XCON Working Group M. Barnes
Internet-Draft Nortel
Expires: January 16, 2006 C. Boulton
Ubiquity Software Corporation
O. Levin
Microsoft Corporation
July 15, 2005
A Framework and Data Model for Centralized Conferencing
draft-ietf-xcon-framework-01
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Abstract
This document defines the framework for Centralized Conferencing
(XCON), which is applicable to participants using different call
control signaling protocols and exchanging media over networks with
potentially different characteristics. The XCON Framework defines
the XCON data model, the XCON logical entities, the naming
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conventions, and outlines the standard conferencing protocols
(complementary to the call control signalling protocols) for building
advanced conferencing applications. The framework binds all the
defined components together for the benefit of conferencing system
builders.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. XCON Data Model . . . . . . . . . . . . . . . . . . . . . . . 9
4.1 Common Conference Information . . . . . . . . . . . . . . 11
4.2 Conference Template . . . . . . . . . . . . . . . . . . . 12
4.3 Conference policies . . . . . . . . . . . . . . . . . . . 12
5. XCON Constructs and Identifiers . . . . . . . . . . . . . . . 13
5.1 Conference Identifier . . . . . . . . . . . . . . . . . . 13
5.2 Conference Instance . . . . . . . . . . . . . . . . . . . 13
5.3 Conference Object . . . . . . . . . . . . . . . . . . . . 14
5.3.1 Conference Object Identifier . . . . . . . . . . . . . 16
5.4 Conference User Identifier . . . . . . . . . . . . . . . . 17
6. Conferencing System Realization . . . . . . . . . . . . . . . 18
6.1 Cloning Tree . . . . . . . . . . . . . . . . . . . . . . . 19
6.2 Ad-hoc Example . . . . . . . . . . . . . . . . . . . . . . 21
6.3 Advanced Example . . . . . . . . . . . . . . . . . . . . . 22
6.4 Scheduling a 'Conference Object for Reservation' . . . . . 24
7. Conferencing Mechanisms . . . . . . . . . . . . . . . . . . . 28
7.1 Call Control Signalling . . . . . . . . . . . . . . . . . 28
7.2 Notifications . . . . . . . . . . . . . . . . . . . . . . 28
7.3 Conference Control Protocol . . . . . . . . . . . . . . . 28
7.3.1 CPCP . . . . . . . . . . . . . . . . . . . . . . . . . 29
7.3.2 CCCP . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.3.3 CSCP . . . . . . . . . . . . . . . . . . . . . . . . . 30
7.3.4 NETCONF . . . . . . . . . . . . . . . . . . . . . . . 30
7.3.5 SOAP . . . . . . . . . . . . . . . . . . . . . . . . . 31
7.4 Floor Control . . . . . . . . . . . . . . . . . . . . . . 31
8. Conferencing Scenario Realizations . . . . . . . . . . . . . . 33
8.1 Participant Manipulations . . . . . . . . . . . . . . . . 33
8.2 Media Manipulations . . . . . . . . . . . . . . . . . . . 35
8.3 Sidebar Manipulations . . . . . . . . . . . . . . . . . . 36
8.4 Whispering or Private Messages . . . . . . . . . . . . . . 38
8.5 Conference Announcements and Recordings . . . . . . . . . 38
9. Relationships between SIPPING and XCON Frameworks . . . . . . 38
10. Security Considerations . . . . . . . . . . . . . . . . . . 38
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . 40
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40
13. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . 41
14. Changes since last Version . . . . . . . . . . . . . . . . . 41
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
15.1 Normative References . . . . . . . . . . . . . . . . . . . 43
15.2 Informative References . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 45
Intellectual Property and Copyright Statements . . . . . . . . 47
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1. Introduction
This document defines the framework for Centralized Conferencing
(XCON), which is applicable to participants using various call
signalling protocols (such as SIP, H.323, Jabber, HTML, PSTN, etc.)
and exchanging media over networks with potentially different
characteristics.
The XCON Framework defines the XCON data model, the XCON logical
entities, the naming conventions, and outlines the standard
conferencing protocols (complementary to the call control signalling
protocols) for building advanced conferencing applications. The
framework binds all the defined components together for the benefit
of conferencing system builders.
The XCON Framework is compatible with the functional model presented
in the SIPPING Conferencing Framework [9] . Section 9 of this
document discusses the relationship between the XCON Framework and
the SIPPING Conferencing framework, in the context of the XCON
architecture.
2. Conventions and Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
The XCON Framework document both generalizes, when appropriate, the
SIPPING Conferencing Framework [9] terminology and introduces new
concepts as listed below.
Active Conference: The term Active Conference refers to a Conference
Object that's been created (for example, using a "blueprint") and
"activated" via the allocation of its identifiers (i.e.
Conference Object Identifier, Conference Identifier) and the
associated Focus.
Call (Control) Signalling: The protocol used between a participant
and a Focus. In this context, the term "call" means a channel or
session used for media streams establishment. Protocol examples
include, but are not limited to, SIP, H.323, MSRP, Jabber, HTML
and PSTN signalling. Other than references to general
functionality required (e.g. establishment and teardown), details
of these protocols are outside the scope of this document.
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Common Conference Information: The data type (i.e. the XML schema)
which is used to represent the fixed information part of a
Conference Object. It includes a common set of definitions for
basic conference features, such as conference identifiers,
membership, signalling, capabilities, media, etc.
Conference Control Protocol (CCP): A protocol used by clients to
manipulate a Conference Object [Section 7.3].
Conference Factory: A logical entity that, upon request, generates
unique URI(s) to identify and represent a conference Focus. The
Conference Factory is typically used in the conference creation
process via a signalling interface and non-signalling methods such
as Conference Control Protocol [Section 7.3] and proprietary
mechanisms.
Conference Identifier(ID): The call signalling protocol-specific URI
that uniquely identifies a conference Focus and its associated
Conference Instance.
Conference Instance: An instantiation of a Conference Object. The
Conferencing System associates a Conference Instance with the
Conference Identifier(s). There is a one-to-one mapping between a
Conference Instance and a conference Focus.
Conference Object: A representation of a conference at a certain
stage (e.g. description upon conference creation, reservation,
activation, etc.), which a Conferencing System maintains in order
to describe the system capabilities and to provide access to the
available services provided by the Conferencing System. All
Conference Objects are of type 'Conference Object Type' which is
comprised of two distinct sub components; the 'Common Conference
Information' and the 'Conference Template' (see definitions in
this section for details).
Conference Object Identifier (ID): A [TBD schema name] URI which
uniquly identifies a Conference Object and is being used by a
Conference Control Protocol [Section 7.3].
Conference policies: A term which is used to collectively refer to a
virtual set of rights, permissions and limitations pertaining to
operations being performed on a certain Conference Object. The
term is described in more details in Section 4.3.
Conference State: The state of a Conference Instance as represented
using the Conference Package mechanism defined in [11].
Conferencing System: The term used to refer to a conferencing
solution (system) that is based on the set of specifications and
is built using the protocols and the data model defined by the
XCON working group within the IETF.
Conference Template: The data type (i.e. the XML schema) which is
used to represent the variable information part of the Conference
Object. It can be included in the Conference Object to represent
enhanced conferencing capabilities (e.g. media mixers, etc.)
and/or user interface abstraction.
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Floor: A term which is used to refer to a set of data or resources
associated with a Conference Instance, for which a conference
participant (or group of participants) is granted temporary input
access.
Floor Chair: A Floor control protocol compliant client (human
participant or automated entity) who is authorized to manage
access to one floor (grants, denies, or revokes a floor). The
floor chair does not have to be a participant in the Conference
Instance.
Focus: Focus is a logical entity that maintains the call signalling
interface between each participating client (i.e. participant) and
the Conference Instance. As such, the Focus acts as an endpoint
for each of the supported signalling protocols and is responsible
for all primary conference membership operations (e.g. join,
leave, update the Conference Instance) and for media negotiation/
maintenance between a conference participant and the Focus. There
is a one-to-one mapping between the Focus and its Conference
Instance. Focus is addressed by explicitly associated unique
conference URIs for each signalling protocol, supported for its
Conference Instance.
Media Graph: The logical representation of the flow of media for a
conference.
Media Mixer: A logical entity that has the capability to combine
media inputs of the same type (or/and transcode the media) and
distribute the result(s) to a single or multiple outputs. In this
context, the term "media" means any type of data being delivered
over the network using appropriate transport means, such as RTP/
RTCP (defined in RFC 3550[7]), Message Session Relay Protocol
(defined in [25]), etc.
Registered Conference Document : An official standards document (RFC)
that defines and registers a Conference Template schema with the
appropriate standards body (IANA). A 'Registered Conference
Document' also includes any complimentary textual information in
relation to the conference template schema and its meaning.
