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

[Justin M. Streiner]

On Fri, 7 Jan 2005, Mikael Abrahamsson wrote:

> 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.
>
> 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.

Indeed.  As a general rule, using SX GBICs with singlemode fiber is not 
recommended, nor is the reverse - LX/LH/ZX GBICs ober multimode.  You can 
run into all kinds of problems related to modal or chromatic dispersion in 
those cases.  This could show up as link flaps, interface errors, or some 
other fun problem :-)  The reverse would be more dangerous because the 
potential exists to fry the receiver optics in your LX/LH/ZX GBICs.

jms