On 28.11.2025 05:40, Mark Tinka wrote:
On the single-lambda side, the 2km plug has been defined under 100G-FR1.
While I like those the most because data centre x-connects will
generally be under 2km long, experience is showing that operators are
carrying their "LR4" habit into 100G-LR1 world :-).
Yes we're seeing the same. And when I ask a customer if they would like
their uplinks to be 100G-LR4 or 100G-LR they ask me what 100G-LR is :-)
Yes, you are right. It can be quite cobbled up. But to summarize it,
there are 3 applications:
* 100G-LR4 (LWDM):
o 4×25G NRZ in O-band with the LAN-WDM 800GHz spacing, 10km class.
o Wavelengths: 1295.56/1300.05/1304.58/1309.14nm.
* 400G-LR4 (CWDM O-band):
o 4×100G PAM4 on CWDM4 wavelengths (wide 20nm spacing), 6km – 10km
class.
o Wavelengths: 1271/1291/1311/1331nm.
* 400G-ER4 (nLWDM):
o 4×100G PAM4 with tighter 400GHz spacing clustered near 1310nm to
keep dispersion low/flat, 30km - 40km class.
o Wavelengths: 1304.58/1306.85/1309.14/1311.43nm
Good summary.
Just don't forget to check if the 400G-ER4 you're buying really uses the
400GHz spacing, everyone. Remember that FiberMall listing from my
earlier email:
https://www.fibermall.com/sale-458209-qsfp-dd-400g-er4-lwdm4-40km.htm
And with ER4-lite all bets are off. It's anyone's guess which shop will
sell which spacing, just make sure your inventory stays consistent for
your own sanity.
Thanks for bouncing back and forth with me on this topic, Mark!
Good weekend to everyone, sooner or later, depending on timezone :-)
Joel
--
Joel Busch,
Network Engineer
Switch, AS559
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