How does Connectify work?

Question

I recently found out about Connectify, which can create a full (as opposed to ad hoc) access point using only a computer. It also allows to share an internet connection from another WiFi network.

Thus, the computer can be "connected" to two WiFis at the same time -- the one it created and the normal one.

How is that achieved, with only one physical WiFi card? This also brings up the question, would it be possible to write a program that would make your computer be able to connect to multiple (normal) WiFis at the same time (without creating any of them, like Connectify does)?

Solution

connectify uses a feature that's built into windows 7 but not actually used, called 'virtual wireless cards', which apparently is supposed to require special drivers. My guess is connectify provides modified drivers, or somehow patches the current drivers to enable this and provides a front end for it.

Bizzarely, the best source of information on the back end of virtual wifi is an abandoned MS project called... virtual wifi - apparently amongst other things, it impliments a protocol called Slotted Seeded Channel Hopping (SSCH) - this allows a wireless card to connect to multiple networks, as long as they arn't on overlapping channels - this is meant for ad-hoc networks but its clear where its being used in this case - to connect to one AP, and create a second one on a different channel. Considering this, chances are its probably possible to write a programme that connects to more than one AP, though trunking the two connections would probably be a pain and half.