JP2999087B2 - Path switching method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a path switching system, and more particularly, to a path switching system suitable for application to an instantaneous uninterrupted path switching system for improving network quality during maintenance operation of an ATM (Asynchronous Transfer Mode) network. Things.

[0002]

2. Description of the Related Art In the operation of a communication network such as an ATM network, it is necessary to perform various path switching such as switching back of a path or a transmission path after restoration from a failure or switching accommodation of a transmission path or a path.
In order to operate the communication network efficiently and to improve the service, it is desirable that such path switching can be executed without interruption. 2. Description of the Related Art Conventionally, a non-instantaneous path switching method for an ATM network described in the following document has already been proposed.

References: "Hideo Takino and Nobuyuki Tokura, ATM"
Study of Non-interruptible Path Switching Method in Transmission Network ", IEICE Technical Report, CS90-47" Hereinafter, a conventional non-interruptible path switching method described in this document will be described. Here, FIG. 2 is a block diagram showing a configuration of a conventional technique, and FIG. 3 shows an arrangement of a switching unit in a network.

[0004] In FIG. 3, a transmission-side switching unit 2 is provided in a transmission-side node accommodating a transmission-side terminal 1.
The receiving-side switching unit 4 is provided in the receiving-side node that accommodates the receiving-side terminal 3, and a plurality of nodes 5a, 5b,...
6n are connected by a working path 5 and a protection path 6 which pass through 6n.

As shown in FIG. 2, the transmission-side switching unit 2 provided at such a position on the network includes a path switching switch 11 and a switching cell insertion unit 12, and the reception-side switching unit 4 As shown in FIG. 2, a switching cell detector 13, a delay circuit 14, and a path switch 15 are provided. The receiving terminal 3 is provided with a buffer 16.

In FIG. 2, a transmitting end 20 is connected to a path changeover switch 11 via a transmission line 21. The path changeover switch 11 is connected to a path control center (not shown) when a path changeover instruction is not given. The cell flow from the transmitting end 20 is transmitted to the working path 5, and when a path switching is instructed by the path management center, the switching cell provided from the switching cell insertion unit 12 via the transmission path 22 (Representing a cell at the timing next to the last cell transmitted to the working path 5) to the working path 5 and the cell flow from the transmitting end 20 to the protection path 6.

In the receiving side switching unit 4, the cell flow via the working path 5 is input to the switching cell detecting unit 13, while the cell flow via the protection path 6 is input to the delay circuit unit 14. .

The switching cell detector 13 determines whether or not the input cell is a switching cell. If the input cell is not a switching cell, the input cell is switched to a path switching switch via the transmission line 23. Give to 15. On the other hand, if the cell is a switching cell, the path switching switch 15 is instructed to switch the path, and a signal indicating that the switching cell has been detected is supplied to the delay circuit unit 14 via the signal line 24.

The delay circuit section 14 is composed of, for example, a selector and a delay circuit (for example, a FIFO configuration).
The delay circuit unit 14 inputs the cell supplied from the backup path 6 to the delay circuit before the detection signal of the switching cell is supplied. When a cell is held in the delay circuit at the time when the detection signal of the switching cell is supplied, the delay circuit unit 14 determines the fixed predetermined period (the cell input period from the standby path 6). The cell stored in the backup path 6 is supplied to the path changeover switch 15 via the transmission line 25 and the cell input from the backup path 6 is stored in the delay circuit. If there are no cells held in the delay circuit while the output and input from the delay circuit are being performed, the transmission line 25 is transmitted without delaying the cell provided from the backup path 6. To the state given to the path changeover switch 15 via the switch. If no cell is held in the delay circuit at the time when the detection signal of the switching cell is provided, the delay circuit unit 14 thereafter transmits the cell provided from the backup path 6 without delaying the transmission path. 25 to the path changeover switch 15.

The transmission path for directly providing the cells from the protection path 6 to the path switch 15 without delay may be different from the transmission path for supplying the cells output from the delay circuit to the path switch 15. .

The path switch 15 connects the cell from the working path 5 input via the switching cell detecting unit 13 to the receiving terminal 3 until the switching cell detecting unit 13 performs the detecting operation. After the switching cell detection unit 13 performs the detection operation, the cell from the protection path 6 input via the delay circuit unit 14 is transmitted to the transmission line 26.

The buffer 1 provided in the receiving terminal 3
Numeral 6 is for smoothing the cell flow rate output from the path changeover switch 15, that is, for absorbing the cell delay fluctuation caused by the switching. The cell flow smoothed by the buffer 16 is supplied to an output terminal 28 via a transmission line 27. In addition, the smoothing of the cell flow, when transmitting and receiving audio and image information,
Works effectively in preventing quality degradation.

Here, as the buffer 16 provided in the receiving terminal 3, for example, a buffer in accordance with the adaptive clock method can be applied. Hereinafter, the adaptive clock method will be considered in consideration of real-time communication such as an ATM moving image. Will be explained.

[0014] The timing cell sent from the transmitting side in a fixed period is written in the receiving timing cell buffer. At this time, a reference accumulation level of the timing cell buffer is determined, and control is performed to advance or delay the cycle of the reproduction clock in accordance with an increase or decrease to this level. For this reason, the receiving side has a local clock oscillator and a PLL circuit for changing the period.

By such an adaptive clock method, an appropriate amount of information is accumulated in the reception data buffer.
It is possible to appropriately prevent underflow and overflow of information. This is because the increase / decrease of data in the data buffer due to a relatively long delay fluctuation can be prevented by controlling the reproduction clock. This also eliminates the need to increase the data buffer amount taking into account relatively long delay fluctuations. As a result, the data buffer amount can be minimized, and the delay time can be minimized.

Here, in the case of real-time communication of a moving image of a fixed bit rate or the like, the timing cell and the data cell can be treated the same. The same applies to the buffer. In the following, for simplicity, the same treatment is described.

FIG. 4 is a flow chart showing an outline of processing of the conventional hitless path switching method (only processing relating to path switching). The processing of both the transmission side switching unit 2 and the reception side switching unit 4 is summarized. Is shown.

In the transmitting terminal 2, when path switching is instructed from a path management center (not shown), the path switch 11 switches from the working path 5 to the protection path 6 and switches the working path 5 The switching cell is inserted and output immediately after the last cell (steps 100 and 10).
1).

On the receiving side, the reception of the switching cell is monitored, and if there is a cell input from the protection path 6 before the reception of the switching cell, the cell is held in the delay circuit in the delay circuit section 14 ( Steps 102 and 103).

