Due to the imperative need to reduce the management costs, operators multiplex several concurrent applications in large datacenters. However, uncontrolled resource sharing between co-hosted applications often results in performance degradation problems, thus creating violations of service level agreements (SLAs) for service providers. Therefore, in order to meet per-application SLAs, per-application performance modeling for dynamic resource allocation in shared resource environments has recently become promising. We introduce Chorus, an interactive performance modeling framework for building application performance models incrementally and on the fly. It can be used to support complex, multi-tier resource allocation, and/or what-if performance inquiry in modern datacenters, such as Clouds. Chorus consists of (i) a declarative high-level language for providing semantic model guidelines, such as model templates, model functions, or sampling guidelines, from a sysadmin or a performance analyst, as model approximations to be learned or refined experimentally, (ii) a runtime engine for iteratively collecting experimental performance samples, validating and refining performance models. Chorus efficiently builds accurate models online, reuses and adjusts archival models over time, and combines them into an ensemble of models. We perform an experimental evaluation on a multi-tier server platform, using several industry- standard benchmarks. Our results show that Chorus is a flexible modeling framework and knowledge base for validating, extending and reusing existing models while adapting to new situations.

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Server-based architectures have recently generated more interests and are currently considered for usage for communication in networks. In parallel, switched Ethernet technology has been widely adopted and used in lots of networked systems. Current requirements of networks for supporting real-time guarantees while being flexible at the same time have made the network designers to consider addition of some features to common switches. The FTT-Enabled Ethernet switch is a switch that has been developed to support the FTT (Flexible Time Triggered) paradigm. Recently, servers have been added in these types of switches in order to efficiently manage their allocated bandwidth to different types of messages. A hierarchical network of Ethernet switches might be designed in different ways according to the overall goals and properties of the network. In this thesis, after a study on different design solutions, an architecture has been proposed based on FTT-enabled switches, motivated by their support of real-time constraints and server-based communication features. After having created the architecture, a protocol for bandwidth reservation for this hierarchically composed Ethernet switch architecture is developed. Behavior of the designed protocol is described in detail and it has been modeled using Uppaal. Moreover, the temporal behavior (timing) of the network is presented.

Medan servervirtualisering växt väldigt mycket det senaste decenniet har Apple nyligen börjat tillåta virtualisering av deras operativsystem Mac OS X. På grund av Apples stora framgångar med att lyckas sälja sina produkter till hemanvändare har nu även Mac-datorer börjat hitta till arbetsplatsen. Detta gör att det kommer finnas ett behov av att virtualisera Mac OS X i företagsmiljöer i framtiden då servervirtualisering är väldigt kostnadseffektivt. För att kunna virtualisera krävs en så kallad hypervisor. Det finns två olika typer, typ 1 och typ 2. I denna uppsats ville vi undersöka prestandaskillnader mellan dessa två typer vid virtualisering av Mac OS X. Detta för att kunna se hur prestandan skiljer dem sinsemellan. Prestandatester genomfördes i en experimentmiljö där resultaten visar att en typ 1-hypervisor ger mindre prestandaförluster än en typ 2- hypervisor.

This thesis investigates TCP connection management mechanisms in order to understand the behaviour and improve the performance of Internet servers during overload conditions such as flash crowds. We study several alternatives for implementing TCP connection establishment, reviewing approaches taken by existing TCP stacks as well as proposing new mechanisms to improve server throughput and reduce client response times under overload. We implement some of these connection establishment mechanisms in the Linux TCP stack and evaluate their performance in a variety of environments. We also evaluate the cost of supporting half-closed connections at the server and assess the impact of an abortive release of connections by clients on the throughput of an overloaded server. Our evaluation demonstrates that connection establishment mechanisms that eliminate the TCP-level retransmission of connection attempts by clients increase server throughput by up to 40% and reduce client response times by two orders of magnitude. Connection termination mechanisms that preclude support for half-closed connections additionally improve server throughput by up to 18%.

