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XCON Working Group                                             M. Barnes
Internet-Draft                                                    Nortel
Intended status: Standards Track                              C. Boulton
Expires: January 11, 2010                                NS-Technologies
                                                               S. Loreto
                                                                Ericsson
                                                           July 10, 2009


       Chatrooms within a Centralized Conferencing (XCON) System
                   draft-boulton-xcon-session-chat-04

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Abstract

   The document "A Framework for Centralized Conferencing" defines a
   centralized conference as both signaling and protocol agnostic.  The
   primary examples within this framework focus on audio and video as
   the media types for the session.  This document provides an overview
   of the mechanisms defined in the centralized conferencing framework
   that can be used to support multi-user chat.  In addition, the
   document describes additional functionality and requirements
   necessary to provide feature rich functionality.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Conventions and Terminology  . . . . . . . . . . . . . . . . .  3
   3.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Basic Protocol Operations  . . . . . . . . . . . . . . . .  5
     3.2.  Chat Session and Conferencing Identifiers  . . . . . . . .  7
   4.  Advanced Operations  . . . . . . . . . . . . . . . . . . . . .  9
   5.  Additional Operations  . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Nicknames  . . . . . . . . . . . . . . . . . . . . . . . .  9
     5.2.  Logging  . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.3.  History  . . . . . . . . . . . . . . . . . . . . . . . . . 11
     5.4.  Indicating Alternate Venue . . . . . . . . . . . . . . . . 11
     5.5.  File Transfer  . . . . . . . . . . . . . . . . . . . . . . 12
     5.6.  Real Time Collaboration  . . . . . . . . . . . . . . . . . 12
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 13
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15

















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1.  Introduction

   A Centralized Conference as defined by the "A Framework for
   Centralized Conferencing" (XCON Framework) [RFC5239] is both
   signaling and protocol agnostic.  The primary examples within the
   framework focus on audio and video as the media types for the
   session.  This document provides an overview of the mechanisms and
   associated framework elements involved when text is the media for the
   conference.  This functionality is often referred to as a "multi-user
   chat" as it enables a participant to join a chatroom (e.g. hosted by
   the conference server) for the exchange of messages between multiple
   participants.  The message can be plain text or can contain different
   format for more advanced functionality.

   Several existing protocols support this multi-user chat
   functionality, such as Extensible Messaging and Presence Protocol
   (XMPP) [RFC3920],[RFC3921] and Internet Relay Chat (IRC) defined in
   [RFC1459] and its successors: [RFC2810],[RFC2811],[RFC2812],
   [RFC2813].  In addition, [I-D.ietf-simple-chat] provides multi-user
   chat functionality for a purely SIP signaling based solution option
   using Message Session Relay Protocol (MSRP) [RFC4975].

   The focus of this document is to describe the interface and provide
   guidelines for the the support of existing multi-user chat
   functionality on a conferencing system based on the XCON framework
   using the Conference Control Manipulation Protocol (CCMP) independent
   of the specific media type used by the chat client.

   The functionality described in this document is not intended to
   replace any of the existing chat protocols, nor is it specifying a
   new chat protocol.  The motivation for this document is to allow
   clients that use the conferencing framework model for other media
   types (e.g. voice/video) to utilize the same conference control
   mechanisms and conferencing system to establish, update and delete a
   chatroom associated with a conference instance, independent of the
   chat protocol.  This approach also allows the conferencing system to
   provide a natural interworking point for various chat protocols - the
   details of the interworking are outside the scope of this document.


2.  Conventions and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This document reuses the terminology defined in the Centralized
   Conferencing Framework [RFC5239] and related protocol document



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   [I-D.ietf-xcon-ccmp].

   Additional terminology used in this document:
   Chat Client:  a Conferencing Client as defined in [RFC5239] that
      participates in a "chatroom".
   Chatroom:  A virtual space that users figuratively enter in order to
      participate in real-time, text-based conferencing with other
      users.
   Multi-user chat:  The functionality that allows multiple users to
      exchange messages in the context of a room or channel, similar to
      Internet Relay Chat (IRC).
   Private message:  A message sent from one participant directly to
      another participant - i.e., not to the chatroom itself to all
      participants.


