| With the fast development of network technology, network-based applications emerge inan endless stream. Some applications especially in electric power and communication fieldsrequire precise network time synchronization. The time synchronization precision of theprecise time synchronization protocol (PTP) can reach sub-microsecond level. However, thereis also a low precision problem of PTP in the application of the asymmetric communicationlink because of the asymmetric uplink and downlink transmission delay. In this paper, theapplied in the asymmetric communication link was studied and implemented, which was partof VDSL top software protocol development project.Several network time synchronization technologies were firstly introduced in the paper,including their theories and models. And then, the impact of asymmetric transmission delayon time synchronization algorithm of PTP and time synchronization algorithm were analyzedin detail.Based on delay and algorithm analysis, dividing transmission delay into fixed part andvariable part, an improved time synchronization algorithm was proposed, which could avoidthe impact of the transmission distance on synchronization.Simulation results showed the synchronization precision of the algorithm proposed in thepaper was not affected by transmission distance. Therefore, it could get higher accuracy thanblock burst transmission synchronization algorithm in the situation of long-distancetransmission, at the same time; it cost narrower bandwidth, shorter synchronization cycle andreduced the complexity of the packet detection.Combining with the characteristics of VDSL, the algorithm proposed in the paper hasbeen applied in the system of VDSL. It can meet the requirements of the system forsynchronization precision, while costing narrower bandwidth and reducing the complexity ofthe system. |
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