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Re: [BP] Question regarding Channels


I don't think we're as far apart as it may seem.  You state that there are a number of customers who do counterboring, and a number who don't.  I agree.  There are certainly different materials and trace dimension out there, both length and width.  -13 is by no means excluded.  It may have challenges reaching the full 40" but that's not excluding it's usage in the majority of the market and that doesn't mean that 40" is not achievable with improved FR4.  I've seen customers do proper engineering to enable upgrade of their systems to 10G, and that of course means taking into account all aspects of high frequency design techniques for their particular system requirements.  You say that for some customers counterboring would be a Greenfield design.  I would say it's their first 10Gbps design (i.e, they didn't design their previous system for upgrade to 10Gbps).

Thanks,        Joe


Joe Abler                                                             abler@us.ibm.com
IBM Microelectronics Division                          919-254-0573
Technical Marketing & HSS Applications    919-254-9616 (fax)
3039 Cornwallis Road                                                                
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"DAmbrosia, John F" <john.dambrosia@TYCOELECTRONICS.COM>
Sent by: owner-stds-802-3-blade@LISTSERV.IEEE.ORG

10/20/2004 05:59 AM
Please respond to "DAmbrosia, John F"

       
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Joe,
I partially disagree with your statement regarding Joel's definition for the channel. First, Joel said his model is based on an 0.030" stub, thus requiring counterboring.  Not everybody has done counterboring, and not everyone has done it to that degree.  Thus, for some vendors counterboring would be a Greenfield thing, and I guarantee that there are vendors out there who will consider counterboring to be Greenfield, simply because they don't do it internally.  Second, Joel's channel is based on "improved FR'4".  However, I believe 4000-13 is about as low a grade as you can go.  Unfortunately, the current definition restricts the ease of use for -13 being used.  I ran into that earlier in the summer, and the new proposal that Joel had suggested at one point would have enabled more constructions of -13 to be used. Unfortunately, this was voted down.  I say unfortunate, because -13 lo! oks to be the next main "FR-4" to be used, and I would like our customers to have as much freedom as possible in using this material.  I have heard from a number of system vendors that they are going to -13 next.  Use of grade beyond it become limited due to relative cost differences, and that is for the backplane.  For the line cards the relative cost difference accumulates even quicker, and it is easy to envision that the relative cost difference will keep the material grade down to the lowest grade material solution.  Different applications will be sensitive to relative cost in different ways.  This is why I had to do line cards in -13 and -13SI.  Thus, while you are entitled to your view, so are a lot of other people, and that fact needs to be observed.  Just because we can build it, does not mean that they will come.
 
One other thing that I wonder about is the use of 6 mil traces on the daughtercards and backplane.  At 40 inches skin effect is an accumulate pain.  Will all applications be able to support the use of 6 mil wide traces on line and fabric cards.  I think this is a key question from system vendors, and ultimately will impact the channel model.  I am assuming from Joel's use of it on his test boards that he can support it.  I would like to hear other vendors confirm this or argue with it.
 
The big thing in my mind comes to the stub effect.  If you look at our objectives it merely talks about 1m of improved FR-4.  It does not say anthing at all about stub effects. There are a number of customers who do it, and a number who don't want to do it.  I believe as part of the process, we need to examine it, and rule it either possible with consequences or rule it out because of those consequences, but the point is we still have to do it.  The industry expects it of us.  The case #6 I proposed was a very mild stub effect, compared to other channel data.  Having a test case in like that is imperative for both marketing reasons and allowing the industry a fair chance to select the best solution.  At the last meeting, you had questioned me on the weighing scheme, and I have no answer to that.  I do not believe whether you can get it to work is the ultimate weighing factor.  There are ! surrounding questions that need to support that fact, such as the things you talked about - power, ease of implementation, etc  All of these things will go into the weighing by each individual as to what is the best solution. .
 
 
My two cents.
 
John
 
-----Original Message-----
From: owner-stds-802-3-blade@listserv.ieee.org [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of Joe M Abler
Sent: Monday, October 18, 2004 10:46 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: Re: [BP] Question regarding Channels
 

In the context of my original note, which was addressing issues of the signaling ad-hoc, the line is as defined by the channel ad-hoc which is where and how the line should be defined.  Some appear to have taken exception to what's been defined and rather than working to address it in the channel ad-hoc the issue has been opened in the signaling ad-hoc, which I don't think is appropriate.

So as not to skirt your question let me comment on the legacy issue that's been raised.  In my view, there's nothing in Joel's definition that exclusively requires greenfield design.  The definition he put together does not require exotic new materials or breakthrough manufacturing techniques from what has been available in the past.  I would very much like to see someone bring in a legacy design that was done for an initial system release at a lower speed, but at the time the system specifically took on the objective of designing for a future upgrade to 10Gbps.  There are systems that have done this, where they have used generally recognized high frequency design techniques, made reasonable assumptions on where the signaling technology would be, analyzed their system to those assumptions, and are now well positioned to meet their objectives.  If system vendors were to bring those designs in and recommend potential ! changes to the channel model to c! onsider limitations we may have missed then I would be very willing to look at changing the model.  What I don't think should be brought to the group is someone's Johnny on the spot 1G or 3G design that was never engineered with the intent of upgrading to 10G.  If in the past Vendor A took on some additional system cost and took additional time to market to properly engineer their system for future upgrade, and Vendor B went for lowest cost and forego engineering for the future in order to rush their product out the door then I don't think we should be penalizing Vendor A with additional power and silicon area in order to service Vendor B.  That's not to say either vendor made a bad initial business decision or that Vendor B is now out in the cold.  There will always be chip vendors who are willing to provide more advanced technologies to service these problem systems.  It's simply a matter of Vendor B taking the eas! y road initially and now it's t! ime to pay the piper.  Of even mor e significance than penalizing hypothetical Vendor A is the fact that we'd be penalizing all vendors going forward who plan to properly engineer their systems for 10G - and power is critical for all these vendors that I know of.  