When the switching cell is detected, the path switch 15 is switched from the working path 5 to the protection path 6, and it is determined whether or not the delay circuit holds the cell at the time of receiving the switching cell. (Steps 104 and 105).

If it is not held, the delay circuit is immediately disconnected to terminate the delay operation, and the cells from the standby path 6 are immediately input to the path switch 15 to complete a series of switching processing (step 106). .

On the other hand, if a cell is held in the delay circuit at the time of reception of the switching cell, reading of the cell from the delay circuit and writing of the cell from the backup path 6 to the delay circuit are performed.
The operation is repeated while confirming that the cells held in the delay circuit remain (steps 107 and 108).
Note that the read cycle is shorter than the write cycle. When there are no more cells held in the delay circuit due to such repetitive processing, the delay circuit is disconnected to terminate the delay operation, and the cells from the backup path 6 are immediately input to the path changeover switch 15 so that a series of operations are performed. Is completed (step 106).

FIG. 5 is an explanatory diagram showing a relationship between path switching and an input cell flow to the receiving side switching unit 4. In addition,
FIG. 5 shows an ideal case in which there is no delay fluctuation in the cell flow and cells arrive at a constant period.

FIG. 5A shows a case where there is no path switching. The cell flows C1, C2,... Shown in FIG. 5A input to the receiving-side switching unit 4 via the working path 5 are output to the receiving-side terminal 3 as they are.

FIGS. 5 (B1) and (B2) show a case where the transmission delay time of the protection path 6 is longer than the transmission delay time of the working path 5. FIG. For example, when the transmission path length of the protection path 6 is longer than the transmission path length of the working path 5 or when the number of passing nodes interposed in the protection path 6 is larger than the number of passing nodes interposed in the working path 5. In addition, the transmission delay time of the protection path 6 may be longer.

For example, when a path switching command is given at the timing when four cells C 1 to C 4 are input from the input terminal 20 to the transmission side switching unit 2, the four cells C 1 to C 4 are provided to the working path 5. And the switching cell CE are transmitted, and FIG.
As shown in 1), the cell flows C1 to CE arrive at the switching cell detecting unit 13 of the receiving-side switching unit 4 with a delay of the transmission delay time of the working path 5, and the cell paths C1 to CE C
5 are transmitted and the cell flows C5, C6,...
As shown in 2), the cell streams C5, C6,... Arrive at the delay circuit section 13 of the receiving side switching section 4 with a delay of the transmission delay time of the protection path 6. In this case, since the transmission delay time of the protection path 6 is longer than the transmission delay time of the working path 5, the cells from the protection path 6 arrive at the delay circuit unit 14 at the timing when the switching cell CE arrives. Not
The delay circuit section 14 receives the cell flows C5 and C6 from the standby path 6.
,... Are input to the path switch 15 without delay processing.

As a result, although not shown, the path changeover switch 15 outputs the cell flows C 1, C 2,..., C 5, C 6,.
... (however, the switching cell CE is excluded) is transmitted. That is, the cell flow in which the cell jump time has occurred between the cells C4 and C5 is output from the path switch 15, and the cell jump time is absorbed by the buffer 16 of the receiving terminal 3.

FIGS. 5 (C1) to 5 (C3) show the active system path 5.
4 shows a case where the transmission delay time of the backup path 6 is longer than the transmission delay time of the protection path 6. For example, when the transmission path length of the working path 5 is longer than the transmission path length of the protection path 6,
For example, when the number of passing nodes interposed in the active path 5 is larger than the number of passing nodes interposed in the backup path 6, the transmission delay time of the working path 5 may be longer.

For example, assuming that a path switching command is given at the timing when four cells C1 to C4 are input from the input terminal 20 to the transmission side switching unit 2, the processing in the transmission side switching unit 2 is the same as that described above. Similarly, four cells C1 to C4 and a switching cell CE are transmitted to the working path 5,
In the standby path 6, the cell flows C5, C6,.
Is sent.

However, in this case, since the transmission delay time of the working path 5 is longer than the transmission delay time of the protection path 6, the receiving side switching unit 4 is shown in FIGS. 5 (C1) and (C2). Thus, the cell flow from the working path 5 and the protection path 6
And the cell flow from a certain part of the time period. For example, cells C3 and C4 from the working path 5 and cells C5 and C6 from the protection path 6 arrive in parallel, and the latter cells C5 and C6 are held in the delay circuit in the delay circuit unit 14. You. As a result, at the timing when the switching cell CE arrives, the cells C5 and C6 are held in the delay circuit, and the delay circuit unit 14 stores the held cells C5 and C6.
(C7, ...) (output to the path changeover switch 15) and writing to the cell streams C7, ... C10 from the standby path 6 are performed in parallel. FIG. 5C3 shows a cell flow output from the delay circuit unit 14. At the timing when the cell C10 is read from the delay circuit, no cell is held in the delay circuit, and the delay circuit section 14 disconnects the delay circuit. As a result, from the delay circuit section 14, as shown in FIG. Arriving cells C11, C12, ... like
Is output as it is as shown in FIG. 5 (C3).

As a result, from the path changeover switch 15,
Although not shown, the cell flows C1, C2,..., C5 to C12, maintaining the phase relationship shown in FIGS. 5 (C1) and (C3).
(However, the switching cell CE is excluded) is transmitted. That is, although there is no cell jump, a cell flow in which a part of the cell interval is closed is output, and the change in the cell interval is absorbed by the buffer 16 of the receiving terminal 3.

Conventionally, there has been proposed a circuit in which a delay circuit section is provided on the transmission-side switching section 2 side to adjust the cell flow at the time of switching on the transmission side. Since the delay control is performed based on the maximum transmission delay difference obtained, the method is inferior to the method in which the receiving-side switching unit 4 includes the delay circuit unit 14 (see the above-mentioned document).

[0033]

However, the above-described conventional path switching method intended for non-stop is a problem when the transmission delay time of the protection path 6 and the transmission delay time of the working path 5 are significantly different. It had the following.

For example, when the transmission delay time of the protection path 6 is considerably longer than the transmission delay time of the working path 5,
In the cell stream output from the path switching switch 15 of the reception-side switching unit 4, the cell jump time from the timing of outputting the last cell from the working path 5 to the timing of outputting the first cell from the protection path 6 ( FIGS. 5B1 and 5B2) are very large.

