Fiber optic communication systems are limited by effects arising from chromatic dispersion and nonlinearities. In this paper, evaluations of nonlinear effects like SPM and XPM are made, in order to determine the limits imposed by these effects on the launched power. These evaluations are done by means of simulation scenarios, where single channel 10Gb/s DPSK optical modulation with direct detection is employed over 100 km of SMF. In addition, the benefits of SPM are shown by applying this effect in an all-optical regeneration scheme, used to compensate residual dispersion over 500 km of SMF.