Two-layer mesh network optimization based on inter-layer decomposition

Presently, backbone data networks are converging toward a typical two-layer architecture of an IP/MPLS layer over an optical layer. In this paper, we study the problem of maximizing a utility function for an Internet service provider (ISP) of a two-layer mesh networks and propose an efficient decomposition method based on Lagrange relaxation. Differing from previous works on two-layer mesh networks, our proposed decomposition method decomposes an original two-layer mathematic optimization problem, respectively, into an IP/MPLS-layer and an optical-layer optimization problem by slacking the constraints between the two layers. This decomposition method enables to control the trade-off between running time and quality of the feasible solution. Numerical results for a variety of networks indicate that our proposed decomposition method is attractive to quickly find near optimal solutions.     

多域光网络生存性的关键技术研究

多域光网络的生存性作为衡量网络性能优劣的关键指标,与实际网络应用的关系最为密切,是当前迫切需要解决的关键问题;聚焦高速化、多业务化驱动的多域光网络环境下的生存性技术.基于光网络的多业务、分布式控制的特性,分析了多域光网络生存性机制的研究现状及面临的挑战;给出了一种针对多域光网络生存性问题的分类方法;结合多域光网络对生存性的需求,对相关关键技术进行了归类和研究,并指明了进一步研究的方向和重点.     

A novel domain-by-domain survivable mechanism in multi-domain wavelength-division-multiplexing optical networks

In multi-domain wavelength-division-multiplexing (WDM) optical networks, the inter-domain routing is a challenge since each single-domain cannot view the full network topology. At the same time, survivability is also an important issue in optical networks since the failures of fiber links or network nodes may lead to a lot of traffic being blocked. In this paper, we study the survivability in multi-domain WDM optical networks, and propose a new survivable mechanism called load balanced domain-by-domain routing (LBDDR). In LBDDR, in order to obtain the efficient inter-domain survivable routes, we present the domain-by-domain routing (DDR) method which can find the intra-domain sub-working path and sub-backup path in each single-domain to form the inter-domain working path and backup path for each demand. In order to reduce the blocking probability, we present the load balanced routing method which can encourage the traffic to be uniformly distributed on the links with more free wavelengths. Simulation results show that, compared with conventional mechanism, LBDDR can obtain better performances.     

Hierarchical routing and traffic grooming in IP/MPLS-based ASON/GMPLS multi-domain networks

Routing, connection setup, and path computation are well-known problems in multi-domain networks, which have been largely analyzed in pure IP (packet) networks. In circuit-switched optical multi-domain networks, there remain, however, a number of routing and path computation challenges. Traffic grooming means combining a number of low-speed traffic streams so that the high capacity of each lightpath may be used as efficiently as possible, as path computation implements the core of the grooming function, it is obvious that solutions for the traffic grooming problem in optical multi-domain networks are still not sufficiently investigated. In this study we propose a methodology to address the problems of routing, connection setup, and traffic grooming in optical multi-domain networks, which adapts a two-level hierarchical routing scheme and full-mesh topology abstraction algorithm to improve routing scalability and lower inter-domain blocking probabilities; additionally our proposed methodology adapts a scheme for traffic grooming in DWDM multi-domain networks to improve the resources usage. To test our proposed methodology we propose a detailed IP/MPLS-based ASON/GMPLS multi-domain multilayer test framework.     

Hybrid protection algorithms based on game theory in multi-domain optical networks

