Spectrum Defragmentation in Elastic Optical Networks

Elastic optical networks (EONs) provide fine bandwidth allocation granularity and enable scalable network management. In this paper, we review the strategies to alleviat e spectrum fragmentation from both the preemptive and proactive perspectives. As for preemptive defragmentation, we inves tigate the characteristics of bandwidth fragmentation in EONs, and then discuss a fragmentation-aware routing and spectrum as signment (RSA) algorithm to relieve spectrum fragmentation when setting up connections. As for proactive defragmentation,we decompose the problem into three subproblem: 1)Connection Selection; 2) RSA Re-optimization; and 3) Traffic Migration . We also discuss the problem of timing selection for defragment ation in dynamic network environments, and investigate how to improve network performance with the minimum operation cost by using intelligent and adaptive timing selection.