Digital data uses discrete discontinuous signals to represent its meanings. In a DC (direct current) transmission system, different voltage (or current) values are used to represent the values (usually 0 and 1). A digital transmission has a very low error rate and can be sent at very high speeds. Weak signals can be regenerated with low probability of cumulative error. Since all signals are made up of 0s and 1s, signals from many sources can be readily multiplexed using digital techniques. See multiplexing.
For transmission over longer distances (over about 50 to 1000 meters) it is common to insert transformers and/or optoisolators to improve the signal integrity by breaking ground loops and eliminating common mode interference. Alternative methods use modems, fiber-optic cables, or wireless links. See also modulation.