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 ______ between sending the notification and notification arriving at the source, thousands of additional ______ may arrive. In ATM network, a major tool for preventing ______ is ______ control. When a host wants a new virtual ______, it must describe the traffic to be offered and the service expected.
A．collision
B．congestion
C．drop
D．delay