NM uses a heuristic to determine which wireless network it should associate
with. IIRC, it keeps the list of SSID to which it has successfully associated, sort from the most recently connected to, to the least recently connected to, and chooses the first one.

The following happens to me. I believe this situation is quite common:

- Connecting from a public place, using a widely deployed wireless network in my city (let's call the SSID "Freewifi")
- Suspend my laptop, go back home
- Open my laptop. Since Freewifi is also visible from my place, it will associate to it instead of my home network.
- I have to manually change the network.

There could be some possible solution to that:
- give control to the user by allowing him to mark a connection as 'preferred'
- uses a more clever heuristic. I can think of the following ones
(1) prefer encrypted network over unencrypted ones (I think that would cover most cases)
(2) do not sort by most recently used, but maybe most 'frequently used' or 'whose total connection time is the longest' (I'm less sure about that one).


This situation is very real and is bound to happen in every big city where telco companies use people's DSL boxes to deploy their own city-wide wifi network.