Structure, Design Principles and Services Offered
Nikolaos Xypolitos, Michael Paraskevas, Emmanouel Varvarigos
Research Academic Computer Technology Institute, University of Patras, Greece
Keywords: Internet services, School Networks.
Abstract: The Greek School Network (GSN) is a closed educational network that offers advanced telematic and
networking services to all units of primary and secondary education schools and administration offices in
Greece. The main objective of GSN is the implementation of a network infrastructure for the
interconnection of the school laboratories and the provision of a wide range of network and telematic
services to students and teachers. The GSN separates its telematic services to two major groups: the
centralized services and the end-user services. The purpose of this paper is to describe the GSN structure,
the services it provides, and its design and operational principles.
The Greek School Network – GSN (Greek School
Network, 1998), described in this report, is the
educational intranet of the Ministry of Education and
Religious Affairs, which interlinks all Greek schools
and educational administration offices, and provides
basic and advanced telematic services to students,
teachers, and administration personnel. It also
contributes to the creation of new educational
communities that use Informatics and
Communication Technologies in the educational
procedure. The telematic services of the GSN are
based on Open Source technologies that are
modified in their source to fit exactly the needs of
the Greek educational community.
The GSN offers a large number of services to
more than 15.000 schools and administrative units,
and over 50.000 teachers in Greece, across all the 51
prefectures of Greece. The services are offered
over the network that GSN has developed and
maintained since 1998. The network is hierarchically
structured into three layers in order to manage the
complexity that comes with the large number of sites
that are covered:
Core Network: The Greek Schools
Network interconnects with the Greek
Research and Technology Network
(GRNET, 1995) in seven main points,
using it as its core network.
Distribution Network: The distribution
network provides for the interconnection of
the schools and educational administrative
units to the core network, and consists of 51
nodes. The GSN has installed in the capital
of each prefecture, network and
computational equipment, to ensure optimal
access of the prefecture‘s schools to the
network and its services, and is further
separated into two distinct layers:
Access network: It is used to directly and
efficiently interconnect the schools to the
prefecture‘s access point. The
telecommunication junctions used to
interconnect each school are selected on the
basis of financial and technical criteria from
an array of available options: Digital ISDN
circuit (bandwidth: 64 - 128 kbps), Analog
leased line (0,128 – 2 Mbps), Wireless link
(10 Mbps), ADSL circuit (384/128 Kbps,
512/128 Kbps, 1024/256 Kbps), VDSL
circuit (10 - 15 Mbps), Public Switched
Telephone Network circuit (56 kbps)
In order to achieve the objectives of e-Europe
2005 regarding the provision of broadband access to
all schools, the Greek Schools Network is upgrading
its distribution network by increasing its installation
Xypolitos N., Paraskevas M. and Varvarigos E. (2006).
THE GREEK SCHOOL NETWORK - Structure, Design Principles and Services Offered.
In Proceedings of the International Conference on e-Business, pages 283-288
DOI: 10.5220/0001425302830288
of broadband connections (ADSL connections and
10 Mbps wireless links). Regarding the wireless
links, 13 distinct wireless networks are in operation.
The wireless networks allow for the provision of
advanced, high-quality telecommunication and
informatics services to the units connected, and
significantly decreases the telecommunication
operational costs.