Role: Represents differing membership categories that a conference
participant can assume within a conference. Each category has a
difference set of conference operations that a participant can
perform. A default (e.g. Standard Conference Participant) 'Role'
will always exist which provides a standard user with a set of
basic conference operations. Any user with appropriate
authentication and authorization may assume a role that has a
wider set of conference operations that are otherwise not
available (to a standard Conference Participant) - e.g. A 'Role'
called 'Conference Moderator' may exist that has additional
conference operations such as 'modify conference end time'.
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Sidebar: TBD.
Whisper: TBD.
3. Overview
A centralized conference is an association of endpoints (called
conference participants) with a central endpoint (called a conference
Focus) where the Focus has direct peer-wise relationships with the
participants by maintaining a separate call control signalling
interface with each. Consequently, in this tightly coupled model,
the call control signalling graph is always a star.
The most basic conference supported would be an ad-hoc unmanaged
conference, which would not necessarily require any of the
functionality defined within this framework. For example, it could
be supported using basic SIP signalling functionality with a
participant serving as the Focus; the SIPPING Conferencing Framework
[9] together with the SIP Call Control Conferencing for User
Agents[15] documents address these types of scenarios.
An XCON-compliant Conferencing System, in addition to the basic
features, can offer richer functionality including dedicated
conferencing applications with explicitly defined capabilities,
reserved reoccurring conferences, and the standard protocols for
managing and controlling different conference aspects.
The core requirements for tightly managed centralized conferencing
are outlined in [10]. These requirements are applicable for
conferencing systems using various call control signalling protocols,
not restricted to SIP alone. Additional conferencing requirements
are provided in [12], [13], and [14].
The XCON architecture is built around a fundamental concept of a
Conference Object. A Conference Object is a logical representation
of a Conference Instance. For conference creation, a Conference
Object provides a "blueprint" representing the System Capabilities.
A conference object also provides the logical representation of a
conference during each of the various stages of a conference (e.g.
reservation, active, completed, etc.). A Conference Object is
accessible using XCON protocols (e.g. a Conference Control Protocol
[Section 7.3].
A Conferencing System can support any subset of the conferencing
functions depicted in the Conferencing System logical decomposition
in Figure 1 and described in this document. Nevertheless, typically
advanced functions could not be implemented without implementing
others. For example, the Notification Service is an essential
component required for implementing almost any advanced functionality
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and being used, among other things, for correlation of information
(such as list of participants with their media streams) between
otherwise distinct functions.
......................................................................
. Conferencing System .
. .
. +-----------------------------------------------------+ .
. | C O N F E R E N C E O B J E C T | .
. +-+---------------------------------------------------+ | .
. | C O N F E R E N C E O B J E C T | | .
. +-+---------------------------------------------------+ | | .
. | C O N F E R E N C E O B J E C T | | | .
. | | | | .
. | | |-+ .
. | |-+ .
. +-----------------------------------------------------+ .
. ^ ^ ^ | .
. | | | | .
. v v v v .
. +-------------------+ +--------------+ +-------+ +------------+ .
. | Conference Control| | Floor Control| |Foci | |Notification| .
. | Server | | Server | | | |Service | .
. +-------------------+ +--------------+ +-------+ +------------+ .
. ^ ^ ^ | .
................|.................|...........|..........|............
| | | |
|Conference |BFCP |SIP/ |SIP NOTIFY/
|Control | |PSTN/ |Etc.
|Protocol | |H.323/ |
| | |T.120/ |
| | |Etc. |
................|.................|...........|..........|............
. V V V V .
. +----------------+ +------------+ +----------+ +------------+ .
. | Conference | | Floor | | Call | |Notification| .
. | Control | | Control | | Control | | Client | .
. | Client | | Client | | Client | | | .
. +----------------+ +------------+ +----------+ +------------+ .
. .
. Conferencing Client .
......................................................................
Figure 1: Conferencing System Logical Decomposition.
The media graph of a conference can be centralized, de-centralized,
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or any combination of both and potentially differ per media type. In
the centralized case, the media sessions are established between a
media mixer controlled by the focus and each one of the participants.
In the de-centralized (i.e. distributed) case, the media graph is a
(multicast or multi-unicast) mesh among the participants.
Consequently, the media processing (e.g. mixing) can be controlled
either by the focus alone or by the participants. The concepts in
this framework document clearly map to a centralized media model.
The concepts can also apply to the de-centralized media case,
however, the details of such are left for future study by the XCON WG
charter.
Section 4 of this document provides more details on the Conference
Object. Section 5 provides an overview of the identifiers necessary
to address and manage the Conference Objects, Instances and Users
associated with a Conferencing System. Section 6 of this document
describes how a Conferencing System is logically built using the
defined data model and how the Conference Objects are maintained.
Section 7 describes the fundamental conferencing mechanisms and
provides a high level overview of the XCON protocols. Section 8 then
provides realizations of various conferencing scenarios, detailing
the manipulation of the Conference Objects using XCON defined
protocols. Section 9 of this document summarizes the relationship
between the XCON Framework and the SIPPING Conferencing Framework.
4. XCON Data Model
The XCON data model defined in this framework has no strict
separation between conference membership, conference media
information and the related policies (i.e. the capabilities and
limitations for each). This approach meets the requirement in many
conference control operations to enable synchronized access to the
conference policies as a whole, to the conference state as a whole,
and for receiving notifications about changes to either.
A Conference Object is of type 'Conference Object Type' which is
comprised of two distinct components: the 'Common Conference
Information Type' and the 'Conference Template Type', as illustrated
in Figure 2. Each of these types is a placeholder for including
potentially multiple sub-types.
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+------------------------------------------------------+
| C O N F E R E N C E O B J E C T T Y P E |
| |
| +--------------------------------------------------+ |
| | COMMON CONFERENCE INFORMATION TYPE | |
| | | |
| | +----------------------------------------------+ | |
| | | Conference Description | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Membership (Roles, Capacity, Names) | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Signaling (Protocol, Direction, Status) | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Floor Information | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Sidebars, Etc. | | |
| | +----------------------------------------------+ | |
| | | |
| +--------------------------------------------------+ |
| +--------------------------------------------------+ |
| | CONFERENCE TEMPLATE TYPE | |
| | | |
| | - Mixer algorithm, inputs, and outputs | |
| | - Floor controls | |
| | - User Control Interface | |
| | - User's View | |
| | - Etc. | |
| +--------------------------------------------------+ |
| |
+------------------------------------------------------+
Figure 2: Conference Object Type Decomposition.
Since, in an XCON-compliant system the same Conference Object Type is
used for representation of a conference for different purposes, such
as expressing Conferencing System capabilities, reserving
conferencing resources or reflecting the state of ongoing
conferences, each of the two components (i.e., the Common Conference
Information and the Conference Template) is syntactically optional to
be included in a particular Conference Object. Section 6 describes
the usage semantics of the Conference Objects.
[Editor's Note: The exact XML schema of the Conference Object (i.e.
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the organization of the Common Conference Information and the
Conference Template) is an open issue (Discussion Point 4 on the
mailing list), which has been summarized as the three potential
alternatives below:
1. The top-level information is the template section, and it
contains a subsection that is the common conference information.
This has the advantage that the schema can all be well defined:
because the common conference information is known at the time the
template is developed, the appropriate schema definition can be
inserted into the template schema. The downside is that this setup
requires navigation of the template information to get to the common
information, which is likely to be manipulated most frequently.
2. The top-level information is the common conference information,
which contains the template information. This has the advantage that
clients don't even need to care about the template being used to
allow rendering and control over basic conference functionality(which
will suffice for many clients (e.g. those with limited screen). The
downside is that the common conference information schema must
include an extension point to allow new templates to hook into the
schema. This may make schema validation more difficult.
3. The template information and common conference information are
conveyed as two separate objects (e.g. using multipart MIME). This
provides the benefits of allowing completely separate schema,
straightforward schema validation, and easy access to the common
conference information. The downside is that any mechanism for
separating the schema is going to add some amount of protocol
complexity and the need for synchronization between the two data
objects. Note that it has been argued that it is increasingly
difficult to find a potential client of the XCON protocols that
doesn't already support multipart MIME).
The model put forth in this document is the result of the consensus
reached during the XCON second interim meeting in Boston and depicts
option 2 above. With slight adaptations it can also support option
3. ]
4.1 Common Conference Information
The common conference information section contains the core
information that is utilized in any conference and can be abstracted
regardless of the specific conference media nature (e.g. the mixing
algorithms performed, the advanced floor control applied, etc.).
Typically, participants with read-only access to the conference
information would be interested in this common information only.
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The basic common conference information can be represented using the
conference-info-type schema as defined in [11]. This schema contains
the definitions for representation of the Conference Object
capabilities, membership, roles, call control signalling and media
statuses relevant to different stages of the conference life-cycle.
