Thesis (M.S.)--Mississippi State University. Department of Electrical and Computer Engineering. / Title from title screen. Includes bibliographical references.

In recent years, multi-tier architectures have become the standard computing environment for web- and enterprise applications. The application server tier is often the heart of the system embedding the business logic. Adaptability, in particular the capability to adjust to the load submitted to the system and to handle the failure of individual components, are of outmost importance in order to provide 7/24 access and high performance. Replication is a common means to achieve these reliability and scalability requirements. With replication, the application server tier consists of several server replicas. Thus, if one replica fails, others can take over. Furthermore, the load can be distributed across the available replicas. Although many replication solutions have been proposed so far, most of them have been either developed for fault-tolerance or for scalability. Furthermore, only few have considered that the application server tier is only one tier in a multi-tier architecture, that this tier maintains state, and that execution in this environment can follow complex patterns. Thus, existing solutions often do not provide correctness beyond some basic application scenarios. / In this thesis we tackle the issue of replication of the application server tier from ground off and develop a unified solution that provides both fault-tolerance and scalability. We first describe a set of execution patterns that describe how requests are typically executed in multi-tier architectures. They consider the flow of execution across client tier, application server tier, and database tier. In particular, the execution patterns describe how requests are associated with transactions, the fundamental execution units at application server and database tiers. Having these execution patterns in mind, we provide a formal definition of what it means to provide a correct execution across all tiers, even in case failures occur and the application server tier is replicated. Informally, a replicated system is correct if it behaves exactly as a non-replicated that never fails. From there, we propose a set of replication algorithms for fault-tolerance that provide correctness for the execution patterns that we have identified The main principle is to let a primary AS replica to execute all client requests, and to propagate any state changes performed by a transaction to backup replicas at transaction commit time. The challenges occur as requests can be associated in different ways with transactions. Then, we extend our fault-tolerance solution and develop a unified solution that provides both fault-tolerance and load-balancing. In this extended solution, each application server replica is able to execute client requests as a primary and at the same time serves as backup for other replicas. The framework provides a transparent, truly distributed and lightweight load distribution mechanism which takes advantage of the fault-tolerance infrastructure. Our replication tool is implemented as a plug-in of JBoss application server and the performance is carefully evaluated, comparing with JBoss' own replication solutions. The evaluation shows that our protocols have very good performance and compare favorably with existing solutions.

Thesis (M.S.)--Georgia State University, 2006. / Rajshekhar Sunderraman, committee chair; Sushil Prasad, Alex Zelikovsky, committee members. Electronic text (58 p.) : digital, PDF file. Description based on contents viewed Aug. 13, 2007. Includes bibliographical references (p. 58).

Thesis (MScEng)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: There is a large variety of telemetry recervmg software currently available for the reception of telemetry information from different satellites. Most of the software used in receiving telemetry data is satellite specific. Hence, a user-friendly way is needed to make telemetry data easily accessible. A satellite-based web server is aimed at providing telemetry information to any standard web browser as a way of bringing space technology awareness to the people. Two different satellite-based web server methods are examined in this thesis. Based on the evaluation, the on-board File server with proxy server was proposed for satellite-based web server development. This requires that the File server be ported to the on-board computer of the satellite. The web proxy server is placed on the ground segment with the necessary communication requirements to communicate with the on-board File server. In the absence of satellite, the satellite-based web server was successfully implemented on two computers, laying a good foundation for implementation on the on-board computer of the satellite (OBe). / AFRIKAANSE OPSOMMING: Daar is 'n groot verskeidenheid telemetrie ontvangs sagteware huidiglik beskikbaar vir die ontvangs van telemetrie informasie vanaf verskillende satelliete. Die meeste van die sagteware wat gebruik word om telemetrie data te ontvang is satelliet spesifiek. Gevolglik, 'n gebruikers vriendelike metode is nodig om telemetrie data maklik beskikbaar te maak. 'n Satelliet-gebaseerde web-bediener word beoog om telemetrie informasie te verskaf aan enige standaard web-blaaier as 'n metode om mense bewus te maak van ruimte tegnologie. Twee verskillende satelliet gebaseerde web-bediener metodes salondersoek word in hierdie tesis. Gebaseer op 'n evaluering, word die aanboord leêr-bediener met instaanbediener voorgestel vir satelliet-gebaseerde webbediener ontwikkeling. Hiervoor is dit nodig dat die leêr-bediener na die aanboord rekenaar van die satelliet gepoort word. Die web instaanbediener word op die grond segment geplaas met die nodige kommunikasie benodighede, om te kommunikeer met die aanboord leêr-bediener. In die afwesigheid van die satelliet was die satellietgebaseerde web-bediener met sukses geïmplementeer op twee rekenaars, met die gevolg dat 'n goeie fondasie gelê is vir die implementering op die aanboord rekenaar van die satelliet (OBC).

