How Low Can You Go? Revisiting (S)NTP Time Synchronization for Industrial Networks

Time synchronization is a fundamental requirement for various industrial automation scenarios. Its use cases range from precise distributed control to deterministic Sequence of Events (SoEs) in case of plant faults. With the advent of Time-Sensitive Networking (TSN), the Generalized Precision Time Protocol (gPTP) has been the protocol of choice to enable sub- $\mu$ s time synchronization between network devices and has superseded the Network Time Protocol (NTP) in most mission-critical systems. However, gPTP requires hardware support in all devices and thus is not compatible with many existing system installations. In this paper, we revisit time synchronization for industrial networks and tackle the question of NTP’s synchronization accuracy in the light of network convergence. We examine the impact of recent capabilities of network devices such as strict priority scheduling and frame preemption on (S)NTP and show that accuracies below 1 ms can be achieved in large networks.