This counts Far End Block Errors (FEBE) reported for the line layer on this SONET/SDH port since the last reset, errors the far end detected and reported back to this port, rather than errors this port detected locally. Because FEBE reflects the far end's error experience rather than this port's own receive quality, a rising count here means the signal this port is transmitting is arriving degraded at the remote end, pointing troubleshooting toward this port's transmit path or the fiber run itself. A port with clean local BIP counters but climbing pportFebeErrors would indicate this port's outbound signal, not its inbound receive path, is the one degrading before it reaches the far end.