Diverse routing for shared risk resource groups (SRRG) failures in WDM optical networks

Failure resilience is one of the desired features of the Internet. Most of the traditional restoration architectures are based on single-failure assumption which is unrealistic. Multiple link failure models, in the form of shared-risk link groups (SRLG\u27s) and shared risk node groups (SRNG\u27s) are becoming critical in survivable optical network design. We classify both these form of failures under a common heading of shared-risk resource groups (SRRG) failures. In our research, we propose graph transformation techniques for tolerating multiple failures arising out of shared resource group (SRRG) failures. Diverse routing in such multi-failure scenario essentially necessitates finding out two paths between a source and a destination that are SRRG disjoint. The generalized diverse routing problem has been proved to be NP-complete. The proposed transformation techniques however provide a polynomial time solution for certain restrictive failure sets. We study how restorability can be achieved for dependent or shared risk link failures and multiple node failures and prove the validity of our approach for different network scenarios

Reliability of Connections in Multilayer Networks under Shared Risk Groups and Costs Constraints

International audienceThe notion of Shared Risk Resource Groups (SRRG) has been introduced to capture survivability issues when a set of resources may fail simultaneously. Applied to Wavelength Division Multiplexing Network (WDM), it expresses that some links and nodes may fail simultaneously. The reliability of a connection therefore depends on the number of SRRGs through which it is routed. Consequently, this number has to be minimized. This problem has been proved NP-complete and hard to approximate in general, even when routing a single request. Some heuristics using shortest paths have already been designed, however the cost (the usual routing cost, not in term of SRRG) was not part of the objective. In this paper we study the problem of minimizing a linear combination of the average number of SRRG per paths and the cost of the routing. The main result of our work is a column generation formulation that allows to solve efficiently the problem of maximizing the reliability of a set of connection requests in MPLS/WDM mesh networks with SRRGs while keeping the cost of the routing low

Two heuristics for calculating a shared risk link group disjoint set of paths of min-sum cost

A shared risk link group (SRLG) is a set of links which share a common risk of failure. Routing protocols in Generalized MultiProtocol Label Switching, using distributed SRLG information, can calculate paths avoiding certain SRLGs. For single SRLG failure an end-to-end SRLG-disjoint path pair can be calculated, but to ensure connection in the event of multiple SRLG failures a set with more than two end-to-end SRLG-disjoint paths should be used. Two heuristic, the Conflicting SRLG-Exclusion Min Sum (CoSE-MS) and the Iterative Modified Suurballes’s Heuristic (IMSH), for calculating node and SRLG-disjoint path pairs, which use the Modified Suurballes’s Heuristic, are reviewed and new versions (CoSE-MScd and IMSHd) are proposed, which may improve the number of obtained optimal solutions. Moreover two new heuristics are proposed: kCoSE-MScd and kIMSHd, to calculate a set of k node and SRLG-disjoint paths, seeking to minimize its total cost. To the best of our knowledge these heuristics are a first proposal for seeking a set of k ðk[2Þ node and SRLG-disjoint paths of minimal additive cost. The performance of the proposed heuristics is evaluated using a real network structure, where SRLGs were randomly defined. The number of solutions found, the percentage of optimal solutions and the relative error of the sub-optimal solutions are presented. Also the CPU time for solving the problem in a path computation element is reported

Diverse Routing with Star SRLGs

International audienceLa notion de groupe de liens partageant un risque (Shared Risk Link Group, SRLG) a été introduite pour modéliser des problèmes de tolérance aux pannes simultanées d'ensembles de liens d'un réseau. Dans ce contexte, le problème du routage diversifié est de trouver un ensemble de chemins SRLG-disjoints entre une paire donnée de noeuds du réseau. Ce problème a été prouvé NP-complet en général et certains cas polynomiaux ont été caractérisés. Nous avons étudié le problème du routage diversifié dans les réseaux satisfaisant la propriété d'étoile. Dans un réseau satisfaisant la propriété d'étoile, un lien peut être affecté par plusieurs SRLGs, mais tous les liens affectés par un même SRLG sont incidents à un même sommet. Nous avons trouvé des contre-exemples à un algorithme polynomial publié pour le calcul de paires de chemins SRLG-disjoints dans les réseaux satisfaisants la propriété d'étoile. Puis, nous avons prouvé que ce problème est en fait NP-difficile. Plus généralement, nous avons montré que le problème du routage diversifié dans les réseaux avec la propriété d'étoile est NP-difficile, APX-difficile, et W[1]-difficile lorsque le paramètre est le nombre de chemins SRLG-disjoints. Enfin, nous avons caractérisé de nouvelles instances polynomiales, en particulier lorsque le degré maximum des sommets est 4, ou lorsque le réseau est acyclique

Shared Risk Resource Group: Complexity and Approximability issues

International audienceThis article investigates complexity and approximability properties of combinatorial optimization problems yielded by the notion of Shared Risk Resource Group (SRRG). SRRG has been introduced in order to capture network survivability issues where a failure may break a whole set of resources, and has been formalized as colored graphs, where a set of resources is represented by a set of edges with same color. We consider here the analogous of classical problems such as determining paths or cuts with the minimum numbers of colors or color disjoint paths. These optimization problems are much more difficult than their counterparts in classical graph theory. In particular standard relationship such as the Max Flow - Min Cut equality do not hold any longer. In this article we identify cases where these problems are polynomial, for example when the edges of a given color form a connected subgraph, and otherwise give hardness and non approximability results for these problems

