Research On Routing And Spectrum Allocation Issues In Elastic Optical Network

With the rapid development of broadband services as well as the Internet,the bandwidth demand for services has shown a dynamic growth trend.The traditional WDM optical network uses a fixed grid allocation method for resource,which is not flexible enough in the management mode of spectrum resources,which resulting in low bandwidth utilization and poor network flexibility.Disadvantages such as poor network flexibility can no longer adapt to the development of information transfer.With the introduction of orthogonal frequency division multiplexing technology,the elastic optical network can provide spectrum division with fine granularity.They can not only form super-wavelength bandwidth channels through sub-carriers to meet the needs of large bandwidths,but also allocate required bandwidth resources for service requests instead of fixed-size bandwidth which reduces the waste of bandwidth resources.This improves the utilization of spectrum resources and reduces the blocking rate of the network.Elastic optical network is the main direction of future optical network development.Routing and spectrum allocation are one of the core technologies of the elastic optical network.In this paper,the routing and spectrum allocation in elastic optical networks is studied,and the improved methods and strategies are proposed.The feasibility of the methods are analyzed theoretically,and the simulation method is used to verify the algorithms.The main works of the thesis are as follows:(1)The paper analyzes the existing spectrum fragmentation assessment schemes and the spectrum allocation schemes used to reduce spectrum fragmentation.For the existing schemes,there is rarely a scheme that links the bandwidth of the request with the spectrum status of the path.This paper proposes an adaptive parameter that measures the size of the service request bandwidth and the path frequency situation.The allocation factor is used to measure the adaptation of the bandwidth of the service request and the condition of the path frequency.When doing spectrum allocation,not only the spectrum status of the path is considered,but also the bandwidth required by the service.(2)Aiming at the problem that the spectrum fragmentation in the network affects the network blocking rate,an RSA algorithm based on service bandwidth awareness(BA-RSA)is proposed.The adaptation factor is used as the criterion for selecting the path,and the smaller adaptation factor is preferred.The spectrum dispersion,which is a parameter to describe the spectrum distribution ofthe allocated spectrum,is defined to measure the spectrum distribution of the path.When the path adaptation factor is the same,the path with the small spectrum dispersion is selected for spectrum allocation.The simulation results show that,in the CERNET network topology,compared with the traditional Dijkstra + FF and Dijkstra + RF algorithms,the BA-RSA algorithm reduces the blocking rate by approximately 8.45% and 17.37% respectively.In terms of spectrum resource utilization,the maximum increases were approximately 9.28% and 15.22%,respectively.(3)Aiming at the problem that traditional routing algorithms are not efficient and only consider path length,an improved version of ant colony algorithm is proposed,which is based on ant colony system and applied to the RSA problem of elastic optical network.The spectrum usage of path is introduced into the state transition heuristic function of the ant colony system,and the volatility factor is redefined so that the volatility factor can adaptively change with the number of iterations to avoid the algorithm falling into a local best.The simulation results show that,in the CERNET network topology,the RSA algorithm based on the improved ant colony system has a maximum reduction of approximately 12.07% in the blocking rate compared to the traditional Dijkstra + FF algorithm,and a maximum increase of approximately 11.54% in the spectrum resource utilization.