1,721,530 research outputs found
An Experimental Evaluation and Characterization of VoIP over an LTE-A Network
No full textMobile telecommunications are converging towards all-IP solutions. This is the case of the Long Term Evolution (LTE) technology that, having no circuit-switched bearer to support voice traffic, needs a dedicated VoIP infrastructure, which often relies on the IP Multimedia Subsystem architecture. Most telecom operators implement LTE-A, an advanced version of LTE often marketed as 4{G} + , which achieves data rate peaks of 300 Mbps. Yet, although such novel technology boosts the access to advanced multimedia contents and services, telco operators continue to consider the VoIP market as the major revenue for their business. In this work, the authors propose a detailed performance assessment of VoIP traffic by carrying out experimental trials across a real LTE-A environment. The experimental campaign consists of two stages. First, we characterize VoIP calls between fixed and mobile terminals, based on a data-set that includes more than 750,000 data-voice packets. We analyze quality-of-service metrics such as round-trip time (RTT) and jitter, to capture the influence of uncontrolled factors that typically appear in real-world settings. In the second stage, we further consider VoIP flows across a range of codecs, looking at the trade-offs between quality and bandwidth consumption. Moreover, we propose a statistical characterization of jitter and RTT (representing the most critical parameters), identifying the optimal approximating distribution, namely the Generalized Extreme Value (GEV). The estimation of parameters through the Maximum Likelihood criterion, leads us to reveal both the short- and long-tail behaviour for jitter and RTT, respectively
Statistical Assessment of IP Multimedia Subsystem in a Softwarized Environment: A Queueing Networks Approach
No full textThe Next Generation 5G Networks can greatly benefit from the synergy between virtualization paradigms, such as the Network Function Virtualization (NFV), and service provisioning platforms such as the IP Multimedia Subsystem (IMS). The NFV concept is evolving towards a lightweight solution based on containers that, by contrast to classic virtual machines, do not carry a whole operating system and result in more efficient and scalable deployments. On the other hand, IMS has become an integral part of the 5G core network, for instance, to provide advanced services like Voice over LTE (VoLTE). In this paper we combine these virtualization and service provisioning concepts, deriving a containerized IMS infrastructure, dubbed cIMS, providing its assessment through statistical characterization and experimental measurements. Specifically, we: i) model cIMS through the queueing networks methodology to characterize the utilization of virtual resources under constrained conditions; ii) draw an extended version of the Pollaczek-Khinchin formula, which is useful to deal with bulk arrivals; iii) afford an optimization problem focused at maximizing the whole cIMS performance in the presence of capacity constraints, thus providing new means for the service provider to manage service level agreements (SLAs); iv) evaluate a range of cIMS scenarios, considering different queuing disciplines including also multiple job classes. An experimental testbed based on the open source platform Clearwater has been deployed to derive some realistic values of key parameters (e.g., arrival and service times)
No-preparation ceramic veneers: a systematic review.
No full textAim The main objective of the present systematic review was to investigate the validation of no-preparation ceramic veneers as restorations.
Materials and Methods Pubmed, Evidence-Based Dentistry, BMJ Clinical Evidence, Embase, Dynamed and Opengrey were analyzed in order to identify randomized controlled clinical trials evaluating the clinical outcomes of no-preparation ceramic veneers; manual researches were performed as well.
Results Database search produced 2551 records. After removal of duplicates and a careful examination of titles and abstracts, the reviewers excluded all of the studies. Manual and grey literature did not yield any other relevant article.
