single mode fiber verse multi mode fiber

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We are building a new Residence Hall on our campus. The question has come up on what type of fiber to install SM verse MM. The backbone is 1GB and the distance is 2500 feet. It looks like Single mode fiber will deteriorate a 1GB connection at 300 meters and is pushing us to use Single mode fiber. What hardware or application limitations will we have by using single mode. There will be 3750's at each end of this fiber run.

I have this problem too.
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ralphcarter Mon, 07/21/2008 - 11:27

Multimode SFP for the 3750's run up to 550meters = 1800 feet.

You would need to run single mode fiber with Single mode LX modules for the 3750.

Model: GLC-LH-SM , these can go up to 10Km I believe.

To answer all your questions, I would ask this question on the optical forum.

michaelchoo Mon, 07/21/2008 - 16:27

Any single-mode fibre should work fine for you. From memory, there are two major single-mode wavelength: 1310nm and 1550nm. 1000BaseLX/LH with 1310nm wavelength can reach up to 10km regardless of the fibre core size. On the contrary, 1550nm can reach 70-100km depending on the fibre core: 9/10-micron core size can reach only up to 70 km, while 8-micron core can go up to 100km.

Here's a handy "cheat sheet" from Cisco that I use quite often:

Edit: as far as required hardware is concerned, all you need is the appropriate SFPs and fibre patch leads for your application. 3750's should be fine. Considering the distance, I think the most appropriate hardware for you is simply 1000BaseLX/LH SFP with single-mode fibre with 8/9/10-micron core diameter. If your fibre terminates on patch panel, you'll need the appropriate single-mode fibre patch lead(s) as well (which is quite expensive).

a.whiting Thu, 07/24/2008 - 02:36

Hi Bryan,

Whilst MM fibre will work over this reach please bear in mind the need to use mode-conditioning cables (in the tx legs) when using LX SFP's over 300m. Where SM fibre scores big points here is the possibility of using wavelength division multiplexing (WDM) technology in the future to provide (a) more bandwidth and (b) separate services within the campus. Cisco have plenty of coarse, dense and extended WDM products; for a quick overview of what can be achieved I've attached a brochure (from MRV, although I'm not plugging them - it's just a clear overview).

Best regards,



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