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What is a Computer Network?




Text 1

Introduction

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I. - , :

teletype terminal

to configure computers

fibre optic cable

microwave dish

cellular phone

switched line

public branch exchange

computer network

II. , :

communications media; voice conversations; computer communications; laser disc player; fax machine; communication channel; fast computer connection; software design

III. :

essential, ubiquitous, distinction, difficulty, primarily, interconnection, microwave, computerize, successfully

IV. , .

V. .

VI. :

1. It is these special properties of sound that are the subject of the present chapter.

2. It was commuter communications that has blurred every distinction between communications media.

3. It was May 1, 1964 when two computers communicated with one another at Dartmouth College in Hanover.

4. It is the gravitation that makes the satellites move round the Earth.

5. It was not in September when the equipment was brought to the laboratory.

VII. .

VIII. , .

IX. . .

1. The first time two computers communicated with one another was May 1, 1964, at Dartmouth College in Hanover, New Hampshire. It was 4 o'clock in the morning when Professor Tom Kurtz successfully transmitted a portion of a BASIC program from one teletype terminal to another.

2. From this simple beginning, computer communications has become not only essential and ubiquitous, but has blurred every distinction between communications media. Today, we not only send data over telephone lines, but we can conduct voice conversations over the Internet and send and receive interactive data via satellites through the medium of television.

3. Computer communications have become easier, as well. The technical difficulties of configuring two computers to "talk" to one another have been surmounted, primarily through software design, moreover, it has become possible for many different types of electronic devices to communicate with other electronic devices computers to fax machines, telephones to television, VCRs and laser disc players to computers.

4. Communication channels have also become interconnected telephone lines connect to fibre optic cable to microwave dishes to satellites to cellular phones and modems. Telecommunications use switched lines through the telephone companies' PBXs (Public Branch Exchange). Even though the computerized PBXs can carry more than simple voice communications, you need a computer network for fast computer connections.

X. .

Text 2

The Purposes of Networks

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I. , .

state university; major supercomputer facility; supercomputer centre; Massachusetts-based insurance company; insurance claim forms; satellite networks; full-color graphic images; entertainment purposes

; ; ; ; ; ; ;

 

 

quickly, justify, justifiably, collection, researcher, supercomputer, worker, clerical, government, entertainment, business, sculpture

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III. . .
, . :

process ()

base ()

form ()

tour (, )

visit ()

change ()

result ()

place ()

aid ()

claim (, , )

IV. " " .

V. " ":

1. The results obtained enabled the solution to be greatly simplified.

2. Existing simulation techniques permit the operations to be easily imitated.

3. This information allowed the assistants to go ahead with the work.

4. Computers enable researchers' data to be sent to a supercomputer centre through the Internet.

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2. .

3. .

4. .

 

 

VI. - . .

VII. - :

1. One laser beam could carry all the radio, TV and telephone messages simultaneously.

2. If you watch a laser operate, you might be surprised at the simplicity of a device capable of such power.

3. This printing technique suggests that a similar method might be used in colour television.

4. Later developments in physics have shown that the electron cannot be accurately considered as if it were in orbital motion about the nucleus.

5. It is essential that a superconductor should be a solid material and it is necessary that it should be cooled to -273C.

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5. , , , -273C.

 

VIII. .

IX. , "to have" , , -.

X. .

1. Because computers process data so quickly, you can justifiably say that they "conquer" time. With a computer, you can perform calculations in seconds that would have taken days, weeks, or even years by hand. Computer networks also enable us to conquer another dimension space.

2. Here are examples:
Researchers at a small state university need a supercomputer to calculate the results of a sophisticated problem. But they don't have the money to travel to a major supercomputer facility. In the past these researchers would have to give up. Today, they can send their data to a supercomputer centre through the Internet. The next day, they receive the results.

3. A Massachusetts-based insurance company has discovered a place where many young, educated workers live. Even better, these workers do not mind taking clerical jobs, such as processing insurance claim forms. The place? Ireland. The company sends forms from Massachusetts to Ireland through a satellite network. Workers process the forms there and send them back to Massachusetts through the same network.

