JP2012151737A - Station side optical network terminal device, optical communication system, abnormality detection method, and device program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and easily detect an abnormality in an Optical Network Terminal (ONU).SOLUTION: An Optical Line Terminal (OLT) comprises: scheduling means which assigns an exclusive transmitting timing to each ONU; control signal transmitting means which transmits to each ONU a control signal for making data transmitted along a transmitting timing assigned by the scheduling means; and monitoring means which monitors an optical signal received through a transmission path. In the scheduling means, scheduling is performed so that all the connected ONUs include a non-communication state where transmission of the optical signal is stopped. In the monitoring means, monitoring is performed including a reception state in the non-communication state.

Description

  The present invention relates to, for example, a station side optical network terminal (OLT) such as a PON (Passive Optical Network) system, a subscriber side terminal (ONT; Optical Network Terminal / ONU; Optical Network Unit, hereinafter ONU). The present invention relates to a station-side optical network terminating device, an optical communication system, an abnormality detection method, and an apparatus program used in an optical communication system configured by being connected via a transmission line.

  Conventionally, one optical fiber (transmission path) is used as one of the technologies to realize FTTH (Fiber To The Home) that draws an optical fiber from a accommodation station (hereinafter referred to as a station) such as a communication carrier. A PON that is branched by a branching device (optical coupler) and drawn into a plurality of subscribers' homes is used.

  A general PON system using time division multiplexing represented by GE-PON (IEEE 802.3ah) and G-PON (ITU-T G984 series) will be described with reference to FIG.

  In many cases, as illustrated in FIG. 5, a PON system is configured in a point-to-multipoint type by connecting a plurality of ONUs installed in a subscriber premises to one OLT installed in a station. .

  Therefore, in the PON system, as shown in FIG. 5, the OLT transmits a transmission control signal (information for permitting data transmission timing) that is controlled so that transmission of each ONU does not overlap with each ONU. Each ONU transmits data to the OLT at a timing permitted by the transmission control signal. As a result, communication between the OLT and each ONU is performed without collision of signals from each ONU.

  Here, in the PON system, as described above, since data of a plurality of ONUs is optically multiplexed on one optical fiber, it is permitted among a number of ONUs installed at the subscriber's home side. If there is an abnormal ONU that transmits data at an unsuccessful timing, there is a risk of collision with data transmitted from another normal ONU. When such a collision occurs, communication between the OLT and a normal ONU may be hindered.

  For this reason, various techniques for detecting abnormal ONUs that do not follow the transmission timing instruction from the OLT have been proposed.

  For example, in Patent Document 1, the abnormality detection means of the OLT counts the duration of an idle pattern transmitted from the ONU during idling, the duration of the idle pattern is longer than a prescribed value defined in the standard, and the logical connection is When there is only one, the ONU is determined to be abnormal.

  Also, in Patent Document 2, if the frame cannot be synchronized with the received signal from the ONU, the OLT compares the predicted value of the signal strength based on the database with the measured value of the received signal, and whether the difference is a certain value or more. The strength of the received signal is checked based on the result. When the difference is equal to or greater than a certain value, the intensity of the received signal is measured at a timing at which a non-light condition in which no uplink signal from the ONU is received is calculated, and the difference from the predicted received signal intensity is calculated. Then, the calculated value is compared with the difference between the registered value registered in advance in the database and the intensity of the received signal to determine the occurrence of abnormality.

  Further, in Patent Document 3, when it is detected that a failure has occurred in which one of the ONUs emits continuous light and a light signal from all other ONUs cannot be received, the OLT detects all of the ONUs. An abnormal ONU is specified by transmitting a command not to allocate a communication band and then sequentially assigning the maximum communication band to each ONU.

  Moreover, in patent document 4, in the optical coupler which branches the optical fiber from OLT toward each ONU, the optical detection part corresponding to each ONU is provided separately, and each optical detection part from the ONU to which each corresponds. By detecting the intensity of the optical signal, the occurrence of a continuous light emission failure is detected, and the ONU where the failure has occurred is specified.

  Further, in Patent Document 5, the optical signal from the optical coupler is branched not only to the OLT but also to the dedicated ONU frame monitoring device, and the ONU frame monitoring device monitors the upstream signal from each ONU. Thus, it is detected whether or not the upstream signal from each ONU exceeds the permitted time region.

