Doctor Educationis / Cybersecurity defense tools, techniques and methodologies are constantly faced with increasing challenges including the evolution of highly intelligent and powerful new generation threats. The main challenges posed by these modern digital multi-vector attacks is their ability to adapt with machine learning. Research shows that many existing defense systems fail to provide adequate protection against these latest threats. Hence, there is an ever-growing need for self-learning technologies that can autonomously adjust according to the behaviour and patterns of the offensive actors and systems. The accuracy and effectiveness of existing methods are dependent on decision making and manual input by human expert. This dependence causes 1) administration overhead, 2) variable and potentially limited accuracy and 3) delayed response time. In this thesis, Autonomous Threat Detection and Response (ATDR) is a proposed general method aimed at contributing toward security related self-protected networks. Through a combination of unsupervised machine learning and Deep learning, ATDR is designed as an intelligent and autonomous decision-making system that uses big data processing requirements and data frame pattern identification layers to learn sequences of patterns and derive real-time data formations. This system enhances threat detection and response capabilities, accuracy and speed. Research provided a solid foundation for the proposed method around the scope of existing methods and the unanimous problem statements and findings by other authors.

This thesis provides a discrete-event simulation framework that can be used to analyze  and  dimension  computing  systems.  The  simulation  framework  can define  and  parametrize  the  flexible  queueing  system.  We  use  the  simulation framework to explore the data collected from the real-world system. We analyze the metrics, including waiting time and server utilization of single-server and multi-server  queueing  systems.  In  particular,  we  study  the  impact  of  the number of servers on waiting time and server utilization. The experiments show it  is  possible  to  increase  server  utilization  and  decrease  the  server  number without  significantly  increasing  waiting  time,  and  flexible  architectures  canlead to significant gains. / Detta  examensarbete  tillhandahåller  ett  ramverk  som  kan  användas  för  att analysera och dimensionera dator-system. Simuleringsramverket kan definera och parameterisera ett flexibelt kösystem baserat på data från ett system i drift. Vi använder simuleringsramverket för att undersöka datat insamlat från skarpa system.  Vi  analyserar  prestandatal,  såsom  väntetid  och  utnyttjandegrad  för system  med  en  och  flera  betjänare.  Framför  allt  undersöker  vi  hur  antalet betjänare  påverkar  väntetid  och  utnyttjandegrad.   Försöken  visar  att  det  är möjligt  att  öka  uttnyttjandegraden  och  minska  antalet  betjänare  utan  att märkbart öka väntetiden, och att en flexibel arkitektur kan leda till märkbaraförbättringar. / <p>Industrial Advisors: Olga Grinchtein and Johan Karlsson </p>

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Este trabalho estuda medidas de desempenho aproximadas em centrais de atendimento, apresentadas pelo modelo M/G/s/r+G. As aproximações são calculadas a partir do modelo M/M/s/r+M(n). Os resultados foram extendidos para o caso de mais de um tipo de cliente, apresentado pelo modelo M/Mi/s/r+Mi(n). Para dois casos particulares com 2 tipos de clientes, as aproximações citadas foram avaliadas numericamente e comparadas com os resultados de referência obtidos através de simulação. Os resultados aproximados comprovam que a aproximação é bastante satisfatória. / We study approximations for performance measures of call centers, represented by M/G/s/r+G queueing model. We use the measures computed in the M/M/s/r+M(n) queueing model. The results were extended for more then one type of customer, represented by M/Mi/s/r+Mi(n) queueing model. For two particular cases with two types of customers, the mentioned approaches were numerically evaluated and compared with the results of reference obtained by simulation. The approximate results show that the approach is quite satisfactory.

