[Cerowrt-devel] SQM Question #5: Link Layer Adaptation Overheads

Tue Jan 7 03:08:27 PST 2014

I'm in the US, but live in a relatively rural area. My only internet
options are DSL and satellite. The local provider is Century Link (it used
to be Sprint, but they sold their copper phone business off). I have the
fastest service that they offer (based on distance from the DSLAM), 4 down
/ .5 up.

I have had SmokePing monitoring my latency to the first hop outside my
network for over a year now (I've been on CeroWRT the whole time). My
baseline (no load) latency is 31ms. I used to have AQM throttling back to
80% of my already pathetic bandwidth. I would still regularly see periods
lasting minutes to hours when latency would be 80 - 120ms.

I only recently grokked what you were talking about with tc_stab since I
got back from the holidays with the family, I set things up as you
suggested for Fred (nfq_codel, "target 25ms" in advanced egress, ATM, per
packet overhead 40, and set my SQM bandwidth limits to 95%). Since the 30th
my "worst case" latency has been 41ms. Plus I get to use more of my actual
bandwidth. I REALLY wish that I'd made the time to read your emails about
setting up the ATM overhead earlier.

Thank you.

-- 
David P.

On Mon, Jan 6, 2014 at 9:27 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:

> Hi Fred,
>
>
> On Jan 6, 2014, at 15:22 , Fred Stratton <fredstratton at imap.cc> wrote:
>
> > The line rate is 11744/1022 kb/s, but changes moment to moment. SNR is
> 12.1 decibel.  I am using 11000/950 kb/s as settings.
>
>         So 100 * 11000 / 11744 = 93.66% of downlink line rate and 100* 950
> / 1022 = 92.95 % of uplink line rate; quite impressive given the common
> wisdom of 85% :).
>
>
> >  I shall try your suggestion when there is something worth watching
> live, to provide a valid comparison, which may not be before 21:30 CET on
> Sunday.
>
>         Oh, take your time, this is really not essential, butit would be a
> nice data point for figuring out how important the correct overhead
> estimate really is in real life, theory being theory and all…
>
> Best Regards
>         Sebastian
>
> >
> > On 06/01/14 14:12, Sebastian Moeller wrote:
> >> Hi Fred,
> >>
> >>
> >> On Jan 6, 2014, at 10:52 , Fred Stratton <fredstratton at imap.cc> wrote:
> >>
> >>> I have been operating the latest build with 6relayd disabled. The
> henet /48 I have been allocated is subnetted correctly, presumably by
> dnsmasq.
> >>>
> >>> I adopted the suggestions to use nfq_codel and an egress target of
> 25ms , with an overhead of 40 on a PPPoE connection.  I chose to watch the
> first 2 episodes of the 3 part third series of 'Sherlock', live on iPlayer,
> and these streamed correctly and uninterrupted for 90 minutes.  This was
> not previously possible.  (Quite whether they were up to the standard of
> previous episodes is another matter.)
> >>>
> >>> I can watch iPlayer with little stutter whilst downloading Arch Linux
> by torrent, downloading other files at the same time.
> >>>
> >>> So, for a relatively slow ADSL2+ line, the current build works well.
> >>      Out of curiosity, to what percentage of the "current line rate"
> (you know the one reported by your modem) you shaped up- and downlink? And
> in case you have too much time on your hand, how does the same feel with an
> overhead of 10 (to see how bad an overhead underestimate would feel for a
> user), since you currently happen to have a quite sensitive subjective
> latency evaluation system set up :)…
> >>
> >> Best Regards
> >>      Sebastian
> >>
> >>>
> >>> On 06/01/14 03:29, Dave Taht wrote:
> >>>> On Sat, Jan 4, 2014 at 10:40 AM, Fred Stratton <fredstratton at imap.cc>
> wrote:
> >>>>> Link Names:
> >>>>>
> >>>>> For consistency, if ADSL is used as a portmanteau term, them VDSL
> should be
> >>>>> used as the equivalent for VDSL and VDSL2.
> >>>>>
> >>>>> CeroWRT has to decide whether it is an experimental build, or
> something that
> >>>>> will eventually be used in production, so these decisions can be made
> >>>>> consistently.
> >>>> Well, what I was aiming for was for us to get the sqm scripts and gui
> >>>> up to where they were better than the standard openwrt qos scripts and
> >>>> then push them up to openwrt to where they could be more widely
> >>>> deployed.
> >>>>
