By equipping vehicles with the on-board wireless facility, the newly emerged vehicular networking targets to provision the broadband serves to vehicles. As such, a variety of novel and exciting applications can be provided to vehicular users to enhance their road safety and travel comfort, and finally raise a complete change to their on-road life. As the content distribution and media/video streaming, such as Youtube, Netflix, nowadays have become the most popular Internet applications, to enable the efficient content distribution and audio/video streaming services is thus of the paramount importance to the success of the vehicular networking. This, however, is fraught with fundamental challenges due to the distinguished natures of vehicular networking. On one hand, the vehicular communication is challenged by the spotty and volatile wireless connections caused by the high mobility of vehicles. This makes the download performance of connections very unstable and dramatically change over time, which directly threats to the on-top media applications. On the other hand, a vehicular network typically involves an extremely large-scale node population (e.g., hundreds or thousandths of vehicles in a region) with intense spatial and temporal variations across the network geometry at different times. This dictates any designs to be scalable and fully distributed which should not only be resilient to the network dynamics, but also provide the guaranteed quality-of-service (QoS) to users. The purpose of this dissertation is to address the challenges of the vehicular networking imposed by its intrinsic dynamic and large-scale natures, and build the efficient, scalable and, more importantly, practical systems to enable the cost-effective and QoS guaranteed content distribution and media streaming services to vehicular users. Note that to effective- ly deliver the content from the remote Internet to in-motion vehicles, it typically involves three parts as: 1.) an infrastructure grid of gateways which behave as the data depots or injection points of Internet contents and services to vehicles, 2.) protocol at gateways which schedules the bandwidth resource at gateways and coordinates the parallel transmissions to different vehicles, and 3.) the end-system control mechanism at receivers which adapts the receiver’s content download/playback strategy based on the available network throughput to provide users with the desired service experience. With above three parts in mind, the entire research work in this dissertation casts a systematic view to address each part in one topic with: 1.) design of large-scale cost-effective content distribution infrastructure, 2.) MAC (media access control) performance evaluation and channel time scheduling, and 3.) receiver adaptation and adaptive playout in dynamic download environment. In specific, in the first topic, we propose a practical solution to form a large-scale and cost-effective content distribution infrastructure in the city. We argue that a large-scale infrastructure with the dedicated resources, including storage, computing and communication capacity, is necessary for the vehicular network to become an alternative of 3G/4G cellular network as the dominating approach of ubiquitous content distribution and data services to vehicles. On addressing this issue, we propose a fully distributed scheme to form a large-scale infrastructure by the contributions of individual entities in the city, such as grocery stores, movie theaters, etc. That is to say, the installation and maintenance costs are shared by many individuals. In this topic, we explain the design rationale on how to motivate individuals to contribute, and specify the detailed design of the system, which is embodied with distributed protocols and performance evaluation. The second topic investigates on the MAC throughput performance of the vehicle-to- infrastructure (V2I) communications when vehicles drive through RSUs, namely drive-thru Internet. Note that with a large-scale population of fast-motion nodes contending the chan- nel for transmissions, the MAC performance determines the achievable nodal throughput and is crucial to the on-top applications. In this topic, using a simple yet accurate Marko- vian model, we first show the impacts of mobility (characterized by node velocity and moving directions) on the nodal and system throughput performance, respectively. Based on this analysis, we then propose three enhancement schemes to timely adjust the MAC parameters in tune with the vehicle mobility to achieve the maximal the system throughput. The last topic investigates on the end-system design to deliver the user desired media streaming services in the vehicular environment. In specific, the vehicular communications are notoriously known for the intermittent connectivity and dramatically varying throughput. Video streaming on top of vehicular networks therefore inevitably suffers from the severe network dynamics, resulting in the frequent jerkiness or even freezing video playback. To address this issue, an analytical model is first developed to unveil the impacts of network dynamics on the resultant video performance to users in terms of video start-up delay and smoothness of playback. Based on the analysis, the adaptive playout buffer mechanism is developed to adapt the video playback strategy at receivers towards the user-defined video quality. The proposals developed in the three topics are validated with the extensive and high fidelity simulations. We believe that our analysis developed in the dissertation can provide insightful lights on understanding the fundamental performance of the vehicular content distribution networks from the aspects of session-level download performance in urban vehicular networks (topic 1), MAC throughput performance (topic 2), and user perceived media quality (topic 3). The protocols developed in the three topics, respectively, offer practical and efficient solutions to build and optimize the vehicular content distribution networks.

