abstract: RF convergence of radar and communications users is rapidly becoming an issue for a multitude of stakeholders. To hedge against growing spectral congestion, research into cooperative radar and communications systems has been identified as a critical necessity for the United States and other countries. Further, the joint sensing-communicating paradigm appears imminent in several technological domains. In the pursuit of co-designing radar and communications systems that work cooperatively and benefit from each other's existence, joint radar-communications metrics are defined and bounded as a measure of performance. Estimation rate is introduced, a novel measure of radar estimation information as a function of time. Complementary to communications data rate, the two systems can now be compared on the same scale. An information-centric approach has a number of advantages, defining precisely what is gained through radar illumination and serves as a measure of spectral efficiency. Bounding radar estimation rate and communications data rate jointly, systems can be designed as a joint optimization problem. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2017

Por muitos anos, a ciência tratou todas as redes como se seus relacionamentos fossem estabelecidos de forma randômica, ou seja, a maioria dos nós teriam aproximadamente o mesmo número de relacionamentos. Porém, o mapeamento de uma variedade de sistemas revelou que a maioria dos nós tinha poucos relacionamentos, enquanto alguns nós têm uma grande quantidade de conexões. Processos microscópicos dinâmicos e estatísticos são duas facetas de sistemas complexos, que estão intimamente ligadas, e a compreensão da sua interdependência é importante tanto para a previsão quanto planejamento estratégico. Os exemplos mais proeminentes incluem o ruído do tráfego em redes de comunicação, sinais ruidosos em sistemas desordenados e auto-organizados, e as séries temporais das flutuações dos preços nos mercados financeiros. Neste trabalho foram analisadas não apenas características globais do tráfego de pacotes em redes complexas, como a presença ou não de congestionamento na rede como um todo, mas também as características locais (isto é, de roteadores específicos) do tráfego no ponto de transição entre a fase livre e a fase de congestionamento. Os resultados mostram, entre outros, que a transição de um estado livre de congestionamento para o estado congestionado de um nó ocorre quando o coeficiente de detrended fluctuation analysis da série temporal do número de pacotes na fila de espera do nó é próximo do valor crítico de 1. / For many years the science networks all treated as if their relationships were set at random, that is, most of us have approximately the same number of relationships. However, the mapping in a variety of systems revealed that most of us had a few relationships, while some of us have a lot of connections. Dynamic and statistical microscopic processes are two facets of complex systems, which are closely linked, and understanding of their interdependence is important both for predicting as strategic planning. Prominent examples include traffic noise in communication networks, noisy signals in disordered systems and self-organized, and the time series of price fluctuations in financial markets. This work analyzed not only the overall characteristics of package traffic in complex networks and the presence or absence of congestion on the network as a whole, but also the local characteristics (ie, specific routers) of the traffic at the point of transition from the free phase, and congested phase. The results show, among others, that the transition from free to congested traffic in a node happens when the detrended fluctuation analysis coefficient of the time series of the number of waiting packets is close to the critical value of 1.

Made available in DSpace on 2014-06-12T16:00:28Z (GMT). No. of bitstreams: 2 arquivo6669_1.pdf: 1298139 bytes, checksum: 82c0aa9def52f663c245e3f57be952ef (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2007 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The Transmission Control Protocol (TCP) is responsible for supplying reliable data transport service on the TCP/IP stack and for carrying most than 90% of all Internet traffic. In addition, the stability and efficiency of the actual TCP congestion control mechanisms have been extensively studied and are indeed well known by the networking community. However, new Internet applications and functionalities continuously modify its traffic characteristics, demanding new research in order to adapt TCP to the new reality of the Internet. In particular, a traffic phenomenon known as "mice and elephants" has been motivating important researches around the TCP. The main point is that the standard TCP congestion control mechanisms were designed for elephants leading small flows to experience poor performance. This is caused by the exponential behavior of Slow Start which often causes multiple packet losses due their aggressive increase. This work examines minutely the problems caused by the standard TCP congestion control to mice flows as well as it studies the most important proposals to solve them. Thus, based on such research studies, a modified TCP startup mechanism was proposed. The Burst TCP (B-TCP) is an intuitive TCP modification that employs a responsive congestion window growth scheme based on the current window size, to improve performance for small flows. Moreover, B-TCP is easy to implement and requires TCP adjustment at the sender side only. Simulation experiments show that B-TCP can significantly reduce both transfer times and packet losses for small flows without causing damage to large flows

