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 (arun.prasath@samsung.com), R.Pradeep (pradeep.r@samsung.com) and Dwaraka

Sreevatsa (srevatsa@samsung.com), 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