Introduction to Computing

Lecture # 11

Introduction to Computing

Lecture # 11

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Outline

• Network Definition

• Benefits of Networks

• Types of Networks

• Types of LANs

• Components of a LAN

• Topology of LANs

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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)

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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 e-mail 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).

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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)

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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

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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

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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.

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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

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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 e-mail.

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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.

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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

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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.

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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.

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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.

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Topology of LANs

• Topology – the logical layout, or shape, of a

network.

• The three basic topologies are bus, ring, and

star.

Bus

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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.

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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.

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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.

– END

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