XI Information Technology - BIEK Chapter 7 - Computer Networks

Computer Network
In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.

In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.




Configurations or Topologies Networks
A network can be arranged or configured in several different ways. This arrangements is called the network's topology. The four principal network topologies are

1. Star Network

2. Bus Network

3. Ring Network

4. Hierarchical Network


1. Star Network

In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.

One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.


2. Bus Network

In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.

The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.


3. Ring Network

In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.

A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.


4. Hierarchical Network

This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.




Strategies of Networks
Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.




Peer-to-Peer Network System
In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.




Client/Server Network System
Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.

One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.




Advantages of Network
Networks provide tremendous benefits. The most compelling advantages of network are as follows.

1. Networks allow users simultaneous access to shared programs and data.

2. Network also allows users to share peripheral devices such as printers and hard disks.

3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.

4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.




Types of Networks
Communications differ in geographical size. Three important types are LANs, MANs, WANs.


Local Area Networks (LANs)

Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).

The figure shows an example of a LAN. This type of arrangement has two benefits.

1. People can share different equipment, which lowers the cos of equipment.

2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.


Metropolitan Area Network (MANs)

These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.


Wide Area Network (WANs)

Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.




Uses of Internet
The most common uses of Internet are


1. Communicating

Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.


2. Shopping

One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.


3. Researching

Internet provides you to have one of the world's largest libraries available from home.


4. Entertainment

Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy.