Harry Li

University of Texas at Austin

Building Robust Cooperative Services


Decentralized approaches are an increasingly effective way to deploy services. Popular examples include peer-to-peer (p2p) applications, content distribution networks, and mesh routing protocols. These approaches are attractive because they can be highly fault-tolerant, scalable, adaptive, and less expensive than a more centralized solution.  Cooperation lies at the heart of these strengths. Yet, in settings where working together is crucial, a natural question is: "What if users stop cooperating?"


This talk explores how to build cooperative services to tolerate Byzantine participants while also incentivizing selfish participants to contribute resources.  I will discuss how to balance obedience against choice in building a robust live streaming system. Imposing obedience is desirable as it leaves little room for users to attack or cheat the system. However, providing choice is also attractive as it allows us to engineer flexible and efficient solutions. My work strikes a balance between obedience and choice by using approximate equilibria in the design and implementation of FlightPath.


FlightPath is a very robust and practical p2p live streaming system. It can maintain a highly reliable stream of data from a source to a large population of peers while using bandwidth efficiently, handling churn, and tolerating malicious activity. In disseminating an hour long video, 98% of peers deliver every packet and 100% of peers miss less than 6 seconds. FlightPath continues to provide good stream quality despite 10% of peers acting maliciously. Moreover, the system can easily absorb flash crowds and sudden massive peer departures.



Harry Li is a Ph.D. candidate at the University of Texas at Austin and works with Professor Lorenzo Alvisi and Professor Mike Dahlin. His current research focuses on designing robust cooperative systems. However, his interests span all things distributed, operating systems, networking, game theory, mechanism design, and formal methods. Harry received an Sc.B. in computer science from Brown University where he also pursued research in model checking.



B17 Upson Hall

Thursday, April 9, 2009

Refreshments at 3:45pm in the Upson 4th Floor Atrium

Computer Science


Spring 2009