JP2000092124A - Packet switching device, packet switching method, network and network restoration method - Google Patents

Abstract

(57) [Problem] To provide a packet switching device capable of monitoring the quality of a transmission path and switching a packet route at high speed. SOLUTION: In a packet switching device having a packet switch having a plurality of receivers and a plurality of transmitters, the quality of a signal on a transmission path for transmitting a signal from the packet switching device to another packet switching device deviates from an allowable value. If there is, the route control means includes means for controlling the packet switch so as to send a signal to another packet switching apparatus by bypassing another transmission path different from the transmission path having deteriorated quality. [Effect] Since the route is switched based on the physical quality information, high-speed switching is possible. As a result, the reliability of the packet network is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet switching device, a packet switching method, a network and a network recovery method, and more particularly to a packet switching device, a packet switching method, a network, and a method for dynamically switching the route of a packet when a failure occurs. Regarding network recovery methods.

[0002]

2. Description of the Related Art A plurality of packet switching devices are provided.
In IP (I nternet P rotocol) packet network (network layer), a routing protocol is used as a function to detect a failure of the root. There is OSPF (O pen S hortest P ath F irst) method as one of them. In this system, communication is periodically performed between packet switching devices using hello packets, a continuity test between the packet switching devices is performed, and the reliability of the route is confirmed. This routing protocol selects a route when a failure is detected,
The communication between the packet switching devices and the updating of the routing table storing the connection information between the packet switching devices are performed.

[0003] In the public network, in conjunction with IP packets switching device synchronous optical trunk system (SONET: S ynchronous O ptical
NET work) transmission equipment is often used. This is because the introduction thereof enables automatic line switching when a failure occurs in the physical layer. Such switching is SONET
Automatic switching: are called (APS A utomatic P rotection S witching ). Optical ring synchronization trunk system network as an example (BLSR: B i-directional L ine S witched R ing)
And a 1: 1 SONET switching device in which a backup optical fiber and a working optical fiber are assigned on a one-to-one basis. Such a network combining IP packets and SONET method is called I
Called the P over SONET method. IEEE as a reference
Communication Magazine, May 1998, p136-142.

In such an IP over SONET system, when a transmission line failure such as an optical fiber disconnection occurs, the APS is activated to quickly switch to a protection line. At this time, high-speed switching in the physical layer is not normally detected in the network layer, and the routing protocol in the network layer does not start.

[0005] However, when recovery by APS is not possible, for example, a failure of the packet switching device can be cited.
At this time, detection of a fault, communication between packet switching devices, updating of a routing table, and selection of a route (route) of an IP packet are performed by a routing protocol. That is, the IP over SONET method includes restoration by the physical layer APS and route restoration by the network layer routing protocol.

As a specific switching time, a recovery time from the occurrence of a failure requires several tens of milliseconds for the APS, and several tens to several minutes for the routine protocol.

However, the use of a SONET switching device increases the reliability of the network, but increases the cost. In particular wavelength multiplex transmission method (WDM: W avelength D ivision M ulti
plex) is used, expensive SONET depending on the number of wavelengths
Since a large number of switching devices are required, the device cost is enormous.

[0008] To solve this problem, IP over WDM has been proposed. In this method, the SONET switching device is not used in order to reduce the device cost, and the packet switching devices are connected using wavelength multiplex transmission. For this reason, since a plurality of signals are transmitted at different wavelengths to one optical fiber, transmission line costs are reduced.

FIG. 1 is a diagram for explaining a conventional packet switching device. In the packet switch 2, a plurality of receivers 10-1, 10-2,..., 10-N (hereinafter, referred to as a receiver 10) and a plurality of transmitters 11-1, 11-
,..., 11-N (hereinafter referred to as the transmitter 11) are connected. Each of the plurality of receivers 10 receives a signal from another packet device, and each of the plurality of transmitters 11 transmits a signal to the other packet device. Input packet signals 5 from a plurality of receivers are switched by a packet switch by selecting a destination from among a plurality of transmitters 11 according to a command of the route control means 1 for each destination. At this time, the route control means 1 issues a command to the packet switch while referring to the destination route information in the routing table 3. That is, a packet switching device is a device that switches a packet based on route information.