The Internet has scaled massively over the past 15 years to extend to billions of users. These users increasingly require extensive applications and capabilities from the Internet, such as Quality of Service (QoS) optimized paths between end hosts. When default Internet paths may not meet their requirements adequately, there is a need to facilitate the discovery of such QoS optimized paths. Fortunately, even though the route offered by the Internet may not work (to the required level of performance), often there exist alternate routes that do work. When the direct Internet path between two Internet hosts for instance is sub-optimal (according to specific user defined criterion), there is a possibility that the direct paths of both to a third host may not be suffering from the same problem owing to path disjointness. Overlay Networks facilitate the discovery of such composite alternate paths through third party hosts. To discover such alternate paths, overlay hosts regularly monitor both Internet path quality and choose better alternate paths via other hosts. Such measurements are costly and pose scalability problems for large overlay networks. This thesis asserts and shows that these overheads could be lowered substantially if the network layer path information between overlay hosts could be obtained, which facilitates selection of disjoint paths. This thesis further demonstrates that obtaining such network layer path information is very challenging. As opposed to the path monitoring which only requires cooperation of overlay hosts, disjoint path selection depends on the accuracy of information about the underlay, which is out of the domain of control of the overlay and so may contain inaccuracies. This thesis investigates how such information could be gleaned at different granularities for optimal tradeoffs between spatial and/or temporal methods for selection of alternate paths. The main contributions of this thesis are: (i) investigation of scalable techniques to facilitate alternate path computation using network layer path information; (ii) a review of the realistic performance gains achievable using such alternate paths; and (iii) investigation of techniques for revealing the presence of incorrect network layer path information, proposal of new techniques for its removal.

The Internet has scaled massively over the past 15 years to extend to billions of users. These users increasingly require extensive applications and capabilities from the Internet, such as Quality of Service (QoS) optimized paths between end hosts. When default Internet paths may not meet their requirements adequately, there is a need to facilitate the discovery of such QoS optimized paths. Fortunately, even though the route offered by the Internet may not work (to the required level of performance), often there exist alternate routes that do work. When the direct Internet path between two Internet hosts for instance is sub-optimal (according to specific user defined criterion), there is a possibility that the direct paths of both to a third host may not be suffering from the same problem owing to path disjointness. Overlay Networks facilitate the discovery of such composite alternate paths through third party hosts. To discover such alternate paths, overlay hosts regularly monitor both Internet path quality and choose better alternate paths via other hosts. Such measurements are costly and pose scalability problems for large overlay networks. This thesis asserts and shows that these overheads could be lowered substantially if the network layer path information between overlay hosts could be obtained, which facilitates selection of disjoint paths. This thesis further demonstrates that obtaining such network layer path information is very challenging. As opposed to the path monitoring which only requires cooperation of overlay hosts, disjoint path selection depends on the accuracy of information about the underlay, which is out of the domain of control of the overlay and so may contain inaccuracies. This thesis investigates how such information could be gleaned at different granularities for optimal tradeoffs between spatial and/or temporal methods for selection of alternate paths. The main contributions of this thesis are: (i) investigation of scalable techniques to facilitate alternate path computation using network layer path information; (ii) a review of the realistic performance gains achievable using such alternate paths; and (iii) investigation of techniques for revealing the presence of incorrect network layer path information, proposal of new techniques for its removal.

