EPA Network Protocol Development And Research On Conformance Test

With the development of computer network, communication and control technology, the application of Ethernet in the industrial control field becomes a research hotspot. However, the inherent disadvantages of Ethernet, such as the uncertainty of communication delay and the deficiency of uniform application layer protocol, highly prevent its step into the industrial control area.EPA (Ethernet for Plant Automation) is a real-time Ethernet solution in field device layer. It expands the data link layer defined by ISO/IEC 8802-3 agreement with a communication scheduling management entity, which schedules the package sending to avoid collision and therefore solves the uncertainty of communication delay. In addition, EPA defines a uniform application layer protocol to meet for the request of device management and data transmission in industry control system, which implements the intercommunication among Ethernet devices in industry control field.The hiberarchy of EPA application layer protocol is studied. According to the modularized structure of the protocol, the development of EPA management information base class EPA_SMIB, socket mapping entity class EPA_SMPE, system management entity class EPA_SME and application access entity class EPA_AAE, which are implemented in Linux application layer, using object oriented design and C++ programming language, is introduced.The architecture of EPA data link layer protocol is studied and the package scheduling principle of EPA communication schedule management entity is analyzed. The timed messages transmission is realized through software/hardware timer. The priority management of messages is implemented through Linux QoS interface. The protocol state machine is developed through the modification of relevant code in Linux LLC layer.Choose conformance test as the verification method of the implemented EPA protocol. According to EPA conformance test principle, the test platform is established and the conformance test is carried out through EPA_Tester, which was developed by SUPCON. Test results show that the implemented EPA protocol is in accordance with EPA standard.