Thanks,        Joe


Joe Abler                                                             abler@us.ibm.com
IBM Microelectronics Division                          919-254-0573
Technical Marketing & HSS Applications    919-254-9616 (fax)
3039 Cornwallis Road                                                                
Research Triangle Park, NC  27709

  "Booth, Bradley" <bradley.booth@INTEL.COM>
Sent by: owner-stds-802-3-blade@listserv.ieee.org

10/14/2004 01:35 AM
Please respond to "Booth, Bradley"

       
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Joe,
 
I wanted to touch on the following statement you made:
Note that when I use the term "line," I'm using it figuratively to refer to channels that fall within all aspects of the channel adhocs definition of a compliant channel.  I'm not solely referring to the SDD21 line.
 
This is the area that I think is the heart of the problem.  Where does that line exist?  What makes a channel compliant?  Compliant with a signaling approach?  Compliant with an installed base?  These questions are rhetorical.  I know that everyone is likely to have a different point of view of what the line is for being compliant.  How can the TF get to 75% consensus while satisfying the Objectives and 5 Criteria?  (Again, another rhetorical question.) :-)
 
Thanks,
Brad



From: owner-stds-802-3-blade@listserv.ieee.org [mailto:owner-stds-802-3-blade@listserv.ieee.org] On Behalf Of Joe M Abler
Sent: Wednesday, October 13, 2004 12:03 PM
To: STDS-802-3-BLADE@listserv.ieee.org
Subject: [BP] Question regarding Channels


Let me finally add my views on the subject.  I haven't been purposefully silent, just swamped lately.

So we have this great debate about channels above the line and those below.  Assuming everyone agrees we evaluate all the channels above the line, let's look at the reason for also considering those below the line.  The primary reason is to assess that the signaling methodology has sufficient margin for the given channel definition.  We must do that, but I would claim the starting point for that is not with use of channels below the line.  The standard is likely to be defined for a BER of e-12, but most system vendors have a backplane requirement of e-17 or better.  We should start by evaluating that the signaling approach has this amount of margin or some other agreed to metric (the performance criteria) for channels above the line .  That's still only a starting point.  I'm much more concerned about potential channels that have severe discontinuities that may all be fully above the defined line, along wi! th xtalk, return loss and other c! ! haracteristics that are also within the compliant definition.  Any of the signaling methodologies we're looking at could well have a problem with some potential killer channels before they have problems with some of the rather well behaved channels below the line (like several of John's).  We need participants to bring in these potential killer channels as part of validating that we have a robust signaling methodology as well as a comprehensive channel definition.  Anyone that has a view that looking at channels below the line is a comprehensive way of evaluating margin is kidding themselves.  The well behaved ones somewhat below the line won't show problems, while the ugly ones well below the line will simply be dismissed because they're well below the line.  

I don't have a problem per se with including channels below the line in our simulation and analysis, and certainly agree we need to do some of it.  However I believe the group has various views as to what it means to include channels into the signaling adhoc evaluation.  In my view, the group should first evaluate the signaling methodology for channels above the line against it's metrics.  I expect many in the group believe we should look at some channels below the line for margin purposes, a view I would agree with.  I also believe some in the group have the view that all channels which are accepted into the signaling ad-hoc need to be solutioned.  I don't agree with this.  Solutioning channels well below the line penalizes those above the line in terms of power, area, complexity (time to market risk), etc.  Issues with definition of where the channel line is drawn need to be dealt within the channel adho! c, not the signaling.  So if! ! we're going to include these channels into the evaluation set, we need to get the group in sync as to how they are used relative to the analysis of the signaling methodology.  Options I see are:
1.        Properly margin the analysis of channels above the line, and don't consider any channels below the line.
2.        Make the channels below the line available but leave it optional as to whether a vendor includes them in their simulation set or not.  Results from these channels would only be used if there is a tie-breaker need of results from channels above the line.  I think the group is self-policing enough that all vendors will bring in results for a reasonable set of these channels, but no one would be discounted for not doing all of them because the simulation and analysis does take a considerable amount of time.
3.        Select a set of channels that are within a reasonable deviation from the line and require they be used as part of the evaluation set in order to show margin.  The problem with this approach is that it requires us to draw another line.  Need I remind anyone that we haven't succeeded in drawing a first line yet?
4.        Require that all channels be used in the evaluation, but somehow weight the results of ones below the line such that they won't overly influence the evaluation and lead to a methodology that is way overdesigned to the objectives and therefore penalizes systems with additional power, area, cost, and risk.  To propose a specific mechanism to do this we'd first need to complete the work of defining the base evaluation metrics.  I believe we'd also need to do #3 because I expect some channels would be weighted differently than others.  Needless to say, this would be a difficult and cumbersome approach.  
5.        Require that all channels be used in the evaluation, and require that a signaling methodology be identified (or perhaps invented) that would adequately solution all channels.

My preference is option 2.  I'm deadset against option 5.  Note that when I use the term "line," I'm using it figuratively to refer to channels that fall within all aspects of the channel adhocs definition of a compliant channel.  I'm not solely referring to the SDD21 line.


Thanks,        Joe


Joe Abler                                                             abler@us.ibm.com
IBM Microelectronics Division                          919-254-0573
Technical Marketing & HSS Applications    919-254-9616 (fax)
3039 Cornwallis Road                                                                
Research Triangle Park, NC  27709