Evaluating the impact of traffic sampling in network analysis

Dissertação de mestrado integrado em Engenharia InformáticaThe sampling of network traffic is a very effective method in order to comprehend the behaviour and flow of a network, essential to build network management tools to control Service Level Agreements (SLAs), Quality of Service (QoS), traffic engineering, and the planning of both the capacity and the safety of the network. With the exponential rise of the amount traffic caused by the number of devices connected to the Internet growing, it gets increasingly harder and more expensive to understand the behaviour of a network through the analysis of the total volume of traffic. The use of sampling techniques, or selective analysis, which consists in the election of small number of packets in order to estimate the expected behaviour of a network, then becomes essential. Even though these techniques drastically reduce the amount of data to be analyzed, the fact that the sampling analysis tasks have to be performed in the network equipment can cause a significant impact in the performance of these equipment devices, and a reduction in the accuracy of the estimation of network state. In this dissertation project, an evaluation of the impact of selective analysis of network traffic will be explored, at a level of performance in estimating network state, and statistical properties such as self-similarity and Long-Range Dependence (LRD) that exist in original network traffic, allowing a better understanding of the behaviour of sampled network traffic.A análise seletiva do tráfego de rede é um método muito eficaz para a compreensão do comportamento e fluxo de uma rede, sendo essencial para apoiar ferramentas de gestão de tarefas tais como o cumprimento de contratos de serviço (Service Level Agreements - SLAs), o controlo da Qualidade de Serviço (QoS), a engenharia de tráfego, o planeamento de capacidade e a segurança das redes. Neste sentido, e face ao exponencial aumento da quantidade de tráfego presente causado pelo número de dispositivos com ligação à rede ser cada vez maior, torna-se cada vez mais complicado e dispendioso o entendimento do comportamento de uma rede através da análise do volume total de tráfego. A utilização de técnicas de amostragem, ou análise seletiva, que consiste na eleição de um pequeno conjunto de pacotes de forma a tentar estimar, ou calcular, o comportamento expectável de uma rede, torna-se assim essencial. Apesar de estas técnicas reduzirem bastante o volume de dados a ser analisado, o facto de as tarefas de análise seletiva terem de ser efetuadas nos equipamentos de rede pode criar um impacto significativo no desempenho dos mesmos e uma redução de acurácia na estimação do estado da rede. Nesta dissertação de mestrado será então feita uma avaliação do impacto da análise seletiva do tráfego de rede, a nível do desempenho na estimativa do estado da rede e a nível das propriedades estatísticas tais como a Long-Range Dependence (LRD) existente no tráfego original, permitindo assim entender melhor o comportamento do tráfego de rede seletivo

The theory and application of bootstrap control charts for statistical process control

Mini Dissertation (MSc (Mathematical Statistics))--University of Pretoria, 2017.Chapter 1 of this mini-dissertation gives an introduction to Statistical Process Control (SPC) and provides some background on the Shewhart, CUSUM and the EWMA control charts. The bootstrap by [9] Efron (1979) is discussed and a brief overview of Phase I and Phase II analysis is given. The chapter concludes with the research objectives of this dissertation. Chapter 2 of this dissertation provides a literature review of bootstrap Shewhart, cumulative sum (CUSUM), exponentially weighted moving average (EWMA) and multivariate control charts. The Shewhart-type control charts mostly focus on the bootstrap procedures proposed by [2] Bajgier (1992), [34] Seppala, Moskowitz, Plante and Tang (1995) and [23] Liu and Tang (1996). An overview of the bootstrap CUSUM charts proposed by [7] Chatterjee and Qiu (2009) and [1] Ambartsoumian and Jeske (2015) is given. A review of the parametric bootstrap control chart used by [33] Saleh, Mahmoud, Jones-Farmer, Zwetsloot and Woodal (2015) to construct EWMA control charts is given. The chapter concludes with a review of the bootstrap T2 control chart proposed by [32] Phaladiganon, Kim, Chen, Baek and Park (2011). In Chapter 3 the design of a potential nonparametric bootstrap EWMA control is given. The chapter concludes with two examples of how the control limits for such a chart can be constructed for two different statistics. Chapter 4 of this mini-dissertation examines conditional in-control (IC) and out-of-control (OOC) average run-length, for the chart proposed in Chapter 3, taking different underlying process distributions into consideration. In Chapter 5 the the mini-dissertation is concluded by summarising the research that has been done and providing recommendations for further research.StatisticsMSc (Mathematical Statistics)UnrestrictedFaculty of Natural and Agricultural Science

Robust longitudinal rate gyro bias estimation for reliable pitch attitude observation through utilization of a displaced accelerometer array

In this thesis, a novel attitude estimation device is proposed utilizing cost-effective measurement sensors. The device fuses a rate gyroscope with an accelerometer array to estimate and eliminate the rate gyro bias online yielding accurate real time aircraft attitude tracking. Attitude determination algorithms are dependent on instantaneous and accurate measurements of translational and rotational body rates for precise estimation of vehicle orientation in three-dimensional space. Measurement error of instantaneous rate sensors, gyroscopes, is introduced via inherent biases and signal noise resulting in gyro drift. Integration of the rate signal for calculation of a net displacement amplifies these minute measurement errors leading to inaccurate and unreliable attitude observation. The proposed device is a departure from typical attitude observers and bias estimators due to its reliance on accelerometers measuring the local gravitational vector in lieu of additional magnetic field sensors or GPS. The end result of this work is a longitudinal attitude estimation device able to compute a rate gyro bias in real-time producing accurate pitch angle tracking while subjected to simulated aircraft flight conditions. The effectiveness of the newly constructed attitude estimation algorithm is demonstrated by comparison of attitude and rate gyro bias estimates produced from noise corrupted and biased sensors with the actual attitude of a nonlinear aircraft model and true rate gyro bias