Lightpath restoration in WDM optical networks

Optical networks employing wavelength-division multiplexing and wavelength routing are potential candidates for future wide area networks. Because these networks are prone to component failures and carry a large volume of traffic, maintaining a high level of service availability is an important issue. This article discusses providing tolerance capability to the optical layer in WDM-based transport networks. It presents a survey on restoration schemes available in the literature, explains the operation of these schemes, and discusses their performance.     

Design protection for WDM optical networks

With wavelength division multiplexing (WDM) networks the failure of a single link or component may cause the simultaneous failure of several optical channels, potentially making impossible restoration by rerouting directly in higher layers directly using the optical network (SDH, ATM, internal protocol (IP)). To address this, we introduce the concept of design protection, which aims at making such failure propagations impossible. We present the disjoint alternate path (DAP) algorithm which places optical channels in order to maximize design protection. We show the result on various network examples     

A heuristic algorithm for lightpath scheduling in next-generation WDM optical networks

We study the routing and wavelength assignment (RWA) problem of scheduled lightpath demands (SLDs) in all-optical wavelength division multiplexing networks with no wavelength conversion capability. We consider the deterministic lightpath scheduling problem in which the whole set of lightpath demands is completely known in advance. The objective is to maximize the number of established lightpaths for a given number of wavelengths. Since this problem has been shown to be NP complete, various heuristic algorithms have been developed to solve it suboptimally. In this paper, we propose a novel heuristic RWA algorithm for SLDs based on the bee colony optimization (BCO) metaheuristic. BCO is a newborn swarm intelligence metaheuristic approach recently proposed to solve complex combinatorial optimization problems. We compare the efficiency of the proposed algorithm with three simple greedy algorithms for the same problem. Numerical results obtained by numerous simulations performed on the widely used realistic European Optical Network topology indicate that the proposed algorithm produces better-quality solutions compared to those obtained by greedy algorithms. In addition, we compare the results of the BCO–RWA–SLD algorithm with four other heuristic/metaheuristic algorithms proposed in literature to solve the RWA problem in the case of permanent (static) traffic demands.     

Power series-based algorithm for dedicated protection in WDM optical networks

WDM optical networks allow the transmission of multiple services with high rates and low cost. Therefore, the occurrence of a failure in any network element can cause loss of several services. Some survival mechanisms may be used to try to overcome this type of failure event. We present in this paper a new dedicated protection algorithm for link-failure survivability in WDM optical networks, referred to as power series routing-based dedicated protection (PSR-DP) algorithm. PSR-DP is based on the evaluation of the network links’ costs by using a power series expansion. This power series expansion uses input variables based on some relevant information of the network such as link physical length and wavelength availability. Other contribution of this paper is to propose a new input variable based on the wavelength continuity constraint. The performance of the proposed algorithm is compared to other well-known algorithms in the literature. We also propose a modification to Suurballe’s algorithm and compare it with our PSR-DP algorithm. Three different topologies are used in our simulations, and statistical analysis is performed on the results of the investigated algorithms. In all simulated cases, PSR-DP algorithm outperformed the other analyzed algorithms.     

Subpath protection for scalability and fast recovery in optical WDM mesh networks

This paper investigates survivable lightpath provisioning and fast protection switching for generic mesh-based optical networks employing wavelength-division multiplexing (WDM). We propose subpath protection, which is a generalization of shared-path protection. The main ideas of subpath protection are: 1) to partition a large optical network into smaller domains and 2) to apply shared-path protection to the optical network such that an intradomain lightpath does not use resources of other domains and the primary/backup paths of an interdomain lightpath exit a domain (and enter another domain) through a common domain-border node. We mathematically formulate the routing and wavelength-assignment (RWA) problem under subpath protection for a given set of lightpath requests, prove that the problem is NP-complete, and develop a heuristic to find efficient solutions. Comparisons between subpath protection and shared-path protection on a nationwide network with dozens of wavelengths per fiber show that, for a modest sacrifice in resource utilization, subpath protection achieves improved survivability, much higher scalability, and significantly reduced fault-recovery time.     

Hybrid connection algorithm: A strategy for efficient restoration in WDM optical networks

In present communication, we propose a modified resource allocation strategy, namely, hybrid connection algorithm, for achieving efficient restoration in WDM optical networks. The main theme of the algorithm is that, while attempting connection establishment, a wavelength is reserved in advance for providing resources for backup lightpaths. The analysis and the comparison of the proposed strategy with other existing strategies has been undertaken using metrics such as, restoration efficiency, number of wavelength links used by primary and backup lightpaths, and the percent link utilization. The proposed strategy provides 100% restoration efficiency and much better performance than the existing techniques.     

