[e2e] Two questions on simulation of AQM

[Damon Wischik]

> (1) Where should the action(Marking/Dropping) be taken?
> In the code of RED, action is taken in enque(), ie., at the input of the
> queue. From intuition, better performance can be got when action is
> taken in deque(), ie., at the output of the queue. The reason is that it
> can shorten the feedback latency, especially when the RTT is similar to
> the queueing delay.  What I want to know is whether there is any
> implemention limitation in the router.