An apparatus and method of measuring the performance of a computer network by determining transit times of packets between two selected sites connected by the computer network and the public switched telephone network and deriving from those transit times a measure of the performance of the computer network. Software establishes a network connection and a circuit switched connection between the two selected sites. A pair of messages is sent, at the same or nearly the same time, over the network connection and the circuit-switched connection and the transit time for a one way trip over the network connection is derived from the trips over the network and circuit-switched connections. This furnishes a measurement from which performance statistics of the computer network can be derived.