A dark fiber path was recently ordered to a remote location on our network, and to my surprise, the engineering report on the path is coming back at around 130 km, which is substantially longer than I expected the span to be.
While I am researching gear that will drive a signal this far without a mid-span regen, I'm also inquiring with the carrier to see if there is any way to shorten the span, but I also have to be prepared for the chance that a shorter span is not possible.
I've seen some pieces from MRV and Transition that might be up to the job, though most of the options I've seen are rated to 120 km, tops.
That said, I'd be interested in hearing about what people who are driving similar spans. I don't think I'm going to have the budget to go out and buy Ciena/Infinera/Cisco ONS kit just for this, since I don't have any at the present time. The link is still being built, so I haven't gotten an engineering report yet. My gut tells me that the 2-point loss on the span at 1550nm will be somewhere around 30-35 dB.
Does anyone know of a good colocation facility in the California Monterey Bay area? I know of got.net but I am looking for alternatives to get a good comparison.
What's your measured chromatic dispersion? You might need
to budget in the hit from compensation too. Some of the
super long range optics have wide tolerance of dispersion,
but probably not without a penalty.
If you don't have a measurement, you can estimate w/ the values
for that fiber type.
You have to be real careful running 10G at those distance. Loss isn't
the only thing you have to worry about...you may need dispersion
compensation, which by itself is going to add to your loss.
If loss is your only worry, then you might be able to do a pre/post
amplification. 130km is far, but you might be able to skip midspan
amplification.
It would be helpful to know what type of fiber you are working with...SMF-28(e) G.652, NZDSF G.655, ...?
You not only need to account for dB loss over the span, but also chromatic dispersion.
At 1550nm, you can expect <= 0.22 dB/km for SMF-28 G.652 if you have a nice clean fiber path...possibly even <= 0.20 dB/km. (Got any OTDR or CD test results? Your provider might be able to give them to you...)
80km DWDM XFPs typically launch between -1 to +3 dBm, and are only sensitive down to about -24 to -25 dBm. Unfortunately, I don't have any data sheets on the 120km versions handy, but I suspect you will be close to the edge.
As Dale mentioned, long-reach optics typically have something like "path penalty at 1450 ps/nm = 2.5dB" in the optical characteristics, so you need to factor that into your budget as well. The amount of chromatic dispersion can either be measured or estimated -- but it will greatly depend on which type of fiber you are using. In general, find out what the maximum amount of chromatic dispersion the receiver can handle for whatever optics you are considering. Then look at a datasheet for the fiber you have (or actually measure it) to see if you are within the spec given in the transceiver datasheet.
That length you're probably going to need Raman amps. As others have
mentioned, if you're planning on 10G or higher you'll need to think about
Chromatic and Polarization dispersion. If the fiber is still in the process
of being laid it shouldn't be too bad assuming the fiber is of high quality.
