1,721,128 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Experimental analysis of the socio-economic phenomena in the BitTorrent ecosystem
Full text linkBitTorrent is the most successful Peer-to-Peer (P2P) application and is responsible for a major portion of Internet traffic. It has been largely studied using simulations, models and real measurements. Although simulations and modelling are easier to perform, they typically simplify analysed problems and in case of BitTorrent they are likely to miss some of the effects which occur in real swarms. Thus, in this thesis we rely on real measurements. In the first part of the thesis we present the summary of measurement techniques used so far and we use it as a base to design our tools that allow us to perform different types of analysis at different resolution level.
Using these tools we collect several large-scale datasets to study different aspects of BitTorrent with a special focus on socio-economic aspects. Using our datasets, we first investigate the topology of real BitTorrent swarms and how the traffic is actually exchanged among peers. Our analysis shows that the resilience of BitTorrent swarms is lower than corresponding random graphs. We also observe that ISP policies, locality-aware clients and network events (e.g., network congestion) lead to locality-biased composition of neighbourhood in the swarms. This means that
the peer contains more neighbours from local provider than expected from purely random neighbours selection process. Those results are of interest to the companies which use BitTorrent for daily operations as well as for ISPs which carry BitTorrent traffic. In the next part of the thesis we look at the BitTorrent from the perspective of the content and content publishers in a major BitTorrent portals. We focus on the factors that seem to drive the popularity of the BitTorrent and, as a result, could affect its associated traffic in the Internet. We show that a small fraction of publishers (around 100 users) is responsible for more than two-thirds of the published content. Those publishers can be divided into two groups: (i) profit driven and (ii) fake publishers. The former group leverages the published copyrighted content (typically very popular) on BitTorrent portals to attract content consumers to their web sites for financial gain. Removing this group may have a significant impact on the popularity of BitTorrent portals and, as a result, may affect a big portion of the Internet traffic associated to BitTorrent. The latter group is responsible for fake content, which is mostly linked to malicious activity and creates a serious threat for the Bit-
Torrent ecosystem and for the Internet in general. To mitigate this threat, in the last part of the thesis we present a new tool named TorrentGuard for the early detec-
tion of fake content that could help to significantly reduce the number of computer infections and scams suffered by BitTorrent users. This tool is available through
web portal and as a plugin to Vuze, a popular BitTorrent client. Finally, we present MYPROBE, the web portal that allows to query our database and to gather different
pieces of information regarding BitTorrent content publishers.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Extending the address space of the Internet
Full text linkIn the nearest future Internet in its current shape will have to face the problem of shortage of IPv4 addresses. IPv4 architecture reserves 32 bits for addressing purposes, which occurs not to be enough in the face of a rapid growth of the Internet. To overcome this problem, the successor of IPv4, IPv6, was designed with 128 bits of addressing space. However, deployment of IPv6 goes very slowly mainly because of the cost of transition, even if many transition mechanisms were already proposed. Therefore, it could be advantageous to explore solutions which can occur better than IPv6 in terms of deployment ease or will allow for IPv4 and IPv6 coexistance with minimal cost. This thesis presents new approach for solving a problem with lack of addresses. xIP architecture creates new address space by extending IPv4 address scheme. xIP can be incorporated as a completely new protocol or can be used as a mechanism which can improve IPv6 and IPv4 coexistance (xIP6). The common characteristics of both of the architectures are integrated routing and addressing and reusing extensive part of IPv4 world. This solution seriously decreases management cost during coexistence period and makes deployment less expensive and easier to accept by users.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Experimental QoE evaluation of multicast video delivery over IEEE 802.11aa WLANs