For this reason, even if the buffer 16 of the receiving terminal 3 according to the above-described adaptive clock method attempts to absorb the cell jump time, it may not be able to absorb the cell jump time. . FIG. 5 shows an ideal input cell flow to the receiving-side switching unit 4 without cell delay fluctuation. However, in practice, cell delay fluctuation is caused by cell competition in an ATM network. In such a case, the transmission delay difference before and after the path switching is added to the cell delay fluctuation, so that the cell jump time is further increased, and the buffer 16 may not be able to absorb the cell jump time.

Therefore, it is conceivable to increase the capacity of the buffer 16 so that a large jump time can be absorbed. However, in this case, another problem that the configuration of the receiving terminal 3 becomes large. Occurs. Also, always preparing the buffer 16 in consideration of the path switching requires preparing a delay difference in consideration of the possibility of all path switching, so that a large buffer 16 is used. Conversely,
If an appropriate delay difference is given in advance, the degree of freedom in path switching is lost.

From the viewpoint of the receiving side terminal 3, the cell flow having a large cell jump time from the receiving side switching unit 4 has a steep cell delay fluctuation, and the buffer 16
In addition to the absorption problem at the point, it can cause inconveniences.

The problem of the delay fluctuation and discontinuity of the cell flow is caused by the fact that the original information itself such as image information and audio information has the characteristics of real time and continuity, and the quality of the network is reduced. It is evaluated and is a major factor affecting network quality. This is the same in the case of an ATM, whether it is a fixed capacity or a variable capacity.

The present invention has been made in view of the above points, and provides a path switching method capable of switching paths so as to appropriately smooth a cell flow without increasing the capacity of a buffer. Another object of the present invention is to provide a path switching system that can improve the network quality by using a network in which cell delay fluctuation in a short time is small.

[0040]

In order to solve the above-mentioned problems, in the present invention, switching between the working path and the protection path is performed by a transmitting side switching section and a receiving side switching section located at both ends of both paths. Is performed by the operation of
The following means are provided in a path switching system in which one of the transmission-side switching unit and the reception-side switching unit includes a delay unit for compensating for cell discontinuity due to switching.

That is, (1) the transmission-side switching unit includes
For the path, a delay difference measurement cell was inserted in the cell row.
After that, a predetermined number of cells are output and cells for the working path are output.
The transmission is completed, and the protection path is set to the working path.
The same timing as the insertion timing of the delay difference measurement cell
Cell for delay difference measurement by
From the transmitting side to output cells after cell transmission from
(2) The receiving-side switching unit includes (2-1)
Cell of delay difference measurement via working path and protection path
Based on the arrival, the transmission delay difference between the transmission delay time of the working path and the transmission delay time of the protection path is determined , and
Empty cells for delay difference measurement in cell train from system path
Delay difference measuring means for, through (2-2) working path
A certain number of cells arrive after the arrival of the delay difference measurement cells.
Sending path that switches to the backup path after waiting for arrival
(3) a transmission-side switching unit and / or a reception-side
The switching unit is provided in the transmission-side switching unit or the reception-side switching unit based on the transmission delay difference obtained by the delay difference measurement unit.
When the amount of delay by the delay means is shorter than one cell period
Delay that can absorb the transmission delay difference by gradually increasing or decreasing
Control to the amount, and its gradual increase or decrease operation time,
It is within the time when a predetermined number of cells arrive at the receiving side switching unit
Control means for performing such control .

Here, if the path switching system of the present invention includes a delay unit for compensating for the discontinuity of the cell due to the switching at the receiving side switching unit, the delay control unit may include:
On the basis of the transmission delay difference obtained by the delay difference measuring means, if the transmission delay time of the protection path is longer than the transmission delay time of the working path, the working path is adjusted by the delay means so as to absorb the transmission delay difference. If the transmission delay time of the working path is longer than the transmission delay time of the protection path, the cells from both paths are delayed. In order to compensate for the irregularity of the order due to the reversal or simultaneous arrival, a delay means gives a predetermined delay time to the cell via the backup path and then gradually reduces the delay time to eliminate the delay.

Further, if the path switching system of the present invention includes a delay unit for compensating for the discontinuity of the cell due to the switching by the transmission-side switching unit, the delay control unit sets the transmission cell to Based on the transmission delay difference calculated by the delay difference measuring means, and the working path arriving at the receiving-side switching unit, based on the separation means for switching and separating the cells to be sent to the working path and the cells to be sent to the protection path. In order to compensate for the continuity of the cell of the protection path and the cell of the protection path, the delay means controls the delay while gradually increasing or decreasing the delay time of the cell transmitted to the working path or the cell transmitted to the protection path.

[0044]

According to the conventional path switching method intended for non-interruption, a delay means is provided in one of the transmission-side switching unit and the reception-side switching unit, and discontinuity such as cell order reversal or cell jump at the time of path switching is provided. Trying to prevent sex.

However, it is overlooked that an actual transmission delay difference between the transmission delay time of the working path and the transmission delay time of the protection path has a great effect on the discontinuity of cells that occurs at the time of path switching. Since path switching control is performed, the discontinuity of the cell cannot be fully compensated for by using the delay means, and the network has large cell delay fluctuations in a short time. The inventor thinks.

Accordingly, in the present invention, a delay difference measuring means is provided to obtain a transmission delay difference between the transmission delay time of the working path and the transmission delay time of the protection path, and based on the obtained transmission delay difference. The path switching is performed by controlling the delay operation of the delay means so as to suppress the discontinuity of the cell.

More specifically, if the receiving-side switching unit includes a delay unit for compensating for the discontinuity of the cell due to the switching, the discontinuity relationship affected by the transmission delay difference may occur. Since a cell flow from a certain working path and a cell flow from the protection path arrive, the discontinuous relation is changed to a continuous relation before switching according to the determined transmission delay difference. The delay control means controls the delay means.

On the other hand, if the transmission-side switching unit is provided with a delay means for compensating for the discontinuity of the cell due to the switching, when the cell flow arrives at the reception-side switching unit, the continuous relationship is established. In accordance with the determined transmission delay difference, the delay control means intentionally causes the cell flow to be output to the working path and the cell flow to be output to the protection path to have a discontinuous relationship. The delay means will be controlled.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) First Embodiment Hereinafter, a first embodiment of a path switching system according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of the first embodiment, in which the same or corresponding parts as in FIG. 3 are denoted by the same reference numerals.

The transmission-side switching section 2 and the reception-side switching section 4 relating to the path switching of the first embodiment are also located on the network as shown in FIG.

In FIG. 1, the transmission side switching unit 2 includes a path switching switch 31 and a delay difference measurement cell insertion unit 30, and the reception side switching unit 4 includes two delay difference measurement cell detection units 32. 33, two delay circuit units 34 and 35, a selector 36, and a switching control unit 37. Also,
In this embodiment as well, the buffer 16
Is provided.

