Regarding the interconnection of different circuit boards of OTN equipment, which of the following statements is correct (multiple choice)

High-risk operations refer to all operations that may affect the stable operation of equipment, the normal operation of customer services, and the normal monitoring of network management. Which of the following are usually included? (multiple choice)

If the low-level crossover of SDH equipment is exhausted, there are several common optimization schemes (multiple choice)

OSN6800 single-master network element master control failure, after replacing the master control, what operations need to be performed (multiple choice)

In the point-to-point WDM networking scenario, the signal-to-noise ratio of a certain single wave is low, and the other channels are normal. The reason is that it is impossible?