Conclusions Due to the lack of data, at the moment achieving a definitive clinical statement regarding the “no-prep” technique is not possible. Further clinical studies are needed to assess the effectiveness of no-preparation ceramic veneers. No-prep veneers can be considered as conservative treatments which should be carefully recommended and request a cautious selection of cases. Further controlled clinical researches are necessary to clearly identify predictable clinical protocols and evaluate the long-term outcomes of such restorations
Teaching quantum physics in the footsteps of Einstein
No full textA teaching-learning sequence designed to introduce some fundamental concepts of quantum physics to high school teachers is proposed. Some parts of the proposal can be adapted to be taught to advanced high school students themselves. The inspiration came from the recognition of the fact that the roots of many pivotal concepts of quantum physics, namely light quanta, wave-particle duality, and probability, were introduced for the first time in some paper by Albert Einstein. Moreover, this was done in a characteristically deep and illuminating way. A critical study of Einstein's papers should therefore be useful for teachers and students as well, in view of the fact that such concepts are often misconceived. The teaching-learning sequence can supplement usual historically oriented treatments of elementary quantum physics and can in turn be complemented by a discussion of some elementary tools of statistical physics, which may be not part of the learners' background. Preliminary results obtained with both teachers and pupils in high schools in southern Italy, which are very promising, are presented
A WNN-Based Approach for Network Intrusion Detection
No full textNowadays, Intrusion Detection Systems (IDSs) are becoming more and more effective since they can benefit from the flexibility offered by Machine Learning (ML) techniques. In this work we investigate the potentiality of the Weightless Neural Networks (WNNs) as a classification method of network attacks. Traditionally, WNNs have been exploited in the image classification field and are implemented through the WiSARD algorithm. Interestingly, our analysis reveals that, applied to the IDS realm, WNNs offer surprising results in terms of performance/time complexity trade-off with respect to other ML-based techniques. The experimental assessment is carried on by considering one of the most updated datasets (CIC-IDS) in the field of the intrusion detection, where two exemplary attacks to be detected are considered: Distributed Denial of Service (DDoS) and PortScan
Experimental Review of Neural-Based Approaches for Network Intrusion Management
No full textThe use of Machine Learning (ML) techniques in Intrusion Detection Systems (IDS) has taken a prominent role in the network security management field, due to the substantial number of sophisticated attacks that often pass undetected through classic IDSs. These are typically aimed at recognizing attacks based on a specific signature, or at detecting anomalous events. However, deterministic, rule-based methods often fail to differentiate particular (rarer) network conditions (as in peak traffic during specific network situations) from actual cyber attacks. In this article we provide an experimental-based review of neural-based methods applied to intrusion detection issues. Specifically, we i) offer a complete view of the most prominent neural-based techniques relevant to intrusion detection, including deep-based approaches or weightless neural networks, which feature surprising outcomes; ii) evaluate novel datasets (updated w.r.t. the obsolete KDD99 set) through a designed-from-scratch Python-based routine; iii) perform experimental analyses including time complexity and performance (accuracy and F-measure), considering both single-class and multi-class problems, and identifying trade-offs between resource consumption and performance. Our evaluation quantifies the value of neural networks, particularly when state-of-the-art datasets are used to train the models. This leads to interesting guidelines for security managers and computer network practitioners who are looking at the incorporation of neural-based ML into IDS
Phase time and transmission probability in the traversal of a PT-symmetric potential: The case of an electromagnetic waveguide
No full textWe study the unconventional transmission properties of a wave packet through a PT-symmetric potential region as describing the actual electromagnetic wave propagation along a waveguide filled with gain and loss media. The nontrivial behavior of the transmission probability manifests in the giant amplification of the incident electromagnetic signal of given wavelengths for well-defined configurations, depending on the gain/loss contrast. Maximum transmission peaks are related to spectral singularities and a strict correlation exists between the "resonant" wavelengths and the gain/loss contrast. The transit times are as well calculated, showing their surprising vanishing in the opaque barrier limit, independently of the gain/loss contrast, which is reminiscent of some sort of Hartman effect. Also, nonlocal effects manifest in the presence of negative delay times for given configurations, while a correlation is apparent between maximum delay times and transmission probability peaks, though appreciably depending on the gain/loss contrast
A road map for Feynman’s adventures in the land of gravitation
No full textRichard P. Feynman’s work on gravitation, as can be inferred from several published and unpublished sources, is reviewed. Feynman was involved with this subject at least from late 1954 to the late 1960s, giving several pivotal contributions to it. Even though he published only three papers, much more material is available, beginning with the records of his many interventions at the Chapel Hill conference in 1957, which are here analyzed in detail, and show that he had already considerably developed his ideas on gravity. In addition, he expressed deep thoughts about fundamental issues in quantum mechanics which were suggested by the problem of quantum gravity, such as superpositions of the wave functions of macroscopic objects and the role of the observer. Feynman also lectured on gravity several times. Besides the famous lectures given at Caltech in 1962–1963, he extensively discussed this subject in a series of lectures delivered at the Hughes Aircraft Company in 1966–1967, whose focus was on astronomy and astrophysics. All this material allows to reconstruct a detailed picture of Feynman’s ideas on gravity and of their evolution until the late sixties. According to him, gravity, like electromagnetism, has quantum foundations, therefore general relativity has to be regarded as the classical limit of an underlying quantum theory; this quantum theory should be investigated by computing physical processes, as if they were experimentally accessible. The same attitude is shown with respect to gravitational waves, as is evident also from an unpublished letter addressed to Victor F. Weisskopf. In addition, an original approach to gravity, which closely mimics (and probably was inspired by) the derivation of the Maxwell equations given by Feynman in that period, is sketched in the unpublished Hughes lectures
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