XCON Working Group C. Boulton
Internet-Draft Ubiquity Software Corporation
Expires: August 27, 2007 M. Barnes
Nortel
February 23, 2007
Centralized Conferencing (XCON) Using the Message Session Relay
Protocol (MSRP)
draft-boulton-xcon-msrp-conferencing-04
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Abstract
The document "A Framework and Data Model 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
defines the mechanisms, in the context of this centralized
conferencing framework, when using the Message Session Relay Protocol
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(MSRP) for instant messaging sessions.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Protocol Operations . . . . . . . . . . . . . . . . . . . 5
3.2. MSRP and Conferencing Identifiers . . . . . . . . . . . . 5
4. Basic Operations . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Creating a Chat Room . . . . . . . . . . . . . . . . . . . 8
4.2. Joining a Chat Room . . . . . . . . . . . . . . . . . . . 10
4.3. Deleteing a Chat Room . . . . . . . . . . . . . . . . . . 12
5. Advanced Operations . . . . . . . . . . . . . . . . . . . . . 13
5.1. Text Sidebar . . . . . . . . . . . . . . . . . . . . . . . 13
5.2. Private Message . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
8.1. Normative References . . . . . . . . . . . . . . . . . . . 20
8.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 22
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1. Introduction
A Centralized Conference as defined by the "A Framework and Data
Model for Centralized Conferencing" [2] is both signaling and
protocol agnostic. The primary examples within this framework focus
on audio and video as the media types for the session. The
requirements to support conferences of session-based instant
messages, private messaging, and sidebars are introduced in [6],
which also provides a purely SIP signaling based solution option.
This document defines the mechanisms and associated framework
elements involved when using the Message Session Relay Protocol(MSRP)
[4] in a centralized conference, as defined by [2], in support of
those requirements.
This document has been constructed to be compatible with both the
XCON Framework and "A Call Control and Multi-party usage framework
for the Session Initiation Protocol (SIP)" [3] document (SIPPING
Conferencing Framework). The Centralized Conferencing Framework
provides the data model and interfaces to be used while the SIPPING
Conferencing Framework provides details of the SIP signaling protocol
operations. For the purpose of this document, MSRP will be discussed
in the context of SIP being the carrying protocol, as defined in the
core MSRP [4] specification.
2. Conventions and Terminology
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, [1] and indicate requirement levels for
compliant implementations.
3. Overview
MSRP is defined as a peer-to-peer protocol that enables a direct
connection between two compliant endpoints, unless an MSRP relay is
inserted in the MSRP signaling path. The MSRP Relay specification
[5] details the associated functionality with a relay in the
signaling path. Centralized conferencing using MSRP can be achieved
by the conferencing system appearing as an MSRP endpoint for
Conference Participants, with the conferencing system distributing
the messages by relaying them to each of the conference participants.
Figure 1 provides an illustration of MSRP clients having a direct,
1:1 connection to the conferencing system. The MSRP conferencing
system can be roughly categorized as a hybrid MSRP entity that
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combines both MSRP client and MSRP relay functionality. An MSRP SEND
sent to the conference will arrive at the conference server and then
be replicated to all appropriate MSRP sessions.
+--------+
| MSRP |
| Client |
| |
+--------+
|
|
|
|
|
|
v
+------------+
+--------+ | | +--------+
| MSRP | | MSRP | | MSRP |
| Client |-------------->|Conferencing|<--------------| Client |
| | | System | | |
+--------+ | | +--------+
+------------+
^
|
|
|
|
|
|
+--------+
| XCON |
| Client |
| |
+--------+
Figure 1: Client Connection
The approach in this document is to minimize the impact on the MSRP
protocol, while taking full advantage of the functionality provided
by the centralized conferencing framework. The solution proposal in
this document meets the requirements identified in the requirements
section of the multiparty IM with MSRP document [6], with the
exception of the requirements (REQ-5, REQ-6 and REQ-7) related to the
concept of nicknames. A solution for nicknames is currently not
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within the scope of the centralized conferencing framework or
associated protocol documents, although it is a useful and desireable
concept.
A basic solution for IM chat sessions, also meeting the Multiparty IM
using MSRP requirements, is documented in [6]. 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 [6] 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. However, that solution approach 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 a reuse of the centralized
conferencing framework model for advanced features, such as sidebars
and private conferences, and manipulation of the conference data.
3.1. Protocol Operations
On issuing an MSRP SEND request to an MSRP media session that is a
member of a conference instance, the SEND request will be replicated
and forwarded, in the relevant context, to all other MSRP media
sessions that are participants of the conference instance.
