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研究了AFDX交换机在采用轮转调度策略,并保证消息传输实时性的前提下,对消息到达时间间隔抖动的容忍能力。采用实时通信中的周期性任务模型,依据实时性保证原则,推导出在已知的轮转调度策略下,交换机允许消息到达最小时间间隔,及交换机对消息抖动的容忍度的数学表达式。最后给出在给定的实时流量下,到达时间间隔抖动容忍度的计算实例,结合算例结果分析了实际情况中容忍度的意义,即容忍度越低,消息延时越容易破坏消息的实时性。
This paper studies the tolerance of AFDX switches to jitter of message arrival time under the premise of adopting round robin strategy and ensuring the real-time transmission of messages. Based on the periodic task model in real-time communication and the principle of real-time guarantee, a mathematic expression of the tolerance of switch jitter to message jitter under the known rotation scheduling strategy is derived. Finally, the calculation example of jitter tolerance of arrival time interval under a given real-time traffic flow is given, and the significance of tolerance in actual situations is analyzed with the result of an example. That is, the lower the tolerance is, the more likely the message delay is to destroy the real-time message Sex.