4. You need some information from the Smithsonian, but you don't have the time to visit it. With the aid of the Web, you can tour several Smithsonian collections while sitting in front of your computer. You will see beautiful, full-color graphic images of sculptures, photographs, and paintings.

5. The United States is becoming abundantly networked for business, government, personal communications, and entertainment purposes. And as it does so, computer networking is changing the very fabric of society.

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XI. .

Text 3

What is a Computer Network?

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I. - , :

communications channel

dumb terminal

keyboard

intelligent terminal

twisted-pair cable

coaxial cable

hardwired

asynchronous communications

synchronous communications

clock signal

II. , :

high-speed connection; communication device; input and output device; tin can; telephone service; television applications; earth station; satellite television; microwave communications channel

III. , :

Special , , , , ,

special feature;

special training in some field;

special interests;

special reason

Effect (n) , , , , , ,

The effect of heat upon ;

cause and effect;

to give effect to the decisions of .

General effect of this report was not favourable.

The new law came into effect last week.

Information , , ;

His mind is well stored with information.

That's a very useful piece of information.

This information enabled us to go ahead with the work.

We need some information from the Smithsonian.

A communication channel is the means of transmitting data or information between the terminals.

IV. , " ". .

V. .

VI. , :

1. To draw correct conclusions we must observe all the conditions.

2. To draw correct conclusions was the aim of our discussion.

3. To record the information is necessary.

4. To record the information the machine is to be properly adjusted.

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2. .

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VII. , , ( ), . .

VIII. .

IX. .

X. . .

1. A computer network is an electronic system that uses hardware, software, and communications devices to connect various terminals together in one or more communications channels in order to share data, information, or both. Computer networks normally speed up connections between computers. A computer network links two or more computers with a direct, high-speed connection. Networks are physically composed of terminals and communications channels, both discussed in the following sections.

Terminals

2. In order for computers or any other communication device to communicate, there must be two or more terminals, connected by a communications channel. A terminal is an input and output device connected to a separate processing device. Typically, a dumb terminal is a keyboard and monitor. A PC is an intelligent terminal because it can perform its own processing. A terminal can be simple or complex; for example, two tin cans, connected by a communications channel made of a length of string, are simple terminals. Today, it is common to see terminals that include telephone, PBXs, PCs and larger computers.

Communications Channels

3. A communications channel is the means of transmitting data or information between the terminals. The simplest communications channel in use today is two copper wires, called twisted-pair, used in basic telephone service. A better channel is coaxial cable, used in various television applications. Better yet is fibre optic cable, used by phone companies, the telecommunications industry, large business, government, colleges and universities and other commercial concerns.

4. These three communication channels are hard-wired; that is, a physical connection between terminals. A fourth channel is microwave, which transmits signals through the air between earth stations or satellites. For example, DSS satellite television uses the microwave communications channel.

Methods of Computer Communications

5. Most communications channels use asynchronous communications to transmit data, meaning the data is transmitted one at a time, from start to stop until everything is completely transmitted. This method is contrasted with synchronous communications, which transmits data by coordinating it to start and stop with an internal clock signal from the computer. Most modern computers and PCs use asynchronous, and older mainframe use synchronous communications.

 

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2. , , , . - , . , - . PC - , . ; , , , , . , , , PBXs, PC .

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Text 4

What is a Computer Network?
(continued)

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I. - , :

bandwidth

transmission speed

frequency

to download

data compression

band

II. , :

voice bandwidth; credit card authorization request; full-motion video clip; data transmission; microwave transmission; voice-grade transmission; multimedia applications; bandwidth channel capabilities; frequency range

III. , .

IV. :

to mean, means, term, issue, number of, instant, case

.

V. , the (more) the (better):

1. The greater the mass of a body, the greater is its kinetic energy.

2. The more messages carried, the better.

3. The better the communications channel, the more data and information it can transmit.

4. The larger the diameter of the wire, the smaller the resistance is, the more current can flow through it.

5. The greater the electromotive force, the greater is the pressure on the electrons moving through the conductor.

VI. , .

VII. .

VIII. - .

IX. , , .

X. , .

XI. . .

1. The better the communications channel, the more data and information it can transmit. The terms used to describe better channels are bandwidth and transmission speeds.

