JPH0795213A - System switching device for digital exchange switch - Google Patents

Abstract

PURPOSE:To make it unnecessary to provide a buffer which temporarily stores a cell for system switching. CONSTITUTION:When a system switching request is issued, a search cell inserting part 11 inserts a search cell. A system switching bit control part 12 switches the system switching bits of a cell after the search cell is inserted so as to be processed by a preliminary system. Each present and preliminary system digital exchange switch 20A and 20B sets the cell as a valid cell when the system switching bits are its own system, and cancel the cell when the system switching bits are the other system according to each cell discriminating part 21A and 21B. A switching control part 31 of an output interface part 30 monitors the output of the present system digital exchange switch 20A, judges that the valid cell is not left in the input buffer of the digital exchange switch 20A when the search cell is detected, and instructs the switching from the present system to the preliminary system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system switching device for a digital exchange switch for performing non-instantaneous disconnection system switching of digital exchange switches such as dual ATM switches.

[0002]

2. Description of the Related Art In digital networks such as broadband ISDN, a communication system called ATM (asynchronous transfer mode) has been introduced. This ATM is a communication mode in which the communication information is divided into bit strings (ATM cells) of a short length like packet communication, and the header at the beginning of each bit string is attached with address information indicating its destination and transferred. is there. Further, in such an ATM, a high speed and large capacity ATM cell exchange requires extremely high reliability. In particular, in the case of image communication, the communication quality is very easily affected, so high-speed and high-quality communication is required.

From this point of view, in the ATM communication system, in order to maintain the reliability of information, a dual redundant configuration of the device is adopted. Here, in the redundant redundancy configuration, when a failure occurs in the ATM switching device, two sets of the devices are prepared in advance in order to minimize the influence on the communication service due to the failure, and one device fails. If
This is a mechanism in which the other device continuously provides services. The duplicated devices are generally called 0-system and 1-system, and normally only one of the systems operates.

For example, if a 0-system device is currently in operation and a failure occurs in the 0-system device, it is switched to the 1-system device. On the contrary, if a failure occurs while the 1-system device is operating, it is switched to the 0-system device to continue the communication service. That is, the reliability of communication is ensured. Also,
In order to further improve reliability, work to periodically check the standby system devices that are not in operation for abnormalities is also performed. This is called device diagnosis, and generally the spare system device is diagnosed once a day or once every several days depending on the reliability required for the device.

Similar to the switching operation when a failure occurs, this diagnosis adopts a method of switching the device and confirming whether or not it can be operated normally, but unlike the case when a failure occurs, it is artificially performed. Further, when diagnosing such a device, it is necessary to perform switching so that communication is not affected at all, because switching is not performed due to the occurrence of a failure. Therefore, the system switching for the purpose of diagnosing the device is required to be performed in a time period with a small communication traffic and to be performed without interruption without stopping the communication. Furthermore, system switching must be performed without interruption even when the device is expanded or maintained.

Hereinafter, a configuration for performing device switching without interruption will be described. First, the ATM switching device will be described. An ATM switching device having a duplicated ATM switch has N input ports for inputting cells carrying information and N output ports for outputting cells switched by the ATM switch, and N × Configure N ATM switch. The cell is an ATM switch operating from the input port (active system)
And two ATs that are on standby and an ATM switch (standby system)
Although it is distributed to the M switches, the input system is switched in the active system (for example, 0 system), and the standby system (1
In the system), the input cell is discarded without being replaced.

Outputs of the 0-system and 1-system ATM switches are guided to a selector, and the selector selects an output cell of the system (0-system) in operation. Therefore, A of 0 system
The cells exchanged by the TM switch are selected by the selector and output to the line. The ATM switch is composed of an input buffer type switch. The input buffer type switch is characterized by having a first-in first-out (FIFO) type buffer for accumulating cells on the input port side. When cells having the same exchange destination are input at the same time, only one cell is stored. The selected cells are exchanged and output, and the cells not selected are stored in the input buffer.

The cells sequentially input from the input port are guided to the input buffer to determine whether they can be exchanged,
If it is selected, it is exchanged to the output port, and if it is not selected, it remains in the input buffer as it is and waits for the determination of the next exchange. Therefore, when a large number of cells are input from the N input ports or cells concentrate at the same output port at a certain time, a large number of cells are accumulated in the input buffer.