New XCON specifications can extend the basic conference-info-type and
introduce additional schemas to be used within the common conference
information type placeholder.
4.2 Conference Template
The concept of a "Conference Template" is introduced to abstract the
complexity and the details of the "mixer" and other conferencing
features and to allow for easy user interface abstraction for
advanced Conferencing Systems.
Each Conference Template needs to be registered with IANA. The IANA
registration needs to point to an RFC having the text description of
the feature behavior and optionally the XML definition allowing the
feature presentation, configuration, and management. RFCs of this
kind are referred by XCON documents as a "Registered Conference
Document".
Typically, a conference template would contain the information about
the specific media mixing details, the associated client roles and
the available floor controls. This information would allow
authorized clients to manipulate mixer's behavior and the resultant
distribution of the media to all or individual participants. By
doing so, a client can change its own state and/or state of other
participants in the conference.
A conference template can also include an abstract user interface
definition in terms of sliders, radio boxes, etc. for simplifying
user interaction with a specific non-trivial feature.
4.3 Conference policies
Conference policies is the term used to collectively refer to a
virtual set of rights, permissions and limitations pertaining to
operations being performed on a certain Conference Object.
The virtual set of rights describes the read/write access privileges
for the Conference Object as a whole. This access would usually be
granted and defined in terms of giving the read-only or read-write
access to clients with certain roles in the conference. For details
see [TBD].
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The permissions and limits are specified as an integral part of the
Conference Object Type, with data objects containing the allowed
ranges for other data objects (e.g. maximum number of participants)
and lists of clients allowed to perform certain operations on a
conference object. For example, the "allowed to join" list of
participants is consulted to decide who is allowed to join. The
entries in the list can specify the identity of an individual user
(joe@example.com), a role, a domain (*@example.com), etc. For
details see [TBD].
A more general rule mechanism, beyond the functionality provided by
the permissions and limits, is an item for future study for the XCON
WG.
5. XCON Constructs and Identifiers
This section provides details of the identifiers associated with the
XCON constructs (e.g. Conference Object and Conference Instance) and
the identifiers necessary to address and manage the clients
associated with a Conferencing System. An overview of the
allocation, characteristics and functional role of the identifiers is
provided.
5.1 Conference Identifier
The Conference Identifier (ID) is the call signalling protocol-
specific URI that uniquely identifies a Conference Instance and a
conference Focus. The Conference Factory is the logical entity that
generates the unique Conference ID to identify and represent a
conference Focus. The Conference Factory is typically used in the
conference creation process via a signalling interface and non-
signalling methods such as Conference Control Protocol [Section 7.3]
and proprietary mechanisms.
5.2 Conference Instance
A Conference Instance is an internal implementation construct of a
conference, which is accessible by call signalling means, thus no
explicit identifier is required. Note that a Conference Instance can
have more than a single Conference Identifier, for example, for each
call signalling protocol supported. There is a one-to-one mapping
between a Conference Instance and a conference Focus. The Focus is
addressed by explicitly associating unique Conference IDs for each
signalling protocol supported by its Conference Instance.
A single Conference Instance can be internally mapped to a single or
multiple Conference Objects; each of them accessible by a Call
Control protocol.
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5.3 Conference Object
A Conference Object is the logical representation of a Conference
Instance at a certain stage, such as a "blueprint" representing a
Conferencing System's capabilities, the data representing a reserved
or scheduled conference, or the conference state during an active
conference. The Conferencing System exposes this data as separate
objects to allow independent access. Consequently, the XCON
specifications allow the association of multiple Conference Objects
with a single Conference Instance.
Figure 3 illustrates the relationships between the Conference
Identifier, the Focus and the Conference Object Identifier within the
context of a logical Conference Instance, with the Conference Object
corresponding to an ongoing conference (i.e. a conference in the
active state). The Conference Object is identified by a single or a
set of call signaling Conference Identifiers, with a one-to-one
mapping, as shown in the figure.
The Conference Objects corresponding to additional conference stages
are addressing using CCP [Section 7.3]. CCP will define the
necessary logical naming conventions for addressing additional
Conference Objects, within the context of the cloning tree concept
introduced in Section 6.
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......................................................................
. Conference Instance .
. .
. .
. +---------------------------------------------------+ .
. | Conference Object Identifier | .
. | | .
. | | .
. +---------------------------------------------------+ .
. ^ ^ .
. | | .
. v | .
. ................................................... | .
. . Focus . | .
. . . | .
. . +----------------------------------+ . | .
. . |Conference Identifier (Protocol Y)| . | .
. . +------------------------------------+ | . | .
. . | Conference Identifier (PSTN) | | . | .
. . +--------------------------------------+ |-+ . | .
. . | Conference Identifier (SIP) | |^ . | .
. . | |-+| . | .
. . | |^ | . | .
. . +--------------------------------------+| | . | .
. ............^...............................|.|.... | .
. | | | | .
................|...............................|.|......|............
| | | |
|SIP | | |Conference
| PSTN | |Y |Control
| | | |Protocol
| +---------------+ | |
| | | |
| | | |
v v v v
+----------------+ +--------------+ +---------------+
| Conferencing | | Conferencing | | Conference |
| Client | | Client | | Client |
| 1 | | 2 | | X |
+----------------+ +--------------+ +---------------+
Figure 3: Conference Identifer, Focus, Conference Instance and
Conference Object Identifier Relationships.
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5.3.1 Conference Object Identifier
In order to make each Conference Object externally accessible, the
Conferencing System allocates a unique URI per distinct Conference
Object in the system, as defined in [ref:TBD]. A Conference Control
Protocol [as outlined in Section 7.3] can then be used for directly
manipulating a particular Conference Object and for obtaining its
current state.
The Conference Object URI acts as a top level identifier for an
'umbrella style' construct within the Conference System for the
purpose of identifying incoming connections for complimentary XCON
protocols (e.g. BFCP). This implicit binding provides a structured
mapping of the various XCON protocols with the associated Conference
Object Identifier. As an example, Figure 4 illustrates how BFCP
connections fall under the general Conference Object identifier
umbrella.
+--------------+
| Conference |
| Object |
| Identifier |
+--------------+
|
|
|
+-------+-------+
| BFCP 'confid' |
+-------+-------+
|
|
+---------------+---------------+
| |
+-------+-------+ +-------+-------+
|BFCP 'floorid' | |BFCP 'floorid' |
+-------+-------+ +-------+-------+
Figure 4: Conference Object Mapping.
In Figure 4, the Conference Object Identifier acts as the top level
key in the identification process. The BFCP protocol, as defined in
[24], defines the 'conf-id' identifier which represents a conference
instance within Floor Control. BFCP also defines the 'floorid'
identifier for specific floors within a Conference instance. When
created within the Conference System, the 'conf-id' has a 1:1 mapping
to the unique XCON Conference Object Identifier. Using the BFCP
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example, the Conference System is able to map the floor request to
the associated Conference Object.
This umbrella style association can be applied to any supplementary
mechanisms that are applied to the XCON model defined in this
document as long as a unique reference per conference instance is
available that can be mapped to a Conference Object.
[Editor's Note: The URI schema name per TBD must be registered with
IANA.]
5.4 Conference User Identifier
Section 5.3.1 discusses the concept of an umbrella mechanism for
associating various protocol identifiers with a top level XCON
identifier. This section outlines a similar umbrella mechanism for
the purpose of correlating users of supplementary XCON protocols
under one universal XCON identity within an XCON Conference System.
It is important to emphasize that the Conference User Identifier
being described must be in the context of the Conference System.
This is due to the requirement for identity of Conference System
users who may not be participating in a Conference Instance.
Examples being a non participating 'Floor Control Chair' or 'Media
Policy' Controller. Users can then be associated with Conference
Objects as defined in Section 5.3.1. This association enables the
Conference System to associate and enforce user level policies at
both a system level and Conference Object level.
Each user within a Conference System is allocated a unique Conference
User Identifier, as defined in [TBD]. This identifier acts as a top
level identifier, in a similar fashion to that defined for the
Conference Object Identifier described in Section 5.3.1. User
identifiers defined in other protocols that are used within a
Conference Instance fall underneath the top level identifier and
enable the Conference System to correlate and map authentication
under the single user umbrella.
Figure 5 illustrates an example using the Conference User Identifier
in association with the user identity defined for BFCP and SIP Digest
user identity as defined in RFC3261[4]
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+---------------+
| Conference |
| User |
| Identifier |
+-------+-------+
|
|
|
+---------------+---------------+
| |
+-------+-------+ +-------+-------+
| BFCP | | SIP Digest |
| 'UserID' | | Username |
+---------------+ +-------+-------+
Figure 5: Conference Object Mapping.
