On 2018/05/01 10:48, Stefan Sperling wrote: > > On 2018/04/30 11:08, Stefan Sperling wrote: > > > Derp. A dBm value of -10 would of course be better than -60. > > > > > > Whatever the numbers shown by tcpdump really mean, the probe response's > > > one is better!!! > > > > Better as in "more accurate". But as the reported value is ridiculously > > high rather than too low, why wasn't 5GHz selected anyway? > > What I wrote in my first mail was not very clear (I wrote it in > a hurry before leaving to catch a train). > > The kernel compares the RSSI values which are shown in debug output. > For reference, the scan debug printfs below again show a 2GHz beacon > vs. a 5GHz "low power" beacon, where measured RSSI on 2Ghz is represented > as "58" and on 5Ghz is represented as "6": > > + b8:ee:0e:cb:b3:08 1 +58 54M ess privacy rsn "ESSID" > + b8:ee:0e:cb:b3:09 112 +6 54M ess privacy rsn "ESSID" > > The "non-reduced" Tx power frames, i.e. probe responses or beacons while > a client is associated, closely matched Tx power seen on 2GHz: > > + b8:ee:0e:cb:b3:08 1 +58 54M ess privacy rsn "ESSID" > + b8:ee:0e:cb:b3:09 112 +61 54M ess privacy rsn "ESSID"
What do the values represent here? I've been reading them as sign-flipped dBm signal strength because (before the +6 outlier) the numbers all matched that (i.e. -61dBm for 5GHz and -58dBm for 2GHz looks right for an access point at typical power levels about 30m away). I didn't interpret them as % in this case because it would be unusual for the 5GHz signal to be stronger than the 2GHz though that is possible and if that's the case, your diff makes sense. > There is a huge amount of material in the 802.11 specs about tx power > management and spectrum management but I haven't read any of that. And even then more reading is needed to understand it all, the specs just provide the framework for implementation, but the actual requirements are in local regulations which aren't in the specs. But fortunately for us (at least in client mode ;) this is mostly AP-led.
