Non-intrusive measurement of end-to-end network properties

A method and apparatus for non-intrusive measurement of end-to-end properties of a network flow uses a passive approach. Data units at the input of a network path are sampled by an ingress monitor, which identifies each data unit with a unique signature and generates measurement data. The same data units at the output of the network path are sampled by an egress monitor, which identifies each data unit with a unique signature and generates measurement data. A data correlator pulls lists of entries from the ingress and egress monitors, each entry having the unique signature and the measurement data for one of the data units, correlates the lists to find entries from the lists that have the same unique signature, and determines from the measurement data for the data units from the two lists that have the same unique signature the end-to-end properties of the network flow.