177 research outputs found
Reti acustiche sottomarine: progettazione di protocolli e problematiche di sicurezza
No full textNonostante le reti sottomarine siano ormai studiate da tempo, esistono an- cora molte difficolt`a da affrontare, causate dell’avversit`a del canale acustico, per poter stabilire una comunicazione wireless affidabile. Inoltre, lo sviluppo di nuovi modem a basso costo apre la strada a nuove applicazioni per le reti sottomarine, come, ad esempio, applicazioni per i futuri porti intelligenti. Ad oggi, comunque, i principali ambiti di utilizzo delle reti sottomarine ri- mangono quello militare e di pubblica sicurezza, la cui rilevanza pone inoltre ulteriori sfide legate anche alla sicurezza delle reti. Infatti, un’interruzione dei servizi forniti dalle reti causata da un attacco potrebbe portare a se- rie conseguenze. Tuttavia fino ad ora, gli aspetti di sicurezza delle reti sottomarine non sono stati adeguatamente studiati e l’utilizzo di contro- misure progettate per reti terrestri non sempre risulta possibile. In questa tesi ci occuperemo sia della progettazione di protocolli di comunicazione efficaci, che dell’analisi di attacchi e contromisure nelle reti sottomarine. Prima di tutto, progetteremo un protocollo MAC per la raccolta di dati da sensori sottomarini in ambiente portuale e analizzeremo le prestazioni com- plessive della rete, dalla trasmissione dei dati dai sensori fino alla ricezione sulla costa. L’analisi delle prestazioni verr`a effettuata sia attraverso sim- ulazioni che attraverso test sperimentali. Successivamente, ci dedicheremo all’analisi della sicurezza nelle reti sottomarine. Cominceremo analizzando degli scenari in cui gli attaccanti dispongono di una conoscenza limitata dei protocolli di rete, studiando gli effetti di attacchi di tipo jamming e re- play. Progetteremo, poi, contromisure basate sulla reputazione di un nodo, a protezione di attacchi piu` sofisticati in cui il nodo attaccante conosce il funzionamento e le vulnerabilit`a dei protocolli e sfrutta queste conoscenze per attaccare la rete. In entrambi i casi, ci concentreremo sulle peculiarit`a delle comunicazioni acustiche che rendono gli attacchi e le contromisure differenti rispetto a quelli in ambito terrestre.Although underwater networks have been developed for considerable time now, the harshness of the acoustic channel still poses a lot of challenges for wireless communications. In addition, the development of low cost modems paves the way for new applications in different scenarios, such as future smart ports. Nevertheless, for the time being, the use of underwater net- works is still mainly related to military and public safety applications, whose relevance arises further challenges related also to network security. Indeed, a network failure caused by an attack could lead to serious consequences. However, security problems have not been deeply investigated so far, and the implementation of terrestrial network countermeasures in the underwater field is not always feasible. In this thesis we focus on both open challenges previously described: the design of efficient communication protocols, and the analysis of attacks and countermeasures in underwater networks. First, we consider a data collection service in a smart port scenario, designing a Medium Access Control (MAC) protocol for this service and analyzing the End-To-End (E2E) transmission, from sensor nodes to the shore. We eval- uate the performance through both simulations and field tests. Afterward, we analyze security issues in underwater networks. We start by analyzing attackers with limited knowledge of the protocol stack, studying the effect of jamming and replay attacks. We then move to the design of a counter- measure based on a trust metric to be employed against more sophisticated attacks in which the malicious node can exploit the protocol’s behavior and vulnerabilities to carry out the attacks. In both cases we specifically focus on the peculiarities of the acoustic channel that differentiate attacks and countermeasures in underwater networks from their terrestrial counterpart
Modeling the performance of optical modems in the DESERT underwater network simulator
No full textWhile in the past decades only low rate acoustic modems were employed for underwater wireless communication, nowadays also high rate optical modems can be used for short range communication, up to a few hundred meters. A key ques- tion is what is the expected performance of a modem in a given scenario, in order to predict the coverage range of the system in a network deployment. In the literature, many models have been proposed, but each of them is limited to simulating a particular device or a limited set of scenarios. However, in the last decade, many sea evaluations of optical communications performance in different water conditions have been performed, and many datasets published and presented to the research community. In this paper we collect a database of performance figures of optical modems, including it in the DESERT Underwater network simulator. In addition, we simulate optical communication in a real scenario, thanks to the water measurements retrieved during the ALOMEX'15 NATO cruise
Multi-hop range extension of a wireless remote control for underwater vehicles
