Two-dimensional Fragmentation-aware Routing And Spectrum Allocation Algorithms In Software Defined Elastic Optical Networks

With the continuous development of online video,cloud computing and video conferencing applications,the bandwidth demand for network users is growing rapidly.Elastic optical network(EON)supports finer spectrum granularity and more flexible adjustment of optical parameters,thus can provide lightpath services for more network requests.Software defined network(SDN)separates control and data forwarding,and combines with EON to form software defined elastic optical network(SD-EON),which makes it easier for control and manage of EON.Therefore,SD-EON has become a hot research point in the next generation optical network.Routing and spectrum allocation(RSA)is a very important problem in SD-EON,which aims to establish an end-to-end lightpath for each network request.In dynamic SD-EON scenarios,with the continuous establishment and removal of lightpaths,a large number of spectrum fragments will be generated in the network,causing serious call blocking.Therefore,in SD-EON,it is of great significance to investigate how to decrease spectrum fragmentation and reduce the bandwidth blocking probability.Firstly,in this thesis,the research background and the state of art of EON,SDN and SD-EON is analyzed,and the network architecture of SD-EON is introduced.And then,the SD-EON simulation environment in built based on Mininet network simulator and RYU controller.In addition,the constraints of RSA and the fragmentation problem are discussed.Moreover,the classical RSA algorithms are summarized,and the characteristics of immediate reservation(IR)requests and advance reservation(AR)requests as well as the related RSA algorithms are investigated.Secondly,for provisioning IR requests in dynamic SD-EON scenarios,in terms of routing,this thesis propose an offline hop and modulation based routing(OHM)algorithm.OHM routing algorithm comprehensively considers hop count and modulation format,so as to calculate several candidate paths with least hop count and highest modulation format.In terms of spectrum allocation,this thesis establishs a two-dimensional path resource model,and design an efficient candidate spectrum block search strategy.Then,by jointly considering distance to frequency boundary,impact on neighboring resources,and resource consumption,this thesis designs a two-dimensional fragmentation metric,namely combined fragmentation degree.Based on this,this thesis proposes a minimum combined fragmentation degree(MCF)spectrum allocation algorithm.Furthermore,by combining the above proposed routing algorithm and spectrum allocation algorithm,this thesis proposes a two-dimensional fragmentation-aware RSA algorithm for dynamic IR requests,namely OHM-MCF.Thirdly,for provisioning AR requests in dynamic SD-EON scenarios,in the routing phase,this thesis proposes a minimum resource consumption(MRC)routing algorithm.MRC routing algorithm can minimize the time-frequency resource consumption of AR requests,thus leaves more available free resources for subsequent requests.In the spectrum allocation phase,this thesis firstly builds a time-frequency two-dimensional path resource model.Then this thesis abstracts the required time-frequency resources to a rectangular block,so that the RSA problem of AR requests is transformed into a two-dimensional rectangle packing problem.In addition,in the case of considering neighborhood fragmentation condition of the pre-assigned resources,this thesis proposes several factors such as the increased number of runs,the neighborhood matching degree,and etc.Based on the above factors,this thesis proposes a two-dimensional fragmentation-aware spectrum allocation(2D-FA)algorithm.According to the above proposed routing algorithm and spectrum allocation algorithm,this thesis proposes a temporal and spectral two-dimensional fragmentation-aware RSA algorithm for dynamic AR requests,namely MRC-2D-FA algorithm.Finally,based on the built SD-EON simulation environment,the performance of the proposed OHM-MCF algorithm and MRC-2D-FA algorithm are evaluated.Simulation results show that compared with the typical benchmark algorithms,the proposed RSA algorithms can further reduce the bandwidth blocking probability and improve the spectrum utilization.