Subject: Re: [PATCH] sch_red: fix red_change

From: Hagen Paul Pfeifer <[email-masked]>
Date: Wed, 7 Dec 2011 23:57:48 +0100

* Ilpo Järvinen | 2011-12-05 13:42:44 [+0200]:

>I disagree. If there's any slow starting flow that alone can fill the 
>bottleneck, anything significantly larger than RTT just harms. RED is 
>just "too slow" if you follow the recommended parametrization..
>
>In a core router you can probably get away with multiple RTTs, but near 
>edge that is a grave mistake due to how slow-start behaves. With average 
>based on many RTTs, RED still estimates that the link has low load while 
>congestion has escalated to higher dimensions due to slow start. As a 
>result, RED graciously falls back to tail-drop once the physical queue 
>runs out and the flows respond allowing the load to decrease. However, 
>finally RED reaches a state where it starts to "pro-actively" react to an 
>"incipient congestion"?!? :-/ => Problem is made worse by those extra 
>drops/marks happening too late.

But then one question Ilpo: drive IW10 or IW14 the behavior even worse?
Especially if n connections start almost simultanously? You did some analysis
on this topic.

HGN