OPC UA and IEEE TSN are game-changing fundamental elements of Industry 4.0 that can revolutionize industrial automation capabilities, from the field device up to enterprise level. How well do the ubiquitous, and sometimes resource-constrained, devices of today’s automation landscape cope with these new technologies?
Alexander Gogolev ABB Corporate Research Ladenburg, Germany, firstname.lastname@example.org
ABB sees Industry 4.0 playing a vital role in the future of industrial automation. Two important elements of Industry 4.0 are OPC UA and IEEE TSN.
OPC UA (open platform connectivity and unified architecture) is the next generation of OPC. OPC UA removes many of the shortcomings of OPC and is a more flexible and secure way to handle data. OPC (OLE for process control, where OLE stands for object linking and embedding) goes back to a software interface standard that allows Windows programs to communicate with any compatible industrial hardware device. OPC works in a server/client mode. The beauty of OPC is that it is an open standard, which means that a hardware manufacturer need only provide an OPC server for their device and it can then easily communicate with any other OPC client. The problem of vendor-specific protocols, interfaces, etc. is then solved in one fell swoop. OPC UA can better cope with the volume and complexity of today’s data world – a challenge that could not have been foreseen by the developers of OPC.
IEEE TSN (time-sensitive networking) is a set of IEEE standards that provides deterministic networking for OPC UA at lower levels. TSN and OPC UA combined have the potential to not only replace, but also outperform  existing fieldbuses. Nowadays, both these technologies claim to be available on the market, at different levels of readiness.
Enabling end devices with OPC UA and TSN can be challenging when those devices are resource-constrained. ABB recently investigated the performance of typical end devices when faced with OPC UA and TSN implementation. In the project, several software and hardware platforms were evaluated to develop three proof-of-concept implementations for different ABB product prototypes. These devices were enabled with OPC UA, then Extended Automation System 800xA and TSN system integration were compared. The question was: “Is the Industry 4.0 concept capable of leveraging deterministic networking and enhanced data access with TSN and OPC UA, and can these new mechanisms be integrated into products to provide broader capabilities and better performance?”
New concepts in industrial automation
Nowadays, the world of industrial automation faces new concepts, such as data analytics, cloud access, edge computing, etc. These concepts have information at their heart: its acquisition, retrieval, representation, processing and distribution.
Process-relevant data originating on devices, on a factory production line, for example, may need to be preprocessed, filtered and communicated to the cloud for management presentation and analytics. Currently, raw production data is often retrieved by fieldbus technologies, which use proprietary specifications both for the data semantics and transport. To access the process data, one needs gateways specific to the particular fieldbus to bridge data and transport formats. However, OPC UA can unify the information models for all system devices to provide enhanced and transparent data access, using TSN as transport means →01. Such an arrangement also provides powerful semantics to represent device business logic and the transparent client-server communication that can connect the factory floor to the cloud.
Apart from vendor-specific interfaces and protocols, other challenges can arise at the production line level. For instance, demanding applications, such as motion control tasks, need high performance and determinism in the data transport between devices. The fieldbus technologies that were designed decades ago struggle to meet today’s requirements. TSN can outperform  the existing fieldbuses and allow for future growth in high-performance data transport.
In summary, the requirement to not just unify enhanced information models but also to provide deterministic data transport poses a serious challenge for existing system architectures. Industry 4.0 suggests this challenge be addressed using IoT mechanisms, such as OPC UA and IEEE TSN. While TSN can provide the low-level data transport, OPC UA can serve as an IoT enabler for higher-level applications. A combination of these two technologies can provide two features vital for the future of industrial automation: a fast and robust data transport, and a client-server combination for elaborate device semantics →02.
Another positive aspect of the adoption of OPC UA and TSN is the shift from a proprietary and custom world to a unified and standard one. An evident advantage here is the unification of the software, interfaces and access models across product ranges. Furthermore, OPC UA and TSN enable the unification of development expertise between businesses, which may eliminate the existence of duplicate or redundant expertise in a bundle of various narrow fields.
Not all plain sailing
Though OPC UA and TSN may bring new capabilities and improve performance, open questions remain:
• Is the market ready to move from the proprietary (but known) in favor of standard and open (but new)?
• How to ensure a smooth evolution of the technology into the new paradigm?
• Are there any pilot solutions enabled with TSN and OPC UA? And what technologies and strategies are needed to fit OPC UA and TSN into a system?
When deciding in favor of adopting Industry 4.0, a system builder should first answer several questions. For instance, “does the system really need all the capabilities and features of OPC UA and TSN?” Not every application requires deterministic networking or low communication latency. Thus, the scope of TSN adoption will, most likely, vary: Cloud-level interaction typically would not require TSN and, in some cases, neither would field sensors. Similarly, not all end devices need elaborate semantics and uniform accessibility of data.
The second of the three questions listed above concerns integration of OPC UA and TSN into existing system design and management tools: What mechanisms should be used and how should they be unified? These are not trivial questions, given the diversity of multivendor systems and the respective tooling.
Once the decision to support OPC UA and TSN is made, the most pressing questions could be summarized as follows:
• Where does the system require new technology and to what extent?
• How would OPC UA and TSN fit into the system architecture and how should they be configured?
