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Re: [10GBT] Summary of issues with PAM12


You are only person on copy.

I've been thinking about you point below and wondering the same. I can think
of two reasons why a detractor of PAM-12 might care about the technical
proposal for PAM-12. First, they are engineers. Need I say more? More
importantly, they might be considering the possibility that this is a Trojan
horse. That is to say that once PAM-12 is adopted, and it is discovered that
it is really hard, a more efficient PAM-12 constellation is introduced.
Presuming that said constellation will be more difficult to implement and
have negative impacts (e.g. number of cells, power, latency...) and that if
it had been introduced prior to the adoption of the PAM-12 proposal it would
have been rejected out of hand, it would live only because of deception (or
incompetence, you pick).

All of this is purely speculation, of course. I can imagine that PAM-12
detractors would not want to directly raise this issue in a public forum as
it would seem at least politically incorrect if not outright accusatory.


> -----Original Message-----
> From: stds-802-3-10gbt@IEEE.ORG [mailto:stds-802-3-10gbt@IEEE.ORG]On
> Behalf Of Hugh Barrass
> Sent: Wednesday, August 18, 2004 9:42 AM
> To:
> Subject: Re: [10GBT] Summary of issues with PAM12
> Hal,
> I don't understand why the "hole in the constellation" is seen as an
> issue. It causes the PAM-12 to be less "efficient" than it could be,
> just like the padding bits and encapsulation overhead. The
> net result is
> that the proposal using PAM-12 needs a symbol rate of 825Mbaud where a
> lower clock rate might be used if the efficiency was better.
> However, if
> the comparison is made using that proposal and PAM-12 still comes out
> better then perhaps the "inefficiency" is acceptable. If, on the other
> hand and as Sailesh maintains, the comparison comes out in favor of
> PAM-8 then the PAM-12 proponents might want to look at ways
> of "trimming
> the fat."
> It would be equally valid to raise the "issue with PAM-8" of "only 12
> bits/baud" and require the PAM-8 fans to address that...
> Personally, I think 10GBASE-T would be best addressed by 4
> pair, bonded,
> 2BASE-TL on steroids :-)
> Hugh.
> Roberts, Hal wrote:
> >All,
> >
> >Sailesh provides a nice compact list of (his) issues with
> regard to PAM12. I
> >have seen responses to some of these but nothing addressing
> or summarizing
> >them all.
> >
> >In addition it would be useful (at least to me) to see a
> similar summary of
> >"Issues with PAM8" from a PAM12 proponent. (Unless based on Sailesh's
> >criticisms there are no longer any PAM12 proponents?   ;-)
> >
> >Finally, Sailesh has a good point that a number of his
> issues have been
> >completely unanswered. I am surprised no one has addressed
> the 'hole in
> >constellation' issue.
> >
> >
> >
> >