Re: Throughput riddle
On Tue, 2016-03-22 at 00:45 -0400, Celejar wrote:
> On Mon, 21 Mar 2016 12:15:56 -0000 (UTC)
> Dan Purgert <dan@djph.net> wrote:
>
> > On 2016-03-18, Celejar <celejar@gmail.com> wrote:
> > > Hi,
> > >
> > > I'm trying to understand the throughput across the different links of
> > > my little home network, and am perplexed by the measured wireless
> > > throughput.
> > >
> > > The three main devices I'm interested in:
> > >
> > > Router: Buffalo WZR-HP-G300NH running OpenWrt (Chaos Calmer 15.05).
> > > Gigabit WAN and LAN, 802.11bgn wireless.
> >
> > I know I'm coming to the party a bit late, and it's probably been
> > answered somewhere else in the posts here, but what channel width are
> > you running here?
> >
> > If you're running 40 MHz, you WILL be getting combined Co-channel
> > contention from all other devices on channels 1 and 6 (or 6 and 11).
> > With 2.4 GHz connections, it's advisable to stick to 20 MHz channels, to
> > limit the amount of contention you're getting.
>
> Running at 20 MHz.
>
> > > [...]
> > >
> > > Here's the part that baffles me - these are with the laptop connected
> > > to the router wirelessly:
> > >
> > > Laptop - router: ~11.8 Mbps
> > >
> > > These numbers actually exhibit significant variance, but they're
> > > generally at least this much, and at most about 15-20 Mbps.
> > >
> > > Laptop - NAS: ~14.7 Mbps
> > >
> > > Once again, these numbers vary widely, but are in line with the laptop
> > > - router numbers.
> > >
> > > But here's the kicker: Ookla's speedtest (run on the laptop with
> > > speedtest-cli) shows 29.01/5.89 (d/u), and this is fairly consistent.
> > >
> > > [...]
> > >
> > > So the wireless link can apparently push at least 30 Mbps or so, so why
> > > are my local wireless throughput numbers so much lower?
> >
> > Given that the router is a 2x2 device, have you tried sending multiple
> > streams with iperf (with the "-P" client option)? As I (likely,
> > incorrectly) recall, iperf defaults to one stream, whereas speedtest
> > will run multiple streams.
>
> Just tried a few runs with "-P 2" - no difference.
>
> > > I was originally using one of the common 1/6/11 channels, and I switched
> > > to 3 since I saw a lot of other stations on those channels. This may
> > > have resulted in some improvement, but I'm still stuck locally as
> > > above. What's the explanation for this - how can I possibly be getting
> > > much better throughput to servers tens of miles away than to my local
> > > stations? Does iperf somehow work fundamentally differently from
> > > speedtest? If so, which is a better representation of actual throughput?
> >
> > Switch back to 1, 6, or 11 (and a 20 MHz channel). As others have
> > explained, being on an "in-between" channel will result in you getting
> > actual interference (rather than simply co-channel contention) ... not
> > to mention causing interference for your neighbors.
> >
> > It might be a good idea to upgrade to a dual-band access point, so that
> > you can use 5 GHz, which is typically has much cleaner channels.
>
> Thanks. See my other response in the thread regarding channel selection.
>
> Celejar
>
Also remember you can have too much RF power in your transmitter, as
well as your neighbours overloading your system, you could be
overloading your own.
Try turning down the transmitters power.
David.
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