No full textIn this paper, we explore the feasibility of controlling an Underwater Autonomous Vehicle (AUV) from a base station, via a multi-hop wireless control channel. As a first step, we identify which networking and data-link protocols can be employed in this system. Then, we design a simple but effective routing protocol for this scenario. Finally, we simulate the performance of the system during missions of interest, and conclude by discussing the effectiveness of wireless multi-hop control methods for AUVs
AUVs Telemetry Range Extension through a Multimodal Underwater Acoustic Network
No full textIn this paper, we describe an underwater multi-hop network scenario based only on acoustic modems operating at different frequencies. The idea is to remotely control an Autonomous Underwater Vehicle (AUV) and verify whether it is able to follow the path sent by a control station (CTR) in the form of consecutive waypoints. The AUV sends back packets that can be monitoring or control information. We tested by simulation different MAC layer protocols to compare their performance in terms of throughput and packet delivery delay, in particular focusing on both contention-free (TDMA-based) and contention-based (CSMA-based) protocols, to analyze which solution performs better in different network conditions varying the amount of traffic generated by the AUV during its mission
Underwater Jamming Attacks as Incomplete Information Games
No full textAutonomous Underwater Vehicles (AUVs) have several fundamental civilian and military applications, and Denial of Service (DoS) attacks against their communications are a serious threat. In this work, we analyze such an attack using game theory in an asymmetric scenario, in which the node under attack does not know the position of the jammer that blocks its signals. The jammer has a dual objective, namely, disrupting communications and forcing the legitimate transmitter to spend more energy protecting its own transmissions. Our model shows that, if both nodes act rationally, the transmitter is able to quickly reduce its disadvantage, estimating the location of the jammer and responding optimally to the attack
On the connection between quark propagation and hadronization
No full textWe investigate the properties and structure of the recently discussed “fully inclusive jet correlator”, namely, the gauge-invariant field correlator characterizing the final state hadrons produced by a free quark as this propagates in the vacuum. Working at the operator level, we connect this object to the single-hadron fragmentation correlator of a quark, and exploit a novel gauge invariant spectral decomposition technique to derive a complete set of momentum sum rules for quark fragmentation functions up to twist-3 level; known results are recovered, and new sum rules proposed. We then show how one can explicitly connect quark hadronization and dynamical quark mass generation by studying the inclusive jet’s gauge-invariant mass term. This mass is, on the one hand, theoretically related to the integrated chiral-odd spectral function of the quark, and, on the other hand, is experimentally accessible through the E and twist-3 fragmentation function sum rules. Thus, measurements of these fragmentation functions in deep inelastic processes provide one with an experimental gateway into the dynamical generation of mass in Quantum Chromodynamics
Quark fragmentation as a probe of dynamical mass generation
No full textWe address the propagation and hadronization of a struck quark by studying the gauge invariance of the color-averaged cut quark propagator, and by relating this to the single inclusive quark fragmentation correlator by means of new sum rules. Using suitable Wilson lines, we provide a gauge-invariant definition for the mass of the color-averaged dressed quark and decompose this into the sum of a current and an interaction-dependent component. The latter, which we argue is an order parameter for dynamical chiral symmetry breaking, also appears in the sum rule for the twist-3 ilde{E} fragmentation function, providing a specific experimental way to probe the dynamical generation of mass in Quantum Chromo Dynamics
?Jacques Roumain, Signori della rugiada, trad. di Alessandro Costantini, Edizioni Lavoro?
No full textPresentation of the book "Signori della rugiada" of the author Jacques Roumain, translated by Alessandro Costantini.Presentazione del romanzo "Signori della rugiada" dell\u27autore Jacques Roumain, tradotto da Alessandro Costantini
Optimality conditions for an extended tumor growth model with double obstacle potential via deep quench approach
No full textIn this work, we investigate a distributed optimal control problem for an extended phase field system of Cahn–Hilliard type which physical context is that of tumor growth dynamics. In a previous contribution, the author has already studied the corresponding problem for the logarithmic potential. Here, we try to extend the analysis by taking into account a non-smooth singular nonlinearity, namely the double obstacle potential. Due to its non-smoothness behavior, the standard procedure to characterize the necessary conditions for the optimality cannot be performed. Therefore, we follow a different strategy which in the literature is known as the “deep quench” approach in order to obtain some optimality conditions that have to be interpreted in a more general framework. We establish the existence of optimal controls and some first-order optimality conditions for the system are derived by employing suitable approximation schemes
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