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RE: [bp] BER Objective for BPE



Jeff,
 
Although you addressed this directly to me, I assume that you put this topic to the reflector for general discussion.
 
As you know, this proposal needs to be brought forward to the study group and agreed to by at least a 75% majority before it become an objective.  I encourage you to make such a motion at our next meeting if you feel that this is a necessary change.

Since you directed the message to me, I'll also make some remarks as a citizen of 802.3 and not SG chair:
 
My personal opinion is that it would help if you elaborated on what this objective would mean in practice (especially for those who do not participate in the OIF). 
 
I am personally aware of system requirements for 1E-15 and below, but as you imply in the phrasing of the proposed objective, it is prohibitive to measure such low error rates.  The specific language you use implies that we will define a system that is guaranteed to work at a BER of 1E-15 but we will only verify its performance by measuring the BER to 1E-12.  Giving this topic only limited thought, I see a couple of ways to approach this:

1.  Define the system (transmitter, channel, receiver) such that simulated performance is 1E-15, but in compliance test performance is only verified to 1E-12.  Presumably, parametric values specified in the standard include margin to account for the difference in what was simulated at 1E-15 and what can actually be measured 1E-12.  For a quick example, consider random jitter.  If the link is defined such the peak-peak random jitter at 1E-15 is 0.15UI, then the specification would presumably incorporate a specification for peak-peak random jitter at 1E-12 of 0.133UI.
 
2.  Define a system for performance to 1E-15, and as part of compliance test rely on extrapolation of measured data (for example, bathtub curves along the vertical or horizontal axis) to derive values for 1E-15 that can be compared with the specified values.

One interesting observation regarding (1) is that, if we were to have a closed eye system (i.e. the solution relies heavily on receiver-based equalization, in that the eye at the receiver input is closed), I would expect receiver compliance to be based on "operation at a given BER when driven by compliant driver through a compliant channel."  This is the model that has been employed in 100/1000M twisted pair links and in 10GBASE-CX4.  Using the model defined in (1), we would drive a compliant channel with a compliant driver and ensure that receiver BER performance was better than 1E-12.  I would argue that this says nothing about the receiver's ability to operate at 1E-15.  Some additional impairment (worse than worst-case transmitter or channel) needs to be included to ensure that the appropriate margin is in the receiver design.
 
With regards to (2), we would run the risk of having a hole in the specification (solutions that are both perceived to be compliant but are not interoperable) since error floors below 1E-12 would be undetected and extrapolation would provide misleading results.

In summary, I do not debate that some applications would like to see BER exceed 1E-12 (and in some cases, exceed 1E-15).  With regards to your proposed objective, I think it would be useful to get a better understanding of how a Backplane Ethernet standard could be judged to have met such an objective or not.
 
I think members of the OIF community who also participate in the SG could share some insight here.  I welcome them to do so.
 

Thank you,
-Adam
 
-----Original Message-----
From: Jeff Warren [mailto:IEEE@nc.rr.com]
Sent: Wednesday, January 28, 2004 11:43 AM
To: stds-802-3-blade@ieee.org
Subject: [bp] BER Objective for BPE

Adam,
 
During the recent IEEE Backplane Ethernet (BPE) study group (SG) interim meeting in Vancouver, BC. Canada a BER objective of 10EE-12 was voted into the initial set of BPE objectives by a vote of 32-yes / 3-no / 1-abstain.
 
I was one of the three negative votes. My reason was simple; because these future 10G backplane links in a modular chassis are critical network links and the environment (inside the box) is much more noisy than external links.
 
I felt the same approach as the OIF CEI implementers agreement makes sense; they require a BER of 10EE-15 per lane with the test requirement of 10EE-12.
 
I suspect that system vendors will have the same concern with this 10EE-12 BER objective for backplane applications and voice their concerns when this objective reaches the 802.3 WG so it might be better to fix this objective now rather than later.
 
I would propose a new BER objective, here's some suggested text:
 
"Support a BER of 10EE-15 or better with the test requirement set at 10EE-12".
 
Cheers,
 
   - Jeff Warren