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PROPOSED STANDARD
Errata Exist
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.




















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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





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1.  Introduction

   This document defines the framework for Centralized Conferencing.
   The framework allows participants using various call signaling
   protocols, such as SIP, H.323, Jabber, 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
   [RFC4353].  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, [RFC2119] and indicate requirement levels for
   compliant implementations.

3.  Terminology

   This Centralized Conferencing Framework document generalizes, when
   appropriate, the SIP Conferencing Framework [RFC4353] 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.







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   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.





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   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.






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   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 [RFC3550]) or Message
      Session Relay Protocol (defined in [RFC4975]).

   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
   [RFC4353] together with the SIP Call Control Conferencing for User
   Agents [RFC4579] documents address these types of scenarios.





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   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
   [RFC4245].  These requirements are applicable for conferencing
   systems using various call signaling protocols, including SIP.
   Additional conferencing requirements are provided in [RFC4376] and
   [RFC4597].

   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 [RFC3265]) 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.








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   ....................................................................
   .  Conferencing System                                             .
   .                                                                  .
   .        +-----------------------------------------------------+   .
   .        |       C o n f e r e n c e   o b j e c t             |   .
   .      +-+---------------------------------------------------+ |   .
   .      |       C o n f e r e n c e   o b j e c t             | |   .
   .    +-+---------------------------------------------------+ | |   .
   .    |       C o n f e r e n c e   o b j e c t             | | |   .
   .    |                                                     | | |   .
   .    |                                                     | |-+   .
   .    |                                                     |-+     .
   .    +-----------------------------------------------------+       .
   .              ^                  ^             ^        |         .
   .              |                  |             |        |         .
   .              v                  v             v        v         .
   .  +-------------------+ +--------------+ +-------+ +------------+ .
   .  | Conference Control| | Floor Control| |Foci   | |Notification| .
   .  | Server            | | Server       | |       | |Service     | .
   .  +-------------------+ +--------------+ +-------+ +------------+ .
   .             ^                 ^           ^          |           .
   ..............|.................|...........|..........|............
                 |                 |           |          |
                 |Conference       |Binary     |Call      |Notification
                 |Control          |Floor      |Signaling |Protocol
                 |Protocol         |Control    |Protocol  |
                 |                 |Protocol   |          |
                 |                 |           |          |
   ..............|.................|...........|..........|............
   .             V                 V           V          V           .
   .  +----------------+  +------------+  +----------+ +------------+ .
   .  | Conference     |  | Floor      |  | Call     | |Notification| .
   .  | and Media      |  | Control    |  | Signaling| | Client     | .
   .  | Control        |  | Client     |  | Client   | |            | .
   .  | Client         |  |            |  |          | |            | .
   .  +----------------+  +------------+  +----------+ +------------+ .
   .                                                                  .
   . Conferencing Client                                              .
   ....................................................................

            Figure 1: Conferencing System Logical Decomposition

   The media graph of a conference can be centralized, decentralized, or
   any combination of both and potentially differ per media type.  In
   the centralized case, the media sessions are established between a
   media mixer controlled by the focus and each one of the participants.
   In the decentralized (i.e., distributed) case, the media graph is a




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   multicast or multi-unicast mesh among the participants.
   Consequently, the media processing (e.g., mixing) can be controlled
   either by the focus alone or by the participants.  The concepts in
   this framework document clearly map to a centralized media model.
   The concepts can also apply to the decentralized media case; however,
   the details of such are left for future study.

   Section 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.































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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



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   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 [RFC4575].  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 [RFC4575].  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.







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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.





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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
   [RFC4579].  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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    ....................................................................
    .  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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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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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.




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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.






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   +---+-----------------------+
   | p |                       |
   | o |   P A R E N T  A      |
   | l |                       |
   | i |   C O N F E R E N C E |
   | c |                       |
   | i |   O B J E C T         |
   | e |                       |
   +-s-+-----------------------+
           |
          \| /
           \/  INDEPENDENT
           /\
          /| \
           V
   +---+-----------------------+
   | p |                       |
   | o |   P A R E N T  B      |
   | l |                       |
   | i |   C O N F E R E N C E |
   | c |                       |
   | i |   O B J E C T         |
   | e |                       |
   +-s-+-----------------------+
           |    |
           |    |
           |    ---------------------------
           |                              |
           V                              V
   +---+-----------------------+    +---+-----------------------+
   | p |                       |    | p |                       |
   | o |   C H I L D  1        |    | o |   C H I L D  2        |
   | 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.







