Re: Throughput riddle
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
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