Content uploaded by Joaquin Salvachua
Author content
All content in this area was uploaded by Joaquin Salvachua
Content may be subject to copyright.
ISABEL: A CSCW Application for the Distribution of Events
Juan Quemada, Tomas de Miguel, Arturo Azcorra, Santiago Pavon, Joaquin Salvachua,
Manuel Petit, David Larrabeiti, Tomas Robles, Gabriel Huecas.
Departamento de Ingenieria de Sistemas Telematicos (DIT)
Technical University of Madrid
Introduction
Many activities which in the past have required physical presence and direct interaction among
participants can be performed in a distributed fashion with the help of advanced information
technologies such as, CSCW [1,2] (Computer Supported Cooperative Work), interactive multimedia
services and broadband communications. Technologies aiming at supporting the collaboration among
individuals or groups are identified under the term groupware technologies. Asynchronous interactions
which do not require physical presence of interacting persons have matured during the last years. Very
successful examples of asynchronous groupware exist. LOTUS Notes [3] is considered probably the
most successful commercial product in this area. The Internet and many of its application can be
considered as groupware technologies to some extend.
Technology can support today also synchronous interaction where real time contact among
individuals is required. We mean by synchronous interaction the exchange of verbal, visual, ...
messages or information, like the exchanges of information carried out typicaly in meetings,
conversations or other activities where several participants collaborate in physical presence.
Remote synchronous interaction is not new, the plain old telephone is a very good example of an old
technology supporting a simple but very effective form of synchronous interaction. POTS is today by
far the most demanded synchronous service. This service has evolved into N to N audioconference or
videoconference facilities. Computers in general and the Internet have also had primitive types of
character oriented synchronous interactive services for a long time, like TALK, IRC, ... Today low
quality voice and video over the Internet is also common practice with applications like, CU-SeeMe,
IVS, VAT, ...
Audio-visual broadcasting is also a highly demanded type of remote synchronous interaction which
has been done since many years. Although broadcasting has really no interaction because the flow of
information is unidirectional, it is nevertheless being addressed in the experiments performed for
creating new synchronous services. One of the most popular services on the multicast backbone of the
Internet, also known as the MBONE, is the conference broadcasting for which a Session Directory
(SD) exists where the list of broadcast conferences is displayed in real time.
Sophisticated forms of remote synchronous interaction requiring good quality telepresence demand
more bandwidth and more reliable communications to achieve a proper interaction. Therefore for
setting up large sacle experiments like the RACE/ACTS Summer Schools [2,5,6,9] a complex
collaboration among a large number of organizations has been needed. In addition, the availability of
large broadband infrastructures is enabling the realization of large scale experiments using broadband
communications which are providing a better understanding of the role which synchronous interaction
will play in the communication services of the future.
Although intensive experimentation is needed, there are many application domains where remote
collaboration seems to have the same usability as physical presence. This could avoid or reduce travel
and/or movement of persons with substantial benefits for the overall productivity of an organization.
Introduction to ISABEL
ISABEL is a CSCW application whose very first version was developed in the European project
ISABEL in 1993. The ISABEL project was leaded by TELEFONICA I+D. The other participants were
CET, the research labs of Telecom Portugal, and the Dept. of Telematic Engineering of the Technical
University of Madrid (DIT-UPM). The development continued in the RACE project IBER with the
same participants. The acronym IBER was chosen due to the iberic nature of the project including only
Spanish and Portuguese participants. The ACTS projects NICE, TECODIS and BONAPARTE have
continued its use and tunning in a variety of application domains.
The ISABEL application was designed from the beginning for the interconnection of audiences.
ISABEL grew associated with the realization of the RACE and ACTS summer schools on Advanced
Broadband Communication, where several auditoriums had to be interconnected to create a unique
large transnational distributed virtual auditorium, where the attendees achieve the sense of participating
in a unique event independently of it´s location. The authors are not aware of other applications which
have targeted at interconnecting audiences and claim ISABEL to be the first application to have
addressed audience interconnection with integrated management of the distributed event. Related
projects where audience interconnection are intended are : the Munin Project [8] which addresses
lecture room interconnection and the ETSIT project addressing lecture room interconnection over
satellite.
