In frame relay, a congestion control mechanism that prevents the frame relay network device (FRND) from accepting incoming frames unless there is an extremely high probability of the network's being able to deliver them without discard. A closed-loop algorithm fairly allocates backbone bandwidth among all the permanent virtual circuits (PVCs) configured on a particular trunk, and in proportion to the Committed Information Rate (CIR) of each PVC. See also backbone, bandwidth, CIR, congestion, frame relay, FRND, PVC, and trunk.