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

[Lindahl, Carl]

Per Cisco 

http://www.cisco.com/en/US/products/hw/switches/ps708/products_data_shee
t09186a008014cb5e.html

You can run LX GBICs on MM Fiber w/ a specific "mode conditoning" patch
cord. 


-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net]On Behalf Of Justin M.
Streiner
Sent: Friday, January 07, 2005 12:34 PM
To: cisco-nsp at puck.nether.net
Subject: Re: [c-nsp] Catalyst SX GBIC's and SMF 


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
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