With the network size increasing, the optical backbone is divided into multiple domains and each domain has its own network operator and management policy. At the same time, the failures in optical network may lead to a huge data loss since each wavelength carries a lot of traffic. Therefore, the survivability in multi-domain optical network is very important. However, existing survivable algorithms can achieve only the unilateral optimization for profit of either users or network operators. Then, they cannot well find the double-win optimal solution with considering economic factors for both users and network operators. Thus, in this paper we develop the multi-domain network model with involving multiple Quality of Service (QoS) parameters. After presenting the link evaluation approach based on fuzzy mathematics, we propose the game model to find the optimal solution to maximize the user’s utility, the network operator’s utility, and the joint utility of user and network operator. Since the problem of finding double-win optimal solution is NP-complete, we propose two new hybrid protection algorithms, Intra-domain Sub-path Protection (ISP) algorithm and Inter-domain End-to-end Protection (IEP) algorithm. In ISP and IEP, the hybrid protection means that the intelligent algorithm based on Bacterial Colony Optimization (BCO) and the heuristic algorithm are used to solve the survivability in intra-domain routing and inter-domain routing, respectively. Simulation results show that ISP and IEP have the similar comprehensive utility. In addition, ISP has better resource utilization efficiency, lower blocking probability, and higher network operator’s utility, while IEP has better user’s utility.     

Evaluation of post-fault restoration strategies in multi-domain networks

Although multi-domain survivability is a major concern for operators, few studies have considered the design of post-fault restoration schemes. This paper proposes two such strategies, based upon hierarchical routing and signaling crankback, to handle single and multi-link failure events in multi-domain IP/MPLS networks (also extendible to optical DWDM networks). Specifically, the hierarchical routing strategy relies upon abstracted domain information to compute inter-domain loose routes, whereas the crankback scheme applies signaling re-tries to restore paths in a domain-by-domain manner. The performance of these proposed solutions is then analyzed and compared via simulation.     

Survivability and scalability of space networks: a survey

Survivability and scalability are key terms for any network. The challenge is greater in space networks than in terrestrial networks. Satellites have various uses, some notable uses are communication, observation, meteorology, navigation etc. In future satellites will aid terrestrial users by providing Internet connectivity. With proliferation of Internet users, demand for satellite services will increase and soon we will suffer from bandwidth limitation. Hence, the scalability and survivability of space networks are very important issues to ensure smooth connectivity to all the users both mobile and immobile. Since, most of the existing works on network survivability and scalability are focused on terrestrial networks. We have categorized the existing works on survivability and scalability of terrestrial networks. In addition, we have performed a comprehensive survey on the popular products available in the market for network survivability and scalability. Finally, we have listed the major issues and challenges of space networks that needs to be considered before applying network scalability and survivability solutions on them. This work can help network engineers to select suitable solutions for space networks considering the available choices and challenges listed in this paper.     

A novel Topology Aggregation approach for shared protection in multi-domain networks

Routing for shared protection in multi-domain networks is more difficult than that in single-domain networks because of the scalability requirements. We propose a novel approach for shared protection routing in multi-domain networks where the key feature is a special Topology Aggregation. In this Topology Aggregation, only some potential intra-domain paths (intra-paths for short) are selected for carrying working and backup traffic between domain border nodes. The abstraction of each intra-path to a virtual edge makes the original multi-domain network to become an aggregated network. On the aggregated network, a single-domain routing algorithm for shared protection can be applied for obtaining the complete routing solutions. The experiments show that the proposed approach is scalable. Moreover it is close to the optimal solution in single-domain networks and outperforms the previously proposed scalable solutions in multi-domain networks.     

智能光网络的多域生存性技术研究

自动交换光网络是传送网的发展趋势,而快速高效的生存性是其重要特点.介绍了光网络生存性,重点分析了多域网络和域间路由问题,并且提出了具体的实现多域网络的生存性方法.     

Sub-Wavelength Solutions for Next-Generation Optical Networks [Topics in Optical Communications]

The recent trend in optical networks is switching packets directly in the optical domain. The aim is to benefit from both packet flexibility and optical transparency. In this article, we review current optical architectures that try to reconcile these two requirements. We discuss the challenges encountered in these new architectures and their respective niches. To meet the requirements of next-generation high-speed optical networks, we also propose a new solution based on the distribution of the aggregation process in the network. The feasibility of this scheme and the benefit that it provides over existing solutions are analyzed in this article.     

