JPH07321810A - Route switching system - Google Patents

Abstract

PURPOSE:To provide a route switching system with high reliability by enabling the normalcy of reception information to be confirmed after a route is switched. CONSTITUTION:A transmission side switching part 2 inserts a cell for switching to the end of the cell to be sent on a route 5 for system in use by a cell insertion part 31 for switching of system in use when the route is switched by the transmission switching part 2, and also, inserts the cell for switching to the leading position of the cell to be sent on a route 6 for spare system by a cell insertion part 32 for switching of spare system. While, a reception side switching part 3 attaches the same number of sequence numbers by a sequence number attaching part 35 for system in use and a sequence number attaching part 36 for spare system setting the cell for switching as a mark, and the loss of the cell or the inversion of order of the cell can be detected by detecting the normalcy of the number by a sequence number detecting part 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a route switching system, and more particularly to an ATM (Asynchronous Transfer)
The present invention relates to a route switching system suitable for application to a non-interruptible transmission line and a path switching system for the purpose of improving network quality in maintenance and operation of a switching network such as an er mode network.

[0002]

2. Description of the Related Art In the operation of a communication network such as an ATM network, switching back of a path or transmission line after recovery of a fault notification,
Various switching such as accommodation replacement of transmission lines and paths is required. In order to operate the communication network efficiently and improve the service, it is desirable that such path switching can be performed without interruption. As a conventional hitless path switching method for an ATM network, for example, Hideo Tatsuno, Nobuyuki Tokura, "Examination of a hitless path switching method in an ATM transmission network", IEICE technical report, CS90-4
7 are listed.

In this non-instantaneous-interruption path switching system, after switching to the standby system on the transmitting side, a switching cell indicating the end of the information sequence is added to the active system and the switching cell is detected on the receiving side. A path switching method is disclosed which avoids cell order inversion at the time of path switching by reading a cell from the standby system that has arrived at the receiving side earlier than the active system after detecting the switching cell from the delay circuit.

[0004]

However, such a conventional route switching system intended for non-disruptive operation has a malfunction of the switching function (when the standby system has a smaller transmission line delay than the active system, Reliability of received information after switching is not provided because there is no detection means for cell loss after switching due to delay addition in the delay circuit not being performed properly, or inversion of order, etc. There may be some inconvenience.

An object of the present invention is to solve the above drawbacks of the prior art and to provide a highly reliable route switching system by making it possible to confirm the normality of received information after switching the route. And

[0006]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention performs switching between a working route and a protection route by a route switching request at a transmitting side switching unit and a receiving side located at both ends of these routes. In the route switching method performed by the operation of the side switching unit, the transmission side switching unit switches the route of the received signal when the route switching request is generated from the working route to the standby route and sends the signal. There is provided a switching cell inserting means for inserting the switching cell, which indicates the switching timing when the switching is performed, at the end of the signal sent to the working path and at the beginning of the signal sent to the protection path. Further, the receiving side switching unit, the switching cell detection means for detecting the switching cell inserted by the switching cell insertion means, and when the path switching request occurs, the switching cell detection means detects the switching cell of the active system. Until detected, the active system sequence number assigning means for assigning a sequence number to the signal from the active path, and the switching cell detecting means for detecting the switching cell of the standby system, the subsequent standby path A sequence number assigning means for assigning a sequence number to the signal from, and a delay means for absorbing the delay difference when the signal from the standby path arrives earlier than the signal from the active path, and the delay means. After absorbing the delay difference between the active route and the standby route by means of the route switching means for switching the system and the sequence number assigned to the active signal and the standby signal And a monitoring means for monitoring the normality of the signals after switched by sequence number.

Further, according to the present invention, a path switching system for switching between the active path and the standby path by the operation of the transmitting side switching section and the receiving side switching section located at both ends of these paths in response to a path switching request. In the transmission side switching unit, the transmission side switching unit switches a route switching means for switching the signal received from the active route to the standby route when the route switching request is generated, and a switching timing when switching the route by the switching unit. The switching cell inserting means for inserting the switching cell shown in the drawing at the end of the signal sent from the working path is provided.
Further, the receiving side switching unit is a switching cell detecting means for detecting a switching cell from the active system path inserted by the switching cell inserting means, and a standby system cell for detecting a signal sent from the standby system path. When a path switching request is generated by the detecting means, an active system sequence number assigning means for assigning a sequence number to a signal from the active system until the switching cell detecting means detects the switching cell of the active system, and a backup. When the system cell detecting means detects the signal sent from the standby system path, the standby system sequence number assigning means for assigning a sequence number to this signal and the signal from the standby system path are faster than the signal from the active system path. When arriving, the delay means for absorbing the delay difference, and the path switching means for performing the system switching after absorbing the delay difference between the active route and the standby route by the delay means , And a monitoring means for monitoring the normality of the signals after switched by the active system signals on the assigned sequence number and a standby system sequence number assigned to the signal of the.

