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The MQTT Sparkplug™ B specification defines a way for subscribing clients (such as MQTT Engine) to notify publishing clients (such as MQTT Transmission) via a STATE message when they are ONLINE online or OFFLINEoffline.

When the subscribing client connects to a server, it can publish its connection state on a topic that contains an ID identifying it as a critical application.

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However as there will still be many existing clients which are only compatible with the MQTT Sparkplug™ B specification v2.2, we have made changes to MQTT Engine to establish a MQTT client whose only function to publish the STATE message in its legacy format. This is a configurable option and will be enabled as default.

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When viewing Ignition logs, you will also note notice a new MQTT Engine client which starts with ME-LS for example: 

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