Category Archives: News

18.12.2012 – Talk by Michele Mazzucco

Title: Revenue Maximization Problems in Commercial Data Centers

Date: 18/12/2012
Time: 1:00 pm
Location: Sala riunioni
Type: industrial application
Speaker: Michele Mazzucco (Demonware, Dublin)


As IT systems are becoming more and more important, one of the main concerns is that users may face major breakdowns and eventually incur major costs if computing systems do not meet the expected performance requirements: customers expect reliability and performance guarantees, while under-performing systems loose revenues. For example, it has been reported that Amazon tried delaying the page generation by 100 ms and found out that even very small delays would result in substantial and costly drops in revenue (1% sales drop for 100 ms delay). In this talk I will discuss some performance models aiming at optimizing the revenue earned by IT providers running ‘jobs’ subject to Quality of Service (QoS) constraints. The presentation is divided into two parts. In the first part I will analyze a business model where the QoS guarantees are formally defined through Service Level Agreements (SLAs), and thus the provider is liable to pay a penalty every time the promised performance level is not met. Experimental results show that revenues can be dramatically improved by imposing suitable conditions for accepting incoming traffic, and that the proposed policies perform well under different traffic conditions.

In the second part of the presentation I will discuss two queueing models for power and performance. The main difference compared to the first part of the talk is that now the QoS is implicit, and thus customers simply leave the system (or wait) if it under-performs, while the provider also takes into account the energy consumed by servers when deciding how many servers to allocate.

Michele Mazzucco graduated in Computer Science at the University of Bologna and obtained his PhD at the University of Newcastle under the supervision of prof. Mitrani. His main reserach interests include models for the performance evaluation and optimization of data centers. He has published in major conferences and journals on topics such as cloud computing and green computing. Since 2012, he works for Demonware.

DemonWare is an Irish software development company and a subsidiary of Activision Blizzard. DemonWare’s products enable games publishers to outsource their networking requirements, allowing them to concentrate on playability. The organisation has offices in Dublin, Ireland; and Vancouver, Canada.Primary products developed by DemonWare include the “DemonWare State Engine” and “Matchmaking+”. The State Engine is a high-performance state synchronization C++ programming framework that eliminates the need to reinvent netcode multiplayer games. Matchmaking+ provides services for multiplayer games such as matchmaking, user profiling, and gaming statistics. DemonWare’s main product has been used to support the development of several online games of success, among which Call of Duty.

12.12.2012 – Tutorial by Stefano Calzavara

Title: An introduction to stochastic process algebras and quantitative security analysis

Date: 12/12/2012
Time: 3:00 pm
Location: Sala riunioni
Type: review of literature
Speaker: Stefano Calzavara (Ca’ Foscari, Venice)

Stochastic process algebras are a popular and convenient specification tool, which have proven successful in many applications from the areas of performance modeling, bioinformatics, and security. However, approaching the world of stochastic process algebras is a nontrivial task, since the very foundations of such models are rather peculiar and the well-known formal machinery of classical (non-deterministic) process algebras does not properly fit them. In this talk we analyze stochastic process algebras from the point of view of the programming languages community, and we try to motivate and understand some apparently weird design choices underlying their development. We then focus on an application of stochastic process algebras to security verification and we propose a personal understanding of the challenges behind such task. We argue that, as the foundations of stochastic process algebras depart from those of classical process algebras, also the approach to their verification may probably benefit from a change of perspective.

Prerequisites: Some notions on process algebras and formal methods may help in appreciating the contents, but the seminar is self-contained.

05.12.2012 – Tutorial by Gian-Luca dei Rossi

Title: Performance evaluation of ARQ protocols

Date: 05/12/2012
Type: review of literature
Speaker: Gian-Luca dei Rossi (Ca’ Foscari, Venice)

Abstract: ARQ (Automatic Repeat Request) protocols are widely used in computer networks in order to provide reliable communications over unreliable  channels such as wireless links. Following the track of the previous lecture, this talk proposes an analysis, based on matrix geometric methods, of ARQ Protocols in wireless networks with Adaptive Modulation and Coding (AMC), modelled as Discrete Time Markov Chains  (DTMCs), as originally proposed in [1]. The derivation of some performance indices is then shown.

[1] Long B. Le, Edkram Hossain, Michele Zorzi: “Queueing Analysis for GBN and SR ARQ Protocols under Dynamic Radio Link Adaptation with Non-Zero Feedback Delay” IEEE Transactions on Wireless Communications, volume 6, issue 9 (september 2007), pages: 3418-3428.

Prerequisites: Some very basic knowledge of linear algebra and computer networks, attendance to the previous seminar on Matrix Geometric Methods.

07.11.2012 – Tutorial by Andrea Marin

Title: From M/M/1 queues to Quasi Birth and Death Processes
Date: 7 November, 2012 – 12.30
Type: tutorial
Speaker: Andrea Marin (Ca’ Foscari, Venice)

Abstract: Markov chains are an important framework for studying queueing systems. However, deriving the steady-state behavior of a queue may be a really hard task because of the large number of states (possibly infinite) of the process. Indeed, the brute-force numerical algorithms quickly become numerically unstable and time-expensive. This tutorial aims at showing how the geometric structure of the Markov chains underlying a class of queues called “Quasi Birth and Death” can be exploited to derive its stationary state probabilities and performance indices.

Prerequisites: Matrix manipulation (product, sum, transposed), solution of linear systems in matrix form (including matrix inversion), rank of a matrix, continuous/discrete time Markov chains (stationary analysis)