Self-* overload control for distributed web systems

Unexpected increases in demand and most of all flash crowds are considered the bane of every web application as they may cause intolerable delays or even service unavailability. Proper quality of service policies must guarantee rapid reactivity and responsiveness even in such critical situations. Previous solutions fail to meet common performance requirements when the system has to face sudden and unpredictable surges of traffic. Indeed they often rely on a proper setting of key parameters which requires laborious manual tuning, preventing a fast adaptation of the control policies. We contribute an original Self-* Overload Control (SOC) policy. This allows the system to self-configure a dynamic constraint on the rate of admitted sessions in order to respect service level agreements and maximize the resource utilization at the same time. Our policy does not require any prior information on the incoming traffic or manual configuration of key parameters. We ran extensive simulations under a wide range of operating conditions, showing that SOC rapidly adapts to time varying traffic and self-optimizes the resource utilization. It admits as many new sessions as possible in observance of the agreements, even under intense workload variations. We compared our algorithm to previously proposed approaches highlighting a more stable behavior and a better performance.Comment: The full version of this paper, titled "Self-* through self-learning: overload control for distributed web systems", has been published on Computer Networks, Elsevier. The simulator used for the evaluation of the proposed algorithm is available for download at the address: http://www.dsi.uniroma1.it/~novella/qos_web

A property of structural numbers and cut sets

The classical theory of structural numbers and its relations with graphs are used in this work to determine a property concerning cut sets in graphs. © 1979 Instituto di Elaborazione della Informazione del CNR

Design and Evaluation of Protocol Stacks for Underwater Communications

The project revolves around three themes: (i) understanding the physics of acoustic propagation and its impact on the design of communication algorithms and network protocols, (ii) design of network protocols that are theoretically sound and suited to the needs of underwater applications, and (iii) experimental demonstration. The latter activity will benefit from Prof. Basagni collaborations with Woods Hole Oceanograhic Institute and with La Spezia NURC (Nato Underwater Research Center). Such collaborations will allow us to test our ideas in real settings, using equipments whose cost (in the million of Euros) would otherwise be not affordable, having impact on cutting edge ocean engineering