波长路由树形全光网中波长转换器配置算法

在波长路由全光网中,波长转换以及路由和波长分配算法（RWA）是降低网络阻塞率、改善网络性能的两个重要方法。研究了树形网络中波长转换器的配置问题,结合树形网络的特点,对影响波长转换器配置的主要因素进行了分析。综合路径长度、路径通信负荷以及节点的度,提出了基于网络直径的波长转换器配置算法和基于网络中心的波长转换器配置算法。通过算法演示和仿真,表明提出的两种算法各有优点。     

树形全光网络中波长转换器配置算法

配置有限数量的波长转换器使网络阻塞率最低,是全光网络中需要解决的一个关键问题.通过考虑网络的直径、中心以及节点和链路的通信量,采用网络分解和迭代的方法,提出树形网络中基于赋权直径的波长转换器配置算法、基于节点加权中心的波长转换器配置算法,以及基于光路加权中心的波长转换器配置算法.算法演示表明,提出的3个算法总是将波长转换器放置在阻塞率较高的节点上,从而大大降低网络整体阻塞率.     

全光网络中波长转换器配置问题的蚁群算法

研究提高网络的利用率,在全光网络中放置波长转换器是打破波长一致性约束,为了降低网络阻塞率,提高网络通信能力的有效途径。但限于波长转换器的高昂成本,不可能为网络中的每个节点都配置波长转换器,所以波长转换器应以最优方案放置在网络中的个别关键节点上。提出了一种基于蚁群算法的波长转换器配置方法,通过蚁群算法寻找给定网络中任意源、目的节点之间的最优路径,并利用蚂蚁对最优路径的记录,统计路径在节点处发生波长转换的次数,将具有较高波长转换次数的节点作为网络中波长转换器放置节点。最后通过对一个5节点的网络进行算法演示和仿真分析,结果表明该算法能求得波长转换器的合理配置,得到较好的通信效果。     

基于WDM传输网的动态路由算法

波分复用技术(WDM)作为一种公认的最佳光纤扩容技术已被广泛应用在国际和国内长途骨干网上。路由算法与波长分配(RWA)是WDM网中的重要技术之一,评价RWA算法的一个重要标准是网络阻塞率。采用合适的路由算法可以大大降低网络的阻塞率。该文采用一种结合了再生节点选择的动态RWA算法来解决WDM网中的波长路由问题,并通过光纤通道拓扑的优化算法来进一步优化。通过建模仿真,研究了NSFNET网络优化前后阻塞率的变化,仿真的结果证明采用该优化算法可以降低网络的阻塞率。     

WDM光网络中固定备选路由算法的实现

路由问题是WDM全光网络中的一个核心问题。该文介绍了常用的固定备选路由FAR算法(前K条最短路由算法)的实现过程,并与固定路由FR算法性能进行了比较。仿真结果表明,能有效降低网络的阻塞率,提高网络的性能。     

光网络中波长转换器的优化放置问题求解

基于分层图模型,提出了一种的简化的计算具有波长转换器光网络中光链路阻塞率的数学模型和公式,并应用于遗传算法的迭代函数,通过遗传算法对波长转换器在光网络中的优化放置问题进行求解,分析了波长转换器的最优放置和波长转换器的最小使用数量。通过在美国自然科学基金网(NSFNet)的仿真模拟,得出了使用部分和全部波长转换时的网络阻塞特性。     

WDM光网络中支持优先级的备用路由算法

论文提出了一种在WDM光网络中支持优先级的备用路由算法,该算法结合波长的使用情况,通过给优先级较高的光路建立请求预留较多的备用路由,从而降低了高优先级的光路连接的阻塞率。同时由于使用了备用路由,使较低优先级的光路建立请求性能得到优化。同现有的支持优先级的算法相比,该算法更多地考虑了路由问题,而且也增强了网络的抗毁性。计算机仿真结果表明,该算法在支持优先级的同时能有效降低网络各优先级光路的阻塞率。     

全光网络中组播路由波长分配的一种遗传算法

在WDM网络中,组播是一种重要的通信需求。组播算法就是要建立一棵从源节点到目的节点的组播树,并给这棵组播树分配波长。但是在网络中有波长转换器的情况下计算的复杂性会大大增加。该文在分层图结构中基础上,提出了组播路由和波长分配的一种遗传算法,可以在满足时延约束的情况下,寻找费用最小的组播树,将路由和波长分配统一进行,同时考虑到了网络中波长转换器的存在。数值仿真实验结果表明该算法具有较好的平均性能和较低的时间复杂度。     