An MSRP capable client wishing to join a conference uses standardized
mechanisms for creating and joining a conference. SIP signaling
mechanisms for creating and joining a conference are defined in
SIPPING Conference Framework [3] and non signaling specific
mechanisms are defined in the Centralized Conferencing Framework [2]
and related protocol document [TBD].
An An MSRP capable client wishing to delete a chat room uses
standardized mechanisms for deleteing a conference. SIP signaling
mechanisms for deleting a conference are defined in SIPPING
Conference Framework [3] and non signaling specific mechanisms are
defined in the Centralized Conferencing Framework [2] and related
protocol document [TBD].
3.2. MSRP and Conferencing Identifiers
As mentioned in the overview, an MSRP client connecting to a
conferencing system has a 1:1 relationship with the MSRP signaling
entity, each having a unique MSRP session ID (session ID's are
contained in MSRP URLs). When referring to MSRP session ID's the
document is making reference to the locally (at conferencing system)
generated session ID that is inserted into the local path SDP
attribute and used for MSRP session signaling identification. An
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important concept in this proposal is the creation and management of
MSRP sessions. It is important that each MSRP session created, as
identified by the unique session ID, is explicitly tied to an
associated conference, represented by the conference identifier (as
defined in the Centralized Conferencing Framework [3]). This
provides the relevant association between MSRP and an XCON
Conference. An example representation is illustrated by the rows
contained in Figure 2.
---------------------------------------------
| Conference Identifier |
---------------------------------------------
| MSRP Session ID=8asjdhk |
| MSRP Session ID=38iuhds |
| MSRP Session ID=djiowid |
| MSRP Session ID=389hewu |
---------------------------------------------
Figure 2: Simple Session Association
The Centralized Conferencing Framework[3] introduces the concept of a
conference user identifier defined in [9]. When a user joins a
conference instance through the signaling protocol, it is allocated
an appropriate conference user identifer either through
authentication or system allocation. The conference user identifer
MUST be used in conjunction with the MSRP 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.
-------------------------------------------------------------------
| Conference Identifier |
-------------------------------------------------------------------
| MSRP Session ID=8asjdhk | Conf User ID=839ULjj |
| MSRP Session ID=38iuhds | Conf User ID=0283hHu |
| MSRP Session ID=djiowid | Conf User ID=ncH37H |
| MSRP 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 MSRP sessions in a single conference
instance, such as multi-lingual conference support. The conference
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representation in Figure 3 allows for such functionality when
separate SIP dialogs represent MSRP sessions. This process becomes
complex when multiple SDP MSRP media sessions (m=) are defined in a
single payload. This internal representation now needs expanding to
enable a conferencing system to explicitly associate a media session
(m=). This involves including the media label, as defined in [7], to
maintain the internal conference association. An example is
illustrated in Figure 4.
----------------------------------------------------------------------------
| Conference Identifier |
----------------------------------------------------------------------------
| MSRP Session ID=8asjdhk | Conf User ID=839ULjj | Label=iede3 |
| MSRP Session ID=38iuhds | Conf User ID=0283hHu | Label=8heus |
| MSRP Session ID=838unaH | Conf User ID=0283hHu | Label=3cnu7 |
| MSRP Session ID=djiowid | Conf User ID=ncH37Hs | Label=jd38J |
| MSRP Session ID=389hewu | Conf User ID=pakdj7H | Label=U83hd |
| MSRP Session ID=Ko03jdk | Conf User ID=pakdj7H | Label=ehy3h |
----------------------------------------------------------------------------
Figure 4: Advanced Session Association + Media Label
In Figure 4 conference user uidentifiers '0283hHu' and 'pakdj7H'
appear twice. The combination of multiple conference user
identifiers and a unique MSRP session ID enables the conference
system to clearly identify a specific MSRP instance. The
representation also includes the media label, as defined in [7],for
identification purposes. This added property, which is extracted
from the SDP media line, enables clear identification when multi SDP
media (m=) lines appear in the same SDP payload.
A client MUST include the media label attribute defined in [7] when
including multiple MSRP sessions in the same SDP payload. Even in
the simplest conferencing system, where users are allowed to enter
anonymously, the internal representation described in this section
should be observed. In this case, the conferencing system would
still internally create a conference user identifier for participant
reference purposes.
4. Basic Operations
This section provides details of the realization of the Multi-party
IM (chat) using MSRP within the context of the centralized
conferencing framework. A brief discussion and diagrams are provided
for the creating, joining and deleting a chat based conference. The
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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 IM chat.
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.
