In the system architecture, the ICR-3211B connects to the elevator lift control PLC over RS-232. A python app on the ICR-3211B polls the Modbus registers on the PLC and sends the values to an MQTT broker. These values communicate information like: door stuck open, door stuck closed, and lift car stuck between floors. The Cloud Monitoring Web App gets this and other data from the MQTT broker and presents in the web portal.