基于改进PCNN算法的光网络RWA问题的研究

针对波分复用光网络在动态业务下的路由和波长分配问题,本文将一种改进的脉冲耦合神经网络(PCNN——Pulse Coupled Neural Networks)算法引入到光网络路由选择中,并将波长分配与分层图模型相结合,通过改变PCNN神经元的点火方式以及控制自动波的传播时间模拟路径代价,使得网络路由选择具有了PCNN的并行处理特性。结合波长分配算法进行仿真,结果表明,本算法与传统的最短路径算法相比,总能得到全局最优解且计算量小,降低了网络的呼叫阻塞率,提高了对网络资源的利用。     

光通信网络中路由与波长分配的算法研究

光通信网络作为下一代网络的主要网络之一,在整个通信网中起着至关重要的作用。目前光通信中主要是采用基于DWDM(密集波分复用)技术组成的光网络,随着波分数量的增加,DWDM网络中的路由与波长分配问题显得十分重要,需要有一种有效的算法来使有限的波长资源得到充分地利用。本文根据原有的数学分析模型,提出了一种分层图模型,并根据此模型提出了一种用来解决DWDM网络中出现的波长分配问题的一种算法,并通过计算机仿真来表明此算法提高了波长资源的利用率,降低了网络的阻塞率。     

部分波长转换全光网阻塞概率的近似计算

该文基于链路波长占用独立性假设，改进了Birman 在1996年提出的分析模型，提出了一种部分波长转换全光网在固定式路由和随机分配波长条件下阻塞性能的近似分析方法，该方法可以适用于任何网络拓扑，任何业务量分布模式条件下网络中任意链路上配置任意数目转换器情况的研究，扩大了Birman模型的适用范围，对于转换器均匀放置的网络，在业务均匀分布或者业务量信中在短跳路径的情况下，近似计算能够较好地与计算机仿真相吻合，对于业务量集中在长跳路径的情况或者转换器非均匀放置的网络，近似计算能够很好地跟随计算机仿真结果。     

Probability based dynamic-alternate routing and the corresponding converter placement algorithm in all-optical WDM networks

This paper proposes a new dynamic-alternate routing algorithm and its corresponding converter placement algorithm in order to reduce the connection blocking probability for all-optical WDM networks. The main idea in the proposed dynamic-alternate routing algorithm is to try to route the traffics according to a predefined optimal probability distribution. The problem for finding the optimal probability distribution was shown as a convex optimization problem. The problem can be solved by flow deviation method or other standard optimization techniques. Simulation results show that the proposed routing algorithm yields lower connection blocking probabilities than the previous works. The proposed routing algorithm produces similar traffic pattern as the optimal traffic pattern. The similarity between the traffic pattern produced by the proposed dynamic-alternate routing algorithm and the optimal traffic pattern can be further employed for solving other network designing problems such as converter placement problem. Since the optimal traffic pattern can be easily predicted, the optimal traffic pattern which minimizes the blocked traffic intensity is utilized for finding the locations of wavelength converters. The key idea is to place the wavelength converters at the nodes where they are needed most. Simulations have been performed to study the performance of the proposed wavelength converter placement method. The simulation results have shown that the proposed placement method combined with the proposed probability based dynamic-alternate routing algorithm yields smaller connection blocking probability than the two converter placement methods with their corresponding alternate routing algorithms.     

A heuristic for placement of limited range wavelength converters in all-optical networks

Wavelength routed optical networks have emerged as a technology that can effectively utilize the enormous bandwidth of the optical fiber. Wavelength converters play an important role in enhancing the fiber utilization and reducing the overall call blocking probability of the network. As the distortion of the optical signal increases with the increase in the range of wavelength conversion in optical wavelength converters, limited range wavelength conversion assumes importance. Placement of wavelength converters is a NP complete problem [K.C. Lee, V.O.K. Li, IEEE J. Lightwave Technol. 11 (1993) 962–970] in an arbitrary mesh network. In this paper, we investigate heuristics for placing limited range wavelength converters in arbitrary mesh wavelength routed optical networks. The objective is to achieve near optimal placement of limited range wavelength converters resulting in reduced blocking probabilities and low distortion of the optical signal. The proposed heuristic is to place limited range wavelength converters at the most congested nodes, nodes which lie on the long lightpaths and nodes where conversion of optical signals is significantly high. We observe that limited range converters at few nodes can provide almost the entire improvement in the blocking probability as the full range wavelength converters placed at all the nodes. Congestion control in the network is brought about by dynamically adjusting the weights of the channels in the link thereby balancing the load and reducing the average delay of the traffic in the entire network. Simulations have been carried out on a 12-node ring network, 14-node NSFNET, 19-node European Optical Network (EON), 28-node US long haul network, hypothetical 30-node INET network and the results agree with the analysis.     

