JP2012089979A - Subscriber side optical line termination apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a subscriber side optical line termination apparatus for changing over an active system and reserve system without the occurrence of collision of signals.SOLUTION: A subscriber side optical line termination apparatus to be used for a passive optical network (PON) type optical transmission system is connected to a center side optical line termination apparatus (OLT 20) via multiple lines of optical transmission paths so as to perform communication with one optical path as an active system and with the other path as a reserve system. The apparatus includes: an abnormality detection part (a monitor control part 12) for detecting abnormality in the active system; a disconnection processing part (the monitor control part 12) for performing processing to disconnect a PON link with the center side optical line termination apparatus when the abnormality detection part detects the abnormality; a disconnection detection part (the monitor control part 12) for detecting the disconnection of the PON link by the operation of the disconnection processing part; and a changeover part (the monitor control part 12) for changing over the active system into the reserve system when the disconnection detection part detects the disconnection of the PON link.

Description

  The present invention relates to a subscriber premises optical line termination device.

  Patent Documents 1 and 2 propose systems in the PON system in which the optical transmission path between the center side optical line terminator and the optical coupler is duplexed, with one as the active system and the other as the standby system.

JP 2007-235504 A JP 2007-311953 A

  Patent Documents 1 and 2 are techniques for duplicating an optical transmission line between a center-side optical line terminator and an optical coupler. On the other hand, it may be desired to duplex between the optical coupler and the customer premises optical line termination device.

  By the way, the upstream optical signal from the subscriber premises optical line terminator to the center side optical line terminator is transmitted based on TDMA. For this reason, each subscriber premises optical line terminator needs to transmit an optical signal at a timing assigned to itself. However, when the duplex between the optical coupler and the customer premises optical line terminator is used, the optical path length of the active system and the standby system may be different. In this case, if the signal is transmitted at the timing assigned in the active system In some cases, a collision occurs with a signal from another subscriber-side optical line terminating device.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a subscriber premises optical line termination device capable of switching between an active system and a standby system without causing signal collision.

In order to solve the above-described problems, the present invention provides a subscriber-side optical line terminator used in a PON (Passive Optical Network) type optical transmission system, the center-side optical line terminator and a plurality of systems of optical transmission. An abnormality detection unit that detects an occurrence of an abnormality in the working system in a subscriber premises optical line terminator that communicates with one of the optical transmission lines as a working system and the other as a protection system, When the occurrence of an abnormality is detected by the abnormality detection unit, the PON link is disconnected by the operation of the disconnection processing unit for executing the processing for disconnecting the PON link with the center-side optical line terminating device and the operation of the disconnection processing unit. A disconnection detecting unit for detecting the disconnection, and a switching unit for switching from the active system to the standby system when the disconnection detecting unit detects disconnection of the PON link.
According to such a configuration, it is possible to switch between the active system and the standby system without causing a signal collision.

According to another invention, in addition to the above invention, the disconnection processing unit outputs a shutdown signal for shutting down an ONU (Optical Network Unit) to the ONU.
According to such a configuration, the PON link can be reliably interrupted by the shutdown signal.

According to another invention, in addition to the above invention, the disconnection processing unit outputs a transmission prohibition signal for prohibiting transmission to the center side to the ONU, and after the switching by the switching unit is completed. The transmission permission signal is output to the ONU.
According to such a configuration, the PON link can be brought down by the transmission prohibition signal, and by prohibiting transmission, it is possible to reliably prevent the transmission signal from being output during switching.

According to another invention, in addition to the above invention, the abnormality detection unit detects an abnormality when an optical input level of the working system becomes smaller than a predetermined threshold value.
According to such a configuration, it is possible to detect an abnormality in the optical transmission line and switch from the active system to the standby system.

In addition to the above invention, another invention is characterized in that the abnormality detection unit detects an abnormality when the optical output level of the working system becomes smaller than a predetermined threshold value.
According to such a configuration, it is possible to detect an abnormality in the laser diode for transmission and switch from the active system to the standby system.

In addition to the above invention, another invention is characterized in that the optical transmission lines of the plurality of systems are connected to one center-side optical line terminator disposed on the center side.
According to such a configuration, even when a failure occurs in the optical transmission line, it is possible to continue communication by switching from the active system to the standby system.

