The BACnet Protocol Engine receives messages from external BACnet devices and holds them until the Protocol Engine can process them. If this queue becomes too large, the Protocol Engine is not capable of holding all of the messages in progress, causing some communications to fail.
If the Protocol Engine input queue is critical, BACnet protocol messages received from the IP port are discarded. The IP port counter, Discarded Frames (under the IP Datalink, Diagnostic tab), displays the number of discarded messages.