Re: [aqm] Questioning each PIE heuristic - moving averages and rate measurement

Michael Menth <menth@uni-tuebingen.de> Thu, 30 March 2017 09:57 UTC

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To: Jonathan Morton <chromatix99@gmail.com>, Bob Briscoe <ietf@bobbriscoe.net>
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From: Michael Menth <menth@uni-tuebingen.de>
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Date: Thu, 30 Mar 2017 11:57:10 +0200
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Subject: Re: [aqm] Questioning each PIE heuristic - moving averages and rate measurement
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Hi all,

Am 30.03.2017 um 11:08 schrieb Jonathan Morton:
> 
>> On 30 Mar, 2017, at 10:46, Bob Briscoe <ietf@bobbriscoe.net> wrote:
>>
>> For PI2 we removed all but 2 and it worked the same or better than PIE in all our tests. I have been assessing each of the other 7 one by one for reinstatement. So far I've rejected 6. I think I can reject this last one by making the sampling time of the base PI algo dependent on the max link rate. Then when the queue goes idle, the base PI algo will decay drop down to zero no slower than the queue drains, without needing this extra heuristic.
> 
> That’s fair enough.
> 
> It sounds like the fairly coarsely discrete time intervals in PIE are the main justification for this particular heuristic, so it might be sufficient to document that WRT PIE itself.  Using finer time intervals is clearly a better choice for the future.
PIE uses time intervals for measurement purposes and several parameters
contribute. We've recently done some basic work on measurement
methodology that facilitates a comparison of different measurement
approaches and better-informed parametrization by introduction of the
"memory" concept.
https://atlas.informatik.uni-tuebingen.de/~menth/papers/Menth17c.pdf
PIE essentially implements TDRM-DTWMA-UEMA illustrated in Fig. 6d.

The concept of "memory" can also be applied to moving averages which are
also used in PIE for several purposes. Configuration via a "memory" can
make some heuristics more intuitive.

Best wishes,

Michael



> 
>  - Jonathan Morton
> 

-- 
Prof. Dr. habil. Michael Menth
University of Tuebingen
Faculty of Science
Department of Computer Science
Chair of Communication Networks
Sand 13, 72076 Tuebingen, Germany
phone: (+49)-7071/29-70505
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mailto:menth@uni-tuebingen.de
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