In optical channel transport unit overhead （OTU OH）， what are general communication channels 1 and 2（GCC1/GCC2） used for？（）
- Afor trail trace identification
- Bas the backward defect indicator
- Cto transmit information between OTU termination points
- Dto extend command and management functions over several frames
- EGeneral communication channels 1 and 2 （GCC1/GCC2） do not belong to OTU OH