New technologies are expected to play a major role for wireless cellular systems beyond the existing 4G paradigm. The need for several orders of magnitude increase in system capacity has led to the proliferation of low-powered cellular layers overlaid on the existing macrocell layer. This type of network consisting of different cellular layers, each with their unique characteristics including transmission power and frequency of operation among others is termed as a heterogeneous network (HetNet). The emergence of HetNets leads to several research challenges and calls for a profound rethinking of several existing approaches for mobility management and interference management among other issues.

Les xarxes WLANs possibiliten un accés de banda ampla a Internet des d'un terminal mòbil, essent una possible solució alternativa a les xarxes cel·lulars. Tanmateix, aquest tipus de tecnologia presenta certes limitacions, com és la difícil coexistència entre fluxos de tràfic rígids (VoIP) i fluxos de tràfic elàstic (TCP), degut al propi protocol d'accés al medi. En aquesta tesi es proposa la utilització d'un nou mecanisme de control d'admissió que utilitzant el nou estàndard de qualitat de servei en xarxes WLAN (EDCA). La utilització del mecanisme de control d'admissió millora notablement les prestacions que es poden obtenir de la xarxa, solucionant les diferents limitacions de la tecnologia. Per a l'avaluació i optimització del mecanisme de control d'admissió s'ha desenvolupat un conjunt d'eines matemàtiques que permeten capturar tant la dinàmica del protocol d'accés com el comportament dels diferents fluxos de tràfic multimèdia que s'han consideren (VoIP i tràfic elàstic, TCP). / WLANs provide a broadband access to Internet from a mobile terminal, which can be a possible alternative solution to cellular networks. However, this technology presents several limitations, as it is the difficult coexistence between rigid traffic flows (VoIP) and elastic traffic flows (TCP), due to the medium access protocol itself. In this thesis a new admission control mechanism is proposed. It uses the set of QoS mechanisms provided by the new EDCA standard. The use of the proposed admission control mechanism improves the overall WLAN performance, solving the different technology limitations. In order to be able to evaluate and optimize the admission control mechanism, several mathematical tools have been developed in order to capture the dynamics of both, the access protocol and of the different multimedia traffic flows that have been considered.

Durante los últimos años las redes móviles celulares han experimentado un considerable crecimiento y desarrollo debido al nuevo modo en que la sociedad crea, comparte y consume información. El enorme impacto y penetración de los servicios móviles telefónicos en la sociedad actual, así como la introducción de un amplio abanico de nuevos servicios de datos y servicios multimedia, han llevado a un crecimiento espectacular del volumen de tráfico transportado por este tipo de redes. Esta tendencia se mantendrá en los próximos años ya que constantemente van apareciendo nuevas aplicaciones que demandan mayor calidad de servicio y ancho de banda. Sin embargo, lasredesmóviles celulares actualestienen fuerteslimitaciones de ancho de banda debido a la escasez de frecuencias en el espectro radioeléctrico. Así, estas nuevas necesidades establecen nuevosretos para la industria de las telecomunicaciones. Es necesario gestionar un creciente número de servicios que demandan elevadas cantidades de recursos, conjuntamente con la escasez del espectro radioeléctrico, para ofrecer servicios que satisfagan las necesidades de los usuarios de un modo eficaz y económico. Dentro de este contexto, la gestión de los recursos radio se presenta como una estrategia clave para hacer frente a las características especiales de estasredes. Concretamente, el control de admisión es un mecanismo clave para utilizar eficientemente los recursos radio disponibles, proporcionando al mismo tiempo las garantías de calidad de servicio requeridas para todoslos usuarios. El presente trabajo se centra en el diseño y evaluación de políticas de control de admisión implementadas en redes móviles celulares multiservicio que transportan diferentes servicios portadores. Además, la presente tesis es una contribución al desarrollo de modelos con los que evaluar diferentes políticas de control de admisión en el desafiante contexto introducido por las redes 4G de próxima aparición. En la primera parte de esta tesis se trata el desarrollo de políticas de control de admisión para redes utilizadas actualmente, mientras que en la segunda parte de esta tesis se proponen políticas de control de admisión novedosas con el objetivo de hacerfrente a los retos introducidos por las redes de próxima aparición, tales como las redes Long TermEvolution o las de tecnología Cognitive Radio / Bernal Mor, E. (2013). Design and evaluation of admission control policies in mobile cellular networks [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27714

