Bluetooth General Architecture

Bluetooth is designed to be used in a short-range radio link between two or
more mobile stations. The system provides a point-to-point connection
between two stations or point-to-multipoint connection where the medium
is shared by several stations. We then have a piconet, where two or more units
share the same medium.
In a piconet, one station acts as master, and the others as slaves. In
effect, the names master and slave refer to the protocol used on the channel:
Any Bluetooth unit (all units are identical) can assume one of the two roles
when required. The master is defined as the unit that initiates the connection
(toward one or more slave units). A piconet can have one master, and up to
seven slaves can be in an active state. Active state means that a unit is communicating
with a master; the station can stay in a parked state if it is synchronized
to the master, but it is not active on the channel. Both active and parked
station are controlled by the master.
A slave unit can be synchronized with another piconet: A station that is
master in one piconet can be slave in another one. In this way, multiple  piconets with overlapping coverage, which are not time or frequency synchronized,
constitute a scatternet. These different scenarios are synthesized in
Figure 6.4.
The main characteristics of the Bluetooth system are presented in
Table 6.1. The Bluetooth system employs a time-slotted access method. A
packet can use up to five slots but must have at least one slot. Bluetooth system
may transport an asynchronous data channel, up to three simultaneous
synchronous voice channels, or a channel that simultaneously supports asynchronous
data and synchronous voice.
The different types of links supported by Bluetooth are:
• A 64-Kbps synchronous link in each direction for voice channel;
• Maximal 723.2 Kbps asymmetric in one direction (still up to 57.6
Kbps in the return direction) or 433.9 Kbps symmetric for asynchronous
link.