dark fiber and sfp distance limitations

Justin M. Streiner streiner at cluebyfour.org
Sat Jan 2 18:37:14 UTC 2010

On Sat, 2 Jan 2010, Mikael Abrahamsson wrote:

> On Fri, 1 Jan 2010, Justin M. Streiner wrote:
>>  The first thing you need to do is test the fiber with an OTDR.  If you
>>  don't have one, you can probably contract a local cabling company to test
>>  it for you.
> Why would you want an OTDR report on the fiber, when an attenuation report is 
> probably more accurate? OTDR is good for locating WHERE a problem is, but if 
> you're seeing .2 dB/km attenuation end-to-end, there is little reason to 
> break out the OTDR.

Some OTDRs (or, more correctly, fiber test sets that include OTDR 
capabilities) are multi-function devices that will show you the overall 
length (assuming the span is not broken somewhere in the middle), 
of the span, plus attenuation and reflections (spikes) at your desired 
wavelength in one complete package.

I'm a big believer in running my own tests when possible, and not just 
relying on $provider's word.  It also allows me to verify what their 
engineering reports tell me about the condition of a span.


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