3.  Overview

   Figure 1 provides a general illustration of chat clients having a
   direct, 1:1 connection to the conferencing system.  Participants can
   use the chat clients to join a room associated with a conference
   instance and send messages.  The conferencing system receives the
   messages sent from a client participating in a conference instance
   and then distributes them to the other clients associated with the
   conference instance, that are also present in the chatroom.


                              +--------+
                              |  Chat  |
                              | Client |
                              +--------+
                                  |
                                  |
                                  |
                                  v
      +--------+            +------------+            +--------+
      | Chat   |            |Conferencing|            |  Chat  |
      | Client |----------->|  System    |<-----------| Client |
      +--------+            +------------+            +--------+
                                  ^
                                  |
                                  |
                                  |
                              +--------+
                              | Chat   |
                              | Client |
                              +--------+




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                        Figure 1: Client Connection

   The approach in this document is to have no impact on the existing
   chat protocols, while taking full advantage of the functionality
   provided by the centralized conferencing framework.

   A basic solution for MSRP based IM chat sessions is documented in
   [I-D.ietf-simple-chat].  It uses the concept of an "MSRP switch" as
   the centralized component, whose role is very similar to the MSRP
   Conferencing Server in this document.  The solution in
   [I-D.ietf-simple-chat] doesn't explicitly take advantage of the
   centralized conferencing framework model, as it primarily intends to
   make use of the basic SIP conferencing framework to provide the basic
   chat functionality.  The MSRP based IM chat solution is compatible
   with the solution components described in this document, with no
   impact on that basic solution proposal.  One of the advantages of
   applying the two solutions in concert would be to take advantage of
   the centralized conferencing framework model for advanced features,
   such as sidebars and private conferences, and manipulation of the
   conference data.

   XMPP assumes a decentralized client-server architecture similar to
   the one showed in Figure 1, wherein a client utilizing XMPP accesses
   a server and servers can also communicate with each other over TCP
   connections, like in the email network.  The XMPP server can provide
   as additional functionality the multi-user conferencing services
   [XEP-0045].  The XMPP multi-user conferencing service is also
   compatible with the solution components described in this document,
   with no impact on the basic solution proposal.  Indeed the
   centralized conferencing framework model is perfectly able to manage
   the XMPP strong room control model, including the ability to kick and
   ban users, to name room moderators and administrators, to require
   membership or passwords in order to join the room.  However it is
   worth to note that the centralized conferencing framework does not
   encompass the communication between servers, as XMPP does.  Then when
   used together the access to a XMPP chatroom SHOULD be only limited to
   client having a direct connection with the server hosting the
   chatroom instance, and the federation between servers SHOULD NOT be
   allowed.

3.1.  Basic Protocol Operations

   The multi-user chat protocol operations, such as create, join and
   delete a chat MAY be performed using both non-signaling specific
   mechanisms or protocol specific mechanism if defined.  Non-signaling
   specific mechanisms are defined in the Centralized Conferencing
   Framework [RFC5239] and related Conference Control Manipulation
   Protocol (CCMP) document [I-D.ietf-xcon-ccmp].  This document



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   provides the details for the non-signaling specific mechanisms using
   CCMP with detailed examples provided in [I-D.ietf-xcon-examples].
   Protocol specific mechanisms are defined in other documents such as
   for SIP in the SIPPING Conference Framework [RFC4353] and for XMPP in
   Multi-User Chat [XEP-0045].

   The privilege to create a chatroom associated with a conference
   instance MAY be restricted to certain users or MAY be reserved to an
   administrator of the conference.  The room creation MAY be performed
   using non-signaling mechanism or protocol specific mechanism if
   defined.  In the case of CCMP, a confRequest message with a "create"
   operation is sent by the chat client.

   A participant MAY query the conferencing system to discover the list
   of the chat rooms associated to a hosted conference instance.  In the
   case of CCMP, a blueprintsRequest message for the chatrooms supported
   by a conferencing system or a confsRequest message for the active
   chatrooms can be sent by the chat client.

