Modelos para el análisis y optimización del control de admisión en redes celulares

En la última década se ha producido una enorme popularización de las redes celulares, siendo incluso muy superior a las previsiones iniciales más optimistas. Este interés que ha despertado entre los usuarios ha provocado que sea en la actualidad el sector de las telecomunicaciones más productivo para los operadores. Aunque el número de usuarios no se prevé que aumente al mismo ritmo a como lo ha hecho hasta ahora porque el número de líneas móviles es superior al de habitantes en muchos países, existe toda una serie de nuevos desafíos para los operadores para poder ofrecer servicios atractivos y competitivos a los usuarios. Estos nuevos servicios se prevé que demanden asimismo una mayor cantidad de recursos. Para el mundo de la investigación, esto supone la necesidad de desarrollar mecanismos cada vez más eficientes y complejos que gestionen los recursos adecuadamente para garantizar unos requisitos de calidad de servicio. Tradicionalmente, para el diseño de estos mecanismos de gestión de recursos se ha partido de las propuestas realizadas para redes fijas. No obstante, las redes celulares introducen nuevos retos por la escasez del espectro radioeléctrico, la aleatoriedad de la propagación y la movilidad de los terminales. La presente tesis doctoral toma como marco de trabajo las redes celulares que implementan políticas de control de admisión. De forma más concreta, en la primera parte de la tesis doctoral se han desarrollado modelos analíticos que permiten estudiar el impacto de los accesos repetitivos que se producen en un sistema cuando el controlador de admisión decide bloquear una petición de acceso al sistema. Esta contribución se realiza en dos aspectos: en el desarrollo de técnicas de resolución de sistemas con reintentos y en la aplicación de esas técnicas a modelos de redes celulares con el fin de comprender el impacto que los reintentos tienen en ellas. La segunda parte de la tesis doctoral está enfocada al diseño de políticas óptimas de control de admisGiménez Guzmán, JM. (2008). Modelos para el análisis y optimización del control de admisión en redes celulares [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/2936Palanci

Torii: Multipath Distributed Ethernet Fabric Protocol for Data Centers with Zero-Loss Path Repair

This paper describes and evaluates Torii, a layer-two data center 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 MAC 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 center topologies. Simulation results show an excellent distribution of traffic load and latencies, similar to shortest path protocols

Torii: Multipath Distributed Ethernet Fabric Protocol for Data Centers with Zero-Loss Path Repair

This paper describes and evaluates Torii, a layer-two data center 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 MAC 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 center topologies. Simulation results show an excellent distribution of traffic load and latencies, similar to shortest path protocols

On the Benefits of Channel Bonding in Dense, Decentralized Wi-Fi 4 Networks

Channel bonding is a technique first defined in the IEEE 802.11n standard to increase the throughput in wireless networks by means of using wider channels. In IEEE 802.11n (nowadays also known as Wi-Fi 4), it is possible to use 40 MHz channels instead of the classical 20 MHz channels. Although using channel bonding can increase the throughput, the classic 802.11 setting only allows for two orthogonal channels in the 2.4 GHz frequency band, which is not enough for proper channel assignment in dense settings. For that reason, it is commonly accepted that channel bonding is not suitable for this frequency band. However, to the best of our knowledge, there is not any accurate study that deals with this issue thoroughly. In this work, we study in depth the effect of channel bonding in Wi-Fi 4 dense, decentralized networks operating in the 2.4 GHz frequency band. We confirm the negative effect of using channel bonding in the 2.4 GHz frequency band with 11 channels which are 20 MHz wide (as in North America), but we also show that when there are 13 or more channels at hand (as in many other parts of the world, including Europe and Japan), the use of channel bonding yields consistent throughput improvements. For that reason, we claim that the common assumption of not considering channel bonding in the 2.4 GHz band should be revised

Design and evaluation of a learning environment to effectively provide network security skills

Information system security and network security are topics of increasing importance in the information society. They are also topics where the adequate education of professionals requires the use of specific laboratory environments where the practical aspects of the discipline may be addressed. However, most approaches currently used are excessively static and lack the flexibility that the education requirements of security professionals demand. In this paper we present NEMESIS, a scenario generation framework for education on system and network security, which is based on virtualization technologies and has been designed to be open, distributed, modular, scalable and flexible. Finally, an example scenario is described and some results validating the benefits of its use in undergraduate computer security courses are shown.La seguridad de redes y sistemas de información es un área de importancia creciente en el ámbito de la sociedad de información. Además, constituye un tema en el que la adecuada formación de profesionales exige el uso de entornos de laboratorio específicos en los que abordar los aspectos prácticas de la disciplina. Sin embargo, la mayoría de las aproximación usadas en la actualidad son excesivamente estáticas y carecen de la flexibilidad que las exigencias de la formación de profesionales de seguridad imponente. En este artículo, presentamos NEMESIS, un entorno para la generación de escenarios para la formación en seguridad de redes y sistemas, basado en tecnologías de virtualización que ha sido diseñado para ser abierto, distribuido, modular, escalable y flexible. Finalmente, se describe un escenario de ejemplo y se muestran resultados que validan los beneficios de su uso en cursos de seguridad informática de grad

All-Path Bridging: Path Exploration Protocols for Data Center and Campus Networks

Today, link-state routing protocols that compute multiple shortest paths predominate in data center and campus networks, where routing is performed either in layer three or in layer two using link-state routing protocols. But current proposals based on link-state routing do not adapt well to real time traffic variations and become very complex when attempting to balance the traffic load. We propose All-Path bridging, an evolution of the classical transparent bridging that forwards frames over shortest paths using the complete network topology, which overcomes the limitations of the spanning tree protocol. All-Path is a new frame routing paradigm based on the simultaneous exploration of all paths of the real network by a broadcast probe frame, instead of computing routes on the network graph. This paper presents All- Path switches and their differences with standard switches and describes ARP-Path protocol in detail, its path recovery mechanisms and compatibility with IEEE 802.1 standard bridges. ARP-Path is the first protocol variant of the All-Path protocol family. ARP-Path reuses the standard ARP Request and Reply packets to explore reactively the network and find the fastest path between two hosts. We compare its performance in terms of latency and load distribution with link-state shortest-path routing bridges, showing that ARP-Path distributes the load more evenly and provides lower latencies. Implementations on different platforms prove the robustness of the protocol. The conclusion is that All-Path bridging offer a simple, resilient and scalable alternative to path computation protocols

All-Path Bridging: Path Exploration Protocols for Data Center and Campus Networks

Today, link-state routing protocols that compute multiple shortest paths predominate in data center and campus networks, where routing is performed either in layer three or in layer two using link-state routing protocols. But current proposals based on link-state routing do not adapt well to real time traffic variations and become very complex when attempting to balance the traffic load. We propose All-Path bridging, an evolution of the classical transparent bridging that forwards frames over shortest paths using the complete network topology, which overcomes the limitations of the spanning tree protocol. All-Path is a new frame routing paradigm based on the simultaneous exploration of all paths of the real network by a broadcast probe frame, instead of computing routes on the network graph. This paper presents All- Path switches and their differences with standard switches and describes ARP-Path protocol in detail, its path recovery mechanisms and compatibility with IEEE 802.1 standard bridges. ARP-Path is the first protocol variant of the All-Path protocol family. ARP-Path reuses the standard ARP Request and Reply packets to explore reactively the network and find the fastest path between two hosts. We compare its performance in terms of latency and load distribution with link-state shortest-path routing bridges, showing that ARP-Path distributes the load more evenly and provides lower latencies. Implementations on different platforms prove the robustness of the protocol. The conclusion is that All-Path bridging offer a simple, resilient and scalable alternative to path computation protocols

Design and evaluation of a learning environment to effectively provide network security skills

Information system security and network security are topics of increasing importance in the information society. They are also topics where the adequate education of professionals requires the use of specific laboratory environments where the practical aspects of the discipline may be addressed. However, most approaches currently used are excessively static and lack the flexibility that the education requirements of security professionals demand. In this paper we present NEMESIS, a scenario generation framework for education on system and network security, which is based on virtualization technologies and has been designed to be open, distributed, modular, scalable and flexible. Finally, an example scenario is described and some results validating the benefits of its use in undergraduate computer security courses are shown.La seguridad de redes y sistemas de información es un área de importancia creciente en el ámbito de la sociedad de información. Además, constituye un tema en el que la adecuada formación de profesionales exige el uso de entornos de laboratorio específicos en los que abordar los aspectos prácticas de la disciplina. Sin embargo, la mayoría de las aproximación usadas en la actualidad son excesivamente estáticas y carecen de la flexibilidad que las exigencias de la formación de profesionales de seguridad imponente. En este artículo, presentamos NEMESIS, un entorno para la generación de escenarios para la formación en seguridad de redes y sistemas, basado en tecnologías de virtualización que ha sido diseñado para ser abierto, distribuido, modular, escalable y flexible. Finalmente, se describe un escenario de ejemplo y se muestran resultados que validan los beneficios de su uso en cursos de seguridad informática de grad

