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IETF RFC 5239
A Framework for Centralized Conferencing
Last modified on Friday, June 6th, 2008
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Network Working Group M. Barnes
Request for Comments: 5239 Nortel
Category: Standards Track C. Boulton
Avaya
O. Levin
Microsoft Corporation
June 2008
A Framework for Centralized Conferencing
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document defines the framework for Centralized Conferencing.
The framework allows participants using various call signaling
protocols, such as SIP, H.323, Jabber, Q.931 or ISDN User Part
(ISUP), to exchange media in a centralized unicast conference. The
Centralized Conferencing Framework defines logical entities and
naming conventions. 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.
Barnes, et al. Standards Track PAGE 1 
RFC 5239 Centralized Conferencing Framework June 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Centralized Conferencing Data . . . . . . . . . . . . . . . . 10
5.1. Conference Information . . . . . . . . . . . . . . . . . . 11
5.2. Conference policies . . . . . . . . . . . . . . . . . . . 12
6. Centralized Conferencing Constructs and Identifiers . . . . . 12
6.1. Conference Identifier . . . . . . . . . . . . . . . . . . 13
6.2. Conference Object . . . . . . . . . . . . . . . . . . . . 13
6.2.1. Conference Object Identifier . . . . . . . . . . . . . 15
6.3. Conference User Identifier . . . . . . . . . . . . . . . . 16
7. Conferencing System Realization . . . . . . . . . . . . . . . 17
7.1. Cloning Tree . . . . . . . . . . . . . . . . . . . . . . . 17
7.2. Ad Hoc Example . . . . . . . . . . . . . . . . . . . . . . 20
7.3. Advanced Example . . . . . . . . . . . . . . . . . . . . . 21
7.4. Scheduling a Conference . . . . . . . . . . . . . . . . . 23
8. Conferencing Mechanisms . . . . . . . . . . . . . . . . . . . 26
8.1. Call Signaling . . . . . . . . . . . . . . . . . . . . . . 26
8.2. Notifications . . . . . . . . . . . . . . . . . . . . . . 26
8.3. Conference Control Protocol . . . . . . . . . . . . . . . 26
8.4. Floor Control . . . . . . . . . . . . . . . . . . . . . . 26
9. Conferencing Scenario Realizations . . . . . . . . . . . . . . 28
9.1. Conference Creation . . . . . . . . . . . . . . . . . . . 28
9.2. Participant Manipulations . . . . . . . . . . . . . . . . 30
9.3. Media Manipulations . . . . . . . . . . . . . . . . . . . 32
9.4. Sidebar Manipulations . . . . . . . . . . . . . . . . . . 33
9.4.1. Internal Sidebar . . . . . . . . . . . . . . . . . . . 35
9.4.2. External Sidebar . . . . . . . . . . . . . . . . . . . 37
9.5. Floor Control Using Sidebars . . . . . . . . . . . . . . . 40
9.6. Whispering or Private Messages . . . . . . . . . . . . . . 42
9.7. Conference Announcements and Recordings . . . . . . . . . 44
9.8. Monitoring for DTMF . . . . . . . . . . . . . . . . . . . 46
9.9. Observing and Coaching . . . . . . . . . . . . . . . . . . 46
10. Relationships between SIP and Centralized Conferencing
Frameworks . . . . . . . . . . . . . . . . . . . . . . . . . . 49
11. Security Considerations . . . . . . . . . . . . . . . . . . . 50
11.1. User Authentication and Authorization . . . . . . . . . . 51
11.2. Security and Privacy of Identity . . . . . . . . . . . . . 53
11.3. Floor Control Server Authentication . . . . . . . . . . . 53
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 53
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 54
13.1. Normative References . . . . . . . . . . . . . . . . . . . 54
13.2. Informative References . . . . . . . . . . . . . . . . . . 54
Barnes, et al. Standards Track PAGE 2
RFC 5239 Centralized Conferencing Framework June 2008
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, Q.931 or ISUP, 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. 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 SIP Conferencing Framework
[RFC 4353]. Section 10 of this document discusses the relationship
between the Centralized Conferencing Framework and the SIP
Conferencing Framework, in the context of the Centralized
Conferencing model presented in this document.
