Virtual environments where users can interact with each other as well as with the environment are today used in many application areas ranging from military simulations to massive multiplayer online games. But no matter the application area, as soon as the number of users reaches a certain threshold, hosting a virtual environment on a single machine can become problematic. Speed and quality of the network connection will limit the number of concurrently connected users in terms of acceptable visual quality and hardware requirements of the server will be strict. With a single point of failure, system reliability could easily be compromised by means of network or host failure. Distribution of the virtual environment therefore seems a reasonable approach in order to address this problem. Hardware and network requirements would not be so critical and it would increase reliability by having no single point of failure. Unfortunately distribution introduces new problems dealing with synchronization of the world state within the distribution network. A possible solution to these problems with the focus on reliability will be presented in this thesis. The solution uses a peer to peer platform that is able to adapt to changes in the network infrastructure as a base for all communication. To improve synchronization efficiency the network will be dynamically divided into multicast groups based on synchronization needs. The solution will be tested for performance with the network fully functioning and in a number of more of less broken states to determine the reliability. The results from the tests conclude that the system is able to perform with what must be seen as acceptable performance levels even in very problematic network environments. The scalability of the system did also meet the expectations but the results would have benefited from more experimentation with larger user populations. / Virtuella världar där användare kan träffas och interagera med både varandra och miljön används idag i inom flera områden så som militära simulatorer och online-spel. Men det spelar ingen roll vad användningsområdet är, när antalet anvädare når en viss gräns blir det problematiskt att hålla den virtuella världen på en maskin. Distribuering kan vara en lösning på detta problem men som i sin tur drar med sig nya problem i form av synkroniseringssvårigheter. En potentiell lösning presenteras i rapporten som använder peer-to-peer-tekniker för att hålla informationen synkroniserad och försöker upprätthålla en hög tillgänlighet under svåra nätverksförhållande. Lösningen har testats och uppvisade låvande resultat inom båda skalbarhet och pålitlighet men skulle behöva fler tester för att ge definitiva resultat.

Background: The network-centric defense requires a method for securing vast dynamic distributed information systems. Currently, there are no efficient methods for establishing the level of IT security in vast dynamic distributed information systems. Purpose: The target of this thesis was to design a method, capable of determining the level of IT security of vast dynamic component-based distributed information systems. Method: The work was carried out by first defining concepts of IT security and distributed information systems and by reviewing basic measurement and modeling theory. Thereafter, previous evaluation methods aimed at determining the level of IT security of distributed information systems were reviewed. Last, by using the theoretic foundation and the ideas from reviewed efforts, a new evaluation method, aimed at determining the level of IT security of vast dynamic component-based distributed information systems, was developed. Results: This thesis outlines a new method, CAESAR, capable of predicting the security level in parts of, or an entire, component-based distributed information system. The CAESAR method consists of a modeling technique and an evaluation algorithm. In addition, a Microsoft Windows compliant software, ROME, which allows the user to easily model and evaluate distributed systems using the CAESAR method, is made available.

Increased wireless connectivity to vehicles invites both existing and new digital methods of attack, requiring the high prioritisation of security throughout the development of not just the vehicle, but also the services provided for it. This report examines such a connected car service used by thousands of customers every day and evaluates it from a security standpoint. The methods used for this evaluation include both direct testing of vulnerabilities, as well as the examination of design choices made which more broadly affect the system as a whole. With the results are included suggestions for solutions where necessary, and in the conclusion, design pitfalls and general considerations for system development are discussed.

