JP2000151634A - VP switching method and VP switching node device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a VP switching control method and apparatus capable of reliably detecting a failure in a duplicated VP segment and quickly switching to a standby VP in an ATM network. SOLUTION: A switching end node device of a redundant VP segment transmits a control cell for VP monitoring and status notification to both an active VP and a standby VP at a fixed period, and receives a control cell from a partner node. Is monitored, and when the reception of the control cell is interrupted for a predetermined time, it is determined that a VP failure has occurred. At the time of failure of the active VP, after confirming the normality of the standby VP, a VP switching request is transmitted to the partner node, and the VP is switched after waiting for the switching response.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ATM (Asynchro
nous Transfer Mode: As for the self-healing technology in the network,
In an ATM network, in a VP segment section in which a virtual path (Virtual Path: hereinafter, referred to as a VP) has a dual structure of an active system and a standby system, when a failure occurs in the active system VP, the VP is quickly switched to the standby system VP. The present invention relates to a method and a VP switching node device.

[0002]

2. Description of the Related Art In an ATM network, a maximum of 40 transmission lines can be used.
Since 96 VPs can be set, a switching control method (hereinafter, referred to as “switching”) that switches connections in the event of a failure in units of VPs.
The VP switching method) can make the switching unit finer than a method in which switching is performed in transmission line units.
Therefore, according to the VP switching method, a switching system (duplexing) can be set for each service, so that it is possible to make a service menu according to the reliability required by the user and to improve the utilization rate of the ATM network.

FIG. 8 shows a conventionally known VP switching control system. In the figure, 10-1 and 10-2 are switching terminal node devices, 11-1 and 11-2 are VP terminal nodes connected to the switching terminal nodes, and a solid line is provided between the two switching terminal node devices. , The relay nodes 12A-1 and 12A-
VP: 110A formed on the transmission line 120A passing through the transmission line 120A and the transmission line 120B passing through the relay nodes 12B-1 and 12B-2 indicated by the broken lines.
The standby system VP: 110B formed above is provided.

Conventionally, as shown by, for example, as shown by the mark x, the relay node device 12A-1 on the active system VP: 110A of the signal path from the switching terminal node device 10-2 to the switching terminal node device 10-1 When a VP failure occurs with the relay node device 12A-2, the relay node device 12A-1 located on the downstream side in the signal transmission direction detects the failure, and a forward VP failure notification cell: VP-AIS (Virtual Path- Alarm Indication
Signal) cells are sent downstream. The switching control from the active VP to the standby VP is performed by the switching end node device 10-1 located downstream of the relay node 12 </ b> A- 1.
Triggered by receiving an AIS cell. That is, upon receiving the VP-AIS cell from the active transmission line, the switching node device 10-1 receives the VP: 110B
Control cell AP indicating a request to switch to the backup VP using
Send S [REQ]. The control cell APS [RE
Q] reaches the other switching end node device 10-2 via the relay node devices 12B-1 and 12B-2. The switching end node device 10-2 transmits the control cell APS [RE
Q], the control cell APS [A] indicating a switching response to the switching-end node device 101 using the standby VP.
CK], and switches from the active VP to the standby VP. The above-mentioned switching control cell has the same VPI (Virtua) as the information cell to be transmitted in the header portion.
By setting the (l Path Identifier) value, the same path as the information cell can be obtained.

[0005] As a conventional technique relating to the above-mentioned VP switching, for example, there is "Study of an integrated VP self-healing system in an ATM network" in the 1995 IEICE Communication Society Conference SB-6-1 (1995). In the above document, a VP-APS (Automatic Protection Switch) in which the same band as the active VP is previously reserved in the standby VP.
A method and a VP-SH (Self-Healing) method in which a backup band is shared by a plurality of backup VPs and a band required for each backup VP is reserved when a failure occurs.

