Abstract: Wireless sensor networks consist of sensor nodes with sensing, communicating, computing & storage with battery capacity. Data aggregation is a process or scheme to eliminate redundant transmission & provide fused information to base station which improves energy efficiency & network .lifetime of energy constrained WSN..In this paper, we present a survey of data aggregation schemes in Flat & Hierarchical wireless sensor networks & compare them on the basis of metrices such as lifetime, latency and data accuracy. Our main focus on data aggregation in cluster based network using LEACH protocol which delivers 10 times more data than the minimum energy transmission routing which improves system lifetime & reliability of data transmission & energy consumption by a factor of 8 compared to direct transmission. This paper highlights some of the drawbacks and issues in LEACH & the proposed protocol LEACH Acess Point(LEACH-AP).