The transmitting end 20 is connected to a path switch 31 via a transmission line 21. The path switching switch 31 is connected to the transmitting end 20 when a path switching instruction is not issued from a path management center (not shown). Is transmitted to the working path 5. When path switching is instructed from the path management center, the path switch 31 switches the delay difference measurement cell provided from the delay difference measurement cell insertion unit 30 via the transmission path 40 to the active path 5 and the active path 5. Backup path 6
At the same time, and then returns to the state of transmitting the cell flow to the working path 5. When a predetermined amount of cells have been transmitted from this return point, the input cell flow is transmitted to the backup path 6. Then, the switching process in the transmission-side switching unit 2 ends.

In the receiving side switching section 4, the working path 5 and the protection path 6 are connected to the corresponding delay difference measuring cell detecting sections 32 and 33, respectively.

When the cell provided via the working path 5 is other than the delay measurement cell, the delay difference measurement cell detection section 32 passes the cell as it is and supplies it to the delay circuit section 34 via the transmission line 41. If the cell provided via the working path 5 is a cell for delay measurement, the detection operation is performed, the detected timing information is notified to the switching control unit 37, and the cell is emptied and the transmission line 41 is transmitted. This is given to the delay circuit section 34 via the oscilloscope. If the cell provided via the protection path 6 is other than the delay measurement cell, the delay difference measurement cell detection unit 33 passes the cell as it is to the delay circuit unit 35 via the transmission line 42, When the cell provided via the path 6 is a delay measurement cell, the detection operation is performed, and the detected timing information is notified to the switching control unit 37.

Each of the delay circuits 34 and 35 is composed of, for example, a selector and a delay circuit (for example, a FIFO configuration). Each of the delay circuit units 34 and 35 includes a switching control unit 3
When the instruction is given from 7, the built-in delay circuit is activated to perform the delay operation of the input cell. The output cycle of the cell from the delay circuit also follows the instruction of the switching control unit 37. The cells transmitted from the respective delay circuits 34 and 35 are input to the selector 36 via the transmission lines 43 and 44.

Under the control of the switching control unit 37, the selector 36 passes the cell passing through the working path 5 given from the delay circuit unit 34 or passing through the protection path 6 given from the delay circuit unit 35. The selected cell is selected and the receiving terminal 3
Is transmitted to the transmission line 45 connected to.

The switching control unit 37 determines the transmission delay difference between the transmission delay time of the working path 5 and the transmission delay time of the protection path 6 based on the detection timing information from both the delay difference measurement cell detection units 32 and 33. Is determined according to the determined transmission delay difference, which of the delay circuit units 34 or 35 is to be delayed, and further, a read cycle from the delay circuit in the delay circuit unit 34 or 35 is determined, The information such as the determined read cycle is given to the determined delay circuit unit 34 or 35. Further, the switching control unit 37 includes a selector 36
Is supplied with a selection control signal.

FIG. 6 is a flowchart showing an outline of the switching process in the receiving side switching section 4 of the first embodiment.

First, the delay difference between the transmission delay time of the working path 5 and the transmission delay time of the protection path 6 is measured, and it is determined which transmission delay time of which system is longer (steps 200 to 202). ).

If the transmission delay time of the protection path 6 is long (Yes at step 201), the delay circuit of the delay circuit unit 34 relating to the working path 5 is made to function and the protection path 6 is activated.
The cells transmitted via the active path 5 are gradually increased by writing the cells transmitted via the active path 5 into the delay circuit and reading out the cells at a cycle determined in accordance with the transmission delay difference. When the transmission delay difference can be absorbed, the delay operation is terminated. When the processing for the last cell from the active path 5 is completed, the selector 36 switches the selection input to perform a series of switching. The process ends (steps 203 to 205). Note that the transmission delay difference may be completely absorbed before the last cell due to the delay fluctuation of the cell. Also, the delay time is changed from 0 to the transmission delay difference.

When the transmission delay time of the working path 5 is equal to the transmission delay time of the protection path 6 (step 201).
And 202), the cells are input to the selector 36 without delaying the input cells while leaving the delay circuits in both the delay circuits 34 and 35 separated, and the final The selector 36 is switched to the standby side at the timing when the cell has passed through the selector 36, and a series of switching processing ends (step 205).

If the transmission delay time of the working path 5 is long (negative result in step 201, affirmative result in step 202), it is set to a state in which the delay circuit in the delay circuit unit 35 relating to the protection path 6 functions. Then, the selector 36 is switched to the standby side at the timing when the selector 36 has passed the last cell that has passed through the active path 5, and the cell transmitted through the standby path 6 is delayed by the delay circuit section 35. By writing into the circuit and reading out at a cycle corresponding to the delay difference (the readout cycle is shorter), the cells transmitted via the backup path 6 are delayed little by little while reducing the delay time. Thus, when the delay time becomes 0, the delay circuit unit 3
A series of switching processes is completed by disconnecting the delay circuit in 5 and selecting cells from the standby path 6 without delay (steps 206 to 209). Note that the delay time is changed from the transmission delay difference to zero.

FIG. 7 is an explanatory diagram showing an input cell flow and an output cell flow of the reception side switching unit 4 when the transmission delay time is longer in the backup path 6. FIG. 7 shows an ideal case where there is no delay fluctuation in the input cell flow.

In this case, as shown in FIGS. 7A and 7B, the delay difference measuring cell CD simultaneously transmitted from the transmission-side switching unit 2 to the working path 5 and the protection path 6 is received. The signal from the working path 5 arrives at the switching unit 4 first, and then the signal from the protection path 6 arrives with a delay of the transmission delay difference TD. The arrival of the delay difference measuring cell CD via the paths 5 and 6 of the two systems causes the reception switching unit 4 to recognize the transmission delay difference TD1, and the cell interval Ta1 (input cell flow) of the cell flow output from the delay circuit unit 34. Is longer than the cell interval Tn1).

FIG. 7 shows a case where, for example, when a delay difference measuring cell CD arrives from the protection path 6, the cell arriving from the working path 5 is immediately subjected to delay processing. Delay processing is applied to the cell C4 to the last cell C K-1 so that the cell interval Ta1 is constant. Here, the delay time of the delay circuit section 34 is the smallest in the cell C4 (= Ta1−Tn1), and the largest in the last cell CK-1 (= TD1). Note that the delay time of the cell before reaching the final cell CK-1 is the transmission delay difference TD
If it is equal to (or more than) 1, then
Thereafter, the delay time is set to the transmission delay difference TD until the last cell.

