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To be effective, applications such as streaming multimedia require both a more stable and more reliable service than the default best effort service from the underlying computer network. To guarantee steady data transmission despite the unpredictability of the network, a single reserved path for each traffic flow is used. However, a single dedicated path suffers from single link failures. To allow for continuous service inexpensively, unreserved backup paths are used in this thesis. While there are no wasted resources using unreserved backup paths, recovery from a failure may not be perfect. Thus, a goal for this approach is to design algorithms that compute backup paths to mask the failure for all traffic, and failing that, to maximize the number of flows that can be unaffected by the failure. Although algorithms are carefully designed with the goal to provide perfect recovery, when using only unreserved backup paths, re-routing of all affected flows, at the same service quality as before the failure, may not be possible under some conditions, particularly when the network was already fully loaded prior to the failure. Alternate strategies that trade off service quality for continuous traffic flow to minimize the effects of the failure on traffic should be considered. In addition, the actual backup path calculation can be problematic because finding backup paths that can provide good service often requires a large amount of information regarding the traffic present in the network, so much that the overhead can be prohibitive. Thus, algorithms are developed with trade-offs between good performance and communication overhead. In this thesis, a family of algorithms is designed such that as a whole, inexpensive, scalable, and effective performance can be obtained after a failure. Simulations are done to study the trade-offs between performance and scalability and between soft and hard service guarantees. Simulation results show that some algorithms in this thesis yield competitive or better performance even at lower overhead. The more reliable service provided by unreserved backup paths allows for better performance by current applications inexpensively, and provides the groundwork to expand the computer network for future services and applications.

The infrastructure used to deploy hypermedia applications over the World Wide Web has also been increasingly used to support software that has the majority of its logic implemented apart from Universal Resource Locators (URLs). We denote such software as web-based applications. Whilst there have been many observations about the difference between web-based application development environments and their more traditional counterparts, it is shown that one aspect of web-based application development that has received less attention is the software architecture of web-based applications. In this thesis we demonstrate the positive impact that an appropriate software architecture can have on creating easy-to-maintain web-based applications. / The first part of the thesis presents a taxonomy of web-based applications that is organised around abstraction layers, that highlight the role of software architecture and tiers that reflect the infrastructure of the web on which applications are deployed. It is shown that there is a systematic way to develop a software architecture for a web-based applications by projecting the high level abstract layers representing the application onto the tiers that define the distributed web infrastructure. The thesis next presents a new architecture for web-based applications targeted at lowering the cost of routine maintenance. Various tools that support the use of this architecture in the development process for web-based applications are then presented. The feasibility and usability of the architecture is demonstrated by the construction of several significant applications using it. Finally the new architecture proposed in the thesis is compared experimentally with the major current competitor architecture, which follows the so called model-view-controller pattern, in relation to an ease of maintenance criteria. It is shown that the new architecture has significant advantages over the model-view-controller pattern in making the maintenance of complex web-based applications easier. / Thesis (PhDInformationTechnology)--University of South Australia, 2006.

Thesis (M.S.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references (leaves 62-63)

Thesis (Ph. D.)--George Mason University, 2007. / Title from PDF t.p. (viewed Jan. 18, 2008). Thesis director: Bijan Jabbari Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical and Computer Engineering. Vita: p. 113. Includes bibliographical references (p. 109-112). Also available in print.