Transmission is the module that is used to publish data, but it's pretty common to also use it in combination with Distributor (the MQTT broker module), and sometimes Engine (allows Ignition to subscribe to MQTT data) https://www.docs.inductiveautomation.com/docs/8.1/system-architectures/iiot-architecture#mqtt-server-broker https://docs.chariot.io/display/CLD80/MQTT+Modules