WDM网络光层保护整数线性规划算法的探讨

针对WDM(波分复用)光网络光层保护问题，提出了两种新的保护算法。这两种保护方法都属于ILP(整数线性规划)，所处理的是通道失效问题，而不是链路失效问题，分别列出两种算法的步骤和计算结果。     

A novel 1:N protection scheme for WDM passive optical networks

This paper presents a 1:N protection scheme based on the cyclic property of an array waveguide grating and a specific connection pattern among the optical network units (ONUs). The proposed scheme requires half the number of wavelengths of existing schemes presented in the literature. Although the current scheme requires more fiber links among the ONUs than previous schemes, the network resource demands are greatly reduced and the protection performance is improved.     

WDM光网络中一种新型的动态共享保护算法

波分复用(WDM)光网络中引入了共享风险链路组(SRLG)的概念 ,要求工作通路与保护通路不能处于同一个SRLG之中.文章提出了一种基于SRLG限制的动态共享通道保护算法,即满足K对业务的动态链路权重配置(K-Dynamic Link Weight Configuration, K-DLWC)算法 ,该算法的     

WDM网络光层保护新算法的探讨

首先介绍了几种按照不同标准划分的WDM网络光层保护方法,然后提出了三种实现光层保护的新算法,对它们的内容和性能做了详细描述。按照提出的算法所求得的解,可以为WDM网络提供新的光层保护方式。     

Power-aware provisioning strategy with shared path protection in optical WDM networks

As the Internet continues to grow, the power consumption of telecommunication networks is rising at a considerable speed, which seriously increases the operational expenditure and greenhouse gas emission. Since optical Wavelength Division Multiplexing (WDM) networks are currently the most promising network infrastructures, power saving issue on these networks has received more attention in recent years. In traditional optical WDM networks, a large amount of power is drained by the redundant idle resources and reserved backup resources although these powered on resources do not carry traffic in most of the time. In order to reduce the network power consumption, turning off the corresponding network components or switching them to a low-power, standby state (or called sleep mode) is a promising greening approach. In this paper, we study the power-aware provisioning strategies and propose a sleep mode based Power-Aware Shared Path Protection (PASPP) heuristic algorithm to achieve the power efficiency of optical WDM networks. By jointly utilizing link-cost and fiber-cost in path routing, resource assignment, and resource release, PASPP makes working paths and backup paths converge on different fibers as much as possible, and switch idle and backup components to sleep mode to realize power saving. Simulation results show that our PASPP can obtain notable power saving and achieve satisfactory tradeoff between power efficiency and blocking probability with respect to Power-Unaware Shared Path Protection (PUSPP).     

WDM网络恢复算法性能的比较

随着波分复用(WDM)技术的迅速商用化,骨干网络传输带宽呈现爆炸式增长的趋势,这使得网络生存性变得越来越重要.传统的网络生存性包括保护和恢复两种机制,而恢复机制直接影响着网络失效以后其承载业务的可靠性.文章综合前人的研究成果,从3个角度出发,提出了3种不同的恢复算法,并通过仿真数据对这3种算法性能进行了分析.     

Protection interoperability for WDM optical networks

The failure of a single optical link or node in a wavelength division multiplexing (WDM) network may cause the simultaneous failure of several optical channels. In some cases, this simultaneity may make it impossible for the higher level (SONET or IP) to restore service. This occurs when the higher level is not aware of the internal details of network design at the WDM level. We call this phenomenon “failure propagation.” We analyze three types of failure propagation, called “bottleneck,” “connectivity,” and “multiple groups.” Then we present a solution based on the definition of appropriate requirements at network design and a WDM channel placement algorithm, protection interoperability for WDM (PIW). Our method does not require the higher level to be aware of WDM internals, but still avoids the three types of failure propagation mentioned above. We finally show the result on various network examples     

Provisioning algorithms for WDM optical networks

This paper concerns connection provisioning for optical networks employing wavelength division multiplexing. A heuristic algorithm is developed and numerically studied for routing and wavelength assignment of a set of static connection requests. The algorithm runs much faster than the optimum solution of this problem. An adaptation of the algorithm is proposed to design restorable networks which can handle a specified set of failures. The proposed algorithm is based on taking all failures into consideration simultaneously, and performs better than developing independent designs for each failure     

