“The name is Hart, W. L. Hart. I have to get out of here. How do I do it?” Our adventurous hero was addressing the ally he had found in this high tech den of thieves. She was blonde, tall, dangerous, and full of information. He found himself confiding in her. The regular status reports from himself and those around him to The Manager made slipping out of this place tricky. Dodging a parole officer or avoiding bed-checks on a co-ed field trip were child’s play in comparison.
“There are three ways Mr. Hart,” she said with a slight accent indicating her birthplace was once on the wrong side of the Iron Curtain. “First, you can tell those in the cubicles around you of your intention to leave and walk out.”
“It sounds too simple.”
“When The Manager determines you are absent from the status report of your neighbors, he will alert those on the outside. Your second possibility is for the manager to order you out.”
“That sounds like a bad idea as well. What’s the third option?”
“You can just leave. When your neighbors discover you are gone, they will send the information to The Manager in their status reports. It gives you the most time before your absence is detected.”
“I’ll take it.”
The real network
In a WirelessHART network, the device can initiate a disconnect by sending a disconnect message in the data link layer to its linked neighbors. When these devices send neighbor status updates to the network manager, the network manager will be able to determine the device has disconnected.
Alternatively, the network manager can send a command to a device to disconnect from the network. This might be necessary if the device is malfunctioning.
Finally, the device could just die. Through loss of power or some catastrophic failure, the device might stop transmitting. When neighboring devices no longer receive signals from the absent device, they will transmit this information to the network manager in their status reports. The network manager may alert the outside world to the loss of the device so maintenance can be performed.