The Greek Schools Network offers a broad package
of services to its units and users that can be
separated into two main categories: the centralized
services and the end-user services. The centralized
services are supporting many of the end-user
services and also offer GSN administrators the
ability to globally monitor the correct operation of
the services. The GSN’s centralized services are the
Directory Service, the Content Filtering service
which controls the access to the Internet, prohibiting
access to web sites with harmful content for
children, and the Web Hosting for static and
dynamic pages
2.1 The LDAP Directory Service
The main centralized service of the GSN network is
the LDAP directory service. The LDAP directory
holds all the teacher and school accounts and is used
to authenticate the users in all services that require a
login process. The attributes in the LDAP directory
have been adjusted for every user in order to suit the
needs of the services offered. The directory service
is supported by an array of four servers, three of
which are exclusively dedicated to supporting the
directory service. The main server is the write
master, where all additions and updates to the
directory information store take place. The
remaining servers store a copy of this information,
which is continually synchronized with the main
server (online replicas). The online replicas
constantly answer to queries of other services
supporting the delivery of email messages, the
dialup access to the network, and the
authentication/authorization operations for the other
services. It is worth noting that in addition to the
typical multimaster replication model, alternative
servers may assume the role of the main write
master, allowing for the smooth and continuous
operation of the directory in case of malfunctioning
of the write master server.
2.2 Controlled Access to the Internet
The GSN has restrictive policies for the sites that
can be accessed by the students. A schema with the
appropriate proxy servers is used to control the
access of GSN users to the Internet. The access is
prohibited to categories like porn, drugs, violence,
gambling etc. There are three ways for the GSN
system to control the access of its users to the
Internet. The first is to examine for words that
identify an illegal category in the URL or in the
metadata of every requested site. The second way is
to communicate with international black list
databases and deny access to the sites listed in these
databases. The third way to control the access to the
Internet is more customized to the GSN needs. The
GSN has built an extra database to explicitly record
sites not allowed to be accessed and sites allowed to
be accessed. The first database helps restrict access
to sites that are not globally black listed but whose
content is not consistent with the GSN terms of use.
A user has the right to suggest a site that must be
blacklisted, and the administrator of the service
examines the site and includes it in the custom black
list database, if its content is found to be ineligible.
A similar database is used to record sites whose
content is not offensive, but which have been
blacklisted for some reason. A user may suggest, by
sending an e-mail to the administrator of the service,
a site that is currently prohibited to become
accessible. The administrator then examines the
content of the site, and if it is found to be
appropriate records it in the while list database so
that GSN users can access it.
2.3 Web Hosting
The Web Hosting service provides space for web
pages and web applications using the GSN Web
servers. The service is provided to the schools and
teachers community to create their own web sites.
The web sites are separated to schools’ web sites and
administration units and teachers’ web sites
Each school or administration unit connected to the
GSN has its own Domain Name (DNS) under the domain. This DNS is the address of a virtual
web hosting server for this unit. If a unit has more
than one accounts, each of them has an independent
web site accessible under the address <unit DNS
The service allows the users to publish static
HTML pages or dynamic pages using PHP and
MySQL. The GSN offers to its users a web based
database administration interface accessible under
the Web Portal. Each school or administration unit is
allowed 100 MB of web space, and each individual
teacher is allowed 50 MB of web space. The GSN
offers four different tools for building web pages.
Two of them focus on building static web pages and
the other two tools focus on building dynamic web
pages. The tools were all developed by the GSN
team and they can be accessed by registered users
through the web portal. In addition to the web page
building tools, GSN users have FTP access to their
web space, so that they can simply upload a site they
have already built elsewhere.
The schools and teachers sites are shown in the
web portal in a special area dedicated to the users’
sites. The sites are grouped according to their
thematic area in a thematic catalogue that is
available to the visitors of the web portal. A rating
mechanism is also available, and the sites with the
highest rates are shown in the first page of the web
portal. Through the web portal, users can add web
sites to their favourite preferences, which are shown
in a special area of the portal. The portal also
provides a search mechanism for the teacher and
school web sites through a graphical interface (a
map of Greece), allowing searches by author, name,
and geographical area.
The end-user services offered by GSN are:
Web Portal (Greek School Network, 1998),
offering news services and personalized
access to all GSN telecommunication and
informatics services under a single login
Ε-mail, accessible through the POP3 and
IMAP protocols, as well as the world wide
web and E-mail lists
News service, forum discussions and
electronic magazine
Wizards for automatic webpage creation
Asynchronous distance learning, for
hosting and distributing digitized courses
High end multimedia services such as
Teleconference, Video On Demand for
delivering streaming educational
multimedia material and Live Web Casting
of various educational events
Automated registration procedure for
educational staff and students
Remote network access (dialup)
All the end user telematic services are implemented
in the GSN Web Portal.
