The sending of data from one
place to another by radio waves or cables is known as telecommunications.
The earliest form of telecommunication in the 1990's was visual signaling with flags, lamps, or smoke. Nowadays, telecommunication refers
to various electrical and electronic systems. Visual images and printed
materials are sent and received in a fraction of a second, via modern
telecommunication systems.
Some common telecommunication systems are televisions, telephones and radios while the other kinds of systems are used solely by industries. Information such as airline reservations and banking transactions (Electronic Funds Transfer) are transmitted by such systems. Teleprinting / telephoto are essential to newspapers for obtaining stories and photographs worldwide. Space stations and the earth communicate through telecommunications systems, which transmit messages via satellite (see telecommunication satellites), radio and underground or seafloor cables. Radio waves are used for transmission of television and radio.
Microwaves relay signals over long distances for television as well as for telephone. Analogue and digital transmissions are two methods of transmission. Analogue transmission makes use of signals that are exact reproductions of the sound or picture being transmitted and the telephone receiver is a good example where this principle is applied. Digital transmission converts signals into codes that has only two elements in most cases such as the on and off switch of a radio or the dot-dashes of Morse code. In other types of digital telephone system, the coded signals are transmitted by a rapidly flashing beam of light (laser) and decoded in the receiver. (see also Fibre Optic and ISDN)