Download - Web laboratory for computer network
Web Laboratory forComputer NetworkNENAD JOVANOVIC,1 RANKO POPOVIC,2 SUZANA MARKOVIC,1 ZORAN JOVANOVIC1
1Department of Computing and Informatics, Advanced Business School, Blace, Serbia
2Department of Computing and Informatics, Singidunum University, Belgrade, Serbia
Received 7 July 2009; accepted 18 January 2010
ABSTRACT: Current technologies give us the ability to enhance and replace developmental classes with
computer-based resources, often called Web laboratories. Web laboratories have become a very useful support for
practical aspects of teachingmethods. This article presents a Web-based laboratory, whichmakes learning of base
principles of computer network possible. �2010 Wiley Periodicals, Inc. Comput Appl Eng Educ; Published online in
Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20417
Keywords: IP; computer network; e-learning
INTRODUCTION
Traditional educational system, which is mostly based on
theoretical learning, does not give good results when it comes
to the qualification of students for solving practical problems.
Theoretical learning must be combined with practical experience,
while laboratories represent ideal places for upgrading theoretical
knowledge with practical skills.
Acceleration in development of technologies, and possibil-
ities of informatical age, intend to change playing rules in
education. Educational system should be adapted and give us new
educational forms which will maintain new students to use
technological achievements in educational processes, without
addition of money expenses, and their physical absence will not
be a disadvantage.
As an answer to this challenge, many educational institu-
tions give response in the development of online educational
programs. When we have a possibility for transfer of educational
content over the Internet, it is necessary to give a student an
online interaction with real or virtual equipment such as
computers, routers, electronic circuits, lasers, microscopes, etc.
When we have online control of equipment, we create an online
laboratory.
In order for online labs to be an adequate tool in the process
of education, they must realize three academic principles [1]:
* Authenticity: Enable easy division of development tools.
* Complex: Possibility of visualizing a complex process.* Collaboration: Possibility of computer communication.
Online laboratories are used in technical [2�6]
and mathematical [7�9] sciences, and in the field of social
sciences.
On the Internet we have different types of online labs. Some
of them have an online interface for access on the physical
devices, where we may adjust, control or read from a remote
place [2]. They enable creation and online publication of
exercises which are based on those devices.
A second type of online laboratories works with simulations
of real equipment with the purpose of representing functionality
of these devices [3,5,6]. These environments allow students to
configure devices in the same way like with the real equipment,
but experiments are derived in a controlled and robust environ-
ment.
Today, we have an online education system which may
simulate real equipment [4]. In distinction of simulation,
emulated devices execute process of information in real time
and can be used in educational purposes, and in process of
researching.
Some online laboratories are realized in the form of Java
applet and enable simple interactive work and visualization of
processes in observed system [7,8].
In this article, educational system is available [10] which has
several tools that are grouped in the group system named ‘‘Web
laboratory for computer network.’’ While preceding systems
belong to some specialized area, our system covers several areas
and has the possibility of use as component for distant learning in
the process of engineer education for informatics. The system isCorrespondence to N. Jovanovic ([email protected]).
� 2010 Wiley Periodicals Inc.
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interactive and covers system simulation and process visualiza-
tion and has the possibility of explaining complicated work of
computer networks.
WEB LABORATORY STRUCTURE
Web laboratory for computer network [10] consists of two parts:
* WNetSim: Computer network simulator [11].* Basic concept of IP networking.
WNetSim: Computer Network Simulator
WNetSim presents an environment which allows us to visualize
and simulate a process in computer network with any topology.
The purpose of the simulator is to help students comprehend basic
principles of acting of one TCP/IP computers network as a part of
the educational system of computer network. Information
technologies progress work on instruction and learning methods
from different domains such as computer networks. Processes
that occur in computer network during data exchange between
network devices are complex and they are executed in very
short time slices, since the consumer is not in the state to follow
and understand what happens in computer network. The main
purpose of our simulator is to present these processes visually. In
addition, its features like topology editor, and simulation of real-
time network scenarios makes it a suitable tool for undergraduate
teaching as well as for research.
WNetSim simulator is Web based and enables animation
and visualization of process data transport in computer network.
