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

[Preethi Natarajan <[e-mail]>]

From:  Michael Welzl <[e-mail]>
Date:  Friday, November 8, 2013 5:30 PM
To:  Preethi Natarajan <[e-mail]>
Cc:  Naeem Khademi <[e-mail]>, "[e-mail]" <[e-mail]>
Subject:  Re: [aqm] AQM schemes: Queue length vs. delay based

> 
> Thanks for the link. My point was just (along with Naeem) that it would be
> useful to compare PIE (or CoDel) against something else except CoDel and RED.
> When I just look at the graphs in the HPSR paper (sorry, didn't get to read it
> yet), again I see only PIE, CoDel, RED.
> 
> We tried ARED and were surprised to see how good it works - which is not to
> say that it is the ideal - but it was surprisingly often better than these
> newer schemes, despite its age of 10+ years... as we all know, there are many
> schemes out there, quite often designed with the goal of removing RED's
> dependence on parameters.

Michael, Naeem:

This is just a follow-up to better understand the ARED results presented at
AQM WG (http://www.ietf.org/proceedings/88/slides/slides-88-iccrg-4.pdf).

Could you please clarify whether the ARED parameters for the tests were set
as specified in the 2001 paper? I.e., when average queueing delay target =
1ms, the min and max thresholds would translate to 0.5ms and 1.5ms, and for
5 ms target the min and max thresh will be 2.5ms and 7.5ms, respectively,
right? Can you confirm?

Assuming ARED logic is intact, ARED drops all packets when average queue
size goes above max_thresh  (max_thresh = 1.5ms or 7.5ms etc.); this would
be semantically similar to a drop tail queue with shallow buffer (can be
confirmed by looking at cumulative packet drops by ARED).

This is probably why the delay values are tight for ARED, and why ARED
translates to poor utilization, especially for the lower target delay
values, as seen in your slides (#8, #11, #13).

Also,  wondering if bursty traffic was considered for evaluations, since
semantics of drop tail with shallow buffering doesn't accommodate bursty
traffic. 

Thanks,
Preethi & Rong