Research On The Methods Of Resource Allocation For Optimizing Spectrum Utilization In Elastic Optical Networks

In recent years,with the continuous appearance of emerging services,the rapid growth of data traffic has brought extremely serious challenges to backbone networks.Compared with the wavelength division multiplexing(WDM)optical networks with fixed wavelength assignment,elastic optical networks(EONs)based on optical orthogonal frequency division multiplexing technology can allocate spectrum at the finer granularity,which greatly improves spectrum resource utilization in the optical layer.Consequently,EONs have been widely looked upon as the technology for upgrading WDM networks.However,when spectrum resources are allocated in EONs,the strict constraints of spectrum consistency,spectrum continuity and spectrum non-overlapping are demanded to follow.That makes the spectrum resources in the network become discrete,producing spectrum fragmentations of different bandwidth sizes,and reducing spectrum utilization ratio in the network.Meanwhile,introducing network virtualization technology into EONs can overcome the "ossification" situation of the Internet development effectively.However,it is more difficult to allocate resources for virtual optical network services in EONs,and it is difficult to improve spectrum utilization ratio.Based on the above,this thesis mainly researches the methods of resource allocation for optimizing spectrum utilization ratio in EONs and virtual optical networks.In order to address the fragmentation problem in the time domain and the spectrum domain in elastic optical networks,the third chapter of thesis proposes a fragmentation-avoiding spectrum assignment strategy based on time-spectrum partition(FASA-TSP).Firstly,a time-spectrum partition method,splitting whole optical spectrum into several spectrum partitions and then split every spectrum partition into multiple time-spectrum partitions,is proposed.On the basis of this,a spectrum assignment policy is proposed,where each time-spectrum partition is preferentially used to transmit requests with same rate and closest holding time.Besides,each spectrum partition is executed last-fit policy to search available spectrum resources when requests with the same rate are not successfully transmitted in dedicated time-spectrum partition.Lastly,other spectrum partitions are used to seek usable spectrum resources when there are no available spectrum resources in dedicated spectrum partition.Meanwhile,when there is only one available spectrum partition,execute last-fit policy.When there are several availablespectrum partitions,we design a partition selection equation to minimize spectrum collision.Moreover,a spectrum collision avoidance reconfiguration mechanism,moving requests which are not transmitted in dedicated time-spectrum partition to dedicated time-spectrum partition,is also proposed.Simulation results show that the FASA-TSP strategy can effectively reduce spectrum fragmentations and improve spectrum resources utilization ratio.In order to address the problems of imbalance physical resources consumption during virtual optical network embedding and spectrum fragmentation in space division multiplexing elastic optical networks,a virtual optical network embedding strategy based on fragmentation awareness is proposed.In the stage of node embedding,considering the embedding state of adjacent virtual nodes and the topological characteristics of physical nodes,then measure the importance of virtual nodes and physical nodes respectively to improve successful probability of virtual optical network embedding.In the stage of link embedding,in order to balance the resource consumption in physical path,the degree of polymerization of physical path is considered,and then according to the average degree of polymerization of each physical path to embed virtual links to improve the balance of resource consumption.In the stage of spectrum allocation,firstly,classify cores based on the number of cores,where each region is set to transmit certain size of service to minimize spectrum fragmentations caused by mixed line rate service.Besides,a fragmentation awareness spectrum allocation strategy based on core classification is proposed to minimize spectrum fragmentations caused by spectrum allocation.Lastly,a spectrum collision avoidance reconfiguration mechanism,moving requests which are not transmitted in dedicated cores to dedicated cores,is also proposed.Simulation results show that the proposed strategy can effectively improve resources utilization ratio and reduce spectrum fragmentations.