Our developed combined system model can be considered under the concept of next generation optical network (NGON) as a model for the future design of backbone networks. Such solution can be topical in the result of different telecom operators’ optical networks convergence. In this case a necessity to transmit differently modulated signals over a single optical fiber even with different bit rates may occur. This research is performed with OptSim 5.2 simulation software that numerically solves nonlinear Schrödinger equation. Authors have revealed the optimal parameter configuration for developed combined transmission systems and obtained in system’s channels detected signals bit-error-rate (BER) correlation diagrams. They represent BER as a function from different system’s parameters such as channel output power level, optical amplifier fixed output power level and system’s channels allotment in C-band of ITU – T (Telecommunication Standardization Sector of the International Telecommunications Union) recommended spectral grid. As well as these obtained BER values were compared with the results for similar system, where instead of standard single mode fiber (according ITU – T Rec. G.652 D) optical signals are transmitted over non-zero dispersion shifted fiber (ITU – T Rec. G. 655).