4B 5B encoding

4B/5B encoding A data-translation
scheme used to precede signal encoding in
FDDI (Fiber Distributed Data Interface)
networks. In 4B/5B, each group of four bits
is represented as a five-bit symbol, which is
then associated with a bit pattern, which in
turn is encoded using a standard method,
often NRZI (non-return to zero inverted).
See also Manchester encoding.