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The objective of this work is to analyze the performance of HDLC Balanced Class of Procedures under saturated, full-duplex transmission on error prone links. This thesis extends work done by Bux et al. [8] by considering errors on both the links. Satellite links have long propogation delays compared to terrestrial links, and hence, have longer error recovery times. For such links, errors in acknowledgements have considerable impact on the throughput. In this analysis, the effect of errors in acknowledgements is taken in to consideration. An analytical approach is used to derive performance measures. The concept of "virtual transmission time" introduced by Bux et al is redefined to accommodate the effect of errors in acknowledgements and used in the analysis. Resulting throughput calculations show how various parameters, (e.g. transmission rate, propagation delay, error rate and packet size), interact and determine the performance. / Master of Science

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No description available.

<p>In this information age, the Internet has found a role in various industries such as transportation, advertising, etc. The travel industry, in which communication between travellers and travel service providers is a very important component, has as much potential as any other industry to make full use of this new medium. Already, most travel agencies and travel service providers promote their products and services using web sites. Searching for information online is now seen by many people as a way to save time and cost, especially in their travel activities. In order to fully deploy the Internet within the travel industry, understanding the use of the Internet in tourism is critical. This research sets out initially to examine the role and the impact of the Internet in the whole of the travel industry. But in order to define an achievable scope of work and because of its importance in South Africa at this time, tourism within the travel industry was chosen as the focus of the work.</p>

Approved for public release; distribution is unlimited / Special Forces are crucial in specific military operations. They usually operate in hostile territory where communications are difficult to establish and preserve, since the operations are often carried out in a remote environment and the communications need to be highly mobile. The delivery of information about the geographical parameters of the area can be crucial for the completion of their mission. But in that highly mobile environment, the connectivity of the established wireless networks (LANs) can be unstable and intermittently unavailable. Existing content transfer protocols are not adaptive to volatile network connectivity. If a physical connection is lost, any information or part of a file already retrieved is discarded and the same information must be retransmitted again after the reestablishment of the lost session. The intention of this Thesis is to develop a protocol in the application layer that preserves the already transmitted part of the file, and when the session is reestablished, the information server can continue sending the rest of the file to the requesting host. Further, if the same content is available from another server through a better route, the new server should be able to continue to serve the content, starting from where the session with the previous server ended. / Lieutenant, Hellenic Navy

Devido à importância dos firewalls para proteção de redes de computadores, muito se estuda no sentido do aprimoramento das técnicas de proteção e no desenvolvimento de novas técnicas para serem utilizadas na análise destes. Com enfoque neste tema, esta dissertação trata a respeito da viabilidade da técnica de injeção de pacotes e observação dos resultados para analisar o comportamento de firewalls de rede para a pilha TCP/IP, resultando em uma técnica alternativa para análise de firewalls. Para mostrar a validade da técnica foi proposta uma arquitetura e, como prova de conceito, foi implementado um protótipo do sistema de análise. Foram também efetuados alguns testes. A técnica de injeção de pacotes e observação dos resultados mostrou-se viável para algumas situações. Para outras, são necessárias estudos adicionais para redução da explosão combinatória. / Due to the importance of the firewalls for protection of network computers, a lot of studies has been done in order of the improvement of the protection techniques and in the development of new techniques to be used in the analysis of them. With focus in this theme, this thesis considers the viability of the technique of injection of packages and observation of the results to analyze the behavior of network firewalls for stack TCP/IP, resulting in an alternative technique for analysis of firewalls. To show the validity of the technique an architecture was proposed and, as a concept proof, a prototype of the analysis system was implemented. Also was implemented some tests. The technique of injection of packages and observation of the results reveled viable for some situations. For others, addictionals studies are necessary for reduction of the combinatory explosion.

Application-layer overlay networks have recently emerged as a promising platform to deploy additional services over the Internet. A virtual network of overlay nodes can be used to regulate traffic flows of an underlay network, without modifying the underlay network infrastructure. As a result, an opportunity to redeem the inefficiency of IP routing and to improve end-to-end performance of the Internet has arisen, by routing traffic over multiple overlay paths. However, to achieve high end-to-end performance over the Internet by means of overlay networks, a number of challenging issues, including limited knowledge of the underlay network characteristics, fluctuations of overlay path performance, and interactions between overlay and the underlay traffic must be addressed. This thesis provides solutions to some of these issues, by proposing a framework to construct a multi-path overlay architecture for improving Internet end-to-end performance and availability. The framework is formed by posing a series of questions, including i) how to model and forecast overlay path performance characteristics; ii) how to route traffic optimally over multiple overlay paths; and iii) how to place overlay nodes to maximally leverage the Internet resource redundancy, while minimizing the deployment cost. To answer those research questions, analytical and experimental studies have been conducted. As a result, i) a loss model and a hybrid forecasting technique are proposed to capture, and subsequently predict end-to-end loss/delay behaviors; with this predictive capability, overlay agents can, for example, select overlay paths that potentially offer good performance and reliability; ii) to take full advantage of the predictive capability and the availability of multiple paths, a Markov Decision Process based multi-path traffic controller is developed, which can route traffic simultaneously over multiple overlay paths to optimize some performance measures, e.g. average loss rate and latency. As there can be multiple overlay controllers, competing for common resources by making selfish decisions, which could jeopardize performance of the networks, game theory is applied here to turn the competition into cooperation; as a consequence, the network performance is improved; iii) furthermore, to facilitate the deployment of the multi-path overlay architecture, a multi-objective genetic-based algorithm is introduced to place overlay nodes to attain a high level of overlay path diversity, while minimizing the number of overlay nodes to be deployed, and thus reducing the deployment cost. The findings of this thesis indicate that the use of multiple overlay paths can substantially improve end-to-end performance. They uncover the potential of multi-path application-layer overlay networks as an architecture for achieving high end-to-end performance and availability over the Internet.

Thesis (Ph.D. (Computer Science)) - Rhodes University, 2008.

Thesis (M.S.)--Mississippi State University. Department of Computer Science and Engineering. / Title from title screen. Includes bibliographical references.