Optical network termination device

Abstract

An ONU (120) is provided with: an optical module transmission unit (141) for transmitting an optical signal to an OLT when a transmission permission is received; an optical output control unit (131) for providing the transmission permission to the optical module transmission unit (141) at a time allocated from the OLT; a failure detection unit (133) for monitoring the transmission permission and the transmission state of the optical signal, and for providing, to the optical module transmission unit (141), a transmission permission invalidation instruction for invalidating the transmission permission when an abnormal light emission state is detected; and an FET switch (150) for, when the transmission permission invalidation instruction is given to the optical module transmission unit (141), cutting off power being supplied to the optical module transmission unit (141). When the transmission permission invalidation instruction is received, the optical module transmission unit (141) stops the transmission of the optical signal even if the transmission permission has been received.

Description

Technical Field

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[0001] The present disclosure relates to an optical line terminal device Place .

Background Art

[0002] In a PON (Passive Optical Network) system, upstream data is transmitted by time division multiplexing (TDMA: Time Division Multiple Access). The OLT (Optical Line Terminal), which is a station-side device, assigns the time available for data transmission as a grant to each ONU (Optical Network Unit). The ONU emits light at the time assigned by the OLT to transmit upstream data.

[0003] Here, the OLT determines the assigned time so that the times assigned to each ONU do not overlap. As a result, only one ONU can emit light and transmit data at the same time.

[0004] If an ONU emits light outside the assigned time due to a failure or the like, the upstream data signal of the non-failed ONU will be disrupted. If the light emission state continues for a predetermined time or more (hereinafter, such a state is referred to as an "abnormal light emission state"), it will affect the communication of all ONUs under the OLT.

[0005] In the conventional ONU described in Patent Document 1, when the failure detection unit detects an abnormal light emission state, it controls the power supply Disable signal to stop the power supply of the optical module transmission unit via the optical module power supply unit. As a result, the optical module transmission unit stops emitting light.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

[0007] However, conventional ONUs have a problem in that they cannot stop the light emission of the optical module transmitter when a power supply disable signal or an abnormality occurs in the optical module power supply unit.

[0008] Therefore, one or more aspects of this disclosure aim to ensure that the light emission of an ONU in which an abnormality has occurred can be reliably stopped. [Means for solving the problem]

[0009] An optical line termination device according to one aspect of the present disclosure includes: an optical signal transmission unit that transmits an optical signal to a central office device when it receives a transmission permission, which is permission to transmit an optical signal; an optical output control unit that gives the transmission permission to the optical signal transmission unit at a time allocated by the central office device for transmitting the optical signal; and an optical signal transmission unit that monitors the transmission permission and the transmission status of the optical signal and, when it detects an abnormal light emission state, issues a transmission permission invalidation instruction, which is an instruction to invalidate the transmission permission. and switch section A fault detection unit that provides the transmission permission invalidation instruction is given If this occurs, the power supplied to the optical signal transmission unit is cut off. The aforementioned The optical signal transmission unit comprises a switch unit and, The power is cut off by the switch, and the transmission of the optical signal is stopped, or The system is characterized in that, upon receiving the instruction to invalidate the transmission permission, it stops transmitting the optical signal even if it has received the transmission permission. [Effects of the Invention]

[0011] According to one or more aspects of this disclosure, it is possible to reliably stop the light emission of an ONU that has malfunctioned. [Brief explanation of the drawing]

[0012] [Figure 1] This is a block diagram that schematically shows the overall configuration of the PON system according to Embodiment 1. [Figure 2]This is a block diagram schematically showing the main components of the ONU according to Embodiment 1. [Figure 3] This is a first time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 1. [Figure 4] This is a second time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 1. [Figure 5] This is a third time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 1. [Figure 6] This is a block diagram schematically showing the main components of the ONU in Embodiment 2. [Figure 7] This is a block diagram schematically showing the configuration of the upstream queue control unit in Embodiment 2. [Figure 8] This is a time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 2. [Figure 9] This is a block diagram schematically showing the main components of the ONU in Embodiment 3. [Modes for carrying out the invention]

[0013] Embodiment 1. Figure 1 is a block diagram schematically showing the overall configuration of the PON system 100 according to Embodiment 1. The PON system 100 comprises an OLT 110, which is a central office-side device, and an ONU 120, which is a subscriber-side termination device or optical line termination device. The OLT110 and the ONU120 are connected via the optical fiber 101 and the optical coupler 102. Although Figure 1 shows multiple ONUs 120, the PON system 100 only needs to be equipped with at least one ONU 120.

