Real Time Communication and Collaboration◆招待論文◆

Real Time Communication
and Collaboration

実時間コミュニケーションとコラボレーション
Sinchai Kamolphiwong
Associate Professor, Center for Network Research (CNR),
Department of Computer Engineering, Faculty of Engineering, Prince of Songkla University
シンチャイ カモルピワォン
ソンクラーナカリン大学工学部准教授

Thossaporn Kamolphiwong
Associate Professor, Center for Network Research (CNR),
Department of Computer Engineering, Faculty of Engineering, Prince of Songkla University
トサポン カモルピワォン
ソンクラーナカリン大学工学部准教授

Suthon Sae-Wong
Lecturer, Center for Network Research (CNR),
Department of Computer Engineering, Faculty of Engineering, Prince of Songkla University
ストン サエ・ワォン
ソンクラーナカリン大学工学部専任講師

In this paper, we first present some proposed extensions based on SIP (Session Initiation Protocol)
conference scenarios. We then show how to use such extensions to enhance interactive distance learning(IDL) applications as an example. Our work describes some enhancements of conference scenarios
based on SIP. The system architecture to support such scenarios as well as signal flows are presented.
Some flow parameters are given, to show real deployment possibility. We have proposed two additional
components to enhance conference features: Conference Manager Server (CMS) and Conference
Repository (CR). We have deployed these scenarios for SIP based e-learning applications. We haveshown some e-learning scenarios when interactive communications are needed, for example, classscheduled learning, class mate group finding. In addition, other rich features can be added, e.g. sharing
on-line objects and documents in real-time, virtual interactive white-board, and multimedia recorder.
We have proposed the implementation architecture, some main features are described. We discussed
for some future challenging works: P2P based SIP may be adopted. Moreover, converging to UCC(Unified Communication and Collaboration), as well as working on multi-platform and multi-devices
are concerned.
本稿では、まず、SIP (Session Initiation Protocol) の会議通話向けの拡張を提案した。次に、この拡張の利用例として、enhance interactive distance learning (IDL) アプリケーションにおける利用例を示した。本研究では、会議向けの拡張のため、Conference Manager Server (CMS) と Conference
Repository (CR) の２つのコンポーネントの追加を提案し、E ラーニング用のアプリケーションへの適用を検討した。E ラーニングにおいては、受講者間の会話など、インタラクティブなコミュニ
ケーションが必要な場合がある。また、教材のリアルタイム共有、黒板の共有、マルチメディア録
音機能の利用も考えられる。本研究では、これらの機能の実装方針を提案した。
Keywords: SIP, Interactive communication, Distance Learning, IDL, VoIPKEIO SFC JOURNAL Vol.8 No.2 2008

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some limitations, e.g., high overhead and transaction

1 Introduction
Conference systems based on the Internet

modification.

infrastructure are widely deployed, in both com-

To make a conference system working on a real

mercial and free services. The most widely usedenvironment with SIP as the protocol, reusing thestandards are H.323[1]

and SIP (Session Initiation

most existing protocols is necessary. This will benefit

Protocol) . Both of them are developed to support

from: no interoperability issues, mature and provenfor a group conference system. H.323 is highlighted(of existing) protocols, and gain all benefits what

to load balancing and management issue. In contrast,

existing protocols have and provide. However, there

SIP is highlighted to light-weighted flexible andis a number of alternative ways to re-use existing

extensible issues. Recently, SIP is more widely

protocols. Some of them, for example, are“Non-SIP[2]

used than H.323[3] [4]. However, SIP may have some

Related Protocols”- e.g. XCAP, LDAP, and MSCML.

difficulties for legacy conference, e.g., a conference

Those of Non-SIP Protocols are engineering

manager.

development issues, depending on their purposes

When we figure out the whole conference

and deployed scenarios.

system, starting at the beginning state, we have

In this paper, we propose enhancements of IP

found that it is hard to find a complete system in

Conference scenarios based on Session Initiation

any literatures. In[12], some parts are left out, e.g.,

Protocol (SIP). Our works have described somea conference mixer. A new protocol, XCCP, which

enhanced conference scenarios based on SIP, as wellis based on XML, was created but it is not suitableas system architecture to support such scenarios.

for real deployment when such service needs to be

A sample flow and some flow parameters, aninstalled on all UAs (User Agent). SOAP (Simple

implementation based on this framework are shown

Object Access Protocol) was proposed to be used

in a real practice. This paper also discusses someas a conference policy control protocol[13]

but it hasfeatures for real-time interactive communications.

