Page History

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• Q: What does the MQTT 'Transmission Control/Refresh' in the MQTT Transmission tag provider do?
• A: This tag is used to 'refresh' the MQTT client(s) associated with MQTT Transmission.  By default, any new tags added to a transmitter definition will not be published to the MQTT server.  By writing to the 'Transmission Control/Refresh' tag any newly added tags will be detected and published.
  
  
• Q: What is the MQTT Client (Transmission) Keep Alive setting?
• A: The Keep Alive setting controls how often the MQTT client (Transmission) is expected to ping the MQTT Server (Distributor) so the MQTT Server can verify the client is still connected. If the server hasn't seen a ping or control packet from the client in 1.5 x 'Keep Alive', it will forcefully close the socket connection and publish the LWT (which for a Sparkplug client is the NDEATH message) for that client denoting it as offline.
  
  
• Q: What is the Primary Host ID and why should I set it?
• A: The 'Primary Host ID' is used for client state notifications to ensure MQTT clients are notified of a loss of connectivity to the primary host which is often MQTT Engine. For example, the 'Primary Host ID' must be set in order for the MQTT Distributor/Server to detect a disconnect between itself and the MQTT Engine and then publish a retained message for all connected clients stating that the MQTT Engine is offline. When MQTT Transmission sees this message stating the Engine/PrimaryHost is offline, it will then go offline itself and begin to store messages locally (assuming Store and Forward is enabled) to be sent once the Engine/PrimaryHost is back online.

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