In such an ATM switching apparatus, when performing system switching for the purpose of diagnosis or maintenance or expansion as described above, in order to prevent loss of cells and maintain cell order, input of an ATM switch during operation is performed. A process to output all cells left in the buffer is required. As means for performing such processing, conventionally, a buffer for temporary storage and a circuit into which a special cell for easy identification can be inserted are prepared for each input port, and the output stage of the ATM switch is Some have provided a circuit capable of sequentially inspecting the exchanged cells and detecting the inserted special cells.

FIG. 2 is a diagram showing the configuration. The device shown in the figure shows a hitless switching configuration of an ATM switch.
Temporary storage buffer memory 1, F cell insertion circuit 2, two ATM switches 3, 4, two F cell detection circuits 5,
6, selector 7, F cell removal / idle cell insertion circuit 8
Consists of.

The temporary storage buffer memory 1 stores the input cells based on the switching instruction of the ATM switch. The F cell insertion circuit 2 is a circuit that inserts an F cell (Filling Cell) as a special identification cell at the end of the cell. The ATM switches 3 and 4 are switches that perform the above-described cell exchange processing, and internally include input buffer memories 3a and 4a for accumulating cells in the exchange processing. F cell detection circuit 5,
6 is the cell output from the ATM switches 3 and 4 and F
This is a circuit for detecting cells, and switches the selector 7 according to the detection signal.

The selector 7 is a selection circuit for selecting the output of the ATM switches 3 and 4, and switches according to the F cell detection signals from the F cell detection circuits 5 and 6. The F cell removal / idle cell insertion circuit 8 is a circuit that removes the F cell from the cell flow selected by the selector 7 and inserts the idle cell into the removed portion.

Next, the operation of such a system switching device will be described. FIG. 3 is a flowchart thereof. First, when the active system is the ATM switch 3 and the standby system is the ATM switch 4, when there is an instruction to switch the ATM switch,
The control unit (not shown) stops sending the input cells to the ATM switches 3 and 4 (step S1), and stores them in the temporary storage buffer memory 1 of the input port (step S2). Further, the F cell is inserted at the end of the cells input to the ATM switches 3 and 4 and sent to the ATM switches 3 and 4 (step S3).

Therefore, after the F cells in the input buffer memory 3a of the ATM switch 3 are exchanged, no cells remain in the ATM switch 3. The F cell detection circuit 5 monitors the output of the ATM switch 3,
When the F cell is output, this is detected (step S4). At this step S4, the ATM switch 3
When all the F cell detection circuits 5 on the output side of 1 detect F cells, it means that no cells remain in the input buffer memory 3a of the operating ATM switch 3.

When the F cell detection circuit 5 detects an F cell in step S4, the control unit (not shown) instructs the selector 7 to switch the selection, and the selector 7
From the ATM switch 3 that has been operating until now, the switching destination A
Select the output port of the TM switch 4 (step S
5).

Thereafter, the transmission of the cells accumulated in the temporary storage buffer memory 1 of the input port while waiting for the switching is started, and the cells are supplied to the switched ATM switch 4 side (step S6). As a result, system switching can be performed without loss or duplication of cells. Further, the F cell removal / idle cell insertion circuit 8 removes the F cell so that the F cell is not mixed in on the line.

[0017]

As described above, in the case of switching the input buffer type ATM switch having the dual structure, in order to realize the non-interruptible switching without affecting the communication information, the input port is required. It is necessary to prepare the buffer memory 1 for temporary storage every time.

However, the temporary storage buffer memory 1 is unnecessary for the original ATM exchange operation. Therefore, this temporary storage buffer memory 1
Since a large amount of hardware is required as the device becomes large in scale, it becomes a factor of increasing the mounting volume of the device and increasing the cost, which has been an obstacle to realizing a large-scale ATM switching device.

The present invention has been made in order to solve the above-mentioned conventional problems, and requires a small amount of hardware and can easily realize a large-scale digital switching device, and a system switching device for a digital switching switch. The purpose is to provide.