Figure 1 XCON Conference Framework

Real Time Communication and Collaboration

This paper is organized as follows: Section 2

3 System Architecture Designpresents some related work and standard reference

3.1 Proposed system architecture

models. System architecture design and signal flows

In this section, we propose the system archi-

are described in section 3. System performance

tecture for a SIP based real-time communication

discussion is made in Section 4. Section 5 presentswith collaboration capability. In our framework [17],the future works with some challenging issues.

we have proposed two main components as shown

Conclusion is made in Section 6.

in Figure 2: Conference Manager Server (CMS) and
Conference Repository (CR). Conference Server

2 Related Works(CS) is equivalent to a Focus in XCON framework [7].

XCON [7] and SIPPING [6] working groups have

Focus is addressed to be the heart component of the[5].

system in XCON to support more complex media

It consists of 5 important components as shown inmanipulations and enhanced conferencing features

Figure 1.

as well as the conference information (e.g. specificdefined a conference framework for SIP protocol

SIPPING framework uses SIP protocol as themedia mixing details, available floor controls). CMS

signaling protocol to establish, tear down and modify

is used for managing information and conference

conferences, while XCON framework does notpolicy before starting a conference. CMS can initiate

depend on any particular signaling protocols. Theya conference by using SIP INVITE to a mixer, using

focus on a standardized suite of protocols for tightly-

SIP REFER for every pre-configured participant tocoupled multimedia conferences. However, XCON

join a conference. The signal flow of the conference

framework is referred by SIPPING framework.

manager is described in the next section. CMS

Although XCON and SIPPING conferencing

does not try to replace any operations of SIP Focus.

framework are widely adopted to implement a

Since Focus is used when a conference session isconference system using SIP, some parts of thecreated while CMS is used to manager a conference

framework are not clearly described, e.g., mechanism

in both before and after conferences, even during a

to configure or manage a conference policy.

conference session. This means that CMS works with

Our work presents a SIP based conference

Focus to help and handle complicated conference

system designed for a practical propose. We design

scenarios, to make it simpler. Moreover, CMS[6]

the conference system based on RFC 4597 , whichhandles more protocols, e.g. XCAP, LDAP, and SIP,

discusses basic and advance conference scenarios

due to its functions (while Focus understands only

for SIP protocol, and RFC 4579

[7]

which discusses a

SIP signals). In addition, the Conference Repository

conference call control for SIP user agent. Our firstwhich store information of participants is managed

proposal was IDLP (Interactive Distance Learning

by CMS.

Protocol) that was presented in[16]. The extension

In our scenarios, a conference can be either open

where more existing(public) or closed (private) conference. Conference

protocols are reused, e.g. LDAP (Lightweight

Repository (CR), which stores conference information

Directory Access Protocol), MSCML (Media Server(e.g. conference URI, type of conference) is the place

Control Markup Language), XCAP (Extensible

to find such conference information, for example a

Markup Language). Furthermore, how to deal withpublic conference can be found by anonymous users

mobility feature e.g., mobile e-learning is presented

while a private conference can only be found by

scheme has been shown inin our previous work[17][18][19].

authenticated users. This mechanism can be done by

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Figure 2 Proposed SIP based conference architecture

Figure 3 Group finding scenario

10Real Time Communication and Collaboration

・Join the given the conference URI. User sends

using conference descriptions and LDAP.
In this framework design[17], we have shown

an INVITE request to join the conference basedsome details and signal flows on how to deal withon the conference information (Conference URI).