This route control means periodically transmits the above-mentioned hello packet to the adjacent packet switching device for a continuity test. Upon receiving the hello packet, the adjacent packet switching device replies to the adjacent packet. As a result,
When a hello packet is not returned from the adjacent packet switching device, the route control means determines that a failure has occurred in the packet route due to a timeout, and updates the routing table so that the packet passes through a route different from the route.

Table 1 and FIG. 2 are tables and diagrams for explaining a conventional routing table and a packet detour route.

[0012]

[Table 1]

[0013] routing table, the destination IP address, the transmitter interface: has (IF I nter F ace) number. For example, if the destination IP address of the packet is A, the received packet is transmitted from the transmitter # 1 because the transmitter IF number indicates # 1. Also, FIG.
This shows a state in which a failure has occurred in the optical fiber connected to the transmitter # 1, and shows a state in which the packet switching device is transmitting a hello packet.

A case will be described in which, as a result of a route continuity test using a hello packet, the route control means determines that a failure has occurred in the transmitter having the IF number # 1 or the optical fiber connected to the transmitter # 1. . The route control means determines a route not using the optical fiber as a substitute so as not to use the transmitter, and updates the routing table based on the result. Table 1
In the updated routing table, when the destination IP addresses of the packets are A and E, the transmitter IF numbers # 2 and # 3 are substituted for the transmitter of the transmitter IF number # 1.
Is set to use the transmitter. By rewriting the routing table in this manner, the packet signal is switched to a route where no failure has occurred.

[0015]

As described above, the first problem of the prior art is that the IP address of the packet switching device is high.
In the over WDM system, it took several tens of seconds to several minutes to recover from a failure or select a route. During that time, the routes are disconnected, and network management becomes impossible. The reason is that a hello packet (failure monitoring packet) from the routing protocol is detected by a timeout, so that a time for the timeout is always required.

The second problem is that if the transmission time of the hello packet is shortened or the number of times of transmission is increased, it is possible to detect the packet at a high speed. Absent.

As described above, when an attempt is made to reduce the construction cost of a transmission line in a large-capacity optical trunk system using a wavelength multiplexing system, the IP over WDM system has a problem in network reliability.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to remedy the above-mentioned problems. That is, an object of the present invention is to detect a failure at a physical layer faster than in the past and to switch the route at a higher speed than in the past. A further object of the present invention is to reduce an increase in network load accompanying detection of a transmission line failure.

The gist of the present invention is to provide a packet switch having a plurality of input signal receiving means and a plurality of output signal transmitting means, and transmitting a packet or signal received by the input signal receiving means of one of the packet switches to the output signal transmitting means. A packet switching apparatus having a route control means for instructing the packet switch to which of a plurality of transmission ends of the means to output, a signal for transmitting a signal from the packet switching apparatus to another packet switching apparatus. When the signal quality of the transmission path is out of the allowable value or when the failure information of the one transmission path is obtained, the other packet switching device is transmitted through another transmission path different from the one transmission path. Wherein the route control means is configured to control the packet switch to send a packet or a signal to the packet switch. In the device, and the like.

The present invention is particularly suitable for application to the IP over WDM system, but is not limited thereto.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of a packet switching device according to the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 3 is a diagram for explaining an embodiment of a packet switching apparatus according to the present invention. In this packet switch 2, a plurality of receivers 10-1, 10-
,..., 11-N (hereinafter, referred to as the transmitter 11) and a plurality of transmitters 11-1, 11-2,. . Multiple receivers 1
0 respectively receives a signal from another packet device, and the plurality of transmitters 11 each transmit a signal to another packet device. Input packet signals 5-1 and 5 from a plurality of receivers
,..., 5-N (hereinafter referred to as an input packet signal 5) are output from a plurality of transmitters 11 in accordance with a command from the route control means 1 by a packet switch. 6-1、6-2 、 ・ ・
, Transmitted from the transmitter 11 selected as 6-N (hereinafter referred to as output packet signal 6).

