Text A. Basic communication systems

Data communications are the transfer of data from one device to another via some form of transmission medium. A data communications system must transmit data to the correct destination in an accurate and timely manner. The five components that make up a communications system are the message, transmitter, receiver, medium, and protocol. Text, numbers, images, audio, and video are different forms of information. The transmitter injects a signal into the channel that delivers it to the receiver. The receiver must recover the information contained in the receiver signal despite the limitations introduced by the channel.

The channel can be a physical one, like a copper cable and an optical fiber, or simply air or even vacuum that transmits electromagnetic waves. Any channel is subject to some kind of electromagnetic “noise” and interference.

In order to transmit a digital signal at a reasonable distance it has to be processed by a modulator. The modulator can:

1) Select the frequency at which the signal will be transmitted over the

channel.

2) Allow for different signals to share the same modulation channel, in a

process known as multiplexing.

3) Adapt the signals parameters to suit the requirements of a given channel

(bandwidth, spectral properties, noise robustness, etc.).

4) Provide the flexibility to exchange spectral efficiency for robustness, as

needed.

Of course, at the receiving end, the inverse operation, called demodulation, needs to be performed. So in bidirectional systems a single device will perform both operations and therefore be called a modem.

The word modem is a combination of the words modulation and demodulation which is precisely what a modem does. A modem can also be viewed as a device that takes information, transfers it on to a medium to allow transportation of the information, and at the other end, removes the information from the medium and restores it to its original form. This brings up two distinguishing characteristics of a modem, the type of information it accepts and the media that it operates upon.

The type of medium employed by the modem dictates the type of modulation it will employ. The medium can be a copper cable, an optical fiber or an electromagnetic wave in free space.

Although the modem is a separate building block, it is often embedded in a laptop or in a wireless router.

Multiplexing is the sharing of a single communication channel among different users. The communication channel can be a copper wire, an optical fiber or the space between a transmitting and a receiving antenna. Different users can be distinguished by means of different frequencies, time slots, codes or regions of space.

3.1 In the text above, find English equivalents for the following:

Обеспечить надежность (прочность); информация, содержащаяся в сигнале; отличительная особенность (свойство); встроенный в компьютер блок; временной интервал.

3.2 Answer the questions:

1) What are the five components of a data communications system?

2) What functions do transmitters and receivers have?

3) What does the process known as multiplexing consist in?

4) What is a modem and what is it designed for?

3.3 Translate into Russian:

1) The type of medium employed by the modem dictates the type of modulation it will employ.

2) Any channel is subject to some kind of electromagnetic “noise” and interference.

3) A modem can also be viewed as a device that takes information and transfers it on to a medium.

4) Of course, at the receiving end, the inverse operation, called demodulation, needs to be performed.

Поиск по сайту: