In this paper, the authors investigate the impact of network size and contention window on the performance of the IEEE 802.11 MAC protocol. The performance of any network needs to be evaluated on certain criteria, these criteria then decide the basis of performance of any system. Study on wireless networks' simulation and measuring performance metrics, mainly packet delivery ratio has been done using NS-2 and AWK scripts. The effect of variations in number of nodes on the network performance is analyzed over a wide range of their values. Results are shown in terms of graph and table.