基于D~*思想的ASON动态均衡恢复策略研究
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摘要
随着Internet的高速发展,全球数据业务呈爆炸式增长。数据业务动态、突发等特性对传统的光传送网(OTN,Optical Transmission Network)提出了更高的要求。自动交换光网络(ASON,Automatically Switched Optical Network)作为一项新的智能光网络技术的出现,赋予了光网络前所未有的灵活性和可扩展性,已经成为下一代网络(NGN,Next Generation Network)的重要发展方向。其中,对多种恢复机制的支持是ASON的一个重要特点。ASON上承载的多种业务要求网络具有快速、智能和多样化的故障恢复能力,同时能够合理有效地分配网络资源。而目前基于传统光传送网设计的一系列恢复机制远远不能满足ASON对生存性的要求。因此,对ASON恢复问题的研究已成为ASON研究的一个重点之一。
     D~*算法(D-star algorithm)是一种动态环境下的启发式(Heuristic)搜索算法,应用于环境为未知、部分已知或不断变化的状态空间搜索中。具有智能、高效、鲁棒性、易于实现分布式等优点。博弈论是研究具有斗争或竞争性质现象的理论和方法。论文在研究探讨了ASON及其恢复相关问题的基础上,运用D~*算法,并结合混合策略博弈理论,设计了一种动态均衡的ASON恢复策略,通过路由和波长分配(RWA,Routing and Wavelength Assignment)为受损业务提供恢复通道。目的是在快速恢复故障的同时,合理利用网络资源。从而提高网络的故障恢复率,增强网络的生存性。
     论文围绕ASON的动态恢复问题展开论述,主要完成的工作和取得的成果如下:
     (1)分析归纳了ASON控制平面的结构、功能,ASON路由体系结构、路由方式、消息分发,ASON的生存性及恢复策略以及ASON动态路由和波长分配(RWA,Route and Wavelength Assignment)技术等与ASON恢复问题相关的背景知识和影响因素。(2)研究了D~*算法和混合策略博弈的相关理论,提出了一种基于D~*思想的ASON动态均衡恢复策略。将网络中的路径代价与当前状态下的波长资源占用情况综合考虑,运用混合博弈原理求解波长占用与路径代价之间的纳什均衡(NashEquilibration),并以此动态建立D~*算法的估计函数,使恢复策略能够在动态通道恢复过程中尽量保证网络资源的合理分配。相对于传统的最短路径恢复策略和简单的动态恢复策略,该策略能够取得更高的恢复率和更低的网络资源占用率。
     (3)根据恢复策略的思路,详细分析并设计实现了均衡D~*算法的原理,包括建立数据结构和数学模型,以及流程设计和性能分析等。针对仿真实验时发现由于求解纳什均衡非线性方程组而造成算法收敛较慢的不足,设计了一种结合Newton迭代法和最小二乘法求解纳什均衡非线性方程组的方法,仿真实验证明,可以大大加快算法的收敛速度。
     (4)采用C#和MATLAB混合编程技术,自行开发了恢复策略的仿真系统,模拟实际网络环境对恢复算法性能进行了测试,并且,用传统的最短路径算法和另行设计的简单D~*算法与之进行了比较。仿真结果表明,该算法在阻塞率、恢复率以及资源占用率上都明显优于相比较的其他算法,且时间性能可以较好满足ASON中恢复时间的要求。
With the rapid development of Internet, the global data traffic growth is exponential. The dynamic, burst characteristics of data traffic present the high requirement to traditional optical transmission network (OTN). As a new technology of intelligent optical network, the appearance of automatically switched optical network (ASON) endue traditional optical transport network with unprecedented flexibility and expansibility. ASON represented the future direction of next generation networks (NGN). Hereinto, supporting many kinds of restoration strategy is an important characteristic of ASON. Multi-traffics carried in ASON demand the fast and multi-schemes restoration ability of network, simultaneity, reasonably and efficiently assign the network resources. However, at present, a series of restoration strategy there are designed for traditional optical transmission network are hardly satisfied with the survivability request of ASON. Therefore, the research on ASON restoration problem became a focus in ASON studies.
     D~* (D-star) algorithm is a heuristic search algorithm in dynamic environments. It is applied to paths planning in unknown, partially known, and changing state spaces, with advantages such as intelligence, high efficiency, robustness, and easy to actualize distributing, etc. Game theory is the method and architecture to research the phenomena with struggling or competitive characters. Based on researching the relative problem of ASON and restoration in ASON, the article design a dynamic equilibrated restoration strategy in ASON using D* algorithm and uniting game theory of mixed strategy to provide the restoration channel for failed traffic by routing and wavelength assignment. The purpose is to restore fault rapidly, simultaneously, to assign the network resources reasonably, and then to improve the rate of restoration and enhance survivability of network.
     In this thesis, the research is focus on restoration in ASON. The main works and innovative results are listed as follow:
     (1) Analyzing and summing up the background knowledge and influence factors related problems of restoration of ASON, which include framework and functions of control plane, architecture and modes of route, message distribution, the strategies of survivability and restoration, the techniques of dynamic route and wavelength assignment (RWA) etc. in ASON.
     (2) Researching the related theories of D~* algorithm and game theory of mixed strategy, and present a D~* principle-based dynamic equilibrated restoration strategy in ASON. Considering of the path cost and the occupancy of wavelength comprehensively, using game theory of mixed strategy to solve Nash equilibration between occupancy of wavelength and path cost, according this, the evaluation function of D~* algorithm is constructed dynamically, for ensuring a more equitable distribution of network resources in the process of dynamic channel restoration. Compared with traditional restoration strategy based on shortest path and simple dynamic restoration strategy, this algorithm can achieve higher restorability and lower resource occupancy.
     (3) According to the idea of the restoration strategy, the article detailedly analyze, design and carry out the principle of equilibrated D~* algorithm, which include constructing data structure and model of mathematic, flow design and capability analysis, etc. Against the disadvantage of slow convergence founded in simulation experiment, due to sloving nonlinear equations of Nash equilibrium, the article design a method which combining Newton iterative method with least square method to solve nonlinear equations of Nash equilibrium. It can be proved to accelerate convergent speed of the algorithm by simulation.
     (4) Using C# and MATLAB integrated programming, the article design simulation system of restoration strategy independently, and test the performance of equilibrated D~* algorithm by simulating actual network environment. In addition, we compare equilibrated D~* algorithm with shortest path algorithm and simple D~* algorithm which designed separately. It shows that the blocked rate, restorable rate and rate of resource occupancy of equilibrated D~* algorithm, are all obviously better than other comparative algorithms, and the performance of time of equilibrated D~* algorithm can sufficiently fit the request of restoration time in ASON.
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