~ >>Just found another case where a non-overlapping channel isn't optimal: ~ >
~ >>* Interference from neighbors on channels 1, 6, and 10 ~ >
~ >>could get a reliable connection on channel 3. ~ >
~ >Well, sure, if there's significant interference from the optimal set ~ >of non-overlapping channels, then go for the non-optimal midpoints. ~ ~ My point is that 1, 6, and 11 aren't necessarily optimal. ~ ~ In fact 1, 6, and 11 are only really optimal in terms of minimizing ~ interference when you control multiple overlapping access points, and even ~ then they aren't necessarily optimal -- 4 channel spacing (e.g., 1, 4, 8, and ~ 11) will allow 4 access points (instead of just 3) to overlap with minimal ~ interference.
Our test results do not concur (assuming that you control your RF environment). The interference created by using 1/4/8/11 rather than 1/6/11 channel spacing will give you less aggregate throughput throughput the 2.4GHz band. With 4 APs, you are better off having two on the same channel.
This is because, with multiple BSSIDs on a single channel, the 802.11 MAC can (potentially) recognize the signals from the other BSSID as being valid
802.11 frames, and can hence do an informed backoff/transmission. With multiple BSSIDs on adjacent overlapping channels, the other BSSID's transmissions are just perceived as noise.
having said that ...
~ In an uncontrolled environment an overlapping channel might be optimal, as it ~ is in my case that started this thread, and in some other cases I know of. ~ ~ It nonetheless makes sense to recommend first trying the non-overlapping ~ channels (1, 6, 11) even in an uncontrolled environment because (a) they are ~ the most likely to be optimal and (b) they are the most "neighbor friendly". ~ But it nonetheless also makes sense to try other channels, particularly the ~ midpoints between the non-overlapping channels, when the non-overlapping ~ channels don't provide optimal results.
agreed - if you don't control your RF environment, then do whatever works best. (Within the bound of the law, of course.)