Networks

Computers and peripherals (pieces of equipment that are connected to the central processing unit of а computer system) connected together form а network. Networks allow communication between computers and the sharing of hardware (such as printers) and software (programs and data). А network that covers а small area e.g. an office or building is known as а LAN (local area network). The main computers that provide services on the network are called servers e.g. а file server provides а central storage area for data files. The computers that use the services are known as clients. The computers can be connected using various types of cabling, including the ordinary telephone system wiring. А main data communications cable connecting LANs together is referred to as а backbone. Various electronic devices are also used to amplify, filter and determine the best path for the signals. These include bridges for dividing а LAN into separate parts or connecting similar networks together, gateways for connecting different types of networks and routers for connecting different networks together and determining the best path (or route) for the signals. Routers are used to connect networks to form the Internet. А modem (modulator/demodulator) is used to convert signals from analogue (havingа variety of levels) to digital (having only two levels, representing on and off) for connection to the ordinary telephone system. Alternatively, an ISDN (integrated services digital network) adapter or а DSL (digital subscriber line) modem can be used to allow digital signals to be used without being converted to analogue signals.

There are different standard methods of connecting computers in а LAN. One of the most common is known as Ethernet. Each computer must have а network adapter (special electronics to control the network connection). This is usually in the form of an expansion card known as а network interface card (NIC). All the computers are connected through another electronic device known as а hub. The electronics in the hub are used to amplify the signals to prevent them from becoming too weak before they reach the desired computer. The cable normally used to connect the computers to the hub is known as twisted-pair cabling. It contains two cables twisted together to eliminate interference from external signals. In а home network, the mains power cables built into the house can be used instead if electronic devices called isolation adapters are used to isolate the computer from the mains electricity running through the cable. In future, wireless networks will use а radio transmitter and receiver tuned to use the same radio frequency, instead of cabling.

In а client/server network, the main server computer provides the services (sharing of printers, programs or data, etc.) and the attached client computers can be normal computers or simple terminals. Terminals require the server to dо most or all of the processing. А thin client (or thin terminal), such as а NetPC, has а processor that does some of the processing but а dumb terminal does not have а processor and all the processing must be done by the server computer.

One character of data is referred to in computing as а byte. In the binary system (а number system that only uses two digits i.e. 1 and 0) used in computers, а byte is made up of 8 bits where а bit is а 1 or а 0. When data is transmitted through а network system, it can be transmitted in different ways. Asynchronous transmission (or stop-start transmission) sends the data one byte (or character) at a time. A start bit (called a control bit) is added to indicate the beginning of each byte and another control bit called a stop bit is added to indicate the end of each byte. Synchronous transmission sends the data in blocks. Extra bytes of data called synch bytes are added at the beginning and end of each block. They are used to synchronise the sending and receiving devices.

When a message is transmitted through a network, it is processed in various ways by the software and the hardware. It is first processed by the applications program e.g. an e-mail program, and then it is processed by the operating system. It is then processed by the hardware such as the network interface card and finally by the network electronics e.g. a muter, as it passes through the network system. When it arrives at its destination, it is similarly processed in reverse order to display the message on the display screen of the receiving computer.

4. Explain the meaning of the terms associated with networks such as:

Backbone, bridge, client, thin client, gateway, hub, network, LAN, muter, server.

5.Pronounce correctly and transcribe. Consult the dictionary if necessary. Give Russian equivalents:

Processing, router, synchronous, asynchronous, dumb, transmission, client, binary, frequency, amplify, sharing, expansion, terminal, transmitter, referred to, interface, pass through, require, device, character, muter, message, server, wireless, attach, convert.