[Bloat] [iccrg] Fwd: [tcpPrague] Implementation and experimentation of TCP Prague/L4S hackaton at IETF104

Dave Taht dave.taht at gmail.com
Fri Mar 15 06:46:28 EDT 2019

Bufferbloat.net's ecn-sane working group members have a co-ordinated
response to your efforts brewing but it's not ready yet. We have a
worldwide team of linux and freebsd developers co-ordinating on landing
code for our competing proposal "Some Congestion Experienced", which we
submitted to tsvwg last sunday.

That draft is under continuous revision, here:


Our Linux and FreeBSD team is also flying into prague for SCE presentations
at netdevconf and ietf.

Some background to this: after the L4S/TCP Prague/and dualpi experiments
appeared stalled out indefinitely in the IETF, and with our own frustration
with IETF processes, bufferbloat.net project members publicly formed our
own working group to look into the problems with ecn, back in august of
last year.

Its charter is here: https://www.bufferbloat.net/projects/ecn-sane/wiki/

We were unaware, until last month, that the cable industry had 16 months
back gone and formed its own private working group also, and was intending
to turn the tcp prague/l4s/dualpi IETF "experiments" into an actual DOCSIS

Our SCE proposal appears to be backward compatible with the existing
10s-100s of millions of ecn-enabled fq_codel[1] and sch_cake[2]
deployments, and doesn't require any changes to any RFC3168 tcps (or any
tcp-friendly congestion control) at all in order to basically work.
tcp-prague is subtly incompatible with that, and dualpi, more so. Our
proposal is different also, it proposes some receiver side changes in order
to get the full benefit of SCE while remaining backward compatible with the
existing meaning of the CE codepoint.

In either case, either approach essentially permanently redefines the ECT_1
codepoint incompatibly, once and for all, and for all time. This is a final
battle over the meaning of a single bit in IP, and I expect the debates to
be as difficult as the ones described in
https://www.ietf.org/rfc/ien/ien137.txt - I would really, really, really
prefer that they stay technical and not veer into politics, but I have
little hope for that.

The members of the ecn-sane working group are delighted to finally hear
that running code for tcp-prague might land this ietf, and look forward to
finally testing the whole l4s/tcpprague/dualpi architecture in conjunction
with the flent.org 's and irtt's exhaustive suite of tests and servers in
the cloud in the coming months, both against our existing, deployed,
fq_codel, fq_pie, cake and pie derived solutions and our new SCE proposal.
We hope to finally be able to write new tests for flent in particular, that
can show tcpprague off in the ways that are important to those developing
it. Flent has some basic dctcp tests, but nothing that can get down below a
20ms sample rate on modern hardware. (currently. It's easy to add tests,
flent is written in python)

We also hope that more test tools and implementations in ns2 and ns3 show
up for tcpprauge  and dualpi show up soon also, from members of those

Note: sunday's dual-pi linux submission was kicked back from the linux
networking developers due to some technical and legal problems with linux
net-next HEAD ( https://patchwork.ozlabs.org/patch/1054521/  ) , and I do
hope that a corrected version lands soon, so we can safely test it with
current versions of OpenWrt, etc.

Finally, running code. Will we find consensus?


[1] https://tools.ietf.org/html/rfc8290
[2] sch_cake was available for 3 years out of tree and was mainlined last
august, in linux 4.19. It is partially described by "Piece of CAKE: A
Comprehensive Queue Management Solution for Home Gateways" "

A second paper describing its fq_codel-derived "cobalt" AQM algorithm is
awaiting publication in a peer reviewed journal. It has been part of
openwrt and the related sqm-scripts for many years and is widely deployed
on multiple commercial products, such as those from eero and evenroute.

Cake has a docsis specific mode which we longed for cablelabs to evaluate.

On Fri, Mar 15, 2019 at 2:33 AM Bob Briscoe <ietf at bobbriscoe.net> wrote:

> Forwarding to tcpm & iccrg - apologies if you were already on one of the
> lists that received this.
> Olivier has been working hard on integrating the pieces of a Linux
> implementation of TCP Prague, and is close to having a version ported
> against the tip of the Linux mainline tree. This is his request for more
> people to get involved.
> Bob
> -------- Forwarded Message --------
> Subject: [tcpPrague] Implementation and experimentation of TCP Prague/L4S
> hackaton at IETF104
> Date: Wed, 6 Mar 2019 10:26:05 +0000
> From: Tilmans, Olivier (Nokia - BE/Antwerp)
> <olivier.tilmans at nokia-bell-labs.com>
> <olivier.tilmans at nokia-bell-labs.com>
> To: hackathon at ietf.org <hackathon at ietf.org> <hackathon at ietf.org>,
> tcpprague at ietf.org <tcpprague at ietf.org> <tcpprague at ietf.org>
> CC: dlebrun at google.com <dlebrun at google.com> <dlebrun at google.com>, Joakim
> Misund <joakim.misund at gmail.com> <joakim.misund at gmail.com>, Bob Briscoe
> <research at bobbriscoe.net> <research at bobbriscoe.net>, Quentin De Coninck
> <quentin.deconinck at uclouvain.be> <quentin.deconinck at uclouvain.be>,
> François Michel <francois.michel at uclouvain.be>
> <francois.michel at uclouvain.be>, Mirja Kuehlewind
> <mirja.kuehlewind at tik.ee.ethz.ch> <mirja.kuehlewind at tik.ee.ethz.ch>,
> Maxime Piraux <maxime.piraux at uclouvain.be> <maxime.piraux at uclouvain.be>,
> Olga Albisser <olga at albisser.org> <olga at albisser.org>, Fabien Duchêne
> <fabien.duchene at uclouvain.be> <fabien.duchene at uclouvain.be>, De Schepper,
> Koen (Nokia - BE/Antwerp) <koen.de_schepper at nokia-bell-labs.com>
> <koen.de_schepper at nokia-bell-labs.com>
> Hi all,
> We'll be working on the "TCP Prague" congestion control/L4S architecture
> during the IETF-104 hackaton.
> This topics aims at accelerating the work that started during the IETF93
> (coincidentally also in Prague), in order to get TCP Prague to an 'usable'
> state—i.e., meet the safety requirements and have supporting materials
> (e.g., VMs, labs) to let people experiment with it. Depending on people's
> interest, prototyping something similar for QUIC is another possible output.
> Details and links to resources/supporting drafts are available at
> https://trac.ietf.org/trac/ietf/meeting/wiki/104hackathon#tcp-prague and
> copied below.
> Additionally, few topics will presented during netdev 0x13 the week before.
> See you in Prague.
> Best,
> Olivier
> Implementation and experimentation of TCP Prague/L4S
> * Champion
> * Olivier Tilmans <olivier.tilmans at nokia-bell-labs.com>
> * Projects
> * Prototype the "TCP Prague" congestion control on Linux
> * Finalize the implementation of accurate ECN (draft conformance), and
> port it on Linux v5.x * Build tooling around L4S to let people experiment
> with the technology (e.g., virtual machine, or mininet labs)
> * Work towards "QUIC Prague"
> * Resources
> * TCP Prague
> * Repository — ​https://github.com/L4STeam/tcp-prague
> * Requirements — ​
> https://tools.ietf.org/html/draft-ietf-tsvwg-ecn-l4s-id-05#page-21
> * Upcoming netdev talk —
> https://netdevconf.org/0x13/session.html?talk-tcp-prague-l4s
> * Accurate ECN
> * Specs — ​https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-07
> * Implementation for Linux v4.17 — ​https://github.com/mirjak/linux-accecn
> * Past netdev talk —
> https://www.netdevconf.org/2.2/session.html?kuhlewind-accecn-talk
> * Paced Chirping * Repository — ​
> https://github.com/JoakimMisund/PacedChirping
> * Upcoming netdev talk —
> https://netdevconf.org/0x13/session.html?talk-chirp
> * L4S architecture
> * Specs — ​https://tools.ietf.org/html/draft-ietf-tsvwg-l4s-arch-03
> * DualPI2 AQM
> * Specs — ​
> https://tools.ietf.org/html/draft-ietf-tsvwg-aqm-dualq-coupled-08
> * Repository — ​https://github.com/L4STeam/sch_dualpi2_upstream
> * Upcoming netdev talk —
> https://netdevconf.org/0x13/session.html?talk-DUALPI2-AQM
> * RITE Project — ​https://riteproject.eu/dctth/#code
> _______________________________________________
> tcpPrague mailing list
> tcpPrague at ietf.org
> https://www.ietf.org/mailman/listinfo/tcpprague
> _______________________________________________
> iccrg mailing list
> iccrg at irtf.org
> https://www.irtf.org/mailman/listinfo/iccrg


Dave Täht
CTO, TekLibre, LLC
Tel: 1-831-205-9740
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