Communication through the Internet is one of the dominant methods of exchanging information. Whether at an individual or large corporate level the Internet has become essential to gathering and disseminating information. TCP and UDP are the transport layer protocols responsible for transit of nearly all Internet communications. Due to the growth of real-time audio and video applications, UDP is being used more frequently as a transport protocol. As UDP traffic increases potential problems arise. Unlike TCP, UDP has no mechanism for congestion control leading to wasted bandwidth and poor performance for other competing protocols. This thesis defines a congestion control protocol called UDPCC to replace UDP. Several other protocols or applications have been proposed to provide UDP-like transport with congestion control. DCCP and UDP-MM are two schemes examined and will be used as comparetors to UDPCC. This thesis will show that the proposed UDPCC can perform at the level of DCCP, UDP-MM or higher while maintaining a simple implementation.

In this thesis, a new model for the slow start phase based on the discrete evolutions of congestion window is developed, and we integrate this part into the improved TCP steady state model for a better prediction performance. Combining these short and steady state models, we propose an extensive stochastic model which can accurately predict the throughput and latency of the TCP connections as functions of loss rate, round-trip time (RTT), and file size. We validate our results through simulation experiments. The results show that our model?s predictions match the simulation results better than the Padhye and Cardwell's stochastic models, about 75% improvement in the accuracy of performance predictions for the steady state and 20% improvement for the short-lived TCP flows.

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A major cause of congestion in queuing situations, that is of immoderate waits and lengthening queues, is often the assumed independence of the arrival and service mechanisms. This dissertation is concerned with single server "correlated" models, defined to be such that either the service mechanism is somehow tailored to the arrival pattern, or vice versa. The greatest attention is given to a particular model in which the service time allotted to the nth arrival is λ Tn , where λ is a non-time dependent constant and numerically has the value of congestion index, and Tn is the interval between the (n-l)th and the nth arrivals which, it is important to note, could be observed by the server before service is initiated. It is shown that the effect of the correlation mechanism is to reduce congestion under a given level of traffic intensity, as compared with single server systems in which arrivals and service are independent. This result is achieved without inflicting on the service facility the penalty of increased periods of idleness. The particular model is a queuing interpretation of a stochastic-kinematic situation studied by B. W. Conolly in connection with a military tactical analysis. The dissertation is divided into two parts. Part I develops the theory of the main model with particular reference to state probabilities, waiting time, busy period, and output. Some consideration is also give to a related model where service depends on the arrival pattern, and to what is referred to as the "dual" problem in which the arrival mechanism is geared to service capability. Further, the state probabilities at arrival epochs for a conventional M/M/l queue are obtained by employing a simple probabilistic argument. This is needed for Part II. Part II applies the theory to give a practical comparison of the correlation mechanism with the elementary "independent" single server queues M/M/I, M/D/l and D/M/l; and it is shown in detail that the practical result referred to above is achieved. The superiority of the correlation mechanism increases with traffic intensity. State probability, busy period and output comparisons are made only with the M/M/l system. The main conclusions are found to extend also to these processes. It is concluded that, where its application is practicable, a mechanism of correlation can achieve important gains in efficiency. / Ph. D.

This discussion develops an approach for using fractal geometry and diffusion limited aggregation to describe highway traffic flow. The formulation is platoon based and is most applicable for describing uninterrupted-flow facilities. The model explains empirical models in terms of fractal dimensions. The concepts of change in length of a platoon and a discrete spacing unit are described for the first time in this paper. Boundary values of various fractal dimensions are calculated for different HCM freeway LOS designations. A state of flow equation established in the model represents both microscopic and macroscopic aspects of a traffic stream. Using the same traffic flow model, recurring and nonrecurring types of congestion were quantified. A congestion evaluation index was developed to address the two types of congestion which can also be used as an performance-measure in monitoring a Congestion Management System (CMS). A few ideas were suggested for quantifying indirect benefits of CMS and furthering the present research trend. / Master of Science