[0008]

According to the present invention, when a route switching request is issued,
The route switching means of the transmitting side switching unit switches the received signal from the active route to the standby route and sends it out.
The switching cell insertion means inserts the switching cell, which indicates the switching timing, at the end of the signal sent from the working path and at the beginning of the signal sent from the protection path. On the other hand, when a path switching request is generated in the receiving side switching unit, the active system sequence number assigning means starts assigning a sequence number to the signal from the active system. Also,
When the switching cell detecting unit detects the switching cell of the standby system, the standby system sequence number assigning unit assigns a sequence number to the signal from the standby system that follows. The signal from the spare system is absorbed by the delay means for the delay difference between the working system path and the spare system path, and then the system is switched by the path switching means on the receiving side and sent to the monitoring means. The monitoring means determines the normality of the signal after switching based on the sequence number given to the signal of the current system and the sequence number given to the signal of the standby system.

Further, according to the present invention, when a route switching request is generated, the switching means of the transmitting side switching section switches the received signal from the working route to the standby route and sends it out. The cell inserting means inserts a switching cell indicating the switching timing at the end of the signal sent from the working path. On the other hand, in the receiving side switching unit, when a path switching request is generated, the active system sequence number assigning means
Start assigning a sequence number to the signal from the active system.
When the signal from the standby system is detected, the standby system sequence number assigning means assigns a sequence number to the signal from the standby system. The signal from the spare system is absorbed by the delay means for the delay difference between the working system path and the spare system path, and then the system is switched by the receiving side path switching means and sent to the monitoring means. The monitoring means determines the normality of the signal after switching based on the sequence number given to the signal of the current system and the sequence number given to the signal of the standby system.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a path switching system according to the present invention applied to a non-interruptible transmission line and path switching will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a first embodiment of a route switching system according to the present invention, and FIG. 2 shows an arrangement of a switching unit in a network.

In FIG. 2, the transmitting side switching unit 2 is provided in the transmitting side node accommodating the transmitting terminal 1, while the receiving side switching unit 3 is provided in the receiving side node accommodating the receiving side terminal 4. Is provided. The transmission side switching unit 2 and the reception side switching unit 3 are connected by an active system route 5 and a standby system route 6. Thus, in the case of the active route 5, the nodes 5a, 5b, ... 5m are passed, and in the case of the standby route 6, the nodes 6a, 6b ,. The received signal is received by the receiving terminal 4 via the transmitting side switching unit 2 and the receiving side switching unit 3.

As shown in FIG. 1, the transmission side switching unit 2 provided at such a position on the network has a path switching switch (SW) 30, an active system switching cell insertion unit 31, and a standby system switching cell. An insertion portion 32 is provided. Further, the receiving side switching unit 3 includes an active system switching cell detection unit 33, a standby system switching cell detection unit 34, an active system sequence number assigning unit 35, a standby system sequence number assigning unit 36, and a delay circuit 3.
7, a path changeover switch (SW) 38, and a sequence number detector 39.

The transmission end 20 is an input end for inputting a signal from the transmission terminal 1, and is connected to the route changeover switch 30 via the transmission line 21. The route changeover switch 30 is a switch for changing over the route from the active system to the standby system when, for example, a route management center (not shown) instructs a route switching (route switching request). The route switching request is also notified to the receiving side switching unit 3.

The path changeover switch 30 is connected to the active system changeover cell inserting section 31 and the standby system changeover cell inserting section 32 via the transmission lines 22 and 23, respectively. The active system switching cell insertion unit 31 inserts the switching cell at the end of the active system cell flow, and the standby system switching cell insertion unit 32 inserts the switching cell at the beginning of the standby system cell flow. These switching cell insertion parts 3
Reference numerals 1 and 32 respectively send the input signal, that is, the cell to the active system path 5 and the backup system path 6, and the switching process in the transmission side switching unit 2 ends.