Bandwidth Issues

2. Bandwidth refers to the capacity of a communications channel to carry data or information. Bandwidth is measured in cycles per second, or Hertz (abbreviated Hz). Voice bandwidth is not much of an issue; the frequency range of the human voice is quite narrow, about 300-3,000 Hz. Obviously, twisted-pair has a limited bandwidth.

3. Bandwidth is measured in two ways. The first is the number of messages the channel can carry, whether voice or data. The more messages carried, the better. This is distinct from transmission speed because the type of message determines the number of messages a channel can carry and how quickly the message can be delivered. For example, a credit card authorization request is typically 1K, or 1,000 bits, and takes only an instant. However, if you are downloading a still photograph or even a full-motion video clip from the Web, it could range upward of several megabits and take minutes or even hours. In such cases, files are often compacted using data compression techniques to save space and speed up transmission. A commonly used program for data compression is WinZip.

4. The second way bandwidth is measured is by the nature and quality of the signal. Data must have a very clear channel; what you hear as noise on the phone line can completely corrupt a data transmission. Coaxial cable can be affected by inclement weather, and falling autumn leaves can downgrade microwave transmissions. Imagine the significance of this to a bank that is electronically transferring several billion dollars. In addition, full-motion video used in multimedia applications requires very high bandwidth channel capabilities. Thus, the communications channel must be as wide and as clean as possible to accommodate a large number of complex signals.

Transmission Speeds

5. Communications bandwidth is measured in kilobits per second (kbps) or gigabits per second (gbps). When considering bandwidth and speed, the channels are classified into three categories:

Narrow band transmission, the slowest at 45-150 band.

Voice-grade transmission, the middle speed at 300-9,600 band.

Wide band transmission, for highest speed at 19,200 band to 500 Kbp or more.

XII. .

Text 5

Networking Protocols

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I. - , :

simplex

half-duplex

full-duplex

host

circuit switching

packet switching

II. , :

protocol standard; voice and data communications channels; computer-to-print channel; host-to-terminal computer systems; data exchange

III. , .

IV. There + to be .

V. :

1. An electronic computer is one of (great) achievements of man.

2. What is (important) unit in the computer?

3. PASCAL is (practical) than BASIC.

4. The business segment is one of (large).

5. Databases, spreadsheets ( ) and word-processors help business to run (efficiently), make administrative work (easy).

6. Computer technology has a great potential for (progressive) transformation of our society.

VI. , , :

1. They (to write) this computer program by June.

2. A hybrid computer (to combine) some properties of digital and analog computers.

3. Computers (to become) smaller, cheaper and more numerous. Designers (to call) these small computers microcomputers or micros since that time.

4. When I came into the room, my friend (to compile) a program.

5. The electronic computer just (to perform) these calculations.

6. The computer of the future (to use) natural languages.

VII. . .

1. Protocol refers to a prescribed manner of doing something. Networking protocols refer to a set of standards that ensure data and information are properly exchanged between communicating computers. The most common protocol standard is referred to as X.25, which is used worldwide. Although most adhere to the X.25 standard, there is no single protocol used by all. Protocols refer to means of transmission, which have improved over the years. The following protocols are listed in chronological order:

2. Simplex, or one direction only, for example from host to recipient;
Half-duplex, meaning one direction at a time although both directions are possible;
Full-duplex, meaning both directions at the same time

3. Today, most voice and data communications channels are full-duplex; the need for information and instantaneous feedback requires it. However, the computer-to-printer channel is simplex, and most large host-to-terminal computer systems still use half-duplex.

4. There are several specific techniques for data exchange within the full-duplex protocol. The first is circuit switching, which routes data along a prescribed path from source to destination. The more common method is packet switching, which sends data in small blocks, or packets, each separate, along the most expedient route to the destination, where they are reassembled in proper order. Although seeming more complex, packet switching is far more efficient.

VIII. .

Text 6





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