Issue
How are BACnet controllers established as being Online / Offline?
Product Line
EcoStruxure Building Operation
Environment
BACnet
Cause
BACnet controllers may appear offline in the system, even though they can still be communicated with. This raises questions about how their online/offline status is determined.
Resolution
The online/offline status of BACnet devices is managed by the BACnet device manager plugin, which processes BACnet I-Am messages to maintain a device table.
The following rules and mechanisms are used to determine the status of BACnet controllers:
Device Discovery and Initial Probing
- When a new device is discovered, an entry is added to the device table.
- The system probes the new entry up to four times at 5-second intervals.
- If the device does not respond within this time, it is declared offline.
Offline Detection via MSTP Driver
- Building Operation uses the MSTP dev driver to monitor token passing.
- If three consecutive tokens are missed, the device is marked as offline.
Probing Offline Devices
- Once a device is offline, the system sends a Who-Is message every 60 seconds.
- Offline devices are probed indefinitely at 60-second intervals until they respond.
- Online devices are never probed.
Status Transition
- A device is considered online once it responds to a request.
- If it fails to respond, its status is updated to offline, and probing resumes.
