The 0s and 1s in a stream of digital data must be translated into physical symbols that can be impressed onto a medium.
It is natural to visualize the bits in a frame being transmitted across a medium by faithfully copying its 0 and 1 bits into physical representations of 0 and 1for example, as distinct voltage levels or optical power levels.
The problem with using a high voltage for 1 and a low voltage for 0 is that a receiver has trouble keeping track of where bits begin and end when it receives a long string of 1s or a long string of 0s.
Over the years, several ways of overcoming this problem have been introduced. For example, for 10BASE5, 10BASE2, and 10BASE-T Ethernet, each 0 or 1 is translated into a ...