Στην παρούσα µεταπτυχιακή διπλωµατική εργασία παρουσιάζεται ο σχεδιασµός, η ανάπτυξη, η εγκατάσταση και λειτουργία ενός ολοκληρωµένου συστήματος παρακολούθησης και διαχείρισης έξυπνων κτιρίων με χρήση ετε- ρογενών ασυρµάτων δικτύων αισθητήρων. Οι συγκεκριµένες συσκευές µπο- ρούν να λειτουργήσουν είτε ως απλοί αισθητήρες είτε ως ελεγκτές συσκευών, με χρήση ασύρµατης επικοινωνίας και state-of-the-art τεχνολογιών του Δια- δικτύου των Συσκευών που διευκολύνουν την αλληλεπίδραση με αυτές αλλά και την εννοποίησή τους με διαδυκτιακές εφαρμογές. Στα πλαίσια της συ- γκεκριµένης διπλωµατικής, εστιάζουµε αρχικά στην υλοποίηση του πρωτο- κόλλου CoAP που προσφέρη τις δυνατότητες ελένχου και αίσθησης μέσω της ασύρµατη επικοινωνία των συσκευών με ένα δομημένο και κοινά κατανοητό τρόπο. Προτείνουµε επίσης, µια ένα συγκεκριµένου συστήµατος το οποίο προ- σφέρει κεντρικά τις υπηρησίες των ασύρματων αισθητήρων για την διευκό- ληνση της αναζήτησης συσκευών και χαρακτηριστικών όπως και την δυνα- τότητα κεντρικής διαχείρισης των συσκευών. Το συγκεκριµένο σύστηµα εί- ναι ανεξάρτητο από τις συσκευές που χρησιµοποιούνται (platform & hardware independent) καθώς οι λειτουργίες και τα δεδοµένα παρέχονται µε δοµηµένο τρόπο με την χρήση RESTful Web Services. Για την µελέτη της συµπεριφο- ράς του συστήµατος αναπτύχθηκαν ολοκληρωµένες εφαρµογές οι οποίες απο- δικνύουν την ευκολία χρήσης των δεδομένων που προέρχονται από τις συ- σκευές και αλληλεπίδρασης με αυτές. Κάθε µία από αυτές υλοποιήθηκε με χρήση διαφορετικών τεχνολογιών όπως HTML5, Android, Microsoft Windows 8 και On{x}, αλλά και διαφορετικές συσκευές αισθητήρων και συγκεκριµένα iSense, Arduino, TelosB και XBee. / Within the scope of this MSc dissertation, we present the design and implementation of pervasive applications on top of heterogeneous wireless sensor network environment. The wireless communication between heterogeneous devices is an inherently difficult research problem due to fundamental differences in system architecture, properties and capabilities of the these devices. Initially, our research focused on the identification of the problems related to the intercommunication among the devices of a heterogeneous wireless sensor network. As a solution, we propose a new abstract system that provides the key qualities needed for a successful pervasive system; expandability, scalability and performance. The new architecture achieves interoperability among the devices by introducing abstraction in the communication protocols (MAC, Transport and Application Layers). In order to demonstrate the applicability of our system we include various representative use case scenarios, that illustrate the usage of our infrastructure. Each scenario focuses on different properties of the system and uses a combination of devices such as iSense, Arduino, SunSPOT, TelosB and XBee.

