computer network is a group of interconnected computers that share information and resources. The most common resource shared today is connection to the Internet. Other shared resources can include a printer or a file server. The Internet itself can be considered a computer network. Two basic network types are local-area networks (LANs) and wide-area networks (WANs). LANs connect computers and peripheral devices in a limited physical area, such as a business office, laboratory, or college campus, by means of links (wires, Ethernet cables, fibre optics, Wi-Fi) that transmit data rapidly.

1. 1/4/2020 1
Samina khan
Fazaia Degree College Risalpur

2. • Chapter 1 Data –Processing Cycle
• Chapter 2 Binary Computing
• Chapter 3 System Software
• Chapter 4 Application Software
• Chapter 5 More on Word
• Chapter 6 More on Spreadsheets
• Chapter 7 Algorithms and Flow charts
• Chapter 8 Introduction to Programming Languages
• Chapter 9 Computer Networks
• Chapter 10 The Internet
• Chapter 11 Communicating through Email1/4/2020
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3. CHAPTER 9

4. The need for being connected
• To share information with other computers,
our computer must be connected to them.
• We connect our computer to a very large and
powerful computer called server.
• A server can store a lot of data and expensive
software. Expensive hardware devices can also
be connected to it.
• We can then share the data, software and
hardware with other computers connected to
the server.

6. Networks
• A network consist of many people or devices
connected to one another in some way.
• Your circle of friends is a network. You share
your problems and joys with them.

7. Networks
• A computer network is a network of computers
and hardware devices connected by wires.
• Computer network consists of some other
important parts.
1. The sending device
2. The receiving device
3. The transmission medium
4. The communication device
5. The network interface card

8. The sending device
• A sending device send data over a network.
• When a computer need to use a printer or a
program on a server, it sends a request to the
server.
• This computer is a sending device.

9. The receiving device
• A receiving device receives data or signals sent
by a sending device.
• If a sender send request to the server then the
server is the receiving device.

10. Transmission medium
• A transmission medium connects computers to
the server.
• It carries signals from the sending device to a
receiving device. The wires or cables connecting
telephones and computers are transmission
media.
• There are three main types of cables.
1. The coaxial cables
2. Twisted-pair cable
3. Fiber-optic cable

11. Coaxial Cable Twisted pair cable
Fibre optic

12. The coaxial cable
• It is the simplest type of cable.
• It consists of a conducting wire made of copper.
• Signals travel along the copper wire. The wire is
covered by layers of insulating material.
• Some wires from one cable can interface with
signals travelling

13. Twisted-pair cable
• It consists of two wires twisted around each
other. This reduce crosstalk and other
disturbance.
• It is thinner and more flexible than coaxial
cable.

14. Fibre-optic cable
• It carries data faster than other types of cables.
• It is made of glass fibres.
• Light signals travel by reflection across the inner
surface of the wire.

15. The communication device
• A communication device helps two devices
understand each other.
• Digital signals that flow in computer are different
from the analog signals carried along telephone
wires.
• Digital signals cannot travel along telephone lines
and computers cannot understand analog signals.
• A communication device that convert digital signals
to analog and vice versa.
• This device is called modem.

16. The Network Interface Card
• An expansion card is connected to mother board
to increase the processing capacity of a
computer.

18. The computer network
• A computer network is a group of computers
connected to each other by a transmission
medium.
• Computers can share data, programs and
hardware devices when they are part of a
network.
• A computer that not part of a network is called a
stand-alone computer.

21. Network is an effective way to share information

23. The Hub
• A hub connects the computers in a network.
• Cables from all the computers are connected to
the hub.
• When a computer sends a message to another
computer, the message is first sent to the hub.

25. The Hub
• The hub then sends the message to all the
computers on the network.
• This is a waste because not every computer
needs the message. A hub is also called the
repeater.

26. The switch
• switch is better than a hub.
• A switch knows the address of each computer on
network.
• When a signal from sending device reaches the
switch, it sends the message only to the
computer that needs the message.

27. The router
• A router connects two networks. It
enables a message to be sent from
one network to another.
• When a message reaches a router,
a router first identifies the network
of the receiving computer. Then it
sends the message to the address
of the receiving computer on that
network.

28. Types of computer network
• There are many types of network.
i. Peer-to-peer network
ii. Client/server network

32. Peer-to-peer network
• In peer-to-peer network there is no central
computer or server.
• Each computer is connected to every other
computer and no computer is more important
than the other.

33. Client/server network
• In a client/server network there is server or a
central computer.
• The server stores data and programs that can
be shared by other smaller computers
connected to it.
• These data and programs are called resources.
• The smaller computers that share these
resources are called clients.

36. Local area network (LAN)
• A Local area network connects computers in a
small building.
• LANs are found in schools, colleges and offices.

37. Metropolitan area network(MAN)
• A metropolitan area network combines two or
more LANs. It connects computers in different
parts of city.
• It is larger and faster than a LAN.
• It is more expensive.

38. Wide area network (WAN)
• A wide area network combines many LANs and
WANs. It connects computers in different cities
or area.
• It is larger than a MAN.
• It uses a lot of cable. Satellite connections are
faster, but they are very expensive.

39. The Internet
• The Internet is a special type of WAN. It can link
all the LANs in the world to create a worldwide
network.
• The internet uses very large and powerful
servers.

40. The Intranet
• The Intranet connects computers within an
office. It doesn’t link computers in one building
only. It connects computer in different cities.
• An intranet uses internet technology.
• It is faster than LAN or WAN and can carry more
data.

41. The extranet
• Sometimes, a company needs to share data with
customers or suppliers. It can do this by creating
an extranet.
• An extranet is created when a company lets its
customers and suppliers connect to the intranet

42. Network topologies
• Topology means arrangement. We can arrange
computers in different ways in a network.
• These different arrangements are called
network topologies.
• There are three main network topologies.

43. The Bus topology
• In a bus topology, all the computers are
connected to the server by a single cable called
a backbone.
• When we send a signal from our computer to
the server, the server sends it to all the
computers. Only the receiving computer
receives the message. It slows down the
network.
• If there is a problem with the cable at any point,
the signal cannot reach the server or the client.

44. The ring topology
• In a ring topology, all the computers are
connected in a loop. Each computer or device is
called a node.
• Computers send signals round the loop by
passing them from one computer to another.
• It is faster and cheaper but if a cable or
computer breaks down, all the computers
become disconnected.

45. The star topology
• In a star topology, each computer is connected
to a hub or a server by a separate cable.
• Data doesn’t travel needlessly.
• If one computer or a cable breakdown, the
other computers can still work normally.