How to use Screen Mirroring. What network protocol does Screen Mirroring use?

I have a Samsung Galaxy SIII (GT-I9300) which supports Screen Mirroring. I would like to use this feature to share my screen with a Samsung Galaxy S Plus (GT-I9001) running Android Gingerbread or with a Windows 7 or Vista computer or Sony Bravia TV. However, when I try to activate the feature on the SIII by clicking Settings -> Connections -> Screen Mirroring I get a message that says "Available Devices Scanning... No devices found". Does Screen Mirroring need to be available (and enabled) on both devices, or on just one device? Do I need to have any special software for it to work? How do I get this feature to work? Thanks.