ABSTRACT
Spectrum fragmentation, is a serious issue in elastic optical networks (EONs), which suppresses the resource utilization and enhances call blocking in the network. This chapter presents the fragmentation problem in EONs. The spectrum fragmentation problem in EONs, where lightpath requests are allocated dynamically while respecting the constraints of spectrum continuity and contiguity. The chapter describes the different metrics that are used to measure spectrum fragmentation in EONs. It discusses the major spectrum allocation policies, which are first fit, random fit, last fit, first-last fit, exact fit, least used, most used, and presents the impact of fragmentation when the network uses these spectrum allocation policies. The free spectrum slots, which have been utilized by the smallest number of fiber links in the network, are the focus of the least used spectrum allocation policy to satisfy lightpath requests. The spectrum allocation of the most used policy is similar to that of the least used policy.
