Topology patterns of a community network: Guifi.net

This paper presents a measurement study of the topology and its effect on usage of Guifi.net, a large-scale community network. It focuses on the main issues faced by community network and lessons to consider for its future growth in order to preserve its scalability, stability and openness. The results show the network topology as an atypical high density Scale-Free network with critical points of failure and poor gateway selection or placement. In addition we have found paths with a large number of hops i.e. large diameter of the graph, and specifically long paths between leaf nodes and web proxies. The usage analysis using a widespread web proxy service confirms that these topological properties have an impact on the user experience

Design and implementation of a simulator to explore cooperation in distributed environments

La manca de recursos computacionals dels ordinadors personals, afegit al increment de requeriments cada vegada mes patent en el software actual, està demanant urgentment a una redefinició dels paradigmes de computació que hi havia fins ara. Les xarxes de computació distribuïda son una de les solucions que actualment s'estan valorant per resoldre el problema de la manca de recursos hardware. No obstant, la aplicació d'aquestes solucions es veu aturada per la manca de coneixement sobre el seu funcionament i la necessitat tecnològica de resoldre reptes que la recerca i la innovació encara no han descobert com encarar. Un dels problemes pendents és com generar la suficient confiança entre els usuaris i per tant, assegurar un cert nivell de cooperació dins de la xarxa, o el que és el mateix: una col·laboració bidireccional. Aquest projecte de màster pretén explorar els diferents mecanismes basats en incentius i topologies per promoure la cooperació utilitzant com a eina un simulador capaç de valorar aquests indicadors sobre múltiples topologies de xarxa, aplicacions i estratègies sobre sistemes GRID distribuïts. Per tant, una primera part est`a enfocada a l'estudi de la cooperació e identificar quins paràmetres poden portar-la a terme, i quins no influeixen. El segon objectiu és la creació d'una eina prou modular i potent com per extreure suficients conclusions de la seva utilització sobre diferents escenaris i, finalment, una ultima part centrada en l'anàlisi de resultats i la creació d'un protocol de negociació verificable per la compartició de recursos en xarxes distribuïdes

Understanding collaboration in volunteer computing systems

Volunteer computing is a paradigm in which devices participating in a distributed environment share part of their resources to help others perform their activities. The effectiveness of this computing paradigm depends on the collaboration attitude adopted by the participating devices. Unfortunately for software designers it is not clear how to contribute with local resources to the shared environment without compromising resources that could then be required by the contributors. Therefore, many designers adopt a conservative position when defining the collaboration strategy to be embedded in volunteer computing applications. This position produces an underutilization of the devices’ local resources and reduces the effectiveness of these solutions. This article presents a study that helps designers understand the impact of adopting a particular collaboration attitude to contribute with local resources to the distributed shared environment. The study considers five collaboration strategies, which are analyzed in computing environments with both, abundance and scarcity of resources. The obtained results indicate that collaboration strategies based on effort-based incentives work better than those using contribution-based incentives. These results also show that the use of effort-based incentives does not jeopardize the availability of local resources for the local needs.Peer ReviewedPostprint (published version

An Analysis of the Consequences of the General Data Protection Regulation on Social Network Research

This article examines the principles outlined in the General Data Protection Regulation in the context of social network data. We provide both a practical guide to General Data Protection Regulation--compliant social network data processing, covering aspects such as data collection, consent, anonymization, and data analysis, and a broader discussion of the problems emerging when the general principles on which the regulation is based are instantiated for this research area

Analysis of Multiplex Social Networks with R

Multiplex social networks are characterized by a common set of actors connected through multiple types of relations. The multinet package provides a set of R functions to analyze multiplex social networks within the more general framework of multilayer networks, where each type of relation is represented as a layer in the network. The package contains functions to import/export, create and manipulate multilayer networks, implementations of several state-of-the-art multiplex network analysis algorithms, e.g., for centrality measures, layer comparison, community detection and visualization. Internally, the package is mainly written in native C++ and integrated with R using the Rcpp package

Design and implementation of a simulator to explore cooperation in distributed environments

La manca de recursos computacionals dels ordinadors personals, afegit al increment de requeriments cada vegada mes patent en el software actual, està demanant urgentment a una redefinició dels paradigmes de computació que hi havia fins ara. Les xarxes de computació distribuïda son una de les solucions que actualment s'estan valorant per resoldre el problema de la manca de recursos hardware. No obstant, la aplicació d'aquestes solucions es veu aturada per la manca de coneixement sobre el seu funcionament i la necessitat tecnològica de resoldre reptes que la recerca i la innovació encara no han descobert com encarar. Un dels problemes pendents és com generar la suficient confiança entre els usuaris i per tant, assegurar un cert nivell de cooperació dins de la xarxa, o el que és el mateix: una col·laboració bidireccional. Aquest projecte de màster pretén explorar els diferents mecanismes basats en incentius i topologies per promoure la cooperació utilitzant com a eina un simulador capaç de valorar aquests indicadors sobre múltiples topologies de xarxa, aplicacions i estratègies sobre sistemes GRID distribuïts. Per tant, una primera part est`a enfocada a l'estudi de la cooperació e identificar quins paràmetres poden portar-la a terme, i quins no influeixen. El segon objectiu és la creació d'una eina prou modular i potent com per extreure suficients conclusions de la seva utilització sobre diferents escenaris i, finalment, una ultima part centrada en l'anàlisi de resultats i la creació d'un protocol de negociació verificable per la compartició de recursos en xarxes distribuïdes

Enhanced geometries of macroporous silicon photonic crystals for optical gas sensing applications

A macroporous silicon photonic crystal is designed and optimized theoretically for its use in gas sensing applications and IR optical filters. Light impinges perpendicularly onto the sample surface (vertical propagation) so a three-dimensional (3d) structure is used. For gas sensing, a sharp resonance is desired in order to isolate an absorption line of the gas of interest. The high Q-factors needed mandate the use of a plane defect inside the PhC to give rise to a resonant mode inside the bandgap tuned to the gas absorption line. Furthermore to allow gas passage through the device, an open membrane is required. This can affect the mechanical resilience. To improve the strength of the photonic crystal the pores are extended after the “active” 3d part. The number of modulations, and the extension length have been optimized to obtain the largest Q-factor with reasonable transmitted power. These proposed structures have been experimentally performed, probing an enhancement of almost an order of magnitude in the Q-factor in respect with the basic case. Simulations considering CO2 have been performed showing that the proposed structures are promising as precise optical gas sensors.Peer ReviewedPostprint (author's final draft

A Twitter-based study of the European Internet of Things

We present a methodology integrating social media data, data from qualitative research and network analysis. Qualitative insights gained from ethnographic fieldwork are used to collect and annotate social network data, and social media data is used as part of the ethnography to identify relevant actors and topics. The methodology is presented in the context of an analysis of the Internet of Things in the European context