It has been a little too long since my last post. It is time to start catching up!
First off, in the last posting, I had asked two short questions.
#1, Can multiple wireless networks co-exist in the same room on the same channel? The answer is yes. When a user connects to a wireless network by network name, they are actually connecting to a specific access point by MAC address.
Take a look at figure 1 below, a screen shot from AP-Finder. (click on the image to enlarge it.)
It shows three APs. Note that two APs outlined in yellow are on the same channel. They have different network names, and most importantly, different MAC addresses. The different MAC addresses of the APs is the key to how two different wireless networks can peacefully co-exist on the same wireless channel at the same time.
This leads us to the the answer for the next question.
#2 Can multiple wireless networks co-exist in the same room on the same channel with the same network (SSID) name? The answer for this one is also yes as well, as long as each wireless AP has a different MAC address. And, every AP will have a different MAC address (unless someone tampers with them. Unique MAC address are, of course, assigned at the factory when they are manufactured.)
A side effect of the fact that two wireless networks can co-exist on the same channel at the same time is that it is possible to monitor wireless communications on multiple networks (as long as they are on the same channel). In fact, it is possible to monitor communications over a wireless network without ever joining the network. In Linux, this can be done by setting the wireless network card into monitor mode. Sniffing a network in “monitor mode” allows for a passive way to collect wireless communications that is undetectable by the network users/owners.