Abstract: A signal in HDBn code is transmitted with an auxiliary binary signal having a lower bit-rate on a digital transmission line. The HDBn code signal comprises predetermined sequences each including n+1 elements, n-1 central elements being zeros and a last element being a bipolarity violation mark. In each sequence of the HDBn code signal transmitted during each of binary elements of the auxiliary signal having a predetermined binary state, a bipolar mark in the sequence is permutated with a zero element having a predetermined rank in the sequence to derive an encoded sequence. The HDBn code signal is an information signal in the transmission line and the auxiliary signal can be a signal for remotely locating the repeater in the line from a monitoring end equipment of a monitoring system or for indicating performance factors of the repeaters, such as error rates, to the monitoring equipment.

Abstract: A step-by-step remote locating system for a digital bidirectional transmission link includes repeater pairs between a monitoring end equipment and a remote equipment. The monitoring equipment transmits remote location sequences and a locate end interruption on a forward channel. The sequences are intended to command closing and opening respective loop-back paths between two repeaters of the pairs. Each sequence comprises a predetermined integral number k of nonconsecutive interruptions in a transmitted digital signal throughout a predetermined period and, with the exception of the first sequence, an interruption preceding the k interruptions intended for opening the loop-back path of the preceding pair. The remote locate circuit associated with each repeater pair comprises an interruption counter. When the count of the counter is k the respective loop-back path to the monitoring equipment is closed. When the count is not equal to k, the loop-back path is opened.

Abstract: The system triggers the relief of a working line amongst N working lines in a bidirectional digital transmission link having at least one spare line. The link is interconnected between two end stations (A, B) which allow a switch-over between a faulty working line and a spare line. The relief of a working line is triggered in response to the detection of an alarm indication signal (AIS) delivered by any end or intermediary terminal included in the working line. An AIS coming from outside the link and related to the working line is detected in an end station and replaced by a switching inhibiting signal that is transmitted via the working line, or perhaps via a spare line, should the working line be faulty and previously relieved, and that is detected in the other station and then replaced by an AIS transmitted outside the link in relation to the other station.

Abstract: The system relieves a transmission working line included in a bidirectional digital link having N working lines and P spare lines between two end stations. In response to the detection of a transmission fault on the working line, the switching units of the stations perform a first exchange of order signals via a selected free spare line, and then a first switch-over of the data related to the faulty working line to the spare line. After the faulty working line has been repaired, to prevent continued data transmission along the spare line, a second exchange of order signals triggers a second switch-over so the system reverts to normal operation. The second exchange of order signals takes place along the repaired line while data related to the repaired line continues to be transmitted via the spare line. During the repair of the preceding faulty working line, a relief procedure of a high priority working line may take place via the selected spare line.