Research On The Spectrum Defragmentation In Elastic Optical Networks

Elastic optical networks (EON), also known as flexible-grid opticalnetworks, were recently proposed to achieve high spectral utilization andefficiency. In EON, it can allocate spectrums with speeds ranging from Gb/sup to Tb/s at tighter channel spacing based on the demands and reachrequirements. The combination of bandwidth adaptive transceivers, adaptiveROADMs and intelligent control plane enable the new flexible opticalnetworks. Varied-bit-rate single optical carrier can dynamically support thedifferent traffic.In the control plane, the traditional wavelength continuity constraintmust be followed. However, the flexible spectral grid leads to an additionalspectrum continuity constraint, which means allocation the same continuousspectrum on each fiber link along the lightpaths of a request. In the dynamiccases, the channel setup and tear down processes lead to fragment ofspectrum. We theoretical analyses the elastic optical networks and find thatfragments may be unevenly distributed among the network and on thespectrum of each link. Based on these two features, we propose two schemesfor the partial defragmentation, namely link-based partial defragmentationand spectrum-based partial defragmentation. Simulation results show thatthe proposed schemes may reduce up to40%defragmentation whilemaintaining the network performance.The thesis has several main contents：I. Theoretical analyses the elasticoptical networks. II. Point out two features of the spectrum fragments in theEON, namely unevenly distributed among the network and on the spectrumof each link. III. Propose two schemes for the partial defragmentation, namely, link-based partial defragmentation and spectrum-based partialdefragmentation. IV. Three triggered methods are compared in numericalresults, periodically defragmentation, rejection triggered defragmentationand departure triggered defragmentation. V. We also consider the networkfairness before and after the defragmentation.