Spray and Focus: Efficient Mobility-Assisted Routing for Heterogeneous and Correlated Mobility

Intermittently connected mobile networks are wireless networks where most of the time there does not exist a complete path from the source to the destination. There are many real networks that follow this model, for example, wildlife tracking sensor networks, military networks, vehicular ad hoc networks (VANETs), etc. To deal with such networks researchers have suggested to use controlled replication or "spraying " methods that can reduce the overhead of flooding-based schemes by distributing a small number of copies to only a few relays. These relays then "look" for the destination in parallel as they move into the network. Although such schemes can perform well in scenarios with high mobility (e.g. VANETs), they struggle in situations were mobility is slow and correlated in space and/or time. To route messages efficiently in such networks, we propose a scheme that also distributes a small number of copies to few relays. However, each relay can then forward its copy further using a single-copy utility-based scheme, instead of naively waiting to deliver it to the destination itself. This scheme exploits all the advantages of controlled replication, but is also able to identify appropriate forwarding opportunities that could deliver the message faster. Simulation results for traditional mobility models, as well as for a more realistic "community-based" model, indicate that our scheme can reduce the delay of existing spraying techniques up to 20 times in some scenarios