Η παρούσα διπλωματική εργασία εστιάζεται στον κλάδο του τουρισμού και πιο συγκεκριμένα στις αντιλήψεις των πελατών και την ικανοποίηση τους με τα ξενοδοχεία. Ο ξενοδοχειακός κλάδος ανήκει στον κλάδο των υπηρεσιών. Πιο συγκεκριμένα, αντικείμενο μελέτης αποτελεί η ποιότητα παρεχόμενων υπηρεσιών στους πελάτες ξενοδοχείων, η ικανοποίηση που αποκομίζουν από την όλη διαμονή τους και ο τρόπος διαχείρισης των παραπόνων που οι ίδιοι υποβάλλουν. / This study focuses on the tourism sector and particularly on the perceptions of customers and their satisfaction from the hotels. The hospitality industry belongs to the category of services. More specifically, this paper studies the quality of service to customers booking, the satisfaction which is derived from the period they stay in the hotel and the way the administration manages their complaints.

Το VoIP (Voice Over IP) αναφέρεται στη μετάδοση και τη σηματοδοσία επικοινωνιών φωνής π.χ τηλεφωνικές κλήσεις πάνω από IP δίκτυα όπως είναι το διαδίκτυο. Σκοπός της παρούσας διπλωματικής ήταν η μελέτη της παρεχόμενης ποιότητας ομιλίας VoIP τηλεφωνικών συσκευών (Sitel,Polycom) κάτω από σενάρια διαφορετικών συνθηκών κίνησης στο δίκτυο. Αρχικά παρουσιάζονται οι εφαρμογές του voip και στη συνέχεια αναλύονται η λειτουργία, η αρχιτεκτονική και τα πρωτόκολλα της τεχνολογίας αυτής. Ακολούθως περιγράφεται η πειραματική διάταξη που απαιτήθηκε για να συγκεντρωθούν οι μετρήσεις από τις συσκευές και στη συνέχεια οι γραφικές αναπαραστάσεις των μετρήσεων αυτών που αφορούν της παρεχόμενη ποιότητα ομιλίας. Γίνεται ανάλυση των γραφικών και σύγκριση με ανάλογες της βιβλιογραφίας. / The VoIP technology refers to the transmission of voice samples over the Internet Protocol. The aim of the thesis is to investigate the QoS of a VoIP call under various networks circumstances when various impairments occur. The devices that we put under test belong to Sitel and Polycom company.

abstract: Demands in file size and transfer rates for consumer-orientated products have escalated in recent times. This is primarily due to the emergence of high definition video content. Now factor in the consumer desire for convenience, and we find that wireless service is the most desired approach for inter-connectivity. Consumers expect wireless service to emulate wired service with little to virtually no difference in quality of service (QoS). The background section of this document examines the QoS requirements for wireless connectivity of high definition video applications. I then proceed to look at proposed solutions at the physical (PHY) and the media access control (MAC) layers as well as cross-layer schemes. These schemes are subsequently are evaluated in terms of usefulness in a multi-gigabit, 60 GHz wireless multimedia system targeting the average consumer. It is determined that a substantial gap in published literature exists pertinent to this application. Specifically, little or no work has been found that shows how an adaptive PHYMAC cross-layer solution that provides real-time compensation for varying channel conditions might be actually implemented. Further, no work has been found that shows results of such a model. This research proposes, develops and implements in Matlab code an alternate cross-layer solution that will provide acceptable QoS service for multimedia applications. Simulations using actual high definition video sequences are used to test the proposed solution. Results based on the average PSNR metric show that a quasi-adaptive algorithm provides greater than 7 dB of improvement over a non-adaptive approach while a fully-adaptive alogrithm provides over18 dB of improvement. The fully adaptive implementation has been conclusively shown to be superior to non-adaptive techniques and sufficiently superior to even quasi-adaptive algorithms. / Dissertation/Thesis / M.S. Engineering 2011

