Chinese Journal of Computers   Full Text
Title	A Load Balancing Method in Superlayer of Hierarchical DHT-Based P2P Network
Authors	ZHANG Yu-Xiang1),2) ZHANG Hong-Ke1)
Address	1)(National Engineering Laboratory on Next Generation Internet Interconnection Devices, School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing 100044) 2)(College of Computer Science, Civil Aviation University of China, Tianjin 300300)
Year	2010
Issue	No.9(1580—1590)
Abstract &   Background	Abstract Compared to flat DHT-based Peer-to-Peer (P2P) networks, hierarchical DHT-based P2P networks can use some stable and powerful peers (called superpeers) to achieve efficient lookup under highly dynamic environments. However, a crucial problem faced by all these networks is the load imbalance among superpeers. This paper proposes a novel load balancing algorithm, 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. On this basis, “moment balance equation” is applied to finding a tradeoff point between balancing linear leaf-peer interval and balancing request loads for a superpeer. Analysis and simulation results show that the method can balance the load among superpeers in proportion to their capacity under Zipf capacities distribution and Gaussian or Pareto requests distribution. Keywords DHT; Chord; hierarchical DHT-based P2P network; load balancing Background This research is partly supported by the National Natural Science Foundation of China under grant Nos.60833002, 60776807, the Beijing Natural Science Foundation under grant No.4091003 and by the Special Fund of Basic Scientific Research of Central Colleges under grant Nos.ZXH2010D016, ZXH2009A006. In flat DHT-based Peer-to-Peer (P2P) networks, as the network size increases, weak peers will seriously limit the performance of DHT networks in a churn environment. To address this problem, several hierarchical DHT-based P2P networks have been proposed so far. However, a crucial problem faced by all these networks is the load imbalance among superpeers. These hierarchical DHT networks are mostly organized into two layers: a superlayer built by superpeers, and a leaf-peer layer built by all peers. The superlayer is mostly implemented using a DHT algorithm such as Chord Protocol. At the same time, each superpeer manages a group of leaf peers, and is responsible for delivering queries on behalf of the leaf peers in its group. This paper presents a novel load balancing algorithm for two-tier DHT system with a connection leaf-peer layer, which we call 2Chord (2-teir Chord). In 2Chord, the basic idea of the load balancing algorithm is that each superpeer, besides being responsible for the circular identifier interval from its identifier to its predecessor’s identifier (this is the Chord identifier interval), maintains the linear leaf-peer interval which is different from the former. On this basis, “moment balance equation” is applied to finding a tradeoff point between balancing linear leaf-peer interval and balancing request loads for a superpeer. Analysis and simulation results show that the method can balance the load among superpeers in proportion to their capacity.