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Mathematical Problems in Engineering
Volume 2012, Article ID 923023, 18 pages
Research Article

Improved Degree Search Algorithms in Unstructured P2P Networks

Guole Liu,1,2,3 Haipeng Peng,1,2,3 Lixiang Li,1,2,3 Yixian Yang,1,2,3 and Qun Luo1,2,3

1Information Security Center, Beijing University of Posts and Telecommunications, P.O. Box 145, Beijing 100876, China
2Research Center on Fictitious Economy and Data Science, Chinese Academy of Sciences, Beijing 100190, China
3National Engineering Laboratory for Disaster Backup and Recovery, Beijing University of Posts and Telecommunications, Beijing 100876, China

Received 1 November 2011; Revised 21 February 2012; Accepted 14 April 2012

Academic Editor: Yi-Chung Hu

Copyright © 2012 Guole Liu et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Searching and retrieving the demanded correct information is one important problem in networks; especially, designing an efficient search algorithm is a key challenge in unstructured peer-to-peer (P2P) networks. Breadth-first search (BFS) and depth-first search (DFS) are the current two typical search methods. BFS-based algorithms show the perfect performance in the aspect of search success rate of network resources, while bringing the huge search messages. On the contrary, DFS-based algorithms reduce the search message quantity and also cause the dropping of search success ratio. To address the problem that only one of performances is excellent, we propose two memory function degree search algorithms: memory function maximum degree algorithm (MD) and memory function preference degree algorithm (PD). We study their performance including the search success rate and the search message quantity in different networks, which are scale-free networks, random graph networks, and small-world networks. Simulations show that the two performances are both excellent at the same time, and the performances are improved at least 10 times.