Adaptive Hybrid Clock Discipline Algorithm for the Network Time Protocol 1

This paper describes the analysis, implementation and performance of a new algorithm engineered to discipline a computer clock to a source of standard time, such as a GPS receiver or another computer synchronized to such a source. The algorithm is intended for the Network Time Protocol (NTP), which is in widespread use to synchronize computer clocks in the global Internet, or with another functionally equivalent protocol such as DTSS or PCS. It controls the computer clock time and frequency using an adaptiveparameter, hybrid phase/frequency-lock feedback loop. Compared with the current NTP Version 3 algorithm, the new algorithm developed for NTP Version 4 provides improved accuracy and reduced network overhead, especially when per-packet or percall charges are involved. The algorithm has been implemented in a special purpose NTP simulator, which also includes the entire suite of NTP algorithms. The performance has been verified using this simulator and both synthetic data and real data from Internet time servers in Europe, Asia and the Americas.