I had a chance to put the AirPcap NX card and Wireshark today to a good use and here are the findings including a screenshot of the network capture.
For about a minute or so I was able to browse a site with wallpapers. As expected traffic suddenly stopped and I wasn't able to ping the ip of the phone from my workstation nor from the access point.
When looking through the network captures I saw that the phone sent the AP a message indicating that it will put its interface to sleep (to preserve power) - while there is active data transfer in progress (the screen wasn't even locked as I was browsing through the site and the power save feature that turns off wi-fi is disabled)
The phone never seem to be able to wake up from dozing off. According to my research stations (phones) should wake up and check periodically listeining to beacon frames to find out if there is data buffered for them. I see in subsequent frames sent from the AP that there is data buffered for the phone but the phone insists that it is in sleep mode... I can post a screenshot of that too if necessary.
I've had exactly the same problem since ICS.
I'm trying to connect to a BT home HUB 3, the Xperia P knocks out every thing in the house running on WIFI
After changing the phone and then every setting going I've finally got it working!!
Change the wireless interface on your router to be 802.11 b/g only - not b/g/n
This resolved it for me, but i'd be interested to know why this is such a problem for ICS but is not getting solved with a patch.
Gary,
you're a genius 
I've just spent an entyire day messing around with this phone bought yesterday from 3 and getting kicked out and non connected from my BT router after ICS update
Problem now solved and alls well but to anyone else out there the problem is easily solved if you're getting a wifi connection problem through a BT router. Gary's solution of changing the wireless settings to 802.11 g/b only will fix the wireless issues
Grazie Mille
see my grateful reply to Gary above
change your router to b/g only - problem fixed
Sorry but this is not a resolution. We are approaching 100 access points in our corporate network and this is not an option. We have mutiple devices using the 2.4 and 5GHz bands without any issues - even wireless VoIP phones and medical devices work just fine.
As you can see from the attached screenshot we see a "few" devices
My old Nokia N900 and various other flavors of smartphones (HTC, Apple, Samsung,etc.) and tablets work just fine. The only device that has an issue is the Xperia P with ICS.
It is also not a fix for you - what are your options when you are at an airport or another place with free wi-fi - ask them to reconfigure their router?
Quoting the CWAP Certified Wireless Analysis Professional Official Study Guide:
Power Management Field
“Legacy power management methods define an option called Power Save mode for 802.11 client stations. When a client station is set for a Power Save mode, it will shut down some of the transceiver components for a period of time to conserve power. The wireless card basically takes a short nap. The station indicates it is using Power Save mode by changing the value of the Power Management bit to 1. When the Power Management bit is set to 1, the access point is informed that the client station is using power management, and the access point buffers all of the client’s 802.11 frames.”
More Data Field
“…when a station receives the beacon…it checks to see…that a buffered unicast frame waits. If so, the station will remain awake…The station will stay awake while the access point transmits the buffered unicast frame.
To summarize, the More Data field is used to inform Power Save mode clients that they still have buffered unicast traffic and that they should not go back into a doze state.”
Translation:
It is OK for the wireless card to go into sleep mode if there is no data traffic and it should check periodically (I think the beacons sent from the APs are every 100ms) to see if there is data destined for it. If there is it should switch to an active state.
I believe in our case the wireless interface goes to sleep regardless of the fact that there is data traffic and remains in that state until the wireless interface is reset, phone is powered off/on, associates to a different SSID (or roams to a different AP).
Hey Guys,
I think I've experienced the same issue as ye. I was at my parents house at the weekend and after a minute or so of browsing on my xperia P it just stopped loading pages. The funny thing was every time this happened my laptop's internet also went down (just like gary.piper said). It seemed to crash my router or something because I had to reset it to get my laptop internet working again. My router had no option to change from b/g/n to just b/g so I couldn't test if the "n" was at fault.
Back at my own house the xperia P works fine on wifi with no problems. I thought this might be because my router was only using b/g but I just checked and it's b/g/n...which kinda confuses me!
Anyway just thought I'd share my experience. Hopefully sony are aware of the issue.
By the way...great debug work by iproute! I'll see if I can produce the same results next weekend
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