Design methodology for WDM backbone networks using FWM-aware heuristic algorithm

The problem of lightpath topology design (LTD) and traffic routing over the lightpaths for wavelength-routed optical backbone networks has been investigated extensively in the past using heuristic as well as linear-programming based approaches. Sensitivity of such long-haul backbones to physical-layer impairments is required to be adequately addressed during LTD phase to improve overall performance. For optical communication using wavelength-division multiplexing (WDM) over a long-haul fiber backbone, four-wave mixing (FWM) may become one of the significant transmission impairments. Intrinsically, for a WDM-based wavelength-routed network with wavelengths assigned using equally-spaced channels, the generated FWM components are found to remain more crowded at the center of the fiber transmission window. Using this observation, we propose an LTD scheme employing a unique wavelength assignment (WA) technique, wherein long lightpaths (traversing through a larger number of fiber links) are allocated wavelengths at the either edges of the fiber transmission window whereas short lightpaths (consisting of fewer fiber links) are placed in the middle of the transmission window, thereby reducing the FWM crosstalk for long lightpaths. Since long lightpaths comprise of large numbers of fiber links and intermediate nodes, they experience large amplified spontaneous emission (ASE) noise and switch crosstalk. Therefore, by using the proposed WA technique, long lightpaths while suffering from more ASE noise and switch crosstalk get subjected to lesser FWM crosstalk leading to a more uniform distribution of overall optical signal-to-noise ratio for all the lightpaths across the network. Analysis of our results indicates that the proposed FWM-aware LTD scheme with the novel WA technique can achieve similar congestion levels (of lightpaths) and bandwidth utilization efficiency without any need of additional network resources as compared with the existing FWM-unaware LTD schemes.     

Shared protection in mesh WDM networks

This article introduces the design principles and state-of-the-art progress in developing survivable routing schemes for shared protection in mesh WDM networks. This article first gives an overview of the diverse routing problem for both types of protection in mesh networks, path-base and segment shared protection; then the cost function and link state for performing diverse routing are defined by which the maximum extent of resource sharing can be explored in the complete routing information scenario. Review is conducted on the most recently reported survivable routing schemes along with state-of-the-art progress in diverse routing algorithms for segment shared protection. The following three reported algorithms are discussed in detail: iterative two-step-approach, potential backup cost, and maximum likelihood relaxation.     

WDM光网络中的业务量疏导

波分复用（WDM）技术在主干传送网中巳广泛应用，WDM光网络的研究进展也非常迅速，光网络中的业务量疏导定义为复用、解复用和交换低速率业务流到大容量的光路中的行为。介绍了WDM光网络的业务量疏导的重要性，研究方法及其最新研究进展情况。     

Differentiated QoS for survivable WDM optical networks

Optical networks based on WDM technology have become a promising solution to realize transport networks that can meet the ever-increasing demand for bandwidth. As WDM networks carry a huge volume of traffic, maintaining a high level of survivability is an important and critical issue. The. development of GMPLS switching technology led to the direct integration of IP and WDM. In these IP-over-WDM networks different applications/end users need different levels of fault tolerance and differ in how much they are willing to pay for the service they get. The current trend in network development is moving toward a unified solution providing support for voice, data, and various multimedia services. Therefore, it imperative that WDM networks incorporate fault tolerance to single or multiple component failures, protection bandwidth, recovery time, and recovery granularity besides resource utilization and call acceptance ratio. This article presents a survey of various methods that have been proposed for providing service differentiation in survivable WDM networks and discuss their performance. Such methods are broadly classified under various paradigms such as differentiated reliability, R-connections, quality of protection, and quality of recovery.     

WDM网络波带交换算法分析

主要介绍了WDM光网络中的波带交换(Waveband Switching)问题的基本概念、技术特点.并分析了研究波带交换问题与波长路由问题(RWA)的不同之处,总结了波带交换算法常用的分析和研究方法.     

Tunable optical filters for dense WDM networks

WDM is currently taking over as the leading technology in point-to-point transmission links. For optical implementation of WDM networks, logical functionalities such as wavelength (channel) selection should be carried out in the wavelength domain; thus, the development of dynamic optical devices is required. One key device is a tunable optical filter. Important features of such a filter include low insertion loss, narrow bandwidth, high sidelobe suppression, large dynamic range, fast tuning speed, a simple control mechanism, small size, and cost effectiveness. Here, an extensive overview of the different technologies used to produce tunable optical filters is presented. Among them, fiber filters such as fiber Bragg gratings and fiber Fabry Perot are the most commercialized, yet inherently limited in their dynamic speeds. For high demanding dynamics, micro-machined and acousto-optic filters can offer a good solution for microsecond tuning speeds. Faster tunable devices, in nanosecond tuning speeds, might emerge out of microresonators, electrooptic filters, and active DBR filters