This counts frames delivered on this circuit carrying the BECN bit, telling this circuit's own transmitting end, since BECN flows back toward the sender, that its outbound traffic is experiencing congestion somewhere along the path in the other direction. An admin sees this rise specifically when this circuit's own sender needs to slow down, distinguishing it from cktOutFECNFrames, which reflects congestion affecting frames sent to this circuit rather than by it. For example, a sudden spike in cktOutBECNFrames right after this circuit's cktInOctets rate spiked would show the network correctly telling this site to throttle its own outbound transmission.