This counts Uncorrected FEC Blocks at the OTU layer: FEC-frame blocks that arrived with more errors than the FEC algorithm could fix, per the MIB's description. Unlike the pre/post-FEC BER estimates, which are modeled rates, this is a hard count of blocks on this specific OTU section that FEC gave up on and passed through with errors intact into the client payload -- any nonzero value here means real, uncorrected corruption reached the ODU/client layer during this bin, not just a close call; 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. On a healthy port this bin should read 0; even 1 uncorrected block would be treated far more seriously than a large FEC-corrected count, since it represents damage the correction scheme could not undo.