In most cases, it’s possible to use beacons without knowing the exact data format of the advertising. It’s usually possible to specify only a few values such as iBeacon UUID, major and minor and the devices and listening apps work together. In some instances it’s necessary to know Bluetooth LE packets formats, for example, to implement your own code.
The Bluetooth packet formats are defined by the Bluetooth specifications but specifications aren’t always the fastest and easiest to understand. There’s a new presentation on SlideShare on Bluetooth Low Energy (BLE) Packet formats.
Winfred Lu from STMicroelectronics describes Link layer, advertising, data channel and physical channel packets.
Read about Using Bluetooth Low Energy (LE)