【作者】 朱智俊；

【导师】 乐孜纯；

【作者基本信息】 浙江工业大学 ， 控制理论与控制工程， 2011， 博士

【摘要】 光突发交换(Optical Burst Switching, OBS)网络将突发包的传输与控制信道相分离,在核心网中实现了突发包的全光传输,克服了电域中的电子处理瓶颈,大大提高了网络的执行效率,被认为是实现大容量、高速交换网络所富有前景的方案。目前光交换方式可分为三种:光线路交换(Optical Circuit Switching, OCS)、光分组交换(Optical Packet Switching, OPS)和光突发交换(Optical Burst Switching, OBS)。OBS是介于OCS和OPS之间的一种过渡技术,其中OBS比OCS具有更高的带宽利用率。与OPS相比,OBS避免了光缓存这一问题,网络的建设成本大大降低。因此,对OBS的研究成为近年来国内外学术界的研究热点。OBS中各项关键技术的研究是将其实用化的重要环节。本文着重分析和讨论了边缘节点的汇聚技术,以及核心节点路由技术和OXC的设计。通过基于NS-2的OBS网络仿真平台OBS-NP的搭建,对OBS中各关键技术进行了分析与比较,并为深入研究打下了良好的基础。本文的主要工作和研究成果如下:1.提出了一种用于光突发交换网络的边缘节点中汇聚模块(OBS-Ethernet自适应汇聚模块)。OBS-Ethernet自适应汇聚模块引入流量检测队列,并通过该队列检测的结果选择合适的时间汇聚门限。同时,OBS-Ethernet自适应汇聚模块还通过突发数据包包长的反馈信息来修正控制曲线。仿真结果表明:与MBMAP汇聚方式相比,OBS-Ethernet自适应汇聚模块在网络数据突发性较强的情况下,具有较小的平均汇聚时延。并且与前者采用两个固定汇聚门限不同,OBS-Ethernet自适应汇聚模块的时间汇聚门限可以随着网络流量的变化而自适应地调整。2.根据光突发交换网(Optical Burst Switching, OBS)网络的特点,分析了在OBS网络边缘节点处进行数据汇聚的一般原则,针对现有的汇聚策略提出了一种新型OBS网络边缘节点的自适应汇聚策略。与以往采用固定汇聚门限的汇聚策略不同,本文设计的汇聚策略引入了穿越计数器,通过测量网络实时业务流量,判断穿越计数器,动态选择合适的汇聚门限。比较前后两次选择的汇聚门限类型来修正门限步长。仿真结果表明:与现有汇聚策略相比,本文设计的汇聚策略在不同参数的自相似流和网络负载情况下丢包率分别降低了69.07%和38.89%;因此,该汇聚策略不仅能根据网络流量变化动态调整汇聚门限,而且该策略更适应具有突发性的业务流,在强自相似情况下有较小的丢包率。3.提出了一种支持多业务等级下的综合考虑拥塞概率的路由选择的数学模型。在有限波长转换情况下,提出一种“分段”的概念。根据波长转换节点将路由分段,并分别计算该转换节点和分段路由的拥塞概率,然后根据所建立的数学模型计算全网的拥塞概率。这种分析方式,充分考虑了波长转换节点在网络中的作用和对阻塞率的影响,可更好的与路由和波长分配算法相结合。高业务等级的请求将获得低拥塞概率的路径进行路由,保证其服务质量(Quality of Service, QoS)。文中采用最短路径算法、k-最短路径算法和着色法等对NSFNET网络拓扑进行了仿真。4.保护机制是WDM光网络生存性的主要研究方向之一。本文主要研究WDM光网络中单链路失效情况下的保护策略,提出了分段保护-分段路由方法(SPSR),并将其用于OBS网络。该算法能根据当前网络状态动态调整链路权重,SPSR计算出对应的工作路径和保护路径。因此,更有利于全网的负载均衡,能有效的提高资源利用率,并降低拥塞概率。5.通过比较和分析三种典型的OBS网络仿真平台的优缺点后,建立了一种基于NS-2的OBS网络通用仿真平台——OBS-NP(OBS-NS2-Platform)。该平台扩展了NS-2中的链路类、节点类、OBS路由模块、OBS汇聚模块、OBS调度模块、控制协议模块和业务量模块,支持对光突发交换(OBS)网络的运行及关键算法的仿真。在详细描述OBS-NP系统结构的基础上,以一个16节点的OBS网络为仿真环境,对网络中突发包的时延、吞吐量和资源利用率等进行了仿真,并给出了业务量建立情况、调度表、下一跳路由信息、突发包动态传输情况和Trace表等结果。最后,分析和讨论了OBS-NP仿真平台的准确性和有效性。6.提出了一种光交叉连接器(Limited-range Wavelength Conversion, L-WIXC)的光学结构和对应的控制算法。对L-WIXC的拥塞概率、交换时间和吞吐量等性能以及设计成本进行了仿真或者计算。同时测试了L-WIXC光学层面中串扰、线性Q因子、误码率和眼图等关键光学参数。更多还原

