FAQ: Ignition Modules

• Q: What do each of the MQTT Modules do in simple terms?
  • A: The MQTT modules for Ignition each have very specific functions.  The very high level overview of each is listed below.  For more detailed information see this page.
    
    • MQTT Distributor - A MQTT v3.1.1 compliant MQTT Server.
    • MQTT Engine - A module which acts as a MQTT to Ignition Tag Bridge.  This module listens for and captures incoming MQTT messages and creates/updates Ignition tags based on those messages.  In addition it listens for tag writes in Ignition and converts those to MQTT messages to send/update data and I/O on the remote MQTT devices.  This module can be thought of as a tool to receive and visualize MQTT data in Ignition.
    • MQTT Injector - A simulation tool for creating MQTT clients which represent edge gateways and field devices
    • MQTT Transmission - An Ignition Tag to MQTT Bridge.  This module listens for tag change events in Ignition and converts those to outgoing Sparkplug MQTT messages.  In addition, it listens for incoming MQTT messages and updates tag values based on those incoming messages.  This module can be thought of as a tool to MQTT enable Ignition Tag providers and push that data to an MQTT Server and MQTT Engine.

Sparkplug

• Q: What is Sparkplug in a nutshell?
  
  • A: Sparkplug is a set of definitions on top of MQTT to serve the following purposes:
    • Define a set of topics to ensure state/quality of data be ensured in a backend MQTT client application
    • Define a standard payload format that allows an edge node/device client to communicated with a backend application
    • Define a flow of messages to ensure the state/quality of data.
• Q: What is the difference between Sparkplug A and Sparkplug B?
  
  • A: The 'A' and 'B' qualifiers differentiate payload encoding formats.  The following points show the similarities and differences between the two:
    • Important note!  Sparkplug A has been deprecated and any new projects being created should use Sparkplug B.  If you need a copy of the Sparkplug A specification you can contact support@cirrus-link.com to get a copy.
    • Both A and B use the same topic format with a qualifier as the first token in the topic namespace to denote the payload encoding format
    • The message flow of both A and B is the same
    • The only difference is the payload encoding format.
    • Both formats are open source
    • Both are based on Google Protobuf definitions
    • Sparkplug A uses Eclipse Kura's payload definition found here: https://raw.githubusercontent.com/eclipse/kura/develop/kura/org.eclipse.kura.core.cloud/src/main/protobuf/kurapayload.proto
    • Sparkplug B uses an expanded definition allowing for more metadata found here: https://raw.githubusercontent.com/Cirrus-Link/Sparkplug/master/sparkplug_b/sparkplug_b.proto