Recent advances in wireless sensor networks have led to many new protocols specifically designed for sensor networks

where energy awareness is an essential consideration. Most of the attention, however, has been given to the

routing protocols since they might differ depending on the application and network architecture. This paper surveys

recent routing protocols for sensor networks and presents a classification for the various approaches pursued. The three

main categories explored in this paper are data-centric, hierarchical and location-based. Each routing protocol is described

and discussed under the appropriate category. Moreover, protocols using contemporary methodologies such as

network flow and quality of service modeling are also discussed. The paper concludes with open research issues