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Data Transmission

When data is transmitted from one device to another, it is sent as a large number of bits.

The speed of data transmission is called the baud rate.

Parallel transmission
  • a number of bits (8, 16 or 32) can be sent at the same time along a number of wires.
  • used internally when data is sent along the buses
  • faster than serial transmission
  • can only be used for short distances
Serial transmission
  • bits are sent one after another along a single wire.
  • used for greater distances
  • can be fast on fibre optic cables.
Simplex Transmission of data can be in one direction only
Half-duplex Transmission can be in both directions but only one direction at a time.
Full-duplex Simultaneous transmission of data in both directions is possible.

 

Digital computer signals generally need to be converted to analogue signals to use communication links such as telephone systems. This process is called modulation.

The reverse process of converting analogue signals back to digital signals is called de-modulation.

A modem (modulator - demodulator) is a device which modulates or de-modulates a signal. It allows a computer to transmit along the telephone system eg to use the Internet.

An alternative to using the telephone system for networks (Internet) is to use ISDN (Integrated Services Digital Network) lines. These transmit digital signals so there is no need for modulation. The bandwidth is high - more data can be sent at a time increasing transmission speeds.

Transmission speeds can also be increased using multiplexing - a method of combining and sending more than one signal at the same time.