Does the WirelessHART network manager serve as a brain, computing and manipulating data as it passes through the network? Or is the network manager more like a conductor, orchestrating the harmonious flow of information? In this tenth installment of our technical discussion of the WirelessHART protocol, we examine how the network manager functions similar to an air traffic controller.
The crowded skies
Commercial airline pilots have very few choices. They are told when and from what runway they may take off, what altitude and vector to fly at to reach their destination, and when and on what runway to land. They are even told what frequency to use to communicate with the control tower. While they certainly take action when something goes wrong, they are even required to report that to the control tower if possible. This is to ensure two planes never occupy the same space at the same time, and passengers arrive safely at their destination in a timely manner.
Nodes in a WirelessHART network are in the same position. Only their control tower is the network manager. The network manager tells each node when, where, and how to send each packet to avoid collisions and ensure data reaches its destination in a timely fashion without collisions.
View from the tower
The network manager keeps track of the network topology, just as an air traffic controller tracks the position of planes. But the network manager goes a step further and creates the “flight schedule” by assigning transmissions to superframes. The network manager then delivers each node only the information the node needs to successfully transmit a packet.
The network manager doesn’t have a radar, but it does get periodic updates from each node about their neighbors, signal strength, and information needing delivery or receipt. The network manager calculates the topology and a superframe schedule, determining who will send, who will listen, and at what frequency for each time-slot. It then sends each device the part of the superframe table the device needs.
The network manager also handles security, preventing nodes from joining the network unless they transmit the necessary code. You could think of this as air defense: no password, no admittance.
Why a central command?
Just try to imagine if each and every airplane had to track every other airplane to avoid collisions, and arrange take-offs and landings at a crowded airport. Every pane would need much more sophisticated radar and at least one individual dedicated solely to negotiating with other pilots.
The WirelessHART network manager allows simpler network devices utilizing less power. Providing the network manager with a global view, both transmission efficiency and network security are enhanced as well.
Without an air traffic controller, safety, security, and efficiency are compromised unless planes are made much more complicated. The WirelessHART network manager is utilized for the same reason.