4.1. Creating a Chat Room
There are different ways to create a conference. A participant can
create a conference using call signaling means only, such as SIP and
detailed in [8]. For a conferencing client to have more flexibility
in defining the charaterisitics and capabilities of a chat based
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 5 provides an example of one client "Alice" determining the
conference blueprints available to support various types of chat
rooms for a particular conferencing system and creating a chat based
conference using 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, | +------------+|
| | chatBlueprintAConfObjID,| +-----------+ | ||
| Client |-------------------------->|Conference | |Conference ||
| | confUserID> | |Control |~~~>|Chat ||
| |<--------------------------|Server | |BlueprintA ||
| |CCP Response | | | +------------+|
+--------+ <chatResvConfObjID | | | \|/ |
confID> | | | /|\ |
| | | V |
| | | +------------+|
| | |~~~>|Conference ||
| | | |Chat ||
| | | |Reservation ||
| +-----------+ +------------+|
"Alice" | | |
+--------+ | | |
| |CCP Request <add, | V |
| | chatResvConfObjID, | +-----------+ +------------+|
| Client |-------------------------->|Conference | |Active ||
| | confID,confUserID> | |Control |~~~>|Chat ||
| |<--------------------------|Server | |Conference ||
| |CCP Response | | | +------------+|
+--------+ <chatActiveConfObjID, | | | |
confID> | +-----------+ |
+--------------------------------+
Figure 5: Client Creation of Chat room
Upon receipt of the Conference Control Protocol request for
blueprints associated with chat rooms, the conferencing system would
first authenticate "Alice" (and allocate a conference user
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identifier, if necessary) and then ensure that "Alice" has the
appropriate authority based on system policies to receive any chat
room based blueprints supported by that system. Any blueprints that
"Alice" is authorized to use are returned in a response, along with
the conference user ID.
Upon receipt of the Conference Control Protocol response containing
the blueprints, "Alice" determines which blueprint to use for the
conference to be created. "Alice" creates a conference object based
on the blueprint (i.e., clones) and modifies applicable fields, such
as membership list, topic details, 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" now creates an active chat room using that
reservation. "Alice" provides the conference information, including
the necessary conference ID, to desired participants to allow them to
join the chat room. "Alice" may also add other users to the chat
room. 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.
4.2. Joining a Chat Room
A participant can join and leave the conference using call signaling
means only, such as SIP. However, in order to perform richer
conference control a user client can implement a conference control
protocol client. By using a conference control protocol, the client
can affect its own state and the state of other participants,
depending upon policies, which may indirectly affect the state of any
of the conference participants.
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In the example in section Section 4.1, "Alice" has reserved a chat
room . "Alice" has also already joined the conference and made the
chat room active. "Alice" can either add additional participants to
the chat room or provide the conference information, including the
necessary conference ID, to desired participants and allow them to
request to join themselves. Any participants that have the authority
to manipulate the conference would receive the conference object
identifier of the active conference object in the response to their
request to join.
Figure 6 provides an example of "Bob" joining the chat room using the
conference ID provided by "Alice" (e.g., in an IM).
+--------------------------------+
| Conferencing System |
"Bob" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | | Active ||
| | Conference Object ID, | |Control |~~~>| Chat ||
+--------+ Add, "Bob" > | |Server | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Alice" | ' ' '|
+--------+ NOTIFY <"Bob"="added"> |+------------+ ' ' '|
| |<-------------------------|Notification|<~~~| ||
| Client |. . ||Service | +-------+ ||
+--------+--+ . || | |"Bob" | ||
| |<----------------------| | +-------+----+|
| Client |NOTIFY <"Bob"="added">|+------------+ |
+--------+ +--------------------------------+
"Bob"
Figure 6: Joining a chat room
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 must determine whether
"Bob" is already a user of this conferencing system or whether he is
a new user. If "Bob" is a new user for this conferencing system, a
Conference User Identifier is created for Bob. The conferencing
system must also ensure that "Bob" has the appropriate authority
based on the policies associated with that specific conference object
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to perform the operation.
Once "Bob" has been successfully added to the chat room, 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.
4.3. Deleteing a Chat Room
Depending upon the conferencing system policies and policies specific
to the chat room, the creator of the chat would typically be the
participant authorized to delete the chat room.
In the example in section Section 4.1, "Alice" has created a chat
room and provided the conference information, including the necessary
conference ID, to desired participants and allow them to request to
join themselves. "Bob" and others are participants in the chat.
Figure 6 provides an example of "Alice" later deleting this same chat
room.
