Survivable WDM mesh networks

In a wavelength-division-multiplexing (WDM) optical network, the failure of network elements (e.g., fiber links and cross connects) may cause the failure of several optical channels, thereby leading to large data losses. This study examines different approaches to protect a mesh-based WDM optical network from such failures. These approaches are based on two survivability paradigms: 1) path protection/restoration and 2) link protection/restoration. The study examines the wavelength capacity requirements, and routing and wavelength assignment of primary and backup paths for path and link protection and proposes distributed protocols for path and link restoration. The study also examines the protection-switching time and the restoration time for each of these schemes, and the susceptibility of these schemes to multiple link failures. The numerical results obtained for a representative network topology with random traffic demands demonstrate that there is a tradeoff between the capacity utilization and the susceptibility to multiple link failures. We find that, on one hand, path protection provides significant capacity savings over link protection, and shared protection provides significant savings over dedicated protection; while on the other hand, path protection is more susceptible to multiple link failures than link protection, and shared protection is more susceptible to multiple link failures than dedicated protection. We formulate a model of protection-switching times for the different protection schemes based on a fully distributed control network. We propose distributed control protocols for path and link restoration. Numerical results obtained by simulating these protocols indicate that, for a representative network topology, path restoration has a better restoration efficiency than link restoration, and link restoration has a faster restoration time compared with path restoration.     

双链路故障时的共享路径保护

在波长路由光网络中,网络的存活性已经受到越来越多的重视.对单链路故障时的保护已经不能满足某些关键性业务对网络存活性的要求,因而研究了双链路故障时的共享路径保护技术.在动态业务下,将共享路径保护问题归结为整数线性规划.在节点无波长转换能力的情况下,分别提出了为当前业务计算最优路径和固定路径两种策略下的整数线性规划.数值结果表明,相对于专用保护,双链路故障时的共享路径保护能够节约30%左右的波长链路资源.     

Dynamic Survivability in WDM Mesh Networks Under Dynamic Traffic

Network survivability is a crucial requirement in WDM mesh networks. In this paper, we systematically consider the problem of dynamic survivability with dynamic single link failure in WDM networks under dynamic traffic demands. Specifically, we investigate various protection schemes, such as dedicated path protection (DPP), shared path protection (SPP), dedicated link protection (DLP), shared link protection (SLP), and two restoration schemes, path restoration (PR) and link restoration (LR). Moreover, two new shared protection methods are proposed, i.e., SRLG-based shared link protection (SRLG-SLP) and SRLG-based shared path protection (SRLG-SPP). The SRLG (shared risk link group) constraint defines the availability of protection resources to a working path, which requires that any two working paths sharing the same risk of failure (or in the same SRLG) cannot share the same protection resources. Furthermore, in our study, we consider a more practical dynamic single-link failure model, in which the link-failure-interarrival time and link-failure-holding time are considered as two independent parameters. Based on this link-failure model, extensive simulations are done to analyze and compare the dynamic survivable performance of various protection and restoration schemes. Resource utilization, protection efficiency, restoration efficiency, and service disruption ratio are employed as survivable performance metrics versus traffic load, link-failure frequency, and link-failure reparation time to evaluate the survivable performance. Many meaningful results are given. In addition, we show that the developed SRLG-SLP and SRLG-SPP protection schemes perform very well in terms of protection efficiency and service disruption ratio, while sacrificing some performance in terms of resource utilization.     

EONs中一种混合路径专有保护算法

为了降低带宽阻塞率,节约频谱资源,在动态业务到达的弹性光网络(EONs)场景下,不同业务请求的路径状况可能不同,因此不能确定单路径专有保护与带宽分割多路径专有保护的优劣。文章结合单路径专有保护和带宽分割多路径专有保护提出了一种混合路径专有保护(HDPP)算法。该算法利用路径的单位频谱效率和路径跳数计算了k条链路不相关候选路径,并提出了一种考虑单位频隙最高频谱效率和路径跳数以及路径上最大可用频谱信息的多路径频谱分配(MPSA)算法,最后,HDPP算法在多种生存性方案中选择出最佳方案。仿真结果表明,与对比算法相比,所提算法在阻塞率和频谱利用率方面都有较好的性能表现。     

