COMPUTER NETWORK
• A computer network is an interconnection of various
computer systems located at different places
• Two or more computers are linked together with a
medium and data communication devices for the
purpose of communicating data and sharing resources
• The computer that provides resources to other
computers on a network is known as server.
• Individual computers in the network, which access
shared network resources, are known as nodes.
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Local Area Network (LAN)
 Networks used to interconnect computers in a single room,
rooms within a building or buildings on one site are called Local
Area Network (LAN).
 LAN transmits data with a speed of several megabits per
second
 The transmission medium is normally coaxial cables.
 LAN links computers, in the same area for the purpose of
sharing information.
 Usually LAN links computers within a limited geographical area
because they must be connected by a cable, which is quite
expensive.
 People working in LAN get more capabilities in data
processing, work processing and other information exchange
compared to stand-alone computers.
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Characteristics of LAN
1) every computer has the potential to
communicate with any other computers of the
network
2) high degree of connection between computers
3) easy physical connection of computers in a
network
4) inexpensive medium of data transmission
5) high data transmission rate
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Use of LAN
1)
2)
3)
4)
5)
6)
File transfers and Access
Word and text processing
Electronic message handling
Remote database access
Personal computing
Digital voice transmission and storage
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Wide Area Network
The term Wide Area Network (WAN) is used
to describe a computer network spanning a
regional, national or global area.
For example, for a large company the head
quarters might be at Cairo and regional
branches at Mansoura, Tanta , and Aswan.
the transmission medium used are normally
telephone lines, microwaves and satellite
links
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The characteristics of WAN
•
•
Communication Facility: For a big company
spanning over the country the employees
can save long distance phone calls and it
overcomes the time lag in overseas
communications.
Computer conferencing is another use of
WAN where users communicate with each
other through their computer system.
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•
•
•
Remote Data Entry is possible in WAN. It means sitting
at any location you can enter data, update data and
query other information of any computer attached to
the WAN
Centralized Information: This means if the organization
is spread over many cities, they keep their important
business data in a single place. WAN permits collection
of this data from different sites and save at a single site
Ethernet: Ethernet developed by Xerox Corporation is a
famous example of WAN
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Difference between LAN and WAN
1) LAN is restricted to limited geographical area of few kilometers.
But WAN covers great distance and operate nationwide or even
worldwide.
2) In LAN, the computer terminals and peripheral devices are
connected with wires and coaxial cables. In WAN there is no
physical connection. Communication is done through telephone
lines and satellite links.
3) Cost of data transmission in LAN is less because the transmission
medium is owned by a single organization. In case of WAN the
cost of data transmission is very high because the transmission
medium used are hired, either telephone lines or satellite links.
4) The speed of data transmission is much higher in LAN than in
WAN. Few data transmission errors occur in LAN compared to
WAN.
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NETWORK TOPOLOGY
Star Topology
• In star topology a number of workstations are directly linked to a
central node as the next figure.
• Any communication between stations on a star LAN must pass
through the central node.
• The central node controls all the activities of the nodes.
The advantages of the star topology are:
• It offers flexibility of adding or deleting of workstations from the
network.
• Breakdown of one station does not affect entire system
The major disadvantage of star topology is that failure of the central
node disables communication throughout the whole network
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Star topolgy
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Bus Topology
 In bus topology all workstations are connected to a
single communication line called bus.
 There is no central node as in star topology.
 Transmission from any station travels the length of the
bus in both directions and can be received by all
workstations.
The advantage of the bus topology is that
 It is quite easy to set up.
 If one station of the topology fails it does not affect
the entire system.
 The disadvantage of bus topology is that any break in
the bus is difficult to identify.
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Bus Topology
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Ring Topology
 In ring topology each station is attached nearby stations on a
point to point basis so that the entire system is in the form of a
ring.
 In this topology data is transmitted in one direction only.
 Thus the data packets circulate along the ring in either
clockwise or anti-clockwise direction.
The advantage of this topology is that any signal transmitted on
the network passes through all the LAN stations.
The disadvantage of ring network is that the breakdown of any
one station on the ring can disable the entire system.
