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MQTT Engine is designed to consume Sparkplug messages and create Ignition tags in the MQTT Engine tag provider.

The topic and payload of the Sparkplug message are parsed in different ways to create the Default Tag or UNS Tag folder hierarchy in the MQTT Engine tag provider.


Default Tags

When configured to create Default Tags, MQTT Engine will parse the topic and payload to create tags under the 'Edge Nodes' folder in the MQTT Engine tag provider.

The metric name in the payload is used for the tag name prefixed by the Sparkplug Descriptors from the message topic resulting in a tag path of:

  • [MQTT Engine]Edge Nodes/GroupID/EdgeNodeID/DeviceID/MetricName

For example the message below:

  • Topic: spBv1.0/Site 1/DDATA/Area 1/Line 1
  • Payload: {"timestamp":1643823757750,"metrics":[{"name":"Conveyer/Batch/Quantity","timestamp":1643823756467,"dataType":"Double","value":33.02}],"seq":23}

creates an MQTT Engine tag:

  • [MQTT Engine]Edge Nodes/Site 1/Area 1/Line 1/Conveyer/Batch/Quantity


If using MQTT Transmission to publish the message and the Transmitter is configured to dynamically pickup the Sparkplug Descriptors, the metric names used in the payload will be the remainder of the tag folder hierarchy not used in the topic namespace.

Prefixing the Sparkplug Descriptors in the topic to the metric name in the payload results in unique tag folder hierarchy's at MQTT Engine  


UNS Tags

When configured to create UNS Tags, MQTT Engine will obfuscate the Sparkplug Descriptors used in the topic and only parse the metric name included in the payload to create the tag structure under the configured UNS Folder prefix.

For example the message below:

  • Topic: spBv1.0/Site 1/DDATA/Area 1/Line 1
  • Payload: {"timestamp":1643823757750,"metrics":[{"name":"Conveyer/Batch/Quantity","timestamp":1643823756467,"dataType":"Double","value":33.02}],"seq":23}

creates an MQTT Engine tag:

  • [MQTT Engine]UNS/Conveyer/Batch/Quantity
    • with custom properties of
      • SparkplugDeviceId - Line1
      • SparkplugEdgeNodeId - Area 1
      • SparkplugGroupId - Site 1


It is a requirement of a UNS is that each tag can only be referenced from a single source ie. the same tag path cannot be published from two edge nodes.

If MQTT Engine receives a second message payload with a metric name it has already created, it will not create the UNS tag. 

For example:

  • Topic: spBv1.0/Site 2/DDATA/Area 2/Line 2
  • Payload: {"timestamp":1643823756250,"metrics":[{"name":"Conveyer/Batch/Quantity","timestamp":1643823732145,"dataType":"Double","value":65.40}],"seq":72}

will not create an MQTT Engine tag as the tag [MQTT Engine]UNS/Conveyer/Batch/Quantity already exists.

If using MQTT Transmission to publish the message and the Transmitter are configured to dynamically pickup the Sparkplug Descriptors, the metric names used in the payload will be the remainder of the tag folder hierarchy not used in the topic namespace.

This can result in collisions at MQTT Engine with duplicate metric names from different edge nodes.


In the example below we have three tag providers simulating edges - Site 1A, Site 1B and Site 2. 

Allowing the Transmitters to create the Sparkplug Descriptors dynamically would result in duplicate metric names in messages published to MQTT Engine.

For example:

Site 1 A publishing with topic "Enterprise/Site 1/Area 1" would contain a payload metric of "BMS/Rooftop"

Site 1 B publishing with topic "Enterprise/Site 1/Area 2" would contain a payload metric of "BMS/Rooftop"

Site 2 publishing with topic "Enterprise/Site 2/Area 1" would contain a payload metric of "BMS/Rooftop"



The recommended approach to create unique metric names is to configure the Sparkplug Descriptors used by each Transmitter which allows the full tag folder hierarchy to be used for the metric name.

In the example below we have set the Sparkplug IDs for each Transmitter: 

such that 

Site 1 A publishing with topic "Enterprise/Site 1 A/UNS" would contain a payload metric of "Enterprise/Site 1/Area 1/BMS/Rooftop"

Site 1 B publishing with topic "Enterprise/Site 1 B/UNS" would contain a payload metric of "Enterprise/Site 1/Area 2/BMS/Rooftop"

Site 2 publishing with topic "Enterprise/Site 2/UNS" would contain a payload metric of "Enterprise/Site 2/Area 1/BMS/Rooftop"


If MQTT Engine is configured for both Default Tags and UNS Tags, this approach will result in some duplication of the folder structure under the Edge Nodes but will ensure that the UNS view is correctly laid out 


At Engine, these tags published from Edge Nodes are then concatenated under the single UNS tag path of UNS > Enterprise


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