A method for testing of a communication network, using a plurality of traffic agents coupled to communicate via the network. The method includes transmitting a sequence of data packets via the network from a first one of the traffic agents to a second one of the traffic agents and recording arrival characteristics of the packets in the sequence, responsive to receiving the packets at the second traffic agent. The arrival characteristics of different packets in the sequence are compared so as to determine a measure of variability in transmission of the packets via the network.