Abstract: The frequency of a clock for a receiving terminal is controlled based on a predetermined clock frequency of a terminal that produces a continuous stream of data at a predetermined frequency for transmission to the receiving terminal over a communications network of the kind in which data is transmitted between the terminals in discrete packets that are delayed on the network by possibly different amounts. Arrivals of packets that are sent to the receiving terminal are detected, time intervals between the arrivals of the successive packets are determined, and the time intervals are processed to generate an estimate that is related to the predetermined frequency. The frequency of the receiving terminal clock is controlled in response to the estimate. In one aspect, the time intervals are determined by measuring time differences of arrival between successive packets, and the measured time differences are filtered to generate the estimate.