The "Biologically-Inspired Computing" Column

Self-managing systems, whether viewed from the perspective of Autonomic Computing, or from that of another initiative, offers a holistic vision for the development and evolution of biologically-inspired computer-based systems. It aims to bring new levels of automation and dependability to systems, while simultaneously hiding their complexity and reducing costs. A case can certainly be made that all computer-based systems should exhibit autonomic properties [6], and we envisage greater interest in, and uptake of, autonomic principles in future system development

Incentive-driven QoS in peer-to-peer overlays

A well known problem in peer-to-peer overlays is that no single entity has control over the software, hardware and configuration of peers. Thus, each peer can selfishly adapt its behaviour to maximise its benefit from the overlay. This thesis is concerned with the modelling and design of incentive mechanisms for QoS-overlays: resource allocation protocols that provide strategic peers with participation incentives, while at the same time optimising the performance of the peer-to-peer distribution overlay. The contributions of this thesis are as follows. First, we present PledgeRoute, a novel contribution accounting system that can be used, along with a set of reciprocity policies, as an incentive mechanism to encourage peers to contribute resources even when users are not actively consuming overlay services. This mechanism uses a decentralised credit network, is resilient to sybil attacks, and allows peers to achieve time and space deferred contribution reciprocity. Then, we present a novel, QoS-aware resource allocation model based on Vickrey auctions that uses PledgeRoute as a substrate. It acts as an incentive mechanism by providing efficient overlay construction, while at the same time allocating increasing service quality to those peers that contribute more to the network. The model is then applied to lagsensitive chunk swarming, and some of its properties are explored for different peer delay distributions. When considering QoS overlays deployed over the best-effort Internet, the quality received by a client cannot be adjudicated completely to either its serving peer or the intervening network between them. By drawing parallels between this situation and well-known hidden action situations in microeconomics, we propose a novel scheme to ensure adherence to advertised QoS levels. We then apply it to delay-sensitive chunk distribution overlays and present the optimal contract payments required, along with a method for QoS contract enforcement through reciprocative strategies. We also present a probabilistic model for application-layer delay as a function of the prevailing network conditions. Finally, we address the incentives of managed overlays, and the prediction of their behaviour. We propose two novel models of multihoming managed overlay incentives in which overlays can freely allocate their traffic flows between different ISPs. One is obtained by optimising an overlay utility function with desired properties, while the other is designed for data-driven least-squares fitting of the cross elasticity of demand. This last model is then used to solve for ISP profit maximisation

A Delay-Constrained Middleware Architecture for Disseminating Information in Wireless Sensor Networks

RÉSUMÉ Les réseaux de capteurs sans fil (WSNs: Wireless Sensor Networks) constituent un domaine de recherche très actif et qui reçoit beaucoup d'attention de la part de la communauté scientifique. Ces réseaux offrent la possibilité de surveiller, de rassembler et de transmettre des données de l'environnement, en utilisant des noeuds appelés capteurs. Ces données sont généralement recueillies par une entité centrale qui les rend disponibles aux utilisateurs et à d’autres réseaux, comme Internet et les réseaux cellulaires. À cette fin, il existe des techniques, dites de diffusion, qui s’occupent de transférer les données à toutes les destinations. En particulier, le choix d’une technique de diffusion dépend de l'application utilisée. Par exemple, les applications à contraintes de délai imposent une contrainte de délai de bout-en-bout au processus de diffusion des données afin de coordonner des opérations de recherche et de sauvetage, et d'alerter les gens lors d’une opération d’urgence. Ce mémoire propose une architecture d'intergiciel qui sert de médiateur entre les applications à contraintes de délai et les techniques de diffusion de données. Une preuve de concept est faite pour montrer la faisabilité de l'architecture et l'efficacité d'un tel médiateur. L’analyse du prototype montre, entre autres, que le pourcentage de succès de transmission de l’intergiciel est largement supérieur à celui des protocoles individuels, tels que le service de messagerie (SMS: Short Message Service), le courriel et Twitter. ----------ABSTRACT Wireless Sensor Networks (WSNs) have been gaining a lot of attention from the research community. They offer the possibility to monitor and collect information from the environment, using small sensor nodes. Generally, the information is later transmitted towards a centralized entity that serves as an interface to users, or to other networks (e.g., cellular networks or Internet). Data dissemination techniques are in charge of the sending process to all destinations. The technique is chosen depending on the application. For instance, delay-constrained applications impose end-to-end delay constraints to coordinate rescue operations and warn people about critical events. This thesis proposes a middleware architecture that serves as a mediator between delay-constrained applications and data dissemination techniques. The architecture is intended to disseminate information from wireless sensor networks to Internet and cellular networks, considering end-to-end delay constraints. A proof of concept is done to validate its feasibility and effectiveness. More specifically, the results show that the percentage of success is much better using a middleware as a mediator than using individual protocols for data dissemination, such as Short Message Service (SMS), email and twitter

Advanced languages and techniques for trust negotiation.

The Web is quickly shifting from a document browsing and delivery system to a hugely complex ecosystem of interconnected online applications. A relevant portion of these applications dramatically increase the number of users required to dynamically authenticate themselves and to, on the other hand, to identify the service they want to use. In order to manage interactions among such users/services is required a flexible but powerful mechanism. Trust management, and in particular trust negotiation techniques, is a reasonable solution. In this work we present the formalization of the well known trust negotiation framework Trust-X, of a rule-based policy definition language, called X-RNL. Moreover, we present the extension of both the framework and of the language to provide advanced trust negotiation architectures, namely negotiations among groups. We also provide protocols to adapt trust negotiations to mobile environments, specifically, we present protocols allowing a trust negotiation to be executed among several, distinct, sessions while still preserving its security properties. Such protocols have also been extended to provides the capability to migrate a ongoing trust negotiation among a set of known, reliable, subjects. Finally, we present the application of the previously introduced trust negotiation techniques into real world scenarios: online social networks, critical infrastructures and cognitive radio networks