This paper presents a simple and efficient switched Ethernet communication protocol for industrial hard real-time LAN applications. The network is founded with end nodes and a switch, and hard real-time communication is handled by software added between the Ethernet protocols and the TCP/IP suites. We established a virtual link of the source and destination node by applying admission control based upon the requested QoS, and manages hard real-time traffic to bypass the TCP/IP stacks. This bypassing considerably reduces the dwell time in the nodes, and increases the achievable data frame rate. After the bypassing, hard real-time traffic schedule is executed according to dynamic-priority EDF algorithm. The protocol does not need any modifications in the Ethernet hardware and coexists with TCP/IP suites, therefore, the LAN with the protocol can be connected to any existing Ethernet networks and support both real-time traffic and best-effort traffic. Compared to some conventional hard real-time network protocols, the proposed one has better real-time performances, and meets the requirements of reliability for hard real-time system applications.
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