【Abstract】 Optical Burst Switching network separates Burst Data Packets and control channel to realize the transferring in all optical manners. It conquers the limit of electrical processing in the electric domain, and improves the efficiency of whole network. OBS network is considered as one of the most promising solutions for the vast-bandwidth and high-speed switching network in the future. The current optical switching can be divided into three types: 1) Optical Circuit Switching; 2) Optical Packet Switching and 3) Optical Burst Switching. OBS has better bandwidth utilization compared with OCS. Meanwhile compared with OPS, OBS avoid the problem of no optical buffer, and reduce the cost of network construction. The study on key technologies in OBS networks will become the important step in the process of deploying the OBS networks. The design of OXC in core node and assembly strategy in edge node are discussed and analyzed in this paper. According to build OBS simulation platform based on NS-2 called OBS-NP, different key technologies in OBS network can be compared and analyzed.The main contributions and numerical results of the dissertation are as follows:1. Proposed an assembly module entitled OBS-Ethernet self-tuning assembly module for the edge node in optical burst switching networks. The traffic detection queue is included in the designed module by whose output is used to choose the suitable assembly time threshold. Moreover, the control curve is adjusted by the feedback of the BDP length. Simulation results demonstrate that the OBS-Ethernet self-tuning assembly module has less average assembly delay when the traffic bursty is strong compared with MBMAP assembly module. In addition, the assembly time threshold in the OBS-Ethernet self-tuning assembly module can be adjusted according to the network traffic, which is different from MBMAP assembly strategy whose assembly thresholds are static.2. In order to improve the assembly performances of Optical Burst Switching (OBS) networks, by analyzing the shortcomings of existing assembly strategies, a novel adaptive assembly strategy for the edge node of OBS networks was proposed in this paper. By means of introducing the cross counter, the strategy presented in this paper adopt a dynamic threshold system, which was different from former assembly strategies that could be considered as a fixed threshold system. The novel strategy estimated the network traffic flow and chose a suitable assembly threshold dynamically by the cross counter, moreover, the value of assembly threshold modified by the step length according to the differences and similarities type of assembly threshold with former one. Simulation results demonstrate that the novel strategy can reduce the burst loss probability by 69.07% and 38.89% compared with the existing assembly strategies. Therefore, the novel strategy not only can adjust the assembly threshold according to the traffic flow, but also can achieve lower burst loss probability under strong self-similar case that be showed adapt to burst traffic.3. Proposed an analytical model for supporting multi-class service with the blocking probability analysis and adaptive routing strategy to solve the potential shortcomings in the real network. Making the use of the idea of segmented routes to separate routes according to the finite wavelength conversion resources. We then combine the each segment to obtain the whole blocking probability. The simulation results demonstrate that, by adopting the adaptive routing algorithms, the whole network can calculate the blocking probability for the candidate routes, and the request which takes the highest priority will choose the route with minimum blocking probability. There are two features in our paper. First, segmented route is designed. Second, use k-shortest routing algorithm to obtain the minimum blocking probability routing between source node and destination node.4. The protection scheme is a key topic in survivable wavelength division multiplexing (WDM) optical networks. In this paper, we investigate the issue of multicast requests in survivable networks against any single-link failure and present a novel scheme called segment protection with segment route (SPSR). Through dynamically adjusting link-cost according to the current network state, SPSR establishes a primary light-tree and corresponding link-disjoint backup segments for each multicast connection request. An analytical model was present for blocking probability analysis and adaptive routing algorithm to solve the potential shortcomings in the real network. We are making the use of the idea of segmented routes according to the branch nodes. Simulation results demonstrate that with the consideration of load balancing SPSR gets better blocking probability and resource utilization performance relative to other schemes.5. According to compare and analyze the advantages and shortcomings of three typical OBS simulation platforms, an OBS network simulation platform called OBS-NP (OBS-NS2-Platform) based on NS-2 was proposed. It extended the link class, node class, routing modular, schedule modular, assembly modular, control modular and traffic modular on the basis of NS-2, and provided the simulation surroundings for key Optical Burst Switching algorithms. After detailed descriptions for the structure of the OBS-NP system, a 16 nodes OBS network was taken as an example to obtain routing results and some significant network parameters such as the delay of the burst packets, throughput and resource utilization. Moreover,traffic result,schedule table,next hope routing information and Trace table are proposed. Finally, the accuracy and efficiency of the simulation results was discussed and analyzed.6. The architecture and corresponding control algorithm for a devised optical cross connect (Limited-range Wavelength Conversion, L-WIXC) are presented. The performance of L-WIXC including blocking probability, switching time, and throughput is simulated, while the cost comparison with wavelength selective cross connect and wavelength interchangeable cross connect is calculated. Key optical parameters, such as crosstalk, linear Q, bit error rate (BER) and eye diagram are also discussed and measured.更多还原