Η παρούσα διπλωματική εργασία πραγματεύεται την προσομοίωση του πρωτοκόλλου Mobile Internet Protocol version 4 (MIPv4), το οποίο έχει προταθεί για τη διαχείριση της κινητικότητας των χρηστών, έχοντας ως στόχο τη διατήρηση των ενεργών συνδέσεών τους. Το βασικό πλεονέκτημα του πρωτοκόλλου MIPv4 αναφέρεται στη διατήρηση των διεπαφών του πρωτοκόλλου με ανώτερα υποστρώματα, όπως το Transmission Control Protocol – TCP, τα οποία ενεργούν με βάση μία σταθερή ΙΡ διεύθυνση, ενώ παράλληλα παρέχουν αδιάλειπτες υπηρεσίες, ανεξάρτητα από τη θέση του τελικού χρήστη. Ωστόσο, το πρωτόκολλο MIPv4 παρουσιάζει κάποια σημαντικά μειονεκτήματα, όπως η τριγωνική δρομολόγηση και η ενθυλάκωση πακέτου, σε περιπτώσεις υποστήριξης υπηρεσιών πραγματικού χρόνου, όπως το Voice over IP – VoIP. Αυτές οι διεργασίες έχουν ως αποτέλεσμα την εμφάνιση αυξημένης συνολικής καθυστέρησης, διεύρυνσης της διακύμανσης της καθυστέρησης (jitter) και εμφάνισης επιπλέοντος επίβαρου στο δίκτυο, κυρίως λόγω των ενθυλακωμένων πακέτων. Στην παρούσα διπλωματική εργασία, η προσομοίωση του πρωτοκόλλου MIPv4 στοχεύει στην μελέτη της επίδρασης αυτών των παραμέτρων, ώστε να γίνουν κατανοητοί οι μηχανισμοί υποστήριξης της κινητικότητας των χρηστών, οι οποίοι χρησιμοποιούν εφαρμογές πραγματικού χρόνου. Η υλοποίηση της προσομοίωσης του πρωτοκόλλου πραγματοποιήθηκε με τη χρήση του λογισμικού προσομοίωσης ΟΡΝΕΤ, το οποίο παρέχει στο χρήστη τη δυνατότητα της ολοκληρωμένης μελέτης πρωτοκόλλων δικτύου, και την πολύπλευρη διερεύνηση των αποτελεσμάτων της προσομοίωσης. / In this diploma thesis, the simulation of the Mobile Internet Protocol version 4 (MIPv4) is presented and analyzed. The MIPv4 has been developed in order to deal with the user mobility problem, by targeting on the continuity of the active connections. The main advantage of the MIPv4 is the provision of uninterrupted applications, while taking into account that upper layer protocols, such as the Transmission Control Protocol (TCP) consider a single (and constant) IP address throughout the connection duration. However, the MIPv4 has a number of disadvantages, such as the triangular routing and the packet encapsulation that limits the performance of the protocol in cases where mobile users activate real-time applications. The degradation of the protocol’s performance is realized through the increase of the end-to-end delay, the enhanced delay jitter and the higher network overload, mainly due to the packet encapsulation. This diploma thesis targets on the study of the effect of these parameters through simulation, in order to provide an insight of the mechanisms that support the user mobility when real-time applications are activated. The simulation environment is developed by using the OPNET simulation tool, which provides a comprehensive implementation of all network layers and offers a versatile investigation of simulation results.

