A communication channel whose input and output each have an alphabet of distinct letters, or, in the case of a physical channel, whose input and output are signals that are discrete in time and amplitude (see discrete and continuous systems). The size of the alphabet, or the number of amplitude levels, is usually finite.

The discrete memoryless channel (DMC) has the property that its treatment of a symbol input at a certain time does not depend on the symbols input, or its treatment of them, at any earlier time.

The discrete memoryless channel (DMC) has the property that its action depends on its inputs at a number of earlier times.

See also channel coding theorem, Shannon’s model.