In this chapter, we will briefly describe the main features of an emerging class of next generation wireless networks, namely, opportunistic networks. After presenting the state of the art in opportunistic networking and related technologies, we will describe representative use cases. Finally, we will present a short overview of the main envisioned technological evolutions, and of the challenges to be faced by opportunistic network designers.
An opportunistic network is a short-range wireless network characterized by a very sparse network topology—see Figure 17.1: if one takes a snapshot of the network at an arbitrary time instant, what is typically observed is a large fraction of isolated nodes, and a small fraction of nodes having active links with a few other nodes in the network. From a networking perspective, what is lacking in the network topology is connectivity, that is, the possibility for a node in the network to establish a (possibly multi-hop) communication path with all the other nodes. However, network connectivity—or at least, as we will see, a weak form of connectivity—can be achieved by exploiting the temporal dimension and node mobility: since nodes in an opportunistic network move, isolated nodes can get in touch with other nodes as time goes by. Similarly, a node A which is currently in touch with node B might later get in touch with another node C, and so on—see Figure 17.1. So, ...