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

A Survey of Wireless Sensor Networks for Industrial Applications 12-3
Application layer
Network layer
MAC layer
Physical layer
Physical medium
FIGURE 12.2
Wireless sensor network stack.
the layer above it, and it receives information and services from the layer below it. This information and
service exchange is performed in a well-defined and standardized message-exchange format.
The most commonly used WSN stack is a simplified version of the seven-layered Open Systems
Interconnection (OSI) Basic Reference Model [X.200]. The WSN stack consists of four layers; the PHY
layer, the MAC layer, the network layer, and the application layer. The structure of the WSN stack is
visualized in Figure 12.2.
The PHY layer handles functionality related to the RF transceiver, and it is the interface to the physical
medium where the communication occurs. It handles the transmission and reception of data packets
and provides control mechanisms for selecting operating channels, performing clear channel assessment,
and RF energy detection.
The MAC layer provides access to the radio channel and is responsible for radio synchronization. It
also handles acknowledgment frames, association/disassociation with other radio devices, and security
control. Its main task is to provide a reliable link between two peer MAC entities.
The network layer handles functions for how to join and leave a network. It provides mechanisms for
end-to-end (source to destination) packet delivery, which for mesh network topologies might involve
multiple hops. To achieve multi-hop routing, it is necessary to have updated routing tables. The discovery
and maintenance of routing tables is also the task of the network layer.
The application layer provides services to user-defined application processes. It handles fragmentation
and reassembly of data packets, and it is responsible for defining the network role (end-device,
router node, or network coordinator) of the device. The application layer is often referred to as the application
programmers interface (API).
12.3 Motivation and Drivers for Wireless Instrumentation
To enable the introduction of any new technology in the industry, a major driver and motivational factor
is the potential financial gains, i.e., reduced costs and/or increased revenue. Secondly, if new technology
has the potential to benefit other important aspects such as health, safety, and the environment (HSE),
they would also be considered interesting.
Wireless sensors/transmitters have many benefits over their traditional wired counterparts.
Eliminating the need for cables, combined with the self-configuring capabilities of WSNs, reduces the
installation cost compared to wired transmitters, both when it comes to the construction of new plants
and facilities and to modification projects on existing facilities. In addition, wireless transmitters allow
© 2011 by Taylor and Francis Group, LLC