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

50-2 Industrial Communication Systems
ZigBee applications
Simple network
applications
Mesh network
applications
Level 3
ZigBee profiles
ZigBee app layer
Interoperability
Level 2
ZigBee network layer
Mesh networks
IEEE802.15.4 MAC Simple wireless networks
Level 1
IEEE802.15.4 wireless microcontroller
Co-existence
FIGURE 50.1
IEEE 802.15.4 and ZigBee protocol stacks.
network topologies such as star, tree, and mesh. ZigBee devices can act as coordinators that initiate
a network, a device with routing capability, or as an end device with no routing capability.
802.15.4 is also the basis for wireless sensor networks (WSN) and mesh networking (see Section 50.5).
Wireless mesh networks (WMN) are an effective solution for building automation and control. A WMN
would enable maintenance workers using mobile handheld devices such as smartphones or personal
digital assistants to gather data from wherever they are in a building.
The mesh access points (MAPs) communicate only with their adjacent routers. In larger mesh network
deployments, some of the access points (APs) would act as intermediate routers or relays between
APs (multi-hopping) not within wireless range (non-line-of-sight) of one another. When an intermediate
router becomes faulty, other routers/APs adapt and pick up the routing; i.e., the mesh network is self
healing, ensuring constant availability of information.
50.3 ZigBee in the Context of Other Wireless Networks
Zigbee belongs to lowest range/data rate wireless technologies. Figure 50.2 illustrates some general
differences among wireless personal area networks (WPANs), wireless metropolitan area networks
(WMANs), wireless local area networks (WLANs), and wireless wide area networks (WWANs).
It is also beneficial to compare ZigBee against other wireless technologies relative to its range,
throughput, power consumption, and cost. Table 50.1 provides such brief overview.
50.4 ZigBee Stack
Although based upon standard seven-layer open systems interconnection (OSI) mode, ZigBee stack
defines specific layers responsible for performing of specific set of services to the layer above it through a
service access point (SAP). While IEEE 802.15.4 standard defines two lower layers—the physical (PHY)
and the medium access control (MAC) sub-layer, the ZigBee Alliance builds on this foundation by providing
the network (NWK) layer and the framework for the application layer (APL)—application support
(APS) sub-layer, the ZigBee device object (ZDO), and the manufacturer-defined application objects
(Figure 50.3). The details on these layers will be further elaborated in following sections.
© 2011 by Taylor and Francis Group, LLC