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Ring Topology
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INTERNET
 The Internet is a network of networks
 Computer users on the Internet can contact one
another anywhere in the world
 In Internet a huge resource of information is
accessible to people across the world
 Information in every field starting from education,
science, health, medicine, history, and geography to
business, news, etc. can be retrieved through
Internet
 You can also download programs and software
packages from anywhere in the world
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Origin of Internet
• In 1969 Department of Defense (DOD) of USA started
a network called ARPANET (Advanced Research
Projects Administration Network )
• Around 1970, NSFNET (National Science Foundation
Network) was created. With the advancement of
modern communication facilities,
• By 1990 many computers were looking up to NSFNET
giving birth to Internet
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Internet functions
 Internet is not a governmental organization.
 The ultimate authority of the Internet is the Internet
Society.
 This is a voluntary membership organization whose
purpose is to promote global information exchange.
 Internet has more than one million computers
attached to it.
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E-mail
• E-mail stands for electronic mail.
• This is one of the most widely used features of
Internet.
• In electronic mail the data are transmitted through
Internet and therefore within minutes the message
reaches the destination may it be anywhere in the
world.
• Therefore the mailing system is excessively fast and is
being used widely for mail transfer
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Features of E-mail
1)
2)
3)
4)
One-to-one or one-to-many communications
Instant communications
Physical presence of recipient is not required
Most inexpensive mail service, 24-hours a
day and seven days a week
5) Encourages informal communication
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Components of an E-mail Address
• As in the case of normal mail system, e-mail is also
based upon the concept of a recipient address.
• The email address provides all of the information
required to get a message to the recipient from
anywhere in the world. Consider the e-mail ID
• john@hotmail.com
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john@hotmail.com
• In the example above, "john" is the local
part, which is the name of a mailbox on the
destination computer, where finally the mail
will be delivered.
• Hotmail is the mail server where the
mailbox "john" exists,
• .com is the type of organization on net
• .edu Educational institutions
• .gov Government site
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File Transfer Protocol (FTP)
• File Transfer Protocol, is an Internet utility software
used to upload and download files.
• It gives access to directories or folders on remote
computers and allows software, data and text files to
be transferred between different kinds of computers.
• FTP works on the basis of same principle as that of
Client/Server.
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• FTP "Client" is a program running on the your
computer that enables you to talk to, and get stuff
from, remote computers.
• The FTP client takes FTP commands and sends them
as requests for information from the remote
computer or known as FTP servers.
• To access remote FTP server it is required but not
necessary to have an account in the FTP server.
• When the FTP client gets connected
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The objectives of FTP
The basic objectives of FTP are
• to give flexibility and promote sharing of
computer programs, files and data
• to transfer data reliably and more efficiently
over network
• to encourage implicit or indirect use of remote
computers using Internet
• to shield a user from variations in file storage
systems among hosts
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Telnet (Remote Computing)
 Telnet or remote computing is telecommunication utility
software, which uses available telecommunication
facility and allows you to become a user on a remote
computer.
 Once you gain access to the remote computer, you can
use it for the intended purpose.
 The TELNET works in a very step by step procedure. The
commands typed on the client computer are sent to the
local Internet Service Provider (ISP), and then from the
ISP to the remote computer that you have gained access.
 Most of the ISP provides facility to TELNET into your
own account from another city and check your e-mail
while you are traveling or away.
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WORLD WIDE WEB (WWW)
• WWW is the short form for the World Wide Web. It is also
commonly known as ‘The Web’.
• The WWW is hypertext based information retrieval tool.
• One can easily surf the Web by jumping from one document to
another using the links in those documents.
• These documents can be in many formats, such as text,
graphics, animation, sound and latest is video. They may also be
a combination of all these.
• All the information on Internet are presented to the user as a
document or more popularly known as Web Page.
• All these Web Pages are link to each other or even to section
within a Web Page. And these links are known as Hyper Links.
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The Web browser
 The tool used to view these Web Pages on Internet is
known as Internet browser or simply browser.
 It is a software program specifically developed to
extract information on user request from the Internet
and present them as a Web Page to the viewer
 The most popular are Internet Explorer from Microsoft
and Netscape from Netscape Inc
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