In addition to the above invention, another invention is characterized in that the optical transmission lines of the plurality of systems are respectively connected to a plurality of center side optical line terminators arranged on the center side.
According to such a configuration, the reliability of communication can be improved by multiplexing the center side optical line terminator.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the customer premises optical line termination | terminus apparatus which can switch an active system and a protection system, without producing a signal collision.

It is a figure which shows the structural example of the PON type | mold optical transmission system containing the subscriber premises optical line termination | terminus apparatus which concerns on 1st Embodiment of this invention. It is a flowchart for demonstrating operation | movement of 1st Embodiment. It is a figure which shows the signal waveform of each part of 1st Embodiment. It is a figure which shows the structural example of the customer premises optical line termination | terminus apparatus which concerns on 2nd Embodiment. It is a flowchart for demonstrating operation | movement of 2nd Embodiment. It is a figure which shows the signal waveform of each part of 2nd Embodiment. It is a figure which shows the structural example of the subscriber optical fiber terminal device concerning a 3rd embodiment. It is a figure which shows the signal waveform of each part of 3rd Embodiment. It is a figure which shows the structural example of the PON type | mold optical transmission system which concerns on 4th Embodiment.

  Next, an embodiment of the present invention will be described.

(A) Description of Configuration of First Embodiment FIG. 1 is a configuration example of a PON (Passive Optical Network) type optical transmission system including a redundant customer premises optical line terminating device 10 according to the first embodiment of the present invention. FIG. As shown in this figure, a PON type optical transmission system includes a redundant subscriber premises optical line terminator 10 (corresponding to “subscriber premises optical line terminator” in the claims), a center side optical line terminator. OLT (Optical Line Terminal) 20 as an ONU 30, ONUs 30 and 40 as subscriber-side optical line terminators, optical fibers 21, 50-1, 50-2, 51-1 to 51-3 (“optical” in claims) And the optical couplers 50 and 51 (corresponding to the “optical transmission line” in the claims). In the following description, the redundant subscriber premises optical line terminator 10 and the ONUs 30 and 40 are appropriately referred to as “subscriber premises optical line terminators”.

  Here, the OLT 20 multiplexes and transmits the information to be transmitted to each subscriber premises optical line terminating device by, for example, TDM (Time Division Multiplexing). The OLT 20 exchanges information with each subscriber premises optical line terminator, and establishes a PON link when each subscriber premises optical line terminator satisfies a predetermined condition. In addition, when the OLT 20 and each subscriber premises optical line terminator are compliant with GE-PON (Gigabit Ethernet (registered trademark) -PON), the establishment of this PON link is a procedure of the IEEE 802.3ah standard. It is based on.

  The optical coupler 50 demultiplexes the light incident from the optical fiber 21 into two, emits the light to the optical fibers 50-1 and 50-2, and transmits the light incident from the optical fibers 50-1 and 50-2. The light is multiplexed and emitted to the optical fiber 21. The optical coupler 51 demultiplexes the light incident from the optical fiber 50-2 into three, emits the light to the optical fibers 51-1 to 51-3, and enters from the optical fibers 51-1 to 51-3. The lights are combined and output to the optical fiber 50-2.

  The redundant subscriber premises optical line terminating device 10 according to the first embodiment includes an optical switch 11 (corresponding to “switching unit” in the claims), a supervisory control unit 12 (“abnormality detection unit, disconnection in claims”). Corresponding to a processing unit and a disconnection detection unit), and an ONU 13 as a main component, installed in a service subscriber's home or premises, and a home network (not shown) (hereinafter referred to as a “home network”) Connected to. The redundant subscriber premises optical line terminator 10 converts the optical signal transmitted from the OLT 20 into an electrical signal and supplies it to the home network, and converts the electrical signal supplied from the home network into an optical signal. To the OLT 20. The optical transmission line between the redundant subscriber premises optical line terminating device 10 and the optical couplers 50 and 51 is duplexed, one is the active system and the other is the standby system, and these are switched as necessary. Used.

