Although OICT convergence (Operational, Information, and Communication Technology) is an industry consensus, its actual implementation is not as simple as it seems. When we discuss various ways to achieve smart manufacturing, including edge computing, big data, industrial internet, and industrial IoT, the first problem we encounter is actually the connectivity problem. Without solving this problem, we cannot advance the realization of other issues.
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What are the challenges in integrating IT and OT?
1.1 Fieldbus to Real-Time Ethernet
Figure 1 provides a brief description of a communication network in a manufacturing field. Compared to traditional PLC centralized control, fieldbus brings many conveniences to industrial control systems. It enables distributed control through a unified bus connection and simplifies wiring, thus reducing the workload of system configuration and diagnostics. Therefore, fieldbus is a technology that brings many conveniences to manufacturing fields. However, various companies have developed their own buses, with over 20 different buses included in the IEC standard. While the bus itself brings convenience, the different buses create new barriers. Due to differences in business focus and technical approaches among companies, various fieldbuses differ in multiple dimensions such as physical medium, voltage level, bandwidth, number of nodes, verification methods, and transmission mechanisms. This results in devices using the same bus standard being able to interconnect, while devices using different buses cannot.
Figure 1 - The fundamental reasons for the emergence of OPCUATSN technology
This is why real-time Ethernet technology began to be used in the early 21st century. In 2001, B&R launched POWERLINK real-time Ethernet, which was the first real-time Ethernet in the industrial field. Compared with traditional buses, the advantage of real-time Ethernet is that the physical medium, number of nodes, distance, bandwidth, verification, and diagnostics all adopt the standard IEEE 802.3 network. Therefore, at this level, everyone has achieved uniformity.
1.2 Interconnection and Interoperability
However, real-time Ethernet only solves the problems of the physical layer and data link layer. For the application layer, it still cannot be connected. According to the IEC standard, communication connection is divided into multiple layers such as interconnection, interoperability and interoperability. Each real-time Ethernet is based on the original three-layer network architecture (physical layer, data link layer and application layer). In the application layer, protocols such as Profibus and CANopen are used, but these protocols cannot achieve semantic interoperability.
Simply put, semantic interoperability means that in automation control, calculations like "5+5" are processed directly from physical signals. However, when IT networks transmit more complex data structures and types, more information is needed, such as units. Obviously, "5 inches + 5 centimeters" cannot be added together. At this point, we need semantic specifications and standards so that different systems can understand the semantics expressed by each parameter.
1.3 Industrial Communication in the Smart Era
Previously, we discussed the acquisition of physical signals and the transmission of information in the horizontal and vertical directions in industrial settings. However, in the era of intelligent manufacturing, we need more comprehensive data acquisition, transmission, calculation, analysis, and optimization to achieve efficient collaboration in manufacturing and improve overall production efficiency.
Figure 2 briefly illustrates this scenario. Data connectivity is needed at every stage from the factory to the supply chain. In this case, the integration of IT and OT will encounter the following complexities:
Figure 2 - Application Scenarios of Industrial Internet of Things
① Obstacles caused by the complexity of the bus
The complexity of the bus not only adds complexity to the manufacturing site but also poses a significant obstacle to IT access to OT. Different network drivers must be written for different data access methods. For older factories using fieldbuses with different physical media, additional network adapter modules need to be configured. Then there are the software-level drivers. Even with real-time Ethernet, different interface programs still need to be written. The rich combination of fieldbuses and application layers creates thousands of possibilities. This makes IT spend a lot of money on configuring networks, data acquisition and connectivity, and data preprocessing, which makes this work uneconomical. This is the primary obstacle to technological advancement. If a project cannot be implemented economically, then there is no need to invest in it.
② Transmission of periodic and non-periodic data
The differences between IT and OT data also lead to different network requirements, which often result in the use of different mechanisms. For OT, the control tasks are periodic, so periodic networks are used, mostly employing a polling mechanism where the master station allocates time slices to the slave stations. IT data, on the other hand, is often non-periodic. Because standard Ethernet cannot meet the requirements of periodic deterministic transmission and microsecond-level real-time performance, Ethernet-based protocols such as POWERLINK and Profinet were developed. However, none of these can transmit two different types of data within a single network.