The thesis investigates how content produced by end-users on the World Wide Web — referred to as user-generated content — can enhance the news vertical aspect of a universal Web search engine, such that news-related queries can be satisfied more accurately, comprehensively and in a more timely manner. We propose a news search framework to describe the news vertical aspect of a universal web search engine. This framework is comprised of four components, each providing a different piece of functionality. The Top Events Identification component identifies the most important events that are happening at any given moment using discussion in user-generated content streams. The News Query Classification component classifies incoming queries as news-related or not in real-time. The Ranking News-Related Content component finds and ranks relevant content for news-related user queries from multiple streams of news and user-generated content. Finally, the News-Related Content Integration component merges the previously ranked content for the user query into theWeb search ranking. In this thesis, we argue that user-generated content can be leveraged in one or more of these components to better satisfy news-related user queries. Potential enhancements include the faster identification of news queries relating to breaking news events, more accurate classification of news-related queries, increased coverage of the events searched for by the user or increased freshness in the results returned. Approaches to tackle each of the four components of the news search framework are proposed, which aim to leverage user-generated content. Together, these approaches form the news vertical component of a universal Web search engine. Each approach proposed for a component is thoroughly evaluated using one or more datasets developed for that component. Conclusions are derived concerning whether the use of user-generated content enhances the component in question using an appropriate measure, namely: effectiveness when ranking events by their current importance/newsworthiness for the Top Events Identification component; classification accuracy over different types of query for the News Query Classification component; relevance of the documents returned for the Ranking News-Related Content component; and end-user preference for rankings integrating user-generated content in comparison to the unalteredWeb search ranking for the News-Related Content Integration component. Analysis of the proposed approaches themselves, the effective settings for the deployment of those approaches and insights into their behaviour are also discussed. In particular, the evaluation of the Top Events Identification component examines how effectively events — represented by newswire articles — can be ranked by their importance using two different streams of user-generated content, namely blog posts and Twitter tweets. Evaluation of the proposed approaches for this component indicates that blog posts are an effective source of evidence to use when ranking events and that these approaches achieve state-of-the-art effectiveness. Using the same approaches instead driven by a stream of tweets, provide a story ranking performance that is significantly more effective than random, but is not consistent across all of the datasets and approaches tested. Insights are provided into the reasons for this with regard to the transient nature of discussion in Twitter. Through the evaluation of the News Query Classification component, we show that the use of timely features extracted from different news and user-generated content sources can increase the accuracy of news query classification over relying upon newswire provider streams alone. Evidence also suggests that the usefulness of the user-generated content sources varies as news events mature, with some sources becoming more influential over time as new content is published, leading to an upward trend in classification accuracy. The Ranking News-Related Content component evaluation investigates how to effectively rank content from the blogosphere and Twitter for news-related user queries. Of the approaches tested, we show that learning to rank approaches using features specific to blog posts/tweets lead to state-of-the-art ranking effectiveness under real-time constraints. Finally this thesis demonstrates that the majority of end-users prefer rankings integrated with usergenerated content for news-related queries to rankings containing only Web search results or integrated with only newswire articles. Of the user-generated content sources tested, the most popular source is shown to be Twitter, particularly for queries relating to breaking events. The central contributions of this thesis are the introduction of a news search framework, the approaches to tackle each of the four components of the framework that integrate user-generated content and their subsequent evaluation in a simulated real-time setting. This thesis draws insights from a broad range of experiments spanning the entire search process for news-related queries. The experiments reported in this thesis demonstrate the potential and scope for enhancements that can be brought about by the leverage of user-generated content for real-time news search and related applications.

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This thesis explores the way in which biological metaphors can be applied to web content mining and, more specifically, the identification of interesting information in web documents. Web content mining is the use of content found on the web, most usually the text found on web pages, for data mining tasks such as classification. Due to the nature of the search domain, i.e. the web content is noisy and undergoing constant change, an adaptive system is required. The discovery of interesting information is an advance on basic text mining in that it aims to identify text that is novel, unexpected or surprising to a user, whilst still being relevant. This thesis investigates the use of Artificial Immune Systems (AIS) applied to discovery of interesting information as AIS are thought to confer the adaptability and learning required for this task. Two novel Artificial Immune Systems are described and tested. AISEC (Artificial Immune System for Interesting E-mail Classification) is a novel, immune inspired system for the classification of e-mail. It is shown that AISEC performs with a predictive accuracy comparable to a naïve Bayesian algorithm when continually classifying e-mail collected from a real user. This section contributes to the understanding of how AIS react in a continuous learning scenario. Following from the knowledge gained by testing AISEC, AISIID (Artificial Immune system for Interesting Information Discovery) is then described. A study involving the subjective evaluation of the results by users is undertaken and AISIID is seen to discover pages rated more interesting by users than a comparative system. The results of this study also reveal AISIID performs with subjective quality similar to the well known search engine, Google. This leads to a contribution regarding a better understanding of the user's perception of interestingness and possible inadequacies in the current understanding of interestingness regarding text documents.