[0020]

According to a first aspect of the present invention, there is provided a system switching device for a digital exchange switch, wherein a digital exchange switch for routing a plurality of data cells is duplicated in an active system and a standby system. In a system switching device for a digital exchange switch for switching between and, a system switching bit indicating which system is to be used for processing is provided in each cell, and a system switching request is generated in front of the digital exchange switch. In this case, a search cell insertion unit that inserts a search cell in the flow of each cell at the generation timing, and when a system switching request occurs, the system switching bits of cells after the search cell are switched from the active system to the standby system. It is provided in the system switching bit control unit and each digital exchange switch. If the system switching bit is its own system, the cell is valid. If the system switch bit is another system, and the output from the cell determination unit that invalidates the cell and the active digital exchange switch is the search cell, the active system switches to the standby system. And a switching control unit for switching the system.

A system switching device for a digital exchange switch according to a second aspect of the present invention is a digital exchange switch for duplicating a digital exchange switch for routing a plurality of data cells into an active system and a standby system and switching between the active system and the standby system. In the system switching device, the system switching bit indicating in which cell the processing is performed is provided in each cell, and the system switching bit is provided in front of the digital exchange switch when a system switching request occurs. Is provided in the system switching bit control unit that switches the active system from the standby system to the standby system and the digital exchange switch of each system. If the system switching bit is its own system, that cell is regarded as an effective cell and the system switching bit is If the cell is a system, a valid cell is no longer output from the cell determination unit that invalidates the cell and the active digital switch. In timing, it is characterized in that a switching control unit for system switching from the active system to the standby system.

[0022]

In the system switching device for the digital exchange switch according to the first aspect of the present invention, when the system switching request is generated, the search cell inserting section of the input interface section inserts the search cell.
Further, the system switching bit control unit switches the system switching bits of cells after the search cell is inserted from the value of the active system to the value of the standby system. The active and standby digital exchange switches receive cells from the input interface unit, and each cell determination unit determines whether the cell is a valid cell for routing or a cell to be discarded. In the output interface section, the switching control section monitors the output of the digital exchange switch, and when a search cell is detected in the output from the active system digital exchange switch, the selector is switched to the standby system and the standby system digital exchange is performed. Instruct the switch to start cell routing.

In the system switching device for the digital exchange switch of the second invention, when the system switching request is generated, the system switching bit control unit switches the system switching bits of the subsequent cells from the current system to the standby system value. . The active and standby digital exchange switches receive cells from the input interface unit, and the respective cell determination units determine whether they are valid cells for routing or cells to be discarded. The output interface unit monitors the output of the digital exchange switch by the switching control unit, switches the selector to the standby system when the effective cell is no longer output from the active system digital exchange switch, and Command to start cell routing.

[0024]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the principle configuration of a first embodiment of a system switching device for a digital exchange switch according to the present invention. The illustrated apparatus comprises an input interface section 10, digital exchange switches 20A and 20B, and an output interface section 30.

The input interface section 10 is an input side interface of the digital exchange switches 20A and 20B, and includes a search cell inserting section 11 and a system switching bit control section 12.
Is equipped with. The search cell insertion unit 11 has a function of inserting a search cell (indicated by S cell in the figure) at the timing of generation of a system switching request. The system switching bit control unit 12, when a system switching request is generated,
It has a function of switching the system switching bits (indicated by C in the figure) of cells after the search cell inserted by the search cell inserting section 11 from the value of the active system to the value of the standby system. The system switching bit indicates in which system the cell is processed, and is stored in the header of the cell.

FIG. 4 is a diagram showing the structure of an ATM cell. That is, an ATM cell consists of a switching tag, a cell header and information, and the cell header and information are 53 bytes. The switching tag is used for routing processing in the device and consists of 1 byte of information, 1 bit of which is a system switching bit (C bit).
Is used as. The value of the system switching bit is set so that, for example, when C = 0, the system 0 digital exchange switch becomes a valid cell, and when C = 1, the system 1 digital exchange switch becomes a valid cell.

Digital exchange switches 20A, 20B
Are 0-system and 1-system ATM switches, and are provided with cell determination units 21A and 21B, respectively. Cell determination unit 21
A and 21B perform control so that the cell is set as an effective cell when the system switching bit is the own system and the cell is discarded when the system switching bit is another system. That is, in the 0-system digital exchange switch 20A, it is set such that cells are exchanged with the system switching bit C = 0 and cells are discarded with C = 1.
In B, the cell is set to be discarded when C = 0, and the cell is set to be exchanged when C = 1.

The output interface section 30 is an output side interface of the digital exchange switches 20A and 20B and has a switching control section 31. Switching control unit 31
Is the active digital exchange switch 20A (or 2
If the valid cell is a search cell from 0B), the digital exchange switch 20A (or 20
It has a function of switching the system of B).

