Nanosecond-scale event synchronization over local-area networks

The research discussed in this paper builds on the success of the network time protocol (NTP) which has been synchronizing clocks on hosts all across the Internet for many years. With a different end goal (NTP seeks to setup and maintain agreement of UTC time in network-connected systems) we augment NTP methods with hardware to improve the accuracy of synchronization that is possible within an ethernet subnet by more than three orders of magnitude. Our approach involves a study of the sources of nondeterminism in NTP exchanges and their removal by special hardware aids. The added hardware has a real-time synchronized clock output and a programmable 'event synch' output that can be used to synchronize attached real-time equipment. The hardware aids allow us to achieve much better synchronization precision (100 nsec) while also facilitating the convergence to synchronization in a vastly shorter time-about one minute rather than hours or days as required by NTP.