Industrial Protocols: We Answer the Questions Everyone Gets Wrong

What industrial protocol should we use? That’s the question we hear most, and it’s the wrong one. The right question is: what problem are we solving, and at which layer? We’ve spent years wiring factories, and we can tell you that protocol choice is rarely about performance alone—it’s about legacy, vendor lock-in, and the skills your team actually has. So let’s bust some myths and give you straight answers.

Is Modbus dead?

No, and it won’t be anytime soon. Modbus, developed in the late 1970s, still uses a master-slave register model and runs over serial (RTU) or Ethernet (TCP). The Modbus Organization calls itself the steward of the world’s most widely adopted industrial communication protocol (Modbus Organization). But here’s the catch: Modbus has no built-in security, no device profiles, and no real-time guarantees. We still deploy it for simple sensor-to-PLC links, but we never expose it to the internet. If you’re building a new line with more than a dozen devices, Modbus alone will hold you back.

Is PROFINET just Siemens’ proprietary Ethernet?

That’s a myth. PROFINET is an open, Ethernet-based real-time protocol developed by Siemens and PROFIBUS/PROFINET International. It supports real-time (RT) and isochronous real-time (IRT) classes for motion control (OPC Foundation). The installed base is massive: PI reports more than 68 million PROFIBUS, over 69 million PROFINET, and over 51 million IO-Link nodes worldwide as of the end of 2023 (PROFIBUS & PROFINET International). Yes, it’s dominant in Siemens shops, but it’s standardized and multi-vendor. If your plant is Siemens-heavy, PROFINET is a no-brainer. If not, you’ll pay a premium in training and spares.

What’s the difference between EtherNet/IP and PROFINET?

Both run over standard Ethernet, but they come from different camps. EtherNet/IP uses the Common Industrial Protocol (CIP) over TCP/UDP and is especially common in North America on Rockwell/Allen-Bradley platforms (OPC Foundation). CIP is object-oriented and media-independent, supported by hundreds of vendors (ODVA Common Industrial Protocol). PROFINET is more prevalent in Europe and Asia. The real difference is in the ecosystem: if you’re a Rockwell shop, EtherNet/IP is the path of least resistance. If you’re Siemens, PROFINET. We’ve seen too many projects try to mix them without a gateway—don’t do that unless you enjoy debugging.

Do we need OPC UA if we already have MQTT?

They solve different problems. OPC UA is a vendor-neutral, platform-independent standard with built-in encryption and authentication, serving as the backbone for IIoT and IT/OT integration (OPC Foundation). It’s standardized as IEC 62541 (IEC 62541 OPC UA Standard). MQTT is a lightweight publish/subscribe messaging transport, standardized as ISO/IEC 20922 (ISO/IEC 20922 MQTT Standard). OPC UA is for structured, secure data modeling from machine to MES/ERP. MQTT is for efficient many-to-many telemetry, often to the cloud. In practice, we use OPC UA for controller-to-SCADA and MQTT for sensor-to-cloud. They complement each other; you don’t have to choose.

Is real-time Ethernet only for motion control?

No. EtherCAT, for example, was designed for hard real-time with cycle times ≤ 100 µs and jitter ≤ 1 µs (EtherCAT Technology Group). It’s used in packaging, printing, and robotics. But real-time Ethernet also matters for high-speed sorting and registration. Sercos offers cycle times from 31.25 µs to 65 ms with synchronization accuracy much less than 1 µs (Sercos International). If your application has axes that must stay in lockstep, you need a deterministic protocol. For basic discrete I/O, standard Ethernet with a managed switch is often enough.

Can we just use MQTT for everything?

We wish. MQTT is brilliant for constrained devices and unreliable networks—it has three QoS levels, supports TLS, and scales to millions of devices (MQTT.org). But it’s not deterministic. You can’t run a servo loop over MQTT. And while MQTT is agnostic to payload, it doesn’t give you the semantic model that OPC UA does. So no, you can’t use it for everything. Use it where it shines: telemetry, remote monitoring, and cloud integration.

What about security? Aren’t legacy protocols fine behind a firewall?

That’s the most dangerous myth. CISA warns that many legacy ICS devices use outdated operating systems and older protocols that lack encryption or authentication, and brownfield deployments are a unique challenge (CISA Industrial Control Systems). A firewall helps, but it’s not enough. We follow ISA/IEC 62443, which defines requirements for secure industrial automation and control systems (ISA/IEC 62443). For new projects, we insist on protocols with built-in security like OPC UA or CIP Security. For legacy, we segment and monitor. NIST SP 800-82 Rev. 3 provides guidance on securing OT (NIST SP 800-82 Rev. 3).

Quick tip: If you’re designing a new line, pick one real-time Ethernet protocol for the field level and OPC UA for northbound data. Mixing three or more fieldbuses on one machine is a maintenance nightmare.

So what should we actually do?

Start with a layered approach. Use the right protocol for each layer: Modbus, PROFINET, or EtherNet/IP for field devices and PLCs; OPC UA and MQTT for SCADA, MES, and cloud (OPC Foundation). Don’t chase trends—chase interoperability and security. The industrial automation market is growing at 8.5% CAGR to reach $326.48 billion by 2032 (Maximize Market Research), and IIoT is growing even faster at 12.2% (Maximize Market Research). That means more devices, more data, and more risk. The protocols you choose today will be with you for decades. Choose wisely, and don’t let a vendor’s sales pitch override your plant’s reality.

Sources

• OPC Foundation - https://opcfoundation.org/
• PROFIBUS & PROFINET International (PI) - https://www.profibus.com/technology/
• ODVA Common Industrial Protocol - https://www.odva.org/technology-standards/key-technologies/common-industrial-protocol-cip/
• ISO/IEC 20922 MQTT Standard - https://www.iso.org/standard/69466.html
• CISA Industrial Control Systems - https://www.cisa.gov/topics/industrial-control-systems
• Maximize Market Research - https://www.maximizemarketresearch.com/