Wireless sensor networks are potentially one of the most important technologies of this century. Advances in hardware development have made available the prospect of low cost, low power, miniature devices for use in remote sensing applications. The combination of these factors has improved the viability of utilizing a sensor network consisting of a large number of intelligent sensors, enabling the collection, processing analysis and dissemination of valuable information gathered in a variety of environments. Typical sensing tasks for such a device could be temperature, light, vibration, sound, radiation, and so on. All these components together in a single device form a so-called sensor node. The current state of art about sensor networks is discussed in this article with solutions under their related protocol stack. This paper also points out the open research issues under each layer.