SIP WG R. Mahy
Internet-Draft N. Ismail
Expires: August 25, 2003 Cisco Systems, Inc.
February 24, 2003
Media Policy Manipulation in the Conference Policy Control Protocol
draft-mahy-sipping-media-policy-control-00.txt
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Copyright Notice
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
The SIP conferencing framework defines a model for tightly-coupled
conferencing in the Session Initiation Protocol (SIP), in which a
Conference Policy Control Protocol is used to manipulate policies
relevant to a specific conference, such as conference membership
policy, authorization policy, and media policy. This document
describes a logical model to describe media processing in a SIP
conference. It also defines specific protocol semantics and a
specific syntax to manipulate that model.
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Table of Contents
1. Conventions . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1 Elements . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.2 Media Topology Graphs . . . . . . . . . . . . . . . . . . . 5
3. Media Policy Control High-Level Functions . . . . . . . . . 8
3.1 Transactions . . . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Inventory and Collection Management . . . . . . . . . . . . 9
4. Semantics . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Server Semantics--Media Topology operation semantics . . . . 9
4.1.1 Connecting input and output media streams to groups,
operators and collections . . . . . . . . . . . . . . . . . 10
4.1.2 Notifications of media policy changes . . . . . . . . . . . 10
4.2 Client Semantics . . . . . . . . . . . . . . . . . . . . . . 11
5. Standard Operations . . . . . . . . . . . . . . . . . . . . 11
5.1 Audio . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.1.1 Loudest Speaker . . . . . . . . . . . . . . . . . . . . . . 11
5.1.2 n-1 mixer . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.1.3 n-mixer . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1.4 n-1 filter . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1.5 Gain control . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2 Video . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.2.1 Video Tiling Operator . . . . . . . . . . . . . . . . . . . 13
5.2.2 Two Input Video Switch Operator (TIVS) . . . . . . . . . . . 13
5.2.3 Voice Activated Switch Operator (VAS) . . . . . . . . . . . 14
6. Standard Collections . . . . . . . . . . . . . . . . . . . . 15
7. Formal Syntax . . . . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 16
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 16
Normative References . . . . . . . . . . . . . . . . . . . . 16
Informational References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 17
Intellectual Property and Copyright Statements . . . . . . . 18
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1. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [2].
2. Overview
The SIP conferencing framework [3] defines a model for
tightly-coupled conferencing in SIP [1], in which a Conference Policy
Control Protocol is used to manipulate policies which are relevant to
a specific SIP conference, such as conference membership policy,
authorization policy, and media policy. While the conference policy
control protocol provides many non-media specific policies such as
membership policy and authorization policy, this document
specifically addresses #requirements# to manipulate the way in which
media in a SIP conference is selected, combined, and modified. It
defines a logical model of this type of media processing using a
"media topology graph". By manipulating the graph, authorized users
can change the media processing behavior of the mixers associated
with a specific SIP conference.
A media topology graph consists of individual media streams, logical
groups of media streams, and functions or "operations" performed on
those streams. These elements are typically associated with a
specific subconference. A subconference simply defines a context
which allows different groups of users to share a media topology and
participant roster with a subset of the participants in a conference.
Subconferences are defined in the conferencing framework, and are
typically used to enable conferencing sidebars. For convenience
purposes, subgraphs consisting of groups and operations, called
collections, can be defined, instantiated, and manipulated just like
individual elements. These elements and their properties are defined
below.
2.1 Elements
First are Streams. These are the actual media streams sent and/or
received by or on behalf of conference participants. Media streams
are typically established when conference participants join a
conference and are described by the SDP media lines in the offer/
answer exchange between the participants and the focus. Within the
media topology graph, each stream is described by a media type,
direction and at least one identifier. Media types can be audio,
video or text. Other media types can also be specified in the future.
Direction is "in" for streams originating from the conference
participants and "out" for streams terminating at the conference
participant. Stream identifiers can be network identifiers or
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aliases. Network identifiers consist of an address family (IPv4 or
IPv6), an IP address, and a port number.
