Terminal device, communication device, and switching control method

Abstract

A first communication device comprises: a redundant terminal device that terminates a signal between the terminal device and a lower-order device; a relay unit that transmits, to a second communication device, a main signal that the terminal device has received from the lower-order device, and transmits, to the lower-order device via the terminal device, a main signal that was received from the second communication device and is destined for the lower-order device; and a notification unit that, if an abnormality of the terminal device has occurred during operation, notifies the second communication device of the occurrence of the abnormality. The second communication device comprises: a transmitting / receiving unit that receives, from the relay unit, a main signal having the lower-order device as the transmission source, and that transmits, to the relay unit, a main signal that is destined for the lower-order device; a switching unit that transmits, to a higher-order device, the main signal received from the relay unit by the transmitting / receiving unit, and transmits, from the transmitting / receiving unit to the relay unit, a main signal that was received from the higher-order device and is destined for the lower-order device; and a control unit that, if notified by the notification unit that an abnormality has occurred in the terminal device, switches from the terminal device in which the abnormality has occurred to a backup terminal device.

Description

[Technical Field]

[0001] The present invention relates to an end station device, a communication device, and a switching control method. [Background technology]

[0002] An OLT (Optical Line Terminal, optical subscriber line termination equipment) can be equipped with multiple PON-PKGs (packages) that provide a PON (Passive Optical Network) interface, some of which are used as redundant PKGs. Figure 17 shows the normal communication path in the OLT, and Figure 18 shows the communication path in the OLT after switching to the redundant PKG. If a malfunction occurs in a PON-PKG while the OLT is in operation, the control panel detects the malfunction and instructs the optical selector to switch. This switches the communication path to the redundant PON-PKG, allowing communication (service provision) to continue. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2013 / 058179 Summary of the Invention [Problem to be solved by the invention]

[0004] The introduction of OLT in rural (low-demand) areas requires the equipment to be compact. One way to achieve this is to eliminate the control panel. In this case, the PON protection function, which switches to a redundant PON-PKG in the event of a failure, becomes unavailable. However, in rural areas, the PON protection function is essential because it takes time to rush to the site in the event of a failure.

[0005] In view of the above circumstances, an object of the present invention is to provide a terminal device, a communication device, and a switching control method that can achieve both miniaturization and interface switching in the event of a failure due to redundancy. [Means for solving the problem]

[0006] One aspect of the present invention is an end station device comprising a first communication device and a second communication device, wherein the first communication device comprises a redundant first termination device that terminates signals between the first communication device and a first lower-level device, a relay unit that performs a process of transmitting a main signal received by the first termination device from the first lower-level device to the second communication device, and a process of transmitting a main signal received from the second communication device and addressed to the first lower-level device to the first lower-level device via the first termination device, and a notification unit that notifies the second communication device of the occurrence of an abnormality when an abnormality occurs in the first termination device during operation, and the second communication device The communication system includes a transmitting / receiving unit that receives the main signal sent from the first lower-level device from the relay unit and transmits the main signal addressed to the first lower-level device to the relay unit, a switch unit that transmits the main signal received by the transmitting / receiving unit from the relay unit to a higher-level device and transmits the main signal received from the higher-level device addressed to the first lower-level device from the transmitting / receiving unit to the relay unit, and a control unit that performs switching control to switch the first terminal device in which the abnormality has occurred to a spare first terminal device when the notification unit notifies the first terminal device of an abnormality.

[0007] A communication device according to one embodiment of the present invention comprises a transceiver unit that receives a main signal transmitted by a first lower-level device from another communication device having a redundant first termination device that terminates signals between the first lower-level device and the other communication device, and transmits a main signal addressed to the first lower-level device to the other communication device; a redundant second termination device that terminates signals between a second lower-level device and the other communication device; a switch unit that transmits the main signal received by the transceiver unit from the other communication device and the main signal received by the second termination device from the second lower-level device to a higher-level device, and transmits, from the transceiver unit to the other communication device, the main signal addressed to the first lower-level device, of the main signals received from the higher-level device, and transmits the main signal addressed to the second lower-level device to the second lower-level device via the second termination device; and a control unit that, when notified by the other communication device of an abnormality in the first termination device, performs switching control to switch the first termination device in which the abnormality has occurred to the spare first termination device.

[0008] One aspect of the present invention is a switching control method in an end station device having a first communication device and a second communication device, the method comprising: a first transmission / reception step in which an active termination device among redundant termination devices of the first communication device transmits and receives a main signal to and from a lower-level device; a relay step in which a relay unit of the first communication device transmits the main signal received in the first transmission / reception step to the second communication device and transmits the main signal received from the second communication device and addressed to the lower-level device to the lower-level device in the first transmission / reception step; a process in which a transmitter / receiver unit of the second communication device receives the main signal from the first communication device and which is transmitted from the lower-level device; the second communication device performs a process of transmitting a main signal addressed to the first communication device to the first terminal device; an upper communication step in which a switch unit of the second communication device performs a process of transmitting the main signal received in the second transmission / reception step to a higher-level device and a process of receiving a main signal addressed to the lower-level device from the higher-level device; a notification step in which a notification unit of the first communication device notifies the second communication device of the occurrence of an abnormality when an abnormality occurs in the terminal device during operation; and a switching step in which a control unit of the second communication device performs switching control to switch the terminal device in which the abnormality has occurred to a spare terminal device when the control unit of the second communication device is notified of the occurrence of an abnormality in the terminal device by the notification step. [Effects of the Invention]

[0009] The present invention makes it possible to achieve both miniaturization and interface switching in the event of a failure due to redundancy. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a configuration diagram of a terminal device according to an embodiment. [Figure 2] FIG. 2 is a configuration diagram of a terminal device according to an embodiment. [Figure 3] FIG. 2 is a functional block diagram of a terminal device according to the first embodiment. [Figure 4] FIG. 4 is a sequence diagram of a master station according to the first embodiment. [Figure 5] FIG. 4 is a sequence diagram of a master station according to the first embodiment. [Figure 6] FIG. 3 is a sequence diagram of the terminal device according to the first embodiment. [Figure 7] FIG. 3 is a sequence diagram of the terminal device according to the first embodiment. [Figure 8] FIG. 10 is a functional block diagram of a terminal device according to a second embodiment. [Figure 9] FIG. 10 is a sequence diagram of a terminal device according to a second embodiment. [Figure 10] FIG. 10 is a sequence diagram of a terminal device according to a second embodiment. [Figure 11] FIG. 10 is a functional block diagram of a terminal device according to a third embodiment. [Figure 12] FIG. 11 is a sequence diagram of a terminal device according to the third embodiment. [Figure 13] FIG. 11 is a sequence diagram of a terminal device according to the third embodiment. [Figure 14] FIG. 10 is a functional block diagram of a terminal device according to a fourth embodiment. [Figure 15] FIG. 10 is a sequence diagram of a terminal device according to a fourth embodiment. [Figure 16] FIG. 10 is a sequence diagram of a terminal device according to a fourth embodiment. [Figure 17] FIG. 1 is a diagram illustrating a communication path in a conventional OLT. [Figure 18] FIG. 1 is a diagram illustrating a communication path in a conventional OLT. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0012] [overview] FIG. 1 is a diagram showing an example of the configuration of a terminal device 1 according to an embodiment of the present invention. The terminal device 1 has a master station OLT 10, an optical selector 20, and a slave station OLT 30. The master station OLT 10 will be referred to as the master station 10, and the slave station OLT 30 will be referred to as the slave station 30. The master station 10 may be provided with the optical selector 20. The master station 10 and the optical selector 20 are examples of a second communication device, and the slave station 30 is an example of a first communication device. The optical selector 20 and the slave station 30 are connected by an optical transmission path 50. The optical transmission path 50 is, for example, an optical fiber.

[0013] The master station 10 is connected to the ONU 60 via an optical selector 20. The master station 10 is also connected to a higher-level device 80. The slave station 30 is connected to the ONU 61 via an optical transmission path 70. The terminal device 1 transfers signals transmitted by optical signals from the lower-level devices, ONU 60 and ONU 61, to the higher-level device 80. The terminal device 1 also transfers signals transmitted from the higher-level device 80 to the destination ONU 60 and ONU 61 by optical signals. The direction from the ONUs 60 and 61 to the higher-level device 80 is referred to as upstream, and the direction from the higher-level device 80 to the ONUs 60 and 61 is referred to as downstream. The normal path and the path after switching shown in FIG. 1 indicate the paths of data communication for the ONU 61.

[0014] The master station 10 has a control panel 11, one or more PON-PKGs 12, one or more redundant PKGs 13, a transfer PKG 14, and a switch (SW) 15. Fig. 1 shows an example in which the master station 10 is equipped with multiple PON-PKGs 12 and one redundant PKG 13. In a normal state, the PON-PKG 12 is an active PKG, and the redundant PKG 13 is a standby PKG.

[0015] The control panel 11 controls each unit in the master station 10. When a failure occurs in the PON-PKG 12, the control panel 11 controls PON protection and switches the failed PON-PKG 12 to the redundant PKG 13. When the control panel 11 is notified by the slave station 30 that a failure has occurred in the PON-PKG 32, the control panel 11 controls PON protection for the slave station 30 and switches the failed PON-PKG 32 to the redundant PKG 33.

[0016] The PON-PKG 12 provides a PON interface for the OSU. The PON-PKG 12 is connected to the ONU 60 via the optical selector 20 and terminates optical signals between the ONU 60. The PON-PKG 12 converts upstream optical signals received from the ONU 60 into electrical signals and outputs them to the SW 15. The PON-PKG 12 also converts downstream electrical signals addressed to the ONU 60 and received from the higher-level device 80 via the SW 15 into optical signals and transmits them to the ONU 60. The redundant PKG 13 has the same functions as the PON-PKG 12. Of the multiple PON-PKGs 12 installed in the master station 10, one that is not in operation is used as the redundant PKG 13.

[0017] The transfer PKG 14 connects the parent station 10 with the child station 30. The transfer PKG 14 receives an upstream optical signal output by the child station 30 from the optical selector 20, converts the received optical signal into an electrical signal, and outputs it to the SW 15. The transfer PKG 14 also converts a downstream electrical signal input from the SW 15 into an optical signal and outputs it to the optical selector 20. The transfer PKG 14 transmits and receives a main signal between the ONU 61 under the control of the child station 30 and the higher-level device 80, as well as a control signal between the control panel 11 of the parent station 10 and the child station 30.

[0018] SW15 is connected to the PON-PKG 12, the redundant PKG 13, the transfer PKG 14, and the higher-level device 80. SW15 outputs upstream electrical signals input from each of the PON-PKG 12, the redundant PKG 13, and the transfer PKG 14 to the higher-level device 80 according to the destination. SW15 also distributes downstream electrical signals received from the higher-level device 80 to the PON-PKG 12, the redundant PKG 13, and the transfer PKG 14 according to the destination, and outputs the signals. That is, SW15 outputs downstream signals addressed to ONU 60 to the PON-PKG 12 or the redundant PKG 13 connected to ONU 60, and outputs downstream signals addressed to ONU 61 to the transfer PKG 14.

[0019] The optical selector 20 includes a control panel 21, an optical switch (optical SW) 22, and a coupler 23. The control panel 21 controls the path of the optical signal in the optical SW 22. The control panel 21 also includes a power supply unit that supplies power to each component of the optical selector 20. The power supply unit may be provided outside the control panel 21. The optical SW 22 has multiple ports, and outputs an optical signal input from one port from another port according to the path set by the control panel 21. The coupler 23 is a 2x2 coupler. Two first ports of the coupler 23 are connected to different ONUs 60. Two second ports of the coupler 23 are connected to the PON-PKG 12 and the optical SW 22, respectively. The coupler 23 branches the optical signal input from the first port into two and outputs the branched optical signals from two second ports. The coupler 23 also branches the optical signal input from the second port into two and outputs the branched optical signals from two first ports.

[0020] The slave station 30 has one or more PON-PKGs 32, one or more redundancy PKGs 33, a transfer PKG 34, and an optical selector 40. Fig. 1 shows an example in which the slave station 30 has a plurality of PON-PKGs 32 and one redundancy PKG 33. The optical selector 40 may be provided outside the slave station 30. In a normal state, the PON-PKG 32 is an active PKG, and the redundancy PKG 33 is a standby PKG.

[0021] The PON-PKG 32 provides an interface for the PON of the OSU. The PON-PKG 32 may have the same functions as the PON-PKG 12. The PON-PKG 32 is connected to the ONU 61 and terminates optical signals between the ONU 61. The PON-PKG 32 converts upstream optical signals received from the ONU 61 into electrical signals and outputs them to the transfer PKG 34. The PON-PKG 32 also converts downstream electrical signals received via the transfer PKG 34 into optical signals and transmits them to the ONU 61.

