Home > Knowledge > Content
Factory level industrial Ethernet protocol to realize effective asset monitoring and interconnection
Mar 16, 2020

Ethernet dominates industrial automation communication, but users need to choose the best industrial protocol at various architecture levels. Contextualization is the key to transfer the original OT data. Object-oriented can improve the consistency and efficiency, and be compatible with the latest programming language.

Industrial automation applications rely on connections from the lowest level to the highest. The most basic field connection is hard wired I / o point, which has been supplemented or even replaced by industrial field bus for many years. Other networks and protocols are more suitable for communication between higher-level automation components.

In the past decade, a significant progress has been the increasing use of Ethernet for industrial connectivity. Ethernet has become the leader of many choices, but even if this seems to simplify the problem, end users still have to choose the appropriate industrial Ethernet protocol.

Installation may require multiple protocols, depending on the application and where each protocol will be used in the automation system architecture. Some industrial Ethernet protocols have strong foundation and mature technology, but many of them are not ideal. Other protocols are optimized for specific applications such as high-speed motion. In the upper layer of the industrial automation architecture, that is, the factory level network above the controller network, there are specific requirements for the selection of driving protocol, and its focus is different from the field equipment and I / O level network at the lower layer.

Factory level network is a place where many different systems interact with each other. It needs a secure network protocol to provide rich context objects, so as to provide the original data as practical information. OPC UA is an industrial protocol that can be considered to provide these characteristics in the plant level network. OPC UA feature set makes it an effective protocol for monitoring and connecting with industrial Internet.

Equipment and network architecture of industrial automation and control system

Industrial automation system is composed of many interconnected or networked devices and components. Field devices such as sensors, actuators, and intelligent systems are connected to the controller. These PLC and PAC monitor and command field devices, communicate with each other, and network to a higher level system for human machine interface (HMI), monitoring and data acquisition (SCADA), history recording, analysis and other functions.

Industrial network architecture is defined by many features, but it is not always a precise definition, because some network layers can be virtualized or folded together on a physical network. The following is a representative of the relevant levels that must be networked within the industrial building:

Level 4: business planning and logistics;

Level 3: for on-site supervision;

Level 2: HMI and SCADA monitoring;

Level 1: local PLC and PAC automatic control;

Level 0: field sensors, devices, and networks.

Controllers can use hardwired I / O, fieldbus networks, and industrial Ethernet to interact with field devices (and with each other) at levels 0 and 1. These connections are local to site connections, usually consisting of small packets that must communicate quickly because of the need for real-time direct control of the physical device.

There are different requirements for communication between and on the controller. Industrial networks connecting level 1 and above are sometimes referred to as factory level networks. Factory level packets may not be as time critical as lower level communications.

Compared with the low-level network with stronger specificity, the factory level network is made up of a wide variety of systems interconnection. This puts forward new requirements for modern industrial plant level network communication:

Security: provide built-in security features;

Situational, object-oriented: be able to define and organize the data transferred;

Platform independent: allows distributed applications to communicate seamlessly.

As mentioned earlier, Ethernet has become the preferred choice for physical networks. This is also true for enterprise and business information technology (it) applications and industrial operating technology (OT) systems. From a physical point of view, Ethernet can be run using copper, fiber, or even wireless. The real difference between Ethernet used in it and ot environment is the communication protocol running on Ethernet.

There are some difficulties in applying commercial it Ethernet to industrial ot applications. Ethernet has many good protocols (such as PROFINET, Ethernet / IP and many others) to choose from, so it becomes the leader of OT field network.

The field network protocol varies according to the task of its ot role, but the field network protocol is generally a dedicated protocol, and often has some legacy problems, which makes it not suitable for a higher level of network level. At these levels, users need more flexible and functional protocols to interact with multiple system types. They prefer open solutions with the security necessary for business and Internet Oriented connectivity.

Over the years, the OPC foundation has developed and maintained specifications for delivering safe and reliable interoperability. The latest specification (first released in 2008) is OPC unified architecture (UA).

At level 1 and above, OPC UA defines how to model and communicate information using specific security, situational, and object-oriented features - making it a good choice for most industrial applications. OPC UA's comprehensive, modular and scalable features allow users to create "systems of the system.". That is to say, an integrated industrial automation system is constructed by many subsystems of different sizes, which interact seamlessly with each other. The client and server are defined as interactive partners.