[0006]

However, in the above-mentioned conventional VP switching control, one of the relay nodes located downstream of the VP failure point generates a VP-AIS cell, and the two switching end node devices It is assumed that one of them detects the VP-AIS cell. Therefore, if a VP-AIS cell cannot be detected by the downstream switching end node device even though a failure has occurred in the active system VP, the standby system V
There is a problem that the switching operation to P is not started.

[0007] The non-detection of a VP-AIS cell in the switching end node device is based on (1) when the relay node device located between the failure point and the switching end node device does not transmit the VP-AIS cell, (2). When the switching end node device cannot recognize the reception of the VP-AIS cell, there are two cases. As a cause of the above (1), since the same VPI value as the information cell is used for the VP-AIS cell, for example, the loss of the VPI value due to the disappearance of the VP path in the upstream node device, or the upstream side VP-AIS in node device
A failure of the cell generation circuit may be considered. Also, (2)
Is caused by the VP-AI in the switching node device.
A failure of the S cell receiving circuit is given.

An object of the present invention is to provide a VP switching method and a VP switching node device capable of performing VP switching even when a relay node device located between switching terminal node devices performing VP switching control fails.

[0009]

In order to achieve the above object, a VP switching method according to the present invention comprises: two switching end node devices located at both ends of a duplicated VP segment section of an ATM network; Each VP of standby system
A control cell for fault monitoring and status notification is transmitted at a fixed interval, and the reception state of the control cell transmitted by the partner node device is monitored. When the reception of the control cell by the active VP is interrupted for a predetermined period, The switching operation from the active VP to the standby VP is started after determining that the active VP has failed and confirming the normality of the standby VP.

In the VP switching method according to the present invention, the control cell for fault monitoring and status notification includes, in addition to the information indicating the type or function of the control cell, a selection status of a duplicate VP and a fault detection status in the source node device. Is included. When each switching-end node device receives a VP-AIS generated by any of the node devices located on the route of the active VP, the switching end node device returns from the active VP in the same manner as when the control cell is interrupted. What is necessary is just to start the switching operation to the system VP.

In the present invention, the operation system VP is switched to the standby system V.
The switching to P is performed when the switching end node device that detects the active VP failure sends the VP to the partner node device via the standby VP.
A second control cell indicating a switching request is transmitted, and the counterpart node device responds to the reception of the second control cell by the VP.
Is switched, and the switching end node device is connected to the standby VP.
By switching the VP in response to a third control cell indicating a switching response received from the partner node device via the VP.

[0012] The VP switching node device according to the present invention comprises an AT
A fault switch is provided to the ATM switch coupled to each of the transmission lines of the operation system and the protection system forming the duplex transmission section of the M network, and to each VP on the transmission line of the operation system and the protection system via the ATM switch. A control cell for transmitting a control cell for notification of a combined state at a fixed period, and monitoring a reception state of the control cell transmitted by the other VP switching node device connected to the other end of the transmission section. When the device stops receiving the control cell in the active VP for a predetermined period, the device determines that the active VP has failed, and after confirming the normality of the corresponding standby VP,
The switching operation from the VP to the standby VP is started.

More specifically, the ATM switch is
At least a duplicated first and second line interface connected to each of the operation system and protection system transmission lines;
A third line interface accommodating a line to be coupled to the duplicated line interface through a TM switching operation, wherein the control device is coupled to the ATM switch, and transmits the control cells and receives control cells. A VP switching control unit for monitoring, and a monitoring control unit coupled to the VP switching control unit. When the VP switching control unit detects an active VP failure, A second control cell indicating a VP switching request is transmitted to the other VP switching node device via the first or second line interface, and the first or second line interface currently serving as a standby system is transmitted to the other VP switching node device. Through the other V
When receiving a second control cell indicating a VP switching request or a third control cell indicating a switching response from the P switching node device,
VP switching is requested to the monitoring control unit, and the monitoring control unit updates a header conversion table provided in the first, second, and third line interfaces in response to a request from the VP switching control unit. It is characterized by the following.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram illustrating an embodiment of the present invention.
2 shows a configuration of a TM network and a transmission operation of a VP switching control cell according to the present invention. VP terminal node device 1
1-1 and 11-2 are two VPs: 110 via different ATM sub-networks 100A and 100B.
A, 110B. Normally, communication between end nodes is performed using the VP 110A indicated by the solid line as the active VP, and when a failure occurs in the active VP, the used VP is switched to the standby VP indicated by the broken line, and subsequent communication is performed. Done. The VP switching control from the active system to the standby system is performed by two switching end node devices 10-1 and 10-2 located in front of the VP terminating devices 11-1 and 11-2. In addition, the two switching end node devices 10-1,
The VP section to be switched between 10-2 is called a VP switching segment.