This thesis researches how individuals make sense of information and find their way in complex online environments. Global information communication networks are today accessible to almost everyone. One consequence of this network is greater ease of interaction with friends and colleagues from around the world. Another consequence is an increase in the amount of information that individuals face on a daily basis. People experience much of this information in fragments, from different sources, and in different media formats. In order to act meaningfully in a particular context, individuals form coherence around the information that they encounter. Making sense of this information is a challenging and on-going task, especially in advanced economies where knowledge-related work is a growing segment of the economy. Developing a coherent view of new information, and how it relates to existing information, is important in preparing individuals and organizations for decision-making, planning, and capacity for action. This research study considers the cognitive, social, technological, and spatial strategies that individuals use when they navigate the structure of, and content in, a large open online course with over 2,200 participants. The research includes a social network analysis of the participation patterns of learners in an open online course as well as a grounded theory exploration of the techniques and strategies those learners utilize in their learning. The theory that emerges from the research is the Sensemaking Wayfinding Information Model (SWIM) that details how individuals orient themselves through self-directed activities, as part of social networked systems, and through the use of technologies. This model centres on the information habits of individuals and emphasizes the centrality of identify formation, navigation, social interactions, and sensegiving activities. The social networks that form as individuals make sense of topics indicate the importance of participation, active engagement, language-based activities and artefact creation (such as naming concepts, creating word images, or creating images, diagrams, and videos), and sustained involvement over time.

Une ville intelligente peut être considérée comme un système complexe dans lequel les différents acteurs coopèrent afin d’améliorer la zone urbaine, la rendant plus efficace et plus durable. Pour atteindre cet objectif, les technologies de l’information et de la communication et, en particulier l’Internet des Objets, sont appelées à jouer un rôle clé pour la mise en œuvre des solutions innovantes, des services et des applications. Cependant, en regardant l’état actuel de la ville intelligente, la réalisation d’un tel concept est encore loin d’être atteinte; le scénario réel est en effet caractérisé par un niveau élevé de fragmentation en raison de la pléthore de technologies et de dispositifs présents dans une ville. Afin de combler cette lacune, dans cette thèse, l’évolution de l’Internet des objets vers le Cloud of Things (CoT) est démontrée. Pour démontrer ce concept, le système d’exploitation VITAL est introduit. Dans le CoT, et en général dans le contexte Smart City, l’un des défis les plus importants est la découverte de données-sources appropriées aux besoins des utilisateurs. Cette découverte est une opération qui peut être exécutée directement in-network et / ou out-network. Dans cette thèse, les deux processus sont discutés en introduisant deux solutions différentes. En ce qui concerne la découverte in-network, la conception d’une passerelle pour le Cloud of Things est introduite. Cette passerelle est capable de découvrir et de gérer différents objets sur une base sémantique et, d’autre part, d’agir comme point final pour la présentation des données aux utilisateurs, combinant ainsi tous les aspects de cette thèse. / A Smart City can be seen as a complex system in which different actors cooperate in order to improve, the urban area, making it efficient and sustainable. To achieve this goal, the Information and Communication Technologies, and especially the prominent Internet of Things, are called to play a key role for implementing innovative solutions, services, and applications. However, looking at the current status, the realization of the Smart City is still far from being realized; the real scenario is indeed characterized with a high level of fragmentation due to the plethora of technologies and devices present in a city. In order to bridge this gap, in this thesis, the evolution of the Internet of Things towards the Cloud of Things (CoT) is demonstrated. To demonstrate this concept, the VITAL operating system is introduced. Within the CoT, and in general in the Smart City context, one of the most important challenges is the discovery of appropriate data-sources that satisfy user requirements. The discovery is an operation that can be performed directly in-network and/or out-network. In this thesis, both processes are discussed by introducing two different solutions. Going deeply towards an horizontal unification of different data-sources and the need to have processing capabilities closer to the network, in the last part of the dissertation, the design of a gateway for the Cloud of Things is introduced. This gateway is capable to discover and manage different semantic-like things and, on the other hand, to act as end-point for the presentation of data to users, bridging the contributions of this thesis.

