Tech-invite3GPPspecsGlossariesIETFRFCsGroupsSIPABNFsWorld Map

RFC 5239


A Framework for Centralized Conferencing

Part 3 of 3, p. 40 to 57
Prev RFC Part


prevText      Top      Up      ToC       Page 40 
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.

Top      Up      ToC       Page 41 
                                      |   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

Top      Up      ToC       Page 42 
   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.

Top      Up      ToC       Page 43 
                                      |   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

Top      Up      ToC       Page 44 
   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

   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

   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.

Top      Up      ToC       Page 45 
                                      |   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

Top      Up      ToC       Page 46 
   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

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

   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

Top      Up      ToC       Page 47 
   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

   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.

Top      Up      ToC       Page 48 
                                      |   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

Top      Up      ToC       Page 49 
   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

   "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

Top      Up      ToC       Page 50 
   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

   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

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

Top      Up      ToC       Page 51 
   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

Top      Up      ToC       Page 52 
   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

   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.

Top      Up      ToC       Page 53 
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,

Top      Up      ToC       Page 54 
   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.

Top      Up      ToC       Page 55 
   [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.

Top      Up      ToC       Page 56 
Authors' Addresses

   Mary Barnes
   2201 Lakeside Blvd
   Richardson, TX


   Chris Boulton
   Building 3
   Wern Fawr Lane
   St Mellons
   Cardiff, South Wales  CF3 5EA


   Orit Levin
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052


Top      Up      ToC       Page 57 
Full Copyright Statement

   Copyright (C) The IETF Trust (2008).

   This document is subject to the rights, licenses and restrictions
   contained in BCP 78, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights.  Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at