In this work we introduce a novel queueing model with two classes of users in which, instead of accessing a resource, users wait in the system to match with a candidate from the other class. The users are selective and the matchings occur probabilistically. This new model is useful for analysing the traffic in web portals that match people who provide a service with people who demand the same service, e.g. employment portals, matrimonial and dating sites and rental portals. We first provide a Markov chain model for these systems and derive the probability distribution of the number of matches up to some finite time given the number of arrivals. We then prove that if no control mechanism is employed these systems are unstable for any set of parameters. We suggest four different classes of control policies to assure stability and conduct analysis on performance measures under the control policies. Contrary to the intuition that the rejection rate should decrease as the users become more likely to be matched, we show that for certain control policies the rejection rate is insensitive to the matching probability. Even more surprisingly, we show that for reasonable policies the rejection rate may be an increasing function of the matching probability. We also prove insensitivity results related to the average queue lengths and waiting times. Further, to gain more insight into the behaviour of probabilistic matching systems, we propose approximation methods based on fluid and diffusion limits using different scalings. We analyse the basic properties of these approximations and show that some performance measures are insensitive to the matching probability agreeing with the results found by the exact analysis. Finally we study the optimal control and revenue management for the systems with the objective of profit maximization. We formulate mathematical models for both unobservable and observable systems. For an unobservable system we suggest a deterministic optimal control, while for an observable system we develop an optimal myopic state dependent pricing.

In recent years, there has been an exponential growth in the use of multimedia applications. A satellite system offers great potential for multimedia applications with its ability to broadcast and multicast a large amount of data over a very large area as compared to a terrestrial system. However, the limited transmission capacity along with the dynamically varying channel conditions impedes the delivery of good quality multimedia service in a satellite system which has resulted in research efforts for deriving efficient radio resource management techniques. This issue is addressed in this thesis, where the main emphasis is to design a CAC framework which maximizes the utilization of the scarce radio resources available in the satellite and at the same time increases the performance of the system for a UMTS based satellite system supporting unicast and multicast traffic. The design of the system architecture for a UMTS based satellite system is presented. Based on this architecture, a CAC framework is designed consisting of three different functionalities: the admission control procedure, the retune procedure and the pre-emption procedure. The joint use of these functionalities is proposed to allow the performance of the system to be maintained under congestion. Different algorithms are proposed for different functionalities; an adaptive admission control algorithm, a greedy retune algorithm and three pre-emption algorithms (Greedy, SubSetSum, and Fuzzy). A MATLAB simulation model is developed to study the performance of the proposed CAC framework. A GUI is created to provide the user with the flexibility to configure the system settings before starting a simulation. The configuration settings allow the system to be analysed under different conditions. The performance of the system is measured under different simulation settings such as enabling and disabling of the two functionalities of the CAC framework; retune procedure and the pre-emption procedure. The simulation results indicate the CAC framework as a whole with all the functionalities performs better than the other simulation settings.

Esta dissertação de mestrado aborda a introdução de reconhecimento de sessões http em um modelo de servidor web com serviços diferenciados (SWDS). Algumas técnicas foram desenvolvidas com o objetivo de produzir diferenciação de serviços junto com garantias de que novas sessões poderiam ser aceitas no sistema. Esses objetivos constituem requisitos essenciais na Internet atual, especialmente para aplicações web modernas. Um novo esquema para controle de admissão de sessões foi desenvolvido e introduzido no modelo SWDS, considerando dois mecanismos para aceitar novas sessões, com garantia de nalização. O mecanismo que estima a capacidade do sistema de aceitar novas sessões, baseado em um modelo de sessão construído dinamicamente a partir da carga do sistema, é destacado. A proposta global deste trabalho também considera um controle de admissão de requisições, baseado em sessões, onde a nova política de atendimento criada mantém o sistema livre de sobrecargas e oferece atendimento diferenciado para as sessões. As políticas de negociação desenvolvidas para o controle de admissão de requisições tiveram um papel importante neste trabalho, contribuindo para a priorização do atendimento das sessões. Os resultados obtidos mostram que os controles propostos constituem estruturas fundamentais para a estabilidade do desempenho do sistema, tanto quanto os mecanismos desenvolvidos têm grande importância no atendimento das sessões e, portanto de seus clientes, através de uma abordagem baseada em diferenciação. / This MSc dissertation approaches the introduction of the HTTP sessions recognition in a web server model with diferentiated services (SWDS). Some techniques have been developed aiming at issuing diferentiation of services together with guarantees that new sessions could be accepted in the system. These aims constitute essential requirements for the current Internet, especially for modern web applications. A new scheme for the admission control system has been developed and introduced in the SWDS model, considering two mechanisms for accepting new sessions, with guarantee of their nalizations. The mechanism that estimates the system capacity of acceptance of a new session, based on a session model built dynamically from system workload information, is highlighted. The global propose of this work also considers a request admission control, based on sessions, where the new attendance polices created keep the system free from overloads and over diferentiated attendance for the sessions. The negotiation polices developed for request admission control had an important place in this work, contributing for the session attendance prioritization. The results reached show that the controls proposed comprise fundamental structures for system performance stability, as well as the mechanisms developed have great importance in attending sessions and, therefore, their clients by means of a diferentiation-based approach.