According to the present invention, the operation-side VP: 110A is connected to two switching-end node devices 10-1 and 10-2 facing each other.
The control cell (hereinafter, referred to as an OAM cell) for fault monitoring and status notification is periodically transmitted in both the backup system and the backup VP: 110B, and the reception status of the OAM cell from the partner device is monitored with each other. And

FIG. 2 shows the switching end node device 10- in the present invention.
VP performed by 1 and 10-2: 110A or 110B
2 shows an operation of transmitting an OAM cell for failure monitoring and status notification (lower stage) and an operation of receiving an OAM cell from a partner device (upper stage). Each switching end node device operates at time t0,
t2, t4,. . . As shown by, an OAM cell is transmitted at a fixed period T to each VP of the active system and the standby system. V
If P is normal, times t1, t3, t5,. . . As shown by, the OAM cells transmitted from each other can be received at a constant period T. As shown by the broken line at time t7, when the reception of the OAM cell that has been received periodically until then is stopped, as shown by t9 and t11,
The subsequent reception state of the cell is monitored, and it is confirmed that an OAM cell is not received within a predetermined VP switching protection period (3T in the illustrated example), and it is determined that a VP failure has occurred.

When a failure of the active VP is detected due to the interruption of the received OAM cell, the normality of the standby VP is confirmed from the reception status of the OAM cell in the standby VP, and then the active VP is switched to the standby VP. VP switching operation is started. The switching of the VPs is performed, as shown at time t12, by the switching end node device detecting the failure transmitting a second control cell (hereinafter, referred to as an OAM [REQ] cell) including a switching request to the standby VP. Be started. In addition, operation system V
When the VP-AIS cell is received from the upstream relay node at P, the switching operation of the system is started by transmitting the OAM [REQ] including the switching request, as in the case of the interruption of the OAM cell.

In the present invention, as shown in FIG. 3, OAM cells for switching control transmitted and received by
It comprises a byte ATM header 50 and a 48-byte payload section (information field) 51. In the first byte of the payload section 51, information indicating a cell type (cell type) and a function is set. Various control information is set in the third byte. The second byte of the payload portion includes, for example, a 6-bit switching control information field and 2 bits.
The switching control information field includes the first OAM cell for failure monitoring and status notification in which the cell is transmitted at a fixed period, or the other node device Second OA requesting VP switching
M [REQ] cell or a third OAM [AC
K] Information indicating a cell type and information indicating a switching request, a switching factor, and the like are set. In the own device VP failure state field, two VP (0
The information indicating whether the system (system and system 1) is in a normal (failure) detection (or recognition) state in its own device is set.

The third byte of the above-mentioned payload portion is
A 1-bit own device switching system field indicating that the VP selected as the active system in the own device is either 0 system or 1 system;
It consists of a 4-bit own device switching detailed information field, and the remaining 3 bits are unused. In the own device switching detailed information field, for example, when the own device is in a state where switching control is impossible, information indicating the cause thereof, and the switching system selection information received from the other device matches the own device. The information indicating whether or not there is.

