I have ongoing problems with wifi power saving mode and my AP which does not seem to like it. For example if I start a sip call via wlan the audio is very choppy and pings to the n900 change from < 100ms to sometimes > 9000ms as soon as the call is established.

If I disable PSM for the connection the high latency is gone so I tried to switch power saving on and off on wlan0 with iwconfig and dbus-scripts which works most of the time but not always.

After all I haven't found a real solution for the PSM problem I experience with my AP till now besides buying a new AP what I want to avoid if possible.

In the wiki I read that the tablets try to optimize performance by remaining in Constant Active Mode (CAM) if there is constant traffic and I think rtp traffic during a sip call does comply to this but wlan0 stays with 'power on' no matter how intensive I use the internet connection.

What do you think - is this the expected behaviour under some circumstances or should the wireless be set to 'power off' as soon as constant traffic is seen and switch back to 'power on' when the traffic stops?

Or in other words: should I file a bug report?

Some more questions:

Do you have interference sources around? Have you tried switching channels? Other equipment in your LAN / WLAN?

What is the value of DTIM setting on your AP (if it can be viewed)?

Manufacturer and model of AP?

I think 'power on' all the time is what Constant Active Mode means.

I use a FritzBox 7270 and I can't access the DTIM setting. There are aprox. 11 other APs around (hope you mean this by asking for 'interface sources').

Switching channels unfortionately doesn't help. The only other equipment in my wlan is a notebook and it makes no difference if it is switched on or off.

Maybe it's from interest that I just noticed that pings to the n900 vary extremly depending if I initiate a sip or a skype call.

With PSM enabled:
Pings to the n900 normaly take ~ 140ms

If I start a sip call pings take between 40ms and 140ms an go up to > 9000ms (if they don't start between 2000ms and 9000ms right after the call is established)

If I start a skype call pings take betwen 3ms and 5ms and sometimes go up to 4000ms.

That, and other equipment working in the 2.4GHz frequency range (there are plenty, ranging from microwave ovens to wireless keyboards to movement detecting radars).

It might be an incompatibility between your AP and the N900. Some APs just don't do the power saving stuff correctly, and the N900 isn't completely free of issues itself.

Before trashing you AP though, I'd try if the setup works different in another location, as it sounds like your current environment might have quite a lot of radio noise. Does it matter how close to your AP you are? Do you have transmit power on the N900 set to 100mW? Also try if you can find people with same/similar AP and ask for their experiences.

Very high (1000ms+) ping times (and breakups in non-TCP traffic) point towards dropped ARP packets (as compared to dropped ICMP echo packets, which would show as packet loss). ARP request/response wait is the reason why the first ping time is higher than the subsequent pings (this is best observable with wired ethernet, where ping times are more stable). Do you get a lot of packet loss with ping?