A Confusion about ODUk mapping

Dear friend!
On an OTN network, all service signals need to be converted into ODUk or ODUflex signals because the WDM-side ports of the equipment transmit OTU signals. Service signals can be converted into OTU signals only after being converted into ODU signals. Then, the data can be transmitted on the OTN network. The process of converting service signals into ODU signals may be performed in the tributary board or the line board.

Tributary board:

Line board:

Thank you!