Maximum Length for 1000Base-SX

Can I calculate the maximum run length for 1000Base-SX based on:

Max dB Loss (7.5dB) > # patch panels * loss per mated pair + distance attenuation

Where loss per mated pair is nominally < .75 dB, but we test for < .3 dB;

and distance attenuation is 3 db / km

And thus exceed 220 m over 62.5/125 =B5m?

Do I count the switch to patch cable as a mated pair, or is that included within the optical budget?

How about modal dispersion? Is there a calculation for that?

Or should I run replacement 50 =B5m fiber?



(P.S. Sorry about cross-posting, but I realise that this is a better forum than comp.dcom.lans.ethernet for this question.)

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You actually have to be more conservative with your margins. 3.75dB/km is more realistic for a standard 62.5/125 mkm fiber. Also, I would still stick with 0.75 dB per connector even if the measured value is 0.3 dB per mated pair. This is simply because if you test the same connector pair again, you will get another value (usually worse, but not necessarily). Test it in a year after couple re-connections and you'll see it drop to

0.75 dB if lucky or even beyond that.

No the connectors on equipment don't count

The degrading effect of modal dispersion is figured into the maximum loss figure.

Or you can use 1000BASE-LX on the same fiber and get 550 meters. That may be much cheaper, depending on how difficult it is to re-pull the fiber.

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