A Região Metropolitana de São Paulo (RMSP) sofre de sérios problemas de congestionamento, assim como muitas outras cidades de grande porte. Uma possível solução, proposta por pesquisadores de transportes, economia e ciências ambientais, é a implantação de um sistema de congestion charging, chamada no Brasil de pedágio urbano. Um dos objetivos do presente trabalho foi estabelecer os conceitos relacionados a este assunto e ilustrar as principais questões relacionadas à sua implantação. Espera-se que este trabalho possa auxiliar o desenvolvimento de estudos de avaliação da viabilidade e de impactos de sistemas propostos de congestion charging. Para atingir este objetivo, toca-se em diversos assuntos, como a definição de congestionamento e as formas de medi-lo, a base conceitual e teórica dos sistemas de congestion charging e seus diversos esquemas de diferenciação. São expostas também as medidas de mitigação de congestionamento que já foram implantadas na RMSP, quais foram os estudos já desenvolvidos considerando este tipo de política para a RMSP, e casos em que sistemas de congestion charging já foi implantado. Neste trabalho, desenvolveu-se também um modelo de escolha discreta a partir dos dados da Pesquisa Origem e Destino 2007 do METRÔ, onde pessoas deveriam escolher entre \"Transporte Coletivo\" e \"Transporte Público\". Este modelo foi utilizado para avaliar o potencial de impacto na divisão modal e de arrecadação de um congestion charge aplicado ao centro expandido de São Paulo. Adverte-se, porém, que os resultados obtidos são meramente ilustrativos. Mostra-se, também, que é possível avaliar a capacidade ociosa do sistema de transporte coletivo a partir dos dados disponíveis de bilhetagem e de GPS dos ônibus. Este processo é exemplificado através do cálculo de capacidade de uma única viagem de um único ônibus, dada a dificuldade de automatização deste processo para abranger toda a frota. / The São Paulo Metropolitan Region (SPMR) suffers from severe traffic congestion, as do many other large-scale urban areas around the world. A possible solution to this issue, which has been suggested by transportation, economics and environmental researchers, is the implementation of a congestion charging system. One of the objectives of this project is to establish clear concepts and shed light on the main issues regarding these systems by means of a comprehensive literary review. It is expected that this project may help the development of in-depth studies carried in order to evaluate the viability and impacts of congestion charging proposals. In order to achieve this goal, many subjects are addressed, such as the definition of congestion, how its measured, the theoretical backgrounds that support congestion charging schemes, their different degrees of differentiation, which policies were enacted in order to reduce traffic congestion in São Paulo, what considerations and studies have already been developed for Brazil and São Paulo regarding these systems and where have these systems been successfully installed. Later chapters deal with another goal of this project: estimating how a congestion charging system would affect SPMR. This was achieved through a multinomial logit model, where decision-makers choose between \"Public Transportation\" and \"Private Automobile\". The results presented at this phase are merely indicative of certain tendencies and should not be considered final. This project also attempts to show that given the available Automated Fare Collection (AFC) data and Automated Vehicle Location (AVL) data, it is possible to estimate the current public transportation system\'s unused capacity. The author shows this by calculating the capacity of one bus trip using these data, but also explains the difficulties of expanding this analysis to the whole of SPMR\'s public transportation system.

The purpose of this thesis is to evaluate and analyze the performance of RED (Random Early Detection) algorithm and our proposed RED algorithm. As an active queue management RED has been considered an emerging issue in the last few years. Quality of service (QoS) is the latest issue in today’s internet world. The name QoS itself signifies that special treatment is given to the special traffic. With the passage of time the network traffic grew in an exponential way. With this, the end user failed to get the service for what they had paid and expected for. In order to overcome this problem, QoS within packet transmission came into discussion in internet world. RED is the active queue management system which randomly drops the packets whenever congestion occurs. It is one of the active queue management systems designed for achieving QoS. In order to deal with the existing problem or increase the performance of the existing algorithm, we tried to modify RED algorithm. Our purposed solution is able to minimize the problem of packet drop in a particular duration of time achieving the desired QoS. An experimental approach is used for the validation of the research hypothesis. Results show that the probability of packet dropping in our proposed RED algorithm during simulation scenarios significantly minimized by early calculating the probability value and then by calling the pushback mechanism according to that calculated probability value. / +46739567385(Rajiv), +46762125426(Mustafa)

