This paper describes an efficient method of estimating the ratio of clock frequency between two clocks used at the two end nodes of a one-way path. This estimation method relies on the local time measurements on the packets in a data stream going from a source node to a sink node. The time durations between adjacent packets are measured at both the source and the sink nodes according to the local clocks. The ratios of clock frequencies of two local clocks can be estimated on the suitable samples of the ratios of the time durations between two adjacent packets. The suitable samples of the ratios are obtained when two adjacent packets have experienced a zero value of the one-way variable delay. A heuristic has been developed to infer the cases when two adjacent packets experienced a zero one-way variable delay. The heuristic is used to select the suitable samples of the ratios of the time duration between two adjacent packets. Evaluation results show that the estimated values of the ratio of clock frequency very closely approximate the actual ratios. The accuracy of this method is robust to packet loss and the out-of-the-order transmission of packets. This estimation method is highly efficient without requiring complicated computations.