dark fiber and sfp distance limitations

Richard A Steenbergen ras at e-gerbil.net
Fri Jan 1 23:19:30 UTC 2010

On Fri, Jan 01, 2010 at 02:52:33PM -0800, Mike wrote:
> I am looking at the possibility of leasing a ~70 mile run of fiber. I 
> don't have access to any mid point section for regeneration purposes, 
> and so I am wondering what the chances that a 120km rated SFP would be 
> able to light the path and provide stable connectivity. There are a lot 
> of unknowns including # of splices, condition of the cable, or the 
> actual dispersion index or other properties (until we actually get 
> closer to leasing it). Its spare telco fibers in the same cable binder 
> they are using interoffice transport, but there are regen huts along the 
> way so it works for them but may not for us, and 'finding out' is 
> potentially expensive. How would someone experienced go about 
> determining the feasibillity of this concept and what options might 
> there be? Replies online or off would be appreciated.

That shouldn't be too difficult, especially at only 1G (though pesonally
I can't imagine why you would bother leasing dark fiber for that :P). 
There are several ways you could do it, including 120km+ rated SFPs
(iirc there have been 200km SFPs out for a while too), an external
optical amplifier (ideally you'd want to amp in the middle, but with a
single channel you should be fine w/pre-amp), and a digital FEC wrapper
to extend the receive sensitivity. Remember that the distance spec on
optics is mostly a rough guideline, so depending on the fiber conditions
and number of splices/panels along the way you could potentially expect
to get the entire distance out of a "standard" 100km optic.

Richard A Steenbergen <ras at e-gerbil.net>       http://www.e-gerbil.net/ras
GPG Key ID: 0xF8B12CBC (7535 7F59 8204 ED1F CC1C 53AF 4C41 5ECA F8B1 2CBC)

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