To directly control your Sky box (e.g. change channels, pause, play and rewind TV) the box must be connected to the same network as the device with the Sky+ app (first available in 2009). This is far greater functionality than was available when the remote recording service was introduced three years earlier in 2006.
To send a remote recording request you need to be logged in to your Sky account on the internet. The request is sent to their servers from where it is encoded to the satellite uplink, and the satellite downlink is decoded by your Sky box.