Capacity Efficiency and Restorability of Path Protection and Rerouting in WDM Networks Subject to Dual Failures

Resilient optical networks are predominately designed to protect against single failures of fiber links. But in larger networks, operators also see dual failures. As the capacity was planned for single failures, disconnections can occur by dual failures even if enough topological connectivity is provided. In our approach the design of the network minimizes the average loss caused by dual failures, while single failures are still fully survived. High dual failure restorability is the primary aim, capacity is optimized in a second step. For WDM networks with full wavelength conversion, we formulate mixed integer linear programming models for dedicated path protection, shared (backup) path protection, and path rerouting with and without stub-release. For larger problem instances in path rerouting, we propose two heuristics. Computational results indicate that the connectivity is of much more importance for high restorability values than the overall protection capacity. Shared protection has similar restorability levels as dedicated protection while the capacity is comparable to rerouting. Rerouting surpasses the protection mechanisms in restorability and comes close to 100% dual failure survivability. Compared to single failure planning, both shared path protection and rerouting need significantly more capacity in dual failure planning.     

Optical layer survivability: a post-bubble perspective

We revisit the topic of optical layer protection from a motivation and deployment perspective. We first discuss the changes that have occurred in optical networking in general and the implications for protection. We then discuss scenarios where optical protection makes sense, recognizing that other fast protection schemes at the client layer provide viable alternatives in certain cases. Our conclusion is that optical protection makes sense for metro networks, as long as they are based on simple dedicated schemes. When it gets to more complex shared ring and mesh protection, we believe that OEO-based schemes are more viable, whether crossconnect-based or packet-switch-based.     

Shared-Risk Logical Span Groups in Span-Restorable Optical Networks: Analysis and Capacity Planning Model

In an optical transport network distinct logical groups of lightwave channels between neighboring OXC nodes (called spans) may sometimes be realized over a common physical resource such as a duct or conduit, and hence share a common cause of failure. This is closely related to the concept of shared risk on individual channels or links, called SRLGs, which is relevant to pre-planned path protection schemes with shared capacity on backup paths. But when considering span-restorable networks, shared risk over logical spans (not individual channels) is the corresponding issue of concern. This work considers several aspect of how such shared-risk span groups (SRSG) affect the protection capacity design and other aspects of span-restorable mesh networks. We provide a model for capacity planning any span-restorable network in the presence of a known set of such shared-risk spans and study the relationship between capacity requirements and the number and placement of such situations. This provides guidelines as to how many SRSGs can be sustained before the capacity penalty becomes severe and methods to diagnose which of them are the most limiting to overall protection efficiency. One finding of interest is that if a given percentage of all possible dual-failure combinations incident to a common node are allowed for in the design, then nearly the same percentage of other dual-span failure combinations (any two spans in the network) will also be restorable. We also show that designing a network to withstand even a small number of multi-span co-incident spared-risk span groups will yield a significant improvement in overall dual-failure restorability and hence also in network availability.Presented at Optical Networking and Communications Conference (Opti Comm 2002), Boston, MA, USA, July-August 2002.     

Availability analysis under multiple link failures in WDM networks with shared-link connections

In optical Wavelength Division Multiplexing (WDM) networks, different protection schemes have been proposed in the literature, namely, dedicated protection and shared protection. Shared protection techniques significantly reduce the required spare capacity by providing the same level of availability as dedicated protection. However, current mission critical applications (which heavily depend on the availability of communication resources) require connection availability in the order of 99.999% or higher, which corresponds to a downtime of almost 5 min a year on the average. Therefore, in order to satisfy a connection serviceavailability requirement defined by the users Service Level Agreement in a cost-effective and resource-efficient way, network operators need a systematic mechanism to evaluate the network availability under multiple failure scenario to ensure that current network configuration can meet the required availability degree; otherwise, a network upgrade is required. Unfortunately, under multiple failure scenario, traditional availability analysis techniques based on reliability block diagrams are not suitable for survivable networks with shared spare capacity. Therefore, a new concept is proposed to facilitate the calculations of network availability. In this paper, we propose an analytical model for evaluating the availability of a WDM network with shared-link connections under multiple link failures. The analytical model is also verified using Monte Carlo simulation. The proposed model significantly contributes to the related areas by providing network operators with a quantitative tool to evaluate the system availability and, thus, the expected survivability degree of WDM optical networks with shared connections under multiple link failures.     

