Telecommunication is the almost instantaneous transmission of sounds, words, pictures, data and information by electronic means.
Every communication system needs three things: a transmitter, a communications link and a receiver.
Transmitters can be telephones or computers with modems. They change the words, pictures, data or sounds into an electrical signal and send it. Similar receivers pick up the signal and change it back into the right form.
Communications links carry the signal from the transmitter to the receiver in two main ways. Some give a direct link through telephone lines and other cables. Some are carried on radio waves through the air, via satellite or microwave links.
Telephone lines used to be mainly electric cables which carried the signal as pulses of electricity. More and more are now fiber optics which carries the signal as coded pulses of light.
Communications satellites are satellites orbiting the Earth in space. Telephone calls are beamed up on radio waves to the satellite, which beams them back down to the right part of the world.
Microwave links use very short radio waves to transmit telephone and other signals from one dish to another in a straight line across Earth’s surface.
Mobile phones or cellular phones transmit and receive phone calls directly via radio waves. The calls are picked up and sent on from a local aerial.
The information superhighway is the network of high-speed links that might be achieved by combining telephone systems, cable TV and computer networks. TV programmes, films, data, direct video links and the Internet could all enter the home in this way.