Research On Routing Spetrum Assignment Strategy And Its Application In Elastic Optical Networks

Both the types and quantity of network traffics have been dramatically increased recently,and the differentiation among these service requirements has become obvious than ever before.The tradional wavelength division multiplexing(WDM)network uses the fixed wavelength grid to allocate service,which cannot meet the dynamic traffic requirements.Elastic optical network(EON)defines finer frequency granularity and achieves more flexible allocation for the incoming service requirements,which can effectively decrease the blocking probabililty and improve the resource utilization.Routing and spectrum assignment(RSA)is the key technology in EON,while the spectrum fragmentation issue is even more difficult to handle for RSA.This thesis presents a comprehensive research focusing on the spectrum defragmentation issues in EON from the defragmentation triggered mechanism to defragmentation algorithm with theoretical analysis and numerical simulation.Firstly,this thesis introduces the fundamental concepts,system structure,and key techniques in EON briefly.Meanwhile,the analysis of RSA problem and description of the spectrum fragmentation in EON are provided.Focusing on current defragmentation triggered mechanisms,this thesis proposes a policy-based comparison-triggered defragmentation mechanism.The improved mechanism defines two parameters called spectrum availability and traffic request.The result of comparing the two parameters is used as the basis for judging whether to trigger defragmentation.The defragmentation will only be triggered when the value of traffic request is bigger than the spectrum availability before defragmentation,and smaller than or equal to the spectrum availability after it,respectively.Theoretical analysis and simulation result show that the proposed mechanism can reduce the blocking probability and improve the network utilization ratio effectively.Finally,this thesis focuses on the spectrum defragmentation algorithm and proposes a blocking-triggered defragmentation algorithm based on the selected path.The proposed algorithm takes the effectiveness and the complexity of spectrum defragmentation into consideration simultaneously.Then it will select a path from source node to destination node then perform the partial defragmentation based on the selected path,i.e.sort the related services and reallocate them.Theoretical analysis and numerical simulation results show that the proposed algorithm has an obvious improvement in reducing the network latency and easing the blocking situation.