ct is similar to the reflection coefficient in matching networks (VSWR). The problem of turbulent networks is that it is difficult to predict the onset of turbulence - the point of instability, the point at which a 'fluid' flow becomes laminar. The reason that it is difficult to predict the onset of turbulence is that turbulence is turbulent. Lewis Fry Richardson (the uncle of Sir Ralph Richardson) produced some seminal work on turbulence just prior to the First World War when there was a particular interest in knowing how well aeroplanes could fly. Richardson was SO inspired by the mathematical complexity (and apparent unpredictability) of turbulence that he wrote a poem about 'little eddy' behaviour - the behaviour of the little eddies or whorls that you notice in dust storms or snow storms. Big whorls have little whorls which feed on their velocity And little whorls have lesser whorls and SO on to viscosity. Figure 17.2 illustrates this concept of the network as a filter, attempting to smooth out offered traffic turbulence. 17.7 So What Do Whorls Have to Do with Telecom Networks? Well, in order to understand network instability, we need to understand the geometry of turbulence. At what point does the flow of a liquid or gas or packet stream go from smooth to laminar (an unsmooth flow) and what are the cumulative causes. 2 The Fractal Geometry of Nature, Benoit B Mandelbrot, 1983 Edition, ISBN 0-7167-1186-9. 3 Self-similar Network Traffic and Performance Evaluation, Edited by Kihong Park and Walter Willinger, Wiley, New York, 2000 Edition, ISBN 0-471-31974-0. Network Software - The User Experience IP RAN IP Core IP RAN Offered Traffic Bulk Delay Group Delay Blow/Flow Back Pressure Blow back effect Figure 17.2 The network as a filter (the turbulent network). In a wireless wide-area network, the root cause is the increasingly wide dynamic range of the traffic being fired into the network from cellular handsets. Release 99 3GPP1 specified that data rates could vary on the uplink between 15 and 960 kbps from frame 