[cs-talks] Upcoming CS Seminars: Bassem PhD Proposal (today)

Conroy, Nora Mairead conroynm at bu.edu
Mon Jan 26 09:04:14 EST 2015

PhD Proposal Defense
Route Coordination in Brokered Environments
Christine Bassem, BU
Monday, January 26, 2015 at 11am in MCS 148
Abstract: With the recent shift towards the integration of federated commodities to provide high quality services, the adoption of brokered environments has increased. In brokered environments, participants share information about their resources and/or workloads with each other and a broker, which acts as an intermediary between them; with varying degrees of involvement.  As many services can be provided in such environments, I focus on the services that require the routing of a set of commodities over a communication/mobility graph, hence the route coordination of autonomous commodities is required.
In this talk, I will briefly present the route coordination models that I study in my thesis, and discuss in details my most recent work on network-constrained packing of brokered workloads in virtualized environments. This work is a form of implicit route coordination on stationary graphs, in which routes’ properties are implicitly defined by their endpoints, and route coordination includes the decision on the endpoints of communication. As we focus on the problem of providing predictability guarantees to data-intensive workloads, we observe the range of data-intensive applications and data center topologies to define an abstraction that allows us to relate the problem to that of bin packing with implicit network properties. Then, we exploit that abstraction to classify the problem model into several special instances, and develop polynomial-time exact algorithms for two of these special instances that occur frequently in reality. Finally, we develop a greedy heuristic to solve the problem in the general model, which we evaluate via extensive simulations.
Azer Bestavros (reader)
Ibrahim Matta (reader)
Evimaria Terzi (reader)
Mark Crovella (chair)
Steve Homer

Wednesdays @ Hariri

Risk and Default Clustering In Large Financial Networks

Konstantinos Spiliopoulos, BU

Junior Faculty Fellow, Hariri Institute for Computing

Assistant Professor, Department of Mathematics & Statistics

Wednesday, January 28, 2015 at 3pm in MCS 180 – Hariri Institute

Abstract: The past several years have made clear the need to better understand the behavior of risk in large interconnected financial networks. Interconnections often make a system robust, but they can act as conduits for risk. In this talk, I will present recent results on modeling the dynamics of correlated default events in the financial market. An empirically motivated system of interacting point processes is introduced and we study how different types of risk, like contagion and exposure to systematic risk, compete and interact in large-scale systems. Network effects are analyzed and computational methods are developed to assess the behavior and the stability of the network. We develop methods for (a) approximating the distribution of the loss from default in large, potentially heterogeneous, portfolios, (b) capturing the most likely paths to systemic failure, (c) quantifying large portfolio losses (e.g., provably efficient Monte Carlo methods), and (d) understanding the network effects. Numerical results illustrate the accuracy of the approximations. The results give insights into how different sources of default correlation interact to generate typical and atypical portfolio losses. Understanding of these issues can be useful to regulators and give useful insights into how to optimally safeguard against bad events such as large portfolio losses.

Bio: Konstantinos Spiliopoulos is a Junior Fellow of the Hariri Institute and an Assistant Professor in the Department of Mathematics and Statistics at BU, which he joined in 2012. After receiving his Ph.D. at the University of Maryland at College Park, he was a Prager Assistant Professor at Brown University. His current research work focuses in two main areas: Monte Carlo methods, rare event simulation and mathematical analysis of multi-scale systems and equilibrium problems, and development of mathematical and computational tools for the quantification of systemic risk in large financial networks.

BUSec Seminar
Private Access to Remote Data via the Melbourne Shuffle
Olya Ohrimenko, MSR
Wednesday, February 4, 2015 at 9:30am in MCS 148

Abstract: A shuffle is an algorithm for rearranging an array to achieve a random permutation of its elements. Early shuffle methods were motivated by the problem of shuffling a deck of cards. An oblivious shuffle is a distributed shuffle executed by a client who permutes an array of encrypted data items stored at a server in such a way that the server cannot determine the output permutation with probability better than a random guess. Several private cloud storage solutions that obfuscate the access pattern to the data use an oblivious shuffle as a fundamental building block. We present the Melbourne Shuffle, a simple and efficient oblivious shuffle that allows a client with O(\sqrt{n}) memory to obliviously shuffle an array of size n stored at a server by exchanging O(\sqrt{n}) messages of size O(\sqrt{n}). The Melbourne Shuffle is the first provably secure oblivious shuffle that is not based on sorting.  This talk is based on the paper “The Melbourne Shuffle: Improving Oblivious Storage in the Cloud”, appeared in International Colloquium on Automata, Languages and Programming (ICALP), 2014. Joint work with Michael Goodrich (UC Irvine), Roberto Tamassia (Brown University) and Eli Upfal (Brown University).

NRG Seminar
Revisiting Network Resource Allocation in Data Centers
Fahad Dogar, Tufts
Monday, February 9, 2015 at 11am in MCS 148

Abstract: Popular applications like Facebook and Google Search perform rich and complex "tasks" (e.g., generating a user's social newsfeed). From a network perspective, these tasks typically comprise multiple flows, which traverse different parts of the network at potentially different times. Existing network resource allocation schemes (e.g., TCP), however, treat all these flows in isolation - rather than as part of a task - which delays completion of tasks (i.e., user requests). In this talk, I will make a case for "task-aware" network scheduling, and present Baraat, a decentralized task-aware scheduling system. Compared to existing approaches (e.g., TCP and other flow based schemes), Baraat improves both the average and tail response times for a wide range of workloads. I will also present a deployment friendly transport framework (PASE) which can support richer resource allocation schemes (e.g., task-aware scheduling) without requiring changes to network switches. Both Baraat and PASE appeared in ACM Sigcomm 2014. Joint work with researchers from MSR, MSU, and LUMS.

Bio: Fahad Dogar is an assistant professor in the computer science department at Tufts University. Earlier he did his PhD from Carnegie Mellon and undergrad from LUMS, Pakistan. Most recently, he was a post-doc in the systems and networking group at Microsoft Research UK. webpage: https://sites.google.com/site/fahaddogar/home
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