The route controller 1 issues a command to the packet switch 2 based on the route information of the packet in the routing table 3 and receives the quality information 7 from the quality detector 4. The quality detecting means 4 constantly monitors the quality of the transmission path or the quality of the signal passing through the transmission path while receiving the quality signal 14. For example, a signal in the transmission path 21 or a signal from a repeater in the transmission path 21 is used as the quality signal 14. The quality of the transmission path indicates a physical state of a signal propagating through the transmission path. For example, if the transmission waveform and the reception waveform exactly match, it is determined that the signal has not deteriorated. Actually, since the transmission path has external disturbance such as a temperature change, the signal is affected by noise, and the signal quality of the transmission path is degraded. Methods for measuring the quality of such signals include the bit error rate of the signal, the power of the signal, the signal-to-noise ratio, and the absolute wavelength shift of the signal. For example, as an example, if the signal error rate is 10 ⁻⁹ or less, it indicates that the quality is poor, and it can be considered that the signal quality is out of the allowable value. When the received power is set to 20 dBm ± 3 dB in the signal power, if the received power is within the range of 17 dBm to 23 dBm, it indicates that the quality is good and it is considered that the quality is within the allowable value of the signal quality. it can.

The route control means 1 is based on the quality information 7
If it is determined that the quality of the downstream transmission line 21 is out of the allowable value, in other words, that a failure is detected, the packet switch is performed so that the packet is transmitted using a route that does not pass through the transmission line 21. Send the command to 2. Since then
A route using a transmission line in which no failure has occurred is referred to as a bypass route.

Table 2 is a table for explaining an embodiment of the routing table of the present invention.

[0026]

[Table 2]

The routing table is the destination IP address and the transmitter interface number corresponding thereto (IF: I nter F
ace) and transmission path quality information. In the routing table before the failure, the destination IP address A
In this case, the transmitter IF number indicates 1. When the destination IP addresses are B, C, D, E, and F, the transmitter IF numbers indicate 2, 3, 4, 1, and 2, respectively.

The method of selecting a bypass route of a transmission line in which a failure has been detected is the same as that of the conventional example. When the destination IP addresses of packets are A and E, the updated routing table indicates that the transmitter IF number # 1 Are set to use the transmitters whose transmitter IF numbers are # 2 and # 3, respectively, as an alternative to the transmitter. When a failure is detected based on the transmission path quality information 7, the packet signal is switched to the bypass route by rewriting the routing table.

FIG. 4 is a diagram for explaining an embodiment of the switching method according to the present invention. In the step (S1) of constantly monitoring the quality of the transmission path, the physical state of the signal is monitored. In the step (S2) of detecting a failure in the transmission line, the route control means determines whether a failure has occurred in the transmission line based on the information. In the step of determining a detour route (S3), when it is determined that a failure has occurred in the transmission path, the detour route is determined from this information and the route information in the routing table.

(Embodiment 2) FIG. 5 is a diagram for explaining an embodiment of the packet switching apparatus of the present invention. A case where a SONET frame transmitter and a receiver are used as a system embodiment according to the present invention will be described. Where SONET receiver and S
The ONET transmitter is a device that can transmit or receive a SONET frame, and does not need to be the above-described SONET switching device that can switch a transmission path. Here, for simplicity, the packet switching device A according to the present invention is used as a part of the network.
A description will be given of a configuration including 30-a, B30-b, and optical fibers 22 and 24, but the present invention is not limited to this configuration.

The SONET transmitters 11-a and 11-b and the SON
The ET receivers 12-a and 12-b can transmit or receive SONET frames, respectively. The SONET frame (b) includes an overhead area and a payload area. The overhead area includes monitoring information of a transmission path, and the payload area includes a packet. When the SONET frame is used, the quality information 7 of the transmission path can be detected by reading the error rate monitoring area (for example, B1, B2, etc.) in the overhead.