Interconnection of audiences imposes different HCI (Human Computer Interaction) needs than
interconnection of desktops. Distributed events based on desktop interconnection are heterogeneous in
nature in the sense that each participant has not the same view of the event. When using CSCW over
desktops each participant in the distributed event shares with the rest only some of the windows he has
on the screen and he adapts the view he has of the shared components to his particular needs.
We call distributed events homogeneous if all participants share the same view of the interaction.
We believe that this is a fundamental requirement when distributing activities where the physical
presence has naturally provided a homogeneous view of the event. Therefore when interconnecting
meeting rooms, classrooms, .. a similar view of the interaction has to be provided in all endpoints. The
homogeneity of views is the only way of achieving a similar perception of the activity by all
participants and also of achieving the sense of participation in the same event.
ISABEL based Service Provision
ISABEL is a CSCW application which provides the basic technological framework for supporting
remote collaboration in various areas of professional activity. ISABEL has been designed as a
configurable CSCW environment which supports several interaction modes. The areas where ISABEL
has been experimented and for which specific operation modes have been included are :
• Teleeducation/training : In education and training the use of tele-lecture-rooms could facilitate
access to education in remote regions or in locations where the expertise is not available.
• Telework : In the working environment the need to facilitate the communication and collaboration
between teams is considered necessary to improve productivity.
• Telemeeting : The meeting is a central management element. The creation of telemeeting rooms
which avoid travelling can substantially change their role. Now meetings are scheduled according to
travelling constraints, whereas telemeetings can be scheduled according to project needs shortening
lead times and increasing productivity.
The experience gained from experimentation shows that in all the above mentioned activities several
types of interactions appear during an event. Therefore, the introduction of different interaction modes
in a CSCW application provides a much more natural understanding and feeling of the course of the
event to the remote participants. Lets take teleeducation as an example of the large variety of interaction
which can appear during the course of an event. We can differentiate different kinds of events and also
different types of interactions in those events. For example :
• Telelecture : A tele-lecture-room covering a large geographical area, where the students can
participate in the lecture from the distance. The interactions occurring during a lecture will be basically
two: 1) a presentation part usually based on viewgraphs or a blackboard ; 2) a questions/answer part.
• Teleseminar : A seminar or brainstorming session where ideas are presented and discussed. A
brainstorm is more unpredictable than a lecture, but it will also consist of sequences of interactions
like: 1) verbal discussions among several participants ; 2) discussions based on sketches on a
blackboard ; 3) discussions based on last minute documents ; 4) more formal presentations based on
viewgraphs ; ....
• Teleconference : Conferences, symposiums, workshops, ... are ussualy massive events where
participants follow the state of the art of their particular fields of knowledge. As the rest of events, the
conference consists of a sequence of interactions like : 1) a presentation part usually based on
viewgraphs, slides or photographs; 2) a questions/answer part ; 3) Panel discussions ; 4) demos ; ...
• ....
The approach used when designing ISABEL has been to define an architecture, where different
interaction patterns can be created and experimented. Service creation with ISABEL will therefore
imply the identification of the interactions to be supported in order to create a new service mode.
Support to a new service is introduced in ISABEL by creating a new management/operation mode
which enables an effective control of the required interactions.
Elements of ISABEL
As in most CSCW application the collaboration process is supported in ISABEL by having WSs or
PCs where a distributed multimedia application allows users to share elements or media by providing a
coherent view of them on all the computer’s screens. We call sites to the physical places where the WSs
or PCs are located and where participants join to a given distributed event. A distributed event consists
therefore in a sequence of intercations performed through the ISABEL application among several sites.
A service provision platform which includes, workstations, audiovisual equipement and a proper
communication subnetwork is used to run ISABEL.
Three conceptual parts can be distinguished in ISABEL :
• Telepresence. The achievement of sense of presence of the remote participants by means of audio
and video transmission. ISABEL supports the most general telepresence paradigm : videoconference
from N to N participants. Up to 16 sites have been connected with simultaneous video transmission
from all to all.
• Shared Workspace. A shared media space which enables users to achieve a common view and
understanding of the objects or ideas subject of the collaboration. Each mode, teleconference,
teleeducation, telemeeting, telework, ... has a different shared workspace in ISABEL.
