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Warning

Setting the Keep Alive to a short interval will increase the data traffic over the TCP connection in the event that the client is idle.

Setting the Keep Alive to 0 will disable the Keep Alive functionality

MQTT Transmission Primary Host

Note
The notion of Primary Host ID is part of the Sparkplug B specification and, as such, both the main application and edge nodes in a system will need to be Sparkplug compliant

The 

The MQTT Sparkplug B specification defines a way for subscribing clients (such as MQTT Engine) to notify publishing clients (such as MQTT Transmission) when they are online or offline. The publishing clients can then key off a particular subscribing clients status to do different things when that subscriber status changes either to offline or online.

MQTT Transmission keys off a Primary Host ID to enable the store and forward of tag changes within the module. 

When Primary Host ID is configured, and MQTT Transmission primary host ID is an ID to identify the main application that is receiving the MQTT data to guarantee that we don't lose the data and ultimately deliver it to the application. The ID is used for state notifications. These notifications are used to notify the Edge Node if the primary application goes offline. If the Edge Node is notified that the primary backend application has gone offline, it'OFFLINE', it will close it's client connection with the MQTT server and walk to the next MQTT server defined in the set. Data will be stored locally until the state of the primary host is "ONLINE" when any stored data will be published.