Telecommunications :: Telephone Radio Television Microwave Satellite

The transmission of words, sounds, images, or data in the form of electronic orelectromagnetic signals or impulses. Transmission media involve the telephone(using wire or optical cable), radio, television, microwave, and satellite. Datacommunication, the fastest growing field of telecommunication, is the process of propagateting data in digital form by wire or radio. Digital data fire begenerated directly in a 1/0 binary code by a computer or can be produced from avoice or visual signal by a process called encoding. A data communication theorynetwork is created by interconnecting a large number of information sources sothat data can flow freely among them. The data may consist of a specific item ofinformation, a group of much(prenominal) items, or computer instructions. Examples include anews item, a bank transaction, a mailing address, a letter, a book, a mailinglist, a bank statement, or a computer program. The devices used can be computers,terminals (devices that transmit and receive information), and peripheralequipment such as printers (see Computer Office Systems). The transmission derivationused can be a normal or a specially purchased telephone line called a leased, orprivate, line (see Telephone). It can also take the form of a microwave or acommunications-satellite linkage, or some combination of some(prenominal) of these varioussystems.Hardw ar and SoftwareEach telecommunications device uses hardware, which connects a device to thetransmission line and software, which makes it possible for a device totransmit information through the line.HardwareHardware usually consists of a transmitter and a cable interface, or, if thetelephone is used as a transmission line, a modulator/demodulator, or modem. Atransmitter prepares information for transmission by converting it from a formthat the device uses (such as a clustered or parallel arrangement of electronicbits of information) to a form that the transmission line uses (such as, usually,a serial arra ngement of electronic bits). Most transmitters are an integralelement of the sending device. A cable interface, as the name indicates,connects a device to a cable. It converts the transmitted signals from the formrequired by the device to the form required by the cable. Most cable interfacesare also an integral element of the sending device. A modem converts digitalsignals to and from the modulated form required by the telephone line to thedemodulated form that the device itself requires. Modems transmit data through atelephone line at various speeds, which are measured in bits per second (bps) oras signals per second (baud). Modems can be either integral or external units.An external unit must be connected by cable to the sending device.