Research On Multicast Defragmentation In Elastic Optical Network

With the rapid development of the Internet,the demand for network bandwidth increases rapidly.Conventional wavelength division multiplexing divides the spectrum with a fixed grid,resulting in a serious waste of spectrum resources.Because EON can utilize spectrum resource more flexibly,it obtains more and more attention.Spectrum fragmentation will occur in the elastic optical network,and it will have a great impact on the blocking probability of a network.In this thesis,a series of researches on spectrum fragmentation of multicast service in elastic optical network are done.With the goal of reducing the blocking probability,new multicast routing and defragmentation algorithms are proposed from two perspectives.First of all,this thesis proposes a multicast routing algorithm based on network spectrum fragmentation.In the process of routing services,not only the distance information of the path is considered,but also the spectrum fragmentation of the network is considered.Therefore,this thesis presents two methods to measure the state of the network spectrum using path fragmentation: spectrum density function and spectral fragmentation function.In the process of constructing multicast tree for multicast service,we take these two kinds of functions respectively as the measure of spectrum state of the network,then select the shorter path with the best spectrum state of the network to join in the establishing multicast tree.Compared with prioritizing access to the shortest path,this method provides more possibility for subsequent successful spectrum allocation by considering the spectrum state of the network in advance,and in theory can reduce the blocking probability of multicast services.In this thesis,we simulate these two methods respectively and the results show that the multicast routing algorithm based on network spectrum fragmentation can significantly decrease the blocking probability of the service.Secondly,on the problem of defragmentation of multicast service in elastic optical network,this thesis studies the triggering timing of spectrum defragmentation.Based on the Push Pull spectrum shift technology,this thesis proposes two spectrum defragmentation algorithms for multicast services that do not cause service interruption: the path constant defragmentation with common link algorithm and the path adjustment defragmentation with common link algorithm,both of which are used to organize the spectrum fragmentation when the new multicast service is blocked.The path constant defragmentation with common link algorithm does not intervene in the routing of the new service and only performs spectrum defragmentation on the existing services on the transmission path and shifts services from the high frequency band to the low frequency band,striving to free up idle spectrum in high frequency for later services.The path adjustment defragmentation with common link algorithm provides a number of candidate paths for routing for new service,and tries to rout and defragment respectively,that is,combining defragmentation and routing together.The simulation results show that the algorithm based on defragmentation has a certain effect on reducing the blocking probability of multicast services in elastic optical networks,and the performance of path adjustment defragmentation with common link algorithm is better when the network size is larger.