The main reason for this simulator development is its educational
usage. WNetSim simulator allows students to design computer
network of arbitrary topology with arbitrary chosen components,
to configure network components by using command line
interface, and to see data frame flow on different locations in
network, as well as, content of encapsulated data. Simulator
facilitates fundamental perception of protocol operating, such as:
Ethernet, IP, ARP, PPP, etc. It is possible to introspect switching,
routing, and other processes in network.
Network simulator also includes a comprehensive lab menu
that contains structured labs for users to run.
Network simulator allows students to design, build, and
configure their own network with drag and drop design. The
WNetSim monitor can be used to observe the real-time path of a
packet as it travels through the devices in a created network.
Students can view the progress of a packet.
Basic Concept of IP Networking
Internet address, or IP address, is a 32-bit numeric address which
is to be written as four 8-bit numbers separated by point, whereby
the 8-bit numbers are to be presented as decimals. For example,
192.101.121.6.
There are following kinds of IP addresses:
Static address:
* Subscribed manually by network administrator.* They are used in small range networks.* They require careful assignment and verification to avoid
repetition.
Dynamic address (bootstrap protocol (BOOTP), dynamic
host configuration protocol (DHCP)):
* Represented by server when the host is to boot.* Subscribed from the corresponding range of address.* At the expiry of ‘‘rented’’ time, address is returned to the
server.
Internet addresses are being qualified as classes A, B, C, D,
and E. IP address consists of two parts: the network part (NetID)
and the HostID. The NetID part uniquely identifies the network
and the HostID indicates the address of the node on the network.
Different types of IP classes are defined in order to fulfill the
needs of different extents of networks.
Class A IP addresses have 7 bits reserved for NetID and 24
bits for HostID. They are designed for very large networks
and can identify 16,777,214 (224� 2) computers in 126
(27� 2) networks. The first octet in class A addresses could
be a number from 1 to 126.
Class B addresses are mid-ranged. They are suitable for
mid-range and large organizations. Network identification
could be done with 14 bits, and network nodes are identified
with 16 nodes. These addresses can identify 65,534 (216� 2)
computers in network. The first octet in an IP address should
be in the range of 128�191.
Class C address is using 21 bits for NetID, and 8 bits for
HostID. These addresses are designed for small networks
and they can identify 254 (28� 2) computers in network.
The first octet in class C IP address should be in the range of
192�223.
Class D addresses are designed for multicast; they are not to
be used for addressing individual computers. The first octet
in the address should be in range of 224�239.
Class E addresses are used in experimental cases. The first
octet in the address should be in range of 240�255.
Several addresses are reserved for special purposes.
* HostID can never be 0. If all bits in HostID are equal to zero,
then the said IP address is used for indicating the network
(network address).* HostID can never be 1. If all bits of HostID are equal to one,
then the package should be delivered in a diffusing manner
to all computers in network and the above-mentioned
address is to be called broadcast address.
The first address in every network (grade) represents the
network address, and the last address is reserved for the broadcast
address.
IP network could be divided into smaller networks, called
subnetworks (subnets). The division of network into subnetworks
enables larger flexibility and more efficient use of IP addresses.
For example, the network with the network address 177.28.0.0
could be divided into subnetworks with addresses: 177.28.1.0,
177.28.2.0, 177.28.3.0, 177.28.4.0, etc.
The subnet address is created by using bits from HostID
fields as subnet fields. The number of borrowed bits is variable
and is determined by subnet’s mask.
The subnet’s mask uses the same format and the same
manner of representation as IP address. The subnet mask contains
2 JOVANOVIC ET AL.
number 1 in the position of all bits belonging to NetID and
SubNet fields, and contains 0 in all bits belonging to HostID
fields.
The procedure of realization of subnetworks requires
previous analysis of the following questions:
* How many addresses are needed for network segments? (A
network segment is an entity separated from other entity by
a router.)* How many network segments will be needed in the future?* What is the maximum number of hosts on the largest
segment?* What will be future hosts’ needs in any of the segments?
IP Calculator. IP address calculator, which is a part of the
system for learning the basic concepts of IP networking, can serve
for calculating all previously mentioned elements of an IP
address. The basic screen of an IP calculator is shown in Figure 1.
IP calculator enables the entry of an arbitrary IP address in the
field IP address and the calculation of all needed data related to
the given address: class, network address, broadcast address. Data
are shown in decimal and binary forms.
