http://hdl.handle.net/2117/3172 2013-05-23T19:06:42Z http://hdl.handle.net/2117/19378 Title: A summary of virtualization techniques Authors: Rodríguez Haro, Fernando; Freitag, Fèlix; Navarro Moldes, Leandro; Hernández Sánchez, Efraín; Farías Mendoza, Nicandro; Guerrero Ibañez, Juan Antonio; González Potes, Apolinar Abstract: Nowadays, virtualization is a technology that is applied for sharing the capabilities of physical computers by splitting the resources among OSs. The concept of Virtual Machines (VMs) started back in 1964 with a IBM project called CP/CMS system. Currently, there are several virtualization techniques that can be used for supporting the execution of entire operating systems. We classify the virtualization techniques from the OS view. First, we discuss two techniques that executes modified guest OSs: operating system-level virtualization and para-virtualization. Second, we discuss two techniques that executes unmodified guest OSs: binary translation and hardware assisted. Finally, we present a summary of resource management facilities for capacity planning and consolidation of server applications. 2013-05-23T10:14:43Z http://hdl.handle.net/2117/19366 Title: IT or not to be: the impact of Moodle in the education of developing countries Authors: García Almiñana, Jordi; Somé, Michel; Ayguadé Parra, Eduard; Cabré Garcia, José M.; Casany Guerrero, María José; Frigola Bourlon, Manel; Galanis, Nikolaos; García-Cervigon Gutiérrez, Manuel; Guerrero Zapata, Manel; Muñoz Gracia, María del Pilar Abstract: E-learning environments, such as Moodle, provide a technology that fosters the improvement of the educational system in developed countries, where education is traditionally performed with relatively high standards of quality. A large number of case studies and research have been conducted to demonstrate how e-learning technologies can be applied to improve both training and learning processes. However, these technologies have not been proved efficient when applied to developing countries. The challenges that must be addressed in developing countries, both technological and societal, are much more complex and the possible solution margins are more constrained than those existing in the context where these technologies have been created. In this paper we show how Moodle can be used to improve the quality of education in developing countries and, even more important, how can be used to turn the educational system more sustainable and effective in the long-term. We describe our experience in implementing a programming course in Moodle for the Higher School of Informatics at the Université Polytechnique de Bobo-Dioulasso, in Burkina Faso (West Africa), joining efforts with local professors in designing and implementing the learning system. The case example has been designed having in mind a number of contextual problems: lack of lecturers, excessive teaching hours per lecturer, massive classes, and curricula organization and stability, among others. We finally discuss how the teaching effort is reduced, the students’ knowledge and capacity improves, and the institutional academic model can be guaranteed with the proposal. For this reason, we claim that information technologies in developing countries are a cost-effective way to guarantee the objectives originally defined in the academic curricula and, therefore, deal with the problem of the education. 2013-05-22T07:16:25Z http://hdl.handle.net/2117/18788 Title: Power management in sensing subsystem of wireless multimedia sensor networks Authors: Alaei, Mohammad; Barceló Ordinas, José María Abstract: A wireless sensor network consists of sensor nodes deployed over a geographical area for monitoring physical phenomena like temperature, humidity, vibrations, seismic events, and so on. Typically, a sensor node is a tiny device that includes three basic components: a sensing subsystem for data acquisition from the physical surrounding environment, a processing subsystem for local data processing and storage, and a wireless communication subsystem for data transmission. In addition, a power source supplies the energy needed by the device to perform the programmed task. This power source often consists of a battery with a limited energy budget. In addition, it is usually impossible or inconvenient to recharge the battery, because nodes are deployed in a hostile or unpractical environment. On the other hand, the sensor network should have a lifetime long enough to fulfill the application requirements. Accordingly, energy conservation in nodes and maximization of network lifetime are commonly recognized as a key challenge in the design and implementation of WSNs. Experimental measurements have shown that generally data transmission is very expensive in terms of energy consumption, while data processing consumes significantly less (Raghunathan et al., 2002). The energy cost of transmitting a single bit of information is approximately the same as that needed for processing a thousand operations in a typical sensor node (Pottie & Kaiser, 2000). The energy consumption of the sensing subsystem depends on the specific sensor type. In some cases of scalar sensors, it is negligible with respect to the energy consumed by the processing and, above all, the communication subsystems. In other cases, the energy expenditure for data sensing may be comparable to, or even greater (in the case of multimedia sensing) than the energy needed for data transmission. In general, energy-saving techniques focus on two subsystems: the communication subsystem (i.e., energy management is taken into account in the operations of each single node, as well as in the design of networking protocols), and the sensing subsystem (i.e., techniques are used to reduce the amount or frequency of energy-expensive samples). 2013-04-15T10:50:13Z http://hdl.handle.net/2117/18785 Title: Chains of trust in vehicular networks: a secure points of interest dissemination strategy Authors: Antolino Rivas, David; Guerrero Zapata, Manel Abstract: This article describes a scheme which to the best of our knowledge is the first one to use user signatures to share information about Points of Interest in Vehicular Ad hoc Networks. In this scheme, users rate restaurants, hotels, etc. and sign those rates with their private key. Then, they broadcast that information and other vehicles store it for future use. When another user needs a Point of Interest recommendation he queries the system for the other users stored reviews and after he visits that Points of Interest for himself, he evaluates it and his level of trust in the reviewers with rates similar to his own increases. In the end, a user will be able to request to his vehicle information on a certain Point of Interest category and itwill respond with the recommendations made by other users, prioritizing the ones in the user’s Web of Trust.poi-Sim is the tool designed to simulate this scheme. It processes a 24 h mobility trace produced by a Multi-Agent Traffic Simulator, which realistically simulates public and private traffic over regional maps of Switzerland. The result is a Chains of Trust simulation with over 260,000 nodes, which shows that the proposed scheme performs satisfactorily in a realistic scenario. 2013-04-15T09:56:22Z http://hdl.handle.net/2117/18201 Title: RSU deployment for content dissemination and downloading in intelligent transportation systems Authors: Reineri, Massimo; Casetti, Claudio; Chiasserini, Carla-Fabiana; Fiore, Marco; Trullols Cruces, Óscar; Barceló Ordinas, José María 2013-03-12T10:50:20Z http://hdl.handle.net/2117/18025 Title: Reducing energy consumption in human-centric wireless sensor networks Authors: Meseguer Pallarès, Roc; Molina Clemente, Carlos; Ochoa, Sergio; Santos, Rodrigo Abstract: Energy consumption is a main research issue in wireless sensor networks; and particularly in those where nodes collaborate to reach a goal. This article explores the energy consumption in mobile devices participating in a human-based wireless sensor network. Specifically, the paper proposes the use of a message predictor to help detect and reduce the number of unnecessary control packets delivered by the nodes as a way to keep updated the network topology. In order to evaluate this proposal, the Optimized Link State Routing protocol was modified to add a message predictor between the routing and the network layers. Eleven simulations were performed using a particular setting. The preliminary results indicate the use of the message predictor can help reduce considerably the nodes energy consumption without affecting the routing capability of the protocol. Although these results are still preliminary, they are highly encouraging. 2013-02-28T17:25:11Z http://hdl.handle.net/2117/18011 Title: Las comunicaciones móviles en los edificios inteligentes Authors: Reyes Muñoz, María Angélica Abstract: Este trabajo presenta una plataforma de red móvil aplicada a los entornos de edificios inteligentes. En primer lugar, los edificios inteligentes han sido definidos como “aquellos que utilizan la tecnología computacional para gestionar de manera autónoma todos los servicios que ofrece un entorno de un edificio tales como optimizar el confort del usuario, el consumo de energía y la seguridad” [Callaghan 00].Desde el punto de vista de las telecomunicaciones específicamente desde el punto de vista de las comunicaciones móviles es muy importante para los edificios inteligentes considerar la comunicación entre sistemas autónomos inteligentes, dispositivos personales inteligentes, gestión de sistemas de información, dispositivos móviles, etc. 2013-02-27T16:31:39Z http://hdl.handle.net/2117/16643 Title: Should next generation wireless mesh networks consider dynamic channel access? Authors: Amiri Nezhad, Maryam; Bellalta, Boris; Guerrero Zapata, Manel; Cerdà Alabern, Llorenç Abstract: In today’s computer architectures, many scientific applications are considered to be memory bound. The memory wall, i.e. the large disparity between a processor’s speed and the required time to access off-chip memory, is a yet-to-be-solved problem that can greatly reduce performance and make us underutilise the processors capabilities. Many different approaches have been proposed to tackle this problem, such as the addition of a large cache hierarchy, multithreading or speculative data prefetching. Most of these approaches rely on the prediction of the application’s future behaviour, something that should not be necessary as this information is known by the programmer and is located in the application itself. Instead of designing hardware that attempts to guess the future, the goal should be to provide the programmer with the hardware support required to decide when the data is transferred and where is it transferred to. With this goal in mind, we introduce the Data Transfer Engine, a runtime-assisted, software prefetcher that exploits the information provided by the programmer in order to place data in the cache hierarchy close to the processor that will make use of it. The DTE can not only significantly reduce stall time due to cache misses but, more importantly, it allows us to design new computer architectures that are able to tolerate very high memory latencies. 