[ieee 2007 international conference on ip multimedia subsystem architecture and applications (imsaa)...
TRANSCRIPT
Abstract— With the increasing proliferation of mobile devices
with advanced capabilities and coupled with increasing
deployments of IMS networks that combine interactive
multiparty communications with quality of service features,
multimedia conferencing is a service that many end-users will
now be able to enjoy. In this paper we propose new techniques to
be adapted while initiating a conference in order to have enriched
user experience and also optimized utilization of network
resources during Conference setup. Specifically we propose two
methods, Presence Based Instant Conference and Ordered Invite,
for initiating conference which the conferencing server applies
before initiating the conference.
I. INTRODUCTION
conference is an association of user agents (i.e.,
conference participants) with a central point (i.e., a
Conference Server), where the Server has direct peer-
wise relationships with the participants by maintaining a
separate dialog with each. The Conference Server has abilities
to host SIP conferences including their creation, maintenance,
and manipulation using SIP call control means. The
conference server maintains the correlation among
conference's dialogs internally. The media sessions are
established between the conference server and each one of the
participants. The media processing (e.g., mixing) can be
performed by the conference server.
The Conference Policy contains the rules that guide the
operation of the conference server. The rules can be simple,
such as an access list that defines the set of allowed
participants in a conference. The rules can also be incredibly
complex, specifying time-of-day-based rules on participation,
conditional on the presence of other participants. The
conference policy can be manipulated using web applications
or voice applications.
Section II of this document describes the existing conference
techniques. Section III proposes the different methods for
initiating a conference. Section IV concludes with the
advantages of the proposed conference initiation methods.
II. EXISTING CONFERENCE TECHNIQUES
There are many ways in which a conference can be created.
The creation of a conference actually constructs several
elements all at the same time. It results in the creation of a
focus and a conference policy. It also results in the
construction of a conference URI, which uniquely identifies
the focus. Since the conference URI needs to be unique, the
conference server is responsible for guaranteeing that
uniqueness. When conference policy is created, it is
established with default rules that are implementation-
dependent. If the creator of the conference wishes to change
those rules, they would do so using a SIP/non-SIP mechanism.
SIP can be used to create conferences hosted in a
conference server by sending an INVITE to a conferencing
application that would automatically create a new conference
and then place user into it. Third party additions with SIP are
done using REFER. The client can send a REFER request to
the participant, asking them to send an INVITE request to the
conference URI. Additionally, the client can send a REFER
request to the focus, asking it to send an INVITE to the
participant. The latter technique has the benefit of allowing a
client to add a conference-unaware participant that does not
support the REFER method. But both techniques require the
conference creator to invite the participant directly or
indirectly after the conference is created. Some different
techniques of initiating a conference are described in the
following section.
III. TECHNIQUES FOR IMPROVING CONFERENCE INITIATION
This document discusses two different ways of initiating a
conference by a user. The Presence based Instant Conference
deals with policy of creating the conference based on presence
status of the participants. The Ordered Invite deals with the
policy of presence of some pre-determined participants to be
part of conference for the conference to take place.
A. Presence Based Instant Conferencing
Presence based Instant Conference creates a conference
instantly with all the available participants for the conference.
The Conference Server is involved in identifying the status of
the requested participants for the conference and its creation.
The conference initiator needs to send the list of participants
along with the request for conference creation. The list can be
either a Buddy list or a Group list. The conference is
established with all the available participants.
Buddy List:
The conference creator requests for a conference with a buddy
list in the request. The buddy list contains a list of users who
need to be invited to the conference by the Conference Server
based on their presence status.
Group List:
Enriched Conference
R.Arunprasath ([email protected]), R.Pradeep ([email protected]) and Dwaraka
Sreevatsa ([email protected]), Samsung India Software Operations Pvt. Ltd
A
The conference creator requests for a conference with a group
list in the request. The group list contains a list of groups who
need to be invited to the conference by the Conference Server
based on their presence status. The members of the group and
their presence status are retrieved from the Resource List
Server (RLS) by the Conference Server.
Figure 1 : Presence Based Instant Conference
In the Presence Based Instant conference the Conference
Server acts as a Watcher and subscribes to the Presence
Information of the conference participants. When initiating a
conference the conference server before inviting the users,
would subscribe to the presence status of all the users. When
their presence status is online they would be invited
immediately to join the conference. The conference server
keeps checking the status of the users who are offline or whose
communication status is closed and once their status changes
to online it immediately sends invitation to them for joining
the conference. By this mechanism unnecessary INVITE
traffic is reduced significantly. The above figure shows the
flow involved in the Presence Based Instant Conference.
Sample Message Flow:
The message flow diagram below shows the detailed flow
involved in the creation of Presence Based instant conference.
Conference
ServerCSCF
Participant
(B)
2.INVITE
1. INVITE
User
(A)
INVITE (B)
3.200 OK
A, B and C are in conference
Presence
Server
5.SUBSCRIBE(B)
200OK
7. NOTIFY (B)
200OK
11. 200 OK
200 OK
8. INVITE(B)
4.200 OK
6. SUBSCRIBE(C)
200OK
9. NOTIFY (C)
.200OK
Participant
(C)
10. INVITE(C)
.INVITE (C)
12. 200 OK
200 OK
A joins conference
B joins conference
Instant Conference : User A invites Participant B & Participant
C to join a conference
1. User A generates a initial INVITE request with a conference
factory URI and a list of participants for the conference.
2. CSCF on receiving the INVITE, forwards it to Conference
Server.
3. Conference Server accepts user’s request and creates the
conference.
4. User A joins the conference.
5. Conference Server sends Subscribe to Presence Server to
know the status of Participant A.
