PChord:a distributed hash table for P2P network

As a solution for data storage and information sharing for peer-to-peer(P2P)networks,a novel distributed hash table(DHT)structure called PChord is presented in this paper.PChord adopts a bi-directional searching mechanism superior to Chord and enhances the structure of the finger table.Based on Hilbert space filling curve,PChord realizes the mapping mechanism for multikeyword approximate searching.Compared with the Chord and Kademlia protocols,PChord evidently increases speed on resource searching and message spreading via theoretic proof and simulation results,while maintaining satisfactory load balance.

Novel load balancing DHT scheme for the heterogeneous system

The capacities of the nodes in the peer-to-peer system are strongly heterogeneous, hence one can benefit from distributing the load, based on the capacity of the nodes. At first a model is discussed to evaluate the load balancing of the heterogeneous system, and then a novel load balancing scheme is proposed based on the concept of logical servers and the randomized binary tree, and theoretical guarantees are given. Finally, the feasibility of the scheme using extensive simulations is proven.

Load distributions of some classic DHTs

The load balance is a critical issue of distributed Hash table （DHT）, and the previous work shows that there exists O（logn） imbalance of load in Chord. The load distribution of Chord, Pastry, and the virtual servers （VS） balancing scheme and deduces the closed form expressions of the probability density function （PDF） and cumulative distribution function （CDF） of the load in these DHTs is analyzes. The analysis and simulation show that the load of all these DHTs obeys the gamma distribution with similar formed parameters.

HAPS:Supporting Effective and Effcient Full-Text P2P Search with Peer Dynamics

Recently, peer-to-peer （P2P） search technique has become popular in the Web as an alternative to centralized search due to its high scalability and low deployment-cost. However, P2P search systems are known to suffer from the problem of peer dynamics, such as frequent node join/leave and document changes, which cause serious performance degradation. This paper presents the architecture of a P2P search system that supports full-text search in an overlay network with peer dynamics. This architecture, namely HAPS, consists of two layers of peers. The upper layer is a DHT （distributed hash table） network interconnected by some super peers （which we refer to as hubs）. Each hub maintains distributed data structures called search directories, which could be used to guide the query and to control the search cost. The bottom layer consists of clusters of ordinary peers （called providers）, which can receive queries and return relevant results. Extensive experimental results indicate that HAPS can perform searches effectively and efficiently. In addition, the performance comparison illustrates that HAPS outperforms a fiat structured system and a hierarchical unstructured system in the environment with peer dynamics.

Modeling structured peer-to-peer systems

Distributed network architecture and dynamic change of nodes makes the operation of structured peer-to-peer networks unpredictable. This article aims to present a research on the running rule of structured peer-to-peer networks through a mathematical model. The proposed model provides a low-complexity means to estimate the performance of a structured peer-to-peer network from two aspects： the average existent time of a node and probability of returning to a temporarily steady state of network. On the basis of the results, it can be concluded that the proposed structured peer-to-peer network is suitable for those conditions where the frequency of node change is under limited value, and this value mainly depends on the initializing time of the node. Otherwise, structured peer-to-peer network can be abstracted as a network queuing system, which is composed of many node queuing systems in a meshy way and the relation between the throughput of the node system and network system is analyzed.

A P2P Load Balancing-Supported ID Management Algorithm

Load balancing is a critical issue in peer-to-peer networks. DHT （distributed hash tables） do not evenly partition the hash-function range, and some nodes get a larger portion of it. The loads of some nodes are as much as O（log n） times the average. In this paper, a low-cost, decentralized algorithm for ID allocation with complete knowledge in DHT-based system is proposed. It can adjust system load on nodes’ departure. It is proved that the ratio of longest arc to shortest arc is no more than 4 with high probability when network scale increases non-strictly. When network scale decreases from one stable state to another, algorithm can repair the unevenness of nodes distribution. The performance is analyzed in simulation. Simulating results show that updating messages only occupy a little of network bandwidth.

Publish/subscribe based information dissemination over VANET utilizing DHT

A vehicular ad-hoc network （VANET） can be visualized as a network of moving vehicles communicating in an asynchronous and autonomous fashion. Efficient and scalable information dissemination in VANET applications is a major challenge due to the movement of vehicles which causes unpredictable changes in network topology. The publish/subscribe communication paradigm provides decoupling in time, space, and synchronization between communicating entities, and presents itself as an elegant solution for information dissemination for VANET like environments. In this paper, we propose our approach for information dissemination which utilizes publish/subscribe and distributed hash table （DHT） based overlay networks. In our approach, we assume a hybrid VANET consisting of stationary info-stations and moving vehicles. These info-stations are installed at every major intersection of the city and vehicles can take the role of publisher, subscriber, or broker depending upon the context. The info-stations form a DHT based broker overlay among themselves and act as rendezvous points for related publications and subscriptions. Further, info-stations also assist in locating vehicles that have subscribed to information items. We consider different possible deployments of this hybrid VANET with respect to the number of info-stations and their physical connectivity with each other. We perform simulations to assess the performance of our approach in these different deployment scenarios and discuss their applicability in urban and semi-urban areas.