Sensor network contains a large number of nodes

whose battery power is very limited.It’s very important for us to use an energy efficient manner to collect sensing information from sensor nodes.If every node transmits the sensing data directly to the sink node

then the nodes which are far from the sink node will deplete their power quickly.LEACH gives a way of aggregating data by forming some clusters.Each cluster head will incorporate data fusion to reduce the amount of information which is received by other nodes in the same cluster

the aggregated result will be transmitted to the sink node.Another protocol—PEGASIS

which is a near optimal chain-based protocol is an improvement over LEACH.In PEGASIS

each node communicates only with a close neighbor and takes turns transmitting the data being aggregated to the sink node.Thus it will reduce the amount of energy spent per round.The simulated result shows that PEGASIS protocol prolongs the lifetime of sensor network effectively.