Research On Load Balancing Mechanism And Its Security In Dht-Based Distributed Networks

With the rapid development of Internet, the emergence and rise of various new business application architectures, and the evolution of future network, DHT-based distributed network is developing dramatically as the features of distributed, self-organization, and resource sharing. It has played an important role in the construction of business model innovation, business applications architecture and the future network architecture. However, it has encountered key technical challenges such as load balancing technology and security technology.On the one hand, due to the imbalance address space and objects of node carrying, the heterogeneity of node capacity, the uneven object size and query distribution, the dynamic of system, the DHT network load becomed not balanced. The problem of load imbalance affects the service quality of DHT system seriously, and has constrained the development of DHT-based distributed network. Thus, the realization of a low consumption and high efficiency load balancing mechanism is an urgent problem to be solved. On the other hand, due to the characteristic of distributed and self-organizing of DHT systems, there are security threats that can not be ignored. With load balancing mechanism, DHT networks can raise the availability of system. However, many threats are also introduced by the load balancing in DHT.In order to address above problems and challenges effectively, based on analyzing and summing up the root causes of the load imbalance and security issues, the DHT load balancing algorithms and their security are investigated. The main contributions of this dissertation include the following aspects:Firstly, considering a DHT network environment in which the load is imbalance caused by the imbalance address space and objects of node carrying and the heterogeneity of node capacity, based on the virtual server strategy, a hybrid load balancing (SDYA) algorithm is proposed. It is divided into load balancing ID generation algorithm and dynamic load adjustment algorithm. The proposed load balancing ID generation algorithm can solve the problem caused by the imbalance address space of node carrying in the homogeneous and heterogeneous environments and the problem of higher routing maintenance and routing overhead which caused by an excessive number of virtual servers, and it can resist the dynamic of the system. The proposed dynamic load adjustment algorithm can mainly solve the load imbalance caused by the uneven object size and query distribution, and the system dynamic. Finally, the effectiveness of SDYA algorithm is verified by simulation and experiment, and the experiment indicated that it improved in terms of the load balancing effect, the routing overhead and load transfer overhead.Secondly, considering a DHT network environment in which the load is imbalance caused by the uneven object size and query distribution and the system dynamic, a dynamic adjustment load mechanism, Ant-based DHT load balancing algorithm, is proposed. It designs a candidate light-load nodes discovery mechanism and a target nodes selection mechanism. Two types of agents, Forward Ant and Backward Ant, were adopted to realize them. The candidate light-load nodes discovery mechanism provides a way for effective and low-cost load collection. The target nodes selection mechanism provides a way for simple and effective load redistribution. The experimental results showed that Ant-based algorithm has better performance in terms of load balancing effect, load collection overhead and load transfer overhead. In addition, this paper in-depth analysis how system and algorithm parameters affect the performance of proposed algorithm. Simulation results demonstrate Ant-based algorithm is effective and scalability.Thirdly, considering the investigated phenomenon of the load redistribution mechanism which just stay on the special case and tightly coupled with scenarios, a general load redistribution algorithm, priority-based iterative multi-objective load re-distribution (PIMO) algorithm, is proposed. It takes into consideration load balancing effect, load balancing overhead and the change of system attributes for resources after load redistribution. PIMO algorithm can maximize load balancing effect, and reduce load balancing overhead, and ensure the system attributes of the transfer resources. The simulation experiments verified the effectiveness of algorithm. In addition, PIMO algorithm can meet the different requirements of load balancing effect, cost, and system attributes through setting different threshold of load deviation rate, the weight vector and the coefficient of relative entropy.Fourthly, considering the security issues of DHT-based load balancing mechanisms, the security threats are studied and analyzed. This dissertation builds the framework model for DHT load balancing mechanisms. Based on the model, we analyze the root causes of the threats introduced by load balancing mechanisms emphatically, and propose the attack tree model of these threats. Combined with the framework model and its threat model, the key entities and flows affecting the security were summarized and classified.Fifthly, to resolve the major security issues, a security load balancing (SLBA) algorithm for DHT system is proposed. It includes two parts: SLBA-ID algorithm and SLBA-DA algorithm. While addressing the load imbalance problem in DHT systems, SLBA algorithm can fend off security threats that arrive by way of the key flow, node ID generation, and the key entities, the nodes who generate the load reassignment strategy and the nodes who are responsible for transfer resource.Summary is given in the end, where the future research directions related to this doctoral dissertation are also putted forward.