In mixed-line-rate (MLR) networks, different line rates can coexist on the same fiber on different wavelengths. MLR brings flexibility to handle diverse demands. High line rates require advanced modulation techniques, such as DQPSK and DP-QPSK. On the other hand, signals being propagated over transparent paths are exposed to detrimental effects of physical layer impairments (PLI). Advanced modulation techniques are more susceptible to PLI, especially to the cross phase modulation (XPM) induced by intensity modulated channels.