On 4/19/24 10:08, Saku Ytti wrote:

Of course there are limits to this, as FEC is hop-by-hop, so in
long-haul you'll know about circuit quality to the transponder, not
end-to-end. Unlike in wan-phy, OTN where you know both.

Technically optical transport could induce FEC errors, if there are
FEC errors on any hop, so consumers of optical networks need not have
access to optical networks to know if it's end-to-end clean.

This would only matter on ultra long haul optical spans where the signal would need to be regenerated, where - among many other values - FEC would need to be decoded, corrected and re-applied.

SD-FEC already allows for a significant improvement in optical reach for a given modulation. This negates the need for early regeneration, assuming other optical penalties and impairments are satisfactorily compensated for.

Of course, what a market defines as long haul or ultra long haul may vary; add to that the variability of regeneration spacing in such scenarios being quite wide, on the order of 600km - 1,000km. Much of this will come down to fibre, ROADM and coherent pluggable quality.

Mark.