IMDEA Networks Institute Digital Repository
Not a member yet
1915 research outputs found
Sort by
New Methods for Ranking Influence in Social Networks
Get PDFIn this work, propagation dynamics on social networks are studied in order to identify the most influential users. For this purpose, diffusion data has been collected during 4 weeks from a microblogging OSN (online social network) called Tumblr. Then, the propagation graph has been built and studied using the first 2 weeks data (period ). Subsequently, this graph has been used to predict th influencers during the last 2 weeks (period ). A ranking of influential nodes is obtained for , set as the ground truth. The aim is to predict this ranking using the data from . Based on the average spread of users’ posts, rankings obtained with several techniques are tested and compared. These techniques include classical centrality measures used in the literature, the ranking itself, and new alternatives based on effective degree using local (network) information. Whilst all methods perform similarly when considering whole global ranking, differences among them appear when ranking the top influencers. For those, in general, the methods proposed here outperform the classical
centrality measures.Mathematics and StatisticsUniversidad Carlos III de Madrid, Spainpu
Multi-resource energy-efficient routing in cloud data centers with network-as-a-service
Get PDFWith the rapid development of software defined networking and network function virtualization, researchers have proposed a new cloud networking model called Network-as-aService (NaaS) which enables both in-network packet processing and application-specific network control. In this paper, we revisit the problem of achieving network energy efficiency in data centers and identify some new optimization challenges under the NaaS model. Particularly, we extend the energy-efficient routing optimization from single-resource to multi-resource settings. We characterize the problem through a detailed model and provide a formal problem definition. Due to the high complexity of direct solutions, we propose a greedy routing scheme to approximate the optimum, where flows are selected progressively to exhaust residual capacities of active nodes, and routing paths are assigned based on the distributions of both node residual capacities and
flow demands. By leveraging the structural regularity of data center networks, we also provide a fast topology-aware heuristic method based on hierarchically solving a series of vector bin packing instances. Extensive simulations show that the proposed routing scheme can achieve significant gain on energy savings and the topology-aware heuristic can produce comparably good results while reducing the computation time to a large extent.TRUEpu
Mobile Network Resource Optimization under Imperfect Prediction
Get PDFA highly interesting trend in mobile network optimization is to exploit knowledge of future network capacity to allow mobile terminals to prefetch data when signal quality is high and to refrain from communication when signal quality is low. While this approach offers remarkable benefits, it relies on the availability of a reliable forecast of system conditions. This paper focuses on the reliability of simple prediction techniques and their impact on resource allocation algorithms. In addition, we propose ICARO, a resource allocation technique that is robust to prediction uncertainties. The algorithm combines autoregressive filtering and statistical models for short, medium, and long term forecasting. We validate our approach by means of an extensive simulation campaign based on real measurement data collected in Berlin. We show that our solution performs close to an omniscient optimizer and outperforms a limited horizon omniscient optimizer by 10-15%. Our solution provides up to 30% saving of system resources compared to a simple solution that always maintains a full buffer and is close to optimal in terms of buffer under-run time.TRUEpu
OpenVLC, an Open-Source Platform for the Internet of Light
Get PDFOpenVLC is an open-source, low-cost research platform for Visible Light Communications Networks. We discuss the challenges to use OpenVLC as a part of the Internet of Light.FALSEpu
Demo: OpenVLC1.0 Platform for Research in Visible Light Communication Networks
Get PDFBuilt around a cost-effective embedded Linux platform, OpenVLC is an open source project (www.openvlc.org) for research in Visible Light Communication (VLC) Networks. In this work, we introduce and demonstrate the OpenVLC1.0 platform, a flexible, software-defined, and low-cost research platform. OpenVLC1.0 consists of a simple electronic design, and a new driver of the Linux operating system that implements the MAC, part of the PHY layers and it offers an interface to Internet protocols. The electronics of OpenVLC implement a flexible optical front-end consisting of commodity low- and high-power Light Emitting Diodes (LEDs), photodiodes (PDs), and ancillary electronic circuitry. In order to quickly start playing with VLC Networks, we have designed and developed a printed circuit board (OpenVLC1.0 cape). The cape can be plugged into the main embedded Beaglebone board. Researchers can then swiftly build PHY and MAC protocols using the software implementation (OpenVLC1.0 driver), and prototype innovative solutions in realistic network setups. In this demo, we show that OpenVLC1.0 can switch between different MAC protocols, it can choose different optical channel for data transmission and reception, and it can be employed jointly with standard TCP/IP diagnostic tools.TRUEpu
Efficient Networking in Millimeter Wave Bands
