Dynamic Deflection Routing with Virtual Wavelength Assignment in Optical Burst-Switched Networks

In optical burst-switched networks, one of the most significant issues is contention resolution. There have been several deflection routing techniques as contention resolution. While contention is resolved by traditional deflection routing, it cannot guarantee that the control packet will reserve all the wavelengths successfully to the destination on the alternate path, especially when traffic load in a network is high. Therefore, in this paper, we propose a Deflection Routing with Virtual Wavelength Assignment (DR-VWA) algorithm in order to provide a higher resource guarantee for loss-sensitive traffic bursts. The proposed DR-VWA scheme (1) dynamically decides the alternate path with the least traffic load and (2) allows high-priority bursts in terms of loss to be assigned available wavelengths over the path virtually. The proposed scheme is evaluated through simulation, and it is shown that significant improvement with regard to burst loss and wavelength conversion cost can be achieved.This work was supported in part by the Korea Science and Engineering Foundation (KOSEF) through OIRC project and by the US National Communications System (NCS).     

全光网络中动态型波长路由算法的研究

分析了光路径的跳数（H）、拥挤程度（C）以及全网剩余波长总数（FW）对选路的影响,进而提出一种新型的动态波长路由算法。该算法利用网络中剩余资源的数量,动态调节选路策略,将业务分布在最短、负载最小以及剩余波长数和跳数比值最大的路径上;当有效资源减少时,增加最短路径选择的概率;当有效资源增加时,增加小负载路径的选择概率。计算机仿真结果表明,该算法的阻塞率比传统算法FAR和FPLC算法分别降低了19．1％和12．7％。     

波分复用光网络中的波长路由分配策略

路由选择和波长分配是WDM光传输网中非常重要的问题.本文结合交叉连接节点,提出了一种基于最短路径的动态路由选择方案;然后利用这种动态的路由选择策略,以网络的阻塞性能为优化目标分配波长,达到充分利用网络资源的目的.计算机仿真结果表明,无论在单纤或者多纤WDM光传输网络中,利用这种策略的RWA算法优于传统的固定路由和单纯动态路由算法     

Wavelength Conversion in WDM Optical Networks: Strategies and Algorithms for Limiting the Number of Converters in the Optical Cross-Connects

This paper considers the problem of wavelength conversion in optical networks using wavelength division multiplexing technique. In the previous literature, two main wavelength routing and assignment strategies have been introduced: wavelength path (WP) and virtual wavelength path (VWP), depending on whether the signal stays on the same wavelength or is converted to another during its travel throughout the network. While the former method does not require any wavelength conversion, the latter needs wavelength conversion in each optical node and, in particular, a wavelength converter per each signal handled by the node itself. From the previous literature emerged that the VWP leads to optical cross-connect (OXC) with lower dimensions compared to the ones required by the WP scheme, and that the difference between the WP and VWP schemes increases as the number of wavelengths carried by each fiber increases. In this paper a new strategy is introduced, named partial virtual wavelength path (PVWP), with the related wavelength routing and assignment algorithm, which makes limited use of wavelength conversion compared to the VWP scheme, and allows the same advantages of VWP to be attained with lower OXC dimensions. The paper reports a comparative analysis among the different strategies, considering both the cases of a network without failures and a network with the possibility of failure restoration. The main result is that the proposed PVWP strategy allows the same advantages of the VWP scheme with a strongly reduced number of wavelength converters (around 5% of the number required by VWP scheme). This figure does not vary appreciably if failure restoration is considered. The new strategy can be adopted by using an opportune OXC architecture, as illustrated in the paper, which allow a limited number of converters to be shared among all the channels as a common pool.     

Dynamic Routing and Wavelength Assignment in Optical Networks by Means of Genetic Algorithms

We propose a novel genetic algorithm for solving the dynamic routing and wavelength assignment (DRWA) problem in wavelength-routed optical networks. The algorithm not only obtains low call blocking probability, but it also employs a very short computation time. Moreover, it is capable of providing fairness among connections, that is, to offer approximately the same quality of service (in terms of blocking probability) for all source-destination node pairs. Since requirements on optical network availability are highly severe, we also propose an extension of the algorithm to provide fault-tolerance capability at the optical layer. It is achieved by means of protection, where each optical connection request is provided with a pair of lightpaths (a primary and a backup lightpath). Again, the genetic algorithm proves to be highly efficient, in this case, at performing routing and wavelength assignment of pairs of lightpaths.     

静态波长路由光网络中路由和波长分配算法的统计修正

本文采用统计的方法对以网络最小所需波长数为优化目标的路由和波长分配算法进行了修正.数值模拟计算表明,经过统计方法修正之后,可以求得更接近波长下限的网络所需波长数.另外本文还首次提出用统计的方法对路由和波长分配算法进行比较,通过比较两个算法在经过统计修正之后求得的网络所需波长数的分布可以知道它们的优劣.     