   In order to participate in the discussions held in a multi-user chat
   room, a participant MUST first enter the room.  A chat client wishing
   to enter a chatroom associated to a conference instance MAY use a
   non-signaling or protocol specific mechanism if defined.  In the case
   of CCMP, a participant can join a conference instance using several
   mechanisms which are described in [I-D.ietf-xcon-ccmp] - e.g.,
   userRequest message with a "create" operation to be added to a
   conference instance.

   The request to send a message is specific to the chat protocol (e.g.,
   MSRP SEND).  Upon receipt of a request to send a message, the
   conferencing system replicate and forwards the message to all other
   chat clients that are participants of the chat room.  Depending upon
   policy, a conferencing system MAY ignore or reject messages, in which
   case they are not distributed to the other chat room participants.

   A participant MAY send a "private message" to a selected participant
   or a group of participant.  This privilege SHOULD be allowed for all
   participants unless local policy dictates otherwise.

   A chat client wishing to exit a chat room MAY uses non-signaling
   mechanism or protocol specific mechanism if defined.  If the chat
   client is the last to exit, the conferencing system MAY be
   responsible for deleting the room or the originator/owner/moderator
   The privilege to delete a chatroom associated with a conference
   instance MAY be restricted to certain users or MAY be reserved to an
   administrator of the conference.  The room deletion MAY be performed
   using non-signaling mechanism or protocol specific mechanism if
   defined.  In the case of CCMP, the client SHOULD send a CCMP



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   confRequest message with an operation of "delete".

3.2.  Chat Session and Conferencing Identifiers

   As highlighted in the overview section, a chat client connecting to a
   conferencing system has a 1:1 relationship with the chat signaling
   entity, each having a unique protocol specific Chat Session
   identifier (ID).  When referring to Chat Session IDs the document is
   making reference to the locally (at conferencing system) generated
   Chat Session ID used for session signaling identification.  In the
   case of MSRP, this Chat Session ID is inserted into the local path
   SDP attribute.  An important concept in this proposal is the creation
   and management of Group Chats.  It is important that each chat
   session created, as identified by a unique chat session ID, is
   explicitly tied to an associated conference, represented by the
   conference identifier (as defined in the Centralized Conferencing
   Framework [RFC5239]).  This provides the relevant association between
   a chat session and a centralized conference.  A generic example
   representation is illustrated by the rows contained in Figure 2.



             +-----------------------------------------+
             |           Conference Identifier         |
             +-----------------------------------------+
             |         Chat Session ID=8asjdhk         |
             |         Chat Session ID=38iuhds         |
             |         Chat Session ID=djiowid         |
             |         Chat Session ID=389hewu         |
             +-----------------------------------------+



                   Figure 2: Simple Session Association

   The Centralized Conferencing Framework[RFC5239] introduces the
   concept of a conference user identifier defined in
   [I-D.ietf-xcon-common-data-model].  When a user joins a conference
   instance through the signaling protocol, it is allocated an
   appropriate conference user identifier either through authentication
   or system allocation.  The conference user identifier MUST be used in
   conjunction with a chat session identifier to internally represent a
   participant in a conference instance.  Figure 2 is then expanded to
   look like Figure 3.  Again a row in the table representing a single
   entry.






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   +--------------------------------------------------------------+
   |                 Conference Identifier                        |
   +--------------------------------+-----------------------------+
   |       Chat Session ID=8asjdhk  |  Conf User ID=839ULjj       |
   |       Chat Session ID=38iuhds  |  Conf User ID=0283hHu       |
   |       Chat Session ID=djiowid  |  Conf User ID=ncH37H        |
   |       Chat Session ID=389hewu  |  Conf User ID=pakdjjH       |
   +--------------------------------+-----------------------------+



                  Figure 3: Advanced Session Association

   A more complex session association is necessary due to potential for
   a user to have multiple group chats in a single conference instance,
   such as multi-lingual conference support.  In an example with SIP and
   MSRP, the conference representation in Figure 3 allows for such
   functionality when separate SIP dialogs represent MSRP sessions.
   This process becomes complex in the case that multiple SDP MSRP media
   sessions (m=) are defined in a single payload.  This internal
   representation needs expanding to enable a conferencing system to
   explicitly associate a media session (m=).  This involves including
   the media label, as defined in [RFC4574], to maintain the internal
   conference association.  An example is illustrated in Figure 4.