Uma série de problemas de filas em sistemas de transportes com picos de tráfego, ou um número finito de elementos no sistema, são usualmente representados pelo modelo de fonte infinita, dadas as dificuldades de utilização do modelo exato de fonte finita. Este trabalho apresenta uma solução alternativa baseada no cálculo de um limitante superior para as probabilidades de equilíbrio do modelo exato de fonte finita, e compara as medidas de desempenho dos sistemas calculadas pelos dois modelos. Mostra-se que para índices de congestionamento menores que um, as diferenças entre estas medidas são tanto menores quanto menor for este índice. A partir destes resultados, compara-se as medidas de desempenho do modelo aproximado proposto com as do modelo de população infinita, para diferentes tamanhos de população e números de servidores. Conclui-se que os modelos conduzem a resultados numéricos muito próximos para uma ampla variação do índice de congestionamento, e que estes resultados são tão melhores quanto maior for o número de servidores no sistema e o número de elementos na população. São também apresentados três estudos de casos comparando os resultados induzidos pelos modelos exato, proposto e usual de fonte infinita, que ilustram a aplicabilidade prática dos resultados deste trabalho em sistemas de transportes. / A set of stochastic queueing problems in transportation systems with traffic peaks, or a finite number of elements in the system, are usually represented by the infinite source model, due to the difficulties of applying the exact finite source model. This study presents an alternative solution based on the upper bound values of the equilibrium probabilities of the exact finite source model, and compares the performance measurements of the two models. It is shown that for congestion factors below one, the smaller the value of the congestion factor, the smaller is the difference between the models. Based on this results the measures of performance of the proposed aproximate model are compared with the results of the usual infinite source model for different population sizes and number of servers. It is concluded that the models lead to very close numerical results for a wide range of congestion factors of the system and that these results are the better the larger is the number of servers and the number of elements in the system. Three case studies ilustrating the pratical applicability of the results of this study to transportation systems are also presented.

Este trabalho estuda medidas de desempenho aproximadas em centrais de atendimento, apresentadas pelo modelo M/G/s/r+G. As aproximações são calculadas a partir do modelo M/M/s/r+M(n). Os resultados foram extendidos para o caso de mais de um tipo de cliente, apresentado pelo modelo M/Mi/s/r+Mi(n). Para dois casos particulares com 2 tipos de clientes, as aproximações citadas foram avaliadas numericamente e comparadas com os resultados de referência obtidos através de simulação. Os resultados aproximados comprovam que a aproximação é bastante satisfatória. / We study approximations for performance measures of call centers, represented by M/G/s/r+G queueing model. We use the measures computed in the M/M/s/r+M(n) queueing model. The results were extended for more then one type of customer, represented by M/Mi/s/r+Mi(n) queueing model. For two particular cases with two types of customers, the mentioned approaches were numerically evaluated and compared with the results of reference obtained by simulation. The approximate results show that the approach is quite satisfactory.

Uma série de problemas de filas em sistemas de transportes com picos de tráfego, ou um número finito de elementos no sistema, são usualmente representados pelo modelo de fonte infinita, dadas as dificuldades de utilização do modelo exato de fonte finita. Este trabalho apresenta uma solução alternativa baseada no cálculo de um limitante superior para as probabilidades de equilíbrio do modelo exato de fonte finita, e compara as medidas de desempenho dos sistemas calculadas pelos dois modelos. Mostra-se que para índices de congestionamento menores que um, as diferenças entre estas medidas são tanto menores quanto menor for este índice. A partir destes resultados, compara-se as medidas de desempenho do modelo aproximado proposto com as do modelo de população infinita, para diferentes tamanhos de população e números de servidores. Conclui-se que os modelos conduzem a resultados numéricos muito próximos para uma ampla variação do índice de congestionamento, e que estes resultados são tão melhores quanto maior for o número de servidores no sistema e o número de elementos na população. São também apresentados três estudos de casos comparando os resultados induzidos pelos modelos exato, proposto e usual de fonte infinita, que ilustram a aplicabilidade prática dos resultados deste trabalho em sistemas de transportes. / A set of stochastic queueing problems in transportation systems with traffic peaks, or a finite number of elements in the system, are usually represented by the infinite source model, due to the difficulties of applying the exact finite source model. This study presents an alternative solution based on the upper bound values of the equilibrium probabilities of the exact finite source model, and compares the performance measurements of the two models. It is shown that for congestion factors below one, the smaller the value of the congestion factor, the smaller is the difference between the models. Based on this results the measures of performance of the proposed aproximate model are compared with the results of the usual infinite source model for different population sizes and number of servers. It is concluded that the models lead to very close numerical results for a wide range of congestion factors of the system and that these results are the better the larger is the number of servers and the number of elements in the system. Three case studies ilustrating the pratical applicability of the results of this study to transportation systems are also presented.