[0014] The terminal 103 is connected to the ONU 120. The upstream data signal is transmitted from the terminal 103 and transmitted to the network 104 via the ONU 120 and the OLT 110.

[0015] FIG. 2 is a block diagram schematically showing the main configuration of the ONU 120 according to Embodiment 1. In Embodiment 1, as the main configuration of the ONU 120, it includes a PON MAC (Media Access Control) 130 as a control unit, an optical module 140 as an optical communication interface, and a FET switch 150.

[0016] The PON MAC 130 includes an optical output control unit 131, an upstream queue control unit 132, and a fault detection unit 133.

[0017] The optical output control unit 131 gives the optical module 140 a transmission permission, which is a permission to transmit an optical signal, at the time allocated from the OLT 110 for transmitting the optical signal. For example, the optical output control unit 131 gives the optical module 140 an optical output Enable signal (also referred to as an optical output permission signal), which is a signal permitting optical output.

[0018] The upstream queue control unit 132 stores the upstream data signal from the terminal 103 in a queue and performs queue control for transmitting it to the OLT 110.

[0019] The fault detection unit 133 monitors the transmission permission and the transmission state of the optical signal, and when detecting an abnormal light emission state, gives the optical module 140 a transmission permission invalidation instruction, which is an instruction to invalidate the transmission permission. For example, the fault detection unit 133 monitors the optical output Enable signal output from the optical output control unit 131 and the optical output state signal output from the optical module 140. Then, when the fault detection unit 133 detects a fault by monitoring the optical output Enable signal and the optical output state signal, it outputs a transmission permission invalidation signal indicating that the optical output permitted by the optical output Enable signal output from the optical output control unit 131 to the optical module 140 is to be invalidated. Specifically, the fault detection unit 133 monitors an optical output permission signal indicating permission to transmit and an optical output status signal indicating whether or not an optical signal is being output. If the optical module 140 is outputting an optical signal for a predetermined period of time or longer, the unit detects an abnormal light emission state as an abnormality.

[0020] The optical module 140 transmits and receives optical signals. The optical module 140 includes an optical module transmitting unit 141 as an optical signal transmission interface. The optical module transmitter 141 is an optical signal transmitter that transmits an optical signal to the OLT 110 when it receives a transmission permission, which is permission to transmit an optical signal. Furthermore, if the optical module transmitter 141 receives a transmission permission invalidation instruction, as described later, it will stop transmitting optical signals even if it has received a transmission permission.

[0021] Furthermore, the optical module transmitter 141 outputs an optical output status signal indicating the optical output status to the fault detection unit 133. When the optical module transmitter 141 receives a transmission permission invalidation signal from the fault detection unit 133, it will not output light even if optical output has been permitted by the optical output Enable signal from the optical output control unit 131.

[0022] The FET switch 150 is a switch that cuts off the power supplied to the optical module transmitter 141 when a transmission permission invalidation instruction is given to the optical module transmitter 141. Here, the FET switch 150 is a switch that turns off the power supplied from the power supply 121 to the optical module transmitter 141 when a transmission permission invalidation signal is output from the fault detection unit 133.

[0023] As described above, in Embodiment 1, the fault detection unit 133 built into the PON MAC 130 monitors the optical output Enable signal output from the PON MAC 130 and the optical output status signal output from the optical module transmission unit 141. If either or both of these signals remain valid or show an output status for a predetermined period of time or longer, it is determined to be an abnormal light emission state. When an abnormal light emission state is determined, the power supply to the optical module transmission unit 141 is stopped, and the transmission permission from the PON MAC 130 to the optical module transmission unit 141 is invalidated, thereby stopping the light emission.

[0024] The PON MAC130 described above can be configured with processing circuits such as a single circuit, a complex circuit, a programmable processor, a programmable parallel processor, an ASIC (Application Specific Integrated Circuit), or an FPGA (Field Programmable Gate Array).

[0025] Next, the method for detecting an abnormal light emission state of the ONU120 according to Embodiment 1, and the method for stopping light emission when an abnormal light emission state is detected, will be explained with reference to Figure 3. Figure 3 is a time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 1.

[0026] The fault detection unit 133 built into the PON MAC 130 monitors the optical output Enable signal output from the PON MAC 130 and the optical output status signal output from the optical module 140.