In this way, the delay processing for the cell from the working path 5 is performed, and when the delay processing for the last cell CK-1 of the cell arriving from the working path 5 is completed, the selector 36 switches the protection path 6 Switches to the state of selecting a cell. At this time, the delay processing for the cell flow from the protection path 6 is not performed, but the delay processing for the cell flow from the working path 5 causes the output cell flow from the selector 36 to be reduced as shown in FIG. In, the last cell CK-1 from the working path 5 and the first cell CK from the protection path 6 have continuity with no cell jump period. That is, the transmission delay difference TD1 between the working path 5 and the protection path 6 is absorbed in the output cell flow from the selector 36. In other words, the output cell flow from the reception-side switching unit 4 can prevent steep cell delay fluctuations such as cell jumps.

The last cell CK-1 from the working path 5
May be detected based on the number of cells arriving after the delay difference measuring cell CD, and information indicating the last cell is inserted into a predetermined field (for example, a part of the information field) of the last cell CK-1. In this case, the reception-side switching unit 4 may detect the signal, and the reception-side switching unit 4 may transmit a cell that instructs switching next to the last cell.

FIG. 8 is an explanatory diagram showing an input cell flow and an output cell flow of the reception side switching unit 4 when the transmission delay time of the active path 5 is longer. FIG. 8 also shows an ideal case where there is no delay fluctuation in the input cell flow.

In this case, as shown in FIGS. 8A and 8B, the delay difference measuring cell CD simultaneously transmitted from the transmitting side switching unit 2 to the working path 5 and the protection path 6 is transmitted to the receiving side. The signal from the protection path 6 arrives at the switching unit 4 first, and then the signal from the working path 5 arrives with a delay of the transmission delay difference TD2. The arrival of the delay difference measuring cell CD via the paths 5 and 6 of the two systems causes the reception switching unit 4 to recognize the transmission delay difference TD2, and the delay circuit unit 35 of the protection system path 6
The cell interval Ta2 (shorter than the average cell interval Tn2 of the input cell flow) of the cell flow to be output from is determined, and the delay circuit unit 35 is set to a state of performing the delay operation. The delay time for the first cell from the protection path 6 is set to the transmission delay difference TD2, and the cell interval T after the delay operation is performed.
a2 is selected so that the delay time becomes gradually smaller.

Therefore, no delay processing is performed on the cell flow from the working path 5, and as shown in FIG.
The cell flows C1 to CK-1 from the working path 5 are transmitted from the selector 36 without any change in the cell interval.

In this case, since the transmission delay time is longer in the working path 5, as shown in FIGS. 8A and 8B, the last cell from the working path 5, for example, the cell C
The first cells, for example, the cells CK and CK + 1, from the protection path 6 arrive in parallel with the arrival of K-2 and CK-1 at the reception-side switching unit 4.

As described above, since the delay circuit section 35 on the protection path 6 is set to perform the delay operation, the first cell CK from the protection path 6 is delayed by the transmission delay difference TD2, The subsequent cells CK + 1, C (K + 2),... Are delayed so as to have the cell interval Ta2 set thereafter (the delay time itself becomes shorter). As a result, as shown in FIG. 8C, in the output cell flow from the selector 36, after the last cell CK-1 from the active path 5 appears and the selector 36 is switched, the output from the backup path 6 The cells CK, CK + 1,... Continue, and the cells from the backup path 6 do not disappear from the output cell stream and the order is maintained.

The delay time reaches 0 while the delay processing for the cell flow from the backup path 6 is performed. At this time, the delay circuit in the delay circuit unit 35 is disconnected and the delay processing is terminated. As a result, the cell flows CL + 1, CL + 2,...
As shown in (C), the output is directly from the selector 36.

As described above, the continuity of the output cell flow,
That is, a small delay fluctuation in a short time is achieved.

When the transmission delay difference is 0, only switching is performed, so that illustration and description of the cell flow are omitted.

According to the first embodiment, the transmission delay difference between the working path 5 and the protection path 6 is measured,
In the above, the cell flow from the working path 5 or the protection path 6 is delay-controlled according to the transmission delay difference.
In the cell flow transmitted from the receiving side switching unit 4, it is possible to prevent the cell jump and the cell interval from being unnecessarily narrowed, and to realize a smooth path switching.

As a result, smoothing of the input cell flow in the buffer 16 is realized without increasing the capacity of the buffer 16 in the adaptive clock receiving terminal 3, and the cell is discarded in the buffer 16. Can be prevented. In addition, even if the transmission information is an image or audio service, the amount of the buffer of the adaptive clock type can be reduced by such smoothing.
Since the transmission delay can be kept to a minimum without causing cell loss, it is possible to prevent a decrease in network quality.

(B) Second Embodiment Hereinafter, a second embodiment of the path switching system according to the present invention will be described in detail with reference to the drawings. FIG. 9 is a block diagram showing the configuration of the second embodiment, in which the same or corresponding parts as in FIG. 1 are denoted by the same reference numerals.

In the above-described path switching system of the first embodiment, it is impossible that the delay circuit units 34 and 35 simultaneously perform the delay operation. In consideration of this point, the path switching system of the second embodiment attempts to realize a path switching system that can obtain the same effect as that of the first embodiment by using one delay circuit unit.

The transmission-side switching unit 2 and the reception-side switching unit 4 relating to the path switching of the second embodiment are also located on the network as shown in FIG.

In FIG. 9, the configuration and operation of the transmission-side switching section 2 are the same as in the first embodiment, and a description thereof will be omitted.

The receiving-side switching section 4 includes a cross-connect switch 50, two delay difference measuring cell detecting sections 51 and 52,
It comprises a delay circuit section 53, a cell adjustment section 54, an exchange switch 55, and a switching control section 56.

In the receiving-side switching section 4, the working path 5 and the protection path 6 are connected to the cross-connect switch 5 respectively.
Connected to 0. This cross connect switch 50
Connects the working path 5 to the transmission path 60 and the protection path 6 to the transmission path 61, or connects the working path 5 to the transmission path 61 and The system path 6 is connected to the transmission path 60. Note that the latter connection state is used for inputting the cell flow from the working path 5 or the protection path 6 which needs the delay processing determined according to the measured delay difference to the delay circuit unit 53 as described later. It is in the state taken.

