The Role of Trace Modulation in Building Mobile Computing Systems

difficulty of accurately re-creating a mobile networking Abstract environment in vitro argues for live experiments. On the In this paper we put forth the view that trace other hand, the difficulty of experimental control in live modulation is an indispensable technique for experiments confounds interpretation of results. building and evaluating mobile computing systems. The essence of our solution is transparent, realReproducibility of the networking environment is time, trace-driven emulation of a target network. important for three reasons. First, it is essential for sound Although conceptually simple, trace modulation performance evaluation of a given system. Second, it is strikes an attractive balance between the necessary for comparative performance evaluation of conflicting demands of realism, ease-of-use, and alternative mobile system designs. Third, it is valuable in reproducibility. It provides three important debugging mobile systems because it enables re-creation benefits. First, it allows control of the complexity of the network environment to which mobile of conditions that trigger bugs. software is exposed. Second, it enables mobile The adaptive nature of mobile computing systems [5, 7] clients to be subjected to reproducible yet realistic makes them especially difficult to debug and evaluate. network performance. Third, it allows easy Modest perturbations in the environment may cause exploration of a mobile system in the context of significant changes in the behavior of such a system. This hypothetical mobility patterns and network complicates debugging as well as interpretation of infrastructures. These benefits suggest that trace modulation will play a central role in the measurements in the absence of stringent environmental development of future mobile computing systems. control.