Fragmentation-aware VONE in elastic optical networks

Due to the accelerated evolution of application services, the sharing of physical network infrastructure among different users and applications can be facilitated by optical network virtualization, which simplifies optical-layer resource management and enables flexibility in spectrum resource allocation. However, fragmentation is one of the great challenges in implementing virtual optical network embedding (VONE) over flexible-grid elastic optical networks (EONs). In this paper, we propose a fragmentation-aware VONE algorithm to reduce spectral fragmentation and improve resource unitization. We first formulate an integer linear programming (ILP) model for multiple static VON requests, while considering the continuity and consecutiveness of the substrate fiber links' (SFLs) optical spectra. Then, to realize the coordinated node and link mapping in the VONE, we constructed a virtual auxiliary graph (VAG) that decomposes the physical infrastructure into several layered graphs, according to the spectrum slot requirement of a VON request. Three different provisioning schemes are designed. The former two benchmark schemes (i.e., spectrum resource traffic balancing and spectrum resource and computing resource traffic balancing) apply a traffic balancing policy on the spectrum resource and computing resource, while another spectrum resource traffic balancing and defragmentation (SR-TB&DF) scheme additionally uses a proactive defragmentation method in the VONE process, with the aid of a novel metric called "fragment block size." The extensive simulations, which consider both static network planning and dynamic service provisioning scenarios, have demonstrated that the proposed fragmentation-aware VONE algorithm with the SR-TB&DF scheme facilitates the reduction of the spectrum slot fragments and improves the request blocking ratio as well, compared with the two other benchmark schemes.