Data transmission by
either medium is either asynchronous or synchronous. Asynchronous transmissions
are typed with the keyboard as it is. Data character by character is
transmitted. Therefore, the distance between the center is the distance.
However, it is cheap to implement because it does not have to be secured before
sending data. In the synchronous mode on the other hand, secure data is
transmitted by one block. There are many factors in each block. It is suitable
for remote communication, for example: card reader and printer, among computers
and related devices.
The main
communication device to be used today:
1. Wire pairs: These are commonly used in local telephone communication and for
short-range digital data communication it is made of copper and twisted pair.
The speed of data transmission is usually 9600 bits per second at a distance of
100 meters.
2. Coaxial Cable: This is a group of specially wrapped insulated wire which transfers
data at a higher speed. They are made of central copper wires around which
insulation happens and the copper network is located on it. It is used for a
long-distance telephone line and local area network, because it has the ability
to transfer data with sound resistance and faster speed.
3. Microwave: This is the use of
high frequency radio signals for data transfer by space. The transmitter and
receiver of the microwave system should be in line-of-sight because the radio
signals are not bend. There is no facility of long-distance transmission by the
microwave. Repeaters are used in the distance between 25 to 30 kilometers of
transmitting and receiving end to remove the line of site problem and the power
amplification of weak signals.
4. Communication Satellite: The problem of line of site and repeaters is overcome
by satellite, which is today the most used data transmission medium.
Communication is a microwave relay station located in satellite outer space.
INSAT-B is the same type of satellite which is accessible from anywhere in
India. In satellite communication, microwave signals are sent to the satellite
located in the space by the transmitter located on the earth. The satellite
amplifies a weak signal and translates the receiver back. Its main advantage is
that it is the only microwave station visible from any point in the larger
area. The data transmission rate in the microwave is 16 gigabytes per second.
These are mostly used to link big cities.
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