半实物网络测试系统从时钟频率漂移影响分析

针对精确时钟协议(PTP)用于半实物网络仿真测试时难以实现精确系统同步的问题,研究从时钟频率漂移对PTP仿真系统同步性能的影响。建立了半实物网络环境下PTP系统模型和时钟模型,解析性推导出单向传输链路中Slave_n对主时钟的时延误差估计,得出从时钟模型时延误差表达式具有一致的加权结构,且各误差项都将累积并渗透到传输线路中,影响整个网络的同步精度。基于此,设计多种半实物网络仿真场景进行验证、分析和测试。仿真结果表明:单个从时钟频率漂移对系统同步精度影响甚微,但系统内从时钟均存在漂移或主时钟存在时间抖动的情况下,造成的同步误差是单个从时钟频率漂移时的10倍,会对系统同步精度产生严重的影响,研究成果能为半实物网络测试环境时钟部署策略提供重要参考。

Influence of slave clock frequency drift on hanwave-in-the-loop network testing system

For the difficulties of achieving accurate clock synchronization in hanwave-in-the-loop network simulation testing using Precise Time Protocol (PTP), the performance of the simulation system of PTP in the face of slave clock frequency drift was studied. The system model and clock model of PTP under hanwave-in-the-loop network environment were established, the time delay estimation error for the master clock estimated by Slave_n in unidirectional transmission line was analytically derived. It turned out that each drifting slave led to an additive error of identical structure, these error terms got added both in the drifting slave and its successor, and were then percolated down the line together with the previous accumulated error. Based on this, various network simulation scenarios were designed for verification, analysis and testing. The simulation results show that if only one slave clock drifts, the error at the end of the line is slight; but when all the slave clocks drift, synchronization error is more than 10 times larger, and the same relationship holds for the master versus all slaves drifting, which makes a serious impact on the system synchronization accuracy. The research provides an important reference for the clock deployment strategy in hanwave-in-the-loop network simulation.