2. What is a Network?
0 A network consists of two or more computers that are
linked together in order to share resources (such as
printers), exchange files, or allow electronic
communications.
0 The computers on a network may be linked through
cables, telephone lines, radio waves, satellites, or
infrared light beams.
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3. Local Area Network (LAN)
0 Local Area Networks (LANs) are networks that are
confined to a relatively small area. It is generally limited
to an area such as a school, office or building.
0 The computers in a LAN are linked together by cable or
wireless connections.
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4. Local Area Network (LAN)
To enable a computer to connect to a LAN
myou require a device called a
network interface card (NIC)
0 On most LANs, cables are used to connect the network
interface cards in each computer to the network.
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5. Local Area Network (LAN)
0 A Network Interface Card (NIC) is fitted to each device
connected to the network.
0 An NIC stores data being transferred to and from a
computer (workstation) and the network.
0 If required the NIC converts the data being transferred to
make sure that it follows the communications rules that
run on the network.
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6. Local Area Network (LAN)
Client/Server Network
0 In most LANs a powerful computer is used as the
server.
0 The server stores all of the software that controls the
network, as well as the software and files that can be
shared by the computers connected to the network.
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8. Local Area Network (LAN)
Client/Server Network
0 Most LANs will have more than one server. For
example:
0 a printer server;
0 a web server;
0 an applications server.
0 Computers connected to the server on a network are
called workstations. These workstations are the
clients.
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9. Local Area Network (LAN)
Client/Server Network Advantages:
0 Centralised - resources and data security are
controlled through the server;
0 Resource Sharing – expensive peripheral
devices such as laser printers and scanners can
be shared by users
0 Reliability – ability to continue operating when
problems occur;
0 Scalability - elements can be added or replaced
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10. Local Area Network (LAN)
Client/Server Network
Advantages Continued:
0 Flexibility - new technology can be easily
integrated into the system;
0 Interoperability - all components should work
together;
0 Accessibility - resources can be accessed
remotely.
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11. Local Area Network (LAN)
Client/Server Network Disadvantages:
0 Expensive – requires initial investment in network
hardware;
0 Maintenance – large networks will need staff to ensure
efficient operation for example, a network
manager, network technicians;
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12. Local Area Network (LAN)
Client/Server Network
Disadvantages continued:
0 Dependence – when a server goes down, operations
will cease across the network.
0 Interoperability - all components may not work
together;
0 Security/Privacy – as data is shared there is a greater
need for security
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13. Wide Area Network
(WAN)
0 Wide Area Networks (WANs) connect computers across large
distances, such as Scotland, Europe, or the world.
0 Telecommunications links are used to connect this type of
network.
For example: connections (links) via telephone lines and
satellites.
0 A computer must have a modem to enable connection.
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14. Transmission Media
0 Networks use different types of media to transmit data.
0 The main types of media used are:
0Copper cabling
0Fibre-optic cabling
0Wireless
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15. Transmission Media
Copper cabling
0 Twisted-pair cabling:
0 twisted pair cabling is the most popular media used in
LANs;
0 It can support data transmission rates of 100 Mbps.
0 Advantage: It is quite cheap to buy.
0 Disadvantage: twisted-pair cabling may be susceptible to
radio and electrical frequency interference.
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16. Transmission Media
Copper cabling
0 Coaxial cabling:
0is highly resistant to signal
interference;
0it can support greater cable lengths
between network devices than twisted
pair cable.
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17. Transmission Media
Fibre-optic cabling
0Fibre optic cabling transmits light
rather than electronic signals
eliminating the problem of electrical
interference.
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18. Transmission Media
Fibre-optic cabling
0 Advantages:
0It has the ability to transmit signals over
much longer distances than coaxial and
twisted pair;
0It has the capability to carry data at much
greater speeds than coaxial and twisted
pair;
0It is a secure medium.
0 Disadvantage: expensive to install.
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19. Transmission Media
Wireless networking
0 Not all networks are connected by cabling; some
networks are wireless.
0 Wireless LANs use high frequency radio
signals, infrared light beams, or lasers to
communicate between workstations and the
server(s).
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20. Transmission Media
Wireless networking
0 Advantages:
0 no need for cabling;
0 portability – network workstations can be moved and
used in different locations.
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21. Transmission Media
Wireless networking
0 Disadvantages:
0 provide poor security;
0 slower than LANs using cabling;
0 limited range (approximately 100m)
0 signals absorbed by walls;
0 susceptible to interference from lights and electronic devices;
0 performance decreases as more computers used.
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22. Multi Access
0 Multi Access allows many users to share(access) the
processor of a large computer(Mainframe).
0 Processor time is divided between the users by
allocating them a time slice.
0 Each time slice lasts only milliseconds and is carried out
on a rotational basis making the users unaware that the
processor is being shared.
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24. Security Measures
0Files stored on the network
must be protected against
loss, corruption, hacking and
viruses.
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25. Security Measures
0 Ways of securing this are to use:
0 user IDs and Passwords to gain access to the network;
0 different access rights for different users;
0 data encryption – data is changed into a code. To read the
data a user must have the key to the code;
0 advanced ID measures – the use of smart cards to store
fingerprint or voiceprint information
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26. Security Measures
continued
Physical Security measures:
0 To prevent unauthorised access:
0 Lock the door of the computer room(s);
0 Put lockable covers over power switches, etc…
and give only authorised users the key or door code.
0 Disable floppy disc drives to prevent:
0 files being saved to floppy disc and taken away;
0 possible loading of viruses from floppy discs.
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28. Mesh
Topology
0 Advantages 0 Disadvantages
Fault in 1 channel Lots of wiring,
doesn’t affect whole
network Expensive
Many transmissions can
take place at any one
time
Excellent Performance
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29. Star Topology
0 Advantages 0 Disadvantages
Shorter paths loss of network if central
node fails
simpler to monitor and
many cables needed
audit
costly to expand
easier fault finding
greater initial costs
simple access protocols
central node slows
easy expansion communication between
nodes
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30. Bus
Topology
0 Advantages 0 Disadvantages
only 1 main channel fault diagnosis is difficult
required a fault in one section of main
easy to extend channel causes a fault in the entire
channel
cheap
more sophisticated protocols &
Station faults have no
hardware required
effect on rest of
network monitoring and auditing becomes
complicated
High rate of data crashes
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31. Ring
Topology
0 Advantages 0 Disadvantages
suitable for fibre optic difficult to diagnose
cables faults
signal is boosted at extension of the network
each station is impossible without
node failure will not bringing the rest of the
cause network network down
failure, just rerouting Control software and
equipment expensive
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32. Tree
Topology
0 Advantages 0 Disadvantages
As the star, and the bus As the star and bus.
If link between branches
goes down, branch can
work on it’s own.
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