A novel shared-path protection algorithm with correlated risk against multiple failures in flexible bandwidth optical networks

In this paper, to decrease the traffic loss caused by multiple link failures, we consider the correlated risk among different connection requests when both the primary and backup paths are routed and assigned spectrum. Therefore, a novel shared-path protection algorithm is developed, named shared-path protection algorithm with correlated risk (SPP_CR), in flexible bandwidth optical networks. Based on the correlated risk, the routing can be diverse and the sharing in backup spectral resource will be restricted by SPP_CR algorithm, then the dropped traffic caused by simultaneous multiple failures between primary and backup path can be efficiently decreased. Simulation results show that, SPP_CR algorithm (i) achieves the higher successful service ratio (SSR) than traditional shared-path protection (SPP), shared-path protection with dynamic load balancing (SPP_DLB) and dedicated path protection (DPP); (ii) makes a better tradeoff in blocking probability, protection ratio (PR), average frequency slots consumed (AFSC) and redundancy ratio (RR) than SPP, SPP_DLB and DPP algorithms.     

Multi-link failure restoration with dynamic load balancing in spectrum-elastic optical path networks

In this paper, we investigate network performance of multi-link failure restoration in spectrum-elastic optical path networks (SLICE). To efficiently restore traffic under multi-link failures, a novel survivable algorithm, named dynamic load balancing shared-path protection (DLBSPP), is proposed to compute primary and link-disjoint shared backup paths. The DLBSPP algorithm employs first fit (FF) and random fit (RF) schemes to search and assign the available spectrum resource. Traffic-aware restoration (TAR) mechanism is adopted in the DLBSPP algorithm to compute new routes for carrying the traffic affected by the multi-link failures and then the multi-link failures can be efficiently restored. Simulation results show that, compared with the conventional shared-path protection (SPP) algorithm, the DLBSPP algorithm achieves lower blocking probability (BP), better spectrum utilization ratio (SUR), more reasonable average hop (AH) and higher failure restoration ratio (FRR). Thus, the proposed DLBSPP algorithm has much higher spectrum efficiency and much better survivability than SPP algorithm.     

Joint optimization method of failure probability and fiber-link load balancing in flexible bandwidth optical network

In order to gain insight into the relationship between the failure probability and the spectrum efficiency,both failure probability (FP) and load balancing (LB) were attempted to minimize in flexible bandwidth optical networks.An optimized FP-LB algorithm was developed to reduce failure probability and to improve the spectrum efficiency,and a traditional algorithm was further introduced for comparison in flexible bandwidth optical networks.Simulation results show that the optimized FP-LB algorithm reduces 69.8% blocking probability,45.3% spectrum occupancy rate,and 41.9% average failure probability compared to the traditional algorithm.Obviously,the optimized FP-LB algorithm achieves the joint optimization of both failure probability and load balancing.     

Resource efficiency improved approach for shared path protection in EONs

For improving the resource efficiency of dynamic shared path protection in elastic optical networks, a survivable RSA (SRSA)-based heuristic algorithm is proposed in the paper. In SRSA, an adaptive adjustment link cost function is devised to effectively select working and protection paths. The cost function sufficiently considers available spectrum resources and the length of light paths for both working and protection paths. In order to achieve high resource efficiency, a spectrum allocation strategy named minimal cost stable set is proposed to allocate spectrum for protection paths with respect to the resource efficiency in the link cost function. And the graph coloring algorithm is introduced to select the shared protection path with the highest resource efficiency for the request. Compared with the shared path protection and dynamic load balancing shared path protection, simulation results show that the proposed SRSA decreases bandwidth blocking probability and achieves high resource efficiency.     

