Analysis And Research On Churn Problem In P2P Networks

In the traditional client-server (C/S) network, as the number of simultaneous client requests to a given server increases, the server can become overloaded. In additional, when a critical server fails under the C/S model, clients' requests cannot be fulfilled. At the same time, with the rapid grothw of internet, the next generation networks should address how to loacate and share the aggregated resources in internet. To solve these problems, peer-to-peer (P2P) networks are developing rapidly and have been widely used.One of the fundamental problems in the DHT-based Peer-to-Peer (P2P) networks is the problem of churn, which is the continuous process of node arrival and departure in the system. The churn can increase maintenance costs or decrease service quality such as dropped messages, data inconsistency, increased user-experienced latency, or increased bandwidth use.The goal of this paper is to optimize the performance of the DHT-based P2P networks under churn. We propose a new hierarchical DHT-based P2P network, which can not only reduce the harmful effect of churn on network performance but also easily solve the load imbalance of superpeers in the hierarchical DHT-based P2P network. This paper bases on the nation 973 project "Fundamental Research on the Architecture of Universal Trustworthy Network and Pervasive Services", the main research results and innovations are as follows:(1) On the basis of the generation mechanism of churn, this study summarizes the major steps of the churn problem solution:precise measurement of Churn, analysis of the impact of Churn on P2P performance, and provision of specific strategies to handle Churn. Under each step, existing problems, solutions, and the newest recent research are explored. This paper also discusses the prospects of future studies.(2) This paper proposes a new hierarchical DHT-based P2P network, called 2Chord, in which each superpeer, besides being responsible for the Chord identifier interval from its predecessor to it, maintains the linear leaf-peer interval within which its leaf peers fall. This new hierarchical DHT network can use some stable and powerful peers (called superpeers) to achieve efficient lookup under highly churn environments and can easily solve the load imbalance among superpeers.(3) In 2Chord system, two types of superpeer load balancing algorithms are proposed:one is to find a balance point between the leaf-peer intervals; another is to find a tradeoff point between balancing linear leaf-peer interval and balancing request loads for a superpeer. Analysis and simulation results show that our method can balance the load among superpeers in proportion to their capacity under Zipf capacities distribution and Gaussian or Pareto requests distribution.(4) This paper presents a fuzzy classification method to analyze the dynamic behaviors of peers and gives a formal definition of stable peers. At the same time, this paper defines the approximate entropy which can be used to analyze the session sequences of stable peers in P2P networks.