On Thu, 2009-05-14 at 14:54 -0400, Dan Williams wrote: > Libertas splits scans up into 3 parts with a short return to the > operating channel between each part. There's nothing that requires > cfg80211 for that to work... Yeah that was my idea too, just return to the operating channel after having scanned a channel or two and wait for the next beacon, and possibly receive traffic if indicated in that beacon. It takes a bit of synchronisation and isn't easy to implement, but it's definitely possible. > The problem here is that at any time an application (say, wifi location > app) could ask for the list of access points. If you don't scan > periodically, all APs other than your associated AP (and others on the > same channel) will gradually drop off because their beacons are > received. Hard to wifi position or get area statistics if there's only > one AP in the list. The other thing we should do is bump the AP list timeout, I think -- 10 seconds is very small. But then again we really need such apps to query NM anyway. > Secondarily, scanning is a tradeoff between better roaming latency and > continuous high throughput. If you don't scan, you have no idea what's > around, and when you move and the current AP becomes marginal, you > *have* to take the hit no matter what, so you can scan and find a new AP > to associate with. Yeah, that too. > I would have though that the periodic scanning would be more of an > annoyance when doing VOIP or SSH other latency sensitive tasks, but when > just downloading a file, a few second drop in transfer rate gets lost in > the bucket in the grand scheme of things. ssh isn't too bad, at least not after I fixed the timings... before I got very annoyed with ar9170. OTOH with VoIP it would suck to have a small hiccup every 2 minutes -- maybe then we should postpone indefinitely and only do it if the signal strength fluctuates? johannes
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