Low-latency Hard Real-Time Communication over Switched Ethernet

Ethernet, the most widely used commodity network, increasingly moves toward switches as implementation technology thus replacing busses. This allows to use traf£c shaping techniques to implement hard real-time distributed systems on commodity networks. However, because Ethernet switches lack build-in policing features, nodes connected by Switched Ethernet need to be cooperative. Although the theory behind traf£c shaping for real-time communication is known for some time, it has not been considered for Ethernet so far. In this paper we present the implementation of traf£c shaping on Switched Ethernet technology. We make thorough experiments to understand the cost and practical limits of using Fast and Gigabit Ethernet for hard real-time communication. We do measurements to analyze properties of switches and delays that we can achieve using these switches. We further analyze the in¤uences of non real-time Linux nodes sharing the network.