This counter tracks received frames whose HDLC address didn't match any of the unit's configured Rx HDLC addresses. This typically indicates the demodulator is correctly locked onto RF energy but is receiving frames addressed to a different remote unit sharing the same carrier or network -- a multi-drop or shared-carrier configuration issue rather than a signal-quality problem. On a network where several remote sites share one outbound carrier, a misconfigured HDLC address on this unit would show this counter climbing steadily even though the RF link itself appears perfectly locked.