I describe the statistical considerations used to design systems whose clocks are compared using dial-up telephone lines or the Internet to exchange timing informaiton. The comparison is usually used to synchronize the time of a client system to the time of a server, which is, in turn, synchronized to the time scale of a national timing laboratory. The design includes a dynamic estimate of the system performance and a comparison between the performance and a parameter that specifies the required stability based on external considerations. The algorithm adjusts the polling interval and other parameters of the algorithm to realize the specified performance at minimal cost, where the cost is taken to be proportional to the inverse of the interval between message exchanges using either the Internet or dial-up telephone calls.
ACTS, Internet Time Service, Network Time Protocol, NTP, Telephone Time Service