Re: [tsvwg] "Pacing" requirement is lost in L4S

[Neal Cardwell <[e-mail]>]

On Thu, Apr 25, 2024 at 2:52 AM Saverio Mascolo <[e-mail]>
wrote:

> Why there no exists a readable description of bbr in a single updated doc?
>

Have you tried the Internet Draft version?

https://datatracker.ietf.org/doc/html/draft-cardwell-iccrg-bbr-congestion-control

Comments welcome!

thanks,
neal




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>
> Il giorno ven 19 apr 2024 alle 16:33 Christian Huitema <
> [e-mail]> ha scritto:
>
>>
>>
>> On 4/19/2024 7:24 AM, Neal Cardwell wrote:
>> > On Fri, Apr 19, 2024 at 4:39 AM Vasilenko Eduard <vasilenko.eduard=
>> > [e-mail]> wrote:
>> >
>> >> Hi Experts,
>> >> I see L4S as the "Congestion Control Next Generation from IETF" (that
>> is
>> >> actually in competition with "Congestion Control Next Generation from
>> >> Google").
>> >>
>> > IMHO BBR is not in competition with L4S.
>> >
>> > BBR is, at its core, about maintaining an explicit model of the network
>> > path using whatever signals are available, and using that model to try
>> to
>> > achieve low/bounded delay, low loss, and high throughput.
>> >
>> > L4S, IMHO, is largely about creating a low-latency, low-loss, scalable
>> > throughput service model (metaphorically a "lane") in Internet
>> bottlenecks,
>> > and using ECN to provide a signal to achieve that.
>> >
>> > There is nothing fundamentally at odds about those two models. And once
>> the
>> > details of the Prague congestion control algorithm are finalized, one
>> goal
>> > (as our team has mentioned for a number of years) is to have a version
>> of
>> > BBR that can use L4S signals and coexist with Prague congestion control
>> in
>> > the L4S lane of Internet bottlenecks.
>>
>> I have done simulations of what happens if QUIC and BBR are used
>> end-to-end, and the bottleneck implements an L4S like ECN marking
>> strategy. My implementation of BBRv3 was modified to monitor the ECN
>> marking rate, and treat excess numbers as a congestion signal, in
>> parallel with other signals such as RTT or delivery rate. Bottom line,
>> it works exactly as expected.
>>
>> Which is good news, because it means we can deploy L4S gradually, use it
>> as a congestion signal if it is deployed on the path, use the other
>> congestion signals if ECN is not deployed yet.
>>
>> -- Christian Huitema
>>
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