Introduction to Computing Lecture # 11 Introduction to Computing Lecture # 11

2 Outline Network Definition Benefits of Networks Types of Networks Types of LANs Components of a LAN Topology of LANs

3 Network Definition Network (or communications network) - a system of interconnected computers, telephones, or other communications devices that can communicate with one another and share applications and data. (Williams and Sawyer) A network is a set of technologies – including hardware, software, and media (such as wires) – that can be used to connect computers together, enabling them to communicate, exchange information, and share resources in real time. (Peter Norton)

4 Benefits of Networks Sharing of peripheral devices –Expensive devices such as printers, disk drives, and scanners can be shared. Sharing of programs and data –People in an organization can use the same software and have access to the same files. Better communications –Networks make possible, keeping everyone posted about important information. Security of information –Information on a network is apt to be backed up (duplicated) somewhere. Thus, a fire or flood is less apt to destroy essential information. Access to databases –Networks enable users to tap into all kinds of databases (whether private or public/online).

5 Types of Networks Networks may be classified into three categories according to their geographical range: –Wide Area Network (WAN) –Metropolitan Area Network (MAN) –Local Area Network (LAN)

6 Types of Networks Wide area network (WAN) - a communications network that covers a wide geographical area, such as a country or the world May use a combination of satellites, fiber- topic cable, microwave, and copper wire connections WANs are used to connect LANs together Examples: internet, most telephone companies

7 Types of Networks Metropolitan area network (MAN) - a communications network covering a city or a district –The purpose of a MAN is often to bypass local telephone companies when accessing long-distance service. –Example: many cell-phone systems are MANs Local area network (LAN) - connects computers and devices in a limited geographical area, such as an office, a building, or a group of buildings closed together. –Small LANs are sometimes called PANs, for Personal Area Networks. –Some terms used in LANs: host computer, node, backbone –Example: a university campus

8 Types of LANs LANs consists of two principal types: –Client/Server LANs –Peer-to-peer LANS Many LANs mix elements from both client/server and peer-to-peer models.

9 Types of LANs Client/Server LAN: –A client/server LAN consists of requesting microcomputers, called clients, and supplying devices that provide a service, called servers. –Clients: microcomputers that request data –Server: a powerful microcomputer that manages shared devices

10 Common Types of Servers File server – a computer that acts like a disk drive, storing the programs and data files shared by users on a LAN. Database server – a computer in a LAN that stores data but doesn’t store programs. Print server – controls one or more printers and stores the print-image output from all the microcomputers on the system. Web server – contains web pages that can be viewed using a browser. Mail server – manages .

11 Types of LANs Peer-to-peer LAN: –The word peer denotes one who is equal in standing with another –All microcomputers on the network communicate directly with one another without relying on a server –Peer-to-peer networks are less expensive than client/server networks and work effectively for up to 25 computers.

12 Components of a LAN Local area networks are made up of several standard components. –Connection or cabling system –Microcomputers with network interface cards –Network OS –Other shared devices –Routers, bridges, gateways, and hubs

13 Components of a LAN Connection or cabling system –LANs may use wired (twisted-pair wiring, coaxial cable, or fiber-optic cable) or wireless (infrared, radio-wave transmission, bluetooth, or WiFi) connection system. Microcomputers with network interface cards –Two or more microcomputers are required, along with network interface cards. –A network interface card (inserted into an expansion slot in a PC) enables the computer to send and receive messages over a cable network.

14 Components of a LAN Network OS –The network operating system (NOS), such as Novell NetWare, Microsoft Windows NT/2000, Unix, and Linux, is the system software that manages the activity of a network. Other shared devices –Printers, scanners, storage devices, and other peripherals may be added to the network as necessary and shared by all users.

15 Components of a LAN Routers, bridges, gateways, and hubs –A LAN normally connects to the Internet. Routers, bridges, gateways, and hubs are used (as necessary) as interfaces to make these connections. –A router is a special device that directs communicating messages when several networks are connected together. –A bridge is an interface used to connect the same types of networks. –A gateway is an interface permitting communication between dissimilar networks—for example, between a LAN and a WAN or between two LANs based on different OS or different layouts. –A hub is a common connection point for devices in a network – a place of convergence where data arrives from one or more directions and is forwarded out in one or more other directions.

16 Topology of LANs Topology – the logical layout, or shape, of a network. The three basic topologies are bus, ring, and star. Bus

17 Topology of LANs Bus network – all nodes are connected to a single wire or cable, the bus, which has two endpoints. Each communication device on the network transmits electronic messages to other devices. –If some of those messages collide, the sending device waits and tries to transmit again. –The advantage of the bus network is that it may be organized as either a client/server or peer-to- peer network. –The disadvantage is that extra circuitry and software are needed to avoid collisions between data; and –Entire network may stop working if a connection in the bus is broken.

18 Topology of LANs Ring network – one in which all microcomputers and other communications devices are connected in a continuous loop. –There are no end points. –Messages are passed around the ring until they reach the right destination. –There is no central server. –The advantage of a ring network is that messages flow in only one direction (no danger of collisions). –The disadvantage is that if a connection is broken, the entire network stops working.

19 Topology of LANs Star network – one in which all microcomputers and other communications devices are connected to a central server. –Messages are routed through the central hub –Hub prevents collisions between messages –If a connection is broken between hub and a device, the rest of the devices will continue operating. –If the hub goes down, the entire network will stop.

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