Modeling the basic performance limits of a wireless sensor network (WSN) is ofparamount importance in understanding WSN behaviors in the worst conditions and in selecting the appropriate design. In this direction, this document contributes to the WSN modeling methodology using Network Calculus. We propose recurrent expressions of closed form for calculating the worst-case delay, buffering, and worstcase throughputs for any source-destination path. We show how to apply our theoretical results to the specific case of IEEE 802.15. 4/ZigBee WSN. Finally, we demonstrate the validity and analyze the accuracy of our methodology through an experimental study using XBee radio modules, thus confirming theoretical results through experiments.