[0027] Under normal conditions, for example, from time t00 to time t01, and from time t02 to time t03, the optical output Enable signal from the optical output control unit 131 is active only for the time allocated by the OLT 110 for uplink data signal transmission. During this time, the optical module transmitter 141 outputs light, and the optical output status signal is in the output state. At all other times, the optical output Enable signal is inactive, and the optical output status signal is in the stopped state.

[0028] Thus, under normal conditions, the transmit permission invalid signal maintains the transmit permission state, the supplied power maintains the supply state, the optical output from the optical module transmitter 141 is output only for the time allocated by the OLT 110 for uplink data signal transmission, and remains in a stopped state at all other times.

[0029] Next, if the optical output control unit 131 of the PON MAC 130 that outputs the optical output Enable signal, or the optical module transmission unit 141 that outputs the optical output status signal, fails, and the optical output Enable signal remains valid, the optical output status signal continues to output, or both, the fault detection unit 133 determines that the ONU 120 has entered an abnormal light emission state.

[0030] Then, at time t05, the fault detection unit 133 changes the output of the transmit permission invalid signal from the transmit permission state to the transmit permission state. Accordingly, the FET switch 150 turns off (stops) the power supplied from the power supply 121. As a result, the light output from the optical module transmitter 141 is stopped (light emission stops).

[0031] Here, if there is an abnormality or failure in the power line supplying power to the optical module transmitter 141, or in the FET switch 150, as shown in Figure 4, even though the fault detection unit 133 has set the transmission permission invalid signal to the transmission disable state at time t15, the power supply to the optical module transmitter 141 may remain in the supply state. In that case as well, if the transmission permission invalid signal input to the optical module transmitter 141 is in the transmission disable state, the optical module transmitter 141 will stop the optical output (stop emitting light).

[0032] Furthermore, if there is an abnormality or fault in the signal line of the transmission permission invalid signal input to the optical module transmitter 141, as shown in Figure 5, at time t25, even though the fault detection unit 133 has set the transmission permission invalid signal to the transmission prohibition state, the transmission permission invalid signal to the optical module transmitter 141 may remain in the transmission permission state. In that case as well, if the transmission permission invalid signal output by the fault detection unit 133 is a transmission prohibition state light, the power supply input to the optical module transmitter 141 will be cut off, and the optical output of the optical module transmitter 141 will stop (light emission will stop).

[0033] As described above, Embodiment 1 is configured such that when an abnormal light emission state is detected, the power supply to the optical module transmitter 141 is stopped and the transmission permission to the optical module transmitter 141 is disabled. Therefore, even if one of the light emission stop measures fails to operate, the other light emission stop measure can still stop the light emission. This allows for more reliable light emission stoppage and avoids communication interference with other ONUs 120. In addition, since the fault detection unit 133 is provided within the PON MAC 130, there is also the effect of suppressing an increase in circuit size and memory capacity.

[0034] Embodiment 2. In Embodiment 1, when the fault detection unit 133 detects an abnormal light emission state, it immediately takes measures to stop the light emission. In Embodiment 2, however, a method is described in which the detection of a continuous light emission state is notified to the OLT 110, and the OLT 110 notifies the maintenance person via an alarm or the like. An ONU that has entered an abnormal illumination state due to a hardware failure cannot be restored by the subscriber restarting the ONU power cycle, and requires replacement by a maintenance technician. Prompt ONU replacement is necessary for early restoration.

[0035] As shown in Figure 1, the PON system 200 according to Embodiment 2 comprises an OLT 110 and an ONU 220. The OLT110 of the PON system 200 according to Embodiment 2 is the same as the OLT110 of the PON system 100 according to Embodiment 1.

[0036] Figure 6 is a block diagram schematically showing the main components of the ONU220 in Embodiment 2. In Embodiment 2, the main components of the ONU220 include a PON MAC230, an optical module 140, and an FET switch 150. The optical module 140 and FET switch 150 of the ONU220 in Embodiment 2 are the same as the optical module 140 and FET switch 150 of the ONU120 in Embodiment 1.

[0037] The PON MAC230 comprises an optical output control unit 131, an uplink queue control unit 232, a fault detection unit 233, and an OAM (Operations, Administration, and Maintenance) processing unit 234.

[0038] The optical output control unit 131 of the PON MAC230 in Embodiment 2 is the same as the optical output control unit 131 of the PON MAC130 in Embodiment 1.