• Interaction control. The means by which an ordered collaboration is achieved in a conference with
remote participants. In ISABEL interaction control acquires the functionality of a management
environment which has full control of all the elements of the application if needed. Each different
application scenario, teleconference, telemeeting, telework, ... is supported in ISABEL with a different
management scheme which supports the interaction roles of the group (hierarchical, brainstorm, flat,
etc.).
In homogeneous events the WSs or PCs all sites will have always the same layout with the same
information presented in order to provide to all participants the same view of the event. In
heterogeneous events this restriction is not necessary. ISABEL supports both kinds of events.
The creation of each particular service platform will require a special mixture of those 3 elements
adapted to the particular HCI characteristics of each case. For example a teleconference service which
has to interconnect large auditoriums will have completely different requirements than a telework
service designed to connect individual workers on their workstations. Therefore, the interaction
between ISABEL components can only be understood on a service by service basis and will be
explained in a later section. We will provide now only a general overview of the main components and
characteristics of ISABEL.
Telepresence
Telepresence is achieved by audio and video transmission among sites such that participants can see
and hear each other despite of the distance. In order to achieve a natural interaction some scenarios
require N to N video transmission. Each interaction mode in each particular service has usually
different HCI requirements and therefore ISABEL has a modifiable telepresence component which can
be tailored to the specific needs of each interaction type.
In each interaction there are active and passive participants. Usually the active members of the
configurations are the audio and video sources which participate in the videoconference among sites.
For example, in the lecture mode only the video of the speaker is distributed, whereas in a panel
discussion the videos of all the panellists are distributed.
The audio and video components of ISABEL have the following characteristics :
• Audio: This component can provide audio channels among all the partners involved in the
conference. It supports different bitrates and qualities ranging from 8 bit PCM to 16 bit CD quality.
Audio codecs which compress the audio bit rate are also supported in ISABEL. In particular, GSM
and G721 codecs are supported. This wide range of audio codings have been included for
experimentation purposes and to allow adaptation to different communication channels.
• Video facilities: This component provides video connections among all the users involved in
the conference. ISABEL can present the video images of all participants in the conference in all
sites. Up to 16 simultaneous video images have been performed. The video component uses MJPEG
compression. The reason for this choice is just the availability of high performance video boards
supporting this algorithm for the SUN WSs used.
Shared Workspace
The Shared Workspace is a shared media space which enables users to achieve a common view and
understanding of the objects or ideas subject of the collaboration. The shared media space is very
dependent on the application domain, tele-education, tele-work, tele-meeting, ... The shared
environment must be able to present to all users a common view of the problems or elements subject of
the collaboration. For tele-education conventional lecture support material like slides, pointers or
blackboards must be shared, whereas in tele-work arbitrary applications running, pointers or documents
must be shared.
Examples of media components existing in the shared workspace of ISABEL are :
• Viewgraph presentation: This component allows one participant to control a viewgraph based
presentation from one of the sites to the rest of the slides.
• Pointer/Pencil: This component allows one or more participants to use pointers and pencils to point
or draw in other components of the shared media space.
• Editor: This component allows users to produce documents in collaboration.
• Whiteboard: This component provides a distributed graphical editor which enables the joint
creation of graphic designs, diagrams, flow charts, etc.
• Display sharing: This component can present part of the workstation display at one site to the rest
of participating sites.
• Window Fax: This component allows to capture any part of the screen and send it over to the other
participants of a collaborative session.
The exact configuration and accesibility of the different components of the shared media space is
definable for each type of interaction by means of the interaction control component of each service
mode.
Interaction Control
Interaction control, also called floor management, is the key component which permits a natural and
easy use of CSCW. Interaction control is the means by which an ordered collaboration is achieved in a
conference with remote participants. The central idea behind the ISABEL interaction control
component is that the management and operation of distributed events must follow a similar approach
as the one used in the original non distributed event.
For example, the ISABEL based management and control of the virtual auditorium created in a
teleconference by interconnecting several auditoria has been conceived as an extention of existing
auditorium control rooms. Auditoria have control rooms from which the audiovisuals are controlled
according to a script which is prepared in advance. An operator controls, open microphones, audio
levels, video cameras, projection, lights, ... according to the script during the course of the event.