2. Conventions
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, [RFC 2119] and indicate requirement levels for
compliant implementations.
3. Terminology
This Centralized Conferencing Framework document generalizes, when
appropriate, the SIP Conferencing Framework [RFC 4353] 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.
Barnes, et al. Standards Track PAGE 3
RFC 5239 Centralized Conferencing Framework June 2008
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 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 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.
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.
Barnes, et al. Standards Track PAGE 4
RFC 5239 Centralized Conferencing Framework June 2008
Conference object identifier (ID): A conference object identifier is
a URI that 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.
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 signaling
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.
Barnes, et al. Standards Track PAGE 5
RFC 5239 Centralized Conferencing Framework June 2008
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/
RTP Control Protocol (RTCP) (defined in [RFC 3550]) or Message
Session Relay Protocol (defined in [RFC 4975]).
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.
4. 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 SIP Conferencing Framework
[RFC 4353] together with the SIP Call Control Conferencing for User
Agents [RFC 4579] documents address these types of scenarios.
Barnes, et al. Standards Track PAGE 6
RFC 5239 Centralized Conferencing Framework June 2008
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
[RFC 4245]. These requirements are applicable for conferencing
systems using various call signaling protocols, including SIP.
Additional conferencing requirements are provided in [RFC 4376] and
[RFC 4597].
The centralized 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., Binary
Floor Control Protocol (BFCP)) provides the interface between a floor
control client and the floor control server. A call signaling
protocol (e.g., SIP, H.323, Jabber, Q.931, ISUP, etc.) provides the
interface between a call signaling client and a focus. A
notification protocol (e.g. SIP Notify [RFC 3265]) provides the
interface between the conferencing client and the notification
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
the list of participants with their media streams, between the
various other components.
Barnes, et al. Standards Track PAGE 7
RFC 5239 Centralized Conferencing Framework June 2008
....................................................................
. 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
Barnes, et al. Standards Track PAGE 8
RFC 5239 Centralized Conferencing Framework June 2008
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 5 of this document provides more details on the conference
object. Section 6 defines the constructs and identifiers that MUST
be implemented to manage the conference objects, instances, and users
associated with a conferencing system. Section 7 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 8 describes the fundamental conferencing
mechanisms and provides a high level overview of the protocols.
Section 9 then provides realizations of various conferencing
scenarios, detailing the manipulation of the conference objects using
the defined protocols. Section 10 of this document summarizes the
relationship between this Centralized Conferencing Framework and the
SIP Conferencing Framework.
Barnes, et al. Standards Track PAGE 9
RFC 5239 Centralized Conferencing Framework June 2008
5. 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.
+------------------------------------------------------+
| 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 7 describes the usage
semantics of the conference objects. The exact XML schema of the
Barnes, et al. Standards Track PAGE 10
RFC 5239 Centralized Conferencing Framework June 2008
conference object, including the organization of the conference
information is detailed in a separate document [XCON-COMMON].
Along with the basic data model, as defined in [XCON-COMMON], the
realization of this framework requires a policy infrastructure. The
policies required by this framework to manage and control access to
the data include local, system level boundaries associated with
specific data elements, such as the membership, and the ranges and
limitations of other data elements. Additional policy considerations
for a system realization based on this data model are discussed in
Section 5.2.
5.1. 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 the SIP conference event
package [RFC 4575]. 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 defined in the
data model [XCON-COMMON], contains additional data beyond that
defined in the SIP conference event package [RFC 4575]. The
information defined in the data model [XCON-COMMON] 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 the state of other participants in the
conference.
New centralized conferencing specifications can extend the basic
conference-type, as defined in the data model [XCON-COMMON], and
introduce additional data elements to be used within the conference
information type.
