Data communication refers to the process of transmitting data signal from one place to another through a communication media.
The basic components of a data transmission system are:
(a) A central computer.
(b) Terminal devices.
(c) Telecommunications link between the central computer & the terminal devices.
Terms used in data communication
Signal modulation and demodulation:
This is the process of converting data signals to a form that can be transmitted over a transmission medium.
E.g., a modem converts a digital signal to an analog signal, which can be transmitted over analog telephone lines. This process is called modulation. A modem at the receiving end converts the analog signal into a digital signal, a process known as demodulation.
Multiplexing and Demultiplexing:
Multiplexing is the process of sending multiple data signals over the same medium, e.g., a wire conductor can be made to carry several data signals either simultaneously or at different times.
Demultiplexing is the process of separating the multiplexed signals at the receiving end.
Town A has 10 computers which want to communicate with 10 other computers in town B. In a normal case, it will need a direct cable linking each of the computers in town A to its partner in town B. However, if multiplexing is used, the computers can be made to share a single cable laid between the two towns, hence, saving cost.
The different data signals have different frequencies on the cable; hence, they do not interfere with one another.
Frequency (f):Frequency of a wave is the number of cycles made by the wave in 1 second. Frequency is measured in units called Hertz (Hz); where 1 Hz is equivalent to 1 cycle/second.
Baud:This is the unit to measure the speed of transmission. Generally, 1BAUD is 1bit/second.
Baud rate:This is the rate at which data is transferred or transmitted. It is measured in Bits per second (bps).
Band:The rate of change of a signal on a transmission line.
Bandwidth:A Bandwidth is the maximum amount of data that a transmission medium can carry at any one time. E.g., a certain cable may have a bandwidth of 100 Mbps (Mega bits per second).
Guardband:This is the range of frequency that is used to separate two channels.
Baseband signal:This is a digital signal that is generated and applied to the transmission medium directly without modulation.
Note. A baseband signal utilizes the full capacity of the transmission medium; hence, at any one time, only one signal can be sent. However, multiple signals can be sent at different times, if they are multiplexed.
Broadband transmission:This is where an analog signal is sent over the transmission medium using a particular frequency. This means that, several data signals can be sent at the same time through the same medium, but at different frequencies so as to prevent them from overlapping.
Attenuation:Attenuation is the decrease in magnitude and energy of a signal as it progressively moves along a transmission medium.
If the signal is not boosted, it will totally be lost along the way, and may never reach the destination.
Attenuation (or signal loss) is usually corrected by placing signal amplifiers (also called repeater stations) along the medium at appropriate distances in order to receive the weak signal, clean it, amplify it, then retransmit it.
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