TCP in the Internet of Things: from ostracism to prominence

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.TCP has traditionally been neglected as a transport-layer protocol for the Internet of Things (IoT). However, recent trends and industry needs are favoring TCP presence in IoT environments. In this article, we describe the main IoT scenarios where TCP will be used. We then analyze the historically claimed issues of TCP in the IoT context. We argue that, in contrast to generally accepted wisdom, most of those possible issues fall in one of the following categories: i) are also found in well-accepted IoT end-to-end reliability mechanisms, ii) can be solved, or iii) are not actual issues. Considering the future prominent role of TCP in the IoT, we provide recommendations for lightweight TCP implementation and suitable operation in such scenarios, based on our IETF standardization work on the topic.Postprint (author's final draft

Concepciones sobre el pensamiento variacional en docentes de matemáticas de educación media en Bogotá

El interés de esta investigación se centra en concepciones presentes sobre el pensamiento variacional en docentes de matemáticas que se desempeñan en la educación media en Bogotá. Se toma como referente la teoría de la socioepistemología y como método un estudio de caso. El trabajo se desarrolla con docentes que se desempeñan actualmente como docentes de matemáticas del colegio Guillermo Cano Isaza de la ciudad de Bogotá

3d numerical model of a confined fracture tests in concrete

The paper deals with the numerical simulation of a confined fracture test in concrete. The test is part of the experimental work carried out at ETSECCPB-UPC in order to elucidate the existence of a second mode of fracture under shear and high compression, and evaluate the associated fracture energy. The specimen is a short cylinder with also cylindrical coaxial notches similar the one proposed by Luong (1990), which is introduced in a largecapacity triaxial cell, protected with membranes and subject to different levels of confining pressure prior to vertical loading. In the experiments, the main crack follows the preestablished cylindrical notch path, which is in itself a significant achievement. The loaddisplacement curves for various confining pressures also seem to follow the expected trend according to the underlying conceptual model. The FE model developed includes zerothickness interface elements with fracture-based constitutive laws, which are pre-inserted along the cylindrical ligament and the potential radial crack plane. The results reproduce reasonably well the overall force-displacement curves of the test for various confinement levels, and make it possible to identify the fracture parameters including the fracture energies in modes I and IIa

Tratamiento escolar de la geometría a través del diseño de actividades integrando materiales manipulativos

En años recientes, un cuerpo creciente de investigaciones en didáctica de las matemáticas han identificado algunas dificultades en relación con la enseñanza y aprendizaje de contenidos temáticos, procesos y contextos relacionados con el pensamiento espacial y sistemas geométricos, siendo comúnmente atribuidas a causas de orden epistemológico, cognitivo, curricular y didáctico. En este marco se genera la necesidad de integrar recursos, específicamente materiales manipulativos, al currículo y a las prácticas escolares, que permitan fortalecer en los estudiantes los conocimientos obtenidos para resolver algunos problemas de su entorno escolar y cotidiano

Desplazamiento forzado y reinserción: factores de incidencia en la inseguridad urbana

El trabajo plantea una hipótesis sobre los factores que convergen en la situación de inseguridad urbana, especialmente en la ciudad de Bogotá, D.C. como, por ejemplo, el flujo de población desplazada y/o los desmovilizados o reinsertados provenientes de grupos al margen de la ley. Pero no me extenderé en este problema, la finalidad del trabajo es analizar la posible incidencia que puede tener en la inseguridad urbana la población en referencia. No afirmo que estos segmentos poblaciones sean determinantes para señalarlos como únicos culpables de la inseguridad en las ciudades, aun cuando no descarto que puede ser una posibilidad, especialmente por los desmovilizados y/o reinsertados. Baso mi hipótesis de la carencia de fuentes estadísticas de entidades gubernamentales que hayan hecho estudios verificables sobre esta problemática.Pregrad

Aproximación al tratamiento escolar de la geometría a través de materiales manipulativos

En años recientes, un cuerpo creciente de investigaciones en didáctica de las matemáticas han identificado algunas dificultades en relación con el aprendizaje de contenidos temáticos, procesos y contextos relacionados con el pensamiento espacial y sistemas geométricos, siendo comúnmente atribuidas a causas de orden epistemológico, cognitivo, curricular y didáctico. En este sentido se revela como prometedor el estudio del proceso de integración al currículo y a las prácticas escolares, de recursos, concretamente lo que se refiere a materiales manipulativos. Esto con la intención de fortalecer en los estudiantes los conocimientos adquiridos para resolver algunos problemas de su entorno escolar y cotidiano, a medida que avanza su proceso de aprendizaje

CoAP congestion control for the Internet of Things

“© © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.” August Betzler, Javier Isern, Carles Gomez, Ilker Demirkol, Josep Paradells, "Experimental evaluation of congestion control for CoAP communications without end-to-end reliability", Ad Hoc Networks, pp. , 2016, ISSN 15708705. DOI: 10.1109/MCOM.2016.7509394CoAP is a lightweight RESTful application layer protocol devised for the IoT. Operating on top of UDP, CoAP must handle congestion control by itself. The core CoAP specification defines a basic congestion control mechanism, but it is not capable of adapting to network conditions. However, IoT scenarios exhibit significant resource constraints, which pose new challenges on the design of congestion control mechanisms. In this article we present CoCoA, an advanced congestion control mechanism for CoAP being standardized by the Internet Engineering Task Force CoRE working group. CoCoA introduces a novel round-trip time estimation technique, together with a variable backoff factor and aging mechanisms in order to provide dynamic and controlled retransmission timeout adaptation suitable for the peculiarities of IoT communications. We conduct a comparative performance analysis of CoCoA and a variety of alternative algorithms including state-of-the-art mechanisms developed for TCP. The study is based on experiments carried out in real testbeds. Results show that, in contrast to the alternative methods considered, CoCoA consistently outperforms the default CoAP congestion control mechanism in all evaluated scenarios.Peer ReviewedPostprint (author's final draft

NAVIGATION, GUIDANCE AND CONTROL FOR PLANETARY LANDING

This dissertation aims to develop algorithms of guidance and control for propulsive terminal phase planetary landing, including a piloting strategy. The algorithms developed here are based on the Embedded Model Control (EMC) principles. Currently, the planetary entry descent and landing are important issues, landing on Mars and Moon has been scientifically rewarding; successful landed robotic systems on the surface of Mars have been achieved. Projects as Mars Science Laboratory MSL inter alia have achieved a successful landing. These new approaches are focused in delivering large amounts of mass with a low uncertainty and in performing the entry, descent and landing sequence for human exploration. The dissertation is divided in two parts, the first part is focused on Pinpoint landing algorithms, piloting definition and its integration with guidance; some simulations runs are provided. The second part of this research describes the Borea project. It shows the modelling of quadrotor dynamics and kinematics. Its propulsive system is studied and an alternative methodology for the propeller modelling is presented. The embedded model control for quadrotor vehicles is developed. Test of GNC algorithms for planetary landing were studied and simulated. The dissertation is divided in two parts, the first part is focused on Pinpoint landing algorithms, piloting definition and its integration with guidance, some simulations runs are provided. The second part of this research describes the Borea project. shows modelling of quadrotor dynamics and kinematics. Its propulsive system is studied and an alternative methodology for the propeller modelling is presented. The embedded model control for quadrotor vehicles is developed. Test of GNC algorithms for planetary landing were studied and simulated