Barnes, et al. Standards Track PAGE 11
RFC 5239 Centralized Conferencing Framework June 2008
5.2. 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 to 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
framework document, the policies represented by the set of rights are
reflected in the system realization (Section 7).
The permissions and limits require explicit policy mechanisms and are
outside the scope of the data model [XCON-COMMON] and this framework
document. However, there are some important policy considerations
for a conferencing system. A conferencing system associates specific
policies in the form of permissions and limitations with each user in
a conferencing system. The permissions may vary depending upon the
role associated with a specific conference user identifier. A
conferencing system should provide a default user role that only
allows participation in a conference through the default signaling
means.
The conference object identifier provides access to the data
associated with a specific conference. It is important to ensure
that elements in the data have individual policy controls to provide
flexibility in defining the various roles and specific data elements
that may be manipulated by users with specific roles.
In addition, the conference notification interface allows specific
data elements to be sent to users that register for such
notifications. It is important that the appropriate access control
is provided so that only users that are authorized to view specific
data elements receive the data in the notifications.
6. Centralized Conferencing Constructs and Identifiers
This section provides details of the identifiers associated with the
centralized conferencing framework constructs and the identifiers
REQUIRED 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.
Barnes, et al. Standards Track PAGE 12
RFC 5239 Centralized Conferencing Framework June 2008
6.1. 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
[RFC 4579]. The conference identifier can also be obtained using the
conference control protocol or other, including proprietary, out-of-
band mechanisms. To realize the centralized conferencing framework
in this document, a conferencing system is REQUIRED to support SIP as
the default call signaling protocol. Other call signaling protocols
(e.g., ISUP) are OPTIONAL.
6.2. 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 (see
Section 8.3). A conferencing system MUST provide a default blueprint
representing the basic capabilities provided by that specific
conferencing system.
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, one
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
object.
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RFC 5239 Centralized Conferencing Framework June 2008
....................................................................
. Conference Instance .
. .
. .
. +---------------------------------------------------+ .
. | Conference Object Identifier | .
. | | .
. | | .
. +---------------------------------------------------+ .
. ^ ^ .
. | | .
. v | .
. ................................................... | .
. . Focus . | .
. . . | .
. . +----------------------------------+ . | .
. . |Conference Identifier (Protocol Y)| . | .
. . +------------------------------------+ | . | .
. . | Conference Identifier (ISUP) | | . | .
. . +--------------------------------------+ |-+ . | .
. . | Conference Identifier (SIP) | |^ . | .
. . | |-+| . | .
. . | |^ | . | .
. . +--------------------------------------+| | . | .
. ............^...............................|.|.... | .
. | | | | .
................|...............................|.|......|..........
| | | |
|SIP | | |Conference
| ISUP | |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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RFC 5239 Centralized Conferencing Framework June 2008
6.2.1. Conference Object Identifier
In order to make each conference object externally accessible, the
conferencing system MUST allocate a unique URI per distinct
conference object in the system. The conference object identifier is
defined in [XCON-COMMON]. A conferencing system allocates 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
through the conference control protocol mechanism, the data model and
conference package, or out-of-band mechanisms such as email.
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. 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 identifier 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 mechanisms such as
email 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 mapping of the conference object identifier
can be viewed to contain sensitive information in many conferencing
systems. The conferencing system must ensure that the data is
protected, that only authorized users can manipulate that information
via the conferencing control protocol, and that only the appropriate
users receive the information through the notification protocol. In
general, this information would not be expected to be distributed to
the average conference participant.
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RFC 5239 Centralized Conferencing Framework June 2008
6.3. Conference User Identifier
Each user within a conferencing system MUST be allocated a unique
conference user identifier. The conference user identifier is
defined in [XCON-COMMON]. The conference 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
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 identifier 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 identifier 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 mapping
of the conference user identifier to signaling specific user
identifiers requires that methods for protecting and securing a
user's identity are considered. Section 11.1 addresses "User
Authentication and Authorization" and Section 11.2 addresses the
"Security and Privacy of User Identity". In addition, the
conferencing system MUST ensure the appropriate access control around
any internal data structure that maintains this persistent data.
