AW: [bp] BER Objective for BPE
Adam, Jeff,
a good thread to start.
I think option.2 seems to be the best way to go i.e. calculating the system
requirements for a 1e-15 ber, and through over-stressed jitter tolerance
measurements at 1e-12, and bathtub extrapolation gaurentee 1e-15.
For the calibration of the over-stressed ejitter tolerance I believe that
the StatEye Channel measurement methodology can accurately predict the
overstressing requirements. And for output transmitters the extrapolation of
the output jitter is also accurate.
Where I believe problems may occur is in the final system itself. This is
agreeing with your issue of noise floors. I believe the link in presence of
the complete system e.g. power supply glitches, could be limited in terms of
BER. Not sure how to deal with this yet.
Cheers,
Anthony
-----Ursprüngliche Nachricht-----
Von: owner-stds-802-3-blade@majordomo.ieee.org
[mailto:owner-stds-802-3-blade@majordomo.ieee.org] Im Auftrag von Jeff
Warren
Gesendet: Donnerstag, 29. Januar 2004 01:15
An: Healey, Adam B (Adam); stds-802-3-blade@ieee.org
Betreff: Re: [bp] BER Objective for BPE
Adam,
Correct I did intend for this to be a general discussion topic, especially
the 'experts' from OIF and UXPi because both of these 10G technical
specifications require a 10EE-15 BER. The 1st approach you've described
which includes all elements of the BPE standard (transmitter, channel,
receiver) with a systems compliance test at 10EE-12 combined with additional
margin to guarantee 10EE-15 seems like a reasonable way to go.
Hopefully subsequent BPE reflector traffic will include input(s) from the
OIF and UXPi experts that established their respective 10EE-15 BER
requirements for 10G backplane applications.
- Jeff
----- Original Message -----
From: Healey, Adam B (Adam)
To: Jeff Warren ; stds-802-3-blade@ieee.org
Sent: Wednesday, January 28, 2004 6:27 PM
Subject: 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