PDM uses a polarization beam splitter to divide the laser into two vertical directions: x and y.

Which of the following statements about the MST functional module is correct? (Multiple choice).

A communication network is a system that interconnects geographically dispersed user terminal devices to achieve communication and information exchange. It is mainly composed of user equipment and transmission equipment.

Among the following recommendations, which of the following protocols are related to WDM?
(Multiple choice)

The SDH frame structure is a rectangular block frame based on which of the following options?