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时间触发以太网(TTE)通过精确的全局时钟同步,使时间触发(TT)消息具有了严格的时间确定性。当系统同步精度降低时,TT消息的实时性也将严重受到影响。利用TTE交换机的流量类型转换功能,提出了一种基于消息时间窗检测的转换策略(TT-TWD)。该策略应用于TT流量向速率限制(RC)流量的转换过程,能够避免在系统同步精度降低时,TT消息出现丢包或不可接受延迟的情况。为保障该策略下网络流量的实时性,设计了一种基于流量转换策略的优先级调度算法(PTCTS)。运用网络演算理论对PTCTS算法的实时性进行了分析,并与先入先出(FIFO)算法结果对比,证明了PTCTS算法有效地减小了由TT流量转换而来的RC流量的延迟上界,同时保证了原始RC流量端到端延迟的确定性。
Time-triggered Ethernet (TTE) With precise global clock synchronization, time-triggered (TT) messages are subject to strict time certainty. When the system synchronization accuracy decreases, the real-time nature of TT messages will also be seriously affected. By using the traffic type conversion function of TTE switch, a transformation strategy based on message time window detection (TT-TWD) is proposed. This strategy is applied to the conversion of TT traffic to rate-limited (RC) traffic to avoid packet loss or unacceptable delay in TT messages when the system synchronization accuracy is degraded. In order to guarantee the real-time of network traffic in this strategy, a priority scheduling algorithm (PTCTS) based on traffic transformation strategy was designed. The real-time performance of PTCTS algorithm is analyzed by using network calculus theory. Compared with the first-in first-out (FIFO) algorithm, it is proved that the PTCTS algorithm effectively reduces the delay upper bound of RC flow converted from TT traffic, meanwhile, Guaranteed end-to-end delay of raw RC traffic.