Performance Analysis And Search Algorithm Improvement Of Structured P2P Network

In recent years,peer-to-peer network has been widely used in the Internet.Each node on the peer-to-peer network is both a content provider and a content consumer. Because of high scalability and good fault-tolerance capabilitysstructured peer-to-peer network becomes current research hotspot.Which identifies and locates resources based on Distributed Hash Table(DHT),hashing resources and nodes to the same key space so that each resource is mapped to the node whose identifier is closest to its resource identifier.While this resource location mechanism effectively addresses the unscalability issue caused by flooding mechanism of unstructured P2P network,new problems emerge and remain unresolved as follows:1) the cost of updating the routing table increases significantly due to the frequent entering and exiting of the nodes;2)Since the information of the node physical location is lost during the hashing process,the physical distance between two neighboring nodes in the overlay network could be very large, thereby causing long query delay in structured P2P network.3)When the churn rate is high,some structured P2P networks's preference decrease sharply.4) the network only supports searches of precise key-value matching but does not support multi-key-words searches.Prior researches on structured P2P network mainly focus on the improvement of DHT protocol in order to solve a specific problem,There are little to resolution based on performance analysis.The method has two weaknesses:At first,the improvement is aimed at a specific DHT protocol e.g.Tapestry,and may not be generalized.The second,the method fails to take a balanced approach,e.g.while the constant-degree DHT algorithm reduces the query hops,its poor ability of handling the abnormal departure of the nodes significantly decreases the fault-tolerance capability of the system.Therefore, to address the problems,the algorithm should be improved based on insights from a detailed analysis of typical structured P2P network focusing on the cost of routing table update,query delay and the scalability in a churn environment.With regard to the churn issue,The concept of inverse-neighbourhood nodes is proposed.Which means the node is in their routing table.The number of inverse-neighbourhood nodes for six DHT netword is computed.we find that the most significant factors affecting churn is routing,neighboring nodes selection,bootstrapping,lookup parallely and recovery policy.In any two existing DHT,there are at least two kind of policy different.Therefore,the method that compares the routing tables update costs of two structured P2P network directly cann't decide which policy could deal with churn,so we proposes a new method of analysis:CSP(A comparation based on single policy),this method analyzed the relationship between routing tables update costs and each single policy.We create F Pastry which uses fast bootstrapping policy and P_Pasty which uses periodic recovery policy.F_Pastry and P_Pastry are compared with the original version Pastry separately.At the same time,I_Chord which uses iterative routing and R_Chord which use recursive routing are compared.It's concluded that iterative routing,fast bootstrapping,periodly recovery and effective neighboring nodes selection algorithm could decrease the consts of updating routing table in high churn.The mechanisms of storing data,routing policy,neighboring nodes selection and sever-selection is the key factor which affect the query delay of tructured peer-to-peer networkBased on the analysis of the query delay and the weakness of the algorithm aimed at reducing the delay,the paper proposes a DCAN algorithm in order to reduce delay between the nodes in the Content-Addressable Network(CAN).This algorithm abstracts nodes of CAN network into a undirected weighted graph.By dijkstra algorithm,the shortest path from source node to destination node is obtained as the query routing.Simulation experiments suggest that this algorithm can reduce the delay between the source nodes and the target nodes in CAN effectively.In order to address the scalability problem of the P2P network underthe condition of churn,a low-bandwidth evaluation(LBE) method is proposed.Which use the variation of delay for success query and percentage for failed query as the standard to evaluate scalability.A series of delay times are getted by changing DHT parameters randomly,The lowest line could be formed by so much points as the overall performance of DHT network.By fixing some parameter and changing other parameters,the optimal design parameter value could be obstained to get the best DHT network performance.We analyze the scalability of three DHT protocols from two respects:overall preference of the network and the change of optimal design parameters relative to the network scale,and get corresponding conclution.Based on the analysis of the weakness of current multi-key-word search algorithm, the paper proposes an ICCCS(Improved Cube-Connected Cycle) search algorithm, which establishes a logical key-word search layer on top of the DHT protocol layer. The search layer is structured using the Improved Cube-Connected Cycle.The top keywords for each object is choosed by Vector Space Model and is mapped to the cyclic index of ICCC nodes.The whole keyword set for each object is mapped to the cubic index of ICCC nodes.The index scheme is build on Inverse Document Index and the search algorithm is created on Spanning Binomial Tree.Experiments suggest that the algorithm results in higher search precision and lower query delay for searches with fewer key words.