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（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 offered and the service expected.
- A.collision
- B.congestion
- C.drop
- D.delay
正确答案及解析
正确答案
B
解析
在低速网络中，通常采用碰到拥塞时，通过向源端反映使其降低发送速率。而在告诉网络中，这种方式将会恶化，因为在发送通告和通告到达之间会有成千上万的其它数据包到达。在ATM网络中，主要采用允许控制来避免拥塞，当有一台主机要建立一条新的虚连接时，它必须描述它所需的流量和服务等级。