Likewise, a virtual auditorium is controlled in ISABEL by a common script which defines all the
interaction modes to be used. An operator in the central event control room will change the interaction
modes through the ISABEL teleconference control panel available in the event control workstation.
In telemeetings the management scheme has particular constraints. In addition, a large variety of
meeting types exist. The telemeeting service of ISABEL provides support to a conventional chaired
working meeting. In it, a chairperson runs the meeting and decides the activities to take place in the
meeting on the basis of a given agenda. The management of a telemeeting service must be controlled
here by the chairperson. The chairperson must decide about the interactions to take place on a more on
the fly way than in a teleconference. No central control room is needed nor convenient now.
ISABEL was developed to support the RACE/ACTS Distributed Summer Schools on Advanced
Broadband Communications [5,7,10]. Those summer schools targeted from the beginning at auditorium
interconnection. Therefore complex event management issues appeared from the beginning. This led to
an application architecture which has a programmable management/control part which has been used to
experiment with management variants and modes. The basic characteristic of ISABEL is that all
telepresence and shared workspace components are dynamically programable. The interaction control
part is built in TCL-TK and allows an easy prototyping of new control functions.
With the experience gained with the distributed summer schools several management modes have
been introduced which enable effective management of distributed events with a large number of sites.
The fourth summer school ABC´96 can be used as an example of its capabilities. It took place in July
1996 and is the largest distributed event supported with ISABEL. In ABC´96 up to 18 sites were
interconnected in 14 countries (Austria, Belgium, France, Germany, Greece, Iceland, Italy, the
Netherlands, Norway, Portugal, Spain, Sweden, Switzerland) on two continents. ABC´96 lasted 4 days
and lecturers were hosted in 6 different auditoriums (Belgium, Canada, Germany, Italy, Portugal and
Spain). The event control center of ABC’96 was located in the auditorium control room of the
Technical University of Madrid site. Without a centralized control scheme such a large event would
have been imposible.
Teleconference Service
Conferences, workshops, seminars are meetings which have required traditionally physical presence.
A teleconference service must enable the interconnection of physically separate auditoriums in order to
create a unique virtual auditorium where participants can interact with any other participant in any
auditorium. A teleconference is clearly an homogeneous event where all the participants must have the
same view of the distributed conference. In this mode the usual types of interactions among participants
must be supported, such as, lectures, talks, demos, panel discussions, question sessions, …
From the cost point of view a teleconference service can be seen as a service platform available to a
large population of potential users. The operations cost of the platform will be shared therefore by the
users. Although the cost of the platform can be high, the cost will be amortized in many events. The
cost of distributing the conference will be shared also by many participants. Therefore the individual
share of the cost of distributing a conference can be affordable even with today’s prices.
In order to understand a distributed conference it is convenient to describe it from two different
views : the participant´s view and the control view. Both are complementary.
The Participant´s View
A distributed conference can be modelled as a set of participating sites, each having an associated
role and functionality. A site is an access point to the virtual auditorium for participants and consists
usually of a physical auditorium which is connected to the rest of the auditoriums by the projection of
the screen of a multimedia WS where the ISABEL application is running. Several types of sites can be
differentiated.
First of all we have Interactive Sites (referred as IS) with a maximum interaction functionality. From
the organizational point of view some ISs can be differentiated due to the fact of holding lecturers or
having a registered attendance. Such sites have been called Main Sites (refered as MS) in the
ACTS/RACE Summer Schools. MSs have ussualy the same functionality as ISs but must provide a
more reliable service. On the other extreme we have Watch Points (referred as WP) which are receive
only sites. There may exist also uncomplete interactive sites which provide to participants only a
limited set of interaction facilities. For example a site which can not support the realization of
presentations by the lecturers but which can pose questions. The next figure ilustrates the structure and
components of a distributed conference.
The core of the conference is formed by a set of ISs, including some MSs, interconnected ussually
by an ATM multicast subnetwork. This core constitutes the interactive part of the conference. Each
interactive site will have an auditorium which can interact with the other auditoria according to the
mode set by the event control center. Additionaly ISABEL can be used to set up Watch Points. A
watch point has exactly the same view of the interaction as the interactive sites, but it can not interact
with the rest. A watch point needs only a unidirectional connection from the core network to the site.