La th´eorie de la complexit´e permet de classifier les probl`emes en fonction de leur difficult´e. Le cadre classique dans lequel elle s’applique est celui d’un algorithme centralis´e qui dispose de toutes les informations. Avec l’essor des r´eseaux et des architectures d´ecentralis´ees, l’algo- rithmique distribu´ee a ´et´e ´etudi´ee. Dans un grand nombre de probl`emes, en optimisation et en ´economie, les d´ecisions et les calculs sont effectu´es par des agents ind´ependants qui suivent des objectifs diff´erents dont la r´ealisation d´epend des d´ecisions des autres agents. La th´eorie des jeux est un cadre naturel pour analyser les solutions de tels probl`emes. Elle propose des concepts de stabilit´e, le plus classique ´etant l’´equilibre de Nash.Une mani`ere naturelle de calculer de telles solutions est de “ faire r´eagir “ les agents ; si un agent voit quelles sont les d´ecisions des autres joueurs ou plus g´en´eralement un “ ´etat du jeu “, il peut d´ecider de changer sa d´ecision pour atteindre son objectif faisant ainsi ´evoluer l’´etat du jeu. On dit que ces algorithmes sont des “ dynamiques “.On sait que certaines dynamiques convergent vers un concept de solution. On s’int´eresse `a la vitesse de convergence des dynamiques. Certains concepts de solutions sont mˆeme complets pour certaines classes de complexit´e ce qui rend peu vraisemblable l’existence de dynamiques simples qui convergent rapidement vers ces solutions. On a utilis´e alors trois approches pour obtenir une convergence rapide : am´eliorer la dynamique (en utilisant par exemple des bits al´eatoires), restreindre la structure du probl`eme, et rechercher une solution approch´ee.Sur les jeux de congestion, on a ´etendu les r´esultats de convergence rapide vers un ´equilibre de Nash approch´e aux jeux n´egatifs. Cependant, on a montr´e que sur les jeux sans contrainte de signe, calculer un ´equilibre de Nash approch´e est PLS-complet. Sur les jeux d ’appariement, on a ´etudi´e la vitesse de dynamiques concurrentes lorsque les joueurs ont une information partielle param´etr´ee par un r´eseau social. En particulier, on a am´elior´e des dynamiques naturelles afin qu’elles atteignent un ´equilibre enO(log(n)) tours (avec n le nombre de joueurs). / Complexity theory allows to classify problems by their algorithmic hardness. The classical framework in which it applies is the one of a centralized algorithm that knows every informa- tion. With the development of networks and decentralized architectures, distributed dynamics was studied. In many problems, in optimization or economy, actions and computations are made by independant agents that don’t share the same objective whose realization depends on the actions of other agents. Game theory is a natural framework to study solutions of this kind of problem. It provides solution concepts such as the Nash equilibrium.A natural way to compute these solutions is to make the agents “react” ; if an agent sees the actions of the other player, or more generally the state of the game, he can decide to change his decision to reach his objective and updates the state of the game. We call �dynamics� this kind of algorithms.We know some dynamics converges to a stable solution. We are interested by the speed of convergence of these dynamics. Some solution concepts are even complete for some complexity classes which make unrealistic the existence of fast converging dynamics. We used three ways to obtain a fast convergence : improving dynamics (using random bits), finding simple subcases, and finding an approximate solution.We extent fast convergence results to an approximate Nash equilibria in negative congestion games. However, we proved that finding an approximate Nash equilibrium in a congestion games without sign restriction is PLS-complete. On matching game, we studied the speed of concurrent dynamics when players have partial information that depends on a social network. Especially, we improved natural dynamics for them to reach an equilibrium inO(log(n)) rounds (with n is the number of players).

Cette thèse traite de la congestion des transports en milieu urbain, et des liens qu'elle entretient avec les localisations des emplois et des ménages. Elle est organisée en trois parties. La première est une analyse bibliographique sur les questions de croissance et de structure urbaine, suivie d'une analyse, de nature systémique, de la congestion des transports. La deuxième partie est consacrée à l'analyse des manifestations spatiales de la congestion en Île-de-France, en s'appuyant notamment sur différentes méthode d'agrégation spatiale d'indicateurs de congestion. Enfin, dans la troisième partie, un modèle d'équilibre urbain décrivant la localisation des ménages par rapport à leur emploi, en présence de congestion, est développé, et utilisé pour analyser le rôle de la dispersion des emplois sur l'étalement urbain / This thesis deals with transport congestion in urban areas, and with the links between it and the locations of jobs and households. It is organized in three parts. The first one is a literature revue on the questions of urban growth and structure, followed by an analysis of congestion in transport systems. The second part is dedicated to the analysis of the spatial expressions of congestion in the Greater Paris Region, based notably on different spatial aggregation methods of congestion indicators. Finally, in the third part, I develop an urban equilibrium model describing the locations of households with respect to their workplace. This model is then used to analyse the role played by job dispersion on urban sprawl

