4B/5B Code

• insert extra bits to break up runs

• 4-bit values sent as 5-bit codeword

• codewords have ɚ leading 0 & ɛ trailing 0; 16 of 32 used (others for ctrl)

• transmitted using NRZI

• 80% efficiency

• used by FDDI & 100Mb/s Ethernet

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