Within a Conference System, a user is identified by a single
Conference User Identifier. Any other XCON mechanisms that contain a
protocol specific user ID can be associated with the 'Conference User
Identifier', as illustrated in Figure 5. This mechanism allows
conference systems to manage and relate system wide user identities
in relation to specific Conference Objects and helps in the
enforcement of system wide policies.
6. Conferencing System Realization
XCON-compliant implementations can range from systems supporting ad-
hoc conferences, with default behavior only, to sophisticated systems
with the ability to schedule re-occurring conferences (each with
distinct characteristics), being integrated with external resource
reservation tools, and providing snapshots of the conference
information at any of the stages of the conference life-cycle.
A Conference Object is the logical representation of a Conference
Instance at a certain stage, such as capabilities description upon
conference creation, reservation, activation, etc., which a
Conferencing System maintains in order to describe the system
capabilities and to provide access to the available services provided
by the Conferencing System.
Consequently, the XCON specifications don't mandate the actual usage
of the Conference Object, but rather defines the general cloning tree
concept and the mechanisms required for its realization, which is
described in detail in Section 6.1.
Adhoc and advanced conferencing examples are provided in Section 6.2
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and Section 6.3, with the latter providing additional description of
the Conference Object in terms of the stages of a conference, to
support scheduled and other advanced conference capabilites.
The scheduling of a conference based on these concepts and mechanisms
is then detailed in Section 6.4
6.1 Cloning Tree
The concept defined in this section is a logical representation only,
as it is reflected through the XCON mechanisms: the URIs and the
protocols. Of course, the actual system realization can differ from
the presented model and doesn't require physical copying of the
information, etc.
Any Conference Object in a Conferencing System is created by either
being explicitly cloned from an existing parent object or being
implicitly cloned from a default system object. This document uses
the "cloning" metaphor instead of the "inheritance" metaphor because
it more closely fits the object replication and extension concept,
rather than data type re-usage and extension concept.
The cloning operation needs to specify whether the link between the
parent and the child needs to be maintained in the system or not. If
no link between the parent and the child exists, the objects become
independent and are not impacted by any operations on the parent
object nor subject to any limitations of the parent object.
By default, all the data existing in the parent object is copied to
the newly created object.
Once the new object is created, it can be addressed by a unique
Conference Object URI assigned by the system, as described in
Section 5.3.1
By default, the newly created object can expand the data it contains,
within the schema types supported by the parent. It can also
restrict the read/write access to its objects. However, unless the
object is independent, it cannot relax the access relative to its
parent's access.
Any piece of data in the child object can be independently accessed
and, by default, can be independently modified without affecting the
parent data.
Unless the object is independent, the parent object can enforce a
different policy by marking certain data elements as "parent
enforceable". The values of these data objects can not be changed by
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directly accessing the child object; neither can they be expanded in
the child object alone.
In the future, XCON specifications may introduce logical
relationships, in addition to the "parent enforceable", between
elements being cloned from one another.
+---+-----------------------+
| p | |
| o | P A R E N T A |
| l | |
| i | C O N F E R E N C E |
| c | |
| i | O B J E C T |
| e | |
+-s-+-----------------------+
|
\| /
\/ INDEPENDENT
/\
/| \
V
+---+-----------------------+
| p | |
| o | P A R E N T B |
| l | |
| i | C O N F E R E N C E |
| c | |
| i | O B J E C T |
| e | |
+-s-+-----------------------+
| |
| |
| ---------------------------
| |
V V
+---+-----------------------+ +---+-----------------------+
| p | | | p | |
| o | C H I L D 1 | | o | C H I L D 2 |
| i | | | l | |
| l | C O N F E R E N C E | | i | C O N F E R E N C E |
| i | | | c | |
| c | O B J E C T | | i | O B J E C T |
| i | | | e | |
+-s-+-----------------------+ +-s-+-----------------------+
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Figure 6: The Cloning Tree.
Using the defined cloning model and its tools, the following sections
show examples of how different XCON-compliant systems can be
realized.
6.2 Ad-hoc Example
Figure 7 illustrates how an ad-hoc conference can be created and
managed in a conferencing system.
A client can create a conference by establishing a call control
signalling channel with a Conference Factory as specified in
Section 5.1. The Conference Factory can internally select one of the
system supported Conference Object blueprints based on the requesting
client privileges and the media lines included in the SDP body.
The selected blueprint with its default values is copied by the
server into a newly created Conference Object, referred to as an
'Active Conference'. At this point the Conference Object becomes
independent from its blueprint. A new Conference Object Identifier,
a new Conference Identifier and a new focus are allocated by the
server.
During the conference lifetime, an authorized client can manipulate
the Conference Object (such as adding participants) using the
Conference Control Protocol [Section 7.3].
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+---+-----------------------+
| p | |
| o | C O N F E R E N C E |
| l | |
| i | S Y S T E M |
| c | |
| i | D E F A U L T |
| e | |
+-s-+-----------------------+
|
\| /
\/
/\
/| \
V
+---+-----------------------+
| p | |
| o | A C T I V E |
| l | |
| i | C O N F E R E N C E |
| c | |
| i | |
| e | |
+-s-+-----------------------+
Figure 7: Conference Ad-hoc Creation and Lifetime.
6.3 Advanced Example
Figure 8 illustrates how a recurring conference can be specified
according to system capabilities, scheduled, reserved, and managed in
a conferencing system.
Firstly, a client would query a Conferencing System for its
capabilities. This can be done by requesting a list of the
Conference Object "blueprints" (or templates) the system supports.
Each blueprint can contain a specific combination of capabilities and
limitations of the conference server in terms of supported media
types (audio, video, text, or combinations of these), participant
roles, maximum number of participants of each role, availability of
floor control, controls available for participants, availability and
type of sidebars, the definitions and names of media streams, etc.
A Client may need to query any templates that it doesn't understand
and then make a decision on compatibility. Interface hints need to
be included as per [21]. The client then selects which specific
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template to use and retrieves the template from the server itself
(and NOT from some centralized repository).
The selected blueprint with its default values is copied by the
client into a newly created Conference Object, referred to as a
'Conference Object for Reservation', that specifies the resources
needed from the system for this Conference Instance. At this point
the 'Conference Object for Reservation' becomes independent from its
blueprint. The client can also change the default values (within the
system ranges) and add additional information (such as the list of
participants and the conference start time) to the 'Conference Object
for Reservation'.
At this point the client can ask the conference server to create a
new conference reservation by attaching the 'Conference Object for
Reservation' to the request. As a result, the server can allocate
the needed resources, create the additional Conference Objects for
each conference occurrence (referred to as a 'Conference Object for
Occurrence') and allocate the Conference Object identifiers for all -
the 'Conference Object for Reservation' and for each 'Conference
Object for Occurrence'.
From this point on, any authorized client is able to access and
modify each of the Conference Objects independently. By default,
changes to an individual 'Conference Object for Occurrence' will
affect neither the 'Conference Object for Reservation' nor its
siblings.
On the other hand, some of the conference sub-objects, such as the
maximum number of participants and the participants list, can be
defined by the system as parent-forcible. As a result, these objects
can be modified by accessing the 'Conference Object for Reservation'
only. The changes to these objects can be applied automatically to
each of the 'Conference Object for Occurrence's (subject to local
policy).
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+---+-----------------------+
| p | |
| o | S E L E C T E D |
| l | |
| i | C O N F E R E N C E |
| c | |
| i | B L U E P R I N T |
| e | |
+-s-+-----------------------+
|
\| /
\/
/\
/| \
V
+---+-----------------------+
| p | |
| o | C O N F E R E N C E |
| l | |
| i | R E S E R V A T I O N |
| c | |
| i | |
| e | |
+-s-+-----------------------+
| | |
| | |
| | |
| | |
+---|--|--V-----------------+
+-+---|--V------------------+ |
+-+-+---V-------------------+ | |
| p | | | |
| o | C O N F E R E N C E | | |
| l | | | |
| i | O C C U R R E N C E | | |
| c | | | |
| i | | |-+
| e | |-+
+-s-+-----------------------+
Figure 8: Advanced Conference Definition, Creation, and Lifetime.
6.4 Scheduling a 'Conference Object for Reservation'
Scheduling conferences forms an important part of the Conferencing
System solution. The concept of an individual Conference Instance
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and its relationship to a specific Conference Object is introduced in
Section 5.2 and Section 5.3. A basic Conference Instance represents
a single occurrence that has a specified 'start' and 'end' time, with
the times being specified relative to a single specified 'fixed'
time (e.g. 'start' = 09.00 GMT, 'end'= 'start'+2), subject to system
considerations . In most advanced conferencing solutions it is
possible to not only schedule an individual conference instance, but
also schedule a series of related conferences (e.g. A weekly meeting
that starts on Thursday at 09.00 GMT).