多域光网络中基于优先级的波长路由分配算法

本文提出一种在多域光网络中基于优先级的路由波长分配算法.算法设计旨在解决复杂网络拓扑下,多任务请求路由波长分配问题.本文首先根据复杂网络拓扑情况与任务请求状况,完成多域的划分,对跨域任务的最短路由进行路由分裂;其次依据域内与域间优先级设定策略,完成多任务请求优先级设定;按照优先级顺序,采用模糊优化波长分配算法完成波长分配.仿真结果表明本算法在处理复杂网络拓扑、多任务路由波长分配问题上效果明显,有效的降低了网络请求阻塞率,提高了光网络资源利用率.     

Routing Mechanisms Employing Adaptive Weight Functions for Shortest Path Routing in Optical WDM Networks

Optical dense wavelength division multiplexed (DWDM) networks are an attractive candidate for the next generation Internet and beyond. In this paper, we consider routing and wavelength assignment in a wide area wavelength routed backbone network that employs circuit-switching. When a session request is received by the network, the routing and wavelength assignment (RWA) task is to establish a lightpath between the source and destination. That is, determine a suitable path and assign a set of wavelengths for the links on this path. We consider a link state protocol approach and use Dijkstras shortest path algorithm, suitably modified for DWDM networks, for computing the shortest paths. In [1] we proposed WDM aware weight functions that included factors such as available wavelengths per link, total wavelengths per link. In this paper, we present new weight functions that exploit the strong correlation between blocking probability and number of hops involved in connection setup to increase the performance of the network. We also consider alternate path routing that computes the alternate paths based on WDM aware weight functions. The impact of the weight functions on the blocking probability and delay is studied through discrete event simulation. The system parameters varied include number of network nodes, wavelengths, degree of wavelength conversion, and load. The results show that the weight function that incorporates both hop count and available wavelength provides the best performance in terms of blocking probability.     

光网络选路和波长分配研究

文章在叙述了光网络中选路和波长分配(RWA)要解决的基本问题后,对有关方面的近年研究作了综述,主要包括:虚拓扑重构、业务量疏导的RWA、多播RWA、抗毁网络的RWA.抗毁问题涉及WDM网络的抗毁选路、区分可靠性、网状网的快速恢复、多故障下的抗毁.     

QoS-Friendly Wavelength Assignment in Dynamic Wavelength-Routed Optical Networks

In-band crosstalk has been widely considered as a major transmission impairment that significantly impacts the bit error rate (BER) performance of lightpaths in circuit-switched all-optical wavelength-routed networks. Such crosstalk usually occurs when multiple wavelengths pass through an optical crossconnect node, and the magnitude of the crosstalk is largely dependent on the wavelengths assigned to the lightpaths. Traditional wavelength assignment (WA) schemes pay little regard to the physical layer quality of service (QoS), and hence cannot provide optimized network performance in practical networks with imperfect physical transmission media. In this paper, we first present our categorization of in-band crosstalk based on the location of crosstalk generation, then we propose two QoS-friendly WA approaches, one of which selects the wavelength based on the estimated BERs, and the other based on the weighted crosstalk number counting. The two approaches have different computation complexities. Numerical results show that both approaches can significantly improve the BER blocking rate by suppressing the created in-band crosstalk, but the BER-based approach generally gives the better performance at the price of more extensive computation.This work was supported in part by DARPA Grants #N66001-00-1-8949 and #66001-01-1-8932 (co-funded by NSA).     

Dynamic Routing and Wavelength Assignment in Survivable WDM Networks

Dense wavelength division multiplexing (DWDM) networks are very attractive candidates for next generation optical Internet and intelligent long-haul core networks. In this paper we consider DWDM networks with wavelength routing switches enabling the dynamic establishment of lightpaths between each pair of nodes. The dynamic routing and wavelength assignment (RWA) problem is studied in multifiber networks, assuming both protection strategies: dedicated and shared. We solve the two subproblems of RWA simultaneously, in a combined way using joint methods for the wavelength selection (WS) and wavelength routing (WR) tasks. For the WS problem in contrast to existing strategies we propose a new, network state based selection method, which tries to route the demand on each wavelength, and selects the best one according to different network metrics (such as available channels, wavelengths per fiber and network load). For the WR problem we propose several weight functions for using in routing algorithms (Dijkstra or Suurballe), adapting dynamically to the load of the links and to the length of the path. The combination of different wavelength selection and routing (WS&WR) methods enables wide configuration opportunities of our proposed algorithm allowing good adaptation to any network state. We also propose the extension of the RWA algorithm for dedicated and shared protection and a new method for applying shared protection in dynamic WDM environment. The detailed analysis of the strategies demonstrate that our RWA algorithm provides significantly better performance than previous methods in terms of blocking probability whether with or without protection methods.     

抗毁WDM网络中支持多优先级的波长分配算法

WDM网络将在未来的骨干网中扮演重要的角色,具备抗毁能力和支持多优先级都很必要.本文提出了两种基于优先级的波长分配算法——波长编号法和分配限额法,并研究了动态业务下,抗毁WDM网络使用这两种波长分配方法后网络的阻塞率性能.研究的内容包括业务量负载、光纤链路的波长通道数和每条链路包含的光纤数对网络性能的影响.本文还给出了仿真结果.     