Στόχος της παρούσας διπλωματικής εργασίας είναι να γίνει μια εκτίμηση και ρύθμιση τη λειτουργίας κάποιων συσκευών ενός «έξυπνου» σπιτιού σε ένα ενσωματωμένο σύστημα. Η λογική είναι να μπορεί ο χρήστης να δει ποια είναι η μέση κατανάλωση ισχύος μιας συσκευής και το αντίστοιχο χρηματικό κόστος που αναλογεί σε αυτήν, για κάποιο χρονικό διάστημα λειτουργίας της και υπολογισμού της βέλτιστης συμπεριφορά της συσκευής έτσι ώστε να επιτύχουμε την ελάχιστη δυνατή κατανάλωση. Τα φορτία τα οποία ελέγχθηκαν είναι ένα κλιματιστικό, ένα πλυντήριο και ένας θερμοσίφωνας. Η υλοποίηση έγινε σε ένα ενσωματωμένο σύστημα και δημιουργήθηκε και ένα περιβάλλον γραφικής απεικόνισης για επικοινωνία με τον χρήστη. / Simulation of the behavior of three home electrical devices with the use of demand response algorithms. Calculation of energy consumption of each device and money charge. Setting the behavior of each device to minimize total cost.

Στην εργασία αυτή, μελετήθηκε η δομή του σύγχρονου ίντερνετ από την σκοπιά του δικτύου και κατέστη σαφές το πως διασυνδέονται οι πάροχοι υπηρεσιών και οι τερματική χρήστες, πως γίνεται η δρομολόγηση και ποιοί αλγόριθμοι χρησιμοποιούνται για τιν επίτευξη της. / This diploma thesis focus on how modern networks connect together in order to create the internet and which algorithms used for the routing of informations that traverse through them.

Βασικό ζητούμενο στον τομέα των δικτύων υψηλής ταχύτητας είναι αυτό της “διατήρησης της διαπερατότητας”. Η προσπάθεια επίτευξης του ζητούμενου αυτού στην περίπτωση παραδοσιακών δικτύων που χρησιμοποιούν προτυποποιημένα πρωτόκολλα μπορεί να γίνει μόνο στην κατεύθυνση του σχεδιασμού και της υλοποίησης του συστήματος επεξεργασίας που εκτελεί τα πρωτόκολλα αφού οι μηχανισμοί και η σύνταξη των ίδιων των πρωτοκόλλων είναι ήδη καθορισμένα. Στην παρούσα εργασία διερευνώνται τρόποι επίτευξης του ζητούμενου αυτού για το πιο βασικό από τα δικτυακά υποσυστήματα, του προσαρμογέα δικτύου. Οι σχεδιαστικές αποφάσεις που αφορούν την αρχιτεκτονική ενός network adapter παίζουν καταλυτικό ρόλο στην απόδοσή του. Στις επόμενες παραγράφους θα παρουσιαστεί η αρχιτεκτονική ενός απλού δομικά αλλά και στην σύλληψή του προσαρμογέα και στην συνέχεια θα διερευνηθούν διάφορες αρχιτεκτονικές παρεμβάσεις που στόχο θα έχουν την βελτίωση της απόδοσης αυτού. Με την βοήθεια της βιβλιοθήκης εξομοίωσης CSIM της Mesquite οι αρχιτεκτονικές που θα προκύψουν μοντελοποιούνται και δίνοντας στα χαρακτηριστικά τους τιμές προϊόντων που διατίθενται αυτή την στιγμή στην αγορά υπολογίζεται η βελτίωση που επιφέρουν. / One of the main challenges in high-throughput networking is the “throughput preservation problem”. The effort to address this problem in the case of standardized protocols should be focused in the design and implementation of the protocol processing systems, for the mechanisms and syntax are already well defined in a standardized protocol. This paper explores the ways of preserving the throughput of network adapters, the most basic of communication systems. Design and architectural issues of network adapters affect their performance characteristics. In the following sections the architecture of a simple structurally and conceptually network adapter will be presented. Next, several architectural modifications will be imposed in order to ameliorate its performance. By using Mesquite's CSIM modeling and simulating tool, models of the produced network adapter configurations will be implemented and their performance will be measured. These measurements will be produced by giving in the models' characteristics values of currently available in market products.

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The Grid provides a novel platform where the scientific and engineering communities can share data and computation across multiple administrative domains. There are several key services that must be offered by Grid middleware; one of them being the Grid Information Service( GIS). A GIS is a Grid middleware component which maintains information about hardware, software, services and people participating in a virtual organisation( VO). There is an inherent need in these systems for the delivery of reliable performance. This thesis describes a number of approaches which detail the development and application of a suite of benchmarks for the prediction of the process of resource discovery and monitoring on the Grid. A series of experimental studies of the characterisation of performance using benchmarking, are carried out. Several novel predictive algorithms are presented and evaluated in terms of their predictive error. Furthermore, predictive methods are developed which describe the behaviour of MDS2 for a variable number of user requests. The MDS is also extended to include job information from a local scheduler; this information is queried using requests of greatly varying complexity. The response of the MDS to these queries is then assessed in terms of several performance metrics. The benchmarking of the dynamic nature of information within MDS3 which is based on the Open Grid Services Architecture (OGSA), and also the successor to MDS2, is also carried out. The performance of both the pull and push query mechanisms is analysed. GridAdapt (Self-adaptive Grid Resource Monitoring) is a new system that is proposed, built upon the Globus MDS3 benchmarking. It offers self-adaptation, autonomy and admission control at the Index Service, whilst ensuring that the MIDS is not overloaded and can meet its quality-of-service,f or example,i n terms of its average response time for servicing synchronous queries and the total number of queries returned per unit time.

Software defined networking (SDN) is a relatively new paradigm that decouples individual network elements from the control logic, offering real-time network programmability, translating high level policy abstractions into low level device configurations. The framework comprises of the data (forwarding) plane incorporating network devices, while the control logic and network services reside in the control and application planes respectively. Operators can optimize the network fabric to yield performance gains for individual applications and services utilizing flow metering and application-awareness, the default traffic management method in SDN. Existing approaches to traffic optimization, however, do not explicitly consider user application trends. Recent SDN traffic engineering designs either offer improvements for typical time-critical applications or focus on devising monitoring solutions aimed at measuring performance metrics of the respective services. The performance caveats of isolated service differentiation on the end users may be substantial considering the growth in Internet and network applications on offer and the resulting diversity in user activities. Application-level flow metering schemes therefore, fall short of fully exploiting the real-time network provisioning capability offered by SDN instead relying on rather static traffic control primitives frequent in legacy networking. For individual users, SDN may lead to substantial improvements if the framework allows operators to allocate resources while accounting for a user-centric mix of applications. This thesis explores the user traffic application trends in different network environments and proposes a novel user traffic profiling framework to aid the SDN control plane (controller) in accurately configuring network elements for a broad spectrum of users without impeding specific application requirements. This thesis starts with a critical review of existing traffic engineering solutions in SDN and highlights recent and ongoing work in network optimization studies. Predominant existing segregated application policy based controls in SDN do not consider the cost of isolated application gains on parallel SDN services and resulting consequence for users having varying application usage. Therefore, attention is given to investigating techniques which may capture the user behaviour for possible integration in SDN traffic controls. To this end, profiling of user application traffic trends is identified as a technique which may offer insight into the inherent diversity in user activities and offer possible incorporation in SDN based traffic engineering. A series of subsequent user traffic profiling studies are carried out in this regard employing network flow statistics collected from residential and enterprise network environments. Utilizing machine learning techniques including the prominent unsupervised k-means cluster analysis, user generated traffic flows are cluster analysed and the derived profiles in each networking environment are benchmarked for stability before integration in SDN control solutions. In parallel, a novel flow-based traffic classifier is designed to yield high accuracy in identifying user application flows and the traffic profiling mechanism is automated. The core functions of the novel user-centric traffic engineering solution are validated by the implementation of traffic profiling based SDN network control applications in residential, data center and campus based SDN environments. A series of simulations highlighting varying traffic conditions and profile based policy controls are designed and evaluated in each network setting using the traffic profiles derived from realistic environments to demonstrate the effectiveness of the traffic management solution. The overall network performance metrics per profile show substantive gains, proportional to operator defined user profile prioritization policies despite high traffic load conditions. The proposed user-centric SDN traffic engineering framework therefore, dynamically provisions data plane resources among different user traffic classes (profiles), capturing user behaviour to define and implement network policy controls, going beyond isolated application management.

Timely identification of critical nodes is crucial for assessing network vulnerability and survivability. This thesis presents two new approaches for the identification of critical nodes in a network with the first being an intuition based approach and the second being build on a mathematical framework. The first approach which is referred to as the Combined Banzhaf & Diversity Index (CBDI) uses a newly devised diversity metric, that uses the variability of a node’s attributes relative to its neighbours and the Banzhaf power index which characterizes the degree of participation of a node in forming the shortest path route. The Banzhaf power index is inspired from the theory of voting games in game theory whereas, the diversity index is inspired from the analysis and understanding of the influence of the average path length of a network on its performance. This thesis also presents a new approach for evaluating this average path length metric of a network with reduced computational complexity and proposes a new mechanism for reducing the average path length of a network for relatively larger network structures. The proposed average path length reduction mechanism is tested for a wireless sensor network and the results compared for multiple existing approaches. It has been observed using simulations that, the proposed average path length reduction mechanism outperforms existing approaches by reducing the average path length to a greater extent and with a simpler hardware requirement. The second approach proposed in this thesis for the identification of critical nodes is build on a mathematical framework and it is based on suboptimal solutions of two optimization problems, namely the algebraic connectivity minimization problem and a min-max network utility problem. The former attempts to address the topological as- pect of node criticality whereas, the latter attempts to address its connection-oriented nature. The suboptimal solution of the algebraic connectivity minimization problem is obtained through spectral partitioning considerations. This approach leads to a distributed solution which is computationally less expensive than other approaches that exist in the literature and is near optimal, in the sense that it is shown through simulations to approximate a lower bound which is obtained analytically. Despite the generality of the proposed approaches, this thesis evaluates their performance on a wireless ad hoc network and demonstrates through extensive simulations that the proposed solutions are able to choose more critical nodes relative to other approaches, as it is observed that when these nodes are removed they lead to the highest degrada- tion in network performance in terms of the achieved network throughput, the average network delay, the average network jitter and the number of dropped packets.

The rapid development in wireless technologies and multimedia services has radically shifted the major function of the current Internet from host-centric communication to service-oriented content dissemination, resulting a mismatch between the protocol design and the current usage patterns. Motivated by this significant change, Information-Centric Networking (ICN), which has been attracting ever-increasing attention from the communication networks research community, has emerged as a new clean-slate networking paradigm for future Internet. Through identifying and routing data by unified names, ICN aims at providing natural support for efficient information retrieval over the Internet. As a crucial characteristic of ICN, in-network caching enables users to efficiently access popular contents from on-path routers equipped with ubiquitous caches, leading to the enhancement of the service quality and reduction of network loads. Performance analysis and optimisation has been and continues to be key research interests of ICN. This thesis focuses on the development of efficient and accurate analytical models for the performance evaluation of ICN caching and the design of optimal caching management schemes under practical network configurations. This research starts with the proposition of a new analytical model for caching performance under the bursty multimedia traffic. The bursty characteristic is captured and the closed formulas for cache hit ratio are derived. To investigate the impact of topology and heterogeneous caching parameters on the performance, a comprehensive analytical model is developed to gain valuable insight into the caching performance with heterogeneous cache sizes, service intensity and content distribution under arbitrary topology. The accuracy of the proposed models is validated by comparing the analytical results with those obtained from extensive simulation experiments. The analytical models are then used as cost-efficient tools to investigate the key network and content parameters on the performance of caching in ICN. Bursty traffic and heterogeneous caching features have significant influence on the performance of ICN. Therefore, in order to obtain optimal performance results, a caching resource allocation scheme, which leverages the proposed model and targets at minimising the total traffic within the network and improving hit probability at the nodes, is proposed. The performance results reveal that the caching allocation scheme can achieve better caching performance and network resource utilisation than the default homogeneous and random caching allocation strategy. To attain a thorough understanding of the trade-off between the economic aspect and service quality, a cost-aware Quality-of-Service (QoS) optimisation caching mechanism is further designed aiming for cost-efficiency and QoS guarantee in ICN. A cost model is proposed to take into account installation and operation cost of ICN under a realistic ISP network scenario, and a QoS model is presented to formulate the service delay and delay jitter in the presence of heterogeneous service requirements and general probabilistic caching strategy. Numerical results show the effectiveness of the proposed mechanism in achieving better service quality and lower network cost. In this thesis, the proposed analytical models are used to efficiently and accurately evaluate the performance of ICN and investigate the key performance metrics. Leveraging the insights discovered by the analytical models, the proposed caching management schemes are able to optimise and enhance the performance of ICN. To widen the outcomes achieved in the thesis, several interesting yet challenging research directions are pointed out.

