[Bloat] Comcast & L4S

[Dave Taht]

Here are the positives:

For the first time, a major ISP has deployed the PIE AQM on all
traffic. Before now Comcast was only doing that on the upstream.
That´s 99.99% of all current comcast traffic getting an AQM on it. WIN.

The L4S side being enabled will also result in some applications
actually trying to use it for cloud gaming. There is a partnership
with valve,
meta, and apple, that implies that we will perhaps see some VR and AR
applications trying to use it. I look forward to a killer app.

Negatives include explicit marking and potential DOS vectors as often
discussed.  I do feel that in order to keep up with the jonesies,
we will have to add optional l4s marking to CAKE, which should
outperform pie (mark-head), I just wish I knew what the right
level was - at 100Mbit it seemed at 2ms was best. We also need to
remove classic RFC3168 style marking and drop instead when the L4S bit
is present - across the entire linux and BSD ecosystem.

There was an abortive attempt last year to get dualpi, accecn, and
prague into mainstream linux, but it stumbled over GSO handing, and
has not been resubmitted. ACCECN seems to be making some progress.
This makes it really hard to fool with this stuff.








On Fri, Jan 31, 2025 at 5:27 AM Sebastian Moeller via Bloat
<bloat at lists.bufferbloat.net> wrote:
>
> Hi Rich,
>
>
> > On 31. Jan 2025, at 14:20, Rich Brown via Bloat <bloat at lists.bufferbloat.net> wrote:
> >
> > Google Alerts sent me this: https://www.webpronews.com/comcasts-latency-leap-a-game-changer-in-network-performance/
> >
> > Key quote: "Compatibility and Ecosystem: For L4S to have a significant impact, it requires an ecosystem where both the network infrastructure and the end-user devices support the standard..."
> >
> > Can anyone spell "boil the ocean"? :-)
> >
> > Or am I missing someting?
>
> Well, the whole safety mechanisms in L4$ are laughably inadequate... this "design" essentially exposes a priority scheduler* without meaningful admission control to the open internet. This is so optimistically naive that it almost is funny again. I wish all the effort and hard work to make L4$ happen, would have been put in a reasonable design... but at least I learned one of the IETF's failure modes, and that is at least something valuable ;)
>
>
> *) Just because something is not a strict preempting priority scheduler does not make it a good idea to expose it blindly... a conditional priority scheduler with e.g. L4$'  weight share of 10:1 already can do a lot of harm.
>
>
> >
> >
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>
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-- 
Dave Täht CSO, LibreQos