A novel multi-link fault-tolerant algorithm for survivability in multi-domain optical networks

With the large-scale deployment of optical network equipments, the problems of separated domains management and the multi-domain-based survivability have become the primary challenge in new generation intelligent optical networks. Aimed at resisting multi-link failures in multi-domain optical networks (MDON), a heuristic multi-link fault-tolerant (MLFT) algorithm for survivability in MDON is proposed in this article, which applied Hamiltonian cycle protection and segment-shared protection to establish a novel survivability strategy for either intra-domain??s or inter-domain??s multiple links, respectively. Furthermore, a new virtual-link mapping scheme and link-cost formulas are presented to encourage the appropriate routing selection and load balancing, which can also contributed to better resource utilization ratio and blocking ratio. Simulation results show that MLFT realizes the multi-link fault-tolerant survivability at a lower cost with better performances in redundancy ratio, blocking ratio, and computation complexity.     

Joint wireless and optical resources allocation for availability-guaranteed service in survivable fiber-wireless access network

The fiber-wireless (FIWi) access network not only leverages the technical merits of wireless and optical access networks, but also provides a potential opportunity for the design of survivable access networks. Previous works have studied the survivability of FiWi access network against network component failure by means of backup fiber deployment and wireless rerouting. However, most of these works put less attention on the connection availability and ignore the joint allocation of wireless and optical resources, which plays an important role in improving the global network performance gain. In this paper, we consider a notable failure scenario in FiWi access network but less mentioned in previous works, i.e., single shared-risk link group failure. We first propose a model for FiWi network to estimate the connection availability of service demand. Then, a novel resource allocation approach is proposed to provide the availability-guaranteed service. Under the requirements of bandwidth and connection availability, we deal with the optimal allocation of joint wireless and optical resources with the objective of minimum resource consumption. Numerical results demonstrate that the proposed scheme can reduce the resource consumption significantly compared to the resource allocation without considering connection availability.     

A Novel Fast Multicast Algorithm with Enhanced Survivability in WDM Optical Networks

WDM optical networking technology is expected to facilitate bandwidth-intensive multicast application by establishing a light-tree which regards the source node as the root and all the destination nodes as the leaves. However, the existing multicast routing algorithms are time-consuming and the generated light-trees are very sensitive to failures, e.g., a single fiber cut can disrupt the information from transmitting to several terminals. In this paper, we propose a novel fast multicast algorithm with enhanced survivability (FMES), which applies a two-stage multicast routing approach, and employs a path protection scheme for each segment of the first stage tree. Analysis and experimental results show that FMES has the significant advantage of a much shorter running time than that in existing schemes, and this advantage can be enlarged in the distributed routing and signaling system of the coming intelligent optical networks. We also compare FMES with non-protection and full-protection schemes. It shows that the FMES scheme achieves the best trade-off between network survivability and resource-utilization. We illustrate our study with numerical experiments based on the real-life ChinaNet topology.     

Survivable deployment of cloud-integrated fiber-wireless networks against multi-fiber failure

Cloud-integrated fiber-wireless (FiWi) networks inheriting advantages of optical and wireless access networks have a broad prospect in the future. As various component failures may occur in cloud-integrated FiWi networks, survivability is becoming one of the key important issues. It is necessary to provide survivability strategies for cloud-integrated FiWi networks. Hence, this paper mainly focuses on the survivability of cloud-integrated FiWi networks against multiple fibers failure. Firstly, in this paper, a novel integer linear programming (ILP) solution is proposed to tolerate the failure of multiple distribution fibers with capacity and coverage constraints in the context of urban area. Then, considering the complexity of ILP models, an efficient heuristic scheme is proposed, in order to get the approximate solutions of ILP. Simulation results and analysis give the configurations of optical network units (ONUs) and wireless routers with different constraints and show the network coverage of clients for different number of ONUs and wireless routers with ILP solution and heuristic approach, respectively.     