6. Conference Server sends Subscribe to Presence Server to
know the status of Participant B.
7. Presence Server notifies Conference Server, the status of
Participant A.
8. If Participant status is “Available”, Conference Server
invites Participant A to join the conference.
9. Presence Server notifies Conference Server, the status of
Participant B.
10. If Participant status is “Available”, Conference Server
invites Participant B to join the conference.
11. Participant A accepts and joins the conference.
12. Participant B accepts and joins the conference.
IMS CORE
(CSCF)
Presence
Server
Conference
server
Participant
B (Online)
Participant
C (Offline)
User (A)
RLS
Conference
ServerCSCF
Participant
(B)
User
(A)
A, B and C are in conference
Presence
Server
2. NOTIFY (C)
.200OK
Participant
(C)
10. INVITE(C)
3..INVITE (C)
4. 200 OK
200 OK
A and B are in conference
1, PUBLISH
PUBLISH
Participant C joins a ongoing conference
Pre-Condition: User A and Participant B are in conference as
Participant C was not invited to join the conference due to his
non-availability.
1. Participant C sends a PUBLISH to Presence Server
indicating his availability.
2. Presence Server notifies Conference Server, the
availability status of Participant C.
3. Conference Server invites Participant C to join the
conference.
4. Participant C accepts and joins the conference.
B. Ordered Invite
Currently while establishing the session for group
communication, server will send the initial INVITE to all users
simultaneously. Note all these INVITEs sent to individual
users will be independent of each other. Currently user can
only mention the users who need to be invited in body of
INVITE request in case of the ad-hoc session, and in case of
pre-arranged group user will maintain the group information
into the server. This is the current state of art for the
establishing the group communication. With the existing
mechanism the user cannot mention priorities using which the
conference server should fork out INVITE requests and also
some conditions for setting up the conference. Following are
some use cases which substantiate the need for Ordered Invite:
1. user A wants to establish a group communication
with user B, C, D, E, and G. He wants to set up a
session only when user B accept the invitation.
2. user A wants to set up a session and if user C accepts
the invitation then only send INVITE to user D other
wise don’t send invitation to user D.
If the user is not given a method where in he/she can set some
priorities and conditions for conference establishment it is a
pain for the conference creator to track the conference
establishment and to decide whether to continue or not. This is
a waste of time in many cases. Especially for the applications
like POC where session initiation time is important unwanted
establish session can waste time for user and resource or
charges for a user. It is very beneficial when if user can specify
some rules while establishing a session.
Figure 2 : Ordered Invite – Conference not created because of
Policy Failure
The diagram above shows that conference creation fails
because one of the required particiapnts failed to join. So the
SIP INVITE is not sent to other users.
Figure 3: Ordered Invite – Conference Created when required
condition is met
The diagram above shows B anc C are invited for the
conference since A accepted to join the conference.
Sample Message Flow:
The following sequence diagram shows the message flow for
the case where the user A wants to invite user C to the
conference only if User B accepts the conference invitation
Conference
ServerCSCF
Participant
(B)
2.INVITE
1. INVITE
User
(A)
5. INVITE (B)
3.200 OK
A, B and C are in conference
Presence
Server
6. 200 OK
6. 200 OK
5. INVITE(B)
4.200 OK
Participant
(C)
7. INVITE(C)
7. INVITE (C)
8. 200 OK
8. 200 OK
A joins conference
B joins conference
Conference Server sends invite to C
only after B has joined conference
Ordered Invite
1. User A generates a initial INVITE request with a
conference factory URI and a list of users for the
conference including the rule to invite. In this
example, User A includes the rule to invite User C
that “Invite User C only if User B accepts the
invitation to join the conference”.
2. CSCF on receiving the INVITE, forwards it to
Conference Server.
3. Conference Server accepts user’s request, stores the
rules to invite other users and creates the conference.
4. User A joins the conference.
5. Conference Server applies the rule “Invite User C
only if User B accepts the invitation to join the
conference” and hence invites User B first to join the
conference.
6. User B accepts the invitation and joins the
conference.
7. Since User B joined the conference, Conference
Server sends the invitation to User C.
8. User C accepts and joins the conference.
IV. CONCLUSION
Advantages of Presence Based Instant conference:
Instant conference is faster compared to AdHoc
conference, in which User invites a participant to
a conference by sending a REFER request to the
participant directly or to the Conference Server.
User need not wait for the conference to be
established to invite other participants.
Conference Server invites participants who are
available ONLY to join the conference.
User can invite members of different groups at
once.
Advantages of Ordered Invite during conference:
This will help user to set priorities for invitation
User can set some rules for sending the invitation
so that this will avoid unnecessary invitations
This also helps in avoiding the unnecessary
session setup, when there is no need for session
set up if particular user reject the invitation
ACKNOWLEDGMENT
We would like to thank Dr.Raghunandan Sreenath (Head of
ATD), and Mr.J.Venkateswar, Samsung India Software
Operations Pvt. Ltd, for giving us an opportunity to present
this paper.
REFERENCES
[1] 3GPP TS 22.229 : “Internet Protocol (IP) multimedia call control
protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3”, 3GPP TS 24.229, Release 6, 2005
[2] J. Rosenberg, “A Framework for Conferencing with the Session Initiation Protocol(SIP), RFC 4353, February 2006
[3] O. Levin, R. Even, “High-Level Requirements for Tightly Coupled SIP Conferencing”, RFC 4245, November 2005
[4] A. Johnston, O. Levin, “Session Initiation Protocol (SIP) Call Control – Conferencing for User Agents, RFC 4579, August 2006
[5] J. Rosenberg, “A Presence Event Package for the Session Initiation Protocol (SIP)”, RFC 3856, August 2004