With the improvement of communication ability of Ethernet and Internet in digital system, it also brings security risks. Information security is defined by confidentiality, integrity and availability (CIA). Traditional fieldbus networks and early industrial Ethernet protocols focus on availability and integrity, with little or no consideration of confidentiality. This is often referred to as availability, integrity, and confidentiality (AIC) or CIA. Whether it's the CIA or the AIC, higher-level networks need a more balanced approach.

Some protocols can be extended by adding security features, such as virtual private network (VPN) or transport layer security (TLS), although this is not ideal. A better way is to design the security architecture into the protocol. OPC UA uses a set of built-in services to process security certificates, and establishes secure client / server sessions at the application layer, channels at the communication layer, and socket connections at the transmission layer.

OPC UA provides a local security mechanism for clients to discover available servers, manage and distribute certificates and trust tables, and coordinate with certification authorities. OPC UA is fully qualified for the role of modern Ethernet protocol, which is used for secure industrial communication from level 0 to level 4.

Classic industrial protocols emphasize the reliable transmission of raw data. The designer is responsible for arranging the input data signals and then processing them in the destination controller to convert the original data into useful information. For example, this processing includes defining what information is and scaling values to engineering units.

If this operation must be performed at every step of the communication channel (for example, from I / O signal to controller, from controller to HMI and SCADA, from SCADA to MES, from SCADA or controller to History), the processing task will become heavy.

There is a better approach, called contextualization, which requires the use of inherent semantics to transmit data, so that there is no need to program and configure the PLC and HMI independently, or to map signals carefully between them, as the meaning of the data is understood by two collaborative applications. Contextualization allows users to work with the same set of source data. OPC UA's excellent self discovery capability enables HMI configuration to navigate into PLC configuration, so as to obtain required data, and all scaling and attributes of data are inherently available in standard format. OPC UA also supports the concept of hierarchy, which can be used by careful designers to organize data into practical arrangement, just like the folder based file system on PC.

Contextualization enables aggregation servers to aggregate information from one or more areas of an industrial automation site. This information can then be provided to numerous clients for visualization, analysis, history, and other applications.

Each client simply points to the node that encapsulates all the required information, because the supplementary data is sent in a structured format, where data variables and attributes are separated by references that define the relationship between them. This approach to a certain extent flattens the level of automation and enables each key stakeholder to have meaningful data at any time.

Object oriented technology is an organizational feature that can be used to develop information models and convey meaning in a standard format. For example, a structure can be used to represent the inlet and outlet temperature and pressure of the pump.

Using object-oriented concepts, designers can develop reusable best practice configurations. Furthermore, the concept can be extended so that objects can also reference and assemble from other objects. Therefore, object-oriented design improves efficiency and consistency.

In addition to disclosing information, OPC UA server also provides a set of complex services for clients, including discovery service, subscription service, query service and node management. It allows users to create object models that can be easily used by any client application.

OPC UA was created to eliminate restrictions imposed by OPC classic, including dependence on Microsoft technology, and to address emerging requirements in terms of security, cross firewall communication, and support for complex data structures. In this way, distributed applications running on various platforms, including real-time operating systems (such as VxWorks or QNX popular in the first level real-time deterministic high-speed PLC / PAC), can communicate with the second level system in a seamless way.

Time sensitive network (TSN) is a complementary standard Ethernet developed in the field of quality of service (QoS), including bandwidth reservation and synchronization. TSN makes the concept of certainty, security and guaranteed bandwidth possible, which is critical for demanding industrial applications, while converging various standards and real-time protocols into a single network. Using opc-ua on TSN is a significant progress in the field of industrial automation. It can make the best of both worlds to realize contextualization, and even safer and more secure bandwidth.

When it comes to industrial automation connections, even if physical Ethernet is so popular, designers still face many protocol choices. Sometimes they are limited by a physical network or digital protocol that is compatible with the selected device. However, the modern architecture of factory level network requires that any communication is secure, situational and object-oriented.

These precise features are built into OPC UA, and security terms follow proven it concepts. Contextualization is the key to transfer raw OT data to many different high-level it / OT systems using a framework supporting information. Object oriented can improve consistency, efficiency and compatibility with the latest programming languages. The combination of these advantages makes opcua the first choice of industrial automation communication protocol