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Hello Steve I’m sorry if I wasn’t able to make my points clear.
Thanks for the second chance. There is no acceptable business case for a 40GBASE-SR4 XR product due
to the expected small size of the market. While the market size for a 100GBASE-SR10 XR product appears larger,
there is still no acceptable business case for a product due to the expected
availability of alternative solutions. Since there will be alternate solutions, modules with a XLAUI/CLAUI
interface, overlap from baseline PPI interface modules, point-to-point
connections, etc., we should take advantage of the situation and enable their
use in a more formal manner than word of mouth. Thanks again for the opportunity to clarify my points. Regards, John From: Swanson, Steven
E [mailto:SwansonSE@xxxxxxxxxxx] John, Thanks for all your work on this; I have
to study it more and would like to see the actual presentation but I would
offer the following comment: If the following statement is true, why do
we have an objective of 100m rather than 150m? "Do nothing to the standard and when
150 m of OM3 or 250 m of OM4 is desired – just plug in the fiber. The odds are overwhelming that it
will work." Thanks, Steve From:
PETRILLA,JOHN [mailto:john.petrilla@xxxxxxxxxxxxx] Colleagues I’m concerned that the proposal of creating a
new objective is leading us into a train wreck. This is due to my belief
that it’s very unlikely that 75% of the project members will find this
acceptable. This will be very frustrating for various reasons, one of
which, almost all the modules expected to be developed will easily support the
desired extended link reaches, will be discussed below. I don’t want to wait until our next phone
conference to share this in the hope that we can make use of that time to
prepare a proposal for the September interim. I’ll try to capture
my thoughts in text in order to save some time and avoid distributing a presentation
file to such a large distribution. I may have a presentation by the phone
conference. Optical modules are expected to either have a
XLAUI/CLAUI interface or a PMD service interface, PPI. Both are
considered. A previous presentation, petrilla_xr_02_0708, http://ieee802.org/3/ba/public/AdHoc/MMF-Reach/petrilla_xr_02_0708.pdf
has shown that modules with XLAUI/CLAUI interfaces will support 150 m of OM3
and 250 m of OM4. These modules will be selected by equipment
implementers primarily because of the commonality of their form factor with
other variants, especially LR, and/or because of the flexibility the
XLAUI/CLAUI interface offers the PCB designer. Here the extended fiber
reach comes for no additional cost or effort. This is also true in PPI
modules where FEC is available in the host. Everyone is welcome to express their forecast of the
timing and adoption of XLAUI/CLAUI MMF modules vs baseline MMF modules. To evaluate the base line proposal for its extended
reach capability, a set of The Tx distribution characteristics follow.
All distributions are Gaussian. Min OMA, mean = -2.50 dBm, std dev = 0.50 dBm
(Baseline value = -3.0 dBm) Tx tr tf, mean = 33.0 ps, std dev = 2.0 ps
(Example value = 35 ps) RIN(oma), mean = -132.0 dB/Hz, std dev = 2.0
dB (Baseline value = -128 to -132 dB/Hz, Example value = -130 dB/Hz) Tx Contributed DJ, mean = 11.0 ps, std dev =
2.0 ps (Example value = 13.0 ps) Spectral Width, mean = 0.45 nm, std dev =
0.05 nm (Baseline value = 0.65 nm). Baseline values are from Pepeljugoski_01_0508
and where no baseline value is available Example values from petrilla_02_0508
are used. All of the above, except spectral width, can be
included in an aggregate Tx test permitting less restrictive individual
parameter distributions than if each parameter is tested individually. In
this example distributions are chosen such that only the mean and one std dev
of the distribution satisfy the target value in the link budget spreadsheet.
If the individual parameter is tested directly to this value the yield loss
would be approximately 16%. The Rx distribution characteristics follow.
