Zhang,”Modeling of a bus-based disruption tolerant network trace”, to appear

We study traces taken from UMass DieselNet, a Disruption-Tolerant Network consisting of WiFi nodes attached to buses. As buses travel their routes, they encounter other buses and in some cases are able to establish pair-wise connections and transfer data between them. We analyze the bus-to-bus contact traces to characterize the contact processes between buses and its impact on DTN routing performance. We nd that the all-bus-pairs aggregated inter-contact times show no discernible pattern. However, the inter-contact times aggregated at a route level exhibit periodic behavior. Based on analysis of the deterministic inter-meeting times for bus pairs running on route pairs, and consideration of the variabil-ity in bus movement and the random failures to establish connections, we construct generative route-level models that capture the above behavior, allowing one to generate synthetic DTN mobility traces. Through trace-driven simulations of epidemic routing, we nd that the epidemic performance predicted by traces generated with this ner-grained route-level model are much closer to the actual performance that would be realized in the operational system than traces generated using the coarse-grained all-bus-pairs aggregated model. This suggests the importance in choosing the right level of model granularity when modeling mobility-related measures such as inter-contact times in DTNs.