Research On Defragmentation In Elastic Optical Networks

With the development of the Internet industry,the demand for network bandwidth increases and the quality of service requirements become higher.Traditional WDM optical networks which fixed wavelength have poor flexibility and serious waste of bandwidth resources,which cannot meet the transmission requirements of future optical networks.While the elastic optical network,which has the advantages of flexible bandwidth allocation and variable modulation mode,has greatly improved the utilization of bandwidth resources.Therefore,the elastic optical network has become the mainstream architecture of the next generation of optical network.Fragmentation is a core problem in elastic optical networks.The existence of spectrum fragments causes waste of spectrum resources and increase the blocking ratio of the network.This thesis studies how to solve the spectrum fragmentation problem in elastic optical networks from two aspects: routing and spectrum allocation algorithm and defragmentation algorithm.The main work of this thesis is as follows:(1)In terms of defragmentation problem in fixed routing,this thesis proposes the downward aggregated defragmentation algorithm(DAD),which uses the services transmitted in the upper spectrum to fill up the underlying spectrum layer by layer.The biggest difference between DAD and the traditional defragmentation algorithm is that it no longer relies on the fixed order to move the business,but chooses the appropriate service to move according to the idle state of each spectrum.This thesis also compared the performance differences between DAD and the traditional defragmentation algorithm using several different sorting strategies.Besides that,this thesis compared the longest path first downward aggregate defragmentation algorithm(LPF-DAD),which has the best performance in the comparison above,with the other two latest fixed routing fragmentation algorithms.This thesis improves the DAD based on the first last fit algorithm(FLF).The blocking ratio of the improved algorithm is significantly reduced,but the complexity is higher,and the number of service refactoring is also higher.(2)In terms of routing and spectrum allocation problem,this thesis proposes a new fragmentation-aware iteration routing and spectrum allocation algorithm(FA-IRSA).In the process of finding path,FA-IRSA considers the continuity of each link's spectrum and the consistency of spectrum among different links,while iterative strategy is used to calculate several paths for the business.Finally,FA-IRSA selects the path with less hops to establish the optical path for the business.The algorithm not only has low blocking ratio,but also effectively reduces the waste of spectrum resources.(3)In terms of defragmentation problem in dynamic routing,this thesis proposes a path adjustment downward aggregated defragmentation(PADAD)algorithm.PADAD algorithm adopts the strategy of filling up the spectrum from bottom to top,but when the service is unable to move,the algorithm attempts to rerouting the service to other paths.The rerouting path has been calculated with FA-IRSA before sorting out,which can greatly reduce the complexity of the algorithm.Simulation results show that the algorithm significantly reduces the blocking ratio of network,while the computation complexity is moderate,and the number of refactoring is also lower.