This information would typically only be available to a conferencing
system administrator.
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7. 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
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 7.1.
Ad hoc and advanced conferencing examples are provided in Section 7.2
and Section 7.3, 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 7.4
As discussed in Section 5.2, 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.
7.1. 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.
Barnes, et al. Standards Track PAGE 17
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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 or not the link
between the parent and child needs to be maintained in the system.
If no link between the parent and child exists, the objects become
independent and the child is not impacted by any operations on the
parent 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 6.2.1. 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 cannot be changed by
directly accessing the child object, nor 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.
Barnes, et al. Standards Track PAGE 18
RFC 5239 Centralized Conferencing Framework June 2008
+---+-----------------------+
| 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 |
| l | | | l | |
| i | C O N F E R E N C E | | i | C O N F E R E N C E |
| c | | | c | |
| i | O B J E C T | | i | O B J E C T |
| e | | | 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.
Barnes, et al. Standards Track PAGE 19
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7.2. 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 6.1. 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
Session Description Protocol (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, by performing operations 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-+-----------------------+
Figure 5: Conference Ad-hoc Creation and Lifetime
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7.3. 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.
Barnes, et al. Standards Track PAGE 21
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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 ad hoc example, the active
conference is independent from the parent, and changes to the
conference reservation will not impact the active conference. Any
Barnes, et al. Standards Track PAGE 22
RFC 5239 Centralized Conferencing Framework June 2008
desired changes must be targeted towards the active conference. An
example of this interaction is shown in Section 9.1.
7.4. 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 [RFC 2445] in union
with the concepts introduced in Section 5 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 that contains scheduling information about
the conference (e.g., 'start' time, 'end' time).
Barnes, et al. Standards Track PAGE 23
RFC 5239 Centralized Conferencing Framework June 2008
+--------------+ +-------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 6.2.1
and defined in [XCON-COMMON]. 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.
Barnes, et al. Standards Track PAGE 24
RFC 5239 Centralized Conferencing Framework June 2008
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
that 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, can
Barnes, et al. Standards Track PAGE 25
RFC 5239 Centralized Conferencing Framework June 2008
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.
8. Conferencing Mechanisms
8.1. 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.
8.2. 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 [RFC 3265] with the specifics to support conferencing
defined in [RFC 4575].
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.
8.3. 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.
8.4. 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
conference users to that floor. Floor control is not a mandatory
Barnes, et al. Standards Track PAGE 26
RFC 5239 Centralized Conferencing Framework June 2008
mechanism for a conferencing system implementation, but it 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 (BFCP)" specification
[RFC 4582].
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 [RFC 4566] offer/answer [RFC 3264] exchange
on the signaling interface with the focus. Section 11.3 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 [RFC 4582] 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 identified by the conference object ID per
Section 6.2.1. This conference object ID must be included in all
floor control messages. When the SDP model is used as described in
[RFC 4583], 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 6.3. 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 [RFC 4583].
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 [RFC 4583], 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 [RFC 4574].
Barnes, et al. Standards Track PAGE 27
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9. Conferencing Scenario Realizations
This section addresses how advanced conferencing scenarios, many of
which have been described in [RFC 4597], 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.
9.1. Conference Creation
There are different ways to create a conference. A participant can
create a conference using call signaling means only, such as SIP
detailed in [RFC 4579]. For a conferencing client to have more
flexibility in defining the characteristics 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.
Barnes, et al. Standards Track PAGE 28
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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
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.
Barnes, et al. Standards Track PAGE 29
RFC 5239 Centralized Conferencing Framework June 2008
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.
9.2. 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.
Barnes, et al. Standards Track PAGE 30
RFC 5239 Centralized Conferencing Framework June 2008
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" [RFC 4579] 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, the
state of other participants, and the state of various resources (such
as media mixers) that 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
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.
