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Versions: (draft-barnes-xcon-framework) 00 01
02 03 04 05 06 07 08 09 10 11 RFC 5239
XCON Working Group M. Barnes
Internet-Draft Nortel
Intended status: Informational C. Boulton
Expires: November 15, 2007 Ubiquity Software Corporation
O. Levin
Microsoft Corporation
May 14, 2007
A Framework for Centralized Conferencing
draft-ietf-xcon-framework-08
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines the framework for Centralized Conferencing.
The framework allows participants using various call signaling
protocols, such as SIP, H.323, Jabber and PSTN, to exchange media in
a centralized unicast conference. The Centralized Conferencing
Framework defines logical entities and naming conventions, along with
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a high level conferencing data model. The framework also outlines a
set of conferencing protocols, which are complementary to the call
signaling protocols, for building advanced conferencing applications.
The framework binds all the defined components together for the
benefit of builders of conferencing systems.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Centralized Conferencing Data . . . . . . . . . . . . . . . . 10
4.1. Conference Information . . . . . . . . . . . . . . . . . . 12
4.2. Conference policies . . . . . . . . . . . . . . . . . . . 12
5. Centralized Conferencing Constructs and Identifiers . . . . . 13
5.1. Conference Identifier . . . . . . . . . . . . . . . . . . 13
5.2. Conference Object . . . . . . . . . . . . . . . . . . . . 13
5.2.1. Conference Object Identifier . . . . . . . . . . . . . 15
5.3. Conference User Identifier . . . . . . . . . . . . . . . . 15
6. Conferencing System Realization . . . . . . . . . . . . . . . 16
6.1. Cloning Tree . . . . . . . . . . . . . . . . . . . . . . . 17
6.2. Ad-hoc Example . . . . . . . . . . . . . . . . . . . . . . 20
6.3. Advanced Example . . . . . . . . . . . . . . . . . . . . . 21
6.4. Scheduling a conference . . . . . . . . . . . . . . . . . 23
7. Conferencing Mechanisms . . . . . . . . . . . . . . . . . . . 26
7.1. Call Signaling . . . . . . . . . . . . . . . . . . . . . . 26
7.2. Notifications . . . . . . . . . . . . . . . . . . . . . . 26
7.3. Conference Control Protocol . . . . . . . . . . . . . . . 26
7.4. Floor Control . . . . . . . . . . . . . . . . . . . . . . 26
8. Conferencing Scenario Realizations . . . . . . . . . . . . . . 28
8.1. Conference Creation . . . . . . . . . . . . . . . . . . . 28
8.2. Participant Manipulations . . . . . . . . . . . . . . . . 30
8.3. Media Manipulations . . . . . . . . . . . . . . . . . . . 32
8.4. Sidebar Manipulations . . . . . . . . . . . . . . . . . . 33
8.4.1. Internal Sidebar . . . . . . . . . . . . . . . . . . . 35
8.4.2. External Sidebar . . . . . . . . . . . . . . . . . . . 37
8.5. Floor control using sidebars . . . . . . . . . . . . . . . 40
8.6. Whispering or Private Messages . . . . . . . . . . . . . . 42
8.7. Conference Announcements and Recordings . . . . . . . . . 44
8.8. Monitoring for DTMF . . . . . . . . . . . . . . . . . . . 46
8.9. Observing and Coaching . . . . . . . . . . . . . . . . . . 46
9. Relationships between SIPPING and Centralized Conferencing
Frameworks . . . . . . . . . . . . . . . . . . . . . . . . . . 49
10. Security Considerations . . . . . . . . . . . . . . . . . . . 50
10.1. Authorization . . . . . . . . . . . . . . . . . . . . . . 51
10.2. Security and Privacy of Identity . . . . . . . . . . . . . 52
10.3. Floor Control Server Authentication . . . . . . . . . . . 52
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 53
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 53
13. Changes since last Version . . . . . . . . . . . . . . . . . . 53
14. Informative References . . . . . . . . . . . . . . . . . . . . 60
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 62
Intellectual Property and Copyright Statements . . . . . . . . . . 63
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1. Introduction
This document defines the framework for Centralized Conferencing.
The framework allows participants using various call signaling
protocols, such as SIP, H.323, Jabber, or PSTN, to exchange media in
a centralized unicast conference. Other than references to general
functionality (e.g., establishment and teardown), details of these
call signaling protocols are outside the scope of this document.
The Centralized Conferencing Framework defines logical entities and
naming conventions, along with a high level conferencing data model.
The framework also outlines a set of conferencing protocols, which
are complementary to the call signaling protocols, for building
advanced conferencing applications.
The Centralized Conferencing Framework is compatible with the
functional model presented in the SIPPING Conferencing Framework [8].
Section 9 of this document discusses the relationship between the
Centralized Conferencing Framework and the SIPPING Conferencing
framework, in the context of the Centralized Conferencing model
presented in this document.
2. Terminology
This Centralized Conferencing Framework document generalizes, when
appropriate, the SIPPING Conferencing Framework [8] terminology and
introduces new concepts, as listed below. Further details and
clarification of the new terms and concepts are provided in the
subsequent sections of this document.
Active conference: The term active conference refers to a conference
object that has been created and activated via the allocation of
its identifiers (e.g., conference object identifier and conference
identifier) and the associated focus. An active conference is
created based on either a system default conference blueprint or a
specific conference reservation.
Call Signaling protocol: The call signaling protocol is used between
a participant and a focus. In this context, the term "call" means
a channel or session used for media streams.
Conference information: The conference information includes
definitions for basic conference features, such as conference
identifiers, membership, signaling, capabilities and media types,
applicable to a wide range of conferencing applications. The
conference information also includes the media and application
specific data for enhanced conferencing features or capabilities,
such as media mixers. The conference information is the data type
(i.e., the XML schema) for a conference object.
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Conference blueprint: A conference blueprint is a static conference
object within a conferencing system, which describes a typical
conference setting supported by the system. A conference
blueprint is the basis for creation of dynamic conference objects.
A system may maintain multiple blueprints. Each blueprint is
comprised of the initial values and ranges for the elements in the
object, conformant to the data schemas for the conference
information.
Conference control protocol (CCP): A conference control protocol
provides the interface for data manipulation and state retrieval
for the centralized conferencing data, represented by the
conference object.
Conference factory: A conference factory is a logical entity that
generates unique URI(s) to identify and represent a conference
focus.
Conference identifier (ID): A conference identifier is a call
signaling protocol-specific URI that identifies a conference focus
and its associated conference instance.
Conference instance: A conference instance refers to an internal
implementation of a specific conference, represented as a set of
logical conference objects and associated identifiers.
Conference object: A conference object represents 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 services available for each object
independently. The conference object schema is based on the
conference information.
Conference object identifier (ID): A conference object identifier is
a URI which uniquely identifies a conference object and is used by
a conference control protocol to access and modify the conference
information.
Conference policies: Conference policies collectively refers to a
set of rights, permissions and limitations pertaining to
operations being performed on a certain conference object.
Conference reservation: A conference reservation is a conference
object, which is created from either a system default or client
selected blueprint.
Conference state: The conference state reflects the state of a
conference instance and is represented using a specific, well-
defined schema.
Conferencing system: Conferencing system refers to a conferencing
solution based on the data model discussed in this framework
document and built using the protocol specifications referenced in
this framework document.
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Conference user identifier (ID): A unique identifier for a user
within the scope of a conferencing system. A user may have
multiple conference user identifiers within a conferencing system
(e.g., to represent different roles).
Floor: Floor refers to a set of data or resources associated with a
conference instance, for which a conference participant, or group
of participants, is granted temporary access.
Floor chair: A floor chair is a floor control protocol compliant
client, either a human participant or automated entity, who is
authorized to manage access to one floor and can grant, deny or
revoke access. The floor chair does not have to be a participant
in the conference instance.
Focus: A focus is a logical entity that maintains the call
signalling interface with each participating client and the
conference object representing the active state. As such, the
focus acts as an endpoint for each of the supported signaling
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.
Media graph: The media graph is the logical representation of the
flow of media for a conference.
Media mixer: A media mixer is the logical entity with the capability
to combine media inputs of the same type, 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[5]) or Message Session Relay Protocol
(defined in [17]).
Role: A role provides the context for the set of conference
operations that a participant can perform. A default role (e.g.,
standard conference participant) will always exist, providing a
user with a set of basic conference operations. Based on system
specific authentication and authorization, a user may take on
alternate roles, such as conference moderator, allowing access to
a wider set of conference operations.
Sidebar: A sidebar is a separate Conference instance that only
exists within the context of a parent conference instance. The
objective of a sidebar is to be able to provide additional or
alternate media only to specific participants.
Whisper: A whisper involves a one-time media input to a specific
participant(s) within a specific conference instance, accomplished
using a sidebar. An example of a whisper would be an announcement
injected only to the conference chair or to a new participant
joining a conference.
