Method and apparatus for aligning time references when separated by an unreliable data packet network

Abstract

A time control mechanism accepts samples of time (true or otherwise) over a network, and enables dynamic compensation for random delays of the network in order to maintain the output of a slave clock that the time control mechanism controls within required bounds relative to the time of a master clock, even when the samples are randomly delayed. In one embodiment, a hardware timestamping method and apparatus is provided. The hardware timestamping method and apparatus is used to achieve the fine resolution required for timestamping both received samples and transmitted requests. In another embodiment, a delay-variation-smoothing method and apparatus is provided. The delay-variation-smoothing method and apparatus allows the time control mechanism to calculate the network delay in order to maintain the slave clock within the required time bounds. Moreover, a method and apparatus is provided that not only compensates for the random delays in the samples but also dynamically adjusts its operations to suit the changing characteristics of the delay path (typically a network).