Highly Accurate Timestamping for Ethernet-Based Clock Synchronization

It is not only for test and measurement of greatimportance to synchronize clocks of networked devices to timelycoordinate data acquisition. In this context the seek for highaccuracy in Ethernet-based clock synchronization has beensignificantly supported by enhancements to the Network TimeProtocol (NTP) and the introduction of the Precision TimeProtocol (PTP). The latter was even applied to instrumentation andmeasurement applications through the introduction of LXI. Theseprotocols are usually implemented in software; however, thesynchronization accuracy can only substantially be improved byhardware which supports drawing of precise event timestamps.Especially, the quality of the timestamps for ingress and egresssynchronization packets has a major influence on the achievableperformance of a distributed measurement or control system.This paper analyzes the influence of jitter sources remainingdespite hardware support and proposes enhanced methods forup to now unmatched timestamping accuracy in Ethernet-basedsynchronization protocols. The methods shown in this paperreach sub-nanosecond accuracy, which is proven in theory andpractice