[e2e] Two questions on simulation of AQM

J Wu jinw at comp.leeds.ac.uk
Wed Apr 11 01:50:08 PDT 2001

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

On Wed, 11 Apr 2001, Zhang Miao wrote:

> Hi, all
>    Recently I did some simulation with single congested gateway in ns-2. 
> I have two questions related to the simulation details. I would be grateful 
> if anyone could provide some advices or references.
> (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.
> (2) What policy should be used in the reverse direction?
>     When we test the performance of one AQM scheme, we only pay attention to the 
> scheme applied in one direction. I just observed that the policy in the reverse 
> diretion also has some influence to the result. ACK packets are controlled by it.
>     Thanks a lot!
> *****************************************************************
> *    Zhang Miao                                                 *
> *    Ph.D candidate,Department of Computer Science & Technology * 
> *    Tsinghua University,Beijing,China(100084)                  *
> *    Tel: (8610)-62785822                                       *
> *    Email: zm at csnet1.cs.tsinghua.edu.cn                        *
> *    Web: http://netlab.cs.tsinghua.edu.cn/~zm (domestic only ) *
> *****************************************************************

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