dark fiber and sfp distance limitations

Rene Avi rene.avi at gmx.net
Sat Jan 2 05:35:15 CST 2010


On 02.01.2010 02:10, William Herrin wrote:
> On Fri, Jan 1, 2010 at 7:24 PM, ML <ml at kenweb.org> wrote:
>> Pardon my ignorance in this area but is too much to ask for OTDR data before
>> signing contracts?  In addition to data on the make of the fiber if you
>> wanted to do xWDM in the future.
> 
> Yes, it's too much to ask. They won't splice your path until you sign
> the contracts and you can't get useful OTDR and loss readings until
> the fiber is spliced.

In my experience the fiber splice/patch-teams have quite accurate 
estimations on the overall attenuation of unprovisioned paths. They know 
the distance (0.25dB/km for G.652 @ 1550nm), the number of connectors 
(0.35dB per plug average here) and splices (0.1dB/spice). YMMV though. 
We add +20% safety, include an escape clause wherever possible and cross 
our fingers.

With regards to suggested EDFA amplification tricks and similar: If the 
requirement is not > 150km at 1G or 80km at 10G/DWDM then I personally 
strongly disencourage the use of optical amps. 200km / 41dB 1G SFPs are 
available with costs way below dual EDFAs plus spare, and the chance for 
the untrained to get eye damages in the process of implementation is far 
less. So put some laser googles at around 400 USD/each to the purchase 
list. If one decides to do so then add a post-amplifier on each *end* of 
the fiber link to increase the signal before hitting the receiver, and 
do not pump in star-wars class laser power at the beginning ;) .

Cheers,
-- 
Rene Avi

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