Progressive Web Apps (PWA) is a concept of enhanced web apps which aim to erase the difference between web and native apps. The concept of PWA introduces several benefits, including simpler distribution and development, which makes web apps a viable option for many businesses. The installation process of a PWA is different from native apps and this study aims to understand whether or not it has an impact on the users will to install the PWA. PWA:s are installed directly from the browser, rather than an app marketplace. Said installation process is suspected to be unknown to many which might influence the impact. In this study, several papers on the topic are studied. A PWA is developed from scratch which is used as a platform for a user test, hosting a brief introduction of the topic as well as guiding participants through the installation process. In conjunction with the user test a survey is conducted to collect the impressions from their experience in the user test. The result of the survey shows indications that the suspected lack of knowledge and experience was correct, and that the installation process is not to complicated.Additionally, results show that many probably will not bother to install a PWA, even if it is available. Therefore, I argue that the installation process does have an impact in its current form. Alternatives to the installation process used in this study do exist and are discussed in this paper.

L'objectif de cette thèse est de fournir des algorithmes d'optimisation pour l'accès aux services vidéo qu’ils soient non-gérés (Internet TV) ou gérés (IPTV). Nous étudions des statistiques récentes concernant les services vidéo non-gérés comme YouTube et nous proposons des techniques d'optimisation appropriées qui pourraient améliorer l'accès aux fichiers vidéos et réduire le coût de cet accès. En outre, l’analyse des coûts joue un rôle important dans les décisions qui concernent la mise en cache des fichiers vidéos et celles liées au choix des périodes temporelles d'hébergement de ces fichiers sur les serveurs. En ce qui concerne les services vidéo gérés appelés IPTV, nous avons mené des expériences sur une architecture ouverte IPTV-collaboration entre différents opérateurs. Ce modèle est analysé selon un critère de coût d’investissement et d'exploitation à l'intérieur de la sphère domestique. En outre, nous avons introduit une solution d’optimisation dynamique de l'arbre « minimum spanning tree » (MST) pour le service IPTV multicast. Lors d’un accès nomade, les arbres statiques pourraient être incapables de fournir le service de manière efficace vu que l'utilisation de la bande passante augmente aux côté des points de streaming (racines de la topologie). Finalement, nous étudions des mesures de sécurité fiables en streaming vidéo basées sur la méthodologie de la chaîne de hachage et nous proposons un nouvel algorithme hybride. Nous effectuons des comparaisons entre les différentes manières utilisées dans la réalisation de la fiabilité des chaînes de hachage basées sur les classifications génériques / The aim of this thesis is to provide optimization algorithms for accessing video services either in unmanaged or managed ways. We study recent statistics about unmanaged video services like YouTube and propose suitable optimization techniques that could enhance files accessing and reduce their access costs. Moreover, this cost analysis plays an important role in decision making about video files caching and hosting periods on the servers. Under managed video services called IPTV, we conducted experiments for an open-IPTV collaborative architecture between different operators. This model is analyzed in terms of CAPEX and OPEX costs inside the domestic sphere. Moreover, we introduced a dynamic way for optimizing the Minimum Spanning Tree (MST) for multicast IPTV service. In nomadic access, the static trees could be unable to provide the service in an efficient manner as the utilization of bandwidth increases towards the streaming points (roots of topologies). Finally, we study reliable security measures in video streaming based on hash chain methodology and propose a new algorithm. Then, we conduct comparisons between different ways used in achieving reliability of hash chains based on generic classifications

This thesis deals with practical implementation of photon mapping algorithm. To achieve better results some basic and some more advanced methods of global illumination has been examined. These time demanding algorithms are often practically unusable and their further optimization is necessary. Optimized ray tracer is essential for practical implementation. Computing diffuse interreflection by Monte Carlo sampling is also very time demanding operation. Therefore it is appropriate to use it along with proper interpolation.

