This table specifies a list of CAS signaling protocols such as
R2 CAS, Feature Group D Oprerator Services ( FGD OS).
Each CAS variant is downloaded to and parsed by
the media gateway.
A CAS variant can be applied to a DS0 group of the DS1
line with CAS signaling. A DS1 line is configured for CAS
signaling when its dsx1SignalMode is set to 'robbedBit(2)'
for T1 or 'bitOriented(3)' for E1.