FIG. 4 shows an example of the configuration of the switching end node 10-1 for performing VP switching based on the periodic transmission and reception of control cells. The same applies to the switching end node 10-2. In the figure, 13A is a transmission line 12 on which VP: 110A is formed.
Line interface for accommodating 0A, 13B
VP: a line interface for accommodating the transmission line 120B in which the VP: 110B is formed, 14 is a line interface for accommodating a transmission line connected to the VP terminal node device, 15 is a line interface for accommodating these line interfaces,
An ATM switch unit for selectively switching the connection route of the line interface 14 to one of the two line interfaces 13A and 13B is shown. Reference numeral 20 denotes a VP switching control unit coupled to the ATM switch unit;
Denotes a monitoring control unit for monitoring the status of each unit in the node and setting various information, and 40 denotes an internal bus for interconnecting the above-described elements in the node.

Here, for the sake of simplicity, only one set of duplex line interfaces 13A and 13B is shown, but in an actual node device, a plurality of line interfaces In correspondence with the interface 14, a plurality of duplexed line interfaces are provided.

FIG. 5 shows an example of the configuration of the VP switching control unit 20 and the monitoring control unit 30 related to the VP switching control. VP
The switching control unit 20 decomposes the control cell received from the ATM switch unit 15 and extracts various control information set in the payload unit, and a state transition for performing a state transition for VP switching. A processing unit 23, an event notification processing unit 24 that notifies the monitoring control unit 30 when the switching state information has changed from the state at the time of receiving the previous control cell,
Timer management memory 25, which constitutes a timer for sending out control cells for failure monitoring and status notification at regular intervals and a timer for periodically monitoring reception of control cells.
And a state transition management memory 26 for storing switching state information, and a connection management memory 27 for storing the destination VPI of the control cell. The switching state information referred to here is the switching control information described in FIG.
It indicates a failure state, switching system selection information, and the like. The monitoring control unit 30 that controls VP switching includes a VP switching command unit 31 for instructing VP switching and an MIB (Management) for managing information such as switching state information and connection setting information.
Information Block) 32, and a bus interface 33 for connecting the internal bus 40 and the VP switching command unit 31.

Next, the switching end nodes 10-1 and 10-
2 will be described.
In the following description, the ATM formed on the transmission path 120A
A VP passing through the subnetwork 100A is defined as a 0-system VP
A VP passing through the ATM sub-network 100B formed on the transmission path 120B is defined as a 1-system VP, and a 0-system VP is defined.
Is the active system and the first system VP is in the standby system state, the active system VP heading from the switching end node device 10-2 to 10-1:
Assume that a failure has occurred in 110A.

Each of the VP switching control units 20 of the switching-end node devices 10-1 and 10-2 transmits the VP: 110A via the ATM switch unit 15 and the interface units 13A and 13B.
The OAM cell is periodically transmitted to the base station 110B every predetermined time T. The transmission of the OAM cell is performed by all duplicated VPs.
Is performed in the same manner.

When a failure occurs in the active VP (0-system VP: 110A) from the switching-end node device 10-2 to 10-1, the switching-end node device 10-2 becomes the 0-system VP: 11
The OAM cell transmitted to 0A2 is the switching end node device 10-
Stop arriving at 1. If the reception of the OAM cell is interrupted for a predetermined time managed by the timer management memory 25, the switching end node device 10-1 determines that a failure has occurred in the 0-system VP: 110A, and changes the active-system VP to the above-described state. To switch from the 0 system VP to the 1 system VP: 110B, the 1 system VP:
Check the normality of 110B. The normality of the first-system VP: 110B is determined such that the OAM cells transmitted to the first-system VP: 110B, which is currently the standby system by the other switching end node device 10-2, are periodically interrupted by the VP switching control unit 109. Can be determined by arriving at or not.

