This read-only counter, in frames, tallies frames this switch itself sent with the FECN bit set toward the receiving end. Because this switch is the one setting FECN here, a rising count means this switch itself is experiencing, or forwarding notice of, congestion somewhere in the path toward the receiving end, making it a leading indicator of a transmit-path problem on this VC before it necessarily shows up as discards. This counter beginning to climb on a previously quiet connection during a peak-hour period is an early sign the path is nearing saturation, even before any frames actually get dropped.