A quality of service monitor adapted to measure a separate value for a quality of service for each of a plurality of monitoring intervals, where each monitoring interval is shorter than the total time duration of a network communications session and longer than the time duration of one data packet in the plurality of packets included in the session. A processor searches for the one monitoring interval with the poorest quality of service value and reports the quality of service for the session as the poorest quality of service for the one monitoring interval.