Multi-hop message forwarding based on geographic coordinates is a fundamental building block for vehicular communication. However, the unstable links and wide range of node densities make it challenging to design an algorithm suitable for vehicular use. We introduce DAZL, a new forwarding protocol that combines three concepts in a novel way. First, multiple nodes cooperate in packet forwarding. Compared with traditional single relay schemes, this provides robustness against changes in topology and packet delivery rates. Second, network-layer slotting is used to control duplication and contention in high density scenarios. Third, a distributed prioritization algorithm is used to opportunistically maximize hop length. Through both experiments and simulations, we show that DAZL provides improvements of up to 60% in throughput over single relay forwarding, while ensuring low latency and replication.
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