General purpose operating systems have been designed to provide fast, loss-free disk service to all applications. However, multimedia applications are capable of tolerating some data loss, but are very sensitive to variation in disk service timing. Present research efforts to handle multimedia applications assume pessimistic disk behaviour when deciding to admit new multimedia connections so as not to violate the real-time application constraints. However, since multimedia applications are ``soft' real-time applications that can tolerate some loss, we propose an optimistic scheme for admission control which uses average case values for disk access. Typically, disk scheduling mechanisms for multimedia applications reduce disk access times by only trying to minimize movement to subsequent blocks after sequencing based on Earliest Deadline First. We propose to implement a disk scheduling algorithm that uses knowledge of the media stored and permissible loss and jitter for each client, in addition to the physical parameters used by the other scheduling algorithms. We will evaluate our approach by implementing our admission control policy and disk scheduling algorithm in Linux and measuring the quality of various multimedia streams. If successful, the contributions of this thesis are the development of new admission control and flexible disk scheduling algorithm for improved multimedia quality of service.

In this thesis we explore precision in measurement of buffer overflow and loss probability. We see how buffer overflow probability compares with queuing delay measurements covered in the literature. More specifically, we measure the overflow probability of a packet buffer for various sampling rates to see the effect of sampling rate on the estimation. There are various reasons for measurement in networks; one key context assumed here is Measurement Based Admission Control. We conduct simulation experiments with analytically derived VoIP and bursty traffic parameters, in Matlab, while treating the buffer under consideration as a two-state Markov Chain. We note that estimation error decreases with increase in sampling gap (or in other words precision improves/variance decreases with decrease in sampling rate). We then perform experiments for VoIP and bursty data using NS-2 simulator and record the buffer states generated therein. We see a similar trend of increase in precision with increase in sampling gap. In our simulations, we have mainly considered static traffic passing through the buffer, and we use elastic traffic (TCP) for comparison. We see from our results that the sampling error becomes constant beyond certain asymptotic level. We thus look into asymptotic error in estimation,for the lowest sampling gap, to establish a lower bound on estimation error for buffer loss probability measurement. We use formulae given in recent literature for computing the experimental and theoretic asymptotic variance of the buffer state traces in our scenarios. We find that the theoretical and experimental asymptotic variance of overflow probability match when sampling a trace of buffer states modelled as a two-state Markov Chain in Matlab. We claim that this is a new approach to computing the lower bound on the measurement of buffer overflow probability, when the buffer states are modelled as a Markov process. Using Markov Chain modelling for buffer overflow we further explore the relationship between sampling rate and accuracy. We find that there is no relationship between sampling gap and bias of estimation. Crucially we go on to show that a more realistic simulation of a packet buffer reveals that the distribution of buffer overflow periods is not always such as to allow simple Markov modelling of the buffer states; while the sojourn periods are exponential for the smaller burst periods, the tail of the distribution does not fit to the same exponential fitting. While our work validates the use of a two-state Markov model for a useful approximation modelling the overflow of a buffer, we have established that earlier work which relies on simple Markovian assumptions will thereby underestimate the error in the measured overflow probabilities.

Esta dissertação de mestrado apresenta a prototipação de uma arquitetura denominada ServidorWeb com Diferenciação de Serviços (SWDS). O trabalho também apresenta a proposta, implementação e a avaliação de desempenho de dois algoritmos de controle de admissão denominados Algoritmo de Negociação e Algoritmo de Reserva de Conexões. O objetivo principal deste trabalho é a avaliação de desempenho dos algoritmos de controle de admissão no protótipo do SWDS. Como resultados, verificou-se que a Classe de maior prioridade consegue atender mais requisições que a Classe de menor prioridade em todos as configurações de carga. Também pode-se observar que o algoritmo de reserva de conexões consegue se adaptar a todas as variações de cargas / This masters dissertation presents the prototype of an architecture named SWDS. This work presents the proposal, implementation and performance evaluation of two admission control algorithms named negotiation algorithm and connection reserve algorithm. The aim of this work is to evaluate the performance of the control admission algorithms in the SWDS prototype. As a result, it could be seen the high priority Class met a higher number of requests than the low priority Class. Also it could be seen the connection reserve algorithm can adapt to all workloads variation

Esta dissertação de mestrado apresenta a prototipação de uma arquitetura denominada ServidorWeb com Diferenciação de Serviços (SWDS). O trabalho também apresenta a proposta, implementação e a avaliação de desempenho de dois algoritmos de controle de admissão denominados Algoritmo de Negociação e Algoritmo de Reserva de Conexões. O objetivo principal deste trabalho é a avaliação de desempenho dos algoritmos de controle de admissão no protótipo do SWDS. Como resultados, verificou-se que a Classe de maior prioridade consegue atender mais requisições que a Classe de menor prioridade em todos as configurações de carga. Também pode-se observar que o algoritmo de reserva de conexões consegue se adaptar a todas as variações de cargas / This masters dissertation presents the prototype of an architecture named SWDS. This work presents the proposal, implementation and performance evaluation of two admission control algorithms named negotiation algorithm and connection reserve algorithm. The aim of this work is to evaluate the performance of the control admission algorithms in the SWDS prototype. As a result, it could be seen the high priority Class met a higher number of requests than the low priority Class. Also it could be seen the connection reserve algorithm can adapt to all workloads variation