Qiao Lian

An Empirical Study of Collusion Behavior in the Maze P2P File-Sharing System

Peer-to-peer networks often use incentive policies to encourage cooperation between nodes. Such systems are generally susceptible to collusion by groups of users in order to gain unfair advantages over others. While techniques have been proposed to combat Web spam collusion, there are few measurements of real collusion in deployed systems. In this paper, we report analysis and measurement results of user collusion in Maze, a large-scale peer-to-peer file sharing system with a non-net-zero point-based incentive policy. We search for colluding behavior by examining complete user logs, and incrementally refine a set of collusion detectors to identify common collusion patterns. We find collusion patterns similar to those found in Web spamming. We evaluate how proposed reputation systems would perform on the Maze system. Our results can help guide the design of more robust incentive schemes.

On the Impact of Replica Placement to the Reliability of Distributed Brick Storage Systems

Data reliability of distributed brick storage systems critically depends on the replica placement policy, and the two governing forces are repair speed and sensitivity to multiple concurrent failures. In this paper, the authors provided an analytical framework to reason and quantify the impact of replica placement policy to system reliability. The novelty of the framework is its consideration of the bounded network bandwidth for data maintenance. The framework was applied to two popular schemes, namely sequential placement and random placement, and showed that both have drawbacks that significantly degrade data reliability. Then the stripe placement scheme was proposed and find the near-optimal configuration parameter such that it provides much better reliability. The possibility of addressing the problem of correlated brick failures in the analytical framework was further discussed

Robust incentives via multi‐level Tit‐for‐Tat

Much work has been done to address the need for incentive models in real deployed peer‐to‐peer networks. In this paper, we discuss problems found with the incentive model in a large, deployed peer‐to‐peer network, Maze. We evaluate several alternatives, and propose an incentive system that generates preferences for well‐behaved nodes while correctly punishing colluders. We discuss our proposal as a hybrid between Tit‐for‐Tat and EigenTrust, and show its effectiveness through simulation of real traces of the Maze system. Copyright

RepStore: a self-managing and self-tuning storage backend with smart bricks

With the continuously improving price-performance ratio, building large, smart-brick based distributed storage system becomes increasingly attractive. The challenges, however, include not only reliability, adequate cost-performance ratio, online upgrades and so on, but also the systems ability to achieve these goals in as self-managing and self-adaptive a manner as possible. In this paper, we describe RepStore, a system that fulfills these goals. RepStore unites the self-organizing capability of P2P DHT and the completely autonomous, per-brick tuning mechanism to derive a scalable and cost-effective architecture. RepStore employs replication for active write-intensive data and erasure-coding for the rest, strives to achieve the best cost-performance balance automatically and transparent to application, and does so in a completely distributed manner. Our preliminary evaluations reveal that the system performs much as expected, achieving performance and reliability closer to a 3-way fully replicated system with only 60% of the cost.

Z-ring: fast prefix routing via a low maintenance membership protocol

In this paper, we introduce Z-ring, a fast prefix routing protocol for peer-to-peer overlay networks. Z-ring incorporates cost-efficient membership protocol to achieve fast routing with small maintenance cost. Z-ring achieves routing in logGN steps, where N is the network size and G is the size of a group that can be maintained by a membership protocol with low cost. With G=4096, it translates to one-hop routing for intranet environments (N<4096), two-hop routing for mid-scale internet applications (N<16 million), and three-hop routing for ultra-large Internet applications (N<64 billion). Z-ring maintains good routing success rate under churn and low maintenance cost even at large network size. Its modularized use of the membership protocol also makes it adaptive to dynamic and wide-range network size changes.

Sigma: a fault-tolerant mutual exclusion algorithm in dynamic distributed systems subject to process crashes and memory losses

This paper introduces the Sigma algorithm that solves fault-tolerant mutual exclusion problem in dynamic systems where the set of processes may be large and change dynamically, processes may crash, and the recovery or replacement of crashed processes may lose all state information (memory losses). Sigma algorithm includes new messaging mechanisms to tolerate process crashes and memory losses. It does not require any extra cost for process recovery. The paper also shows that the threshold used by the Sigma algorithm is necessary for systems with process crashes and memory losses.