M4E #35: What is OPC-UA Pub Sub?
In M4E #18 we explained what is OPC-UA. In today’s video we will see one of the most interesting features that has been incorporated into the standard and its implementation in the last years: Publication-Subscription capabilities, also known as Pub-Sub. See next the video from the 4.0 Solutions.
Time for Insights
The next pictures will help you understand the main difference in the communication model of a client-server structure and pub-sub. You can see how the number of connections reduces quite a lot, making communications much more scalable. Also, polling is eliminated, so clients don’t have to query servers continuously to ask for information, they receive data updates when needed.
Of course, in the pub-sub model the broker figure acts as a single-point of failure, but typically in a real deployment parallel instances are used in order to avoid this problem.
Client-server
Pub-sub
A pub-sub architecture allows also to decouple software from upper layers from what is at the bottom. As you can see, publishers and subscribers are decoupled from each other through the broker and the communications protocol. Thus, you can have interoperability between modules from different vendors, programmed in dispare languages, etc. Changes in features or components doesn’t force to change the whole system, only a part of it.