IMDEA Networks Institute Digital Repository
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On the persistence of wireless advertising without infrastructure support
Get PDFThe number of devices connected to the Internet keeps growing, and the traffic they collectively generate grows even faster, creating congestion issues, especially in the network access segment. Some of the newer Internet applications can however be served with device-to-device (D2D) opportunistic communications, thus offloading a portion of the traffic from the network.
This thesis studies and presents experiments on the possibility of providing content availability to end user terminals by exploiting D2D infrastructureless connectivity and opportunistic communication. In order to avoid unrealistic assumptions on the behavior of D2D communications, the work includes and builds upon the implementation of an Android application that supports infrastructureless distributed content sharing between
wireless devices using Wi-Fi Direct. The collected experimental data permit to analyze the occurring events and to assess and compare the performance of the class of services under evaluation against existing communication protocols.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Evaluation of a Learning Analytics Application for Open edX Platform
Get PDFMassive open online courses (MOOCs) have recently emerged as a revolution in education. Due to the huge amount of users, it is difficult for teachers to provide personalized instruction. Learning analytics computer applications have emerged as a solution. At present, MOOC platforms provide low support for learning analytics visualizations, and a challenge is to provide useful and effective visualization applications about the learning process. At this paper we review the learning analytics functionality of Open edX and make an overview of our learning analytics application ANALYSE. We present a usability and effectiveness evaluation of ANALYSE tool with 40 students taking a Design of Telematics Applications course. The survey obtained very positive results in a system usability scale (SUS) questionnaire (78.44/100) in terms of the usefulness of visualizations (3.68/5) and the effectiveness ratio (92/100) of the actions required for the respondents. Therefore, we can conclude that the implemented learning analytics application is usable and effective.pu
Software-Defined Underwater Acoustic Modems: Historical Review and the NILUS Approach
Get PDFFlexible/adaptive acoustic modems that are reprogrammable/reconfigurable at all layers of the communication stack, either by a user or by means of autonomous decisions, are considered as an important enabler for interoperability and cognitive networking in the underwater domain. In this paper, we review the existing literature on software-defined acoustic modems (SDAMs) for underwater communications and networking, considering past and ongoing academic efforts, as well as industrial developments and European collaborations centered on software-defined modem structures and functionalities. We then zoom in on relevant R&D efforts currently taking place in a defense cooperation between The Netherlands and Norway, targeting the design of a software-defined modem for the NILUS MK 2 sensor node. This modem is built using general-purpose (GP) computing architectures running open-source operating system and tools, thereby making a further step toward software-defined open-architecture underwater acoustic modems. The first field tests of the NILUS MK 2 node in multihop underwater acoustic networks are presented, showing satisfactory performance in shallow and open waters.pu
Multimodal Underwater Networks: Recent Advances and a Look Ahead
Get PDFThe recent uptake of non-acoustic underwater transmission systems suggests that in the near future it will be common for underwater devices to incorporate different physical communication technologies. Such devices are typically described as \emph{multimodal}. They seek flexibility by compensating for the shortcomings of a given technology through the advantages of another. For example, a system encompassing acoustic and optical communication systems can provide long-range, low-bit rate communications, while enabling faster data transfer at very short range.\sloppy
As the development of non-acoustic underwater communications is taking momentum, so is the research on how to optimally exploit the multimodal communications capabilities in different scenarios. This paper presents a survey of past and recent work on this topic, covering the development both of the communication technologies and of the networking schemes and protocols for multimodal networks. As an example of the opportunities offered by multimodal communications, we discuss two different case studies. We conclude with an outlook on likely future developments for multimodal communications.TRUEpu
Millimeter-wave networking tutorial
No full textThe tutorial will highlight some of the challenges of and possible approaches for networking in the millimeter-wave (mm-wave) band. Communication at such high frequencies brings unique challenges, primarily due the high signal attenuation, which can only be overcome by the use of highly directional antennas. On the one hand side, this results in much less interference compared to omni-directional communication at lower frequencies, allowing for a high degree of spatial reuse and potentially simpler Medium Access Control Protocols (MAC) and interference management mechanisms. On the other hand, high directionality may cause deafness due to beam misalignments, whereas channels may appear and disappear over very short time intervals and cause sudden communication blockages, in particular for mobile devices. The tutorial specifically focuses on networking aspects of the MAC layer and above. It starts by an overview of mm-wave communication aspects and characteristics, and then delves into the most important network and protocol design aspects, ranging from beam-training and medium access to the impact on transport protocols and efficient network architectures.TRUEpu
Analyzing the Behavior of Students Regarding Learning Activities, Badges, and Academic Dishonesty in MOOC Environments
Get PDFThe 'big data' scene has brought new improvement opportunities to most products and services, including education. Web-based learning has become very widespread over the last decade, which in conjunction with the MOOC phenomenon, it has enabled the collection of large and rich data samples regarding the interaction of students with these educational online environments.
