Content distribution in large?scale vehicular ad hoc networks is difficult due to the scalability issue. A message may need to be carried by several vehicles till it reaches the destination. To select an appropriate next?hop carrier, the current carrier should exchange control messages with a large number of vehicles encountered, and thus the pure ad hoc solution is not scalable. In this paper, we introduce a hybrid?network solution. We first divide the area into regions, and select a hot spot in each region to install a road?side unit (RSU). RSUs can coordinate message exchanges between vehicles, and storage devices are used to temporarily hold a message waiting for the next?hop carrier. The RSUs and the vehicles traveling between them construct an overlay store?carry?and?forward content distribution network. Two types of vehicles exist, one with fixed mobility patterns such as buses, and the other with random patterns such as taxis. Considering one or both types of vehicles, utility?based optimization problems can be formulated to find the optimal routing solutions. Using the bus and taxi traces of Shanghai city, we demonstrate the effectiveness of the hybrid framework in terms of delivery delay, delivery ratio and overhead ratio.
content distribution; VANETs; utility?based routing; store?carry?and?forward