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1. What is the importance of a broker in the enterprise architecture? If the broker breaks the connection does it ensure QoS policies?
In a OPC UA Pub/Sub architecture, consider below two scenarios.
- No-Broker use case: Resulting in faster cycle times and within the network
- Broker use case: Resulting in slower cycle times and outside of the network
However, OPC UA pub/sub by itself doesn’t cover the QoS policies. It maps to the QoS of the brokers. So, if the brokers have the QoS, the messages are handled as per that QoS policies.
For example, if MQTT is being used, both publisher to Broker and Broker to subscriber can be configured with different QoS and the message delivered is ensured as per that set of QoS policies.
2. Can you restrict the read/write control in the OPC UA Server architecture at the tag level? Can the broker functionality be implemented in the pub-sub model? If yes, then at which end? Client or Sever?
Yes. In the OPC UA client server architecture, it is possible to have read/write control defined/ restrictions applied at the tag level at the server end.
3. How many OPC clients can be connected to a broker?
The Pub/Sub model doesn’t place a limit on the number of maximum client connections. However, it depends on system configuration of your application.
4. Is it mandatory for an OPC client to be a publisher or a server can also publish the data?
To answer your question, being a publisher or a subscriber doesn’t necessarily mean that they are forced to be a client or a server. It depends on the datatype that they require at that particular moment.
5. Is the broker used between the OPC client and Server for security purposes?
Yes, it’s possible to use brokers for the OPC UA PubSub middleware module integration. However, brokers are not implemented for the providing security measures. They are used to transfer the load in the OPC UA Server.
6. Does Edge device have both the OPC Client and OPC Server capabilities?
This is a common question raised by all. Yes, it is possible to have edge devices to have both OPC Client and OPC server capabilities. Utthunga has already executed at least 3 projects with both client and server in single device.
Consider the scenario where you have 3 PLCs with OPC UA running on them and you have a separate edge gateway. In this case, the edge gateway will have OPC UA Client to connect to the PLCs gather data and expose the aggregated data again via OPC UA using a OPC UA server.
7. What is the role played by the MQTT Broker? How does OPC UA leverage MQTT?
To answer your question, MQTT broker is the middleman between subscribers and publisher, i.e. it manages the channels where in messages are transmitted. OPC UA Pub-Sub does message exchange over MQTT protocol.
8. How to handle the data from the ASCII controller?
Please share the specific machine model and controller details and we shall get back to you.
9. What is the difference between MQTT OPC Connector available in the market and Utthunga’s interface software?
All the open connectors have basic functionality that would be limited in terms of flexibility and maintenance. We provide interface software that is certified, flexible and provide support services.
10. Can OPC UA Server be introduced at the ISA-95 level-1?
In general, level 2 and above is recommenced but based on the specifics of the plant and operational requirements.
11. Is MQTT suite better than OPC for some use cases?
MQTT only handles the message exchange. Nothing more. The data harmonisation across different solutions that use MQTT is possible only if the data that is being exchanged, is harmonized to begin with. OPC Information Models and PubSub specification does that.
12. Do unidirectional gateways support OPC UA to achieve communication from OT to IT layers?
No, OPC UA does not work with unidirectional gateways (diodes). OPC UA communication supports a Client-Server and/or PubSub communication mode. The unidirectional feature of data diodes does not allow OPC UA to work.