Next, the operation of the system switching device of the digital exchange switch thus configured will be described. When a system switching request from the 0-system to the 1-system occurs after the cell A passes through the input interface unit 10, in the input interface unit 10, the search cell insertion unit 11 immediately inserts the search cell (S cell). Further, the system switching bit control unit 12
Is the value of the system switching bit of the cell (cell B) that arrives after the insertion of the search cell is C = 1 (In the initial state, the 0 system (C = 0) is selected as the active system).

In the system 0 digital exchange switch 20A, the system switching bit of the cell is set to C = 0 for switching and C = 1 for discarding. Therefore, the cell A and the search cell are valid cells and are not shown. It is accumulated in the input buffer and is subjected to routing processing, and cell B is discarded. As a result, there is no cell stored in the input buffer of the digital exchange switch 20A and subjected to the routing process after the search cell.

On the other hand, the system 1 digital exchange switch 20
In B, the system switching bit of the cell is set to C = 1 for exchange and C = 0 for discard, so that cell A and the search cell are discarded and cell B becomes a valid cell. Therefore, the cell input to the input interface unit 10 after the search cell is inserted is stored in the input buffer of the digital exchange switch 20B.

The output interface unit 30 monitors the cells output from the digital exchange switches 20A and 20B, and detects the search cell from the output of the 0-system digital exchange switch 20A to detect the digital exchange switch 20A. After determining that there is no cell accumulated in the input buffer and discarding the search cell, the switching control unit 31 switches the selector (not shown) from the 0 system to the 1 system, and the 1 system digital exchange switch 20B.
A control signal for starting cell routing is sent to the. As a result, the 1-system digital exchange switch 20B starts cell routing immediately after receiving the control signal.

FIG. 5 is a flowchart of the above operation. That is, when a system switching request is generated, first, it is investigated whether or not valid cells are accumulated in the input buffer in the active system digital exchange switch 20A (or 20B) (step S1). In this embodiment, this check is determined by the presence or absence of detection of a search cell. In addition, the cells input during the investigation in step S1 are stored in the input buffer of the digital switching switch 20B (or 20) in the standby system (step S2). That is, the cells after the search cell are stored in the spare digital exchange switch 20B (or 20).

Next, the active digital exchange switch 2
It is confirmed that valid cells are not accumulated in the input buffer in 0A (or 20B) (step S3). That is, the active digital exchange switch 20A (or 2
When a search cell is detected from the output of 0B), it is confirmed that valid cells are not accumulated. After that, the outputs of the digital exchange switches 20A and 20B are switched to the standby system, and the standby system digital exchange switch 20B (or 20) is operated (step S4).

Next, a specific structure of the first embodiment will be described. FIG. 6 is a block diagram thereof. The device shown is
0-system and 1-system input interface units 10A and 1 respectively
0B, digital exchange switches 20A and 20B, and output interface units 30A and 30B.

Input interface units 10A and 10B
Are search cell insertion units 11A-1 to 11A-n, respectively.
And 11B-1 to 11B-n, and system switching bit control units 12A-1 to 12A-n and 12B-1 to 12B-n.
And have. In addition, these search cell insertion units 11
A-1 to 11A-n, 11B-1 to 11B-n and system switching bit control units 12A-1 to 12A-n and 12B-1
12B-n have the same configurations and operations as the search cell insertion unit 11 and the system switching bit control unit 12 in FIG. 1, and therefore description thereof will be omitted here.

Digital exchange switches 20A and 20
B corresponds to each of the n ports and the cell determination unit 2
1A-1 to 21A-n and 21B-1 to 21B-n,
Selectors 22A-1 to 22A-n and 22B-1 to 22
2B-n, input buffers 23A-1 to 23A-n and 23B-1 to 23B-n, and switch units 24A and 2
4B and.

The cell determination units 21A-1 to 21A-n and 21B-1 to 21B-n are the cell determination units 2 in FIG.
The configuration is the same as that of 1A and 21B, and it is determined based on the system switching bit of an input cell whether the cell is a valid cell or is discarded. Also, the selector 22
A-1 to 22A-n and 22B-1 to 22B-n are
0-system or 1-system input interface unit 10A, 10B
One of these outputs is selected. Furthermore,
Input buffers 23A-1 to 23A-n and 23B-1
23B-n are buffer memories for accumulating cells corresponding to n input ports. The switch units 24A and 24B are cell switching units that perform cell routing.