Aliases can also be created for any of the streams, either
automatically or when created manually. One such automatic alias
consists of a participant identifier and optionally either the media
stream identification "mid" as specified in SDP or the position of
the media line describing the stream in SDP. Another set of automatic
aliases can be created automatically when per media line i-lines
appear in the SDP.
Conference Policy servers provide clients with stream descriptions
either as part of the SIP conferencing package or as responses to
inventory requests specified in section x. Clients use the stream
identifier that is part of the stream description to associate and
connect the stream to other media topology elements to achieve the
media policy required. open issue 2.1.1: Should we allow stream
identifiers to be a URL?. An example of that is notifications that
are either stored locally by the focus or one of its controlled
mixers or stored on an external web page.
Next are Groups. Media groups are created by clients within the
context of a sub-conference as specified in section y. A media group
has a media type and a name. Groups can be connected to streams,
operators and collections. An example is a group of audio streams
that are associated with the main sub-conference and is connected to
an operator that determines the loudest speaker.
Next are Operators. Operators are basic elements that perform simple
media operations. They select among media streams, combine streams,
or perform other media processing. Each operator has a type, one or
more inputs, one logical output, and an optional set of parameters.
The type uniquely identifies the operator and specifies the media
service offered. The input connectors specify the number and type of
streams required by the operator to perform its operation. An input
or output of an operator can be connected to streams, operators,
collections or groups. The number and type of parameters depend on
the type of the operator. Each type defines the semantics of the
operation and any parameters. Parameters define aspects of the
operator's function that can differ from one instance of the operator
to another.
This specification defines a set of standard operators (see section
z). Each standard operator has a unique type that will be registered
with IANA and an XML schema describing the operator. Server
implementations can support any of the set of standard operators.
Implementors can define their own operators and operator types. Each
newly defined operator needs a unique type and a published XML
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schema. Clients make inventory requests to a Server to get the set of
operators supported by the server.Clients can then instantiate
operators using the method specified in section y.
OPEN ISSUE: Should we use name spaces with types to guarantee uniqueness?
Finally there are Collections. Collections are complex elements
created by connecting different operators, groups, streams and other
collections together. Each collection provides a sophisticated media
service. Like operators, a collection has a type that uniquely
identifies it and specifies its function. Each collection has one or
more inputs, one logical output and an optional set of parameters.
This specification defines a set of standard collections that offer
the most common mixing and switching media functions available. Each
standard collection has a unique type that will be registered with
IANA and an XML schema describing the collection. Server
implementations can support any of the set of standard collections
and they can also define their own proprietary collections. Each
newly defined collection needs a unique type and a published XML
schema. Clients make inventory requests to Server to get the set of
collections supported by the server. Clients can then instantiate
collections using the method specified in section zz. Clients can
also make their own collections to provide new media services by
using the method specified in section y.
OPEN ISSUE: Likewise should we use namespaces here?
2.2 Media Topology Graphs
Below is a diagram which shows a sample media topology with streams,
collections, and groups.
Audio and Video Conference with one Audio Sidebar
(streams) (streams) (streams)
A B D E F H J A C D F G H I B E J
| | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | |
V V V V V V V V V V V V V V V V V
+-------------------+ +-------------------+ +-------------------+
| Main Video In | | Main Audio In | | Sidebar Audio Out |
| (group) | | (group) | | (group) |
+-------------------+ +-------------------+ +-------------------+
|| // || ||
|| // || ||
|| // || +-----+ ||
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|| // || | | ||
\/ // \/ | V \/
...................V. ..................... | .....................
. . . . | . .
. . . . | . .
. vendor . . standard . | . standard .
. defined . . conference . | . sidebar .
. video . . audio . | . audio .
. collection . . collection . | . collection .
. . . . | . .
. . . . | . .