Barnes, et al. Standards Track PAGE 31
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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.
9.3. 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.
Barnes, et al. Standards Track PAGE 32
RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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.
9.4. 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 7.1.
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
Barnes, et al. Standards Track PAGE 33
RFC 5239 Centralized Conferencing Framework June 2008
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
cannot 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 6.2.1. 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 7.1. 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 7.1).
Barnes, et al. Standards Track PAGE 34
RFC 5239 Centralized Conferencing Framework June 2008
9.4.1. 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.
Barnes, et al. Standards Track PAGE 35
RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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" | ||
+--------+ || | +-------+----+|
|+------------+ |
+--------------------------------+
Figure 12: Client Creation of a Sidebar Conference
Barnes, et al. Standards Track PAGE 36
RFC 5239 Centralized Conferencing Framework June 2008
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 receive
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.
9.4.2. 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
Barnes, et al. Standards Track PAGE 37
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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 ||
| | | |Conference ||
| +-----------+ +-------+ ||
Barnes, et al. Standards Track PAGE 38
RFC 5239 Centralized Conferencing Framework June 2008
| |"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
Barnes, et al. Standards Track PAGE 39
RFC 5239 Centralized Conferencing Framework June 2008
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.
9.5. Floor Control Using Sidebars
Floor control with sidebars can be used to realize conferencing
scenarios 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.
Barnes, et al. Standards Track PAGE 40
RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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
Barnes, et al. Standards Track PAGE 41
RFC 5239 Centralized Conferencing Framework June 2008
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, who's 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.
9.6. 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 9.4.1, 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 targeted 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" who's chairing a
fixed length conference with "Bob" and "Carol". The configuration is
such that only the chair is providing a warning when there are 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.
Barnes, et al. Standards Track PAGE 42
RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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 > || | +---/---+\---+|
|+------------+ / \ |
+--------------------------------+
Figure 15: Whisper
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RFC 5239 Centralized Conferencing Framework June 2008
When the conferencing system determines that there are only 10
minutes left in the conference which "Alice" is chairing, rather than
creating a reservation as was done for the sidebar in Section 9.4.1,
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
sidebar, 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.
9.7. 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 9.8. 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 dual tone multi-frequency (DTMF), within the context
of this framework, is shown in Figure 16.
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RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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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RFC 5239 Centralized Conferencing Framework June 2008
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 that
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.
9.8. 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.
9.9. 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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RFC 5239 Centralized Conferencing Framework June 2008
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 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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RFC 5239 Centralized Conferencing Framework June 2008
+--------------------------------+
| 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" | ||
+--------+ || | +-------+----+|
|+------------+ |
+--------------------------------+
Figure 17: Supervisor Creating a Sidebar for Observing/Coaching
Barnes, et al. Standards Track PAGE 48
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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.
10. Relationships between SIP and Centralized Conferencing Frameworks
The SIP Conferencing Framework [RFC 4353] provides an overview of a
wide range of centralized conferencing solutions known today in the
conferencing industry. The document introduces a terminology and
logical entities in order to systemize the overview and to show the
common core of many of these systems. The logical entities and the
listed scenarios in the SIP Conferencing Framework are used to
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RFC 5239 Centralized Conferencing Framework June 2008
illustrate how SIP [RFC 3261] can be used as a signaling means in
these conferencing systems. The SIP Conferencing Framework does not
define new conference control protocols to be used by the general
conferencing system. It uses only basic SIP [RFC 3261], the SIP
Conferencing for User Agents [RFC 4579], and the SIP Conference
Package [RFC 4575] 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) 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 [RFC 3261],
the SIP Conferencing for User Agents [RFC 4579], and the SIP
Conference Package [RFC 4575] are fully compatible with both framework
documents. The basis for compatibility is provided by including the
basic data elements defined in [RFC 4575] in the Conference
Information Data Model for Centralized Conferencing (XCON)
[XCON-COMMON]. User agents that only support [RFC 4579] and do not
support the Conferencing Control Protocol are still provided basic
SIP conferencing, but cannot take advantage of any of the advanced
features.
