Dispersion-Adaptive First–Last Fit Spectrum Allocation Scheme for Elastic Optical Networks

The quality-of-transmission (QoT) degradation due to the dispersion effect in longer lightpaths is higher than that of shorter lightpaths in a dispersion uncompensated network. To overcome this shortcoming, this letter proposes a dispersion-adaptive first-last fit spectrum allocation scheme for elastic optical networks to decrease the call blocking in the network. The proposed scheme assigns longer lightpath requests from the smallest indexed spectrum slot, where the dispersion effect is less, and shorter lightpath requests from the largest indexed spectrum slot, where the dispersion effect is more. As a result, a less robust modulation technique is used to maintain the QoT threshold level for the longer lightpath requests, and hence a lower number of spectrum slots are required for lightpath establishment. Simulation results show that the proposed scheme outperforms the conventional scheme in terms of blocking probability and contiguous aligned available slot ratio.