In case if we want to divide a given network on a certain
number of subnetworks, we need to define how many bits have to
be borrowed from the HostID part of an IP address. We can do this
in two ways. We can define the number of bits which define the
network and the subnetwork through a slider or we can enter the
IP address in the form of a Classless Inter-Domain Routing
(CIDR) notation (e.g., 198.123.56.23/28).
For example, an IP network address 198.123.56.0 which
belongs to class C is given. If we want to divide the given IP
address into at least 10 subnetworks, then we need to separate
from the HostID part of an IP address 4 bits, because 24> 10. In
that case, bit of a subnetwork address is 28 (Fig. 1a).
We can see that the subnetwork mask is 255.255.255.240
and that in this way we can form a maximum of 14 subnetworks
with a maximum of 14 hosts in each subnetwork.
By pressing the button, near the maxSubNet field, we can
get a list of all available subnetwork addresses, with a range of
valid IP address hosts, as well as the broadcast address for each
subnetwork (Fig. 1b).
Work With the System. After entering the name and the surname
of a student and pressing the button START, the first window of
application for the work with IP addresses opens. This application
consists of seven parts:
(1) Numerous systems.
(2) The classes of IP address.
(3) IP network subnetting.
(4) Calculating the subnet and broadcast.
(5) CIDR.
(6) Network topology 1.
(7) Network topology 2.
The first part is the Web application for work with numerous
systems, which is made of an interactive system in which
questions to which students give answers are generated.
Questions are related to the conversion of randomly generated
values from one into another number system. Number systems
with the base of 2, 8, 10, and 16 are dominant. After answering
the questions, the student can see the statistics for correct/
incorrect answers (Fig. 2).
By clicking the button next, we go onto the next part.
In the second part, it is necessary to answer questions
regarding the given IP address, which is generated randomly
(Fig. 3). It is necessary to write down the binary code of the
address, the class of address, to define address’ scope, the extent
of the first octet of given IP address’ scope, considered subnet’s
mask and network address. Then we need to determine the class
of four IP addresses, generated randomly, and enter the answers in
the adequate text fields.
In this example, there is a randomly generated C class
address 195.45.123.19. The value of first octet for C class
is between 192 and 223. This IP address has a place in
network with the following address: 195.45.123.0. The
defaults network mask is 255.255.255.0. The binary address
is 11000011001011010111101100010011. Generated IP
addresses, in this example, 170.119.35.197, 179.111.75.78,
Figure 1 IP calculator. (a) The basic screen of IP calculator and (b) a list of all needed data.
WEB LABORATORY FOR COMPUTER NETWORK 3
25.195.42.97, and 73.118.33.102 belong to classes B, B, A, and
A, respectively.
In the third part of the exercise (Fig. 4) it is necessary to
define how many data bits should be borrowed from the host part,
so that the given network address (201.45.123.17), which is
generated randomly, could be divided into a distinctive number of
subnets. Then, it is necessary to define the subnet’s mask and to
show the subnet’s mask in binary form.
In this example, the task is to divide the network into
10 subnetworks. Since 24¼ 16, the conclusion is that 4 bits
should be borrowed from the host part. The mask for 4 bits is
240, or to be more precise the subnet’s mask will be
255.255.255.240.
It is necessary to fill the table with several valid subnet
addresses. Also, one should define the scope of useful addresses
for every subnet and broadcast addresses. The possible numbers
Figure 3 Web application—the second part.
Figure 2 Web application—the first part.
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of subnets in this examples (according to defined formula:
2n� 2): 24� 2¼ 14. The numbers of hosts in each subnet are
24� 2¼ 14. For example, first subnet could be 201.45.123.16.
Broadcast address for this subnet is 201.45.123.31. The range of
useful hosts addresses is 201.45.123.17�201.45.123.30.
In the fourth part (Fig. 5), it is necessary to fill the table. In
every row of the chart IP address and subnet mask are randomly
generated, and the user should calculate the subnet and broadcast
to fill it in the appropriate field.
In the specific example shown in Figure 5, the first generated
IP address is 7.213.175.179 (class A) and the subnet mask is
255.255.255.128. Which subnet is this address part of?
According to the subnet mask we can conclude the
following: there are 131,070 (217� 2) subnets, and the increment
for each is 128 (27). The address of first subnet is 7.0.0.128,
the second one 7.0.1.0, etc. and the address of the last subnet
will be 7.255.255.0. IP address 7.213.175.179 is between subnet
7.213.175.128 and subnet 7.213.176.0. Therefore, we can
Figure 4 Web application—the third part.