11. 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 8 and policy control. The protocols
used for manipulation and retrieval of confidential information need
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RFC 5239 Centralized Conferencing Framework June 2008
to support a confidentiality and integrity mechanism. Similar
requirements apply for the floor control protocols. Section 11.3
discusses an approach for client authentication of a floor control
server. It is RECOMMENDED that all the protocols that interface with
the conferencing system implement Transport Layer Security (TLS).
There are also security issues associated with the authorization to
perform actions on the conferencing system to invoke specific
capabilities. Section 5.2 discusses the policies associated with the
conference object to ensure that only authorized entities are able to
manipulate the data to access the capabilities. Another set of
issues involves the privacy and security of the identity of a user in
the conference, which is discussed in Section 11.2.
A final issue is related to Denial of Service (DoS) attacks on the
conferencing system itself. In order to minimize the potential for
DoS attacks, it is recommended that conferencing systems require user
authentication and authorization for any client participating in a
conference. It is recommended that the specific signaling and media
protocols include mechanisms to minimize the potential for DoS.
11.1. User Authentication and Authorization
Many policy authorization decisions are based on the identity of the
user or the role that a user may have. Conferencing systems
typically require authentication of users to validate their identity.
There are several ways that a user might authenticate its identity to
the system. For users joining a conference using one of the call
signaling protocols, the user authentication mechanisms for the
specific protocol often suffice. For the case of users joining the
conference via SIP signaling or using the conference control
protocol, TLS is RECOMMENDED.
The conferencing system may also know (e.g., out-of-band mechanisms)
about specific users and assign passwords to allow these users to be
authorized. In some cases (e.g., Public Switched Telephone Network
(PSTN) users), additional authorization may be required to allow the
user to participate in the conference. This may be in the form of an
Interactive Voice Response (IVR) system or other means. The users
may also be authorized by knowing a particular conference ID and a
Personal Identification (PIN) for it. Sometimes, a PIN is not
required and the conference ID is used as a shared secret.
In the cases where a user is authorized via multiple mechanisms, it
is up to the conferencing system to correlate (if desired) the
authorization of the call signaling interface with other
authorization mechanisms. A conferencing system can avoid the
problem with multiple mechanisms by restricting the methods by which
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a conference can be joined. For example, many conferencing systems
that provide a web interface for conferences correlate the PSTN call
signaling by forcing a dial-out mode for joining the conference.
Thus, there is only the need for a single PIN or password to join the
conference.
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 to 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 authorizes 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 refers to the usual, reasonable sized and hard to
predict shared secret. Today, users often have passwords containing
up to 30 bits (8-16 characters) of entropy. A 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 or 3
digits). 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 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.
Once a user is authenticated and authorized through the various
mechanisms available on the conferencing system, a conference user
identifier is associated with any signaling specific user identifiers
that may have been used for authentication and authorization. This
conference user identifier may be provided to a specific user through
the conference notification interface and will be provided to users
that interact with the conferencing system using the conference
control protocol. This conference user identifier is required for
any subsequent operations on the conference object.
Barnes, et al. Standards Track PAGE 52
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11.2. 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,
"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'
identity (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.
Since a conferencing system based on this framework allocates a
unique conference user identifier for each user of the conferencing
system, it is not necessary to distribute any signaling specific user
identifier to other users or participants. Access to any signaling
specific user identifiers can be controlled by applying the
appropriate access control to the signaling specific user identifiers
in the data schema.
11.3. Floor Control Server Authentication
The floor control protocol contains mechanisms that clients can use
to authenticate servers, and that servers can use to authenticate
clients, as described in Section 9 of [RFC 4582]. The precise
mechanisms used for such authentication can vary depending on the
call control protocol used. Clients using call control protocols
that employ an SDP offer/answer model, such as SIP, use the mechanism
described in Section 8 of [RFC 4583]. Clients using other call
control protocols make use of the mechanisms described in the BFCP
Connection Establishment document [RFC 5018].
