An analysis of transmission performance of optical transport networks employing two different types of wavelength conversion (based on four wave mixing and cross phase modulation) and adopting two different node architectures is reported. The performance is evaluated by means of a system modeling which allows one to consider physical phenomena occurring during transmission and all the important impairments that introduce system penalties. The limits of these kinds of network are investigated and the main features are reported. The analysis reveals that both the types of converters can be employed with different features and limitations, according to the considered architecture. An example of geographical network is discussed and its simulated transmission performance is reported.