  Here, the optical switch 11 selects one of the optical fiber 50-1 (A system) and the optical fiber 51-1 (B system) according to the switching signal from the monitoring control unit 12, and connects to the ONU 13. To do. The optical switch 11 detects the intensity of the optical signal input from the optical fiber 50-1 and supplies it to the monitoring controller 12 as an optical input A monitor signal, and the optical signal input from the optical fiber 51-1. Is detected in the same manner and supplied to the monitoring controller 12 as an optical input B monitor signal.

  The monitoring control unit 12 detects an abnormality with reference to the monitor signal of the working system among the optical input A monitor signal and the optical input B monitor signal supplied from the optical switch 11, and when an abnormality is detected A switching signal is output to the optical switch 11 to switch the connection. In addition, when an abnormality is detected, the monitoring control unit 12 outputs a shutdown signal to the ONU 13 to shut down the ONU 13 and disconnect the PON link. At this time, the PON link state is monitored to confirm that the PON link has been disconnected.

  The ONU 13 acquires a packet addressed to itself from the time-division multiplexed optical signal received from the OLT 20 and sends it to the home network. The ONU 13 converts an electrical signal received from the home network into an optical signal, and transmits the optical signal to the OLT 20 at a timing assigned from the OLT 20.

  ONU 30 and ONU 40 are normal subscriber-side optical line terminators that are not duplexed. The ONU 30 is connected to the optical coupler 51 by an optical fiber 51-2, and the ONU 40 is connected to the optical coupler 51 by an optical fiber 51-3.

(B) Description of Operation of First Embodiment Next, the operation of the first embodiment will be described. FIG. 2 is a flowchart for explaining an example of processing executed in the first embodiment. FIG. 3 is a diagram showing signal waveforms at various parts of the redundant customer premises optical line terminating device 10 shown in FIG. In the following, when the optical fiber 50-1 is the active system and the optical fiber 51-1 is the standby system, an abnormality occurs and an optical signal transmitted through the optical fiber 50-1 is transmitted. The operation when the level is lowered and the active system is switched to the standby system will be described as an example.

  When the processing of the flowchart shown in FIG. 2 is started, the following steps are executed.

  Step S <b> 1: The monitoring control unit 12 detects the active optical input monitor value M from the optical switch 11. In this example, since the optical fiber 50-1 is selected as the active system, the monitoring controller 12 detects the optical input A monitor value M input via the optical fiber 50-1.

  Step S2: The monitoring control unit 12 compares the optical input monitor value M detected in Step S1 with a predetermined threshold Th, and if M <Th is satisfied (Step S2: Yes), the process proceeds to Step S3, otherwise In the case of (Step S2: Yes), the process returns to Step S1 and the same process as described above is repeated. For example, as shown in FIG. 3A, when the optical input A monitor value starts to decrease at time t1 and falls below the threshold Th at time t2, it is determined Yes and the process proceeds to step S3.

  Step S3: The monitoring controller 12 outputs an ONU shutdown signal to the ONU 13. Here, the ONU shutdown signal is a signal for resetting the ONU 13, and upon receiving this signal, the ONU 13 returns to the initial state and disconnects the PON link with the OLT 20. FIG. 3B shows an example of the shutdown signal. In this example, the shutdown signal is “H” at time t3 and “L” at time t4. When receiving such a shutdown signal, the ONU 13 executes the shutdown.

  Step S4: The monitoring controller 12 detects the link state of the ONU 13. Specifically, the monitoring control unit 12 detects whether the PON link is maintained or is down with reference to the PON link state signal supplied from the ONU 13.

  Step S5: The monitoring controller 12 refers to the link state detected in Step S4, and proceeds to Step S6 when the PON link is down (disconnected) (Step S5: Yes), and otherwise (Step S5) In step S5: No), the process returns to step S4 to repeat the same process as described above. In the example of FIG. 3C, since the PON link down is detected at time t5, as a result, the determination is Yes and the process proceeds to step S6.

  Step S6: The monitoring controller 12 switches the optical switch 11 from the active system to the standby system. In the present example, since the optical fiber 50-1 is the active system and the optical fiber 51-1 is the standby system, the selection of the optical switch 11 is changed from the optical fiber 51-1 to the optical fiber 50-1. In the example of FIG. 3D, at time t6, the switching signal is changed from “L” to “H”, and switching from the working system to the B system that is the standby system is performed.