To be able to achieve such functionality, a Conferencing System needs
to be able to appropriately schedule and maintain Conference
Instances that form part of a recurring conference schedule. The
mechanism proposed in this document makes use of the 'Internet
Calendaring and Scheduling Core Object' specification defined in
RFC2445[8] in union with the concepts introduced in Section 4 for the
purpose of achieving advanced conference scheduling capability.
Figure 9 illustrates a simplified view of a Client interacting with a
Conference System. The Client is using the Conference Control
Protocol (Section 7.3) to add a new Conference Instance to the
Conference System by interfacing with the Conference Control Server.
A Conference Control Protocol request contains a valid 'Conference
Object for Reservation' and reference by value to an 'iCal' object
which contains scheduling information about the conference instance
(e.g. start time, end time).
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+--------------+ +-------Conferencing System-----------------+
| Generic ICAL | | |
| Resource | | ..Conference Instance.... |
+--------------+ | . . +-----------+|
^ ^ | . +-------------------+ . | Conference||
| | | . |Conference Objects |<--| Control ||
| ----------------->. +-------------------+ . | Server ||
| | . . +-----------+|
| | ......................... ^ |
| | ^ | |
+-----|--------------+ | | |
| v | | |
| +--------------+ | | |
| | Resource |<------------------+ | |
| | Scheduler | | |
| +--------------+ | |
| | |
+---------------------------------------------------------|------+
|
|
+-Request-+
| |
+----+ |
|ICAL| |
+----+----+
|
|
|
Conference Control|
Protocol |
|
+-------------+
| Conferencing|
| Client |
+-------------+
Figure 9: Resource Scheduling
A successful creation of a Conference Instance using the Conference
Control Protocol results in a new 'Conference Object for
Reservation'. A Conference Control Protocol request is validated,
including the associated iCal object, and the resultant 'Conference
Object for Reservation' is created. The Conference Object is
uniquely represented within the Conference System by Conference
Object Identifier (e.g. xcon:hd87928374) as discussed in
Section 5.3. The unique URI is returned to the client and can be
used to reference the 'Conference Object for Reservation'
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representation if any future manipulations are required (e.g. Alter
start time) using a Conference Control Protocol.
The previous example explains how a client creates a basic
'Conference Object for Reservation' using an iCal reference in
association with a Conference Control Protocol. Figure 9 can also be
applied when explaining how a series of Conferences are scheduled in
the system. The description is almost identical with the exception
that the iCal definition that is included in a Conference Control
Request represents a series of recurring Conference Instances (e.g.
conference start time, end time, occur weekly). The Conference
system will treat this request the same as the first example. The
protocol request will be validated, along with the associated iCal
object, and the 'Conference Object for Reservation' will be created.
The 'Conference Object for Reservation' and the Conference Object ID
created for this example represent the entire series of recurring
Conference Instances rather than a single Conference. If the client
uses the Conference Object ID provided and a Conference Control
Protocol to adjust the 'Conference Object for Reservation', every
Conference Instance in the series will be altered. This includes all
future occurrences, such as a conference scheduled as an infinite
series, subject to the limitations of the available calendaring
interface.
A Conferencing System that supports the scheduling of a series of
Conference Instances should also be able to support manipulation
within a series range. A good example might be that a 'Conference
Object for Reservation' has been scheduled to occur every Monday at
09.00 GMT. For the next three weeks only, the meeting has been
altered to occur at 10.00 GMT in an alternative venue. With
Figure 9 in mind, the client will construct a Conference Control
request whose purpose is to modify the existing 'Conference Object
for Reservation' representing the recurring Conference Instance. The
Client will include the Conference Object ID provided by the
Conference System to explicitly reference the 'Conference Object for
Reservation' within the Conference System. A Conference Control
request will contain all the required changes to the 'Conference
Object for Reservation'(e.g. Change of venue). The Conference
System matches the incoming request to the existing 'Conference
Object for Reservation' but identifies that the associated iCal
object only refers to a range of the existing series. The Conference
System creates a child clone of the original 'Conference Object for
Reservation' to represent the altered Conference Instances within
the Series. The cloned 'Conference Object for Reservation'
representing the altered series of Conference Instances has its own
associated Conference Object ID which is returned to the Client using
a Conference Control Protocol. This Conference Object ID is then
used by the client to make any future alterations on the newly
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defined sub-series. This process can be repeated any number of times
as the newly returned Conference Object ID representing an altered
(cloned) series of Conference Instances, can itself be manipulated
using the Conference Control Protocol and the newly created
Conference Object ID representation. This provides a flexible
approach to the scheduling of recurring Conference instances.
7. Conferencing Mechanisms
7.1 Call Control Signalling
The focus is the central component of the conference. Participants
interface with the focus using an appropriate Call Control Signalling
protocol. Participants request to establish or join a conference
using the Call control signalling interface. A focus then either
accepts (after checking the policies), sends a progress indication
(e.g. for a parked call while awaiting moderator approval to join) or
rejects that request using the call control signalling interface.
During an active conference, a Conference Control Protocol
[Section 7.3] can be used to affect the conference state. For
example, Conference Control Protocol requests to add and delete
participants will be communicated to the focus and checked against
the conference policies. If approved, the participants will be added
or deleted using the call signalling to/from the focus.
7.2 Notifications
A Conferencing System is responsible for implementing a Conference
Notification Service. The Conference Notification Service provides
updates about the Conference Instance state to authorized parties
(e.g. participants) according to [11].
The Conference User Identifier and associated Role are used by the
conferencing system to filter the notifications such that they
contain only information that is allowed to be sent to that user.
7.3 Conference Control Protocol
The XCON working group charter includes the development of a protocol
or a set of protocols for controlling the state of a Conference
Object and for retrieving its state. The nature of this protocol is
currently under discussion in the XCON working group. The proposals
span from data manipulation (management-like) protocols (CPCP and
NETCONF) to semantic-oriented (CCCP and CSCP) . Details of the
proposed protocols are in the sections below. The following
paragraphs summarize the fundamental issues around the selection of
the protocol(s). [Editor's Note: Discussion Point 5 on the XCON WG
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mailing list].
It is recognized that semantic manipulations make for a cleaner
protocol design, with the disadvantage that extensions to the
underlying data model require extensions to the protocol used to
manipulate it. Syntactic manipulations allow for extensions to the
data model without requiring protocol extensions, with the
disadvantage that the server generally has to infer intent from data
manipulations instead of having intent explicitly signaled.
It is worth noting that one portion of the data to be manipulated,
the Common Conference Information, will not be extended, and would
naturally lend itself to semantic manipulation. Another part of the
data, the Conference Template, is intended to be extended, and would
naturally lend itself to syntactic manipulation. However, there has
been a stated desire to use a single protocol (and presumably a
single mode of operation within this protocol) to manipulate all
conference object state (common and template).
The third statement in the paragraph above makes the first two
solution options mutually exclusive. A proposal was made that by
allowing more than one protocol, a hybrid approach could be taken
such that CPCP and CSCP can both be used, since they are based on
other protocols that are likely to be supported by the clients (XCAP
and BFCP, respectively). However, the very rough consensus of the WG
supports a single protocol for Conference Control and SOAP has most
recently been put forth as that protocol. A basic overview of SOAP
in the context of Conference control is provided in Section 7.3.5
7.3.1 CPCP
A Conference Policy Control Protocol (CPCP) is a data manipulation
protocol being proposed as a standard means of storing and
manipulating the conference policy. According to CPCP, the
conference policy is comprised of the rules associated with a
specific Conference Instance. Requirements for the CPCP are defined
in the CPCP Requirements document [13]. The Conference Policy
Control Protocol document [17] defines the XML Schema for the
conference policy data elements.
The privileges as to which users are allowed to read and/or
manipulate a specific Conference Instance are defined in a separate
Extensible Markup Language (XML) Schema[19]. This schema is based on
the common policy model being used for geographic privacy information
and for presence information.
A separate document [18] proposes XCAP as one protocol mechanism for
storing and manipulating this conferencing policy data. XCAP is a
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HTTP 1.1 based protocol that allows clients to read, write, modify
and delete application data stored in XML format on a server. One of
the main advantages of XCAP is that it maps XML document elements and
attributes to HTTP URIs that can be directly accessed by HTTP.
7.3.2 CCCP
A Centralized Conferencing Control Protocol [20] is a semantic-
oriented protocol defined to allow participants or otherwise
authorized entities to directly manipulate an active Conference
Instance. CCCP is defined as a set of transactions issued over a
reliable transport protocol. A transaction consists of a Request
carrying the required information in an XML body and a corresponding
Response carrying an appropriate XML body.
CCCP requests are submitted to the CCCP server and can be prioritized
and queued, based on the CCCP client Role and the requested
primitives. CCCP requires no single lock per document, and the CCCP
server can locally implement an optimization strategy independent of
CCCP client behavior.
