Re: 400G ER4 wavelengths - two grids

[Mark Tinka via NANOG <nanog () lists nanog org>]

On 26/11/2025 15:40, Joel Busch via NANOG wrote:
> Does anyone have any parts sourced directly from a router 
> manufacturer? Could you share what they went with optically?

I have not seen any OEM's selling the 400G-ER4 or 400G-ER4 Lite in the 
wild. Most of the ones I have come across are from the open market.

What OEM's seem to be selling are 400G-DR4/FR4/LR4.

> Or any other pertinent insider knowledge? :-)

The bottom line is that the ER4-Lite was built for shorter distances 
(30km), while the ER4 proper is designed for up to 40km. Of course YMMV 
re: fibre quality, so the better numbers to work with are up to 15.5dB 
for the ER4-Lite and up to 18.5dB for the ER4 proper.

The ER4-Lite is cheaper, and also explains why it has been out of stock 
for some time now. I see that suppliers have resumed providing units in 
the last 2 or so months.

It would not be advisable to run an ER4 and ER4-Lite over a link. Better 
to match them for optical compatibility.

Of course, it goes without saying that if you need to go father than 
40km for 400G, or solve for poor fibre OSNR, you are better off going 
coherent.

Hope this helps.

Mark.
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