(bit-robbing) The exchange of call control information on the same channel as the telephone call or data transmission. Since one bit in a frame is periodically used for signalling instead of data, this is often referred to as bit robbing.

This is the reason why a D1 channel in the T-carrier system can only carry 56 Kbps of usable data instead of the 64 Kbps carried by the D0 channel in the E-carrier system.