   +-----------------------------------------------------------------+
   |                   Conference Identifier                         |
   +-----------------------------------------------------------------+
   | Chat Session ID=8asjdhk  | Conf User ID=839ULjj  | Label=iede3  |
   | Chat Session ID=38iuhds  | Conf User ID=0283hHu  | Label=8heus  |
   | Chat Session ID=838unaH  | Conf User ID=0283hHu  | Label=3cnu7  |
   | Chat Session ID=djiowid  | Conf User ID=ncH37Hs  | Label=jd38J  |
   | Chat Session ID=389hewu  | Conf User ID=pakdj7H  | Label=U83hd  |
   | Chat Session ID=Ko03jdk  | Conf User ID=pakdj7H  | Label=ehy3h  |
   +-----------------------------------------------------------------+



           Figure 4: Advanced Session Association + Media Label

   In Figure 4, conference user identifiers '0283hHu' and 'pakdj7H'
   appear twice.  The combination of multiple conference user
   identifiers and a unique Group Chat session ID enables the conference
   system to clearly identify a specific Group Chat instance.  Even in
   the simplest conferencing system, where users are allowed to enter
   anonymously, the internal representation described in this section



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   should be observed.  In this case, the conferencing system would
   still internally create a conference user identifier for participant
   reference purposes.


4.  Advanced Operations

   Advanced chat features, such as sidebars and private messages can
   also be supported within the context of the centralized conferencing
   framework using CCMP.  Additional protocol details for these advanced
   features are provided in [I-D.ietf-xcon-examples].


5.  Additional Operations

   This section discusses additional operations or features required to
   provide chat room functionality.  Most of the operations are not
   explicitly defined in the centralized conferencing framework.  While
   most of the features and operations are achievable using the XCON
   data model [I-D.ietf-xcon-common-data-model] and data maintained by a
   conferencing system per the XCON framework, some advanced features
   require extensions to the XCON data model and may be optimized with
   more discrete CCMP messages.

5.1.  Nicknames

   Nicknames allow a user to define a text string that uniquely
   identifies the user within a particular chatroom without necessarily
   reflecting any protocol specific identity (e.g., SIP URI, Conference
   User Identifier, etc.).  It is also important to note that the
   functionality to provide nicknames is not limited to users involved
   in chatrooms, thus it should be a general feature of the conferencing
   system.

   Within a conferencing system, all nicknames should map to a
   conference user identifier.  The nicknames are unique only to the
   specific conferencing system.  There may be multiple nicknames
   associated with a single conference user identifier (e.g., a user
   that has different nicknames for different chat rooms and/or voice/
   video conferences).  In order to support nicknames, a 'nickname'
   attribute is defined in the XCON data model within the 'user'
   element.  A nickname can be assigned to the conference user when an
   XCON-USERID is assigned to the user.  The conferencing client MAY
   include a preferred nickname in the CCMP userRequest with a "create"
   operation.

   The conferencing system allocates a conference user identifier and a
   nickname using system specific mechanisms, which may also include



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   authentication.  The conferencing system associates the assigned
   nickname with the specific conference user identifier that has been
   allocated.  Another option would be to define a new CCMP message to
   just manipulate the nickname element.

   As described Section 3.2, the conference user identifier MUST be used
   in conjunction with a chat session identifier to internally represent
   a participant in a conference instance.  This association is created
   when a conferencing client requests to create or join a specific
   chatroom.  The nickname allocated for the specific conferencing user
   identifier MUST also be associated with the chat session ID.
   Figure 5 provides an example of the association between the chat
   session identifier, the conference user identifier and conference
   nickname for a specific Group Chat represented by the conference
   identifier.



