A spectrum allocation scheme based on first–last-exact fit policy for elastic optical networks

In elastic optical networks, bandwidth fragmentation refers to the existence of non-aligned and non-contiguous available subcarrier slots in the set of all subcarrier slots. Since spectrum for a connection must be allocated on contiguous subcarrier slots and aligned along the routing path in the absence of wavelength converter, non-aligned and non-contiguous available subcarrier slots could cause blocking. This paper proposes a spectrum allocation scheme based on first–last-exact fit allocation policy for elastic optical networks in order to increase the number of aligned available slots and avoid small contiguous available slots. The proposed scheme separates the allocation of disjoint and non-disjoint connections. Connections with disjoint paths are allocated using the first-exact fit allocation policy, whereas connections with non-disjoint paths are allocated using the last-exact fit allocation policy. The separation of the disjoint and non-disjoint connections provides a higher number of aligned available slots. The exact fit policy provides a higher number of contiguous available slots. The contiguous aligned available slots reduce the bandwidth fragmentation, and hence the blocking probability is suppressed. Simulation results show that the proposed scheme outperforms the conventional scheme in terms of blocking probability.