Research On Bandwidth Fairness Based Restoration Algorithms In Post-disaster WDM Optical Networks

Since large amount of broadband services emerges in our life,the WDM(Wavelength Division Multiplexing)optical networks have been extensively applied because of its tremendous transmission rate and huge transmission capacity.However,as the scale of these networks continuously increases,optical networks are increasingly threatened by various kinds of disaster events(e.g.earthquake,tsunami,hurricane,or even human attack).The damages and destructions from disaster events might cause massive service disruptions and critical data loss,leading to significant economic loss for both customers and carrier companies.Therefore,optical network survivability mechanism against large-scale disasters has become an important subject in the optical network research area.Aiming at large-scale disasters,this thesis researched the bandwidth fairness based restoration algorithms in post-disaster optical networks,which is based on a static traffic model.The specific research contents are as follows:To allocate bandwidth resources fairly among different levels of disrupted services,hierarchical bandwidth fairness based cyclic stepwise restoration are studied.Aiming at service recovery issue in disaster-damaged networks,the proposed algorithm conducts fairness based bandwidth recovery for various levels of disrupted service connections in accordance with a strategy of multipath provisioning and bandwidth degradation.In which,we flexibly classify services into levels and set a step-length metric,then conduct a multistage(stepwise)recovery for disrupted services in the sequence of their levels to achieve a relative fairness of bandwidth recovery among different service levels.In each stage,we dynamically adjust the recovery priorities of disrupted services of the same level according to their bandwidth loss ratio,then cyclically increase a minimum unit of bandwidth for each of them to achieve a fairness of bandwidth recovery for the same service level.Simulation results indicate that,compared with the self-adaptive bandwidth degradation restoration and no bandwidth degradation restoration,the proposed algorithm can effectively improve the fairness of bandwidth restoration for disrupted services,particularly for high-and medium-level ones,and can also improve,to some degree,the performances in terms of traffic loss ratio and connection loss ratio.To implement fair allocation of bandwidth resources among different levels of services,a global optimization algorithm on the basis of the restoration algorithm proposed in Chapter III are studied.With a global resource optimization thought,we conduct the cyclic stepwise restoration for both disrupted and undisrupted service connections in the post-disaster network.During the global optimization for the whole network resource,the strategy of multipath provisioning and bandwidth degradation shows a distinct effect,which can take good advantage of the fragmented bandwidth resource in the network,and significantly enhanced the bandwidth fairness for various levels of services.The simulation results indicate that,compared with hierarchical bandwidth fairness based cyclic stepwise restoration,self-adaptive bandwidth degradation restoration and no bandwidth degradation restoration,the global optimization algorithm can effectively improve the performances in terms of bandwidth fairness,traffic loss ratio,and connection loss ratio.