  Step S7: The OLT 20 executes P2MP (Point to Multipoint) discovery, and again establishes the PON link between the redundant customer premises optical line terminating device 10 and the OLT 20 via the optical fiber 51-1, which is a standby system. Establish. Specifically, after the PON link goes down, the OLT 20 detects the redundant subscriber premises optical line terminating device 10 via the optical fiber 51-1, which is a standby system, and assigns an LLID (Logical Link ID) thereto. And establish a PON link. As a result, as shown at time t7 in FIG. 3C, the PON link changes from the down state to the established state. At this time, the OLT 20 extends from the OLT 20 through the optical fiber 21, the optical coupler 50, the optical fiber 50-2, the optical coupler 51, and the optical fiber 51-1, to the redundant customer premises optical line terminating device 10. The RTT (Round Trip Time) is measured, and the redundant customer premises optical line terminating device 10 performs time synchronization with the OLT 20. When the redundant subscriber premises optical line terminator 10 transmits an upstream signal, a packet is transmitted at a timing set based on the standby RTT, so that it collides with upstream signals from other ONUs. You can avoid that. As shown in FIG. 3D, a period from time t6 to time t7 is referred to as an ONU re-registration period.

  As described above, according to the first embodiment of the present invention, when an abnormality occurs in the working system, the shutdown signal is output to shut down the ONU 13, and after the PON link down is detected, the working The system was switched from the standby system to the standby system. In this way, by switching from the active system to the standby system after the PON link down is detected, the standby system transmits packets at the timing assigned to the active system (timing based on the active system RTT), and the packets collide. Can be avoided. Also, by bringing down the PON link, P2MP discovery for the standby system can be quickly executed and the PON link can be established.

(C) Description of Configuration of Second Embodiment Next, the second embodiment will be described. FIG. 4 is a block diagram illustrating a configuration example of the redundant customer premises optical line terminating device 10A according to the second embodiment. 4 is connected to a PON type optical transmission system in place of the redundant subscriber premises optical line termination device 10 shown in FIG.

  As shown in FIG. 4, the redundant subscriber premises optical line terminating device 10A includes TRxA 70, TRxB 71, switches 72 and 73 (corresponding to “switching unit” in the claims), AND elements 74 and 75, and a supervisory control unit. 76 (corresponding to “abnormality detection unit, disconnection processing unit, disconnection detection unit”) and MAC (Media Access Control) unit 77 are the main components.

  Here, the TRxA 70 converts the optical signal received from the optical fiber 50-1 into an electrical signal, supplies it to the switch 73 as an Rx (reception) signal, and transmits the transmission (Tx) signal supplied from the switch 72 to the optical signal. And transmitted to the optical fiber 50-1. In addition, the TRxA 70 detects the intensity of the optical signal input from the optical fiber 50-1, and outputs it to the monitoring controller 76 as an optical input A monitor signal. Note that transmission from the TRxA 70 is controlled by a TxEN (Tx Enable: transmission permission) signal supplied from the AND element 74. When the TxEN signal is “H” (High), transmission is permitted, and “L”. In the case of (Low), transmission is prohibited.

  The TRxB 71 converts the optical signal received from the optical fiber 51-1 into an electrical signal, supplies it to the switch 73 as an Rx signal, converts the transmission signal supplied from the switch 72 into an optical signal, and converts the optical signal into the optical fiber 51-1. Send to. Also, the TRxB 71 detects the intensity of the optical signal input from the optical fiber 51-1, and outputs it to the monitoring controller 76 as an optical input B monitor signal. Note that transmission from the TRxB 71 is controlled by the TxEN signal supplied from the AND element 75, and transmission is permitted when the TxEN signal is “H”, and transmission is prohibited when the signal is “L”.

  The switch 72 is controlled by the control signal 1 supplied from the monitoring control unit 76. When the control signal 1 is “L”, the Tx signal from the MAC unit 77 is supplied to the TRxA 70, and the control signal 1 is set to “H”. In the case of “,” the Tx signal is supplied to the TRxB 71. The switch 73 is controlled by the control signal 1 supplied from the supervisory control unit 76. When the control signal 1 is “L”, the Rx signal from the TRxA 70 is supplied to the MAC unit 77, and the control signal 1 is set to “H”. In the case of “,” the Rx signal from the TRxB 71 is supplied to the MAC unit 77.

