In order to send information using 4B5B encoding, the data byte to be sent is first broken into two nibbles. If the byte is 0E, the first nibble is 0 and the second nibble is E. Next each nibble is remapped according to the 4B5B table. Hex 0 is remapped to the 4B5B code 11110. Hex E is remapped to the 4B5B code 11100.
In 100BASE-FX and 100BASE-TX, the 4B5B replacement happens at the PCS sublayer of the Physical layer. Information is then further encoded for transmission using NRZI in 100BASE-FX at the PMA sublayer, and MLT-3 in 100BASE-TX at the PMD sublayer.
|4B5B Encoding Table|
|Data (Hex)||(Binary)||4B5B Code|
In order to send information using 8B6T encoding, the value of the data byte is compared to the values in the 8B6T table. Every possible byte has a unique 6T code, a set of 6 tri-state symbols. Unlike 4B5B, 8B6T completely prepares the data for transmission; no further encoding is required.
100BASE-T4 is currently the only technology which uses 8B6T encoding. It performs 8B6T encoding at the PCS sublayer of the Physical layer. 100BASE-T4 then demultiplexes the 6T codes onto three wire pairs.
|8B6T Encoding Table|
|Data (Hex)||(Binary)||8B6T Code|
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