We recently came a cross a very useful diagram, from a research paper, that clearly shows the main Bluetooth LE advertising formats for Bluetooth 4.2, used by beacons:
This clearly shows how the formats, iBeacon, AltBeacon and Eddystone, all sit within a Bluetooth LE advertising protocol data unit (PDU). i.e. They are all use standard Bluetooth LE. Notice also that the advertising data is always short which is partly why it doesn’t use much transmit power and battery. Advertising is sent periodically, every 100ms to 10 seconds, depending on the beacon settings. It only takes of the order of 1ms or 2ms to send the advertising which means the beacon can sleep most of the time, another reason for the low power use.