Improving the accuracy of timing in scalable WSN simulations with communication software execution models

Abstract

Emerging infrastructure-less network architectures such as WSNs consist of devices that perform packet processing in software. General-purpose network simulators do currently not possess models to simulate the intra-node delay of such devices. For example, a TelosB mote with TinyOS spends seven ms on processing packets with a size of 36 bytes and fifteen ms on packets of 124 bytes. The core problem addressed in this work is that simulation does not include such delays, and therefore, the results are inaccurate. To overcome this problem, we create a communication software execution model of TelosB that accounts for its temporal behavior to enable more accurate WSN simulations in the ns-3 simulator. A challenge is to create a tracing framework for TinyOS that can be used to accurately and reliably trace the behavior of a very resource-constrained system. By analyzing the software execution of TelosB running TinyOS in the emulator Cooja/MSPSim and on a real device, we discover discrepancies in the temporal behavior. The evaluation of our model shows that it is scalable and accurate; the simulated intra-OS delay deviates at most 5% from the intra-OS delay in the real mote. When we include the model in simulations, the forwarding capacity of a mote is decreased by 36%. The WSN community can use this model for more realistic simulations, and future WSN mote models will be easier to make with it as a foundation.