Orientador: Regiane Máximo de Souza / Banca: Enzo Barberio Mariano / Banca: Reinaldo Morabito Neto / Resumo: Vários Sistemas de Atendimento Emergenciais (SAE's) sofrem com as variações diárias da demanda e da disponibilidade das ambulâncias. Nesses sistemas pode haver flutuação do desempenho ao longo do dia devido, por exemplo, a mudança no número de servidores e nas taxas de chegada, levando à necessidade de considerar explicitamente tais variações em uma extensão ao modelo hipercubo ainda não explorada na literatura. Como ocorre em alguns SAE's, as ambulâncias melhor equipadas são reservadas para o atendimento exclusivo de chamados com risco de vida. Dessa maneira, a política de despacho pode ser diferenciada com a finalidade de reservar totalmente o atendimento de alguns servidores para certas gravidades de ocorrências. Além disso, somam-se à natureza aleatória desses sistemas, como por exemplo, as incertezas da disponibilidade das ambulâncias, a chegada de um novo chamado e sua localização. Nesse contexto, os objetivos do presente estudo são: (i) estender o modelo hipercubo de filas para reserva total de capacidade, dependendo do tipo do chamado; (ii) estender o modelo hipercubo de filas para torná-lo mais eficiente computacionalmente, sem haver perda de precisão durante a modelagem e resolução; e (iii) propor uma abordagem baseada no modelo hipercubo não-estacionário para organização do trabalho das ambulâncias em qualquer momento do dia. Para verificar a viabilidade e a aplicabilidade dessas abordagens, é realizado um estudo de caso no SAMU da cidade de Bauru (SAMU-Bauru) que,... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Many Emergency Service Systems face daily variations on demand and ambulance availability. These systems may suffer, for example, performance fluctuations throughout the day, changes on the number of servers and on arrival rates, leading to the need to explicitly consider such variations in a hypercube model extension not yet explored in the literature. As occurs in some SAMU's, which reserve their best equipped ambulances to exclusively serve life-threating requests. Therefore, the dispatch policy can be differentiated in order to completely reserve the service of some ambulances to more severe requests. These problems add up to the random nature of these systems with uncertainties upon ambulance availability or the arrival of a new request and its location. Thus, this study aims to: (i) extend the hypercube queueing model to be able to capture the complete capacity reservation of advanced ambulances, depending on the request classification; (ii) extend the hypercube model in order to make it more computationally efficient, without losing any information during modeling and resolution. (iii) propose an approach based on nonstationary hypercube queueing model to organize the operation of ambulances at any time of the day. To verify the feasibility of these approaches, a case study is carried out on the SAMU from Bauru city (SAMU-Bauru), which, in addition to the advanced ambulance reservation for life-threating requests, is affected by daily variations in demand and ambulance availability. In addition to the original configuration of SAMU-Bauru, studied on a two-step approach, we studied a total of four alternative scenarios that exploited important matters as: the impact of average demand increase on the congestion peak; mitigation of this impact by including a new ambulance; changing the schedule of daily breaks; and the... (Complect abstract electronic acess below) / Mestre

The objective of this dissertation is to enhance the overall understanding of practical manufacturing systems by using rigorous academic approaches, primarily queueing theory. The scope spans from the performance of a single manufacturing process to the performance of a manufacturing system. Queueing models are commonly used to evaluate the performance of manufacturing systems. Exact M/M/1 or approximations of G/G/1 models are usually adopted to describe the behavior of a single machine system. However, when applying queueing models to a single machine, some practical issues are encountered. A real machine is subject to different types of interruptions, such as breakdowns, setups and routine maintenance. The proper queueing models under interruptions are presented. The behavior of manufacturing systems is explored by first investigating the underlying structure of tandem queues. We introduce two properties describing the dependence among servers in tandem queues, namely the intrinsic gap and intrinsic ratio, and develop a new approximation approach. The approach exploits what we call the nearly-linear and heavy-traffic properties of the intrinsic ratio. Across a broad range of examined cases, this new approach outperforms earlier approximations that are based on the parametric-decomposition and diffusion approximation approaches. We also demonstrate its use with historical data to achieve very accurate queue time estimates. Furthermore, based on the structure of tandem queues, a way to model the performance of manufacturing systems has been developed.