+--------------------------------+
| Conferencing System |
"Alice" | +---------+--+|
+--------+ | |policies | ||
| |CCP Request < | +-----------+ +---------+ ||
| Client |-------------------------->|Conference | | Active ||
| | Conference Object ID, | |Control |~~~>| Chat ||
+--------+ Delete > | |Server | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Alice" | ' ' '|
+-------+ NOTIFY <confObjID, |+------------+ ' ' '|
| |<-------------------------||Notification|<~~~| ||
| Client| "deleted"> ||Service | +-------+ ||
+-------+--+ . || | |"Bob" | ||
| |<----------------------|| | +-------+----+|
|Client |NOTIFY<"Bob"="removed">|+------------+ |
+-------+ +--------------------------------+
"Bob"
Figure 7: Deleting a chat room
Upon receipt of the Conference Control Protocol request to "delete"
the specific chat room as identified by the conference object ID, the
conferencing system must determine whether "Alice" has the authority
to delete this conference. Since "Alice" is the creator of the
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conference, the "delete" operation is performed, with the appropriate
signalling sent to the participants.
One step in the deletion of the chat room may include notifitying the
participants (including "Bob") that they have been removed via the
Conference Notification Service.
5. Advanced Operations
This section provides details of the realization of advanced chat
features, such as sidebars and private messages, within the context
of the centralized conferencing framework. As with Section 4, 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 advance IM chat features.
5.1. Text Sidebar
The Multi-party IM using MSRP document [6] identifies the requirement
(REQ-GEN-12) to set up a sidebar conference with one or more
participants of the conference.
The concept of a 'sidebar' in an XCON compliant conference system is
fully described in the Sidebar section and related subsections within
the Conferencing Scenarios Realization section of the centralized
conferencing framework document [2]. The creation, manipulation and
deletion of sidebars for MSRP based sessions follows the same
principles.
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
implicitly linked to the parent conference object (i.e. it is not an
independent object) and is associated with the parent conference
object identifier. A conferencing system manages and enforces the
parent and appropriate localized restrictions on the sidebar
conference object (e.g., no members from outside the parent
conference instance can join, sidebar conference can not exist if
parent conference is terminated, etc.).
Figure 8 provides an example of one client "Alice" involved in active
chat conference with "Bob" and "Carol". "Alice" wants to create a
sidebar to have a side discussion with "Bob" while still receiving
the session based messaging associated with the main chat conference.
Whether the text is interleaved with the main chat or whether a
separate window is created for the sidebar is implementation
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specific. "Alice" initiates the sidebar by sending a request to the
conferencing system to create a conference chat reservation based
upon the active chat 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 the text sidebar conference is occurring.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active Chat || | |Conference ||
"Alice" | +-------+ ||
+--------+ | |"Alice"| ||
| |CCP Req <createSidebar, | +-------+ ||
| | activeChatConfObjID, | +-----------+ |"Bob" | ||
| Client |-------------------------->|Conference | +-------+ ||
| | confUserID> | |Control |~~~>|"Carol"| ||
| |<--------------------------|Server | +-------+----+|
| |CCP Response | | | | |
+--------+ <sidebarResvConfObjID, | | | | |
confID> | | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | | ||
| +-----------+ | Sidebar ||
"Alice" | | Chat ||
+--------+ | | Reservation||
| |CCP Request <update, | +-----------+ | ||
| | sidebarResvConfObjID,| | | | ||
| Client |-------------------------->| |~~~>| ||
| | confID,confUserID, | | | +------------+|
| | video=parent, | | | | |
| | audio=sidebar> | |Conference | | |
| | | |Control | V |
| | | |Server | +---------+--+|
| |CCP Response | | | |policies | ||
| |<activeChatSideConfObjID,| | | +---------+ ||
| |<--------------------------| | |Active Chat ||
+--------+ confID> | | | |Sidebar ||
| | | |Conference ||
| +-----------+ +-------+ ||
| |"Alice"| ||
"Bob" | | | ||
+--------+ NOTIFY <"Bob"=added> |+------------+ +-------+ ||
| |<-------------------------|Notification|<~~~| | ||
| Client | ||Service | |"Bob" | ||
+--------+ || | +-------+----+|
|+------------+ |
+--------------------------------+
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Figure 8: Client Creation of a Sidebar Conference
Upon receipt of the Conference Control Protocol request to "reserve"
a new sidebar chat conference, based upon the active chat conference
received in the request, the conferencing system uses the received
active chat conference to clone a conference chat 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 chat 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 text from the original conference, but
wants the text within the sidebar to be restricted to the
participants in the sidebar. "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 chat 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.
5.2. Private Message
The case of private messages can be handled as a sidebar with just
two participants, identical to the example in section Section 5.1.
The other context, referred to as whisper, in this document refers to
situations involving one time media targetted to specific user(s).
An example of a whisper would be a text message injected only to the
conference chair or to a new participant joining a conference.
