Re: Open Request to Del Hanson and David Cunningham: Link Model for10 Gig Et...
The "Gigabit Ethernet Model" served very well for many members who do not
deal Fiber Optic Communication issues daily. The benefit and contribution
of the Model to committee were well appreciated by all members, which
provided instant, quantitative answers to various, complex input parameters
without being an expertise in this field. Truly, it was a SUPER
The Model is a Cook Book of the GbE optical communication issues. In the
process of accomplishing a Cook Book, many assumptions have to be made to
represent most likely occurrences, but not every possible occurrences. As a
result, in the event of a different occurrence from the original assumption,
the Cook Book will provide an approximate result, but not an accurate result.
In most cases, the approximated answer is good enough; however, it is also
possible that the approximated answer may do disservice to users.
The ISI issue in the GbE is a typical case of the Cook-Book failure.
The ISI power penalty in the IEEE 802.3z specification is 2.6 dB which is
over 40% of the useful power 5.83 dB in 1000BASE-SX specification using 62.5
um fiber. The ISI calculated based on the Gimlet's ISI power penalty
equation and the system BW equation (BER of 10^12), is around 0.5 dB, but
not 2.6 dB. Experimentally, it is impossible to have an ISI penalty of 2.6
dB measured from any 230 meter of 62.5 um fiber using a transmitter with
negligible ISI. The actually measured ISI penalty was, again, near 0.5 dB,
but not 2.6 dB. The impact of the error is very significant: over 40% of the
useful power were wasted, and there is no power budget left for distance
extension. - poor cost-effectiveness.
When this 40% of ISI wasted power issue was brought up, we were unable to
determine where the errors came from. The Model, a Cook Book, did not
provide the analysis and derivation process to demonstrate how the model was
made. A big disadvantage. Even many of the experts in the Fiber Optic
communication field could not determine what is the problem due to the
lacking of the traceably of a model.
The GbE model was established in a very short time period without sufficient
I believe it is necessary for a model, or a cook-book, to not only provide
the spread-sheet, but also the brief analyses which created the "Model"
spread sheet for optimization.
Besides ISI issue, there are many other issues:
1. Fiber bandwidth.
Using the BW of 160 MHz-km for a 62.5 um fiber in the Model is wrong. A
fiber itself does not have a BW in the first place.
2. The K factor, which caused lots of headache for us, without knowing how
the K factor was established in the Model.
3. A random jitter of a fiber, true?
In addition to the spread sheet, provide the mathematical equations, and
reasoning in the Appendix.
NetWorth Technologies, Inc
I would like to request, in behalf of the HSSG, a presentation at the York
meeting regarding the applicability of the "Gigabit Ethernet Model (i.e.,
Hanson; Cunningham spreadsheet)" for use in our work on "ten Gig."
This model was extremely helpful to us in 1000BASE-X in discussing
Variations to the specifications and resolving issues. I expect, as with any
model, that there are certain underlying assumptions which might have to be
corrected (or at least tuned) for application in 10 Gig. At very least,
there will be new techniques needed to use it for multilevel encoding, as an
Some things to consider:
1. Use of truly single mode LW lasers (Vs multiple longitudinal; single
1.1 Compensated by adjusting K only?
1.2 Measurement of spectral width (rate of drift of "single mode" Vs
Characterization of spectra)
2. The inherent difference between rise and fall times
3. Assumptions about ISI penalty maximums for a link
4. Simultaneous support for:
4.1 Serial up to 12.5 Gig
4.2 Parallel / WDM down to ?
4.3 Support of various multi-level schemes
4.4 Channel to channel crosstalk issues
4.6 Assumptions for SMF and high performance BW MMF
5. Replacement of the E/R (per FC proposals)
6. The various recommendations made by Petar Pepeligoski (IBM)