Preemptive switched Ethernet for real-time process control system

Abstract

The real-time performance of control network between process control system(PCS) in a nuclear power plant is an important factor to ensure safety and reliability of power plant. Ethernet network is widely adopted in modern PCS even though it does not guarantee hard real-time performance in the non-safety region of a nuclear power plant. To achieve better real-time performance and QoS(Quality of Service), PCS usually uses switched Ethernet with the priority feature, which is based on the IEEE 802.1Q/p protocol. However, the IEEE 802.1Q/p protocol also has a priority inversion problem when transmission of a higher-priority frame is requested during transmission of a lower-priority frame. To resolve this problem, this paper proposes Preemptive Switched Ethernet(PSE) that is based on the IEEE 802.1Q/p protocol with a preemption mechanism. This paper shows that PSE provides better real-time performance than the standard IEEE 802.1Q/p protocol especially when non-real-time and real-time traffics are mixed together. This paper also implements PSE controller using the FPGA (Virtex-4) and MicroBlaze processor. From the implementation results, PSE controller shows an improved latency and jitters of transmission period compare to the normal Ethernet controller. Experiment result shows that the jitter of real-time packet is 50% less than the standard 802.1Q/p protocol.