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I
agree with John that short is not always better, and the SDD12 is not the only
criteria that defines if a channel can be equalized correctly or
not.
Since
we have not converged on a signalling and electrical specification for
TX and RX devices, I think it may be counter-productive to spend too much time
debating the informative channel, especially if it excludes many of the
existing, measured channels that have been presented. Since the data presented
by John and Peter can easily be reproduced in other practical systems, I
feel it is a mistake to discard it because it does not meet the informative mask
for SDD12.
I
really think the signaling commitee should continue work related to defining an
objective simulation methodology. This would not only allow us to compare
signalling methods, but it would also give everyone involved a clearer picture
of what channels are "solvable". The signalling ad hoc should simulate as
many channels as possible, with the goal of objectively picking the best
signalling approach.
Once a
signalling approach has been selected, the next step can be to extend the
simulation models to take into account implementation specific limitations that
may further reduce the number of channels that can be supported, but at the same
time it should give some guidance to the channel ad hoc with respect to where
the limits on the masks should be. Hopefully, we will emerge with a robust
signalling approach and a clearer picture of what the reasonable
limits of the channel are. This will include loss, xtalk, reflections, and
anything else that is considered an impairment.
In summary, let's accelerate discussion around
what assumptions to include in simulations, how to define a common
simulation methodology, and which signalling techniques we want evaluated. I'd
like to see less talk about limiting the channels we will simulate with
until we know that none of the signalling schemes proposed can solve
them.
Riccardo
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