Industrial automation systems rely on connectivity from the lowest to the highest levels. Ethernet has proven to be a dominant networking technology, but the right protocol must be selected for each application. My article in The Industrial Ethernet Book, Choosing the Right Plant-Level Industrial Ethernet Protocol, discusses the specific needs for plant-level networks, and why OPC UA is a good fit.
Plant-level networks are those where on-site devices like programmable logic controllers (PLCs) and programmable automation controllers (PACs) communicate with other intelligent devices and systems, such as higher-level systems for human-machine interface (HMI), supervisory control and data acquisition (SCADA), historization, and analysis.
Building a Plant NetworkHere is one way of representing network levels in an industrial plant:
Level 0 field-level communications contain relatively small data packets which must be communicated quickly for real-time control. Industrial networking levels at Level 1 and above are sometimes collectively called plant-level networks, and usually carry somewhat larger data packets with less stringent communication time requirements. Modern plant-level network communications must be:
Ethernet has long been the physical network of choice for information technology (IT) systems, and more recently for operational technology (OT) systems at the plant level.
ProtocolsThere are many protocol choices for OT industrial Ethernet field networking at Level 0 such as ProfiNET, EtherNet/IP, and many others.
Field networking protocols are quite mission-specific for their OT roles, but the specialized nature and legacy roots of field networking protocols makes them less suitable for higher levels of the networking hierarchy.
To handle communications at Levels 1 and 2, the OPC Foundation in 2008 released the OPC Unified Architecture (UA) specification to define how information can be modelled and communicated with security, contextualization, and object-oriented features.
The comprehensive, modular, and scalable nature of OPC UA allows users to create a "system of systems" … built from many subsystems of all sizes interacting seamlessly with each other.
The OPC UA industrial communications protocol provides security and data contextualization using a platform independent architecture.
SecuritySecure networking demands a balance of confidentiality, integrity, and availability. Some older protocols can be improved by adding security features like virtual private networks (VPNs), but a better approach is for security mechanisms to be built into to protocol, as with OPC UA.
Context and Object-OrientationClassic industrial communication protocols focused more on reliable transmission of raw data, leaving burdensome organizational tasks and interpretation to end users. OPC UA supports object-oriented techniques of contextualization where the data conveys its own meaning, and hierarchy to organize the data.
Object-oriented techniques improve efficiency, enabling designers to create, re-use, and combine information models.
Platform IndependenceUnlike older protocols, OPC UA can seamlessly be implemented on a variety of Level 1 and Level 2 platforms, and considers emerging requirements for security, firewalls, and complex data structures.
TSN is Next Level TechnologyTime Sensitive Networking (TSN) is a developing evolution of Ethernet. Using OPC UA over TSN, even in conjunction with other protocols, will enable Quality of Service (QoS) features like bandwidth reservation and synchronization.
OPC UA Built for IndustryPhysical Ethernet works for many levels of industrial networking, and OPC UA is a comprehensive plant-level Ethernet protocol for delivering the required security, contextualization, and object-oriented capabilities.