Full text linkAbstract. The IEEE 802.11aa amendment standardised the Group Addressed Transmission Service (GATS), which extends 802.11 WLANs with a novel set of MAC mechanisms to support an effective and efficient multicast video service. The key challenge with GATS is the selection of the best scheme and its configuration for a given network scenario, as the standard does not provide any guidelines nor any assessment of the performance of each mechanism. Although some previous studies have addressed this challenge, their evaluation is either via analysis or simulations under non-realistic assumptions, or based on Quality of Service (QoS) metrics instead of video quality metrics, which are required for a proper video performance assessment. In this paper, we deploy a mid-size real-life testbed and develop a thoughtful methodology to perform an extensive Quality of Experience (QoE) evaluation of GATS under a variety of scenarios. We analyse the performance of the novel schemes under ideal conditions, as well as under controlled and non-controlled interference, assessing their ability to provide an adequate QoE and quantifying the resources left for other type of traffic. Ours is the first thorough QoE evaluation of GATS in a real-life scenario, providing key insights on their performance, and can be used to derive configuration guidelines for the schemes.The work of P. Serrano and I. Ucar were partially supported by the EC in the framework of H2020-ICT-2014-2 project Flex5Gware (Grant agreement no. 671563), by the Spanish Ministry of Economy and Competitiveness throught the 5G-City project (TEC2016-76795-C6-3-R), and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
uNap: Practical micro-sleeps for 802.11 WLANs
Full text linkIn this paper, we revisit the idea of putting interfaces to sleep during packet overhearing (i.e., when there are ongoing transmissions addressed to other stations) from a practical standpoint. To this aim, we perform a robust experimental characterisation of the timing and consumption behaviour of a commercial 802.11 card. We design μNap, a local standard-compliant energy-saving mechanism that leverages micro-sleep opportunities inherent to the CSMA operation of 802.11 WLANs. This mechanism is backwards compatible and incrementally deployable, and takes into account the timing limitations of existing hardware, as well as practical CSMA-related issues (e.g., capture effect). According to the performance assessment carried out through trace-based simulation, the use of our scheme would result in a 57% reduction in the time spent in overhearing, thus leading to an energy saving of 15.8% of the activity time
Filtering Noisy 802.11 Time-of-Flight Ranging Measurements from Commoditized WiFi Radios
Full text linkTime-of-flight (ToF) echo techniques have been recently suggested for ranging mobile devices over WiFi radios. However, these techniques have yielded only moderate accuracy in indoor environments because WiFi ToF measurements suffer from extensive device-related noise which makes it challenging to differentiate between direct path from non-direct path signal components when estimating the ranges. Existing multipath mitigation techniques tend to fail at identifying the direct path when the device-related Gaussian noise is in the same order of magnitude, or larger than the multipath noise. In order to address this challenge, we propose a new method for filtering ranging measurements that is better suited for the inherent large noise as found in WiFi radios. Our technique combines statistical learning and robust statistics in a single
filter. The filter is lightweight in the sense that it does not require specialized hardware, the intervention of the user, or cumbersome on-site manual calibration. This makes our method particularly suitable for indoor localization in largescale deployments using existing legacy WiFi infrastructures. We evaluate our technique for indoor mobile tracking scenarios in multipath environments and, through extensive evaluations across four different testbeds covering areas up to 1000m2, the filter is able to achieve a median 2D positioning error between 2.0 and 3.4 meters.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
An entropy-based methodology for detecting Online Advertising Fraud at scale
Full text linkProgrammatic online advertising allows advertisers to di-
versify their budget dynamically, set the desired context of
publishers content, and target a specific audience. Besides,
it is accessible to all budgets. Despite these notable benefits, programmatic advertising has the drawback of being highly exposed to fraud.
The detection of fraudulent activities is a difficult task due to the limited information exchanged between ad-networks
and the large volume of publishers and traffic sources (IPs). In general, identifying participants in ad-fraud requires a large effort, while recreating a fraudulent system from different IPs targeting new publishers is relatively easy.
In this paper, we propose an efficient and scalable solution
to deterministic ad-fraud. The traffic patterns of ad-fraud
bots can be identified using the concept of entropy from
information theory. We develop a normalized entropic score
to identify the domains involved in ad-fraud and the IPs
from which the ad-fraud bots operate. We also describe a
lightweight and scalable modular system for fraud mitigation
that allows not only to filter out evident fraud, but also
configure diffeerent levels of suspicious activity.
Given the complexity of evaluating the potential fraud,
the system is configurable letting advertisers to decide the
level of risk they are willing to take. As reducing the risk involves increasing the number of false positives, we propose a multi-level scheme with a bank of bloom filters with different price limits to soften the trade-off.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
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