Achieving Resource-Efficient Survivable Provisioning in Service Differentiated WDM Mesh Networks

A resource-efficient provisioning framework (RPF) is proposed in this paper for optical networks providing dedicated path protection (DPP) and shared path protection (SPP) services. The framework reduces resource consumption by considering spare capacity reservation of DPP and SPP cooperatively while provides 100% survivability guarantee and maintains the recovery time for both protection types against the predominant single link failures. To tackle the service provisioning problem under the framework, an integer linear programming (ILP) formulation is presented to find the optimal routing solution for a given set of traffic demands. The objective is to minimize total capacities consumed by working and backup paths of all demands. Then, heuristics are developed for on-line routing under dynamic change of traffic. Numerical results show that compared with traditional provisioning framework (TPF), the RPF has the following advantages: 1) Over 10% capacity savings are achieved for static service provisioning; 2) blocking probability of both protection types is greatly reduced; 3) lower resource overbuild is achieved; and 4) average backup-path hop distance of shared-path-protected flows is reduced. Finally, network survivability in face of double link failures is discussed under the framework.      

Availability-Aware Provisioning Strategies for Differentiated Protection Services in Wavelength-Convertible WDM Mesh Networks

In an optical WDM mesh network, different protection schemes (such as dedicated or shared protection) can be used to improve the service availability against network failures. However, in order to satisfy a connections service-availability requirement in a cost-effective and resource-efficient manner, we need a systematic mechanism to select a proper protection scheme for each connection request while provisioning the connection. In this paper, we propose to use connection availability as a metric to provide differentiated protection services in a wavelength-convertible WDM mesh network. We develop a mathematical model to analyze the availabilities of connections with different protection modes (i.e., unprotected, dedicated protected, or shared protected). In the shared-protection case, we investigate how a connection's availability is affected by backup resource sharing. The sharing might cause backup resource contention between several connections when multiple simultaneous (or overlapping) failures occur in the network. Using a continuous-time Markov model, we derive the conditional probability for a connection to acquire backup resources in the presence of backup resource contention. Through this model, we show how the availability of a shared-protected connection can be quantitatively computed. Based on the analytical model, we develop provisioning strategies for a given set of connection demands in which an appropriate, possibly different, level of protection is provided to each connection according to its predefined availability requirement, e.g., 0.999, 0.997. We propose integer linear programming (ILP) and heuristic approaches to provision the connections cost effectively while satisfying the connections' availability requirements. The effectiveness of our provisioning approaches is demonstrated through numerical examples. The proposed provisioning strategies inherently facilitate the service differentiation in optical WDM mesh networks.     

Models of Restoration Probability in WDM Networks Employing Active Restoration

The ever-increasing demand for network bandwidth makes network survivability an issue of great concern. Lightpath restoration is a valuable approach to guaranteeing an acceptable level of survivability in WDM optical networks with better resource utilization than that of its protection counterpart. Active restoration (AR) is a newly proposed lightpath restoration scheme [M. Mostafa et al. OSA Journal of Optical Networking, vol. 3, no. 4, pp. 247–260] that combines the best of protection and reactive restoration while avoiding their shortcomings. In this paper, we conduct detailed performance analysis on the restoration probability of AR-based WDM networks. In particular, analytical models of restoration probability are developed respectively for networks with full-wavelength conversion capability and for networks without wavelength conversion capability under different backup path searching schemes. Based on the new models, we investigate the effects of wavelength availability, wavelength conversion capability, path length as well as backup path seeking methods on the restoration probability.     

