A Study of Path Protection in Large-Scale Optical Networks

We consider the problem of designing a network of optical cross-connects (OXCs) which provides end-to-end lightpath services to large numbers of client nodes, under the requirement that the network will survive any single-link failure. Our main objective is to quantify the additional resource requirements of implementing path protection schemes over a network with no survivability properties. To this end, we present heuristic routing and wavelength assignment algorithms for dedicated path protection and two variants of shared path protection, and integrate them into the physical and logical topology design framework we developed in an earlier study. We apply our heuristics to networks with up to 1000 client nodes, with a number of lightpaths that is an order of magnitude greater than the number of clients, and for a wide range of values for system parameters such as the number of wavelengths per fiber, the number of optical transceivers per client node, and the number of ports per OXC. Our results provide insight into the relative resource requirements of dedicated and shared path protection schemes. We also find that, using shared path protection schemes, it is possible to build cost-effective survivable networks that provide rich connectivity among client nodes with only a modest additional amount of resources over a network with no survivability properties.     

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。     

Inter group shared protection (I-GSP) for survivable WDM mesh networks

This paper focuses on the survivable routing problem in WDM mesh networks where the objective is to minimize the total number of wavelengths used for establishing working and protection paths in the WDM networks. The past studies for survivable routing suffers from the scalability problem when the number of nodes/links or connection requests grows in the network. In this paper, a novel path-based shared protection framework, namely inter group shared protection (I-GSP), is proposed where the traffic matrix can be divided into multiple protection groups (PGs) based on specific grouping policy. Optimization is performed on these PGs such that sharing of protection wavelengths is considered not only inside a PG, but between the PGs. Simulation results show that I-GSP based integer linear programming model, namely, ILP-II solves the networks in a reasonable amount of time for which a regular integer linear programming formulation, namely, ILP-I becomes computationally intractable. For most of the cases the gap between the optimal solution and the ILP-II stays within 6%. The proposed ILP-II model yields a scalable solution for the capacity planning in the survivable optical networks based on the proposed I-GSP protection architecture.     

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.     

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.     

光网络中基于SRLG约束的动态RWA算法

在IPoverWDM光网络中,需要为每条工作光路提供光通路保护,即提供一条保护光路。光网络中引入了共享风险链路组(SRLG)的概念,要求工作光路与保护光路不共享风险链路组。不考虑波长分配提出一种新的启发式算法,该算法同时计算两条SRLG分离且总费用低;在此算法基础上利用分层图的思想,提出WDM网络中的一种在SRLG约束条件下的动态选路波长分配算法。     

A New Shared Segment Protection Method for Survivable Networks with Guaranteed Recovery Time

Shared segment protection (SSP), compared with shared path protection (SPP), and shared link protection (SLP), provides an optimal protection configuration due to the ability of maximizing spare capacity sharing, and reducing the restoration time in cases of a single link failure. This paper provides a thorough study on SSP under the GMPLS-based recovery framework, where an effective survivable routing algorithm for SSP is proposed. The tradeoff between the price (i.e., cost representing the amount of resources, and the blocking probability), and the restoration time is extensively studied by simulations on three networks with highly dynamic traffic. We demonstrate that the proposed survivable routing algorithm can be a powerful solution for meeting stringent delay upper bounds for achieving high restorability of transport services. This can significantly improve the network reliability, and enable more advanced, mission critical services in the networks. The comparison among the three protection types further verifies that the proposed scheme can yield significant advantages over shared path protection, and shared link protection.     

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.     

Partial SRLG-disjoint shared path protection with differentiated reliability in survivable WDM network

This paper addresses the problem of shared path protection algorithm in survivable wavelength-division-multiplexing (WDM) optical networks, taking into consideration of differentiated reliability (DiR) under Shared-Risk-Link-Group (SRLG) constraint. A subset of network links that share the risk of failure at the same time are said to be in a common SRLG. Rather than the conventional complete SRLG-disjoint shared path protection, we introduce a heuristic Partial SRLG-disjoint Shared Path Protection algorithm (Pd-SPP) based on the concept of SRLG conditional failure probability, to provide differentiated reliability protection. The main target of our work is to improve the network resource utilization ratio under the DiR constraint. We adopt the ideas of partial SRLG-disjoint and the K-shortest paths algorithm such we can efficiently solve the “trap” problem. The experimental results show that our algorithm outperforms the complete SRLG-disjoint shared path protection in both blocking probability ratio and network resource utilization, i.e. the results are found to be promising.     