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3. Overview
A centralized conference is an association of endpoints, called
conference participants, with a central endpoint, called a conference
Focus. The Focus has direct peer relationships with the participants
by maintaining a separate call signaling interface with each.
Consequently, in this centralized conferencing model, the call
signaling graph is always a star.
The most basic conference supported in this model 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 signaling functionality with a
participant serving as the Focus; the SIPPING Conferencing Framework
[8] together with the SIP Call Control Conferencing for User Agents
[12] documents address these types of scenarios.
In addition to the basic features, however, a conferencing system
supporting the centralized conferencing model proposed in this
framework document can offer richer functionality, by including
dedicated conferencing applications with explicitly defined
capabilities, reserved recurring conferences, along with providing
the standard protocols for managing and controlling the different
attributes of these conferences.
The core requirements for centralized conferencing are outlined in
[7]. These requirements are applicable for conferencing systems
using various call signaling protocols, including SIP. Additional
conferencing requirements are provided in [10], and [11].
The centralizing conferencing system proposed by this framework is
built around a fundamental concept of a conference object. A
conference object provides the data representation of a conference
during each of the various stages of a conference (e.g., creation,
reservation, active, completed, etc.). A conference object is
accessed via the logical functional elements, with whom a
conferencing client interfaces, using the various protocols
identified in Figure 1. The functional elements defined for a
conferencing system described by the framework are a Conference
Control Server, Floor Control Server, any number of Foci and a
Notification Service. A Conference Control Protocol (CCP) provides
the interface between a conference and media control client and the
conference control server. A floor control protocol (e.g., BFCP)
provides the interface between a floor control client and the floor
control server. A call signaling protocol (e.g., SIP, H.323, PSTN,
etc.) provides the interface between a call signaling client and a
Focus. A notification protocol (e.g. SIP Notify) provides the
interface between the conferencing client and the Notification
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Service.
A conferencing system can support a subset of the conferencing
functions depicted in the conferencing system logical decomposition
in Figure 1 and described in this document. However, there are some
essential components that would typically be used by most other
advanced functions, such as the Notification Service. For example,
the notification service is used to correlate information, such as
list of participants with their media streams, between the various
other components.
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....................................................................
. 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 |Binary |Call |Notification
|Control |Floor |Signaling |Protocol
|Protocol |Control |Protocol |
| |Protocol | |
| | | |
..............|.................|...........|..........|............
. V V V V .
. +----------------+ +------------+ +----------+ +------------+ .
. | Conference | | Floor | | Call | |Notification| .
. | and Media | | Control | | Signaling| | Client | .
. | Control | | Client | | Client | | | .
. | Client | | | | | | | .
. +----------------+ +------------+ +----------+ +------------+ .
. .
. Conferencing Client .
....................................................................
Figure 1: Conferencing System Logical Decomposition.
The media graph of a conference can be centralized, decentralized, 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 decentralized (i.e., distributed) case, the media graph is a
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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 decentralized media case, however,
the details of such are left for future study.
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 high level data model and how the conference objects are
maintained. Section 7 describes the fundamental conferencing
mechanisms and provides a high level overview of the protocols.
Section 8 then provides realizations of various conferencing
scenarios, detailing the manipulation of the conference objects using
the defined protocols. Section 9 of this document summarizes the
relationship between this Centralized Conferencing Framework and the
SIPPING Conferencing Framework.
4. Centralized Conferencing Data
The centralized conference data is logically represented by the
conference object. A conference object is of type 'Conference
information type', as illustrated in Figure 2. The conference
information type is extensible.
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+------------------------------------------------------+
| C o n f e r e n c e o b j e c t |
| |
| +--------------------------------------------------+ |
| | Conference information type | |
| | | |
| | +----------------------------------------------+ | |
| | | Conference description (times, duration) | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Membership (roles, capacity, names) | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Signaling (protocol, direction, status) | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Floor information | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Sidebars, Etc. | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Mixer algorithm, inputs, and outputs | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Floor controls | | |
| | +----------------------------------------------+ | |
| | +----------------------------------------------+ | |
| | | Etc. | | |
| | +----------------------------------------------+ | |
| +--------------------------------------------------+ |
+------------------------------------------------------+
Figure 2: Conference Object Type Decomposition.
In a system based on this conferencing framework, the same conference
object type is used for representation of a conference during
different stages of a conference, such as expressing conferencing
system capabilities, reserving conferencing resources or reflecting
the state of ongoing conferences. Section 6 describes the usage
semantics of the conference objects. The exact XML schema of the
conference object, including the organization of the conference
information is detailed in a separate document [16].
Along with the basic data model as defined in [16], the realization
of this framework requires a policy infrastructure. The policies
required by this framework to manage and control access to the data
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include local, system level boundaries associated with specific data
elements, such as the membership, and by the ranges and limitations
of other data elements. Additional policy considerations for a
system realization based on this data model are discussed in
Section 4.2.
4.1. Conference Information
There is a core set of data in the conference information that is
utilized in any conference, independent of the specific conference
media nature (e.g., the mixing algorithms performed, the advanced
floor control applied, etc.). This core set of data in the
conference information contains the definitions representing the
conference object capabilities, membership, roles, call signaling and
media status relevant to different stages of the conference life-
cycle. This core set of conference information may be represented
using the conference-type as defined in [9]. Typically, participants
with read-only access to the conference information would be
interested in this core set of conference information only.
In order to support more complex media manipulations and enhanced
conferencing features the conference information, as reflected by the
data model defined in [16], contains additional data beyond that
defined in [9]. The information defined in [16] provides specific
media mixing details, available floor controls and other data
necessary to support enhanced conferencing features. This
information allows authorized clients to manipulate the mixer's
behavior via the focus, with 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.
New centralized conferencing specifications can extend the basic
conference-type as defined in [16] and introduce additional data
elements to be used within the conference information type.
4.2. Conference policies
Conference policies collectively refers to a set of rights,
permissions and limitations pertaining to operations being performed
on a certain conference object.
The 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. Managing this access
would require a conferencing system have access to basic policy
information to make the decisions, but doesn't necessarily require an
explicit representation in the policy model. As such, for this
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framework document, the policies represented by the set of rights are
reflected in the system realization (Section 6).
The permissions and limits require explicit policy mechanisms and are
outside the scope of the data model [16] and this framework document.
5. Centralized Conferencing Constructs and Identifiers
This section provides details of the identifiers associated with the
centralized conferencing framework constructs 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 (conference ID) is a call signaling
protocol-specific URI that identifies a specific conference focus and
its associated conference instance. A conference factory is one
method for generating a unique conference ID, to identify and address
a conference focus, using a call signaling interface. Details on the
use of a conference factory for SIP signaling can be found in [12].
The conference identifier can also be obtained using the conference
control protocol or other, including proprietary, out-of-band
mechanisms.
5.2. Conference Object
A Conference object provides the logical representation of a
conference instance in a certain stage, such as a conference
blueprint representing a conferencing system's capabilities, the data
representing a conference reservation, and the conference state
during an active conference. Each conference object is independently
addressable through the conference control protocol interface
[Section 7.3].
Figure 3 illustrates the relationships between the conference
identifier, the focus and the conference object ID within the context
of a logical conference instance, with the conference object
corresponding to an active conference.
A conference object representing a conference in the active state can
have multiple call signaling conference identifiers; for example, for
each call signaling protocol supported. There is a one-to-one
mapping between an active conference object and a conference focus.
The focus is addressed by explicitly associating unique conference
IDs for each signaling protocol supported by the active conference
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object.
....................................................................
. 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: Identifier Relationships for an Active Conference.
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5.2.1. 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. The conference object identifier is created
both by the conferencing system based on internal actions as well as
based on specific conference protocol requests. A conferencing
system will allocate a conferencing object identifier for every
conference blueprint, for every conference reservation and for every
active conference. The distribution of the conference object
identifier depends upon the specific use case and includes a variety
of mechanisms, such as the through the conference control protocol
mechanism, the data model and conference package or out of band
mechanisms such as E-Mail.
When a user wishes to create or join a conference and the user does
not have the conference object identifier for the specific
conference, more general signaling mechanisms apply, such that a user
may have a pre-configured conference object identifier to access the
conferencing system or other signaling protocols may be used and the
conferencing system maps those to a specific conference object
identifier. Once a conference is established, a conference object
identifier is required for the user to manipulate any of the
conferencing data or take advantage of any of the advanced
conferencing features. The same notion applies to users joining a
conference using other signaling protocols. They are able to
initially join a conference using any of the other signaling
protocols supported by the specific conferencing system, but the
conference object identifer must be used to manipulate any of the
conferencing data or take advantage of any of the advanced
conferencing features. As mentioned previously, the mechanism by
which the user learns of the conference object identifier varies and
could be via the conference control protocol, using the data model
and conference package or entirely out of band such as E-Mail or a
web interface.
The conference object identifier logically maps to other protocol
specific identifiers associated with the conference instance, such as
the BFCP 'confid'. The conference object identifier is defined in
[16].
5.3. Conference User Identifier
Each user within a conferencing system is allocated a unique
conference user identifier. The user identifier is used in
association with the conference object identifier to uniquely
identify a user within the scope of conferencing system. There is
also a requirement for identifying conferencing system users who may
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not be participating in a conference instance. Examples of these
users would be a non participating 'Floor Control Chair' or 'Media
Policy Controller'. The conference user identifier is required in
conference control protocol requests to uniquely determine who is
issuing commands, so that appropriate policies can be applied to the
requested command.
A typical mode for distributing the user identifer is out of band
during conferencing client configuration, thus the mechanism is
outside the scope of the centralized conferencing framework and
protocols. However, a conferencing system must also be capable of
allocating and distributing a user identifier during the first
signaling interaction with the conferencing system, such as an
initial request for blueprints or adding a new user to an existing
conference using the conference control protocol. When a user joins
a conference using a signaling specific protocol, such as SIP for a
dial-in conference, a conference user identifier must be assigned if
one is not already associated with that user. While this conference
user identifier isn't required for the participant to join the
conference, it is required to be allocated and assigned by the
conferencing system such that it is available for use for any
subsequent conference control protocol operations and/or
notifications associated with that conference. For example, the
conference user identifer would be sent in any notifications that may
be sent to existing participants, such as the moderator, when this
user joins.
The conference user identifier is logically associated with the other
user identifiers assigned to the conferencing client for other
protocol interfaces, such as an authenticated SIP user. The
conference user identifier is defined in [16].
6. Conferencing System Realization
Implementations based on this centralized conferencing framework can
range from systems supporting ad-hoc conferences, with default
behavior only, to sophisticated systems with the ability to schedule
recurring 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
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by the conferencing system. Consequently, this centralized
conferencing framework does not mandate the actual usage of the
conference object, but rather defines the general cloning tree
concept and the mechanisms required for its realization, as described
in detail in Section 6.1.
Adhoc and advanced conferencing examples are provided in Section 6.2
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 capabilities. The
scheduling of a conference based on these concepts and mechanisms is
then detailed in Section 6.4
As discussed in Section 4.2, the overall policy in terms of
permissions and limitations is outside the scope of this framework
document. The policies applicable to the conference object as a
whole in terms of read/write access would require a conferencing
system have access to basic policy information to make the decisions.
In the examples in this section, the policies are shown logically
associated with the conference objects to emphasize the general
requirement for policy functionality necessary for the realization of
this framework.
6.1. Cloning Tree
The concept defined in this section is a logical representation only,
as it is reflected through the centralized conferencing mechanisms:
the URIs and the protocols. Of course, the actual system realization
can differ from the presented model. The intent is to illustrate the
role of the logical elements in providing an interface to the data,
based on conferencing system and conferencing client actions, and
describe the resultant protocol implications.
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 conference blueprint. A
conference blueprint is a static conference object used to describe a
typical conference setting supported by the system. Each system can
maintain multiple blueprints, typically each describing a different
conferencing type using the conference information format. This
document uses the "cloning" metaphor instead of the "inheritance"
metaphor because it more closely fits the idea of object replication,
rather than a 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
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object nor subject to any limitations of the parent 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 5.2.1. By default, the newly created object contains all the
data existing in the parent object. 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 modify the
access restrictions imposed by the parent object.
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 elements can not be changed
by directly accessing the child object; neither can they be expanded
in the child object alone.
Figure 4 illustrates an example of a conference (Parent B), which is
created independent of its Parent (Parent A). Parent B creates two
child objects, Child 1 and Child 2. Any of the data elements of
Parent B can be modified (i.e. there are no "parent enforceable" data
elements) and depending upon the element, the changes will be
reflected in Child 1 and Child 2 , whereas changes to Parent A will
not impact the data elements of Parent B. Any "parent enforceable"
data elements as defined by Parent B cannot be modified in the child
objects.
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+---+-----------------------+
| 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-+-----------------------+
Figure 4: The Cloning Tree.
Using the defined cloning model and its tools, the following sections
show examples of how different systems based on this framework can be
realized.
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6.2. Ad-hoc Example
Figure 5 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 signaling channel with a conference factory as
specified in Section 5.1. The conference factory can internally
select one of the system supported conference 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.
+---+-----------------------+
| p | |
| o | System Default |
| l | |
| i | Conference |
| c | |
| i | Blueprint |
| e | |
+-s-+-----------------------+
|
\| /
\/
/\
/| \
V
+---+-----------------------+
| p | |
| o | Active |
| l | |
| i | Conference |
| c | |
| i | |
| e | |
+-s-+-----------------------+
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Figure 5: Conference Ad-hoc Creation and Lifetime.
6.3. Advanced Example
Figure 6 illustrates how a recurring conference can be specified
according to system capabilities, scheduled, reserved, and managed in
a conferencing system. A client would first query a conferencing
system for its capabilities. This can be done by requesting a list
of the conference blueprints the system supports. Each blueprint
contains a specific combination of capabilities and limitations of
the conference server in terms of supported media types (e.g., 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.
The selected blueprint with its default values is cloned by the
client into a newly created conference object, referred to as a
conference reservation, that specifies the resources needed from the
system for this conference instance. At this point the conference
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 reservation.
At this point the client can ask the conference server to create new
conference reservations by attaching the conference reservation to
the request. As a result, the server can allocate the needed
resources, create the additional conference objects for the child
conference reservations and allocate the conference object
identifiers for all - the original conference reservation and for
each child conference reservation.
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 child conference reservation will affect
neither the parent conference reservation, from which it was created,
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 enforceable. As a result, these
objects can be modified by accessing the parent conference
reservation only. The changes to these objects can be applied
automatically to each of the child reservations, subject to local
policy.
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+---+-----------------------+
| p | |
| o | Selected |
| l | |
| i | Conference |
| c | |
| i | Blueprint |
| e | |
+-s-+-----------------------+
|
\| /
\/
/\
/| \
V
+---+-----------------------+
| p | |
| o | Conference |
| l | |
| i | Reservation |
| c | |
| i | |
| e | |
+-s-+-----------------------+
| | |
| | |
| | |
| | |
+---|--|--V-----------------+
+-+---|--V------------------+ |
+-+-+---V-------------------+ | |
| p | | | |
| o | Child Conference | | |
| l | | | |
| i | Reservation | | |
| c | | | |
| i | | |-+
| e | |-+
+-s-+-----------------------+
Figure 6: Advanced Conference Definition, Creation, and Lifetime.
When the time comes to schedule the conference reservation, either
via the system determination that the 'start' time has been reached
or via client invocation, an active conference is cloned based on the
conference reservation. As in the adhoc example, the active
conference is independent from the parent and changes to the
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conference reservation will not impact the active conference. Any
desired changes must be targeted towards the active conference. An
example of this interaction is shown in Section 8.1
6.4. Scheduling a conference
The capability to schedule conferences forms an important part of the
conferencing system solution. An individual conference reservation
typically 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 occurrence of a
conference reservation, 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
reservations that form part of a recurring conference. The mechanism
proposed in this document makes use of the 'Internet Calendaring and
Scheduling Core Object' specification defined in RFC2445[6] in union
with the concepts introduced in Section 4 for the purpose of
achieving advanced conference scheduling capability.
Figure 7 illustrates a simplified view of a client interacting with a
conferencing system. The client is using the Conference Control
Protocol to add a new conference reservation to the conferencing
system by interfacing with the conference control server. A CCP
request contains a valid conference reservation and reference by
value to an 'iCal' object which contains scheduling information about
the conference (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 7: Resource Scheduling
A CCP request to create a new conference reservation is validated,
including the associated iCal object, and the resultant conference
reservation is created. The conference reservation is uniquely
represented within the conferencing system by a conference object
identifier (e.g., xcon:hd87928374) as introduced in Section 5.2.1 and
defined in [16]. This unique URI is returned to the client and can
be used to reference the conference reservation, if any future
manipulations are required (e.g., alter start time), using a CCP
request.
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The previous example explains how a client creates a basic conference
reservation using an iCal reference in association with a conference
control protocol. Figure 7 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 CCP request represents a series of recurring
conference instances (e.g., conference start time, end time, occur
weekly). The conferencing system will treat this request the same as
the first example. The CCP request will be validated, along with the
associated iCal object, and the conference reservation is created.
The conference reservation and its 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 CCP request to adjust the
conference 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 specific range of the series. A good example is a
conference reservation that 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 7
in mind, the client will construct a CCP request whose purpose is to
modify the existing conference reservation for the recurring
conference instance. The client will include the conference object
ID provided by the conferencing system to explicitly reference the
conference reservation within the conferencing system. A CCP request
will contain all the required changes to the conference reservation
(e.g., change of venue).
