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Re: [10GBT] Summary of issues with PAM12


I still maintain that the "hole in the constellation" is not an issue
per se. It can be demonstrated that a PAM-12 solution *could* operate
with a baud rate lower than 800Mbaud whereas the proposal in July showed
a solution with a baud rate of 825Mbaud. If, this solution does not work
then perhaps those who favor PAM-12 modulation might want to rethink
their constellations. On the other hand, if the "inefficient" PAM-12
proposal is deemed workable and superior to any other proposal then
perhaps the proponents like the "convenience" of 14 bits/baud instead of
14.33 bits/baud.

I find all of the bombast and hyperbole distracting. We are engineers;
we can read graphs; we can review equations. I do not think that we
should be making decisions based on who can coin the snappiest phrase or
whether we get constellations made of chocolate. Can we please get back
to the regular programming - post simulation results, analysis etc.

Of Sailesh's list - the first and second a relevant points although
there seems to be sufficient dispute over the details to warrant more
analysis. The fourth point is a reasonable argument against the PCS
proposal although it has no relevance to the modulation. The third and
fifth points are redundant as the effects of inefficiency are taken into
account by the increased baud rate. The last point is just plain dumb!
Frame delineation is always overhead; fixed length frames are usually
delineated by fixed patterns that contain no information other than the
frame delineation - well, duh!


Roberts, Hal wrote:

>Ignoring the hilarious 'confidential' e-mails that this posting seemed to have inspired, the 'hole in the constellation' just seems to me to be a particularly obvious waste of margin in the PAM-12 proposal. What I am really looking for is a PAM-12 proponent to summarize the issues with PAM-8 (like Sailesh did for PAM-12) so as to make a comparison. So far nobody has attempted to create this summary.
>Your analogy of an 'issue with PAM-8' being 'only 12 bits/baud' is not a good one since trading bits per baud for increased baud rate is a valid engineering trade off. It is not an outright inefficiency like the constellation problem.
>Like Sailesh said, "Did 10GBASE-T become a greatly simplified problem in the intervening period
>that these margins are no longer important?"