[0022] The redundancy PKG 33 has the same functions as the PON-PKG 32. That is, of the multiple PON-PKGs 32 installed in the slave station 30, one that is not in operation can be used as the redundancy PKG 33. The redundancy PKG 33 is not connected to the ONU 61 in a normal state in which no abnormality has occurred in any of the PON-PKGs 32. If an abnormality is detected in a PON-PKG 32, the redundancy PKG 33 changes from the standby state to the operational state in place of the PON-PKG 32 in which the abnormality has been detected, based on an instruction from the control panel 11 of the master station 10, and is connected to the ONU 61.

[0023] The transfer PKG 34 connects the local station 30 with the master station 10. The transfer PKG 34 receives an upstream electrical signal from either the PON-PKG 32 or the redundant PKG 33, whichever is in operation, converts the received electrical signal into an optical signal, and outputs it to the optical transmission path 50. The transfer PKG 34 also converts a downstream optical signal received from the optical transmission path 50 into an electrical signal, and distributes and outputs the signal to either the PON-PKG 32 or the redundant PKG 33, whichever is in operation, according to the destination. The transfer PKG 34 also transmits and receives control signals related to PON protection between the slave station 30 and the control panel 11 of the master station 10.

[0024] The optical selector 40 includes a control panel 41, an optical switch 42, and a coupler 43. The control panel 41 controls the path of the optical signal in the optical switch 42. If an abnormality is detected in the PON-PKG 32, the control panel 41 changes the path based on an instruction from the control panel 11 of the master station 10 so that the ONU 61 is connected to the redundant PKG 33 instead of the PON-PKG 32 in which the abnormality was detected. The control panel 41 also includes a power supply unit that supplies power to each unit of the optical selector 40. The power supply unit may be provided outside the control panel 41. The optical switch 42 has multiple ports, and outputs an optical signal input from one port from another port according to the path set by the control panel 41.

[0025] The coupler 43 is a 2x2 coupler. Two first ports of the coupler 43 are connected to different ONUs 61. Two second ports of the coupler 43 are connected to the PON-PKG 32 and the optical SW 42, respectively. The coupler 43 branches an optical signal input from the first port into two and outputs the branched optical signals from the two second ports. The coupler 43 also branches an optical signal input from the second port into two and outputs the branched optical signals from the two first ports. With this configuration, the optical selector 40 can communicate without using the optical SW 42 during normal operation when the redundant PKG 33 is not operating. In addition, the optical selector 40 can switch the connection destination of the ONU 61 between the PON-PKG 32 and the redundant PKG 33 without stopping communication.

[0026] As described above, the master station 10 is equipped with a control panel 11, but the slave station 30 is not. The master station 10 is equipped with transfer PKGs 14 in place of some of the PON-PKGs 12 to communicate with the transfer PKGs 34 of the slave stations 30. The control panel 11 of the master station 10 manages the status of both the master station 10 and the slave stations 30. That is, the control panel 11 manages the status of the PON-PKG 12 and the redundant PKG 13 of the master station 10, and the status of the PON-PKG 32 and the redundant PKG 33 of the slave station 30, as to whether they are in operation. When the control panel 11 of the master station 10 detects a malfunction in the PON-PKG 32 through a notification from the slave station 30, it outputs a PON-PKG switching instruction and an optical selector switching instruction to the transfer PKG 34 of the slave station 30 for PON protection.

[0027] Under normal conditions when no abnormality occurs in the PON-PKG 12 of the parent station 10, the coupler 23 of the optical selector 20 splits the upstream optical signal transmitted from the ONU 60 into two, outputs one of the split optical signals to the PON-PKG 12, and outputs the other split optical signal to the optical SW 22. The optical SW 22 does not detect the switching and therefore discards the input optical signal without outputting it. The PON-PKG 32 converts the optical signal received from the optical selector 20 into an electrical signal and outputs it to the SW 15.

[0028] Under normal conditions when no abnormality occurs in the PON-PKG 32 of the remote station 30, the optical selector 40 inputs an optical signal transmitted from the ONU 61 and outputs the input optical signal to the PON-PKG 32. Specifically, the coupler 43 of the optical selector 40 splits the upstream optical signal transmitted from the ONU 61 into two, outputs one of the split optical signals to the PON-PKG 32, and outputs the other split optical signal to the optical SW 42. Because the optical SW 42 does not detect switching, it discards the optical signal input from the coupler 43 without outputting it. The PON-PKG 32 converts the optical signal received from the optical selector 40 into an electrical signal and outputs it to the transfer PKG 34. The transfer PKG 34 converts the electrical signal input from the PON-PKG 32 into an optical signal and transmits the optical signal to the master station 10 via the optical transmission path 50. The optical SW 22 of the optical selector 20 outputs the optical signal input from the optical transmission path 50 to the transfer PKG 14 of the master station 10. The transfer PKG 14 converts the input upstream signal into an electrical signal and outputs it to the SW 15. The SW 15 transfers the upstream electrical signal received from the PON-PKG 32 and the upstream electrical signal received from the transfer PKG 14 to the higher-level device 80 according to the destination.

[0029] Furthermore, the higher-level device 80 transmits a downstream signal addressed to ONU 60 or ONU 61. SW15 outputs the downstream signal addressed to ONU 60 to PON-PKG 12, which is connected to ONU 60. PON-PKG 12 converts the electrical signal input from SW15 into an optical signal and outputs it to the optical selector 20. The optical selector 20 transmits the optical signal input from PON-PKG 12 to ONU 60.

[0030] Meanwhile, SW15 outputs a downstream signal addressed to ONU 61 to transfer PKG 14. Transfer PKG 14 converts the downstream signal from an electrical signal to an optical signal and outputs it to the optical selector 20. Optical SW22 of the optical selector 20 transmits the optical signal input from transfer PKG 14 to the slave station 30 via the optical transmission path 50. Transfer PKG 34 of the slave station 30 converts the downstream optical signal transmitted over the optical transmission path 50 into an electrical signal and outputs it to the PON-PKG 32 corresponding to the destination ONU 61. PON-PKG 32 converts the input electrical signal into an optical signal and outputs it to the optical selector 40. A coupler 43 of the optical selector 40 branches the optical signal input from PON-PKG 32 into two and transmits the branched optical signals to ONU 61 via the optical transmission path 70.

[0031] When a failure occurs in the PON-PKG 32, the transfer PKG 34 outputs a notification of the occurrence of the failure in the PON-PKG 32 to the master station 10 via the optical transmission path 50. When the control board 11 of the master station 10 receives the notification from the transfer PKG 14, it outputs a PON-PKG switching instruction and an optical selector switching instruction to the slave station 30 via the optical transmission path 50. The slave station 30 switches the PON-PKG 32 in which the failure occurred to the redundant PKG 33 in accordance with the PON-PKG switching instruction. Furthermore, the control board 41 of the optical selector 40 changes the line of the optical SW 42 so that the optical transmission path 70 connected to the PON-PKG 32 in which the failure occurred is connected to the redundant PKG 33.

[0032] After the switching is performed as described above, the optical selector 40 receives the upstream optical signal transmitted by the ONU 61 and outputs the received optical signal to the redundancy PKG 33. Specifically, the coupler 43 of the optical selector 40 branches the upstream optical signal transmitted by the ONU 61 into two, outputs one of the branched optical signals to the PON-PKG 32, and outputs the other branched optical signal to the optical SW 42. The PON-PKG 32 discards the optical signal received from the coupler 43. Meanwhile, the optical SW 42 outputs the optical signal received from the coupler 43 to the redundancy PKG 33. The redundancy PKG 33 converts the upstream optical signal received from the optical SW 42 into an electrical signal and outputs it to the transfer PKG 34. The transfer PKG 34 converts the electrical signal output from the redundancy PKG 33 into an optical signal and transmits the optical signal to the master station 10 via the optical transmission path 50. The optical selector 20 and the master station 10 operate in the same manner as before the switching.

[0033] Furthermore, the higher-level device 80 transmits downstream signals addressed to ONUs 60 and 61. The parent station 10 and the optical selector 20 operate in the same manner as before the switching. The transfer PKG 34 of the child station 30 converts the downstream optical signal transmitted through the optical transmission path 50 into an electrical signal and outputs it to the redundancy PKG 33 according to the destination ONU 61. The redundancy PKG 33 converts the input electrical signal into an optical signal and outputs it to the optical selector 40. The optical SW 42 of the optical selector 40 outputs the optical signal input from the redundancy PKG 33 to the coupler 43 connected to the destination ONU 61. The coupler 43 branches the optical signal input from the optical SW 42 into two and transmits the branched optical signals to the ONU 61 via the optical transmission path 70.

[0034] As described above, when a failure occurs in the PON-PKG 32 of the slave station 30, the transfer PKG 34 transmits failure information to the transfer PKG 14 of the master station 10. When the control panel 11 of the master station 10 receives the failure information, it instructs the PON-PKG 32 of the slave station 30 and the optical selector 40 to switch. In this way, to enable the control panel 11 of the master station 10 to control the slave station 30, the transfer PKG 14 of the master station 10 and the transfer PKG 34 of the slave station 30 are provided with the function of sending and receiving monitor and control signals. The same optical transmission path 50 as for the main signal is used to transmit the control signal between the master station 10 and the slave station 30. The transfer PKG 14 of the master station 10 and the transfer PKG 34 of the slave station 30 perform priority control for the main signal and the control signal.

[0035] According to the terminal device 1 of this embodiment, even if the slave station 30 does not have a control panel, if a malfunction is detected in the PON-PKG 32 of the slave station 30, it is possible to switch to the redundant PKG 33 using the control panel 11 of the master station 10. Furthermore, the space required for installing the control panel of the slave station 30 can be saved, allowing for the device to be made more compact.

[0036] Furthermore, the communication route between the master station and the slave stations may be made redundant. FIG. 2 is a diagram showing an example of the configuration of a terminal device 1a according to an embodiment. In FIG. 2, the same components as those in the terminal device 1 shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. The terminal device 1a includes a master station 10a, an optical selector 20, and a slave station 30a. Redundancy is provided between the optical selector 20 and the slave station 30a by optical transmission paths 50-1 and 50-2. The optical transmission paths 50-1 and 50-2 are, for example, optical fibers. The normal path and the path after switching shown in FIG. 2 indicate the paths of data communication for the ONU 61.

[0037] The master station 10a includes a control panel 11, one or more PON-PKGs 12, one or more redundant PKGs 13, a transfer PKG 14a, and a switch 15. The transfer PKG 14a is connected to the optical transmission paths 50-1 and 50-2 via an optical selector 20. The transfer PKG 14a checks which of the two communication routes using the optical transmission paths 50-1 and 50-2 is a valid link. The transfer PKG 14a transmits and receives control signals between the master station 10a and the slave station 30a via the valid communication route.

[0038] The slave station 30a includes a PON-PKG 32, a redundant PKG 33, a transfer PKG 34a, and an optical selector 40. The transfer PKG 34a is connected to the optical selector 20 via optical transmission paths 50-1 and 50-2. The transfer PKG 34a checks which of the two communication routes using the optical transmission paths 50-1 and 50-2 is a valid link. The transfer PKG 34a transmits and receives control signals between the master station 10a and the slave station 30a via the valid communication route.

[0039] As described above, the optical transmission path 50-1 or 50-2 for transmitting the main signal is used to transmit the control signal between the master station 10a and the slave station 30a. The transfer PKG 14a of the master station 10a and the transfer PKG 34a of the slave station 30a perform priority control for the main signal and the control signal. The terminal device 1a may transfer the main signal and the control signal via different communication routes, such as transmitting the main signal via one of the optical transmission paths 50-1 and 50-2 and transmitting the control signal via the other. Furthermore, the terminal device 1a may load balance the main signal between the optical transmission paths 50-1 and 50-2.

[0040] In the terminal device 1 shown in FIG. 1, the slave station 30 is not equipped with a control panel. Therefore, even if the communication route between the master station 10 and the slave station 30 is redundant, if one of the systems fails on the communication route, the PON protection function may not be controlled. Therefore, the terminal device 1a shown in FIG. 2 provides redundancy between the transfer PKG 14a of the master station 10a and the transfer PKG 34a of the slave station 30a, and transmits and receives control signals using an available communication route. Therefore, in addition to realizing the same functions as the terminal device 1 shown in FIG. 1, even if one of the systems fails on the communication route, it is possible to issue a switchover command from the PON-PKG 32 of the slave station 30a to the redundant PKG 33 and a line switchover command to the optical selector 40. This improves fault tolerance.