..................... ..................... | .....................
|| || | ||
\/ \/ | \/
+-------------------+ +-------------------+ | +-------------------+
| Main Video Out | | Main Audio Out | | | Sidebar Audio Out |
| (group) | | (group) | | | (group) |
+-------------------+ +-------------------+ | +-------------------+
| | | | | | | | | | | | | | | | | | | |
| | | | | | | | | | | | | | | | | | | |
V V V V V V V V V V V V V V V +--+ V V V
A B C D E F H J A C D F G H I B E J
(streams) (streams) (streams)
Still need an ASCII art example of a topology graph (audio and
video?). Perhaps show tiled video example
This document defines numerous standard operations (in section x.y)
to facilitate interoperability. Implementors are free to extend this
list of operations, and an IANA registration process is defined for
this purpose. Note that specific conference servers may (MAY) support
as few or as many operations as they choose, however each conference
server needs to (MUST) support at least one standard collection
(these are defined in section x.y) per media type which the
conference server is capable of handling.
Media manipulation is generally media-specific. When a subconference
is created, an input group and an output group are automatically
created for each media type supported by the conference server, and a
specific collection can be instantiated (again, for each media type).
Once instantiated, collections are simply operations and groups
connected in some way. The resulting graph can be modified, attached,
detached, and deleted without affecting the collection from which the
graph was copied. Note also that more than one collection can be
incorporated into the topology graph for a given subconference and
media type.
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Manipulating the topology graph for a SIP conference enables a number
of useful features, many of which are described in the SIP
conferencing high-level requirements [4] document. Noisy participants
can be "muted" from a conference by disconnecting their audio from
the appropriate input group.
OPEN ISSUE: would you instead just set the media to send only
or inactive? doesn't seem as elegant. the participant gets
a new offer answer that way which does not seem desirable.
Participants can be moved to a sidebar by disconnecting their media
streams (some or all of them) and reconnecting them to the input and
output groups created for the corresponding subconference.
Interaction with #floor control# is coordinated by including an
operation which selects only media streams corresponding to
participants who have the appropriate floor. The resulting logical
output stream or group of streams can be connected to a suitable
mixing or combining operation (for example tiling for video), or
connected directly to a specific physical stream or streams.
Obviously, authorization is required to allow manipulation of media
topology by multiple parties (participants and non-participants
alike). The effects of manipulating the media topology graph can
range from simple, benign changes which only affect the participant
requesting the change, to complete failure of the conference. Clearly
no one-size-fits-all policy can be applied. However it is useful to
recognize several different categories or severities of impact.
o connecting and disconnecting your own streams to a group
o connecting and disconnecting another participants streams
o creating subconferences
o instantiating arbitrary operations or collections
o creating new groups
o connecting and disconnecting operations and collections to your
own groups
o connecting and disconnecting operations and collections which
affect an existing conference or subconference
The rest of the functions of the Conference Policy Control Protocol
(CPCP for brevity) are mostly orthogonal to media manipulation and so
they will be defined in a separate document. However it is important
to mention the interaction between the media topology-specific and
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other aspects of the policy. Conferences and subconferences can be
created and deleted by CPCP. Although not topology dependent, when
these are created the media topology will change automatically to
reflect this. Also, one participant may wish to invite several other
participants to a subconference (sidebar), but the initiating
participant may not have permission to change the stream connection
properties of all of the participants. In this case, the initiator
places the participant in a pending state. This informs the
participant that the initiator would like the participant to join the
sidebar. Then the participant (or an agent acting on his or her
behalf) either makes the requested change to the media topology by
connecting his or her streams to the appropriate groups (a media
topology task), or removes himself or herself from the pending list
(a non-media related task). Finally, in many cases authorized users
can set authorization policy related to a variety of aspects of
conference policy. While setting these policies is non-media related,
many uses of these policies do affect the media topology. Note that
because of this separation, it is possible to produce an
implementation of CPCP which runs on two separate servers, one
responsible for media topology and the other responsible for the
balance of conference policy functions.
3. Media Policy Control High-Level Functions
Manipulations of the media topology graph are performed as
transactions. This insures that the media graph transitions from one
consistent state to another. It should never be in a partially
connected or disconnected state. Note that operations are
automatically deleted unless they have at least one input connection
and at least one output connection. As a result, a transaction which
instantiates an operation must connect it to an input source and an
output source during the same transaction, otherwise adding the
operation would have no effect.
