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Grooming-enhanced multicast in multilayer networks

In this paper we investigate and evaluate the performance of multicast routing in grooming capable multi-layer optical wavelength division multiplexing (WDM) networks. New wavelength-graph models are proposed for network equipments capable of optical-layer branching of light-paths. We evaluate the cost-effectiveness of electronic and optical-layer multicast and unicast as well. The high scalability of optical multicast against unicast is also showed. All routing and technical constraints are formulated in ILP and realized in our versatile simulator.

Realization strategies of dedicated path protection: A bandwidth cost perspective

Communication networks have to provide a high level of availability and instantaneous recovery after failures in order to ensure sufficient survivability for mission-critical services. Currently, dedicated path protection (or 1+1) is implemented in backbone networks to provide the necessary resilience and instantaneous recovery against single link failures with remarkable simplicity. However, in order to satisfy strict availability requirements, connections also have to be resilient against Shared Risk Link Group (SRLG) failures. In addition, switching matrix reconfigurations have to be avoided after a failure in order to guarantee instantaneous recovery. For this purpose, there are several possible realization strategies improving the characteristics of traditional 1+1 path protection by lowering reserved bandwidth while conserving all its favorable properties. These methods either utilize diversity coding, network coding, or generalize the disjoint-path constraint of 1+1. In this paper, we consider the cost aspect of the traditional and the alternative 1+1 realization strategies. We evaluate the bandwidth cost of different schemes both analytically and empirically in realistic network topologies. As the more complex realizations lead to NP-complete problems even in the single link failure case, we propose both Integer Linear Programming (ILP) based optimal methods, as well as heuristic and meta-heuristic approaches to solve them. Our findings provide a tool and guidelines for service providers for selecting the path protection method with the lowest bandwidth cost for their network corresponding to a given level of reliability.

Regular reconfiguration of light-trees in multilayer optical networks

In this paper we study dynamically changing multicast trees (light-trees) in double-layer optical networks. In this scenario, the continuous changing of multicast endpoints causes the degradation of the tree. Therefore a huge amount of network resources can be spared by regular reconfiguration. The benefit of reconfiguration is investigated for different routing algorithms and reconfiguration periods.

A meta-heuristic approach for non-bifurcated dedicated protection in WDM optical networks

Survivable routing serves as an important issue in core optical mesh networks. Operators are mainly interested in the protection of single link failures and a set of multiple link failures with high failure probability. In order to consider failure dependencies among links, Shared Risk Link Groups (SRLG) are defined in the network. Against a given set of SRLG failures the connection needs to be resilient to fulfill the required quality of service (QoS) level. Currently, 1+1 dedicated path protection is reported to be the most widely deployed network resilience mechanism because it offers instantaneous recovery from network failures. However, 1+1 protection in most cases unable to provide SRLG-disjoint paths, thus, it is not resilient against all SRLG failures under consideration. In this paper, a novel Bacterial Evolutionary Algorithm for the Integer (or non-bifurcated) Generalized Dedicated Protection (IGDP) is introduced to protect each SRLG in the operators list. The proposed evolutionary algorithm aims to minimize the amount of reserved spare bandwidth. As a result, the solution is resilient against all failures in the SRLG list while the simplicity of 1+1 protection in signaling and switching is maintained. Extensive simulation is conducted to compare our evolutionary approach with previously reported optimal and heuristic solutions for the IGDP problem, by which its merits are further demonstrated.

Physical impairment aware multicast routing heuristics

Need for efficient and reliable network transport technologies has led to the introduction of all optical networks and routing technologies. With the spreading of new, bandwidth consuming services, like 3D-TV, where multicast can be used and with the introduction of new technologies where the operators have the ability to fine tune nearly all the properties of the optical signals it gets more and more important to present a reliable, fast, easy to use heuristic for the problem of Physical Impairment Constrained Routing (PICR). Various papers have been written to solve this problem; however, none of them has proposed a joint solution for routing, wavelength assignment and physical constraints awareness together if there is only limited or no regeneration or splitting capability. Our goal in this paper is to fill in this gap by extending the Accumulative Shortest Path (ASP) and the Minimum Path Heuristic (MPH). We show, by simulations, the beneficial properties of our PICR aware low-level multicast heuristics against application level multicasting and routing methods that do not consider physical impairment at all.

Shared protection of demands with Physical Impairment Constrained Routing

The difference between dedicated and shared protection is well known. In this paper we investigate these ideas applied to sharing power budgets of links. When defining protection paths not as a “hot stand-by” but rather as a “cold stand-by” the power needed for protection will be lower; therefore the routeable distance of certain connections should be longer, that increases the number of routeable demands. In this paper we present simulation results to show that in reality with the introduction of shared protection for Physical Impairment Constrained Routing (PICR) in large or saturated networks the number of routeable demands is lowered.

Network Resilience Requirements and Algorithms for Multicasting and Broadcasting Digital TV

In this paper we give an overview of the network architecture and of the resilience requirements for both, metro and core networks.

Restoration of multi-cast trees in optical-beared grooming-capable two-layer networks

We consider dynamically changing multicast trees (light-trees) in two-layer optical-beared grooming-capable networks. The continuous changing of the tree ldquoleavesrdquo causes the degradation of the tree in time. Therefore, a huge amount of network resources can be spared by reconfigurations performed periodically or upon failures and reparations. In this paper we focus onto restoration of trees if a link (or any other network element) fails. The failures are more critical if they affect the tree closer to its root, while less critical if closer to a leave. We propose and evaluate four simple restoration strategies and investigate their performance for different multicast routing algorithms.

Preplanned restoration of multicast demands in optical networks

The evolution of multicast applications has speeded up. providers have to offer cheap and reliable services for their customers. One way to achieve this is to use a restoration method that provides relatively fast restoration calculated upon a failure, where nearly the minimal amount of resources is allocated. In this paper we propose a new, faster way of restoring multicast demands after link failure that is based on preplaning. We prove its optimality if a few preconditions hold. To do so a new formalization of the wavelength graph transformation (WGT) is presented. We show, based on simulations, that the beneficial properties of our method hold even when one or more preconditions are not kept.

Generalized shared protection (GSP): Simulation results and proof of optimality

Among various protection and restoration schemes it is hard to decide which is the best to be used in a certain situation. First, we propose a method to find the best possible shared protection scheme among all possible shared protection schemes. We provide optimisation and simulation results. Second, we prove the optimality of the proposed method in terms of minimal resource usage for any single demand to be routed with any shared protection: shared link, shared segment, and shared end-to-end path protection.