Fault Monitoring and Localization in Transparent Optical Networks Open Access
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Emerging transparent all-optical networks (TONs) introduce the need for new monitoring and fault localization techniques at the optical layer due to inherent protocol transparency, unique fault-propagation, strict time constraints, and scalability requirements. This problem is especially important for enabling resilient TONs and is more challenging than in traditional networks that regenerate signals at every node. In a TON, a single fault may propagate to various parts of the network, generating a potentially large number of redundant alarms, complicating localization, delaying restoration, and causing churn from multiple protocol layers that may all report alarms or initiate recovery mechanisms. This dissertation introduces several novel and efficient approaches for monitoring and fault-localization in TONs and conducts a comprehensive empirical and analytical study of their performance. We first formulate the centralized optimal monitor activation problem, prove its NP-completeness, formulate its optimal integer linear program (ILP) solution, and introduce an efficient heuristic algorithm whose solution quality is compared to the optimal ILP solution. Next, we introduce a novel hierarchically-distributed monitoring approach and prove identical fault detection between centralized and hierarchically-distributed monitoring. The impact of network connectivity on localization complexity in randomly generated network topologies is also studied. Furthermore, we introduce an efficient algorithm for fault localization and present its simulation results for centralized and hierarchically-distributed monitoring. This is followed by a novel monitoring approach that efficiently exploits the provisioned user lightpaths for in-band monitoring and achieves complete fault localization coverage at the minimum resource cost through the use of optimally-selected, complementary supervisory lightpaths/lightcycles. We formulate the problem, present its optimal ILP solution, and introduce an efficient heuristic for provisioning a near-optimal set of complementary supervisory lightpaths/lightcycles. Finally, we propose an efficient approach for adaptive monitor optimization and localization. We formulate the optimal ILP solution and introduce efficient adaptive heuristics. The impact of the heuristic's re-optimization period using ILP is also studied. Extensive numerical analysis and comparisons with several recently published algorithms demonstrate the efficiency and the advantages of our proposed approaches. This work contributes novel, rapid, and scalable methods for TON monitoring and fault localization, leading to faster service recovery while minimizing required supervisory resources.
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