  The AND element 74 calculates a logical product of the EN (Enable) signal supplied from the MAC unit 77 and the control signal 2 supplied from the monitoring control unit 76, and outputs the calculation result to the TRxA 70 as a TxEN signal. The AND element 75 calculates the logical product of the EN signal supplied from the MAC unit 77 and the control signal 3 supplied from the monitoring control unit 76, and outputs the calculation result to the TRxB 71 as a TxEN signal.

  The supervisory control unit 76 monitors the active monitor signal of the optical input A monitor signal and the optical input B monitor signal. If the optical input level becomes smaller than a predetermined threshold, it is assumed that an abnormality has occurred. By setting the active control signal out of the control signal 2 and the control signal 3 to the “L” state, the TxEN signal is set to “L” and the transmission of the upstream signal is prohibited. As a result, since the PON link goes down, the PON link status signal from the MAC unit 77 is referred to. When the PON link goes down, the control signal 1 is inverted to switch between the active system and the standby system. .

  The MAC unit 77 has a function of performing medium access control conforming to IEEE 802.3ah, receives a signal supplied from a home network (not shown), supplies it to the switch 72 as a Tx signal, and is supplied from the switch 73. Rx signal is supplied to the home network. Also, a process of establishing a PON link with the OLT 20 is executed, and when the PON link is established, the PON link status signal is set to the “H” state. Further, when the PON link with the OLT 20 goes down, the PON link state signal is set to the “L” state.

(D) Description of Operation of Second Embodiment Next, the operation of the second embodiment will be described. FIG. 5 is a flowchart for explaining an example of processing executed in the second embodiment. FIG. 6 is a diagram showing signal waveforms at various parts of the redundant subscriber premises optical line terminating device 10A shown in FIG. In the following, when TRxA 70 and optical fiber 50-1 are the active system, and TRxB 71 and optical fiber 51-1 are the standby system, some abnormality occurs and the level of the optical signal received by TRxA 70 is The operation when switching from the active system to the standby system will be described as an example.

  When the processing of the flowchart shown in FIG. 5 is started, the following steps are executed.

  Step S10: The monitoring controller 76 detects the active optical input monitor value M. In this example, since TRxA70 is the active system, the monitoring control unit 76 detects the signal value M of the optical input A monitor signal output from TRxA70.

  Step S11: The supervisory control unit 76 compares the active optical input monitor value M detected in step S10 with a predetermined threshold Th, and if M <Th is satisfied (step S11: Yes), the process proceeds to step S12. In other cases (step S11: No), the process returns to step S10 and the same processing is repeated. For example, when TRxA 70 is the active system, as shown in FIG. 6A, if the optical input A monitor signal starts to decrease from time t1 and falls below threshold value Th at time t2, Yes in step S11. And the process proceeds to step S12.

  Step S12: The supervisory control unit 76 sets the active control signal of the control signal 2 and the control signal 3 to the “L” state in order to set the active TxEN signal to “L”. For example, when TRxA 70 is the active system, as shown in FIG. 6B, the monitoring control unit 76 sets the control signal 2 to the “L” state at time t3. As a result, since the TxEN signal output from the AND element 74 is in the “L” state, transmission of the TRxA 70 is prohibited. When TRxB 71 is the active system, the control signal 3 is set to the “L” state, and as a result, the TxEN signal output from the AND element 75 is set to the “L” state, so that transmission of the TRxB 71 is prohibited. .

  Step S13: The supervisory control unit 76 refers to the PON link status signal output from the MAC unit 77 and detects the status of the PON link.

  Step S14: When the PON link status signal output from the MAC unit 77 is in the “L” state (step S14: Yes), the monitoring control unit 76 determines that the PON link is down and determines whether the PON link is down. In other cases (step S14: No), the process returns to step S13 to repeat the same process as described above. In this example, since transmission of TRxA 70 is prohibited in step S12, the MAC unit 77 cannot respond to a periodic inquiry from the OLT 20 for maintaining the PON link. As shown, the PON link state signal changes from “H” to “L” at time t4, and PON link down is detected. When the PON link goes down, the Tx signal from the MAC unit 77 is not output, so that collision of transmission signals is avoided.