Physical layer performance benchmarking of two metropolitan area network configurations

This paper investigates the problem of dynamic survivable lightpath provisioning against single-node/link failures in optical mesh networks employing wavelength-division multiplexing (WDM).We unify various forms of segment protection into generalized segment protection (GSP). In GSP, the working path of a lightpath is divided into multiple overlapping working segments, each of which is protected by a node-/link-disjoint backup segment. We design an efficient heuristic which, upon the arrival of a lightpath request, dynamically divides a judiciously selected working path into multiple overlapping working segments and computes a backup segment for each working segment while accommodating backup sharing. Compared to the widely considered shared-path protection scheme, GSP achieves much lower blocking probability and shorter protection-switching time for a small sacrifice in control and management overhead.On the basis of generalized segment protection, we present a new approach to provisioning lightpath requests according to their differentiated quality-of-protection (QoP) requirements. We focus on one of the most important QoP parameters—namely, protection-switching time—since lightpath requests may have differentiated protection-switching-time requirements. For example, lightpaths carrying voice traffic may require 50 ms protection-switching time while lightpaths carrying data traffic may have a wide range of protection-switching-time requirements. Numerical results show that our approach achieves significant performance gain which leads to a remarkable reduction in blocking probability.While our focus is on the optical WDM network, the basic ideas of our approaches can be applied to multi-protocol label switching (MPLS) networks with appropriate adjustments, e.g., differentiated bandwidth granularities.     

面向业务的弹性光网络光路损伤感知能效路由策略

针对弹性光网络中物理损伤导致业务频谱利用率低和传输能耗高问题,该文提出一种面向业务的链路损伤感知频谱分区(LI-ASP)能效路由策略。在LI-ASP策略中,为降低不同信道间非线性损伤,基于负载均衡设计一个综合考虑链路频谱状态和传输损伤的路径权重公式,根据调制方式的频谱效率和最大传输距离构造分层辅助图,从最高调制等级开始,为高质量业务选择K条边分离的最大权重传输路径;为低质量业务选择K条边分离的最短能效路径。然后,LI-ASP策略根据业务速率比值对频谱分区,采用首次命中(FF)和尾端命中(LF)联合频谱分配方式,减少不同传输速率业务间的交叉相位调制。仿真结果表明,该文所提LI-ASP策略在有效降低带宽阻塞率的同时,减少了业务传输能耗。     

基于联合故障概率的频谱灵活光网络生存性业务认知算法

This paper addresses the problem of survivable traffic assignment with failure probability requirement in flexible bandwidth optical networks. We describe a Survivable Traffic Cognition (STC) algorithm with joint failure probability. Survivable Traffic Assign-ment (STA) algorithm and Conventional Traf-fic Assignment (CTA) algorithm are added to illustrate the effectiveness of our proposed STC. We investigate the effect of joint failure probability on blocking probability, spectral utilization ratio, average joint failure probabil-ity, and the average hops. Simulation results show that our proposed STC not only achieves better performance in terms of blocking probability and spectral utilization ratio than CTA and STA, but also does not cause higher average joint failure probability or larger average hops compared with STA. As a result, STC makes the best use of spectral resources and does not cause large average joint failure probability.     

Survivable routing,spectrum and waveband assignment strategy in cloud Optical and Data Center Network

These years, data centers are developing quickly and cloud Optical and Data Center Network (ODCN) has been shown to be the most viable solution for inter-data-center network implementation with less energy consumption and higher transmit rate. At the same time, elastic optical networks and waveband switching can address the problems caused by dramatic increase in network scale. In cloud hierarchical ODCN with flexible spectrum and waveband switching, survivability is an important and complex issue which is needed to be researched. So, we study the survivable routing, spectrum and waveband assignment strategy in cloud hierarchical ODCN, and in this paper, a novel hierarchical shared-protection (HSP) strategy is proposed. We consider spectrum fragmentation, waveband and shared-protection simultaneously. By quantifying the influence of spectrum assignment and the emergence of fragmentation, slots are assigned to the optimal paths. In order to share protection resource or wavebands, a heuristics algorithm named HSPGA is proposed for optimally picking out the two protection paths. Simulation results show that the proposed HSP strategy decreased the amount of employed ports significantly. In addition, the spectrum efficiency is improved.     

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.     

An efficient network‐side path protection scheme in OFDM‐based elastic optical networks

