$20\mathrm{.}5$ For a frame relay network to be able to detect and then signal congestion, it is neces$-$

sary for each frame handler to monitor its queueing behavior. If queue lengths begin

to grow to a dangerous level, then either forward or backward explicit notification or

a combination should be set to try to reduce the flow of frames through that frame

handler. The frame handler has some choice as to which logical connections should

be alerted to congestion. If congestion is becoming quite serious, all logical connec$-$

tions through a frame handler might be notified. In the early stages of congestion,

the frame handler might just notify users for those connections that are generating

the most traffic.

Figure $20\mathrm{.}14$ Network of Packet$-$Switching Nodes