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Old 12-01-2005, 02:00 PM
Kolja Sulimma
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Default Re: Multi-layer switch network?

Davy schrieb:

> But why not use single-layer instead of multi-layer switch network?


A very abstract answer:
I a single layer network every input connects to N other pins.
These everage wire length for each input is at least proportional to
(n*sqrt(n)), same for the capacitance.
Therefor the bandwidth is reciprocal to n^3, the latency is proportional
to n^3.

The other extreme is a tree of 2-way switches. Each path has log(n)
switches. Each connection has 2 pins. The area is n^2 (n*log(n) is only
true for unbounded number of rounting layers). The average wire length
is n. The bandwidth is constant, the latency is proportional to log(n).

Of course the latency of the switch will have a larger constant value
than the wire. But the difference between log and n^3 is extreme, so the
break even point will be for rather small n.

Kolja Sulimma
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