Relay Node placement in Vehicular Delay-tolerant Networks

Delay-tolerant networking (DTN) is an architecture to enable data communications between isolated or remote regions, where long delays and intermittent connectivity can be tolerated. An emerging class of DTN, called vehicular DTNs (VDTN), exploits transportation systems as the transport layer to transfer data. In these networks, vehicles (e.g., busses, boats, trains) act as mobile nodes and carry data messages around. Mobile nodes can exchange data messages using devices called relay nodes. Relay nodes, placed in strategic positions along vehicle routes, have the capability to download, store, and upload the data messages from/to the mobile nodes. An important issue in VDTN is the optimal placement of the relay nodes such that delay-tolerant connectivity in VDTN is ensured at minimum cost. In this paper we show that the problem of optimal relay node placement is an NP-hard problem. Other contributions of this paper are the formulation of the relay node placement problem using ILP and the proposal of heuristic algorithms solving the optimization problem. Using simulation results, we compare the performance of each algorithm under different network constraints, such as node storage capability and network topology.