Yuan Chen, Karsten Schwan,
Opportunistic Overlays: Efficient Content Delivery in Mobile Ad Hoc Networks
Current content-based publish/subscribe systems assume a fixed network
environment in which nodes do not move and where the network topology remains
relatively stable. For mobile environments, the 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
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. Adaptation techniques include the dynamic construction of broker
overlay networks and runtime changes of mobile clients' assignments to
Opportunistic overlays and the adaptive methods they use are realized by a set
of distributed protocols implemented in a Java-based publish/subscribe
infrastructure. Performance evaluations use simulation, system emulation, and
also involve running a representative application on an experimental testbed.
Experimental results demonstrate that the opportunistic overlay approach is
practically applicable and the performance advantages attained from the use of
opportunistic overlays can be substantial.