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Opportunistic Overlays: Efficient Content Delivery in Mobile Environments

Middleware has become a key enabler for the development of
distributed applications. Unfortunately, conventional middleware
technologies do not yet offer sufficient functionality to make them
suitable for mobile environments. This dissertation proposes a novel
middleware approach termed opportunistic overlays and its
dynamically reconfigurable support framework for building efficient
mobile applications. Specifically, we address the inefficiency of
content delivery introduced by node mobility and by dynamically
changing system loads, in the context of publish/subscribe systems.
In response to changes in physical network topology, in nodes'
physical locations, and in network node behaviors, the opportunistic
overlay approach dynamically adapts event dissemination structures
(i.e., broker overlays) with the goal of optimizing end-to-end
delays in event delivery. Adaptation techniques include the dynamic
construction of broker overlay networks, runtime changes of mobile
clients' assignments to brokers, and dynamic broker load balancing.
Essentially, opportunistic overlays implement a middleware-level
analogue of the networking routing protocols used in wireless
communications (i.e., Mobile IP, AODV, DSR and DSDV). By thus
coordinating network- with middleware-level routing, opportunistic
overlays can attain substantial performance improvements over
non-adaptive event systems. Such improvements are due to their use
of shorter network paths and better balancing of loads across event

Opportunistic overlays and the adaptive methods they use are
realized by a set of distributed protocols implemented in a
Java-based publish/subscribe infrastructure. Comprehensive
performance evaluations are performed via simulation, emulation, and
with two representative applications on actual networks.
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, in both infrastructure-based mobile environments and
mobile ad hoc networks.
Date13 April 2005
CreatorsChen, Yuan
PublisherGeorgia Institute of Technology
Source SetsGeorgia Tech Electronic Thesis and Dissertation Archive
Detected LanguageEnglish
Format1903157 bytes, application/pdf

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