Bluetooth connects portable equipment such as mobile phones. Low-cost transceivers are embedded in the devices. Up to 8 devices can be connected at the same time, and each device provides a unique 48-bit address. The piconet or Bluetooth network is composed of a personal area network that contains 2 to 8 Bluetooth peer devices.
There’s usually up to 7 slaves and one master, the device that initiates a connection with other devices. It controls the traffic and communications link between itself and the slaves, the devices that respond to the master device. Slaves need to synchronize their receive/transmit timing with that of the master device. Slave devices can only start its transmissions either in a time slot reserved for use by the slave device or immediately after the time slot that was addressed by the master.
The master’s Bluetooth device address defines the frequency hopping sequence. The master device sends radio signal demanding a response from the slave devices included in the range of addresses. The slave devices respond and synchronize their clock and hop frequency with that of the master.
Scatternets, an ad hoc computer network composed of 2 or more piconet, are made when a device becomes an active member of more than one Bluetooth network. Bluetooth’s core specification is composed of 5 layers – radio, baseband layer, Logical Link Control & Adaptation Protocol (L2CAP), Link Manager Protocol (LMP) and Service Discovery Protocol (SDP). Radio defines the radio transmission requirements including power characteristics, frequency, and modulation for a Bluetooth transceiver.
LMP dictates the process for setting up and managing link. The baseband layer identifies the logical and physical types of link and logical channels. It also defines the packet formats, device addressing, channel control, receive and transmit timing and frequency hopping mechanism. Logical Link Control & Adaptation Protocol adapts any upper-layer protocol to the baseband layer. Service Discovery Protocol allows a Bluetooth device to ask other Bluetooth devices for services provided and device information.