See Resource Breakdown Structure
The Resource Breakdown Structure (RBS) is the reserved Enterprise Resource Outline Code 30 that is used for Resource Management. It can be used to represent hierarchical structures and groupings of resources (be they logical or physical).
robbed bit signaling. A form of signaling that "robs" a bit from the user's data stream to provide supervisory and signaling information to and from the switch. RBS emulates older analog trunk and line signaling methods by providing a 1:1 mapping of analog supervisory signaling to the signaling bits (A, B, C, D).
Robbed Bit Signaling is used in T1 circuits. Instead of having a specific timeslot dedicated to provide signal (as is true with ISDN) , signaling bits for on-hook and off-hook are within the sixth, twelfth, eighteenth and twenty-fourth frames of each time slot. RBS is sometimes called CAS (Channel Associated Signaling) because it takes bits from the bearer channels for signaling.