This read-write TruthValue indicates whether Robbed Bit Signalling is turned on for this DS0, applying only to T1 (DS1) links since E1 lines always report false. RBS steals signaling bits from the voice channel itself, so an admin configuring a T1 for CAS signaling would expect this to default to true, while CCS or unsignaled lines default to false. For example, if a T1 channel configured for CAS shows this object as false, that mismatch would explain why on-hook/off-hook signaling isn't being detected correctly on that DS0.