Re: 100G over 100 km of dark fiber

[Ariën Vijn via NANOG <nanog () nanog org>]

Hi Jared,

4x25Gbit/s, 'directly detected' MAY work but it won't be easy at all. As many already have suggested, coherent 
detection will give you much much less headaches. 

If you want to go with directly detected for financial reasons than first make sure you know the type(s) of fibers and 
the dispersion you can expect. Fiber-operators tend to splice different types of fiber together. Don't just assume that 
it will be all G.652 compatible fiber.

If there is G.655 or even G.653 compatible fiber in your path then it is unlikely that you can operate in the O-band 
(1310nm). 

In that case you need to go with the C-band (1550nm), which is easier to amplify than the O-band, because you can use 
commonly available EDFAs. 

You probably need to compensate the chromatic dispersion in the C-band. For that it is again very important to know the 
fiber type(s) in your path.Because a '100km DCM', assumes 100km G.652 fiber. If your path consists of 50km G.652 and 
50km G.655 then you need to compensate for 50km. 

Last but not least, your hardware or optics probably need to be able to do FEC to get a bit of a decent BER.

-- Ariën



> On 30 Oct 2020, at 15:19, Jared Brown <nanog-isp () mail com> wrote:
>
> Hello NANOG!
>
> I need to push 100G over 100 km of dark fiber. Since there are no 100G pluggable optics with this reach (~25 dB), I 
> have been offered coherent transport systems to solve my problem. This is all good and well, except total system 
> costs start from high five figures.
>
> So, my question is, do I have any other options?
>
> I can't help noticing that you can break out a 100G QSFP into four 25G QSFPs. 25G DWDM systems are relatively 
> inexpensive (low five figures), but can you make 25G DWDM go 100 km?
>
> I only need the one 100G, so I don't really need a highly scalable DWDM system. I can't put anything midspan, or if I 
> could it would cost more than just going with a coherent system.
>
>
> Jared