Many studies have been performed proposing optimization solutions for off-line (or static) RSA in Elastic Optical Networks. In the last 3 years, however, focus have migrated to the dynamic performance of RSA. In this version of the problem the main issue to be solved is the spectrum fragmentation. The spectrum fragmentation occurs when connections with diverse rate are dynamically established and torn down, leaving gaps of available spectrum that may be smaller than connections requests that are dynamically arriving and therefore increasing demands blocking probability. In this sense solutions for the fragmentation problem may be sub classified into a fragmentation-aware RSA or a defragmentation technique with spectrum re-allocation.
Dynamic RSA algorithms may RSA be designed as one or two step approach. In two-step approaches, RSA problem is divided into routing and spectrum assignment sub-problems. In the one step approach routing and spectrum allocation are solved in tandem as one problem.
