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CH/S4CS/Sept. 2006
Networking (Ch. 8)

A network
devices.

Networking is the process of connecting computers that permits the transfer of data and programs between
them.

Today networking is the fastest growing area in information technology.
is a communication system that connects two or more computers and their peripheral
Need for networking (8-3)

There are several reasons why a company or an organisation would choose to implement a network. The four
most important ones are:
i.
Fast response: a network system allows users at various locations to get immediate responses to inquiries.
ii.
Up-to-the-minute database: a major benefit of a network system is that a user can maintain an
up-to-the-minute database.
iii.
Hardware resource sharing: Every computer on the network is allowed to use certain expensive devices.
iv.
Information resource sharing: It allows using a computer on the network to access data and software stored
on any other computer or the host computer in the network.
Distributed processing: Rather than using a large mainframe, several smaller computers can be used around the
organisation and in each branch office, by connecting together in networks. A distributed system is a system in
which a job is performed by a number of computers that are linked through a communication network..
Types of Networks - a geographical distribution (p. 68 – p. 69)

Local Area Network (LAN).
i.
Local area networks are networks in which all the computers and terminals are located in the same offices or
buildings.
ii.
They enable all the computers on the site to communicate with each other, and share peripherals such as hard
disk, printers and external communications links.
iii.
LANs represent a low-cost solution for low-volume data transfer over relatively short distances.
iv.
Network models of a LAN
a.
b.
Client / Server model

It uses a central computer, known as the server
, to maintain all the files used by the
users. Each individual computer (workstation) on the network can have access to the files on the
server.

Advantage: handles very large networks efficiently.
Peer-to-peer model

It has no server. It allows any computer to share the hardware, software, or information located on
any other computer in the network. It is commonly found in small organisations.

Advantage: Low cost and easy to set up.
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
Wide Area Network (WAN).
i.
Wide area networks (WANs) use telephone lines, microwave relays and satellites to reach data over long
distances in the same country or outside country on different continents between various centres.
ii.
Under a WAN, each location needs to access resources locally but also needs to share data with the other
locations.
** This is another type of network namely the Metropolitan Area Network (MAN) with its scale larger than LAN
and smaller than WAN.
Hardware for Networking (8-8 to 8-10)

Telephone line. The telephone system, originally set up for voice communication, is used to handle data
communications.


Modem.
i.
Computers deal with data in digital form but most telephone lines are designed to carry analog signals.
ii.
An interface is needed to change the data from digital to analogue form and vice versa, i.e. a modem (for
both modulator and demodulator).
Coaxial cable. Coaxial cable contains electrical wire and is constructed to permit high-speed data
transmission over this wire with a minimum of signal distortion.

Unshielded Twisted Pair (UTP) Cable.

Fibre optics cable.

i.
Eventually replacing the copper wire traditionally used in the telephone system.
ii.
A fibre optics cable consists of a number of thin tubes of glass which carry data as pulses of light. The
pulses are very rapid, large in data capacity, more reliable and more secure at transmitting data.
Microwave radio. Microwave transmission consists of high-frequency waves that travel in straight lines
through the air rather than through wires.

Communication satellite. In satellite communications, data are first transmitted to an Earth station, where
giant antennas route signals to another Earth station via a communications satellite.


Network Interface Card (NIC).
i.
An interface between a computer and the network.
ii.
It is an expansion card installed on the motherboard.
iii.
A network cable is plugged into the NIC from the wall socket.
Connecting Devices.
i.
ii.
iii.
Hub
. It connects all network cables together and broadcasts every packet of data to every port.
Switch
. It also connects all network cables together but it forwards each packet of data to the
destined port only.
Bridge
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. It connects different networks together.
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iv.
Router
. It also connects different networks. Network data is routed to different networks
based on the program in it.
Software for Networking (p. 73)

The network operating system (NOS) manages the resources on the network. It monitors the data exchange,
ensure data security by incorporating users’ account and password system.

Common samples of network OS: Windows NT, Windows 2000, Linux.

In order to ensure that different manufacturers’ products can be connected properly in one network, International
Standards Organisation set up a strict set of rules called
protocol
for communication. It describes
the following things:
i.
the language to be used.
ii.
the speed at which the data is sent.
iii.
odd or even parity check being used.
iv.
the types of codes that identify stations and data storage devices on the network.
v.
the type of line control in use i.e. how an individual station gains control of the communication line so that it
can talk without interrupting others or being interrupted.

A network operating system must have the ability to communicate with each network using a common protocol.

Sample protocols: NetBEUI and TCP/IP
Network Topology

Network topology is used to describe the physical organisation of the network. The basic patterns are usually
classified as:
i.
Star topology.
a.
The central control unit handles the communication tasks of receiving and routing messages to the
various workstations.
b.
Advantage:

Easy to install

No disruption to the network when connecting or removing devices

Easy to detect faults (control)
main resource
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Fig.
ii.
iii.
(a) Star-network
Highest speed
topology gives the
and security.
Ring topology.
a.
It involves computers that are approximately the same size, has all devices connected by a single
communication cable that forms a closed circle. Ring topology is used for more local communication.
b.
Advantage:

East to connect computer or peripheral to a linear bus

Requires less cable
Bus topology.
a.
All devices in the network are connected to and share a single cable. An advantage of the bus topology is
that if one computer on the network fails, this does not affect the rest of the network.
b.
There are usually two rings running in parallel.
c.
Advantage:

Does not rely on a single hosting computer and can function even though one of the nodes is broken.
main resource
Fig9(b) Ring-network based on a ‘continuous’ loop
main resource
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Fig. 9(c) Bus-network is versatile and
cheap – but less secure.
Common Network Service (8-13 to 8-14)


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Simultaneous Access
i.
When separate copies of certain data are stored in different computer, it is difficult to determine when
copy of the data is the most up-to-date.
ii.
Using a client/server network, a single copy of data is store in a server, which can be accessed through
different workstation at the same time.
Device Sharing
i.
When several people can share a device, e.g. printer, in a network, the use of the device becomes less
expensive and easier to manage.
ii.
Spooling.
a.
Users send documents to a networked printer.
b.
Each document is temporarily stored in the printer server.
c.
The printer server stores the print job in a queue.
d.
When the printer finishes the current job, it printer server sends the next print job of the queue to the
printer.
Communication
i.
Electronic mail system – A system for exchanging written messages through a network.
Wireless Network

Using a wireless network, data are transmitted by radio wave.

Wireless network connections perform the same functions as wired connection.

Each computer that is to be part of the wireless network must have a
(or a wireless PC card for a notebook computer).

A
wireless access point
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wireless adapter
allows computer to access a wired network.
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