Elastic optical networks (EONs) based on orthogonal frequency division multiplexing (OFDM) technologies are seen as a promising solution for next‐generation optical transport networks to support the rapidly growing and heterogeneous traffic. In EONs, the elastic bandwidth allocation and modulation format agilities combined with reconfiguration capabilities pave the new way for leveraging the network efficiency. In this paper, we recast the network‐side path protection in EONs considering the opportunities and challenges enabled by the flexible operation of OFDM technologies. For the first time, we propose to take advantages of the reconfiguration capabilities of OFDM transponders for adapting to transmission condition variations when switching from the working to protection path in network‐side protection. The idea is inspired by the observation that in reach‐diverse networks, the transmission margin between the working path and protection path of a connection might be large enough, and thus, the most spectrum‐efficient modulation format for each path could be separately tailored, rather than imposed by a common one based on the worse condition as with current fixed transmission technologies. We formulate survivable transparent network designs for both dedicated and shared path protection in the form of integer linear programming model taking into account our proposal for enabling different transmission operations between working and protection mode. Numerical results based on extensive simulations on a realistic network topology, COST239, are presented to highlight the benefits of our proposal compared to conventional approaches in terms of spectrum efficiency for un‐capacitated scenarios and improvements in blocking ratio for capacitated scenarios.     

Multiple link failure recovery in survivable optical networks

Survivability is of critical importance in high-speed optical communication networks. A typical approach to the design of survivable networks is through a protection scheme that pre-determines and reserves backup bandwidth considering single/double link failure scenarios. In this article, a greedy algorithm is presented to reserve backup bandwidth considering multiple (F > 2) link (SRLG) failure scenarios. A bandwidth-saving joint selection scheme of working and protection paths is presented for protection against random multiple-link failures under dynamic traffic. Simulation shows that the algorithm can achieve maximum sharing of backup bandwidth for protection against random multiple-link failure with significant amount of bandwidth saving.     

多域光网络中一种支持区分可靠性的通路保护算法

区分可靠性的通路保护方案既能为光网络中具有不同可靠性需求的业务提供有效的故障保护,又能优化网络资源的利用,是一种高效的生存性机制。但目前此类问题的研究主要是集中于传统的单域光网络中,所得的研究成果无法直接运用于具有多域特点的下一代光网络中。针对这一问题,在对以往通路保护算法进行改进的基础上提出了一种适用于多域光网络中的支持区分可靠性的通路保护算法,并对其性能进行了计算机仿真研究。仿真结果表明,该算法不仅能满足多域光网络中不同业务的可靠性需求,而且能提高网络资源的利用率、降低业务连接的阻塞率。     

ACO-based routing and spectrum allocation in flexible bandwidth networks

Optical networks with flexible bandwidth provisioning are a very promising networking architecture. It enables efficient resource utilization and supports heterogeneous bandwidth demands. In this paper, we focus on the dynamic routing and spectrum allocation (RSA) problem which emerges in such networks and propose a novel dynamic RSA algorithm by means of ant colony optimization (ACO). In our proposed algorithm, ants are launched to modify the routing table according to the length and the spectrum fragmentation information along the path. A simulation study is performed considering five algorithms in terms of blocking probability: WDM-based RWA approach, KSP-based RSA approach, Slot-based RSA algorithm, and our proposed ACO-based RSA approach. We then compare the deterioration degree of blocking probability by adding more types of line rate. Simulation results indicate that our proposed ACO-based RSA approach achieves lower blocking probability, complexity, and higher adaptability to more line rates mixture.     

Multicast service protection algorithm based on elastic optical network

With the rapid growth of the network traffic,the elastic optical network (EON) has been proposed as a promising solution due to its high spectrum efficiency and flexible bandwidth provision.Meanwhile,multicast routing and spectrum allocation,and the survivability of the network become more challenging than that in the conventional optical network.The routing for multicast traffic and its protection algorithm in EON was investigated.An integer linear programming (ILP) formulation with the objective to minimize total spectrum consumption was presented.In addition,a heuristic algorithm called multicast sub-tree protection algorithm (MSPA) to achieve sufficient protection and satisfy resources savings was designed.The simulation results demonstrate that comparing with the traditional multicast routing and protection algorithm,MSPA performs well in improving the blocking probability and the spectrum utilization of the network.     