7.3.3 CSCP
A Conference State Change protocol [26] is a client server protocol
used to change the state of a conference object. CSCP extends the
BFCP protocol [16] with new commands. A client sends the server a
request representing a sequence of commands. Each command can set,
get, add, or delete a single field in the conference object. Changes
to the conference object are performed on a hierarchal set of
elements and unique attributes within those elements. A series of
changes can be pipelined in a single BFCP message. The server
executes each action in series. If one of them fails, the server
returns an error for the action that failed and does not execute any
of the actions after that. Each individual action is atomic but the
pipelined series is not.
The item to which a command applies is specified by a unique ID and,
where appropriate, attribute name. The ID is an unsigned 32 bit
integer called the Element ID. The server discovery of the Element
ID is outside of CSCP. Typically this is done by using the
conference notification service per Section 7.2. Each field in the
data received in the notification contains a unique field ID
attribute that can be used in BFCP requests.
7.3.4 NETCONF
The Network Configuration (NETFCONF) protocol [27] defines a simple
mechanism through which a network device can be managed,
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configuration data information can be retrieved, and new
configuration data can be uploaded and manipulated. The protocol
allows the device to expose a full, formal, application programming
interface (API).
NETCONF is proposed as the mechanism for object content manipulation
and state retrieval for the XCON data. NETCONF provides a flexible
configuration retrieval mechanism, with extensibility. It allows for
incremental configuration and commits. NETCONF supports stored
configurations (e.g. for startup, running, etc.). It also supports
XPath and subtree filtering. With NETCONF, there are no constraints
on the configuration content.
7.3.5 SOAP
The SOAP protocol is fundamentally an XML messaging scheme, capable
of supporting remote procedure calls. SOAP defines a simple message
format composed of a "header" and a "body" contained within an
"envelope". The "header" contains meta-information relating to the
message, and can be used to indicate such things as store-and-forward
behaviour or transactional characteristics. In addition, SOAP
encoding is optimized for ease of automated deserialization.
SOAP is proposed as the mechanism for object content manipulation and
state retrieval for the XCON data. In general, SOAP is a good fit
for Conference Control, essentially because of its remote procedure
call characteristics and its inherently synchronous and client-driven
nature.
7.4 Floor Control
[Editor's Note: This text still requires further updating to reflect
new model and pending new WG agreements. Amongst the things TODO
are:
1. Need to be able to fetch from the Conference Object the
credentials required for BFCP. This includes the conference id, user
id, and password.
4. Evaluation of an alternative proposal [TBD as a stand alone draft
as well] for using Templates as the means for correlating Floor
Control identifiers.
5. Still need to condense this section - propose to add a scenario
to section 8 and thus remove some of the details, leaving this
description a very basic overview and mapping of the identifiers.
]
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A mechanism for floor control within a Conferencing System is defined
in the 'Binary Floor Control Protocol' specification [16]. Floor
control is not a mandatory mechanism for a Conferencing System
implementation but provides advanced media input control features for
participants.
An XCON compliant client supporting floor control needs to obtain
information for connecting to a floor control server to enable it to
issue floor requests. This connection information can be retrieved
using information provided by mechanisms such as negotiation using
the SDP[2] offer/answer[5] exchange on the signalling interface with
the focus.
As well as the Client --> Floor Server connection information, a
client wishing to interact with a Floor Control server requires
access to additional information. This information associates Floor
Control interactions with the appropriate Floor instance. Once a
connection has been established and authenticated (see [16] for
authentication details), a specific floor control message requires
detailed information to uniquely identify a user, a floor and a
conference. This information, defined in the next set of bullet
points, can be obtained using methods such as negotiation using the
SDP offer/answer exchange on the signalling interface with the focus:
o Conference Object ID - Each Conference Object has a unique
identifier per Section 5.3.1, obtained from the Conference
server, which MUST be included in all Floor messages. When the
SDP model is used as described in [24] this identifier maps to the
'confid' SDP attribute.
o Conference User Identifier - Each user has a unique identifier
within the Conference Object per Section 5.4, obtained from the
Conference server, which MUST be included in all Floor messages.
When using SDP offer/answer exchange to negotiate a Floor control
connection with the focus using the call control signalling
interface, the unique conference identifier is contained in the
'userid' SDP attribute, as defined in [24]
o Floor ID - A media session with a Conferencing System can have any
number of 'Floors' (0 or more) that are represented by a unique
identifier within the Conference Instance (as represented by
Conference ID). When using SDP offer/answer exchange to negotiate
a Floor control connection with the focus using the call control
signalling interface, the unique conference identifier is
contained in the 'floorid' SDP attribute, as defined in [24]
e.g.a=floorid:1 m-stream:10 . Each 'floorid' attribute,
representing a unique floor, has an 'm-stream' tag containing one
or more identifiers. The identifiers represent individual SDP
media sessions (as defined using 'm=' from SDP) using the SDP
'Label' attribute as defined in [23].
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Clients can authenticate a BFCP server using the TLS certificates.
Requests submitted on a successfully created BFCP connection may
additionally require digest authentication within the BFCP protocol
to authenticate the Floor control client to the server. For this to
take place a shared secret needs to be exchanged between the BFCP
client/server entities. This can be achieved out of band using a
mechanism such as the 'k=' SDP attribute. The shared secret can also
be exchanged using un-specified 'out of band' mechanisms. When using
Digest authentication of BFCP client messages the exchange of an
active 'Nonce' is also required. This can be achieved using a BFCP
request response interaction as defined in BFCP (A request is
submitted without a Nonce TLV and the server generates an error
response with either an Error Code 7 (DIGEST TLV Required) or 6
(Invalid Nonce) containing the valid nonce). The BFCP 'Nonce' value
can also be obtained 'out of band' using information provided in the
Offer/Answer exchange. As with the other SDP Floor attributes
referenced in this section and defined in [24], the 'nonce' attribute
can be inserted in the SIP response e.g. a=nonce:dhsa8hd0dwqj.
8. Conferencing Scenario Realizations
This section addresses how advanced conferencing scenarios, many of
which have been described in [14], are realized using this XCON
framework. The objective of this section is to further illustrate
the model, mechanisms and protocols presented in the previous
sections and also serves to validate that the model, mechanisms and
protocols are sufficient to support advanced conferencing scenarios.
Section 6.2 and Section 6.3 provide examples of the creation of a
basic adhoc conference and a more advanced scheduled conference.
8.1 Participant Manipulations
There are different ways to affect a participant state in a
conference. A participant can join and leave the conference using
call signalling means only, such as SIP. This kind of operation is
called "1st party signalling" and does not affect the state of other
participants in the conference.
Limited operations for controlling other conference participants (a
so called "3rd party control") through the Focus, using call
signalling only, may also be available for some signalling protocols.
For example, "Conferencing for SIP User Agents" [15] shows how SIP
with REFER can be used to achieve this functionality.
In order to perform richer conference control a user client needs to
implement a conference control protocol client. By using a
conference control protocol, the client can affect its own state,
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state of other participants, and state of various resources (such as
media mixers) which may indirectly affect the state of any of the
conference participants.
Figure 11 provides an example of one client "Alice" impacting the
state of another client "Bob". This example assumes an established
conference. In this example, "Alice" wants to add "Bob" to the
conference.
It should be noted that not all entities impacted by the request are
shown in the diagram (e.g. Focus), but rather the emphasis is on the
new entities introduced by XCON.
+--------------------------------+
| Conference System |
"Alice" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | |Conference ||
| | Conference Object ID, | |Control |~~~>|Object of ||
+--------+ Add, "Bob" > | |Server | |occurrence ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Bud" | ' ' '|
+--------+ NOTIFY <"Bob"="added"> |+------------+ ' ' '|
| |<-------------------------|Notification|<~~~| ||
| Client |. . ||Service | +-------+ ||
+--------+--+ . || | |"Bob" | ||
| |<----------------------| | +-------+----+|
| Client |NOTIFY <"Bob"="added">|+------------+ |
+--------+ +--------------------------------+
"Bob"
Figure 10: Client Manipulation of Conference - Add a party
Upon receipt of the Conference Control Protocol request to "add" a
party ("Bob") in the specific conference as identified by the
Conference Object ID, the Conference System ensures that "Alice" has
the appropriate authority based on the policies associated with that
specific Conference Object to perform the operation. The Conference
System must also determine whether "Bob" is already a user of this
Conference System or whether he is a new user.
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If "Bob" is a new user for this conference system, a Conference User
Identifier is created for Bob. Based upon the addressing information
provided for "Bob" by "Alice", the call signalling to add "Bob" to
the conference is instigated through the Focus.