Referring to FIG. 5, consider a case where the optical fiber 24 is disconnected in the transmission path from the packet switching device A to the packet switching device B. S of packet switching device B
The ONET receiver 10-b separates the transmission path quality information 7-1 and the packet signal 5-b. This quality information 7-1
Control means 1-b of the packet switching device B which has received the
Notifies the upstream packet switching device A30-a of this information. As a way to send this information upstream, SONET
The overhead area of the frame is used. For example, the overhead area K1, K2 byte and data communication channels (DCC: D ata C ommunication C hannel) the like. In the SONET transmission 11-b, the packet signal 6-
b and the quality information 7-2 are allocated to the SONET frame and transmitted to the packet switching device A. SONET receiver 10-a
Reads the quality information 7-3 from the SONET frame, and the route control means 1-a of the packet switching device A receives it. The route control means 1-a of the packet switching device A
The detour of the signal 6-a is determined based on the quality information 7-3. However, since FIG. 5 is a part of the network, the detour route is not drawn. in this way
Since the quality detection time is several tens of milliseconds using a SONET frame, high-speed detection of the quality of the transmission path is possible.

(Embodiment 3) FIG. 6 is a diagram for explaining an embodiment of the packet switching device of the present invention. Consider the case where an optical supervisory signal is used as a system embodiment according to the present invention. Here, for simplicity, the packet switching devices A30-a and B30
A description will be given of a configuration including 30-b and the optical fibers 23 and 24, but the configuration is not limited to this configuration. The light monitoring signal uses the signal 9-a and the signal 8-b. The packet signal is transmitted from the packet switching device A30-a as the output packet signal 6, transmitted as the signal 20 from the transmitter 11 to the receiver 10, and received as the input packet signal 5 by the packet switching device B30-b. At this time, the optical monitoring signal 9-a and the packet signal 20 are wavelength-multiplexed and transmitted.

In FIG. 6, the packet switching device A30-
Let us consider a case where the optical fiber 24 is disconnected in the transmission path from the packet transmission device a to the packet switching device B30-b. The optical supervisory signal receiver 12-b on the packet switching device B side detects the quality of the transmission path. For example, in the receiver 12-b, the quality of the transmission path can be detected by monitoring the signal power of the optical monitoring signal 9-a. Route control means 1-b of the packet switching device B receiving the quality information 7-1
Is transmitted from the optical monitoring signal transmitter 13-b to the upstream packet switching apparatus A as quality information 7-2. Receiver 12-
a receives the quality information 7-3 and transmits it to the route control means of the packet switching device A. The route control means 1-a of the packet switching device A, based on the quality information 7-3,
The detour of the signal 6 is determined.

As described above, by using the optical supervisory signal and the wavelength multiplexing technique together, it is possible to communicate the quality information of a plurality of packet signals by using the optical supervisory signal of one wavelength. For example, N
In wavelength multiplex transmission of waves, N-
By using one wave and one wavelength for the optical monitoring signal, the cost for monitoring the quality of the transmission path can be reduced.

Since no special fault monitoring packet is required, no load is applied to the packet network. In the present invention, the SONET frame transceiver and the optical supervisory signal can be used together, and they can be freely combined depending on the connection form of the transmission path.

(Embodiment 4) FIG. 7 is a diagram for explaining an embodiment of the packet switching apparatus of the present invention. The packet switch 2 has the same configuration as that of FIG. The packet switching device has a plurality of routing tables 3-1, 3-2,..., 3-N corresponding to the failure state of the transmission path. The route control means 1 selects a routing table corresponding to the failure state of the transmission path from the quality information based on the quality information. By previously determining the bypass route corresponding to the failure state of the transmission line, the load on the route control unit can be reduced.