ISABEL can de used also to set up gateways to the MBONE.
The set of ISs of a given event form the core of a distributed event, whereas the WPs are only able
to follow what is happening in the ISs. During the course of a distributed event the interactive sites
follow a sequence of interaction patterns which are derived from the script and content of the event. In
each interaction among the N interactive sites of the event, there will exist A active sites and P passive
sites. The active sites of an interaction deliver information content defined by the role they are playing,
such as a speech, slides, video images, computer demos,... to all the participants in the event. Of course
the roles and attributes of the ISs change when the interaction mode changes. For example : During a
lecture, usually only the site where the lecturer is present is active and has the lecturing role which
enables the speaker to control the shared components needed for his presentation, like viewgraphs,
pointer, pencil, display sharing,... When the talk finishes and questions are raised, the sites which pose
questions get active and are able to send audio and video. In a panel discussion all the sites which host
a panellist are active sites and the rest passive.
Watch Point (WP)
Core Multicast
ATM Network
(Fiber+Satellite)
IS
IS
IS
MS
Interactive Site (IS)
IS
Main Site (MS)
IS
MS
WP
ATM
MBONE Gateway
ATM (Satellite)
The Control View
The change of roles and attributes in the core of the distributed event is performed by the operation
team in the Event Control Center. As in any non distributed conference or TV production studio, local
control rooms which selects the right microphones, cameras, lightening,... must also exist in all the
auditoriums participating in the distributed event.
The next figure illustrates the control model used in ISABEL for a distributed conference. Each site
has two ISABEL WSs. The first WS is used to project the shared media space and the telepresence
components in a large screen in the auditorium. From this screen, the lecturer controls his presentation.
The second WS, also called the control WS, is used to control and manage de distributed event. This
acts as the conference creator and all sites must connect to it when joining the event. The rest of the
control WSs have only a marginal role in the event, related to the adjustment of the local audioinput to
the ISABEL audio component. Control workstations are ussually located in the control rooms of the
auditoriums. Of course, local control of audio, video, microphone, video cameras,.. must also be
performed in each auditorium complementing the overall interaction mode control performed in the
event control center.
Site
Display WS
Event
Control
Center
Display WS
Local
Control
WS
Display WS (lecturer)
Local
Control
WS
Display WS
Local
Control
WS
Site
Site
Site
- Configuration contr.
- Intersite comms.
- Lecturer role assig.
- Conference monit.
- Active site definition
- Video layout
-Audio channel contr.
- …….
- Local audio
- Local video
- Slides
- Pointer
- Pencil
- Video
- Audio
The control WS in the event control center can select the interaction mode established between the
sites with the control panel of the interaction control component which is depicted in the next figure.
This control panel controls the configuration of all the WSs participating in the distributed event.
Pressing a button in this control panel creates a chain of signals to all the workstations participating in
the event which will configure in each WS the appropiate layout and state. This panel includes several
types of buttons. For example the middle column is used to select interaction modes such as:
One site in large (1 large video)
Two sites interacting (2 videos)
Three sites interacting (3 videos)
Show all sites (all vieos)
Presentation/lecture mode (with three video sizes and several locations on the screen)
Question-answer mode
The lower part of the includes some audio and video related controls. The right side column is used
for selecting the presentation which is going to be given. The left side column is used for selecting the
sites of the interaction. Finally the row on the bottom is used for adjusting the bandwith used by
ISABEL.
The ISABEL operation manual describes in detail the precise meaning of each button.
A properly designed conference should include a script which precisely defines the sequence of
changes. Each change is performed ussualy by pressing one (or more) button.
There exist more control and monitoring panels in the event control center. Those are described in
the operation manual.
Telemeeting Service
Ideally, a telemeeting service should interconnect geographically disperse meeting rooms where the
attendees can interact among them as if they were in a single room. There are many kinds of meetings
which are potential candidates for being transformed into a distributed meeting and not all can be
covered with a single service. The ISABEL telemeeting service supports to a conventional chaired
working meeting. Such a meeting has two conflicting requirements. It must support, on one hand, the
chairperson running the meeting and provide him the instruments to control the interaction modes when
needed. On the other hand, it must facilitate an unplanned and easy change of interaction modes as
decided by participants, in order to encourage active involvement of the participants in the meeting.
