Re: constant FEC errors juniper mpc10e 400g

[Mark Tinka <mark@tinka.africa>]

On 4/20/24 14:41, Dave Cohen wrote:

> LAN PHY dominates in the US too. Requests for WAN PHY were almost exclusively for terrestrial backhaul extending off of 
> legacy subsea systems that still commonly had TDM-framed services. It’s been a couple of years since I’ve been in 
> optical transport directly but these requests were essentially non-existent after 2018 or so. OTN became somewhat more 
> common from 2014 onward as optical system interop improved, but actually was more common in the enterprise space as 
> providers would generally go straight to fiber in most use cases, and with dark fiber opex costs coming down in many 
> markets, I see OTN requests as winnowing here as well.

What really changed the game was coherent detection, which breathed new 
life into legacy subsea cables that were built on dispersion-managed 
fibre. Post-2014 when uncompensated (and highly dispersed) fibre has 
been the standard for subsea builds (even for SDM cables), coherent 
optical systems are the mainstay. In fact, because linear dispersion can 
be accurately calculated for the cable span, uncompensated cables are a 
good thing because the dispersion compensation happens in very advanced 
coherent DSP's in the optical engine, rather than in the fibre itself.

WAN-PHY did not extend to 40G or 100G, which can explain one of the 
reasons it lost favour. For 10G, its availability also depended on the 
type of device, its NOS, line card and/or pluggable at the time, which 
made it hard to find a standard around this if you built multi-vendor 
networks or purchased backhaul services from 3rd party providers that 
had non-standard support for WAN-PHY/OTN/G.709. In other words, LAN-PHY 
(and plain Ethernet) became the lowest common denominator in the 
majority of cases for customers.

In 2024, I find that operators care more about bringing the circuit up 
than using its link properties to trigger monitoring, failover and 
reconvergence. The simplest way to do that is to ask for plain Ethernet 
services, particularly for 100G and 400G, but also for 10G. In practice, 
this has been reasonably reliable in the past 2 - 3 years when procuring 
100G backhaul services. So for the most part, users of these services 
seem to be otherwise happy.

Mark.