Made available in DSpace on 2016-06-02T19:07:10Z (GMT). No. of bitstreams: 1 PAULA_Anderson_2015.pdf: 815177 bytes, checksum: b64e699dd3ec918452fa1075460274f9 (MD5) Previous issue date: 2015-06-29 / Paxos is an active replication algorithm that keeps the same shared state consistently among servers that handle requests from an application. It is unusual to find applications where the main processing happens through a replication algorithm such as Paxos, mostly due to the high number of exchanged messages required to keep the state consistent. This restricts the system scalability to a handful of replicas. To increase the applicability of active replication, we would like be able to not only make the capacity of processing proportional to the number of servers employed, but also change dynamically the number of server according to demand. In this dissertation we explored reconfiguration on systems that use active replication. We proposed two mechanisms: (1) efficient protocolo for state transfer; and (2) incorporation of new replicas in the system with no significant increase in the cost to keep the whole system consistent. Our approach uses both mechanisms to create reader replicas, capable of answering all application requests without taking an active part in the costly operations of the Paxos algorithm. / Paxos é um mecanismo de replicação ativa que consegue manter um mesmo estado compartilhado entre servidores que atendem a requisições de uma aplicação. É incomum encontrar aplicações onde a parte principal do processamento acontece através de um algoritmo de replicação como Paxos devido ao seu custo em termos do número de mensagens trocadas, o que limita a escalabilidade do sistema para algumas poucas réplicas. Para aumentar a aplicabilidade de replicação ativa, gostaríamos de ser ser capazes de, não só tornar a capacidade de processamento proporcional ao número de servidores empregados, mas também de variar essa capacidade dinamicamente em resposta às mudanças da demanda gerada. Nessa dissertação exploramos a questão da reconfiguração em sistemas de replicação ativa. Em particular, cobiçamos transformar a biblioteca de replicação Treplica em um sistema reconfigurável. Propomos dois novos mecanismos: (1) protocolo eficiente para transferência de estado; e (2) adição de novas réplicas sem aumentar de forma significativa o custo de manutenção da consistência do sistema como um todo. Nossa estratégia utiliza os dois mecanismos para criação de réplicas leitoras, que são capazes de atender todas as requisições da aplicação sem no entanto participarem ativamente das operações custosas do algoritmo Paxos.

The objective of this thesis was to design and implement a scalable and load efficient back-end system for web game services. This is of interest since web applications may overnight gain a significant increase in user base, because of viral sharing. Therefore designing the web application to service an increasing amount of users can make or break the application, in regard to keep the user base. Because of this, testing how well the system performs during heavy load can be used as a foundation when making a decision of when and where to scale up the application. The system was to be generically accessible through an Application Programming Interface (API) by the different game services. This was done using a RESTful architecture where emphasise was put on building the system scalable and load efficient. This thesis focuses on designing and implementing such a system, and how load testing can be used to evaluate this systems performance for an increasing amount of simultaneous clients using the web application. The results from load testing the implemented system was above the expectations, considering the hardware used when running the tests and hosting the system. The conclusion of this thesis is that by following REST when designing a web service, scalability becomes a natural part of how one would design the system.

