The core protocol stack of Bluetooth has the above three main layers:
Physical Layer: Decides how the bits are transmitted over the air, like the modulation schemes and the packet structures to be used for communication.
Logical Layer : Bluetooth is a connection oriented protocol, this means that there is a connection set up, maintenance and tear down. This layer handles these activities. Each type of connection has its own set of associated packets and each connection type is tailored for different purposes like music playback, hands free etc.
L2CAP : L2CAP multiplexes data of various applications (or BT profiles) over the lower layer logical links and connections.
A typical Bluetooth architecture will look like above diagram, L2CAP and above layers will sit on the host while Logical and Physical layers will sit on the controller. “Host” usually means the main processor, and the controller is a small BT chip sold by guys like Broadcom and CSR. “Host” processors in Laptops are usually Intel CPUs running Windows/Linux, in hand held market the host is usually an ARM SoC which may be running Android/iOS/WP7 or any other embedded OS.
There is usually a transport layer which connects the host to the BT controller, usually this is a high speed UART interface. There is one more hardware which is the lowest and below all the layers, this is the analog RF which actually transmits the bits over the air, receives the response and passes it to the physical layer, this analog logic is usually outside of the BT controller chip. An interesting aspect is that the main consumer of power or current in this system will be the RF, better the RF more optimized will be the power consumption.