Server Placement with Shared Backups for Disaster-Resilient Clouds

A key strategy to build disaster-resilient clouds is to employ backups of virtual machines in a geo-distributed infrastructure. Today, the continuous and acknowledged replication of virtual machines in different servers is a service provided by different hypervisors. This strategy guarantees that the virtual machines will have no loss of disk and memory content if a disaster occurs, at a cost of strict bandwidth and latency requirements. Considering this kind of service, in this work, we propose an optimization problem to place servers in a wide area network. The goal is to guarantee that backup machines do not fail at the same time as their primary counterparts. In addition, by using virtualization, we also aim to reduce the amount of backup servers required. The optimal results, achieved in real topologies, reduce the number of backup servers by at least 40%. Moreover, this work highlights several characteristics of the backup service according to the employed network, such as the fulfillment of latency requirements.Comment: Computer Networks 201

Trace Selection for Improved WLAN Monitoring

International audienceExisting measurement techniques for IEEE 802.11-based networks assume that the higher the density of monitors in the target area, the higher the quality of the measure. This assumption is, however, too strict if we consider the cost involved in monitor installation and the necessary time to collect and merge all traces. In this paper, we investigate the balance between number of traces and completeness of collected data. We propose a method based on similarity to rank collected traces according to their contribution to the monitoring system. With this method, we are able to select only a subset of traces and still keep the quality of the measure, while improving system scalability. In addition, based on the same rank, we identify monitors that can be relocated to enlarge the monitored area and increase the overall efficiency of the system. Finally, our experimental results show that the proposed solution leads to a better tradeoff in terms of unique captured frames over the number of merge operations

The Power of Quasi-Shortest Paths: ρ-Geodesic Betweenness Centrality

International audienceBetweenness centrality metrics usually underestimate the importance of nodes that are close to shortest paths but do not exactly fall on them. In this paper, we reevaluate the importance of such nodes and propose the ρ-geodesic betweenness centrality, a novel metric that assigns weights to paths (and, consequently, to nodes on these paths) according to how close they are to shortest paths. The paths that are just slightly longer than the shortest one are defined as quasi-shortest paths, and they are able to increase or to decrease the importance of a node according to how often the node falls on them. We compare the proposed metric with the traditional, distance-scaled, and random walk betweenness centralities using four network datasets with distinct characteristics. The results show that the proposed metric, besides better assessing the topological role of a node, is also able to maintain the rank position of nodes overtime compared to the other metrics; this means that network dynamics affect less our metric than others. Such a property could help avoid, for instance, the waste of resources caused when data follow only the shortest paths and reduce associated costs

Padrões de Mobilidade de Vizinhança em Redes de Contato Intermitente

A modelagem dinmica de redes oportunsticas se baseia no conhecimento dual dos contatos e dos intercontatos. Este trabalho prope o uso de uma viso estendida, na qual os ns rastreiam sua vizinhana estendida (a alguns saltos) e no somente seus vizinhos diretos. Para tal, introduzido um mtodo que permite aos ns preverem se outros estaro em alcance dada a posio atual e os movimentos anteriores. Essa abordagem contrria s existentes nas quais os padres de contato so extrados da mobilidade espacial dos ns. O mtodo proposto aplicado a vrios traos reais e sintticos. Inicialmente, um novo algoritmo provido bem como uma modelagem intuitiva para compreender o entorno de um n. Em seguida, so destacadas duas cadeias principais de comportamento da vizinhana. Finalmente, trs principais tipos de movimento (nascimento, morte e sequencial) so identificados assim como os seus padres predominantes

Eficiência dos Caminhos Quase Mais Curtos em Redes Dinâmicas

National audienceMétricas de centralidade de intermediação frequentemente subestimam a importância dos nós próximos do caminho mais curto, mas que raramente participam deles. Em redes dinâmicas, esses nós podem se encontrar momentaneamente em posições topologicamente estratégicas. Este artigo avalia a importância desses nós reutilizando a ideia de centralidade de intermediação por espalhamento. Essa métrica considera, além dos caminhos mais curtos, os múltiplos ``caminhos quase mais curtos'', atribuindo-lhes um peso proporcional. O impacto da métrica na rede é avaliado através de comparações com outras métricas de intermediação. Os resultados mostram que o uso da ideia de espalhamento pode reclassificar nós, reduzindo o número de pontos de articulação na rede que estão dentre os nós mais bem classificados. Considerando falha nos nós mais centrais, a vazão da rede em geral mantém-se mais elevada quando o espalhamento é aplicado. Essa propriedade pode ajudar a escolher melhor o papel executado pelos nós de forma a melhorar o desempenho de redes com dinâmica temporal

Unsupervised Detection of Adversarial Collaboration in Data-Driven Networking

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Network Design Requirements for Disaster Resilience in IaaS Clouds

International audienceMany corporations rely on disaster recovery schemes to keep their computing and network services running after unexpected situations, such as natural disasters and attacks. As corporations migrate their infrastructure to the cloud using the infrastructure as a service model, cloud providers need to offer disaster-resilient services. This article provides guidelines to design a data center network infrastructure to support a disaster-resilient infrastructure as a service cloud. These guidelines describe design requirements, such as the time to recover from disasters, and allow the identification of important domains that deserve further research efforts, such as the choice of data center site locations and disaster-resilient virtual machine placement

Latency versus survivability in geo-distributed data center design

A hot topic in data center design is to envision geo-distributed architectures spanning a few sites across wide area networks, allowing more proximity to the end users and higher survivability, defined as the capacity of a system to operate after failures. As a shortcoming, this approach is subject to an increase of latency between servers, caused by their geographic distances. In this paper, we address the trade-off between latency and survivability in geo-distributed data centers, through the formulation of an optimization problem. Simulations considering realistic scenarios show that the latency increase is significant only in the case of very strong survivability requirements, whereas it is negligible for moderate survivability requirements. For instance, the worst-case latency is less than 4~ms when guaranteeing that 80% of the servers are available after a failure, in a network where the latency could be up to 33 ms

VEER: Um Algoritmo de Seleção de Pares em Redes Ad Hoc Veiculares

National audienceThis paper introduces Veer, a peer selection algorithm for vehicular ad hoc networks running peer-to-peer file exchange applications. Contrary to existing approaches that basically consider vehicular networks as ordinary mobile ad hoc networks, Veer relies on the individual mobility patterns of the vehicles when making peer selection, and this at low control overhead. In Veer, replies are only sent by peers that share part of their trajectories with the requesting node. The file transfer is then scheduled to the time interval when both vehicles meet. In this way, Veer avoids multi-hop file transfers, thus reducing contention areas and increasing the global capacity of the network. We show through extensive simulation that using such an opportunistic one-hop transfer mechanism gives better results than multi-hop file tranfers. In order to support our simulation results, we show through real experiments the capacity of car-to-car links with off-the-shelf hardware