The conferencing system matches the incoming CCP request to the
existing conference reservation but identifies that the associated
iCal object only refers to a range of the existing series. The
conferencing system creates a child, by cloning the original
conference reservation, to represent the altered conference instances
within the series. The cloned child object is not independent of the
original parent object, thus preventing any potential conflicts in
scheduling (e.g., a change to the whole series 'start time'). The
cloned conference reservation, representing the altered series of
conference instances, has its own associated conference object ID
which is returned to the client using a CCP response. This
conference object ID is then used by the client to make any future
alterations on the newly 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,
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can itself be manipulated using a CCP request for the newly created
conference object ID . This provides a flexible approach to the
scheduling of recurring conference instances.
7. Conferencing Mechanisms
7.1. Call Signaling
The focus is the central component of the conference. Participants
interface with the focus using an appropriate call signaling protocol
(CSP). Participants request to establish or join a conference using
the CSP. After checking the applicable policies, a focus then either
accepts the request, sends a progress indication related to the
status of the request (e.g., for a parked call while awaiting
moderator approval to join) or rejects that request using the call
signaling interface.
During an active conference, a Conference Control Protocol can be
used to affect the conference state. For example, CCP requests to
add and delete participants are communicated to the focus and checked
against the conference policies. If approved, the participants are
added or deleted using the call signaling 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,
including participants. A model for notifications using SIP is
defined in [4] with the specifics to support conferencing defined in
[9].
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 conference control protocol provides for data manipulation and
state retrieval for the centralized conferencing data, represented by
the conference object. The details of the conference control
protocol are provided in separate documents.
7.4. Floor Control
A floor control protocol allows an authorized client to manage access
to a specific floor and to grant, deny or revoke access of other
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conference users to that floor. Floor control is not a mandatory
mechanism for a conferencing system implementation but provides
advanced media input control features for conference users. A
mechanism for floor control within a conferencing system is defined
in the Binary Floor Control Protocol specification [13].
Within this framework, a 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[1] offer/answer[3] exchange on the
signaling interface with the focus. Section 10.3 provides a
discussion of client authentication of a floor control server.
As well as the client to the floor control 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 [13] for authentication details), a specific floor control
message requires detailed information to uniquely identify a
conference, a user and a floor.
The conference is uniquely identifed by the conference object ID per
Section 5.2.1. This conference object ID must be included in all
floor control messages. When the SDP model is used as described in
[15] this identifier maps to the 'confid' SDP attribute.
Each authorized user associated with a conference object is uniquely
represented by a conference user ID per Section 5.3. This conference
user ID must be included in all floor control messages. When using
SDP offer/answer exchange to negotiate a Floor control connection
with the focus using the call signaling protocol, the unique
conference user identifier is contained in the 'userid' SDP
attribute, as defined in [15]
A media session within a conferencing system can have any number of
floors (0 or more) that are represented by the conference identifier.
When using SDP offer/answer exchange to negotiate a floor control
connection with the focus using the call signaling interface, the
unique conference identifier is contained in the 'floorid' SDP
attribute, as defined in [15] 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 [14].
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8. Conferencing Scenario Realizations
This section addresses how advanced conferencing scenarios, many of
which have been described in [11], are realized using this
centralized conferencing 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.
The scenarios provide a high level primitive view of the necessary
operations and general logic flow. The details shown in the
scenarios are for illustrative purposes only and don't necessarily
reflect the actual structure of the conference control protocol
messages nor the detailed data, including states, which are defined
in separate documents. 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 this
centralized conferencing framework.
8.1. Conference Creation
There are different ways to create a conference. A participant can
create a conference using call signaling means only, such as SIP and
detailed in [12]. For a conferencing client to have more flexibility
in defining the charaterisitics and capabilities of a conference, a
conferencing client would implement a conference control protocol
client. By using a conference control protocol, the client can
determine the capabilities of a conferencing system and its various
resources.
Figure 8 provides an example of one client "Alice" determining the
conference blueprints available for a particular conferencing system
and creating a conference based on the desired blueprint.
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+--------------------------------+
| Conferencing System |
"Alice" | +------------+|
+--------+ | | ||
| |CCP Request <blueprints> | +-----------+ | ||
| Client |-------------------------->|Conference | |Conference ||
| |<--------------------------|Control |~~~>|Blueprint(s)||
+--------+CCP Response<blueprintA, | |Server | | ||
... | +-----------+ +------------+|
blueprintZ, | |
confUserID> | |
"Alice" |
+--------+ | |
| |CCP Request <reserve, | +------------+|
| | blueprintAConfObjID,| +-----------+ | ||
| Client |-------------------------->|Conference | |Conference ||
| | confUserID> | |Control |~~~>|BlueprintA ||
| |<--------------------------|Server | | ||
| |CCP Response | | | +------------+|
+--------+ <reservationConfObjID, | | | \|/ |
confID> | | | /|\ |
| | | V |
| | | +------------+|
| | |~~~>|Conference ||
| | | |Reservation ||
| +-----------+ +------------+|
"Alice" | | |
+--------+ | | |
| |CCP Request <add, | V |
| |reservationConfObjID, | +-----------+ +------------+|
| Client |-------------------------->|Conference | |Active ||
| | confID,confUserID> | |Control |~~~>|Conference ||
| |<--------------------------|Server | | ||
| |CCP Response | | | +------------+|
+--------+ <activeConfObjID, | | | |
confID> | +-----------+ |
+--------------------------------+
Figure 8: Client Creation of Conference using Blueprints
Upon receipt of the Conference Control Protocol request for
blueprints, the conferencing system would first authenticate "Alice"
(and allocate a conference user identifier, if necessary) and then
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ensure that "Alice" has the appropriate authority based on system
policies to receive any blueprints supported by that system. Any
blueprints that "Alice" is authorized to use are returned in a
response, along with the conference user ID.
Upon receipt of the Conference Control Protocol response containing
the blueprints, "Alice" determines which blueprint to use for the
conference to be created. "Alice" creates a conference object based
on the blueprint (i.e., clones) and modifies applicable fields, such
as membership list and start time. "Alice" then sends a request to
the conferencing system to create a conference reservation based upon
the updated blueprint.
Upon receipt of the Conference Control Protocol request to "reserve"
a conference based upon the blueprint in the request, the
conferencing system ensures that the blueprint received is a valid
blueprint (i.e. the values of the various field are within range).
The conferencing system determines the appropriate read/write access
of any users to be added to a conference based on this blueprint
(using membership, roles, etc.). The conferencing system uses the
received blueprint to clone a conference reservation. The
conferencing system also reserves or allocates a conference ID to be
used for any subsequent protocol requests from any of the members of
the conference. The conferencing system maintains the mapping
between this conference ID and the conference object ID associated
with the reservation through the conference instance.
Upon receipt of the conference control protocol response to reserve
the conference, "Alice" can now create an active conference using
that reservation or create additional reservations based upon the
existing reservations. In this example, "Alice" has reserved a
meetme conference bridge. Thus, "Alice" provides the conference
information, including the necessary conference ID, to desired
participants. When the first participant, including "Alice",
requests to be added to the conference, an active conference and
focus are created. The focus is associated with the conference ID
received in the request. Any participants that have the authority to
manipulate the conference would receive the conference object
identifier of the active conference object in the response.
8.2. Participant Manipulations
There are different ways to affect a participant state in a
conference. A participant can join and leave the conference using
call signaling means only, such as SIP. This kind of operation is
called "1st party signaling" and does not affect the state of other
participants in the conference.
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Limited operations for controlling other conference participants (a
so called "3rd party control") through the Focus, using call
signaling only, may also be available for some signaling protocols.
For example, "Conferencing for SIP User Agents" [12] 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,
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 9 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.
+--------------------------------+
| Conferencing System |
"Alice" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | | Active ||
| | Conference Object ID, | |Control |~~~>|Conference ||
+--------+ Add, "Bob" > | |Server | | ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Carol" | ' ' '|
+--------+ NOTIFY <"Bob"="added"> |+------------+ ' ' '|
| |<-------------------------|Notification|<~~~| ||
| Client |. . ||Service | +-------+ ||
+--------+--+ . || | |"Bob" | ||
| |<----------------------| | +-------+----+|
| Client |NOTIFY <"Bob"="added">|+------------+ |
+--------+ +--------------------------------+
"Bob"
Figure 9: 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
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conference object ID, the conferencing system ensures that "Alice"
has the appropriate authority based on the policies associated with
that specific conference object to perform the operation. The
conferencing system must also determine whether "Bob" is already a
user of this conferencing system or whether he is a new user.