Online algorithms are characterized by operating on an input sequence revealed over time versus a single static input. Instead of generating a single solution, they produce a sequence of incremental solutions corresponding to the input seen so far. An online algorithm's ignorance of future inputs limits its ability to produce optimal solutions. The incremental nature of its solutions is also an obstacle. The two factors can be differentiated by examining the corresponding incremental algorithm, which has knowledge of future inputs, but must still provide a competitive solution at each step. In this thesis, the lower bound of the incremental constraint of k-server is shown to be to 2.

The rapidly increasing expansion of the Internet has brought dramatic impact to our life and education alike. The major feature differentiates e-learning from the traditional learning is its ability to train anyone, anytime, and anywhere attributed to the Internet. Many experts tell us that e-learning will plays the key-enabling role in knowledge management for individual, schools, and enterprise. Nevertheless, the lack of standard in courseware and learning management system (LMSs) makes courseware in different LMS platforms can not be exchanged directly, and there is no way to monitor and evaluate learner¡¦s behavior from one platform to another. And there are LMS platforms do not provide the effective protection mechanism for courseware in the LMS platforms; this will let an unauthorized user can retrieve courseware as well as he knows the correct URL in the LMS. In this thesis, in order to overcome those hurdles, we refer to the e-learning standard, called Sharable Content Object Reference Model (SCORM), to enhance this feature on our existing LMS platform. And we propose an effective courseware access control mechanism which implement at the kernel of the web server.

This dissertation presents a scalable web framework leaning system, Web-based Learning System (WebLS), addressing the distance learning scenario. Since the speed popularity of the Internet infrastructure and World Wide Web Services that have become the most commonly used information platform and an important medium for education; and expand to the Web-based e-Learning model. The Web-based e-Learning is not subject to the boundary of time or space that has greatly enhanced the effectiveness of online distance learning. The WebLS aims at bringing together the most promising web technologies and standards, in order to attain a scalability and highly availability online learning environment. Moreover, the scalable web framework includes a SCORM based learning management system (named LMS), a server cluster infrastructure, a learning content management service, an information and content repository (named LMS database), and an agent system supporting the innovative solutions taken to implement scalability, availability, portability, reusability, and standardization. The WebLS can store and provide Web access portal to learning contents from teachers, voluntaries, and institutions that lack resources or expertise to offer curriculums over the Internet. So, in the first we design and implement the web-based learning managemnt sytem, Learning Management System (LMS), which conform the e-Learning standard, SCORM 1.2 specification, that established by ADL, and satisfy the requirements of the basic functionality at online web-based learning. Besides, in point of the research topic of learning behavior analysis, we propose a study result for extracting better learning path, Experience Matrix System with Time Fragment Extraction (EMST), which can analyse the learner¡¦s study behavior in Web-based learing environment. Then the information is used to explore, analyse students¡¦ learning path in order to find out the suitable learning path for the more learners. As masses of learners concurrently enter the learning system, the system is often unable to serve such a massive workload, particularly during peak periods of learning activity. We use the server-cluster architecture as a way to create scalable and highly available solutions. However, hosting a variety of learning contents from different owners on such a distributed server system faces new design and management problems and requires new solutions. This dissertation describes the research work we are pursuing for constructing a system to address the challenges faced by hosting learning content on a server farm environment.

One of the most crucial decisions when developing a system based on Service Oriented Architecture is to select an appropriate server which will be the ground for building the application. Similar to databases, an application server has significant influence on efficiency, stability, and security of entire system. During the preparation of architecture for system development one has to decide which available application server would be optimal for hosting and maintaining v Web Services in the given case. There are multiple significant criteria that lead to the proper choice. The impact on a decision among other things is type of the physical machine on which the application server is installed, estimated number of simultaneous clients, and sizes of requests and responses between clients and server. The goal for this thesis is to conduct the comparative analysis of the most commonly used application servers using Service Oriented Architecture and to determine which server should be applied in which particular cases. Performance and load tests will be conducted using SoapUI application.