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XAUI and 64b/66b


Jonathan just sent me a note saying that I was even confusing
him right now so I want to stop and ask my question again. I'll
try to make this as clear as possible.

In the layer diagram that Brad showed in Albuquerque, the XAUI
was shown as an XGMII extender. To me this means that the
reconcilation sub-layer speaks using XGMII language and the PCS
listens using XGMII language. The XAUI can extend this interface
by translating from XGMII to XAUI but it must translate back
again before it gets to the PCS. The XGXS block is the translator.

The 64b/66b proposal as written ignores the XGXS block between
XAUI and the PCS. It is my contention that, though this would
work, it is unnecessary and even burdensome to those implementors
that choose to not use XAUI. 64b/66b would work equally as well
without the XAUI specific control codes as they add nothing to
the efficiencies of 64b/66b (that I can tell). The XGMII specific
control codes are completely adequate for 64b/66b. In my opinion,
a serial PCS should be specified as if XAUI didn't exist.

I'll even go so far as to state that, in my opinion, even a
parallel/CWDM PCS should be specified as if XAUI didn't exist.
If this PCS turns out to be identical to the XGXS block then some
implementors may choose to avoid the encode/decode/encode as
specified in the standard, but I believe that is how it should
be specified.

Is the question/comment still confusing or do you merely disagree?


Benjamin Brown
Router Products Division
Nortel Networks
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Kilton Road
Bedford, NH 03110
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