Providing Freshness for Cached Data in Unstructured Peer-to-Peer Systems

Replication is a popular technique for increasing data availability and improving perfor- mance in peer-to-peer systems. Maintaining freshness of replicated data is challenging due to the high cost of update management. While updates have been studied in structured networks, they have been neglected in unstructured networks. We therefore confront the problem of maintaining fresh replicas of data in unstructured peer-to-peer networks. We propose techniques that leverage path replication to support efficient lazy updates and provide freshness for cached data in these systems using only local knowledge. In addition, we show that locally available information may be used to provide additional guarantees of freshness at an acceptable cost to performance. Through performance simulations based on both synthetic and real-world workloads from big data environments, we demonstrate the effectiveness of our approach

DSL-Lab: a Platform to Experiment on Domestic Broadband Internet

This report presents the design and building of DSL-Lab, a platform for distributed computing and peer-to-peer experiments over the domestic broadband Internet. Experimental platforms such as PlanetLab and Grid'5000 are promising methodological approaches for studying distributed systems. However, both platforms focus on high-end services and network deployments on only a restricted part of the Internet, and as such, they do not provide experimental conditions of residential broadband networks. DSL-Lab is composed of 40 low-power and noiseless nodes, which are hosted by participants, using users' xDSL or cable access to the Internet. The objective is twofold: 1) to provide accurate and customized measures of availability, activity and performance in order to characterize and tune the models of such resources~; 2) to provide an experimental platform for new protocols, services and applications, as well as a validation tool for simulators and emulators targeting these systems. In this article, we report on the software infrastructure (security, resources allocation, power management) as well as on the first results and experiments achieved

Comparative indicators for cancer network management in England: Availability, characteristics and presentation

BACKGROUND: In 2000, the national cancer plan for England created 34 cancer networks, new organisational structures to coordinate services across populations varying between a half and three million people. We investigated the availability of data sets reflecting measures of structure, process and outcome that could be used to support network management. METHODS: We investigated the properties of national data sets relating to four common cancers - breast, colorectal, lung and prostate. We reviewed the availability and completeness of these data sets, identified leading items within each set and put them into tables of the 34 cancer networks. We also investigated methods of presentation. RESULTS: The Acute Hospitals Portfolio and the Cancer Standards Peer Review recorded structural characteristics at hospital and cancer service level. Process measures included Hospital Episode Statistics, recording admissions, and Hospital Waiting-List data. Patient outcome measures included the National Survey of Patient Satisfaction for cancer, and cancer survival, drawn from cancer registration. Data were drawn together to provide an exemplar indicator set a single network, and methods of graphical presentation were considered. CONCLUSION: While not as yet used together in practice, comparative indicators are available within the National Health Service in England for use in performance assessment by cancer networks

Systematizing Decentralization and Privacy: Lessons from 15 Years of Research and Deployments

Decentralized systems are a subset of distributed systems where multiple authorities control different components and no authority is fully trusted by all. This implies that any component in a decentralized system is potentially adversarial. We revise fifteen years of research on decentralization and privacy, and provide an overview of key systems, as well as key insights for designers of future systems. We show that decentralized designs can enhance privacy, integrity, and availability but also require careful trade-offs in terms of system complexity, properties provided, and degree of decentralization. These trade-offs need to be understood and navigated by designers. We argue that a combination of insights from cryptography, distributed systems, and mechanism design, aligned with the development of adequate incentives, are necessary to build scalable and successful privacy-preserving decentralized systems