extended conferences scenarios, for example, justconferencing (a few clicks to conference), group

Approach 2: using HTTP

finding (a few click to create and reach the group),

・Use search function via web application.

and conference scheduling. Based on the proposed

・Click on the link to the Conference URI.

architecture, we will show only one sample scenario,

・CMS initiates an invite conference. CMS willi.e., group finding, as shown in Figure 3. It shows

send REFER request to Focus.
・The conference server consults the policy server

how to search the conference information. This
will allow users to find conferences of their interest

whether the participant can join.
・Participant then can join the conference.

without being asked to sign-in. There are two
approaches as follows:

Figure 4 shows an example of a conference

Approach 1: using LDAP

group finding using HTTP signaling flows. A

・ Search entries in the conference repository.

User Agent (UA) queries a Conf-ID URI from theUser uses LDAP to query conference information

Conference Manager using HTTP request F1. Thenfrom the Conference Repository. The results are

the Conference Manager answers HTTP response F2

the conference URIs.

with Conf-ID to the UA. The UA sends HTTP request

Figure 4 Group finding signal flow using HTTP

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Figure 5 Group finding signal flow using LDAP

F3 to the Conference Manager. When the Conference

Mixer sends 200 (OK) to response. The ConferenceManager receives HTTP request F3, it sends INVITE

Server is ready for conferencing.

request F4 containing a conference information to
the Conference Server for establishing conference.

3.2 System development

The Conference Server uses XCAP PUT to store

Based on our design framework, we developed

conference information in the Policy Server. Afterthe prototype software, named IDL (Interactivethat the Conference Server sends INVITE request

Distance Learning). Some important features are:containing Contact header field with parameter isconference facility, interactive white board, on-line

Focus to the UA. After that system is ready for thechat, file transfer and sharing, real-time presentation,

conferencing.

and multimedia recorder. Figure 6 shows ourdevelopment architecture [20]. They are:Figure 5 shows an example of group finding
using LDAP signal flow. A UA queries a Conf-ID
URI from the Conference Repository using LDAP・Conference Manager is the heart component to

F1. The Conference Repository answers with LDAP

manage a conference, for example, to create a

Acknowledge containing Conf-ID URI. The UA sends

conference, to maintain a contact list.

INVITE method F3 to Conference Server for initialing

・Conference UI is a main part of showing eachthe conference. The Conference Server replies

conference information and GUI. Our idea iswith 180 (Ringing) response. Then the Conference

the Conference UI is independent from theServer requests the Mixer using INVITE request

Conference Manager, to allow GUI layout forF5 containing MSCML data for specific Mixer. The

skin changing.

12Real Time Communication and Collaboration

・Component is a software module for each

IDL’s presentation layer (Figure 6). All participants

function under Component Manager. There arecan share the white board as a single entity. All2 types of the component:

documents, e.g., PowerPoint, PDF, can be brought- Component is the module to handle com-

to the white-board as an object for presentation. Any

mands and events.

actions, such as drawing lines or objects, can be- Visual component is the same as theshared among all participants in real time. A policy

component with the Conference UI inter-may be used for sharing objects, for example, only

action.

object owner can edit such object. To make objects

・Service is the common service elements of IDL,

independent, the objects are drawn on anotherfor example, doing a file transfer. We developed

layer, on top of the presentation layer, so called

the service layer where these components“transparency”. One presentation page may havecan be shared and re-used by higher service

several transparencies, so called“3D-transparency”.

components.

Figure 7 shows a sample GUI of the interactive whiteboard.

When interactive communication is concerned,

In our implementation, the video conference canproviding services to serve this requirement is aselect its source from multiple sources. The video ischallenge. The interactive white board (similar to aconsidered as a media stream, and all video sources

virtual white-bard with real-time interaction between

that have the same behavior should be able to use

participants) is such the tool needed, appeared on

this session. For example, conference participants

Figure 6 Interactive Distance Learning (IDL) Architecture

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should be able to switch between USB camera, IP

usage, a special tool is needed (considering that it iscamera, and any video files, such as MPEG or WAV

a slow moving screen).

files. IDL treats all of them as the same media source.

