[c-nsp] Catalyst SX GBIC's and SMF

[Mikael Abrahamsson]

On Fri, 7 Jan 2005, Robert Walton wrote:

> 	I've currently got two catalyst 4000's connected via a single mode
> fibre using SX GBIC's in an ad-hoc network configuration - at present
> I've seen no service degredation and the link from box-to-box is about
> 40m. According to the cisco spec's these gbics should only be used with
> multi-mode fibre, does anyone know over what distance you would start
> hitting problems when using SMF with SX GBIC's?

It is not really a distance problem, it's a getting-light-into-the-hole
problem. You're using a laser designed to put light into a 50 or 62.5
mikrometer diameter hole, into a 10 mikrometer hole. Basically the surface 
area of this hole is much less than designed. On the other hand, the light 
that actually gets in there will be less degraded over distance.

On the other hand, I have even seen smf patched with mmf fiber and it 
worked (most of the time). At certain temperatures the link started 
flapping wildly. Took some time to find that (the customer had moved our 
CPE and put their own patch cable from the ODF to the CPE). 

I guess best bet is to use a light meter to measure the amount of light
that comes out the other end of your SMF.

I would definately not recommend using SX gbics over SM fiber for 
production purposes. Better to purchase some LX GBICs off of ebay if your 
budget is tight.

-- 
Mikael Abrahamsson    email: swmike at swm.pp.se