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*To*: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx*Subject*: Re: [802.3BA] 802.3ba XR ad hoc next step concern*From*: Scott Kipp <skipp@xxxxxxxxxxx>*Date*: Fri, 22 Aug 2008 09:07:57 -0600*Delivered-to*: mhonarc@xxxxxxxxxxxxxxxx*In-reply-to*: A<4.2.0.58.20080822070205.00dd64d0@xxxxxxxxxxxxxxxxxxxxxx>*List-help*: <http://listserv.ieee.org/cgi-bin/wa?LIST=STDS-802-3-HSSG>, <mailto:LISTSERV@LISTSERV.IEEE.ORG?body=INFO%20STDS-802-3-HSSG>*List-owner*: <mailto:STDS-802-3-HSSG-request@LISTSERV.IEEE.ORG>*List-subscribe*: <mailto:STDS-802-3-HSSG-subscribe-request@LISTSERV.IEEE.ORG>*List-unsubscribe*: <mailto:STDS-802-3-HSSG-unsubscribe-request@LISTSERV.IEEE.ORG>*References*: <9C4A066E2B2E714BA6A0AA7FE46B32AA015B392B@xxxxxxxxxxxxxxxxxxxxxxx> <9C4A066E2B2E714BA6A0AA7FE46B32AA015B392B@xxxxxxxxxxxxxxxxxxxxxxx> A<4.2.0.58.20080822070205.00dd64d0@xxxxxxxxxxxxxxxxxxxxxx>*Reply-to*: Scott Kipp <skipp@xxxxxxxxxxx>*Thread-index*: AckEYjq3qmB/or58TaGkEiWKfbhXpgAASqdQ*Thread-topic*: [802.3BA] 802.3ba XR ad hoc next step concern

All,

I disagree with some premises that have been put
forward and feel that we need to proceed on the present course to defining how
to extend the reach beyond 100 meters. The time to throw in the towel has
not come.

Let's run through a little scenario. Joe the
installer needs to go 130 meters and begins plugging in the ends of the fiber to
different modules and a combination finally works and the link comes up.
The link works fine for a few months or even years and then the module
degrades a little (but is still within the 100 meter specification) and the
link begins to have bit errors. Joe the installer is long gone (or
should hide after the link fails) and nobody knows what
happened. Both modules still pass any tests based on the
standard, but the link is failing and no one is responsible.

The reason we have standards (like Geoff says) is
because we want reliable links to work all of the time over the lifetime of the
parts. When a link fails, we can determine the cause and have
responsibility. I agree that the links are defined conservatively and
will work longer most of the time, but I disagree with John's premise
that there is no value in the XR solution that goes significantly farther.
Responsible installers will rely on standards based parts to go the rated
distance. We have several ways we can make OM3 links work for
longer than 100 meters.

Do we have the difficult task of choosing only one way
to extend the link or can we talk about several ways to do this in an
informative annex? The hard part is choosing one solution because we have
so many camps with different solutions. The usual problem is that we have
no clear winner - no Usain Bolt - in the XR race beyond 100
meters.

TGIF,

Scott

In answer to your question

What I believe that John has argued for (and not unreasonably) is the following.

We provide assured operation at 100 meters

If you want to go to 150 meters, the odds are very strong that you can succeed as long as you are will to lower your expectations from plug and chug to trying your way through a half dozen parts at each end in order to get a set that works.

His thesis, as I understand it, is:

1) It is not worth the extra investment (time and money both) to get a different standard with the extra reach.

2) Even if we do #1, the market won't pay anything for it. They will just go through the select and try route in order to save the extra money and separate inventory hassle.

Given the odds that it will work over 90% of the time, I would agree.

Am I willing to reduce our customers' overall chance of success to 92%?

No !!

Sincerely,

Geoff Thompson

At 08:55 AM 8/21/2008 , Swanson, Steven E wrote:

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]Sent:Wednesday, August 20, 2008 11:23 PMTo:STDS-802-3-HSSG@xxxxxxxxxxxxxxxxxSubject:[802.3BA] 802.3ba XR ad hoc next step concern

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 Monte Carlo, MC, analyses were run. The first MC evaluates just a Tx distribution against an aggregate Tx metric. This is to estimate the percentage removed by the aggregate Tx test. The second MC evaluates the same Tx distribution in combination with an Rx distribution and 150 m of worst case OM3. The third MC repeats the second but replaces the 150 m of OM3 with 250 m of worst case OM4. Worst case fiber plant characteristics were used in all link simulations.

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.

**Follow-Ups**:**Re: [802.3BA] 802.3ba XR ad hoc next step concern***From:*Brad Booth

**References**:**[802.3BA] 802.3ba XR ad hoc next step concern***From:*PETRILLA,JOHN

**Re: [802.3BA] 802.3ba XR ad hoc next step concern***From:*Geoff Thompson

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