弹性光网络中基于自适应调制的碎片感知共享通路保护算法

为了提高弹性光网络(EON)的频谱利用率,提出一种基于自适应调制的碎片感知共享通路保护算法。该算法利用频谱块承载权重(SBBW)衡量不同频谱块接纳业务的能力,优先选择SBBW大的链路构成候选工作路径,并利用分配前、后SBBW差值最小的频谱块建立工作路径。然后选择可用频谱块和保护频谱块承载能力大的链路构成候选保护路径,建立保护路径时优先使用分配前、后SBBW差值最小的保护频谱块,建立失败时才选择分配前、后SBBW差值最小的可用频谱块。仿真结果表明:该算法可以降低带宽阻塞率、频谱碎片率和备用容量冗余。     

WDM网基于混合共享和SRLG约束的通路保护

研究了网状波分复用（WDM）网中动态生存性路由配备问题，提出了一种新颖的基于共享风险链路组（SRLG）束的混合共享通路保护（MSPP）方案。MSPP为每个业务请求分配丁作通路和SRLG分离的保护通路，因此能完全保护单SRLG故障。与传统的共享通路保护（SPP）方案不同，在满足某些约束条件下，MSPP允许部分工作通路和保护通路共享资源。仿真结果表明，MSPP性能优于SPP。     

Experimental demonstration of time-aware software defined networking for OpenFlow-based intra-datacenter optical interconnection networks

Nowadays, most service providers offer their services and support their applications through federated sets of data centers which need to be interconnected using high-capacity optical networks in intra-datacenter networks. Many datacenter applications in the environment require lower delay and higher availability with the end-to-end guaranteed quality of service. In this paper, we propose a novel time-aware software defined networking (TaSDN) architecture for OpenFlow-based intra-datacenter optical interconnection networks. Based on the proposed architecture, a time-aware service scheduling (TaSS) strategy is introduced to allocate the network and datacenter resources optimally, which considers the datacenter service scheduling with flexible service time and service bandwidth according to the various time sensitivity requirements. The TaSDN can arrange and accommodate the applications with required QoS considering the time factor, and enhance the data center responsiveness to quickly provide for intra-datacenter service demands. The overall feasibility of the proposed architecture is experimentally verified on our testbed with real OpenFlow-enabled tunable optical modules. The performance of TaSS strategy under heavy traffic load scenario is also evaluated based on TaSDN architecture in terms of blocking probability and resource occupation rate.     

Performance enhancement for impairment-aware SRLG failure protection in wavelength-routed optical networks

With the increase of size and number of shared risk link groups (SRLGs) in WDM networks, path protection tends to have longer working paths and backup paths due to SRLG-disjoint constraints, which makes physical impairment a major concern in working path and backup path provisioning, particularly in large-sized all optical networks. As a simple and efficient algorithm, the working path first algorithm is often used for path protection against SRLG failures, where the working path is calculated first by using the shortest-path algorithm on the graph, followed by using the SRLG-disjoint shortest path as backup path. Compared with the working path, the backup path calculated after the working path in the working path first algorithm is more vulnerable to physical impairment, since it may be much longer than the working path. As a result, if we reject those connections that cannot meet the physical impairment requirement, with SRLGs the blocking probability of path protection will be much higher. We argue that impairment must be taken into account together with capacity efficiency in a comprehensive way during SRLG-disjoint working path and backup path selection. To solve this problem, we motivate the needs to study physical impairment-aware shared-path protection by considering two policies. Policy I uses two SRLG-disjoint least impairment paths as working path and backup path, respectively, and Policy II tries to benefit from both the shortest path and the least impairment path by choosing them intelligently. Analytical and simulation results show: (1) compared with impairment-unawareness, impairment-aware SRLG failure protection performs much better in terms of blocking probability especially with strong physical impairment constraints; (2) impairment-aware SRLG failure protection can significantly reduce physical-layer blocking probability; and (3) the algorithm based on Policy II achieves a good balance between capacity efficiency and physical impairment requirement.     

串扰感知的空分弹性光网络频谱转换器稀疏配置和资源分配方法

针对大容量多芯光纤空分复用弹性光网络(SDM-EON)中芯间串扰导致业务传输质量下降和阻塞率上升的问题,该文提出了节点稀疏配置频谱转换器降低芯间串扰的路由纤芯频谱分配方法。该方法根据网络中节点中介中心性稀疏配置频谱转换器。在业务路由阶段,设计综合考虑光路负载和节点频谱转换能力的光路选择的权重方法;为了降低串扰,在纤芯频谱分配阶段,设计纤芯分组和频谱分区分配方法;最后,针对串扰较大的业务,采用频谱转换以降低业务串扰和改善带宽阻塞率。仿真结果表明,所提算法能有效地提高频谱利用率,降低因芯间串扰导致的带宽阻塞率。     

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.