This thesis is concerned with queueing models where demand is allowed to exceed the system capacity, and also with the capacity sizing and pricing problem for heterogeneous products and resources under demand uncertainty. Our aim is to improve productivity and profitability. In the first part of the thesis, we consider the dynamic assignment of servers to tasks in queueing networks where demand may exceed the capacity for service. The objective is to maximize the system throughput. We use fluid limit analysis to show that several quantities of interest, namely the maximum possible throughput, the maximum throughput for a given arrival rate, the minimum arrival rate that will yield a desired feasible throughput, and the optimal allocations of servers to classes for a given arrival rate and desired throughput, can be computed by solving linear programming problems. We develop generalized round robin policies for assigning servers to classes for a given arrival rate and desired throughput, and show that our policies achieve the desired throughput as long as this throughput is feasible for the arrival rate. We conclude with numerical examples that illustrate the points discussed and provide insights into the system behavior when the arrival rate deviates from the one the system is designed for. In the second part of the thesis, we consider the effects of inspection and repair stations on the production capacity and product quality in a serial line with possible inspection and repair following each operation. We consider multiple defect types and allow for possible inspection errors that are defect dependent. We construct a profit function that takes into account inspection, repair, and goodwill costs, as well as the capacity of each station. Then we compare the profitability of different inspection plans and discuss how to identify the optimal inspection plan. Finally, in the third part of the thesis, we consider the capacity and pricing decisions made by a monopolistic firm producing two heterogeneous products under demand uncertainty. The objective is to maximize profit. Our model incorporates dedicated and flexible resources, product substitutability, and processing rates that may depend on the product and on the resource type. We provide the optimum prices and production quantities as functions of resource capacities and demand intercepts. We also show that investment in flexible capacity is only desirable when it is optimal to invest in dedicated capacities for both products, and obtain upper bounds for the costs of the dedicated capacities that need to be satisfied for investment in the flexible resource. We conclude with numerical examples that illustrate the points discussed and provide insights into how the optimal capacities and expected production quantities, prices, and profit depend on various model parameters.

Distributed Discrete Event Simulation (DDES) has received much attention in recent years, owing to the fact that uniprocessor based serial simulations may require excessive amount of simulation time and computational resources. It is therefore natural to attempt to use multiple processors to exploit the inherent parallelism in discrete event simulations in order to speed up the simulation process. In this dissertation we study the performance of distributed simulation of queueing networks, by analysing queueing models of message flows in distributed discrete event simulators. Most of the prior work in distributed discrete event simulation can be catego­rized as either empirical studies or analytic (or formal) models. In the empirical studies, specific experiments are run on both conservative and optimistic simulators to see which strategy results in a faster simulation. There has also been increasing activity in analytic models either to better understand a single strategy or to compare two strategies. Little attention seems to have been paid to the behaviour of the interprocessor message queues in distributed discrete event simulators. To begin with, we study how to model distributed simulators of queueing networks. We view each logical process in a distributed simulation as comprising a message sequencer with associated message queues, followed by an event processor. A major contribution in this dissertation is the introduction of the maximum lookahead sequencing protocol. In maximum lookahead sequencing, the sequencer knows the time-stamp of the next message to arrive in the empty queue. Maximum lookahead is an unachievable algorithm, but is expected to yield the best throughput compared to any realisable sequencing technique. The analysis of maximum lookahead, therefore, should lead to fundamental limits on the performance of any sequencing algorithm We show that, for feed forward type simulators, with standard stochastic assump-tions for message arrival and time-stamp processes, the message queues are unstable for conservative sequencing, and for conservative sequencing with maximum lookahead and hence for optimistic resequencing, and for any resequencing algorithm that does not employ interprocessor "flow control". It follows that the resequencing problem is fundamentally unstable and some form of interprocessor flow control is necessary in order to make the message queues stable (without message loss). We obtain some generalizations of the insta­bility results to time-stamped message arrival processes with certain ergodicity properties. For feedforward type distributed simulators, we study the throughput of the event sequencer without any interprocessor flow control. We then incorporate flow control and study the throughput of the event sequencer. We analyse various flow control mechanisms. For example, we can bound the buffers of the message queues, or various logical processes can be prevented from getting too far apart in virtual time by means of a mechanism like Moving Time Windows or Bounded Lag. While such mechanisms will serve to stabilize buffers, our approach, of modelling and analysing the message flow processes in the simulator, points towards certain fundamental limits of efficiency of distributed simulation, imposed by the synchronization mechanism. Next we turn to the distributed simulation of more general queueing networks. We find an upper bound to the throughput of distributed simulators of open and closed queueing networks. The upper bound is derived by using flow balance relations in the queueing network and in the simulator, processing speed constraints, and synchronization constraints in the simulator. The upper bound is in terms of parameters of the queueing network, the simulator processor speeds, and the way the queueing network is partitioned or mapped over the simulator processors. We consider the problem of choosing a mapping that maximizes the upper bound. We then study good solutions o! this problem as possible heuristics for the problem of partitioning the queueing network over the simulator processors. We also derive a lower bound to the throughput of the distributed simulator for a simple queueing network with feedback. We then study various properties of the maximum lookahead algorithm. We show that the maximum lookahead algorithm does not deadlock. Further, since there are no syn­chronization overheads, maximum lookahead is a simple algorithm to study. We prove that maximum lookahead sequencing (though unrealisable) yields the best throughput compared to any realisable sequencing technique. These properties make maximum lookahead a very useful algorithm in the study of distributed simulators of queueing networks. To investigate the efficacy of the partitioning heuristic, we perform a study of queue­ing network simulators. Since it is important to study the benefits of distributed simula­tion, we characterise the speedup in distributed simulation, and find an upper bound to the speedup for a given mapping of the queues to the simulator processors. We simulate distributed simulation with maximum lookahead sequencing, with various mappings of the queues to the processors. We also present throughput results foT the same mappings but using a distributed simulation with the optimistic sequencing algorithm. We present a num­ber of sufficiently complex examples of queueing networks, and compare the throughputs obtained from simulations with the upper bounds obtained analytically. Finally, we study message flow processes in distributed simulators of open queueing networks with feedback. We develop and study queueing models for distributed simulators with maximum lookahead sequencing. We characterize the "external" arrival process, and the message feedback process in the simulator of a simple queueing network with feedback. We show that a certain "natural" modelling construct for the arrival process is exactly correct, whereas an "obvious" model for the feedback process is wrong; we then show how to develop the correct model. Our analysis throws light on the stability of distributed simulators of queueing networks with feedback. We show how the stability of such simulators depends on the parameters of the queueing network.

