Shared Risk Link Group Constraints Research Articles

QoT-aware elastic bandwidth allocation and spare capacity assignment in flexible island-based optical transport networks under shared risk link group constraints

This paper focuses on the problem of provisioning multi-granularity static lightpath connections with fault-tolerant requirements in survivable island-based translucent optical networks with traffic grooming capabilities. The problem is tackled for the first time, to the best of our knowledge, taking into account both Quality of Transmission (QoT) and Shared Risk Link Group (SRLG) constraints. A two phase heuristic algorithm is proposed relying on a novel generic purpose-built auxiliary graph model that may support various factors of network heterogeneity (i.e., network nodes with different wavelength-conversion, regeneration and traffic grooming capabilities), and represent numerous network constraints related mainly to QoT requirements and network-resources. The purpose of the proposed heuristic is to optimize the utilisation of the available network resources and hence the network throughput through the simultaneous use of traffic grooming and two resource sharing techniques namely the Generalized Backup-Backup multiplexing (GBBM) and the Generalized Adaptive Primary-Backup Multiplexing (GAPBM) which are combined for the first time, as far as we know, under a static traffic scenario, and performed in such a way that 100% QoT-aware SRLG-fault recoverability is still guaranteed for all serviced lightpath requests. The performances of the proposed solution are demonstrated through multiple simulation experiments conducted on different network topologies.

Application of <formula formulatype="inline"><tex Notation="TeX">${p}$</tex></formula>-Cycle Protection for the Substation Communication Network Under SRLG Constraints

In order to improve the security and stability of the intelligent substation communication networks, a novel shared risk link group (SRLG) weighted -cycle algorithm (SWCA) is proposed by considering the diversity of different substation links and the associated fiber core. The proposed approach is dedicated to solve the problems of multiple failures by sharing risk analysis. Hybrid integer linear programming and heuristic algorithm implementation are presented to reduce the complexity of optimizing bandwidth allocation under SRLG constraints. The performance of bandwidth utilization, service reject rate, and protection resource redundancy is investigated under the dynamic traffic environment, and the optimum SRLG number is discussed. The experimental results from two demonstration networks with randomly set SRLGs show that SWCA can reserve more bandwidths and, therefore, more service requests can be served at the expense of protection redundancy. Completely separated SRLG protection will decrease simultaneous failure probability of the working path and protection path and, thus, improve the survivability of the substation communication network compared with the classical capacitated iterative design algorithm-grow and shortest path pair protection method. Meanwhile, the approach can restore multiple failures within intelligent substation commu- nication networks, and can therefore enhance the survivability of the electric power communication network.

Backup Reprovisioning After Shared Risk Link Group (SRLG) Failures in WDM Mesh Networks

In this paper, we study the impact of shared risk link group (SRLG) failures on shared-path protection by examining the percentage of connections that are vulnerable after SRLG failures, investigate the benefits of backup reprovisioning after SRLG failures, and evaluate different policies for backup reprovisioning. Compared with single-link failures, SRLG failures leave many more connections unprotected and vulnerable to the next failures and make the network topology much sparser. The major challenge of backup reprovisioning after SRLG failures is how to find SRLG-disjoint backup paths for those unprotected connections with a recovery ratio that is as high as possible within reasonable computational complexity. We are motivated to consider three reprovisioning policies by considering different sequences of reprovisioning according to the degree of SRLG constraints. The first policy is to reprovision backup paths for connections whose working paths traverse more SRLGs first (Policy I), and the second policy is to reprovision backup paths for connections whose working paths traverse fewer SRLGs first (Policy II). The third policy is to do backup reprovisioning randomly, i.e., we pick up an unprotected working path randomly (random reprovisioning). Extensive simulation results show that 1) SRLG failures will leave more connections unprotected compared with single-link failures, and the percentage of connections left vulnerable tends to be proportional to the SRLG size; 2) the network performance based on the first reprovisioning policy always performs best in recovery ratio; and 3) the network performance based on Policy II even underperforms the random reprovisioning. These results can be explained by the fact that connections whose working paths traverse fewer SRLGs are more flexible in finding SRLG-disjoint backup paths, and thus priority given to connections whose working paths traverse more SRLGs in Policy I can significantly improve the recovery ratio.

