This Counter32 counts AAL5 PDUs dropped due to length violations, applicable to CCS PVCs, since HDLC frames must meet a minimum frame size for correct interpretation by the upper-layer protocol. Frames arriving smaller than the required HDLC minimum are effectively unparseable by the signaling protocol above, so this counter directly reflects malformed signaling frames being discarded. An engineer troubleshooting intermittent signaling failures on a CCS PVC would check this counter to see if undersized HDLC frames are being silently dropped rather than assuming a higher-layer protocol issue.