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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.







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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



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   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 [RFC2445] 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).




















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   +--------------+     +-------Conferencing System-----------------+
   | Generic ICAL |     |                                           |
   |   Resource   |     |    ..Conference Instance....              |
   +--------------+     |    .                       . +-----------+|
         ^ ^            |    . +-------------------+ . | Conference||
         | |            |    . |Conference Objects |<--| Control   ||
         | ----------------->. +-------------------+ . | Server    ||
         |              |    .                       . +-----------+|
         |              |    .........................       ^      |
         |              |                ^                   |      |
   +-----|--------------+                |                   |      |
   |     v                               |                   |      |
   |  +--------------+                   |                   |      |
   |  |   Resource   |<------------------+                   |      |
   |  |   Scheduler  |                                       |      |
   |  +--------------+                                       |      |
   |                                                         |      |
   +---------------------------------------------------------|------+
                                                             |
                                                             |
                                                        +-Request-+
                                                        |         |
                                                        +----+    |
                                                        |ICAL|    |
                                                        +----+----+
                                                             |
                                                             |
                                                             |
                                           Conference Control|
                                               Protocol      |
                                                             |
                                                    +-------------+
                                                    | Conferencing|
                                                    | Client      |
                                                    +-------------+

                       Figure 7: Resource Scheduling

   A CCP request to create a new conference reservation is validated,
   including the associated iCal object, and the resultant conference
   reservation is created.  The conference reservation is uniquely
   represented within the conferencing system by a conference object
   identifier (e.g., xcon:hd87928374), as introduced in Section 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.




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   The previous example explains how a client creates a basic conference
   reservation using an iCal reference in association with a conference
   control protocol.  Figure 7 can also be applied when explaining how a
   series of conferences are scheduled in the system.  The description
   is almost identical with the exception that the iCal definition that
   is included in a CCP request represents a series of recurring
   conference instances (e.g., conference 'start' time, 'end' time,
   occur weekly).  The conferencing system will treat this request the
   same as the first example.  The CCP request will be validated, along
   with the associated iCal object, and the conference reservation is
   created.  The conference reservation and its conference object ID,
   created for this example, represent the entire series of recurring
   conference instances rather than a single Conference.  If the client
   uses the conference object ID provided and a CCP request to adjust
   the conference reservation, every conference instance in the series
   will be altered.  This includes all future occurrences, such as a
   conference scheduled as an infinite series, subject to the
   limitations of the available calendaring interface.

   A conferencing system that supports the scheduling of a series of
   conference instances should also be able to support manipulation
   within a specific range of the series.  A good example is a
   conference reservation that has been scheduled to occur every Monday
   at 09.00 GMT.  For the next three weeks only, the meeting has been
   altered to occur at 10.00 GMT in an alternative venue.  With Figure 7
   in mind, the client will construct a CCP request whose purpose is to
   modify the existing conference reservation for the recurring
   conference instance.  The client will include the conference object
   ID provided by the conferencing system to explicitly reference the
   conference reservation within the conferencing system.  A CCP request
   will contain all the required changes to the conference reservation
   (e.g., change of venue).

   The conferencing system matches the incoming CCP request to the
   existing conference reservation but identifies that the associated
   iCal object only refers to a range of the existing series.  The
   conferencing system creates a child, by cloning the original
   conference reservation, to represent the altered conference instances
   within the series.  The cloned child object is not independent of the
   original parent object, thus preventing any potential conflicts in
   scheduling (e.g., a change to the whole series ''start' time').  The
   cloned conference reservation, representing the altered series of
   conference instances, has its own associated conference object ID
   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



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   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 [RFC3265] with the specifics to support conferencing
   defined in [RFC4575].

   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



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   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
   [RFC4582].

   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 [RFC4566] offer/answer [RFC3264] 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 [RFC4582] 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
   [RFC4583], 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 [RFC4583].

   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 [RFC4583], 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 [RFC4574].





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9.  Conferencing Scenario Realizations

   This section addresses how advanced conferencing scenarios, many of
   which have been described in [RFC4597], 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 [RFC4579].  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.

















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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.




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   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.









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   Limited operations for controlling other conference participants (a
   so called "3rd party control") through the focus, using call
   signaling only, may also be available for some signaling protocols.
   For example, "Conferencing for SIP User Agents" [RFC4579] 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.




