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Re: [HSSG] BER Objective


just a quick comment on the measurement method that Howard
was referring to. The idea is somewhat similar to the Q measurement
that I was talking about. In both cases, you reduce the optical power
at the optical frontend and measure the BER at higher values. Howard
mentioned BER values of 1E-10. In the Q-factor measurement approach you
typically measure a power range in which the BER changes say from
BER 1E-3 to 1E-9 or 1E-10, and then you extrapolate that curve. You
do this both for errors dominated by ONEs (marks) and by ZEROs (spaces).
The intersection of both curves gives theoretically the minimum BER.

The problem is that you are extrapolating with either method. You measure
at BER 1E-10 or higher and you draw some conclusions that the BER
should be about 1E-15 but you never know because there could be an error
floor at 1E-14 due to some other sources.

The method that Howard mentioned or that Q-factor method is
somewhat a "quick and dirty" test. It is not really usable to fully
determine what the true BER is. There is a paper about that
from Agilent:


Mike Bennett wrote:

Thank you for making a key point regarding packet loss and it's impact on getting work done.  A fair amount of the CFI material referenced high throughput flow data.  Jugnu illustrates one case in which packet loss doesn't have much of a noticeable affect - high transaction rate, low throughput flows such as web hosting services, etc.  On the other hand, sites that transport fewer high-throughput flows will suffer greatly from an error per second.  The following link illustrates the impact of packet loss on TCP sessions (and what some folks are attempting to do about it):  There are many more examples and a multitude of research regarding TCP performance degradation due to packet loss.

I've not see a response to Howard's suggestion of using a method similar to that of the one found in EFM.  Can someone tell me what's wrong with that idea?



Roger Merel wrote:



Indeed some applications will not truly be adversely affected with a poorer BER even if the errors occurred once per second or more on such a high speed link (although no one really likes looking at a the error racking up that fast.  While this requires a packet resend, this does not in these applications significantly degrade working throughput.


However there are applications where such an error rate does have a serious impact (and these represent some of Ethernet’s important early adopters).  When the data is being used in a computational pipeline, such a resend stalls the pipeline and wastes all of the time until the resent data arrives.  In a multi-processor world which seeks to have all N processors cache sync’ed, this can effectively stall the entire system and since the system may be composed of up to N^2 links, the effect of BER can be very significant… 1 error per second per link could mean that no productive work is occurring.




From: OJHA,JUGNU [mailto:jugnu.ojha@xxxxxxxxxxxxx]
Sent: Tuesday, August 29, 2006 10:48 AM
To: Roger Merel; STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: RE: [HSSG] BER Objective




I understand that test time is the issue.  The point I’m getting at (and which I’ve always wondered about) is, if the errors are so few and far between that it takes so long to find them, how much impact can they really be having on the system/network performance?  I.e., are we being too demanding with the BER requirements.  




From: Roger Merel [mailto:roger@xxxxxxxxxxx]
Sent: Tuesday, August 29, 2006 10:44 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective


It’s not hard to measure, just time consuming.  If one wants to keep optics affordable, one need manufacturing test to be <minutes, not >10 minutes.


Although my position is that 1E-15 BER is not required; but only 1E-13 at most.


From: OJHA,JUGNU [mailto:jugnu.ojha@xxxxxxxxxxxxx]
Sent: Tuesday, August 29, 2006 10:37 AM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective


All of this raises the following question:  If this is so hard to measure, how much impact can it really have in the real world?  Why not back the BER requirement off to 10e-10? 





From: Petar Pepeljugoski [mailto:petarp@xxxxxxxxxx]
Sent: Monday, August 28, 2006 8:03 PM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective


I agree with Howard. It is impractical and expensive to test for very low BERs - the specs should be such that the power budget is capable of achieving BER =1e-15, yet the testing can be some kind of accelerated BER at lower value that is derived from the curve interpolation.

However, the as with any extrapolation of testing results one has to be careful, so in this case it will be manufacturers' responsibility to guarantee the BER=1e-15.  


Petar Pepeljugoski
IBM Research
P.O.Box 218 (mail)
1101 Kitchawan Road, Rte. 134 (shipping)
Yorktown Heights, NY 10598

e-mail: petarp@xxxxxxxxxx
phone: (914)-945-3761
fax:        (914)-945-4134

Howard Frazier <hfrazier@xxxxxxxxxxxx>

08/28/2006 05:39 PM

Please respond to
Howard Frazier <hfrazier@xxxxxxxxxxxx>






Re: [HSSG] BER Objective




For the 100 Mbps EFM fiber optic links (100BASE-LX10 and 100BASE-BX10)
we specified a BER requirement of 1E-12, consistent with the BER requirement
for gigabit links. We recognized that this would be impractical to test in a
production environment, so we defined a means to extrapolate a BER of 1E-12
by testing to a BER of 1E-10 with an additional 1 dB of attenuation.  See
58.3.2 and 58.4.2.
Howard Frazier
Broadcom Corporation

From: Roger Merel [mailto:roger@xxxxxxxxxxx]
Monday, August 28, 2006 1:54 PM
Re: [HSSG] BER Objective

Prior to 10G, the BER standard (for optical communications) was set at 1E-10 (155M-2.5G).  At 10G, the BER standard was revised to 1E-12.  For unamplified links, the difference between 1E-12 and 1E-15 is only a difference of 1dB in power delivered to the PD.  However, the larger issue is one of margin and testability (as the duration required to reliably verify 1E-15 for 10G is impractical as a factory test on every unit) especially since we’d want to spec worst case product distribution at worst case path loss (cable+connector loss) and at EOL with margin.  Thus in reality, all products ship at BOL from the factory with a BER of 1E-15 and in fact nearly all will continue to deliver 1E-15 for their entire life under their actual operating conditions and with their actual cable losses.
Thus, if by “design target”, you mean a worst case-worst case with margin to be assured at EOL on every factory unit, then this is overkill.  I might be willing to entertain a 1E-13 BER as this would imply that same number of errors per second (on an absolute basis; irrespective of the number of bits being passed; this takes the same time in the factory as verifying 1E-12 at 10G although this is in fact a real cost burden which adversely product economics); however, this would not substantially change the reality of the link budget.  It would make for a sensible policy for the continued future of bit error rate specs (should their be future “Still-Higher-Speed” SG’s).


From: Martin, David (CAR:Q840)
Friday, August 25, 2006 12:22 PM
BER Objective

During the discussion on Reach Objectives there didn’t appear to be any mention of corresponding BER.
Recall the comments from the floor during the July meeting CFI, regarding how 10GigE has been used more as infrastructure rather than as typical end user NICs. And that the application expectation for 100GigE would be similar.
Based on that view, I’d suggest a BER design target of (at least) 1E-15. That has been the defacto expectation from most carriers since the introduction of OC-192 systems.
The need for strong FEC (e.g., G.709 RS), lighter FEC (e.g., BCH-3), or none at all would then depend on various factors, like the optical technology chosen for each of the target link lengths.


David W. Martin
Nortel Networks

+1 613 765 2901 (esn 395)


Michael J. Bennett
Sr. Network Engineer
LBLnet Services Group
Lawrence Berkeley Laboratory
Tel. 510.486.7913

Marcus Duelk
Bell Labs / Lucent Technologies
Data Optical Networks Research

Crawford Hill HOH R-237
791 Holmdel-Keyport Road
Holmdel, NJ 07733, USA
fon +1 (732) 888-7086
fax +1 (732) 888-7074