Research On Spectrum Defragmentation Algorithm For Elastic Optical Networks

With the development of Internet technology,the number of services on the network has increased dramatically,and the types of services have tended to diversify.The traditional wavelength division multiplexing optical network cannot meet the flexible network requirements and will cause a lot of waste of bandwidth resources.In order to solve these problems,elastic optical networks have been proposed.However,with the arrival and departure of a large number of services,the state of spectrum resources becomes messy,and spectrum fragments are generated,resulting in the subsequent transmission of normal services,which seriously affects network performance.The thesis conducts an in-depth study on the problem of spectrum fragmentation in elastic optical networks.In order to reduce the spectrum fragmentation in EONs with mixed line rate requests,an odd-even partition spectrum assignment algorithm based on holding-time is proposed in the third chapter.The algorithm comprehensively considers different types of requests,holding time of request and other factors.First,the spectrum resources are divided into different dedicated partitions according to different types of requests.Then,the dedicated partitions is divided into odd types and even types.The requests in the odd and even partition adopt first-fit policy and last-fit policy to form a shared partition with free spectrum blocks on the link.Finally,the requests in the parity partition are adjusted according to the holding time of the requests to enhance the successful transmission rate of request.Simulation results show that the algorithm can effectively reduce the generation of spectrum fragments in combination with the service duration,and optimized the bandwidth blocking probability and improve the spectrum utilization ratio.Due to the network continuously allocates and releases spectrum resources for a large number of arriving and leaving requests,the spectrum fragmentation increases and the available spectrum resources decrease in the network.Without regular spectrum defragmentation,the network performance will not be further improved.Therefore,a spectrum defragmentation algorithm based on fragment evaluation is proposed in the fourth chapter.The algorithm comprehensively considers the spectrum fragmentation in the frequency domain and time domain to propose the fragmentation degree of network,then sets a threshold based on the fragmentation degree of network,and triggers spectrum fragmentation according to the threshold.Spectrum defragmentation moves some of the requests in the network to integrate the free spectrum blocks in the network to provide the largest free spectrum blocks for the transmission of subsequent requests;and adjust the subsequent requests according to the holding time of request duration to improve utilization of spectrum resources in network.Finally,Simulation results show that the algorithm can integrate free spectrum blocks to transmit subsequent requests according to the holding time when there is too much spectrum fragmentation,which improves the performance in terms of bandwidth blocking probability and spectrum utilization ratio.