the RSTU skips a pair, so the 8 ports that it uses are on the first 8 odd numbered pairs. the evens aren't used.
the BSLU is the same, for the first 8 ports. IF you have the BSLS daughter card, then you get the other 8 ports on pairs 16-24 (I think, I can't find the right manual for that right now)
on both cards pair 25 is for power failure cutover.
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