  Step S15: The monitoring controller 76 controls the switches 72 and 73 to switch from the active system to the standby system. In this example, since the control signal 1 is in the “L” state and the TRxA 70 is selected as the active system, the control signal 1 is changed from “L” to “L” at time t5 as shown in FIG. Inverted to H ″. As a result, the switches 72 and 73 both select TRxB71.

  Step S16: The supervisory control unit 76 sets the control signal corresponding to the standby system of the control signal 3 and the control signal 2 to the “H” state in order to set the standby TxEN signal to “H”. For example, when TRxB 71 is a standby system, as shown in FIG. 6E, the control signal 3 is set to the “H” state at time t6. As a result, since the TxEN signal output from the AND element 75 is in the “H” state, transmission of the TRxB 71 is permitted. When TRxA 70 is the active system, the control signal 2 is set to the “H” state. As a result, the TxEN signal output from the AND element 74 becomes equal to the EN signal, so that transmission of the TRxA 70 is controlled by the EN signal. Is done.

  Step S17: The OLT 20 executes P2MP discovery and re-establishes a PON link between the redundant subscriber premises optical line terminating device 10A and the OLT 20 via the standby system. Specifically, after the PON link goes down, the OLT 20 detects the redundant subscriber premises optical line terminating device 10A via the optical fiber 51-1, which is a standby system, and assigns an LLID to establish the PON link. To do. As a result, as shown at time t7 in FIG. 6E, the PON link changes from the down state to the established state. At this time, the OLT 20 passes from the OLT 20 through the optical fiber 21, the optical coupler 50, the optical fiber 50-2, the optical coupler 51, and the optical fiber 51-1, to the redundant customer premises optical line terminating device 10A. Measure RTT. Also, the redundant subscriber premises optical line termination device 10A performs time synchronization with the OLT 20. When the redundant subscriber premises optical line terminator 10A transmits an uplink signal, a packet is transmitted at a timing set based on the standby RTT. It is possible to avoid collision with the upstream signal.

  As described above, according to the second embodiment of the present invention, when an abnormality occurs in the active system, the transmission is prohibited by setting the TxEN signal, which is a transmission permission signal, to the “L” (Disable) state. After the PON link down is detected, the active system is switched to the standby system. In this way, by switching from the active system to the standby system after the PON link down is detected, it is possible to avoid a packet being transmitted to the standby system at the timing assigned to the active system and the packet colliding. Also, by bringing down the PON link, P2MP discovery for the standby system can be quickly executed and the PON link can be established. Furthermore, the TxEN signal of the active system is set to “L” to bring down the PON link, and after the switching between the active system and the standby system is completed, the TxEN signal of the standby system is set to “H” to re-establish the PON link. Therefore, by prohibiting transmission at the time of switching, it is possible to reliably avoid a transmission signal being erroneously output from both the active system and the standby system and collision of the upstream signal.

(E) Description of Configuration of Third Embodiment FIG. 7 is a block diagram for explaining a configuration example of a redundant customer premises optical line terminating device 10B according to a third embodiment of the present invention. In FIG. 7, portions corresponding to those in FIG. 4 are denoted by the same reference numerals, and description thereof is omitted. In the third embodiment shown in FIG. 7, an optical output level monitor signal line is newly added between the TRxA 70 and TRxB 71 and the monitoring control unit 76, as compared with the case of FIG. The rest is the same as in FIG. The optical output level monitor signal line detects the level of the optical signal transmitted from the system (operation system) used at that time among TRxA 70 and TRxB 71 and notifies the monitoring control unit 76 of the level. The redundant subscriber premises optical line terminator 10B is connected to a PON type optical transmission system instead of the redundant subscriber premises optical line terminator 10 shown in FIG.

(F) Description of Operation of Third Embodiment In the operation of the third embodiment, the optical output level monitor value Mo of the operational system is detected in step S10 of FIG. In S11, the optical output level monitor value Mo is compared with the threshold value Th. If Mo <Tho (step S11: Yes), the process proceeds to step S12. Otherwise (step S11: No), the process proceeds to step S12. Returning to S10, the same processing as described above is repeated. The other processes are the same as those in the second embodiment.

