How are BACnet b3 controllers established as being Online / Offline?
EcoStruxure Building Operation
Controllers show Offline, but they can still be communicated with.
The BACnet device online/offline status is managed by the BACnet plugin device manager. The device manager handles all BACnet I-Am messages and used these information to build the device table.
Here are the rules:
When a new device is discovered, an entry is added to the device table. A new entry is probed up to four times at a 5 second intervals. If it does not respond in that time, it is declared offline.
To detect b3s going offline, StruxureWare Building Operation uses the MSTP dev driver, and watches token passing. 3 missed tokens = device offline . Once detected offline, then the probing rules apply: StruxureWare Building Operation will send a who-is message every 60 seconds.
Offline devices are probed at 60 second intervals, indefinitely, until they respond.
Online devices are never probed. Once resolved, a device is considered online until it fails to respond to a request and its status
is then set to offline.