[Cake] A few puzzling Cake results

Jonathan Morton chromatix99 at gmail.com
Thu Apr 19 05:32:35 EDT 2018

> If you turn off the AQM entirely for the
> first four packets, it is going to activate when the fifth packet
> arrives, resulting in a tail loss and... an RTO!

That isn't what happens.

First of all, Cake explicitly guards against tail loss by exempting the last packet in each queue from being dropped.  If a tail loss and RTO actually occurs, it's extremely unlikely that Cake caused it, unless it's been driven far beyond its design load in terms of flow count.

Secondly, and as you should very well know, Codel only starts marking or dropping when the *standing* queue exceeds the threshold set.  COBALT implements that logic in a different way to the reference version, but it's still there.  It's not a case of the fifth packet in a flow getting dropped, but of a five-packet standing queue being the smallest that *can* experience drops.

So please don't strawman this.

 - Jonathan Morton

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