Bit Robbing

Bit robbing is often defined as a variation of in-band signaling. This technique is most effective when used with a traditional T-carrier system. In this scenario, a 193-bit frame that serves 24 channels is transmitted in a 12 frame sequence, more commonly known as a superframe. Specific data signals that may indicate whether or not a voice channel is on-hook or off-hook, is included with the superframe. This is made possible by using what is called an a-bit and a b-bit. The a-bit is robbed from the 6th signaling frame while the b-bit is robbed from the 12th frame. Bit robbing is well suited for data transmission and voice conversations that are received by a modem. It is not very useful in a pure data transmission in which every bit is of importance. Bit robbing is the reason why a 64 Kbps channel is only able to carry 56 Kbps of accessible data.