Wireless Sensor Networks (WSN) shares a wireless communication medium for sending and receiving data packets. Therefore, there are varieties of protocols that manage access to the medium, such as medium traffic adaptive access (TRAMA), medium sensor access control (S-MAC) and multiple access with signaling (PAMAS) with access to feeding. In this document, the S-MAC is simulated and investigated using the network simulator. The NS2.S-MAC protocol is considered one of the contention-based protocols. The main objective of S-MAC is to reduce energy consumption. The protocol employs a work cycle approach, which means that nodes change periodically between a listening state and the suspend state.