Re: Carrier Ethernet Demarc

[Joel Busch via NANOG <nanog () nanog org>]

On 26.11.2024 05:31, Mark Tinka wrote:
> But getting 100G beyond 10km without amplification and dispersion 
> compensation means you will need to go coherent.
>
> NRZ-based 100G-ZR4 says it will do 80km, but real life has shown things 
> can be vastly different, primarily due to generally poor fibre 
> characteristics.

I agree on the struggle with bad fiber, and we've had to use 100G ER4 
"Lite" on links around 10km before too. But I think you are a little too 
pessimistic with putting the limit of what NRZ can do at 10km.

From my experience 30km is also possible with NRZ. We have a few ER4 
and ER4 "Lite", that is Flexoptix Q.161HG.40 and Q.161HG.25, running 
between cities, with one span being a bit over 30km. That one is muxed 
parallel to our DWDM, so take an additional 2.5dB for our filters.

> That said, you might find OpenXR's latest work exciting for GPON. That
> group has put out a 400G coherent plug that uses digital subcarriers
> (wavelengths nested within a wavelength) to deliver 16x 25G channels in
> a p2mp topology, right in the plug itself. It can run both in normal or
> BiDi mode, and certainly makes future GPON and Active-E p2mp
> architectures very interesting.

That's very interesting, even if we don't use PON. I hadn't heard of 
this before. On the face of it, it sounds expensive to have to use a 
400G capable coherent receiver for a 25G customer. But I'm curious to 
see how the prices shake out in the end, with potential mass adoption.

Best,
Joel

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Joel Busch, Network

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