To ensure secure communications links, 802.15.4 radios can be set up to require registration with their network monitors. This registration or “pairing” process, which takes less than five seconds, is performed only once to establish the linkage. Once a device and its monitor have been paired, the two continually exchange information as long as both have power.
IEEE 802.15.4 security techniques are part of the pairing process. When registration is activated, the monitor provides the switch with several pieces of information. The first is the monitor’s individual 16-bit network identification number, which the monitor selects at power-up to avoid conflict with other networks in the vicinity. The second is a unique 16-bit address for the wireless devices, which the monitor creates. The third piece of data is a 128-bit encryption key that the pair will use to encode future communications. Once the information is exchanged, the switch and monitor use it to address and encode the signals they exchange.
Once established, the pairing is maintained even if the monitor loses power or a battery is replaced in the switch. This ensures a self-healing network and simplifies system maintenance. The monitor is able to automatically re-establish any dropped link to a registered switch. Replacement or reconfiguration of the devices is performed through a clearing and repairing process.
The combination of addressing and encryption helps to ensure the uniqueness and security of each wireless device’s channel. No two monitors or switches will have the same network address, so the monitors and the sensors/switches will not respond to signals originating from other networks. This means a monitor will not confuse signals within its network, and switches will not respond to signals intended for other switches.
Even if an addressing error occurs somewhere, the network will not react to the erroneous signal, because the encryption keys for decoding the message will not match. The use of encryption further ensures that no unregistered node can successfully insert erroneous signals into a network or decode signals from a network, making the network secure from both eavesdropping and hacking.
Cost savings, greater flexibility
Using an 802.15.4 radio network to connect switches and sensors to a central controller frees industrial and manufacturing equipment developers and users from many of the costs and restrictions of wired solutions. It also expands the range of possible uses and placement of monitoring devices, making it easier and faster to reconfigure the factory floor for new product designs. As a result, the commissioning and lifetime cost of the network drops, while significantly increasing reliability and integrity.
When plant managers evaluate the advantages and drawbacks of wired versus wireless networks, they need to consider cost savings, maintenance issues, ease of installation, and configurability, uptime, and security.
802.15.4-based wireless networks have proven themselves reliable, robust, and cost-effective for a wide range of industrial, warehousing, and facility applications.
Joseph Citrano III is global product manager for Honeywell Sensing and Control.