Telecommunications

The transmission of words, sounds, images, or data in the form of electronic or

electromagnetic signals or impulses. Transmission media include the telephone

(using wire or optical cable), radio, television, microwave, and satellite. Data

communication, the fastest growing field of telecommunication, is the process of

transmitting data in digital form by wire or radio. Digital data can be

generated directly in a 1/0 binary code by a computer or can be produced from a

voice or visual signal by a process called encoding. A data communications

network is created by interconnecting a large number of information sources so

that data can flow freely among them. The data may consist of a specific item of

information, a group of such items, or computer instructions. Examples include a

news item, a bank transaction, a mailing address, a letter, a book, a mailing

list, a bank statement, or a computer program. The devices used can be computers,

terminals (devices that transmit and receive information), and peripheral

equipment such as printers (see Computer; Office Systems). The transmission line

used can be a normal or a specially purchased telephone line called a leased, or

private, line (see Telephone). It can also take the form of a microwave or a

communications-satellite linkage, or some combination of any of these various

systems.

Hardware and Software

Each telecommunications device uses hardware, which connects a device to the

transmission line; and software, which makes it possible for a device to

transmit information through the line.

Hardware

Hardware usually consists of a transmitter and a cable interface, or, if the

telephone is used as a transmission line, a modulator/demodulator, or modem. A

transmitter prepares information for transmission by converting it from a form

that the device uses (such as a clustered or parallel arrangement of electronic

bits of information) to a form that the transmission line uses (such as, usually,

a serial arrangement of electronic bits). Most transmitters are an integral

element of the sending device. A cable interface, as the name indicates,

connects a device to a cable. It converts the transmitted signals from the form

required by the device to the form required by the cable. Most cable interfaces

are also an integral element of the sending device. A modem converts digital

signals to and from the modulated form required by the telephone line to the

demodulated form that the device itself requires. Modems transmit data through a

telephone line at various speeds, which are measured in bits per second (bps) or

as signals per second (baud). Modems can be either integral or external units.

An external unit must be connected by cable to the sending device.