Robbed bit signaling was (is) used to encode signaling information on a digital circuit (typically a T1 in North America) without a dedicated signaling channel.

Robbed bit signaling was (is) used to encode signaling information on a digital circuit (typically a T1 in North America) without a dedicated signaling channel. There were a variety of multiplexing systems to get more than a single line on a copper pair, but they didn't have anything to do with robbed bit signaling.