Abstract: An improved system for allowing a digital transmission line element, such as a regenerative repeater, to communicate with a remote location. The line element is interconnected to a digital transmission line, which receives an incoming data stream. The data stream follows predetermined coding rules. The line element includes a detector and an error generator. The detector senses when a status inquiry is made and responsively enables the error generator to then selectively introduce errors into the data stream along the digital transmission line. The errors may then be detected at a remote location to a provide information regarding the line element, such as its location or operating mode.