  FIG. 8 is a diagram showing waveforms of respective parts of the third embodiment shown in FIG. For example, when TRxA70 is the active system and TRxB71 is the standby system, as shown in FIG. 8A, the level of the upstream optical signal output from TRxA70 begins to decrease at time t1, and at time t2, It is assumed that the value becomes smaller than the threshold value Th. Then, as shown in FIG. 8B, at time t3, the control signal 2 is set to the “L” state. As a result, since the TxEN signal output from the AND element 74 is in the “L” state, transmission of the TRxA 70 is prohibited and the PON link goes down. When the PON link goes down, as shown in FIG. 8 (C), the PON link status signal becomes “L” at time t4. Therefore, as shown in FIG. 8 (D), the control signal 1 at time t5. Is set to "H", and the active system is switched to the standby system. Then, as shown in FIG. 8E, at time t6, the control signal 3 is set to the “H” state, and the output of the AND element 75 becomes the EN signal, so that transmission of the standby TRxB 71 is permitted. The As a result, P2MP discovery is executed, a PON link is established with the standby system, and the PON link status signal becomes “H” at time t7 as shown in FIG. 8C.

  As described above, according to the third embodiment, it is detected that the output light level has decreased, and based on this, the active system and the standby system are switched. When a laser diode that fails to operate fails, this can be detected quickly, and the active system can be switched to the standby system without causing a collision of transmission signals.

(G) Description of Configuration of Fourth Embodiment FIG. 9 is a diagram illustrating a configuration example of the fourth embodiment of the present invention. As shown in FIG. 9, in the fourth embodiment, the center side is also duplicated. That is, in FIG. 4, two OLTs 20A and 20B are arranged on the center side, and the redundant subscriber premises optical line terminator 10 is arranged in each home. Further, the center side and each redundant subscriber premises optical line terminating device 10 include optical fibers 21A and 21B, optical couplers 50A and 50B, and optical fibers 50A-1 to 50A-3, 50B-1 to 50B-3. (Corresponding to “optical transmission line” in claims). Each redundant subscriber premises optical line terminator 10 is the redundant subscriber premises optical line terminator 10A shown in FIG. 4 or the redundant subscriber premises optical line terminator 10B shown in FIG. Also good.

  Here, the OLT 20A is connected to the optical coupler 50A via the optical fiber 21A. The downstream optical signal transmitted from the OLT 20A is demultiplexed into three by the optical coupler 50A, and is incident on each redundant customer premises optical line terminating device 10 via the optical fibers 50A-1 to 50A-3. The Further, the optical signals transmitted from the respective redundant subscriber premises optical line terminators 10 are combined by the optical coupler 50A and are incident on the OLT 20A via the optical fiber 21A. On the other hand, the OLT 20B is connected to the optical coupler 50B via the optical fiber 21B. The downstream optical signal transmitted from the OLT 20B is demultiplexed into three by the optical coupler 50B, and is incident on each redundant customer premises optical line terminating device 10 via the optical fibers 50B-1 to 50B-3. The Further, the optical signals transmitted from the respective redundant subscriber premises optical line terminators 10 are combined by the optical coupler 50B and are incident on the OLT 20B via the optical fiber 21B.

(G) Description of Operation of Fourth Embodiment Next, the operation of the fourth embodiment will be described. In the following, the redundant subscriber premises optical line terminating device 10 displayed at the top of FIG. 9 will be described as an example. For example, when the optical fiber 50A-1 connected to the redundant subscriber premises optical line terminating device 10 displayed at the top is the active system and the optical fiber 50B-1 is the standby system, the OLT 20A Alternatively, when a failure occurs in the optical fiber 50A-1 and the level of the input light becomes smaller than the threshold value, an ONU shutdown signal is output in step S3 in the process shown in FIG. Disconnected. When the PON link down is detected by the PON link state signal, the optical switch 11 is switched, and the ONU 13 and the OLT 20B are connected by the optical switch 11. As a result, P2MP discovery is executed by the OLT 20B, and a PON link is established between the ONU 13 and the OLT 20B to enable communication.

