AJAX clients/server web app.

I need a (multi)client/server AJAX solution to activate and deactivate a sine wave sound on my PC (server) using an ON/OFF button on a remote web page (client(s)). This remote button page will be used simultaneously by multiple persons in different browsers/PCs so its appearance (button ON or button OFF) must be updated in real-time everywhere. I mean, if an user switches the button ON it must IMMEDIATELY change its appearance (ON) in the browsers of the other active users too, and viceversa for OFF. ALL the updates between server and client(s) must happen in real-time therefore you CAN'T use a "polling" method. You must use a "push" (real-time) method, like a permanent TCP connection.