Again, all distributions are Gaussian. Unstressed sensitivity, mean = -12.0 dBm, std
dev = 0.75 dB (Baseline value = -11.3 dBm) Rx Contributed DJ, mean = 11.0 ps, std dev =
2.0 ps (Baseline value = 13.0 ps) Rx bandwidth, mean = 10000 MHz, std dev = 850
MHz (Baseline value = 7500 MHz). For the Tx MC, only 2% of the combinations would
fail the aggregate Tx test. For the 150 m OM3 MC, only 2% of the combinations
would have negative link margin and fail to support the 150 m reach. This
is less than the percentage of modules that would have been rejected by the Tx
aggregate test and a stressed Rx sensitivity test and very few would actually
be seen in the field. For the 250 m OM4 MC, only 8% of the combinations
would have negative link margin. Here approximately half of these would
be due to transmitters and receivers that should have been caught at their
respective tests. The above analysis is for a single lane. In
the case of multiple lane modules, the module yield loss will increase
depending on how tightly the lanes are correlated. Where module yield
loss is high, module vendors will adjust the individual parameter distributions
such that more than one std dev separates the mean from the spread sheet target
value. This will reduce the proportion of modules failing the extended
link criteria. Also, any correlation between lanes results in a module
distribution of units that are shipped having fewer marginal lanes than where
the lanes are independent. So while there’s a finite probability that a
PPI interface module doesn’t support the desired extended reaches, the
odds are overwhelming that it does. Then with all of one form factor and more than 92%
of the other form factor supporting the desired extended reach, the question
becomes, ‘what’s a rational and acceptable means to take advantage
of what is already available?’ A new objective would enable this
but, as stated above getting a new objective for this is at best
questionable. Further, it’s expected that one would test to see
that modules meet the criteria for the new objective, set up part numbers,
create inventory, etc. and that adds cost. Finally, users, installers,
etc. are intelligent and will soon find this out and will no longer accept any
cost premium for modules that were developed to support extended reach - they
will just use a standard module. There’s little incentive to invest
in an extended reach module development. I’ll make a modest proposal: Do nothing
– just hook up the link. Do nothing to the standard and when 150 m
of OM3 or 250 m of OM4 is desired – just plug in the fiber. The
odds are overwhelming that it will work. If something is really needed in
the standard, then generate a white paper and/or an informative annex
describing the statistical solution. Background/Additional thoughts: Even with all the survey results provided to this
project, it’s not easy to grasp what to expect for a distribution of
optical fiber lengths within a data center and what is gained by extending the
reach of the MMF baseline beyond 100 m. Here’s another attempt. In flatman_01_0108, page 11, there’s a
projection for 2012. There for 40G, the expected adoption percentage of
links in Client-to-Access (C-A) applications of 40G is 30%, for
Access-to-Distribution (A-D) links, it is 30%, and for Distribution-to-Core
(D-C)links it is 20%. While Flatman does not explicitly provide a
relative breakout of link quantities between the segments, C-A, A-D & D-C,
perhaps one can use his sample sizes as an estimate. This yields for C-A
250000, for A-D 16000 and for D-C 3000. Combining with the above adoption
percentages yields an expected link ratio of C-A:A-D:D-C = 750:48:6. Perhaps Alan Flatman can comment on how outrageous
this appears. This has D-C, responsible for 1% of all 40G links,
looking like a niche. Arguments over covering the last 10% or 20% or 50%
of D-C reaches does not seem like time well spent. Even A-D combined with
D-C, AD+DC, provides only 7% of the total. Similarly for 100G: the 2012 projected
percentage adoption for C-A:A-D:D-C is 10:40:60 and link ratio is
250:64:18. Here D-C is responsible for 5% of the links and combined with
A-D generates 25% of the links. Now the last 20% of AD+DC represents 5%
of the market. Since the computer architecture trend leads to the
expectation of shorter link lengths and there are multiple other solutions that
can support longer lengths, activating FEC, active cross-connects, telecom
centric users prefer SM anyway, point-to-point connections, etc., there is no
apparent valid business case supporting resource allocation for development of
an extended reach solution. |