Research On Cross-Layer Spectrum Defragmentation For IP Over Elastic Optical Network

Elastic optical network(EON)has received extensive interest in recent years due to its flexibility in spectrum allocation and high spectrum efficiency.Setting up and tearing down lightpaths with different numbers of frequency slots(FSs)dynamically will lead to severe spectrum fragmentation,which would degrade the overall network spectrum utilization of an EON.Various spectrum defragmentation strategies have been proposed to smooth the network spectrum usage for future lightpath service connections.However,most of the existing studies have only focused on the optical layer,not jointly considering the IP layer.Actually,the service request arrival and departure in the IP layer is the root cause leading to the spectrum fragmentation in the optical layer since the latter provides transport capacity for the former.Thus,there is an important open question:can we further improve the network service provisioning performance by jointly considering the reconfiguration of IP traffic flows in addition to implementing the spectrum defragmentation?We for the first time propose cross-layer spectrum defragmentation for the IP and optical layers.Specifically,we consider not only rerouting traffic flows in the IP layer but also changing the route and spectrum of each established lightpath in the optical layer.To implement the defragmentation,we have employed the periodic triggering mechanism and the triggering mechanism of defragmentation upon blocking.Also,when we implement the defragmentation,two defragmentation strategies are employed,i.e.,defragmentation with sequentially releasing and re-establishing service connections(SR-D)and defragmentation with jointly releasing and re-establishing service connections(JR-D).Also,for efficient network resource allocation under the multi-layer environment,we employ the AG-based traffic grooming algorithm,which can allocate network resources more efficiently and improve the utilization of network resources of the IP layer.For the optical layer service resource allocation,we consider the spectrum window plane(SWP)-based routing and spectrum allocation algorithm(RSA)which greatly improves the efficiency of path and spectrum resource allocation,and increases the resource utilization of the multi-layer network.Under these defragmentation strategies,the proposed cross-layer spectrum defragmentation scheme is evaluated in comparison with other two schemes,i.e.,IP-layer reconfiguration only and optical-layer defragmentation only.Simulation results show that the proposed cross-layer scheme is efficient to significantly outperform the other two schemes in terms of bandwidth blocking probability(BBP).By comparing the bandwidth blocking performance of the cross-layer spectrum defragmentation under different triggering mechanisms,simulation results show that the bandwidth blocking performance of the BD mechanism is better than the BTD when the defragmentation frequency is low,the bandwidth blocking performance of the BTD is gradually improved or even better than the BD when the defragmentation frequency is increased to a certain extent.By comparing SR-D and JR-D,simulation results show that JR-D can achieve better bandwidth blocking performance than SR-D regardless of the defragmentation scheme.