Information Technology Reference
User software Î
Host driver Î
Bluetooth module Î
Figure 5: The Bluetooth protocol stack.
The RF layer is concerned with the physical data transfer, carrier
generation and modulation, and power management. It includes design
specifications to be followed for the construction of a Bluetooth transmitter,
such as spurious emissions inside and outside the band, the accuracy in
frequency and the interference among channels.
The Baseband layer manages physical connections and channels, offering
a variety of services: Bluetooth units synchronization, selection of frequency
hopping sequence, error correction, data flow control and security.
The main task of the Link Manager layer is to create, manage and
terminate connections, to manage the master-slave role switch and low-
power modes (hold, sniff and park). Furthermore, it is responsible for the
quality of service, authentication and encryption.
The L2CAP layer (Logical Link Control & Adaptation Protocol)
provides higher layers with services for sending data . To this end it
supports multiplexing for higher levels of protocol, segmentation and
reassembly of large packets, and management of logical connections with
the upper layer.
The HCI host-controller interface (HCI) defines standardised communi-
cations between the host stack (e.g. a PC or mobile phone OS) and the
controller (the Bluetooth module) . This standard allows the host stack or
Bluetooth module to be swapped with minimal adaptation. There are several
HCI transport layer standards, each using a different hardware interface to
transfer the same command, event and data packets. The most commonly used
are USB (in PCs) and UART (in mobile phones and PDAs). Figure 6 shows the
lower layers of a Bluetooth device. Upper layers interact with the baseband
using the commands made available by the HCI through the HCI driver.