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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.



















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                                      +--------------------------------+
                                      |   Conferencing System          |
    "Alice"                           |                  +---------+--+|
   +--------+                         |                  |policies |  ||
   |        |CCP Request <            | +-----------+    +---------+  ||
   | Client |-------------------------->|Conference |    |Active      ||
   |        |  Conference Object ID,  | |Control    |~~~>|Conference  ||
   +--------+  Mute, "Bob" >          | |Server     |    |            ||
                                      | +-----------+    +-------+    ||
                                      |                  |"Alice"|    ||
      "Carol"                         |                  '       '    '|
   +--------+  NOTIFY <"Bob"=mute">   |+------------+    '       '    '|
   |        |<-------------------------|Notification|<~~~|            ||
   | Client |.          .             ||Service     |    +-------+    ||
   +--------+--+          .           ||            |    |"Bob"  |    ||
      |        |<----------------------|            |    +-------+----+|
      | Client |  NOTIFY <"Bob"=mute">|+------------+                  |
      +--------+                      +--------------------------------+
          "Bob"

        Figure 10: Client Manipulation of Conference - Mute a Party

   Upon receipt of the conference control protocol request to "mute" a
   party ("Bob") in the specific conference as identified by the
   conference object ID, the conference server ensures that "Alice" has
   the appropriate authority based on the policies associated with that
   specific conference object to perform the operation.  "Bob's" status
   is marked as "recvonly" and the conference object is updated to
   reflect that "Bob's" media is not to be "mixed" with the conference
   media.

   Depending upon the policies, other participants (including "Bob") may
   be notified of this change via the conference notification service.

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






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   implicitly linked to the parent conference object (i.e., it is not an
   independent object) and is associated with the parent conference
   object identifier, as shown in Figure 11.  A conferencing system
   manages and enforces the parent and appropriate localized
   restrictions on the sidebar conference object (e.g., no members from
   outside the parent conference instance can join, sidebar conference
   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).








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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.






































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                                      +--------------------------------+
                                      |   Conferencing System          |
                                      |                  +---------+--+|
                                      |                  |policies |  ||
                                      |                  +---------+  ||
                                      |                  |Active      ||
                                      |                  |Conference  ||
   "Alice"                            |                  +-------+    ||
   +--------+                         |                  |"Alice"|    ||
   |        |CCP Req <createSidebar,  |                  +-------+    ||
   |        |     activeConfObjID,    | +-----------+    |"Bob"  |    ||
   | Client |-------------------------->|Conference |    +-------+    ||
   |        |    confUserID>          | |Control    |~~~>|"Carol"|    ||
   |        |<--------------------------|Server     |    +-------+----+|
   |        |CCP Response             | |           |           |      |
   +--------+  <sidebarResvConfObjID, | |           |           |      |
                          confID>     | |           |           V      |
                                      | |           |    +---------+--+|
                                      | |           |    |policies |  ||
                                      | |           |~~~>+---------+  ||
                                      | |           |    |            ||
                                      | +-----------+    |            ||
    "Alice"                           |                  | Sidebar    ||
   +--------+                         |                  | Reservation||
   |        |CCP Request <update,     | +-----------+    |            ||
   |        |    sidebarResvConfObjID,| |           |    |            ||
   | Client |-------------------------->|           |~~~>|            ||
   |        |  confID,confUserID,     | |           |    +------------+|
   |        |  video=parent,          | |           |           |      |
   |        |  audio=sidebar>         | |Conference |           |      |
   |        |                         | |Control    |           V      |
   |        |                         | |Server     |    +---------+--+|
   |        |CCP Response             | |           |    |policies |  ||
   |        |    <activeSideConfObjID,| |           |    +---------+  ||
   |        |<--------------------------|           |    |Active      ||
   +--------+    confID>              | |           |    |Sidebar     ||
                                      | |           |    |Conference  ||
                                      | +-----------+    +-------+    ||
                                      |                  |"Alice"|    ||
     "Bob"                            |                  |       |    ||
   +--------+  NOTIFY <"Bob"=added>   |+------------+    +-------+    ||
   |        |<-------------------------|Notification|<~~~|       |    ||
   | Client |                         ||Service     |    |"Bob"  |    ||
   +--------+                         ||            |    +-------+----+|
                                      |+------------+                  |
                                      +--------------------------------+

            Figure 12: Client Creation of a Sidebar Conference



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   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