No full textState-of-the-art wireless communication already operates close to Shannon capacity and one of the most promising options to further increase data rates is to increase the communication bandwidth. Very high bandwidth channels are only available in the extremely high frequency part of the radio spectrum, the millimeter wave band (mm-wave). Upcoming communication technologies, such as IEEE 802.11ad, are already starting to exploit this part of the radio spectrum to achieve data rates of several GBit/s. However, communication at such high frequencies also suffers from high attenuation and signal absorption, often restricting communication to line-of-sight (LOS) scenarios and requiring the use of highly directional antennas. This in turn requires a radical rethinking of wireless network design. On the one hand side, such channels experience little interference, allowing for a high degree of spatial reuse and potentially simpler MAC and interference management mechanisms. On the other hand, such an environment is extremely dynamic and channels may appear and disappear over very short time intervals, in particular for mobile devices. This talk will highlight some of the challenges of and possible approaches for networking in the mm-wave band.TRUEpu
Probabilistic bounds on the length of a longest edge in Delaunay graphs of random points in d-dimensions
Get PDFMotivated by low energy consumption in geographic routing in wireless networks, there has been recent interest in determining bounds on the length of edges in the Delaunay graph of randomly distributed points. Asymptotic results are known for random networks in planar domains. In this paper, we obtain upper and lower bounds that hold with parametric probability in any dimension, for points distributed uniformly at random in domains with and without boundary. The results obtained are asymptotically tight for all relevant values of such probability and constant number of dimensions, and show that the overhead produced by boundary nodes in the plane holds also for higher dimensions. To our knowledge, this is the first comprehensive study on the lengths of long edges in Delaunay graphs.pu
A Measurement-based Characterization of the Energy Consumption in Data Center Servers
Get PDFIn this work we present an exhaustive empirical characterization of the power requirements of multiple components of data center servers. To do so, we devise different experiments to stress these components, taking into account the multiple available frequencies and the fact that we are working with multicore servers. In these experiments, we measure energy consumption of server components and identify their optimal operational points. Our study proves that the curve defining the minimal CPU power utilization, as a function of the load in Active Cycles Per Second, is neither concave nor purely convex. Instead, it definitively shows a superlinear dependence on the load. Similarly, we present results on how to improve the efficiency of network cards and disks. Finally, we validate the accuracy of the model derived from our characterization by comparing the real energy consumed by two Hadoop applications?PageRank and WordCount?with the estimation from our model, obtaining errors below 4:1% on average.pu
Evidence of MOOC Students Using Multiple Accounts to Harvest Correct Answers
Get PDFMassive Open Online Courses (MOOCs) give “honor certificates” of accomplishment for successful completion of their courses. In part because these certificates are given without any verification of the identity of the student, such tokens have little professional value – they would seem to have value mostly for personal reasons. However, although the value of the certificates is not clear, we have found that a substantial number of students do not obey the code of honor, but apparently are using multiple accounts to harvest the correct answers for questions that they later submit with their main account. This is enabled because most MOOCs provide an instant feedback about the correctness of a student’s
answers. In this paper we present evidence for, and detailed patterns of such behavior; we then briefly
discuss ways to prevent it.
To the best of our knowledge, our study is the first to report on this type of cheating in MOOCs. The topic of academic dishonesty in online learning environments was addressed by various studies, see for example [1-3], but in the context of MOOCs research, it still did not get a lot of attention. We believe that it is very important to discuss the various aspects of this sensitive issue, as if it is not handled properly, it can jeopardize the value of MOOCs as academic credentials.TRUEpu
Radio-Signal Correlation for Collaborative Wideband Spectrum Monitoring System
Get PDFToday's spectrum measurements are mainly performed by governmental agencies which drive around using expensive specialized hardware. The idea of collaborative spectrum monitoring has recently gained attention to capture the usage of the wireless spectrum at larger geographical scale. We present in this report the main challenges address in collaborative spectrum monitoring and we propose a methodology for making decisions based on signal correlation similarity between sensors. To reach this goal, we build a software-defined sensor architecture that enables distributed data collection in real-time over Internet. Our sensor design builds upon low-cost commercial hardware components with a total cost per sensor device below $100. Our results suggest that our architecture can be useful to coordinate a large number of sensors scanning at the same or different frequencies in order to reach the target collaboratively. Interesting application areas could be dynamic spectrum access in cognitive radios, re-construct a large-bandwidth signals or simply to gain an understanding of the spectrum usage at large scale to detect elevated electro-smog regions, anomalies in the signals or set policy enforcement in the electromagnetic space.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu