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1915 research outputs found
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A Declarative and Expressive Approach to Control Forwarding Paths in Carrier-Grade Networks
Get PDFSDN simplifies network management by relying on declarativity (high-level interface) and expressiveness
(network flexibility). We propose a solution to support those features while preserving high robustness and
scalability as needed in carrier-grade networks. Our solution is based on (i) a two-layer architecture separating connectivity and optimization tasks; and (ii) a centralized optimizer called DEFO, which translates high-level goals expressed almost in natural language into compliant network configurations. Our evaluation on real and synthetic topologies shows that DEFO improves the state of the art by (i) achieving better trade-offs for classic goals covered by previous works, (ii) supporting a larger set of goals (refined traffic engineering and service chaining), and (iii) optimizing large ISP networks in few seconds. We also quantify the gains of our implementation, running Segment Routing on top of IS-IS, over possible alternatives (RSVP-TE and OpenFlow).TRUEpu
A Predictive Model of Learning Gains for a Video and Exercise Intensive Learning Environment
No full textThis work approaches the prediction of learning gains in an environ- ment with intensive use of exercises and videos, specifically using the Khan Academy platform. We propose a linear regression model which can explain 57.4% of the learning gains variability, with the use of four variables obtained from the low level data generated by the students. We found that two of these variables are related to exercises (the proficient exercises and the average number of attempts in exercises), and one is related to both videos and exercises (the total time spent in both) related to exercises, whereas only one is related to videos.TRUEpu
Energy-optimal base station density in cellular access networks with sleep modes
Get PDFSleep modes are widely accepted as an effective technique for energy-efficient networking: by adequately putting to sleep and waking up network resources according to traffic demands, a proportionality between energy consumption and network utilization can be approached, with important reductions in energy consumption. Previous studies have investigated and evaluated sleep modes for wireless access networks, computing variable percentages of energy savings. In this paper we characterize the maximum energy saving that can be achieved in a cellular wireless access network under a given performance constraint. In particular, our approach allows the derivation of realistic estimates of the energy-optimal density of base stations corresponding to a given user density, under a fixed performance constraint. Our results allow different sleep mode proposals to be measured against the maximum theoretically achievable improvement. We show, through numerical evaluation, the possible energy savings in today’s networks, and we further demonstrate that even with the development of highly energy-efficient hardware, a holistic approach incorporating system level techniques is essential to achieving maximum energy efficiency.pu
Combining Learning Analytics and the Flipped Classroom in a MOOC of maths
Get PDFThis paper describes the configuration, setup and initial analysis ex- amples of an experience for introducing learning analytics in a MOOC of maths for adult high school education, using the flipped the classroom methodology. An overview of the MOOC of maths is provided, as well as an overview of the ANALYSE learning analytics tool which is used to analyze the learning pro- cess. We describe how the learning analytics tool can be useful in this setup and methodology and we illustrate specific examples of conclusions in the MOOC of maths.TRUEpu
Torii: Multipath Distributed Ethernet Fabric Protocol for Data Centers with Zero-Loss Path Repair
Get PDFThis paper describes and evaluates Torii, a layer 2 data centre network fabric protocol. The main features of Torii are being fully distributed, scalable, fault-tolerant and with automatic setup. Torii is based on multiple, tree-based, topological media access control addresses that are used for table-free forwarding over multiple equal-cost paths, and it is capable of rerouting frames around failed links on the fly without needing a central fabric manager for any function. To the best of our knowledge, it is the first protocol that does not require the exchange of periodic messages to work under normal conditions and to recover from link failures, as Torii exchanges messages just once. Moreover, another important characteristic of Torii is that it is compatible with a wide range of data centre topologies. Simulation results show an excellent distribution of traffic load and latencies, similar to the shortest path protocols.pu
Impact of BGP filtering on Inter-Domain Routing Policies
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Internet-Draft
Intended status: Informational
Expires: December 11, 2015This document describes how unexpected traffic flows can emerge across an autonomous system, as the result of other autonomous systems filtering, or restricting the propagation of more specific prefixes. We provide a review of the techniques to detect the occurrence of this issue and defend against it.pu
Behind the NAT – A Measurement Based Evaluation of Cellular Service Quality
Get PDFMobile applications such as VoIP, (live) gaming, or video streaming have diverse QoS requirements ranging from low delay to high throughput. The optimization of the network quality experienced by end-users requires detailed knowledge of the expected network performance. Also, the achieved service quality is affected by a number of factors, including network operator and available technologies. However, most studies focusing on measuring the cellular network do not consider the performance implications of network configuration and management. To this end, this paper reports about an extensive data set of cellular network measurements, focused on analyzing root causes of mobile network performance variability. Measurements conducted over four weeks in a 4G cellular network in Germany show that management and configuration decisions have a substantial impact on the performance. Specifically, it is observed that the association of mobile devices to a Point of Presence (PoP) within the operator’s network can influence the end-to-end RTT by a large extent. Given the collected data a model predicting the PoP assignment and its resulting RTT leveraging Markov Chain and machine learning approaches is developed. RTT increases of 58% to 73% compared to the optimum performance are observed in more than 57% of the measurements.TRUEpu
An Analysis of the Economic Impact of Strategic Deaggregation
Get PDFThe advertisement of more-specific prefixes provides network operators with a fine-grained method to control the interdomain ingress traffic. Prefix deaggregation is recognized as a steady long-lived phenomenon at the interdomain level, despite its well-known negative effects for the community. In this paper, we look past the original motivation for deploying deaggregation in the first place, and instead we focus on its aftermath. We identify and analyze here one particular side-effect of deaggregation regarding the economic impact of this type of strategy: decreasing the transit traffic bill. We propose a general Internet model to analyze the effect of advertising more-specific prefixes on the incoming transit traffic burstiness. We show that deaggregation combined with selective advertisements has a traffic stabilization side-effect, which translates into a decrease of the transit traffic bill. Next, we develop a methodology for Internet Service Providers (ISPs) to monitor general occurrences of prefix deaggregation within their customer base. Thus, the ISPs can detect selective advertisements of deaggregated prefixes, and thus identify customers which impact the business of their providers. We apply the proposed methodology on a complete set of data including routing, traffic, topological and billing information provided by a major Japanese ISP and we discuss the obtained results.pu
A Software-defined Sensor Architecture for Large-scale Wideband Spectrum Monitoring
Get PDFToday’s spectrum measurements are mainly performed by governmental agencies which drive around using expensive specialized hardware. The idea of crowdsourcing spectrum monitoring has recently gained attention as an alternative way to capture the usage of wide portions of the wireless spectrum at larger geographical and time scales. To support this vision, we develop a flexible software-defined sensor architecture that enables distributed data collection in real-time over the Internet. Our sensor design builds
upon low-cost commercial off-the-shelf (COTS) hardware components with a total cost per sensor device below $100. The low-cost nature of our sensor platform makes the sensing approach particularly suitable for large-scale deployments but imposes technical challenges regarding performance and quality. To circumvent the limits of our solution, we have implemented and evaluated different sensing strategies and noise reduction techniques. Our results suggest that our sensor architecture may be useful in application areas
such as dynamic spectrum access in cognitive radios, detecting regions with elevated electro-smog, or simply to gain an understanding of the spectrum usage for advanced signal intelligence such as anomaly detection or policy enforcement.TRUEpu