JPS6216588B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a transmission line switching system that monitors the error rate of the transmission line to switch the transmission line and prevents errors during switching back.

The error rate of the working transmission line is constantly monitored, and when the error rate exceeds a predetermined value, it automatically switches to the backup transmission line. A method is adopted in which the transmission line is automatically switched back to the current transmission line. In such conventional methods, after switching the faulty working transmission line to the backup transmission line, the working transmission line is repaired and the backup transmission line is switched back to the working transmission line. , there was a risk that transmission information would be lost.
That is, several bits of transmitted information may be lost due to a momentary interruption due to cutback or a difference in transmission delay time between the backup transmission line and the working transmission line.

The present invention has been made to improve the conventional drawbacks as described above, and aims to prevent transmission information from being lost when switching back from a backup transmission line to a working transmission line. Examples will be described in detail below.

FIG. 1 is an explanatory block diagram of the active and backup transmission lines, where 1 is a transmitter, 2a and 2b are repeaters,
Reference numeral 3 denotes a receiving section, and when the repeater 2a side is used as the active transmission path, the error rate is measured in the receiving section 3, and when the error rate exceeds a predetermined value, the backup section on the repeater 2b side is transmission line. At this time, the transmission information or monitoring information is also transmitted to the current transmission path, so the receiver 3 can monitor the status of the current transmission path, and if the error rate falls below a predetermined value, the backup transmission path is From then on, switching back to the current transmission line is performed.

In this switchback, although the transmission information on the backup transmission line and the transmission information on the working transmission line are the same, there is a difference in transmission delay time, so simply switching will result in instantaneous interruptions or missing several bits. It turns out.
Therefore, the switching back is performed after time adjustment is performed in the receiving section 3.

FIG. 2 is a block diagram of an embodiment of the present invention, showing the main parts of the receiving section 3, in which 10 is a shift register consisting of elements 10a to 10n such as flip-flops, 11 is a signal selection section, 12 is a comparator, 13 and 14 are switches, and 15 is an OR circuit. The information transmitted through the backup transmission path B is received and processed via the switch 14 and the OR circuit 15. When switching back from the backup transmission path B to the working transmission path A, the information transmitted through the transmission path A is The transmitted information is input to the shift register 10, and the signal selection unit 11 sequentially selects the output of each stage of the shift register 10 and applies it to the comparator 12, where it is compared with the information transmitted through the backup transmission line B. .

For example, the current transmission line A is used for the backup transmission line B.
Assuming that the transmission delay time of
A comparison of the bit correspondences in 2 can be found. If this comparison match state continues for a predetermined plurality of bits, the comparator 12 controls the switch 13 to close, and continues outputting the second stage element 10b of the shift register 10 to the signal selection section 11. Instructs to output selectively. As a result, the time alignment between the information transmitted through the backup transmission path B and the information transmitted through the current transmission path A is completed, and the information transmitted through both transmission paths A and B is transmitted from the OR circuit 15. It will be sent to the reception processing section, and if the switch 14 is turned off after a predetermined time,
The operation of switching back to the currently used transmission line A is completed, and this switching back operation eliminates the loss of even one bit.

As explained above, in the present invention, after a failure occurs in the current transmission line, the current transmission line is switched to the backup transmission line, and then the current transmission line is repaired and the backup transmission line is switched back to the current transmission line. At this time, the information transmitted through the current transmission path is added to the shift register 10, and the output of each stage of this shift register 10 is compared with the information transmitted through the backup transmission path, and the output of the shift register 10 that matches the output is compared. The output of the stage is selected and added to the OR circuit together with the information transmitted through the backup transmission line, and then the backup transmission line is disconnected to complete the switchback operation. When switching back, the backup transmission line is also used as the current one. Since the transmission paths are also sound, there is no problem even if it takes a little longer to cut back after the information transmitted by both transmission lines matches the bit correspondence. The effect of preventing bit loss is very large and can be applied to PCM transmission lines.

Note that if the transmission delay time of the backup transmission path is longer than the transmission delay time of the current transmission path, it is sufficient to provide a delay circuit for the backup transmission path in advance. In addition, when the error rate of the current transmission path deteriorates and a switch is made to the backup transmission path, the switching is done quickly as before, and in this case, bit loss due to the difference in transmission delay time has already been detected as an error in the current transmission path. This is not a problem as there are many of them.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a transmission system using active and backup transmission lines, and FIG. 2 is a block diagram of main parts of an embodiment of the present invention. 1 is a transmitter, 2a and 2b are repeaters, 3 is a receiver, 10 is a shift register, 11 is a signal selector,
12 is a comparator, 13 and 14 are switches, and 15 is an OR circuit.

Claims (1)

[Claims] 1 Monitor the error rate of the currently used transmission line, and when the error rate exceeds a threshold value, switch to a backup transmission route, and after switching to the backup transmission route, when the error rate of the currently used transmission route becomes equal to or less than the threshold value. , in the transmission line cutback method for switching back to the working transmission line, the output of each stage of a shift register which adds the information transmitted by the backup transmission line and the information transmitted by the working transmission line; and selecting the output of the shift register of the stage that matches the comparison and outputting the information transmitted by the spare transmission line via an OR circuit, and then disconnecting the spare transmission line. A transmission line switching method characterized by: