Modeling and Delay Analysis of Intermittently Connected Roadside Communication Networks

Vehicular networks outline a challenging terrestrial application of the emerging delay-tolerant networking (DTN) paradigm where wireless links experience frequent disruptions. Thus, continuous end-to-end paths are unguaranteed. Under such conditions, mobile vehicles present opportunistic relaying capabilities that promote network connectivity, particularly between stationary and isolated roadside units. In this context, we investigate a challenging information-delivery-delay minimization problem. Information is encapsulated into bundles buffered at the source, and vehicles opportunistically transport them to the destination. Consequently, bundles undergo both queueing and transit delays. We propose a probabilistic bundle release scheme (PBRS) under which a roadside unit performs typical Internet-like forwarding where a single bundle is only released to an arriving relatively high-speed vehicle. This ensures a minimized bundle transit. In contrast, under a greedy bundle release scheme (GBRS), a bundle is released to any arriving vehicle, regardless of its speed. Two queueing models are developed to characterize a roadside unit and evaluate its performance under both schemes. A simulation framework is set up to validate these models. Results indicate the inefficiency of the typical Internet packet-like release mechanism as it incurs excessive bundle queueing delays. A bulk bundle release (BBR) extension is proposed as an effective solution. We show that GBRS-BBR outperforms PBRS-BBR.