(Embodiment 5) FIG. 8 is a diagram for explaining an embodiment of the packet switching apparatus of the present invention. The packet switch 2 has the same configuration as that of FIG. One or more interface tables 8-1, 8-2,...
8-N and one or more routing tables 3-
1, 3-2,..., 3-N. The routing table 3 stores the transmitter information according to the destination of the packet, and the interface table 8 stores the transmitter information and the quality information corresponding thereto. When a failure has occurred, the routing control means 1 issues a command to the packet switch 2 to transmit a packet from a transmitter other than the transmission path in which the failure has occurred, based on the quality information in the interface table 8.

Table 3 is a table for explaining an embodiment of the routing table and the interface table according to the present invention.

[0040]

[Table 3]

The routing table stores the destination IP address and the logical IF number of the transmitter. The interface table stores the logical IF number and the output IF number of the transmitter corresponding to the logical IF number.

In the interface table before the occurrence of the failure, the logical IF numbers # 1, 2, 3, and 4 correspond to the output IFs # 1, 2, 3, and 4 of the transmitter, respectively. what if
Consider a case where a failure is detected in IF # 4. The route control means 1 determines a bypass route based on the information on the quality of the transmission path so that the packet transmitted from IF # 4 is transmitted from another transmitter interface. In the updated interface table, the logical IF number of the transmitter # 4
Indicates that the packet is transmitted from the transmitter corresponding to the output IF number # 1.

Further, the load on the route control means can be reduced by presetting the interface tables 8-1, 2,..., N according to the failure state.

(Embodiment 6) FIG. 9 is a diagram for explaining an embodiment of a network according to the present invention.

This network is a packet switching device 30
-1, 30-2, 30-3, 30-4, 30-5 and transmission lines 100-1, 100-2, 100-3, 100-4,
100-5, and are connected as shown in FIG.

The packet switching device 30-1 is connected to the transmission line 100
Consider the case where the quality information of the transmission line is detected as -1 and the quality of the transmission line is out of the allowable value. The packet switching device 30-1 instructs the packet switch to transmit a packet signal being transmitted to the packet switching device 30-4 from another transmitter. For example, as a detour route of 100-1, packet signals are transmitted on transmission lines 100-2 and 100-5.
Is transmitted to the packet switching devices 30-1 to 30-4. As another alternative route, the packet signal is transmitted using the transmission paths 100-3, 100-4, and 100-5. Also, the packet signals are transmitted on transmission lines 100-7 and
It is transmitted using 0-6.

[0047]

According to the present invention, packet switching can be performed at a higher speed than in the prior art based on quality information of a transmission line. As a result, the reliability of the packet network is improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a conventional packet switching device.

FIG. 2 is a diagram illustrating a detour route.

FIG. 3 is a diagram illustrating a packet switching device according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a packet switching method according to an embodiment of the present invention.

FIG. 5 is a diagram illustrating a packet switching device according to a second embodiment of the present invention.

FIG. 6 is a diagram illustrating a packet switching device according to a third embodiment of the present invention.

FIG. 7 is a diagram illustrating a packet switching device according to a fourth embodiment of the present invention.

FIG. 8 is a diagram illustrating a packet switching device according to a fifth embodiment of the present invention.

FIG. 9 is a diagram illustrating a network according to a sixth embodiment of the present invention.

[Explanation of symbols]

1 ... route control means, 2 ... packet switch, 3 ...
Routing table, 4 ... quality detection means, 5 ... input packet signal, 6 ... output packet signal, 7 ... quality information, 8 ... interface table, 9 ... optical monitoring signal 10. ..Receiver, 11 ... Transmitter, 12 ... Light monitoring signal receiver, 13 ... Light monitoring signal transmitter 14 ... Quality signal 20 ... Signal, 21-24 ... Light Fiber 30: packet switching device, 100: transmission line.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5K030 GA12 HA08 HB06 HB11 HB28 JL03 KA04 KA13 LB08 MA04 MB04 MD02 5K035 AA03 BB04 CC08 DD02 EE01 JJ01 LL18 MM01

Claims (19)

