Data Communications Networking Devices - 4th Ed.pdf

316 ________________________________________________________ LOCAL AREA NETWORKS4B5B codingThe use of a 4B5B coding scheme enables data and control information to be carriedin each symbol represented by a ®ve bit code group. In addition, an inter-stream ®llcode IDLE) is de®ned, as well as a symbol used to force signaling errors. Sincefour data bits are mapped into a ®ve bit code, only 16 symbols are required toTable 3.11Code group4320 Name4B5B 100BASE-TX code groupsTXD/RD3210 InterpretationData11110 0 0000 Data 001001 1 0001 Data 110100 2 0010 Data 210101 3 0011 Data 301010 4 0100 Data 401011 5 0101 Data 501110 6 0110 Data 601111 7 0111 Data 710010 8 1000 Data 810011 9 1001 Data 910110 A 1010 Data A10111 B 1011 Data B11010 C 1100 Data C11011 D 1101 Data D11100 E 1110 Data E11101 F 1111 Data FIdle11111 I IDLE: used as inter-stream ®ll codeControl11000 J Start-of-stream Delimiter, Part 1of 2; always used in pairs with K10001 K Start-of-stream Delimiter, Part 2of 2; always used in pairs with J01101 T End-of-stream Delimiter, Part 1 of2; always used in pairs with R00111 R End-of-stream Delimiter, Part 2 of2; always used in pairs with TInvalid00100 V Transmit error; used to forcesignaling errors00000 V Invalid code00001 V Invalid code00010 V Invalid code00011 V Invalid code00101 V Invalid code00110 V Invalid code01000 V Invalid code01100 V Invalid code10000 V Invalid code11001 V Invalid code