Änderungen von Datenstromanfragen zur Laufzeit werden insbesondere durch zustandsbehaftete Datenstromoperatoren erschwert. Da die Zustände im Arbeitsspeicher abgelegt sind und bei einem Neustart verloren gehen, wurden in der Vergangenheit Migrationsverfahren entwickelt, um die inneren Operatorzustände bei einem Änderungsvorgang zu erhalten. Die Migrationsverfahren basieren auf zwei unterschiedlichen Ansätzen - Zustandstransfer und Parallelausführung - sind jedoch aufgrund ihrer Realisierung auf eine zentrale Ausführung beschränkt. Mit wachsenden Anforderungen in Bezug auf Datenmengen und Antwortzeiten werden Datenstromsysteme vermehrt verteilt ausgeführt, beispielsweise durch Sensornetze oder verteilte IT-Systeme. Zur Anpassung der Anfragen zur Laufzeit sind existierende Migrationsstrategien nicht oder nur bedingt geeignet. Diese Arbeit leistet einen Beitrag zur Lösung dieser Problematik und zur Optimierung der Migration in Datenstromsystemen. Am Beispiel von präventiven Instandhaltungsstrategien in Fabrikumgebungen werden Anforderungen für die Datenstromverarbeitung und insbesondere für die Migration abgeleitet. Das generelle Ziel ist demnach eine möglichst schnelle Migration bei gleichzeitiger Ergebnisausgabe. In einer detaillierten Analyse der existierenden Migrationsstrategien werden deren Stärken und Schwächen bezüglich der gestellten Anforderungen diskutiert. Für die Adaption von laufenden Datenstromanfragen wird eine allgemeine Methodik vorgestellt, welche als Basis für die neuen Strategien dient. Diese Adaptionsmethodik unterstützt zwei Verfahren zur Bestimmung von Migrationskonfigurationen - ein numerisches Verfahren für periodische Datenströme und ein heuristisches Verfahren, welches auch auf aperiodische Datenströme angewendet werden kann. Eine wesentliche Funktionalität zur Minimierung der Migrationsdauer ist dabei die Beschränkung auf notwendige Zustandswerte, da in verteilten Umgebungen eine Übertragungszeit für den Zustandstransfer veranschlagt werden muss - zwei Aspekte, die bei existierenden Verfahren nicht berücksichtigt werden. Durch die Verwendung von neu entwickelten Zustandstransfermethoden kann zudem die Übertragungsreihenfolge der einzelnen Zustandswerte beeinflusst werden. Die Konzepte wurden in einem OSGi-basierten Prototyp implementiert und zudem simulativ analysiert. Mit einer umfassenden Evaluierung wird die Funktionsfähigkeit aller Komponenten und Konzepte demonstriert. Der Performance-Vergleich zwischen den existierenden und den neuen Migrationsstrategien fällt deutlich zu Gunsten der neuen Strategien aus, die zudem in der Lage sind, alle Anforderungen zu erfüllen.

Software as a service is an emerging but important aspect of the web. WebServices play a vital role in providing it. Web Services are commonly provided in one of two architectural styles: a "REpresentational State Transfer" (REST), or using the "Simple Object Access Protocol" (SOAP.) Originally most web content was text and small images. But more recent services involve complex data structures including text, images, audio, and video. The task of optimizing data to provide delivery of these structures is a complex one, involving both theoretical and practical aspects. In this thesis work, I have considered two architectures developed in the REST architectural style and tested them on mixes of data types (plain text, image, audio) being retrieved from a file system or database. The payload which carries the actual content of a data transmission process can either be in Extensible Markup Language (XML) or JavaScript Object Notation (JSON). Both of these language notations are widely used. The two architectures used in this thesis work are titled as Scenario 1 and Scenario 2. Scenario 1 proposes two different cases for storing, retrieving and presenting the data via a REST web service. We investigate the question of what is the best way to provide different data types (image, audio) via REST Web Service. Payload size for JSON and XML are compared. Scenario 2 proposes an enhanced and optimized architecture which is derived from the pros of the first two cases in Scenario 1. The proposed architecture is best suited for retrieving and serving non-homogeneous data as a service in a homogenous environment. This thesis is composed of theoretical and practical parts. The theory part contains the design and principles of REST architecture. The practical part has a Web Service provider and consumer model developed in Java. The practical part is developed using the Spring MVC framework and Apache CXF, which provides an implementation using JAX-RS, the Java API for RESTful services. A glossary of acronyms used in this thesis appears in the appendix on page 101.

