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By default the MQTT messages from Transmission are send only upon Value or Quality changes. and there is no provision to resend a single Tag or Device level Tags at any interval if the values have not changed.

However, MQTT Transmission has control tags that allow you to request the Edge for a Node Refresh or a full Transmission refresh.

These can be scripted for either period or on specific Tag changes with the Gateway Events script tools.

Full Transmission Refresh

A full Transmission refresh is requested using the '[MQTT Transmission]Transmission Control/Refresh' tag.  This forces all Edge Nodes to disconnect and reconnect resulting in the sending of NDEATH, NBIRTH and DBIRTH messages for all Edge Nodes. 

Edge Node Refresh

An Edge Node specific refresh is requested using the '[MQTT Transmission]Transmission Info/Transmitters/TRANSMITTER_NAME/Edge Nodes/GROUP_ID/EDGE_NODE_ID/Refresh Edge Node' tag. This forces the Edge Node to disconnect and reconnect resulting in the sending of NDEATH, NBIRTH and DBIRTH messages for this one Edge Node.

Please reference the Using the MQTT Transmissions 'Refresh' Mechanism tutorial and the MT: Tags document for additional information for these control tags.