Research On Spectrum Optimization Mechanism Of Elastic Optical Network Based On Fragmentation Awaring

With the emergence of high traffic applications,the elastic optical network based on orthogonal frequency division multiplexing(OFDM)has attracted extensive attention due to its finer grid and flexible allocation technology.However,in the process of service transmission and resource allocation,elastic optical networks also face the problem of spectrum fragmentation,which has become the key to optimize network resources..Due to the constraints of spectrum allocation,as well as the continuous establishment and removal of service connection requests in the network,the available spectrum resources in the network become more discrete,resulting in the formation of spectrum fragments,which improves the service blocking rate in the network and seriously affects the service transmission efficiency of the network.In this thesis,by combining the duration,this thesis proposes a time-frequency fragment awareness measurement model based on the preventive spectrum resource allocation method and a time-frequency defragmentation model based on the maintenance of defragmentation,respectively.Through in-depth research on the probability of fragments generated in the allocation process and the selection of service migration strategies in the defragmentation process,the impact of fragments on the network is mitigated and the network blocking rate is reduced.The main contents of this thesis are as follows:(1)From the perspective of preventive spectrum allocation,to address the problem of incomplete fragmentation avoidance in the spectrum allocation process,this thesis first constructs a time-frequency fragmentation metric model by considering the fragmentation resources in both frequency and time domains comprehensively.Based on this,a time-frequency fragmentation-aware spectrum allocation algorithm is proposed to reduce fragmentation by allocating the spectrum resources with the least fragmentation degree for connection requests as well as minimizing the probability of network fragmentation when a connection request leaves the network.The algorithm aims at minimizing the fragmentation level,improving the network resource utilization and reducing the network blocking rate.From the simulations,it can be seen that the algorithm can effectively reduce the spectrum fragmentation and reduce the fragmentation rate by 19% when the service volume is 360 Erl under NSFNET.(2)From the perspective of maintenance-based defragmentation,to address the problem of incomplete utilization of fragmentation resources in the spectrum,this thesis first considers the impact of the service move strategy on the spectrum fragmentation resources in the network and constructs a duration-aware fragmentation metric model.On this basis,the time-frequency resource-aware fragmentation algorithm is proposed.When a connection request is blocked,the fragmentation algorithm is triggered,the time-frequency fragmentation amount in the link is combined,the service moving threshold is set to be selected,and different moving strategies are selected according to the comparison result between the fragmentation amount and the threshold to achieve the purpose of efficient utilization of fragmentation resources.The algorithm aims to re-integrate the fragmented resources and improve the utilization of network resources.From the simulation,it can be seen that the algorithm can effectively reduce the spectrum fragmentation and reduce the fragmentation rate by 17% when the service volume is 360 Erl under NSFNET.