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Figure 9 provides an example of one user "Alice" whose chairing a
fixed length conference with "Bob" and "Carol". The configuration is
such that only the chair is providing a warning when there is only 10
minutes left in the conference. At that time, "Alice" is moved into
a sidebar created by the conferencing system and only "Alice"
receives that text message announcing the 10 minute warning.
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+--------------------------------+
| Conferencing System |
| +---------+--+|
| |policies | ||
| +---------+ ||
| |Active Chat ||
| |Conference ||
| +-------+ ||
| |"Alice"| ||
| +-------+ ||
| +-----------+ |"Bob" | ||
| |Conference | +-------+ ||
| |Control |~~~>|"Carol"| ||
| |Server | +-------+----+|
| | | | |
| | | | |
| | | V |
| | | +---------+--+|
| | | |policies | ||
| | |~~~>+---------+ ||
| | | | ||
| +-----------+ |Sidebar Chat||
"Alice" | |Conference ||
+--------+ NOTIFY <"Alice"=added, |+------------+ +-------+ ||
| |<-------------------------|Notification| | | ||
| Client | activeChatSideConfObjID,||Service |<~~~|"Alice"| ||
+--------+ confID > || | +-------+----+|
|+------------+ |
~~~Text message delivered to "Alice"~~~
| +-----------+ |
| |Conference | |
| |Control | |
| |Server | |
| | | |
| | | \---------+--/|
| | | |\ /||
| | |~~~>+ \ / ||
| | | | \ / ||
| +-----------+ |Sid\bar /hat||
"Alice" | |Conf\re/ce ||
+--------+ NOTIFY <"Alice"=removed,|+------------+ +-----\/+ ||
| |<-------------------------|Notification|<~~~| /\| ||
| Client | activeChatSideConfObjID,||Service | |"Ali/ce\ ||
+--------+ confID > || | +---/---+\---+|
|+------------+ / \ |
+--------------------------------+
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Figure 9: Whisper
When the conferencing system determines that there is only 10 minutes
left in the conference which "Alice" is chairing, rather than
creating a reservation as was done for the sidebar in Section 5.1,
the conferencing system directly creates an active chat sidebar
conference, based on the active chat 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 chat 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 chat sidebar conference, the
text announcement 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 text messages from the main conference.
Upon delivery of the text 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.
6. Security Considerations
As discussed in the XCON 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 in the context of MSRP conferencing would include 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 attempting to create conferences it is not allowed to
create.
Since this solution makes use of existing protocols (e.g. MSRP,
Conference Control Protocol, SIP), it also re-uses the security
solutions for those protocols and the associated authorization
mechanisms. There are security issues associated with the
authorization to specifically perform the MSRP conferencing
capability. Since this solution makes use of the XCON framework, it
makes use of the policy associated with the conference object to
ensure that only authorized entities are able to manipulate the data
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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 XCON Framework.
7. Acknowledgements
The authors would like to thank Miguel Garcia-Martin for his comments
on this document and discussion of the solution options.
8. References
8.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[2] Barnes, M., "A Framework and Data Model for Centralized
Conferencing", draft-ietf-xcon-framework-07 (work in progress),
January 2007.
[3] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol (SIP)", RFC 4353, February 2006.
[4] Campbell, B., "The Message Session Relay Protocol",
draft-ietf-simple-message-sessions-18 (work in progress),
December 2006.
[5] Jennings, C., "Relay Extensions for the Message Sessions Relay
Protocol (MSRP)", draft-ietf-simple-msrp-relays-10 (work in
progress), December 2006.
[6] Niemi, A. and M. Garcia-Martin, "Multi-party Instant Message
(IM) Sessions Using the Message Session Relay Protocol (MSRP)",
draft-niemi-simple-chat-05 (work in progress), June 2006.
[7] Levin, O. and G. Camarillo, "The Session Description Protocol
(SDP) Label Attribute", RFC 4574, August 2006.
[8] Johnston, A. and O. Levin, "Session Initiation Protocol (SIP)
Call Control - Conferencing for User Agents", BCP 119, RFC 4579,
August 2006.
[9] Boulton, C. and M. Barnes, "A User Identifier for Centralized
Conferencing (XCON)", draft-boulton-xcon-userid-00 (work in
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progress), October 2006.
Authors' Addresses
Chris Boulton
Ubiquity Software Corporation
Building 3
Wern Fawr Lane
St Mellons
Cardiff, South Wales CF3 5EA
Email: cboulton@ubiquitysoftware.com
Mary Barnes
Nortel
2201 Lakeside Blvd
Richardson, TX
Email: mary.barnes@nortel.com
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