Opportunistic Overlays: Efficient Content Delivery in Mobile Ad Hoc Networks

Current content-based publish/subscribe systems assume network environments with stable nodes and network topologies. For mobile environments, one resulting problem is a mismatch between static broker topologies and dynamic underlying network topologies. This mismatch will result in inefficiencies in event delivery, especially in mobile ad hoc networks where nodes frequently change their locations. This paper presents a novel middleware approach termed opportunistic overlays, and its dynamically reconfigurable support framework to address such inefficiencies introduced by node mobility in publish/subscribe systems. The opportunistic overlay approach dynamically adapts event dissemination structures (i.e., broker overlays) to changes in physical network topology, in nodes’ physical locations, and in network node behaviors, with the goal of optimizing end-to-end delays in event delivery. Runtime adaptations include the dynamic construction of broker overlay networks and changes of mobile clients’ assignments to brokers. Experimental results demonstrate that the opportunistic overlay approach is practically applicable and that the performance advantages attained from the use of opportunistic overlays can be substantial.