No description available.

The work describes possibilities, which the electronic store can offer its customers and due to which it is possible to gain a competitive advantage over other stores. Aside from the description of the functioning of the store itself, there are also described the possibilities of the store´s promotion and marketing on the Internet and basic programming techniques, that should be used for the programming of the store.

No description available.

Information monitoring systems are publish-subscribe systems that continuously track information changes and notify users (or programs acting on behalf of humans) of relevant updates according to specified thresholds. Internet-scale information monitoring presents a number of new challenges. First, automated change detection is harder when sources are autonomous and updates are performed asynchronously. Second, information source heterogeneity makes the problem of modelling and representing changes harder than ever. Third, efficient and scalable mechanisms are needed to handle a large and growing number of users and thousands or even millions of monitoring triggers fired at multiple sources. In this dissertation, we model users' monitoring requests using continual queries (CQs) and present a suite of efficient and scalable solutions to large scale information monitoring over structured or semi-structured data sources. A CQ is a standing query that monitors information sources for interesting events (triggers) and notifies users when new information changes meet specified thresholds. In this dissertation, we first present the system level facilities for building an Internet-scale continual query system, including the design and development of two operational CQ monitoring systems OpenCQ and WebCQ, the engineering issues involved, and our solutions. We then describe a number of research challenges that are specific to large-scale information monitoring and the techniques developed in the context of OpenCQ and WebCQ to address these challenges. Example issues include how to efficiently process large number of continual queries, what mechanisms are effective for building a scalable distributed trigger system that is capable of handling tens of thousands of triggers firing at hundreds of data sources, how to effectively disseminate fresh information to the right users at the right time. We have developed a suite of techniques to optimize the processing of continual queries, including an effective CQ grouping scheme, an auxiliary data structure to support group-based indexing of CQs, and a differential CQ evaluation algorithm (DRA). The third contribution is the design of an experimental evaluation model and testbed to validate the solutions. We have engaged our evaluation using both measurements on real systems (OpenCQ/WebCQ) and simulation-based approach. To our knowledge, the research documented in this dissertation is to date the first one to present a focused study of research and engineering issues in building large-scale information monitoring systems using continual queries.

The performance of Internet-based services depends on many server-side, client-side, and network related factors. Often, the interaction among the factors or their effect on service performance is not known or well-understood. The complexity of these services makes it difficult to develop analytical models. Lack of models impedes network management tasks, such as predicting performance while planning for changes to service infrastructure, or diagnosing causes of poor performance. We posit that we can use statistical causal methods to model performance for Internet-based services and facilitate performance related network management tasks. Internet-based services are well-suited for statistical learning because the inherent variability in many factors that affect performance allows us to collect comprehensive datasets that cover service performance under a wide variety of conditions. These conditional distributions represent the functions that govern service performance and dependencies that are inherent in the service infrastructure. These functions and dependencies are accurate and can be used in lieu of analytical models to reason about system performance, such as predicting performance of a service when changing some factors, finding causes of poor performance, or isolating contribution of individual factors in observed performance. We present three systems, What-if Scenario Evaluator (WISE), How to Improve Performance (HIP), and Network Access Neutrality Observatory (NANO), that use statistical causal methods to facilitate network management tasks. WISE predicts performance for what-if configurations and deployment questions for content distribution networks. For this, WISE learns the causal dependency structure among the latency-causing factors, and when one or more factors is changed, WISE estimates effect on other factors using the dependency structure. HIP extends WISE and uses the causal dependency structure to invert the performance function, find causes of poor performance, and help answers questions about how to improve performance or achieve performance goals. NANO uses causal inference to quantify the impact of discrimination policies of ISPs on service performance. NANO is the only tool to date for detecting destination-based discrimination techniques that ISPs may use. We have evaluated these tools by application to large-scale Internet-based services and by experiments on wide-area Internet. WISE is actively used at Google for predicting network-level and browser-level response time for Web search for new datacenter deployments. We have used HIP to find causes of high-latency Web search transactions in Google, and identified many cases where high-latency transactions can be significantly mitigated with simple infrastructure changes. We have evaluated NANO using experiments on wide-area Internet and also made the tool publicly available to recruit users and deploy NANO at a global scale.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: PI; PISA; PIMC; cwnd; TCP. Includes bibliographical references (p. 49-50).