It is important to consider that each system starts (or finishes) at the end device. These ubiquitous devices often have limited resources. Historically, OPC UA was not used in devices with computing power, memory, or power supply that was constrained. Furthermore, full TSN support requires specific hardware to provide real-time capabilities. How much enhancement would the end device need to support the new technologies? What exactly has to happen to prepare end devices for Industry 4.0 and the IIoT? Enabling such resource-constrained devices with OPC UA and TSN can be the most challenging implementation aspect of all.
OPC UA and TSN enablement for ABB end devices
In ABB, a cross-competency team enabled OPC UA for three end devices: an ABB FCB400 Coriolis mass flowmeter, an ABB LLT100 laser level transmitter and an ABB UMC universal motor controller. The detailed description of the OPC UA enablement will be covered in detail in a later article.
During the OPC UA evaluation, the team tackled the TSN enablement for the three prototypes, using third-party infrastructure equipment. The test setup uses several TSN switches (from TTTech), two industrial PCs and the ABB end-device prototypes →03. The test setup is configured using the prototype software, combining the legacy command-line tools with new technologies such as NETCONF (Network Configuration Protocol) and YANG, a data modeling language.
With time-aware shaping (TAS) of traffic , TSN switching infrastructure can offer real-time data exchange, with up to microsecond precision. However, resource-constrained end devices often cannot match the data transmission times to the microsecond-granular forwarding windows on the TSN switches. To evaluate the consequences under such circumstances, this scenario was tackled in the first steps of the TSN evaluation.
The assessment focused on the application requirements, such as the duration of the control cycles (1 to 5 ms) and the quantity of data exchanged (typically, a read-write operation on several variables). The first phase of the project evaluated the latency and jitter of the OPC UA traffic in scenarios with different traffic loads. The application synchronization and system integration for TSN will be the focus of the second phase of the project, which will be reported in a future article.
Results and spin-offs
The TSN enablement evaluation showed that the latency of the OPC UA data exchange can be significantly reduced and bound to a narrower spread. →04 shows the difference in latency for OPC UA read requests to and from the embedded OPC UA server (in this case, the LLT100) in a network where 95 percent of the throughput is consumed by disturbing traffic and with particular reference to the quality of service (QoS). It indicates that even just the introduction of QoS reduces latency despite the high-throughput disturbance traffic. QoS in TSN switches can distinguish messages based on eight priority levels to ensure that important messages are sent first. With TSN mechanisms such as time-aware traffic shaping, OPC UA latency further shortens and becomes more stable. Clearly, even basic TSN support on the end device software improves the determinism in data access, using TSN-ready infrastructure.
The software concepts developed within the project will evolve in the second phase of TSN adoption, which will focus on automated end device integration in TSN-enabled systems.
The IIoT Device project enabled new device prototypes with OPC UA. Indeed, product development has already started for some of the target devices. Another bonus is that the research project has made available tools and best practices for OPC UA enablement. For instance, an automated code generator that translates the development artifacts (such as device description files) into C-based code ready to be compiled and loaded onto the device for use with an OPC UA server. Another example is the Device Integration (DI) model guidelines that help developers from different areas to represent the device business logic in a standard and functional manner.
A game-changer for industrial automation
TSN-ready switches that deliver the expected determinism in networking are already available on the market. OPC UA client-server software is also available as a product that is ready for integration. The OPC UA PubSub extension, which is more relevant for high-performance applications, is expected soon. According to the OPC Foundation , “PubSub enables further adoption of OPC UA at the deepest levels of the shop-floor where controllers, sensors and embedded devices typically require optimized, low-power, and low-latency communications on local networks.”
ABB end devices can already be enabled with basic TSN support today. Full TSN support, including hardware, can be provided in the foreseeable future. The full system integration of TSN is still largely an open question: Switch vendors do not aim at solutions for full system integration, but rather add-on modules for network configuration. Automation vendors and system integrators such as ABB hold the know-how for the automation systems, own engineering tools and possess the relevant expertise to decide on the scale of TSN application and integration →05. Therefore, automation vendors, network equipment manufacturers and system integrators continue the joint work to create standard integration mechanisms for TSN that can be adopted throughout the industry.
To grow into a widely adopted technology paradigm, the basic elements of Industry 4.0 needs to be harmonized and standardized. ABB representatives are actively driving the respective standardization efforts on both OPC UA and TSN. The standardization community is drawing in more and more actors with new considerations that, in turn, bring new features that need to be harmonized with the previously defined ones. Unification at such a scale requires considerable effort. Progress, however, is evident and becomes more and more prominent.
 D. Bruckner, R. Blair, M-P. Stanica et al “OPC UA TSN A new Solution for Industrial Communication,” WEKA Fachmedien, Available: https://cdn.weka-fachmedien.de/whitepaper/files/OPC_UA_TSN_-_A_new_Solution_for_Industrial_Communication.pdf. [Accessed Dec. 3, 2019].
 OPC Foundation, “OPC Foundation announces OPC UA PubSub release as important extension of OPC UA communication platform.” Available: https://opcfoundation.org/news/press-releases/opc-foundation-announces-opc-ua-pubsub-release-important-extension-opc-ua-communication-platform [Accessed Dec. 3, 2019].
This article would not have been possible without the ideas, work and dedication of the entire project team. Special thanks to Francisco Mendoza, Roland Braun, Philipp Bauer and Thomas Gamer.