Combinatorial optimization in networks with Shared Risk Link Groups

International audienceThe notion of Shared Risk Link Groups (SRLG) captures survivability issues when a set of links of a network may fail simultaneously. The theory of survivable network design relies on basic combinatorial objects that are rather easy to compute in the classical graph models: shortest paths, minimum cuts, or pairs of disjoint paths. In the SRLG context, the optimization criterion for these objects is no longer the number of edges they use, but the number of SRLGs involved. Unfortunately, computing these combinatorial objects is NP-hard and hard to approximate with this objective in general. Nevertheless some objects can be computed in polynomial time when the SRLGs satisfy certain structural properties of locality which correspond to practical ones, namely the star property (all links affected by a given SRLG are incident to a unique node) and the span 1 property (the links affected by a given SRLG form a connected component of the network). The star property is defined in a multi-colored model where a link can be affected by several SRLGs while the span property is defined only in a mono-colored model where a link can be affected by at most one SRLG. In this paper, we extend these notions to characterize new cases in which these optimization problems can be solved in polynomial time. We also investigate the computational impact of the transformation from the multi-colored model to the mono-colored one. Experimental results are presented to validate the proposed algorithms and principles

Designing multi-layer provider networks for circular disc failures

We examine the issue of disaster recovery after zonal outages in core networks, especially IP-over-WDM multi-layer networks. In particular, we consider the network design problem for a regional failure of circular area of radius R. Our goal is to design a network that can withstand a randomly located single failure of radius R. To this end, we formulate the problem as a constrained optimization problem whose solution for both IP-over-optical networks and pure ROADM-based networks is proposed. Subsequently, we develop an efficient heuristic based on a divide and conquer strategy that gives acceptable results. We also discuss the role of SDN in design and restoration of such networks. Simulation results are showcased over a core network topology thereby realizing the plausibility of such network design

Towards Scalable Cost-Effective Service and Survivability Provisioning in Ultra High Speed Networks

Optical transport networks based on wavelength division multiplexing (WDM) are considered to be the most appropriate choice for future Internet backbone. On the other hand, future DOE networks are expected to have the ability to dynamically provision on-demand survivable services to suit the needs of various high performance scientific applications and remote collaboration. Since a failure in aWDMnetwork such as a cable cut may result in a tremendous amount of data loss, efficient protection of data transport in WDM networks is therefore essential. As the backbone network is moving towards GMPLS/WDM optical networks, the unique requirement to support DOE’s science mission results in challenging issues that are not directly addressed by existing networking techniques and methodologies. The objectives of this project were to develop cost effective protection and restoration mechanisms based on dedicated path, shared path, preconfigured cycle (p-cycle), and so on, to deal with single failure, dual failure, and shared risk link group (SRLG) failure, under different traffic and resource requirement models; to devise efficient service provisioning algorithms that deal with application specific network resource requirements for both unicast and multicast; to study various aspects of traffic grooming in WDM ring and mesh networks to derive cost effective solutions while meeting application resource and QoS requirements; to design various diverse routing and multi-constrained routing algorithms, considering different traffic models and failure models, for protection and restoration, as well as for service provisioning; to propose and study new optical burst switched architectures and mechanisms for effectively supporting dynamic services; and to integrate research with graduate and undergraduate education. All objectives have been successfully met. This report summarizes the major accomplishments of this project. The impact of the project manifests in many aspects: First, the project addressed many essential problems that arisen in current and future WDM optical networks, and provided a host of innovative solutions though there was no invention or patent filing. This project resulted in more than 2 dozens publications in major journals and conferences (including papers in IEEE Transactions and journals, as well as a book chapter). Our publications have been cited by many peer researchers. In particular, one of our conference papers was nominated for the best paper award of IEEE/Create-Net Broadnets (International Conference on Broadband Communications, Networks, and Systems) 2006. Second, the results and solutions of this project were well received by DOE Labs where presentations were given by the PI. We hope to continue the collaboration with DOE Labs in the future. Third, the project was the first to propose and extensively study multicast traffic grooming, new traffic models such as sliding scheduled traffic model and scheduled traffic model. Our research has sparkled a flurry of recent studies and publications by the research community in these areas. Fourth, the project has benefited a diverse population of students by motivating, engaging, enhancing their learning and skills. The project has been conducted in a manner conducive to the training of students both at graduate and undergraduate levels. As a result, one Ph.D., Dr. Abdur Billah, was graduated. Another Ph.D. student, Tianjian Li, will graduate in January 2007. In addition, four MS students were graduated. One undergraduate student, Jeffrey Alan Shininger, completed his university honors project. Fifth, thanks to the support of this ECPI project, the PI has obtained additional funding from the National Science Foundation, the Air Force Research Lab, and other sources. A few other proposals are pending. Finally, this project has also significantly impacted the curricula and resulted in the enhancement of courses at the graduate and undergraduate levels, therefore strengthening the bond between research and education