A method of determining a representative frequency for data packets, each data packet having an associated time, the method comprising: receiving a sequence of time-differentials, wherein a time-differential represents a difference between the time associated with a corresponding first data packet and the time associated with a corresponding second data packet; and determining the representative frequency based on the steps of: grouping a predetermined number N of the time-differentials into one or more groups based on the magnitudes of the N time-differentials; selecting one or more of the one or more groups for use in determining a representative time-differential; determining the representative time-differential as a function of the time-differentials of the selected one or more groups; outputting an inverse of the representative time-differential as the representative frequency.