Therefore the control of the telemeeting shall be in the meeting room and not in a separate control room
as in the teleconference.
The ISABEL telemeeting falls into the category of homogeneous event where all the participants
must have the same view of the event. Its main target is interconnecting meeting rooms, but it can be
also used to connect directly from a workstation to the distributed event.
From the cost point of view a telemeeting service can be seen as a service platform available to a
large population of potential users. A regular telemeeting service should be based on a set of
telemeeting rooms available to projects which should be booked and used by projects. The operations
cost of the platform will be shared therefore by the users. Although the cost of the platform can be high,
the cost will be amortized in many telemeetings. The cost of the meeting will be also shared by the
participants. Therefore the individual share of the cost of distributing a meeting can be affordable with
today’s prices.
The Participant´s View
A distributed meeting can be modelled as a set of participating sites, each having an associated role
and functionality. Each site is an access point to the virtual meeting room for participants and consists
usually of a meeting room where a WS connects through a multimedia application to the rest of the
sites. If the number of attendees to a meeting room is large a screen projector can be used. Usually all
sites will be interactive (IS) with full interaction capabilities. Although in some particular meetings WPs
may play a role, this is rare and we will deal only with telemeetings formed of interactive sites.
Some of the sites may be individuals sitting in their WSs and attending to the meeting as shown in
the picture.
During the course of a distributed meeting the sites will pass through a sequence of activities, each
having a particular interaction pattern. The chairperson shall have the possibility of taking the last
decision about the activities performed, but he is also a participant and must therefore be able to
participate as anybody else. Typical interactions occurring during a meeting are : 1) A speech from one
site ; 2) A viewgraph based presentation ; 3) A discussion among some or all sites ; 4) the distribution
and discussion of a document ; 5) To show a demo ; 6) To discuss a paper ; 7) ...
Network
Shared
Blackboard
ISABEL Appl. Shared
Blackboard
ISABEL Appl.
Shared
Blackboard
ISABEL Appl.
The Control View
The change of roles and attributes of the sites must be performed in a natural way. On the other
hand the chairperson has to have the last word about the decisions taken. The ISABEL telemeeting
mode tries to harmonize both requirements by giving to the sites the capability of requesting resources
and roles directly.
The control panel of the ISABEL telemeeting mode appears in the same WS where the telepresence
and shared media components are presented. Therefore only one WS per site is needed to set up a
telemeeting platform. The next figure shows the control panel used to interact in a telemeeting , which
has been made as simple as possible to facilitate its use by any participant with a short training.
The interaction rules are as follows : To facilitate the interaction the audio channels are always open
such that any participant can always communicate verbaly with the rest of the sites. The controls allows
the change of the video layout and the creation of elements of the media space, like pointers/pencils,
presentations, shared display, notepad, blackboard,...
The following functions are supported in the control panel:
1) Set big video : the video image of a site is set in large.
2) Set debate mode : The video image off all sites participating in the telemeeting are presented in
the largest size possible. This interaction mode should be used for discussions where only voice
is used.
3) Set intermediate mode : The video image off all sites participating in the telemeeting are
presented in a medium size such that a large part of the screen is still free for the shared media
space. This interaction mode should be used when video image is important, but other
components of the shared work space should be used.
4) Set work mode : The video image off all sites is presented in a small size at the righ hand side of
the screen. This interaction mode should be used when other components of the shared work
space should be used, such as shared blackboard or shared display.
5) No video mode : all the videos are removed from the screen. This interaction mode has been
included for the case that participants would like to remove all video information from the
screen.
6) Set presentation mode : All the elements of a presentation are assigned to the site requesting it.
This includes : presentation video in the upper right corner, presentation selection panel, slides,
and pointer/pencil.
7) Shared display : A window is created by the site requesting it and the window is displayed in all
the remaining sites.
8) Pointer/pencil : A pointer which can point and draw in any window or part of the screen is
created. The pointer can be used by all participants.
9) Shared Blackborad : A shared blackborad where all the sites can draw and interact is created.
10) Shared Notepad : a text editor where all the sites can write.
