This read-only counter, in frames, tallies frames received from the network with the Backward Explicit Congestion Notification bit set, a signal meant to reach the sender and trigger a rate reduction. A high count here with no corresponding drop in casfVcCountSentFrames indicates the sending device either doesn't support BECN-based flow control or has it disabled, and will keep contributing to the very congestion being reported. A router configured without adaptive frame-relay traffic shaping would keep transmitting at full rate despite a climbing count here, worsening the congestion it's being warned about.