In optical channel transport unit overhead (OTU OH), what are general communication channels 1
and 2 (GCC1/GCC2) used for?

A.
for trail trace identification

B.
as the backward defect indicator

C.
to transmit information between OTU termination points

D.
to extend command and management functions over several frames

E.
General communication channels 1 and 2 (GCC1/GCC2) do not belong to OTU OH.