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

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

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

Bandgap widening in macroporous silicon photonic crystals by multiperiodic structures

Large bandgaps with low transmission in 3D macroporous silicon photonic crystals have been proved as an interesting technology for the development of optical filters and spectroscopic MIR gas sensors. The aim of this study is the investigation of different bandgap widening methods based on multiperiodic structures for 3D macroporous silicon photonic crystals. To do so, chirped modulations and structures with different periodicity groups have been modelled and theoretically analysed by means of 3D FDTD simulations. They have revealed that by using different decreasing periodicity groups, bandgaps with null transmission and widths as high as 1800 nm, 4 times the original single periodicity photonic crystal bandgap, can be obtained. Furthermore, it has been shown that a resonant cavity with a 20% transmission can be placed in a 1 µm wide bandgap. The results open a way to use this type of structures not only for gas sensing but also for other purposes such as wide stop-band filters, selective filters or broadband mirrors.Peer ReviewedPostprint (published version

A technological overview of the guifi.net community network

This work presents a technological analysis of guifi.net, a free, neutral, and open-access community network. Guifi.net consists of more than 27,000 operational nodes, which makes it the world’s largest community network in terms of the number of nodes and coverage area. This paper describes the characteristics of the network, the link level topology, its growth over a decade, and its resilience in terms of availability and reachability of network nodes. Our study is based on open data published by guifi.net regarding its nodes and wireless links, monitoring information, community database, and its web portal. The data includes historical information that covers the lifetime of the network. The scale and diversity of the network requires a separate analysis of the subsets of the entire dataset by area or by separating the core from the leaf nodes. This shows some degree of diversity in local characteristics caused by several demographic, geographic, technological, and network design factors. We focus on the following aspects: technological network diversity, topology characteristics, evolution of the network over time, analysis of robustness, and its effect on networking service availability. In addition, we analyse how the community, the technology used, the geographical region where the network is deployed, and its self-organised structure shape the network properties and determine its strengths and weaknesses. The study demonstrates that the guifi.net community network is diverse in technological choices for hardware, link protocols, and channels and uses a combination of routing protocols yet provides a common private IP network. The graph topology follows a power- law distribution for links in regions up to a few thousand Km 2 , limited to the scope of wireless links. Network growth has two aspects: a geographic growth of the network core using long distance links with wireless or fibre, and the local growth in density with leaf low-cost leaf nodes. The resilience of the network derived from the nodes’ uptime and the structure of the graph varies across different regions with more fragile leafs than core nodes and diverse degrees of graph resilience to random failures or coordinated attacks, such as natural causes, depending on the network planning, structure, and maturity. The guifi.net community network results from a loosely coupled and decentralised organic growth that exhibits large local differences, diverse growth, and maturity under a common community license and social network.Peer ReviewedPostprint (author's final draft

Time series analysis to predict link quality of wireless community networks

Community networks have emerged under the mottosCommunity networks have emerged under the mottos “break the strings that are limiting you”, “don't buy the network, be the network” or “a free net for everyone is possible”. Such networks create a measurable social impact as they provide to the community the right and opportunity of communication. As any other network that mixes wired and wireless links, the routing protocol must face several challenges that arise from the unreliable nature of the wireless medium. Link quality tracking helps the routing layer to select links that maximize the delivery rate and minimize traffic congestion. Moreover, link quality prediction has proved to be a technique that surpasses link quality tracking by foreseeing which links are more likely to change its quality. In this work, we focus on link quality prediction by means of a time series analysis. We apply this prediction technique in the routing layer of large-scale, distributed, and decentralized networks. We demonstrate that it is possible to accurately predict the link quality in 98% of the instances, both in the short and the long terms. Particularly, we analyse the behaviour of the links globally to identify the best prediction algorithm and metric, the impact of lag windows in the results, the prediction accuracy some time steps ahead into the future, the degradation of prediction over time, and the correlation of prediction with topological features. Moreover, we also analyse the behaviour of links individually to identify the variability of link quality prediction between links, and the variability of link quality prediction over time. Finally, we also present an optimized prediction method that considers the knowledge about the expected link quality values.Peer ReviewedPostprint (author's final draft