University of Macau / Faculty of Science and Technology / Department of Civil and Environmental Engineering

Latency is becoming a significant factor in many Internet applications such as P2P sharing and online gaming. Coupled with the fact that an increasing number of people are using online services for backup and replication purposes and it is clear that congestion increases exponentially on the network. One of the ways in which the latency problem can be solved is to remove core network congestion or to limit it in such a way that it does not pose a problem. In South Africa, Telkom rolled out MSAN cabinets as part of their Fibre-to-the-curb (FTTC) upgrades. This created an unique opportunity to provide new services, like BaRaaS, by implementing micro data centres within the MSAN to reduce congestion on the core network. It is important to have background knowledge on what exactly latency is and what causes it on a network. It is also essential to have an understanding of how congestion (and thus latency) can be avoided on a network. The background literature covered helps to determine which tools are available to do this, as well as to highlight any possible gaps that exist for new congestion control mechanisms. A simulation study was performed to determine whether implementing micro data centres inside the MSAN will in fact reduce latency. Simulations must be done as realistically as possible to ensure that the results can be correlated to a real-world problem. Two different simulations were performed to model the behaviour of the network when backup and replication data is sent to the Internet and when it is sent to a local MSAN. In both models the core network throughput as well as the Round Trip Times (RTTs) from the client to the Internet and the MSAN cabinets, were recorded. The RTT results were then used to determine whether latency had been reduced. Once it was established that micro data centres will indeed help in reducing congestion and latency on the network, the design of a storage server, for inclusion inside the MSAN cabinet, was done. A cost benefit analysis was also performed to ensure that the project will be financially viable in the long term. The cost analysis took into account all the costs associated with the project and then expanded them over a certain period of time to determine initial expenses. Extra information was then taken into consideration to determine the possible income per year as well as extra expenditure. It was found that the inclusion of a micro data centre reduces latency on the core network due to the removal of large backup data traffic from the core network, which reduces congestion and improves latency. From the Cost Benefit Analysis (CBA) it was found that the BaRaaS service is viable from a subscription point of view. Finally, the relevant conclusions with regard to the effects of data centres in MSAN cabinets on latency and services were drawn. / Vertraagtyd word 'n belangrike faktor in baie Internet toepassings soos P2P-deel en aanlyn-speletjies. Gekoppel met die feit dat 'n toenemende getal mense internetdienste gebruik vir rugsteun en replisering, word opeenhoping in die datanetwerk eksponensieel verhoog. Een van die maniere waarop die vertraagtydsprobleem opgelos kan word, is om opeenhoping in die kern-datanetwerk te verwyder of om dit op so 'n manier te beperk dat dit nie 'n probleem veroorsaak nie. In Suid Afrika het Telkom MSAN-kaste uitgerol as deel van hulle "Fibre-to-the-Curb" (FTTC) opgraderings. Dit het 'n unieke geleentheid geskep om nuwe dienste te skep, soos BaRaaS, deur mikro-datasentrums in die MSAN-kas te implementeer om opeenhoping in die kernnetwerk te verminder. Dit is belangrik om agtergrondkennis te hê van presies wat vertraagtyd is en waardeur dit op die netwerk veroorsaak word. Dit is ook belangrik om 'n begrip te hê van hoe opeenhoping (en dus vertraagtyd) op die netwerk vermy kan word. Die agtergrondsliteratuur wat gedek is help om te bepaal watter instrumente beskikbaar is, asook om moontlikhede na vore te bring vir nuwe meganismes om opeenhoping te beheer. 'n Simulasiestudie is uitgevoer om vas te stel of die insluiting van datasentrums in die MSAN-kaste inderdaad 'n verskil sal maak aan die vertraagtyd in die datanetwerk. Twee simulasies is uitgevoer om die gedrag van die netwerk te modelleer wanneer rugsteun- en repliseringsdata na onderskeidelik die Internet en die plaaslike MSAN gestuur word. In altwee is die deurset van die kernnetwerk sowel as die sogenaamde Round Trip Times (RTTs) van die kliënt na die Internet en die MSAN-kaste aangeteken. Die RTTs-resultate sal gebruik word om te bepaal of vertraagtyd verminder is. Nadat dit bepaal is dat mikro-datasentrums wel die opeenhoping in die netwerk sal verminder, is die ontwerp van 'n stoorbediener gedoen, vir insluiting in die MSAN-kas. 'n Koste-ontleding neem alle koste wat met die projek verband hou in ag en versprei dit dan oor 'n bepaalde tydperk om die aanvanklike kostes te bepaal. Verdere inligting word voorts in ag geneem om die moontlike inkomste per jaar sowel as addisionele uitgawes te bepaal. Daar is bevind dat die insluiting van 'n mikro-datasentrum vertraagtyd verminder deur groot rugsteen-dataverkeer van die kernnetwerk af te verwyder. Die koste-ontleding het gewys dat uit 'n subskripsie-oogpunt, die BaRaaS diens lewensvatbaar is. Uiteindelik word relevante gevoltrekkings gemaak oor die effek van datasentrums in MSAN-kaste op vertraagtyd en dienste. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

