Consider the problem of implementing timers in your current practical. Selective Repeat does not resend all packets on timeout, so it must timeout packets individually. However, in our implementation we only have one timer. How might we solve this problem? What would happen if we re-start the timer every time a packet is sent? What would happen if we re-start the timer when the oldest packet is ACKed?
考虑在当前实际应用中实现计时器的问题。选择性重复不会在超时时重新发送所有数据包，因此它必须单独地发送超时数据包。然而，在我们的实现中，我们只有一个计时器。我们如何解决这个问题？如果每次发送数据包时重新启动计时器，会发生什么情况？如果我们在最早的包被确认时重新启动计时器，会发生什么？