DWDM on 250 Km dark fiber without re-amplification
lists.nanog at monmotha.net
Sun Dec 25 08:41:12 UTC 2016
On 12/23/2016 07:14 PM, Jeremy wrote:
> Hi all,
> First, i'm sorry for my english, i'm french and i don't have a good
> level in this language. But i want some informations and i'm sure,
> someone will be give the good anwser about my question.
> So, i'm regarding to rent a dual dark fiber in France, the estimated
> distance is 225 Km, but i know there are a lot of optical switching on
> the highway where it's fiber is installed (in theory, all 80 Km). So, i
> used the bad scenario, in adding 25 Km on my need.
> I would like to buy a amplificator and multiplexer DWDM to add some
> 10Gb/s waves on this dark fiber. I've see that the amplification is
> better on 100 Gb/s synchronised ports, but we don't have enoug capacity
> on our router to add 100 Gb/s interfaces.
> So, someone has installed this type of hardware on a dark fiber without
> regeneration on 250 Km of distance ?
> If yes, with what kind of hardware ? If you are commercial for this
> hardware, please contact me in private message.
Look up Raman amplification. The short of what this does is it pumps a
ton of power into the near end of the fiber span and creates what looks
somewhat like a typical color-blind amplifier somewhere several dozen km
out on the span. You'll also need to dump a ton of power into the span
at the far end using an EDFA or similar. Even with both of those, that
distance is still going to push the raw optical power budget of even
most state-of-the-art transceivers especially if the fiber is old or of
low quality (high loss, high dispersion, etc.).
The longest span I've ever gotten a vendor to commit to an engineered
design for was about 140km, and of course they needed full
characterization of the span before they'd do it. At those distances,
distance alone is no longer sufficient to throw together a design.
It seems highly likely that there's at least one re-gen facility along
that span. I'd definitely see if there is one and if you can get some
space in it. That will knock you down into the 100-130km range on both
sides of the re-gen, hopefully, which is perfectly doable.
You are somewhat correct that 100Gb interfaces often handle longer
distances better, but it's because they are often using coherent
receivers and carrier-synchronous transmitters rather than raw power
receivers and ASK pulsed transmitters. There are vendors that sell
coherent 10Gb transceivers, too, and they'll be cheaper than 100Gb
solutions especially if you don't need the extra capacity anyway. I'd
definitely check them out for this type of application especially if you
can't get any dispersion compensation in the middle since coherent
optics are usually much more tolerant of chromatic dispersion.
The big vendor I've worked with in the past on this sort of stuff is
Ciena (and they're certainly a juggernaut in the industry) though I have
no connection to them other than as a satisfied (if occasionally broke
after a PO or out of breath after seeing a quotation) customer/integrator.
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