explicit congestion notification (FR) (ECN)
Explicit Congestion Notification (ECN) is a mechanism in IP protocol and Frame Relay( FR) that is used to notify network congestion.
The ECN mechanism uses two bit values to indicate congestion. Both bit values are located in the IP header in the DSCP field, Differential Service Code Point. One bit is the Backward Explicit Congestion Notification( BECN), the other is the Forward Explicit Congestion Notification( FECN).
In the Frame Relay header, the Backward Explicit Congestion Notification (BECN) is transmitted in the direction opposite to the congestion and is intended to inform the sending node that the transmission link is congested. The Forward Explicit Congestion Notification (FECN) is inserted into the Frame Relay header and transmitted in the direction in which the congestion occurs. The FECN is to inform the receiving node of the congestion.
The congestion mechanism is triggered by setting a bit in the header.