链路的传输速度为10 6位/秒。它使用每个大小为1000字节的数据包。假定该确认具有可忽略的传输延迟，并且其传播延迟与数据传播延迟相同。还假定节点处的处理延迟可以忽略不计。在此设置中，停止等待协议的效率正好是25％。单向传播延迟的值(以毫秒为单位)为___________。
(A) 4
(B) 8
(C) 12
(D) 16答案： (C)
解释：
In stop and wait, protocol next packet is sent only when
acknowledgement of previous packet is received. This
causes poor link utilization.
Tansmission speed = 106
Time to send a packet = (1000 * 8) bits / 106
= 8 miliseconds
Since link utilization or efficiency is 25%, total time
taken for 1 packet is 8 * 100/25 = 32 miliseconds.
Total time is twice the one way propagation delay plus
transmission delay. Propagation delay has to be considered
for packet and ack both.
Transmission delay is considered only for packet as the
question says that trans. time for ack is negligible.
Let propagation delay be x.
2x + 8 = 32.
x = 12.这个问题的测验