Highly Accurate Timestamping for Ethernet-Based Clock Synchronization

Abstract

It is not only for test and measurement of great importance to synchronize clocks of networked devices to timely coordinate data acquisition. In this context the seek for high accuracy in Ethernet-based clock synchronization has been significantly supported by enhancements to the Network Time Protocol (NTP) and the introduction of the Precision Time Protocol (PTP). The latter was even applied to instrumentation and measurement applications through the introduction of LXI. These protocols are usually implemented in software; however, the synchronization accuracy can only substantially be improved by hardware which supports drawing of precise event timestamps. Especially, the quality of the timestamps for ingress and egress synchronization packets has a major influence on the achievable performance of a distributed measurement or control system. This paper analyzes the influence of jitter sources remaining despite hardware support and proposes enhanced methods for up to now unmatched timestamping accuracy in Ethernet-based synchronization protocols. The methods shown in this paper reach sub-nanosecond accuracy, which is proven in theory and practice.