For 10PASS-TS, 2BASE-TL, and 1000BASE-PX PHYs, it is a count of uncorrectable FEC blocks. This counter will not increment for other PHY Types. Increment the counter by one for each FEC block that is determined to be uncorrectable by the FEC function in the PHY. This object is applicable for an OLT and an ONU. At the OLT, it has a distinct value for each virtual interface. Discontinuities of this counter can occur at re-initialization of the management system and at other times, as indicated by the value of the ifCounterDiscontinuityTime object of the Interface MIB module.