Several decades after A.K. Erlang originated the theory of queues and queueing networks, D.V. Lindley added impetus to the development of this field by determining a recursive relation for waiting times. Part I of this thesis provides a theoretical treatment of single-server and multiserver queues described by the basic Lindley relation and its extensions, which are referred to collectively as Lindley-Loynes equations. The concepts of stability, and minimal and maximal solutions are investigated. The interdependence of theory and practice becomes evident in Part II, where the results of recent and current research are highlighted. While the main aim of the first part of the thesis is to provide a firm theoretical framework for the sequel, the objective in Part II is to derive generalised forms of the Lindley-Loynes equations from different network protocols. Such protocols are regulated by different switching rules and synchronization constraints. Parts I and II of the thesis are preceded by Chapter 0 in which several fundamental ideas (including those on notation and probability) are described. It is in this chapter too that a more detailed overview of the concept of the thesis is provided. / Thesis (M.Sc.)-University of Natal, Durban, 1993.

Design and management decisions require an accurate prediction of the performance of the network. Network performance estimation techniques require accurate network traffic models. In this thesis we are concerned with the modelling of network traffic for the wireless mesh network (WMN) environment. Queueing theory has been used in the past to model the WMN environment and we found in this study that queueing theory was used in two main methods to model WMNs. The first method is to consider each node in the network in terms of the number of hops it is away from the gateway. Each node is then considered as a queueing station and the parameters for the station is derived from the number of hops each node is away from the gateway. These topologies can be very limiting in terms of the number of physical topologies they can model due to the fact that their parameters are only dependent on the number of hop-counts each node is away from the gateway. The second method is to consider a fixed topology with no gateways. This method simplifies analysis but once again is very limiting. In this dissertation we propose a queueing based network traffic model that uses a connection matrix to define the topology of the network. We then derive the parameters for our model from the connection matrix. The connection matrix allows us to model a wider variety of topologies without modifying our model. We verify our model by comparing results from our model to results from a discrete event simulator and we validate our model by comparing results from our model to results from models previously proposed by other authors. By comparing results from our model to results of other models we show that our model is indeed capable of modelling a wider variety of topologies. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Design and management decisions require an accurate prediction of the performance of the network. Network performance estimation techniques require accurate network traffic models. In this thesis we are concerned with the modelling of network traffic for the wireless mesh network (WMN) environment. Queueing theory has been used in the past to model the WMN environment and we found in this study that queueing theory was used in two main methods to model WMNs. The first method is to consider each node in the network in terms of the number of hops it is away from the gateway. Each node is then considered as a queueing station and the parameters for the station is derived from the number of hops each node is away from the gateway. These topologies can be very limiting in terms of the number of physical topologies they can model due to the fact that their parameters are only dependent on the number of hop-counts each node is away from the gateway. The second method is to consider a fixed topology with no gateways. This method simplifies analysis but once again is very limiting. In this dissertation we propose a queueing based network traffic model that uses a connection matrix to define the topology of the network. We then derive the parameters for our model from the connection matrix. The connection matrix allows us to model a wider variety of topologies without modifying our model. We verify our model by comparing results from our model to results from a discrete event simulator and we validate our model by comparing results from our model to results from models previously proposed by other authors. By comparing results from our model to results of other models we show that our model is indeed capable of modelling a wider variety of topologies. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013.