[Claims] 1. A packet switch having a plurality of input signal receiving means and a plurality of output signal transmitting means, and a packet or signal received by said input signal receiving means of one of said packet switches being output to a plurality of said output signal transmitting means. In a packet switching device having a route control means for instructing the packet switch which of the transmitting ends to output, a packet transmission device for transmitting a signal from the packet switching device to another packet switching device. When the signal quality is out of the allowable value or when the failure information of the one transmission path is obtained, the packet or signal is transmitted to the other packet switching device through another transmission path different from the one transmission path. Wherein the route control means controls the packet switch to send the packet switch. 2. The method according to claim 1, wherein the route control unit transmits the packet or signal received by the input signal receiving unit of the packet switch to the plurality of transmission units of the output signal transmitting unit based on the route information stored in a routing table. 2. The packet switching device according to claim 1, wherein the packet switching device has a function of deciding which of the ends to output. 3. When there is a plurality of routing tables, when the signal quality of the one transmission line is out of an allowable value or when the failure information of the one transmission line is obtained, according to the failure, 3. The packet switching device according to claim 1, wherein the packet switching device is configured to select one of the plurality of routing tables, control the packet switch, and recover from a failure. 4. A routing table having information on a destination of a packet and one output terminal of the packet switch to which the packet is to be transmitted corresponding to the destination, wherein when a failure in the one transmission path is detected, the failure is detected. 2. The packet switching device according to claim 1, wherein the packet switching device is configured to update or change the routing table based on information. 5. The system according to claim 1, wherein when the failure of said one transmission line is detected, said routing table is updated or changed so as to send a signal or a packet to said another packet switching device via said another transmission line. 5. The packet switching device according to claim 4, wherein: 6. A first and a second routing table for restoring a first and a second fault state, respectively, wherein the first and second routing tables are determined based on the signal quality of the transmission path or the quality of the transmission path.
When detecting the occurrence of a failure state, the packet switch is controlled to determine one of the other transmission paths for transmitting the packet based on the first or second routing table. The packet switching device according to claim 1, wherein 7. The routing table, the first or second routing table.
And updating or changing the association between the destination of the received packet and one output terminal corresponding to the destination while updating or changing the routing table of the packet switch. The packet switching device according to any one of the above. 8. A transmitter or a transmitter between one output terminal of said packet switch and said another transmission line for determining said another transmission line to be a new transmission destination of a packet. 2. The packet switching device according to claim 1, wherein the packet switching device recognizes whether the interface is normal or not, and determines the one other transmission path only when the interface is normal. 9. An apparatus according to claim 1, further comprising an interface table having a transmitter logical interface number, a corresponding transmitter interface number, and information on whether each transmitter interface is normal or not. The packet switching device according to any one of the above. 10. A packet switch having a plurality of input signal receiving means and a plurality of output signal transmitting means, and a packet or a signal received by said input signal receiving means of one of said packet switches being output to a plurality of said output signal transmitting means. Preparing a packet switching device having a route control means for instructing the packet switch to which of the transmitting ends to output, one transmission for sending a signal from this packet switching device to another packet switching device; When the signal quality of the path is out of the allowable value or when the failure information of the one transmission path is obtained, the packet is transmitted to the other packet switching device through another transmission path different from the one transmission path. Or, the packet switching method, wherein the route control means controls the packet switch to send a signal. 11. The plurality of transmission means of the output signal transmitting means, wherein the route control means transmits the packet or signal received by the input signal receiving means of one of the packet switches based on the route information stored in a routing table. 11. The packet switching method according to claim 10, further comprising a step of determining which of the ends to output. 12. In a network having first and second packet switching devices and first and second transmission paths serving as signal paths between the two, a failure of the first transmission path is detected by the second packet switching apparatus. Means for causing the first packet switching device to recognize the information via the second transmission path when the packet switching device recognizes the information, and the first packet switching device recognizing the information comprises: A network comprising means for stopping transmission of a packet or signal to a first transmission path and transmitting the packet or signal to another transmission path. 13. A second SONET receiver on the side of the second packet switching device receives a first SONET frame, and the second SONET receiver receives fault information in the first SONET frame. Or, the quality information of the transmission path is extracted and the information is put on the second SONET frame transmitted from the second SONET transmitter on the side of the second packet switching device, and the second SONET frame is stored in the second SONET frame. Send to a first SONET receiver on the side of the first packet switching device,