This thesis presents two modern control methods to address the Internet traffic congestion control issues. They are based on a distributed traffic management framework for the fast-growing Internet traffic in which routers are deployed with intelligent or optimal data rate controllers to tackle the traffic mass. The first one is called the IntelRate (Intelligent Rate) controller using the fuzzy logic theory. Unlike other explicit traffic control protocols that have to estimate network parameters (e.g., link latency, bottleneck bandwidth, packet loss rate, or the number of flows), our fuzzy-logic-based explicit controller can measure the router queue size directly. Hence it avoids various potential performance problems arising from parameter estimations while reducing much computation and memory consumption in the routers. The communication QoS (Quality of Service) is assured by the good performances of our scheme such as max-min fairness, low queueing delay and good robustness to network dynamics. Using the Lyapunov’s Direct Method, this controller is proved to be globally asymptotically stable. The other one is called the OFEX (Optimal and Fully EXplicit) controller using convex optimization. This new scheme is able to provide not only optimal bandwidth allocation but also fully explicit congestion signal to sources. It uses the congestion signal from the most congested link, instead of the cumulative signal from a flow path. In this way, it overcomes the drawback of the relatively explicit controllers that bias the multi-bottlenecked users, and significantly improves their convergence speed and throughput performance. Furthermore, the OFEX controller design considers a dynamic model by proposing a remedial measure against the unpredictable bandwidth changes in contention-based multi-access networks (such as shared Ethernet or IEEE 802.11). When compared with the former works/controllers, such a remedy also effectively reduces the instantaneous queue size in a router, and thus significantly improving the queueing delay and packet loss performance. Finally, the applications of these two controllers on wireless local area networks have been investigated. Their design guidelines/limits are also provided based on our experiences.

>Magister Scientiae - MSc / IP multicast is an efficient mechanism for simultaneously transmitting bulk data to multiple receivers. Many applications can benefit from multicast, such as audio and videoconferencing, multi-player games, multimedia broadcasting, distance education, and data replication. For either technical or policy reasons, IP multicast still has not yet been deployed in today’s Internet. Congestion is one of the most important issues impeding the development and deployment of IP multicast and multicast applications.

Mean-field games (MFG) are models of large populations of rational agents who seek to optimize an objective function that takes into account their state variables and the distribution of the state variable of the remaining agents. MFG with congestion model problems where the agents’ motion is hampered in high-density regions. First, we study radial solutions for first- and second-order stationary MFG with congestion on Rd. The radial case, which is one of the simplest non one-dimensional MFG, is relatively tractable. As we observe, the Fokker-Planck equation is integrable with respect to one of the unknowns. Consequently, we obtain a single equation substituting this solution into the Hamilton-Jacobi equation. For the first-order case, we derive explicit formulas; for the elliptic case, we study a variational formulation of the resulting equation. For the first case, we use our approach to compute numerical approximations to the solutions of the corresponding MFG systems. Next, we consider second-order stationary MFG with congestion and prove the existence of stationary solutions. Because moving in congested areas is difficult, agents prefer to move in non-congested areas. As a consequence, the model becomes singular near the zero density. The existence of stationary solutions was previously obtained for MFG with quadratic Hamiltonians thanks to a very particular identity. Here, we develop robust estimates that give the existence of a solution for general subquadratic Hamiltonians. Additionally, we study first-order stationary MFG with congestion with quadratic or power-like Hamiltonians. Using explicit examples, we illustrate two key difficulties: the lack of classical solutions and the existence of areas with vanishing densities. Our main contribution is a new variational formulation for MFG with congestion. With this formulation, we prove the existence and uniqueness of solutions. Finally, we devise a discretization that is combined with optimization algorithms to numerically solve various MFG with congestion.