2012-10-04T11:47:56Z http://hdl.handle.net/2117/16006 Title: Impact of the infrastructure in mobile opportunistic networks Authors: Trullols Cruces, Óscar; Morillo Pozo, Julián David; Barceló Ordinas, José María Abstract: Epidemic modeling has been used to analyze many disciplines such as biology, ecology and medicine. In the last years, it also has been applied to networking paradigms such as social networks, virus spreading in Internet and lastly to opportunistic networking in mobile networks. In this paper we revise some of the facts of epidemic modeling in mobile networks and use these models to analyze the impact of adding infrastructure to sparse opportunistic mobile networks. We show how the position in which infrastructure is placed takes an important impact in the dissemination delay. Description: Invited paper 2012-06-10T13:02:26Z http://hdl.handle.net/2117/15644 Title: Limits of energy saving for the allocation of data center resources to networked applications Authors: León Gutiérrez, Xavier; Navarro Moldes, Leandro Abstract: Energy related costs are becoming one of the largest contributors to the overall cost of operating a data center, whereas the degree of data center utilization continues to be very low. Energy-aware dynamic provision of resources based on the consolidation of existing application instances can simultaneously address under-utilization of servers while highly reducing energy costs. Thus, energy costs cannot be treated separately from resource provision and allocation. However, current scheduling techniques based on market mechanisms do not specifically deal with such scenario. In this paper we model the problem of minimizing energy consumption of the allocation of resources to networked applications as a Stackelberg leadership game to find an upper bound of energy saving. The model is applied to a proportional-share mechanism where resource providers can maximize their profit by minimizing energy costs while users can select resources ensuring the minimum requirements are satisfied. We show that our mechanism can determine the optimal set of resources on and off, even in realistic conditions considering incomplete information, and heterogeneous applications. 2012-03-22T12:01:58Z http://hdl.handle.net/2117/15378 Title: An abstraction methodology for the evaluation of multi-core multi-threaded architectures Authors: Zilan, Ruken; Verdú Mulà, Javier; García Vidal, Jorge; Nemirovsky, Mario; Milito, Rodolfo; Valero Cortés, Mateo Abstract: As the evolution of multi-core multi-threaded processors continues, the complexity demanded to perform an extensive trade-off analysis, increases proportionally. Cycle-accurate or trace-driven simulators are too slow to execute the large amount of experiments required to obtain indicative results. To achieve a thorough analysis of the system, software benchmarks or traces are required. In many cases when an analysis is needed most, during the earlier stages of the processor design, benchmarks or traces are not available. Analytical models overcome these limitations but do not provide the fine grain details needed for a deep analysis of these architectures. In this work we present a new methodology to abstract processor architectures, at a level between cycle-accurate and analytical simulators. To apply our methodology we use queueing modeling techniques. Thus, we introduce Q-MAS, a queueing based tool targeting a real chip (the Ultra SPARC T2 processor) and aimed at facilitating the quantification of trade-offs during the design phase of multi-core multi-threaded processor architectures. The results demonstrate that Q-MAS, the tool that we developed, provides accurate results very close to the actual hardware, with a minimal cost of running what-if scenarios. 2012-02-27T12:31:37Z http://hdl.handle.net/2117/15321 Title: Self-regulated trade-off among timeliness, messages and accuracy for approximate queries in large-scale information aggregation Authors: Brunner, René; Freitag, Fèlix; Navarro Moldes, Leandro Abstract: In data management for large-scale applications such as Peer-to-Peer networks, and Grid and Cloud Computing arise challenges in regard to the decentralization of the application and in regard to an increasing number of failures. A consequence of these conditions is an increasing retrieval time, inaccurate results and higher network consumption. A solution to restrain an increasing retrieval time and an increasing number of messages is the introduction of approximate queries. The introduction of approximate queries limits the querying of all nodes of a network to a subset of nodes in the cost of the results' accuracy. Thus, a conflict to provide a large-scalability lies in guaranteeing accurate data, in the provision of fast results and in a low consumption of network bandwidth. Therefore, we propose an information aggregation that is based on an analytic hierarchical process (AHP) to find a trade-off among the unpredictable factors of time, messages and accuracy. After a user defines the preferences for the retrieval process, the AHP-based algorithm makes autonomous decisions on each node. The algorithm decides autonomously about pruning the approximate queries to reach an optimal trade-off from a global perspective. Applying the self-regulated pruning of the approximate queries allows reducing the messages from an exponential in crease to a constant factor. At the same time, the retrieval time is reduced from a linear increase to a constant factor in regard to an increasing number of nodes. At the same time of reducing the retrieval time and network bandwidth, the AHP-based self-regulation guarantees certain level of accuracy 2012-02-23T10:26:28Z http://hdl.handle.net/2117/15114 Title: CARMA: Composable-Adaptive Resource Management Authorization for ubiquitous environments Authors: Morales Pacheco, Roberto Antonio; Serna Olivera, Jetzabel Maritza; Medina Llinàs, Manuel; Luna García, Jesús Abstract: The ever increasing diversity and mobility of devices have originated a marked rise in ubiquitous resources; a great number of collaborative applications could be exploited just by employing an efficient ubiquitous resource management mechanism. The CARM (Composable-Adaptive Resource Management) middleware-based architecture provides a flexible infrastructure where personal devices create seamlessly on demand interconnections links to share ubiquitous resources. In this article we address CARM's security challenges and to overcome these we propose the CARM Authorization (CARMA) module; in CARMA each user acts as an Attribute Authority (AA) responsible of issuing Attribute Certificates (ACs) and defining for each resource a set of policy-based authorization decisions; CARMA's Alerting System (AS) allows users to work in a collaborative mode by warning others of malicious nodes even when no infrastructure is available. This research mainly describes ongoing work towards a proof-of-concept implementation in the given scenarios. Our proposal enforces security considering the bandwidth efficiency and therefore enhancing the dynamic resource management experience in ubiquitous environments. 2012-02-14T10:15:02Z http://hdl.handle.net/2117/14030 Title: VANET mobility modeling challenged by feedback loops Authors: Meyer, Harald; Trullols Cruces, Óscar; Hess, Andrea; Hummel, Karin Anna; Barceló Ordinas, José María; Casetti, Claudio; Karlsson, Gunnar Abstract: VANET applications are often providing street traffic information to vehicles and drivers, regarding, for instance, traffic conditions and parking space availability. This information influences in turn the driving behavior in real-world settings. Mobility models used in current VANET simulations are mostly ignoring this feedback entirely. In cases the feedback is included, it is mainly based on ad-hoc approaches with lack of generality. With this paper, we contribute to the investigation of such feedback loops within VANETs by describing the levels at which feedback loops can be introduced, i.e., on strategic, tactical, and operational levels of mobility. We further describe how feedback loops can be introduced in arbitrary mobility models and in particular in elementary mobility models. We exemplify our approach by introducing two types of feedback loops for the Manhattan Mobility model, the Random Trip model, and the Constrained Random Trip model. One feedback loop represents points of interest attracting vehicles, such as free parking spaces attracting vehicles searching for parking. The other feedback loop focuses on repelling vehicles, such as a traffic jam. We discuss the impacts of the feedback in terms of the mobility metrics: vehicle density per area, number of direction changes, and intensity of direction changes. Furthermore, we discuss the effects in terms of information availability and delays of transmission in an opportunistic vehicular network. 2011-11-23T13:05:18Z http://hdl.handle.net/2117/14012 Title: Power saving trade-offs in delay/disruptive tolerant networks Authors: Trullols Cruces, Óscar; Morillo Pozo, Julián David; Barceló Ordinas, José María; García Vidal, Jorge Abstract: Wireless nodes such as smart-phones in which the WiFi wireless card is continuously on, consume battery energy in just a few hours. Moreover, in many scenarios, an always-on wireless card is useless because there is often no need for transmission and/or reception. This fact is exacerbated in Delay/Disruptive Tolerant Network (DTN) environments, in which nodes exchange Delay Tolerant Objects (DTO) when they meet. Power Saving Management (PSM) techniques enable the lifetime of the nodes to be extended. This paper analyses the trade-offs that appear when wireless nodes periodically turn off the wireless card in order to save battery in DTN environments. The paper shows the conditions in which a node can switch off the battery without impacting the peer-to-peer contact probability, and those in which this contact probability is decreased. For example, it is shown that node lifetime can be doubled while keeping the peer-to-peer contact probability equal to one. But, further increase of the node lifetime quickly decreases peer-to-peer contact probability. Finally, the impact of power savings in DTO dissemination time is also analyzed. 2011-11-22T12:14:09Z