Nortel Networks CG030601 - Manual (Page 4)

Configuration Guide
Contivity Secure IP Services Gateway
Frame Relay on Contivity Secure IP Services Gateway
CG030601 2.00 July 2003 Page: 4 of 14
Congestion control
Network congestion can degrade network performance. Congestion occurs when a node
receives more frames than it can process, or sends more frames than the transmission line
can handle. The frame relay network informs the nodes of congestion so that they can
reduce the amount of traffic across the network.
In the frame relay packet header, there are two bits that the network sets to alert nodes of
network congestion. These bits, as defined by the frame relay specification, are the
forward explicit congestion notation (FECN) bit and the backward explicit congestion
notation (BECN) bit.
If the network detects congestion, it alerts the CES in the same direction as the received
frame by changing the frame’s FECN bit from 0 to 1. For nodes in the opposite direction
of the received frame, it changes the frame’s BECN bit from 0 to 1.