wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

49-6 Industrial Communication Systems
(a)
(b)
Master
Slave
FIGURE 49.2
Bluetooth piconets.
master device. The master device is used as the reference for communication between all the piconets,
while any device can belong to multiple piconets. A piconet offers the same frequency-hopping channel
to the connected devices.
49.2.8.2 Scatternet
Once a device belongs to multiple piconets, the master devices of the corresponding piconets need to be
connected among themselves in order to make this access available, which ultimately forms a scatternet.
The frequency distribution is simple and can work without interfering with others, as each piconet is
responsible for the distribution to its connected devices (Figure 49.2).
49.2.9 Bluetooth Security
There are three modes of security for Bluetooth access between two devices.
• Security Mode 1: Nonsecure
• Security Mode 2: Service-level enforced security
• Security Mode 3: Link-level enforced security
It is the responsibility of the vendor to implement the security mode. The devices have a two-level
security consisting of “trusted devices” and “un-trusted devices.” The trusted device can pair with any
of the devices and has unrestricted access to the services.
There are different levels of security in services as well, such as
• Services that require authorization and authentication
• Services that require authentication only
• Services that are open to all devices
In general, a personal identification number (PIN) is selected by the user, which must be a 48 bit
number. Additionally, a private link key (128 bit random numbers) and a private encryption key (8–128
bit) are used as a security measure for data transfer.
49.3 Bluetooth Protocol Stack
A protocol stack (often referred to as a communications stack) designates a software implementation
of a computer networking protocol suite. The modularization within the definition (suite) of protocols
enhances design and evaluation. These protocols are commonly described as layers in a stack of protocols,
the lowest protocol always being the low-level, physical interaction of the hardware, all the way to
© 2011 by Taylor and Francis Group, LLC