Reliable comparison of clock discipline algorithms for time synchronization protocols

Worst-case synchronization error is probably the most interesting performance index of clock synchronization protocols when used in real-time control applications. It depends on several factors, among which jitters on timestamp measurements and thermal variations in oscillators, which are very difficult to replicate in real systems. As a consequence, it makes little sense comparing the errors measured in different experiments, which means that assessing synchronization quality in real-time systems in a meaningful way is not a trivial task. In this paper, a methodology is described that permits different clock discipline algorithms to be experimentally evaluated and reliably compared. It was applied to a testbed where the reference broadcast infrastructure synchronization protocol is implemented over Wi-Fi, and permitted to define some guidelines for the optimal selection of the algorithm and its parametrization.