  The above is an example of the case where the redundant subscriber premises optical line terminator 10 shown in FIG. 1 is used, but the redundant subscriber premises optical line terminator 10A shown in FIG. 4 or FIG. It is also possible to use the redundant subscriber premises optical line terminating device 10B. In that case, the active system can be switched to the standby system by the processing shown in FIG.

  As described above, according to the fourth embodiment of the present invention, since the center side can also be duplicated, it is possible to further improve the reliability of communication.

(G) Modified Embodiment Each of the above embodiments is an example, and there are various modified embodiments other than this. For example, the duplexing of the optical transmission path shown in FIG. 1 is an example, and duplexing by other methods is also possible. Specifically, if the optical fibers connected to the redundant subscriber premises optical line termination device 10 (redundant subscriber premises optical line termination devices 10A and 10B) are connected to the OLT 20 via different paths, FIG. The connection method shown in FIG. In each of the above embodiments, the case of duplexing has been described as an example, but triplet or more may be used. In that case, since there is one active system and a plurality of standby systems, if an abnormality occurs in the active system, one of the plurality of standby systems can be selected to switch the connection. Good. Similarly, in the case of the fourth embodiment shown in FIG. 9, the center side can be configured to be more than triple.

  In the first embodiment shown in FIG. 1, the PON link is brought down by the shutdown signal. However, as in the second and third embodiments, the transmission enable signal (TxEN) (not shown) built in the ONU 13 is used. The PON link may be brought down by setting the signal to “L” (Disable).

10, 10A, 10B Redundant subscriber premises optical line terminator (subscriber premises optical line terminator)
11 Optical switch (switching part)
12 Monitoring control unit (abnormality detection unit, cutting processing unit, cutting detection unit)
13 ONU
20, 20A, 20B OLT
30, 40 ONU
21, 21A, 21B, 50-1, 50-2, 51-1 to 51-3, 50A-1 to 50A-3, 50B-1 to 50B-3 Optical fiber (optical transmission line)
50, 51 Optical coupler (optical transmission line)
70 TRxA
71 TRxB
72, 73 switch (switching part)
74, 75 AND element 76 Monitoring control unit (abnormality detection unit, cutting processing unit, cutting detection unit)
77 MAC section

Claims (7)

A subscriber-side optical line termination device used in a PON (Passive Optical Network) type optical transmission system, which is connected to the center side via a plurality of optical transmission lines, and any one of the optical transmission lines is used as an active system In a subscriber premises optical line terminating device that performs communication using the other as a standby system,
An anomaly detector that detects the occurrence of an anomaly in the active system;
When occurrence of an abnormality is detected by the abnormality detection unit, a disconnection processing unit that executes processing for disconnecting the PON link with the center side,
A disconnection detecting unit for detecting that the PON link is disconnected by the operation of the disconnection processing unit;
When a disconnection of the PON link is detected by the disconnection detection unit, a switching unit for switching from the active system to the standby system,
A subscriber's premises optical line terminating device comprising:   The subscriber premises optical line termination device according to claim 1, wherein the disconnection processing unit outputs a shutdown signal for shutting down an ONU (Optical Network Unit) to the ONU.   The disconnection processing unit outputs a transmission prohibition signal for prohibiting transmission to the center side to the ONU, and outputs a transmission permission signal to the ONU after the switching by the switching unit is completed. 2. The subscriber premises optical line terminator according to claim 1.   4. The subscriber premises side according to claim 1, wherein the abnormality detection unit detects an abnormality when an optical input level of the active system becomes smaller than a predetermined threshold value. 5. Optical line termination equipment.   5. The subscriber premises side according to claim 1, wherein the abnormality detection unit detects an abnormality when an optical output level of the active system becomes smaller than a predetermined threshold value. Optical line termination equipment.   6. The subscriber premises side according to any one of claims 1 to 5, wherein the plurality of optical transmission lines are connected to one center side optical line terminating device disposed on the center side. Optical line termination equipment.   6. The subscriber premises according to claim 1, wherein the plurality of optical transmission lines are respectively connected to a plurality of center-side optical line terminators arranged on the center side. Side optical line terminator.

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