256B datasheet(10/21 Pages) IBM

10 / 21 page

256b/257b Transcoding for 100 Gb/s Backplane and Copper Cable

IBM

256b/257b Transcoding w/ at least 1 CB

Step 1: Delete 01 header bits of all DBs and 10 header bits of all CBs.

Step 2: Insert header bit 0 (sent first) indicating 256-bit payload of transcoded block contains at

least 1 CB

Step 3: Delete the second 4-bit nibble in the first byte of the first control block in a transcoded block.

The first 4-bit nibble in the first byte of the first control block indicating the type of the first control

block is kept. There are a total of 11 CB-type indicators without accounting for alignment markers

(AM).

Step 4: Insert 4-bit pattern x1 x2 x3 x4 following header bit 0 where xi=0 indicates that i-th block is

control block CBi whereas xi=1 indicates that i-th block is data block DBi.

64-bit data in all second, third and fourth control blocks in a transcoded block are kept unchanged

and therefore first byte of second, third and fourth control blocks indicating block type field is

protected by distance-4 Hamming code.

No reshuffling of the order of data/control blocks after transcoding

256B Datasheet(PDF) 10 Page - IBM