Context: Cloud computing is rapidly emerging in the area of distributed computing. In the meantime, many organizations also attributed the technology to be associated with several business risks which are yet to be resolved. These challenges include lack of adequate security, privacy and legal issues, resource allocation, control over data, system integrity, risk assessment, software vulnerabilities and so on which all have compromising effect in cloud environment. Organizations based their worried on how to develop adequate mitigation strategies for effective control measures and to balancing common expectation between cloud providers and cloud users. However, many researches tend to focus on cloud computing adoption and implementation and with less attention to vulnerabilities and attacks in cloud computing. This paper gives an overview of common challenges and mitigation techniques or practices, describes general security issues and identifies future requirements for security research in cloud computing, given the current trend and industrial practices. Objectives: We identified common challenges and linked them with some compromising attributes in cloud as well as mitigation techniques and their impacts in cloud practices applicable in cloud computing. We also identified frameworks we consider relevant for identifying threats due to vulnerabilities based on information from the reviewed literatures and findings. Methods: We conducted a systematic literature review (SLR) specifically to identify empirical studies focus on challenges and mitigation techniques and to identify mitigation practices in addressing software vulnerabilities and attacks in cloud computing. Studies were selected based on the inclusion/exclusion criteria we defined in the SLR process. We search through four databases which include IEEE Xplore, ACM Digital Library, SpringerLinks and SciencDirect. We limited our search to papers published from 2001 to 2010. In additional, we then used the collected data and knowledge from finding after the SLR, to design a questionnaire which was used to conduct industrial survey which also identifies cloud computing challenges and mitigation practices persistent in industry settings. Results: Based on the SLR a total of 27 challenges and 20 mitigation techniques were identified. We further identified 7 frameworks we considered relevant for mitigating the prevalence real-time software vulnerabilities and attacks in the cloud. The identified challenges and mitigation practices were linked to compromised cloud attributes and the way mitigations practices affects cloud computing, respectively. Furthermore, 5 and 3 additional challenges and suggested mitigation practices were identified in the survey. Conclusion: This study has identified common challenges and mitigation techniques, as well as frameworks practices relevant for mitigating real-time software vulnerabilities and attacks in cloud computing. We cannot make claim on exhaustive identification of challenges and mitigation practices associated with cloud computing. We acknowledge the fact that our findings might not be sufficient to generalize the effect of the different service models which include SaaS, IaaS and PaaS, and also true for the different deployment models such as private, public, community and hybrid. However, this study we assist both cloud provider and cloud customers on the security, privacy, integrity and other related issues and useful in the part of identifying further research area that can help in enhancing security, privacy, resource allocation and maintain integrity in the cloud environment. / Kungsmarksvagen 67 SE-371 44 Karlskrona Sweden Tel: 0737159290

The focus of this dissertation is on large-scale and long-running networked real-time multiplayer games. In this type of games, each player controls one or many entities, which interact in a shared virtual environment. Three attributes - scalability, security, and fault tolerance - are considered essential for this type of games. The normal approaches for building this type of games, using a client/server or peer-to-peer architecture, fail in achieving all three attributes. We propose a server-network architecture that supports these attributes. In this architecture, a cluster of servers collectively manage the game state and each server manages a separate region of the virtual environment. We discuss how the architecture can be extended using proxies, and we compare it to other similar architectures. Further, we investigate how a distributed database management system can support the proposed architecture. Since efficiency is very important in this type of games, some properties of traditional database systems must be relaxed. We also show how methods for increasing scalability, such as interest management and dead reckoning, can be implemented in a database system. Finally, we suggest how the proposed architecture can be validated using a simulation of a large-scale game.

The specification of communication standards and increased availability of sensors for mobile phones and mobile systems are responsible for a significantly increasing sensor availability in populated environments. These devices are able to measure physical parameters and make this data available via communication in sensor networks. To take advantage of the so called acquiring information for public services, other parties have to be able to receive and interpret it. Locally measured datacould be seen as a means of describing user context. For a generic processing of arbitrary context data, a model for the specification ofenvironments, users, information sources and information semantics has to be defined. Such a model would, in the optimal case, enable global domain crossing context usage and hence a broader foundation for context interpretation and integration.This thesis proposes the CII-(Context Information Integration) model for the persistence and retrieval of context information in mobile, dynamically changing, environments. It discusses the terms context and context modeling under the analysis of former publications in thefield. Further-more an architecture and prototype are presented.Live and historical data are stored and accessed by the same platform and querying processor, but are treated in an optimized fashion.Optimized retrieval for closeness in n-dimensional context-spaces is supported by a dedicated method. The implementation enables self-aware,shareable agents that are able to reason or act based upon the global context,including their own. These agents can be considered as being a part of the wholecontext, being movable and executable for all context-aware applications.By applying open source technology, a gratifying implementation of CII is feasible. The document contains a thorough discussion concerning the software design and further prototype development. The use cases at the end of the document show the flexibility and extendability of the model and its implementation as a context-base for three entirely different applications. / MediaSense

In distributed systems it is often useful to ensure that messages sent between processes in a group are received by all group members. This thesis presents Reliable Non-Ordered Multicast Protocol (RNOMP). We argue that it achieves reliable multicast between processes in groups that processes can leave and join arbitrarily. The protocol has been implemented on top of a group membership simulation which allows evaluation of the performance of the protocol while varying packet loss and the frequency at which processes leaves and joins groups. After analyzing how the protocol handles certain situations we conclude that our protocol achieves reliability and performs well within certain parameter values.

