Saturday, 7 May 2011

Bluetooth definitions


Bluetooth definitions

It is well to aquaint oneself with the terminology used in Bluetooth, if one is to understand the descriptions on these webpages. One could say that there are 3 types of connections in Bluetooth, as shown to the right:
• a) Single-slave
• b) Multi-slave (up to 7 ”slaves” on one master)
• c) Scatternet


Piconet:

A collection of devices connected via Bluetooth technology in an ad hoc fashion. A piconet starts with two connected devices, such as a portable PC and a mobile phone. The limit is set at 8 units in a piconet (that´s why the required address-space is limited to 3 bits). All Bluetooth devices are peer units and have identical implementations. However, when establishing a piconet, one unit will act as a master for synchronization purposes, and the other unit(s) will be slave(s) for the duration of the piconet connection.


Scatternet:

Two or more independent and non-synchronized piconets that communicate with each other. A slave as well as a master unit in one piconet can establish this connection by becoming a slave in the other piconet. It will then relay communications between the piconets, if the need arises.

Master unit:

The device in a piconet whose clock and hopping sequence are used to synchronize all other devices in the piconet. The master also numbers the communication channels.


Slave units:

All devices in a piconet that are not the master (up to 7 active units for each master).

Mac address:

A 3-bit Media Access Control address used to distinguish between units participating in the piconet.

Parked units:

Devices in a piconet which are regularly synchronized but do not have MAC addresses. They are woken up by the Master with a ”beacon signal”.

Sniff mode and hold mode:

Devices that are synchronized to a piconet, and which have temporarily entered power-saving modes in which device activity is lowered. They keep their MAC-addresses.


The Beacon-channel:

To support slaves, the Master establishes a beacon channel when one or more slaves are parked. This channel consists of one beacon slot, or a train of equidistant beacon slots transmitted at constant time interval.

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