Figure 5 Web application—the fourth part.
WEB LABORATORY FOR COMPUTER NETWORK 5
conclude that our randomly generated IP address belongs to
subnet 7.213.175.128. This value is to be written in appropriate
fields in Figure 8. Broadcast address for this subnet is
7.213.175.255.
In the fifth part (Fig. 6), IP address in CIDR notation is
given, generated randomly. The user should determine an
equivalent subnetwork mask, the number of addresses in a given
CIDR block, subnetwork address, the first and the last addresses
in the given CIDR block, and the broadcast address.
In the sixth part (Fig. 7a), a network topology is given, and a
student must assign a proper subnet mask, for a random generated
network IP address, and bring in text fields with valid subnet
addresses.
In the seventh part (Fig. 7b), a network topology and a
randomly generated network IP address are given. A student must
determine an adequate subnetwork mask and to fill in the adequate
text fields the IP addresses of the interface router and the computer
IP address, taking care of where special subnetworks belong.
At the end or after each part of the application, the user can
see his achieved results by clicking the results button (Fig. 8).
ASSESSMENT
Assessment of knowledge is usually done in a traditional way, by
oral examination or by written tests. However, nowadays a large
number of tests for studying and assessing which is done by a
computer are developed. The suggested system generates
computer tests which represent a very efficient way of knowledge
assessment. The assessment time is decreased as well as the
distribution of results. Basically, at the time when the examinee
finishes a test, the system generates a report (a grade or a
percentage and a recommendation for studying those fields, the
questions from which were badly done, etc.).
Learning styles represent different approaches or ways of
studying. Every student, when acquiring knowledge, gives
advantage to the information which he/she receives through a
certain hearing modality and therefore, by using that informa-
tion, learns in the most efficient way. According to that
modality, the basic topology of learning styles is as follows
[12]: visual, auditory, and tactile/kinesthetic learning styles.
The visual learning is dominant in those who acquire
information when it is presented visually in the form of text
(graphical-visual) or a picture. They mostly prefer individual
learning. Those who find it easier to learn by listening to
lectures, discussions, exchange of ideas use the auditory
learning style. This is the reason why it is characteristic of
this learning style for students to work in pairs or groups. Those
who take notes, draw pictures and diagrams during the learning
process, in order to memorize the information more easily use
the tactile/kinesthetic learning style. They learn best through
movement, games, acting, or concrete action, actively explor-
ing the physical world around them.
According to the previously mentioned learning styles, we
have tested a group of students (25 students) and arrived at the
following results.
First, preliminary testing was done which was carried
out in order to determine the learning styles of students and
the way to express knowledge (http://www.businessballs.com/
vaklearningstylestest.htm).
The results of the test were as follows: 24% of the students
(6 of them) prefer to study based on seeing—the visualists, 36%
(9 students) prefer to study by listening—the auditory, and 40%
of the students (10 of them) prefer to study by practical activity—
kinesthetic.
Based on this, the students were divided into three groups
(V—visualists, A—auditory, K—practical).
Based on three types of testing, it is interesting to note that
the results of the students on tests were mainly coherent to their
affinities expressed through preliminary testing. The following
graph demonstrates this:
The testing showed that the system described in this
article proved to be accessible to the three groups of students.
Students were graded with the mark from 5 to 10. The results of
Figure 6 Web application—the fifth part.
6 JOVANOVIC ET AL.
the testing are illustrated in Table 1 and in the following
graph:
The metric characteristics of these tests are: reliability,
validity, objectivity, and discriminatoriness. Besides this, these
kinds of tests are characterized by an equal working time and the
same working regime—less time for examination, exactly
determined range of knowledge needed for a certain grade, an
equal dominance of all course parts, the influence of the luckiness
and coincidence factor reduced to a minimum.
Knowledge assessment through computers has been carried
out in schools in the last few years and it has proved to be very
successful. Most importantly, the disadvantages of the teacher as
Graph 2
Graph 1
WEB LABORATORY FOR COMPUTER NETWORK 7
Figure 7 Web application—the sixth part. (a) Network topology 1 and (b) network topology 2.
