An efficient spectrum assignment algorithm based on variable-grouping mechanism for flex-grid optical networks

Flex-grid optical networks (FONs) employ dynamic routing and spectrum assignment (RSA) algorithms to support diverse services with heterogeneous bit-rates. Although these RSA algorithms can increase the flexibility and efficiency of spectrum allocation, they may also possibly induce spectrum fragments when allocating spectrum to accommodate different service requests. The generated spectrum fragments may exhaust the available spectrum resources and degrade networking performances. Therefore, many schemes referred as defragmentation algorithms have been proposed to reduce spectrum fragments at the cost of traffic disruption or extra components, which are usually required to handle the fragmented spectrum via resource re-optimization. Although some grouping RSA algorithms have been proposed to prevent the generation of spectrum fragments with no traffic disruption or extra components, the pre-divided fixed spectrum groups reduce the flexibility in a dynamic spectrum assignment and thus degrade the blocking performance of the network. In this paper, we propose a RSA algorithm based on variable-grouping mechanism, namely Minimized Variable Grouping (MVG) RSA algorithm, which can not only efficiently restrain the generation of spectrum fragments, but also improve the blocking performance compared to the typical ungrouped and the conventional grouping RSA algorithms. By employing variable grouping mechanism, the proposed algorithm sorts services into different kinds according to their bandwidth requirements and then divides the spectrum resources into several variable groups according to the kinds of services. And the generation of the spectrum fragments is restricted in the spectrum intervals between two adjacent groups. In this way, the proposed algorithm can dramatically restrain the generation of fragments. In addition, the proposed algorithm can reduce the blocking probability by minimizing the grouped spectrum resources to maximize the remained vacant spectrum resources in the spectrum intervals between two adjacent groups for future service requests and thus helps improve the blocking performance. The simulation results show that the proposed MVG RSA algorithm can dramatically reduce the fragments with no traffic disruption while exhibiting a low blocking probability.