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When looking at the impact of the specified link BER on test requirements, the receiver sensitivity measurement is only one aspect that must be considered.
Rx measurement – for a well behaved receiver being driven by a “golden” transmitter followed by an optical attenuator, the BER curves are normally very predictable and extrapolation from measurements in the region of 1E-10 to 1E-12 will generally not generate any surprises if the spec is conservative (e.g. 1 dB margin where a penalty of about 0.5 dB is expected). Of course, the slope of BER vs power is different for APD receivers and any system involving amplifiers so care is required with this. Also, if the bit rate in question was not well established this approach might be dangerous. (I would not propose to do this with current technology if the transmission were 100 Gbit/s serial).
A problem with defining a link with a specified BER of 1E-15 is that for the link power budget, any penalties must be specified at that BER too or the budget won’t add up properly. This means that the transmitter dispersion penalty would need to be specified at 1E-15. Now, compared to extrapolation of receiver BER in a back-to-back configuration, extrapolation of dispersion penalties at 1E-15 from measurements made in the region of 1E-12 is very likely to generate surprises. In an extreme case a modest penalty at 1E-12 can turn in to a very large penalty at 1E-15.
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_____________________________________________
From: Chris Cole [mailto:chris.cole@xxxxxxxxxxx]
Sent: 29 August 2006 06:15
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective
Marcus,
You are right that the concern was about other sources. The process Ft used for most first generation 40G ICs is 110GHz, so design of decision and timing circuits did not have a lot of margin. It was important to verify that there were no low level error events.
Chris
________________________________
From: Marcus Duelk [mailto:duelk@xxxxxxxxxx]
Sent: Mon 8/28/2006 9:38 PM
To: Chris Cole
Cc: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective
Couldn't you just do a quick Q measurement which gives an estimate for the 0/1 amplitude levels and the noise variances from which you derive the minimum BER ? This is a common technique in optical transmission experiments. Such a measurement will take only a few seconds and you will extrapolate your data down to very low BER values (this method assumes that there are no other flaws or background errors from other sources, but it would give a quick estimate ...)
marcus
Chris Cole wrote:
> 40G VSR Transceivers have receiver sensitivity specified at BER=1e-12. This is defined in the ITU application code G.693. 40G Transceivers are also production tested at BER=1e-12.
>
> System OEM customers have been satisifed with data from the design verification phase that demonstrate there are no error floors down to BER=1e-15. That takes two days per point, with a high confidence level. To verify a unit over five supply/temperature corners takes a week and half . Multiple test stations can be set up to test units in parallel.
>
> At 100G, the test time will be reduced by a factor of 3, so a requirement for error free operation down to BER=1e-15 is reasonable for design verification, and BER=1e-12 is reasonable for production.
>
> Chris Cole
> Finisar
>
> ________________________________
>
> From: Petar Pepeljugoski [mailto:petarp@xxxxxxxxxx]
> Sent: Mon 8/28/2006 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.
>
> Regards,
>
> 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>
>
>
> To
> STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
> cc
> Subject
> 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]
> Sent: Monday, August 28, 2006 1:54 PM
> To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
> Subject: Re: [HSSG] BER Objective
>
> David,
>
> 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).
>
> -Roger
>
>
>
>
>
> ________________________________
>
>
> From: Martin, David (CAR:Q840)
> Sent: Friday, August 25, 2006 12:22 PM
> To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
> Subject: 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.
>
> ...Dave
>
> David W. Martin
> Nortel Networks
> dwmartin@xxxxxxxxxx <mailto:dwmartin@xxxxxxxxxx>
> +1 613 765 2901 (esn 395)
> ~~~~~~~~~~~~~~~~~~~~
>
>
--
___________________________
Marcus Duelk
Bell Labs / Lucent Technologies
Data Optical Networks Research
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