Information Technology Reference
In-Depth Information
device it previously paired with. Once a link key has been generated, an
authenticated ACL link between the devices may be encrypted so that the
data that they exchange over the airwaves is protected against eavesdropping.
Link keys can be deleted at any time by either devices: if done by both
devices, this will implicitly remove the bonding between the devices. It is
therefore possible one of the device to have a link key stored but not be aware
that it is no longer bonded to the device associated with the given link key.
2.3
Scatternets
As described earlier, there can be up to seven slaves at a time in a piconet
communicating with one master. It is possible to increase the number of com-
municating devices by means of
inter-piconet units
(IPUs) that set up s
catternets
.
An IPU is a Bluetooth unit that is part of more than one piconet. Each
IPU can communicate with one piconet at a time, since it has only one
Bluetooth radio, but it can switch from one piconet to another from time to
time, keeping clock and address of respective masters. Each IPU can act
independently in the piconets (Figure 4(a)) or act as a gateway between the
piconets, forwarding packets from one to the other (Figure 4(b)). A group of
piconets in which connections consists between different piconets by means
of IPUs is called a
scatternet
.
2.4
The Bluetooth stack
Besides all radio specifications, Bluetooth defines a layer protocol archi-
tecture consisting of core protocols, cable replacement protocols, telephony
control protocols and adopted protocols.
Figure 5 shows the Bluetooth-layered stack, in which every layer within
a device logically interacts with the peer layer in another device with the
appropriate protocol. Physically, each layer supply services to the upper
one exploiting services from the lower one, similar to the Open Systems
Interconnection (ISO-OSI) model [3].
(a)
(b)
Figure 4: IPUs and Scatternets.
