Given a level of node density, a larger number of xsinks will decrease the probability of isolated clusters of nodes that cannot deliver their dataowing to unfortunate signal propagation conditions. In principle, a multiple-xsink WSN can be scalable (i.e., the same performance can be achieved even by increasing the number of nodes), while this is clearly not true for a single-xsink network. However, a multi-xsink WSN does not represent a trivial extension of a single-xsink case for the network engineer. In many cases, nodes send the data collected to one of the xsinks, selected among many, which forwards the data to the gateway, toward the final user (see Fig. 1.1).