Bluetooth ability

The used frequencies determine opportunities Bluetooth to the data transfer. Width of the channel for Bluetooth devices makes 723 2 Kbit/second with in asynchronous modes (however, even in this mode all the same remain up to 57.6 Kb/sec with for simultaneous transfer m the opposite direction), or 4339 Kb/sec with in completely synchronous mode. If data is not transferred, then the connection can be transmitted through Bluetooth up to 3 audio channels. Each of audio channels supports synchronous channels with speed 64 Kb/sec in each direction. Besides, it is possible combined transfer of data and vote.

Distance on which Bluetooth connection can be established is insignificant, and makes from 10 up to 100 meters. But even now for Bluetooth it is not required direct visibility or directed aerial. The connection can be established even through a wall (certainly, if the wall is not shielded).

The main feature of Bluetooth is that various Bluetooth devices connect with each other automatically, if it only appears within the limits of reach. Cables, drivers and so on are not required to the user. The user will take care only that Bluetooth devices would be closely to each other enough. Bluetooth device and software would take care about all the rest.

How is connection established?

Being situated beside, Bluetooth device can establish not only connection of a type a point - - to - point, when there are only two devices, but also the point to - many points, when one device works simultaneously with several others. At connection of one device with several by others, the device which serves some connections is called master, and connected devices –slave. To one master can be connected up to seven active slaves. There are can be a set inactive slave, which can not exchange data with master while all channels are engaged, except for active slave (that is, devices which actively exchange data), remain are synchronized with it (Such structure is called piconet).

There can be only one master in one piconet but everyone slave can be master for other devices simultaneously, and form piconet. Several piconets connected thus form scatternet. In scatternet different devices can not only to be at the same time master and slave simultaneously for various piconet, but also only slave for different piconets.

It is possible to familiarize with this structure in the submitted below figure more evidently.

Moreover, in case of necessity any slave can become master in piconet. Previous master thus becomes slave.

Thus, in scatternet can be united so much Bluetooth devices, how much it is necessary. The logic connections can be formed how it is required, and can change somehow, m case of necessity. A unique condition, various piconet included in one scatternet should have the different channels of communication, that is work on various frequencies and have various hopping channel. Hopping is a regular change of frequencies determined in parameters hopping sequence. Specification provides 10 variants hopping sequence, 5 with a cycle in 79 changes and 5 with a cycle in 23 changes. With any hopping sequence of frequency are replaced 1600 hops/ sec. Hopping used to prevent attenuation of a radio signal and interference.

As was already spoken, the automatic installation of connection between Bluetooth devices situated within the limits of reach is one of major Bluetooth features. Therefore, Bluetooth device starts its work in a unfamiliar environment from device discovery, in other words search others Bluetooth devices. For this purpose the inquiry is sent, and the answer to it depends not only on presence in radius of communication active Bluetooth devices, but also from a mode in which there are these devices. On this stage it is possible three basic modes.