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(C) Herbert Haas
2005/03/11
GE 8B/10B Coding
8B/10B Encoder/Decoder
PMA
PCS
GMII
256 code groups
1024 code groups
8 x 125 Mbit/s
125 million code
groups per
second
1250 Mbaud
1
Only used
by
1000BaseX
1111111
11111111 11
8B10B block coding is very similar to 4B5B block coding but allows fully
balanced 10-bit codewords. Actually, there are not enough balanced 10-bit
codewords available. Note that there are 256 8-bit codewords which need to be
mapped on 1024 10-bit codewords. But instead of using a fully balanced 10-bit
codeword for each 8-bit codeword, some 8-bit codewords are represented by two
10-bit codewords, which are sent in an alternating manner. That is, both
associated 10-bit words are bit-complementary.
Again, the signaling overhead is 12.5%, that is 1250 Mbaud is necessary to
transmit a bit stream of 1000 Mbit/s.