Abstract-An IEEE 802.15.4-based Wireless Sensor Network is considered, and the relationship between the IEEE 802.15.4 topology formation mechanism and possible routing strategies at the network layer is studied. Two alternative routing schemes proposed in the framework of the ZigBee Alliance are analyzed. The first is the well-known Ad-hoc On demand Distance Vector (AODV) routing protocol, which was designed for highly dynamic application scenarios in wireless ad-hoc networks. The second is a tree-based routing scheme based on a hierarchical structure established among nodes during the network formation phase. This latter approach, referred to as HERA (HiErarchical Routing Algorithm) in the paper, routes packets from sensors to sink based on the parent-child relationships established by the IEEE 802.15.4 topology formation procedure.An extensive simulation analysis is carried out to compare HERA and AODV. It is shown that a hierarchical routing scheme based on the MAC association procedures offers several benefits with respect to reactive routing in typical sensor network applications. Moreover, it is to be noted that most sensor network scenarios are concerned with delivery of packets from a series of static sensors to a single, static, sink.

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In this paper we address the problem of optimal data gathering in wireless sensor networks (WSN)