Once the call signalling indicates that "Bob" has been successfully
added to the specific conference, per updates to the state, and
depending upon the policies, other participants (including "Bob") may
be notified of the addition of "Bob" to the conference via the
Conference Notification Service.
8.2 Media Manipulations
There are different ways to manipulate the media in a conference.
A participant can change its own media streams by, for example,
sending re-INVITE with new SDP content using SIP only. This kind of
operations is called "1st party signalling" and they do not affect
the state of other participants in the conference.
In order to perform richer conference control a user client needs to
implement a conference control protocol client. By using a
conference control protocol, the client can manipulate the state of
various resources, such as media mixers, which may indirectly affect
the state of any of the conference participants.
Figure 11 provides an example of one client "Alice" impacting the
media state of another client "Bob". This example assumes an
established conference. In this example, the Client, "Alice" whose
Role is "moderator" of the conference, wants to mute "Bob" on a
medium-size multi-party conference, as his device is not muted (and
he's obviously not listening to the call) and background noise in
his office environment is disruptive to the conference.
It should be noted that only entities impacted by the request are
shown in the diagram (e.g. there is no Focus shown).
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+--------------------------------+
| Conference System |
"Alice" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | |Conference ||
| | Conference Object ID, | |Control |~~~>|Object of ||
+--------+ Mute, "Bob" > | |Server | |occurrence ||
| +-----------+ +-------+ ||
| |"Alice"| ||
| ' ' '|
+--------+ NOTIFY <"Bob"=mute"> |+------------+ ' ' '|
| |<-------------------------|Notification|<~~~| ||
| Client |. . ||Service | +-------+ ||
+--------+--+ . || | |"Bob" | ||
| |<----------------------| | +-------+----+|
| Client | NOTIFY <"Bob"=mute">|+------------+ |
+--------+ +--------------------------------+
Figure 11: Client Manipulation of Conference - Mute a party
Upon receipt of the Conference Control Protocol request to "mute" a
party ("Bob") in the specific conference as identified by the
Conference Object ID, the Conference Server ensures that "Alice" has
the appropriate authority based on the policies associated with that
specific Conference Object to perform the operation. "Bob's" status
is marked as "recvonly" and the Conference Template of the Conference
Object (if included) is updated to reflect that "Bob's" media is not
to be "mixed" with the conference media.
Depending upon the policies, other participants (including "Bob") may
be notified of this change via the Conference Notification Service.
8.3 Sidebar Manipulations
A sidebar can be viewed as a separate Conference instance that only
exists within the context of a parent Conference instance. Although
viewed as an independent Conference instance, it can not exist
without a parent. A Sidebar is created using the same mechanisms
employed for a standard conference as described in Section 6.1 A
Conference object representing a Sidebar is created by cloning the
parent associated with the existing conference, copying the
information from the parent and updating any information specific to
the sidebar. A Sidebar Conference Object is implicitly linked to the
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parent Conference Object (i.e. it is not an independent object). A
Conference System manages and enforces the parent and appropriate
localized restrictions on the Sidebar Conference Object (e.g. No
members from outside the parent conference instance can join, Sidebar
conference can not exist if parent Conference is terminated, etc.).
The Sidebar mechanism uses the umbrella approach for association of
XCON Conference Object Identifiers as introduced in other sections of
this document.
+--------------+
| Conference |
| Object |
| Identifier |
+--------------+
|
|
|
+---------------------+---------------------+
| | |
+-------+-------+ +-------+-------+ +-------+-------+
| Sidebar | | Sidebar | | Sidebar |
| Conference | | Conference | | Conference |
| Object | | Object | | Object |
| Identifier | | Identifier | | Identifier |
+-------+-------+ +-------+-------+ +---------------+
Figure 12: Conference Object Mapping.
Figure 12 illustrates the relationship between a Conference Object
and associated Sidebar Conference Objects within a Conference System.
Each Sidebar Conference Object has a unique Conference Object
Identifier as described in Section 5.3.1. The main Conference Object
Identifier acts as a top level identifier for associated Sidebars.
A sidebar Conference Object Identifier follows many of the concepts
outlined in the Cloning tree model described in Section 6.1. A
Sidebar Conference Object contains a subset of members from the
original Conference object. Properties of the Sidebar Conference
Object can be manipulated by a Conference Control Protocol
(Section 7.3 using the unique Conference Object identifier for the
sidebar. It is also possible for the top level Conference Object to
enforce policy on the Sidebar Object (similar to parent enforceable
as discussed in Section 6.1).
[Editor's Note: this needs more detail - especially around cloning
tree.]
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8.4 Whispering or Private Messages
[Editor's Note: TBD. Once we get full agreement on terminology and
the basic ideas in the other sections, we'll tackle this.]
8.5 Conference Announcements and Recordings
[Editor's note: TBD. Use Cullen's comments on the previous version
of the doc .]
9. Relationships between SIPPING and XCON Frameworks
The SIPPING Conferencing Framework [9] provides an overview of a wide
range of centralized conferencing solutions known today in the
conferencing industry. The document introduces a terminology and
logical entities in order to systemize the overview and to show the
common core of many of these systems. The logical entities and the
listed scenarios in the SIPPING Conferencing Framework are being used
to illustrate how SIP [4] can be used as a signalling means in these
conferencing systems. SIPPING Conferencing Framework does not define
new conference control protocols to be used by the general
conferencing system. It uses only basic SIP [4], the SIP
Conferencing for User Agents [15], and the SIPPING Conference
Package [9] for basic SIP conferencing realization.
The XCON framework defines a particular centralized Conferencing
System and the logical entities implementing it. It also defines a
particular XCON Data Model and refers to the standard protocols
(beyond call signalling means) being defined by the XCON WG to be
used among the XCON logical entities for implementing advanced
conferencing features. The purpose of XCON working group and this
framework is to achieve interoperability between the XCON entities
from different vendors for controlling different aspects of advanced
conferencing applications.
The logical entities defined in the two frameworks are not intended
to be mapped one-to-one. The two frameworks differ in the
interpretation of the internal conferencing system decomposition and
the corresponding operations. Nevertheless, the basic SIP [4], the
SIP Conferencing for User Agents [15], and the SIPPING Conference
Package [9] are fully compatible with both Framework documents.
10. Security Considerations
There are a wide variety of potential attacks related to
conferencing, due to the natural involvement of multiple endpoints
and the many, often user-invoked, capabilities provided by the
conferencing system. Examples of attacks include the following: an
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endpoint attempting to listen to conferences in which it is not
authorized to participate, an endpoint attempting to disconnect or
mute other users, and theft of service, by an endpoint, in attempting
to create conferences it is not allowed to create.
There are several issues surrounding security of this conferencing
framework. One set of issues involves securing the actual protocols
and the associated authorization mechanisms. This first set of
issues should be addressed in the specificiations specific to the
protocols described in Section 7. The protocols used for
manipulation and retrieval of confidential information MUST support a
confidentiality and integrity mechanism. Similar requirements apply
for the floor control protocols.
There are also security issues associated with the authorization to
perform actions on the conferencing system to invoke specific
capabilities. Section 4.3 discusses the policies associated with the
Conference Object to ensure that only authorized entities are able to
manipulate the data to access the capabilities. The final set of
issues involves the privacy and security of the identity of a user in
the conference.
Many policy authorization decisions are based on the identity of the
user or the Role that a user may have. There are several ways that a
user might authenticate its identity to the system. The conferencing
system may know about specific users and assign passwords to the
users. The users may also be authenticated by knowing a particular
Conference ID and a PIN for it. Sometimes, a PIN is not required and
the Conference ID is used as a shared secret. The call signalling
means can provide a trusted form of the user identity or it might
just provide a hint of the possible identity and the user still needs
to provide some authentication to prove it has the identity that was
provided as a hint in the call signalling. This may be in the form
of an IVR system or other means. The goal for the Conferencing
System is to figure out a user identity and a Role for any attempt to
send a request to the Conferencing System.
When a Conferencing System presents the identity of authorized users,
it may choose to provide information about the way the identity was
proven to or verified by the system. A user may also come as a
completely unauthenticated user into the system - this fact needs
also be communicated to interested parties.
When guest users interact with the system, it is often in the context
of a particular conference. In this case the user may provide a PIN
or a password that is specific to the conferences and authenticates
the user to take on a certain role in that conference. The guest
user can then perform actions that are allowed to any user with that
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Role.
The term password is used to mean the usual, that is to say a
reasonable sized, in number of bits, hard to predict shared secret.
Today users often have passwords with more than 30 bits of randomness
in them. PIN is a special password case - a shared secret that is
only numeric and often contains a fairly small number of bits (often
as few as 10 bits). When Conferencing Systems are used for audio on
the PSTN, there is often a need to authenticate using a PIN.
