A method of testing a digital mobile phone network such as a GPRS or 3G network comprises either using real traffic or creating test traffic using test mobile phone coupled to a computer, and using the computer to measure a parameter associated with the network's response to the traffic. The measurements made by the computer are themselves sent as traffic to create one or more data streams within the mobile phone network comprising the traffic, measurements relating to the traffic, and signalling relating to the traffic, whereby this data stream or these streams can be captured at interface points within the network and analysed to investigate the functioning of the network dynamically as the network is exercised with the traffic. Software and test equipment for performing the method are also described.