We define here a concrete syntax here in XML for specifying media
topology manipulation transactions, collection management, and
inventories.
3.1 Transactions
A <transaction> tag encloses one or more topology graph manipulation
steps which must all succeed or all fail. Within the transaction,
individual steps consist of either creating or instantiating elements
or connecting them together. Note that there is an important
distinction between groups and aliases and collections and
operations. Groups and aliases are created (they don't exist
before they are created), while collections and operations are
instantiated (a copy of the original is created). A summary of the
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steps within a transaction is below.
Transaction
instantiateOperation
instantiateCollection
createGroup
createAlias
destroyOperation
destroyCollection
deleteGroup
deleteAlias
connect
disconnect
3.2 Inventory and Collection Management
In addition there are primitives for fetch inventories and
manipulating Collections. A summary of these functions is below:
Inventory
inventoryCollections
showCollectionDetails
inventoryOperations
Collection
makeCollection
deleteCollection
4. Semantics
4.1 Server Semantics--Media Topology operation semantics
Servers must maintain a list of all operator and collection types
that can be used by Clients within a conference. Servers must return
such a list to all authorized Clients in response to inventory
queries. For operators and collections that have parameters, a list
of acceptable parameter values must also be specified for each
parameter.
For each transaction received by the Server it must proceed with the
steps that follow. For each request within the transaction the Server
must verify that the party initiating the request is authorized to
initiate this specific request in the context of the sub-conference
specified within the request. If the initiator is not authorized, the
Server must not execute any part of the transaction and return the
appropriate "Authorization Failure" response to the initiator. An
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example if user A requests to connect the input audio stream of user
B to group X in sub-conference "sidebar-1" and the output audio
stream of user B to group Y in sub-conference "sidebar-1". The Server
must verify that user A is authorized to manipulate the media policy
of user B and is authorized to manipulate "sidebar-1".
For each request the Server must verify that any changes in the media
policy of any participant as a result of the execution of the request
is authorized by the conference policy. If any party is not
authorized for the media policy changes that result from the
execution of any request within the transaction then the server must
not execute any part of the transaction and return the appropriate
"Authorization Failure" response to the initiator. In the example
used in the previous point, the Server must verify that user B is
authorized to join "sidebar-1".
The Server should verify that all requests to instantiate, create
and/or connect elements are conforming to the XML schema and
descriptions of the elements. If any request does not conform to the
XML schema of the elements that it is operating on then the Server
must not execute any part of the transaction and return the
appropriate "XML Schema Error" response to the initiator. For example
an operator that take one input connector of type video can not be
connected to an audio stream.
The Server should verify that all the relevant mixers have enough
resources to perform the actual media processing required as a result
of the execution of the transaction. If no enough resources are
available the Server must not execute any part of the transaction and
return the appropriate "No Available Resources" response to the
initiator. Note that resources needed for trans-coding and
trans-rating should be accounted for. Editor Note: More details and
some examples need to be provided to explain this section and
specially the last bullet.
4.1.1 Connecting input and output media streams to groups, operators and
collections
TBD [This section should specify where media streams should be
connected when a participant first join a conference or a
sub-conference. It also specify how Clients can use stream
identifiers to connect streams as well as participants to other
elements and what should the behaviour of the Server be.
4.1.2 Notifications of media policy changes
TBD [This sections specify the interactions needed between the media
policy server and the notification server to report the relevant
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changes to media policy to the relevant parties. Note that the
protocol should allow hidden transactions for which no notifications
will be sent as a result of the media policy change. All
authorization consideration specfified in section 5.2 should still be
followed.]
4.2 Client Semantics
To be written.
5. Standard Operations
Much more to do. A Partial list is below:
selectFloorHolder
smilLayout
xsltLayout
stereo2mono
selectByName
containsContributor
doesNotContainContributor
text2speech
speech2text
speech2gesture
speech2signlanguage
This sections specifies a set of operators that are needed to provide
the most common media processing operations used in conferencing
today. Each opertaor performs a specific function. Each operator has
a type to be registerd with IANA and an XML schema that defines how
Clients might use the operator. Each Server implementation is free to
support any number of these operators as well as define its own.