   +-----------------------------------------------------------------+
   |                   Conference Identifier                         |
   +-----------------------------------------------------------------+
   | Chat Session ID=8asjdhk  | Conf User ID=839ULjj  | Nick=Alice   |
   | Chat Session ID=38iuhds  | Conf User ID=0283hHu  | Nick=Bob     |
   | Chat Session ID=838unaH  | Conf User ID=0283hHu  | Nick=Cliff   |
   | Chat Session ID=djiowid  | Conf User ID=ncH37Hs  | Nick=Dude    |
   | Chat Session ID=389hewu  | Conf User ID=pakdj7H  | Nick=Elliott |
   | Chat Session ID=Ko03jdk  | Conf User ID=pakdj7H  | Nick=Fluffy  |
   +-----------------------------------------------------------------+



             Figure 5: Nickname Associations for a Group Chat

   Depending upon the conferencing system, the conference system may
   allocate the preferred nickname for that user or return a different
   nickname in the CCMP userResponse message.

   In the future, if a more generic nickname mechanism is available,
   rather than provide nicknames that are specific to the conferencing
   system, a conferencing system may interface with a nickname registry,
   for example, in order to allocate a new nickname for a specific
   conferencing client.  This change in how a conferencing system
   allocates nicknames should not impact the CCMP protocol interface to
   support nicknames.







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5.2.  Logging

   A common chat feature involves logging the history of a chat room.
   This provides a record of a chat room that can be used when a user
   first joins a chat room as discussed in Section 5.3.  It can also be
   used to provide a complete capture of a specific chat room session.
   When a participant enters a room in which the discussions are logged,
   the conferencing system MUST warn the participant that the
   discussions are logged.

   The centralized conferencing framework does not fully describe the
   role of recording or logging of active conferences.  However, this
   functionality can be realized with the manipulation of the
   appropriate elements in the data model using the general conference
   control protocol operations.  One approach for implementing this
   function would be to have it be based on specific manipulation of the
   conference by a user with the appropriate permissions (i.e.,
   confRequest messaage with an "update" operation to start and stop
   recording).  Another mechanism for implementing this function would
   be to have a specific user as part of the conference to perform this
   function, by defining a specific role such as "observer" and having
   the media proxied to a logging device.

5.3.  History

   A common chat feature allows users to view the past history of chat
   rooms.  This operation is common when a user first joins a chat room
   that is underway.  A user is often offered the option to review a
   specific number of past messages.

   Conferencing systems that maintain the history associated with
   specific chat rooms through logging, as described in Section 5.2,
   should provide a mechanism, using the conference identifier, to
   access the specific information requested by a user based on a
   specific timestamp.  The user request for the information and the
   rendering of the information is specific to the user's session based
   messaging protocol and may not be supported by all the messaging
   protocols.

5.4.  Indicating Alternate Venue

   Another chat room feature provides the details of an alternate chat
   room venue for previously active chat rooms that have been closed,
   with a related topic.  While not detailed in the centralized
   conferencing framework, this functionality can be accomplished by
   creating the new chat room as a child or sibling of the previous chat
   room and providing the Active chat conference object identifier to
   any valid users that attempt to join a previous chat room.  The



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   information about the new chat room can also be provided at the end
   of a chat room that is being de-activated at the end of the session.

5.5.  File Transfer

   The ability to send files to a selected participant or group of
   participants is another common functionality, supported by messaging
   protocols.  This functionality also enables the exchange of
   information (e.g. name, size, and date) about the file to be
   transferred and usually provide a mechanism to show an image
   thumbnail for files such as photos.  This capability could be
   reflected in the conference data (in the conference instance) and
   requires at least an extension to the "available-media" element.  The
   thumbnail rendering of the image is outside the scope of the data
   model and is specific to the client application.  Additional
   functionality to support this capability requires further study.

5.6.  Real Time Collaboration

   The messaging protocols can be used, and are being used, in
   applications quite different from a simple exchange of text messages
   between two participants in the context of a chatroom.  Real-time
   collaboration tools (e.g.  Whiteboarding, screen-share, co-browse or
   document-share) are some of these applications.

   The Conferencing Systems are usually bound to Real-time collaboration
   tools to increase the productivity of distributed teams.  In terms of
   correlating this functionality with CCMP, the mechanisms for
   manipulating the conference are the same in terms of updating the
   data associated with the conference with the additional attributes to
   reflect the multiple sources of media for the chatroom.  This
   capability could be reflected in the conference data (in the
   conference instance) with an extension to the "available-media"
   element.  Some current systems using SIP embed the attributes in the
   media stream.  Overall, supporting this functionality requires
   further study.