Materialfluss-Systeme für den Stückgut-Transport auf der Basis von Stetigförderern sind meist modular aufgebaut. Das Verhalten gleichartiger Materialfluss-Elemente unterscheidet sich durch technische Parameter (z.B. geometrische Größen) und durch unterschiedliche logistische Belastungen der Elemente im System. Durch die in der Arbeit getroffenen Modellannahmen werden für die Elemente nur lokale Steuerungsregeln zugelassen und für das System Blockierfreiheit vorausgesetzt. Das Verhalten eines Materialfluss-Elements hängt dann nicht mehr von Zuständen anderer Elemente des Systems ab sondern nur noch von den stochastischen Prozessen des Eintreffens von Transporteinheiten. Die Auslastung eines Elements, die Quantile der Warteschlangenlängen an seinen Eingängen und die Variationskoeffizienten seiner Abgangsströme sind statistische Kenngrößen. Sie hängen im Wesentlichen nur von der Klasse des Elements, seinen technischen Parametern, den Parametern der Eingangsströme und der lokalen Transportmatrix ab. Diese funktionellen Abhängigkeiten sind im Allgemeinen nicht analytisch handhabbar. Da diese Funktionen stetig differenzierbar und beschränkt sind und von relativ viele Eingansgrößen anhängen, sind neuronale Netze gut geeignet für numerische Näherungen. Mit Hilfe von einfachen neuronalen Netzen können die statistischen Kenngrößen numerisch approximiert werden. Aus einzelnen Teilmodellen kann ein hybrides Modell des gesamten Systems zusammengesetzt werden. Anhand von einigen Beispielen wird die Güte der Modellierung bewertet. / Material flow systems are normally built with a modular structure. The behavoir of similar elements only differs by technical parameters (e.g. geometriy), and by different logistic loads of the elements in the system. In this paper, a new model is being developed for a non-blocking system with non-global control rules. The behavior of a flow of a material flow element is assumed not to depend on the conditions of other elements of the system, but only on stochastic processes of the arrival of transportation units. The rate of utilization of an element, the quantiles of the queue lengths at its inputs, and the dispersion of its output stream are statistic characteristics. They depend only on the type of the element, its technical parameters, the parameters of the input streams, and the local transportation matrix. These functional dependencies are not analytically manageable. But due to their properties, neural nets are well suited for numeric approximations of these statistic functions. The single models can be used to compose a hybrid model of the whole system. A few examples show the quality of the new modeling technique.