Two-stage EDA-based approach for all optical WDM mesh network survivability under SRLG constraints

In this paper, a two-stage evolutionary algorithm is proposed to solve an N P -complete telecommunication problem—all optical wavelength-division multiplexing (WDM) mesh network survivability under shared-risk-link-group (SRLG) constraints. First of all, a novel greedy heuristic with two control parameters is developed to construct feasible solutions of the telecommunication problem. An estimation of distribution algorithm (EDA) with guided mutation is applied to search for optimum settings of the two control parameters in respective two stages. Given the found best control parameters, an optimal solution of the considered problem can be constructed by the greedy heuristic. Experimental results show that the proposed approach compares favorably against the best-known evolutionary-based algorithm in 26 out of 30 test instances in terms of solution quality within given time limit.

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.

Evolutionary Algorithms Refining a Heuristic: A Hybrid Method for Shared-Path Protections in WDM Networks Under SRLG Constraints

An evolutionary algorithm (EA) can be used to tune the control parameters of a construction heuristic to an optimization problem and generate a nearly optimal solution. This approach is in the spirit of indirect encoding EAs. Its performance relies on both the heuristic and the EA. This paper proposes a three-phase parameterized construction heuristic for the shared-path protection problem in wavelength division multiplexing networks with shared-risk link group constraints and applies an EA for optimizing the control parameters of the proposed heuristics. The experimental results show that the proposed approach is effective on all the tested network instances. It was also demonstrated that an EA with guided mutation performs better than a conventional genetic algorithm for tuning the control parameters, which indicates that a combination of global statistical information extracted from the previous search and location information of the best solutions found so far could improve the performance of an algorithm.

A new shared-path protection algorithm under shared risk link group constraints for survivable WDM mesh networks

In this paper, we investigate the protection design under shared risk link group constraints in survivable wavelength-division-multiplexing mesh networks, and present a new shared-path protection algorithm, called solution approach with backtracking (SAB). Differing from other shared-path protection algorithms, which are called two-step approach (TSA), SAB not only can solve the trap problem but also find K path pairs and select an optimal path pair as the result. We also study the relationship between the protection recovery time and the resource utilization, and suggest a new method to compute the least-cost path pairs. Under dynamic traffics with different load, the simulation results show that SAB not only perform better than the previous TSA but also determine the appropriate tradeoffs between the resource utilization ratio and the protection recovery time.

Joint routing-selection algorithm for a shared path with differentiated reliability in survivable wavelength-division-multiplexing mesh networks

A routing-selection algorithm is important in survivable wavelength-division networks. A sound algorithm should carefully consider the efficiency of resource utilization and the protection-switching time. Under shared-risk link group constraints with differentiated reliability (DiR), a novel algorithm for a shared path, called a joint routing-selection algorithm (JRSA) with DiR, is proposed. The simulation results show that a JRSA with DiR not only can efficiently satisfy the specific requirements of users but also can produce nearly optimal performance and determine the appropriatetrade-offs between the resource utilization ratio and the protection-switching time.

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.

Demonstration of the highly reliable Hikari router network based on a newly developed disjoint path selection scheme

Integration of multiprotocol label switching functions and multiprotocol lambda switching functions can enhance the throughput of IP networks and remove bottlenecks that are derived from electrical packet processing. To enhance the packet forwarding capability, NTT proposed a photonic MPLS concept that includes MP/spl lambda/S, and demonstrated IP, MPLS, and photonic MPLS integrated router systems called the photonic MPLS router. This router system is now called the Hikari router. The word Hikari is Japanese meaning beam, light, lightwave, optical, photonic, and sunshine. The amount of IP data traffic has grown remarkably. Massive IP routers and flexible route control mechanisms are now required to cope with the increased amount of traffic. The Hikari router can offer two solutions utilizing photonic switching technologies, and photonic network operation and management technologies. The first solution is utilizing photonic switching technologies realized using optical-switch-based crossconnect systems. The other solution is realized using the MPLS and MP/spl lambda/S signaling protocol and photonic network protection functions. In this article we report on the implementation of the Hikari router systems, propose a newly developed disjoint path selection scheme for generalized MPLS networks with shared risk link group constraints, and demonstrate the signaling protocol and network protection functions. The demonstration system achieves a distributed optical path set-up/tear-down protocol with an extended constraint-based routing label distribution protocol. Fast self-healing through automatic protection switching and a new restoration scheme are also implemented. These functions are successfully implemented, and the performance is verified on a demonstration network. The protection switching scheme achieves protection in less than 20 ms, and the optical path restoration scheme achieves restoration in less than 500 ms.