The delay difference measuring cell detecting section 51 is connected to the transmission line 6.
0, which detects a delay measurement cell from the active path 5 given via the active path 0. When the delay measurement cell is detected, the timing information is notified to the switching control unit 56, and the cell is made empty and the transmission path 62 Is given to the cell adjustment unit 54 via. On the other hand, the delay difference measurement cell detector 52
Is for detecting a delay measurement cell from the protection path 6 given via the transmission line 61. When the cell is detected, the timing information is notified to the switching control unit 56 and the cell is made empty. This is given to the delay circuit section 53 via the transmission line 63. When a cell other than the delay measurement cell is provided, each of the delay difference measurement cell detectors 51 and 52 passes the cell as it is.

The delay circuit 53 comprises, for example, a selector and a delay circuit (for example, a FIFO configuration). The delay circuit unit 53 functions as a built-in delay circuit when instructed by the switching control unit 56 to input a cell (the cell may be a cell from the active path 5, and the standby path 6
From the delay circuit), and the output cycle of the cell from this delay circuit is also changed by the switching control unit 5.
6. Follow the instructions in No. 6. The fact that the cell interval from the delay circuit 53 is constant means that the delay time
The delay time is gradually increased or decreased, and the switching control unit 56 also sets the initial delay time, the delay time when terminating the delay operation, and the like. The cell transmitted from the delay circuit unit 53 is input to the cell adjustment unit 54 via the transmission line 64.

Under the control of the switching control unit 56, the cell adjusting unit 54 selects the cells provided from the transmission lines 62 and 64, and secures the cell order even after the control of the cell flow by the delay circuit unit 53. If the cell flow cannot be performed, a process for securing the cell order (buffering process) is also performed, and the adjusted cell flow is supplied to the exchange switch 55 via the transmission line 65.

The exchange switch 55 performs exchange on a channel-by-channel basis, and supplies the exchanged cell flow to the receiving terminal 3 via the transmission line 66. Note that the exchange switch 55 may be a path switch.

The switching control unit 56 determines the transmission delay difference between the transmission delay time of the working path 5 and the transmission delay time of the protection path 6 based on the detection timing information from the two delay difference measuring cell detection units 61 and 62. According to the obtained transmission delay difference, it is determined which cell flow from which path is to be given to the delay circuit unit 53 from which timing, what kind of delay operation is to be performed by the delay circuit unit 53, etc. According to the determined contents, not only the delay circuit section 53 but also the cross connect switch 50 and the cell adjustment section 54 are controlled.

FIG. 10 is a flowchart showing an outline of the switching process in the receiving side switching unit 4 of the second embodiment.

First, the delay difference between the transmission delay time of the working path 5 and the transmission delay time of the protection path 6 is measured, and it is determined which transmission delay time is longer (step 30).
0-302). The cross connect switch 50 is
In the initial state, the cell flow from the working path 5 is supplied to the delay difference measuring cell detection unit 51, and the cell flow from the protection path 6 is supplied to the delay difference measurement cell detection unit 52.

If the transmission delay time of the protection path 6 is long (Yes at step 301), the cross-connect switch 50 controls the cell flow from the working path 5 (via the delay difference measurement cell detector 52). T) given to the delay circuit unit 53,
The cell flow from the standby path 6 is switched so as to be supplied to the cell adjustment unit 54 (via the delay difference measurement cell detection unit 51), and the cell adjustment unit 54 is switched to the transmission line 64 connected to the delay circuit unit 53. , And the function of the delay circuit of the delay circuit unit 53 is operated to write the cell transmitted via the working path 5 into the delay circuit, and at a cycle corresponding to the delay difference. By reading, the current path 5
Is delayed while gradually increasing the delay time, whereby the transmission delay difference can be absorbed, and the delay processing for the last cell from the active path 5 and the selection processing of the cell adjustment unit 54 are completed. Then, the cell adjustment unit 54
Is switched from the transmission path 62 to the transmission path 64, and a series of switching processing ends (steps 303 to 30).
6).

If the transmission delay time of the working path 5 is equal to the transmission delay time of the protection path 6 (step 30).
1, 302), the last cell from the active path 5 is output as the transmission path selected by the cell adjustment unit 54 without delay processing while keeping the delay circuit in the delay circuit unit 53 disconnected. At this time, the transmission path is switched from the transmission path 62 to the transmission path 64 to end a series of switching processing (step 30).
6).

If the transmission delay time of the working path 5 is long (negative result in step 301, affirmative result in step 302), the delay circuit in the delay circuit unit 53 is changed without changing the state of the cross-connect switch 50. At the timing when the cell adjustment unit 54 passes the last cell that has passed through the working path 5.
Is switched to the transmission line 64 side (steps 307 to 30).
9). Then, the cells transmitted via the backup path 6 are written into the delay circuit in the delay circuit unit 53 and read out at a cycle corresponding to the delay difference (the read cycle is shorter), so that the backup system is used. The cells transmitted via the path 6 are delayed little by little while reducing the delay time, and when the delay time becomes 0, the delay circuit in the delay circuit unit 53 is cut off and a series of switching processes is completed (step 310, 3
11).

As described above, the configuration and operation of the second embodiment are slightly different from those of the first embodiment. However, the relationship between the input cell flow and the output cell flow of the receiving side switching unit 4 is different from that of the first embodiment. 7 and 8 described above, and the description of the cell flow is omitted.

Therefore, also according to the second embodiment, the transmission delay difference between the working path 5 and the protection path 6 is measured, and the reception side switching unit 4 determines whether the working path 5 or the protection path Since the cell flow from the path 6 is delay-controlled, it is possible to prevent cell jumps and cell intervals in the cell flow sent from the receiving-side switching unit 4 from being unnecessarily narrowed, and to realize smooth path switching. Can be.

As a result, it is possible to realize smoothing in the buffer 16 without increasing the capacity of the buffer 16 in the receiving terminal 3, prevent cells from being discarded in the buffer 16, and transmit information such as an image or the like. Even in the case of voice, it is possible to prevent quality deterioration.

Further, the delay fluctuation of the output cell flow from the receiving side switching unit 4 is made smaller than before, and the processing load on the receiving side terminal 3 can be reduced.

(C) Third Embodiment Hereinafter, a third embodiment of the path switching system according to the present invention will be described in detail with reference to the drawings. Here, FIG. 11 is a block diagram showing the configuration of the third embodiment, and the same or corresponding parts as in FIG. 1 are denoted by the same reference numerals.

In the above-described path switching systems of the first embodiment and the second embodiment, the case where the information of the measured transmission delay difference is used in the receiving side switching unit has been described. Is an attempt to use information on the measured transmission delay difference in the transmission-side switching unit 2.

The transmission-side switching unit 2 and the reception-side switching unit 4 relating to the path switching of the third embodiment are also located on the network as shown in FIG.

