Resources such as available memory and internal queues are continually monitored by the BACnet® communications software including the IP communications and MS/TP components of the controllers. If any resource becomes overloaded, the BACnet communications software reduces the throughput (throttles it back) to allow the controller a chance to recover.
Exceeded resources are classified into degrees of severity as follows:
Warning means the resource is in short supply.
Trouble means the resource may cause some observable problems.
Alarm means the resource is causing observable problems.
Critical means the resource is almost exhausted and operation may fail.
In some cases, there are statistical counters that count when recovery actions have been taken. The following sections define four resources monitored by the BACnet software and describe what you may notice if the resource throughput is reduced.