PCE-based routing and spectrum assignment in OFDM-based bandwidth-variable optical networks

Bandwidth-variable optical networks can not only provide bandwidth-flexible lightpaths, but also complete high capacity all-optical switching, and improve the spectrum efficiency. However, for the spectrum assignment in orthogonal frequency-division multiplexing (OFDM)-based bandwidth-variable optical networks, a lot of sub-carrier resources will be overlapped during the process of reservation with distributed signaling, whether for the first fit (FF) algorithm or for the random fit (RF) algorithm. In order to solve the issue of resource reservation collision, we propose two path computation element (PCE)-based spectrum assignment algorithms and two corresponding optimization algorithms. But, even for PCE-based spectrum assignment, a lot of fragments of sub-carrier resources will be generated during the process of resource reservation, and service LSP establishment and teardown, which will deteriorate the performance of the entire network seriously. This paper proposes a PCE-based defragmentation algorithm for sub-carriers spectrum resource in OFDM-based bandwidth-variable optical networks, the simulation results of which show that this algorithm can reduce sub-carriers fragments considerably and improve the continuity of spectrum resource.