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．

（74）处填（）。

A．flow

B．admission

C．traffic

D．time

元数据一般分为（）、管理型元数据、结构性元数据、保存性元数据等等。

A.内容元数据

B.描述性元数据

C.资源集合元数据

D.数字对象元数据