[0041] In the above, the main signal and the control signal are transmitted and received between the master station 10 and the slave station 30, and between the master station 10a and the slave station 30a, by optical signals. However, the present invention is not limited to this. For example, the main signal and the control signal may be transmitted and received by electrical signals. In this case, an electrical signal transfer device transfers the main signal and the control signal instead of the optical selector 20. The transfer device transfers the electrical main signal and the control signal between the master station 10 and the slave station 30, and between the master station 10a and the slave station 30a, in the same manner as the optical selector 20. The transfer PKGs 14, 14a, 34, and 34a transmit and receive the main signal and the control signal as electrical signals without converting them to optical signals.

[0042] In the above, the case where electrical signals are transmitted and received between the PON-PKG 12 and the redundant PKG 13 and the SW 15, and between the PON-PKG 32 and the redundant PKG 33 and the transfer PKG 34 has been described, but optical signals may also be transmitted and received. In this case, the transfer PKG 14 and the transfer PKG 34 transfer the optical signals without converting them into electrical signals.

[0043] In the above description, the lower-level devices connected to the terminal device 1 are ONUs 60 and 61 that transmit and receive optical signals, but the present invention is not limited to this. That is, the lower-level devices may transmit and receive electrical signals, wireless signals, etc. In this case, instead of the PON-PKG 12, the redundant PKG 13, the PON-PKG 32, and the redundant PKG 33, a termination device that terminates signals between the lower-level devices is used. And instead of the optical selectors 20 and 40, a transfer device that transfers signals between the lower-level devices and the termination device is used. The signals between the termination device and the transfer PKGs 14 and 14a, and between the termination device and the SW 15, are, for example, electrical signals, but the present invention is not limited to this.

[0044] Although the above describes an example in which the host device 80 and the master stations 10 and 10a transmit and receive electrical signals, the present invention is not limited to this. For example, the host device 80 and the master stations 10 and 10a may transmit and receive optical signals. When the host device 80 and the master stations 10 and 10a transmit and receive optical signals, the PON-PKG 12, the redundant PKG 13, and the transfer PKG 14 output upstream main signals to the SW 15 as optical signals and receive downstream main signals from the SW 15 as optical signals. The PON-PKG 12, the redundant PKG 13, and the transfer PKG 14 do not need to convert optical signals to and from electrical signals. Alternatively, the SW 15 may transmit and receive optical signals to and from the optical selector 20 without passing through the PON-PKG 12 and the redundant PKG 13.

[0045] The terminal equipment of this embodiment will be described in more detail below.

[0046] [First embodiment] In the first embodiment, the master station controls the on / off of light emission of the PON-PKG and redundant PKG of the slave station, and the communication route between the master station and the slave station is not made redundant.

[0047] 3 is a functional block diagram of a terminal device 2 according to the first embodiment. The terminal device 2 includes a master station 100, an optical selector 200, a slave station 300, and an optical selector 400. The terminal device 2, the master station 100, and the optical selector 200 are used as the terminal device 1, the master station 10, and the optical selector 20 in FIG. 1, respectively. The slave station 300 and the optical selector 400 are used as the slave station 30 in FIG. 1.

[0048] The master station 100 includes a control panel 110, a transfer PKG 140, and a line concentrator SW 150. The control panel 110, the transfer PKG 140, and the line concentrator SW 150 are examples of the control panel 11, the transfer PKG 14, and the SW 15, respectively, included in the master station 10 shown in Fig. 1. The master station 100 includes an OSU that uses the PON-PKG 12 and the redundant PKG 13 shown in Fig. 1 as PON interfaces, but these are not shown in Fig. 3.

[0049] The control panel 110 includes an operation processing unit 111, a PKG status management unit 113, and an optical switch control unit 114. When the operation processing unit 111 receives notification of a failure in the PON-PKG 322 from the slave station 300, it controls PON protection for the slave station 300. The operation processing unit 111 includes an emission control unit 112. The PON-PKG 322 and the redundant PON-PKG 332 of the slave station 300 each have a light source for generating an optical signal. The emission control unit 112 controls the start and stop of light emission from the light source for the PON-PKG 322 and the redundant PON-PKG 332 of the slave station 300 in PON protection. The PKG status management unit 113 manages the status of the PKGs included in each of the master station 100 and the slave station 300. The optical switch control unit 114 controls the optical selectors 200 and 400. The optical switch control unit 114 holds information about the lines in the switching unit 220 of the optical selector 200 and the switching unit 420 of the optical selector 400 .

[0050] The transfer PKG 140 includes a transfer processing unit 141. The transfer processing unit 141 converts an upstream optical signal output by the slave station 300 into an electrical signal, outputs the electrical main signal to the line concentrator SW 150, and outputs a control signal to the control board 110. The transfer processing unit 141 also receives a downstream main signal transmitted by the higher-level device 80 from the line concentrator SW 150, and receives a control signal from the control board 110. The transfer processing unit 141 converts the downstream main signal and control signal from an electrical signal into an optical signal and outputs them to the optical selector 200.

[0051] The line concentrator SW 150 includes a SW control unit 151 and a multiplexing unit 152. The SW control unit 151 controls the multiplexing unit 152. The multiplexing unit 152 multiplexes upstream main signals output from the transfer PKG 140 and an operating OSU (not shown), and outputs the multiplexed signals to the destination higher-level device 80. The multiplexing unit 152 also distributes downstream main signals received from the higher-level device 80 to the transfer PKG 140 and an operating OSU (not shown) according to the destination, and outputs the multiplexed signals.

[0052] The optical selector 200 includes an optical selector control unit 210 and a switching unit 220. The optical selector control unit 210 corresponds to the control panel 21 included in the optical selector 20 shown in FIG. 1. The optical selector control unit 210 controls the path of the optical signal in the switching unit 220. The switching unit 220 is the optical SW 22 included in the optical selector 20 shown in FIG. 1. Alternatively, the switching unit 220 may be realized by the optical SW 22 and the coupler 23 included in the optical selector 20. The switching unit 220 has a plurality of ports. The switching unit 220 outputs an optical signal input from one port from another port according to the path set by the optical selector control unit 210.

[0053] The slave station 300 includes an OSU 320, an OSU 330, and a transfer PKG 340. The OSU 320 is an operating OSU, and the OSU 330 is a spare OSU. The slave station 300 may include any number of OSUs 320 and OSUs 330. For simplicity, the following description will be given assuming that the slave station 300 includes one OSU 320 and one OSU 330.

[0054] The OSU 320 includes a PON control unit 321, a PON-PKG 322, and a PON signal processing unit 323. The PON control unit 321 controls communications with the ONUs 61 under its control. This control includes registering and managing the ONUs 61 and allocating upstream bandwidth. The PON control unit 321 retains information related to these controls as configuration information and uses this information when performing control. The PON-PKG 322 corresponds to the PON-PKG 32 included in the master station 10 in FIG. 1. The PON-PKG 322 provides a PON interface to the ONUs 61. The PON-PKG 322 converts upstream optical signals received from the ONUs 61 via the optical transmission path 70 into electrical signals and outputs the electrical signals to the PON signal processing unit 323. The PON-PKG 322 also converts the electrical signals output by the PON signal processing unit 323 into downstream optical signals and transmits them to the ONUs 61 via the optical transmission path 70. The PON signal processing unit 323 acquires a main signal addressed to the higher-level device 80 from the upstream signal output by the PON-PKG 322 and outputs it to the transfer PKG 340. The PON signal processing unit 323 also converts the downstream main signal input from the transfer PKG 340 into an optical signal format and outputs it to the PON-PKG 322.

[0055] The OSU 330 includes a PON control unit 331, a redundant PON-PKG 332, and a PON signal processing unit 333. The functions of the PON control unit 331, the redundant PON-PKG 332, and the PON signal processing unit 333 are similar to those of the PON control unit 321, the PON-PKG 322, and the PON signal processing unit 323 included in the OSU 320. That is, the PON control unit 331 uses configuration information to perform control for communication with the ONUs 61 under the control of the OSU 330. The PON control unit 331 controls the PON signal processing unit 323 and the redundant PON-PKG 332. The redundant PON-PKG 332 corresponds to the redundant PKG 33 included in the master station 10 in FIG. 1. The redundant PON-PKG 332 provides a PON interface to the ONUs 61. The redundant PON-PKG 332 converts upstream optical signals received from the ONU 61 via the optical transmission path 70 into electrical signals and outputs the signals to the PON signal processing unit 333. The redundant PON-PKG 332 also converts electrical signals output by the PON signal processing unit 333 into downstream optical signals and transmits the downstream optical signals to the ONU 61 via the optical transmission path 70. However, under normal conditions, the ONU 61 is not connected to the redundant PON-PKG 332. The PON signal processing unit 333 acquires a main signal addressed to the higher-level device 80 from the upstream signal output by the redundant PON-PKG 332 and outputs the acquired main signal to the transfer PKG 340. The PON signal processing unit 333 also converts downstream main signals input from the transfer PKG 340 into an optical signal format and outputs the acquired main signal to the redundant PON-PKG 332.

[0056] The transfer PKG 340 includes a transfer processing unit 341. The transfer processing unit 341 converts an upstream main signal received from one of the OSUs 320 and 330 that is in operation and a control signal to be transmitted to the master station 100 into an optical signal, and transmits the converted upstream optical signal to the master station 100 via the optical transmission path 50. The transfer processing unit 341 also receives a downstream optical signal transmitted by the master station 100 from the optical transmission path 50 and converts it into an electrical signal. The transfer processing unit 341 distributes and outputs the converted downstream main signal to the OSUs 320 and 330 that are in operation according to their destinations. The transfer processing unit 341 also outputs the converted control signal to the OSUs 320 and 330 and the optical selector 400.

[0057] The optical selector 400 includes an optical selector control unit 410 and a switching unit 420. The optical selector control unit 410 corresponds to the control panel 41 included in the optical selector 40 shown in FIG. 1. The optical selector control unit 410 controls the path of the optical signal in the switching unit 420. The switching unit 420 is implemented by the optical SW 42 and coupler 43 included in the optical selector 40 shown in FIG. 1. The switching unit 420 has multiple ports. These multiple ports are connected to the PON-PKG 322 of the OSU 320, the redundant PON-PKG 332 of the OSU 330, and the ONU 61, respectively. The switching unit 420 outputs an optical signal input from one port from another port in accordance with the path set by the optical selector control unit 410.

[0058] The data communication processing of the terminal device 2 under normal circumstances when no abnormality occurs in the PON-PKG 322 of the slave station 300 will be described. An ONU 60 (not shown) under the master station 100 transmits an upstream signal by optical signal. This upstream signal is a main signal addressed to the upper device 80. An optical selector 200 outputs the optical signal transmitted by the ONU 60 to an OSU (not shown) provided in the master station 100. The OSU of the master station 100 converts the received optical signal into an electrical signal and outputs it to the line concentrator SW 150.

[0059] Meanwhile, the ONU 61 under the control of the slave station 300 transmits an upstream signal as an optical signal. This upstream signal is a main signal addressed to the upper device 80. The switching unit 420 of the optical selector 400 inputs the optical signal transmitted by the ONU 61 from the optical transmission path 70 and outputs the input optical signal to the OSU 320. The PON-PKG 322 of the OSU 320 converts the received optical signal into an electrical signal and outputs it to the PON signal processing unit 323. The PON signal processing unit 323 acquires an upstream signal addressed to the upper device 80 from the received signal output by the PON-PKG 322 and outputs it to the transfer PKG 340. The transfer processing unit 341 of the transfer PKG 340 converts the upstream signal output from the PON signal processing unit 323 from an electrical signal to an optical signal and transmits the optical signal to the master station 100 via the optical transmission path 50. The switching unit 220 of the optical selector 200 outputs the optical signal input from the optical transmission path 50 to the transfer PKG 140 of the master station 100. The transfer processing unit 141 of the transfer PKG 140 converts the input upstream signal into an electrical signal and outputs it to the line concentrator SW 150. The multiplexing unit 152 of the line concentrator SW 150 transfers the upstream signals received from the OSU (not shown) of the master station 100 and the transfer PKG 140 to the higher-level device 80.

