[Ecn-sane] rtt-fairness question

[Dave Taht <dave.taht@gmail.com>]

I have managed to drop most of my state regarding the state of various
dctcp-like solutions. At one level it's good to have not been keeping
up, washing my brain clean, as it were. For some reason or another I
went back to the original paper last week, and have been pounding
through this one again:

Analysis of DCTCP: Stability, Convergence, and Fairness

"Instead, we propose subtracting α/2 from the window size for each marked ACK,
resulting in the following simple window update equation:

One result of which I was most proud recently was of demonstrating
perfect rtt fairness in a range of 20ms to 260ms with fq_codel
https://forum.mikrotik.com/viewtopic.php?t=179307 )- and I'm pretty
interested in 2-260ms, but haven't got around to it.

Now, one early result from the sce vs l4s testing I recall was severe
latecomer convergence problems - something like 40s to come into flow
balance - but I can't remember what presentation, paper, or rtt that
was from. ?

Another one has been various claims towards some level of rtt
unfairness being ok, but not the actual ratio, nor (going up to the
paper's proposal above) whether that method had been tried.

My opinion has long been that any form of marking should look more
closely at the observed RTT than any fixed rate reduction method, and
compensate the paced rate to suit. But that's presently just reduced
to an opinion, not having kept up with progress on prague, dctcp-sce,
or bbrv2. As one example of ignorance, are 2 packets still paced back
to back? DRR++ + early marking seems to lead to one packet being
consistently unmarked and the other marked.

-- 
I tried to build a better future, a few times:
https://wayforward.archive.org/?site=https%3A%2F%2Fwww.icei.org

Dave Täht CEO, TekLibre, LLC