Au cours des dernières années, le trafic réseau nécessitant une qualité de service (QoS) a augmenté de façon exponentielle. Dans cette thèse, notre objectif est de trouver des routages dans les réseaux câblés et sans fil en prenant en compte les contraintes liées à la QoS et en minimisant le coût de la communication. Nous nous intéressons tout d’abord à la résolution du problème du chemin multi-contraint (MCP) pour lequel un algorithme exact efficace est proposé. Cet algorithme permet d'améliorer le temps d'exécution tout en maintenant la qualité de la solution. En ce qui concerne le problème de la diffusion multipoint (multicast) multi-contraint de coût minimal (MCMCM), une nouvelle formulation utilisant la Programmation Linéaire en Nombres Entiers est proposée. Elle permet de calculer les hiérarchies optimales, structures les plus pertinentes pour résoudre de manière exacte le problème MCMCM. Un algorithme de prétraitement efficace est également conçu pour accélérer le temps de résolution dans les réseaux de grande taille. En ce qui concerne le problème du routage avec QoS dans les « Low Power et Lossy Networks » (LLN), une solution basée sur une nouvelle fonction objective est présentée. Cette solution minimisant une longueur non linéaire est la première à prendre en compte un nombre quelconque de contraintes pour le routage avec QoS. Nous avons conçu un algorithme exact et deux algorithmes de routage heuristique pour résoudre ce problème dans les réseaux LLN avec QoS. / In recent years, the network traffic requiring Quality of Service (QoS) has been growing explosively. In this thesis, we study the multi-constrained QoS routing in networks. The objective is to find routes in wired and wireless networks taking into account constraints related to the QoS and minimizing the cost of the communication. We present several propositions. To solve the Multi-Constrained Path problem (MCP), an efficient exact algorithm is proposed. This algorithm is shown to be able to improve the execution time while maintaining the quality of the solution. Concerning the Multi-Constrained Multicast Minimum Cost problem (MCMCM), a new Integer Linear Programming (ILP) formulation is proposed to compute hierarchies, which are the exact solutions for MCMCM. An efficient preprocessing-based algorithm is also designed to accelerate the resolution time in large size networks. Regarding the problem of QoS routing in Low Power and Lossy Networks (LLNs), a new Objective Function (OF)-based solution is presented. This solution uses a non-linear length function. It is the first that takes into account any number of metrics and constraints for QoS routing. We designed an exact and two heuristic routing algorithms with QoS constraints for LLNs.

Abstract Background: The quality of service is considered as an essential component in any service industry. It has been evolved in service marketing and has often been used in other research fields and sectors. Further, researchers have emphasized the importance of measuring the quality dimensions over years and in various industries in order to manage it. Also, they have proposed that enhancing the quality of services enhances customer satisfaction and loyalty, in turn that will enable the service provider to meet the changes and challenges in its business environment. Purpose: Based on listed companies’ perception at Nasdaq Stockholm OMX, the study seeks to evaluate the service quality provided by accounting firms in Sweden and determine the situation of its dimensions, as well as to explore their direct impact on the client satisfaction and client loyalty. In addition, the study utilizes the SERVPERF model to measure the service quality’s dimensions. Approach/methodology: To achieve the purpose, the study conducts a deductive and quantitative approach with explanatory purpose. Also, the data has been collected based an online questionnaire. It was sent to 450 listed companies at Nasdaq Stockholm OMX, resulting in a sample of 58 respondents. The analysis has been conducted based on regression analysis. Result/discussion: the research presents and discusses the result based on two hypotheses groups separately. The first hypotheses group regarding the impact of service quality and its dimensions on customer satisfaction. The second hypotheses group concerning the impact of service quality and its dimensions on customer loyalty. Originality: To the researcher’s knowledge this study is considered as a first attempt using a multi-dimension scale to assess the service quality of the accounting firms in Sweden based on the perception of Swedish listed companies.