In the receiving side switching unit 3, the active system route 5 and the backup system route 6 respectively correspond to the cell detecting unit 33,
It is connected to 34. Active system switching cell detection unit 33
When the cell provided via the active path 5 is other than the switching cell, the cell is allowed to pass through and is provided to the active sequence number assigning section 35 via the transmission path 51. on the other hand,
When the cell provided through the active path 5 is a switching cell, the detection operation is performed, and when the switching cell does not arrive at the standby system switching cell detection unit 34, the reading timing is read to the delay circuit 37. Notify the information of.

The standby system switching cell detection unit 34 detects the switching cell provided via the standby system path 6,
After the detection, the standby system sequence number assigning unit 36 is notified of the start of sequence number assignment. When the standby system switching cell detector 34 receives a cell from the standby system path 6 when the switching cell has not arrived at the active system switching cell detector 33, the cell holding timing is delayed by the delay circuit 37.
To notify. Then, the standby system switching cell detection unit 34
If the cell provided via the backup system path 6 is other than the switching cell, the cell is passed through as it is and provided to the backup system sequence number assigning unit 36 via the transmission path 52. When a cell is input from the standby system switching cell detection unit 34, the standby system sequence number assigning unit 36 receives the active system sequence number assigning unit 3
Give these cells the same number of sequence numbers as given in 5.

After receiving the route switching request from the route management center (not shown), the active system sequence number assigning unit 35 assigns the sequence number to the cell given through the transmission line 51 and detects the switching cell. Based on the detection information from the unit 33, the sequence number assignment is stopped.

Based on the notification from the switching cell detection unit 34, the backup system sequence number assignment unit 36 assigns the working system sequence number assignment unit 3 to the cell given via the transmission path 52.
Assign the same number of sequence numbers as given in 5. The cell transmitted from the active sequence number assigning unit 35 is input to the path changeover switch 38 via the transmission line 53. The sequence number may be assigned to the cell by using the extension bit of the cell in the device, for example.

The delay circuit section 37 includes a switching cell detection section 3
Based on the information notified from 3, 34, the built-in delay unit is made to function to delay the input cell.
The cell transmitted from the delay circuit 37 is input to the path changeover switch 38 via the transmission line 55. The delay circuit 3
In No. 7, when all the cells from the active system path 5 are sent to the path changeover switch 38 and the cells from the standby system path 6 that have undergone the delay process have been sent to the path changeover switch 38, the delay unit is disconnected and the delay process ends. .

The path changeover switch 38 is a cell given from the sequence number giving section 35 via the transmission path 53,
Alternatively, switching is performed to send the cells given from the delay circuit unit 37 via the transmission line 55 to the same transmission line,
It is sent to the transmission line 56.

The sequence number detecting section 39 confirms the normality of the sequence number given by the sequence number assigning sections 33 and 34, and when an abnormality is detected, issues an alarm or the like and collects the details of the abnormality. The cell sent from the sequence number detecting unit 39, in which no abnormality is detected, is sent to the transmission path 57 connected to the receiving end 60 and sent to the receiving terminal 4 (FIG. 2) connected to the receiving end 60. To be

FIG. 3 and FIG. 4 are flowcharts showing the outline of the switching confirmation processing of the first embodiment. A series of processing flows are shown in FIGS. 3 and 4.

First, a path is switched on the transmitting side, a switching cell is inserted at the end of the active system information sequence and at the beginning of the standby system information sequence, and after generation of a switching request, the receiving side sequence number is set to the active system cell. Is given (steps 200 to 202).

When the receiving side receives the working switching cell earlier than the standby switching cell (step 20)
In (3), after detecting a spare cell for switching, a sequence number is given to the subsequent spare cells (step 2).
05, 207).

On the receiving side, when the standby system switching cell is received earlier than the active system switching cell (step 20).
In 4), a sequence number is assigned to the spare cell and the spare cell is held in the delay circuit section (step 20).
6, 208).

When the switching cell detection unit 33 detects the active switching cell, the delay circuit unit 37 starts reading out the cells, and when the delay circuit 37 has no cells, the delay unit of the delay circuit 37. (Steps 209-21)
2).