[0060] Furthermore, the higher-level device 80 transmits a downstream signal, which is a main signal, addressed to either ONU 60 or ONU 61. The line concentrator SW 150 of the master station 100 outputs the downstream signal to the transfer PKG 140 depending on the destination. That is, the multiplexer 152 of the line concentrator SW 150 outputs the downstream signal addressed to ONU 60 to an OSU (not shown) provided in the master station 100. The OSU of the master station 100 converts the input downstream signal from an electrical signal to an optical signal and transmits it to ONU 60 via the optical selector 20. On the other hand, the multiplexer 152 outputs the downstream signal addressed to ONU 61 to the transfer PKG 140.

[0061] The transfer processing unit 141 of the transfer PKG 140 converts the downstream signal from an electrical signal to an optical signal and outputs it to the optical selector 200. The switching unit 220 of the optical selector 200 transmits the optical signal input from the transfer PKG 140 to the slave station 300 via the optical transmission path 50. The transfer processing unit 341 of the transfer PKG 340 provided in the slave station 300 converts the downstream optical signal transmitted over the optical transmission path 50 into an electrical signal and outputs it to the OSU 320 according to the destination. The PON signal processing unit 323 of the OSU 320 converts the input electrical signal into an optical signal format and outputs it to the PON-PKG 322. The PON-PKG 322 converts the downstream signal input from the PON signal processing unit 323 from an electrical signal to an optical signal and outputs it to the optical selector 400. The switching unit 420 of the optical selector 400 transmits the optical signal input from the OSU 320 to the ONU 61 via the optical transmission path 70.

[0062] Next, a description will be given of the PON protection processing of the terminal device 2 when an abnormality occurs in the PON-PKG 322 of the slave station 300. A failure occurs in the PON-PKG 322 of the slave station 300 (step S11). The slave station 300 notifies the operation processing unit 111 of the control panel 110 provided in the master station 100 of the failure in the PON-PKG 322 (step S12). Specifically, when the PON control unit 321 detects the failure in the PON-PKG 322, it outputs a failure detection notification to the transfer PKG 340. The failure detection notification includes identification information of the slave station 300 and identification information of the PON-PKG 322 in which the failure has occurred. The failure detection notification is transmitted from the transfer PKG 340 to the transfer PKG 140 of the master station 100 in the same manner as the upstream signal in the data communication processing described above. The transfer processing unit 141 of the transfer PKG 140 provided in the master station 100 converts the received upstream signal into an electrical signal and outputs the resulting failure detection notification to the control panel 110 .

[0063] The operation processing unit 111 of the control panel 110 identifies the PON-PKG 322 of the slave station 300 in which the failure has occurred based on the failure detection notification. The operation processing unit 111 references the states of the PON-PKG 322 and the redundant PON-PKG 332 of the slave station 300 managed by the PKG state management unit 113, and selects the redundant PON-PKG 332 as the switching destination. The PKG state management unit 113 updates the state of the PON-PKG 322 in which the failure has occurred to "failed," and rewrites the state of the redundant PON-PKG 332 selected as the switching destination to "switching."

[0064] The operation processing unit 111 instructs the slave station 300 to switch the PON-PKG 322 in which the failure has occurred and the optical selector 400 (step S13). Specifically, the operation processing unit 111 outputs a PON-PKG switching instruction and an optical selector switching instruction to the transfer PKG 140. The optical selector switching instruction is generated by, for example, the optical switch control unit 114. The PON-PKG switching instruction and the optical selector switching instruction include identification information of the PON-PKG 322 in which the failure has occurred and identification information of the switching destination redundant PON-PKG 332. Alternatively, the optical selector switching instruction may include information on the line before switching and the line after switching. The line before switching is the line between the port to which the ONU 61 is connected and the port to which the PON-PKG 322 in which the failure has occurred is connected. The line after switching is the line between the port to which the ONU 61 is connected and the port to which the redundant PON-PKG 332 is connected.

[0065] The transfer processing unit 141 of the transfer PKG 140 converts the PON-PKG switching instruction and the optical selector switching instruction from an electrical signal to an optical signal and outputs them to the optical selector 200. The PON-PKG switching instruction and the optical selector switching instruction are transmitted from the transfer processing unit 141 to the transfer PKG 340 of the slave station 300 in the same manner as the downstream signal in the above-described data communication. The transfer processing unit 341 of the transfer PKG 340 provided in the slave station 300 converts the downstream optical signal to an electrical signal to obtain the PON-PKG switching instruction and the optical selector switching instruction. The transfer processing unit 341 outputs the PON-PKG switching instruction to the OSU 320 and the OSU 330. As a result, the PON control unit 321 of the OSU 320 transfers the setting information of the OSU 320 to the PON control unit 331 of the OSU 330. The PON control unit 331 of the OSU 330 holds the transferred setting information.

[0066] Furthermore, the forwarding processing unit 341 transmits an optical selector switching instruction to the optical selector 400 (step S14). In accordance with the optical selector switching instruction, the optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420, which previously had the PON-PKG 322 of the OSU 320 as the destination, so that the redundant PON-PKG 332 of the OSU 330 becomes the destination. When the optical selector control unit 410 completes the line switching, it responds with an optical selector switching completion (step S15). That is, the optical selector control unit 410 outputs the optical selector switching completion to the forwarding PKG 340. The optical selector switching completion includes information about the line before switching and the line after switching. The optical selector switching completion is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 100 by the same process as in step S12 described above. The operation processing unit 111 outputs the received optical selector switching completion to the optical switch control unit 114. When the optical switch control unit 114 receives the optical selector switching completion notification, it rewrites the information of the line before switching of the switching unit 420 that it holds with the information of the line after switching.

[0067] Next, the light emission control unit 112 of the operation processing unit 111 outputs an instruction to stop light emission of the PON-PKG 322 to the transfer PKG 140. Identification information of the PON-PKG 322 is set in the light emission stop instruction. The light emission stop instruction is transmitted to the slave station 300 by processing similar to that of step S13 (step S16). The transfer processing unit 341 of the slave station 300 outputs the light emission stop instruction to the OSU 320. The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 in accordance with the light emission stop instruction.

[0068] When the PON control unit 321 stops the light emission of the PON-PKG 322, it outputs an light emission stop completion response to the transfer PKG 340. The light emission stop completion response is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 100 by processing similar to that for the failure detection notification in step S12 described above (step S17). When the light emission control unit 112 of the operation processing unit 111 receives the light emission stop completion response, it outputs an instruction to start light emission of the redundant PON-PKG 332 to the transfer PKG 140. Identification information of the redundant PON-PKG 332 is set in the light emission start instruction. The light emission start instruction is transmitted to the slave station 300 by processing similar to that in step S13 (step S18).

[0069] The transfer processing unit 341 of the slave station 300 outputs an optical emission start instruction to the OSU 330. The PON control unit 331 of the OSU 330 starts optical emission of the redundant PON-PKG 332 in accordance with the optical emission start instruction. When the redundant PON-PKG 332 starts optical emission, the PON control unit 331 outputs an optical emission start / switching completion response to the transfer PKG 340. The optical emission start / switching completion response is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 100 by processing similar to that of step S12 described above (step S19). The operation processing unit 111 rewrites the status of the redundant PON-PKG 332 managed by the PKG status management unit 113 to "in operation." This completes the switching.

[0070] The data communication processing of the ONU 61 in the terminal device 2 after switching will be described. The switching unit 420 of the optical selector 400 inputs the optical signal transmitted by the ONU 61 from the optical transmission path 70 and outputs the input optical signal to the OSU 330. The redundant PON-PKG 332 of the OSU 330 converts the received optical signal into an electrical signal and outputs it to the PON signal processing unit 333. The PON signal processing unit 333 obtains an upstream signal addressed to the higher-level device 80 from the received signal output by the redundant PON-PKG 332 and outputs it to the transfer PKG 340. Thereafter, the terminal device 2 performs upstream data communication using the same processing as in the normal state.

[0071] Furthermore, the upper level device 80 transmits a downstream signal addressed to the ONU 61. The terminal device 2 transmits the downstream optical signal to the slave station 300 by the same processing as in the normal state. A transfer processing unit 341 of a transfer PKG 340 provided in the slave station 300 converts the downstream optical signal into an electrical signal and outputs it to the OSU 330 according to the destination. A PON signal processing unit 333 of the OSU 330 converts the input electrical signal into an optical signal format and outputs it to the redundant PON-PKG 332. The redundant PON-PKG 332 converts the downstream signal input from the PON signal processing unit 323 from an electrical signal to an optical signal and outputs it to the optical selector 400. A switching unit 420 of the optical selector 400 transmits the optical signal input from the OSU 330 to the ONU 61 via the optical transmission path 70.

[0072] Next, a description will be given of the operation of switching the PON-PKG in the terminal device 2. First, the operation of the master station 100 when switching the PON-PKG will be described.

[0073] 4 is a sequence diagram of command switching in the master station 100. An operator inputs a command switching command to the control panel 110 of the master station 100 to instruct switching of the PON-PKG of the master station 100 (step S101). The control panel 110 transmits a switching preparation instruction to the source OSU, the destination OSU, and the optical selector 200 (steps S102, S103, S104). The source OSU is an OSU that uses the source PON-PKG, and the destination OSU is an OSU that uses the destination PON-PKG.

[0074] The source OSU transfers its setting information to the destination OSU (step S105). The optical selector control unit 210 of the optical selector 200 switches the line of the switching unit 220, which previously had the source OSU as the transmission / reception destination, so that the destination OSU now becomes the transmission / reception destination (step S106). The optical selector control unit 210 transmits a line switching completion response to the control board 110 (step S107). The line switching completion response includes information on the line before switching and the line after switching. Upon receiving the line switching completion response from the operation processing unit 111, the optical switch control unit 114 of the control board 110 rewrites the stored information on the line before switching of the switching unit 220 to information on the line after switching. Upon completing the transfer of the setting information, the source OSU and the destination OSU transmit a switching preparation completion response to the control board 110 (steps S108 and S109).

[0075] The control panel 110 of the master station 100 manages accommodation information. The accommodation information includes information on the OSUs provided in the master station 100, the OSUs 320 and 330 provided in the slave station 300, and the ONUs 61 connected to each of these OSUs. The operation processing unit 111 rewrites the accommodation information so that the connection destination of the ONUs connected to the source OSU becomes the destination OSU (step S110).

[0076] The control board 110 transmits an instruction to stop light emission to the source OSU (step S111). The source OSU stops light emission from its PON-PKG in accordance with the light emission stop instruction, and then returns an light emission stop completion response (step S112). The control board 110 transmits an instruction to start light emission to the destination OSU (step S113). The destination OSU starts light emission from its redundant PON-PKG in accordance with the light emission start instruction, and then returns an light emission start / switching completion response (step S114).

[0077] FIG. 5 is a sequence diagram of switching due to a PON-PKG failure in the master station 100. In FIG. 5, the same processes as those in FIG. 4 are assigned the same reference numerals. A failure occurs in the PON-PKG of the master station 100 (step S151). The source OSU using the failed PON-PKG transmits failure occurrence information to the control panel 110 (step S152). The control panel 110 transmits switching preparation instructions to the source OSU, the destination OSU, and the optical selector 200 (steps S102, S103, and S104). The control panel 110 transfers the setting information of the source OSU to the destination OSU (step S153). The master station 100 performs the processes from step S106 onward in FIG. 4.

[0078] Next, the operation of switching the PON-PKG of the slave station 300 will be described. Fig. 6 is a sequence diagram of command switching of the PON-PKG of the slave station 300 in the terminal device 2. An operator inputs a command switching instruction to switch the PON-PKG of the slave station 300 to the control panel 110 of the master station 100 (step S201). The command switching may be input through a user interface (not shown) provided in the master station 100, or may be input from a monitoring and control system connected to the master station 100. The operation processing unit 111 of the control panel 110 transmits a switching preparation instruction to OSU 320, which is the source OSU of the slave station 300, OSU 330, which is the destination OSU of the slave station 300, and the optical selector 400 (steps S202, S203, S204).

[0079] The PON control unit 321 of the OSU 320 transfers the setting information of the OSU 320 to the PON control unit 331 of the OSU 330 (step S205). The optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420, which previously had the PON-PKG 322 of the OSU 320 as the destination, so that the redundant PON-PKG 332 of the OSU 330 becomes the destination (step S206). The optical selector control unit 410 transmits a line switching completion response to the control panel 110 of the master station 100 (step S207). The line switching completion response corresponds to the completion of the optical selector switching in step S15 of FIG. 3 and includes information about the line before switching and the line after switching. Based on the line switching completion response, the optical switch control unit 114 of the control panel 110 rewrites the stored information about the line before switching of the switching unit 420 to information about the line after switching. After completing the transfer of the setting information, the PON control unit 321 of the OSU 320 and the PON control unit 331 of the OSU 330 transmit a switching preparation completion response to the control panel 110 of the master station 100 (steps S208 and S209).

