Gain Nonuniformity and Gain Transients
Amplifiers must be gain-flattened and must have automatic gain control (AGC).
AGC must be done rapidly if signal degradation after a protection switch or link failure is to be avoided.
Need to have dynamic gain equalization (DGE) to optimize power levels each time wavelengths are added or dropped.
Optical channel monitors are also required to provide feedback to the DGEs.