GBIC's and Fibre

[Andy Haigh_1]

Hi,
We are about to connect two sites together which are approx 250m apart with fibre. The switches at each end are a 2824 and a 2610 the tranceivers I am looking at using are J4858C which have listed distances of:
220 m (62.5 m core diameter, 160 MHz/km)
275 m (62.5 m core diameter, 200 MHz/km)
500 m (50 m core diameter, 400 MHz/km)
550 m (50 m core diameter, 500 MHz/km)
I am looking at using 50 micron fibre but my question is how do I select the bandwidth to use? Is it automatic or an option within the CLI?
If say we need to go with 62.5 micron due to costs how would I force it use 200 MHz/km, or does it work it out for itself?

Thanks

Andy

[Marco Wessel · Accepted solution]

You don't 'select' this bandwidth, this is a quality of the fiber. The higher the better.

You should get 50µ core diameter fiber, either OM2 (the 500MHz/km kind) or (better) OM3, which is a newer kind optimized for lasers at 850nm such as the ones used for 1000BASE-SX. The latter is also what you want if you'd ever want to upgrade to 10gigE. For GigE however, either kind of 50µ fiber is fine.

I quickly googled and found this doc from Corning (large fiber manufacturer) with some more details: http://www.corning.com/WorkArea/downloadasset.aspx?id=7671

[Andy Haigh_1]

Thank's for the reponse, I understand now.

Andy

[Andy Haigh_1]

So just to be 100% sure I can use either 50 micron OM2 or OM3 cable with these tranceivers. The OM3 cable provides an upgrade path to 10Gb if I replace the tranceivers whereas OM2 is currently a max of 1Gb.

Thanks

Andy

[Marco Wessel]

That is correct: OM3 is simply a higher quality fiber, optimized for exactly the kind of light used by 1000BASE-SX and the multimode versions of 10gigE so it can reach farther.

[Marco Wessel]

Oh, I see I didn't answer that entirely.

OM2 will technically support 10gigE too, but only for short distances. Much shorter than the 250m you indicate. Beyond that, the dispersion is too high so, to put it simply, the bits as sent over the fiber are 'blurred' too much to be reliably read.

I once saw a very nice graphic representation of what happened with the light in the various kinds of fiber, but I can't find it right now. If I find it later I'll add it.