Data link protecting system

A method of protecting a data link providing communication between supervisory and control units using communication lines, supervised by the supervisory control units, which transmit main data signals between terminal units using multiplexing by multiplexing/demultiplexing circuits, said method of protecting the data link comprising the steps of:

• (a) detecting, in a line interface unit, a failure of a first communication line available for transmission of the main data signals and in use for data link communication from a transmitting side to a receiving side;
• (b) informing a supervisory and control unit on the receiving side of the failure detected by the line interface unit on the receiving side;
• (c) switching a second communication line, corresponding to the first communication line, but in use for data link communication from the receiving side to the transmitting side, to a third communication line available for transmission of the main data and unused for data link communication from the receiving side to the transmitting side;
• (d) informing a superfvisory and control unit on the transmitting side of the failure of the first communication line via the third communication line by the supervisory and control unit on the receiving side;
• and
• (e) switching to a fourth communication line available for transmission of the main data and unused for data link communication from the transmitting side to the receiving side by the supervisory and control unit on the transmitting side.

A method of protecting a data link providing communication between a supervisory and control unit on a transmitting side and a supervisory and control unit on a receiving side using communication lines which transmit main data signals between terminal units using multiplexing by multiplexing/demultiplexing circuits, said method of protecting the data link comprising the steps of:

• (a) detecting, in a line interface unit on the receiving side, restoration of a first communication line in which a failure had occurred;
• (b) informing the supervisory and control unit on the receiving side of said detecting of the restoration of the communication line by the line interface unit on the receiving side;
• (c) switching a second communication line in use for data link communication from the receiving side to the transmitting side to a third communication line from the receiving side to the transmitting side, corresponding to the first communication line which has been restored;
• (d) informing the supervisory and control unit on the transmitting side of the restoration of the first communication line via the third communication line by the supervisory and control unit on the receiving side;
• and
• (e) switching to the first communication line from the transmitting side to the receiving side by the supervisory and control unit on the transmitting side.