Study On Some Key Techniques Of Network Precise Time Service

With the development of network technology, network is closely connected with social production and living. More and more applications in the areas of defense industry, electric power, telecommunication network, etc. require high precision time synchronization, and traditional Network Time Protocol(NTP) network timing cannot meet the requirements of high precision timing services. Precise Time Protocol(PTP) network precision timing is important supplement of the traditional NTP network timing services, and its precise time synchronization service for specific networks. Since the second edition PTP protocol published in 2008, its research and application are becoming more and more widely. NTP network timing controls of the timing precision were independent and discrete, which lead to the timing accuracy is not high. PTP network precision timing compared with traditional NTP network timing services, its timing services are designed as a whole system, the need to consider series of problems such as the clock performance of network nodes, network packet transmission and algorithm processing, make network timing accuracy is a system-wide problem, also caused the complexity of its analysis and design.This article mainly aims at several key problems in the modeling and simulation, test and design in the PTP network precision timing analysis and research. Modeling and simulation are against the clock feature and network topology for algorithm optimization and scheme evaluation, and test and design are oriented in the practical application environment, the two complements are important aspects in PTP network precision timing system.The main analysis and research are in the following aspects:1. The analyses are in the synchronization mechanism, path delay, time offset and deviation calculation, the relationship with the UTC time scales of PTP protocol. PTP ordinary clock, boundary clock and transparent clock structure are parsed, and PTP local clock correction and counter structure are analyzed.2. Studied the network clock model. The three-state clock model is derived from the stochastic differential equation, combining with Allan variance and the diffusion coefficient.The simulation of the clock model is made, and the two-state clock model is deduced. From the analysis of frequency oscillator model, the time synchronization iterative equation is deduced. According to the research of the influence of the uncertainty of the clock synchronization, the synchronous clock time model is designed.3. The clock servo system and the filtering algorithm are research and analysis. Derived from the combination of two-state clock model and the synchronous clock time model structure, building a kalman filter model, combined with Allen variance analysis method, the uncertainty for direct-link single and comprehensive timestamps are analysis.4. Based on the structural feature of PTP boundary clock and transparent clock, modeling simulation are made respectively, the cumulative error is also analysis and research. And according to the structure and simulation model, methods are proposed to improve the synchronization precision clock and reduce cumulative error.5. The network precision clock servo performance is studied. On the basis of the research and design of network precision timing terminal, the performance of the timing terminal is evaluated firstly, then the synchronization performance under different topologies is analyses, the-filter is test. The non-PTP and PTP network timing topology are analyzed in the test and the test results are given.6. The network two-way delay precision test and measurement method is studied. The network precision measuring instrument is designed according to PTP test clock built first. Packet delay variation data were analyzed respectively, and the time variance metrics and minimum time dispersion analysis methods are research, test and analysis results are given.To sum up, this article analyzed and research the key issues in the modeling and simulation, test and design in the PTP network precision timing. Firstly, the PTP structural clock is analysis, and a reasonable simulation model of the clock is established, a kalman filter and Allen variance curve analysis method are improved, factors affecting the synchronization accuracy and uncertainty has carried on the comprehensive analysis of the simulation, and then the cascade errors of PTP boundary clocks and transparent clocks are modeling and simulation analysis. The actual tests are built using network precision timing terminal, and the network precision measuring instrument is designed to meet the need to precision measurement and analysis, and the comparison test is research, the precision testand measurement method is analysis.Based on the research of the above key issues, the feasible PTP network precision timing theory simulation and test platform is set up, to further improve the network precision accuracy of timing synchronization and optimize the clock servo algorithm, developing the PTP network precision timing has great significance in the research and application.