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This is maybe the simplest part of the Sparkplug infrastructure. Once you have an MQTT V3.1.1 compliant server up and running on hardware sized to manage all the expected traffic, configure the appropriate access controls for the level of risk of your application, and that's it!
MQTT communicates over a single (inbound to the server) TCP port. This means every other node in the network need only have outbound firewall rules, which on most systems are allow all by default.
If required, many Open Source MQTT Server implementations are available which offer multiple server instances for redundancy, high availability, and scalability. Sparkplug is able to take advantage of these MQTT features with no extra effort.

MQTT Edge of Network Node (Edge)

An MQTT Edge of Network Node (EoN) is any V3.1.1 compliant MQTT Client application that manages an MQTT Session and provides the physical and/or logical gateway functions required to participate in the Topic Namespace and Payload definitions of Sparkplug over MQTT.
In CODESYS context the EoN is instantiated once within a program on a PLC near the edge of the network.
Usually a single EoN instance per outgoing connection is necessary. The EoN node is responsible for any local protocol interface to existing legacy devices like other PLCs, RTUs, Flow Computers, Sensors, etc. and/or any local discrete I/O or any logical internal variables.

MQTT Enabled Device (a 'Sparkplug')

This represents any device, sensor, or hardware that directly connects to MQTT infrastructure using a compliant MQTT 3.1.1 connection with the payload and topic notation as outlined in the Sparkplug specification.
Note that it will be represented as an EoN node in the Sparkplug topic payload.


The Device/Sensor represents any physical or logical device connected to the MQTT EoN providing any data, process variables or metrics. This can be seen as any data from PLCs, RTUs, Flow Computers, Sensors, etc. and/or any local discrete I/O or any logical internal variables.

SCADA/IIoT Host Node (Primary Node)

The SCADA/IIoT Host Node is any MQTT Client application that subscribes to and publishes messages.
In typical SCADA/IIoT infrastructure implementations, there will be only one Primary SCADA/IIoT Host Node responsible for the monitoring and control of a given group of MQTT EoN nodes. Sparkplug does support the notion of multiple critical Host applications. This does not preclude any number of additional MQTT SCADA/IIoT Nodes participating in the infrastructure that are in either a pure monitoring mode, or in the role of a hot standby should the Primary MQTT SCADA/IIoT Host go offline.

MQTT Application Node

An MQTT Application Node is any non-primary MQTT SCADA/IIoT Client application that consumes the real-time messages or any other data being published with proper permission and security.We

Roles and functions

Function MQTT Broker EoN Node Device/Sensor SCADA/IIot Host node Application Node
Relay Messages x
publish xDATA x
publish xBIRTH x
publish DDEATH x
Last will NDEATH x
Read xCMD x ? x
Read xDATA x x
publish xCMD x
publish STATE x
last will STATE x
Read STATE x x x
Read xBIRTH x x
Read xDEATH x x