JP 2008-28451 A JP 2010-68362 A JP 2002-359596 A JP 2010-2112778 A JP-A-11-98078

  However, in Patent Document 1 described above, each ONU is sent an idle pattern, and ONU abnormality determination is performed based on the duration, and abnormality determination is performed by setting all ONUs to a non-communication state. It was not something that was taken into consideration.

  Further, in the above-mentioned Patent Document 2, after it is detected that the frame cannot be synchronized with the received signal from the ONU, the strength of the received signal is checked using a pre-registered database and compared with the calculated value. The abnormality determination is performed, and it has not been taken into account that the abnormality determination can be performed quickly and easily by setting all the ONUs to the non-communication state.

  Further, in the above-mentioned Patent Document 3, when a continuous light emission failure that makes it impossible to receive optical signals from all other ONUs occurs in any one of the ONUs, each of the ONUs is specified as an abnormal ONU specific operation. The maximum communication bandwidth is assigned to only ONUs in order, and all ONUs are set to the no-communication state in the normal operation state, and it is considered that the abnormality determination is performed quickly and easily. There wasn't.

  Further, the above-mentioned Patent Document 4 has a complicated structure because the optical detection unit corresponding to each ONU is individually provided in the optical coupler. In other words, it has not been considered to perform the abnormality determination with a simple configuration.

  Also, the above-mentioned Patent Document 5 monitors the upstream signal from each ONU by providing a dedicated ONU frame monitoring device, and the configuration is complicated. In other words, it has not been considered to perform the abnormality determination with a simple configuration.

  The present invention has been made in view of such a situation. By setting a no-communication state in which all ONUs stop transmission during normal operation, it is possible to detect an abnormality quickly and easily on the station side optical network termination. An object is to provide an apparatus (OLT), an optical communication system, an abnormality detection method, and an apparatus program.

  In order to achieve the above object, a station side optical network termination device according to the present invention is used by being connected to a plurality of subscriber side termination devices via a transmission line branched by a branching device. A scheduling means for allocating exclusive transmission timing to each subscriber-side terminal device, and a control signal for causing data transmission to be performed along the transmission timing assigned by the scheduling means to each subscriber-side terminal device. A control signal transmitting means for transmitting and a monitoring means for monitoring an optical signal received via the transmission line, and the scheduling means stops transmission of the optical signal by all connected subscriber-side terminators. Scheduling to include a no-communication state, and the monitoring means monitors the reception state including the no-communication state.

  Further, the optical communication system according to the present invention is configured by connecting a plurality of subscriber-side terminators to the above-mentioned station-side optical network terminator according to the present invention via a transmission line branched by the branching device. It is characterized by that.

  Further, the abnormality detection method according to the present invention is an abnormality detection method by a station-side optical network termination device used by being connected to a plurality of subscriber-side termination devices via a transmission path branched by a branching device, A scheduling step for assigning exclusive transmission timings to the subscriber-side terminal devices, and a control signal transmission for transmitting a control signal for performing data transmission along the transmission timings assigned by the scheduling step to each subscriber-side terminal device And a monitoring step of monitoring an optical signal received via the transmission line, and the scheduling step includes a non-communication state in which all connected terminal devices on the subscriber side stop sending the optical signal. In the monitoring step, monitoring is performed including the reception state in the no-communication state.

  The program according to the present invention is a program for a station-side optical network terminator used by being connected to a plurality of subscriber-side terminators via a transmission line branched by a branching device. A scheduling procedure for allocating exclusive transmission timing to a device, a control signal transmission procedure for transmitting a control signal for transmitting data along the transmission timing allocated by the scheduling procedure to each subscriber-side terminal device, and transmission The monitoring procedure for monitoring the optical signal received via the path is executed by the computer of the optical network terminating device on the station side, and in the scheduling procedure, all connected subscriber-side terminating devices stop sending optical signals. It is scheduled to include the no-communication state, and the monitoring procedure is characterized by monitoring including the reception state in the no-communication state. .

  As described above, according to the present invention, it is possible to detect an abnormality quickly and easily by setting the no-communication state in which all the subscriber-side terminal devices stop transmission during normal operation.

