What statement about DCC tunneling in the ONS 15454 is true?

What statement about DCC tunneling in the ONS 15454 is true?

A.
Only the first STS frame in any OC-n signal is used for tunneling.

B.
For security reasons, the 15454 randomly assigns an STS frame from within any OC-n signal to be used for tunneling.

C.
A different STS frame is used on each section of the ring, to prevent overlap or conflict on the protection path.

D.
Only the last STS frame in any OC-n signal is used for tunneling (this feature is also used as a bit rate indicator).