* Power Class 2 – normal or standard range devices (10m), and

* Power Class 3 – short (10cm)-range operation

• Baseband Layer

The next “floor” in the Bluetooth protocol stack is the Baseband Layer, which is the physical layer of the Bluetooth. It is used as a link controller, which works with the link manager to carry out routines like creating link connections with other devices. It controls device addressing, channel control (how devices find each other) through paging and inquiry methods, power-saving operations, and also flow control and synchronization among Bluetooth devices.

• Link Manager Protocol (LMP)

A Bluetooth device’s Link Manager Protocol (LM) carries out link setup, authentication, link configuration and other protocols. It discovers other LMs within the area and communicates with them via the Link Manager Protocol (LMP).

• Host Controller Interface (HCI)

Next in the protocol stack, above the LMP is the Host Controller Interface (HCI), which is there to allow command line access to the Baseband Layer and LMP for control and to receive status information. It’s made up of three parts: 1) The HCI firmware, which is part of the actual Bluetooth hardware, 2) The HCI driver, which is found in the software of the Bluetooth device, and 3) The Host Controller Transport Layer, which connects the firmware to the driver.

Above the HCI level is the Logical Link Control and Adaptation Protocol (L2CAP), which provides data services to the upper level host protocols. The L2CAP plugs into the Baseband Layer and is located in the data link layer, rather than riding directly over LMP. It provides connection-oriented and connectionless data services to upper layer protocols.

Protocol types are first identified in the L2CAP. Data services are provided here using protocol multiplexing, segmentation and reassembly operation, and group abstractions occur. L2CAP allows higher-level protocols and applications to send and receive data packets up to 64 kilobytes. The L2CAP spends a lot of its time handling segmentation and reassembly tasks.   

• RFCOMM

Above L2CAP, the RFCOMM protocol is what actually makes upper layer protocols think they’re communicating over a RS232 wired serial interface, so there’s no need for applications to know anything about Bluetooth.

• Service Discovery Protocol (SDP)

Also relying on L2CAP is the Service Discovery Protocol (SDP). The SDP provides a way for applications to detect which services are available and to determine the characteristics of those services.