The operation of the third embodiment will be explained while explaining the operation.

In FIG. 11, in the case of normal operation, a cell flow input from the input terminal 20 and input to the path switch 70 of the transmission-side switching unit 2 via the transmission line 21 is transmitted by the path switch 70. The signal is output to the transmission line 80 and provided to the delay circuit unit 71, passes through the delay circuit unit 71 without delay, and is sent out to the working path 5. The cell flow that has passed through the working path 5 and input to the delay difference measurement cell detection unit 72 of the reception-side switching unit 4 passes through the delay difference measurement cell detection unit 72 and passes through the transmission line 81. The signal reaches the path switch 73 and is transmitted to the transmission line 82 connected to the receiving terminal 3 by the switching operation of the path switch 73.

In such a state, the switching control section 74 of the transmission-side switching section 2 to which a switching request is given from a path management center (not shown) firstly outputs the delay difference measuring cell inserting section 75
And controls the path changeover switch 70 to
The delay difference measuring cell output from the delay difference measuring cell insertion unit 75 to the transmission line 83 is output from the path switch 70 to the two transmission lines 80 and 84 at the same time.
The delay difference measurement cells output to 0 and 84 are simultaneously transmitted to the working path 5 and the protection path 6 via the delay circuit 71 or 76 that is controlled to pass.

When the transmission operation of the delay difference measurement cell to the working path 5 and the protection path 6 is completed, the transmission-side switching unit 2 returns to the state of sending the input cell to the working path 5. I do.

Even if the signals are sent to the working path 5 and the protection path 6 at the same time, the difference in the transmission delay time causes the receiving side switching unit 4 to measure the delay difference via the working path 5 and the protection path 6. Cells arrive at different timings. The delay difference measurement cell detection unit 72 detects the delay difference measurement cell via the working path 5 and supplies the detection timing information to the switching control unit 77 in the reception-side switching unit 4, and converts the detection timing information into an empty cell. It is given to a path switch 82 via a transmission line 81. The other delay difference measuring cell detecting unit 78 provides the detection timing information to the switching control unit 77 in the receiving side switching unit 4 for the delay difference measuring cell via the protection path 6 in a similar manner. Perform processing.

The switching control unit 77 given the two pieces of detection timing information (or the path management center notified from the control unit 77) transmits the transmission delay difference between the working path 5 and the protection path 6. Ask for. The transmission delay difference thus obtained is notified to the switching control unit 74 of the transmission-side switching unit 4. For example, notification may be made from the path management center, or notification may be made from the switching control unit 77 to the switching control unit 74 via a reverse route.

Transmission-side switching unit 2 receiving notification of transmission delay difference
The switching control unit 74 determines the delay circuit unit 71 or 76 to be subjected to delay processing, determines the content of delay control, and determines the switching timing of the path switch 70 based on the transmission delay difference. Note that such a determination process may be performed by the path management center.

When the transmission delay time of the protection path 6 is longer, the switching control section 74 activates the delay circuit section 71 to delay the cell to be transmitted to the working path 5 and, at the same time, delays the cell. The time is gradually increased (note that the cell intervals are the same, for example). Further, the switching control unit 74
The path changeover switch 70 is operated at the timing when the cell next to the cell whose delay time of the cell transmitted to the working path 5 has become equal to the transmission delay difference is input to the path changeover switch 70 to delay the input cell. Given to the circuit section 76 side,
The backup path 6 is passed through the delay circuit section 76 as it is.
To terminate the series of switching processing.

As a result, the cells transmitted from the transmission-side switching unit 2 to the working path 5 and the cells transmitted to the protection path 6 partially overlap each other and are discontinuous.
When the signal reaches the receiving-side switching unit 4, continuity between cells from the working path 5 and cells from the protection path 6 is obtained.

When the transmission delay time of the active path 5 is longer, the switching control section 74 immediately activates the path switch 70 to switch the input cell to the delay circuit section 7.
6 and activates the delay circuit unit 76 to delay the cells to be transmitted to the protection path 6. At this time, a transmission delay difference is set as an initial delay time, The delay time is gradually reduced as the transmission proceeds (for example, the cell interval is the same). And
The switching control unit 74 terminates the delay operation of the delay circuit unit 76 when the delay time of the cell transmitted to the standby path 6 becomes 0, sets the delay circuit unit 76 to pass the cell as it is, and performs a series of switching. The process ends.

As a result, a jump period (blank period) occurs between the cells transmitted from the transmission-side switching unit 2 to the working path 5 and the cells transmitted to the protection path 6, and the cells are discontinuous. However, when the signal reaches the receiving-side switching unit 4, continuity between cells from the working path 5 and cells from the protection path 6 is obtained.

When the transmission delay time of the working path 5 is equal to the transmission delay time of the protection path 6, the switching control unit 74 delays the input cell by immediately operating the path switch 70, for example. To the circuit section 76,
A series of switching processing is completed by passing the signal through the delay circuit section 76 as it is and sending it to the backup path 6.

As a result, the cells transmitted from the transmission-side switching unit 2 to the working path 5 and the cells transmitted to the protection-system path 6 become continuous, and when the cells reach the reception-side switching unit 4, they are also used. The cells from the system path 5 and the cells from the standby system path 6 are continuous.

When the last cell arrives from the working path 5, the receiving-side switching unit 4 performs a switching operation of the path switching switch 73 to end a series of switching processing.

According to the third embodiment, the transmission delay difference between the working path 5 and the protection path 6 is measured, and the transmission-side switching unit 2 determines the working path 5 or the protection path according to the transmission delay difference. 6, the flow of cells from the working path 5 and the flow of cells from the protection path 6 reaching the receiving-side switching unit 2 become continuous, and the whole network becomes smooth. Path switching can be realized.

As a result, it is possible to realize smoothing in the buffer 16 without increasing the capacity of the buffer 16 in the receiving terminal 3, to prevent cells from being discarded in the buffer 16, and to reduce the transmission information to image information. Quality can be prevented even in the case of audio information.

Also in the third embodiment, the cell delay fluctuation in the entire network can be reduced, and the transmission quality can be improved.

(D) Other Embodiments In the first and second embodiments, the receiving-side switching unit 4 recognizes a switching request based on cell flows from the working path 5 and the protection path 6. However, for example, a switching request is also given from the path management center to the receiving side switching unit 4,
The delay control may be executed after receiving this request.

In each of the above embodiments, the present invention is applied to an ATM network. However, the present invention can be applied to other communication networks requiring similar path control.