Submitted by Cláudia Bueno (claudiamoura18@gmail.com) on 2015-12-10T14:45:42Z No. of bitstreams: 2 Dissertação - Murilo Antonio de Oliveira - 2015.pdf: 1647647 bytes, checksum: 5b2f01764dbbc90bb9c3b4c20c2a32f7 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-12-11T09:25:38Z (GMT) No. of bitstreams: 2 Dissertação - Murilo Antonio de Oliveira - 2015.pdf: 1647647 bytes, checksum: 5b2f01764dbbc90bb9c3b4c20c2a32f7 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2015-12-11T09:25:38Z (GMT). No. of bitstreams: 2 Dissertação - Murilo Antonio de Oliveira - 2015.pdf: 1647647 bytes, checksum: 5b2f01764dbbc90bb9c3b4c20c2a32f7 (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2015-08-27 / Waiting lines are boldly present in our society following us since the beginnings of civilization. Sometimes they occur in a traditional way with a well-seen aspect and thus look like similar to the model we already have in mind, but also there are times in which waiting lines occur in di erent formats becoming unperceivable to the common observer not yet introduced to the Queuing Theory. The present study aims in demonstrating the applicability of Mathematics. Statistics and the Queuing Theory to real tasks such as the waiting line of a bank cashier in the City of Jataí-Goiás. In this regard we present a short history of the Queuing Theory embracing its advent, the rst task to be dealt with, the de nitions and the adopted terminology looking forward to subsidize a theoretical base in an introductory level. As our object of observation is a waiting line of a bank cashier we additionally present a short history of the National Financial System in which comprehends every bank, and also the municipal law that rules the maximum waiting time in a line. After the choice of a bank agency in the City of Jataí-Goiás we succeeded to get access to the detailing tape of the cashiers under managers authorization. The tape has all the data about daily transactions. The time of analysis refers to the month of November 2014. After appropriate organization and data cataloging, they were processed according to the Queuing Theory illustrating its applicability. Results allowed us to work a few mathematical concepts, specially the idea of average. However, more detailed results and analysis were not dealt with in this work due to its complexity but will be considered in future studies that might take the present work as a starting point. / As las tem presença marcante em nossa sociedade e nos acompanham desde o início da civilização. Algumas vezes manifestam-se de forma tradicional e apresentam caráter bastante visual assemelhando-se assim ao modelo que temos em nossas mentes, mas às vezes manifestam-se de formas variadas e tornam-se imperceptíveis ao olhar não familiarizado com a Teoria das Filas. O presente texto teve como propósito mostrar a aplicabilidade da matemática, estatística e Teoria das Filas a problemas reais tal como a la de guichê de caixa de uma agência bancária da cidade de Jataí-Go. Para isso apresentamos um breve histórico da Teoria das Filas, contemplando o seu surgimento, o primeiro problema estudado, as de nições e os termos empregados visando subsidiar um embasamento teórico em nível básico. Por ter se pautado na análise da la do caixa de uma agência bancária complementarmente apresentamos um breve histórico do Sistema Financeiro Nacional - SFN no qual todos os bancos encontram-se inseridos e a lei municipal que normatiza o tempo máximo de espera em la. Após escolhido uma agência bancária na cidade de Jataí-Go conseguimos com a autorização do gerente a ta detalhe dos caixas, a qual nos apresenta os dados referentes a movimentação diária. O período de análise refere-se ao mês de novembro do ano de 2014. Após a devida organização e catalogação os dados foram tratados sob o olhar da Teoria das Filas ilustrando a aplicabilidade desta teoria. Os resultados possibilitaram trabalhar alguns conceitos básicos da matemática, em especí co o conceito de média. Contudo, resultados e análises mais elaboradas deixaram de ser tratadas no presente texto, devido a sua complexidade, mas serão analisados em textos futuros que poderão ter este como ponto de partida.

The advancement of wireless technology has led to an increase in the employment of wireless sensor networks (WSNs). Traditionally, WSNs are powered by batteries. However, the high power consump- tion and the need to change the batteries regularly has made these networks costly to maintain. The nodes in the WSNs are increasingly strained as power consumption increases and the batteries are depleted faster. This has consequently decreased the overall lifetime of the WSNs. Although many energy-conserving techniques exist, for example energy-efficient medium access control and energy-efficient routing protocols, energy consumption remains one of the significant constraints in the development of WSNs. A natural solution to this constraint is harvesting energy from the environment. However, unlike conventional energy, energy harvested from the environment is random in nature, making it challenging to realise energy-harvesting transmission schemes. Although energy harvesting might be considered a solution to many problems, it brings about new challenges with regard to the usage and management of the energy harvested. Some of these challenges include uneven consumption of power in the network, resulting in dead nodes in some portion of the network and the batteries used in the network are being affected negatively by the energy usage; they may consequently sustain the nodes for long or short periods. To analyse the usage and consumption of energy, a number of techniques have been proposed, namely; information theory, game theory and queueing theory. By this time, the performance of the sensor nodes in WSNs has been analysed making use of a queueing-theoretic model for each sensor. The aforementioned model inadequately expresses the physical constraints, namely, the energy drawing process and the finite battery capacity. This research focuses on developing a model that captures the harvesting, accumulation and dissipation of energy, utilising queueing theory. A rechargeable battery with a finite storage capacity will be used. To ensure that the battery does not lose its capability to store charge after being recharged repeatedly, the leaky bucket model is proposed to check the network data flow as the harvested energy in the WSN is analysed. To capture real-world WSNs with energy harvesting in which there is energy leakage, the energy- harvesting sensor node performance is analysed with two assumptions: data transmission and energy leakage occurring and the token buffer being subjected to a threshold. The system had finite buffers for the data and energy. To make it possible to have some influence over the system performance measures a threshold is imposed on the token buffer. Four models are developed: a basic model, a basic model with leakage incorporated, a basic model with leakage and priority incorporated and a basic model with leakage, priority and threshold incorporated. The developed models are simulated and results for the performance measures are obtained. / Dissertation (MEng (Computer Engineering))--University of Pretoria, 2021. / BWMC, NRF / Electrical, Electronic and Computer Engineering / MEng (Computer Engineering) / Unrestricted