We have detected different areas in the literature that still need improvement and more research studies. Particularly, in the context of MOOC and SPOC, where we focus our data analysis on the platforms Khan Academy, Open edX and Coursera. More specifically, we are going to work towards learning analytics visualization dashboards, carrying out an evaluation of these visual analytics tools. Additionally, we will delve into the activity and behavior of students with regular and optional activities, badges and their online academically dishonest conduct. The analysis of activity and behavior of students is divided first in exploratory analysis providing descriptive and inferential statistics, like correlations and group comparisons, as well as numerous visualizations that facilitate conveying understandable information. Second, we apply clustering analysis to find different profiles of students for different purposes e.g., to analyze potential adaptation of learning experiences and pedagogical implications. Third, we also provide three machine learning models, two of them to predict learning outcomes (learning gains and certificate accomplishment) and one to classify submissions as illicit or not. We also use these models to discuss about the importance of variables.
Finally, we discuss our results in terms of the motivation of students, student profiling, instructional design, potential actuators and the evaluation of visual analytics dashboards providing different recommendations to improve future educational experiments.Telematics EngineeringUniversidad Carlos III de Madrid, Spainpu
Empirical Comparison of Power-efficient Virtual Machine Assignment Algorithms
Get PDFThe advent of cloud computing has changed the way many companies do computation, allowing them to outsource it to the cloud. This has given origin to a new kind of business, the cloud providers, which run large datacenters. In order to be competitive, cloud providers must keep their operational costs low. One way to reduce these costs is reducing the energy consumed with smart task assignment algorithms, which decide where tasks are to be placed upon their arrival. Unfortunately, almost no task assignment algorithm used is power aware.
In this paper we compare the performance of multiple task assignment algorithms for saving energy. We assume that tasks are in fact virtual machines that have to be assigned to physical machines, and we assume that the physical machines have a power consumption that increases superlinearly with the load. First, we propose two tunable power-aware task assignment algorithms (that subsume the algorithms studied in [15]). These algorithms are then compared with multiple state-of-the-art algorithms in different meaningful scenarios. Both algorithms prove themselves as interesting assignment algorithms since, properly configured, they outperform the other algorithms in most of the cases.pu
Video upload from public transport vehicles using multihomed systems
Get PDFDOI: https://doi.org/10.1109/INFCOMW.2016.7562091We consider a surveillance system for public transport vehicles, which is based on the collection of on-board videos, and the upload via mobile network to a central security system of video segments corresponding to those cameras and time intervals involved in an accident. We assume that vehicles are connected to several wireless interfaces, provided by different Mobile Network Operators (MNOs), each charging a different cost. Both the cost and the upload rate for each network interface change over time, according to the network load and the position of the vehicle. When a video must be uploaded to the central security, the system has to complete the upload within a deadline, deciding i) which interface(s) to use, ii) when to upload from that interface(s) and iii) at which rate to upload. The goal is to minimize the total cost of the upload, which we assume to be proportional to the data volume being transmitted and to the cost of using a given interface. We formalize the optimization problem and discuss greedy heuristics to solve it. Then, we discuss scientific and technical challenges to solve the system.TRUEpu
An Analysis of the Privacy and Security Risks of Android VPN Permission-enabled Apps
Get PDFMillions of users worldwide resort to mobile VPN clients to either circumvent censorship or to access geo-blocked content, and more generally for privacy and security purposes. In practice, however, users have little if any guarantees about the corresponding security and privacy settings, and perhaps no practical knowledge about the entities accessing their mobile traffic.
In this paper we provide a first comprehensive analysis of 283 Android apps that use the Android VPN permission, which we extracted from a corpus of more than 1.4 million apps on the Google Play store. We perform a number of passive and active measurements designed to investigate a wide range of security and privacy features and to study the behavior of each VPN-based app. Our analysis includes investigation of possible malware presence, third-party library embedding, and traffic manipulation, as well as gauging user perception of the security and privacy of such apps. Our experiments reveal several instances of VPN apps that expose users to serious privacy and security vulnerabilities, such as use of insecure VPN tunneling protocols, as well as IPv6 and DNS traffic leakage. We also report on a number of apps actively performing TLS interception. Of particular concern are instances of apps that inject JavaScript programs for tracking, advertising, and for redirecting e-commerce traffic to external partners.TRUEpu