The use of visual aesthetics has been found to contribute to feelings of a positive Web experience. Accordingly, studies report strong correlations between aesthetics and facets of user experience like usability and credibility, but does this hold for accessibility also? Some believe that Web aesthetics impedes accessibility, while most Web designers perceive that the accessibility initiative is restrictive design-wise. These misconceptions have slowed down the advancement of an inclusive Web. Firstly, it is clear that the relationship between Web aesthetics and accessibility is still poorly understood. Secondly, tools capable of analysing the aesthetic quality of Web pages and relaying associated accessibility status information are lacking. This thesis addresses these two problems. In order to investigate this relationship, the aesthetic judgements of 180 users were elicited to help classify Web pages based on their visual quality using Lavie and Tractinsky's framework. The classified Web pages were then technically and manually audited for accessibility compliance using 4 automated tools, and 11 experts who used a heuristic evaluation technique known as the Barrier Walkthrough (BW) method to check for barriers which could affect people with visual impairments. Our results consistently showed that Web pages judged on Lavie and Tractinsky's classical aesthetic dimension as being `clean' had significant correlations with accessibility, suggesting `cleanness' to be a suitable proxy measure for accessibility. Expressive dimensions showed no such correlations. This insight was used to develop the EIVAA tool aimed at predicting the aesthetic quality of Web pages and using the information to provide accessibility ratings for the pages. Quantitative evaluations show that the tool is able to predict aesthetic quality in a way that mimics gold standards, especially along the design dimension `clean' where we observed tool-human correlations as strong as 0.703, thus making the associated accessibility predictions also acceptable. We envision that our findings will give the Web community a more holistic understanding of the interactions between the use of aesthetics and accessibility, and that our tool would inform Web developers of the implications of their designs.

Ο μεγάλος όγκος σελίδων και υπηρεσιών στο Διαδίκτυο αρκετές φορές δημιουργεί προβλήματα πλοήγησης με αποτέλεσμα η αναζήτηση εγγράφων και πληροφοριών να είναι μια εξαιρετικά χρονοβόρα και δύσκολη διαδικασία. Για το λόγο αυτό είναι απαραίτητη η πρόβλεψη των αναγκών των χρηστών με στόχο τη βελτίωση της χρηστικότητας του Διαδικτύου αλλά και της παραμονής του χρήστη σε έναν δικτυακό τόπο. Ο στόχος αυτής της διπλωματικής εργασίας είναι αρχικά να παρουσιάσει μεθόδους και τεχνικές που χρησιμοποιούνται για την εξατομίκευση και προσαρμογή στα ενδιαφέροντα του χρήστη, δικτυακών τόπων. Η εξατομίκευση περιλαμβάνει τη χρήση πληροφοριών που προέρχονται από τα ενδιαφέρονται και τη συμπεριφορά πλοήγησης του χρήστη σε συνδυασμό με το περιεχόμενο και τη δομή του δικτυακού τόπου. Στη συνέχεια παρουσιάζεται ένα σύστημα αναδιοργάνωσης της δομής ενός δικτυακού τόπου, του οποίου η υλοποίηση βασίστηκε στη δημοτικότητα των σελίδων για κάθε χρήστη όπως αυτή προκύπτει από τα log αρχεία που διατηρεί ο server του δικτυακού τόπου. Τέλος, το σύστημα αυτό εφαρμόζεται σε έναν πειραματικό δικτυακό τόπο και γίνεται αξιολόγηση των αποτελεσμάτων εφαρμογής του. / The large number of web pages on many Web sites has raised navigation problems. As a result, users often miss the goal of their inquiry, or receive ambiguous results when they try to navigate through them. Therefore, the requirement for predicting user needs in order to improve the usability and user retention of a Web Site is more than ever, indispensable. The primary purpose of this thesis is to explore methods and techniques for improving or “personalizing” Web Sites. Web personalization includes any action that adapts the information or services provided by a Web site to the needs of a particular user or a set of users, taking advantage of the knowledge gained from the users’ navigation behavior and interests in combination with the content and structure of the Web Site. Secondly, this thesis describes the implementation of a tool (reorganization software) which parses log files and uses specific metrics related to web page accesses, in order to reorganize the structure of a web site according to its users’ preferences. Finally, the tool is applied in an experimental Web Site and the results of this reorganization process are evaluated.

