In low-speed network，it is usually adequate to wait for congestion to occur and then react to it bytelling the source of packets to slow down．In high-speed networks，this approach often works poorly，because in the (71) 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 offeredand the service expected．
（75）处填（）。
A．path
B．rout
C．circuit
D．way
参考答案：C
解析：
当拥塞发生时，便通告信源要放慢速度，在低速网络中，等待通告时间通常是足够的。但在高速网络中，这种方法工作起来有时会很差，这是因为，在发出通告与通告到达信源这段时间内(interval)，可能又有成千上万个数据包(packets)已经到达。在ATM网络中，主要的拥塞(congestion)避免工具是通信量(traffic)控制。当一台主机想建立一条新的虚电路(circuit)时，必需要描述其通信量和服务要求。