Wide-area optical networks face significant transmission challenges due to the relentless growth of bandwidth demands experienced nowadays. Network operators must consider the relationship between modulation format and maximum reach for each connection request due to the accumulation of physical layer impairments in optical fiber links, to guarantee a minimum quality of service (QoS) and quality of transmission (QoT) to all connection requests. In this work, we present a BER-adaptive solution to solve the routing, modulation format, and spectrum assignment (RMLSA) problem for wide-area elastic optical networks. Our main goal is to maximize successful connection requests in wide-area networks while choosing modulation formats with the highest efficiency possible. Consequently, our technique uses an adaptive bit-error-rate (BER) threshold to achieve communication with the best QoT in the most efficient manner, using the strictest BER value and the modulation format with the smallest bandwidth possible. Additionally, the proposed algorithm relies on 3R regeneration devices to enable long-distances communications if transparent communication cannot be achieved. We assessed our method through simulations for various network conditions, such as the number of regenerators per node, traffic load per user, and BER threshold values. In a scenario without regenerators, the BER-Adaptive algorithm performs similarly to the most relaxed fixed BER threshold studied in blocking probability. However, it ensures a higher QoT to most of the connection requests. The proposed algorithm thrives with the use of regenerators, showing the best performance among the studied solutions, enabling long-distance communications with a high QoT and low blocking probability.

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This work introduces two novel approaches for the selection of active lightpaths that perform a spectrum defragmentation process in elastic optical networks (EONs). The algorithms, named DF-Ants and DF-Gen, are based on ant colony optimization and genetic metaheuristics, respectively, and their objective is to minimize the fragmentation of the entire network, evaluated with two different fragmentation metrics. In this way, the blocking probability is expected to be minimized with the fewest number of reconfigured possible connections. Furthermore, a new performance metric for spectrum defragmentation is also presented, named weighted blocking rate (WBR). Unicast traffic simulations were conducted, showing the feasibility of the proposal.

The study of protection against failures in WDM optical networks plays strategic importance due to huge bandwidth of optical fiber. The p-Cycle is a novel protection approach based on pre-configured cycles to provide a fast recovery for single link failure. The optimal selection of cycles is the central problem to get a high protection performance of p-Cycle approach. In that sense, the importance of the length of a cycle for fast restoration is studied in this paper, because it affects directly the quality of restoration, therefore, the quality-of-service can be affected. This paper proposes a new heuristic approach and a new evaluation metric to solve the p-Cycle protection problem which simultaneously optimizes cost, protection, length and fairness of solutions in a mono-objective approach. Experimental results show a good performance of the heuristic proposed, when is compared with a recent Genetic Algorithms approach and the state-of-the-art ILP method.

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