[Bloat] Comcast & L4S

[Dave Taht]

https://www.lightreading.com/cable-technology/comcast-wields-low-latency-as-broadband-differentiator


On Fri, Jan 31, 2025 at 4:40 PM David Collier-Brown via Bloat
<bloat at lists.bufferbloat.net> wrote:
>
> What Comcast/L4S is doing was once called, by a Polish colleague,
> "Peeing in the soup, so it smells more like me."
>
> --dave
>
> On 1/31/25 18:57, Dave Taht via Bloat wrote:
> > 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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> >
> >
> --
> David Collier-Brown,         | Always do right. This will gratify
> System Programmer and Author | some people and astonish the rest
> davecb at spamcop.net           |              -- Mark Twain
>
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-- 
Dave Täht CSO, LibreQos