On Fri, 19 Apr 2024 at 10:55, Mark Tinka <mark@tinka.africa> wrote:> FEC is amazing.
At higher data rates (100G and 400G) for long and ultra long haul optical networks, SD-FEC (Soft Decision FEC) carries a higher overhead penalty compared to HD-FEC (Hard Decision FEC), but the net OSNR gain more than compensates for that, and makes it worth it to increase transmission distance without compromising throughput.
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. Much like cut-through switching can induce errors via some symbols to communicate the CRC errors happened earlier, so the receiver doesn't have to worry about problems on their end. -- ++ytti