The Study of Implementation Technology of Time Synchronization for Packet Transport Networks
|School||Nanjing University of Posts and Telecommunications|
|Course||Communication and Information System|
|Keywords||PTP System FPGA Hardware Timestamp Prototype Design and Implementaion Precision of Synchronization|
At present, the transport network is evolving from TDM to a packet transferring network. The packet transport network need bring into the function of high accurate time synchronization, so that it can be compatible with the legacy PSTN services based on TDM and meet the requirements of the mobile backhaul of 3G/LTE network. IEEE1588 defines for LANs a protocol called Precision Time Protocol (PTP), which is being extended in various scenarios of packet transport network. The PTP system and its implementation technology are the important subjects of both the reseach and application in packet transport network.In this thesis, the design and realization of PTP prototype system are based on the embedded FPGA board. The hardware board uses MicroBlaze soft-core CPU, the operating system is based on PetaLinux, and the application is on the open source package PTPd. In the thesis, a soft-core PTP module is designed in VHDL to adjust clock and to process hardware assisted timestamp. The improvement of PTPd timestamp extraction procedure is made and the function of monitoring and debugging is added. Upon the basis, a prototype system, which is compatible with 10Mbps and 100Mbps MII, can reach sub-microsecond in precision.Moreover, the performance of time synchronization is analyzed in four kinds of netwoking environments. Factors that affect synchronization accuracy, have been studied, including the way to obtain timestamps, the netwoking method and the structure of wireless relay. According to the results, the synchronization accuracy of the PTP prototype system based on the hardware timestamp is three orders of magnitude better than the system based on software timestamp. Besides, the synchronization accuracy of wireless relay network is three orders of magnitude degrading.