We study the utility of dynamic frequency agility in real-world wireless sensor networks. Many view such agility as essential to obtaining adequate reliability in industrial environments. We introduce two facets of connectivity graphs --- Multichannel Links (MCLs) and Multichannel Triangles (MCTs) --- that identify instances in the network where switching channels may improve reliability. We study, empirically, how frequently MCLs and MCTs occur in live networks and determine whether multihop provides a comparable solution without the complexity of switching channels. We examine connectivity graphs of live networks over each 802.15.4 channel and find that MCLs and MCTs are extremely rare in practice. Almost no MCLs are found in any connectivity graph while MCTs occur between 0-200 parts per million (ppm). Furthermore, we show that MCLs are rarely important for routing while each MCT has a single-channel routing solution. We also find that there are channels that are always good for connectivity and offer comparable routing costs, with respect to transmission count, in comparison to multichannel communication. Thus, the justification for channel agility in industrial environments applies in the absence but not in the presence of multihop routing.




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