WDM网络中基于负载平衡的动态波长路由算法

在WDM网络中，路由和波长分配（RWA）算法是一个焦点问题．当前的RWA算法多是考虑路径跳数或全网拥塞程度，并没有分析各个链路的具体情况．文中提出一种WDM网络中能实现负载平衡的路由算法——最大波长跳数比值（MWHR）算法。基本思想是：根据各备选路径的跳数和其经过的各链路上的可用波长数信息。计算该路径的优先选取权值，优先选取权值最大的路径．仿真表明，该算法在保证较低的阻塞率情况下，能有效的将业务负载均衡分布在网络中的所有链路上．     

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.     

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.     

一种新型的动态路由和波长分配算法

本文讨论了WDM光网中，在动态业务流量和有限范围波长变换情况下的动态路由和波长分配（RWA）问题，基于Moone-Dijkstra算法，考虑到动态波长变换的可能和限制，提出了一种新型的、可实现动态最小代价路由和最佳虚波长通道的综合启发式算法（DMC－OVMP）。该算法对路由子问题和波长分配子问题既相互独立，又相互结合，优化了RWA，保证了网络信息传输的安全性。对中国教育和科研计算机网（CERNET）基于本算法进行了计算机仿真，实现了低的网络阻塞率。     

混合光波长转换在波分复用光网络中的应用

在全光网络中，如何合理利用波长转换来降低光网络的阻塞率是一个非常关键的问题。研究了最新的波长转换体系结构和波长转换手段，提出一种全新的混合波长转换方法，在减少网络中波长转换器个数的同时，维持拥塞概率类似于全波长转换。提出了5种不同的波长转换器使用策略，并利用数值模拟的方法，比较了这5种不同的波长转换器使用策略，分析结果，得出了最小化光网络的阻塞概率的波长转换使用策略。结合混合波长转换和波长转换器使用策略，进一步提出了光网络中优化波长转换器配置的遗传算法，通过对14个节点的美国自然科学基金网(NSF Net)的数值模拟，结果表明它是十分有效的，在减少光网络中波长转换器数量，且不增加光网络波长数量的情况下，基本保持原有网络性能。     

A Comparison of Allocation Policies in Wavelength Routing Networks*

We consider wavelength routing networks with and without wavelength converters, and several wavelength allocation policies. Through numerical and simulation results we obtain upper and lower bounds on the blocking probabilities for two wavelength allocation policies that are most likely to be used in practice, namely, most-used and first-fit allocation. These bounds are the blocking probabilities obtained by the random wavelength allocation policy with either no converters or with converters at all nodes of the network. Furthermore, we demonstrate that using the most-used or first-fit policies gives an improvement on call blocking probabilities that is equivalent to employing converters at a number of nodes in a network with the random allocation policy. These results have been obtained for a wide range of loads for both single-path and general mesh topology networks. The main conclusion of our work is that the gains obtained by employing specialized and expensive hardware (namely, wavelength converters) can be realized cost-effectively by making more intelligent choices in software (namely, the wavelength allocation policy).     

部分共享波长转换光网络动态路由的改进算法

提出了一种应用于部分共享波长转换（PWC）的波长路由光网络（WRON）中的基于节点阻塞的动态路由算法,它不需要共享复杂的波长转换信息,而是将各节点的阻塞特性考虑到路由过程中。为评价算法性能,在14节点的国家科学基金网（NSFNET）拓扑中进行了仿真。结果表明,新的路由算法显著改善了网络的阻塞性能和建路失败的概率,尤其是随着网络负载的降低,网络性能的改善更显著。     

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％。     

Study on a Distributed Wavelength Routing Algorithm in WDM Optical Transport Networks

A new design scheme for a distributed algorithm for routing and wavelength assignment (RWA) is developed in this paper, and the communication rules between the nodes to exchange signaling packets are discussed. The Adaptive-Alternate-Routing-Least-Load (AARLL) algorithm is implemented in the distributed scheme for the first time. Under dynamic traffic circumstances, the influence of the race condition, which does not exist in centralized scheme, on the network performance is analyzed and the analyzed results show that the race condition has a major impact on network performance only under light traffic load, while under medium and heavy traffic load the impact is very small. To analyze the performance loss caused by adopting the distributed algorithm for RWA, the capacity loss factor (CLF) is introduced and the calculated results show that CLF does not exceed 6% under medium traffic load.     

一种基于波分复用的光控波束合成网络

提出了一种基于波分复用光控波束合成网络,其核心是采用了由波分复用器、可调衰减器和光反射镜构成的光延时模块,通过光反射镜的光程调节获得通道之间的延时。根据该方案制作了18 GHz工作频率下,波束指向为0°和-45°的两个16通道光延时模块。测试结果表明,模块的相位精度达到了±15°,幅度一致性优于±0.1 dB,仿真方向图显示了较高的波束指向精度。     

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.     

波长动态调度TWDM光接入网中的生存性保证

摘要：如何在波长动态调度的时分波分复用光接入网中正确定位故障并进行保护倒换,以保证强生存性是需要解决的关键技术问题。为解决上述问题,提出了一种具有成本效益的利用控制信道定位故障的和基于动态波长调度的生存性保证方案,并对方案进行了生存性和成本的综合定量分析。分析计算表明,所提方案最优时只需付出1%的生存性保证成本,就能带来54%的生存性提高,并且保护倒换能控制在50 ms内完成。     

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.     

