We apply a complete perturbation theory of solitons (for position, phase, frequency, and amplitude) to the cases of amplitude, intensity, or phase modulation, filtering, and soliton interaction. We show that on-line intensity modulation and filtering act in the same way in reducing noise-induced jitter. Soliton interaction can be reduced with initial phase and filtering control or with a periodic pi-phase change for consecutive solitons (as in the case of amplitude modulation). Finally, we design a 30-Gbit/s transoceanic soliton transmission system, using filtering and initial phase control techniques.