② Differences in real-time performance
Due to different real-time requirements, IT and OT networks differ. For microsecond-level motion control tasks, the network must have very low latency and jitter, while IT networks often do not have special requirements for real-time performance, but do have requirements for data load.
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OPCUATSN's role
Figure 3 illustrates the position of OPCUA and TSN in the entire ISO-OSI model. We can see that OPCUA mainly solves problems at the application layer, while TSN is actually at the data link layer.
Figure 3 - The positions of OPCUA and TSN in the ISO-OSI model
Comparatively speaking, OPCUA appeared earlier, so we will first introduce the role and significance of OPCUA before discussing TSN.
2.1 The Role and Significance of OPCUA
➀ The role of OPCUA
The role of OPCUA is mainly based on the following issues. The IEC report on interconnection technology mentions multiple levels of issues such as interconnection, interoperability, and semantic interoperability (incompatibility and coexistence in Figure 4 are not considered, and interchangeability is currently not possible). OPCUA mainly solves the problem of semantic interoperability.
Figure 4 - IEC Technical Report's Hierarchical Definition of Communication Interconnection
② The core issue of OPCUA - Information Model
Figure 5 - OPCUA Architecture
Although there are many reasons to use OPCUA, including non-profit organizations, IEC standards, and security, for smart manufacturing, OPCUA is needed for collaboration between multiple devices (M2M), business management systems and production lines (B2M), and data between business units (B2B).
Figure 6 shows an information model for the plastics industry—developed using the OPCUA standard and specifications, applied to information interaction between injection molding machines and auxiliary equipment, and between injection molding machines and MES systems. Similarly, the OPCUA Foundation collaborates with OMAC/PackML—a vertical industry information model for the packaging industry, MTConnect—for machine tools, AutomationML—for the automotive industry, BacNet—for building systems, ISA—for MES systems, and various fieldbus foundations such as PI, EPSG, and ETG, making OPCUA a commonly supported semantic interoperability layer specification and standard.
Figure 6 - Information Model for the Plastics Industry
Figure 7 shows an example of the definition of AdministrationShell in Industry 4.0 described using OPCUA.
Figure 7 - OPCUA-based management shell design
Therefore, we can see that OPCUA plays a very important role in the entire OICT convergence. Due to the non-profit nature of the OPCUA Foundation and the IEC62451 standard, OPCUA has gained the support of the world's major automation manufacturers. Currently, the OPCUA Foundation is the most active global standardization organization with more than 4,000 manufacturers.
2.2 TSN and the Role of TSN
In comparison, TSN technology has only just begun to enter the industry's field of vision. However, TSN technology is not something that has only emerged in recent years. Initially, it was applied to audio/video synchronization scenarios. Later, with the need for autonomous driving/assisted driving technologies in the automotive industry, TSN was also incorporated into the development. In 2012, the original IEEE 802.1Q established a real-time working group for the Industrial Internet, called IEEE 802.1TSN.
TSN is used to solve the problems we discussed in the first section: the transmission of periodic and non-periodic data, and the transmission of real-time and non-real-time data. The original standard Ethernet IEEE 802.3 was not deterministic, which is why various real-time Ethernet systems were developed. Today, TSN enables standard Ethernet to transmit real-time data and allows periodic and non-periodic data to be transmitted in the same network. This greatly simplifies the workload of the entire intelligent integration process and makes it much simpler.
Figure 8 - TSN Network Reference
Figure 8 shows the TSN network reference. Like other networks, it uses IEEE 802.1ASRev to define precise clock synchronization and then organizes data using data queues. The difference is that IEEE 802.1Qbu+IEEE 802.3br uses preemptive MAC to transmit high real-time data, while IEEE 802.1Qbv uses TimeAwareShaper to provide a dedicated time channel for high real-time data, and BestEffort to transmit other non-real-time data.
