[BP] Project Objectives
The important initial step in our process was to set the project objectives.
These objectives and criteria framed a very viable and valuable project,
and were carefully considered and ratified by the larger 802.3 body.
Early Task Force work and consensus solidified the direction we are taking.
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The project objectives specify operation over Improved FR-4. This
objective establishes some very key guidelines:
a) First, it means that the project is dealing with newly designed
backplanes, as there is no prevalence of Improved FR-4 in legacy backplanes.
b) Further, the group focused very intently on defining the Dk and
Df of Improved FR-4 due to the wide understanding that the material properties
would be the prime determinant of channel capacity. This means that
layout discontinuities were not going to be made the prime determinant
of channel capacity.
c) Finally, the PHYs for 1G and 4-lane 10Gbps are specifically designated
in the Objectives as running over the Improved FR-4 channel. So accommodation
of pre-existing channels that ran other 1G and 4-lane 10Gbps PHYs is out
of this project's scope.
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The directive we were given was to look at the channel model as a bilateral
Contract between backplane and signaling. It was directed that the
signaling must perform to at least under the line, and the backplanes must
perform to at least above the line. (In this email, I will not deal
with the over-simplicity of our present model approach) The bilateral
nature of the contract means that if signaling is asked to provide margin
to the contractual infractions of the backplane, the backplane will be
asked to provide margin to the contractual infractions of the signaling.
The net effect is mutually-contributed, balanced margin.
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The directive given to the 802.3ap members was to unilaterally define the
channel prior to any signaling considerations. The rationale was
that this provided a more deterministic, linear progression through the
project, which is admirable. The direction was that in the subsequent
signaling evaluations, we could expect that any problems that such channel
presented to the signaling could be dealt with by easing up on the channel
at that later time.
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The Channel Ad Hoc directive was to find the worst, reasonable channel
and solidify the contractual line. And now, initial signaling evaluations
have been performed on the channel. In what I believe surprised a
number of people, the results show that the channel model does not require
relief. All the signaling proved able to hit the target, even the
most simple, available and low power. Instead of being ecstatic for
the industry, it seemed this frustrated a number of people.
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It would seem that the Task Force has done quite well in meeting objectives.
Since we have been successful in meeting objectives, and our timeline says
that signaling decisions are the next item, it is appropriate to be focusing
on requirements consistent with our objectives.
BrianS