8b/10b Encoding

8b/10b Encoding

In telecommunications, 8b/10b is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. This means that the difference between the count of 1s and 0s in a string of at least 20 bits is no more than 2, and that there are not more than five 1s or 0s in a row. This helps to reduce the demand for the lower bandwidth limit of the channel necessary to transfer the signal.

An 8b/10b code can be implemented in various ways, where the design may focus on specific parameters such as hardware requirements, dc-balance etc. One implementation was designed by K. Odaka for the DAT digital audio recorder. Kees Schouhamer Immink designed an 8b/10b code for the DCC audio recorder. Another implementation was described in 1983 by Al Widmer and Peter Franaszek.