Efficient Resource Discovery in Wireless AdHoc Networks: Contacts Do Help

In this chapter, we provided an overview of the main approaches for resource discovery in wireless networks. The problem of resource discovery is becoming more challenging and pressing as more emerging infrastructure-less networks are designed and implemented. The various approaches described in this chapter included flooding-based approaches, including expanding ring search and reduced broadcast heuristics, on-demand ad hoc routing, hierarchical cluster-based and dominating set schemes, and hybrid loose hierarchy schemes including zone routing and contact based architectures. Reduced broadcast approaches and dominating set approaches attempt to reduce the redundancies of flooding but attempt to all discovery requests to all nodes in the network. On-demand ad hoc routing utilizes information caching to reduce effects of flooding, but is greatly affected by network dynamics that cause cache invalidation. Hybrid approaches, such as zone and contact-based routing use the proactive approach within the zones, and the reactive approach for out-of-zone discovery. Zone routing uses bordercasting, while contact-based schemes select out-of-zone contact nodes to avoid bordercasting. After conducting an extensive comparative study between the above schemes, it was observed that hybrid approaches are useful when the cost of zone maintenance is amortized over a reasonable number of requests, otherwise flooding-based approaches work better. In general, if power control is used such that only active nodes participate in zone construction and maintenance, then hybrid approaches seem to scale best. In particular the contact based approach is promising as it performs well for a fixed set of parameters over a relatively wide array of scenarios and network sizes.