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,
Barnes, et al. Standards Track PAGE 53
RFC 5239 Centralized Conferencing Framework June 2008
Rohan Mahy, Brian Rosen, Pierre Tane, Bob Braudes, Gregory Sperounes,
and Gonzalo Camarillo for their reviews and constructive input. In
addition, the authors would like to thank Scott Brim for his gen-art
review comments and Kurt Zeilenga for his secdir review comments.
13. References
13.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
13.2. Informative References
[RFC 4566] Handley, M., Jacobson, V., and C. Perkins, "SDP:
Session Description Protocol", RFC 4566, July 2006.
[RFC 3261] 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.
[RFC 3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
Model with Session Description Protocol (SDP)",
RFC 3264, June 2002.
[RFC 3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC 3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC 2445] Dawson, F. and Stenerson, D., "Internet Calendaring
and Scheduling Core Object Specification (iCalendar)",
RFC 2445, November 1998.
[RFC 4245] Levin, O. and R. Even, "High-Level Requirements for
Tightly Coupled SIP Conferencing", RFC 4245,
November 2005.
[RFC 4353] Rosenberg, J., "A Framework for Conferencing with the
Session Initiation Protocol (SIP)", RFC 4353,
February 2006.
[RFC 4575] Rosenberg, J., Schulzrinne, H., and O. Levin, "A
Session Initiation Protocol (SIP) Event Package for
Conference State", RFC 4575, August 2006.
Barnes, et al. Standards Track PAGE 54
RFC 5239 Centralized Conferencing Framework June 2008
[RFC 4376] Koskelainen, P., Ott, J., Schulzrinne, H., and X. Wu,
"Requirements for Floor Control Protocols", RFC 4376,
February 2006.
[RFC 4597] Even, R. and N. Ismail, "Conferencing Scenarios",
RFC 4597, August 2006.
[RFC 4579] Johnston, A. and O. Levin, "Session Initiation
Protocol (SIP) Call Control - Conferencing for User
Agents", BCP 119, RFC 4579, August 2006.
[RFC 4582] Camarillo, G., Ott, J., and K. Drage, "The Binary
Floor Control Protocol (BFCP)", RFC 4582,
November 2006.
[RFC 4574] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574,
August 2006.
[RFC 4583] Camarillo, G., "Session Description Protocol (SDP)
Format for Binary Floor Control Protocol (BFCP)
Streams", RFC 4583, November 2006.
[XCON-COMMON] Novo, O., Camarillo, G., Morgan, D., and R. Even,
"Conference Information Data Model for Centralized
Conferencing (XCON)", Work in Progress, March 2008.
[RFC 4975] Campbell, B., Mahy, R., and C. Jennings, "The Message
Session Relay Protocol (MSRP)", RFC 4975,
September 2007.
[RFC 5018] Camarillo, G., "Connection Establishment in the Binary
Floor Control Protocol (BFCP)", RFC 5018,
September 2007.
Barnes, et al. Standards Track PAGE 55
RFC 5239 Centralized Conferencing Framework June 2008
Authors' Addresses
Mary Barnes
Nortel
2201 Lakeside Blvd
Richardson, TX
EMail: mary.barnes@nortel.com
Chris Boulton
Avaya
Building 3
Wern Fawr Lane
St Mellons
Cardiff, South Wales CF3 5EA
EMail: cboulton@avaya.com
Orit Levin
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
EMail: oritl@microsoft.com
Barnes, et al. Standards Track PAGE 56
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Full Copyright Statement
Copyright © The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
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Barnes, et al. Standards Track PAGE 57
A Framework for Centralized Conferencing
RFC TOTAL SIZE: 146927 bytes
PUBLICATION DATE: Friday, June 6th, 2008
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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