Bluetooth PAN Basics
Communication Topology
8 | P a g e
Chapter 5: Communication Topology
For the communication between two Bluetooth devices, the one requesting the
connection acts as the master, whereas the other is known as the slave. A given master
can maintain up to seven connections to active slaves. As a result very small networks
called piconets can be established. The master can acknowledge new slaves into the
piconet by putting the already active slaves into ‘sleep’ mode.
Bluetooth is a piconet, consisting of a master and from one to seven active slave
devices. The radio designated as the master makes the determination of the channel
(frequency-hopping sequence) and phase (timing offset—that is, when to transmit) that
will be used by all devices on this piconet. The radio designated as master makes this
determination using its own device address as a parameter, while the slave devices
must tune to the same channel and phase.
A slave may only communicate with the master and may only communicate when
granted permission by the master. A device in one piconet may also exist as part of
another piconet and may function as either a slave or master in each piconet. This
form of overlapping is called a scatternet.
A collection of overlapping piconets is called scatternet. The Nodes/Active Slaves
specification for Bluetooth V3.0 is 7/16,777,184.
Figure 7: Piconets with a single slave operation, a multi-slave operation, and a scatternet operation
The advantage of the piconet/scatternet scheme is that it allows many devices to
share the same physical area and make efficient use of the bandwidth. A Bluetooth
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