Research And Improvement Of Chord Protocol And Algorithm In P2P Network

One of fundamental problems confronted by peer-to-peer(P2P) applications is how to efficiently locate the node that stores a particular data item, different strategies are adopted by different P2P search algorithms, in which the efficiency is different.One of distributed search algorithms, named Chord was analysed. As the second generation of P2P algorithm, distributed hash table is adopted by Chord as the search strategy. Chord is scalable, with communication cost and the state maintained by each node scaling logarithmically with the number of Chord nodes, many advantages are hold by Chord algorithm, such as balance load, reliability, expansibility and so on, but the search efficiency of Chord is low.The Full-Chord algorithm which addressed the disadvantage of Chord was presented. The finger table of Chord was improved by Full-Chord algorithm, the formula which calculated the finger table was extended into two, so that the calculating procedure could be conducted in both of clockwise and anti-clockwise directions. At the beginning of the search procedure, the range of the search could be restricted in a half Chord-Circle by Full-Chord. In such a way, the target node could be approached more easily and the search efficiency also could be improved. Theoretical analyses had showed that the efficiency of Full-Chord algorithm is clearly superior to original Chord algorithm.It is very common to insert or delete a node in a P2P network, and therefore the adaptability of P2P network must be considered. Through lots of work in this aspect, an assumption of creating a table having r successors for each node was presented and this will solve the problem better.The research results in small-world field were also used for reference to extend Chord algorithm. Through the analysis of the node degree, a concept which is called "super node" was presented. Referencing to the search technology of Google called PageRank, a formula which can calculate the node range called noderange was found and the super node can be determined easily through this formula. The resource could be efficiently located by super node, and the search efficiency also could be improved.Finally, the simulated testings had showed that the efficiency of Full-Chord is clearly superior to the original Chord in two aspects of average search path length and average search time.