IDL can create a conference in two ways,

Some commercial software allow to share a working

as shown in Figure 9, using a central mixer (fordesktop, and this can also be treated as the same

voice and video), and mixerless. When creating a

media source. However, in order to reduce bandwidth

conference using a central mixer, media streams (e.g.,

Figure 7 A sample GUI of interactive white-board

Figure 8 Input sources can be re-directed to other multimedia source.
The sample picture shows the input source is from a movie.

14Real Time Communication and Collaboration

voice and video) from all participants are sent to thefrom other participants directly. The main benefit tomixer. Mixed stream is sent back to all participants

this scenario is there is no need for voice and video

via multicast protocol. This method will reduce themixers; no single of failure. However, this scenario

consumed bandwidth. However scalability is a big

consumes more bandwidth than the former. It isissue due to a performance of a mixer, and it is asuitable for a small group of conference. We note

single point of failure. Alternatively, IDL can createthat this model can be extended to Peer to Peera conference without using a mixer. In this way,

conference in the future.

each node sends and receives media streams to and

(a)

(b)
Figure 9 Two conference modes can be made: (a) using a central mixer, (b) mixerless

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Another proposed component to enhance ourvideo stream. The most advantageous feature of our

features is the Multimedia Recorder and Player

prototype is it allows us to edit, insert, and delete(M-RP). The recorder is considered as a SIP client,such recorded stream any time, for example whento reduce the system complexity. We use standard

playing back we are able to move all objects freely,

SIP signals for this design purpose. This will gain

to re-produce a new presentation. The proposed

the benefit that the recorder can be any clients ofcomponents are shown in Figure 10.

conference participant. This means that there can be
many recorders, and there is no need to specify to any

4 System Performance Discussion

particular clients. In this case, the source information,

In communication system, to connect both end

such as PowerPoint files, PDF files, and video

parties, there are three main steps: (1) connection

streams, are stored together with drawing objects

establishment, (2) media flow, and (3) connection

drawn by conference participations on the interactive

tear down, as shown in Figure 10. After a connection

whiteboard, as well as synchronized actions (events/

is established, media flows (e.g. voice and video) are

actions created by conference participations, andexchanged. SIP has been involved on step 1 and 3

handled by the action synchronizer). The system

which describes a procedure of creating a connection,

does not record all media sources into a single

terminal capability exchanging, and finally, how to

Figure 10 Multimedia Recorder (MR) components

16Real Time Communication and Collaboration

terminal a connection. Some mobility issues are also

SIP has been heavily investigated and widelyconcerned by the connection establishment, e.g.

deployed. There are research on the performance. We notedof SIP server [22], security [23], 3G and beyond [24][25].

in [29], hand-over may be done separately between

It seems that SIP performs well in most cases in

MIPv6 and SIP applications. In most cases, hand-terms of light overhead, simplicity, less processing

over by SIP applications directly perform faster but

power, a large number of call handling, real timecreate more complexity. Less expensive overhead,communication signal handling. We may conclude

however, for a hand-over mechanism for a mobility

that SIP is a good signaling protocol to support a wide

node regardless of application capability has beenvariety of communications. It can create rich features

performance issues during hand-overproposed

[29]

[30]

of multimedia communications.

.

Regarding to step 2 in Figure 11, the media
flow, all media stream are exchanged in this step.
When dealing with interactive communications,the main performance issues are: low delay, packet
lost toleration, and less bandwidth consume.
For low delay, it means that low end-to-end timedelay is preferred to allow fast actions between allparties. Packet lost toleration means conversationis still maintained in some good quality event

Figure 11 Three main steps of creating a communication:
channel establishment, media flow, and teardown

bandwidth is fluctuated. A number of voice andFigure 12 MPEG 4 throughput change when using media flow control mechanisms