[0080] When the operation processing unit 111 receives the switching preparation completion response, it rewrites the accommodation information so that the connection destination of the ONU 61 that was connected to the switching source OSU 320 is changed to the OSU 330 (step S210). The light emission control unit 112 of the operation processing unit 111 transmits an light emission stop instruction to the switching source OSU 320 (step S211). The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 in accordance with the light emission stop instruction and returns an light emission stop completion response (step S212). The light emission control unit 112 of the master station 100 transmits an light emission start instruction to the switching destination OSU 330 (step S213). The PON control unit 331 of the OSU 330 starts the light emission of the redundant PON-PKG 332 in accordance with the light emission start instruction and returns an light emission start / switching completion response (step S214). As described above, the control panel 110 of the master station 100 instructs the PON-PKG 322 and the redundant PON-PKG 332 of the slave station 300 to start and stop light emission.

[0081] 7 is a sequence diagram of switching due to a PON-PKG failure in the slave station 300 in the terminal device 2. In FIG. 7, the same processes as those in FIG. 6 are assigned the same reference numerals. In the slave station 300, a failure occurs in the PON-PKG 322 (step S251). The OSU 320 including the PON-PKG 322 in which the failure occurred becomes the source OSU for switching. The PON control unit 321 of the source OSU 320 transmits failure occurrence information to the control panel 110 of the master station 100 (step S252). The operation processing unit 111 of the control panel 110 selects the OSU 330 to be the destination OSU for switching. The operation processing unit 111 transmits a switching preparation command to the OSU 320, which is the source OSU for switching of the slave station 300, the OSU 330, which is the destination OSU for switching, and the optical selector 400 (steps S202, S203, and S204).

[0082] The slave station 300 transfers the setting information of the original OSU 320 to the destination OSU 330. For example, the setting information of each OSU 320 is stored in advance in the operation processing unit 111 of the master station 100. The operation processing unit 111 transfers the setting information of the original OSU 320 to the PON control unit 331 of the destination OSU 330. Alternatively, the setting information of the original OSU 320 may be transferred to the destination OSU 330 by the following two methods.

[0083] One method is to store the setting information of the OSU 320 in advance in the transfer PKG 340 of the slave station 300. The transfer PKG 340 transfers the setting information of the OSU 320, which is the switching source, to the PON control unit 331 of the OSU 330 (step S253). This reduces the communication time required for transferring the setting information between the master station 100 and the slave station 300.

[0084] Another method is for the PON control unit 331 of the OSU 330 to always hold the setting information of the OSU 320 as a backup even in the normal state. When the PON control unit 331 receives a switching preparation instruction, it reads out the backed-up setting information of the switching source OSU 320 (step S254). This saves the time required to transfer the setting information. After the processing of step S253 or step S254, the terminal device 2 performs the processing from step S206 onwards in FIG. 6.

[0085] Note that a control line other than the optical transmission path 50 may be used to transmit control signals between the master station 100 and the slave stations 300. The master station 100 may also be connected to multiple slave stations 300. For example, the master station 100 may include multiple transfer PKGs 140, each connected to a different slave station 300. When the terminal device 2 includes multiple slave stations 300, the master station 100 does not need to include an OSU.

[0086] [Second embodiment] In the first embodiment, the master station controls the on / off of light emission of the PON-PKG and redundant PKG of the slave station. In the second embodiment, the slave station controls the on / off of light emission of the PON-PKG and redundant PKG of its own station. The second embodiment will be described focusing on the differences from the first embodiment.

[0087] 8 is a functional block diagram of the terminal device 3 according to the first embodiment. In FIG. 8, the same components as those of the terminal device 2 shown in FIG. 3 are assigned the same reference numerals, and their description will be omitted. The terminal device 3 has a master station 103, an optical selector 200, a slave station 303, and an optical selector 400. The terminal device 3, the master station 103, and the optical selector 200 are used as the terminal device 1, the master station 10, and the optical selector 20 in FIG. 1, respectively. The slave station 303 and the optical selector 400 are used as the slave station 30 in FIG. 1.

[0088] The master station 103 differs from the master station 100 shown in Fig. 3 in that it includes a control panel 160 instead of the control panel 110. The control panel 160 differs from the control panel 110 shown in Fig. 3 in that it includes an operation processing unit 161 instead of the operation processing unit 111. The operation processing unit 161 differs from the operation processing unit 111 shown in Fig. 3 in that it does not include the light emission control unit 112.

[0089] The slave station 303 differs from the slave station 300 shown in Fig. 3 in that it includes a transfer package 350 instead of the transfer package 340. The transfer package 350 includes a transfer processing unit 351. The transfer processing unit 351 has the same function as the transfer processing unit 341 of the transfer package 340 included in the slave station 300 shown in Fig. 3. Furthermore, the transfer processing unit 351 includes a light emission control unit 352. The light emission control unit 352 has the same function as the light emission control unit 112 of the control panel 110 included in the master station 100 shown in Fig. 3.

[0090] The data communication process of the terminal device 3 in normal times when no abnormality occurs in the PON-PKG 322 of the slave station 303 is the same as that in the first embodiment.

[0091] The PON protection process of the terminal device 3 when an abnormality occurs in the PON-PKG 322 of the slave station 303 will be described. A failure occurs in the PON-PKG 322 of the slave station 303 (step S31). The PON control unit 321 of the slave station 303 notifies the operation processing unit 161 of the control panel 160 provided in the master station 103 of the failure of the PON-PKG 322 by processing similar to step S12 in the first embodiment (step S32). By processing similar to that in the first embodiment, the operation processing unit 161 of the control panel 160 selects the redundant PON-PKG 332 as the switching destination, and the PKG status management unit 113 rewrites the status of the PON-PKG 322 and the redundant PON-PKG 332.

[0092] The operation processing unit 161 performs the same process as in step S13 in the first embodiment, and instructs the slave station 303 to switch the PON-PKG 322 in which the failure has occurred and the optical selector 400 (step S33). As in the first embodiment, the transfer processing unit 351 of the slave station 303 outputs a PON-PKG switching instruction to the OSU 320 and the OSU 330, and the PON control unit 331 of the OSU 330 holds the setting information of the OSU 320 transferred from the PON control unit 321 of the OSU 320.

[0093] Furthermore, the slave station 303 performs the same processes as steps S14 and S15 in the first embodiment. That is, the forwarding processing unit 351 transmits an optical selector switching instruction to the optical selector 400 (step S34). The optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420 so that the redundant PON-PKG 332 of the OSU 330 becomes the transmission / reception destination instead of the PON-PKG 322 of the OSU 320, and outputs an optical selector switching completion signal (step S35). The optical selector switching completion signal is transmitted to the operation processing unit 161 of the control panel 160 provided in the master station 103 by the same process as in the first embodiment. When the optical switch control unit 114 receives the optical selector switching completion signal via the operation processing unit 161, it rewrites the held information about the line before switching of the switching unit 420 to information about the line after switching.

[0094] The operation processing unit 161 transmits a switching start instruction to the slave station 303 (step S36). When the transfer processing unit 351 of the transfer PKG 350 included in the slave station 303 receives the switching start instruction, the light emission control unit 352 outputs a light emission stop instruction to the OSU 320 (step S37). The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 in accordance with the light emission stop instruction.

[0095] When the PON control unit 321 stops the light emission of the PON-PKG 322, it outputs an light emission stop completion response to the transfer PKG 350 (step S38). When the light emission control unit 352 of the transfer PKG 350 receives the light emission stop completion response, it outputs an light emission start instruction to the OSU 330 (step S39). In accordance with the light emission start instruction, the PON control unit 331 of the OSU 330 starts light emission of the redundant PON-PKG 332.

[0096] When the redundant PON-PKG 332 starts to emit light, the PON control unit 331 outputs an emission start / switching completion response to the transfer PKG 350 (step S40). When the emission control unit 352 of the transfer PKG 350 receives the emission start / switching completion response, it transmits a switching completion response to the master station 103 (step S41). The transfer processing unit 141 of the transfer PKG 140 of the master station 103 outputs the switching completion response to the operation processing unit 161. The operation processing unit 161 rewrites the status of the redundant PON-PKG 332 managed by the PKG status management unit 113 to "in operation." This completes the switching. The data communication processing of the terminal device 3 after switching is the same as in the first embodiment.

[0097] Next, we will explain the operation of switching the PON-PKG in the terminal device 3. Fig. 9 is a sequence diagram of command switching of the PON-PKG of the slave station 303 in the terminal device 3. In Fig. 9, the same processes as those in the terminal device 2 of the first embodiment shown in Figs. 6 and 7 are denoted by the same reference numerals.

[0098] An operator inputs a command switch to instruct switching of the PON-PKG of the slave station 303 to the control panel 160 of the master station 103 (step S201). The operation processing unit 161 of the control panel 160 transmits a switching preparation command to the OSU 320, which is the source OSU of the slave station 303, the OSU 330, which is the destination OSU of the slave station 303, and the optical selector 400 (steps S202, S203, S204).

[0099] The slave station 303 performs the process of step S253 or step S254. That is, the transfer PKG 350 of the slave station 303 transfers the setting information of the OSU 320 that has been stored in advance to the PON control unit 331 of the OSU 330 (step S253). The PON control unit 331 stores the transferred setting information. Alternatively, the PON control unit 331 of the OSU 330 reads out the setting information of the OSU 320 that has been stored as a backup in the normal state (step S254).

[0100] The terminal device 3 performs the same processes as steps S206 to S210 in Fig. 6. That is, the optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420, which previously had the PON-PKG 322 of the OSU 320 as the destination, so that the redundant PON-PKG 332 of the OSU 330 becomes the destination (step S206). The optical selector control unit 410 transmits a line switching completion response to the control board 160 of the master station 103 (step S207). The optical switch control unit 114 of the control board 160 rewrites the stored information about the line before switching of the switching unit 420 to information about the line after switching, based on the line switching completion response. The PON control unit 321 of the OSU 320 and the PON control unit 331 of the OSU 330 transmit a switching preparation completion response to the control board 160 of the master station 103 (steps S208 and S209). The operation processing unit 161 in the control panel 160 of the parent station 103 rewrites the accommodation information so that the connection destination of the ONU 61 that was connected to the switching source OSU 320 is changed to OSU 330 (step S210). The operation processing unit 161 transmits a switching start instruction to the child station 303 (step S301).

[0101] When the transfer PKG 350 of the slave station 303 receives the switching start instruction, the light emission control unit 352 outputs a light emission stop instruction to the switching source OSU 320 (step S302). The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 in accordance with the light emission stop instruction and returns an light emission stop completion response (step S303). The light emission control unit 352 of the master station 103 sends a light emission start instruction to the switching destination OSU 330 (step S304). The PON control unit 331 of the OSU 330 starts the light emission of the redundant PON-PKG 332 in accordance with the light emission start instruction and returns an light emission start / switching completion response (step S305). The light emission control unit 352 of the slave station 303 sends the switching completion response to the master station 103 (step S306).

[0102] 10 is a sequence diagram of switching due to a PON-PKG failure in the remote station 303 in the terminal device 3. In FIG. 10, the same processes as those in the terminal device 2 of the first embodiment shown in FIG. 7 and those in the terminal device 3 of the second embodiment shown in FIG. 9 are denoted by the same reference numerals. In the remote station 303, a failure occurs in the PON-PKG 322 included in the OSU 320 (step S251). The OSU 320 including the PON-PKG 322 in which the failure has occurred becomes the source OSU for switching. The PON control unit 321 of the source OSU 320 transmits failure occurrence information to the control panel 160 of the master station 103 (step S252). The subsequent processes in the terminal device 3 are the same as those from step S202 onwards shown in FIG. 9.

[0103] Normally, the control panel 160 of the master station 103 controls the start and stop of light emission for the PON-PKG 322 and redundant PON-PKG 332 of the slave station 303. When switching PON-PKGs, as described above, the transfer PKG 350 of the slave station 303 controls the start and stop of light emission for the PON-PKG 322 and redundant PON-PKG 332. This makes it possible to omit communication between the master station 103 and the slave station 303, thereby reducing the time and communication bandwidth required for sending and receiving control signals for starting and stopping light emission.

[0104] [Third embodiment] In the third embodiment, the communication route between the master station and the slave station is made redundant, and the master station controls the on / off of the light emission of the PON-PKG and the redundant PKG of the slave station. The third embodiment will be described, focusing on the differences from the first and second embodiments.

