The simulation analysis is important approach to developing and evaluating the systems in terms of development time and cost. The simulation study analysis, how the number of nodes impacts the reliability of data transmission and the end-to-end communication delay, based on the simulation model that was implemented in the OPNET Modeler. This paper analyzes three parameters; throughput, end-to-end delay and utilization. The IEEE 802.15.4 protocol proposes a flexible communication solution for low-rate wireless personal area networks including sensor networks. It presents the advantage to fit different requirements of potential applications by adequately setting its parameters.