题目内容：
根据下列材料，回答题：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 often works poorly, because in the（ 1 ）between sending the notification and notification arriving at the source, thousands of additional（ 2 ）may arrive．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．
请选择（ 1 ）处最佳答案：
参考答案：
答案解析：