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*To*: STDS-802-3-10GMMF@xxxxxxxxxxxxxxxxx*Subject*: Re: [10GMMF] Corrected Monte Carlo Model as LRM standard model fo r OM1*From*: "Lingle, Jr, Robert (Robert)" <rlingle@xxxxxxxxxxxxx>*Date*: Sun, 10 Jul 2005 18:06:56 -0400*Reply-To*: "IEEE P802.3aq 10GBASE-LRM"<stds-802-3-10gmmf@xxxxxxxx>*Sender*: owner-stds-802-3-10gmmf@xxxxxxxx

Jonathon, Thanks for your thoughtful comments. My responses corresponds to your numbering: 1. John Abbott and I believe that a Monte Carlo model should be used validate any spreadsheet approach to 10GbE, not vice versa. The spreadsheet models assume that "bandwidth" means a Gaussian pulse, and the ISI statistics are calculated based on that. This is overly simplistic for 10Gb transmission; the standard for 10 GbE work was set by 802.3ae where the Monte Carlo delay set approach was applied. The Monte Carlo set has non-Gaussian pulses and a log normal distribution to the BW. 2. The OFL-BW measurement scheme used for grading MM fiber has long been based on gamma-scaling from 6-8km to 300m fibers. 3. I agree that effect of mode-mixing on single mode launch is complicated, and I have pages of notes detailing different cases. That is why John Abbott and I got away from trying to sort out that complex problem in favor of focusing on a problem we know how to treat quantitatively: the impact of mode-mixing on OFL-BW data that was used to construct the MC delay set, using a universally accepted expression and following extensive precendent within the industry for length-scaling of OFL values. (Unfortunately a careful experimental study of DMD variation with length would be very expensive in both fiber and time, given the complication of axial variation.) 4. The manufacturing margin is consumed by the need to account for 1) gamma-scaling when cutting from 8km to 300m length as well as 2) sensitivity of MM fiber to axial variation. Fibers cut to 300m can be expected to have OFL-BW all the way down to 500MHz-km. Regardless, a 50MHz-km shift in minimum OFL-BW (a large value) would only change a given PIE-D %tile by 0.05dB. Robert Robert Lingle, Jr, Manager Fiber Design and Transmission Simulation OFS R&D, Atlanta, GA -----Original Message----- From: Jonathan King [mailto:jking@BIGBEARNETWORKS.COM] Sent: Thursday, July 07, 2005 4:13 PM To: STDS-802-3-10GMMF@listserv.ieee.org Subject: Re: [10GMMF] Corrected Monte Carlo Model as LRM standard model for OM1 Hi Robert thanks for your e-mail, and the summary of the sensitivity analysis to OFL Bw cutoff I personally still have a few objections to the revision of GEN67YY you are proposing. I have two main objections and a couple of perhaps less significant ones, in order of significance: 1) Its not been 'baselined' against other applications: GEN67YY has been shown to be largely consistent with preceding applications which have been successfully proven in the field (Ewen_1_1104.pdf). I could not support transitioning to a model which has not undergone similar scrutiny. 2) Gamma factor scaling from 6-8km fibre length measurements has not been validated with short fibre (300m) measurements. I've raised this issues a few times, but to date it has not been addressed; I apologize for repeating myself. the ones I'm less sure of are 3) I am not convinced that gamma correction is as straight forward for OSL launches as with OFL: My thinking is this: there are three mode mixing regimes - zero mode coupling, which corresponds best to the <300m LRM application, weak mode coupling (where significant power couples into initially unexcited modes) which corresponds to several km or so of fibre , and strong mode mixing (significant power couples back and forth between modes); a fibre would be expected to transition from zero mode mixing at short fibre lengths, through weak mode mixing at intermediate lengths, to strong mode mixing at long lengths. Normalized OFL bandwidth would be expected to increase monatonically with fibre length, because all modes are excited and any degree of mode mixing would tend to average out propagation delay differences between modes. However, for launches exciting just a few modes (eg OSL), weak mode mixing couples power into initially unexcited modes, resulting in an increase in measured propagation delay spread, and a decrease in normalized bandwidth with length - the opposite of effect on OFL. (One symptom of weak mode mixing would be an emerging correlation between measured bandwidths or PIE-D for OSL launches with different offset values - I believe this was visible in the OFS 1998 fibre set Lingle_1_0305.pdf) So I think that whereas the correction for mode mixing effects for OFL may be relatively straightforward (albeit requiring an educated guess which requires validation with measurements), the necessary length correction for mode mixing effects on an OSL would be difficult to predict, and may require the opposite of that required for OFL. 4) The effect of OFL bandwidth manufacturing margin should probably be included in any model revision - the installed base model in GEN67YY is sharply truncated to 500MHz.km. In practice, there would be very few fibres actually at 500MHz.km, because standard manufacturing margining practices would dictate a test criteria at a higher level than the spec limit to guarantee compliance of any individual measured fibre. The effect on the ensemble of fibres is a shift to a higher cutoff OFL Bw. This effect would be similar in magnitude to the sensitivity analysis of the lower OFL Bw cutoff, which you summarize below, and like the wavelength issue would probably result in a 0.1-0.2dB correction in PIE-D values, depending on the details. best wishes Jonathan tel: 1 408 524 5110 e-mail: jking@bigbearnetworks.com fax: 1 408 739 0568 Jonathan King Director, Optical Systems BigBear Networks 345 Potrero Avenue Sunnyvale, CA 94085 -----Original Message----- From: owner-stds-802-3-10gmmf@ieee.org [mailto:owner-stds-802-3-10gmmf@ieee.org] On Behalf Of Lingle, Jr, Robert (Robert) Sent: Saturday, July 02, 2005 2:33 PM To: STDS-802-3-10GMMF@listserv.ieee.org Subject: [10GMMF] Corrected Monte Carlo Model as LRM standard model for OM1 All, At the London meeting, several of us made a presentation on the Monte Carlo set corrected for mode mixing (the gamma correction). I showed duplex coverage PIE-D results for the recommended correction of gamma = 0.9, and recommended that this model be used henceforth for LRM coverage calculations. See http://grouper.ieee.org/groups/802/3/aq/public/upload/Implicationsofdupl exco veragewithcorrectedMonteCarlomodelforTP3stressors.pdf At the meeting Jon Abbott and I received useful feedback from Jon King that sensitivity analysis of the choice of lowest OFL-BW value admitted into coverage calculations was needed to assess the robustness of the fiber model. Fiber modeling for LRM typically uses 500MHz-km as the lower cutoff for OM1 fiber in all calculations to date. Kasyapa Balemarthy (GaTech) has done this analysis, and it increases the credibility of using the Monte Carlo model to assess OM1 coverage for LRM. Kasyapa varied the LOWER limit of OFL-BW fibers retained in the MC model and found that the 99%tile duplex PIE-D point changes linearly by 0.05dB for each 50MHz-km change between 400 and 600 MHz-km. This relative insensitivity arises from the fact that a wide range of both low and high PIE-D fibers exist in a selected range of OFL-BW, and the distribution of PIE-D values within a range of OFL values varies smoothly as OFL rises from 400 to 600MHz-km. This is very good news and means that the MC model is robust to the choice of this parameter, i.e. coverage results obtained are rather insensitive to picking 500 MHz-km vs. 475 or 525 MHz-km. I would like to assess whether there are any remaining technical objections to using the Monte Carlo model at 1355nm with a gamma=0.90 correction as the standard model for LRM coverage calculation. Robert Robert Lingle, Jr, Manager Fiber Design and Transmission Simulation OFS R&D, Atlanta, GA

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