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User experience (UX) is one of the most popular subjects in the industry nowadays and plays a significant role in the business success. As the growth of a business depends on customers, it is essential to emphasize on the UX that can help to enhance customer satisfaction. There has been statements that the overall end-user experience is to a great extent influenced by page load time, and that UX is primarily associated with performance of applications. This paper analyzes the effectiveness of performance optimization techniques and their impact on user experience. Principally, the web performance optimization techniques used in this study were caching data, fewer HTTP requests, Web Workers and prioritizing content. A profiling method Manual Logging was utilized to measure performance improvements. A UX survey consists of User Experience Questionnaire (UEQ) and three qualitative questions, was conducted for UX testing before and after performance improvements. Quantitative and qualitative methods were used to analyze collected data. Implementations and experiments in this study are based on an existing tool, a web-based application. Evaluation results show an improvement of 45% on app load time, but no significant impact on the user experience after performance optimizations, which entails that web performance does not really matter for the user experience. Limitation of the performance techniques and other factors that influence the performance were found during the study. / Användarupplevelse (UX) är idag en av de mest populära ämnena inom IT-branschen och spelar en viktig roll i affärsframgångar. Eftersom tillväxten av ett företag beror på kunder är det viktigt att betona på UX som kan bidra till att öka kundnöjdheten. Det har konstaterats att den övergripande slutanvändarupplevelsen i stor utsträckning påverkas av sidladdningstiden och att UX huvudsakligen är förknippad med applikationernas prestanda. I denna studie analyseras effektiviteten av optimeringstekniker och deras inverkan på användarupplevelse. Huvudsakligen, optimeringstekniker som användes i denna studie var cache-lösning, färre HTTP-förfrågningar, Web Workers och prioritering av innehåll. Profileringsmetoden "Manual Logging" användes för att mäta prestandaförbättringar. En enkätutvärdering som består av User Experience Questionnaire (UEQ) och tre kvalitativa frågor, genomfördes med fokus på användarupplevelsen före och efter prestandaförbättringar. Kvantitativa och kvalitativa metoder användes för att analysera insamlade data. Implementeringar och experiment i denna studie är baserade på ett befintligt verktyg, en webbaserad applikation. Utvärderingsresultatet visar en förbättring på 45% när det gäller sidladdningstid men ingen signifikant inverkan på användarupplevelsen efter prestandaförbättringar, vilket innebär att webbprestanda inte spelar någon roll för användarupplevelsen. Begränsning av optimeringstekniker och andra faktorer som påverkar prestationen hittades under studien.

<p dir="ltr">Network models are essential for representing a myriad of real-world problems. Two of the most important categories of networks are centralized and distributed networks. In this thesis, we investigate the efficient resource allocation for one centralized communication network and two distributed epidemic networks.</p><p dir="ltr">In Chapter 2, we study three proposed centralized coded caching schemes with uncoded pre-fetching for scenarios where end users are grouped into classes with different file demand sets. We provide a lower bound for the transmission rate for the system with heterogeneous user profiles. Then the transmission rates of the three schemes are compared with the lower bound to evaluate their gap to optimality, and also compared with each other to show that each scheme can outperform the other two when certain conditions are met. Finally, we propose a cache distribution method that results in a minimal peak rate and a minimal average rate for one of the schemes when the users’ storage is relatively small compared with the size of the library.</p><p dir="ltr">In Chapter 3, we examine a discrete-time networked SIR (susceptible-infected-recovered) epidemic model, where the infection, graph, and recovery parameters may be time-varying. We propose a stochastic framework to estimate the system states from observed testing data and provide an analytic expression for the error of the estimation algorithm. We validate some of our assumptions for the stochastic framework with real COVID-19 testing data. We identify the system parameters with the system states from our estimation algorithm. Employing the estimated system states, we provide a novel distributed eradication strategy that guarantees at least exponential convergence to the set of healthy states. We illustrate the results via simulations over northern Indiana, USA.</p><p dir="ltr">In Chapter 4, we propose a novel discrete-time multi-virus SIR model that captures the spread of competing SIR epidemics over a population network. First, we provide a sufficient condition for the infection level of all the viruses over the networked model to converge to zero in exponential time. Second, we propose an observation model which captures the summation of all the viruses’ infection levels in each node, which represents the individuals who are infected by different viruses but share similar symptoms. We present a sufficient condition for the model to be strongly locally observable. We propose a distributed Luenberger observer for the system state estimation. We demonstrate how to calculate the observer gain for the estimator and prove that the estimation error of our proposed estimator converges to zero asymptotically with the observer gain found. We also propose a distributed feedback controller which guarantees that all viruses are eradicated at an exponential rate. We then show via simulations that the estimation error of the Luenberger observer converges to zero before the viruses die out.</p><p dir="ltr">We conclude in Chapter 5, where we summarize the findings of this thesis and introduce several challenging open research questions that arise from its results. These questions encompass a range of topics, including the design of optimal testing strategies for large populations, the investigation of estimation techniques in the presence of noisy measurement models, the extension of the SIR epidemic model to more complex models like SEIR and SAIR, and the exploration of efficient vaccine allocation schemes.</p>