[0105] 11 is a functional block diagram of a terminal device 5 according to the third embodiment. In FIG. 11, the same components as those of the terminal device 2 shown in FIG. 3 are assigned the same reference numerals, and their description will be omitted. The terminal device 5 has a master station 105, an optical selector 200, a slave station 305, and an optical selector 400. The terminal device 5, the master station 105, and the optical selector 200 are used as the terminal device 1a, the master station 10a, and the optical selector 20 in FIG. 2, respectively. The slave station 305 and the optical selector 400 are used as the slave station 30a in FIG. 2.

[0106] 3 in that the master station 105 includes a transfer PKG 170 instead of the transfer PKG 140. The transfer PKG 170 includes a transfer processing unit 171 and a link checking unit 172.

[0107] The forwarding processor 171 is connected to two links, the optical transmission path 50-1 and the optical transmission path 50-2, via the optical selector 200. The forwarding processor 171 receives an upstream optical signal output from the slave station 305 via one or both of the communication routes using the two links. The forwarding processor 171 converts the received upstream optical signal into an electrical signal and outputs it to the line concentrator SW150. The forwarding processor 171 also receives a downstream signal transmitted from the upper device 80 via the line concentrator SW150 and converts the received downstream signal from an electrical signal to an optical signal. The forwarding processor 171 distributes the converted optical signal to either the communication route using the optical transmission path 50-1 or the communication route using the optical transmission path 50-2, or to both communication routes by load balancing, and outputs the signal. The forwarding processor 171 outputs a control signal addressed to the slave station 305 from the control panel 110 of the master station 105 to the communication route specified by the link checker 172.

[0108] The link check unit 172 determines the status of two links, the optical transmission path 50-1 and the optical transmission path 50-2. The link check unit 172 determines that an optical transmission path 50-i (i=1, 2) in which no failure has occurred is valid, and determines that an optical transmission path 50-i in which a failure has occurred is invalid. Furthermore, the link check unit 172 determines whether or not an active link is congested. Any technique can be used to check the link status. The link check unit 172 instructs the transfer processing unit 171 on the communication route to be used based on the link status.

[0109] 3 in that the slave station 305 includes a transfer package 360 ​​instead of the transfer package 340. The transfer package 360 ​​includes a transfer processing unit 361 and a link checking unit 362.

[0110] The forwarding processor 361 is connected to two links, the optical transmission path 50-1 and the optical transmission path 50-2. The forwarding processor 361 converts an upstream signal received from one of the OSU 320 and the OSU 330 that is in operation into an optical signal. The forwarding processor 361 distributes the upstream optical signal to either the communication route using the optical transmission path 50-1 or the communication route using the optical transmission path 50-2, or to both communication routes by load balancing, and outputs the signal. The forwarding processor 361 also converts a control signal addressed to the master station 105 into an optical signal and outputs the signal to the communication route specified by the link confirmation unit 362.

[0111] Furthermore, the forwarding processor 361 receives downstream optical signals output by the parent station 105 from either or both of the communication route using the optical transmission path 50-1 and the communication route using the optical transmission path 50-2. The forwarding processor 361 converts the received downstream optical signals into electrical signals to obtain downstream main signals and / or control signals. The forwarding processor 361 distributes and outputs the downstream main signals to the OSUs 320 and 330 in operation according to their destinations. The forwarding processor 361 also outputs the control signals converted into electrical signals to the OSUs 320, 330, and the optical selector 400.

[0112] The link check unit 362 determines the status of two links, the optical transmission path 50-1 and the optical transmission path 50-2. The link check unit 362 determines that an optical transmission path 50-i (i=1, 2) in which no failure has occurred is valid, and determines that an optical transmission path 50-i in which a failure has occurred is invalid. Furthermore, the link check unit 362 determines whether or not an active link is congested. Any technique can be used to check the link status. The link check unit 362 instructs the transfer processing unit 361 on the communication route to be used based on the link status.

[0113] The data communication process between the PON-PKG 322 of the remote station 305 and the terminal device 5 under normal circumstances when no abnormality occurs in the optical transmission lines 50-1 and 50-2 is the same as in the first embodiment, except for the following points.

[0114] That is, the transfer processing unit 361 of the transfer PKG 360 included in the slave station 305 converts the upstream electrical signal output from the PON signal processing unit 323 of the OSU 320 into an optical signal. It is assumed that the link confirmation unit 362 instructs the use of a communication route using the optical transmission path 50-1. The transfer processing unit 361 transmits the upstream optical signal to the master station 105 via the optical transmission path 50-1. The switching unit 220 of the optical selector 200 outputs the optical signal input from the optical transmission path 50-1 to the transfer PKG 170 of the master station 105. The transfer processing unit 171 of the transfer PKG 170 converts the input upstream signal into an electrical signal and outputs it to the line concentrator SW 150.

[0115] Furthermore, the transfer processing unit 171 of the transfer PKG 170 included in the parent station 105 converts a downstream signal received from the upper device 80 via the line concentrator SW 150 from an electrical signal to an optical signal. It is assumed that the link confirmation unit 172 instructs the use of a communication route using the optical transmission path 50-1. The transfer processing unit 171 outputs a downstream optical signal addressed to the ONU 61 to the communication route using the optical transmission path 50-1. The switching unit 220 of the optical selector 200 transmits the optical signal input from the transfer PKG 170 to the child station 305 via the optical transmission path 50-1. The transfer processing unit 361 of the transfer PKG 360 included in the child station 305 converts the downstream optical signal transmitted through the optical transmission path 50-1 into an electrical signal and outputs it to the OSU 320 according to the destination.

[0116] Next, a PON protection process of the terminal device 5 when an abnormality occurs in the PON-PKG 322 of the slave station 305 and the optical transmission path 50-1 will be described. A failure occurs in the PON-PKG 322 of the slave station 305 and the optical transmission path 50-1 (step S51). The link check unit 172 of the transfer PKG 170 provided in the master station 105 and the link check unit 362 of the transfer PKG 360 provided in the slave station 305 check a communication route with a valid link (step S52). For example, the link check unit 172 of the master station 105 and the link check unit 362 of the slave station 305 check a communication route with a valid link at predetermined time intervals. The link check unit 172 and the link check unit 362 detect that the communication route using the optical transmission path 50-1 is not a communication route with a valid link, and that the communication route using the optical transmission path 50-2 is a communication route with a valid link. The link confirmation unit 172 instructs the transfer processing unit 171 to use the communication route using the optical transmission path 50-2. Upon receiving the instruction, the transfer processing unit 171 transmits and receives control signals via the communication route using the optical transmission path 50-2. Similarly, the link confirmation unit 362 instructs the transfer processing unit 361 to use the communication route using the optical transmission path 50-2. Upon receiving the instruction, the transfer processing unit 361 transmits and receives control signals via the communication route using the optical transmission path 50-2.

[0117] The slave station 305 notifies the operation processing unit 111 of the control board 110 included in the master station 105 of the failure of the PON-PKG 322 (step S53). Specifically, when the PON control unit 321 detects a failure of the PON-PKG 322, it outputs a failure detection notification to the transfer PKG 360. The transfer processing unit 361 of the transfer PKG 360 converts the failure detection notification input from the PON-PKG 322 into an optical signal and outputs it to a communication route using the optical transmission path 50-2. The transfer processing unit 171 of the transfer PKG 170 included in the master station 105 inputs the optical signal transmitted through the optical transmission path 50-2 from the optical selector 200, converts the input upstream signal into an electrical signal, and outputs the obtained failure detection notification to the control board 110. The operation processing unit 111 of the control board 110 selects the redundant PON-PKG 332 as the switching destination through processing similar to that in the first embodiment, and the PKG status management unit 113 rewrites the status of the PON-PKG 322 and the redundant PON-PKG 332.

[0118] The operation processing unit 111 instructs the slave station 305 to switch the PON-PKG 322 and the optical selector 400 in which the failure has occurred (step S54). Specifically, the operation processing unit 111 outputs a PON-PKG switching instruction and an optical selector switching instruction to the transfer PKG 170. The transfer processing unit 171 of the transfer PKG 170 converts the PON-PKG switching instruction and the optical selector switching instruction from an electrical signal to an optical signal, and outputs them to a communication route using the optical transmission path 50-2. The switching unit 220 of the optical selector 200 outputs the PON-PKG switching instruction and the optical selector switching instruction to the optical transmission path 50-2. The transfer processing unit 361 of the transfer PKG 360 included in the slave station 305 converts the downstream optical signal transmitted through the optical transmission path 50-2 into an electrical signal, and obtains the PON-PKG switching instruction and the optical selector switching instruction. The transfer processing unit 361 outputs a PON-PKG switching instruction to the OSU 320 and the OSU 330. As a result, the PON control unit 331 of the OSU 330 holds the setting information of the OSU 320 transferred from the PON control unit 321 of the OSU 320, as in the first embodiment.

[0119] Furthermore, the slave station 305 performs the same processes as steps S14 and S15 in the first embodiment. That is, the forwarding processing unit 361 transmits an optical selector switching instruction to the optical selector 400 (step S55). The optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420 so that the redundant PON-PKG 332 of the OSU 330 becomes the transmission / reception destination instead of the PON-PKG 322 of the OSU 320, and outputs an optical selector switching completion (step S56). The optical selector switching completion is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 105 by the same process as in step S53 described above. When the optical switch control unit 114 receives the optical selector switching completion via the operation processing unit 111, it rewrites the held information about the line before switching of the switching unit 420 to information about the line after switching.

[0120] Next, the light emission control unit 112 of the operation processing unit 111 outputs an instruction to stop light emission of the PON-PKG 322 to the transfer PKG 170. The light emission stop instruction is transmitted to the slave station 305 by the same process as in step S54 (step S57). The transfer processing unit 361 of the slave station 305 outputs the light emission stop instruction to the OSU 320. The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 in accordance with the light emission stop instruction.

[0121] When the PON control unit 321 stops the light emission of the PON-PKG 322, it outputs an light emission stop completion response to the transfer PKG 360. The light emission stop completion response is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 105 by processing similar to that of step S53 described above (step S58). When the light emission control unit 112 of the operation processing unit 111 receives the light emission stop completion response, it outputs an instruction to start light emission of the redundant PON-PKG 332 to the transfer PKG 170. The light emission start instruction is transmitted to the slave station 305 in the same manner as in the processing of step S54 (step S59). The transfer processing unit 361 of the slave station 305 outputs the light emission start instruction to the OSU 330.

[0122] The PON control unit 331 of the OSU 330 starts light emission from the redundant PON-PKG 332 in accordance with the light emission start instruction. When the redundant PON-PKG 332 starts light emission, the PON control unit 331 outputs an light emission start / switching completion response to the transfer PKG 360. The light emission start / switching completion response is transmitted to the operation processing unit 111 of the control panel 110 provided in the master station 105 by processing similar to that of step S53 described above (step S60). The operation processing unit 111 rewrites the status of the redundant PON-PKG 332 managed by the PKG status management unit 113 to in operation. This completes the switching.

[0123] The data communication process of the terminal device 5 after switching is the same as that in the first embodiment except for the following points.

[0124] That is, the transfer processing unit 361 of the transfer PKG 360 included in the slave station 305 converts the upstream electrical signal output from the PON signal processing unit 333 of the OSU 330 into an optical signal and transmits the optical signal to the master station 105 via the optical transmission path 50-2. The switching unit 220 of the optical selector 200 outputs the optical signal input from the optical transmission path 50-2 to the transfer PKG 170 of the master station 105. The transfer processing unit 171 of the transfer PKG 170 converts the input upstream signal into an electrical signal and outputs it to the line concentrator SW 150.

[0125] Furthermore, a transfer processing unit 171 of a transfer PKG 170 included in the parent station 105 converts a downstream signal addressed to the ONU 61 received from the upper device 80 via the line concentrator SW 150 from an electrical signal to an optical signal, and outputs the signal to a communication route using the optical transmission path 50-2. A switching unit 220 of the optical selector 200 transmits the optical signal input from the transfer PKG 170 to the child station 305 via the optical transmission path 50-2. A transfer processing unit 361 of a transfer PKG 360 included in the child station 305 converts the downstream optical signal transmitted through the optical transmission path 50-2 into an electrical signal, and outputs the electrical signal to the OSU 330 according to the destination.

[0126] Next, we will explain the operation of switching the PON-PKG in the terminal device 5. Fig. 12 is a sequence diagram of command switching of the PON-PKG of the slave station 305 in the terminal device 5. In Fig. 12, the same processes as those in the terminal device 2 of the first embodiment shown in Fig. 6 are assigned the same reference numerals.

