假设有5个批处理作业J1，…，J5几乎同时到达系统，它们的估计运行时间为10，6，2，4和8分钟，它们的优先级别为3，5，2，1和4(5为最高优先级)，若采用优先级作业调度算法，假设忽略作业切换所用的时间，则平均作业周转时间为______。

(73)

(72)

(71)

(70)

(68)

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．

(69)

(67)

电视信号的标准也称电视的制式，制式的区别在于其帧频的不同、分辨率的不同、信号带宽及载频的不同、彩色空间的转换关系不同等。我国电视采用的制式是(58)，对应帧频是(59)帧/妙，对应分辨率为(60)。

(66)

(65)

(64)