> >>>> Aside from being able to dynamically assign priorities in the gui, we
> >>>> are there.  Except that nfq_codel is currently getting better results
> >>>> than fq_codel at low bandwidths, and I'm tempted to pour all of
> >>>> simple.qos into C.
> >>>>
> >>>> As for cero's future - certainly since all the snowden revelations
> >>>> I've been going around saying that "friends don't let friends run
> >>>> factory firmware". I would like a stable build of sqm and cerowrt to
> >>>> emerge, and to then go off and work on improving wifi. Regrettably
> >>>> what seems to be happening is more backwards than forwards on the
> >>>> former, and ramping up on the ath9k and ath10k is taking more time
> >>>> than I'd like, and it seems likely I'll be working on those primarily
> >>>> on another platform and only eventually pushing the results out to
> >>>> cero, mainline kernel
> >>>>
> >>>> So it's still at the "keep plugging away" point for sqm, ipv6, cero in
> >>>> general, with the stable release always just out of sight.
> >>>>
> >>>> Tackling the ipv6 problem is next on my agenda on cero, and getting a
> >>>> test suite going is next on my day job.
> >>>>
> >>>>> I concur with your ADSL setup suggestion as default. I have been
> running the
> >>>>> Sebastian Moeller ping script overnight to calculate ADSL overhead
> for the
> >>>>> last several days. After several hours of curve fitting using
> Octave, an
> >>>>> overhead result is displayed. This novel approach works well.
> >>>> It would be nice to get to where we could autoconfigure a router using
> >>>> tools like these with no human intervention. This includes bandwidth
> >>>> estimation.
> >>>>
> >>>>> The overhead for the particular setup I use was 40 for PPPoE, and 10
> for
> >>>>> PPPoA.
> >>>>>
> >>>>> The default you suggest is a suitable starting point, I suggest.
> >>>>>
> >>>>>
> >>>>> On 04/01/14 18:16, Rich Brown wrote:
> >>>>>> QUESTION #5: I still don’t have any great answers for the Link Layer
> >>>>>> Adaptation overhead descriptions and recommendations. In an earlier
> message,
> >>>>>> (see
> >>>>>>
> https://lists.bufferbloat.net/pipermail/cerowrt-devel/2013-December/001914.html
> >>>>>> and following messages), Fred Stratton described the overheads
> carried by
> >>>>>> various options, and Sebastian Moeller also gave some useful advice.
> >>>>>>
> >>>>>> After looking at the options, I despair of giving people a clear
> >>>>>> recommendation that would be optimal for their equipment.
> Consequently, I
> >>>>>> believe the best we can do is come up with “good enough”
> recommendations
> >>>>>> that are not wrong, and still give decent performance.
> >>>>>>
> >>>>>> In this spirit, I have changed Draft #3 of the “Setting up SQM”
> page to
> >>>>>> reflect this understanding. See
> >>>>>>
> http://www.bufferbloat.net/projects/cerowrt/wiki/Setting_up_AQM_for_CeroWrt_310
> >>>>>>
> >>>>>>         ADSL/ATM link: Choose “ADSL/ATM", and set Per Packet
> Overhead to
> >>>>>> 40
> >>>>>>         VDSL2 link: Choose “VDSL”, and set Per Packet Overhead to 8
> >>>>>>         Other kind of link (e.g., Cable, Fiber, Ethernet, other not
> >>>>>> listed): Choose “None (default)”, and set Per Packet Overhead to 0
> >>>>>>
> >>>>>> NB: I have changed the first menu choice to “ADSL/ATM” and the
> second to
> >>>>>> “VDSL” in the description. I would ask that we change to GUI to
> reflect
> >>>>>> those names as well. This makes it far easier/less confusing to
> talk about
> >>>>>> the options.
> >>>>>>
> >>>>>> As always, I welcome help in setting out clear recommendations that
> work
> >>>>>> well for the vast majority of people who try CeroWrt. Thanks.
> >>>>>>
> >>>>>> Rich
> >>>>>> _______________________________________________
> >>>>>> Cerowrt-devel mailing list
> >>>>>> Cerowrt-devel at lists.bufferbloat.net
> >>>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >>>>> _______________________________________________
> >>>>> Cerowrt-devel mailing list
> >>>>> Cerowrt-devel at lists.bufferbloat.net
> >>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >>>>
> >>> _______________________________________________
> >>> Cerowrt-devel mailing list
> >>> Cerowrt-devel at lists.bufferbloat.net
> >>> https://lists.bufferbloat.net/listinfo/cerowrt-devel
> >
>
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