4B/5B Encoding Data coded as symbols of 5 line bits >4 data bits, so 100 Mbps uses 125 MHz Uses less frequency space than manchester encoding Uses nrzi to encode the 5 code bits Each valid symbol has at least two 1s So never get three os in a row (Why dont we care about 3 ones in a row? 16 data symbols, 8 control symbols Data symbols: 4 data bits Control symbols: idle, begin frame, etc Example: FDDI ecture 6 15441@2008 124B/5B Encoding •Data coded as symbols of 5 line bits → 4 data bits, so 100 Mbps uses 125 MHz. – Uses less frequency space than Manchester encoding •Uses NRZI to encode the 5 code bits •Each valid symbol has at least two 1s – So never get three 0s in a row – (Why don’t we care about 3 ones in a row?) •16 data symbols, 8 control symbols – Data symbols: 4 data bits – Control symbols: idle, begin frame, etc. •Example: FDDI. Lecture 6 15-441 © 2008 12