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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  ||
                                      | +-----------+    +-------+    ||



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                                      |                  |"Alice"|    ||
     "Bob"                            |                  +-------+    ||
   +--------+  NOTIFY <"Bob"=added,   |+------------+    |"Bob"  |    ||
   | Client |<-------------------------|Notification|<~~~+-------+    ||
   +--------+         "Ethel"=added,  ||Service     |    |"Ethel"|    ||
                      "Fred"=added,>  ||            |    +-------+    ||
     "Ethel"                       +---|            |    |"Fred" |    ||
   +--------+  NOTIFY <"Bob"=added,|  |+------------+    +-------+----+|
   | Client | <--------------------+  +--------------------------------+
   +--------+  "Ethel"=added,"Fred"=added,>

             Figure 13: Client Creation of an External Sidebar

   Upon receipt of the conference control protocol request to "reserve"
   a new sidebar conference, based upon the active conference received
   in the request, the conferencing system uses the received active
   conference to clone a conference reservation for the sidebar.  As
   discussed previously, the sidebar reservation is NOT independent of
   the active conference (i.e., parent).  The conferencing system also
   reserves or allocates a conference ID to be used for any subsequent
   protocol requests from any of the members of the conference.  The
   conferencing system maintains the mapping between this conference ID
   and the conference object ID associated with the sidebar reservation
   through the conference instance.

   Upon receipt of the conference control protocol response to reserve
   the conference, "Alice" can now create an active conference using
   that reservation or create additional reservations based upon the
   existing reservations.  In this example, "Alice" wants only "Bob" and
   "Ethel", along with the new participant "Fred" to be involved in the
   sidebar; thus, she manipulates the membership.  "Alice" sets the
   media such that the participants in the sidebar don't receive any
   media from the main conference.  "Alice" sends a conference control
   protocol request to update the information in the reservation and to
   create an active conference.

   Upon receipt of the conference control protocol request to update the
   reservation and to create an active conference for the sidebar, as
   identified by the conference object ID, the conferencing system
   ensures that "Alice" has the appropriate authority based on the
   policies associated with that specific conference object to perform
   the operation.  The conferencing system must also validate the
   updated information in the reservation, ensuring whether members like
   "Fred" are already a user of this conferencing system or whether he







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   is a new user.  Since "Fred" is a new user for this conferencing
   system, a conference user identifier is created for "Fred".  Based
   upon the addressing information provided for "Fred" by "Alice", the
   call signaling to add "Fred" to the conference is instigated through
   the focus.

   Depending upon the policies, the initiator of the request (i.e.,
   "Alice") and the participants in the sidebar (i.e., "Bob" and
   "Ethel") may be notified of his addition to the sidebar via the
   conference notification service.

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.









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                                      +--------------------------------+
                                      |   Conferencing System          |
                                      |                  +---------+--+|
                                      |                  |policies |  ||
                                      |                  +---------+  ||
                                      |                  |Active      ||
                                      |                  |Conference  ||
                                      |                  +-------+    ||
                                      |                  |"Alice"|    ||
                                      |                  +-------+    ||
                                      | +-----------+    |"Bob"  |    ||
                                      | |Conference |    +-------+    ||
                                      | |Control    |~~~>|"A1"   |    ||
                                      | |Server     |    +-------+    ||
                                      | |           |    |"A2"   |    ||
                                      | |           |    +-------+    ||
                                      | |           |    |"A3"   |    ||
                                      | |           |    +-------+----+|
                                      | |           |           |      |
                                      | |           |           V      |
                                      | |           |    +---------+--+|
                                      | |           |    |policies |  ||
                                      | |           |~~~>+---------+  ||
                                      | |           |    |Active      ||
                                      | +-----------+    |Sidebar     ||
     "A1"                             |                  |Conference  ||
   +--------+  Floor Request <"A1",   |+------------+    +-------+    ||
   |        |------------------------->|Floor Ctrl  |    |"Carol"|    ||
   |Client  |     activeSideConfObjID,||Server      |~~~>|       |    ||
   +--------+     confID    >         ||            |    +-------+----+|
                                      |+------------+           |      |
                                      |                         V      |
                                      |                  +---------+--+|
                                      |                  |policies |  ||
                                      |                  +---------+  ||
                                      |                  |Active      ||
                                      |                  |Sidebar     ||
     "A1"                             |                  |Conference  ||
   +--------+ Floor Granted <"A1",    |+------------+    +-------+    ||
   |        |<-------------------------|Floor Ctrl  |<~~~|"Carol"|    ||
   | Client |     activeSideConfObjID,||Server      |    +-------+    ||
   +--------+     confID    >         ||            |    |"A1"   |    ||
                                      |+------------+    +-------+----+|
                                      +--------------------------------+

                  Figure 14: Floor Control with Sidebars





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   When "A1" wishes to ask a question, he sends a Floor Request message
   to the floor control server.  Upon receipt of the request, the floor
   control server notifies the moderator, "Carol" of the active sidebar
   conference, 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.


