6.  Security Considerations

   As discussed in the Centralized Conferencing Framework, 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 associated with chatrooms includes the following: an
   endpoint attempting to receive the messages for conferences in which
   it is not authorized to participate, an endpoint attempting to
   disconnect other users, and theft of service, by an endpoint, in



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   attempting to create conferences it is not allowed to create.

   Since this document describes the use of existing protocols (e.g.
   MSRP/SIP, CCMP, XMPP, etc.), it depends on the security solutions for
   those protocols and the associated authorization mechanisms.  This
   solution is based on the Centralized Conferencing framework and makes
   use of the policy associated with the conference object to ensure
   that only authorized entities are able to manipulate the data to
   access the capabilities.  This solution also makes use of the privacy
   and security of the identity of a user in the conference, as
   discussed in the Centralized Conferencing Framework.


7.  IANA Considerations

   This document requires no IANA registrations.


8.  Acknowledgments

   The authors appreciate the input and comments from Miguel Garcia-
   Martin and Dave Morgan.


9.  References

9.1.  Normative References

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

   [RFC5239]  Barnes, M., Boulton, C., and O. Levin, "A Framework for
              Centralized Conferencing", RFC 5239, June 2008.

   [I-D.ietf-xcon-common-data-model]
              Novo, O., Camarillo, G., Morgan, D., and J. Urpalainen,
              "Conference Information Data Model for Centralized
              Conferencing (XCON)", draft-ietf-xcon-common-data-model-13
              (work in progress), April 2009.

   [I-D.ietf-xcon-ccmp]
              Barnes, M., Boulton, C., Romano, S., and H. Schulzrinne,
              "Centralized Conferencing Manipulation Protocol",
              draft-ietf-xcon-ccmp-02 (work in progress), March 2009.







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9.2.  Informative References

   [I-D.roach-xcon-chatroom-analysis]
              Roach, A., "An Analysis of Feature Parity Between XCON/
              SIMPLE-Based Chatrooms and Other  Chatrooms",
              draft-roach-xcon-chatroom-analysis-00 (work in progress),
              August 2007.

   [I-D.ietf-xcon-examples]
              Barnes, M., Boulton, C., Miniero, L., and S. Romano,
              "Centralized Conferencing Manipulation Protocol (CCMP)
              Call Flow Examples", draft-ietf-xcon-examples-00 (work in
              progress), July 2009.

   [RFC2664]  Plzak, R., Wells, A., and E. Krol, "FYI on Questions and
              Answers - Answers to Commonly Asked "New Internet User"
              Questions", RFC 2664, August 1999.

   [RFC1459]  Oikarinen, J. and D. Reed, "Internet Relay Chat Protocol",
              RFC 1459, May 1993.

   [RFC2810]  Kalt, C., "Internet Relay Chat: Architecture", RFC 2810,
              April 2000.

   [RFC2811]  Kalt, C., "Internet Relay Chat: Channel Management",
              RFC 2811, April 2000.

   [RFC2812]  Kalt, C., "Internet Relay Chat: Client Protocol",
              RFC 2812, April 2000.

   [RFC2813]  Kalt, C., "Internet Relay Chat: Server Protocol",
              RFC 2813, April 2000.

   [RFC3920]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Core", RFC 3920, October 2004.

   [RFC3921]  Saint-Andre, P., Ed., "Extensible Messaging and Presence
              Protocol (XMPP): Instant Messaging and Presence",
              RFC 3921, October 2004.

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

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

   [I-D.ietf-simple-chat]



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              Niemi, A., Garcia, M., and G. Sandbakken, "Multi-party
              Chat Using the Message Session Relay Protocol (MSRP)",
              draft-ietf-simple-chat-04 (work in progress), March 2009.

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

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

   [XEP-0045]
              Saint-Andre, P., "Multi-User Chat", XSF XEP 0045,
              July 2007.


Authors' Addresses

   Mary Barnes
   Nortel

   Email: mary.barnes@nortel.com


   Chris Boulton
   NS-Technologies

   Email: chris@ns-technologies.com


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420, Finland

   Email: salvatore.loreto@ericsson.com















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