8 JOVANOVIC ET AL.
an assessor are eliminated (the same criteria of assessment for all
students). Statistics has shown that students’ success has a
tendency to grow. The data also show a quantitative and
qualitative progress in the sense of the increase in the number
of students who have passed an exam with very good grades.
CONCLUSION
In this article, the Web-based system is presented, the purpose of
which is learning practical aspects from IT area. The system
enables the user, with an access to the Internet, to study, to
accomplish laboratory practice and test the knowledge he/she has
obtained.
In order to offer the possibilities of contemporary testing to
our students as well, the creating system has been experimentally
conducted at a school. The system provides learning contents and
methods suitable for the learners of different learning
styles. Experimental results on the system show that the
system can establish an individualized learning environment
which will improve the efficiency of learning. Also, the
experiment has shown that in our circumstances it is possible to
implement testing by applying IT and logic of computerized
adaptive testing and to open the doors to further research and
perfection.
The system is realized in Java. Primary requests for the
development environment have been the supporting of all
facilities of the IP networking as well as to minimize the cost.
A zero cost environment based on Java has been used. Major
characteristics of Java such as hardware independence,
internal security, and network-based environment compel the
use of Java environment as quite promising. Java is the
predominant language used for Web-based system because of
its portability, reusability, object orientation, and graphical
capabilities. This system is 100% pure Java, and Java is an
interpreted language. This limitation becomes apparent as the
number of simultaneous users and the number of active
components grows, as manifested by many students accessing
our educational system or a full-featured educational system. In
fact, most of students’ complaints about system performance
were about time responses from the server side. One solution
under consideration is the optimization of the server modules
based on a combination of native and Java code. Presently, we are
carefully profiling the system to be able to select the best
combination possible.
REFERENCES
[1] N. Jensen, S. Seipel, and G. Voigt, Heuristic evaluation of a virtual
lab system, Technical Report L3S Q4 2003, VASE 3, L3S,
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[3] I. Stiubiener, W. V. Ruggiero, R. M. Silveira, I. Korolkovas, S.
Skopp, and C. Meiler, NETLAB: A framework for remote network
experiences, IEEE Frontiers in Education Conference, 2006.
[4] A. Weyland, E. Kurt, T. Braun, and F. Baumgartner, Virtual routers:
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[5] J. Djordjevic, B. Nikolic, and A. Milenkovic, Flexible Web-based
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Figure 8 The realized results statistics.
Table 1 The Results of the Testing
Five Six Seven Eight Nine Ten
Visual 0 0 0 2 2 2
Auditory 0 3 3 2 1 0
Practical 0 2 3 2 2 1
WEB LABORATORY FOR COMPUTER NETWORK 9
[7] P. Falstad’s, Math and physics applets, http://www.falstad.com/
mathphysics.html.
[8] Virtual labs: curves & surfaces, http://www.math.tuberlin.de/
geometrie/lab/curvesnsurfaces.shtml.
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383�396.
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style. Available at: http://homeworktips.about.com/od/homewor-
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BIOGRAPHIES
Nenad M Jovanovic is a professor in the
Department of Computing and Informatics at
the Advanced Business School in Blace. His
research interests include computer network,
simulation and educations sistems. He received
a BSc in computer engineering from the
University of Pristina, a MPhil from the
University of Belgrade and a PhD in computer
science from the University of Pristina.
Ranko Popovic is an Associate Professor of
Computer Science at Singidunum University,
Serbia. He received his Diploma (M.Sc.) in
Electrotechnics at University of Nis and his
Doctorate (Ph.D.) in Computer Science at
University of Pristina., in 1988 and 1996,
respectively. Since 2007 he has been with
Singidunum University. He has taught many
courses on computer science and authored a
few books in Serbian on the same subject. His research interests
include operating systems, computer networks, distributed systems,
graph theory, multimedia, and distance learning.
Suzana Markovic is a Professor of Computer
Science at Adavanced Buissines School of
Blace, Serbia. She received his BS degree in
Electrotechnics at University of Pristina and
her MS in Computer Science at University of
Belgrade. Her research interests include dis-
tance learning systems.
Zoran Jovanovic is a researcher in the
Computer And Informatics Department at the
Adavanced Buissines School---Blace, Serbia.
He received his MS in Computer Science at
Singidunum University, Serbia. His research
interests include computer netvorks and dis-
tance learning.
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