Network Issues
The availability of event specific broadband multicast subnetworks is the main limiting element for
the set up of distributed events. Events with two sites have some usefulness, but the real impact of
distributing events comes from minimizing movements of persons. Therefore service platforms must be
scalable and support an increasing number of participating sites. Multicast is the only effective way of
sharing the bandwidth. The cost of establishing a full mesh network grows quadratically and this is
unacceptable for more than two sites.
Experiments performed [16] show that the traffic aggregation in a CSCW application is much lower
than the sum of the individual peak traffics of the sources, due to the strong correlation existing among
shared media sources in the most frequent interaction modes. Therefore the bandwidth needed for the
realization of a distributed event is not too large. For example, ABC´96 was a distributed event with up
18 interactive sites. An ATM multicast network was created for it with 6Mbit/sec connections. The
average traffic was under 3 Mbit/sec and the quality was good. This was achieved with an MJPEG
compression for video signals. As video is the most bandwidth demanding signal, a higher compression
rate algorithm could have reduced the bandwidth needs.
Different approaches can be taken for creating a broadband multicast network. Let’s describe
briefly three of them which have been used for distributing events.
To perform multicast at the application level with the help of application routers and by using only
unicast communications at the network level. This approach has the big advantage of needing only
standard point to point connections at the network level. WSs are cheap and can perform copies of
application packets with a reasonable efficiency when the number of copies is not very large. It is a very
cost effective choice when the performance obtained allows its use. In the 1994 summer school this
approach was used to interconnect 5 sites with ISABEL [7].
To use an IP multicast service like the MBONE. This approach works fine, except that the tests
performed with some of the existing routers have shown a quick saturation of routers with a small
number of copies (4 or 5).
To perform multicast at the ATM level. This approach is technologically very effective as most
ATM processing operations. Multicast nodes making over 10 copies have been successfully setup for
ABC´96.
The lack of efficient and flexible multicast servers which facilitate the creation of tailored multicast
zones is one of the main hindrances for setting up distributed events. In the experiments performed for
setting up the ACTS/RACE distributed summer schools, the deployment of broadband multicast
subnetworks connecting the sites participating in the event took a very large share of the total effort.
Network architectures supporting distributed events not only have to adapt to the heterogeneous
quality of end-point equipment. Furthermore, when the available bandwidth is not constant throughout
the network, the quality of service at the application level or even the functionalities have to flexibly
and smoothly adapt to the QoS provided by the network. In practice this implies the existence of QoS-
adaptors connected to the backbone multicast network supporting the event at high quality, and taking
the job of reducing the quality of service or the number of components transported in the multimedia
stream towards the sites being serviced fitting each link's bandwidth. This enables easily scenarios with
users connected through narrow-band access networks.
Conclusions and Further Work
ISABEL is a multimedia CSCW application which was created associated to the realization of
distributed events. The experience and understanding gained during the four summer schools shows a
significant progress but there seems to be room for further additional expansion of this cost effective
approach to training in future summer schools or other educational events. The 1993 Summer School
was the seminal event with only two auditoriums interconnected. In 1994 five auditoriums were
connected. For ABC´95 ten sites were connected. ABC´96 has been the largest event organized with
ISABEL with 18 interactive sites connected trough terrestrial ATM links and satellite. Additionally 5
ISABEL watch points have been receiving the summer school with the same quality as in the interactive
sites. Growth in terms of size seems unpractical if interactivity among the sites is demanded. Of course,
with broadcasting an unlimited growth seems feasible. The advancement in the following years is
expected in functionality and reliability.
The experience gained shows that management of distributed multi-conferences is a central aspect
in distributed event organiztion. Proper models identifying the roles of each actor at each site have to be
developed and clear procedures have to be defined. Future developments which further develop the
ISABEL interaction control part are planned for the future.
Very significant improvements in the quality of the interaction among attendes are notizable from
the first versions of ISABEL. Nevertheless technology is advancing very rapidly and incorporation of
many new elements like better components, more effective video codecs, audio codecs or echo
cancellers,... is considered convenient to achieve a more interaction.
References
[1] P.Wilson: "Computer Supported Cooperative Work". Computer Networks and ISDN Systems, pp 91-95,
volume 23 1991, North Holland.
