Comment 17 for bug 984552

I'm also getting this periodic loss of connection problem. I've had it with 10.04, 11.10 and now 12.04 but it is much much worse on 12.04.

Dell Latitude E6400 with a Broadcom chipset wireless card (I think it was a BCM4312)
Dell Latitude E6420 with both a Broadcom (BCM43228) and Intel (AGN5300) chipset wireless card

On the first laptop (E6400) when I was running 10.04 the problem resulted in sluggish response when using SSH or browsing. I was getting about 2% one-way packet loss (i.e. pinging out from the laptop to the WAP showed packet loss, but pinging from another machine to the laptop showed no lost packets.) When first booted the network was fine but would deteriorate over a period of about 60 minutes.

On the same laptop using Ubuntu 11.10 the problem became worse with frequent disconnects. Only rebooting the laptop would reconnect the wireless.

Again, on the same laptop with 12.04 the wireless was completely unusable. It would associate with the WAP and could send and receive a few hundred packets before reporting any host I tried to ping as unreachable. With all three versions of Ubuntu on this laptop I only experienced the problem at home and not at work so put it down to my WAP at home being incompatible with the laptop's wireless card.

On the second laptop (E6420) I've only ever tried Ubuntu 12.04. With the Broadcom wireless card I found that, at home, it would work for a couple of hours then either drop the connection completely or suffer from heavy packet loss (>20%). At work it would appear to be associated with the WAP but trying to ping another machine would result in "network unreachable" messages. Routing tables were all correct.

I then tried an Intel AGN5300 wireless card in the same laptop. It is better but I see more or less the same symptoms: at home I get disconnections or high packet loss after a couple of hours use; at work I see the wireless is associated with a WAP but get "network unreachable" when pinging, or high packet loss. I also get wildly varying connection bit-rates and excessively high "Invalid misc" count from iwconfig. This was reported just five minutes after rebooting:

iwconfig wlan0

wlan0 IEEE 802.11abg ESSID:"Linguamatics"
          Mode:Managed Frequency:2.412 GHz Access Point: F8:D1:11:50:C9:4C
          Bit Rate=48 Mb/s Tx-Power=15 dBm
          Retry long limit:7 RTS thr:off Fragment thr:off
          Power Management:off
          Link Quality=70/70 Signal level=-31 dBm
          Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
          Tx excessive retries:15 Invalid misc:125154 Missed beacon:0

I'm currently running iwlwifi with the following options:

    swcrypto=1 11n_disable=1 power_save=0

which helps a lot but doesn't completely remove the problem.

The fact that I've had similar problems with two laptops, two different WAPs, and three different chipset wireless cards seems to suggest this problem is not a fault with the hardware or drivers but something in Ubuntu itself.

Note that I do not have access to the first laptop any more but I do still have both wireless cards for the new one. I will also try the latest kernel but this may take a while as this is a work laptop and I'm on-call until late next week so can't really be dicking about with it too much.