As jaervosz wrote the other day, the iwl3945 driver has some serious issues with it. I think I have it narrowed down to what conditions cause the problem.

Problem: When downloading large files for non-trivial amounts of time, the download speed drops to <80 K/s. This is unacceptable, the whole pipe is limited to that by the way. I am not sure what exactly causes this but I have narrowed down the conditions to which it happens.

Encryption does not matter.. it falters on wep/wpa{1,2} or open networks. However, I found that this condition only exists on mode B APs. This includes “mixed” APs as well. I do not know enough about drivers but if the AP offers B & G, then it should select G, right? Well, based on the condition of the speeds, I would have to say that it is selecting B mode and then hitting this bug again.

Anyway, for the time being…Do not use B APs. Easier said that done because I’m sure most every sys-admin would select Mixed AP over G only. So, if you are experiencing this issue as well, please comment on the [upstream bug][2], which has been open for 7 months by the way. Annoying. Maybe we can convince them to look at this issue some more? Even intel employees are CC’d on the bug because they have the issue too..

Workaround: Convert your AP to G only or use G only APs.

[2]: http://www.intellinuxwireless.org/bugzilla/show_bug.cgi?id=1592