Finding the sweet spot for frame aggregation in 802.11 WLANs

This letter proposes an algorithm for the dynamic tuning of the maximum size of aggregated frames in 802.11 WLANs. Traffic flows with opposed requirements may coexist in these networks: traditional services as web browsing or file download that need high throughput, and services with real-time requirements that need low latency. The proposed algorithm allows the network manager to find an optimal balance (i.e. the ''sweet spot'' between throughput and latency: a ''delay budget'' can be assigned to real-time flows, with the objective of keeping the latency as close as possible to that budget, while penalizing the throughput of traditional services as little as possible. © 1997-2012 IEEE

Analyzing the effect of tcp and server population on massively multiplayer games

Many Massively Multiplayer Online Role-Playing Games (MMORPGs) use TCP flows for communication between the server and the game clients. The utilization of TCP, which was not initially designed for (soft) real-time services, has many implications for the competing traffic flows. In this paper we present a series of studies which explore the competition between MMORPG and other traffic flows. For that aim, we first extend a source-based traffic model, based on player’s activities during the day, to also incorporate the impact of the number of players sharing a server (server population) on network traffic. Based on real traffic traces, we statistically model the influence of the variation of the server’s player population on the network traffic, depending on the action categories (i.e., types of in-game player behaviour). Using the developed traffic model we prove that while server population only modifies specific action categories, this effect is significant enough to be observed on the overall traffic. We find that TCP Vegas is a good option for competing flows in order not to throttle the MMORPG flows and that TCP SACK is more respectful with game flows than other TCP variants, namely, Tahoe, Reno, and New Reno. Other tests show that MMORPG flows do not significantly reduce their sending window size when competing against UDP flows. Additionally, we study the effect of RTT unfairness between MMORPG flows, showing that it is less important than in the case of network-limited TCP flows

IoTsafe, Decoupling Security from Applications for a Safer IoT

The use of robust security solutions is a must for the Internet of Things (IoT) devices and their applications: regulators in different countries are creating frameworks for certifying those devices with an acceptable security level. However, even for already certified devices, security protocols have to be updated when a breach is found or a certain version becomes obsolete. Many approaches for securing IoT applications are nowadays based on the integration of a security layer [e.g., using transport layer security, (TLS)], but this may result in difficulties when upgrading the security algorithms, as the whole application has to be updated. This fact may shorten the life of IoT devices. As a way to overcome these difficulties, this paper presents IoTsafe, a novel approach relying on secure socket shell (SSH), a feasible alternative to secure communications in IoT applications based on hypertext transfer protocol (HTTP and HTTP/2). In order to illustrate its advantages, a comparison between the traditional approach (HTTP with TLS) and our scheme (HTTP with SSH) is performed over low-power wireless personal area networks (6loWPAN) through 802.15.4 interfaces. The results show that the proposed approach not only provides a more robust and easy-To-update solution, but it also brings an improvement to the overall performance in terms of goodput and energy consumption. Core server stress tests are also presented, and the server performance is also analyzed in terms of RAM consumption and escalation strategies

Can a Wi-Fi WLAN support a first person shooter?

In corporate and commercial environments, the deployment of a set of coordinated Wi-Fi APs is becoming a common solution to provide Internet coverage to moving users. In these scenarios, real-time services as online games can also be present. This paper presents a set of experiments developed in a test scenario where an end device moves between different APs while generating game traffic. A WLAN solution based on virtual APs is used, in order to make the handoffs transparent for Layer 3. The results show that it is possible to maintain an acceptable level of subjective quality during the handoff. At the same time, it is set clear that the fact of having a gamer in an AP could be taken into account by radio resource management algorithms, in order to provide a better quality

COMPETENCIA EN EL MERCADO ESPAÑOL DE CRÉDITOS BANCARIOS: UN MODELO DE VARIACIONES CONJETURALES

The main objective of this work is to propose an oligopolistic competition model thatincorporates product differentiation through quality of service in the Spanish bank loansmarket. This model allows us to detect the competitive behavior patterns in terms of the outputof all the financial entities with respect to three strategic groups defined in terms of size. Thismodel of competitive interactions is tested with a sample of 100 firms in the Spanish bank loanmarket between 1992 and 1994. This period of time is characterized by both, the end of a longprocess of deregulation and the integration of the Spanish Banking System in the EuropeanBanking System. The findings evidence a stronger aggressiveness from the larger-size groupwhen the medium and smaller-size groups increase their output. Besides, the results detect anaggressive conduct between the entities within the larger-size group. El objetivo de este trabajo consiste en proponer un modelo de competencia oligopolísticacon diferenciación de producto vía calidad de servicio en el mercado de créditos bancarios, elcual permite detectar el patrón de conducta competitiva del output (variaciones conjeturales anivel de cantidades de créditos vendidos) para todas y cada una de las entidades financierasrespecto de cada uno de los grupos estratégicos definidos por tamaño. Este modelo deinteracciones competitivas es contrastado con 100 entidades del mercado español de créditosbancarios entre 1992 y 1994, período temporal que marca la culminación de un proceso dedesregulación e integración europea del sistema bancario español y que incide directamente enla competencia en términos de cantidades de créditos vendidos. Los resultados obtenidosevidencian que el grupo de entidades de mayor tamaño tiene una actitud agresiva ante unaumento del output de los grupos de entidades pequeñas y medianas. Además, se detecta unaconducta agresiva entre las entidades del grupo de mayor tamaño.Variación Conjetural, Comportamiento Competitivo, Grupos Estratégicos, Banking; Competition; Strategic Groups.

A refraction/wide-angle reflection seismic profile through the Iberian Chain: preliminary report

As a result of the Eurasian and African plates convergence, Tertiary intraplate deformation of the Iberian plate gave rise to the basement-involved thrust-system of the Iberian Chain. Subsequently, a crustal thickening beneath the Iberian Chain was produced, as deduced from Bouguer anomaly maps. A very preliminary interpretation of a new seismic profile through the Iberian Chain is presented, which leads us to infer a crustal thickening beneath the central part of the profile, where Moho depths of at least 40 km should be reached

Attention to Wi-Fi Diversity: Resource Management in WLANs with Heterogeneous APs

Many home networks integrate a small number (typically 2-4) of Wi-Fi Access Points (APs), with heterogeneous characteristics: different 802.11 variants, capabilities and security schemes. This paper proposes the consideration of these specific characteristics in order to improve the management of network resources. Three use cases are presented in order to showcase the potential benefits. By the use of a user-space AP, which works in coordination with a controller, the network is able to assign each connected station to the AP that best fits with its characteristics. The system also manages security, avoiding the need of adding specific elements for authentication, encryption or decryption. Extensions are proposed to an existing protocol that defines the communication between the AP and the controller, in order to communicate and store the specific characteristics of each AP and end device. This includes new association and handoff schemes that do not introduce any additional delay. The system has been implemented in a real environment, and a battery of tests has been run using three hardware platforms of different characteristics. The results show that handoffs between bands are possible, and estimate the processing delays, the Round-Trip Time and the handoff delay, which is small enough in order not to produce any significant disruption to the user (10-50 ms). Finally, the scenarios of interest have been replicated in a simulation environment, showing that significant benefits can be achieved if the specific characteristics of each AP and station are considered

Leveraging on Digital Signage Networks to Bring Connectivity IOT Devices

The number of Internet-connected devices exceeds the world’s population by more than three times and this figure is expected to be doubled within the next five years. The Internet of Things is a concept that describes this trend and outlines certain aspects of design and functionality that new devices should incorporate for a successful integration into the Internet. In this respect, Digital Signage networks traditionally used for audiovisual media, accomplish many of the characteristics of the Internet of Things devices: interoperability, mobility, scalability and ubiquity, both in terms of access and control of devices and regarding the information they generate. This paper raises the power to employ a proposed Digital Signage network as a substrate to connect other types of devices that can benefit from the advantages of this kind of networks. For that aim, the main problems for this integration are discussed, mainly those related to the bidirectional tunneling scheme used in the proposed Digital Signage solution. The effects of this tunneling approach are analyzed in scenarios with bandwidth constraints, and different solutions are proposed. Tunneling performance in mobility is improved, to increase the amount of Internet of Things devices and applications that can benefit from this type of network. El número de dispositivos conectados a Internet supera actualmente a la población mundial por más de tres veces y se espera que esta cifra se duplique en los próximos cinco años. El Internet de las Cosas es un concepto que describe esta tendencia y perfila ciertos aspectos de diseño y funcionalidad que los nuevos dispositivos deben incorporar para lograr una integración exitosa en Internet. En este sentido, las redes digital signage utilizadas tradicionalmente para los medios de comunicación audiovisual cumplen muchas de las características requeridas en el contexto del Internet de las Cosas: interoperabilidad, movilidad, escalabilidad y ubicuidad; relativas tanto al acceso y control de dispositivos como a la información que estos generan. En este trabajo se plantea el poder de emplear la red digital signage propuesta como sustrato para poder conectar otros tipos de dispositivos para que así puedan aprovechar las ventajas de estas redes. Para ese fin, se discuten los principales problemas existentes en esta integración, prestando especial atención al esquema de túnel bidireccional utilizado en la solución digital signage propuesta. Los efectos de este enfoque de tunelación se analizan en escenarios con limitaciones de ancho de banda y se proponen diferentes soluciones. Con ello se consigue mejorar el rendimiento del túnel en movilidad, facilitando la integración de más dispositivos al Internet de las Cosas al permitir que puedan integrarse en este tipo de redes

On the presence of Scaurus puncticollis Solier, 1838 (Coleoptera: Tenebrionidae) in Qatar

As part of the biodiversity surveys conducted by the Department of Biodiversity at the Qatar Environment and Energy Research Institute (QEERI), we can report the presence of Scaurus puncticollis Solier, 1838 in Qatar, and confirm the first record for the tribe Scaurini Billberg, 1820 in the country. We found two living specimens and remains of a third one distributed over the year (February, April and October) in three different locations of the Al Rayyan Municipality in Qatar. These findings reveal that the fauna of darkling beetles of Qatar is, despite previous efforts, still underestimated. To document and report the actual Biodiversity Heritage of Qatar, new exhaustive field biodiversity surveys should be conducted to complete the catalogue of Tenebrionoidae for the State of Qatar.Peer Reviewe