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OPC Unified Architecture (OPC UA) is an industrial M2M communication protocol for interoperability developed by the OPC Foundation. It is the successor to Open Platform Communications (OPC). Although developed by the same organization, OPC UA differs significantly from its predecessor. The Foundation's goal for this project was to provide a path forward from the original OPC communications model (namely the Microsoft Windows only process exchange COM/DCOM) to a cross-platform service-oriented architecture (SOA) for process control, while enhancing security and providing an information model.〔Mahnke, Wolfgang; Leitner, Stefan-Helmut (OPC Unified Architecture - The future standard for communication and information modeling in automation ), 3/2009 (ABB Review 3/2009, page 56-61 )〕 After more than three years of specification work and another year for a prototype implementation, the first version of the Unified Architecture was released in 2006. The current version of the specification is on 1.02. == Innovations == Although the original binding to COM/DCOM helped OPC to distribute well, it had several drawbacks: * Frequent configuration issues with DCOM; * No configurable time-outs; * Microsoft Windows only; * Lower security; * No control over DCOM (COM/DCOM is kind of a black box, developers have no access to sources and therefore have to deal with bugs or insufficient implementations). These drawbacks along with a number of other considerations pushed the decision to develop a new and independent stack for OPC UA, which replaces COM/DCOM. The main characteristics of this communication stack were: * Multi-platform implementation, including portable ANSI C, Java and .NET implementations; * Scalability: from smart sensors and smart actuators to mainframes; * Multi-threaded, as well as single-threaded/single-task operation—necessary for porting the stack to embedded devices; * Security, based on new standards; * Configurable time-outs for each service; * Chunking of big datagrams. This communication stack reflects the beginning of various innovations. The OPC UA architecture is a service-oriented architecture (SOA) and is based on different logical levels. OPC Base Services are abstract method descriptions, which are protocol independent and provide the basis for OPC UA functionality. The transport layer puts these methods into a protocol, which means it serializes/deserializes the data and transmits it over the network. Two protocols are specified for this purpose. One is a binary TCP protocol, optimized for high performance and the second is Web service-oriented. The OPC information model is a so-called Full Mesh Network based on nodes. These nodes can include any kind of meta information. Think of nodes as objects, as in object-oriented programming (OOP). This object can own attributes for read access (DA, HDA), methods that can be called (Commands), and triggered events that can be transmitted (AE, DataAccess, DataChange). Nodes hold for process data as well all other types of metadata. The OPC namespace contains the type model. Client software can verify what Profiles a server supports. This is necessary to obtain information, if a server only supports DA functionality or additionally AE, HDA, etc. Additionally, information can be obtained about whether a server supports a given profile. New and important features of OPC UA are: * Redundancy support * Heartbeat for connections in both directions (to indicate whether the other end is "alive"). This means that both server and client recognize interrupts. * Buffering of data and acknowledgements of transmitted data. Lost connections don't lead to lost data anymore. Lost datagrams can be refetched. At the OPC UA DevCon in October 2006 in Munich the first prototypes were presented live. Various UA Servers have been shown on a Beckhoff programmable logic controller and an embedded test board from Euros. The Beckhoff PLC is based on Windows XP Embedded and the embedded controller is based on the real-time operating system Euros. The company Embedded Labs Ltd demonstrated an OPC-UA Server based on their own C++ UA Stack executing on a single chip ARM microcontroller with 64kB RAM. In October 2012 the German Fraunhofer-Application Center IOSB-INA and the Institute for industrial Information Technologies (inIT) shows, that an OPC-UA server is scalable downto 15 kB RAM and 10 kB ROM and therefore usable at chip level.〔(The smallest OPC-UA server )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「OPC Unified Architecture」の詳細全文を読む スポンサード リンク
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