Abstract: The focus that switched Ethernet is applied in the networked control system is ability of real-time.For this，a new analytic tool：network calculus is used to determinately analyze the special performances of the real-time data via a switched Ethernet.With scheduling algorithms FIFO（First Input First Output），the communication model is set up and network elements’ arrive curves and service curves are derived for a switched industrial Ethernet model with two levels’ tree topology.Then，analytic expressions of the worst case end-to-end delay，buffer size and output burstiness are presented，the maximum network delays of real-time data are calculated based on derived results.

Key words: network calculus, switched Ethernet, worst case delay bound

摘要： 交换式以太网在网络控制系统中的应用关键问题是实时能力，为此采用一种新型实时性能分析工具——网络演算，对交换式以太网实时能力进行确定性的分析和研究。针对FIFO调度算法，对两级树型拓扑结构的交换式以太网系统建立了通信模型，推导出各网络元素的到达曲线和服务曲线，由此得到了最大时延、所需缓冲区大小、输出突发量等实时业务流的主要参数解析表达式；利用推导所得结论计算了实时业务流的最大网络时延。

关键词: 网络演算, 交换式以太网, 时延上界