It is a figure which shows the PON system as an embodiment of this invention, and an example of data transmission timing. It is a block diagram which shows the structural example of OLT1 as embodiment of this invention. It is a figure which shows the example of a data transmission timing at the time of abnormality occurrence. It is a figure which shows the PON system and data transmission timing example as other embodiment of this invention. It is a figure which shows a general PON system and a data transmission timing example.

  Next, an embodiment of a PON system to which a station-side optical network terminating device (OLT), an optical communication system, an abnormality detection method, and a device program according to the present invention are applied will be described in detail with reference to the drawings.

First, this embodiment will be schematically described.
In this embodiment, as shown in FIG. 1, a single optical fiber 3 connected to the OLT 1 is branched by an optical coupler 2 and connected to a plurality of ONUs 4. Each ONU 4 is OLT 1 at a timing permitted by the OLT 1. In the optical communication system for transmitting signals by light emission respectively, a non-communication section in which all ONUs 4 stop transmitting optical signals when the OLT 1 is in normal operation is prepared, and the optical reception level in this section By monitoring this, it is possible to quickly detect the presence of an abnormal ONU 4 that does not comply with the transmission timing instruction permitted by the OLT 1.

  As shown in FIG. 2, the optical reception level measurement unit 13 of the OLT 1 measures the optical reception level from the ONU 4. The transmission timing control unit (scheduling means) 15 provides exclusive ON timing to each ONU 4 and prepares a no-communication state in which all ONUs 4 stop transmission during normal operation. Notify The abnormal ONU detection unit 14 reads the optical reception level from the optical reception level measurement unit at the timing notified by the transmission timing control unit, thereby monitoring the reception level in the non-communication state where transmission of the optical signal is stopped, When a reception level higher than a prescribed level is detected, it is determined that an abnormal ONU has occurred.

  As described above, the OLT 1 according to this embodiment prepares a non-communication state in which all ONUs 4 always stop sending optical signals during normal operation, and monitors the optical reception level at that timing, thereby transmitting from the OLT 1. It is possible to quickly detect the presence of an abnormal ONU that does not follow the timing instruction.

Next, the configuration of the OLT 1 in the present embodiment will be described in detail with reference to FIG.
As shown in FIG. 2, the OLT 1 is connected to the optical fiber 3, transmits an optical transmission signal from the optical transmission unit 16 to the optical fiber 3, and transmits an optical reception signal from the optical fiber 3 to the optical reception unit 12. An optical multiplexer / demultiplexer 11, an optical receiver 12 that receives an optical signal from the ONU 4, and an optical reception level measuring unit 13 that measures the optical reception level received by the optical receiver 12. Furthermore, in addition to instructing each ONU 4 during normal operation, an exclusive transmission timing is provided, and a non-communication state in which all ONUs 4 stop transmission at regular intervals is provided, and the timing is provided to the abnormal ONU detection unit. Unit 15 and an optical transmission unit 16 that transmits transmission data and transmission control signals to ONU 4 as optical signals. In addition, the optical reception level is read from the optical reception level measurement unit 13 at the timing instructed by the transmission timing control unit 15, the reception level in the no-communication state is monitored, and the transmission timing is detected when a reception level higher than a prescribed level is detected. An abnormal ONU detection unit 14 that determines that an abnormal ONU has occurred is provided.

  Next, an operation example according to the present embodiment will be described with reference to FIGS.

The transmission timing control unit 15 assigns exclusive transmission timing to each ONU 4 and performs scheduling so as to periodically prepare a non-communication period in which all the ONUs 4 are in a non-communication state where no optical signal is transmitted. This non-communication state time is shown as a non-communication section t in FIG.
Thus, information such as the uplink signal transmission timing in each ONU 4 (# 1 to #n) assigned by the transmission timing control unit 15 is transmitted from the OLT 1 to each ONU 4 as a transmission control signal.

  Each ONU 4 (# 1 to #n) transmits uplink data to the OLT 1 at the timing assigned to itself according to the transmission control signal received from the OLT 1. At this time, the abnormal ONU detection unit 14 of the OLT 1 acquires the optical reception level in the non-communication period t shown in FIG. 1 using the optical reception level measurement unit 13, and continuously determines the optical reception level in the non-communication period t. Monitor.

  During normal operation, upstream data from each ONU 4 is transmitted at exclusive timings such as “A”, “B”, and “C” in FIG. 1, and all ONUs 4 transmit optical signals in the non-communication period. Since it is not transmitted, the optical reception level is the same as the level in the no-communication state.