With the increase in wireless technology devices and mobile users, wireless radio spectrum is coming under strain. Networks are becoming more and more congested and free usable spectrum is running out. This creates a resource allocation problem. The resource, wireless spectrum, needs to be allocated to users in a manner such that it is utilised efficiently and fairly. The objective of this research is to find a solution to the resource allocation problem in radio networks, i.e to increase the efficiency of spectrum utilisation by making maximum use of the spectrum that is currently available through taking advantage of co-existence and exploiting interference limits. The solution proposed entails adding more secondary users (SU) on a cognitive radio network (CRN) and having them transmit simultaneously with the primary user. A typical network layout was defined for the scenario. The interference temperature limit (ITL) was exploited to allow multiple SUs to share capacity. Weighting was applied to the SUs and was based on allowable transmission power under the ITL. Thus a more highly weighted SU will be allowed to transmit at more power. The weighting can be determined by some network-defined rule. Specific models that define the behaviour of the network were then developed using queuing theory, specifically weighted processor sharing techniques. Optimisation was finally applied to the models to maximize system performance. Convex optimization was deployed to minimize the length of the queue through the power allocation ratio. The system was simulated and results for the system performance obtained. Firstly, the performance of the proposed models under the processor-sharing techniques was determined and discussed, with explanations given. Then optimisation was applied to the processor-sharing results and the performance was measured. In addition, the system performance was compared to other existing solutions that were deemed closest to the proposed models. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

No / Over the last few years, cloud computing has become quite popular. It offers Web-based companies the advantage of scalability. However, this scalability adds complexity which makes analysis and predictable performance difficult. There is a growing body of research on load balancing in cloud data centres which studies the problem from the perspective of the cloud provider. Nevertheless, the load balancing of scalable web servers deployed on the cloud has been subjected to less research. This paper introduces a simple queueing model to analyse the performance metrics of web server under varying traffic loads. This assists web server managers to manage their clusters and understand the trade-off between QoS and cost. In this proposed model two thresholds are used to control the scaling process. A discrete-event simulation (DES) is presented and validated via an analytical solution.

This paper presents a new analytical framework for the congestion control of Internet traffic using a queue threshold scheme. This framework includes two discrete-time analytical models for the performance evaluation of a threshold based congestion control mechanism and compares performance measurements through typical numerical results. To satisfy the low delay along with high throughput, model-I incorporates one threshold to make the arrival process step reduce from arrival rate ¿1 directly to ¿2 once the number of packets in the system has reached the threshold value L1. The source operates normally, otherwise. Model-II incorporates two thresholds to make the arrival rate linearly reduce from ¿1 to ¿2 with system contents when the number of packets in the system is between two thresholds L1 and L2. The source operates normally with arrival rate ¿1 before threshold L1, and with arrival rate ¿2 after the threshold L2. In both performance models, the mean packet delay W, probability of packet loss PL and throughput S have been found as functions of the thresholds and maximum drop probability. The performance comparison results for the two models have also been made through typical numerical results. The results clearly demonstrate how different load settings can provide different tradeoffs between throughput, loss probability and delay to suit different service requirements.