The output interface units 30A and 30B are
Switching control units 31A-1 to 31A corresponding to the n output ports of the digital exchange switches 20A and 20B, respectively.
It has A-n and 31B-1 to 31B-n. Also,
These switching control units 31A-1 to 31A-n, 31B-1
31B-n, the switching control units 31A and 31 of FIG.
The same as B.

Next, the operation will be described. FIG. 7 is a flowchart of system switching. ATM switch is now 0
It is assumed that the system is operating. Therefore, the system switching bit control units 12A-1 to 12A-n set the value of the system switching bit of the cell as C = 0. Further, the selectors 22A-1 to 22A-n of the digital exchange switches 20A and 20B,
22B-1 to 22B-n select the output of the 0-system input interface unit 10A. Further, the selector of the output interface unit 30A is also the digital exchange switch 20.
It is set to select the output of A.

When a system switching request is generated in such an operating state, the search cell insertion units 11A-1 to 11A-n are
A search cell is inserted (step S1). The destinations of the search cells to be inserted are set corresponding to # 0 to #n on the output side. Also, the system switching bit control unit 1
2A-1 to 12A-n set the value of the system switching bit of the effective cell input after inserting the search cell to C = 1 (step S2).

In the digital exchange switches 20A and 20B, the cell determination units 21A-1 to 21A-n and 21B-.
The cells to which 1 to 21B-n are input are determined, and the cell determination units 21A-1 to 21A-n determine that the system switching bit of the cell passes at C = 0 and is discarded at C = 1. In the cell determination units 21B-1 to 21B-n, the cell is passed at C = 1,
When C = 0, it is determined that the card is discarded (step S3).
After that, normal cell routing is performed, and the corresponding destination cell is output from each output port of the digital switching switches 20A and 20B.

In the output interface unit 30A, the switching control units 31A-1 to 31A-n allow the cells input from the digital exchange switch 20A to pass through as they are, and all the switching control units 31A-1 to 31A-n. , The search cell is monitored (step S4). When the search cells are detected by all the switching control units 31A-1 to 31A-n, the search cells are discarded and the selector (not shown) is switched to the 1-system (step S5), and the 1-system digital exchange switch 20B. A control signal is sent to operate (step S6). As a result, the digital exchange switch 20B starts operating, and the operation is continued in the input interface unit 10B, the digital exchange switch 20B, and the output interface unit 30B of the 1-system.

Next, a second embodiment capable of reducing the amount of hardware as compared with the first embodiment will be described. In the first embodiment, the search cell insertion units 11A-1 to 11A-n are
The destination of the search cell is set to the relationship of the input port number = the output port number, for example, the destination of the search cell from # 0 is the output port of # 0, but in the second embodiment, it is set from all the input ports. A search cell is inserted to a specific output port.

That is, the output interface units 30A, 30
B switching control units 31A-1 to 31A-n, 31B-1 to
31B-n has only one switching control unit having a search cell detection function, and the search cell insertion unit 11B
A-1 to 11A-n and 11B-1 to 11B-n use the switching control unit as the destination of all the search cells to be inserted.

For example, the search cell insertion units 1 of # 0 to #n
The destinations of the search cells to be inserted in 1A-1 to 11A-n are all addressed to the switching control unit 31A-1 of # 0. Also,
In the digital exchange switches 20A and 20B, similarly to the above-described embodiment, it is determined whether the cell is a valid cell or abandoned based on the cell switching bit of the cell. Then, the switching control unit 31A-1 of the output interface unit 30A detects the search cells and counts the number of the search cells. When n search cells are detected, the digital exchange switch 20
All input buffers 23A-1 to 23A-n in A
It is determined that there are no valid cells left, and a control signal for system switching is sent.

Next, a third embodiment will be described in which system switching is performed without using a search cell. That is, this third embodiment is
In the case of the configuration of the apparatus shown in FIG. 1, the input interface unit 10 does not have the search cell insertion unit 11, but has only the system switching bit control unit 12. Then, when a system switching request is generated, the system switching bit control unit 12 switches the values of the system switching bits of the cells thereafter, as in the first and second embodiments, and the digital switching switches 20A, 2A and 2B.
0B determines whether the cell is valid or discarded according to the value of the system switching bit.

