What is the mechanism used by the Continuum system to determine the communication status of third party BACnet devices?
To maintain the communication status of third party BACnet devices
Continuum sends a read property message to read the vendor id from the device once a minute by default (or whatever the probe time is set to), as long as a timely response is received from the device Continuum keeps it online, if no response is received the device will be marked OFFLINE (after a retry)
Once a device is marked OFFLINE Continuum will perform a WHO-IS once a minute (ARP if CyberStation) until an I-AM is received which will cause the device to be tagged back online, once the device is back online Continuum will resume probing the device via the read property message once a minute.
Note that Continuum allows several probe options for BACnet devices, the behavior explained above is for when the probe type is set to 'Probe'
ProbeOnDemand - Probing does not occur unless a communications transaction with the target device fails. Once a transaction fails then probing occurs at the interval specified in Probe Time until the device comes back online. The advantage is that additional requests to the controller fail immediately. The disadvantage if that node failure is not detected until a CyberStation application needs to communicate with a controller.
ProbeOff - Probing does not occur. The advantage is that there is never probe traffic to the device. The disadvantage is that each request to the device fails only after the transaction times out.