<P> Data transmission (also data communication or digital communications) is the transfer of data (a digital bitstream or a digitized analog signal) over a point - to - point or point - to - multipoint communication channel . Examples of such channels are copper wires, optical fibers, wireless communication channels, storage media and computer buses . The data are represented as an electromagnetic signal, such as an electrical voltage, radiowave, microwave, or infrared signal . </P> <P> Analog or analogue transmission is a transmission method of conveying voice, data, image, signal or video information using a continuous signal which varies in amplitude, phase, or some other property in proportion to that of a variable . The messages are either represented by a sequence of pulses by means of a line code (baseband transmission), or by a limited set of continuously varying wave forms (passband transmission), using a digital modulation method . The passband modulation and corresponding demodulation (also known as detection) is carried out by modem equipment . According to the most common definition of digital signal, both baseband and passband signals representing bit - streams are considered as digital transmission, while an alternative definition only considers the baseband signal as digital, and passband transmission of digital data as a form of digital - to - analog conversion . </P>

Group of wires that transfer data are known as