Telecommunications refers to the transmission of information across a distance. Visual signaling with flags, lamps, or smoke was the earliest form of telecommunication. Today, the term most often refers to a wide variety of electrical and electronic communication systems that transmit information throughout the world. This information may include sound, images, or text, or any combination of these elements. It may be in either analog or digital format, or a combination of both. The analog format uses a constantly changing form, such as a radio wave, that represents information and transmits it. The digital format represents and transmits information as a computer code.
Most telecommunication systems transmit information through a wire or through the air. The physical medium (carrier) of such information is called the channel. In the mid-1800’s, people used telegraphs to send simple coded messages over a wire. The coming of the telephone resulted in the creation of a vast network of telephone lines and cables, which could transmit voices and other sounds.
Today, billions of computers around the world use the telephone network to transmit vast amounts of information to each other, forming the Internet. The modern network also uses radio links and fiber-optic cables (see Fiber optics ). A device called a modem enables computer users to send digital information to one another over the network (see Modem ).
Other forms of telecommunication include television and radio broadcasts, cellular telephone signals, and navigation signals, which use radio waves. Super high frequency (SHF) radio waves called microwaves transmit television signals and telephone communication signals over long distances. Communications satellites use microwaves to transmit telephone, television, and other communication signals throughout the world. Such wireless channels are supported by a worldwide network of fiber-optic cables.
