Polje tehnologije koje se bavi komunikacijom na daljinu. Obuhvata, ali nije obavezno na njih ograničeno, telefoniju, telegrafiju, komercijalne radio programe, emitovanje TV programa, kablovsku televiziju, satelitsku televiziju, radar, radio amatere.
The vast discipline encompassing the methods, mechanisms, and media involved in information transfer. In computer-related areas, communications involves data transfer from one computer to another through a communications medium, such as a telephone, microwave relay, satellite link, or physical cable. Two primary methods of computer communications exist: temporary connection of two computers through a switched network, such as the public telephone system, and permanent or semipermanent linking of multiple workstations or computers in a network. The line between the two is indistinct, however, because microcomputers equipped with modems are often used to access both privately owned and public-access network computers. See also asynchronous transmission, CCITT, channel (definition 2), communications protocol, IEEE, ISDN, ISO/OSI model, LAN, modem, network, synchronous transmission. Compare data transmission, telecommunications, teleprocess.
The transmission and reception of information of any type, including data, television pictures, sound, and facsimiles, using electrical or optical signals sent over wires or fibers or through the air.
Communications over a distance, generally by electronic means.
Long-distance voice communication was pioneered 1876 by Scottish scientist Alexander Graham Bell when he invented the telephone. Today it is possible to communicate with most countries by telephone cable, or by satellite or microwave link, with over 100,000 simultaneous conversations and several television channels being carried by the latest satellites. Integrated-Services Digital Network (ISDN) makes videophones and high-quality fax possible; the world's first large-scale center of ISDN began operating in Japan 1988. ISDN is a system that transmits voice and image data on a single transmission line by changing them into digital signals. The chief method of relaying long-distance calls on land is microwave radio transmission.
The first mechanical telecommunications systems were the semaphore and heliograph (using flashes of sunlight), invented in the mid-19th century, but the forerunner of the present telecommunications age was the electric telegraph. The earliest practicable telegraph instrument was invented by William Cooke and Charles Wheatstone in Britain 1837 and used by railroad companies. In the US, Samuel Morse invented a signaling code, Morse code, which is still used, and a recording telegraph, first used commercially between England and France 1851. Following German physicist Heinrich Hertz’s discoveries using electromagnetic waves, Italian inventor Guglielmo Marconi pioneered a “wireless” telegraph, ancestor of the radio. He established wireless communication between England and France 1899 and across the Atlantic 1901. The modern telegraph uses teleprinters to send coded messages along telecommunications lines. Telegraphs are keyboard-operated machines that transmit a five-unit Baudot code (see baud). The receiving te
leprinter automatically prints the received message.
The drawback to long-distance voice communication via microwave radio transmission is that the transmissions follow a straight line from tower to tower, so that over the sea the system becomes impracticable. A solution was put forward 1945 by the science-fiction writer Arthur C Clarke, when he proposed a system of communications satellites in an orbit 35,900 km/22,300 mi above the equator, where they would circle the Earth in exactly 24 hours, and thus appear fixed in the sky. Such a system is now in operation internationally, by Intelsat. The satellites are called geostationary satellites (syncoms). The first to be successfully launched, by Delta rocket from Cape Canaveral, was Syncom 2 in July 1963. Many such satellites are now in use, concentrated over heavy traffic areas such as the Atlantic, Indian, and Pacific oceans. Telegraphy, telephony, and television transmissions are carried simultaneously by high-frequency radio waves. They are beamed to the satellites from large dish antennae or Earth stations,
which connect with international networks. Recent advances include the use of fiber-optic cables consisting of fine glass fibers for telephone lines instead of the usual copper cables. The telecommunications signals are transmitted along the fibers on pulses of laser light.