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Re: dark fiber and sfp distance limitations
From: Alexander Harrowell <a.harrowell () gmail com>
Date: Sat, 2 Jan 2010 00:23:09 +0000

On Friday 01 January 2010 23:19:30 Richard A Steenbergen wrote:
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.

There was an excellent thread on this list last year about using "unusual" 
high power lasers for long range optical networking.


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