Opportunistic Overlays: Efficient Content Delivery in Mobile Ad Hoc Networks [chapter]

Yuan Chen, Karsten Schwan
2005 Lecture Notes in Computer Science  
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
more » ... 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-toend delays in event delivery. Adaptation techniques include the dynamic construction of broker overlay networks and runtime changes of mobile clients' assignments to brokers. 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. Publish/subscribe is a widely used method for providing anonymous, inherently asynchronous group communications in distributed settings. A publish/subscribe system has three main elements: (1) an event producer generating (publishing) events (messages), (2) an event consumer who declares its interest in receiving certain events via a subscription, and (3) an event broker responsible for collecting and processing event subscriptions and for routing processed events to corresponding consumers. Most publish/subscribe architectures employ an application-level broker network(i.e., overlay) to perform content-based routing of events at application-level. Past work has created numerous publish/subscribe systems, in industry and in academia [27, 2, 8, 26, 12, 29, 10, 36] . With the increased availability of powerful mobile computing devices like laptops and IPAQs, and the widespread deployment and use of wireless data communications, there is a pressing need to extend such middleware to the mobile computing domain. Moreover, certain features of publish/subscribe make it well-suited to mobile environments, including asynchronous event delivery, anonymity, multipoint communication and content-based routing [15, 7, 11] . Current systems targeting Internet-based communications, however, commonly assume a fixed network environment in which clients do not move and where the network topology remains relatively stable. Stated more technically, they assume statically deployed broker networks(i.e., overlays) mapped to static network topologies. The resulting problem for mobile environments is a mismatch between static broker topologies and dynamic underlying network topologies. This mismatch will result in inefficiencies in
doi:10.1007/11587552_18 fatcat:hh7e4qb4jjb5npjtbc53skfpli