Re: [Cerowrt-devel] [Cerowrt-users] QOS settings vs speedboost and random bandwidth

[Jim Gettys <jg@freedesktop.org>]

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On Mon, Nov 26, 2012 at 3:32 AM, Dave Taht <dave.taht@gmail.com> wrote:

> there are not presently a lot of cerowrt-users members, so I'm cc-ing
> cerowrt-devel.
>
> On Mon, Nov 26, 2012 at 12:20 AM, Marc MERLIN <marc@merlins.org> wrote:
> > I'm setting up QOS as explained in the FAQ
> > http://www.bufferbloat.net/projects/cerowrt/wiki/FAQ
>
>
> >
> > Not surprisingly
> > speednest.net
>
> gives me 33Mbit/7.65Mbit while dslreports.com/speedtest
>
> gives
> > me a meager 16.2Mbit/2.5Mbit (for a line that's supposed to be
> 22Mbit/5Mbit).
>
> Yes, you get a boost for about 10 seconds.
>
> > I understand the queuing and that if I put too high a number, I'll fill
> > queues and end up with bad latency.
>
> yep.
>
> >
> > At the same time, am I correct that if I put numbers that are lower than
> > what I can really get when the line doesn't suck, I'll cap myself to
> those
> > numbers (here 16.2Mbit instead of 22Mbit or so)?
>
>
> yep.
>
> >
> > Is it also possible for linux/cerowrt to dynmically detect the
> queuing/delay
> > in my cable modem and dynamically adjust the QOS values to limit
> buffering
> > on the comcast side without throttling me down to lower than what the
> line
> > can do at any given time?
>
> Nope. The right answer is to not have to rate shape in the router, but
> to move the fq_codel algorithm into the cable modem, OR to have the
> cable modem exert flow control like ADSL modems do. Then have the
> smarter device (the router) then do smarter queuing.
>
> There are other dynamic bandwidth effects on a cable network that
> result in more widely varying backend bandwidth.
>

Yes, and under conditions of overall network congestion, if you are using
your link at a high fraction (> 80% or so, IIRC), they may also take some
action after an extended period (something like 10-15 minutes), as part of
their protocol neutral congestion management system.

There are also physical effects (temperature) that can cause some bandwidth
variation.


>
> A little birdie tells me that the cable modem guys are on this...
> speedboost is a good idea but the only way to not lose it is to move
> the smarts around.
>

Yup.  It's a good feature and it's sad to have to defeat it (unless someone
does a Powerboost emulator).

>
> That said, it does seem possible to develop a speedboost emulator on
> the router that would give you most of the benefit.
>

The details of at least Comcast's "Powerboost" may be documented in the RFC
published describing their provisioning.   I don't have the RFC handy.  I
think the algorithm they use is described there, even if the exact
parameters for a particular provisioning tier is not...

>
>
> >
> > I'm also a bit concerned of what happens when comcasts ups my bandwidth
> > without telling me (they do that sometimes) and me never finding out if I
> > have a static QOS value in cerowrt.
>

They certainly tell you in the advertising spam that we all delete ;-(.
                         - Jim


> >
> > Can others advise?
> >
> > Thanks,
> > Marc
> > --
> > "A mouse is a device used to point at the xterm you want to type in" -
> A.S.R.
> > Microsoft is to operating systems ....
> >                                       .... what McDonalds is to gourmet
> cooking
> > Home page: http://marc.merlins.org/
>
>
> > _______________________________________________
> > Cerowrt-users mailing list
> > Cerowrt-users@lists.bufferbloat.net
> > https://lists.bufferbloat.net/listinfo/cerowrt-users
>
>
>
>
>
> --
> Dave Täht
>
> Fixing bufferbloat with cerowrt:
> http://www.teklibre.com/cerowrt/subscribe.html
>
>
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> https://lists.bufferbloat.net/listinfo/cerowrt-devel
>
>
>

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