一种波长转换范围受限全光网中的波长分配算法

本文研究了波长转换范围受限全光网中的动态路由和波长分配问题,提出了一种固定备选路由条件下新的路由和波长分配算法.算法引入了波长相关性的概念,用波长关联权值定量描述了各路由的前后链路上不同波长之间的相互依赖关系.在建立连接时首先使用那些依赖性强,对其他路由影响小的波长,从全局的角度出发选择最优的路由和波长分配方案.计算机仿真表明,本文算法能够适用于稀疏网络和网状网,在均匀业务强度或者大部分业务量来自于长跳路由的情况下,本文算法能够显著降低网络阻塞概率和使用的波长转换器数目,有效提高系统性能.     

WDM网络中基于阻塞公平性的业务疏导和波长分配

在具有多速率级别连接请求的WDM网络中，通过为较高速率的请求预留更多的波长集合，结合网络节点对较低速率业务更强的输导能力，解决网络的阻塞公平性和全网的流量问题。在中国教育科研网的仿真实验，本文的策略比First-fit算法取得了更好的阻塞公平性能，并接纳了更多的网络流量。当负载为170Erlang时，多接纳的流量约为12％。     

多约束条件下WDM光网中多播选路和波长分配算法

在光层构建多播选路和波长分配时,必须考虑一些约束条件。主要的约束条件有以下4种：稀疏分光器配置约束、波长连续性约束、能量损伤约束及稀疏波长转换器约束。目前,研究人员只是针对其中一个或两个约束条件进行了算法研究。该文在详细分析各种约束条件之后,提出了一种基于多约束条件下多播选路和波长分配启发式算法。最后在CERNET和NSFNET两种网络拓扑上进行了仿真实验。根据算法仿真结果可以得出该算法可以有效地解决多约束条件下的多播路由及波长分配问题。     

波长路由网络选路时的光信号质量限制研究

光网络中,路由与波长分配(RWA)算法是最优化网络性能的核心问题之一,传统的RWA算法都假设光网络的物理层状态是理想的,即不存在光信号传输损伤的问题.通过对这个缺陷的分析,将光信号的传输损伤问题充分考虑到路由与波长分配算法中,从算法的角度来实现对光信号的传输保护,这样做不仅能有效防止业务的物理损伤阻塞,还能极大地提高光网络的性能.     

应用于分级复用系统的全光网波长分配算法

研究了全光网中采用分级复用系统的波长分配问题,充分考虑到分级复用系统在降低整个网络成本上的重要意义,以最小化光纤数量和波长路径为优化目标,提出一种启发式波长分配算法。     

波分复用光网中的一种新型波长分配算法

目前网络承载业务的趋势是以IP为中心的数据业务,从而促进了以WDM光网络向高速和宽带多波长的应用和普及,为了进一步提高网络的性能并提高资源利用率,出现了光网络控制面技术.路由选择与波长分配问题是WDM光传输网络控制面中非常重要的问题之一.目前实际应用最广泛的波长分配算法是First-Fir(FF)算法.本文基于FF算法,研究动态业务下波分复用光网络在固定选路下的波长分配问题,提出了一种新的波长分配启发式算法——Joint First Fit.计算机仿真试验表明,与常用的FF算法相比,该算法显著的降低了网络呼叫阻塞率,有利于提高网络资源的利用率.     

Sparse Wavelength Conversion in Wavelength-Routed WDM Optical Networks*

A wavelength-routed optical network can suffer inefficiencies due to the wavelength-continuity constraint (under which a signal has to remain on the same wavelength from the source to the destination). In order to eliminate or reduce the effects of this constraint, a device called a wavelength converter may be utilized. Due to the high cost of these wavelength converters, many studies have attempted to determine the exact benefits of wavelength conversion. However, most of these studies have focused on optical networks that implement full wavelength conversion capabilities. An alternative to full wavelength conversion is to employ only a sparse number of wavelength converters throughout the network, thereby reducing network costs. This study will focus on different versions of sparse wavelength conversion--namely, sparse nodal conversion, sparse switch-output conversion, and sparse (or limited) range conversion--to determine if most of the benefits of full conversion can be obtained using only sparse conversion. Simulation and analytical results on these three different classes of sparse wavelength conversion will be presented. In addition, this study will present heuristic techniques for the placement of sparse conversion facilities within an optical network.     

Optimal Wavelength Assignment Algorithms for Permutation Traffic in Multi-Fiber WDM Ring Networks*

Permutation traffic occurs in a number of networking applications. In this paper, the problem of wavelength assignment for permutation traffic in multi-fiber WDM rings with and without wavelength conversion is considered. We focus on a special class of permutation traffic and analyze the bounds on the number of wavelengths required to establish the connections. Lower bounds and optimal algorithms are presented for all the cases. The results indicate that a small number of fibers is sufficient to provide most of the benefits that wavelength conversion provides for this class of permutation traffic.