Efficient time-stable geocast routing in delay-tolerant vehicular ad-hoc networks

Time-Stable Geocast is a group communication pattern where the destination is composed of a set of nodes that, at any time during a predefined time interval, have been located within a given geographic destination region. Time-Stable Geocast is well suited to supporting Smart City and Intelligent Transportation Systems (ITS) applications such as road safety, crowdsensing, entertainment, and business applications that can benefit from disseminating position and time-based abiding information. In this paper, we present GeoTemporal-cast, an opportunistic time-stable geocast routing protocol for Delay-Tolerant Vehicular Ad Hoc Networks (DT-VANETs) that, unlike previous proposals, does not assume that either data messages are generated inside the geographic destination region or that an underlying routing protocol will deliver the packets there. GeoTemporal-cast computes shortest-path trees over the street-layout graph that are rooted at a connected component that includes all the nodes representing intersections located inside the destination region. By traveling along the edges of these trees, data messages can reach the destination region from all the streets with access to the destination region. We evaluate the performance of GeoTemporal-cast using detailed simulations in NS-3 that consider city-wide realistic scenarios involving up to 9,080 vehicles. Our results show that GeoTemporal-cast outperforms a set of time-stable protocols for Delay-Tolerant Networks, including Time-Stable Geographically-Restricted Epidemic and variations of Spray & Wait, in terms of delivery ratio, delivery delay, and overhead.