[BP] Channel Inclusion

[Brian Seemann <brian.seemann@xxxxxxxxxx>]

I was one who, during the recent Ottawa meeting, opposed inclusion of certain
channels in the "group of 20".  Here are some thoughts on that.

1. We have "about 20" cases to be in our official evaluation list.  These should be used to carefully stake out the edges of the reasonable problem space.
2. "Relevant" channels are those that either:
• a) Fit the project objectives AND meet the channel model, or
• b) Meet the channel model
3. Minor deviations from the channel model should be considered "relevant" and studied.
4. Major deviations from the channel model usually represent implementations inconsistent with the project objectives and are not "relevant" or "reasonable", but may be "of interest".  Namely, they may have a characteristic that would be interesting to study, but it doesn't mean that they fit the target application.
5. The channel model we have today is simplistic, but still has value.  Here is why:
• If all frequency domain plots (SDD21, SDD11, NEXT, FEXT) are well behaved, it is a good indicator that the channel will work.
• A large number of channels have been presented that are well-behaved within the channel model.  This demonstrates that backplanes can very feasibly be built to the requirements.
• If a channel doesn't work, the frequency domain plots are discernably bad.
6. Some channels in between require more complex analysis.  This is the false positive / false negative region.  This region may need to allow trading off between the different frequency domain parameters, such as the ANR and Voltage Ratio methods.
7. I'm disappointed that only one connector is represented in all the channels offered to the group.
8. Relative to the above points, here are my opinions on certain channels:
• D'A Case 1:    Fits objectives, minor deviations from model - Include as Relevant.
• D'A Case 2:    Fits objectives, minor deviations from model - Include as Relevant.
• D'A Case 3:    Doesn't fit objectives (50% of length is not Improved FR-4), significant deviations from model - Don't include.
• D'A Case 4:    Fits objectives, meets model - Include as Relevant.
• D'A Case 5:    Fits objectives, meets model - Include as Relevant.
• D'A Case 6:    Fits objectives, minor deviations from model - Include as Relevant.
• D'A Case 7:    Fits objectives, meets model - Include as Relevant.
• Peters  Cases:    Without going through each one, I'd apply my criteria above.  There were a number of channels that I feel fit in the "major deviations / inconsistent with objectives" category.
9. I'm supportive of using our methodologies to look at specific "major deviations / inconsistent with objectives" cases for the informative purposes for that backplane maker to see whether he could use our standardized ICs.  But I am unsupportive of perpetuating those types of design practices by changing the objectives of this project.

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