Robbed-bit signaling

In communication systems robbed-bit signaling is a scheme to provide maintenance and line signaling services on many T1 digital carrier circuits using channel-associated signaling (CAS).

The T1 carrier circuit is a type of dedicated circuit currently employed in North America and Japan. The T1 circuit is divided into 24 channels, each carrying 8,000 samples per second, each 8 bits long. The Super Frame (SF) consist of 12 frames of 24 channels. The DS1 designation consist of 24 frames called, Extended Super Frame (ESF). In either designation, these channels are multiplexed together and sample at 8000 bit/s. In the DS0 designation, each of the channels induces eight bits into the multiplex output stream, ten are utilized entirely for voice/data and two are utilized partially for voice. Hence, each of the two partial channels yields 7 x 8000 bit/s = 56 kbit/s for voice data and the remaining channels yields 8 x 8000 bit/s = 64 kbit/s.