Furthermore, in the first and second embodiments, the switching control unit in the receiving-side switching unit 4 determines the delay circuit unit for performing the delay operation and the delay time. It may be performed by a path management center.

Further, in each of the above embodiments, the cell for outputting the delay difference measurement cell to the working path 5 and the protection path 6 at the same time is shown. However, if the time difference between the transmission timings is specified, the delay difference measurement cell is output. The measurement cells may be output to the working path 5 and the protection path 6 at different timings.

As a modified example of the second embodiment, there can be cited one in which the delay difference measuring cell detectors 51 and 52 are provided in front of the cross connect switch 50.

Further, in each of the above embodiments, the case where only one delay difference measuring cell is transmitted / received has been described. However, a plurality of delay difference measuring cells are transmitted / received to obtain the transmission delay difference with high accuracy. May be.

Here, it is effective that the cell delay is controlled at a speed at which the clock of the adaptive clock controlled by the cell flow can be reproduced, and at a speed which does not hinder the reproduction of the image and the sound. Even if this is not the case, if a cell fluctuation rule (short time) is determined in the network, it is effective to control the cell fluctuation so that it falls within this rule. Further, it is preferable that the control is performed in consideration of a speed that does not violate the capacity limitation of the path (speed of the cell flow).

Although the present invention has a great effect when the buffer of the receiving terminal complies with the adaptive clock method, it can also be applied to a network in which the receiving terminal has a fixed clock buffer. .

[0126]

As described above, according to the present invention, the transmission delay difference between the working path and the protection path is measured, and the transmission delay from the working path or the protection path is measured according to the measured transmission delay difference. Since the cell flow is delay-controlled, a smooth path switching method can be realized in which continuity of the cell flow output from the receiving-side switching unit can be ensured and the cell delay fluctuation of the entire network can be reduced as compared with the conventional art. be able to.

Further, according to the present invention, a short-term cell fluctuation can be suppressed to a small level, the buffer of the receiving terminal (especially of the adaptive clock type) can be reduced, and the delay can be minimized by the current path. In this sense, the network quality can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a first embodiment.

FIG. 2 is a block diagram showing a conventional configuration.

FIG. 3 is a block diagram showing a network configuration to which the present invention is applied.

FIG. 4 is a flowchart showing a conventional switching process.

FIG. 5 is an explanatory diagram of a conventional decision.

FIG. 6 is a flowchart illustrating a switching process according to the first embodiment.

FIG. 7 is an explanatory diagram (part 1) illustrating an input / output cell flow of the receiving-side switching unit of the first embodiment.

FIG. 8 is an explanatory diagram (part 2) illustrating an input / output cell flow of the receiving side switching unit of the first embodiment.

FIG. 9 is a block diagram illustrating a configuration of a second embodiment.

FIG. 10 is a flowchart illustrating a switching process according to the second embodiment.

FIG. 11 is a block diagram showing a configuration of a third embodiment.

[Explanation of Codes] 2 ... Transmission-side switching section, 3 ... Reception-side terminal, 4 ... Reception-side switching section, 5 ... Working path, 6 ... Protection path, 30, 75 ... Delay amount measurement cell insertion section, 31 , 70, 73 ... path changeover switch, 32, 33, 51, 52, 72, 78 ... delay amount measuring cell detector, 34, 35, 53, 71, 76 ... delay circuit section, 36 ... selector, 37, 56 , 74, 77: Switching control unit, 50: Cross connect switch, 54: Cell adjustment unit, 55: Exchange switch.

Continuation of the front page (56) References JP-A-4-369140 (JP, A) JP-A-4-98944 (JP, A) IEICE Technical Report, CS 88-55 (1988-9-27) , Hideo Tatsuno et al., Uninterrupted path switching in high-speed burst multiplex transmission systems, p. 19-24 (58) Field surveyed (Int. Cl. ⁷ , DB name) H04L 12/28 H04L 12/56

Claims (3)

(57) [Claims] The switching between a working path and a protection path is performed by the operation of a transmission-side switching section and a reception-side switching section located at both ends of both paths. In a path switching system in which one of the receiving-side switching units includes a delay unit for compensating for the discontinuity of the cell accompanying the switching, the transmitting-side switching unit includes, for the working path, a cell train. Cell for delay difference measurement
After inserting the cells, a predetermined number of cells are output and the
Cell transmission to the backup path
Is the insertion of the cell for measuring the delay difference into the working path.
At the same timing as the input timing.
Of the cell transmission from the working path.
Equipped with a transmission-side path switching unit that outputs cells after cancellation
For example, the receiving side switching unit, the delay difference through the working path and the backup path
Based on the arrival of the measurement cell, a transmission delay difference between the transmission delay time of the working path and the transmission delay time of the protection path is determined , and the difference between the transmission delay time of the protection path and the cell delay from the working path is determined.
Delay difference measuring means for emptying the delay difference measurement cell, and arrival of the delay difference measurement cell via the working path.
Wait for the specified number of cells to arrive,
Transmission path switching means for switching to a system path, wherein the transmission-side switching section and / or the reception-side switching section are based on the transmission delay difference obtained by the delay difference measurement means, and the transmission- side switching section Or, provided in the receiving side switching unit
From the one cell period
Absorb the above transmission delay difference by gradually increasing or decreasing the short time
Control to the amount of delay possible and gradually increase or decrease
When the operation time reaches the predetermined number of cells,
Equipped with delay control means for controlling to be within the wearing time.
Path switching method characterized by the fact that: 2. The path switching system according to claim 1, wherein said receiving side switching unit includes a delay unit for compensating for a discontinuity of a cell due to the switching. If the transmission delay time of the protection path is larger than the transmission delay time of the working path based on the transmission delay difference obtained by the measuring means, the delay means absorbs the working delay so as to absorb the transmission delay difference. If the transmission delay time of the working path is longer than the transmission delay time of the protection path, the cells via the system path are delayed while gradually increasing the delay time until a predetermined delay time is reached. The delay means gradually reduces the delay time from a predetermined delay time from a predetermined delay time by the delay means so as to compensate for the disorder of the order due to the reversal or simultaneous arrival of cells from the path. Path switching scheme wherein the delaying while. 3. The path switching system according to claim 1, wherein said transmission-side switching unit includes a delay unit for compensating for a discontinuity of a cell accompanying the switching. On the basis of the transmission delay difference obtained by the measuring means, the delay means is configured to compensate for the continuity of the cells of the working path and the cells of the protection path arriving at the receiving side switching unit. A cell transmitted to the backup path or a cell transmitted to the backup path is delayed while gradually decreasing or gradually increasing the delay time.