The protocol stack of BLE maintains a similar lower layer struc-ture as Classic Bluetooth, but also provides revised implementa-tions and a few new layers, such as the General Attribute Pro-file (GATT) and the Attribute Protocol (ATT). Fig. 2 shows the sim-plified stack for three major types of Bluetooth chipsets: ClassicBluetooth, Dual Mode, and BLE-only. For compatibility reasons, theBluetooth Dual Mode chipsets were introduced to support both LowEnergy and BR/EDR communications, which are commonly seenon phones and tablets. BLE-only chipsets are typically installed oncost- and resource-constrained devices.