Which three of these are optical channel data unit (ODU) overhead fields? (Choose three)

A.
general communication channel 0 (GCC0)

B.
section monitoring

C.
reserved (RES)

D.
general communication channels 1 and 2 (GCC1 GCC2)

E.
tandem connection monitoring activation deactivation (TCM ACT)

Explanation:
Optical Data Unit (ODU)
The ODU overhead is broken into several fields: RES, PM, TCMi, TCM ACT, FTFL, EXP,
GCC1/GCC2 and APS/PCC. The reserved (RES) bytes are undefined and are set aside for future
applications.
The path monitoring (PM) field is similar to the SM field described above. It contains the TTI, BIP-
8, BEI, BDI and Status (STAT) sub-fields.
There are six tandem connection monitoring (TCMi) fields that define the ODU TCM sub-layer,
each containing TTI, BIP-8, BEI/BIAE, BDI and STAT sub-fields associated to each TCM level (i=1
to 6). The STAT sub-field is used in the PM and TCMi fields to provide an indication of the
presence or absence of maintenance signals.
The tandem connection monitoring activation/deactivation (TCM ACT) field is currently undefined
in the standards. The fault type and fault location reporting communication channel (FTFL) field is
used to create a message spread over a 256-byte multiframe. It provides the ability to send
forward and backward path-level fault indications.
The experimental (EXP) field is a field that is not subject to standards and is available for network
operator applications.
General communication channels 1 and 2 (GCC1/GCC2) fields are very similar to the GCC0 field
except that each channel is available in the ODU.
The automatic protection switching and protection communication channel (APS/PCC) supports
up to eight levels of nested APS/PCC signals, which are associated to a dedicated-connection
monitoring level depending on the value of the multiframe.