TSN consists of a series of technical standards. Table 1 lists the industry-related standards, application areas, and names:
Table 1 - TSN Related Sub-standards
IEEE 802.1Qcc is a standard for network and user configuration. As shown in Figure 9, it is divided into centralized user configuration and network configuration, and can configure networks under various mechanisms such as Qbu, Qbv, and QCB.
Figure 9 - Network configuration based on IEEE 802.1Qcc
As can be seen, TSN is actually a new data link layer standard developed to enable heterogeneous data interaction and the transmission of real-time and non-real-time data in the same channel.
With the growing demand for the Industrial Internet and the advancement of smart manufacturing, OPCUA and TSN technologies will become more urgent and critical.
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OPCUATSN architecture for future smart manufacturing networks
The second section introduces OPCUA and TSN separately, and as shown in Figure 1, these two standards will work together to provide the foundation for interconnectivity in the manufacturing industry in the future.
3.1 Foundations for the Implementation of the Industrial Internet
Figure 10 shows the position of OPCUA and TSN in the entire OSI model. However, it is not that simple in reality. We can see from the mechanism of OPCUA that OPCUA, including sessions and connections, actually covers the session layer and presentation layer. Similarly, although TSN only refers to the data link layer, its network mechanism and configuration management can be understood as covering layers 1-4.
Figure 10 - Network architecture of OPCUATSN
If we understand OPCUA and TSN in this way, we will find that OPCUA and TSN actually run through the entire OSI seven-layer model, enabling a true "Industrial Internet" through unified standards and specifications.
Figure 11 - Future Industrial Communication Architecture Based on OPCUATSN
Figure 11 shows the entire industrial internet architecture based on OPCUA. As we can see, devices with controllers from different brands can be integrated horizontally through OPCUA, while vertically, devices can be connected from the factory to the cloud.
TSN enables physical information transmission between controllers and underlying sensors and drivers, while OPCUA can be combined with traditional real-time Ethernet to form multi-dimensional data integration. In the future, the integration of TSN and OPCUA can also realize a brand-new manufacturing field network integration.
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OPCUATSN Technology Progress
4.1 Standardization process of OPCUATSN
OPCUA has become an IEC standard and a Chinese national recommended standard in 2017. In 2018, a Pub/Sub-based mechanism was released as a supplementary mechanism to OPCUA, published by the IEC in Part 13.
The TSN standard is currently being developed by the IEEE standards organization, and the current status is shown in Table 2.
Table 2 - TSN Standard Progress - Completed standards include IEEE 802.1 Qbv and Qca. Table 2 shows the status as of 2017. To learn about the progress of the IEEE 802.1 standard, please visit the official website ieee802.org for detailed information.
Table 2 - Current Standard Progress of TSN
4.2 Industry Promotion
Currently, OPCUA and TSN are mostly in the research and development stage, with few publicly released products. At the 2016 SPS exhibition in Germany, B&R released a test system based on OPCUA and TSN, as shown in Figure 12. In this system, the OPCUA and TSN network, consisting of 200 I/O nodes and 5 high-definition video, achieved a response time of 100μS for a single data refresh.
Figure 12 - Test unit based on OPCUATSN
At the 2018 Hannover Messe, many manufacturers, including Siemens, also began to release TSN products.
4.3 Testing and Verification Platform
At the Hannover Messe in April 2018, Huawei, together with ABB, B&R, Schneider, ARM and other companies, jointly launched the OPCUATSN testbed. This represents the latest progress in the convergence of IT and OT and is a milestone for OPCUATSN to enter the substantive stage.
Figure 13 - TSN-OPCUA Testbed Launch at Hannover Messe 2018
Summarize
OPCUA and TSN represent the technological trends of the future industrial internet and the path to OICT convergence. This article mainly understands OPCUA and TSN from the perspective of OT. For IT applications, OPCUA and TSN provide convenient access, which in turn leads to business model innovation, industrial application scenarios based on edge computing, intelligent optimization based on cloud connectivity, and the transformation of industrial business models, truly realizing digital transformation.