Further, in the output interface section 30, the switching control section 31 has a valid cell identifying function. Then, the output from the active digital exchange switch 20A is monitored, and when valid cells are no longer output from all ports (when invalid cells such as idle cells are detected from all ports), the digital exchange switch 20A is operated. It is determined that valid cells are not stored in the input buffer, the selector is switched to the 1-system, and a control signal is sent to the 1-system digital exchange switch 20B to start the routing. Incidentally, the 1-system digital exchange switch 20B
Is set so that the cells are accumulated in the input buffer and the routing is not performed until the switching control unit 31 of the output interface unit 30 gives an instruction to start the routing.

As described above, in the third embodiment, a circuit for inserting and detecting a search cell is unnecessary, so that the amount of hardware can be further reduced as compared with the first and second embodiments.

In each of the above-mentioned embodiments, the system switching of the ATM switching device has been described, but the device can be similarly applied to other data switching as long as it is a device for routing data blocks such as packet switching.

[0051]

As described above, according to the system switching device of the digital exchange switch of the first invention, in each cell,
A system switch bit indicating which system should be used is provided, and when a system switch request occurs, a search cell is inserted at the timing of the request, and the system switch bits of subsequent cells are transferred from the active system to the standby system. Switching is performed so that when a search cell is output from the digital switching switch of the active system, the system is switched from the active system to the standby system, thus eliminating the need for a temporary storage buffer for conventional system switching. hand,
The amount of hardware can be reduced, and a large-scale digital switching device can be realized.

Further, according to the system switching device for the digital exchange switch of the second invention, as in the first invention, a system switching bit indicating which system performs processing is provided in each cell, and a system switching request is issued. If it occurs, the system switching bit of the subsequent cells is switched from the active system to the standby system, and the system is switched from the active system to the standby system when valid cells are no longer output from the active system digital exchange switch. As a result, in addition to the effect of the first aspect of the invention, the amount of hardware can be further reduced.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a principle configuration of a system switching device for a digital exchange switch of the present invention.

FIG. 2 is a block diagram showing a system switching configuration of a conventional digital exchange switch.

FIG. 3 is a flowchart of a system switching operation of a conventional digital exchange switch.

FIG. 4 AT in the digital exchange switch of the present invention
It is a block diagram of M cell.

FIG. 5 is a flowchart of a system switching operation in the system switching device for the digital exchange switch of the present invention.

FIG. 6 is a block diagram showing a specific example of a system switching device for a digital exchange switch of the present invention.

FIG. 7 is a flowchart of a system switching operation in a specific example of the system switching device for a digital exchange switch of the present invention.

[Explanation of symbols]

 11 search cell insertion unit 12 system switching bit control unit 20A, 20B digital exchange switch 21A, 21B cell determination unit 31 switching control unit

Claims (2)

[Claims] 1. A system switching device of a digital switching switch for duplicating a digital switching switch for routing a plurality of data cells into an active system and a standby system, and switching between the active system and the standby system. A system switch bit indicating which system is to be used is provided, and a search cell is provided in the preceding stage of the digital exchange switch, and when a system switch request occurs, a search cell is inserted in the flow of each cell at the generation timing. A search cell insertion unit, a system switching bit control unit that switches the system switching bits of cells after the search cell from the active system to the standby system when a system switching request is generated, and provided in each digital exchange switch, If the system switching bit is the own system, the cell is regarded as a valid cell,
If the system switch bit is another system, the cell determination unit that invalidates the cell concerned, and if the output from the active digital exchange switch is the search cell, the system switch from the active system to the standby system is performed. A system switching device for a digital exchange switch, comprising: 2. A system switching device of a digital exchange switch for duplicating a digital exchange switch for routing a plurality of data cells into an active system and a standby system, and switching between the active system and the standby system. A system switching bit indicating which system is to be used is provided, and the system switching bit is provided in the preceding stage of the digital exchange switch and switches the system switching bit from the active system to the standby system when a system switching request occurs. It is provided in the control unit and the digital exchange switch of each system, and if the system switching bit is its own system, that cell is a valid cell, and if the system switching bit is another system, that cell is invalid. The cell switching unit from the active system to the standby system is switched at the timing when no valid cell is output from the cell determining unit and the active system digital exchange switch. System switching apparatus in a digital exchange switch, characterized in that a Cormorant switching control unit.