This counts the total number of inbound frames on this physical port that the switch discarded rather than forwarding. Since this counter does not distinguish cause, a rising value here on a specific port is a trigger to check that port's congestion, buffer, and admission-control counters, like cardFrameMemoryThreshold, to find out why frames are being dropped. A frame relay port suddenly discarding hundreds of frames per minute after a bandwidth increase upstream would point to this port's own queue or shaping being unable to keep up with the new offered load.