You install a new sensor which needs to join your WirelessHART network. How does it find its way into the network? In this installment of our technical discussion of the wireless industrial protocol, we find the network is secure, but not exclusive. It actively searches for new members.
Lost in the Pacific
Imagine a WWII pilot shot down and alone on an island in the Pacific. He is equipped with a small radio which can send and receive on a few select channels used by search and rescue. He patiently listens – switching periodically between channels – trying to hear a friendly ship, plane or sub.
Finally he intercepts a transmission. Once the channel is available, he transmits the password he was given before he took-off using a secure code. The friendly craft forwards his message to HQ, which arranges for the pilot to be pick-up. Instructions are relayed to the friendly craft who forward the information to our downed pilot.
Joining the club
While the above scenario may be a little melodramatic, it does basically describe the process for how a node joins the network. A device in the network transmits an “advertisement”, containing timing information necessary for a new node to know when to transmit a join request. The new node will only accept the advertised information if its network ID is the one pre-configured in the new node. Then with this information and the pre-programmed join key (our password), the new node can request entrance.
The advertising device becomes a proxy for the new node. It forwards the request to join to the network manager, which transmits detail such as network address and topography for the new node back to the proxy (or a better one). The proxy then forwards the information to the new node.
Once the new node receives the information sent by the network manager, it immediately becomes part of the network. In fact, it could even receive instructions to communicate with another node. Sort of like our downed pilot receiving orders to join a guerrilla unit on the island.
Security is extremely important in the joining process for a WirelessHART network. We will take a closer look at the security aspects in another installment of our technical discussion.