We present Viptos (Visual Ptolemy and TinyOS), a joint modeling and design environment for wireless networks and sensor node software. Viptos is built on Ptolemy II, a graphical modeling and simulation environment for embedded systems, and TOSSIM, an interrupt-level discrete event simulator for homogeneous TinyOS networks. Viptos includes the full capabilities of VisualSense, a Ptolemy II environment that can model communication channels, networks, and non-TinyOS nodes. Viptos presents a major improvement over VisualSense by allowing developers to refine high-level wireless sensor network simulations down to real-code simulation and deployment, and adds much-needed capabilities to TOSSIM by allowing simulation of heterogeneous networks. Viptos provides a bridge between Ptolemy II and TOSSIM by providing interrupt-level simulation of actual TinyOS programs, with packet-level simulation of the network, while allowing the developer to use other models of computation available in Ptolemy II for modeling the physical environment and other parts of the system. This framework allows application developers to easily transition between high-level simulation of algorithms to low-level implementation, simulation, and deployment. In this paper, we discuss how we integrate the semantics of two different simulation systems. We show that the Viptos simulator performance scales linearly in the number of nodes, and even without aggressive performance tuning, can simulate moderately large, heterogeneous sensor networks effectively.




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