One document matched: draft-boulton-xcon-msrp-conferencing-03.txt
Differences from draft-boulton-xcon-msrp-conferencing-02.txt
XCON Working Group C. Boulton
Internet-Draft Ubiquity Software Corporation
Expires: December 28, 2006 M. Barnes
Nortel
June 26, 2006
Centralized Conferencing (XCON) Using the Message Session Relay
Protocol (MSRP)
draft-boulton-xcon-msrp-conferencing-03
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Copyright (C) The Internet Society (2006).
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. Protocol and Framework Overview . . . . . . . . . . . . . . . 3
3.1. Framework operations . . . . . . . . . . . . . . . . . . . 5
4. Text Sidebar . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Private Message . . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
Intellectual Property and Copyright Statements . . . . . . . . . . 12
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1. Introduction
A Centralized Conference as defined by the "A Framework and Data
Model for Centralized Conferencing" (XCON Framework) [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]. 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.
[Editors Note: This document is still in early stages of development
and is intended to invoke discussion. It is not intended to provide
exact solutions at his stage, but rather explores a potential
approach to a solution.]
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 XCON 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, RFC 2119 [1] and indicate requirement levels for
compliant implementations.
3. Protocol and Framework 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.
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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
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 XCON and SIPPING conferencing frameworks. The solution
proposal in this document, as described in Section 3.1, meets many of
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the requirements identified in the requirements document for
multiparty MSRP [6]. Some of the requirements introduce additional
concepts that are not specifically addressed within the context of
the XCON framework or associated protocol documents, however, they
are general enough that they should be addressed either by the XCON
framework or possibly even within the context of a more general SIP
solution, such as the notion of nicknames. [Editor's Note: Further
elaboration of how this solution proposal meets those requirements is
likely required, although a simple checklist in the appendix, or
inline references to those requirements (e.g. ...solution
text...(REQ-GEN-10) might suffice. ]
A basic solution for IM chat sessions, also meeting the Multiparty
MSRP requirements, is documented in [7]. 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 [7] doesn't explicitly take advantage of the XCON FW data
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 XCON FW model for
sidebars and private conferences and manipulation of the conference
data.
3.1. Framework operations
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
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 XCON Conference 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.
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---------------------------------------------
| Conference Identifier |
---------------------------------------------
| MSRP Session ID=8asjdhk |
| MSRP Session ID=38iuhds |
| MSRP Session ID=djiowid |
| MSRP Session ID=389hewu |
---------------------------------------------
Figure 2: Simple Session Association
The XCON Framework[3] introduces the concept of a conference user
identifier, which is also defined in [TODO]. 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
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 [8], to
maintain the internal conference association. An example is
illustrated in Figure 4.
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----------------------------------------------------------------------------
| 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 [8],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.
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
XCON defined 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 XCON Framework [2]. A client
MUST include the media label attribute defined in [8] 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. Text Sidebar
The Session Based Messaging Conferencing requirements document [6]
identifies the requirement (REQ-GEN-12) to set up a sidebar
conference with one or more participants of the conference.
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The concept of a 'sidebar' in an XCON compliant conference system is
fully described in section 7.3 of the XCON Framework document [2].
The creation, manipulation and deletion of sidebars for MSRP based
sessions has the same principles.
Creating a sidebar representation for MSRP would have internal
ramifications in a conferencing system. It would involve the
creation of a cloned conference object that associates the
appropriate conference users. This would then involve a new session
being established to convey the sidebar information. Further detail
on this mechanism is provided in the sidebar section of the XCON FW
document.
[Editors note: Lots more detail to insert once fundamentals are
agreed, including adding an example showing the use of sidebars in
the context of MSRP.]
5. Private Message
[Editors note: This section needs updating to align with updates to
niemi-simple-chat in terms of providing the equivalent functionality
in the context of the XCON FW.]
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
to access the capabilities. This solution also makes use of the
privacy and security of the identity of a user in the conference, as
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discussed in the XCON Framework.
[Editor's Note: Are there any security issues unique to MSRP
conferencing that aren't covered by based MSRP, MSRP relays or the
conferencing 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-04 (work in progress),
June 2006.
[3] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol",
draft-ietf-sipping-conferencing-framework-05 (work in progress),
May 2005.
[4] Campbell, B., "The Message Session Relay Protocol",
draft-ietf-simple-message-sessions-14 (work in progress),
February 2006.
[5] Jennings, C., "Relay Extensions for the Message Sessions Relay
Protocol (MSRP)", draft-ietf-simple-msrp-relays-07 (work in
progress), February 2006.
[6] Niemi, A. and M. Garcia-Martin, "Requirements for Private
Messaging in Centralized Conference Environments",
draft-garcia-xcon-private-messaging-reqs-01 (work in progress),
June 2005.
[7] Niemi, A. and M. Garcia-Martin, "Multi-party Instant Message
(IM) Sessions Using the Message Session Relay Protocol (MSRP)",
draft-niemi-simple-chat-04 (work in progress), February 2006.
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[8] Levin, O. and G. Camarillo, "The SDP (Session Description
Protocol) Label Attribute", draft-ietf-mmusic-sdp-media-label-01
(work in progress), January 2005.
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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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