If the standby VP fails while the active VP is normal, the OA is sent to the active VP at regular intervals.
This is notified to the partner node device by the M cell, stored in the state transition management memory 26, notified to the monitoring control unit, and stored in the MIB file 32. Therefore,
The normality of the backup system (system 1) VP may be confirmed by referring to the state transition management memory 26. 1 system VP:
When the normality of 110B is confirmed, the switching node device 10
-1 uses the above-mentioned 1-system VP and sets the operating system to the 1-system VP: 110-
A control cell (OAM [REQ]) including a switch request message for switching to B is transmitted. The above OAM [RE
Q] cell is connected to the switching end node device 1 via the first system VP.
The VP switching control unit 0-2 is reached. Upon receiving the OAM [REQ] cell, the VP switching control unit of the switching terminal node device 10-2 is linked with the monitoring control unit 30-2 to receive the first system V.
P: Check the normality of 110B and change the active VP to 1
After switching to P: 110B, the control cell (OAM [ACK]) indicating that the VP switching has been completed is changed to the 1-system VP:
Send to 110B. Switching end node 10-of a switching request source
The switching control unit 20 of OAM [A] [AAM]
CK] In response to the reception of the cell, the active VP is changed from 0 to 1
Switch to the system.

FIG. 6 shows a control cell communication sequence between the two switching end nodes 10-1 and 10-2 when the active VP is normal. In the following description, among the components of the switching end node, those belonging to the node 10-1 are denoted by the numeral 1 and those belonging to the node 10-2 are denoted by the numeral 2 and quoted. Switching end node device 10-1, 10-2
Adds the VPI value set in the connection management memory 27 and periodically repeats the sending operation of the OAM cell for fault monitoring and status notification to each of the 1-system VP and the 0-system VP. When an OAM cell is received from the partner node device, the cell receiving unit 21 extracts switching state information. As long as the VP is normal, the transmission of the OAM cell is repeated with the same switching state information as the previous time set in the payload section. State transition processing units 23-1, 23 of each switching end node
-2 indicates that the switching state information indicated by the current received cell is stored in the state transition management memory 2 each time a control cell is received from the partner node.
6 is compared with the previous switching state information stored in step S6. If there is no change in the switching state information, the reception of the next control cell is waited without updating the storage contents of the state transition management memory 26. In this case, the event notification to the monitoring control unit 30 is not performed.

FIG. 7 shows a communication sequence of a switching control cell between two switching end nodes when a failure occurs in the active VP (system 0 VP). As indicated by the mark x, the OAM VP for the failure monitoring and status notification from the other switching end node 10-2 is interrupted by the 0-system VP, and when this continues for a predetermined period, the VP switching of the switching end node 10-1 is performed. Control unit 20-1
Determines that a failure has occurred in the active VP. After confirming the normality of the primary VP, the state transition processing unit 23-1 switches the active VP to the primary VP in the state transition management memory 26-1 in order to switch the switching status information corresponding to the failure VP. (Operation VP) makes a state transition to the first system VP (step 701). Next, an OAM [REQ] cell including the VP switching request message is transmitted to the partner node device 10-2, and the state change is notified to the monitoring control unit 30-1 via the event notification processing unit 24-1 (step 702). ), And waits for a response message indicating the completion of VP switching from the other switching end node device 10-2.

The VP switching control unit 20-2 of the switching end node device 10-2 performs the switching request cell OAM [REQ].
Is received, via the event notification processing unit 24-2,
A VRT (VP Routing Tag) update request for switching the active VP to the first system is issued to the monitoring controller 30-2 (step 703). Upon receiving the VRT update request, the VP switching command unit 31-2 of the monitoring control unit 30-2 receives the VRT update request via the bus interface 33-2 and the internal bus 40-2.
Connection management memory 27, line interface 13
Rewrite the header conversion tables of A, 13B and 14 and change the line interface 1
Instead of 3A, VP switching is performed so that user cells are communicated between the line interface 13B and the line interface 14 (step 704). When the VP switching is completed, the VP switching instruction unit 31-2 notifies the state transition processing unit 23-2 of the VP switching control unit 20-2 of the completion of the VRT update (Step 705).