An efficient hybrid protection scheme with shared/dedicated backup paths on elastic optical networks

Fast recovery and minimum utilization of resources are the two main criteria for determining the protection scheme quality. We address the problem of providing a hybrid protection approach on elastic optical networks under contiguity and continuity of available spectrum constraints. Two main hypotheses are used in this paper for backup paths computation. In the first case, it is assumed that backup paths resources are dedicated. In the second case, the assumption is that backup paths resources are available shared resources. The objective of the study is to minimize spectrum utilization to reduce blocking probability on a network. For this purpose, an efficient survivable Hybrid Protection Lightpath (HybPL) algorithm is proposed for providing shared or dedicated backup path protection based on the efficient energy calculation and resource availability. Traditional First-Fit and Best-Fit schemes are employed to search and assign the available spectrum resources. The simulation results show that HybPL presents better performance in terms of blocking probability, compared with the Minimum Resources Utilization Dedicated Protection (MRU-DP) algorithm which offers better performance than the Dedicated Protection (DP) algorithm.     

On the improvement of network resource utilization efficiency for the establishment of static dependable connections in SRLG-constrained WDM translucent networks

In this paper, we investigate the problem of establishing static connections with fault-tolerant requirements, also known as dependable connections, taking into account quality of transmission constraints. To the best of our knowledge, this is the first study that tackles the aforementioned problem under shared risk link group (SRLG) constraints in translucent WDM optical mesh networks where typically a set of strategically localized network nodes are equipped with regeneration capability to overcome physical-layer impairment effects. A novel cross-layer heuristic approach is introduced to solve the problem for an heterogeneous networked scenario relying on a cost-effective two-stage protection procedure which combines the well-known path protection and partial path protection schemes in order to ensure instantaneous recovery from any SRLG-failure event. The proposed heuristic integrates a generic auxiliary graph model that incorporates various network heterogeneity factors such as the number of transceivers at each network node, the number of wavelengths on each fiber link, and the regeneration capability of each node, represented by different edges in the constructed graph. Moreover, the integrated auxiliary graph can be applied efficiently to model either single- or mixed-line-rate translucent WDM optical networks wherein different modulation formats are employed in order to support the transmission at different line rates. Our solution approach aims at maximizing the total number of accommodated requests by reducing network resource consumption through the simultaneous use of the backup–backup and primary–backup multiplexing techniques. We, here, present extended versions of these two techniques that generalize the sharing concept to some other important node resources—specifically, regeneration equipments which constitute the major cost factor in optical transport networks—in addition to link resources (i.e., wavelength channels). As far as we know, this is the first attempt to deploy simultaneously generalized versions of the backup–backup and primary–backup multiplexing techniques when considering static traffic patterns without compromising the 100 % fault-recoverability guarantee. The performances of the proposed heuristic are evaluated and discussed through extensive numerical experiments carried out on different network topologies. Significant improvements are demonstrated, either in terms of network blocking performance or in terms of resource utilization efficiency, in comparison with previously proposed approaches.     

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.     

Performance evaluation of the survivability schemes in WOBAN: a quality of recovery (QoR) method

The hybrid wireless optical broadband access network (WOBAN) is a combination of an optical backhaul and a wireless front‐end, which combine the huge amount of available bandwidth of optical networks and the ubiquity and mobility of wireless access networks with the objective of reducing their cost and complexity. Survivability is one of the most important issues in WOBAN. In this paper, the survivability schemes in WOBAN are addressed from a particular point of view of the quality of recovery (QoR) method. The QoR is a comprehensive measure to evaluate the survivability schemes in terms of availability, recovery time, redundancy, and bandwidth of backup path. The specific procedures to set up the analytical models for the survivability schemes in WOBAN are given based on the QoR concept, including abstract, normalization, and application. Besides, the weights assignment is provided to calculate the QoR value for the operators, home users, or business users with different requirements, which in turn offers the user‐perceptive quality of service. To verify the performance of the survivability schemes by the QoR method, extensive simulations are made under different WOBAN configurations. Numerical results show that for the intra‐domain survivability schemes, the wireless and optical mixed protection scheme is the best choice for failure recovery in WOBAN. The wireless scheme is the second choice for the solution, which emphasizes cost control, while for the solution that emphasizes the network performance, the 1:1 scheme is the second choice. The 1:N scheme obtains the worst QoR value as the splitter ratios increase. For the inter‐domain survivability schemes, optimizing backup optical networking units selection and backup fibers deployment scheme outperforms maximum protection with minimum cost scheme from the point of view of QoR. Copyright © 2013 John Wiley & Sons, Ltd.     