The sequence number assigned to the cells in the sequence number assigning units 35 and 36 is detected in the sequence number detecting unit 39, and after confirming the normality of the cell flow, if an abnormality is detected, an alarm is issued if necessary. Etc. and collects information such as the number of lost cells (step 21).
3-215).

FIGS. 5A1 to 5A3 show the receiving side switching unit 3 when the transmission delay time is longer in the backup path 6.
FIG. 3 is an explanatory diagram showing an input cell flow and an output cell flow of FIG.

In this case, the switching cells SC0 and SC1 inserted from the transmission side switching unit 2 to the end of the cell flow of the active path 5 and the head of the cell flow of the standby path 6 are (A1) and (A2). As shown in FIG. 5, the one from the working path 5 arrives first at the receiving side switching unit 3, and then the one from the backup path 6 also arrives after a delay of the transmission delay difference. After the path switching request is generated, the sequence number given to the active cell ends counting when the switching cell SC0 arrives, and becomes the active cell for the subsequent standby cells from the time when the switching cell SC1 arrives. The same number of sequence numbers as those given are given. A sequence number is assigned to each of the cell streams output from the path switching switch 38 as shown in (A3) (here, sequence number 1
~ 5 examples are shown). Therefore, the normality of the cell flow can be confirmed by monitoring the sequence number assigned to the cell in the sequence number detection unit 39.

6 (B1) to (B5) and FIG. 7 (B)
6) to (B8) are explanatory diagrams showing the input cell flow and the output cell flow of the reception side switching unit 3 when the transmission delay time is longer in the active path 5.

In this case, the switching cells SC0 and SC1 inserted from the transmission side switching unit 2 to the end of the cell flow of the active path 5 and the head of the cell flow of the standby path 6 are (B1) and (B2). As shown in FIG. 5, the receiving side switching unit 3 first arrives from the backup system route 6, and then also arrives from the working system route 5 with a delay of the transmission delay difference. After the switching request is generated, the sequence number assigned to the active cell is stopped when the switching cell SC0 arrives, and is assigned to the active cell in the spare cells from the time when the switching cell SC1 arrives. The same number of sequence numbers as those that have been added are added.

In this case, since the delay of the working path 5 is larger than the delay of the protection path 6, cells arrive overlappingly as shown in (B1) and (B2). If a cell is sent from the route changeover switch 38 as it is, cell order inversion or the like occurs, so that the changeover cell SC1 is changed to the changeover cell S.
If the receiving side switching unit 3 arrives before the C0, the delay circuit unit 37 waits until the switching cell SC0 arrives in the spare cell.
Delay. The cell flow output from the path switching switch 38 is given a sequence number as shown in (B3) (in this case, sequence numbers 1 to 5).
Is shown as an example). Therefore, the normality of the cell flow can be confirmed by monitoring the sequence number assigned to the cell in the sequence number detection unit 39.

In the example of FIG. 6, by adjusting the transmission delay difference between the active system and the standby system by the delay circuit 37, (B
3) and (B4), when the delay adjustment is normally performed, the cell order after switching is normal as shown in (B5) (sequence number: 123451).
2345). However, (B6) and (B
As shown in 7), when the delay adjustment is not normally performed, the cells arrive at the path changeover switch 38 in duplicate such as C4, C6, C5, and C7 of the cells of the active system and the standby system. Assuming that the reading order from the path changeover switch is C4, C6, C5, and C7, the sequence number is 123421345, and the sequence number detecting unit 39 can detect the reversal of the cell order of C6 and C5.

If the path changeover switch unit 38 does not normally change the cell destination, cell misdistribution or loss occurs. In the example of (D1) of FIG. 7, the sequence number is 12352345, and the sequence number detecting unit 39 can detect the loss of C6.

Next, a second embodiment of the route switching system according to the present invention will be described in detail with reference to the drawings. Here, FIG. 8 is a block diagram showing the configuration of the second embodiment.

In the above-mentioned first embodiment, the switching cell is sent to the working system and the protection system, but in the second embodiment, the switching cell is inserted only in the working system and the protection system is used. Is an attempt to realize the method by detecting the head of the arriving cell and using it as a timing for switching and assigning a sequence number.

