Time synchronization over the Internet using "autolock"

This paper describes the operation of an algorithm for synchronizing the time of computers using messages transmitted over packet-switched networks such as the Internet. The algorithm configures itself to realize any specified performance level at minimum cost (measured in computer cycles or network bandwidth). If the highest-possible accuracy is requested, the performance will be limited by the larger of the instability of the local clock oscillator or the noise in the measurement process between the client and the server. Lower accuracy can be realized at substantially lower cost. The algorithm uses a frequency-locked loop with unequal spacing between the calibration messages. It makes better use of scarce network bandwidth than previous methods. In addition, the algorithm is an improvement over the pure-FLL "Interlock" algorithm because it is self-configuring. In addition to supporting an explicit trade-off between cost and accuracy, the algorithm provides better performance than previous methods because it is better able to adapt itself to fluctuations in the asymmetry of the network delay. This robustness can be realized without the preliminary tuning that was necessary to realize optimum performance using previous methods.