This research investigates whether Transportation Network Companies (TNCs), such as Uber and Lyft, live up to their stated vision of reducing congestion by complementing transit and reducing car ownership in major cities. The objective of this research study is to answer the question: are TNCs are correlated to traffic congestion in the city of San Francisco? If found to be so, do they increase or decrease traffic congestion for the case of San Francisco? If and how TNC pickups and drop-offs impact traffic congestion within San Francisco? And finally, how does the magnitude of this measured command of TNCs on congestion compare to that caused by pre-existing conventional drivers of traffic and congestion change? Apart from answering these questions, it is also sought to establish a framework to be able to include TNCs, a seemingly fledgling mode of transportation but one that is demonstrably shaping and modifying extant transportation and mode choice trends, as part of the travel demand models estimated by any geographic jurisdiction. Traffic congestion has worsened noticeably in San Francisco and other major cities over the past few years. Part of this change could reasonably be explained by strong economic growth or other standard factors such as road and transit network changes. The sharp increase in travel times and congestion also corresponds to the emergence of TNCs, raising the question of whether the two trends may be related. Existing research has produced conflicting results and been hampered by a lack of data. Using data scraped from the Application Programming Interfaces (APIs) of two TNCs, combined with observed travel time data, this research finds that contrary to their vision, TNCs are the biggest contributor to growing traffic congestion in San Francisco. Between 2010 and 2016, weekday vehicle hours of delay increased by 62%, compared to 22% in a counterfactual 2016 scenario without TNCs. The findings provide insight into expected changes in major cities as TNCs continue to grow, informing decisions about how to integrate TNCs into the existing transportation system. This research also decomposes the contributors to increased congestion in San Francisco between 2010 and 2016, considering contributions from five incremental effects: road and transit network changes, population growth, employment growth, TNC volumes, and the effect of TNC pick-ups and Drop-offs. It is so done through a series of controlled travel demand model runs, supplemented with observed TNC data. The results show that road and transit network changes over this period have only a small effect on congestion, population and employment growth are important contributors, and that TNCs are the biggest contributor to growing congestion over this period, contributing about half of the increase in vehicle hours of delay, and adding to worsening travel time reliability. This research contradicts several studies that suggest TNCs may reduce congestion and adds evidence in support of a recent empirical analysis showing that their net effect is to increase congestion. This research gives transportation planners a better understanding of the causes of growing congestion, allowing them to more effectively craft strategies to mitigate or adapt to it.

Intelligent Transportation Systems (ITS) play an important role in supporting motorists and first responders to handle major incidents, hazmat spills, security measures and other emergency operations. Increasingly, technology advancements and applications are providing invaluable integration opportunities to interconnect safety, maintenance, ITS, traffic operations, facilities, and transportation equipment programs to maximize available resources and achieve efficiency in transportation operations. This research focuses on one of the prominent ITS devices: Dynamic Message Signs (DMS) operations. Using real time incident management operations data and ITS operations data, an attempt is made to develop ITS Operations Evaluations Models (ITSOEMs) that are capable of quantifying the operations value of DMS and their complementing ITS surveillance and detection systems, such as CCTV, Safety Service Patrol (SSP) and Computer Aided Dispatch (CAD) systems. The I-95 corridor in the state of Virginia is selected as the Study Corridor. Operations data from the Virginia Department of Transportation (VDOT) on DMS and ITS detection systems and incident management is analyzed to accomplish four key research objectives: a) To collect, extract and evaluate real time operations data from VDOT ITS and incident management operations programs and identify the factors contributing to the successful operation of DMS for the duration of incidents and events occurring on the I-95 Study Corridor; b) To develop analytical models to determine measurable influence of incident detections in successfully disseminating messages on DMS; c) To develop ITS Operations evaluation models to determine the effectiveness of DMS messages during incidents by quantifying the influence of DMS messages in the deterrence of secondary incidents on the I-95 Study Corridor; and d) To develop guidelines on the application of these quantitative ITS evaluation models so that transportation engineers can effectively use these models to perform ITS evaluations at other ITS locations. The ITS evaluation framework developed in this research work is expected to assist transportation engineers in the prioritization, selection and implementation of operations and technology integration strategies.

Thesis (M.A.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 57-58).