单项选择题

案例分析题

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 oftenworks poorly，because in the（1）between sending the notification and notification arriving at the source，thousands of additional（2）may aITive．In ATM network，a major tool for preventing（3）is（4）control．when a host wants a new virtual（5），it must describe the traffic to be offered and the service expected．

文中（ 1 ）处正确的答案是（）。