I nternational Journal of E merging Trends & Technology in Computer Science (I JE TTCS) Web Site: www.ijettcs.org Email: editor@ijettcs.org, editorijettcs@gmail.com Volume 2, Issue 3, May – June 2013 ISSN 2278-6856 Volume 2, Issue 3 M ay – June 2013 Page 284 Abstract: Wireless sensor networks (WSNs) provide a valuable capability to autonomously monitor Remote activities. It consists of a large number of small and low-cost sensor nodes powered by small batteries and equipped with various sensing devices. Energy efficient is the kernel issue in the designing of wireless sensor network. In this paper, we propose an energy efficient token-based MAC protocol integrated with sleep scheduling for WSNs, in order to reduce energy consumption of each sensor nodes. To reduce energy consumption most of the MAC protocols in WSN exploits low duty-cycle; among those RMAC, HEMAC allows a node to transmit data packet for multi-hop in a single duty-cycle. In the above said Mac protocol, due to the synchronized scheduling and transmission collision, flooding increases resulting in energy waste and low throughput. By allowing nodes to operate with a new token-based approach, we intend to produce energy efficiency in an event based approach by reducing flooding, collision and traffic congestion. Keywords: WSN, MAC protocol, Duty-cycles, Token, Traffic Congestion. 1. INTRODUCTION A wireless sensor network is a network composed of hundreds to thousands of communicating sensors and deployed in an area to collect environment events. In a sensor network, each node is a small sensor with low processing, storage and energy capacity. Sensors are often battery powered and we expect a lifetime of several months to several years. Hence, the major difference between the sensor network and the traditional wireless network is that sensors are very sensitive to energy consumption. In the future when sensor manufacture becomes massive, sensor price will be much lower and it is preferable to change sensors rather than batteries after use. Now a day’s wireless sensor networks have wide range of potential applications such as in environmental monitoring, medical systems, agriculture, robotics exploration, traffic surveillance, earth quake monitoring etc. In the wireless sensor networks energy consumption is the most important factor to determine the life of a sensor network because usually sensors nodes are driven by batteries and have very low energy resources. This makes energy optimization more complicated in sensor networks because it involved not only reduction of energy consumption but also prolonging the life of the network. In wireless sensor networks each sensor node can be in either of the mentioned states: Active state and Idle or Sleep state. With the objective of prolong the life time of WSN, reducing the energy consumption token-based MAC protocol is designed. 1.1 WSN sources of energy wastage:- 1) Overhearing: A node wastes its energy when it receives the packets that are destined to other nodes. 2) Collision: Since a radio channel is shared by many nodes, a collision take place when two nodes send their packets at the same time. Collision increase energy consumption and latency packets deliverance mechanism due to retransmissions. 3) Idle Listening: when nodes have nothing to send or receive, the nodes still remain in active state and do idle listening to the network. This process consumes equal amount of energy as during transmitting or receiving process. Thus resulting into wastage of energy. 4) Control packets (overhead): packet headers and control packets (RTS/CTS/ACK) used by a MAC protocol do not contain application data, thus they are considered as supplementary data and they consumes some energy. In order to decrease or if possible to eliminate these various sources of energy wastage, several protocols have been proposed which are divided into two main classes:-  Scheduled-based protocols: these protocols are employed to avoid collision by associating a slot time for each sensor node in a given cluster, and to mitigate the effects of overhearing problem, because in this situation each node knows his corresponding slot time to transmit data packet.  Contention-based protocols: These protocols known as CSMA-based are usually used in wireless networking due to their simplicity. To decrease collision and to reduce other sources of energy wastage, the Wake- up/Sleep mechanisms/ or the control messages RTS/CTS/ACK are used to design energy efficient MAC protocols for WSN. In this paper, by allowing nodes to operate with a new token-based approach, we intend to produce energy A Token Based MAC Protocol – To Reduce Energy Consumption in Wireless Sensor Network Anjali Varshney 1 , Pawan Prakash Singh 2 , Savita Shiwani 3 1 M.Tech Scholar, Suresh Gyan Vihar University, Jaipur, India 2&3 Assistant Professor, Suresh Gyan Vihar University, Jaipur, India