In this paper, we study end-to-end performance characteristics of S-MAC, an energy-aware medium access control (MAC) protocol for wireless sensor networks (WSN). WSNs are composed of battery-driven communication entities. In order to complete a given task, all sensor nodes, which are deployed in an ad-hoc fashion, have to collaborate by exchanging and forwarding measurement data. S-MAC was proposed to provide an energy-efficient MAC protocol for wireless sensor networks. It provides similar features like