Wireless Sensor Networks (WSN) which are battery powered, present a challenge of long term sustainability. So power management is an import concern which can be done at two levels such as sensor subsystems and network subsystem. This paper mainly concentrates on the network subsystem aspect of the power management touching the energy conservation schemes like duty cycling, data driven approaches and mobility. This in turn deals with the data driven approaches such as data reduction and energy efficient data acquisition. An in depth study of data reduction techniques is done in this paper which includes in network processing, data compression and data prediction. A proper comparison has been tabulated between the fore mentioned techniques based on certain parameters.