In low-speed network,it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down.In high-speed networks,this approach often works poorly,because in the（本题）between sending the notification and notification arriving at the source,thousands of additional（72）may arrive.In ATM network,a major tool for preventing（73）is（74）control.When a host wants a new virtual（75）,it must describe the traffic to be offered and the service expected.

In low-speed network,it is usually adequate to wait for congestion to occur and then react to it by telling the source of packets to slow down.In high-speed networks,this approach often works poorly,because in the（本题）between sending the notification and notification arriving at the source,thousands of additional（72）may arrive.In ATM network,a major tool for preventing（73）is（74）control.When a host wants a new virtual（75）,it must describe the traffic to be offered and the service expected.