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                                      +--------------------------------+
                                      |   Conferencing System          |
                                      |                  +---------+--+|
                                      |                  |policies |  ||
                                      |                  +---------+  ||
                                      |                  |Active      ||
                                      |                  |Conference  ||
                                      |                  +-------+    ||
                                      |                  |"Alice"|    ||
                                      |                  +-------+    ||
                                      | +-----------+    |"Bob"  |    ||
                                      | |Conference |    +-------+    ||
                                      | |Control    |~~~>|"Carol"|    ||
                                      | |Server     |    +-------+----+|
                                      | |           |           |      |
                                      | |           |           |      |
                                      | |           |           V      |
                                      | |           |    +---------+--+|
                                      | |           |    |policies |  ||
                                      | |           |~~~>+---------+  ||
                                      | |           |    |            ||
                                      | +-----------+    |Sidebar     ||
     "Alice"                          |                  |Conference  ||
   +--------+  NOTIFY <"Alice"=added, |+------------+    +-------+    ||
   |        |<-------------------------|Notification|    |       |    ||
   | Client |     activeSideConfObjID,||Service     |<~~~|"Alice"|    ||
   +--------+     confID    >         ||            |    +-------+----+|
                                      |+------------+                  |
                                  ~~~Announcement provided to "Alice"~~~
                                      | +-----------+                  |
                                      | |Conference |                  |
                                      | |Control    |                  |
                                      | |Server     |                  |
                                      | |           |                  |
                                      | |           |    \---------+--/|
                                      | |           |    |\          /||
                                      | |           |~~~>+ \        / ||
                                      | |           |    |  \      /  ||
                                      | +-----------+    |Sid\bar /   ||
     "Alice"                          |                  |Conf\re/ce  ||
   +--------+ NOTIFY <"Alice"=removed,|+------------+    +-----\/+    ||
   |        |<-------------------------|Notification|<~~~|     /\|    ||
   | Client |     activeSideConfObjID,||Service     |    |"Ali/ce\    ||
   +--------+     confID    >         ||            |    +---/---+\---+|
                                      |+------------+       /      \   |
                                      +--------------------------------+

                            Figure 15: Whisper



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   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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                                      +--------------------------------+
                                      |   Conferencing System          |
 "Alice"                              | +-----------+                  |
+--------+                            | |Conference |                  |
|        |CCP Request <               | |Control    |                  |
| Client |--------------------------->| |Server     |                  |
|        |Bob's Conference ID,        | |           |                  |
+--------+ Join >                     | |           |                  |
                                      | |           |                  |
                                      | ~           ~                  |
                                 ~~~Announcement provided to "Alice"~~~
                                  ~~~ Digits collected from  "Alice"~~~
                                      | ~           ~    +---------+--+|
                                      | |           |~~~>|policies |  ||
                                      | |           |    +---------+  ||
                                      | |           |    |Active      ||
                                      | |           |    |Conference  ||
                                      | |           |    +-------+    ||
                                      | |           |    |"Bob"  |    ||
                                      | |           |    +-------+    ||
                                      | |           |    |"Carol"|    ||
                                      | |           |    +-------+----+|
                                      | ~           ~                  |
                                 ~~~Announcement provided to "Alice"~~~
                                        ~~~ Alice records her name ~~~
                                      | ~           ~    +---------+--+|
                                      | |           |    |policies |  ||
                                      | |           |    +---------+  ||
                                      | |           |~~~>|Active      ||
                                      | +-----------+    |Conference  ||
                                      |                  +-------+    ||
                                      |                  |"Bob"  |    ||
     "Bob  "                          |                  +-------+    ||
   +--------+  NOTIFY <"Alice"=added, |+------------+    |"Carol"|    ||
   |        |<-------------------------|Notification|    +-------+    ||
   | Client |     activeSideConfObjID,||Service     |<~~~|"Alice"|    ||
   +--------+     confID    >         ||            |    +-------+----+|
                                      |+------------+                  |
                              ~~~Announcement provided to All Parties~~~
                                      |                                |
                                      +--------------------------------+

