This counts Forward Error Correction activity at the OTU layer: the number of bit errors the FEC decoder found and corrected within this bin, per the MIB's description. A raw FEC count on this OTU section isn't itself alarming -- FEC is designed to soak up routine noise -- but tracking how it trends bin over bin tells an admin whether the link's error floor is creeping up before it turns into uncorrected blocks or SES; as a 'total' bin it never rolls over on its own the way the 15-minute and 24-hour bins do -- it only resets on an explicit clear or a card reset, so a high count here just reflects long uptime, not necessarily an active problem. A stable DWDM span might correct on the order of 2287801 bit errors in this bin purely from ordinary optical noise, with no visible impact on the client traffic riding on top of it.