[0127] The master station 105 and the slave station 305 constantly perform link confirmation without a command. Specifically, the link confirmation unit 172 of the master station 105 transmits a link confirmation to the slave station 305 via a communication route using the optical transmission path 50-i (i = 1, 2) (step S501). That is, the link confirmation unit 172 instructs the transfer processing unit 171 to output a link confirmation signal via the communication route using the optical transmission path 50-i. The link confirmation unit 172 may set information about the communication route to be used in the link confirmation signal. The transfer processing unit 171 outputs the link confirmation signal converted into an optical signal to the communication route using the optical transmission path 50-i. The switching unit 220 of the optical selector 200 transmits the optical signal input from the transfer PKG 170 to the slave station 305 via the optical transmission path 50-i. The transfer processing unit 361 of the transfer PKG 360 included in the slave station 305 converts the downstream optical signal transmitted through the optical transmission path 50-i into an electrical signal to obtain a link confirmation signal. The transfer processing unit 361 outputs the link confirmation signal and the communication route through which the link confirmation signal was transmitted to the link confirmation unit 362. The link confirmation unit 362 determines that the communication route using the optical transmission path 50-i is a communication route of a valid link.

[0128] On the other hand, if the link confirmation unit 362 does not receive the next link confirmation signal within a predetermined time after the last time it received a link confirmation signal via a communication route using the optical transmission path 50-i, it determines that the communication route using the optical transmission path 50-i is not a valid link communication route.

[0129] Upon receiving the link confirmation signal, the link confirmation unit 362 returns a link confirmation result response to the master station 105 (step S502). That is, the link confirmation unit 362 instructs the transfer processing unit 361 to output the link confirmation result response via the communication route over which the link confirmation signal was transmitted. The transfer processing unit 361 outputs the link confirmation result response, converted into an optical signal, to the optical transmission path 50-i. The switching unit 220 of the optical selector 200 outputs the optical signal transmitted via the optical transmission path 50-i to the transfer PKG 170 of the master station 105. The transfer processing unit 171 of the transfer PKG 170 converts the input optical signal into an electrical signal to obtain the link confirmation result response. The transfer processing unit 171 outputs the link confirmation result response and the communication route over which the link confirmation result response was transmitted to the link confirmation unit 172. When the link confirmation unit 172 receives the link confirmation result response transmitted via the communication route using the optical transmission path 50-i, it determines that the communication route using the optical transmission path 50-i is a communication route of a valid link.

[0130] On the other hand, if the link confirmation unit 172 does not receive a link confirmation result response within a predetermined time after sending a link confirmation signal via the communication route using the optical transmission path 50-i in step S51, it determines that the communication route using the optical transmission path 50-i is not a valid link communication route.

[0131] The terminal device 5 performs the processes of steps S501 and S502 for each of the optical transmission lines 50-1 and 50-2. The processes of steps S501 to S502 correspond to the process of step S52 in FIG.

[0132] The link check unit 172 of the master station 105 may determine that the communication route has been cut off by the disappearance of the idle signal emitted by the transfer processing unit 361 of the slave station 305 .

[0133] The subsequent processing of the terminal device 5 from step S201 to step S214 is the same as that of the terminal device 2 of the first embodiment shown in Fig. 6. However, the transfer processing unit 171 of the master station 105 and the transfer processing unit 361 of the slave station 305 transmit and receive signals using a communication route where the link is valid and not congested. Furthermore, the transfer processing unit 171 of the master station 105 and the transfer processing unit 361 of the slave station 305 may transmit and receive main signals and control signals using different communication routes.

[0134] Fig. 13 is a sequence diagram of switching due to a PON-PKG failure in the slave station 305 in the terminal device 5. In Fig. 13, the same processes as those in the terminal device 2 of the first embodiment shown in Fig. 7 and those in the terminal device 5 of the third embodiment shown in Fig. 12 are denoted by the same reference numerals.

[0135] The terminal device 5 constantly executes the processes of steps S501 and S502 shown in Fig. 12. When a failure occurs in the PON-PKG 322 included in the switching source OSU 320 in the slave station 305, the terminal device 5 executes the same processes as steps S251 to S214 in Fig. 7. However, the transfer processing unit 171 of the master station 105 and the transfer processing unit 361 of the slave station 305 transmit and receive signals using a communication route where the link is valid and which is not congested. Furthermore, the transfer processing unit 171 of the master station 105 and the transfer processing unit 361 of the slave station 305 may transmit and receive main signals and control signals using different communication routes.

[0136] [Fourth embodiment] In the fourth embodiment, when the communication route between the master station and the slave station is made redundant, the slave station controls the on / off of light emission of its own PON-PKG and redundant PKG. The fourth embodiment will be described, focusing on the differences from the first to third embodiments.

[0137] 14 is a functional block diagram of a terminal device 6 according to the fourth embodiment. In FIG. 14, the same components as those of the terminal device 3 of the second embodiment shown in FIG. 8 and the terminal device 5 of the third embodiment shown in FIG. 11 are designated by the same reference numerals, and their description will be omitted. The terminal device 6 has a master station 106, an optical selector 200, a remote station 306, and an optical selector 400. The terminal device 6, the master station 106, and the optical selector 200 are used as the terminal device 1a, the master station 10a, and the optical selector 20 in FIG. 2, respectively. The remote station 306 and the optical selector 400 are used as the remote station 30a in FIG. 2.

[0138] The master station 106 differs from the master station 105 shown in FIG. 11 in that the master station 106 includes the control panel 160 shown in FIG. 8 instead of the control panel 110.

[0139] 11 in that the transfer PKG 370 is provided instead of the transfer PKG 360. The transfer PKG 370 is also different from the transfer PKG 360 shown in FIG. 11 in that the transfer PKG 370 is provided with a transfer processing unit 371 instead of the transfer processing unit 361. The transfer processing unit 371 performs the same processing as the transfer processing unit 361 shown in FIG. 11. Furthermore, the transfer processing unit 371 includes the light emission control unit 352 of the transfer station 303 shown in FIG. 8.

[0140] The data communication process between the PON-PKG 322 of the remote station 306 and the terminal device 6 under normal circumstances when no abnormality occurs in the optical transmission lines 50-1 and 50-2 is the same as that of the terminal device 5 of the third embodiment.

[0141] The PON protection process of the terminal device 6 will be described below when an abnormality occurs in the PON-PKG 322 and the optical transmission path 50-1 of the remote station 306. The terminal device 6 performs the same processes (steps S71 to S76) as those of the terminal device 5 shown in FIG. 11, steps S51 to S56.

[0142] That is, a failure occurs in the PON-PKG 322 of the slave station 306 and the optical transmission path 50-1 (step S71). The link check unit 172 of the transfer PKG 170 provided in the master station 106 and the link check unit 362 of the transfer PKG 370 provided in the slave station 306 detect that the communication route using the optical transmission path 50-1 is not a communication route with a valid link, and that the communication route using the optical transmission path 50-2 is a communication route with a valid link (step S72). The link check unit 172 and the link check unit 362 instruct the transfer processing unit 171 and the transfer processing unit 371, respectively, to use the communication route with the optical transmission path 50-2.

[0143] The PON control unit 321 of the slave station 306 notifies the operation processing unit 161 of the control panel 160 provided in the master station 106 of the failure of the PON-PKG 322 via a communication route using the optical transmission path 50-2 (step S73). The operation processing unit 161 selects the redundant PON-PKG 332 as the switching destination, and the PKG status management unit 113 rewrites the status of the PON-PKG 322 and the redundant PON-PKG 332.

[0144] The operation processing unit 161 instructs the slave station 306 to switch the PON-PKG 322 in which the failure has occurred and the optical selector 400 via a communication route using the optical transmission path 50-2 (step S74). The transfer processing unit 371 of the transfer PKG 370 included in the slave station 306 converts the received downstream optical signal into an electrical signal to obtain a PON-PKG switching instruction and an optical selector switching instruction. The transfer processing unit 371 outputs the PON-PKG switching instruction to the OSU 320 and the OSU 330. As a result, as in the first embodiment, the PON control unit 331 of the OSU 330 holds the setting information of the OSU 320 transferred from the PON control unit 321 of the OSU 320.

[0145] Furthermore, the forwarding processing unit 371 transmits an optical selector switching instruction to the optical selector 400 (step S75). The optical selector control unit 410 of the optical selector 400 switches the line of the switching unit 420 so that the redundant PON-PKG 332 of the OSU 330 becomes the transmission / reception destination instead of the PON-PKG 322 of the OSU 320, and outputs an optical selector switching completion (step S76). The optical selector switching completion is transmitted to the operation processing unit 161 of the control panel 160 provided in the master station 106. When the optical switch control unit 114 receives the optical selector switching completion via the operation processing unit 161, it rewrites the held information about the line before switching of the switching unit 420 to information about the line after switching.

[0146] The terminal device 6 performs the same processes (steps S77 to S82) as steps S37 to S41 of the terminal device 3 shown in Fig. 8. That is, the operation processing unit 161 transmits a switching start instruction to the slave station 306 via a communication route using the optical transmission path 50-2 (step S77).

[0147] When the transfer processing unit 371 of the transfer PKG 370 included in the slave station 306 receives the switching start instruction, the light emission control unit 352 outputs a light emission stop instruction to the OSU 320 (step S78). The PON control unit 321 of the OSU 320 stops the light emission of the PON-PKG 322 and outputs a light emission stop completion response (step S79). The light emission control unit 352 outputs a light emission start instruction to the OSU 330 (step S80). The PON control unit 331 of the OSU 330 starts the light emission of the redundant PON-PKG 332 and outputs a light emission start / switching completion response (step S81).

[0148] Upon receiving the light emission start / switching completion response, the light emission control unit 352 of the transfer PKG 370 transmits a switching completion response to the master station 106 (step S82). Upon receiving the switching completion response, the operation processing unit 161 of the master station 106 rewrites the state of the redundant PON-PKG 332 managed by the PKG state management unit 113 to "in operation." The data communication processing of the terminal device 6 after switching is the same as that of the terminal device 5 of the third embodiment.

[0149] Next, we will explain the operation of switching the PON-PKG in the terminal device 6. Fig. 15 is a sequence diagram of command switching of the PON-PKG of the slave station 306 in the terminal device 6. In Fig. 15, the same processes as those in the terminal device 3 of the second embodiment shown in Fig. 9 and those in the terminal device 5 of the third embodiment shown in Fig. 12 are assigned the same reference numerals.

[0150] The master station 106 and the slave station 306 constantly check the link by the processing of steps S501 and S502 shown in Fig. 12. The processing of steps S501 to S502 corresponds to the processing of step S72 in Fig. 14. The link check unit 172 of the master station 106 may determine that the communication route is disconnected by the disappearance of the idle signal emitted by the transfer processing unit 371 of the slave station 306.

[0151] The subsequent processing of the terminal device 6 from step S201 to step S306 is the same as the processing of the terminal device 3 of the second embodiment shown in Fig. 9. However, the transfer processing unit 171 of the master station 106 and the transfer processing unit 371 of the slave station 306 transmit and receive signals using a communication route where the link is valid and not congested. Furthermore, the transfer processing unit 171 of the master station 106 and the transfer processing unit 371 of the slave station 306 may transmit and receive main signals and control signals using different communication routes.

[0152] Fig. 16 is a sequence diagram of switching due to a PON-PKG failure in the slave station 306 in the terminal device 6. In Fig. 16, the same processes as those in the terminal device 3 of the second embodiment shown in Fig. 10 and those in the terminal device 5 of the third embodiment shown in Fig. 12 are denoted by the same reference numerals.

[0153] The master station 106 and the slave station 306 constantly check the link by the processes of steps S501 and S502 shown in Fig. 12. The link check unit 172 of the master station 106 may determine that the communication route has been cut off by the disappearance of the idle signal emitted by the transfer processing unit 371 of the slave station 306.

[0154] The subsequent processing of the terminal device 6 from step S251 to step S306 is the same as the processing of the terminal device 3 of the second embodiment shown in Fig. 10. However, the transfer processing unit 171 of the master station 106 and the transfer processing unit 371 of the slave station 306 transmit and receive signals using a communication route where the link is valid and not congested. Furthermore, the transfer processing unit 171 of the master station 106 and the transfer processing unit 371 of the slave station 306 may transmit and receive main signals and control signals using different communication routes.

[0155] In the first and second embodiments, even if the communication route to the installation location of the slave station is made redundant, the slave station is not equipped with a control panel, so if one system on the route fails, it may become impossible to control the PON protection function.The third and fourth embodiments make it possible to reduce the size of the device and realize a PON protection function that functions even if one system on the communication route fails.

