With when a frame relay router experiences congestion, it sends a congestion signal forward to the destination station, which in turn tells the originating station to slow down the transfer of data.

The correct answer is letter "A": forward explicit congestion notification (FECN).

Explanation:

A Forward Explicit Congestion Notification (FECN) is a frame relay message that informs there is not enough network bandwidth in a given time. The message is sent to the same destination where the frame is headed. This problem arises when the network infrastructure is not correct or when there is heavy network traffic.