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Re: [BP] Data Presented in Goergen_02_0904



Title:
Bill,
My comments are in-line. -joel

The channels submitted in goergen_02_0709 and goergen_02_0904 certainly do have great value and should be used by the working group for further work.  However, they should not be used to the exclusion of other channels that represent complete channels.  Both the signaling work and the setting of the channel limit should be based on a wide selection of data and must include data that represents real channels.  I submit the following reasons to support this conclusion.

I have never advocated using only these channels.  They are not meant to be used as golden.  I'm not sure where you or anyone else would have gotten that as the objectives had been clearly stated in many phone conference calls.  I would recommend taking some time to review past discussions on this matter.

Your choice of the words 'wide selection' is interesting.  What you imply is that you want the channel limit to include a wide variety of channel design practices.
 

1)       A connector agnostic test system is a worthy goal.  However, this is not achieved by omitting the connectors.  Additionally, each connector is accompanied by two via fields with their associated breakouts.  This is not well represented by a single via transition.

If you actually take the time to employ the research, it is easily shown that in short segments, the second set of holes you describe is not seen as a double effect.  It's the first set that both determine and dominate the response, the second being absorbed within the first.   The dominant factor is the first holes, combined with the short segments.  Again, show me what flavors of nets I have not been able to show in these cards.  I have matched everything to data, good and bad, yours and everyone else's.

2)       A test system does not necessarily take into account the tradeoffs that inevitably occur in the design of a cost-effective, high density system.

What you imply is this test system is too good of a model.  It should be in most respects.  It uses over 20 years of research and design practice in back plane design, combined with proper routing and geometry shapes.  I took the cards further and employed poor design practice in the aggr signals ... sort of a two for one when including multi-disturber NEXT/FEXT.  It shows the effects of stubs, as well as the effects of xtalk from passing in and out of poor geometry via shapes.  I clearly identified this in my presentations.  It matches quit well with your data.

A test system DOES take into account trade-offs.  Otherwise, what's the point of creating it.  All of the methods employed in these test cards are used everyday in a 'cost-effective, high density system'.  I think the market speaks well enough that this system implementation is cost effective.  And the data of my work is clearly, in terms of the market, more dense then ATCA applications.

What you fail to state is that the real issue here is the inclusion of both gross and severe stub effects within the channel, further disturbed with one-two combinations of short traces.  My data shows this quit well, as does other public data.  Stub effects are very nasty on the channel.  There are cost effective ways to deal with them.  You chose not to deal with them at all in your data.  Your solution is to lower the channel model and let the silicon deal with this problem you call ' a design trade-off'.  I disagree.  The channel should not include severe and gross stub effect.  We've gone through this path in xaui ... one of two major reasons people believe the xaui model is broken.  So instead of attacking my data, why not stick to the issue ... stub effect and short traces.

If you stick to the issue and clearly examine the OIF approach in CEI,  the reason for stateye becomes clear ... you need something very complex to simulate a system with channels registering effects of gross design practice termed by you to be trade-offs in a cost effective and dense design.  Stateye is barely used AND understood by those using it and is clearly unnecessary to simulate just the channel effects (not discussing the system here with tx and rx as there are benefits) when good design practice is employed.  Stubs are easy to both control and effectively design around.

Once I understand the protocol for identification, I will show a trace with stubs, and the same trace with stubs that is influenced by patented technology.

So, you want stubs, I don't.  Stop attacking the validity of my data and test cases.  Start focusing on getting acceptance on the inclusion of gross and severe  stubs into the channel model.

The problem in dealing with both short track effects AND stubs is that the power and die size are going to be larger then I think we can include in a telecom design ... our systems are too dense to support the kind of power required for a 5Ghz drop-off ... I thought it would be 6Ghz, but when you evaluate the stub and short tracks, the data shows a falling off the graph before 5Ghz.  You can see this on the public xaui data.

If we are going to include channels such as this, then I would strongly suggest two channel models and perhaps two sets of phys.  It is my humble opinion that this would happen anyway because the dense systems employed by the telecom group will not be able to handle the power and cooling that a fractional dense ATCA system could handle, essentially making the standard unusable for the telecom market.  I'm not even sure any of the signaling discussed to date can handle that severe channel. 

3)       We can only compare the public data and there are significant differences.  It is difficult to predict how these differences will impact the performance for any particular line code / equalization as illustrated in sinsky_01_0904.

These test cards show several types of channels, not just one type.  Hence that was one of the reasons for doing the cards.  To purposefully identify several types of conditions in such a manor as to evaluate without getting lost in the volume of data.  Again, I have never stated that these are replacements for use of anything.  They are channels used as a common point of reference so when two people show different conclusions of different data, if they both verify similar results on a set of test cards such as mine, we know the data is accurate and taken in a similar manor ... calibrated to some extent.  Thus making the conclusions interesting and relevant.

This topic has been with us on several channel discussion in various bodies since before the days of 802.3z, fiber or copper.  How do we verify everyone is taking data the same way and if they don't, how does that effect the outcome?  We have answered that question after xaui, CEI, and others, as well as ours.  There is a difference,  That was one reason we spent so much time on recommended VNA set-ups.

 

 Again, the test board data from goergen_02_0709 and goergen_02_090 should be considered, but must be put into perspective.  We cannot rely exclusively on incomplete test systems or contrived models however valuable they may be.

 

-Bill Peters

 


From: owner-stds-802-3-blade@listserv.ieee.org [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of Joel Goergen
Sent: Friday, October 01, 2004 4:27 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] Data Presented in Goergen_02_0904

 

Fellow collegues,

During the back plane meeting this week in Ottawa, it was pointed out on several occasions by one colleague that the channels submitted for review and simulation as reported in goergen_02_0709 and goergen_02_0904 are not real channels and therefore, should not be used by the working group in any capacity.  I've studied this concern at length and defend my work in whole as follows.

1) The intent of a connector-less test card was agreed to in part by the members of the channel ad-hoc.  It's creation, though not a new concept at all, was to prevent a common set of test cards from becoming connector evaluation boards by the industry.  My understanding of the ATCA platform is that this MSA has agreed to 'ONE' connector.  Therefore, evaluating comparative back planes in an ATCA environment is easy.  It does not address the diverse nature of the telecom segment, which is the primary intent of the connector-less cards.

2) I've examined all the channel data presented to the public, as well as that submitted to me in private.  All of the public data submitted to IEEE as presentations, and all of the private data sent to me directly correlates to the data from the connector-less back plane cards.  Do the comparison yourself ... Look at every channel and compare it to all the data submitted and you will see the same likeness.  The data speaks for itself.  All the effects form various degrees of inferior channel design are included, certainly not excluding any of those seen in Peters_01_0904.

Therefore, if my data is not valid to consider, then what data 'IS' valid for consideration?  It's clearly acceptable to simulate a channel and then measure the likeness to real before continuing with the remaining simulations/approximations.  These test back planes correlate perfectly and I stand by the design, implementation, and data collected.  If the majority body feels the data is not valid, I am perfectly fine with recalling the data and the cards.  It's cheaper for me.

Joel Goergen