Context: In telecommunications, it is important for network providers to have a knowledge of generic relationships between multi-dimensional QoE and QoS parameters to be able to provide quality service to the customers, keeping in mind the real-time constraints such as time, money and labor. So far, there have been several research works on formulating a generic quantitative relationship between a single QoE and a single QoS parameter in literature. As per the research conducted, the most common examples of mapping between a QoS parameter and QoE were found to be the exponential model (the IQX hypothesis), the logarithmic model (the WeberFechner law), and the power model. However, it has been less common to study the multi-dimensional relationship between QoE and QoS parameters. Objective: The purpose of this paper here is to discuss the impact of several QoS parameters on QoE. The proposal put forth by existing literature is that a multiplicative model better explains the impact of QoS parameters on the overall quality as perceived by the user. The proposal was, however, never backed by subjective data. Method: We have performed several subjective tests in this regard to test our hypothesis. Non-adaptive streaming of videos in a monitored server-client setup was used. In these tests, the objective was to obtain the Mean Opinion Scores(MOS) for varying QoS parameters such as the initial delay and the number of stalls. Network shaping was used for introducing the disturbances in the videos. The experimental setup consisted of a total of 27 experiments per user and each user was handed over a questionnaire. The questionnaire mainly consisted of four questions aimed at gathering feedback from the users regarding the quality of the videos shown to them. Users were asked to mark their MOS on a continuous scale. The videos were subjected to three different values of Initial Delay, Stalls and Resolution, each. The average duration per stalls throughout the experiments was maintained at 2 seconds. Results: Data was collected from 15 users. Thus, in total 405 MOS values were recorded for 27 combinations of Initial Delay, number of Stalls and Resolution. The impact of initial delay and stalls on the QoE as indicated by the MOS was then categorized and studied for each Resolution. With the help of regression tools in MATLAB and Solver in Excel, possible models that explain the multi-dimensional QoS-QoE relationship were studied. Conclusion: The results mostly indicated towards the multiplicative model just as proposed by the existing literature. Also, it was observed that Initial Delay alone has not much impact on the overall QoE. So, the impact of Initial Delay could be described either by an additive or a multiplicative model. However, the impact of Stalls on QoE was found to be multiplicative.

Sistemas supervisórios são sistemas computacionais que permitem a monitoração de informações de processos produtivos ou de dispositivos de automação e de plantas industriais. Neste trabalho é proposto um framework para construção de tais sistemas, direcionada a dispositivos móveis, tais como Personal Digital Assistants (PDAs), telefones celulares e computadores de bolso. O framework proposto define uma arquitetura que é implementada gerando sistemas supervisórios com três características principais: (i) as telas de supervisão são construídas com base em um modelo orientado a objetos que utiliza conceitos da área da aplicação, mapeando o mundo real para um modelo computacional; (ii) o projeto de sistemas supervisórios apresenta flexibilidade com relação aos recursos computacionais disponíveis, oferecendo opções para armazenamento local ou remoto de dados multimídia, com o objetivo de não sobrecarregar os dispositivos móveis onde são executados; (iii) os sistemas supervisórios são capazes de se adaptarem dinamicamente às variações na Qualidade de Serviços (QoS) oferecidos pela infra-estrutura de comunicação, ajustando as suas telas gráficas em função de uma especificação de requisitos definidos em tempo de projeto e do nível de QoS obtido na rede em tempo de execução. Duas ferramentas computacionais são propostas e desenvolvidas no âmbito deste trabalho: (i) a primeira responsável pelo ambiente de desenvolvimento dos projetos de sistemas supervisórios, que resulta na geração automática de código em linguagem Java, correspondente à aplicação de supervisão; (ii) a segunda é responsável pela adaptação de mensagens e comunicação de dados entre as aplicações de supervisão projetadas e outros sistemas supervisórios e de controle, disponíveis no mercado. Os conceitos propostos neste trabalho foram validados através de três estudos de caso descritos na presente dissertação. / Supervisory systems are computational systems which allow information monitoring of production processes or automation and technical plant devices. This paper proposes a framework for building supervisory systems, targeted to mobile devices, such as Personal Digital Assistants (PDAs), cell phones and Pocket PCs. The proposed framework allows the development of supervisory systems with three main characteristics: (i) supervision screens, which graphically depict the technical plant, are built using an object oriented model that uses concepts of the application area, allowing a direct mapping of real world concepts, such as automation devices to a computational model; (ii) the supervisory systems project presents flexibility about the available computational resources, offering options for local or remote storing of multimedia and graphical data, with the purpose of not overloading the mobile devices where they are executed; (iii) the supervisory systems runtime environment can dynamically adapt to variations in the Quality of Services (QoS) offered by the communication infrastructure, adjusting their graphic displays by comparing required and offered QoS. Two computational tools are proposed and developed in this work: (i) the first one supports the development of supervisory systems and allows, from an object-oriented model of the application, an automatic code generation - in Java language - of the supervision application; (ii) the second one is responsible for the online adaptation of messages and data communication among the projected supervision applications and other control and supervisory systems. The proposed concepts are validated through three case studies described in the present dissertation.