This paper relates to the formal analysis of S-MAC, a medium-access protocol designed for wireless sensor networks. We study the synchronization mechanism of mobile nodes and the 4-way handshake mechanism of the Carrier Sense Multiple Access with Collision Avoidance scheme implemented by S-MAC. We model these previous mechanisms with the ?-calculus and the proof of their deadlocks-freeness is achieved by using the Mobility Workbench tool. A performance evaluation of S-MAC is also conducted by modeling and simulating the communications between ?xed nodes with the Performance Evaluation Process Algebra (PEPA). The performance measurements are carried-out with the PEPA Eclipse plug-in. For further information, please visit this web site.