Upon receiving the VRT update completion notification, the state transition processing unit 23-2, via the cell transmission unit 22-2, controls the control cell OAM [ACK] including a response message indicating that the VP switching has been completed. ] Is sent out. The control cell OAM [ACK] includes switching control information indicating that this cell is a switching response, and switching state information indicating that the own device switching system has selected the first system. The cell header includes a connection management memory. 27 and a routing tag for the line interface 13B-2. The state transition processing unit 23-2 performs the OAM [ACK]
After the cell is transmitted, the VP switching state information managed by the state transition management memory 26 undergoes a state transition to the first system VP (step 706), and the state is transmitted to the monitoring control unit 30 via the event notification processing unit 24-2. Notify the change (step 70)
7).

Upon receiving the OAM [ACK] cell including the switching response message, the switching end node 10-1 as the switching request source causes the VP switching control unit 20-1 to transmit the OAM [ACK] cell via the event notification processing unit 24-1. The monitoring controller 30-1 is notified of a VRT update request for switching the active VP to the first VP (step 708). VP of the monitoring control unit 30-1
The switching command section 31-1 is connected to the ATM switch section 15-1 via the bus interface 33-1 and the internal bus 40-1.
VP switching is performed so that the line interface 14 is coupled to the 1-system line interface 13B (step 709). When the VP switching is completed, V
The P switching command section 31-1 notifies the state transition processing section 23-1 of the VP switching control section 20-1 of the completion of the VRT update (Step 710). The state transition processing unit 23-1 performs the VR
Upon receiving the T update completion notification, the state transition management memory 26
After the switching state information managed by the above is changed to the 1-system VP (step 711), the event notification processing unit 24-
Then, the status change is notified to the monitoring control unit 30-1 via the server 1 (step 712).

In FIG. 7, when the reception of the control cell OAM from the other switching end node is interrupted for a predetermined period, it is determined that a VP failure has occurred, and the control cell for the VP switching request is transmitted. Segment VP from upstream relay node
-When the AIS cell is received, the control cell OA
As in the case of the interruption of M, by using the transmission condition of the control cell including the VP switching request message, it is possible to reliably detect a VP failure and realize a network capable of promptly switching to the standby VP.

In the above embodiment, the operation in the case where a failure has occurred in the active VP has been described. However, if the standby VP stops receiving control cells, the control cell transmitted to the active VP depends on the control cell transmitted to the active VP. For the other switching end node,
What is necessary is just to notify the standby system that the VP failure has been detected. Each node constantly compares the detection status of the VP failure at the partner node with the detection status of its own node, and provides information to the network administrator to detect in advance a failure that cannot be detected by the VP-AIS cell method, Appropriate maintenance work can be performed on the standby system before VP switching occurs.

[0034]

According to the present invention, control nodes are transmitted at regular intervals to switching end nodes located at both ends of a VP segment, and by monitoring the reception status of control cells from each other, mutual relay nodes can be controlled. Even if a VP-AIS cell cannot be generated, a failure on the VP path can be reliably detected, so that the VP switching can quickly perform the transfer control of the interruption time of the communication path at the time of the failure. Also,
Since the two switching nodes notify each other of the status information of the own node to the partner node by the control cell, inconsistent switching operation at the time of a VP failure can be avoided, and when a failure of the standby VP is detected, Maintenance work can be performed while the operating system is operating normally.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of an ATM network to which the present invention is applied.

FIG. 2 is a diagram for explaining transmission and reception of control cells in VP switching according to the present invention.

FIG. 3 is a diagram showing an example of a format of a control cell used in VP switching according to the present invention.

FIG. 4 is a diagram illustrating a node device having a VP switching function according to the present invention;
The figure which shows an Example.

FIG. 5 is a block diagram showing a configuration of a main part of the node device shown in FIG. 4;

FIG. 6 is a diagram showing a communication state of control cells between switching end node devices when the VP is normal.

FIG. 7 is a diagram showing a communication sequence of a control cell between switching end node devices and a communication sequence of a control signal in each switching end node in VP switching according to the present invention.

FIG. 8 is a diagram illustrating a VP switching control method according to the related art.

