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Vehicular ad hoc networks (VANETs) enable the timely broadcast dissemination of event-driven messages to interested vehicles. Especially when dealing with broadcast communication, data dissemination protocols must achieve a high degree of scalability due to frequent deviations in the network density. In dense networks, suppression techniques are designed to prevent the so-called broadcast storm problem. In sparse networks, protocols incorporate store-carry-forward mechanisms to take advantage of the mobility of vehicles to store and relay messages until a new opportunity for dissemination emerges. Despite numerous efforts, most related works focus on either highway or urban scenarios, but not both. Highways are mostly addressed with a single directional dissemination. For urban scenarios, protocols mostly concentrate on either using infrastructure or developing methods for selecting vehicles to perform the store-carry-forward task. In both cases, dense networks are dealt with suppression techniques that are not optimal for multi-directional dissemination. To fill this gap, we present an infrastructure-less protocol that combines a generalized time slot scheme based on directional sectors and a store-carry-forward algorithm to support multi-directional data dissemination. By means of simulations, we show that our protocol scales properly in various network densities in both realistic highway and urban scenarios. Most importantly, it outperforms state-of-the-art protocols in terms of delivery ratio, end-to-end delay, and number of transmissions. Compared to these solutions, our protocol presents up to seven times lower number of transmissions in dense highway scenarios.

Vehicular Ad-hoc Networks (VANETs) enable the timely broadcast dissemination of event-driven messages to interested vehicles. However, when dealing with broadcast communication, suppression techniques must be designed to prevent the so-called broadcast storm problem. Numerous suppression schemes aim to reduce broadcast redundancy by assigning vehicles to different delay values, i.e., time slots, that are inversely proportional to their distance to the sender. In this way, only the farthest vehicles would rebroadcast, thereby allowing for quick data dissemination. Despite many efforts, current delay-based schemes still suffer from high levels of contention and collision when the number of vehicles rebroadcasting nearly simultaneously is high in dense networks. Even choosing appropriate values for the total number of time slots does not prevent situations where simply no vehicle is assigned to the earliest time slot, what may result in high end-to-end delay. In this paper, we tackle such scalability issues with a scheme that controls with precision the density of vehicles within each time slot. To reach this goal, we exploit the presence of beacons, periodic messages meant to provide cooperative awareness in safety applications. Simulations results show that our protocol outperforms existing delay-based schemes and is able to disseminate data messages in a scalable, timely, and robust manner.

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