Abstract The Internet of Things vision proposes a global platform in an unforeseen scale for distributed applications that rely on data provided by interconnected resource-constrained things. In such large-scale systems, centralized control of system operation by a single component through vertical interactions becomes unfeasible. Ideally, decentralized control in the proximity of things enables to take into account the local dynamic resource availability and environmental characteristics that are used to optimize the application execution. To realize decentralization, capabilities for horizontal interactions, that complement the vertical interactions, and for opportunistic participation of things are needed. This thesis explores mobile agent technology to implement distributed Internet of Things applications that benefit from both vertical and horizontal interactions of the application components. First, a resource-oriented reactive mobile agent architecture and a software framework are presented. The framework facilitates RESTful interactions between agents and other system components and provides a REST-based interface to build opportunistic agent-based applications. Two agent platforms are presented that integrate resource-constrained things into the framework as mobile agent hosts. Second, mobile agent based mobile crowdsensing and edge computing applications are evaluated with large-scale simulations and real-world experiments. The results show that energy consumption is decreased in the participating things, in comparison with the existing approaches, by agent-based in-network data processing and control of the thing operation. This thesis makes a valuable contribution by enabling mobile agent operations in a heterogeneous set of resource-constrained things. The presented empirical evidence shows how mobile agent technology increases energy efficiency in distributed application execution. The presented mobile agent architecture and software framework potentially accelerate the utilization of mobile agent technology in the Internet of Things. / Tiivistelmä Esineiden Internet liittää resurssirajoitteiset sulautetut laitteet laajamittaisesti Internet-verkkoon, jossa niiden tuottamaa tietoa hyödynnetään hajautettujen järjestelmien sovelluksissa. Esineiden Internetin järjestelmien odotetaan skaalautuvan niin laajoiksi, ettei keskitetty, vertikaaliseen vuorovaikutukseen perustuva järjestelmähallinta ole enää käyttökelpoinen ratkaisu. Hajautettu hallinta lähellä tietoa tuottavia laitteita tuo etuja, kun paikallisesti sovelluksen suorituksessa otetaan huomioon toimintaympäristön tila ja voidaan reagoida dynaamisesti resurssien saatavuuteen. Hajautus Esineiden Internetin sovellusalustoilla edellyttää menetelmiä sekä laitteiden vertikaaliseen ja horisontaaliseen vuorovaikutukseen, että niiden dynaamisen osallistumisen mahdollistamiseksi sovelluksen suorittamisessa. Tässä työssä tutkittiin mobiiliagentti-teknologiaa hajautettujen sovellusten toteuttamiseen Esineiden Internet-ympäristössä. Työssä esitettiin resurssisuuntautunut arkkitehtuuri reaktiivisille mobiiliagenteille sekä ohjelmistokehys, joita käyttäen voidaan toteuttaa agenttipohjaisia hajautettuja sovelluksia. Ohjelmistokehys perustuu REST-arkkitehtuurimalliin, jonka pohjalta esitettiin yhdenmukainen rajapinta agenttien ja järjestelmäkomponenttien väliseen vuorovaikutukseen. Ohjelmistokehyksen osana toteutettiin kaksi mobiiliagentti-ohjelmistoalustaa resurssirajoitteisille sulautetuille laitteille. Työssä tarkasteltiin mobiiliagentti-pohjaisten Esineiden Internet-sovellusten energiatehokkuutta simuloinneilla sekä tosielämän kokeilla. Tarkastelun kohteeksi valittiin joukkoistettu mobiilihavainnointi sekä reunalaskennan ulottaminen resurssirajoitteisiin laitteisiin. Saadut tulokset osoittavat, että laitteiden energiankulutusta voidaan pienentää verrattuna aiemmin esitettyihin ratkaisuihin hyödyntämällä mobiiliagentteja tiedonkäsittelyyn laitteessa sekä laitteen toiminnan ohjaamiseen. Työssä esitetty resurssisuuntautunut mobiiliagenttiarkkitehtuuri sekä ohjelmistokehys edesauttavat mobiiliagentti-teknologian hyödyntämistä resurssirajoitteisissa sulautetuissa laitteissa. Tosielämän kokeista saadut tulokset osoittavat mobiiliagenttiteknologian hyötyjä hajautettujen sovellusten toteuttamisessa Esineiden Internetiin.

In general, migration is one of the most important global challenges. The topic of regulating migration flows came to the fore in relation to the current Europe's migration, or more precisely, refugee crisis. It has been described as the most massive migrant's crisis since the WW2. Unprecedented influx of immigrants and refugees in 2015 resulted in that even the best prepared European countries, such as Sweden, have reached a tipping point with regard to respect EU standards related to reception and processing of asylum applications. Master thesis covered two main analyses - the relevance of the refugee crisis in the EU in regards to the Swedish welfare state and the subsequent implications arising from the refugee crisis for the Swedish welfare state.

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Master’s thesis deals with implementation of a European standard DATEX II. This standard specifies the data format for information transmission in road transport. The road traffic is flowing streams of current information. For the work was selected network of meteorological stations, which will publish the measured data, ie weather conditions of road transport. Measured data will be available to consumers in the format DATEX II. Implementation will be operational in its entirety meteorological station from design to the actual web service that will produce data information for consumers.