[Explanation of symbols]

10 switching end node device 11 VP terminal node device
DESCRIPTION OF SYMBOLS 12 ... Relay node apparatus 100 ... ATM subnetwork 13, 14 ... Line interface 15 ... ATM switch unit 20 ... VP switching control unit 30 ... Monitoring control unit 40 ... Internal bus

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Atsushi Iwamura 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside the Hitachi, Ltd.Information and Communications Division (72) Hiroo Nogi 216 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture F-term in Hitachi, Ltd. Information and Communication Division (Reference) 5K030 GA12 HA10 HB14 HB29 JA11 JA12 LB08 MD02

Claims (8)

[Claims] 1. A VP switching method in a redundant virtual path (VP) segment section constituting an ATM network, wherein two switching end node devices located at both ends of the VP segment are an active system and a standby system. A control cell for fault monitoring and status notification is transmitted to each VP of the system at a fixed cycle, and
The reception state of the control cell transmitted by the partner node device is monitored, and when the reception of the control cell in the active VP is interrupted for a predetermined period, it is determined that the active VP has failed, and the backup VP is determined.
After confirming the normality of the
A VP switching method, wherein a switching operation to P is started. 2. The control cell according to claim 1, wherein the control cell transmitted periodically includes control information indicating a selection state and a failure detection state of the duplicated VP in a source node device. VP switching method. 3. When each of the switching-end node devices receives a VP-AIS (Alarm Indication Signal) generated by one of the node devices located on the path of the active VP, an active VP failure occurs. 3. The V according to claim 1, wherein the switching operation from the active VP to the standby VP is started in the same manner as the control cell interruption.
P switching method. 4. The switching from the active VP to the standby VP is performed by the switching end node device that has detected the active VP failure indicating a VP switching request to the partner node device via the standby VP. , And the other node device switches the VP in response to the reception of the second control cell, and the switching end node device switches the VP received from the other node device via the standby VP. The VP switching method according to any one of claims 1 to 3, wherein the VP switching is achieved by switching a VP in response to a third control cell indicating a response. 5. A VP switching node device connected to one end of a duplicated transmission section of an ATM network, wherein the ATM is coupled to each of the active and standby transmission lines forming the duplicated transmission section. Switch and the above AT
Via the M switch, a control cell for fault monitoring and status notification is sent to each of the VPs on the active and standby transmission lines at a fixed cycle, and the other VP connected to the other end of the transmission section is switched. A control device that monitors a reception state of the control cell transmitted by the node device, wherein the control device determines that an active VP failure has occurred when reception of the control cell in the active VP has been interrupted for a predetermined period. A switching operation from the active VP to the standby VP after confirming the normality of the standby VP corresponding to the VP switching node device. 6. An ATM switch comprising: at least first and second duplex line interfaces connected to each of the active and standby transmission lines; and the duplicated line interface through an ATM switching operation. A third line interface accommodating a line to be coupled, wherein the control device is coupled to the ATM switch, and transmits a control cell and monitors a reception state of the control cell; A monitoring control unit coupled to the switching control unit. When the VP switching control unit detects the active VP failure, the VP switching control unit is connected via the first or second line interface currently serving as the standby system. Transmitting a second control cell indicating a VP switching request to the other VP switching node device, and transmitting the first or second line interface currently serving as a standby system. Via chromatography scan, V from the other VP switching node device
Upon receiving a second control cell indicating a P switching request or a third control cell indicating a switching response, the monitoring control unit requests the VP switching, and the monitoring control unit requests the VP switching from the VP switching control unit. The VP switching node device according to claim 5, wherein a header conversion table provided in the first, second, and third line interfaces is updated in response to the request. 7. The system according to claim 1, wherein the VP switching control unit transmits, to each of the control cells transmitted at a constant period, a duplicated V in its own node device.
7. The VP switching node device according to claim 6, wherein control information indicating a selection state of P and a failure detection state is set and transmitted. 8. The interruption of the control cell when the VP switching control unit receives a VP-AIS (Alarm Indication Signal) generated by any one of the node devices located on the currently operating transmission line. The VP switching node device according to any one of claims 5 to 7, wherein the switching operation is started in the same manner as in the case of detecting the VP.