/>
<xs:element name="videoLayout"
type="basicVideoLayoutType" minOccurs="0"/>
</xs:all>
<xs:attribute name="id" type="confID.datatype" use="required"/>
<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>
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<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"/>
<xs:attribute name="id2" type="independentID.datatype" use="required"/>
<xs:attribute ref="mark"/>
</xs:complexType>
</xs:element>
<xs:element name="modifystream">
<xs:complexType>
<xs:sequence>
<xs:element name="stream" type="streamType" maxOccurs="4"/>
</xs:sequence>
<xs:attribute name="mark" type="mark.datatype"/>
</xs:complexType>
</xs:element>
<xs:element name="unjoin">
<xs:complexType>
<xs:sequence>
<xs:element name="stream" type="basicStreamType"
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"/>
</xs:complexType>
</xs:element>
<xs:element name="send">
<xs:complexType>
<xs:attribute name="event" type="msmlEvent.datatype" use="required"/>
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<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>
</xs:group>
<xs:complexType name="basicStreamType">
<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:complexType>
<xs:complexType name="streamType">
<xs:complexContent>
<xs:extension base="basicStreamType">
<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>
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<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:choice>
<xs:attribute name="preferred" type="boolean.datatype"/>
<xs:attribute name="display" type="xs:string"/>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="basicAudioMixType">
<xs:attribute name="id" type="xs:string" use="required"/>
</xs:complexType>
<xs:complexType name="audioMixType">
<xs:complexContent>
<xs:extension base="basicAudioMixType">
<xs:all>
<xs:element name="asn" minOccurs="0">
<xs:complexType>
<xs:attribute name="ri" type="posDuration.datatype"/>
</xs:complexType>
</xs:element>
<xs:element name="n-loudest" minOccurs="0">
<xs:complexType>
<xs:attribute name="n" type="xs:positiveInteger" use="required"/>
</xs:complexType>
</xs:element>
</xs:all>
</xs:extension>
</xs:complexContent>
</xs:complexType>
<xs:complexType name="basicVideoLayoutType">
<xs:attribute name="id" type="xs:string" use="required"/>
<xs:attribute name="type" type="xs:string"
use="required" fixed="text/msml-basic-layout"/>
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</xs:complexType>
<xs:complexType name="videoLayoutType">
<xs:complexContent>
<xs:extension base="basicVideoLayoutType">
<xs:choice>
<xs:element name="selector">
<xs:complexType>
<xs:complexContent>
<xs:extension base="selectorType">
<xs:sequence>
<xs:element name="root" type="rootType"/>
</xs:sequence>
</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:extension>
</xs:complexContent>
</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">
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<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>
<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">
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<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">
<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 elementFormDefault="qualified"
attributeFormDefault="unqualified"
xmlns:xs="http://www.w3.org/2001/XMLSchema">
<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>
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<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="operatorID.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="dialogID.datatype">
<xs:restriction base="xs:string">
<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"/>
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<xs:pattern value="msml.conf.nomedia"/>
<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:pattern value="conf:[a-zA-Z0-9.:_-]+(/oper:[a-zA-Z0-9.:_-]+|\*)*"/>
<xs:pattern value="conn:[a-zA-Z0-9.:_-]+(/oper:[a-zA-Z0-9.:_-]+|\*)+"/>
</xs:restriction>
</xs:simpleType>
<xs:simpleType name="msmlEventSource.datatype">
<xs:restriction base="xs:string">
<xs:pattern value="conf:[a-zA-Z0-9.:_-]+"/>
<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>
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14. Security Considerations
MSML is invoked through other languages and protocols and as such
security considerations depend on those environments. MSML being an
XML based language, security considerations as defined by RFC 3023
[9]. are applicable.
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15. IANA Considerations
IANA registration for 'application/msml+xml' media type is planned.
MGCP and Megaco/H.248 packages are registered with IANA so that there
is no conflict between packages developed by different authors. The
package scheme planned for future extensibility of MSML/MOML will
also require IANA registry of packages.
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16. Acknowledgements
Version -06 was derived from earlier versions co-authored by Tim
Melanchuk (contact: "<tim.melanchuk@gmail.com>") and Garland
Sharratt.
Adnan Saleem and Yong Xin of Convedia provided key insights, both
theoretic and through development experience, on several earlier
versions of the drafts. Stephen Buko and George Raskulinec of Intel
made numerous valuable contributions for new feature additions to
MSML and MOML versions -06. Gilles Compienne and Ben Smith, both of
Ubiquity Software, provided feedback on several versions. Chris
Boulton of Ubiquity, and Michael Rice of VocalData helped clarify
several issues in the -00 draft, while Bruce Walsh and Kevin
Fitzgerald, both of Spectel, provided important feedback on that
draft. Peter Danielsen of Lucent has contributed thoughtful and
detailed reviews for several versions of the draft.
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17. References
17.1. 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", 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.
17.2. 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] Sharratt, G., Saleem, A., and T. Melanchuk, "Media Objects
Markup Language (MOML)", draft-melanchuk-sipping-moml-06 (work
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in progress), October 2005.
[13] 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.
[14] Van Dyke, J., Burger, E., and A. Spitzer, "Basic Network Media
Services with SIP", draft-burger-sipping-netann-11 (work in
progress), February 2005.
[15] 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.
[16] 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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Authors' Addresses
Adnan Saleem
Convedia
4190 Still Creek Drive, Suite 300
Vancouver, BC V5C 6C6
Canada
Phone: +1 604 918 6376
Email: asaleem@convedia.com
Garland Sharratt
Convedia
4190 Still Creek Drive, Suite 300
Vancouver, BC V5C 6C6
Canada
Phone: +1 604 918 6393
Email: gsharratt@convedia.com
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