If "Bob" is a new user for this conferencing system, a Conference
User Identifier is created for Bob. Based upon the addressing
information provided for "Bob" by "Alice", the call signaling to add
"Bob" to the conference is instigated through the Focus.
Once the call signaling 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.
8.3. 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
operation is called "1st party signaling" 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 10 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.
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+--------------------------------+
| Conferencing System |
"Alice" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | |Active ||
| | Conference Object ID, | |Control |~~~>|Conference ||
+--------+ Mute, "Bob" > | |Server | | ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Carol" | ' ' '|
+--------+ NOTIFY <"Bob"=mute"> |+------------+ ' ' '|
| |<-------------------------|Notification|<~~~| ||
| Client |. . ||Service | +-------+ ||
+--------+--+ . || | |"Bob" | ||
| |<----------------------| | +-------+----+|
| Client | NOTIFY <"Bob"=mute">|+------------+ |
+--------+ +--------------------------------+
"Bob"
Figure 10: 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 object 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.
8.4. 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 and updating any
information specific to the sidebar. A sidebar conference object is
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implicitly linked to the parent conference object (i.e. it is not an
independent object) and is associated with the parent conference
object identifier as shown in Figure 11. A conferencing 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.).
+--------------+
| Conference |
| Object |
| Identifier |
+--------------+
|
|
|
+---------------------+---------------------+
| | |
+-------+-------+ +-------+-------+ +-------+-------+
| Sidebar | | Sidebar | | Sidebar |
| Conference | | Conference | | Conference |
| Object | | Object | | Object |
| Identifier | | Identifier | | Identifier |
+-------+-------+ +-------+-------+ +---------------+
Figure 11: Conference Object Mapping.
Figure 11 illustrates the relationship between a conference object
and associated Sidebar conference objects within a conferencing
system. Each Sidebar conference object has a unique conference
object Identifier as described in Section 5.2.1. 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 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).
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8.4.1. Internal Sidebar
Figure 12 provides an example of one client "Alice" involved in
active conference with "Bob" and "Carol". "Alice" wants to create a
sidebar to have a side discussion with "Bob" while still viewing the
video associated with the main conference. Alternatively, the audio
from the main conference could be maintained at a reduced volume.
"Alice" initiates the sidebar by sending a request to the
conferencing system to create a conference reservation based upon the
active conference object. "Alice" and "Bob" would remain on the
roster of the main conference, such that other participants could be
aware of their participation in the main conference, while an
internal-sidebar conference is occurring.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Conference ||
"Alice" | +-------+ ||
+--------+ | |"Alice"| ||
| |CCP Req <createSidebar, | +-------+ ||
| | activeConfObjID, | +-----------+ |"Bob" | ||
| Client |-------------------------->|Conference | +-------+ ||
| | confUserID> | |Control |~~~>|"Carol"| ||
| |<--------------------------|Server | +-------+----+|
| |CCP Response | | | | |
+--------+ <sidebarResvConfObjID, | | | | |
confID> | | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | | ||
| +-----------+ | ||
"Alice" | | Sidebar ||
+--------+ | | Reservation||
| |CCP Request <update, | +-----------+ | ||
| | sidebarResvConfObjID,| | | | ||
| Client |-------------------------->| |~~~>| ||
| | confID,confUserID, | | | +------------+|
| | video=parent, | | | | |
| | audio=sidebar> | |Conference | | |
| | | |Control | V |
| | | |Server | +---------+--+|
| |CCP Response | | | |policies | ||
| | <activeSideConfObjID,| | | +---------+ ||
| |<--------------------------| | |Active ||
+--------+ confID> | | | |Sidebar ||
| | | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Bob" | | | ||
+--------+ NOTIFY <"Bob"=added> |+------------+ +-------+ ||
| |<-------------------------|Notification|<~~~| | ||
| Client | ||Service | |"Bob" | ||
+--------+ || | +-------+----+|
|+------------+ |
+--------------------------------+
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Figure 12: Client Creation of a Sidebar Conference
Upon receipt of the Conference Control Protocol request to "reserve"
a new sidebar conference, based upon the active conference received
in the request, the conferencing system uses the received active
conference to clone a conference reservation for the sidebar. As
discussed previously, the sidebar reservation is NOT independent of
the active conference (i.e., parent). The conferencing system also
reserves or allocates a conference ID to be used for any subsequent
protocol requests from any of the members of the conference. The
conferencing system maintains the mapping between this conference ID
and the conference object ID associated with the sidebar reservation
through the conference instance.
Upon receipt of the conference control protocol response to reserve
the conference, "Alice" can now create an active conference using
that reservation or create additional reservations based upon the
existing reservations. In this example, "Alice" wants only "Bob" to
be involved in the sidebar, thus she manipulates the membership.
"Alice" also only wants the video from the original conference and
wants the audio to be restricted to the participants in the sidebar.
Alternatively, "Alice" could manipulate the media values to recieve
the audio from the main conference at a reduced volume. "Alice"
sends a conference control protocol request to update the information
in the reservation and to create an active conference.
Upon receipt of the conference control protocol request to update the
reservation and to create an active conference for the sidebar, as
identified by the conference object ID, the conferencing system
ensures that "Alice" has the appropriate authority based on the
policies associated with that specific conference object to perform
the operation. The conferencing system must also validate the
updated information in the reservation, ensuring that a member like
"Bob" is already a user of this conferencing system.
Depending upon the policies, the initiator of the request (i.e.,
"Alice") and the participants in the sidebar (i.e., "Bob") may be
notified of his addition to the sidebar via the conference
notification service.
8.4.2. External Sidebar
Figure 13 provides an example of one client "Alice" involved in an
active conference with "Bob", "Carol", "David" and "Ethel". "Alice"
gets an important text message via a whisper from "Bob" that a
critical customer needs to talk to "Alice", "Bob" and "Ethel".
"Alice" creates a sidebar to have a side discussion with the customer
"Fred" including the participants in the current conference with the
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exception of "Carol" and "David", who remain in the active
conference. "Alice" initiates the sidebar by sending a request to
the conferencing system to create a conference reservation based upon
the active conference object. "Alice", "Bob" and "Ethel" would
remain on the roster of the main conference in a hold state. Whether
or not the hold state of these participants is visible to other
participants depends upon the individual and local policy.
+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Conference ||
"Alice" | +-------+ ||
+--------+ | |"Alice"| ||
| |CCP Req <createSidebar, | +-------+ ||
| | activeConfObjID, | +-----------+ |"Bob" | ||
| Client |-------------------------->|Conference | +-------+ ||
| | confUserID> | |Control |~~~>|"Carol"| ||
| |<--------------------------|Server | +-------+ ||
| |CCP Response | | | |"David"| ||
+--------+ <sidebarResvConfObjID, | | | +-------+ ||
confID> | | | |"Ethel"| ||
| | | +-------+----+|
| | | | |
| | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| +-----------+ | ||
"Alice" | | Sidebar ||
+--------+ | | Reservation||
| |CCP Request <update, | +-----------+ | ||
| | sidebarResvConfObjID,| | | | ||
| Client |-------------------------->| |~~~>| ||
| | confID,confUserID, | | | +------------+|
| | video=sidebar, | | | | |
| | audio=sidebar> | |Conference | | |
| | | |Control | V |
| | | |Server | +---------+--+|
| |CCP Response | | | |policies | ||
| | <activeSideConfObjID,| | | +---------+ ||
| |<--------------------------| | |Active ||
+--------+ confID> | | | |Sidebar ||
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| | | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Bob" | +-------+ ||
+--------+ NOTIFY <"Bob"=added, |+------------+ |"Bob" | ||
| Client |<-------------------------|Notification|<~~~+-------+ ||
+--------+ "Ethel"=added, ||Service | |"Ethel"| ||
"Fred"=added,> || | +-------+ ||
"Ethel" +---| | |"Fred" | ||
+--------+ NOTIFY <"Bob"=added,| |+------------+ +-------+----+|
| Client | <--------------------+ +--------------------------------+
+--------+ "Ethel"=added,"Fred"=added,>
Figure 13: Client Creation of an External Sidebar
Upon receipt of the Conference Control Protocol request to "reserve"
a new sidebar conference, based upon the active conference received
in the request, the conferencing system uses the received active
conference to clone a conference reservation for the sidebar. As
discussed previously, the sidebar reservation is NOT independent of
the active conference (i.e., parent). The conferencing system also
reserves or allocates a conference ID to be used for any subsequent
protocol requests from any of the members of the conference. The
conferencing system maintains the mapping between this conference ID
and the conference object ID associated with the sidebar reservation
through the conference instance.
Upon receipt of the conference control protocol response to reserve
the conference, "Alice" can now create an active conference using
that reservation or create additional reservations based upon the
existing reservations. In this example, "Alice" wants only "Bob" and
"Ethel", along with the new participant "Fred" to be involved in the
sidebar, thus she manipulates the membership. "Alice" sets the media
such that the participants in the sidebar don't receive any media
from the main conference. "Alice" sends a conference control
protocol request to update the information in the reservation and to
create an active conference.
