chapter 8 modern computer and information technology (hkcee) core module section b computer systems...

Modern Computer and Information Technology (HKCEE) Core ModuleSection B Computer Systems and Networking

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Chapter 8

Basic Concepts of a Computer Network

• 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

Objectives


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Chapter 8

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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• 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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8.1.2 Why do We Need a Computer Network ?

A network is a way to connect computers for :

Most companies have PCs connected to form a network in their offices

• Communication

• Data exchange

• Resource sharing


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Video conferencing is available in the network environment

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


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Chapter 8

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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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


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Chapter 88.2.2 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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An illustration of a Wide Area Network (WAN)


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Chapter 8

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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Chapter 8

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.

client client

client

Server

A client/server model


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Chapter 8

Table 8.1 Advantages and disadvantages of peer-to-peer and client/server models

Network model Advantages DisadvantagesPeer-to-peer Inexpensive and easy to set up Lacks of management software to effectively

monitor the activities of a network

Client/server Handles very large networksefficiently

The cost of installation and administration is high


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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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Chapter 8

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.


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Chapter 8

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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Chapter 8

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

The main function of a network interface card is to convert data of a computer into electrical signals

• 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.


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Chapter 8

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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Chapter 8

8.4.5 Connecting Devices

A connecting device acts as a switching board for transmitting data from one computer to another.

Computer ComputerComputerComputer

Hub

A network hub is used to connect different computers together by joining all the network cables


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Chapter 8

Table 8.2 Functions of different connecting devices

Connecting Device FunctionsHub A hub is a device that connects all network cables together. We can

think of the hub as being a joining point of all network media.Bridge A bridge is a device that connects different networks together, e.g.

connecting an electrical network to an optical network, or a wirednetwork to a wireless network.

Router A router is a sophisticated device that connects different networks.Network data is routed to different networks based on the rules thatare programmed in the router. We can think of a router as a kind ofhighway roundabout for data traffic.

Access point An access point is a station that transmits and receives data in awireless network. It connects users to other users within the network.Each access point can serve multiple users within a defined networkarea. When users move beyond the range covered by


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Chapter 8

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

• 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.


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Bus 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.


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Ring topology

• 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.


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Chapter 8

Table 8.3 Advantages and disadvantages of the three different network topologies

Topology Advantages DisadvantagesBus • Easy to connect a computer or

peripheral to a linear bus

• Requires less cable length than a startopology

• Entire network shuts down if there is abreak in the main cable

• Terminators are required at both ends ofthe backbone cable

• Difficult to identify the problem if the entirenetwork shuts down

Star • Easy to install and wire

• No disruptions to the network whenconnecting or removing devices

• Easy to detect faults and to removeparts

• Requires more cable length than a bustopology

• If the hub fails, nodes attached are disabled

• More expensive than the bus topology

Ring • Does not rely on a single hostingcomputer and can function even thoughone of the nodes is broken

• The channel can handle only one messageat a time

• Performance will be degraded if there is ahigh-volume of network traffic


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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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Table 8.4 A summary of different types of Ethernet

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.

Network technology Cable Data transfer rate TopologyEthernet Twisted Pair, Coaxial,

Fibreoptic10 Mbps Bus, Star

Fast Ethernet Twisted Pair, Fibre-optic

100 Mbps Star

Gigabit Ethernet Twisted Pair,Fibre-optic

1 Gbps Star


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8.5 Common Services Available ina 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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Example Quarterly sales report of a company

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.

PC

PC

PC

client

client

clientServer


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Chapter 8

8.5.2 Shared Peripheral Devices

The ability to share peripheral devices is one of the most important services that a network can provide.

Example Sharing of Printers

Client A

Client B

Client C

Print Server Printer

Print queue


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Chapter 8

8.5.3 Communications

Another useful application of a network is electronic mail (e-mail), which is a system for exchanging written messages through a network.

An illustration of how an e-mail is sent and received over a network


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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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8.7 Case Studies of Setting aComputer Network

8.7.1 Network at Home

( Click here for a larger view )


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8.7.2 Network in Workplace

( Click here for a larger view )


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Chapter 8

End of Chapter 8

chapter 8 modern computer and information technology (hkcee) core module section b computer systems...

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