Thesis (Ph. D.)--University of Florida, 2004. / Title from title page of source document. Document formatted into pages; contains 114 pages. Includes vita. Includes bibliographical references.

Thesis (M.P.A.)--University of Hong Kong, 1996. / Includes bibliographical references (leaves 130-136). Also available in print.

Thesis (MTech (Civil Engineering))--Cape Peninsula University of Technology, 2008. / Includes bibliographical references (leaves 91-94). Also available online.

Dans cette thèse, nous proposons un mécanisme appelé Initial Spreading qui permet une optimisation remarquable des performances de TCP pour les connexions de petites tailles, représentant plus de 90% des connexions échangées dans l’Internet. Cette solution est d’autant plus intéressante que pour certaines technologies telles qu’un lien satellite, le temps d’aller-retour particulièrement long est très pénalisant, et des solutions spécifiques ont dû être implantées qui empêchent l’intégration du satellite dans un système de communication plus large. Nous montrons que l’Initial Spreading est non seulement plus performant, mais surtout plus général car pertinent dans toutes les situations. De plus, peu intrusif, il ne compromet aucune des évolutions de TCP passées ou à venir. / In this Ph.D. Thesis, we propose a mechanism called Initial Spreading that significantly improves the TCP short-lived connexions performance, and so more than 90% of the Internet connections. Indeed, if regular TCP without our mechanism can be considered as efficient for terrestrial networks, its behavior is strongly damaged by the long delay of a satellite communication. Satellite community developed then some satellite specific solutions that provide good performance, but prevent the joint use of satellite and other technologies. We show therefore that Initial Spreading is not only more efficient than regular solutions but enables also the use of an unique protocol whatever the context. Moreover, being non-intrusive, it is suitable for past and future TCP evolutions.

Video conferencing applications have significantly changed the way in which people communicate over the Internet. Web real-time communication (WebRTC), drafted by the World Wide Web Consortium (W3C) and the Internet Engineering Task Force (IETF), has added new functionality to web browsers, allowing audio/video calls between browsers without the need to install any video telephony applications. The Google Congestion Control (GCC) algorithm has been proposed as WebRTC’s receiver congestion control mechanism, but its performance is limited due to using a fixed incoming rate decrease factor, known as an alpha (α). In this thesis, we have proposed a dynamic alpha model to reduce the receiving bandwidth estimate during overuse, as indicated by the overuse detector. Experiments using our specific testbed show that our proposed model achieves a higher incoming rate and a lower Round-Trip Time while slightly increasing the packet loss rate in some cases compared to fixed alpha model. Our mathematical model proves that it is necessary to use an adaptive alpha α as the receiver side controller. The experimental results show improvement in the term of incoming rate, Round-Trip Time, and packet fraction loss rate in some cases. Our model increases the amount of incoming rate and decreases Round-Trip Time and fraction loss.

The dynamic nature of vehicular ad hoc network (VANET) induced by frequent topology changes and node mobility, imposes critical challenges for vehicular communications. Aggravated by the high volume of information dissemination among vehicles over limited bandwidth, the topological dynamics of VANET causes congestion in the communication channel, which is the primary cause of problems such as message drop, delay, and degraded quality of service. To mitigate these problems, congestion detection, and control techniques are needed to be incorporated in a vehicular network. Congestion control approaches can be either open-loop or closed loop based on pre-congestion or post congestion strategies. We present a general architecture of vehicular communication in urban and highway environment as well as a state-of-the-art survey of recent congestion detection and control techniques. We also identify the drawbacks of existing approaches and classify them according to different hierarchical schemes. Through an extensive literature review, we recommend solution approaches and future directions for handling congestion in vehicular communications.

published_or_final_version / Urban Planning / Master / Master of Science in Urban Planning

In this work, we focus on congestion control mechanisms in Transmission Control Protocol (TCP) for emerging very-high bandwidth-delay product networks and suggest several congestion control schemes for parallel and single-flow TCP. Recently, several high-speed TCP proposals have been suggested to overcome the limited throughput achievable by single-flow TCP by modifying its congestion control mechanisms. In the meantime, users overcome the throughput limitations in high bandwidth-delay product networks by using multiple parallel TCP flows, without modifying TCP itself. However, the evident lack of fairness between the high-speed TCP proposals (or parallel TCP) and existing standard TCP has increasingly become an issue. In many scenarios where flows require high throughput, such as grid computing or content distribution networks, often multiple connections go to the same or nearby destinations and tend to share long portions of paths (and bottlenecks). In such cases benefits can be gained by sharing congestion information. To take advantage of this additional information, we first propose a collaborative congestion control scheme for parallel TCP flows. Although the use of parallel TCP flows is an easy and effective way for reliable high-speed data transfer, parallel TCP flows are inherently unfair with respect to single TCP flows. In this thesis we propose, implement, and evaluate a natural extension for aggregated aggressiveness control in parallel TCP flows. To improve the effectiveness of single TCP flows over high bandwidth-delay product networks without causing fairness problems, we suggest a new TCP congestion control scheme that effectively and fairly utilizes high bandwidth-delay product networks by adaptively controlling the flow’s aggressiveness according to network situations using a competition detection mechanism. We argue that competition detection is more appropriate than congestion detection or bandwidth estimation. We further extend the adaptive aggressiveness control mechanism and the competition detection mechanism from single flows to parallel flows. In this way we achieve adaptive aggregated aggressiveness control. Our evaluations show that the resulting implementation is effective and fair. As a result, we show that single or parallel TCP flows in end-hosts can achieve high performance over emerging high bandwidth-delay product networks without requiring special support from networks or modifications to receivers.

Since the 1960’s, high-occupancy vehicle (HOV) lanes have been successfully used as a travel demand management technique. In recent years, there has been a growing interest in the use of high-occupancy toll (HOT) lanes as an alternative to HOV lanes to help manage the increasing demand for travel. HOT lanes combine pricing and vehicle occupancy restrictions to optimize the demand for HOV lanes. As two of the four HOT lanes in the world, the HOT lane facilities in Houston, Texas received relatively low patronage after operating for over 6 years on the Katy Freeway and over 4 years on the Northwest Freeway. There existed an opportunity to increase the usage of these HOT lanes by allowing single-occupancy vehicle (SOV) travelers to use the lanes, for an appropriate toll. The potential SOV demand for HOV lane use during the off-peak periods from the Katy Freeway and Northwest Freeway general-purpose lane (GPL) travelers was estimated in this study by using the data collected from a 2003 survey of travelers on the Katy and Northwest Freeway GPLs who were not enrolled in QuickRide. Based on survey results, more travelers would choose to drive on the HOT lanes as SOV travelers during the off-peak periods when the facilities provided higher travel time savings and charged lower tolls. Two important factors influencing travelers’ use of the HOV lanes were their value of travel time savings (VTTS) and penalty for changing travel schedule (VPCS). It was found that respondents had VTTS approximately 43 percent of their hourly wage rate and VPCS approximately 3 percent of their hourly wage rate. Combining this information with current travel time savings and available capacity on the HOV lanes, it was found that approximately 2000 SOV travelers per day would pay an average toll of $2.25 to use the HOV lanes during the off-peak periods.

Thesis (Ph.D.)--University of Texas at Arlington, 2008.