Byzantine Fault-Tolerant Web Services for n-Tier and Service Oriented Architectures

Web Services that provide mission-critical functionality must be replicated to guarantee correct execution and high availability in spite of arbitrary (Byzantine) faults. Existing approaches for Byzantine fault-tolerant execution of Web Services are inadequate to guarantee correct execution due to several major limitations. Some approaches do not support interoperability between replicated Web Services. Other approaches do not provide fault isolation guarantees that are strong enough to prevent cascading failures across organizational and application boundaries. Moreover, existing approaches place impractical limitations on application development by not supporting long-running active threads of computation, fully asynchronous communication, and access to host specific information. We present Perpetual-WS, middleware that supports interaction between replicated Web Services while providing strict fault isolation guarantees. Perpetual-WS supports both synchronous and asynchronous message passing and enables an application model that supports long-running active threads of computation. We present an implementation based on Axis2 and performance evaluations demonstrating only a moderate decrease in throughput due to replication

An effective services framework for sharing educational resources

Nowadays, the growing number of software tools to support e-learning and the data they rely upon are valuable resources, supporting different aspects of the complex learning and teaching processes, including designing learning content, delivering learning activities, and evaluating students’ learning performance. However, sharing these educational resources efficiently and effectively is a challenge: there are many resources, these have not been described accurately and in general they do not interoperate, and it is common for the tools to rely on different technologies. This thesis explores a solution – a novel educational services framework – to improve the sharing of current e-resources, by applying the latest service technologies in the context of higher education. Our findings suggest that the proposed framework is effective to deal with the technical and educational issues in resource discovery, interoperability and reusability, however, there are still technical challenges remaining for implementing this service framework. This research is divided into 3 phases. The first phase investigates the sharing of elearning resources through a literature survey, and identifies limitations on current developments. In the second phase, the current problems relating to resource sharing are addressed by a proposed educational service framework, which contains both educational and technical components. Through a case study, nine e-learning services and their dataflows are identified. To determine the technical components of the framework, a novel Educational Service Architecture is proposed, which allows resources to be better described, structured and connected, by following the principles of discoverability, interoperability and reusability in service technologies. In the third phase, part of the framework is implemented and evaluated by two studies. In the first study, users’ experiences were collected via a simulation experiment, to compare the effectiveness of a service prototype with that of the use of current technologies. During the second part of the evaluation, technical challenges for implementing the services framework were identified via a case study, involving the implementation of another service prototype

Lab4ws: A Testbed For Web Services

Web services are increasingly being deployed in clusters located at geographically distributed datacenters linked via the Internet. Ideally, before the actual deployment of such a complex service, engineers would like to have a way to quantitatively analyze aspects such as performance, availability, and the load balancing achieved by the different solutions available. In this paper we present the Lab4WS, a testbed designed to reduce the difficulties associated with the evaluation of LAN and/or WAN deployed web services. The key features of Lab4WS are illustrated by using it to compare four WAN load balancing mechanisms (DNS-based, server-based, dispatcher-based, and client-based). © 2009 IEEE.(2002) TPC Benchmark W - Specification 1.8, , http://www.tpc.org/tpcw/spec/tpcwV1.8.pdf, FebruaryColajanni, M., Yu, P.S., A performance study of robust load sharing strategies for distributed heterogeneous web server systems (2002) IEEE Transactions on Knowledge and Data Engineering, 14 (2), pp. 398-414Cardellini, V., Colajanni, M., Yu, P.S., Dynamic load balancing on web-server systems (1999) IEEE Internet Computing, 3 (3), pp. 28-39Ye, X., Shen, Y., A middleware for replicated web services (2005) Proceedings - 2005 IEEE International Conference on Web Services, ICWS 2005, 2005, pp. 631-638. , DOI 10.1109/ICWS.2005.8, 1530855, Proceedings - 2005 IEEE International Conference on Web Services, ICWS 2005Salas, J., Perez-Sorrosal, F., Patio-Martnez, M., Jimnez-Peris, R., (2006) Wsreplication: A Framework for Highly Available Web Services, pp. 357-366. , WWW, L. Carr, D. D. Roure, A. Iyengar, C. A. Goble, and M. Dahlin, Eds.ACMFang, C.-L., Liang, D., Lin, F., Lin, C.-C., Fault tolerant Web Services (2007) Journal of Systems Architecture, 53 (1), pp. 21-38. , DOI 10.1016/j.sysarc.2006.06.001, PII S1383762106000609Osrael, J., Froihofer, L., Weghofer, M., Gschka, K.M., Axis2-based replication middleware forweb services (2007) Proceedings of the IEEE International Conference on Web Services 2007 (ICWS 2007), pp. 591-598. , IEEE Computer SocietyChatterjee, D., Tari, Z., Zomaya, A., A task-based adaptive TTL approach for Web server load balancing (2005) Proceedings - IEEE Symposium on Computers and Communications, pp. 877-884. , Proceedings - 10th IEEE Symposium on Computers and Communications, ISCC 2005Cardellini, V., Colajanni, M., Yu, P.S., Request redirection algorithms for distributed web systems (2003) IEEE Trans. Parallel Distrib. Syst., 14 (4), pp. 355-368Liu, L., Lu, Y., Dynamic traffic controls for web-server networks (2004) Comput. Networks, 45 (4), pp. 523-536Conti, M., Gregori, E., Lapenna, W., Client-side content delivery policies in replicated web services: Parallel access versus single server approach (2005) Perform. Eval., 59 (2-3), pp. 137-157Mendonça, N.C., Silva, J.A.F., Anido, R.O., Client-side selection of replicated web services: An empirical assessment (2008) The Journal of Systems and Software, 81, pp. 1346-136