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 hat 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 ommunications-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 its 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 elephone 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. Most modems can dial a telephone number or answer a telephone automatically. Software Among the different kinds of software are file-transfer, host, and network programs. File-transfer software is used to transmit a data file from one device to another. Host software identifies a host computer as such and controls the flow of data among devices connected to it. Network software allows devices in a omputer network to transmit information to one another.
Applications Three major categories of telecommunication applications can be discussed here: host-terminal, file-transfer, and computer-network communications. Host-Terminal In these types of communications, one computerthe host computeris connected to one or more terminals. Each terminal transmits data to or receives data from the host computer. For example, many airlines have terminals that are located at the desks of ticket agents and connected to a central, host computer. These terminals obtain flight information from the host computer, which may be located undreds of kilometers away from the agent’s site.
The first terminals to be designed could transmit data only to or from such host computers. Many terminals, however, can now perform other functions such as editing and formatting data on the terminal screen or even running some computer programs. Manufacturers label terminals as “dumb,” “smart,” or “intelligent” according to their varying capabilities. These terms are not strictly defined, however, and the same terminal might be labeled as dumb, smart, or intelligent depending upon who is doing the labeling and for what purposes.
