[tsvwg] Related to "Non-L4S traffic abusing the L-queue" discussion during the interim

["De Schepper, Koen (Nokia - BE/Antwerp)" <[e-mail]>]

Hi Jonathan,

It seems that the following open issue identified by the chairs:

Non-L4S traffic abusing the L-queue
* 'DualQ gives a large throughput bonus to L queue traffic, ie. a "fast lane"'
* Is this a matter specific for DualQ that can be left for experimentation?

is based on the following experiment you performed:


>             simple two-flow competition test on a standard dumbbell topology,

>             with the bottleneck running a DualQ qdisc into a 50Mbps shaper.

>             Both flows were configured to use CUBIC congestion control with

>             ECN negotiated, but one was additionally tweaked to set ECT(1)

>             instead of ECT(0) on all data segments, and to pace its output at

>             40Mbps. This latter measure prevents the L queue from seeing any

>             need to apply congestion signals, because it is always empty.  These

>             tweaks allowed that flow to use 80% of the link capacity, gaining a

>             fourfold advantage over its competitor,

If there is capacity seeking traffic in the Classic queue, then it is even desired that the L4S queue does not add extra marks. The L4S marks should come only from the Classic coupling.
Before diving into details, can you first explain why in your experiment the coupling from the Classic Q has no effect on your paced and ECT(1) labeled Cubic flow?

I would expect that this ECT(1) labeled Cubic flow would get even less throughput than the Classic Cubic flow, as the first gets the doubled coupled CE marking probability (eg 2*10% = 20%) for L4S flows instead of the squared CE marking probability (10%^2 = 1%) which ECT(0) traffic would get.

Thanks,
Koen.