Caching is a fundamental technique widely used in the field of computing to reduce network traffic, server load, and latency. Storing frequently accessed data in a high-speed cache layer can make future requests process faster by involving fewer system components when generating and serving the response. Kalix is a software product that demands a caching solution since it faces latency and is frequently processing partially repeated queries. However, a cache does not guarantee improved performance, which is why the main problems of caching are: determining what content to cache, when to insert or remove cache content, implementing the caching logic, and deciding where to store the cache efficiently. Therefore, this paper theoretically investigates where a cache solution should be implemented within the Kalix system architecture to decrease latency and server load, and evaluates the subsequent cache implementation experimentally. As a result, a client-side cache is implemented which decreases the latency of Kalix by up to 74%, while reducing the I/O load and memory utilization on the server by 98%. The reason for the decrease is that the cache in the client can directly serve the majority of the content, allowing the servers of Kalix to do substantially fewer computations. The evaluation acts as a recommendation for the company behindKalix, Polystar, as to if a cache is beneficial and where the cache can efficiently be deployed, and this paper gives valuable insights into the decision-making of cache placement. Concludingly, implementing the cache positively impacts the Kalix user experience.

En synthèse d'images réalistes, l'intensité finale d'un pixel est calculée en estimant une intégrale de rendu multi-dimensionnelle. Une large portion de la recherche menée dans ce domaine cherche à trouver de nouvelles techniques afin de réduire le coût de calcul du rendu tout en préservant la fidelité et l'exactitude des images résultantes. En tentant de réduire les coûts de calcul afin d'approcher le rendu en temps réel, certains effets réalistes complexes sont souvent laissés de côté ou remplacés par des astuces ingénieuses mais mathématiquement incorrectes. Afin d'accélerer le rendu, plusieurs avenues de travail ont soit adressé directement le calcul de pixels individuels en améliorant les routines d'intégration numérique sous-jacentes; ou ont cherché à amortir le coût par région d'image en utilisant des méthodes adaptatives basées sur des modèles prédictifs du transport de la lumière. L'objectif de ce mémoire, et de l'article résultant, est de se baser sur une méthode de ce dernier type[Durand2005], et de faire progresser la recherche dans le domaine du rendu réaliste adaptatif rapide utilisant une analyse du transport de la lumière basée sur la théorie de Fourier afin de guider et prioriser le lancer de rayons. Nous proposons une approche d'échantillonnage et de reconstruction adaptative pour le rendu de scènes animées illuminées par cartes d'environnement, permettant la reconstruction d'effets tels que les ombres et les réflexions de tous les niveaux fréquentiels, tout en préservant la cohérence temporelle. / In realistic image synthesis, a pixel's final intensity is computed by estimating a multi-dimensional shading integral. A large part of the research in this domain is thus aimed at finding new techniques to reduce the computational cost of rendering while preserving the fidelity and correctness of the resulting images. When trying to reduce rendering costs to approach real-time computation, complex realistic effects are often left aside or replaced by clever but mathematically incorrect tricks. To accelerate rendering, previous directions of work have either addressed the computation of individual pixels by improving the underlying numerical integration routines; or have sought to amortize the computation across regions of an image using adaptive methods based on predictive models of light transport. This thesis' - and resulting paper's - objective is to build upon the latter of the aforementioned classes of methods[Durand2005], and foray into fast adaptive rendering techniques using frequency-based light transport analysis to efficiently guide and prioritize ray tracing. We thus propose an adaptive sampling and reconstruction approach to render animated scenes lit by environment lighting and faithfully reconstruct all-frequency shading effects such as shadows and reflections while preserving temporal coherency.

