I know the data antennas (3G, WiFi, etc.) power down to save battery, but push notifications still seem to come almost immediately. My iPhone and iPad will chime before the email shows up on my desktop. I'd hooked up a TCP/IP sniffer on my Wifi iPad and noticed the push notifications didn't come via TCP/IP. I understand the sending and receiving of push notifications from the App point of view (register the device, send notification to Apple, who sends it to the device), but would like to know more about this last leg of the trip. I see that Apple says port 5223 is involved somehow, but much in the way of details.
I've searched around the web some and not found anything that explains the mechanism of delivering push notifications from Apple to an iOS device. Is it UDP? Is it an existing always on connection? Why doesn't it kill the battery? Basically, how can the notification happen almost immediately without keeping the radio always on, thus killing the battery?