[e2e] Two questions on simulation of AQM

Alhussein Abouzeid hussein at ee.washington.edu
Wed Apr 11 00:38:31 PDT 2001

i believe this is called drop-from-front (vis-a-vis tail-drop). the issue
has received considerable investigation before in the context of
traditional FIFO queuing and some recent work relevant to AQM- check
publications (don't remember exact ones right now).

i believe the action in the orignial RED drops/marks a packet randomly
(with a prob. dependent on the avg queue size) from the packets in the
queue - i.e. not necessarily the arrviving or the "about to depart"
packet. performance implications and trade-offs don't seem to be
obvious, i think.

as for your second question, i think you might want to consider exactly
what you mean by "reverse direction" from a gateway prespective.

hope this helps.

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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