Trends in technology and pressures of the market-place are changing telecommunications networks at an increasing rate worldwide. The meaning of the phrase `speech channel' may change, no longer corresponding with a physical circuit. In this new world, subtle and unexpected quality impairments might affect network operators who lack a broad and customer facing technical viewpoint. In these revolutionary times, DSP techniques can create powerful new ways of measuring performance and of mixing the traditionally separate disciplines of network modelling and DSP simulation. This mixed modelling promises benefits in better and more far-sighted specification, design and implemention of future networks and services.