[2] Ralf Steinmetz: "Multimedia: Advanced Teleservices and High-Speed Communication Architectures", Ed.,
Springer-Verlag - Lecture Notes in Computer Science, Volume 868, September 1994.
[3] L. Lindop, T. Relph-Knight, K. Taylor, A. Eager, G. Einon, K. Joyce, A. Stevens: "Groupware : Let’s
work Together". PC Magazine, August 1995.
[4] S. Pavón, T.P. de Miguel, M. Petit, J. Salvachua, J. Quemada, L. Rodriguez, P.L. Chas, C. Acuna, V.
Lagarto, J. Bastos: "Integracion de Componentes en la Aplicacion de Trabajo Cooperativo ISABEL",
Jornadas Telecom 94, Noviembre, 1994.
[5] T.P. de Miguel, S. Pavón, J. Salvachua, J. Quemada, P.L. Chas, J. Fernandez-Amigo, C. Acuna, L.
Rodríguez, V. Lagarto, J. Bastos: "ISABEL - Experimental Distributed Cooperative Work Application
over Broadband Networks", pp 353--362, Springer-Verlag - Lecture Notes in Computer Science, Volume
868, September 1994.
[6] Arturo Azcorra et al.: "Multicast IP support for distribuited conferencing over ATM". INTEROP 95. Las
Vegas (USA).
[7] A. Azcorra, T. Miguel, J. Quemada, S. Pavon, Department of Telematics from UPM, P. Chas, C. Acuña, P.
Aranda, Telefonica I + D, V. Lagarto, J. Bastos, J. Domingues: “Distance Learning: Networks and
Applications for RACE Summer School '94”, Centro de Etudos de Telecomunicacoes, The ATM Forum
Newsletter September, 1994 - Volume 2 Issue 3.
[8] K. Age Bringsund and G. Pederson: "The Munin Project", Research Report, University of Oslo, 1993.
[9] J. Quemada, T. Miguel, A. Azcorra, S. Pavon, J. Salvachua, M. Petit, J. I. Moreno, P. L. Chas, C. Acuna,
L. Rodriguez, V. Lagarto, J. Bastos, J. Fontes, J. Domingues: “Distribution of ABC´95 over the European
ATM Pilot Network with the ISABEL Application”, Broadband Islands Conference, Dublin September
1995.
[10] J. Quemada, T. Miguel, A. Azcorra, S. Pavon, J. Salvachua, M. Petit, J. I. Moreno, L. Chas, C. Acuna, L.
Rodriguez, V. Lagarto, J. Bastos, J. Fontes, J. Domingues: ABC´95: A Tele-education Case Study”, High
Performance Networking for Teleteaching - IDC´95, Madeira November 1995.
[11] J. Quemada, T. Miguel, A. Azcorra, S. Pavon, J. Salvachua, M. Petit, J. I. Moreno, P. L. Chas, C. Acuna,
L. Rodriguez, V. Lagarto, J. Bastos, J. Fontes, J. Domingues.“Tele-education Experiences with the
ISABEL Application”, High Performance Networking for Tele-teaching - IDC´95, Madeira November
1995.
[12] Carolina Cruz-Neira, Daniel J. Sandin, Thomas A. DeFanti: “Surround-Screen Projection Based Virtual
Reality : The Design and Implementation of the CAVE”.Annual Conference on Computer Graphics,
ACM-0-89791-601-8/93/008/0135, 1993.
[13] Michael E. Luckacs, David G. Boyer: “A Universal Broadband Multipoint Teleconferencing Service for
the 21st Century”, IEEE Communications Magazine, November 1995, Vol. 33, No 11, pp36-43.
[14] Jose Encarnacao, Martin Gobel, Lawrence Rosenblum: “European Activities in Virtual Reality”, IEEE
Computer Graphics and Applications, January 1994, pp 66-74.
[15] Jeffrey HSU, Tony Lockwood: “Collaborative Computing”.Byte, March 1993.
[16] José I. Moreno: “Propuesta de Arquitectura de Red de Banda Ancha para Servicios de Telecomunicación
de Trabajo Cooperativo”. PhD Thesis. Dpto. Ingeniería de Sistemas Telemáticos. Universidad Politécnica
de Madrid. Junio 1996.