[0039] The fault detection unit 233, similar to the fault detection unit 133 in Embodiment 1, monitors the optical output Enable signal output from the optical output control unit 131 and the optical output status signal output from the optical module 140. The fault detection unit 233 then monitors the optical output Enable signal and the optical output status signal, and if it detects a fault, it notifies the OAM processing unit 234 of an abnormal light emission state detection interrupt. Furthermore, if the fault detection unit 233 detects a fault, it outputs a transmission permission invalidation signal to the optical module transmission unit 141 after a predetermined time has elapsed. In other words, the fault detection unit 233 gives the transmission permission invalidation instruction to the optical module transmission unit 141 after being notified of information indicating that an abnormal light emission state has been detected.

[0040] The OAM processing unit 234 is a signal processing unit that, when an abnormal light emission state is detected, notifies the OLT 110 via the optical module transmission unit 141 of information indicating that an abnormal light emission state has been detected. For example, when the OAM processing unit 234 receives an abnormal light emission interrupt notification from the fault detection unit 233, it sends an abnormal light emission notification signal to the up queue control unit 232.

[0041] The uplink queue control unit 232 stores the uplink data signal from terminal 103 and the abnormal light emission status notification signal from OAM processing unit 234 in a queue and performs queue control for transmission to OLT 110.

[0042] Figure 7 is a schematic block diagram showing the configuration of the upstream queue control unit 232 in Embodiment 2. The upstream queue control unit 232 comprises a user queue 232a, a system queue 232b, and a queue processing unit 232c.

[0043] User queue 232a stores user data signals from terminal 103. System queue 232b stores the abnormal light emission status notification signal from the OAM processing unit 234.

[0044] The queue processing unit 232c reads signals from the user queue 232a and the system queue 232b, and provides the read signals to the optical module transmission unit 141 as uplink data signals. Here, the queue processing unit 232c controls the system queue 232b and the user queue 232a with complete priority, giving high priority to the system queue 232b and low priority to the user queue 232a. As a result, when an abnormal light emission status notification signal is generated, it is always read and transmitted from the abnormal light emission status notification signal.

[0045] Figure 8 is a time chart showing the optical output Enable signal or optical output status signal, the transmit enable invalid signal, the supplied power, and the optical output in Embodiment 2.

[0046] In the PON system supported by PON system 200, the OLT 110 allocates a period of time during which data transmission is possible to periodically check for the presence or absence of uplink data signal transmission requests from each ONU 220. This period is called the polling period, and its value is predetermined by the PON system.

[0047] The fault detection unit 233 built into the PON MAC230 monitors the optical output Enable signal output from the PON MAC230 and the optical output status signal output from the optical module 140.

[0048] For example, according to the time allocated by the OLT 110 for uplink data signal transmission, at time t30, the optical output Enable signal from the optical output control unit 131 becomes active, during which time the optical module transmitter 141 outputs light, and the optical output status signal becomes the output state.

[0049] When an abnormal light emission state is detected at time t31, the fault detection unit 233 notifies the OAM processing unit 234 of the abnormal light emission state detection interrupt. When the OAM processing unit 234 receives an abnormal light emission interrupt notification, it generates an abnormal light emission notification signal and provides this abnormal light emission notification signal to the uplink queue control unit 232. Specifically, the OAM processing unit 234 generates an OAM frame containing information to notify that an abnormal light emission condition has occurred. Such an OAM frame becomes the abnormal light emission notification signal.

[0050] Then, when the uplink queue control unit 232 receives an OAM frame indicating an abnormal light emission state, it stores the OAM frame in the system queue 232b. It then waits for the allocation of data transmission time (grant) from the OLT 110.

[0051] Then, when a grant is allocated from OLT110, the optical output control unit 131 confirms that the OAM frame is stored in system queue 232b and requests OLT110 to transmit the uplink data signal.

[0052] Upon receiving an uplink data signal transmission request from ONU220, OLT110 allocates a grant to ONU220 for uplink data signal transmission. The queue processing unit 232c of ONU220 then reads the OAM frame stored in the system queue 232b and provides it to the optical module transmission unit 141, which then transmits the OAM frame to OLT110.

[0053] In this case, the ONU220 must refrain from taking action to stop the light emission until it has sent an OAM frame indicating an abnormal light emission state to the OLT110, and then take action to stop the light emission after the transmission. One method involves the fault detection unit 233 detecting an abnormal light emission state and then outputting a transmission permission invalidation signal after a predetermined time has elapsed. The predetermined time can be any time required for an OAM frame indicating the abnormal light emission state to be reliably transmitted. In Figure 8, the predetermined time is shown as the delay in implementing the light emission stop measure.