Segment shared protection in WDM networks with partial wavelength conversion

In this paper, we propose a novel approach of survivable routing for segment shared protection (SSP) in mesh wavelength division multiplexing networks with partial wavelength conversion capability, with which spare capacity is allocated dynamically for a given working lightpath. The survivable routing process is formulated into a shortest path searching problem on the transferred graph of cycles (TGC) and wavelength graph of paths (WGP).     

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.     

A novel survivable routing algorithm for shared segment protection in mesh WDM networks with partial wavelength conversion

In this paper, a survivable routing algorithm is proposed for shared segment protection (SSP), called optimal self-healing loop allocation (OSHLA), which dynamically allocates spare capacity for a given working lightpath in mesh wavelength-division-multiplexing (WDM) networks with partial wavelength conversion capability. Two novel graph transformation approaches, namely graph of cycles and wavelength graph of paths, are introduced to solve this problem, in which the task of survivable routing is formulated as a series of shortest path searching processes. In addition to an analysis on the computation complexity, a suite of experiments is conducted to verify OSHLA on four networks with different topologies and traffic loads. We find that the blocking probability and computation complexity are dominated by the upper bound on the length of the working and protection segments. Comparison is made between OSHLA and four other reported schemes in terms of blocking probability. The results show that OSHLA can achieve the lowest blocking probability under the network environment of interest. We conclude that OSHLA provides a generalized framework of survivable routing for an efficient implementation of SSP in mesh WDM partial wavelength convertible networks. With OSHLA, a compromise is initiated by manipulating the upper bound on the length of working and protection segments such that the best performance-computation complexity gain can be achieved.     

Resource efficient network design and traffic grooming strategy with guaranteed survivability

In WDM networks, path protection has emerged as a widely accepted technique for providing guaranteed survivability of network traffic. However, it requires allocating resources for backup lightpaths, which remain idle under normal fault-free conditions. In this paper, we introduce a new design strategy for survivable network design, which guarantees survivability of all ongoing connections that requires significantly fewer network resources than protection based techniques. In survivable routing, the goal is to find a Route and Wavelength Assignment (RWA) such that the logical topology remains connected for all single link failures. However, even if the logical topology remains connected after any single link fault, it may not have sufficient capacity to support all the requests for data communication, for all single fault scenarios. To address this deficiency, we have proposed two independent but related problem formulations. To handle our first formulation, we have presented an Integer Linear Program (ILP) that augments the concept of survivable routing by allowing rerouting of sub-wavelength traffic carried on each lightpath and finding an RWA that maximizes the amount of traffic that can be supported by the network in the presence of any single link failure. To handle our second formulation, we have proposed a new design approach that integrates the topology design and the RWA in such a way that the resulting logical topology is able to handle the entire set of traffic requests after any single link failure. For the second problem, we have first presented an ILP formulation for optimally designing a survivable logical topology, and then proposed a heuristic for larger networks. Experimental results demonstrate that this new approach is able to provide guaranteed bandwidth, and is much more efficient in terms of resource utilization, compared to both dedicated and shared path protection schemes.     

A novel dynamic survivable routing in WDM optical networks with/without sparse wavelength conversion

In this paper, we study the dynamic survivable routing problem, both in optical networks without wavelength conversion and in optical networks with sparse wavelength conversion, and propose a novel hybrid algorithm for it based on the combination of mobile agents technique and genetic algorithms (GA). By keeping a suitable number of mobile agents in the network to cooperatively explore the network states and continuously report cycles (that are formed by two disjoint-link routes) into the routing tables, our new hybrid algorithm can promptly determine the first population of cycles for a new request based on the routing table of its source node, without the time consuming process associated with current GA-based lightpath protection schemes. We further improve the performance of our algorithm by introducing a more advanced fitness function that is suitable for both the above networks. Extensive simulation studies on the ns-2 network simulator show that our hybrid algorithm achieves a significantly lower blocking probability than the conventional survivable routing algorithms for all the cases we studied.     

