1,721,030 research outputs found
On the Performance and Effectiveness of Digital Contact Tracing in the Second Wave of COVID-19 in Italy
Full text linkContact-tracing smartphone applications have been developed and used as a complement to manual contact tracing in the COVID-19 pandemic. The goal of these apps is to trace contacts between people and notify the mobile phone owners when one of their contacts tested positive. People who receive a notification should behave as exposed people, take a test, and possibly isolate themselves until they receive the result. Unfortunately, identifying contacts based on distance is technically a daunting task: apps can be configured conservatively (a very small number of people are notified, limiting the effectiveness of the app) or they may be more tolerant and produce a high number of notifications but also of false positives. We review the data available from Immuni, the Italian app, which provides detailed figures on the notifications sent and the positive users, and we show that Immuni was configured to generate a very large amount of notifications. We estimate the testing resources that the health system would have needed if the app was downloaded by 100% of the adult population, and every notified person would require a test. In such conditions, Immuni would have generated a number of tests orders of magnitude higher than what was available. We compare the performance of Immuni with the currently available literature on other apps and observe that contact-tracing apps had a limited impact on the second wave of the COVID-19 pandemic. As contact tracing exposes citizens to privacy risks, we discuss some ways to reshape the goal of the apps to achieve a better tradeoff between social benefit and risk
A collaborative firewall for wireless ad-hoc social networks
No full textA collaborative firewall can be realized in a multi-hop distributed wireless network when all or some of the nodes in the network agree on a filtering policy and enforce it when routing a packet. Cooperative firewalling introduces many challenges, how to distribute the rules, how to enforce them, how to reduce the global rule-set in order to limit the impact on the network performance. This paper studies the performance of a collaborative firewall when only a subset of the nodes of the ad-hoc network filter the packets. In order to achieve higher performances the integration with OLSR protocol is proposed. Simulations on realistic scenarios are performed and the source code of the simulator is released
Pharmacophore-based optimization of affinity and selectivity toward a1-adrenergic receptors
No full textLa misurazione del rischio di credito per il settore delle costruzioni in Italia
No full textIl settore delle costruzioni in Italia si caratterizza per un’elevata probabilità di insolvenza delle
imprese e la recente crisi dell’immobiliare ha dimostrato l’importanza di una corretta misurazione
del rischio del settore. L’articolo si propone di misurare il rischio delle imprese di costruzioni
utilizzando la metodologia proposta da Moody’s e di valutare i limiti dell’approccio
applicato alla realtà italiana. I risultati dimostrano che la metodologia basata unicamente su dati
di bilancio non permette di prevedere correttamente il rischio di un settore con forte presenza
di imprese di piccole dimensioni e tale limite risulta più evidente nelle fasi di crisi del mercat
On the Properties of Next Generation Wireless Backhaul
Full text linkWith the advent of 5G, cellular networks require a high number of base stations, possibly interconnected with wireless links, an evolution introduced in the last revision of 5G as the Integrated Access and Backhaul (IAB). Researchers are now working to optimize the complex topologies of the backhaul network, using synthetic models for the underlying visibility graph, i.e., the graph of possible connections between the base stations. The goal of this paper is to provide a novel methodology to generate visibility graphs starting from real data (and the data sets themselves together with the source code for their manipulation), in order to base the IAB design and optimization on assumptions that are as close as possible to reality. We introduce a GPU-based method to create visibility graphs from open data, we analyze the properties of the realistic visibility graphs, and we show that different geographic areas produce very different graphs. We run state-of-the-art algorithms to create wireless backhaul networks on top of visibility graphs, and we show that the results that exploit synthetic models are far from those that use our realistic graphs. Our conclusion is that the data-based approach we propose is essential to design mobile networks that work in a variety of real-world situations
Infective flooding in low-duty-cycle networks, properties and bounds
