It is necessary to perform the () operation before querying the error code and optical power on the network management system, otherwise the corresponding teaching data cannot be queried.

When light passes through a passive optical device, the drop in optical power caused is called the () of the device.

40Gbit/s and 100Git/s coherent systems do not require dispersion compensation because the coherent board has a large dispersion tolerance. NG WDM does not support mixed transmission between non-coherent and coherent networks.

The frame structure of the OTUk signal consists of 4 rows and 4080 columns, and the value of k can be an integer of 0 to 6, representing line rates of 1.25G, 2.5G, 10G, 40G, 100G, 200G and 400G.

Which of the following is correct about the processing of data frames by the ports of the data board? (Multiple choice)