Dynamic light trail routing in WDM optical networks

Fiber optics have replaced copper as the primary transmission medium. Wavelength Division Multiplexing (WDM) networks effectively increase single-link bandwidth from 10 Mbps to over 160 Gbps, and have been considered as a promising candidate for the next-generation backbone network. All optical circuits each on a separate wavelength called lightpaths represent the first major method for optical communication. The granularity provided between a source and destination node is that of a complete wavelength. Once a lightpath is set up, the entire wavelength is used exclusively by the connection’s source and destination node-pair. No sub-wavelength sharing between nodes along the lightpath is allowed. However, it is often observed that the bandwidth requirement in today’s network is often dynamically varying and does not justify the need for allocating an entire wavelength. Therefore, the wavelength capacity may be underutilized. A new technology termed light trail was proposed to avoid the inability of intermediate nodes to use a connection wavelength, and the constant reconfiguration of switches. In this article, we study dynamic light trail routing in a WDM optical network. We present an efficient algorithm for establishing a light trail routing for a new connection request, while using minimum network resources. We also study survivable network routing using the proposed light trail technology. We present an efficient heuristic for computing a pair of working and protection light trails for a dynamic incoming connection request. Simulation results are presented which demonstrate the advantages of our routing schemes.     

IP/MPLSoverWDM网中基于共享风险链路组限制的共享通路保护算法

本文研究了IP/MPLS over WDM网中,如何建立两条共享风险链路组(SRLG)分离的标记交换路径(LSP)问题,提出一种新的基于SRLG分离的共享通路保护算法.该算法既可以保证用户业务的可靠性要求,同时又能够有效提高全网的资源利用率,从而大大降低全网LSP建立请求的阻塞率.本文还对所提算法进行了仿真研究,并给出了仿真结果.     

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.     

Shared partial path protection in WDM networks with shared risk link groups

For 100% shared risk link group (SRLG) failure protection, conventional full path protection has to satisfy SRLG-disjoint constraints, i.e., its working path and backup path cannot go though the same SRLG. With the increase of size and number of SRLGs, capacity efficiency of conventional shared full path protection becomes poorer due to SRLG-disjoint constraints and the blocking probability becomes much higher due to severe traps. To solve these problems, we present a partial path protection scheme where SRLG-disjoint backup paths may only cover part of the working path. Full path protection becomes a special case of partial path protection, in which the backup path covers the full working path. By choosing the most survivable partial backup path as backup path, we can make the impact of SRLG failures as low as possible and accept as many as possible connection requests. Assuming every SRLG has the same probability to fail, we present a heuristic algorithm to find the most survivable partial backup path by choosing full path protection first, iteratively computing partial backup paths and choosing the most survivable one. The benefit of this heuristic algorithm is that it can find the optimal results within less iteration. Analytical and simulation results show that, compared to conventional full path protection, our proposed scheme can significantly reduce blocking probability with little sacrifice on survivability. The proposed scheme is very useful particularly when the network contains a lot of SRLGs and the blocking probability of conventional full path protection becomes too high.

Heuristics for Diverse Routing in Wavelength-Routed Networks with Shared Risk Link Groups

In this paper, we consider path protection in wavelength-routed networks with shared risk link groups (SRLGs). Specifically, we study diverse routing, where two paths without sharing any SRLG have to be found between each pair of source–destination nodes, and its applications in dynamic shared protection as well. For the NP-complete diverse routing problem, a heuristic method is proposed, which steadily outperforms an existing algorithm within the first few iterations. When more iterations of calculations are allowed, we demonstrate that the two different algorithms perform nearly the same. This interesting observation helps to achieve some insight into how to further improve the performance of the heuristics in the future.     

Selective survivability with disjoint nodes and disjoint lightpaths for layer 1 VPN

This paper deals with the problem of survivable routing and wavelength assignment in layer 1 virtual private networks (VPNs). The main idea is routing the selected lightpaths by the layer 1 VPN customer, in a link-disjoint manner. The customer may freely identify some sites or some connections, and have their related lightpaths routed through link-disjoint paths through the provider’s network. This selective survivability idea creates a new perspective for survivable routing, by giving the customer the flexibility of selecting important elements (nodes or connections) in its network. This study is different from previous studies which aim to solve the survivable routing problem for the whole VPN topology. The proposed scheme is two-fold: disjoint node based, and disjoint lightpath based. In disjoint node scheme, all lightpaths incident to a node are routed mutually through link-disjoint paths. In disjoint lightpath scheme, a lightpath is routed in a link-disjoint manner from all other ligthpaths of the VPN. We present a simple heuristic algorithm for selective survivability routing. We study the performance of this algorithm in terms of resources allocated by the selective survivability routing scheme compared to shortest path routing with no survivability. The numerical examples show that the amount of used resources by the selective survivability scheme is only slightly more than the amount used in shortest path routing, and this increase is linear. The extra resources used by the new scheme are justified by better survivability of the VPN topology in case of physical link failures, and the simplicity of the implementation.