EPA网络跨网段延迟数学模型

A mathematical model of delay across segments in EPA network

为了实现EPA跨网段实时传输,建立了一个跨网段的端到端传输延迟数学模型.根据EPA标准给出了EPA网络跨网段通信链路模型,EPA网桥是该链路中的关键设备.通过对EPA网络跨网段数据传输过程的分析和对EPA网桥工作过程的分解,得出影响跨网段传输延迟的主要因素有:跨网段数量、传输距离、网桥处理能力、各网段调度算法、不同网段时基差、节点实时负载变化和网络速率.将数量、距离、速率、时基差等确定性因素用独立变量描述;对能力、算法、变化等不确定因素,通过计算找出它们的最大变化域,然后用影响系数描述,提出跨网段数据传输的端到端延迟数学模型.此模型可以用于分析影响因素的作用大小及可控性.此研究为实现EPA跨网段数据的实时传输提供了理论依据.

In order to realize the real-time transmission between two ends across segments in the EPA （Ethernet for plant automation） network, a mathematical model that formulates the delay across seg- ments is constructed. A communication link model across segments in the EPA network is given ac- cording to the standard of EPA, in which the EPA bridge is a key device. Based on the analysis of the data transmission across segments in the EPA network and the EPA bridge process, several im- portant factors that influence delay are derived, including： the numbers of segments, the transmis- sion distance, the processing capacity of the bridge, the scheduling algorithms in segments, the difference of the time-basis between segments, the variation of the load in a node and the transmis- sion speed of the EPA network. Certainty factors such as number, distance, speed, the difference of the time-basis are represented as independent variables while the uncertainty factors such as capacity, algorithm and variation, the change range of which are found by calculation, are represented as quo- tiety. Consequently, a mathematical model of the end-to-end data transmission delay across segments is proposed. This model can be utilized to analyze the controllability and importance of each factor. And this work provides the theoretical basis for the realization of real-time transmission of data across segments in the EPA network.