Dear friend!
Optical line protection:
Protects the optical fiber links (OTS) between FIU boards. The signals are dually fed and selectively received on the OLP.

ODUk/ODUFix protection:
Protects ODU trails. The signals are dually fed and selectively received on the cross-connect board or OTU board.

Intra-board 1+1:
Protects OCh trails. The signals are dually fed and selectively received on the OLP or DCP.

Tributary protection:
It protects the tributary board or the link between the tributary board and the client equipment. The signals are dually fed and selectively received on the cross-connect board or OTU board.

More: Network Level Protection (OTN)
Thank you!