Not Your Father’s Fieldbus

Aug. 2, 2018
As big as the move from fieldbuses to Ethernet-based networks was, the move toward Time-Sensitive Networking will be equally significant because it places all protocols on the same footing. This change puts the focus on protocol capabilities and ease of use.

The fieldbus wars from the days of yore are over. Closed fieldbuses simply don’t cut it anymore when it comes to running a modern manufacturing plant. Sure, they achieve the necessary performance, but at the expense of flexibility. Industrial Ethernet was a step in the right direction with its openness. Now that Ethernet is becoming deterministic by design, performance is no longer the deciding factor. Now, it’s all about the data.

But in reality, it’s always been about the data. If you think back to what made fieldbuses so revolutionary—the move from analog to digital—it was nothing short of a step change. And though replacing 25 wires with just one wire was great, the real cost savings came from less tangible benefits. Increased data capacity, high-speed networks, diagnostics—these were the features that made it possible for us to sell 60 million Profibus nodes. They led to benefits like decreased downtime, increased transparency, shorter throughputs and overall higher efficiency.

The move from fieldbuses to Ethernet-based networks was another step change. Serial fieldbuses achieved their determinism by virtue of the fact that they were a closed network. Likewise, a control network that leverages standard unmodified Ethernet to allow deterministic data exchange to coexist with other protocols—all on the same physical layer—is monumental. This is what made it possible for us to sell 25 million Profinet nodes.

Now, as we move toward Time-Sensitive Networking (TSN), we can see the move to industrial Ethernet as an evolutionary step in the right direction.

Where does the future lie?

As Ethernet evolved, latency was sacrificed in favor of flexibility, since its largest use case was, and is, the Internet. But now the IEEE is adopting and standardizing many of the concepts we’ve invented for factory automation to engineer a deterministic-by-design version of Ethernet known as TSN.

This is a fundamental shift. It means any Ethernet-based protocol can theoretically gain the performance benefits previously associated only with deterministic control networks. You read that correctly: Any. Protocol. Think about this for a second. What does it mean for the future? It means that all protocols can share an equal footing, making the primary differences between them data access and feature functionality.

You might be asking yourself, “Why TSN? This is nothing new!” The answer is that TSN ensures robustness even in heavily loaded networks. Latency is low in lightly loaded Ethernet networks today. But as more traffic gets transmitted over the network, a near certainty in the future, TSN will ensure latency doesn’t suffer for time-sensitive control data.

Using the right tool for the task

Numerous Internet-based protocols exist, such as HTTP, FTP, SMTP, POP, SSH, DHCP, SNMP, LDAP and RSTP. The reason we have so many is that each is suited to its purpose. The same can be said for automation networks that now share a common TSN foundation. Just because you can use a protocol for a certain task doesn’t mean you should.

A common example is Profinet vs. OPC UA Pub/Sub. It doesn’t make sense to use Profinet for information exchange between office-level computers due to routability and data format. Similarly, it doesn’t make sense to use OPC UA for data exchange between field-level devices due to telegram size and overhead. OPC UA simply doesn’t have the characteristics of a modern-day fieldbus, but it is great for modeling and moving information. As a result, Profinet and OPC UA Pub/Sub are complementary technologies, not competing ones.

Though your father’s fieldbus in the 1990s may have been focused on data exchange, modern fieldbuses do much more. Today, an industrial Ethernet protocol must be capable of motion control, data semantics, comprehensive diagnostics, functional safety, scalable media/system redundancy, energy management, process control and flexible topologies—including wireless and fiber, painless commissioning, asset management, IT integration and last-meter connectivity (IO-Link).

The key point to remember is that not all protocols situated for the same task are created equal. With performance otherwise guaranteed via TSN, and more than one flavor of industrial Ethernet on the market, differentiation comes from their capabilities and how easy they are to use. As manufacturing complexity increases, data access and usability should be your core areas of focus for any future-proof industrial Ethernet.

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