Virtual Source Based Multicast Routing in WDM Optical Networks

Wavelength-division multiplexed (WDM) networks using wavelength-routing are considered to be potential candidates for the next generation wide-area backbone networks. Multicasting is the ability to transmit information from a single source node to multiple destination nodes and is becoming an important requirement in high-speed networks. As WDM technology matures and multicast applications become increasingly popular, supporting multicast routing at the WDM layer becomes an important and yet a challenging topic. This paper concerns with the problem of optical multicast routing in WDM networks. A few nodes in the network may have wavelength conversion and/or splitting capabilities. In this paper, a new multicast tree construction algorithm is proposed. This algorithm is based on a concept called virtual source. A virtual source is a node having both the splitting and wavelength conversion capabilities. By exploiting the presence of virtual source nodes, the proposed algorithm achieves improved performance. To further improve the performance, the algorithm assigns priorities to nodes based on their capabilities. The effectiveness of the proposed algorithm is verified through extensive simulation experiments.     

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.     

一种基于时延信息的多QoS快速自适应路由算法

本文在分析现有自适应蚁群算法局限性的基础上，提出了一种基于时延的自适应多QoS路由算法，它在满足带宽和时延波动约束条件下，直接利用前一周期的时延信息来更新路由表，以作为当前寻找路径的依据。仿真和分析结果表明，该算法具有快速准确的特点，能够及时协调网络拥塞和资源有效利用两者间的矛盾。     

Performance of Adaptive Routing in Wavelength-Routed Networks with Wavelength Conversion Capability

This paper concerns itself with the performance of adaptive routing in wavelength-routed networks with wavelength conversion capability. Exploiting the concept of load balancing, we propose an adaptive weighted-shortest-cost-path (WSCP) routing strategy. The salient feature of WSCP is that it seeks the path that minimizes the resource cost while simultaneously maintaining the traffic load among the links as balanced as possible. In our simulation, we compare the blocking probability, average hops and link utilization of WSCP with traditional shortest-cost-path (SCP) strategy, fixed routing and alternate routing. The numerical results show that WSCP can enhance blocking performance and just lengthen hop distances a little longer. The improvement is more significant in denser networks or with more wavelengths. We also develop an analytical model to estimate blocking performance of WSCP and compare analyses with simulations. Because of the benefit from load balancing, the proposed WSCP strategy can be used as a path selection algorithm in traffic engineering.     

A Distributed Fault Management Scheme for Wavelength Routed All-Optical Networks

This paper presents a distributed algorithm to determine fault avoiding routes between source-destination end-node pairs in an all-optical network. Fault-tolerant routing for WDM routed all-optical networks has not been studied in details in the literature except for using protection switching or loopback recovery. Such schemes use predetermined protection mechanism and hence assume that the protection path is not faulty. This paper considers extensions to a dynamic routing scheme (presented earlier by these authors for fault-free networks) to handle rerouting in case of fault occurrence. The performance degradations of the network because of fault occurrence are then studied in terms of blocking probability and set-up time through simulations.     

波分复用波长路由节点的阻塞特性分析

利用概率统计理论的方法，从节点层次上定量分析了节点规模、复用波长数目以及波长转换对波分复用(WDM)波长路由网络中波长路由节点的影响。提出了基于概率统计的节点阻塞模型。数值结果突出表明波长转换能力越强的全光节点，其性能越优。为了提高网络资源的使用效率并增强全光网络的灵活性，必须实现全光网络中的虚波长路由波长转换器。通过数值计算找到了阻塞性能和代价的折中，研究中发现配置较低波长转换能力波长转换器的波长路由节点将会具备更强的性价比优势，当前在构建光通信系统时使用弱波长转换能力的光节点更可行。     

Routing and Wavelength Assignment in Optical Networks Using Logical Link Representation and Efficient Bitwise Computation

In this paper, we propose and evaluate a new approach for implementing efficient routing and wavelength assignment (RWA) in wavelength division multiplexing (WDM) optical networks. In our method, the state of a fiber is given by the set of free wavelengths in this fiber and is efficiently represented as a compact bitmap. The state of a multiple-fiber link is also represented by a compact bitmap computed as the logical union of the individual bitmaps of the fibers in this link. Likewise, the state of a lightpath is represented by a similar bitmap computed as the logical intersection of the individual bitmaps of the links in this path. The count of the number of 1-valued bits in the bitmap of the route from source to destination is used as the primary reward function in route selection. A modified Dijkstra algorithm is developed for dynamic routing based on the bitmap representation. The algorithm uses bitwise logical operations and is quite efficient. A first-fit channel assignment algorithm is developed using a simple computation on the bitmap of the selected route. The resulting bitwise routing algorithm combines the benefits of least loaded routing algorithms and shortest path routing algorithms. Our extensive simulation tests have shown that the bitwise RWA approach has small storage overhead, is computationally fast, and reduces the network-wide blocking probability. The blocking performance of our RWA method compares very favorably with three routing methods: fixed alternate routing, shortest path using flooding, and Dijkstra’s algorithm using mathematical operations. Our simulation experiments have also evaluated the performance gain obtained when the network access stations are equipped with finite buffers to temporarily hold blocked connection requests.