XAUI channel group delay
The XAUI compliance channel group delay limit of 160 ps p-p (adopted in
Irvine and included in D2.1) appears to be impractically restrictive. A plot
of several compliance channels is attached to illustrate. The best channel
measures 628 ps p-p. The best channel having connectors measures 1425 ps
p-p! (Apertures close to the 3% of span allowed by the draft were used.)
I see a few options to fix this in the next draft:
1. Loosen the limit to about 2 ns p-p to accommodate valid channel data. But
such a loose limit will have little value in preventing manipulated
channels, which was the original purpose of the limit.
2. Develop a more complex limit to make distinction between valid channels
and inlikely ones. This will take a committed person or group of persons to
analyze the problem, gather more data and propose the solution. It also
complicates compliance testing. The benefit in preventing manipulated
channels is not worth this effort in my opinion, particularly in view of
likely interoperability tests and other practical requirements that will
exist for XAUI component performance.
3. Eliminate the group delay limit. Given the complexity of preventing
manipulation and the doubtful benefit of testing with a manipulated channel,
I no longer see a need for this limit. I propose we remove it.
Thoughts?
-Dawson
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