5.1 Audio
5.1.1 Loudest Speaker
The Loudest Speaker operator takes a set of audio streams in and
produces one output stream that is of the loudest speaker of the
list. The operator has two optional parameters. The "rank" paramreter
takes a value from one to the number of input audio streams available
to the operator. A rank value of "1" specifies the loudest speaker of
the set, a rank value of "2" specifies the second loudest speaker of
the set and so on. The second parameter is the "timeShift" parameter.
This parameter takes a value from "0" to maxTimeShift where
maxTimeShift is implementation dependent. A "timeShift" value of 0
specfies the current loudest speaker where as a "timeShift" value of
1 specfies the last loudest speaker and so on. The default rank
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parameter is 1 and the default timeShift parameter is 0. Below is the
XML schema describing the operator and using a maxTimeShift value of
3.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- definition of simple type elements -->
<xs:element name="operator"/>
<xs:complexType>
<xs:sequence>
<xs:element name="input" type=audio minOccurs="1" maxOccurs="unbounded"/>
<xs:elemnet name ="output" type=audio />
</xs:sequenec>
</xs:complexType>
<xs:attribute name="type" type=xs:string value="Loudest Speaker" use ="required"/>
<xs:attribute name="rank" type=xs:integer value=[1-]/>
<xs:attribute name="timeShift" type=xs:integer value=[0-3]/>
</xs:element>
</xs:schema>
5.1.2 n-1 mixer
The n-1 mixer mixes a set of audio streams and distribute them so
that participants do not receive their own stream. The operator has a
set of audio input connectors and opne "logical" output connector.
Note that the logical sonnector can actually consist of up to n
different streams. The first stream is distributed to the set of
participants that are not currently particpitaing in the mix. Each of
the other n-1 streams will be distributed to one of the participants
that are currently contributing to the mix. Each of the n-1 mixes
will consist of the normal mix after subtracting the input stream of
the participant to which the mix is distributed. Note that all the
logistic of the n-1 mixing and the correct distribution of the right
mix to the right participant will be handled by the implementation of
this operator. All the Client needs to worry about is instantiating
the n-1 mixer and connecting its input connectors to a set of
elements and typically connecting its output connector to an audio
group. Later we will see other implementations where the whole
process of handling the n-1 mixing has to be described by the Client
in details. The n-1 mixer has one optional parameter which determines
the number of input connectors it has (n). The values that "n" can
take differs from one implentation to another. Below is the XML
schema describing the n-1 mixer operator that has an n parameter than
can be 3 or 4.
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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- definition of simple type elements -->
<xs:element name="operator"/>
<xs:complexType>
<xs:sequence>
<xs:element name="input" type=audio minOccurs=n maxOccurs=n/>
<xs:elemnet name ="output" type=audio />
</xs:sequenec>
</xs:complexType>
<xs:attribute name="type" type=xs:string value="n-1Mixer" use ="required"/>
<xs:attribute name="n" type=xs:integer value=[3-4]/>
</xs:element>
</xs:schema>
5.1.3 n-mixer
TBD
5.1.4 n-1 filter
TBD
5.1.5 Gain control
TBD
5.2 Video
5.2.1 Video Tiling Operator
This operator combines the input video in a grid of x horizontal, by
y vertical panes (each input corresponding to a single pane).
5.2.2 Two Input Video Switch Operator (TIVS)
The two input video switch operator has two input-connectors. The
operator connects the stream connected to the first input connector
to all streams connected to the ouput connector that match the input
stream. The stream connected to the second input-connector is mapped
to the rest of the output stream(s).
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<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- definition of simple type elements -->
<xs:element name="operator"/>
<xs:complexType>
<xs:sequence>
<xs:element name="input" type=video minOccurs=2 maxOccurs=2/>
<xs:elemnet name ="output" type=video />
</xs:sequenec>
</xs:complexType>
<xs:attribute name="type" type=xs:string value="TIVS" use ="required"/>
</xs:element>
</xs:schema>
OPEN ISSUE: Should the matching criteria be fixed or should
it be definable as a parameter to the operator? Current
suggestion is that it would be fixed as following:
"two streams match if they belong to the same participant".
