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

"Rong Pan (ropan)" <ropan@cisco.com> Fri, 26 May 2017 18:30 UTC

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From: "Rong Pan (ropan)" <ropan@cisco.com>
To: Bob Briscoe <ietf@bobbriscoe.net>, Michael Menth <menth@uni-tuebingen.de>
CC: tsvwg IETF list <tsvwg@ietf.org>, AQM IETF list <aqm@ietf.org>
Thread-Topic: [aqm] Questioning each PIE heuristic - moving averages and rate measurement
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Date: Fri, 26 May 2017 18:29:57 +0000
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References: <9ddba389-e368-9050-3b14-aa235c99fcb8@bobbriscoe.net> <D4FDD717.2636D%ropan@cisco.com> <77D4FC66-C99F-49D0-BB73-27A0CEF70F31@gmail.com> <99a7b737-fc3c-efd0-b6c8-d71a089b7de8@bobbriscoe.net> <FB0F3D38-63E2-441E-BAB4-2541D7E9FE94@gmail.com> <471e91b1-c469-3d36-9af1-0411e5661286@uni-tuebingen.de> <abadc87c-49f2-46e2-ae43-0853ac81e794@bobbriscoe.net> <da895a48-6b9c-c67f-1f52-d9eb52844ad6@uni-tuebingen.de> <404874be-32a9-4425-b2ff-5fbff804b5ee@bobbriscoe.net>
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Subject: Re: [aqm] Questioning each PIE heuristic - moving averages and rate measurement
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Michael and Bob,

The depart_rate is inversed in calculation delay….
Delay = queue_length/depart_rate; 
Hence, current_qdelay = queue_.byte_length() * PIE- >avg_dq_time_/DQ_THRESHOLD;

Basically the average dq_time for dequeueing DQ_THRESHOLD is PIE->dq_time; What is the approximate time to deque the current_qlen?
Current_qlen/DQ_THRESHOLD(what portion is current queue length relative to DQ_THRESHOLD)? * avg_dq_time.

That is the rationale behind it.

Thanks,

Rong

    >> (EWMA) of the rate should be:
    >>
    >>      ewma(depart_rate) = DQ_THRESHOLD ∗ ewma(1/t1,1/t2,1/t3,...)
    >>                       != DQ_THRESHOLD / ewma(t1,t2,t3,...)
    >> "
    >> PIE uses the second (incorrect) formula. In the review, I discuss how
    >> wrong this could be, with an example.
    > Thanks, Bob, for pointing this out to me.
    >
    > Rong, is PIE doing this by intent (if so, what's the reason?) or is this
    > a flaw?
    >