In FIG. 8, the transmission side switching unit 7 is composed of a path switching switch (SW) 42 and a switching cell insertion unit 41. The transmission end 20 is connected to a path changeover switch 42 via a transmission line 21. The path changeover switch 42 is used, for example, when the path management center (not shown) has not instructed to change the path.
When the path management center gives an instruction to switch the path, the switching cell inserted from the switching cell inserting unit 41 via the transmission path 22 (the active system (Representing the cell at the timing next to the last cell sent to the path 5) is sent to the active path 5 and the cell flow from the sending end 20 is sent to the backup path 6.

The receiving side switching unit 8 includes the switching cell detection unit 4
3, a standby system cell detection unit 44, an active system sequence number assignment unit 45, a standby system sequence number assignment unit 46, a delay circuit 47, a changeover switch 48, and a sequence number detection unit 49.

In the receiving side switching unit 6, the active route 5 is connected to the switching cell detecting unit 43 for detecting the active switching cell transmitted from the transmitting side switching unit 5, and the standby route 6 is connected.
Is connected to a spare cell detection unit 44 that detects the arrival of cells switched to the spare path 6. The switching cell detection unit 43 is a detection unit that detects the switching cell sent from the active path 5, and is connected to the active sequence number assigning section 45 via the transmission path 51. The active system sequence number assigning unit 45 assigns the sequence number of the active cell after the path switching request is generated, and stops assigning the sequence number according to the switching cell detection information from the switching cell detection unit 43.

The backup system cell detection unit 44 is a detection unit for detecting a cell from the backup system route 6, and when a cell is detected, arrival information is received by the backup system sequence number assigning unit 46 connected via the transmission line 46. To send. When the standby system sequence number assigning unit 46 receives the arrival information of the standby system cell from the standby system cell detecting unit 44, it starts assigning the sequence number to the standby system cell. The standby system sequence number assigning unit 46 is connected via a transmission line 54 to a delay circuit 47 that adjusts the delay relationship between the active and standby cell flows based on the switching cell arrival information and the standby cell arrival information.

The active system sequence number assigning section 45 and the delay circuit 47 are connected to a path changeover switch 48 for changing over the paths via transmission lines 53 and 55, respectively. The path changeover switch 48 is connected via a transmission line 56 to a sequence number detecting section 49 which confirms the normality of the cell flow by detecting the sequence number of the cell given by the sequence number giving section.

FIG. 9 and FIG. 10 are flow charts showing the outline of the switching confirmation processing of the second embodiment, and these drawings show a series of processing flows.

First, on the transmission side, the path changeover switch 4
In step 2, the active system route is switched to the standby system route, and the switching cell insertion unit 41 inserts the switching cell at the end of the active system flow (steps 300 and 301).

After the switching request is generated, the active system sequence number assigning section 45 assigns a sequence number to the active cell (step 302).

On the receiving side, when the head cell of the spare system arrives at the spare cell detector 44 before the switch cell detector 43 detects the switch cell, the spare sequence number assigner 46 makes a sequence number. Is started, and the cells from the standby system path 6 are held in the delay circuit 47. After that, when the switching cell detection unit 43 detects a switching cell, the changeover switch 48 switches the path from the active system to the standby system. Further, when the switching cell detection unit 43 first detects the switching cell, the delay circuit 47 does not delay the cell from the standby system path 6, and the changeover switch 48 switches from the active system to the standby system. The path is switched (steps 303 to 305).

If cells remain in the delay circuit 47,
The delay circuit 47 is separated when the cell reading is completed, and if there is no cell left in the delay circuit 47, it is separated as it is (steps 306 to 309).

In the sequence number detecting section 49, the sequence number of the receiving cell is inspected, and if an abnormality is detected, an alarm or the like is issued if necessary (step 3).
10-312).

The second embodiment is different from the first embodiment in the method of detecting the switching timing as described above, but the confirmation of the normality of the cell on the receiving side is the same as in FIGS. The description of the overlapping cell flow is omitted. Therefore, also in the second embodiment, the normality of the cell flow after switching can be confirmed as in the first embodiment.

[0050]

As described above, according to the route switching system of the present invention, when the route is switched from the active system to the standby system,
When a cell loss or cell order inversion occurs, this can be detected, so that an error in the received information after switching can be detected, and the reliability and the like are higher than in the prior art. Therefore, by applying the present invention to an uninterruptible transmission line or path switching for the purpose of improving network quality related to network maintenance and operation, it is possible to form a highly reliable network.

