Regarding the bit error test of the entire network during commissioning, which of the following statements is correct? (Multiple choice)

In the troubleshooting scenario, which of the following descriptions about the alarms reported when the optical monitoring board receives abnormal light is correct?

Since different frequency (or wavelength) components of the light source have different group velocities, in the transmission process, the time delay of different frequency beams is different and the dispersion is called ()

NG WDM system fault analysis methods include signal flow analysis method, alarm analysis method, instrument test method, () and replacement method.

If the intermediate leveling method is used, the adjustment target of the single-wavelength optical power at the transmitting end and the receiving end is to keep the flatness of the single-wavelength input optical power within the range of the nominal single-wavelength input optical power?