13. The system according to claim 12, wherein the failure information or the quality information of the transmission path is extracted from the second SONET frame received by the first SONET receiver, and the presence or absence of the failure is recognized based on the information. Network. 14. A signal sent from the first packet switching device to the first transmission line is superimposed with a first monitoring signal for monitoring the presence or absence of a failure in the transmission line. The second packet switching device extracts a first monitoring signal from the signal, and outputs a second monitoring signal having information on the presence or absence of a failure based on the signal to the second packet switching device. The second packet is transmitted to the first packet switching device through the second transmission path, and the presence or absence of the failure is recognized based on the second monitoring signal received at the first packet switching device. Claims characterized by the following:
12 described network. 15. A packet switch having a plurality of input signal receiving units and a plurality of output signal transmitting units, respectively, wherein said first and second packet switching devices receive a plurality of input signal receiving units and a plurality of output signal transmitting units. Route control means for instructing the packet switch which of the plurality of transmitting ends of the output signal transmitting means to output the output packet or signal, and wherein the first packet switching device outputs the second When the signal quality of one transmission path for sending a signal to the packet switching device is out of an allowable value or when the failure information of the one transmission path is obtained, another signal different from the one transmission path is used. The route control means of the first packet switching device transmits the packet or the signal to the second packet switching device via a transmission line. 13. The network according to claim 12, wherein the network is configured to control the packet switch. 16. A method for restoring a network having first and second packet switching devices and first and second transmission lines serving as signal paths between the first and second packet switching devices, comprising the steps of: When the second packet switching device recognizes the information, the information is made to be recognized by the first packet switching device via the second transmission path, and the first packet switching device that recognizes the information is used. Stopping transmission of a packet or signal to the first transmission path and transmitting the packet or signal to another transmission path. 17. A second SONET receiver on the side of said second packet switching device receives a first SONET frame, and said second SONET receiver receives fault information in said first SONET frame. Alternatively, the quality information of the transmission path is extracted and the information in the second SONET frame transmitted from the second SONET transmitter on the side of the second packet switching device is placed, and the second SONET frame is placed in the second SONET frame. It sends to the first SONET receiver on the side of the first packet switching device, from the second SONET frame received by the first SONET receiver, the fault information or the quality information of the transmission path in the frame from the second SONET frame. 17. The network restoration method according to claim 16, wherein the network is extracted and the presence or absence of the failure is recognized based on the information. 18. A signal transmitted from the first packet switching device to the first transmission line is superimposed with a first monitoring signal for monitoring the presence or absence of a failure in the transmission line. The second packet switching device extracts a first monitoring signal from the signal, and outputs a second monitoring signal having information on the presence or absence of a failure based on the signal to the second packet switching device. The second packet is transmitted to the first packet switching device through the second transmission path, and the presence or absence of the failure is recognized based on the second monitoring signal received at the first packet switching device. Claims characterized by the following:
Network recovery method described in 16. 19. The first and second packet switching devices each include a packet switch having a plurality of input signal receiving units and a plurality of output signal transmitting units, and a packet switch for receiving the input signal of one of the packet switches. Route control means for instructing the packet switch which of the plurality of transmitting ends of the output signal transmitting means to output the packet or the signal to the output signal transmitting means; When the signal quality of one transmission path for sending a signal to the packet switching device is out of an allowable value or when the failure information of the one transmission path is obtained, another signal different from the one transmission path is used. The route control means of the first packet switching device transmits the packet or the signal to the second packet switching device via a transmission path. 17. The method for restoring a network according to claim 16, wherein said packet switch is controlled.