In this thesis, we investigate several defragmentation techniques, with both proactive and reactive triggering strategies, in the context of dynamic Routing, Modulation and Spectrum Assignment
(RMSA) in optical flexible networks.

Proactive defragmentation is executed periodically or according to some fragmentation degradation thresholds in order to maintain spectral defragmentation at an acceptable level, the defragmentation
is independent of the request connection events. Reactive defragmentation, on the other hand, is performed when a new request is blocked due to insufficient spectral resources. In the
context of dynamic traffic in a flexible optical network, we looked into different combinations of proactive/reactive push-pull and make-before-break defragmentations.

Extensive numerical results show that reactive push-pull defragmentation performs quite well in terms of network throughput and request blocking ratio. Consequently, it is efficient in order
to improve network throughput. For proactive push-pull defragmentation, we investigated two different triggering events, namely, time-driven and throughput-driven. We observed that both
triggering strategies have a good performance on maintaining an efficient spectrum usage in networks. Throughput-driven strategy performs better when the network is heavily loaded, whereas
time-driven strategy is a better option when the network is less loaded.