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RE: [EFM-OAM] RE: [EFM] Re: Loopback and BERT

I don't know Roy, if I were a network operator I'd have a tendency to want
to leave a mysterious "error-correcting endpoint" in place if it made it
through that deliberate error-injection test ;o).  Seems like a functional
test of the silicon more than anything, i.e. not a system-level test.

Bob: In your whitepaper regarding bit error rate test, have you calculated
how long such a test would take for BER <= 10^-12? If you wanted 95%
confidence the measured error rate was within 10% of the true error rate,
back of the napkin (and only on a P2P link where entire BW is dedicated to
BERT, and ignoring header overhead)would be over 100 hours. If you're
talking about a crude test just to see that it's better than say 10^-7,
that's a different story. I think you were talking about characterizing the
link at install time though. Just wondering what shortcuts are taken when
they run such a test, and what other hooks we might need to provide since
100+ hours isn't going to cut it. There are ways to accelerate it by adding
calibrated stress (e.g. precision attenuator), but that definitely can't be
a required addition for EFM products. 

Also was wondering how you'd distinguish between a downstream problem versus
one on the upstream if loopback is used? Do you insert a downstream bit
error count in a header before you loop a corrected test pattern back



One function that was always part of BERT testing when I was working in 
field operations was the deliberate introduction of errors in the encoded 
data stream to be sure that the customer premise equipment was properly 
able to detect errors.  This is part of the originating conformance 
testing, and part of the conformance testing that was done after a 
repair.  I do not think that your "loop back plug" would qualify for that 
level of conformance BERT testing.

Thank you,
Roy Bynum

At 08:55 PM 2/24/2002 +0000, Bob Barrett wrote:

>Dear all
>Rather than put up a presentation on this at the March meeting I have
>written a white paper expressing what I think are the key issues (and the
>key reasons and benefits) of including loopback and BERT functions in the
>EFM subscriber access standard. It can be found at:
>or from a link at
>I have written this as an individual, and not included references to my
>company or products, and I have put it on my personal web site. Inevitably
>do mirror my views into the technolgy that my company produces, as do most
>of we equipment vendors.
>By putting this paper up for discussion now I hope to reach the broad
>audience of all EFM streams and stimulate debate in advance of the March
>meeting, to help us to reach consensus.
>Bob Barrett