This is Part 4 of our “25 Things to Consider when Choosing an OPC Tunnel” series. Performance matters when choosing a tunneler.
Performance is always an important consideration when choosing the best tunneler. It is even more important if one or more of the following is true:
- You need to transfer a lot of data very fast.
- You are using networks with limited bandwidth.
- You are using cellular or satellite networks that charge based on the amount of data used.
This blog post will cover some important aspects to consider when evaluating different tunneling solutions, their methods and the resulting performance relative to such variables.
There are two basic types of OPC tunneling products on the market today, each with a different approach to the problem.
The first approach extends the OPC transaction across the network link.
The second approach keeps all OPC transactions local to the sending or receiving computer.
Think of a train. It has a locomotive, cars, and cargo. When a tunneler passes an entire OPC command across your network, it’s sending the entire train, when all you care about is the cargo. Tunnelers that move the entire OPC command and the data will not be as fast as one that only tunnels the data with as little extra infrastructure as needed to carry the data.
An effective tunneler passes data only on data change events. Why move the entire train when you can move only the cargo in a lightweight package? This metaphor suggests moving contents of train cars without a train; in reality, the idea is that if you only need the data, use an express bullet train, not a lumbering freight train.
Tunnelers that only tunnel the OPC calls typically do not have a means to restrict what data is exposed from the OPC server over the tunnel. An effective tunneler will have the option to either expose all the tags in an OPC server, or only the tags that you want exposed. Only exposing what you need also increases the speed of OPC client configuration, because item discovery and browse operations on the OPC client occur faster with smaller data sets.
Some tunnelers poll for data changes and even send data that has not changed. An effective tunneler will only transmit data changes.
Ask potential suppliers for their performance data. Do they know the latency—a fancy word for “delay”— added as the data passes through their application? As speed is important for your application, this conversation will be critical. If the supplier doesn’t want to reveal this information publicly, you might have to ask for the data. A reputable supplier will be glad to share what they know, and communicate by phone with engineers to discuss your concerns, without sales pressure.
How a tunneler performs is just one of the many considerations when choosing an OPC tunnel. To reiterate from our last post, choosing an effective tunneler that takes into account your application requirements will make a big difference in your operational effectiveness, resiliency, and profitability. Learn about the other reasons in the free whitepaper “25 Considerations when choosing a tunneling solution”.