Upon receipt of the conference control protocol request to update the
reservation and to create an active conference for the sidebar, as
identified by the conference object ID, the conferencing system
ensures that "Alice" has the appropriate authority based on the
policies associated with that specific conference object to perform
the operation. The conferencing system must also validate the
updated information in the reservation, ensuring whether members like
"Fred" are already a user of this conferencing system or whether he
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is a new user. Since "Fred" is a new user for this conferencing
system, a conference user identifier is created for "Fred". Based
upon the addressing information provided for "Fred" by "Alice", the
call signaling to add "Fred" to the conference is instigated through
the Focus.
Depending upon the policies, the initiator of the request (i.e.,
"Alice") and the participants in the sidebar (i.e., "Bob" and
"Ethel") may be notified of his addition to the sidebar via the
conference notification service.
8.5. Floor control using sidebars
Floor control with sidebars can be used to realize conferencing
scenario such as an analyst briefing. In this scenario, the
conference call has a panel of speakers who are allowed to talk in
the main conference. The other participants are the analysts, who
are not allowed to speak unless they have the floor. To request
access to the floor, they have to join a new sidebar with the
moderator and ask their question. The moderator can also whisper to
each analyst what their status/position in the floor control queue,
similar to the example in Figure 15
Figure 14 provides an example of the configuration involved for this
type of conference. As in the previous sidebar examples, there is
the main conference along with a sidebar. "Alice" and "Bob" are the
main participants in the conference, with "A1", "A2" and "A3"
representing the analysts. The sidebar remains active throughout the
conference, with the moderator, "Carol", serving as the chair. As
discussed previously, the sidebar conference is NOT independent of
the active conference (i.e., parent). The analysts are provided the
conference object ID associated with the active sidebar when they
join the main conference. The conferencing system also allocates a
conference ID to be used for any subsequent manipulations of the
sidebar conference. The conferencing system maintains the mapping
between this conference ID and the conference object ID associated
with the active sidebar conference through the conference instance.
The analysts are permanently muted while in the main conference. The
analysts are moved to the sidebar when they wish to speak. Only one
analyst is given the floor at a given time. All participants in the
main conference receive audio from the sidebar conference, as well as
audio provided by the panelists in the main conference.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Conference ||
| +-------+ ||
| |"Alice"| ||
| +-------+ ||
| +-----------+ |"Bob" | ||
| |Conference | +-------+ ||
| |Control |~~~>|"A1" | ||
| |Server | +-------+ ||
| | | |"A2" | ||
| | | +-------+ ||
| | | |"A3" | ||
| | | +-------+----+|
| | | | |
| | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | |Active ||
| +-----------+ |Sidebar ||
"A1" | |Conference ||
+--------+ Floor Request <"A1", |+------------+ +-------+ ||
| |------------------------->|Floor Ctrl | |"Carol"| ||
|Client | activeSideConfObjID,||Server |~~~>| | ||
+--------+ confID > || | +-------+----+|
|+------------+ | |
| V |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Sidebar ||
"A1" | |Conference ||
+--------+ Floor Granted <"A1", |+------------+ +-------+ ||
| |<-------------------------|Floor Ctrl |<~~~|"Carol"| ||
| Client | activeSideConfObjID,||Server | +-------+ ||
+--------+ confID > || | |"A1" | ||
|+------------+ +-------+----+|
+--------------------------------+
Figure 14: Floor Control with sidebars
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When "A1" wishes to ask a question, he sends a Floor Request message
to the floor control server. Upon receipt of the request, the floor
control server notifies the moderator, "Carol" of the active sidebar
conference, whose serving as the floor chair. Note, that this
signaling flow is not shown in the diagram. Since no other analysts
have yet requested the floor, "Carol" indicates to the floor control
server that "A1" may be granted the floor.
8.6. Whispering or Private Messages
The case of private messages can be handled as a sidebar with just
two participants, similar to the example in section Section 8.4.1,
but rather than using audio within the sidebar, "Alice" could add an
additional text based media stream to the sidebar. The other
context, referred to as whisper, in this document refers to
situations involving one time media targetted to specific user(s).
An example of a whisper would be an announcement injected only to the
conference chair or to a new participant joining a conference.
Figure 15 provides an example of one user "Alice" whose chairing a
fixed length conference with "Bob" and "Carol". The configuration is
such that only the chair is providing a warning when there is only 10
minutes left in the conference. At that time, "Alice" is moved into
a sidebar created by the conferencing system and only "Alice"
receives the announcement.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Conference ||
| +-------+ ||
| |"Alice"| ||
| +-------+ ||
| +-----------+ |"Bob" | ||
| |Conference | +-------+ ||
| |Control |~~~>|"Carol"| ||
| |Server | +-------+----+|
| | | | |
| | | | |
| | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | | ||
| +-----------+ |Sidebar ||
"Alice" | |Conference ||
+--------+ NOTIFY <"Alice"=added, |+------------+ +-------+ ||
| |<-------------------------|Notification| | | ||
| Client | activeSideConfObjID,||Service |<~~~|"Alice"| ||
+--------+ confID > || | +-------+----+|
|+------------+ |
~~~Announcement provided to "Alice"~~~
| +-----------+ |
| |Conference | |
| |Control | |
| |Server | |
| | | |
| | | \---------+--/|
| | | |\ /||
| | |~~~>+ \ / ||
| | | | \ / ||
| +-----------+ |Sid\bar / ||
"Alice" | |Conf\re/ce ||
+--------+ NOTIFY <"Alice"=removed,|+------------+ +-----\/+ ||
| |<-------------------------|Notification|<~~~| /\| ||
| Client | activeSideConfObjID,||Service | |"Ali/ce\ ||
+--------+ confID > || | +---/---+\---+|
|+------------+ / \ |
+--------------------------------+
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Figure 15: Whisper
When the conferencing system determines that there is only 10 minutes
left in the conference which "Alice" is chairing, rather than
creating a reservation as was done for the sidebar in Section 8.4.1,
the conferencing system directly creates an active sidebar
conference, based on the active conference associated with "Alice".
As discussed previously, the sidebar conference is NOT independent of
the active conference (i.e., parent). The conferencing system also
allocates a conference ID to be used for any subsequent manipulations
of the sidebar conference. The conferencing system maintains the
mapping between this conference ID and the conference object ID
associated with the active sidebar conference through the conference
instance.
Immediately upon creation of the active sidebar conference, the
announcement media is provided to "Alice". Depending upon the
policies, Alice may be notified of her addition to the sidebar via
the conference notification service. "Alice" continues to receive
the media from the main conference.
Upon completion of the announcement, "Alice" is removed from the
siebar and the sidebar conference is deleted. Depending upon the
policies, "Alice" may be notified of her removal from the sidebar via
the conference notification service.
8.7. Conference Announcements and Recordings
Each participant can require a different type of announcement and/or
recording service from the system. For example, "Alice", the
conference chair, could be listening to a roll call while "Bob" may
be using a telephony user interface to create a sidebar. Some
announcements would apply to all the participants such as "This
conference will end in 10 minutes". Recording is often required to
capture the names of participants as they join a conference,
typically after the participant has entered an access code as
discussed in Section 8.8. These recorded names are then announced to
all the participants as the new participant is added to the active
conference.
An example of a conferencing recording and announcement , along with
collecting the DTMF, within the context of this framework, is shown
in Figure 16.
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+--------------------------------+
| Conferencing System |
"Alice" | +-----------+ |
+--------+ | |Conference | |
| |CCP Request < | |Control | |
| Client |--------------------------->| |Server | |
| |Bob's Conference ID, | | | |
+--------+ Join > | | | |
| | | |
| ~ ~ |
~~~Announcement provided to "Alice"~~~
~~~ Digits collected from "Alice"~~~
| ~ ~ +---------+--+|
| | |~~~>|policies | ||
| | | +---------+ ||
| | | |Active ||
| | | |Conference ||
| | | +-------+ ||
| | | |"Bob" | ||
| | | +-------+ ||
| | | |"Carol"| ||
| | | +-------+----+|
| ~ ~ |
~~~Announcement provided to "Alice"~~~
~~~ Alice records her name ~~~
| ~ ~ +---------+--+|
| | | |policies | ||
| | | +---------+ ||
| | |~~~>|Active ||
| +-----------+ |Conference ||
| +-------+ ||
| |"Bob" | ||
"Bob " | +-------+ ||
+--------+ NOTIFY <"Alice"=added, |+------------+ |"Carol"| ||
| |<-------------------------|Notification| +-------+ ||
| Client | activeSideConfObjID,||Service |<~~~|"Alice"| ||
+--------+ confID > || | +-------+----+|
|+------------+ |
~~~Announcement provided to All Parties~~~
| |
+--------------------------------+
Figure 16: Recording and Announcements
Upon receipt of the Conference Control Protocol request from "Alice"
to join "Bob's" conference, the conferencing system maps the
identifier received in the request to the conference object
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representing "Bob's" active conference. The conferencing system
determines that a password is required for this specific conference,
thus an announcement asking "Alice" to enter the password is provided
to "Alice". Once "Alice" enters the password, it is validated
against the policies associated with "Bob's" active conference. The
conferencing system then connects to a server which prompts and
records "Alice's" name. The conferencing system must also determine
whether "Alice" is already a user of this conferencing system or
whether she is a new user.
