In this paper we explore the problem of achieving efficient packet transmission over unreliable links with worst case occurrence of errors. In such a setup, even an omniscient offline scheduling strategy cannot achieve stability of the packet queue, nor is it able to use up all the available bandwidth. Hence, an important first step is to identify an appropriate metric for measuring the efficiency of scheduling strategies in such a setting. To this end, we propose a relative throughput metric which corresponds to the long term competitive ratio of the algorithm with respect to the optimal. We then explore the impact of the error detection mechanism and feedback delay on our measure. We compare instantaneous error feedback with deferred error feedback that requires a faulty packet to be fully received in order to detect the error. We propose algorithms for worst-case adversarial and stochastic packet arrival models, and formally analyze their performance. The relative throughput achieved by these algorithms is shown to be close to optimal by deriving lower bounds on the relative throughput of the algorithms and almost matching upper bounds for any algorithm in the considered settings. Our collection of results demonstrates the potential of using instantaneous feedback to improve the performance of communication systems in adverse environments.

​We describe the design and implementation of DeepDive, a system for transparently identifying and managing performance interference between virtual machines (VMs) co-located on the same physical machine in Infrastructure-as-a-Service cloud environments. DeepDive successfully addresses several important challenges, including the lack of performance information from applications, and the large overhead of detailed interference analysis. We first show that it is possible to use easily-obtainable, low-level metrics to clearly discern when interference is occurring and what resource is causing it. Next, using realistic workloads, we show that DeepDive quickly learns about interference across co-located VMs. Finally, we show DeepDive’s ability to deal efficiently with interference when it is detected, by using a low-overhead approach to identifying a VM placement that alleviates interference.

In this self-contained talk I will describe few combinatorial results that were initiated by problems from several application areas. These results include the following: (1) the use of the Cycle Lemma in deriving statistics about several classes of trees (this includes, as a start, a very simple proof for the Catalan number of binary trees), (2) a new characterization of tree medians, (3) an algorithm for generation of permutations, (4) a result about the volume of discrete spheres, and (5) a combinatorial problem that resulted in a paper with Paul Erdős

WoWMoM 2013 is the 14th IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks. WoWMoM addresses research challenges and advances towards a world of wireless, mobile, and multimedia pervasive communications.

Institute IMDEA Networks annually holds a by-invitation-only thematic workshop in Madrid. The workshop accompanies a meeting of our Scientific Council comprised of prominent researchers. In addition to talks by Scientific Council members, the workshop includes invited talks by external experts in the research theme of the workshop. The goal of the 2013 event is to foster discussion on a critical aspect of research in networking: 'Reliable Networked Systems'. The workshop will be held on June 5th at University Carlos III of Madrid.

We are entering an era where accurately synchronized clocks are economical and are becoming commonplace. Commercial GPS units synchronize clocks within 10’s of micro-­‐seconds. Chip sets that implement the IEEE 1588 standard are synchronizing clocks within a fraction of a nano-­‐second to improve the probability of collisions in particle colliders.

En este trabajo proponemos una solución para la asignación de tareas en un entorno distribuido complejo y auto-organizado (sería el caso de las redes entre iguales o ́ P2P). Estamos interesados en las tareas que son comunes a todos los participantes o nodos del sistema. Cada uno de los nodos puede ejecutar estas tareas y, además, está interesado en que éstas se ejecuten. Cada nodo dispone de capacidad para la ejecución de cada una de las tareas. El coste para cada nodo es una información que no puede ser auditada y que es únicamente conocido por el nodo en cuestión. Suponemos que los nodos pueden mentir sobre su coste si eso les supone un beneficio; por ejemplo, por el ahorro que implicaría verse libre de ejecutar las tareas.

To meet the increasing demand for wireless capacity, future networks are likely to consist of dense layouts of small cells. Thus, the number of concurrent users served by each base station (BS) is likely to be small which results in diminished gains from opportunistic scheduling, particularly under dynamic traffic loads. We propose user-initiated BS-transparent traffic spreading that leverages user-to-user communication to increase BS scheduling flexibility.

The increasing demand for higher data rates in cellular network results in increasing network density. As a consequence, inter-cell interference is becoming the most serious obstacle towards spectral efficiency. Therefore, considering that radio resources are limited and expensive, new techniques are required for efficient radio resource allocation in next generation cellular networks. In this paper, we propose a pure frequency reuse 1 scheme based on base station scheduling rather than the commonly adopted user scheduling. In particular, we formulate a base station scheduling problem to determine which base stations can be scheduled to simultaneously transmit, without causing excessive interference to any user of any of the scheduled base stations. We show that finding the optimal base station scheduling is NP-hard, and formulate the BASICS (BAse Station Inter-Cell Scheduling) algorithm, a novel heuristic to approximate the optimal solution at low complexity cost. The proposed algorithm is in line with the ABSF (almost blank sub-frame) technique recently standardized at the 3GPP. By means of numerical and packet-level simulations, we prove the effectiveness and superiority of BASICS as compared to the state of the art of inter-cell interference mitigation schemes.

The IEEE Standard 802.3az, namely Energy Efficient Ether- net (EEE), has been recently introduced to reduce the power consumed in LANs. Since then, researchers have proposed various traffic shaping techniques to leverage EEE in order to boost power saving. In particular, packet coalescing is a promising mechanism which can be used on top of EEE to tradeoff power saving and packet delay.