3.1 The Web Portal
The framework used for the implementation of the
GSN Web Portal has been mainly based on the
Jetspeed Portal of the Apache Software Foundation.
The framework used offers a programming
context oriented towards the implementation of web
portals that have a large number of users. At this
moment, Jetspeed is actively being developed and its
feature set is constantly being expanded. The GSN
developing team is further expanding the
functionality of the framework engine to develop a
portal environment that suits the needs of the GSN
The Web Portal Design adheres to the following
general specifications:
The portal permits the execution of micro-
applications that are integrated in it as
portlets. This specification allows for the
natural separation of the application and the
presentation layer, by offering virtually
unlimited potential regarding the
presentation location and format of the
output of each portlet. The output of all
portlets is well defined on the basis of
XML/DTD schemas.
A number of services are currently being
implemented as Web Services. This will
dramatically increase the re-utilization of
these services as well as their distribution to
the end users. Public access may be offered
to Web Services (through UDDI) separately
from the web portal; for instance such
services may be incorporated in the users’
pages (e.g. services that deliver maps based
on the G.I.S.).
The usage of Jetspeed as the underlying
framework offers clear advantages, since
issues related to security, user
authentication and authorization, content
display mechanisms in a customized
THE GREEK SCHOOL NETWORK - Structure, Design Principles, and Services Offered
environment, separation from the portlet
implementation programming language,
velocity engine template support for
content display and integration with other
Open Source applications have already
been solved.
The GSN has developed further the Open Source
portal to support LDAP authentication over secure
password encryption (encrypted with the Unix
Encryption algorithm according to the SUN ONE
LDAP Server), to support personalized pages for
every registered user and to make the login
procedure easier by keeping the navigation of an
anonymous user when he/she decides to login to the
portal. Furthermore, the appropriate modules have
been created so that all the available portlets of the
Jetspeed portal can support LDAP authentication. A
single sign-on system has been implemented which
allows all GSN members to use all services
requiring login after they have logged-in once in the
GSN web portal. The web portal has more than
50.000 users who have their own customized views
of the web portal.
To support a higher number of concurrent users
we have implemented a load balancing technique.
The Apache httpd server (Apache Server Project,
1996) is the main web server in use, combined with
at least one application server, which offers the
execution environment for Servlets and JSP pages.
The Apache web server handles all incoming
requests, forwarding them to the application servers
using the mod_jk module. Each application server
hosts an identical version of the Web Portal.
3.2 E-mail and E-mail Lists
This service is used by the Greek educational
community and by the Vocational Training
personnel. The accounts for the service are separated
in the following user groups: a) Accounts for
Schools and Administrative units, b) Accounts for
Teachers, c) Accounts for Students.
The service has all the standard characteristics of
an e-mail service, plus some additional
characteristics we have developed in order to
provide a more flexible and secure service to the
educational community. The extra features provided
include, virus protection using the Sophos antivirus
software that is installed in all GSN mail servers and
spam protection with new anti-spamming filters.
Spam protection is activated only upon user
request (through a corresponding checkbox in the
web portal), and when it is activated a new folder,
named “spam”, appears in the users mailbox. When
a message is tagged as “spam” (in the GSN mail
server, when the message has been sent more than a
predefined number of times and the sender does not
have the right to send multiple messages), it is
automatically placed in the spam folder. The user
may also choose to categorize as spam all the e-
mails arriving from known spam sources that are in
GSN's rbl lists.
