Fibre Channel 8B/10B Encoding - How IT Works For The IBM Code - Encoding Tables - Control Symbols

Control Symbols

The control symbols within 8b/10b are 10b symbols that are valid sequences of bits (no more than six 1s or 0s) but do not have a corresponding 8b data byte. They are used for low-level control functions. For instance, in Fibre Channel, K28.5 is used at the beginning of four-byte sequences (called "Ordered Sets") that perform functions such as Loop Arbitration, Fill Words, Link Resets, etc.

Resulting from the 5b/6b and 3b/4b tables the following 12 control symbols are allowed to be sent:

Control symbols
Input RD = −1 RD = +1
DEC HEX HGF EDCBA abcdei fghj abcdei fghj
K.28.0 28 1C 000 11100 001111 0100 110000 1011
K.28.1 † 60 3C 001 11100 001111 1001 110000 0110
K.28.2 92 5C 010 11100 001111 0101 110000 1010
K.28.3 124 7C 011 11100 001111 0011 110000 1100
K.28.4 156 9C 100 11100 001111 0010 110000 1101
K.28.5 † 188 BC 101 11100 001111 1010 110000 0101
K.28.6 220 DC 110 11100 001111 0110 110000 1001
K.28.7 ‡ 252 FC 111 11100 001111 1000 110000 0111
K.23.7 247 F7 111 10111 111010 1000 000101 0111
K.27.7 251 FB 111 11011 110110 1000 001001 0111
K.29.7 253 FD 111 11101 101110 1000 010001 0111
K.30.7 254 FE 111 11110 011110 1000 100001 0111

† Within the control symbols, K.28.1, K.28.5, and K.28.7 are "comma symbols". Comma symbols are used for synchronization (finding the alignment of the 8b/10b codes within a bit-stream). If K.28.7 is not used, the unique comma sequences 0011111 or 1100000 cannot be found at any bit position within any combination of normal codes.

‡ If K.28.7 is allowed in the actual coding, a more complex definition of the synchronization pattern than suggested by † needs to be used, as a combination of K.28.7 with several other codes forms a false misaligned comma symbol overlapping the two codes. A sequence of multiple K.28.7 codes is not allowable in any case, as this would result in undetectable misaligned comma symbols.

K.28.7 is the only comma symbol that cannot be the result of a single bit error in the data stream.

Read more about this topic:  Fibre Channel 8B/10B Encoding, How It Works For The IBM Code, Encoding Tables

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