[Cake] Fwd: [bbr-dev] BBR v2 ECN

Dave Taht dave.taht at gmail.com
Tue May 28 11:51:03 EDT 2019

At least there will be a testable version of a L4S compliant BBRv2
before it goes upstream. (see below)

I fear for what this will do to every inbound shaper in the world.
(and also network namespaces, the fq_codel for wifi stuff, and the
entire fq_codel deployment in general).

All along (regardless of the SCE idea) I'd hoped for a simple,
conservative rfc3168 compliant response in BBR to CE markings, and I
didn't like how much BBR ignores packet loss as a signal in the first
place. I thought, when the end users are desperately inbound shaping
to keep their networks usable for all traffic, explicit signalling
from that existing userbase with that expectation for a reasonable
response seemed so reasonable...

/me logs out for the day

---------- Forwarded message ---------
From: 'Neal Cardwell' via BBR Development <bbr-dev at googlegroups.com>
Date: Tue, May 28, 2019 at 7:11 AM
Subject: Re: [bbr-dev] BBR v2 ECN
To: Ingemar Johansson <info at ijdata.com>
Cc: BBR Development <bbr-dev at googlegroups.com>

On Tue, May 28, 2019 at 8:35 AM Ingemar Johansson <info at ijdata.com> wrote:
> Hi
> Looking through the v5.2-rc2 code I can see that a parameter 'delivered_ce' is defined in tcp_sock but other than that I don't see any evidence for the support of ECN (L4S) in BBRv2. Do you still plan to include L4S support for BBRv2 ?

Hi Ingemar,

Yes, we still plan on including L4S support for BBRv2.

BBRv2 is not upstream in the Linux TCP code base yet. We are working
on getting the code ready for a pre-release/RFC version that we plan
on posting at:

But indeed tp->delivered and tp->delivered_ce are part of the
infrastructure inside the Linux TCP stack that BBRv2 makes use of.


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

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