[0054] As shown in Figure 8, the fault detection unit 233 detects an abnormality at time t31, and at time t32, after the delay in implementing the light emission stop measure has elapsed, it changes the output of the transmit permission invalid signal from the transmit permission state to the transmit permission state. Accordingly, the FET switch 150 turns off (stops) the power supplied from the power supply 121. As a result, the light output from the optical module transmitter 141 is stopped (light emission stops).

[0055] Generally, when the OLT110 receives an OAM frame from the ONU220 that notifies an alarm, it notifies the maintenance personnel of the alarm using SNMP (Simple Network Management Protocol) Trap or similar methods. This allows the maintenance personnel to understand that the ONU220 has entered an abnormal illumination state.

[0056] In Embodiment 2, the fault detection unit 233 detects an abnormal light emission state and then initiates the light emission stop measure after a certain period of time has elapsed. However, it is also possible to have the up queue control unit 232 transmit an OAM frame indicating an abnormal light emission state, then transmit a transmission completion signal to the fault detection unit 233, and then initiate the light emission stop measure when the fault detection unit 233 receives the transmission completion signal.

[0057] As explained above, the system is configured to notify the OLT110 and the maintenance personnel when an abnormal light emission condition is detected, enabling the maintenance personnel to quickly identify the abnormal light emission condition and promptly restore service by replacing the ONU220.

[0058] Embodiment 3. Generally, the OLT110 can control the illumination of the ONU (e.g., stop illumination or resume illumination) and reset the ONU according to instructions from the maintenance personnel. If an abnormal illumination state is detected and the ONU is in an illumination-stopped state, and the maintenance personnel instruct the ONU to resume illumination, and the ONU accepts this instruction, the ONU will enter an abnormal illumination state again. Similarly, if an abnormal illumination state is detected and the ONU is in an illumination-stopped state, and the maintenance personnel instruct the ONU to reset, and the ONU accepts this instruction, the ONU will enter an abnormal illumination state again.

[0059] In Embodiment 3, when the ONU320 receives a light emission control instruction or an ONU reset instruction from the OLT110, it checks whether an abnormal light emission state is being detected. If an abnormal light emission state is being detected, it ignores the light emission control instruction or ONU reset instruction from the OLT110 and maintains the light emission stopped state.

[0060] As shown in Figure 1, the PON system 300 according to Embodiment 3 comprises an OLT 110 which is a central office-side device and an ONU 320 which is a subscriber-side termination device. The OLT110 of the PON system 300 according to Embodiment 3 is the same as the OLT110 of the PON system 100 according to Embodiment 1.

[0061] Figure 9 is a block diagram schematically showing the main components of the ONU320 in Embodiment 3. In Embodiment 3, the main components of the ONU320 include a PON MAC330, an optical module340, and an FET switch150. The FET switch 150 of the ONU320 in Embodiment 3 is the same as the FET switch 150 of the ONU120 in Embodiment 1.

[0062] If the fault detection unit 333 detects an abnormal light emission state, it stores information indicating that an abnormal light emission state has been detected. For example, the fault detection unit 333 performs the same processing as the fault detection unit 133 in Embodiment 1, and also includes an abnormal light emission status flag 333a that indicates whether or not an abnormal light emission state is being detected. If an abnormal light emission state is detected, the abnormal light emission status flag 333a indicates that an abnormal light emission state is being detected until the power to the ONU 320 is turned off and then turned on again. Furthermore, when the ONU320 is turned off and then on again, the power supply interruption by the FET switch 150 is also released, and power is supplied to the optical module transmitter 141.

[0063] The optical module 340 comprises an optical module transmitting unit 141 and an optical module receiving unit 342. The optical module transmitter 141 of the optical module 340 in Embodiment 3 is the same as the optical module transmitter 141 of the optical module 140 in Embodiment 1.

[0064] The optical module receiver 342 receives downlink OAM frames from the OLT110. ONU light emission control instructions or reset instructions from the OLT110 are transmitted in OAM frames. The downlink OAM frames from the OLT110 are forwarded via the optical module receiver 342 to the OAM processing unit 334 inside the PON MAC330.

