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17 Computer Networks
·A computer network is a collection of computers linked together so
that they can communicate with each other
·A computer that is not connected to a network is called a stand-
alone computer
·There are two different sorts of computer network:
·`Local Area Network' or `LAN' - the computers are all in the
same building or in different buildings on one site permanently
connected to each other with special cables.
·`Wide Area Network' or `WAN' - the computers are spread over
a large geographical area not permanently connected to each
other communicate using telephone lines, radio transmitters or
satellite links.…read more

Slide 2

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Advantages of a LAN
·Workstations can share peripheral devices like printers. This is
cheaper than buying a printer for every workstation;
·Workstations don't necessarily need their own hard disk or CD-ROM
drives which makes them cheaper to buy than stand-alone PC's;
·Users can save their work centrally on the network's file server. This
means that they can retrieve their work from any workstation on the
network. They don't need to go back to the same workstation all the
·Users can communicate with each other and transfer data between
workstations very easily;
·One copy of each application package such as a word processor,
spreadsheet etc can be loaded onto the file server and shared by all
users. When a new version comes out, it only has to be loaded onto
the server instead of onto every workstation.…read more

Slide 3

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Disadvantages of a LAN
·Special security measures are needed to stop users from using
programs and data that they shouldn't have access to;
·Networks are difficult to set up and must be maintained by skilled
ICT Technicians;
·If the file server develops a serious fault all the users are affected,
rather than just one user in the case of a stand-alone machine.…read more

Slide 4

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Network security measures
·To protect programs and data
·Main threats come from other users and hackers
·Data can be kept secure by giving each network user their own user
identity and password
·Unauthorised access can be reduced by allowing different users
different levels of access
·Local area networks can be protected by physically restricting access
to the computer room by locking the door or providing users with an
entry code or special `swipe card' key.…read more

Slide 5

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Wide Area Network (WAN)
·Computers in a wide area network are often connected to each other
using telephone lines.
·When a computer uses an ordinary telephone line to connect to
another computer, a modem is needed at each end of the link.
·If an entire LAN needs to be connected to a WAN a special gateway
needs to be set-up.…read more

Slide 6

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A Wide Area Network (WAN)
Print Server File Server
Gateway Modem
Remote PC
Remote PC Modem
network cables
telephone lines…read more

Slide 7

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