If device A is sending data to device B
accross a Frame Relay intrastructure and one of the intermediate Frame Relay switches
encounters congestion, congestion being full buffers, over subscribed port, overloaded
resources, etc, it will set the BECN bit on packets being returned to the sending device
and the FECN bit on the packets being sent to the receiving device. This has the
effect of telling the sending router to Back off and apply flow control like traffic
Shaping and informs the receiving device that the flow is congested and that it should
inform upper layer protocols, if possible, that it should close down windowing etc to
inform the sending application to slow down.
A FECN tells the receiving device that the path is congested so that the upper layer protocols should expect some delay. The BECN
tells the transmitting device that the Frame Relay network is congested and that it should
"back off" to allow better throughput.
FECN (Forward Error Congestion Notification)
BECN (Backward Error Congestion Notification)
NMIS from Opmantek includes full support for FECN and BECN collection and reporting for free.