Typically if the user fails to provide the correct PIN a few times in
a row, the PSTN call is disconnected. The rate of making the calls
and getting to the point to enter a PIN makes is fairly hard to do an
exhaustive search of the PIN space even for 4 digit PINs. When using
a high speed interface to connect to a Conferencing System, it is
often possible to do thousands of attempts per second and the PIN
space could quickly be searched. Because of this, it is not
appropriate to use PINs for authorization on any of the interfaces
that provide fast queries or many simultaneous queries.
This conferencing system has an idea of the identity of a user but
this does not mean it can reveal this identity to other users, due to
privacy considerations. Users can set select various options for
revealing their identity to other users. A user can be "hidden" such
that other users can not see they are involved in the conference, or
they can be "anonymous" such that users can see that another user is
there, but not see the identity of the user, or they can be "public"
where other users can see their identity. If there are multiple
"anonymous" users, other parties will be able to see them as
independent "anonymous" parties and will be able to tell how many
"anonymous" parties are in the conference. Note, that the visibility
to other participants is dependent on their Roles. For example,
users' visibility (including "anonymous" and "hidden") may be
displayed to the moderator or administrator, subject to a
Conferencing System's local policies. "Hidden" status is often used
by robot participants of a conference and is also used in many call
center conference situations.
11. IANA Considerations
This is an informational draft, with no IANA considerations required.
12. Acknowledgements
This document is a result of architectural discussions among IETF
XCON working group participants. The authors would like to thank
Henning Schulzrinne for the "Conference Object Tree" proposal, Cullen
Jennings for providing input for the "Security Considerations"
section and Keith Lantz for his careful reviews and constructive
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input.
13. Open Issues
Several open issues are identified in the body of the document. This
list is intended as a summary to facilitate the tracking of the
primary open issues that require WG input.
1. DP4. Object Schema structure and Template definition.
Clarification of Templates versus Blueprints and details of XML
schema.
2. DP5. CCP Protocol.
14. Changes since last Version
Changes from WG 00 to 01::
- Section 2 (Conventions and Terminology). Slight modifications to
definitions of Call (control) signalling, Conference Identifer,
Conference Instance, Conference Object.
- Section 2 (Conventions and Terminology).Renaming of term
"Registered Template Definition" to "Registered Conference Document"
(per agreement at interim meeting).
- Section 3 (Next to the last paragraph on the media model).
Clarified the text such that it doesn't read that the focus performs
media mixing. Changed "focus" to "media mixer controlled by the
focus" in the 2nd sentence and "performed" to "controlled" in the
4th.
- Section 5. Rearranged the sub-sections a bit for better flow.
First describe the Conference ID, then the Conference Instance,
followed by the Conference Object, with the Conference Object
Identifer described in a subsection of the Conference Object
section. Added a diagram showing the relationship between Conference
Identifer/Focus and Conference Object Identifier, within the context
of a Conference Instance to the Conference Object section.
- Section 6.1 (Cloning Tree). Rewording to clarify which operations
apply to independent objects (and non-independent).
- Section 6.3 (Advanced Example). Added additional text with regards
to future conferences, introducing the concept of infinite series
(which would be limited by calendaring interface).
- Section 7.3 (Conference Control Protocol). Updated to include
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reference to SOAP option.
- Section 8.3 (sidebars) - reworded 1st paragraph to be more explicit
about the XCON FW constructs used.
Changes from individual 02 to WG 00:
- few minor editorial changes
- Section 2. Removed second sentence of definition of Conference
ID, as that's now included/described in context in new Identifier
section.
- Section 3. Clarified that TBD in Figure 1 is "Conference Control
Protocol" (per Keith's comment to be more explicit).
- Section 4.1. Identifiers. Moved this to a new section (
Section 5).
- New section for Identifiers ( Section 5), thus all section
references beyond 4 are incremented in the new version.
- Section 4. Since section 4.1 was removed, section 4.2 became the
body text for section 4.
- Section 4.2. Added "Floor Information" to Figure 2 as part of
Common Conference Information, also added "Floor Control" to
Conference Template (per text and Cullen's draft).
- Section 4.5. Conference policies. Reworded to not introduce new
terms, but use the general terms identified in the 1st paragraph.
- Section 5.2. Removed "Instance" from "Active Conference Instance"
in Figure 4.
- Section 5.3. Added text clarifying that templates are retrieved
from server (not central repository) (per DP3 conclusion).
- Section 5.4. Added text that there is a single time and that the
times are all relative the one time (per DP1 conclusion).
- Section 5.4. Added text clarifying that changes to a series impact
"all future occurrences (per DP1 discussion/conclusion).
- Section 6.3 - Added subsections for discussion of CSCP and NETCONF
as the CCP.
- Section 6.4 - Floor Control. Removed Editor's notes 2 and 3.
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Condensed the text only slightly, but added explicit references to
new identifier section.
- Section 6.4.1 Moved to new Identifier section ( Section 5)
- Section 7.1 - moved example to 7.2. Included a new (more
appropriate example) in 7.1, although this may be too basic.
- Section 7.3 - added some proposed text for Sidebars.
15. References
15.1 Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
15.2 Informative References
[2] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[3] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[4] 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.
[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[6] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[7] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[8] Dawson, F. and Stenerson, D., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)", RFC 2445,
November 1998.
[9] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol",
draft-ietf-sipping-conferencing-framework-05 (work in
progress), May 2005.
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[10] Levin, O. and R. Even, "High Level Requirements for Tightly
Coupled SIP Conferencing",
draft-ietf-sipping-conferencing-requirements-01 (work in
progress), October 2004.
[11] Rosenberg, J., "A Session Initiation Protocol (SIP) Event
Package for Conference State",
draft-ietf-sipping-conference-package-12 (work in progress),
July 2005.
[12] Schulzrinne, H., "Requirements for Floor Control Protocol",
draft-ietf-xcon-floor-control-req-03 (work in progress),
January 2005.
[13] Koskelainen, P. and H. Khartabil, "Requirements for Conference
Policy Control Protocol", draft-ietf-xcon-cpcp-reqs-04 (work in
progress), August 2004.
[14] Even, R. and N. Ismail, "Conferencing Scenarios",
draft-ietf-xcon-conference-scenarios-04 (work in progress),
April 2005.
[15] Johnston, A. and O. Levin, "Session Initiation Protocol Call
Control - Conferencing for User Agents",
draft-ietf-sipping-cc-conferencing-07 (work in progress),
June 2005.
[16] Camarillo, G., "The Binary Floor Control Protocol (BFCP)",
draft-ietf-xcon-bfcp-04 (work in progress), May 2005.
[17] Khartabil, H., "The Conference Policy Control Protocol (CPCP)",
draft-ietf-xcon-cpcp-01 (work in progress), October 2004.
[18] Khartabil, H., "An Extensible Markup Language (XML)
Configuration Access Protocol (XCAP) Usages for Conference
Policy Manipulation and Conference Policy Privelges
Manipulation", draft-ietf-xcon-cpcp-xcap-03 (work in progress),
October 2004.
[19] Khartabil, H. and A. Niemi, "Privileges for Manipulating a
Conference Policy",
draft-ietf-xcon-conference-policy-privileges-01 (work in
progress), October 2004.
[20] Levin, O. and G. Kimchi, "Centralized Conference Data Model",
draft-levin-xcon-cccp-02 (work in progress), February 2005.
[21] Jennings, C., "Media Conference Server Control for XCON",
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draft-jennings-xcon-media-control-02 (work in progress),
February 2005.
[22] Rosen, B., "SIP Conferencing: Sub-conferences and Sidebars",
draft-rosen-xcon-conf-sidebars-01 (work in progress),
July 2004.
[23] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute",
draft-ietf-mmusic-sdp-media-label-01 (work in progress),
January 2005.
[24] Camarillo, G., "Session Description Protocol (SDP) Format for
Binary Floor Control Protocol (BFCP) Streams",
draft-camarillo-mmusic-sdp-bfcp-00 (work in progress),
October 2004.
[25] Campbell, B., "The Message Session Relay Protocol",
draft-ietf-simple-message-sessions-10 (work in progress),
February 2005.
[26] Jennings, C. and A. Roach, "Conference State Change Protocol
(CSCP)", draft-jennings-xcon-cscp-00 (work in progress),
February 2005.
[27] Enns, R., "NETCONF Configuration Protocol",
draft-ietf-netconf-prot-07 (work in progress), June 2005.
Authors' Addresses
Mary Barnes
Nortel
2201 Lakeside Blvd
Richardson, TX
Email: mary.barnes@nortel.com
Chris Boulton
Ubiquity Software Corporation
Building 3
Wern Fawr Lane
St Mellons
Cardiff, South Wales CF3 5EA
Email: cboulton@ubiquitysoftware.com
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Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Email: oritl@microsoft.com
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