[zaphod12]

that's incorrect. contention is the reason being next to all of those other wifi networks tanks your speed. Only 1 device can transmit on a given channel at a time. It's as if everyone is plugged into the same handful of ethernet cables.

[gascan]

Ok, maybe I used the wrong word, but I meant the bandwidth of the air. As you say, only 1 device can transmit at a time.