Full text linkFlooding information is an important function in many networking applications. In some networks, as wireless sensor networks or some ad-hoc networks it is so essential as to dominate the performance of the entire system. Exploiting some recent results based on the distributed computation of the eigenvector centrality of nodes in the network graph and classical dynamic diffusion models on graphs, this paper derives a novel theoretical framework for efficient resource allocation to flood information in mesh networks with low duty-cycling without the need to build a distribution tree or any other distribution overlay. Furthermore, the method requires only local computations based on each node neighborhood. The model provides lower and upper stochastic bounds on the flooding delay averages on all possible sources with high probability. We show that the lower bound is very close to the theoretical optimum. A simulation-based implementation allows the study of specific topologies and graph models as well as scheduling heuristics and packet losses. Simulation experiments show that simple protocols based on our resource allocation strategy can easily achieve results that are very close to the theoretical minimum obtained building optimized overlays on the network
WiMAX Network Security
No full textThe possible usage scenarios of a WiMAX service network are extremely various. The network can support static and mobile users roaming in a metropolitan area, the kind of traffic can be the typical Internet browsing or real-time traffic with stringent QoS constraints. The components of a WiMAX network must assure that all these needs are fulfilled. To reach this goal, all the layers of the OSI stack are required to co-operate in order to guarantee security, session establishment, fast handover and correct quality levels
Security analiysis of IEEE 802.16
No full textThis paper analyzes some critical security issues in the family of IEEE 802.16 standard that has not been addressed so far. In particular two of the key features of the standard, the dynamic resources allocation and the mesh mode revealed to be vulnerable to attacks that represent serious threats to the robustness and privacy of the communications. In the first case the attacker is able to reduce bandwidth assigned to its neighbors, with the aim of obtaining more resources for himself;
in the second case, we observed that there might be no real privacy in communications between two nodes of the mesh network. These vulnerabilities are still present even after the latest amendment to the standard, IEEE 802.16e that solved some previously addressed security flaws
S.T.R.E.S.S. : Stress Testing and Reverse Engineering for System Security
Full text linkIn modern wireless networks the functions included into layer
II have to deal with complex problems, such as security and
access control, that were previously demanded to upper layers.
This growing complexity led some vendors to implement layer
II primitives directly in software, e.g. IEEE 802.11i has been
largely distributed as a software patch to be used with legacy
802.11b/g hardware. In any extremely complex software the
likelihood of committing errors during the implementation raises,
and it is well known that software bugs can lead to instability
of the system and possibly to security vulnerability. Software
bugs are the most common cause of successful attacks against
any kind of network and represent a real plague for system
administrators. Stress test is a widely used methodology to
find and eliminate software bugs. In this paper we present a
platform to perform a stress test of generic network protocols
implementations but especially optimized for Layer II stress tests,
that present specific problems. With our approach a generic
network protocol described with ABNF language can be tested
transmitting arbitrary frame sequences and interpreting the
responses to verify consistence with the communication standard
used. Our platform can interact dynamically with the tested
machine (an access point, a router etc.) to verify its robustness
and its compliance with the standard. Experiments confirmed the
validity of our approach both as a stress test technique for system
under development and as a reverse engineering technique for
interaction with closed source system
On Cost-Effective, Reliable Coverage for LoS Communications in Urban Areas
Full text linkThe use of ultra high frequencies in 5G and future networks to improve transmission speeds and capacity requires that users' equipment remain in Line of Sight with the access antennas most of the service time. This requirement implies a change in perspective to plan the coverage: Antennas cannot be placed on roofs or remote antenna sites, and a robust coverage is based on multi-antenna visibility from any point. This paper tackles the problem of public street coverage in urban areas with a data-driven methodology. Starting from 3D digital maps, we formalize the problem of antenna placement as a set coverage problem and leverage powerful heuristics to implement a general algorithm that allows the exploration of different policies, returning the detailed coverage, the antenna placement, and the cost of the coverage. Results on 15 areas in 3 Italian cities show the properties of different policies and confirm for the first time on large scale real data the feasibility of Line of Sight communications with a sustainable number of antennas per km2
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