[e2e] Two questions on simulation of AQM

Zhang Miao zm at csnet1.cs.tsinghua.edu.cn
Wed Apr 11 02:12:21 PDT 2001

Hi, Wu
   Your argument seems reasonable for dropping. If a packet is dropped earlier,
it may provide a room for another packet. There is indeed a tradeoff between 
feeding back faster and the hazard of dropping more packets. But how about marking?
Is there also such tradeoff?
   For question 2, I agree that the effect is slight. But this effect becomes more
important when the performance of two AQM schemes are very similar. In the paper of
REM(http://netlab.caltech.edu), the difference of goodput between RED and REM is
very little. So several percent effect also becomes important. Perhaps this little
difference has no meaning in simulation results.

>For question 1, I agree with u that, if the Marking or Dropping action is
>in deque(), it will obviously shorten the feedback latency, but will
>increase the potential of "Lock-Out".
>As I think, if u drop or marking the packet from the beginning of the
>queue, some burst traffic will monopolize the queue space (or let all the
>packets in queue being marked), preventing other connection from getting
>room in the queue. Simply change the Marking or Dropping action the
>deque() will not work, it will let the burst traffic grasp will the
>For question 2, as far as I can remember, a single ACK loss will just
>have a slight effect to TCP performance, so reverse direction policy will
>not change the TCP performance a lot. There have already some research
>work being done around this. U can find the paper "The Effects of
>Asymmetric Links on TCP Performance and Its Solutions" in JOURNAL OF
>(Chinese). It solves the problem when the bottleneck is in reverse
>Jin Wu
>School of Computing,
>University of Leeds,
>Leeds,  LS2 9JT,
>Tel: (44)113 2336806

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