Impairment-aware spectrum allocation in elastic optical networks: A dispersion-sensitive approach

The degradation of quality-of-transmission (QoT) due to the dispersion effect is a critical issue in elastic optical networks (EONs). To satisfy the required quality of transmission, a robust modulation level needs to be adopted. Thus, the number of required slots for spectrum allocation is increased. Although dispersion compensation devices reduce the effect of dispersion, they require an additional cost. This paper presents a dispersion-sensitive spectrum allocation approach for EONs to suppress the call blocking in the network. The presented spectrum allocation approach does not use any dispersion compensating device for suppressing the dispersion effect. It allocates shorter lightpath requests from the largest indexed spectrum slot, where the effect of dispersion is higher, and longer lightpath requests from the smallest indexed spectrum slot, where the effect of dispersion is lower. To satisfy the required QoT threshold level for the longer lightpath requests, the presented approach uses a less robust modulation level. Thus, for lightpath establishment, a lower number of spectrum slots are required. In the presented approach, lightpath requests are separated as longer and shorter lightpath requests using either the predetermined-threshold policy or the lightpath threshold selection algorithm. When the traffic condition is not known in advance, the predetermined-threshold policy is not applicable. In that case, the lightpath threshold selection algorithm is used to find the distance threshold value, which provides the lowest blocking probability. Simulation results indicate that the presented dispersion-sensitive spectrum allocation approach outperforms the conventional spectrum allocation scheme in terms of available contiguous aligned slot ratio and blocking probability.