The mailing list service enables the development
and maintenance of mailing lists that can be used to
deliver a large number of messages to large numbers
of GSN users. There are two main categories of
mailing lists currently active in GSN: lists with
dynamic subscription of members, and lists with
static subscription of members. In the lists that allow
dynamic subscription, the members are coming from
the LDAP directory Server of the GSN. The list mail
address may, for example, look like,
where the above list may identify all the first grade
schools of Greece. In the lists with static
subscription, the list administrator can enlist one or
more users, or the users themselves can become
members of the lists of their choice, by filling in
their e-mail and some personal data in the
appropriate web form.
To prevent the members of the lists from
accessing material that is inconsistent with the GSN
terms of use, most of the lists have a moderator who
is responsible for the material that is distributed
through the lists. Some lists are completely open, but
these are a minority. The use of a moderator is
mandatory in most cases, because the educational
community is a very special community of people
and messages that contain spam, viruses,
pornography and other related content must not be
allowed in the users’ mailboxes.
3.3 News Service, Forum
Discussions and Electronic
The news service allows registered users, such as
schools and teachers, to post announcements. The
announcements are hierarchically grouped, based on
their content to different categories and topics. Each
announcement has a certain scope: it may apply to
the users of a specific educational unit, a prefecture,
the group of all registered units, etc. The GSN portal
also offers to its members a forum discussion board
which allows the users to create new posts, reply to
messages in a particular post and create new
The electronic magazine of GSN is a classic
newsletter service used to inform GSN users of
educational news and new services introduced. The
service was built from scratch, and gives the
opportunity in all schools to construct their own
newsletter. An archive system keeps all the versions
of the newsletter and every newsletter can be
accessed as a web page through the GSN portal.
3.4 Asynchronous Distance
The software used for this service is Moodle
(Moodle, 2002), which is a software package for the
production of online courses and web pages,
offering a complete set of internet education
services. GSN users can subscribe to an available
course and also, following a particular procedure,
become trainers in a course. The e-learning service
is accessed through the GSN web portal. The e-
learning environment is fully translated into Greek
together with all the modules of the platform, and a
great deal of content has already been developed and
organized in various thematic areas.
3.5 Teleconference Service
The teleconference service of GSN enables a
conference between two or more participants located
at different sites by using the IP network of GSN to
transmit audio, video and text (chat) data in real
time. A teleconference also offers the possibility of
having a presentation from one participant to the
others (e.g., a PowerPoint presentation) or sharing
an application. There are two different categories of
teleconference services, a point-to-point (two-
person) conferencing system and a multipoint
conferencing (point to multipoint), which allows
three or more participants to sit in a virtual
conference room and communicate as if they were
sitting right next to each.
The teleconference service is integrated with the
instant messaging service. The teleconference
system has been tested under various use scenarios,
including synchronous teleconferences among a
number of schools all over Greece and the central
offices of the Greek Ministry of Education. Users
participating in the teleconference can see each other
(the screen is separated to show the input from the
web cameras of all participating users), and when a
user is speaking he is shown in the central screen, so
that all the others can see and understand who is the
speaker at any time.
All European countries have developed or are in the
process of developing telematic services that focus
on the needs of their respective educational
communities. The Greek School Network has
developed a number of services for the educational
community in Greece, using state of the art
technology. The online services offered to the
educational communities must include a variety of
tools for helping in the communication between their
members and in the introduction of new educational
methods. The needs of the educational communities
around the world for online services and educational
material are growing rapidly, making it necessary
for all countries to try to find ways to meet these
demands. One parameter that must be always kept in
mind during this effort is the cost of the services
offered, since these services must be provided to the
students and teachers free of charge. This makes
Open Source solutions preferable to commercial
options. Since the educational communities and
especially the pupils must be protected from
ineligible material, extra care must be taken
regarding content delivery and security. A great deal
of research has taken place in recent years on new
methods and e-learning environments, new ways of
approaching e-learning, and new tools that people
can use. The GSN participates in these efforts by
providing an asynchronous e-learning environment
and a variety of online services to the educational
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