1. Basic Concepts of a Computer Network
Objectives
Understand why a computer network is needed
Understand what types of services are available on a network
Understand how computers can be connected locally to form a Local Area Network (LAN) and over long distances to form a Wide Area Network (WAN)
Be aware of how and why computers are connected to form a network at home, in school and in workplace
Be able to use and describe the common services available in a networked environment
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2. 8.1 Need for a Computer Network
8.1.1 Case Studies
Case 8.1: In school, Jane needs to save her working files in A1 computer laboratory into a floppy disk and give it to her classmate in A2 laboratory for review.
With computer network: Jane can save files in a file server. When Jane amends files in A1 computer laboratory, her classmates can see the new updates in A2 computer laboratory at the same time.
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3. Case 8. 2 : John works in a shipping company
Case 8.2 : John works in a shipping company. He is responsible for data entry and often needs to print the shipping orders of the company. However, no printer is connected to his computer. John must save all files into a floppy disk and use another computer to print the shipping orders. This is very inconvenient for John.
With computer network: John can now directly print the shipping orders to a networked printer from his computer. One printer can handle all the printing tasks.
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4. 8.1.2 Why do We Need a Computer Network ?
A network is a way to connect computers for :
Communication
Data exchange
Resource sharing
Most companies have PCs connected to form a network in their offices
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5. It makes electronic communications easier
Three of the most important benefits that are brought by network include the following:
It allows many users to access the same programs and data simultaneously
It makes electronic communications easier
It allows users to share peripheral devices, such as printers and scanners
Video conferencing is available in the network environment
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking

6. 8.2 Types of Network
When two or more computers are connected, a network is formed. There are two main types of network:
Local Area Network (LAN)
Wide Area Network (WAN)
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7. 8.2.1 Local Area Network (LAN)
A Local Area Network (LAN) consists of computers that are relatively near to each other
It can consist of just two or three PCs connected together to share resources. It can also connect hundreds of computers of different kinds
The connection can be made either by cables, infrared links, or small wireless devices
An example of a local area network connecting several PCs, printers, a file server and a network gateway
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking

8. 8.2.2 Wide Area Network (WAN)
8.2.3 Metropolitan Area Network (MAN)
A typical Wide Area Network (WAN) consists of two or more local area networks connected together across a wide geographical area
Public utilities, such as the telephone line system, are usually used for the transmission of data
The cost associated with transmitting data is another major difference between WAN and LAN. It is relatively more expensive in WAN than that of in LAN.
Metropolitan Area Network (MAN) is a network that interconnects computers in a geographic area larger than that covered by LAN but smaller than that covered by WAN.
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9. An illustration of a Wide Area Network (WAN)
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10. 8.3 Network Models 8.3.1 Peer-to-peer Model
A peer-to-peer model is a LAN where computers are simply connected together
Each computer has equal relations with each other and controls which computer can use its resources
A peer-to-peer model
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11. 8.3.2 Client/Server Model In a client/server network model, we have:
Server: A computer that has central control over all network resources.
Clients: Other computers connected to the server.
A client/server model
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12. Table 8.1 Advantages and disadvantages of peer-to-peer and client/server models
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13. 8.4 Basic Requirements for Establishing a Computer Network
The basic requirements of a network are:
Each computer must have a network card
Network protocol
A hub or a router
Cables or microwaves
Network operating system
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14. 8.4.1 Protocols
Networks are governed by protocols, which are rules for sending and receiving data. Devices on the network must be able to “talk the same language ” or use the same protocol.
Two common protocols used today are:
NetBEUI : It is a protocol that broadcasts messages to every computer on the network.
TCP/IP : It is the protocol of the Internet and is required on any computers that communicate across the Internet. It is a very powerful protocol to connect every computer in the world.
Modern Computer and Information Technology (HKCEE) Core Module
Section B Computer Systems and Networking

15. 8.4.2 Network Operating System (NOS)
A network operating system (NOS) is an operating system that has the ability to control the networking components of a computer system.
It also provides services such as:
Printer sharing
File sharing
Database sharing
Application sharing
The ability to manage a naming directory for the network
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16. 8.4.3 Network Interface Card (NIC)
A network cable is plugged into the network interface card and physically connects a computer to a network
In a network, each computer must have a network interface card to connect to other computers and devices.
In a wireless connection, a wireless adapter is required.
The main function of a network interface card is to convert data of a computer into electrical signals
Modern Computer and Information Technology (HKCEE) Core Module
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17. 8.4.4 Types of Communication Media
In a wired network, data is transmitted through physical media, mostly cables, such as twisted-pair cable , coaxial cable and fibre-optic cable.
In a wireless network, data is transmitted through microwave.
A fibre-optic cable is a thin strand of glass that transmits pulsating beams of light instead of electric current.
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18. 8.4.5 Connecting Devices
A connecting device acts as a switching board for transmitting data from one computer to another.
Computer
Hub
A network hub is used to connect different computers together by joining all the network cables
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19. Table 8.2 Functions of different connecting devices
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20. 8.4.6 Network Topologies
Topology is the physical or logical layout of cables and devices that make up a network. There are three main types of network topology:
Star topology : Several nodes are connected to a central one. All the communications travel through this central node.
It requires the largest amount of connecting cables.
Star topology
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21. It is less expensive than the star topology.
Bus topology : Nodes are connected by a common bus, which can be as simple as a single wire.
It is less expensive than the star topology.
Bus topology
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22. Ring topology : Each node is connected to two others forming a ring
Ring topology : Each node is connected to two others forming a ring. Data is transmitted around this ring.
There are usually two rings running in parallel so that when one segment of the ring is broken, the other ring can take over immediately.
Ring topology
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23. Table 8.3 Advantages and disadvantages of the three different network topologies
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24. 8.4.7 Network Technologies
Network technology is the type of cabling equipment used to create a LAN
Each network technology is designed to work with a certain type of network topology.
Each one has certain standard features
The most common types of network technology include:
Ethernet
Local Talk
Token Ring
Asynchronous Transfer Mode (ATM)
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25. Ethernet is the most popular network technology because it is inexpensive to implement. It is essentially a bus topology where every node “taps ” into a central cable.
Table 8.4 A summary of different types of Ethernet
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26. 8.5 Common Services Available in a Networked Environment
8.5.1 Simultaneous Access
Simultaneous access of information is one of the three common services that can be provided by a network.
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27. Example Quarterly sales report of a company
client
Server PC
Without a network, each computer has its own copy of data file. It is hard to decision which one is the most up-to-dated.
In a client/server network, the data is stored at the central server. Staffs can retreive the file at any time and changes on the data can be seen immediately.
Example Quarterly sales report of a company
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28. 8.5.2 Shared Peripheral Devices
The ability to share peripheral devices is one of the most important services that a network can provide.
Client A
Print Server
Printer
Client B
Print queue
Client C
Example Sharing of Printers
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29. 8.5.3 Communications
Another useful application of a network is electronic mail ( ), which is a system for exchanging written messages through a network.
An illustration of how an is sent and received over a network
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30. 8.6 Wireless Network
Wireless network connections perform the same functions as wired connections.
To connect to a wireless network, we need wireless adapters and wireless network
An illustration of how notebook computers can connect to a network through access points
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31. 8.7 Case Studies of Setting a Computer Network
8.7.1 Network at Home
( Click here for a larger view )
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32. 8.7.2 Network in Workplace ( Click here for a larger view )
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33. End of Chapter 8
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