PTP Over Wide Area Networks With Offset Measurement Outlier Filtering

Abstract

The IEEE 1588 Precision Time Protocol (PTP) is capable of achieving nanosecond-level accuracy over standard Ethernet, making it widely used in industrial and scientific facilities. However, its time offset measurement process is highly sensitive to asymmetries and dynamic variation in the packet delays, hindering its applicability in wide-area use cases. In this paper, we demonstrate that PTP can be enhanced and used for Internet point-to-point time transfer with equal or better performance than the traditional Network Time Protocol (NTP). For this purpose, we propose a technique called offset measurement outlier filtering (OMOF), which leverages the short-term stability of the local clock to discard offset measurements affected by packet delay variation. We implemented OMOF in an open-source PTP client and validated it on a production network connection between two sites located more than 300 km apart. Both sites were fitted with high-performance reference clocks synchronized to less than a nanosecond of error using the GNSS-based common-view technique, enabling accurate measurement of our solution’s performance with state-of-the-art metrology techniques. Results show that our approach achieves a 95% improvement in peak-to-peak time error over the most popular open-source PTP implementation and 71% over NTP synchronization.