Study On Time Synchronization Technology In Time-Sensitive Network

After decades of rapid development,Ethernet has maturely applied in numerous fields.Whether the real-time Ethernet for industrial control applications or automotive Ethernet for automobiles,or carrier-class Ethernet supporting telecommunications services,they all face the problem of the real-time nature of data transmission and the need for high accuracy of synchronization.With the trend of IP development in the whole network,the Packet Transport Network(PTN)based on packet services has gradually replaced the traditional TDM network,Accordingly,it is the top priority for researchers at the moment on how to solve the synchronization of time-sensitive data in the network.Nowadays,the most widely used time synchronization technology in packet networks is the IEEE 1588v2 precise time protocol,i.e.,PTP.It transmits the clock information of the master node to each slave node through the data packets carrying the time stamp under the transmission of the original Ethernet data cable,then the slave nodes calculate the time offset between the master and the slave according to the received time information to adjust the local clock,which therefor achieve the time synchronization of the entire network.The accuracy of the synchronization depends on the accuracy and stability of the master clock,the time stamping accuracy,and the efficiency of the protocol,and currently it's usually at submicro level.This thesis conducts in-depth research and analysis on the IEEE 802.1AS protocol gPTP used in TSN,which is adaptation of the Precision Time Protocol.As well focusing on the design and implementation of the time synchronization subsystem in the Time Sensitive Network(TSN)system.Finally,based on the TSN system prototype developed by our laboratory,we implement a hybrid technology solution that combines synchronous Ethernet SyncE and gPTP algorithm software through hardware optimization and reasonable clock distribution scheme.Via experimental analysis and board-level test verification,we preliminarily achieved nanosecond-level precision time synchronization.The main content and work presented in this thesis are as follows:1.The working mechanism of the time-sensitive network was studied,and the key technologies were introduced,which include the precise clocks and synchronization functions,stream reservation protocols for the maintenance and management of transmission paths,queuing forwarding,scheduler functions and preemption mechanisms and so on.2.Combined with the characteristics of packet networks,the synchronization principle and clock model of the IEEE 1588v2 precise time protocol PTP are studied.Based on this,the data frame format of the IEEE 802.1AS protocol gPTP are described in detail.3.The design of the time synchronization subsystem of the TSN prototype is provided.The main function blocks and their functional properties of the time synchronization subsystem are described.Combined with the advantages of the gPTP protocol and SyncE technology,the subsystem using high-accuracy timestamping techniques in the PHY layer,and using SyncE to provide a timing reference for the network nodes.The gPTP software residing in the control model provide time error calculations and BMCA.The connection between the software and the PHY is implemented by the capture and insertion function blocks in the FPGA.A DPLL block is used to realize onboard clock configuration and precise frequency and time error correction.The design supports a physical and protocol hybrid synchronization scheme.In order to facilitate TSN scheduling more precisely,we suppose a new frequency error correction method.4.On the FPGA-based TSN prototype system,the experimental test analysis and board-level test verification show that the SyncE frequency synchronization effect of this design scheme is stable,and the gPTP phase synchronization is accurate.Either in single-hop or multi-hop scenarios,it achieves nanosecond-level high-precision time synchronization.