Piconets are miniature radio cells. They consist of at least one master and one slave. With Bluetooth, the devices in a piconet always join together to form a self-configuring ad hoc network.
A Bluetooth piconet can consist of a maximum of eight active Bluetooth devices. Since communication among the Bluetooth devices takes place in master-slave mode, one of the devices in such a miniature radio cell assumes the role of master. The master has contact to all slaves. It controls the data exchange and the frequency change for the frequency hopping system( FHSS). Since the frequencies change randomly, 1,600 times per second, several piconets can be operated side by side without interfering with each other. In addition, several piconets can be combined to form a functional network, a scatternet.
In addition to the eight active devices, up to 255 passive devices, which can be in various idle modes, can be connected to a Piconet. Since stationary and mobile, battery-powered devices can be connected to a Bluetooth network, Bluetooth knows several standby modes in addition to the transmission mode, which differ in functionality and especially in power consumption: Active mode, Sniff mode, Hold mode and Park mode.
In the operating state known as active mode, a slave is in wait mode. It can be activated by the master via data packets to transfer data in connection mode. Sniff mode is another standby mode. In this mode the slave can only be addressed by the master via its address. In sniff mode, the current consumption is already significantly reduced. If the transmission activity from the master to a slave is stopped for a predefined time, the slave goes into hold mode. The hold time can be requested from the master. In park mode, the slave is no longer involved in communication, it only maintains synchronization. In this mode the slaves synchronize themselves continuously with the master. The master can switch them from the park mode to the communication state.
For establishing connections with unknown devices there is the Inquiry, and for establishing connections with known addresses there is the Page.