Multi-hop Precision Time Protocol: an Internet Applicable Time Synchronization Scheme

Precise time synchronization is essential for 5G systems, data centers, industrial automation systems, military fields, and more. Although the precision of IEEE 1588 PTP can achieve sub-hundred-nanosecond accuracy, it works only when being deployed hop-by-hop within a LAN with limited range. Hop-by-hop deployment leads to high deployment costs and makes it inapplicable over the Internet. In this paper, we propose the multi-hop precision time protocol (M-PTP), a high-precision and low-cost time synchronization protocol, which does not require hop-by-hop deployment, and no special functions need to be added to the network relay devices such as routers and switches. M-PTP leverages two key ideas. First, to mitigate the "asymmetry in forward delay and reverse delay" problem, SVM-based delay estimation is used to calculate the distribution of positive and negative random delays, then L-estimator is leveraged to estimate the time offset. Second, based on time offset, M-PTP exploits loop effect optimization among nodes. We implemented the protocol and tested its performance on variance hops under different traffic conditions and CPU loads. The experimental results show that M-PTP can achieve a precision of 11.61ns at 5 hops, which is approximately 3 times the precision of HUYGENS and approximately 30 times the precision of PTP.