[0156] In the above description, a case where main signals and control signals are transmitted and received by optical signals between the master station 100 and the slave station 300, between the master station 103 and the slave station 303, between the master station 105 and the slave station 305, and between the master station 106 and the slave station 306 (hereinafter collectively referred to as between the master station and the slave station) has been described as an example. However, this is not limiting, and for example, transmission and reception may be by electrical signals. In this case, instead of the optical selector 200, an electrical signal forwarding device forwards signals between the master station and the slave station. The forwarding processing units 141 and 171 transmit downstream main signals and control signals addressed to the slave stations as electrical signals, and receive upstream main signals and control signals addressed to the respective stations as electrical signals. The forwarding processing units 341, 351, 361, and 371 transmit upstream main signals and control signals addressed to the master stations as electrical signals, and receive downstream main signals and control signals addressed to the respective stations as electrical signals. Furthermore, the main signal and the control signal may be transmitted and received between the master station and the slave station by radio signals.

[0157] In the above description, the PON-PKG 322 and the redundant PON-PKG 332 convert upstream optical signals from the ONU 61 into electrical signals and output the converted signals, and convert downstream electrical signals into optical signals and transmit them to the ONU 61. However, the PON-PKG 322 and the redundant PON-PKG 332 may output upstream optical signals from the ONU 61 without converting them into electrical signals, and may receive downstream optical signals and transmit them to the ONU 61. In this case, the transfer processing units 341, 351, 361, and 371 transmit and receive optical signals to and from the OSUs 320 and 330.

[0158] In the above description, the lower-level device connected to the slave station 300 is the ONU 61 that transmits and receives optical signals, but this is not limiting. That is, the lower-level device may transmit and receive electrical signals, wireless signals, etc. In this case, a termination device that terminates signals between the lower-level device is used instead of the OSUs 320 and 330. The signals between the termination device and the transfer processing units 341, 351, 361, and 371 are, for example, electrical signals or optical signals, but are not limited to these.

[0159] In the above description, the multiplexing unit 152 of the line concentrator SW 150 and the higher-level device 80 transmit and receive electrical signals, but the present invention is not limited to this. For example, the multiplexing unit 152 and the higher-level device 80 may transmit and receive optical signals. When the multiplexing unit 152 and the parent stations 10 and 10a transmit and receive optical signals, the forwarding processing units 141 and 171 output upstream main signals to the multiplexing unit 152 as optical signals, and receive downstream main signals from the multiplexing unit 152 as optical signals. The forwarding processing units 141 and 171 do not need to convert between optical signals and electrical signals.

[0160] The above-described operation processing units 111 and 161, package status management unit 131, optical switch control unit 114, SW control unit 151, PON control units 321 and 331, and light emission control unit 352 may each include a processor, memory, auxiliary storage device, and the like, which are connected via a bus, and the processor may execute a program to realize the above functions. The processor may be, for example, a central processing unit (CPU) or a graphics processing unit (GPU). Note that all or part of the functions of the operation processing units 111 and 161, package status management unit 131, optical switch control unit 114, SW control unit 151, PON control units 321 and 331, and light emission control unit 352 may be realized using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The programs for the operation processing units 111 and 161, the package status management unit 131, the optical switch control unit 114, the SW control unit 151, the PON control units 321 and 331, and the light emission control unit 352 may be recorded on a computer-readable recording medium. Examples of computer-readable recording media include portable media such as flexible disks, magneto-optical disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The programs for the operation processing units 111 and 161, the package status management unit 131, the optical switch control unit 114, the SW control unit 151, the PON control units 321 and 331, and the light emission control unit 352 may be transmitted via telecommunications lines.

[0161] According to the above-described embodiment, the terminal device includes a first communication device and a second communication device. For example, the terminal device corresponds to the terminal devices 1, 1a, 2, 3, 5, and 6 of the embodiment, the first communication device corresponds to the slave stations 30, 30a, 300, 303, 305, and 306 of the embodiment, and the second communication device corresponds to the master stations 10, 10a, 100, 103, 105, and 106 of the embodiment.

[0162] The first communication device includes a redundant first terminal device, a relay unit, and a notification unit. For example, the first terminal device corresponds to PON-PKG 32, redundant PKG 33, OSU 320, and OSU 330; the relay unit corresponds to transfer PKGs 34, 34a, 340, 350, 360, and 370; and the notification unit corresponds to PON control unit 321. The first terminal device terminates signals between the first lower-level device and the first lower-level device. The first lower-level device corresponds to, for example, ONU 61 in the embodiment. The relay unit transmits a main signal received by the first terminal device from the first lower-level device to the second communication device, and transmits a main signal received from the second communication device and addressed to the first lower-level device to the first lower-level device via the first terminal device. The notification unit notifies the second communication device of the occurrence of an abnormality when an abnormality occurs in the first terminal device during operation.

[0163] The second communication device includes a transceiver unit, a switch unit, and a control unit. For example, the transceiver unit corresponds to the transfer PKGs 14, 14a, 140, and 170 of the embodiments, the switch unit corresponds to the SW 15 and the line concentrator SW 150 of the embodiments, and the control unit corresponds to the control panels 11, 110, and 160 of the embodiments. The transceiver unit receives a main signal from the relay unit, the main signal being transmitted from the first lower-level device, and transmits the main signal addressed to the first lower-level device to the relay unit. The switch unit transmits the main signal received by the transceiver unit from the relay unit to the higher-level device, and transmits the main signal received from the higher-level device and addressed to the first lower-level device from the transceiver unit to the relay unit. When the control unit is notified by the notification unit that an abnormality has occurred in the first terminal device, it performs switching control to switch the first terminal device in which the abnormality has occurred to a spare first terminal device.

[0164] The first terminal device may terminate an optical signal between the first terminal device and the first lower-level device. The control unit or the first communication device may also include an emission control unit. The emission control unit instructs the first terminal device in which an abnormality has occurred to stop emitting light and the first terminal device to which the switchover is to be made to start emitting light.

[0165] The relay unit may store the setting information of the first terminal device. The first terminal device as the switching destination acquires the setting information of the first terminal device in which the abnormality has occurred from the relay unit.

[0166] The relay unit and the transceiver unit may transmit and receive the control signal for switching control and the main signal via a redundant communication route, which may be, for example, an optical transmission line.

[0167] The second communication device may further include a second termination device. The second termination device corresponds, for example, to the PON-PKG 12 and redundant PKG 13 in the embodiments. The second termination device terminates signals between the second lower device and the second lower device. The second lower device corresponds, for example, to the ONU 60 in the embodiments. The switch unit performs the following processes: transmitting the main signal received by the transmitter / receiver from the relay unit and the main signal received by the second termination device from the second lower device to the higher device; transmitting, from the transmitter / receiver unit to the relay unit, the main signal addressed to the first lower device among the main signals received from the higher device; and transmitting the main signal addressed to the second lower device to the second lower device via the second termination device.

[0168] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the present invention that do not deviate from the gist of the present invention. [Explanation of symbols]

[0169] 1, 1a, 2, 3, 5, 6 Terminal equipment 10, 10a, 100, 103, 105, 106 Master station 11 Control Panel 12 PON-PKG 13 Redundancy PKG 14, 14a Transfer PKG 15 Switch 20 Optical Selector 21 Control Panel 22 Optical Switch 23 Coupler 30, 30a, 300, 303, 305, 306 slave station 32 PON-PKG 33 Redundancy PKG 34, 34a Transfer PKG 40 Optical Selector 41 Control Panel 42 Optical Switch 43 Coupler 50, 50-1, 50-2, 70 Optical transmission line 60, 61 ONU 80 Upper device 110, 160 control panel 111, 161 Operation processing section 112 Light emission control unit 113 PKG status management unit 114 Optical switch control unit 131 PKG status management unit 140 Transfer PKG 141 Transfer processing unit 150 Concentration SW 151 SW control unit 152 Multiplex section 170 Transfer PKG 171 Transfer Processing Unit 172 Link Verification Section 200 Optical Selector 210 Optical selector control section 220 Switching section 320, 330 OSU 321, 331 PON control unit 322 PON-PKG 323, 333 PON signal processing unit 332 Redundant PON-PKG 340, 350, 360, 370 Transfer PKG 341, 351, 361, 371 Transfer processing section 352 Light Emission Control Unit 362 Link Verification Section 400 Optical Selector 410 Optical selector control unit 420 Switching section

Claims

1. A terminal device including a first communication device and a second communication device, The first communication device a redundant first termination device that terminates signals between the first lower-level device and the first lower-level device; a relay unit that performs a process of transmitting a main signal received by the first terminal device from the first lower-level device to the second communication device, and a process of transmitting a main signal received from the second communication device and addressed to the first lower-level device to the first terminal device via the first terminal device; a notification unit that notifies the second communication device of the occurrence of an abnormality when an abnormality occurs in the first terminal device during operation, The second communication device a transmitting / receiving unit that receives the main signal originating from the first lower-level device from the relay unit and transmits the main signal addressed to the first lower-level device to the relay unit; a switch unit that performs a process of transmitting the main signal received from the relay unit by the transceiver unit to a higher-level device, and a process of transmitting a main signal received from the higher-level device and addressed to the first lower-level device from the transceiver unit to the relay unit; a control unit that performs switching control to switch the first terminal device in which an abnormality has occurred to a standby first terminal device when the notification unit notifies the occurrence of an abnormality in the first terminal device, Terminal equipment.

2. the first terminal device terminates an optical signal between the first terminal device and the first downstream device; the control unit or the first communication device includes a light emission control unit that instructs the first terminal device, where an abnormality has occurred, to stop emitting light and the first terminal device, which is a switching destination, to start emitting light; 2. The terminal device according to claim 1.

3. the relay unit stores setting information of the first terminal device; the first terminal device as a switching destination acquires, from the relay unit, the setting information of the first terminal device in which the abnormality has occurred; 2. The terminal device according to claim 1.

4. The relay unit and the transmission / reception unit transmit and receive the control signal for the switching control and the main signal via a redundant communication route. The terminal device according to any one of claims 1 to 3.

5. the communication route is an optical transmission path; 5. The terminal device according to claim 4.

6. the second communication device further includes a second termination device that terminates signals between the second communication device and a second lower-level device; the switch unit performs a process of transmitting the main signal received by the transmitting / receiving unit from the relay unit and the main signal received by the second terminal device from the second lower device to a higher-level device, and a process of transmitting, from the transmitting / receiving unit to the relay unit, a main signal addressed to the first lower-level device among the main signals received from the higher-level device, and transmitting a main signal addressed to the second lower-level device to the second lower-level device via the second terminal device.

2. The terminal device according to claim 1.

7. a transceiver unit that receives a main signal transmitted by a first lower-level device from another communication device having a redundant first termination device that terminates a signal between the first lower-level device and the other communication device, and transmits a main signal addressed to the first lower-level device to the other communication device; a redundant second termination device that terminates signals between the second lower-level device and the second lower-level device; a switch unit that performs a process of transmitting the main signal received by the transmitting / receiving unit from the other communication device and the main signal received by the second terminal device from the second lower device to a higher-level device, and a process of transmitting, from the transmitting / receiving unit to the other communication device, a main signal addressed to the first lower device among the main signals received from the higher-level device, and transmitting a main signal addressed to the second lower device to the second lower device via the second terminal device; a control unit that performs switching control to switch the first terminal device in which an abnormality has occurred to a standby first terminal device when the other communication device notifies the first terminal device of an abnormality occurrence; A communication device comprising:

8. A switching control method in an end station device including a first communication device and a second communication device, a first transmission / reception step in which an active terminating device among redundant terminating devices of the first communication device transmits and receives a main signal to and from a lower-level device; a relay step in which a relay unit of the first communication device performs a process of transmitting the main signal received in the first transmission / reception step to the second communication device, and a process of transmitting the main signal received from the second communication device and addressed to the lower device in the first transmission / reception step to the lower device; a second transmission / reception step in which a transmission / reception unit of the second communication device receives the main signal originating from the lower device from the first communication device, and transmits the main signal destined for the lower device to the first communication device; an upper communication step in which a switch unit of the second communication device transmits the main signal received in the second transmission / reception step to an upper device and receives a main signal addressed to the lower device from the upper device; a notification step in which, when an abnormality occurs in the terminating device during operation, a notification unit of the first communication device notifies the second communication device of the occurrence of the abnormality; a switching step in which a control unit of the second communication device performs switching control to switch the termination device in which an abnormality has occurred to a standby termination device when the control unit is notified of the occurrence of an abnormality in the termination device by the notifying step; A switching control method comprising:

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