Le contexte universitaire de formation hybride, articulant des cours en présentiel et à distance, est appréhendé ici comme un terrain d’étude sur les pratiques de communication et la médiatisation des savoirs entre apprenants. La question principale de notre recherche est la suivante : Comment expliquer l’usage ou le non usage des outils de communication de plateformes d’apprentissage de l’enseignement supérieur ? Est-ce que les activités des apprenants avec les outils de communication de plateforme (forums de discussion) constituent des activités du savoir ? Notre étude privilégie une épistémologie interprétative qui oriente notre attention sur les discours des interviewés (enseignants et étudiants) dans deux contextes socioculturels différents, à l’université de Lorraine en France et aux universités de Tlemcen et de Ouargla en Algérie. Nous examinons la médiatisation des savoirs en convoquant les concepts des activités du savoir (Gérard, 2000) afin d’analyser les discours sur les activités que font les étudiants des outils de communication. Au terme de notre étude empirique, nous montrons que dans un dispositif hybride les outils de communication de plateforme d’apprentissage ouvrent un éventail de possibilités mais ne sélectionne pas d’eux-mêmes le chemin qui sera suivi pour la médiatisation des savoirs entre apprenants. Celui-ci répond à des contraintes sociales et pédagogiques qui pèsent sur les usages. La médiatisation des savoirs est le produit d’interactions entre l’ensemble des possibilités ouvert par les forums de discussion de plateforme d’apprentissage, les autres pratiques de communication, et les contraintes sociales et pédagogiques (rôle de l’enseignant, engagement des étudiants,...) qui caractérisent le contexte d’insertion de ces dispositifs de communication. Dans un tel contexte pédagogique, nous avons constaté qu’il est presque impossible d’imaginer un processus d’appropriation des forums de discussion qui soit exclusivement individuel. Il passe toujours à travers les autres et les rapports sociaux et de même pour le processus de construction des savoirs / The university context of hybrid formation, articulating group lessons and distance is apprehended here as a field of study on communication practices and media coverage of knowledge between learners. The question that guides our research is: How to explain the use or non-use communication tools of learning platforms of higher education? Are the activities of learners with platform communication tools (discussion forums) are knowledge activities? We have been situated in an interpretative epistemology, which oriente our attention on the discourses of interviewees (teachers and students) in two different cultural contexts, the University of Lorraine in France and universities of Tlemcen and Ouargla in Algeria. We examine media coverage of knowledge by convening the concepts of knowledge activities (Gérard, 2000) to analyze the discourse on activities that students are communication tools.At the end of our empirical study, we show that a hybrid device communication tools platform for learning open a range of possibilities but does not select for themselves the path that will monitoring for mediatisation of knowledges among learners. It responds to social and educational constraints facing uses. The mediatisation of knowledges is the product of interactions between all opened by the communication tools of learning platform opportunities, other communication practices, and social and educational constraints (role of the teacher, student engagement, ...) which characterize the context of inserting these communication devices. In this educational context, we found it almost impossible to imagine a process of appropriation discussion forums it is exclusively individual. It always passes through others and social relationships and even the process of knowledge construction