Re: [aqm] CoDel's control law that determines drop frequency

Polina Goltsman <polina.goltsman@student.kit.edu> Wed, 30 September 2015 15:43 UTC

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Date: Wed, 30 Sep 2015 17:43:56 +0200
From: Polina Goltsman <polina.goltsman@student.kit.edu>
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To: Bob Briscoe <ietf@bobbriscoe.net>
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Subject: Re: [aqm] CoDel's control law that determines drop frequency
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Bob,

May I ask how curvy red is supposed to perform in those situations?

If I understand Codel's law correctly, Codel "starts fresh" every time 
it enters dropping state, so when the load increases it will take more 
time for the control law to reach the correct "count" value for the 
queue to drop. Thus with higher load latency is increased.

Now, if I understood your curvey red report correctly, you argued that 
AQM should increase latency when load increases since otherwise it will 
cause too much loss. Which makes Codel's behavior at least justified ...

BTW, I haven't seen any place in the original specification that 
suggested that fixed target delay is the intended design goal.

Does this make any sense?

Regards,
Polina

On 09/30/2015 02:59 PM, Bob Briscoe wrote:
> Polina,
>
> I think this was it:
> <https://www.ietf.org/proceedings/85/slides/slides-85-iccrg-2.pdf>
>
> I have a set of charts from Rong with many more tests showing CoDel's 
> sluggish responsiveness, but I believe the above was the published 
> summary.
>
>
> Bob
>
> On 30/09/15 10:13, Polina Goltsman wrote:
>> Dear Bob,
>>
>> On 09/30/2015 10:50 AM, Bob Briscoe wrote:
>>>
>>> Early on, Rong Pan showed that it takes CoDel ages to bring high 
>>> load under control. I think this linear increase is the reason.
>>
>> Is there a link to this ?
>>
>> Polina
>>
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