[PATCH] WLAN: --power maxperf shot into the dark

Werner Almesberger werner at openmoko.org
Tue Jan 27 10:03:00 CET 2009

John Sullivan wrote:
>> --power maxperf. Perhaps this depends also on time. Do DHCP and DNS
>> continue to work after you had ping failures ?
> They do continue to work, yes.

Grrr ;-)

> root at calvino:~# ping gnu.org

Do the ping problems also persist when you ping a system that's more
local, e.g., the AP or the DNS server ? What happens if you switch to
a different protocol and, say, use httping instead ?

It may well be that your AP or the ISP is applying some ICMP filtering
that causes losses of long-distance pings but leaves TCP and local
ping intact. This wouldn't explain why maxperf makes a difference, but
maybe there's more than one problem at play.

When using httping, this utility may be useful:

Run it as "snmp 1" and it will print the changes of many of the
kernel's networking statistics counters. That way you can see if
there have been packet losses or similar.

> I am seeing some oddness in the frequencies. My laptop connected to this
> router says frequency 2.422 GHz. But the FR says 2.417 GHz.

And which channel does the router advertize ?

> Link quality is also... weird. Here is some info from the FR:
>          Tx excessive retries:31  Invalid misc:0   Missed beacon:124

This may point to a problem on the wireless segment. Do you also
get these if you start a fresh session ? I.e., after

echo s3c2440-sdi >/sys/bus/platform/drivers/s3c2440-sdi/unbind
echo s3c2440-sdi >/sys/bus/platform/drivers/s3c2440-sdi/bind

followed by configuration but then no experiments (channel changes
or such).

>           Cell 02 - Address: 00:18:01:FB:17:87
>                     ESSID:"LAMW6"
>                     Mode:Master
>                     Frequency:2.412 GHz (Channel 1)
>                     Quality=46/94  Signal level=-49 dBm  Noise level=-95 dBm
>           Cell 05 - Address: 00:18:01:FD:1C:F5
>                     ESSID:"wjsullivan.net"
>                     Mode:Master
>                     Frequency:2.412 GHz (Channel 1)
>                     Quality=39/94  Signal level=-56 dBm  Noise level=-95 dBm

Fierce competition on channel 1. Is LAMW6 by any chance an AP you
can turn off ? If not, perhaps try switching yours to, say, channel
6, where the competition is much weaker.

Thanks a lot for all the data ! I think the next steps should be to
make sure you're using a channel with a low SNR and to find a more
general failure pattern than just ping losses.

After that, it might help to sniff the traffic between Neo and AP
with your laptop. There's plenty of nastiness an AP can put into
its signaling messages ...

- Werner

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