5.2.3 Voice Activated Switch Operator (VAS)
This is one of the most popular video operations. This operation has
two input connectors; one is typically connected to a group of video
streams and the other is connected to an audio stream. The audio
stream is typically the output of an audio operator (see Video
collections) such as the "Loudest Speaker". If any of the streams
connected to first input connector match the stream connected to the
second input connector then the operator maps the stream connected to
the first input connector to all the video stream(s) connected to the
output connector.
<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<!-- definition of simple type elements -->
<xs:element name="operator"/>
<xs:complexType>
<xs:sequence>
<xs:element name="input" type=video />
<xs:element name="input" type=audio />
<xs:elemnet name ="output" type=video />
</xs:sequenec>
</xs:complexType>
<xs:attribute name="type" type=xs:string value="VAS" use ="required"/>
</xs:element>
</xs:schema>
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6. Standard Collections
To do.
7. Formal Syntax
The following syntax specification uses XML schema as described in
xref target="***". This document includes several options for syntax,
including an XML Schema, a SOAP encoding, and an XML RPC encoding.
While drawing a conclusion at this time may be inappropriate, the XML
Schema provides the largest amount of semantic data and is also the
least verbose.
Example of proposed soap encoding:
<?xml version="1.0">
<env:Envelope xmlns:env="http://www.w3c.org/2002/12/soap-envelope">
<env:Body>
<transaction>
<conf>main</main>
<instantiateOperation>
<type>tileXbyY</type>
<id>xyz</id>
<x>2</x>
<y>2</y>
</instantiateOperation>
<connect>
<input>operation:main:tileXbyY:xyz</input>
<output>group:main:video:main.out</output>
</connect>
</transaction>
</env:Body>
</env:Envelope>
An XML schema encoding:
<transaction conf="main">
<instantiateOperation type="tileXbyY" id="xyz" x="2" y="2" />
<connect>
<input kind="operation" type="tileXbyY" id="xyz" conf="main" />
<output kind="group" media="video" name="main.out" conf="main"/>
</connect>
</transaction>
And finally an XML RPC encoding.
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<?xml version="1.0"?>
<methodCall>
<methodName>mpcpTransaction</methodName>
<params>
<param><value>main</value></param>
<param><value><struct>
<member><name>action</name> <value>instantiateOperation</value></member>
<member><name>type</name> <value>tileXbyY</value></member>
<member><name>id</name> <value>xyz</value></member>
<member><name>x</name> <value><int>2</int></value></member>
<member><name>y</name> <value><int>2</int></value></member>
</struct></value></param>
<param><value><struct>
<member><name>action</name> <value>connect</value></member>
<member><name>input</name> <value>operation:main:tileXbyY:xyz</value></member>
<member><name>output</name> <value>group:main:video:main.out</value></member>
</struct></value></param>
</params>
</methodCall>
8. Security Considerations
Need to write some real text. Authorization rules are discussed in
Section *n*.
9. IANA Considerations
This document defines an IANA registry
10. Acknowledgments
This work was the result of discussions among the SIP Conferencing
Design Team.
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] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Informational References
[3] Rosenberg, J., "A Framework for Conferencing with the Session
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Internet-Draft Media Policy for SIP Conferencing February 2003
Initiation Protocol",
draft-rosenberg-sipping-conferencing-framework-01 (work in
progress), February 2003.
[4] Levin, O., "Requirements for Tightly Coupled SIP Conferencing",
draft-levin-sipping-conferencing-requirements-02 (work in
progress), November 2002.
Authors' Addresses
Rohan Mahy
Cisco Systems, Inc.
101 Cooper St
Santa Cruz, CA 95060
USA
EMail: rohan@cisco.com
Nermeen Ismail
Cisco Systems, Inc.
170 W Tasman Dr
San Jose, CA 95134
USA
EMail: nismail@cisco.com
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