256852.fig.001
Figure 1: Aggregation phase. The nodes 1, 2, 3, 4, 5, 6, and 7 are sensor nodes, and the nodes 8, 9, and 10 are aggregators while node 3 works as both sensor node and aggregator. Without losing generality, we assume that every intermediate node is able to sense raw data and performs aggregation like node 3 does.