                  Figure 16: Recording and Announcements

   Upon receipt of the conference control protocol request from "Alice"
   to join "Bob's" conference, the conferencing system maps the
   identifier received in the request to the conference object




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   representing "Bob's" active conference.  The conferencing system
   determines that a password is required for this specific conference;
   thus, an announcement asking "Alice" to enter the password is
   provided to "Alice".  Once "Alice" enters the password, it is
   validated against the policies associated with "Bob's" active
   conference.  The conferencing system then connects to a server 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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   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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                                      +--------------------------------+
                                      |   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



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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 [RFC4353] 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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   illustrate how SIP [RFC3261] 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 [RFC3261], the SIP
   Conferencing for User Agents [RFC4579], and the SIP Conference
   Package [RFC4575] 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 [RFC3261],
   the SIP Conferencing for User Agents [RFC4579], and the SIP
   Conference Package [RFC4575] are fully compatible with both framework
   documents.  The basis for compatibility is provided by including the
   basic data elements defined in [RFC4575] in the Conference
   Information Data Model for Centralized Conferencing (XCON)
   [XCON-COMMON].  User agents that only support [RFC4579] 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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   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.







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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 [RFC4582].  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 [RFC4583].  Clients using other call
   control protocols make use of the mechanisms described in the BFCP
   Connection Establishment document [RFC5018].

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,



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   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

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

13.2.  Informative References

   [RFC4566]      Handley, M., Jacobson, V., and C. Perkins, "SDP:
                  Session Description Protocol", RFC 4566, July 2006.

   [RFC3261]      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.

   [RFC3264]      Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
                  Model with Session Description Protocol (SDP)",
                  RFC 3264, June 2002.

   [RFC3265]      Roach, A., "Session Initiation Protocol (SIP)-Specific
                  Event Notification", RFC 3265, June 2002.

   [RFC3550]      Schulzrinne, H., Casner, S., Frederick, R., and V.
                  Jacobson, "RTP: A Transport Protocol for Real-Time
                  Applications", STD 64, RFC 3550, July 2003.

   [RFC2445]      Dawson, F. and Stenerson, D., "Internet Calendaring
                  and Scheduling Core Object Specification (iCalendar)",
                  RFC 2445, November 1998.

   [RFC4245]      Levin, O. and R. Even, "High-Level Requirements for
                  Tightly Coupled SIP Conferencing", RFC 4245,
                  November 2005.

   [RFC4353]      Rosenberg, J., "A Framework for Conferencing with the
                  Session Initiation Protocol (SIP)", RFC 4353,
                  February 2006.

   [RFC4575]      Rosenberg, J., Schulzrinne, H., and O. Levin, "A
                  Session Initiation Protocol (SIP) Event Package for
                  Conference State", RFC 4575, August 2006.



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RFC 5239           Centralized Conferencing Framework          June 2008


   [RFC4376]      Koskelainen, P., Ott, J., Schulzrinne, H., and X. Wu,
                  "Requirements for Floor Control Protocols", RFC 4376,
                  February 2006.

   [RFC4597]      Even, R. and N. Ismail, "Conferencing Scenarios",
                  RFC 4597, August 2006.

   [RFC4579]      Johnston, A. and O. Levin, "Session Initiation
                  Protocol (SIP) Call Control - Conferencing for User
                  Agents", BCP 119, RFC 4579, August 2006.

   [RFC4582]      Camarillo, G., Ott, J., and K. Drage, "The Binary
                  Floor Control Protocol (BFCP)", RFC 4582,
                  November 2006.

   [RFC4574]      Levin, O. and G. Camarillo, "The Session Description
                  Protocol (SDP) Label Attribute", RFC 4574,
                  August 2006.

   [RFC4583]      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.

   [RFC4975]      Campbell, B., Mahy, R., and C. Jennings, "The Message
                  Session Relay Protocol (MSRP)", RFC 4975,
                  September 2007.

   [RFC5018]      Camarillo, G., "Connection Establishment in the Binary
                  Floor Control Protocol (BFCP)", RFC 5018,
                  September 2007.

















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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

























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RFC 5239           Centralized Conferencing Framework          June 2008


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