WDM光网络中基于交叉共享保护的绿色多播疏导算法(英文)

Currently,multicast survivability in optical network obtains more attention.This paper focuses on the field of multicast grooming shared protection in green optical network and designs a novel auxiliary graph and a shared matrix to address the survivable multicast resource consumption.This paper also proposes a new heuristic called Green Multicast Grooming algorithm based on spanning path Cross-Shared protection(GMGCSP),in which network reliability,energy efficiency and resource utilization are jointly considered.Simulation results testify that,compared to other algorithms,the proposed GMG-CSP not only has lower blocking probability and higher bandwidth utilization ratio,but also saves more energy.     

A framework for service-guaranteed shared protection in WDM meshnetworks

In this article a framework for end-to-end service-guaranteed shared protection in dynamic wavelength division multiplexing (WDM) mesh networks, called short leap shared protection (SLSP), is introduced. The idea of SLSP is to divide each working path into several overlapped protection domains, each of which contains a working and protection path pair. In addition to a guaranteed restoration service, SLSP is designed to satisfy the future requirements of wavelength-routed optical mesh networks in scalability, class of service, and capacity efficiency. Tutorial-like discussions are given in the architecture design and signaling mechanisms for implementing the SLSP framework in a dynamic network environment with examples and illustrations. To show that SLSP can improve capacity efficiency, simulations are conducted using four networks (22-, 30-, 79-, 100-node) for a comparative study between ordinary shared protection schemes and SLSP     

节点中介性和频谱离散度感知虚拟光网络生存性协同映射

虚拟网络的映射策略影响弹性光网络(EON)资源可用性和网络生存性。该文提出一种基于节点间距离和频谱离散度感知的虚拟光网络生存性协同映射(CM-DSDA)算法,研究节点计算资源和拓扑位置中介性的光节点排序策略,设计频谱离散度方法评价链路频谱碎片化程度。在虚拟链路的生存性映射中,选择邻接已映射节点中消耗频隙数少且频谱离散度低的工作光路和保护光路协同映射虚拟网络。仿真结果表明所提算法能有效地提高EON的频谱占用率和减少带宽阻塞率。     

Survivability and reliability of a composite-star transport network with disconnected core switches

This paper deals with the design and dimensioning of a novel survivable optical network structure, called Petaweb, that can reach a total capacity of several Pb/s (10¹⁵ bit/s). The Petaweb has a composite-star architecture that allows two-hop connections between edge nodes through disconnected core nodes. Prior studies of the same authors have tackled the optimization of a Petaweb network architecture with regular and quasi-regular topologies. In this paper, reliability and survivability issues are addressed by introducing a dedicated path protection strategy into the design model. We present by extensive numerical results the reliability and survivability properties of the Petaweb core architecture with respect to single fiber link, core node, or switching plane failure and to switching site disconnection.     

Optimized dimensioning of resilient optical grids with respect to grade of services

An optical grid network geographically integrates distributed computing/information resources with high speed communications. Network dimensioning, maximization of services, and job scheduling are some of today key arising issues in optical grids. Since the last decade, many projects have been conducted in order to provide computational and information facilities in the academic as well as in the business communities. In this paper, we study the network dimensioning and the maximization of IT services in optical grids. We propose a scalable optimization model for maximizing IT services under link transport capacities. We assume the use of the anycast routing principle to identify the server nodes for executing the jobs, and a shared path protection mechanism in order to offer protection against single link/node failures. We also investigate different calculation methods of the link transport capacities in order to maximize the grade of services, while taking into account the bandwidth requirements. Computational results are presented on different traffic distributions. They show that the proposed link dimensioning can save more than 35 % bandwidth in optical grid networks, in comparison with the classical link dimensioning strategies. We also investigate the different protection schemes against single link failures, single node failures, single node and server node failures, and compare their bandwidth requirements, as well as their impact on the grade of services (GoS). Results show that there is no significant increase of the bandwidth requirements and no meaningful impact on the GoS when moving from a single link protection scheme to a single node (including server nodes) protection scheme.