Client (MQTT JSON Schema A)
An MQTT client can be a Geo SCADA Expert server that is running the MQTT driver, or any device, such as a sensor, or third-party server, that can communicate using the MQTT protocol.
An MQTT client sends PUBLISH and/or SUBSCRIBE messages to the MQTT brokers that are online.
A PUBLISH message is used to send data to the brokers, which then pass that data onto the other clients that are online and have subscribed to the topic with which that data is associated.
A SUBSCRIBE message is used by the receiving clients to request data from the brokers. The clients only receive data for the topics to which they have subscribed. When Geo SCADA Expert is running the MQTT driver, it is an MQTT client that can subscribe to topics.
When Geo SCADA Expert 2019 is running the MQTT driver, the server functions as a host MQTT client (one that can receive messages), rather than a remote MQTT client (one that can publish messages).
With the MQTT JSON Schema A driver, you use MQTT Device items in the database to reference the brokers to which Geo SCADA Expert connects, and the topics to which it is subscribed.