[Brief description of drawings]

FIG. 1 is a block diagram showing a first embodiment of a route switching system according to the present invention.

FIG. 2 is a network layout to which an embodiment of a route switching system according to the present invention is applied.

FIG. 3 is a process flow of path switching in the first embodiment shown in FIG.

FIG. 4 is a process flow of path switching in the first embodiment shown in FIG.

FIG. 5 is an operation explanatory diagram showing an input cell flow and an output cell flow in the present embodiment.

FIG. 6 is an operation explanatory diagram showing an input cell flow and an output cell flow in the present embodiment.

FIG. 7 is an operation explanatory diagram showing an input cell flow and an output cell flow in the present embodiment.

FIG. 8 is a block diagram showing a second embodiment of the route switching system according to the present invention.

9 is a processing flow of path switching in the second embodiment shown in FIG.

FIG. 10 is a process flow of path switching in the second embodiment shown in FIG.

[Explanation of symbols]

 2, 7 Transmission side switching unit 3, 8 Reception side switching unit 30, 38, 42, 48 Path switching switch 31 Working system switching cell insertion unit 32 Spare system switching cell insertion unit 33 Working system switching cell detection unit 34 Spare System switching cell protection unit 35 Working system sequence number assigning unit 36 Backup system sequence number assigning unit 37, 47 Delay circuit 39, 49 Sequence number detecting unit

Claims (4)

[Claims] 1. A route switching method in which a switching between a working route and a protection route is performed by the operation of a transmitting side switching unit and a receiving side switching unit located at both ends of these routes in response to a route switching request. And a route switching unit that switches the signal received when the route switching request is generated from the active route to the standby route and sends the signal, and a switching indicating the switching timing when the route is switched by the switching unit. A cell for switching, which is inserted at the end of the signal to be sent to the working path and at the beginning of the signal to be sent to the standby path, and the receiving-side switching section is for inserting the switching cell. Switching cell detecting means for detecting the switching cell inserted by the means, and when the path switching request is generated, the working cell is detected by the switching cell detecting means. Until the switching cell of the system is detected, the active system sequence number assigning means for assigning a sequence number to the signal from the active path, and the switching cell detection means detects the switching cell of the standby system. Then, a backup system sequence number assigning means for assigning a sequence number to the signal from the backup system path that follows, and when the signal from the backup system path arrives earlier than the signal from the working system path. Is a delay unit that absorbs the delay difference, a path switching unit that switches the system after the delay unit absorbs the delay difference between the active path and the standby path, and a sequence number assigned to the active signal. And a monitoring means for monitoring the normality of the signal after switching based on the sequence number given to the signal of the standby system. 2. The path switching system according to claim 1, wherein the switching cell inserting means inserts a switching cell into a working path and a switching cell into a protection path. And a standby system switching cell insertion unit to be inserted, wherein the switching cell detection means is inserted in the standby system path and a current system switching cell detection unit for detecting the switching cell inserted in the current system route. A route switching method comprising: a standby system switching cell detection unit that detects a switching cell. 3. A route switching method in which a switching between a working route and a standby route is performed by an operation of a transmitting side switching unit and a receiving side switching unit located at both ends of these routes in response to a route switching request. And a switching unit that switches the signal received when the route switching request is generated from the active route to the standby route and sends the signal, and a switching timing indicating the switching timing when the route is switched by the switching unit. And a switching cell inserting means for inserting a working cell at the end of the signal sent from the working path, the receiving side switching section is a switching cell from the working path inserted by the switching cell inserting means. Switching cell detecting means for detecting, a standby cell detecting means for detecting a signal sent from the backup path, and when the path switching request occurs Until the switching cell detecting unit detects the switching cell of the working system, a working system sequence number assigning unit that assigns a sequence number to a signal from the working system, and the standby system cell detecting unit When a signal sent from the system route is detected, a backup system sequence number assigning means for assigning a sequence number to this signal, and when the signal from the backup system route arrives earlier than the signal from the working route Is a delay unit that absorbs the delay difference, a path switching unit that switches the system after the delay unit absorbs the delay difference between the active path and the standby path, and a sequence number assigned to the active signal. And a monitoring means for monitoring the normality of the signal after switching by the sequence number given to the signal of the standby system. Switching system. 4. The route switching system according to claim 1, wherein the switching system is applied to an asynchronous communication network (ATM).