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

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. Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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. Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

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

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

8.2.2 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. Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

An illustration of a Wide Area Network (WAN) Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

Table 8.1 Advantages and disadvantages of peer-to-peer and client/server models Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

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

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 Section B Computer Systems and Networking

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. Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

Table 8.2 Functions of different connecting devices Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

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

Table 8.3 Advantages and disadvantages of the three different network topologies Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

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. Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

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

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

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

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

8.7 Case Studies of Setting a Computer Network 8.7.1 Network at Home ( Click here for a larger view ) Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

8.7.2 Network in Workplace ( Click here for a larger view ) Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking

End of Chapter 8 Modern Computer and Information Technology (HKCEE) Core Module Section B Computer Systems and Networking