Webbens framgång har lett till tendens att stora IT-system byggda enligt en centralistisk arkitektur är på väg att ersättas av samverkande distribuerade system. De processorienterade, verksamhetsstödjande systemen utgör inget undandag. I enlighet med denna tendens så finns det ett behov för processtödjande verksamhetssystem att synkronisera och utbyta resultat med med andra verksamhetssystem. Målet med denna undersökning har varit att utreda hur kommunikationen mellan distribuerade verksamhetsprocesser byggda enligt BPMN 2.0-standarden kan implementeras. Ansatsen har varit att en tjänsteorienterad arkitektur baserad på principerna för REST skulle vara en framkomlig väg för att lösa detta problem. Teoretiska studier av tjänsteorienterad arkitektur, BPMN 2.0 samt REST har lett till en minimal implementation baserad på en ”proof-of-concept”-arkitektur i tjänsteplattformen Motrice från Motrice AB. Det konkreta lösningsförslaget utvärderas enligt Richardsons mognadsmodell, där mognadsnivån för lösningsförslaget avgörs i enlighet med denna modell. Slutsatsen är kommunikation mellan distribuerade verksamhetsprocesser bygger på meddelandeflöden, där dessa meddelandeflöden är helt förenliga med principerna för REST. / The success of the web has led to a tendency by which monolithic systems constructed according to a centralistic architecture,are replaced by distributed cooperating systems. Process and business oriented systems are no exception in this regard. This tendency has led to increased demand for process oriented systems to be able to synchronize and exhange results with other business systems. The purpose of this study has been to investigate how communication between distributed business processes built according to the BPMN 2.0 standard can be implemented. The hypothesis was that a service oriented architecture based on the principles of REST would be a viable approach to solve the problem. The theoretical study of service oriented architectures, BPMN and REST have resulted in a minimal implementation based on a proof-of-concept architecture. The concrete solution is then evaluated using Richardsons maturity model, and the maturity level of the solution is assessed according to this model. The conclusions are that communication between distributed BPMN 2.0 processes are based on message flows, where the concrete implementation of message flows are fully compatible with the principles of REST.

The study of large-scale decentralised systems composed of numerous interacting agents that self-organise to perform a common task is receiving growing attention in several application domains. However, real world implementations are limited by a lack of well-established design methodologies that provide performance guarantees. Engineering such systems is a challenging task because of the difficulties to obtain the micro-macro link: a correspondence between the microscopic description of the individual agent behaviour and the macroscopic models that describe the system's dynamics at the global level. In this thesis, we propose an engineering methodology for designing decentralised systems, based on the concept of design patterns. A design pattern provides a general solution to a specific class of problems which are relevant in several application domains. The main component of the solution consists of a multi-level description of the collective process, from macro to micro models, accompanied by rules for converting the model parameters between description levels. In other words, the design pattern provides a formal description of the micro-macro link for a process that tackles a specific class of problems. Additionally, a design pattern provides a set of case studies to illustrate possible implementation alternatives both for simple or particularly challenging scenarios. We present a design pattern for the best-of-n, decentralised decision problem that is derived from a model of nest-site selection in honeybees. We present two case studies to showcase the design pattern usage in (i) a multiagent system interacting through a fully-connected network, and (ii) a swarm of particles moving on a bidimensional plane. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

The main goal of this thesis is to create a monitoring platform and library that can be used to monitor distributed Java-based applications. This work is inspired by Google Dapper and shares a concept called "Span" with the aforementioned project. Spans represent a small specific part of the computation and are used to capture state among multiple communicating nodes. In order to be able to col- lect spans without recompiling the original application's code, instrumentation techniques are highly used in the thesis. The monitoring tool, which is called Distrace, consists of two parts: the native agent and the instrumentation server. Users of the Distrace tool are supposed to extend the instrumentation server and specify the points in their application's code where new spans should be created and closed. In order to achieve high performance and affect the running appli- cation at least as possible, the instrumentation server is used for instrumenting the code. The Distrace tool is aimed to have a small foot-print on the monitored applications, should be easy to deploy and is transparent to target applications from the point of view of the final user. 1