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Re: [10GBT] Summary of issues with PAM12


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?"


-----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 11:42 AM
Subject: Re: [10GBT] Summary of issues with PAM12


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 :-)


Roberts, Hal wrote:

>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.