Particle swarm optimization-based DRWA for wavelength continuous WDM optical networks using a novel fitness function

Greater demand of bandwidth and network usage flexibility from customers along with new automated means for network resource management has led to the concept of dynamic resource provisioning in WDM optical networks where unlike the traditional static channel assignment process, network resources can be assigned dynamically. This paper examines a novel particle swarm optimization (PSO)-based scheme to solve dynamic routing and wavelength assignment (dynamic RWA) process needed to provision optical channels for wavelength continuous Wavelength Division Multiplexed (WDM) optical network without any wavelength conversion capability. The proposed PSO scheme employs a novel fitness function which is used during quantization of solutions represented by respective particles of the swarm. The proposed fitness function takes into account the normalized path length of the chosen route and the normalized number of free wavelengths available over the whole route, enabling the PSO-based scheme to be self-tuning by minimizing the need to have a dynamic algorithmic parameter ‘α’ needed for better performance in terms of blocking probability of the connection requests. Simulation results show better performance of the proposed PSO scheme employing novel fitness function for solving dynamic RWA problem, not only in terms of connection blocking probability but also route computation time as compared to other evolutionary schemes like genetic algorithms.     

Topology-aware wavelength partitioning for DWDM OBS networks: A novel approach for absolute QoS provisioning

Optical Burst Switching (OBS) is a promising switching technology for the next generation all-optical networks. An OBS network without wavelength converters and fiber delay lines can be implemented simply and cost-effectively using the existing technology. However, this kind of networks suffers from a relatively high burst loss probability at the OBS core nodes. To overcome this issue and consolidate OBS networks with QoS provisioning capabilities, we propose a wavelength partitioning approach, called Optimization-based Topology-aware Wavelength Partitioning approach (OTWP). OTWP formulates the wavelength partitioning problem, based on the topology of the network, as an Integer Linear Programming (ILP) model and uses a tabu search algorithm (TS) to resolve large instances efficiently. We use OTWP to develop an absolute QoS differentiation scheme, called Absolute Fair Quality of service Differentiation scheme (AFQD). AFQD is the first absolute QoS provisioning scheme that guarantees loss-free transmission for high priority traffic, inside the OBS network, regardless of its topology. Also, we use OTWP to develop a wavelength assignment scheme, called Best Effort Traffic Wavelength Assignment scheme (BETWA). BETWA aims to reduce loss probability for best effort traffic. To make AFQD adaptive to non-uniform traffic, we develop a wavelength borrowing protocol, called Wavelength Borrowing Protocol (WBP). Numerical results show the effectiveness of the proposed tabu search algorithm to resolve large instances of the partitioning problem. Also, simulation results, using ns-2, show that: (a) AFQD provides an excellent quality of service differentiation; (b) BETWA substantially decreases the loss probability of best effort traffic to a remarkably low level for the OBS network under study; and (c) WBP makes AFQD adaptive to non-uniform traffic by reducing efficiently blocking probability for high priority traffic.     

Network Performance Improvement of All-Optical Networks Through an Algorithmic Based Dispersion Management Technique

Network blocking performance due to wavelength continuity constraint in a well-connected all-optical network can be efficiently reduced by utilizing wavelength converters. Nevertheless, the introduction of high bit rate optical services with strict tolerance to signal quality would have a serious impact on the overall network performance since in this circumstance, a request can be blocked due to unacceptable signal quality of potential routes. Chromatic dispersion tolerance, for example, is reduced by the square of the bit rate. By extending the typical application of parametric wavelength converter in solving a wavelength continuity problem, this paper aims to enhance chromatic dispersion management through an improved wavelength conversion algorithm. Consequently, significant improvement in network performance has been demonstrated through reduction in the dispersion effect when the proposed engineering rule is included in the conversion process.