[Bloat] less than best effort: TCP - flexis - A New Approach To Incipient Congestion Detection and Control

[Dave Taht]

On Tue, Apr 5, 2022 at 8:44 AM Qian Li <biz.tinalee at gmail.com> wrote:
>
> Dear Dave,
>
> Thank you for your interest in my work.
>
> I have read another paper authored by D. Rossi at el. presenting the priority inversion problem of LEDBAT when it is used together with AQM. And it has become one of the factors that motivated me to devise a new LBE CC that can preserve low priority even when AQM is used.

We'd given up hope circa 2014 as of the publication of the paper I
cited, and moved on.

>However, I could not test FlexiS with CoDel on the CORE emulator probably because CoDel drops packets at the dequeue time.

I don't really understand that statement.

> More tests should be done to verify that FlexiS does preserve low priority in the presence of various AQM algorithms.

Yes. until fairly recently I had had a testbed setup that allowed
testing of various tcps and aqm systems, but its been in storage since
covid.

> I am now adapting FlexiS to the receiver side. The main motivation to do so is that there might be HTTP/TCP proxies between the sender and the receiver. A receiver side LBE CC and make the connection between the proxy and the receiver LBE. In this work, I am going to tackle some open issues with FlexiS. For example, I am going to test if trend analysis can be done based on one way delay so that the throughput is less affected by ack path congestion. And I am going to evaluate various techniques to reduce rate below 2 mss per RTT. This may include what you have suggested -- use small packets and sub-packet window. I am also interested in using pacing to slow down sending rate and maybe more alternative solutions.

Cool!

>
> I don't have a git tree for the source code mainly because I don't know if I am allowed to publish the code as open source. If you are interested in the source code, I can ask the University of Oslo if I am allowed to distribute it freely?

I would hope they would allow publication. The world is full of half
baked projects that if only someones new also stepped in, were
completed. An example of this is BBR which originally was about half
what it is today, until source was released among the right people.

>
> Best regards,
> Qian
>
>
>
> On Sun, Apr 3, 2022 at 6:38 AM Dave Taht <dave.taht at gmail.com> wrote:
>>
>> Dear Qian:
>>
>> Pretty promising paper. I liked that it tackled congestion on the ack
>> path, among other things.
>>
>> https://www.techrxiv.org/articles/preprint/TCP_FlexiS_A_New_Approach_To_Incipient_Congestion_Detection_and_Control/19077161/1/files/33905018.pdf
>>
>> I like also that you tackled, inter-rtt fairness, and, ledbat's
>> latecomer advantage problem, and in fig 9, the basic problem with
>> delay based LBE vs AQMs (in that ledbat degrades to reno)... [1]
>>
>> Towards your conclusion...
>>
>> I have always disagreed with the "don't reduce segment size" crowd,
>> btw. If you have a rate where you need to go below 2mss, it doesn't
>> hurt the network to reduce the size of the packet, and you can keep
>> the signal strength up by reducing that size and continuing to sample
>> rtt, to respond quickly.
>>
>> Even if you are only passing a single byte of data, by lowering this
>> below everyone else's 2mss noise floor, you still eventually win, and
>> also you occupy space in packet fifos, reducing overall latency, as
>> bytes=time. IMHO.
>>
>> elsewhere, sub-packet windows are being experimented in bbrv2, I'm
>> told, but not in LBE.
>>
>> I'm also a big believer in packet pacing, and I think this is the
>> first paper I've seen that attempted LBE with it. Thx!
>>
>> Got a git tree?
>>
>> [1] do wish you'd had cited
>> https://perso.telecom-paristech.fr/drossi/paper/rossi14comnet-b.pdf
>>
>> --
>> 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



-- 
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