Re: [aqm] AQM schemes: Queue length vs. delay based

[Preethi Natarajan <[e-mail]>]

From:  Naeem Khademi <[e-mail]>
Date:  Wednesday, November 13, 2013 12:14 PM
To:  Preethi Natarajan <[e-mail]>
Cc:  Michael Welzl <[e-mail]>, "[e-mail]" <[e-mail]>
Subject:  Re: [aqm] AQM schemes: Queue length vs. delay based

> 
> Very true, though that's what ARED *is* with very low thresholds (e.g.
> resonate between 1 or 2 packets on the average in the queue). Indeed there can
> possibly be some future work on ARED's (or any other similar AQM) burst
> allowance but I don't think e.g. letting a 100 ms burst of packets to pass
> through can be a good way of fixing it as this can lead to massive variance in
> overall RTT distribution.

If you are referring to the burst_allowance parameter in PIE, this parameter
allows burst to go through when a system goes from an idle state into some
congestion state. The one we are talking about is accommodating bursts when
the system is in equilibirum -- how does the AQM scheme accommodate bursts
when already operating around target delay or congestion? Delay-based ARED
behaves similar to tail drop at max threshold. This is unacceptable of an
AQM even for max thresholds around 50ms.
Clearly delay-based ARED needs significant and careful redesign. I suppose
one can argue this task is as laborious as designing a new AQM scheme as
opposed to previous notions that delay-based ARED would work right out of
the box. 
Preethi