Roger,
Thanks for summarizing
this for me. I got from Petar’s message that it would impact
computing clusters. I guess we have to define things for the most
stringent case.
Thanks,
Jugnu
From: Roger Merel
[mailto:roger@xxxxxxxxxxx]
Sent: Tuesday, August 29, 2006
11:03 AM
To:
STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [HSSG] BER Objective
Jugnu,
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.
-Roger
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
Roger,
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.
Jugnu
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?
Regards,
Jugnu
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.
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>
|
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|
To
|
STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
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cc
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Subject
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Re: [HSSG] BER Objective
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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
+1 613 765 2901 (esn 395)
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