OPC UA Standard

Open Platform Communications United Architecture

OPC UA standard or OLE (Object Linking and Embedding) for Process Control Unified Architecture is an open source standard for communication in industrial automation. The purpose of OPC UA is to connect higher-layer software systems with lower layers.

Higher-layer systems include HMI screens, SCADA or MES and ERP systems, while lower-layer systems are PLC and DCS. It is based on the TPC/IP protocol and combines OLE and DCOM technologies.

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    Compatibility and scalability

    OPC UA architecture

    The OPC UA standard is a platform-independent architecture that was created due to the need for compatibility and scalability in various projects and applications. OPC UA, unlike OPC, is not based on Microsoft’s OLE and DCOM technology and is thus extensible to other platforms such as OS X, Linux (JAVA) and Android.

    OPC UA is a secure and reliable standard that specifies communications between devices (M2M) and between the machines and the IT and OT system. It is based on the concept of client-server, where the server is an application that provides its data to other applications, and the client is an application that requires or obtains data. In practice, developers strive to make applications that are clients and servers at the same time.

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    Independent architecture OPC UA standard

    OLE for Process Control Unified Architecture provides a Service Oriented Architecture (SOA) that is based on different logical levels.

    All of the basic services are abstract method descriptions which are protocol independent.

    They provide the basis for Unified Architecture (UA) functionality in the OPC standard.

    The basic components of UA functionality are the transport mechanism and the architecture of the standard.

    Meet the elements of the OPC UA architecture

    OPC UA architecture elements

    Transport layer

    The transport layer serializes or deserializes the data. It encapsulates them into a data set suitable for transmission or storage and transmits them over the network.

    Transport layer is defined by protocols based on TCP/IP. The first layer is the optimized TCP protocol UA binary, and the second layer is designed as an XML-SOAP web service. There is also a hybrid of both called UA-Binary via HTTPS.

    Service layer is an architectural pattern, applied within the service-oriented design and represents a data model.

    The data model is not hierarchical but a distributed node-based network service system. The service performs operations autonomously, which you can also use outside of application context. The client can access diagnostic and metadata even if he does not know the entire data model. The model therefore represents the basic building blocks for new applications.

    A node represents an object known as a basic building block in object-oriented programming. The building consists of different properties or attributes.

    A node can have attributes for read access Data Access (DA), Historical Data Access (HDA). We can read properties, call methods on them, and trigger various events. These include Alarm and Events (AE) and DataChange (DA). This feature is very useful when exchanging information between devices.

    Above the transport layer is a session layer and a layer to establish secure communication between the server and the client. Above the latter is SSL, HTTP or HTTPS. Security is based on the X.509 certificate, which checks the client that it cannot be inserted or changed.

    UA is based on TCP / IP and follows the ISO OSI model. The individual layers of the model thus define the specifications, which are divided into core properties, access methods and tools.

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