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video codec has been proposed, well studied anda number of literatures proposing P2P based

deployed. The performance does not only depend

SIP. In our on-going work, we will describe theon voice and video codec performance but alsoarchitecture designed to construct P2P network[27]

collaborating with the existing traditional SIP

shows MPEG 4 throughput change when using

for conferencing system [19] . Comparing tomedia flow control mechanisms, where CNR is ourothers, our proposed scheme is more attractive

proposed scheme. The performance also depends

in terms of scalability (e.g. based on pure

on a network transport mechanisms, e.g. RTP (RealP2P), interoperability with traditional SIP, asTime Transport Protocol), STCP (Stream Transport

well as interactive communication approacha flow control mechanism

Control Protocol)[31]

Control Protocol)[32][26][28]. Figure 12, DCCP (Datagram Congestion

for all SIP clients (simultaneously interactive. The situation is more hardercommunications). However, media flow design isto handle when it is a multi-point communications

still a big issue when real-time communication isespecially when a call party is a mobile node.

concerned. Moreover, security in P2P is still an

In conclusion, this paper addresses a singling

issue.

capability design to create a rich features of・Convergence of communication services

communications.

We are extending this work to UCC (Unified

5 Future Works

Communication and Collaboration). UCC is

The following topics are expected to carry out inthe integration of all kinds of communications

our on- going works:

into one single service. We consider IDL as aparticular application of UCC. Based on our・P2P based SIP Conference

recently work, more features and services will be

P2P (Peer-to-Peer) based SIP VoIP is anadded, for example, we will allow a regular SIP

alternative approach proposed recently. Most ofphone system to call in, and it may be describedtoday implementations are using the traditional

as passive or active participants. Voice mail box

SIP conference which is a centralized approach,as well as a part of CRM (Customer Relationshipwhile P2P is a de-centralized system. There isManagement) will be added.

Table 1 Comparisons of P2P SIP-based features
Reference

Registration & Lookup

CallManagement

ConferenceManagement

Realtime Media

Non-realtime
Media

[31]

SIP and P2P-SIP simultaneously

P2P-SIP

N/A−

P2P-SIP[34]

P2P-SIP

P2P-SIP

−

−

−

[35]

SIP and P2P-SIP simultaneously

P2P-SIP

−

−

−

[36]

P2P-SIP

P2P-SIP

−

−

−

[37]

P2P

SIP

−

−

−

[38]

N/A

N/A

N/A

ALM

−

[39]

P2P-SIP

P2P-SIP−−−

Proposed

SIP

SIP

P2P-SIP

ALM

P2P-SIP

18

Real Time Communication and Collaboration

・Working on multiplatform and multi-devices for

Acknowledgement

ubiquitous application needs to work on seamlessThis work was partly supported byaccess in any-where and any-time. There are・Multimedia Architecture and Applications Basedchallenging issues need to be solved especiallyon SIP Project (MySIP), STIC-Asia Program 2006.

when dealing with multimedia communications,・Faculty of Engineering, Prince of Songkla

e.g., bandwidth limitation and fluctuation,

University, Hat-Yai, Thailand.
・UniNet, Commission of Higher Education,

bandwidth mis-match, device capability (e.g.
display, computer power, energy). For example,

Ministry of Education, Thailand.

voice and video transcoding is needed if the
bandwidth in some links is too small. Several
techniques of overlay multicast may help for thisproblem.

6 Conclusion
In this paper, we have presented someextensions of SIP based conference scenarios.
System architect and signal flows have been
described. We have proposed two additional
components to enhance conference features:
Conference Manager Server (CMS) and Conference
Repository (CR). Based on the proposed framework,in our implementation, we have demonstrated some
services. Recently, we are deploying these scenarios
for SIP based e-learning applications, called IDL:
Interactive Distance Learning. We believe that the
proposed scenarios will make SIP in more effectively
use. We noted in the system performance analysis
where this work concerns on signaling flow, how tocreate a rich feature of communications. Some future
works are discussed to extend this development. For
example, deploying SIP application over P2P overlay
network, extending to UCC (Unified Communication
and Collaboration), and working on multi-platformand devices.

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