If "Alice" is a new user for this conferencing system, a conference
user identifier is created for "Alice". Based upon the addressing
information provided by "Alice", the call signaling to add "Alice" to
the conference is instigated through the Focus.
Once the call signaling indicates that "Alice" has been successfully
added to the specific conference, per updates to the state, and
depending upon the policies, other participants (e.g., "Bob") are
notified of the addition of "Alice" to the conference via the
conference notification service and an announcement is provided to
all the participants indicating that "Alice" has joined the
conference.
8.8. Monitoring for DTMF
The conferencing system also needs the capability to monitor for DTMF
from each individual participant. This would typically be used to
enter the identifier and/or access code for joining a specific
conference.
An example of DTMF monitoring, within the context of the framework
elements, is shown in Figure 16.
8.9. Observing and Coaching
The capability to observe a conference allows a participant with the
appropriate authority to listen to the conference, typically without
being an active participant and often as a hidden participant. When
such a capability is available on a conferencing system, there is
often an announcement provided to each participant as they join the
conference indicating the call may be monitored. This capability is
useful in the context of conferences which might be experiencing
technical difficulties, thus allowing a technician to listen in to
evaluate the type of problem.
This capability could also apply to call center applications as it
provides a mechanism for a supervisor to observe how the agent is
handling a particular call with a customer. This scenario can be
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handled by a supervisor adding themselves to the existing active
conference, with a listen only audio media path. Whether the agent
is aware of when the supervisor joins the call should be
configurable.
Taking the supervisor capability one step further introduces a
scenario whereby the agent can hear the supervisor, as well as the
customer. The customer can still only hear the agent. This scenario
would involve the creation of a sidebar involving the agent and the
supervisor. Both the agent and supervisor receive the audio from the
main conference. When the agent speaks, it is heard by the customer
in the main conference. When the supervisor speaks, it is heard only
by the agent in the sidebar conference.
An example of observing and coaching is shown in figure Figure 17.
In this example, call center agent "Bob" is involved in a conference
with customer "Carol". Since "Bob" is a new agent and "Alice" sees
that he has been on the call with "Carol" for longer than normal, she
decides to observe the call and coach "Bob" as necessary.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active ||
| |Conference ||
"Alice" | | ||
+--------+ | | ||
| |CCP Req <createSidebar, | +-------+ ||
| | activeConfObjID, | +-----------+ |"Bob" | ||
| Client |-------------------------->|Conference | +-------+ ||
| | confUserID> | |Control |~~~>|"Carol"| ||
| |<--------------------------|Server | +-------+----+|
| |CCP Response | | | | |
+--------+ <sidebarResvConfObjID, | | | | |
confID> | | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | | ||
| +-----------+ | ||
"Alice" | | Sidebar ||
+--------+ | | Reservation||
| |CCP Request <update, | +-----------+ | ||
| | sidebarResvConfObjID,| | | | ||
| Client |-------------------------->| |~~~>| ||
| | confID,confUserID> | | | +------------+|
| | | | | | |
| | | |Conference | | |
| | | |Control | V |
| | | |Server | +---------+--+|
| |CCP Response | | | |policies | ||
| | <activeSideConfObjID,| | | +---------+ ||
| |<--------------------------| | |Active ||
+--------+ confID> | | | |Sidebar ||
| | | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Bob" | | | ||
+--------+ NOTIFY <"Bob"=added, |+------------+ +-------+ ||
| |<-------------------------|Notification|<~~~| | ||
| Client | "chair"="Alice" ||Service | |"Bob" | ||
+--------+ || | +-------+----+|
|+------------+ |
+--------------------------------+
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Figure 17: Supervisor Creating a Sidebar for Observing/Coaching
Upon receipt of the Conference Control Protocol request from "Alice"
to "reserve" a new sidebar conference, based upon the active
conference received in the request, the conferencing system uses the
received active conference to clone a conference reservation for the
sidebar. The conferencing system also reserves or allocates a
conference ID to be used for any subsequent protocol requests from
any of the members of the conference. The conferencing system
maintains the mapping between this conference ID and the conference
object ID associated with the sidebar reservation through the
conference instance.
Upon receipt of the conference control protocol response to reserve
the conference, "Alice" can now create an active conference using
that reservation or create additional reservations based upon the
existing reservations. In this example, "Alice" wants only "Bob" to
be involved in the sidebar, thus she manipulates the membership.
"Alice" also wants the audio to be received by herself and "Bob" from
the original conference, but wants any outgoing audio from herself to
be restricted to the participants in the sidebar, whereas "Bob's"
outgoing audio should go to the main conference, so that both "Alice"
and the customer "Carol" hear the same audio from "Bob". "Alice"
sends a conference control protocol request to update the information
in the reservation and to create an active conference.
Upon receipt of the conference control protocol request to update the
reservation and to create an active conference for the sidebar, as
identified by the conference object ID, the conferencing system
ensures that "Alice" has the appropriate authority based on the
policies associated with that specific conference object to perform
the operation. Based upon the addressing information provided for
"Bob" by "Alice", the call signaling to add "Bob" to the sidebar with
the appropriate media characteristics is instigated through the
Focus.
"Bob" is notified of his addition to the sidebar via the conference
notification service, thus he is aware that "Alice" the supervisor is
available for coaching him through this call.
9. Relationships between SIPPING and Centralized Conferencing
Frameworks
The SIPPING Conferencing Framework [8] 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
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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 [2] can be used as a signaling 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 [2], the SIP
Conferencing for User Agents [12], and the SIPPING Conference Package
[9] for basic SIP conferencing realization.
This centralized conferencing framework document defines a particular
centralized conferencing system and the logical entities implementing
it. It also defines a particular data model and refers to the set of
protocols (beyond call signaling means) being defined by the XCON WG
to be used among the logical entities for implementing advanced
conferencing features. The purpose of the XCON working group and
this framework is to achieve interoperability between the logical
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 [2], the
SIP Conferencing for User Agents [12], 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
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 specifications 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. Section 10.3 discusses an approach
for client authentication of a floor control server.
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There are also security issues associated with the authorization to
perform actions on the conferencing system to invoke specific
capabilities. Section 4.2 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, which is discussed in Section 10.2
10.1. Authorization
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 signaling
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 signaling. 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 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
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 it fairly hard to do an
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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.
10.2. Security and Privacy of Identity
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 select various options for
revealing their identity to other users. A user can be "hidden" such
that other users can not see they are participants 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 automated or machine participants of a conference (e.g., call
recording) and is also used in many call center situations.
10.3. Floor Control Server Authentication
Clients can authenticate a floor control server using the TLS
certificates. Requests submitted on a successfully created
connection between the client and floor control server 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 floor
control 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 floor control 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 [15], the 'nonce' attribute
can be inserted in the SIP response e.g., a=nonce:dhsa8hd0dwqj.
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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 and
general feedback, Cullen Jennings for providing input for the
"Security Considerations" section and Keith Lantz, Dave Morgan, Oscar
Novo, Roni Even, Umesh Chandra, Avshalom Houri, Sean Olson, Rohan
Mahy, Brian Rosen, Pierre Tane, Bob Braudes and Gregory Sperounes and
Gonzalo Camarillo for their reviews and constructive input.
13. Changes since last Version
NOTE TO THE RFC-Editor: Please remove this section prior to
publication as an RFC.
Changes from WG 07 to 08 (post-WGLC comments, reflecting IETF-68
discussions on policy):
1) added Intended Status as Informational.
2) Removed data model from Title and clarified reference to data
model in this document as "high level data model". Renamed section 5
from "Centralized Conferencing Data Model" to "Centralized
Conferencing Data".
3) Deleted Conventions section with reference to 2119.
4) Moved terminology to just after intro, before overview.
5) Changed "Common Conference Information" to "Conference
Information".
6) Removed references to policies as an integral part of data model:
updated text discussing policies in section 5 and section 5.2, with
section 7 text changed to be consistent with the updated text in
section 5 and 5.2.
7) Removal of references to individual conference-URI and Userid
documents, bringing some background back into the framework, since
those identifiers are defined in the data model.
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8) Miscellaneous editorial nits.