Thesis (M. Tech. Engineering: Electrical--Vaal University of Technology. / This dissertation discusses the design and implementation of a voice over internet protocol system for the multi-user enterprise. It is limited to small to medium enterprises of which the Vaal University of Technology is an example. Voice communications over existing Internet protocol networks are governed by standards, and to develop such a system it is necessary to have a thorough understanding of these standards. Two such standards namely the International Telecommunications Unions H.323 and the Internet Engineering Task Force's SIP were evaluated and compared to each other in terms of their complexity, extensibility and scalability as well as the services they offer. Based on these criteria it was decided to implement a SIP system. A SIP network consists of application software that act as clients and servers, as well as hardware components such as a proxy and redirect and registrar or location servers that allow users of this network to call each other on the data network. Gateways enable users of the network to call regular public switched telephone network numbers. A test network was set up in the laboratory that contained all the hardware and software components. This was done to understand the installation and configuration options of the different software components and to determine the suitability and interoperability of the software components. This network was then migrated to the network of the Vaal University of Technology which allowed selected users to test and use it. Bandwidth use is a major point of contention, and calculations and measurements showed that the codec being used during the voice call is the determining factor. This SIP system is being used on a daily basis and the users report excellent audio quality between soft phones and soft phones, soft phones and normal telephones and even cellular phones.

Le Cloud computing a gagné beaucoup de popularité et a reçu beaucoup d'attention des deux mondes, industriel et académique, puisque cela les libère de la charge et le coût de la gestion de centres de données locaux. Toutefois, le principal facteur motivant l'utilisation du Cloud est sa capacité de fournir des ressources en fonction des besoins du client. Ce concept est appelé l’élasticité. Adapter les applications Cloud lors de leur exécution en fonction des variations de la demande est un grand défi. En outre, l'élasticité de Cloud est diverse et hétérogène car elle englobe différentes approches, stratégies, objectifs, etc. Nous sommes intéressés à étudier: Comment résoudre le problème de sur/sous-approvisionnement? Comment garantir la disponibilité des ressources et surmonter les problèmes d'hétérogénéité et de granularité des ressources? Comment standardiser, unifier les solutions d'élasticité et de modéliser sa diversité à un haut niveau d'abstraction? Dans cette thèse, trois majeures contributions ont été proposées: Tout d’abord, un état de l’art à jour de l’élasticité du Cloud ; cet état de l’art passe en revue les différents travaux relatifs à l’élasticité des machines virtuelles et des conteneurs. Deuxièmement, ElasticDocker, une approche permettant de gérer l’élasticité des conteneurs, notamment l’élasticité verticale, la migration et l’élasticité combinée. Troisièmement, MoDEMO, un nouveau cadre de gestion d'élasticité unifié, basé sur un standard, dirigé par les modèles, hautement extensible et reconfigurable, supportant plusieurs stratégies, différents types d’élasticité, différentes techniques de virtualisation et plusieurs fournisseurs de Cloud. / Cloud computing has been gaining popularity and has received a great deal of attention from both industrial and academic worlds since it frees them from the burden and cost of managing local data centers. However, the main factor motivating the use of cloud is its ability to provide resources according to the customer needs or what is referred to as elasticity. Adapting cloud applications during their execution according to demand variation is a challenging task. In addition, cloud elasticity is diverse and heterogeneous because it encompasses different approaches, policies, purposes, etc. We are interested in investigating: How to overcome the problem of over-provisioning/under-provisioning? How to guaranty the resource availability and overcome the problems of heterogeneity and resource granularity? How to standardize, unify elasticity solutions and model its diversity at a high level of abstraction? In this thesis, we solved such challenges and we investigated many aspects of elasticity to manage efficiently the resources in the cloud. Three contributions are proposed. Firstly, an up-to-date state-of-the-art of the cloud elasticity, this state of art reviews different works related to elasticity for both Virtual Machines and containers. Secondly, ElasticDocker, an approach to manage container elasticity including vertical elasticity, live migration, and elasticity combination between different virtualization techniques. Thirdly, MoDEMO, a new unified standard-based, model-driven, highly extensible and reconfigurable framework that supports multiple elasticity policies, vertical and horizontal elasticity, different virtualization techniques and multiple cloud providers.