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Bluetooth PAN Basics Bluetooth Stack
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Chapter 3: Bluetooth Stack
The Bluetooth standard has made an attempt to enable devices for ad-hoc connections and to provide flexible and expandable data and voice transfer. To accommodate all these tasks, special efforts has been made at each layer of the Bluetooth protocol stack. It contains the hardware and software portions of the system. Figure 1 shows the graphic representation.
The Bluetooth Stack has the following components:
Figure 4: Bluetooth Stack
A. The RF layer
This layer deals with the electrical specifications of the transmission and reception of data over the wireless channel. The transmission scheme used is Adaptive Frequency Hopping (AFH) that uses pseudo-random ordering of the 79 frequencies which helps in combating interference and removes the frequencies that give low performance.
Figure 5: International Radio Frequency for Bluetooth v 2.
The radio frequency layer of Bluetooth V2.1 uses 2.4 GHz as the carrier frequency but Bluetooth V3.0 offers the use of two carrier frequencies, 2.4 GHz and 5 GHz.
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Bluetooth PAN Basics Bluetooth Stack
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B. The baseband layer
This layer has a microcontroller to process all the sent and received bitstreams. It administers the flow control, framing and synchronization.
C. The Link Management (LM) layer
This unit is responsible for the management of connections, power and access. It provides authentication and encryption services to upper layers. This layer also performs link configuration and controls setup. This layer works with the baseband layer to perform link establishment in the network.
D. The Host Controller Interface (HCI)
In some books, the HCI is not considered a stack layer. It is the dividing line between the software and hardware units.
E. The Logical Link and Adaptation Layer (L2CAP)
The L2CAP is the first layer for the software unit of the Bluetooth stack. It allows higher-level protocols and applications to transmit and receive packets up to 64kB, providing connection oriented and connectionless data services. This layer only supports data traffic; the audio data is sent directly to the baseband.
F. Service Discovery Protocol (SDP)
This layer uses the SDP to find out the services on offer, neighbouring device information, and helps querying the neighbouring devices for connection establishment.
G. Telegraphy Control Specification Protocol (TCS):
The TCS uses call control signalling procedures for establishing speech and data calls between Bluetooth devices.
H. Radio Frequency Communication (RFCOMM) Layer:
RFCOMM is a transport protocol. This layer is used for cable replacement. It excels the RS-232 serial ports (a standard for serial binary data communication between DTE and DCE), hence offering transport capacity to applications that use serial lines for transport.
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