The concept of digital transmission is entirely different from its analog counterpart. With
an analog signal there is continuity, as contrasted with a digital signal that is concerned
with discrete states. The information content of an analog signal is conveyed by the value
or magnitude of some characteristic(s) of the signal such as amplitude, frequency, or phase
of a voltage; the amplitude or duration of a pulse; the angular position of a shaft; or the
pressure of a fluid. To extract the information it is necessary to compare the value or magnitude
of the signal to a standard. The information content of a digital signal is concerned
with discrete states of the signal, such as the presence or absence of a voltage, a contact in
an open or closed position, a voltage either positive- or negative-going, or that a light is on
or off. The signal is given meaning by assigning numerical values or other information to
the various possible combinations of the discrete states of the signal