Bluetooth Connection Protocol

The Bluetooth connection protocol describes the set of rules by which all Bluetooth devices must abide in order to establish a link a communicate with one another. Although the Bluetooth protocol has its foundations in the IEEE 802.11 standard it incorporates many significant changes. The essence of Bluetooth is based upon dynamically configured units. Hopping very quickly between frequencies, the protocol specifically caters for many different modes to allow for minimal power consumption.

Standby

Devices not connected in a piconet are in standby mode. In this mode, they listen for messages every 1.28 seconds - over 32 hop frequencies (fewer in Japan, Spain, and France due to local bandwidth regulation).

Page/Inquiry

If a device wishes to make a connection with another device, it sends out a page message if the address is known, or an inquiry followed by a page message if it is unknown. The master unit sends out 16 identical page messages on 16 hop frequencies to the slave unit. If there is no response, the master retransmits on the other 16 hop frequencies. The inquiry method requires an extra response from the slave unit, since the MAC address is unknown to the master unit.

Active

Data transmission occurs.

Hold

When either the master or slave wishes, a hold mode can be established, during which no data is transmitted. The purpose of this is to conserve power. Otherwise, there is a constant data exchange. A typical reason for going into hold mode is the connection of several piconets .

Sniff

The sniff mode, applicable only to slave units, is for power conservation, though not at as reduced a level as hold. During this mode, the slave does not take an active role in the piconet, but listens at a reduced level. This is usually a programmable setting.

Park

Park mode is a more reduced level of activity than the hold mode. During it, the slave is synchronised to the piconet, thus not requiring full reactivation, but is not part of the traffic. In this state, they relinquish their MAC addresses , but only listen enough to keep their synchronisation with the master and check for broadcast messages.

Back to the index