[0065] The OAM processing unit 334 is a signal processing unit that, in accordance with instructions from the OLT 110, restarts the transmission of optical signals by the optical module transmission unit 141, which has stopped transmitting optical signals in accordance with the instruction to disable transmission permission. However, as long as the fault detection unit 333 is holding information indicating that an abnormal light emission state has been detected, the OAM processing unit 334 will not restart the transmission of optical signals by the optical module transmission unit 141, even if instructed to do so by the OLT 110. Specifically, if the transmitted OAM frame is an ONU light emission control instruction or a reset instruction, the OAM processing unit 334 ignores the light emission control instruction or ONU reset instruction if the abnormal light emission status flag 333a of the fault detection unit 333 indicates that an abnormal light emission state is being detected. On the other hand, if the abnormal light emission status flag 333a does not indicate that an abnormal light emission state is being detected, the OAM processing unit 334 performs light emission control or reset according to the instruction.

[0066] Specifically, the abnormal light emission status flag 333a can take on two states: "normal state (flag not set)" and "abnormal light emission status detected (flag set)."

[0067] When the fault detection unit 333 detects an abnormal light emission state, it sets the abnormal light emission state flag 333a to indicate "Abnormal light emission state detected".

[0068] When the OAM processing unit 334 receives a downlink OAM frame, it interprets the contents of the OAM frame. If the OAM frame is a light emission control instruction or an ONU reset instruction, the OAM processing unit 334 refers to the abnormal light emission status flag 333a. If the flag is set, the OAM processing unit 334 ignores the light emission control instruction or ONU reset instruction. If the flag is not set, the OAM processing unit 334 performs light emission control or reset according to the instruction.

[0069] As described above, according to Embodiment 3, when an abnormal light emission state is detected, the light emission control instruction or ONU reset instruction from OLT110 is ignored and the light emission stop state is maintained, so it is possible to avoid the recurrence of abnormal light emission and the effect of not affecting the communication of other ONU320s is obtained. [Explanation of symbols]

[0070] 100, 200, 300 PON system, 110 OLT, 120 ONU, 130 PON MAC, 131 Optical output control unit, 132, 232 Upstream queue control unit, 232a User queue, 232b System queue, 232c Queue processing unit, 133, 233, 333 Fault detection unit, 234, 334 OAM processing unit, 140 Optical module, 141 Optical module transmitter, 342 Optical module receiver, 150 FET switch.

Claims

1. An optical signal transmission unit that transmits the optical signal to the station-side equipment when it receives a transmission permission, which is permission to transmit an optical signal, An optical output control unit that grants the optical signal transmission unit permission to transmit the optical signal at a time allocated by the station-side equipment in order to transmit the optical signal, A fault detection unit monitors the transmission permission and the transmission status of the optical signal, and when it detects an abnormal light emission state, it issues a transmission permission invalidation instruction, which is an instruction to invalidate the transmission permission, to the optical signal transmission unit and the switch unit. The system includes a switch unit that cuts off the power supplied to the optical signal transmission unit when the instruction to invalidate the transmission permission is given, The optical signal transmitting unit will stop transmitting the optical signal if the power is cut off by the switch unit and the transmission of the optical signal is stopped, or if it receives the instruction to invalidate the transmission permission, even if it has received the transmission permission. A fiber optic network termination device characterized by the following.

2. The optical output control unit outputs an optical output permission signal indicating permission to transmit to the optical signal transmission unit. The optical signal transmission unit outputs an optical output status signal to the fault detection unit, which indicates whether or not it is outputting the optical signal as the transmission status. The fault detection unit monitors the optical output permission signal and the optical output status signal, and detects the abnormal light emission state if the optical signal transmission unit has been outputting the optical signal for a predetermined period of time or longer. The optical network termination device according to claim 1, characterized by the following:

3. The system further includes a signal processing unit that, when the abnormal light emission state is detected, notifies the station-side device via the optical output control unit of information indicating that the abnormal light emission state has been detected. The fault detection unit, after the notification of the information, gives the instruction to invalidate the transmission permission to the optical signal transmission unit. An optical network termination device according to claim 1 or 2, characterized by the above.

4. The system further includes a signal processing unit that, in accordance with instructions from the station-side equipment, restarts the transmission of the optical signal by the optical signal transmission unit, which has stopped transmitting the optical signal in accordance with the transmission permission invalidation instruction, When the fault detection unit detects the abnormal light emission state, it stores information indicating that the abnormal light emission state has been detected. The signal processing unit shall not resume the transmission of the optical signal by the optical signal transmission unit, even if instructed by the station-side device, while the information indicating that the abnormal light emission state has been detected is being held. An optical network termination device according to claim 1 or 2, characterized by the above.

5. The fault detection unit shall cease to retain information indicating that the abnormal light emission state has been detected when the power to the optical line termination device is turned on after being turned off. The optical network termination device according to claim 4, characterized by the above.

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