Le trafic vidéo s’est considérablement accru et est prévu de doubler pour représenter 82% du trafic Internet d’ici 2021. Une telle croissance surcharge les fournisseurs de services Internet (ISP), nuisant à la Qualité d’Expérience (QoE) perçue par les utilisateurs. Cette thèse vise à améliorer la QoE des utilisateurs de streaming vidéo sans hypothèse de changement d’infrastructure physique des opérateurs. Pour cela, nous combinons les technologies de caching réseau, de streaming HTTP adaptatif (HAS), et de transport multipath. Nous explorons d’abord l’interaction entre HAS et caching, pour montrer que les algorithmes d’adaptation de qualité vidéo ont besoin de savoir qu’il y a un cache et ce qui y est stocké, et proposons des algorithmes bénéficiant de cette connaissance. Concluant sur la difficulté d’obtenir la connaissance de l’état du cache, nous étudions ensuite un système de distribution vidéo à large échelle, où les caches sont représentés par un réseau de distribution du contenu (CDN). Un CDN déploie des caches à l’intérieur des réseaux des ISP, et dispose de ses propres serveurs externes. L’originalité du problème vient de l’hypothèse que nous faisons que l’utilisateur est simultanément connecté à 2 ISP. Ceci lui permet d’accéder en multipath aux serveurs externes aux ISP (pouvant ainsi accroître le débit mais chargeant plus les ISP), ou streamer le contenu depuis un cache plus proche mais avec un seul chemin. Ce désaccord entre les objectifs du CDN et de l’ISP conduit à des performances sous-optimales. Nous développons un schéma de collaboration entre ISP et CDN qui permet de nous rapprocher de l’optimal dans certains cas, et discutons l’implémentation pratique. / Video traffic volume grew considerably in recent years and is forecasted to reach 82% of the total Internet traffic by 2021, doubling its net volume as compared to today. Such growth overloads Internet Service Providers' networks (ISPs), which negatively impacts users' Quality of Experience (QoE). This thesis attempts to tackle the problem of improving users' video QoE without relying on network upgrades. For this, we have chosen to combine such technologies as in-network caching, HTTP Adaptive Streaming (HAS), and multipath data transport. We start with exploration of interaction between HAS and caching; we confirm the need of cache-awareness in quality adaptation algorithms and propose such an extension to a state-of-the-art optimisation-based algorithm. Concluding on the difficulty of achieving cache-awareness, we take a step back to study a video delivery system on a large scale, where in-network caches are represented by Content Delivery Networks (CDNs). They deploy caches inside ISPs and dispose of their own outside video servers. As a novelty, we consider users to have a simultaneous connectivity to several ISP networks. This allows video clients either to access outside multipath servers with aggregate bandwidth (which may increase their QoE, but will also bring more traffic into ISP), or stream their content from a closer cache through only single connectivity (bringing less traffic into ISP). This disagreement in ISP and CDN objectives leads to suboptimal system performance. In response to this, we develop a collaboration scheme between two actors, performance of which can approach optimal boundary for certain settings, and discuss its practical implementation.

With a new United States Army initiative to exploit commercially developed information technology, there is a heightened interest in using Internet protocols over the military's geosynchronous satellite links. TCP is the dominant Internet protocol used for reliable data exchange, but its own design limits performance when used over long delay network links such as satellites. Initially this research set out to compare TCP with another proposed protocol, the Satellite Transport Protocol (STP). However through a series of tests, we found that STP does not fulfill its claims of increased throughput over TCP and uncovered a flaw in STP's founding research. In addition, this thesis proposes and demonstrates novel performance enhancing techniques that significantly improve transport protocol throughput.