Efficient Method to Approximately Solve Retrial Systems with Impatience

We present a novel technique to solve multiserver retrial systems with impatience. Unfortunately these systems do not present an exact analytic solution, so it is mandatory to resort to approximate techniques. This novel technique does not rely on the numerical solution of the steady-state Kolmogorov equations of the Continuous Time Markov Chain as it is common for this kind of systems but it considers the system in its Markov Decision Process setting. This technique, known as value extrapolation, truncates the infinite state space using a polynomial extrapolation method to approach the states outside the truncated state space. A numerical evaluation is carried out to evaluate this technique and to compare its performance with previous techniques. The obtained results show that value extrapolation greatly outperforms the previous approaches appeared in the literature not only in terms of accuracy but also in terms of computational cost.This work has been supported by the Spanish government under Projects TIN2010-21378-C02-02 and TIN2008-06739-C04-02/TSI and by Comunidad de Madrid through Project S-2009/TIC-1468.Giménez Guzmán, JM.; Doménech Benlloch, MJ.; Pla, V.; Martínez Bauset, J.; Casares Giner, V. (2012). Efficient Method to Approximately Solve Retrial Systems with Impatience. Journal of Applied Mathematics. 2012(1):1-18. https://doi.org/10.1155/2012/186761S11820121Tran-Gia, P., & Mandjes, M. (1997). Modeling of customer retrial phenomenon in cellular mobile networks. IEEE Journal on Selected Areas in Communications, 15(8), 1406-1414. doi:10.1109/49.634781Artalejo, J. R. (2010). Accessible bibliography on retrial queues: Progress in 2000–2009. Mathematical and Computer Modelling, 51(9-10), 1071-1081. doi:10.1016/j.mcm.2009.12.011Artalejo, J. R., & Pozo, M. (2002). Annals of Operations Research, 116(1/4), 41-56. doi:10.1023/a:1021359709489Marsan, M. A., de Carolis, G., Leonardi, E., Lo Cigno, R., & Meo, M. (2001). Efficient estimation of call blocking probabilities in cellular mobile telephony networks with customer retrials. IEEE Journal on Selected Areas in Communications, 19(2), 332-346. doi:10.1109/49.914511Doménech-Benlloch, M. J., Giménez-Guzmán, J. M., Martínez-Bauset, J., & Casares-Giner, V. (2005). Efficient and accurate methodology for solving multiserver retrial systems. Electronics Letters, 41(17), 967. doi:10.1049/el:20051982Neuts, M. F., & Rao, B. M. (1990). Numerical investigation of a multiserver retrial model. Queueing Systems, 7(2), 169-189. doi:10.1007/bf01158473Gaver, D. P., Jacobs, P. A., & Latouche, G. (1984). Finite birth-and-death models in randomly changing environments. Advances in Applied Probability, 16(4), 715-731. doi:10.2307/142733

Evaluating Native Load Distribution of ARP- Path Bridging Protocol in Mesh and Data Center

RP-Path is a simple, low latency, shortest path bridging protocol for campus, enterprise and data center networks. We recently found that this protocol natively distributes the traffic load in networks having redundant paths of similar characteristics. The reason is that every new path between hosts is selected on-demand in a race among ARP Request packet replicas over all available paths: the first arriving replica gets its path selected on the fly. This means a continuous adaptation of new paths to variations on the load at links and bridges. To show this unique load distribution capability and path diversity property we use a number of simulations for complex scenarios, including two different simulators: one flow- based and one packet-based, and two basic topologies: data center and a regular mesh. We also verify this behavior on real hardware on a network of nine ARP-Path NetFPGA switches. The conclusion is that the ARP-Path protocol efficiently distributes traffic via alternative paths at all load levels, provided that multiple paths of similar propagation delays are availableComunidad de Madri