光网络中基于路径计算单元的路由机制研究

针对大规模多层多域光网络群故障发生时的网络受损情况,提出基于路径计算单元(PCE)架构的跨域路由算法进行快速恢复,并基于OMNet平台对多层多域路由方案进行了性能仿真分析。结果表明,基于PCE架构的路由策略在群故障发生时能够大大减少网络中的路径计算请求泛洪信息,降低路由计算收敛时间,可以提高全网剩余资源的资源利用率,为业务的快速恢复提供了路由基础。     

Survivable traffic grooming with path protection at the connection level in WDM mesh networks

Survivable traffic grooming (STG) is a promising approach to provide reliable and resource-efficient multigranularity connection services in wavelength-division-multiplexing (WDM) optical networks. In this paper, we study the STG problem in WDM mesh optical networks employing path protection at the connection level. Both dedicated-protection and shared-protection schemes are considered. Given network resources, the objective of the STG problem is to maximize network throughput. To enable survivability under various kinds of single failures, such as fiber cut and duct cut, we consider the general shared-risk-link-group (SRLG) diverse routing constraints. We first resort to the integer-linear-programming (ILP) approach to obtain optimal solutions. To address its high computational complexity, we then propose three efficient heuristics, namely separated survivable grooming algorithm (SSGA), integrated survivable grooming algorithm (ISGA), and tabu-search survivable grooming algorithm (TSGA). While SSGA and ISGA correspond to an overlay network model and a peer network model, respectively, TSGA further improves the grooming results from SSGA and ISGA by incorporating the effective tabu-search (TS) method. Numerical results show that the heuristics achieve comparable solutions to the ILP approach, which uses significantly longer running times than the heuristics.     

A Novel Survivable Routing Algorithm With Partial Shared-Risk Link Groups (SRLG)-Disjoint Protection Based on Differentiated Reliability Constraints in WDM Optical Mesh Networks

Previous research on survivability with differentiated reliability in wavelength-division-multiplexing (WDM) optical mesh networks mostly considered the failure probability of a fiber link with the link length that may not be a good solution for consideration of shared-risk link groups (SRLGs). In this paper, we propose a new model of failure probability with the SRLG constraints in WDM optical mesh networks. Based on this model, we present the backup resources assignment and the routing selection method with the differentiated reliable requirements of users. To evaluate the performances of this model, we propose a novel survivable routing algorithm called partial SRLG-disjoint protection (PSDP) to tolerate the single-SRLG failure. Compared with the previous algorithm, PSDP can obtain a better resource utilization ratio and lower blocking probability. Simulation results are shown to be promising.     

地理分布的光网络脆弱性评估研究

从光网络地理分布模型出发,采用通用模型下的最坏圆形切割算法,对网络拓扑结构进行了建模和仿真,计算出了网络的最坏圆形切割集,进而算出了网络的节点风险概率,并根据节点风险概率对网络的脆弱性做出了评估,这些工作对提高光网络的抗毁能力具有一定的参考意义。     

Application-aware protection in DWDM optical networks

Fast recovery time and reduced resource utilization are the two main criteria for determining the quality of survivability mechanism. Now, it is well known that link-based protection and path-based protection provide, respectively, a short recovery time and reduced use of resources. To benefit from the both of these saliencies, we propose in this paper to use these mechanisms simultaneously. Indeed, demands mandating shorter recovery time will be protected using link-based protection. Meanwhile, other demands (e.g., no-critical) will be protected using path-based protection. Simulation results show that the proposed solution achieves a good trade-off between resource utilization and recovery time.     

A survivable multicast routing mechanism in WDM optical networks

In Next Generation Networks (NGN), survivability and availability are becoming more and more key features. Reliability gains more importance in high- capacity networks where IP and optical technologies have converged toward a common control plane, such as GMPLS. In most previous research works, survivability aspects were mainly limited to a single fiber failure and a few considered the differentiated reliability concepts when routing new connection requests. In this article, a novel survivable multicast routing mechanism under SRLG constraints is proposed. We first formulate the problem as an Integer Linear Programming (ILP) model that is shown NP-Complete. We then propose a heuristic algorithm that alleviates the problem’s complexity by decomposing it into two sub-problems resolved separately. Compared with another algorithm proposed in the literature, our algorithm allows for higher acceptance rates even for stringent reliability requirements.