Transmission of signals that vary discretely with time between two values of some physical quantity, one value representing the binary number 0 and the other representing 1.
With copper cabling, the variable quantity is typically the voltage or the electrical potential. With fiber-optic cabling or wireless communication, variation in intensity or some other physical quantity is used.
Digital signals use discrete values for the transmission of binary information over a communication medium such as a network cable or a telecommunications link. On a serial transmission line, a digital signal is transmitted 1 bit at a time.
The opposite of digital transmission is analog transmission, in which information is transmitted as a continuously varying quantity. An analog signal might be converted to a digital signal using an analog-to-digital converter (ADC) and vice versa using a digital-to-analog converter (DAC). ADCs use a method called “quantization” to convert a varying AC voltage to a stepped digital one.
Graphic D-22. Digital transmission.