Changes from WG 06 to 07 (WGLC comments):
1) Section 4: Added definition for Conference User Identifier,
including concept of a single user having multiple identifiers.
2) Section 9: Clarified text to indicate that details of message
flows are illustrative and exact states, etc. will be defined by the
detailed data model, etc.
3) Section 9.4.1: Clarified that "Alice" and "Bob" remain in roster
of main conference while in sidebar.Clarified text that Bob must
already be a user of the conferencing system for internal sidebar
scenario.
4) Section 9.4.1/9.4.2: Clarified text in last paragraph to indicated
that notifications may also go to the initial requestor.
5) Section 9.5: Clarified text to explicitly state that sidebar
participants also receive the audio from the main conference.
6) Fixed Editorial nits including updating references to published
RFC numbers and miscellaneous typos.
Changes from WG 05 to 06:
1) Section 9.4.2: Added a statement that whether the hold state is
visible to other participants is subject to user and local policy.
2) Fixed Editorial nits including updating references to published
RFC numbers, adding references for userid and uri definitions,
removing unused references, fixing names in detailed scenarios
(section 9.4.2: "Frank" -> "Fred", section 9.5: "Alice" -> "Carol" as
moderator), aligning with data model (section 9.5: "allowed to join"
list -> "allowed-users-list") and miscellaneous typos.
Changes from WG 04 to 05:
1) Removed all references to "Conference Template":
Section 4:
- Updated "Common Conference Information" definition, merging details
from "Conference Template" definition, which was removed.
- In definition of "conference blueprint"
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- In definition of "conference object"
- Removed definition of "Registered conference document"
Section 5:
- 1st paragraph. Reworded.
- Figure2: added "boxes" for all the data listed in the Conference
Template type in the diagram.
- Paragraph following Figure 2. Reworded.
Section 5.1/5.2: Merged 5.2 into section 5.1 and reworded
appropriately.
Section 7.1: Second paragraph, 3rd sentence.
Section 7.3:
- Second paragraph, 2nd and 3rd sentences. Deleted. Remaining
sentence merged with 1st paragraph
- Third paragraph. Deleted.
Section 8.4, 1st paragraph. Removed Editor's note containing
reference to alternative proposal for floor control using templates.
Section 9.3, 1st paragraph after Figure 10.
2) Section 4:
- Sidebar. Clarified definition.
- Whisper. Added definition.
3) Section 5, last paragraph, added reference to
draft-ietf-xcon-common-data-model.
4) Section 8.3. Deleted Editor's note. Deleted subsections
containing details of separate protocol proposals.
5) Section 9.4. Sidebar. Added another example - an external
sidebar (i.e. one involving a participant not in the main conference
and with no media from the main conference).
6) New section 9.5. Floor control with sidebars.
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7) Section 9.5 (new 9.6) Whisper. Added more detail and an example
diagram.
8) Section 9.8. (new 9.9) Observing a Conference. Added more details
to example, including concept of coaching and added a corresponding
diagram.
9) Removed Appendix A and Appendix B and updated references to these.
The content will be in separate documents (references TBD).
10) Updated references. Changed drafts to RFCs as appropriate and
removed unused references.
Changes from WG 03 to 04:
- Editorial nits and clarifications.
- Section 4. Template: Removed reference to "user interface
abstractions".
- Section 5.2. Conference Template: deleted references to user
interface abstraction (1st paragraph, last phrase and 4th paragraph).
- Section 9.6. Conference Announcements and Recording: text
expanded. Moved discussion of DTMF to a new section.
- Added two new sections 9.7 (DTMF) and 9.8 (Observing a Conference),
with some initial text.
Changes from WG 02 to 03:
- Updated the definition of Blueprint (per DP 4/4.1 discussions)
- Added definition for Sidebar.
- Section 5.2 Added text indicating that adding new elements or
modifying elements requires the definition of a new template. (per
DP4.2 conclusion).
- Section 7.3. Added text reiterating that the blueprint comprises
both the common conference information and a template (per DP4/4.1
discussions.
- Section 7.3. Added text per resolution of DP 4.3 indicating that a
blueprint is common conference information + one template and that
multiple templates is FFS.
- Section 8.3 - Updated Conference Control Protocol section to
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include the protocols on the table for WG discussion as of 31 Dec
2005 deadline.
- Section 9.4 - Sidebars - added Ascii art to show FW interactions
- Section 9.5 - Whisper - Added some text, reflecting past WG
discussions. Basic definition and further details/example still
needed.
- Section 9.6 - Conf Anncs and Recordings - Added some basic text.
Further details/example still needed.
Changes from WG 01 to 02:
- Editorial nits -i.e. consistent terminology, capatilization, etc.
- Revamped abstract and introduction
- Global removal of XCON as a qualifier (we had previously done this
in a previous version with all the identifiers).
- Global change of "call control signalling" to "call signaling"
- Moved the terminology section after the Overview section:
- - Modified the definitions to be more concise and per some of
Henning's recommendations.
- - Added definitions for blueprint and conference reservation.
- Clarified the definition of policy and added more explicit text as
to how policy is accomplished via the data model and system
realization (section 4.3 and 6.1)
- Removed the Editor's note/text in section 4 about the options for
the schema; added a reference to a TBD schema document.
- Section 5:
- - clarified the identifiers. Kept the logical definition as
"identifiers", although most will be realized as URIs.
- - deleted the section on conference instance.
- - removed the term "umbrella" from sections conference User and
conference object identifier sections
- - moved alot of detail from Conference User Identifier and
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conference Object Identifier sections into appendices, and added
additional detail, that will become the basis for separate documents.
- In section 6:
- - added a bit of explanation as to the intent of the cloning tree
model - it's not implementation binding, but rather to illustrate the
data model and context for the protocol interactions.
- - removed the term copying altogether. Cloning is the model and
the idea is that the cloned object contains data indentical to the
parent when it was created (whether it gets "copied" or whatever from
the parent is an implementation issue).
- - introduce the blueprint concept in section 6.1 prior to its
implied usage in 6.2 and 6.3.
- - removed the usage of the term occurrence (which is just a child
reservation).
- Removed security related details from Floor Control section and
moved those to the security section. As a result removed most of the
editorial notes from the front of the Floor control section and
integrated the remaining ones inline into that section, where the
resolution should be documented.
- Section 8:
- - Added new example 8.1 - conference creation
- - Added a placeholder for a more detailed example to the sidebar
section to show a sidebar which has some media specifically
associated with the sidebar (i.e. audio), yet still use the main
conference for other media (visual presentation).
- Section 11: As a result of adding additional information to the
security section, divided this section into subsections for clarity.
Changes from WG 00 to 01::
- Section 2 (Conventions and Terminology). Slight modifications to
definitions of Call (control) signaling, Conference Identifier,
Conference Instance, Conference Object.
- Section 2 (Conventions and Terminology).Renaming of term
"Registered Template Definition" to "Registered Conference Document"
(per agreement at interim meeting).
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- 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
Identifier described in a subsection of the Conference Object
section. Added a diagram showing the relationship between Conference
Identifier/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
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
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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.
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.
14. Informative References
[1] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[2] 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.
[3] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[4] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
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[5] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications", STD 64,
RFC 3550, July 2003.
[6] Dawson, F. and Stenerson, D., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)", RFC 2445,
November 1998.
[7] Levin, O. and R. Even, "High-Level Requirements for Tightly
Coupled SIP Conferencing", RFC 4245, November 2005.
[8] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol (SIP)", RFC 4353, February 2006.
[9] Rosenberg, J., Schulzrinne, H., and O. Levin, "A Session
Initiation Protocol (SIP) Event Package for Conference State",
RFC 4575, August 2006.
[10] Koskelainen, P., Ott, J., Schulzrinne, H., and X. Wu,
"Requirements for Floor Control Protocols", RFC 4376,
February 2006.
[11] Even, R. and N. Ismail, "Conferencing Scenarios", RFC 4597,
August 2006.
[12] Johnston, A. and O. Levin, "Session Initiation Protocol (SIP)
Call Control - Conferencing for User Agents", BCP 119,
RFC 4579, August 2006.
[13] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor Control
Protocol (BFCP)", RFC 4582, November 2006.
[14] Levin, O. and G. Camarillo, "The Session Description Protocol
(SDP) Label Attribute", RFC 4574, August 2006.
[15] Camarillo, G., "Session Description Protocol (SDP) Format for
Binary Floor Control Protocol (BFCP) Streams", RFC 4583,
November 2006.
[16] Novo, O., "Conference Information Data Model for Centralized
Conferencing (XCON)", draft-ietf-xcon-common-data-model-05
(work in progress), April 2007.
[17] Campbell, B., "The Message Session Relay Protocol",
draft-ietf-simple-message-sessions-19 (work in progress),
February 2007.
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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
Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
Email: oritl@microsoft.com
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