When there is an ONU having a transmission timing abnormality, as illustrated in FIG. 3, there is data transmitted at the timing of the non-communication section t. In the example of FIG. 3, a state in which “C” data by ONU 4-n (#n) is transmitted in the non-communication section t is shown.
In this case, since it can be determined that the optical reception level in the no-communication section t is more than a predetermined value from the normal ONU no-communication level, the abnormal ONU detection unit 14 does not follow the transmission timing instruction from the OLT 1. The occurrence of ONU can be detected.

  As described above, in the above-described embodiment, the single optical fiber 3 connected to the OLT 1 is branched by the optical coupler 2 and connected to each of the plurality of ONUs 4, and each of the ONUs 4 permitted by the OLT 1 is used for each timing. In an optical communication system in which a signal by light emission is transmitted from the ONU 4 to the OLT 1, all the ONUs 4 are in each period for assigning exclusive transmission timings to all ONUs 4 to which transmission timings are assigned during normal operation. Set the no-communication section to stop transmission.

  According to this embodiment, when the optical reception level abnormality is detected by monitoring the optical reception level in the non-communication section, the OLT 1 indicates that there is an abnormal ONU that does not follow the transmission timing instruction permitted by the OLT 1. It can be detected promptly.

[Other Embodiments]
Next, another embodiment of the present invention will be described with reference to FIG.
In the other embodiment shown in FIG. 4, the basic configuration is the same as in the above-described embodiment, but a non-communication section is inserted between the optical signal transmission timings assigned to each ONU 4 to make it easier to identify an abnormal ONU. I am trying to do it. A description of the same components as those in the above-described embodiment is omitted.

  When the transmission timing control unit 15 assigns exclusive transmission timings to the ONUs 4 (# 1 to #n), all the ONUs 4 are optically transmitted immediately after the optical signal transmission timings of the ONUs 4 thus assigned. Scheduling is performed so as to prepare a non-communication period in which no signal is transmitted. This non-communication state time is shown as non-communication sections t1 to t3 in the example of FIG.

  The transmission timing control unit 15 thus determines the transmission timing of each ONU 4 so as to include the non-communication section between the communication timings of each ONU 4, and transmits information such as the transmission timing in each ONU 4 to the ONU 4 by a transmission control signal. Each ONU 4 transmits uplink data to the OLT 1 according to the received transmission control signal at a timing exclusively assigned to the own device.

  The abnormal ONU detection unit 14 uses the optical reception level measurement unit 13 to acquire the optical reception level in the non-communication period (t1 to t3 in the example of FIG. 4) set between the communication timings of the respective ONUs 4. When the abnormal ONU detection unit 14 acquires the optical reception level of each non-communication section and determines that the acquired optical reception level is different from the ONU non-communication level by a predetermined value or more, transmission from the OLT 1 Detects that an abnormal ONU that does not follow the timing instructions has occurred.

  At this time, for example, when the abnormality ONU detection unit 14 detects no abnormality in the non-communication section t1 in FIG. 4 and detects an abnormality in the next non-communication section t2, the transmission timing is assigned immediately before the non-communication section t2. It is determined that there is a high possibility that there is an abnormality in the transmission timing of ONU4-2 (# 2). That is, it is determined that there is a high possibility that the ONU 4-2 (# 2) that finally performed the optical signal transmission operation based on the transmission control signal from the OLT 1 has caused the timing abnormality.

  As described above, in another embodiment illustrated in FIG. 4, the single optical fiber 3 connected to the OLT 1 is branched by the optical coupler 2 and connected to the plurality of ONUs 4, and each ONU 4 permitted by the OLT 1 is used. In an optical communication system in which a signal by light emission is transmitted from each ONU 4 to the OLT 1 at each timing, every ONU 4 stops transmission every time an exclusive transmission timing is assigned to each ONU 4 during normal operation. The communication section is set immediately after the transmission timing.

  According to another embodiment, when the no-communication state is arranged between the transmission timings of the respective ONUs 4 and the OLT 1 detects the optical reception level abnormality by monitoring the optical reception level in the no-communication section, the OLT 1 It is possible to quickly detect the occurrence of an abnormal ONU that does not follow the permitted transmission timing instruction, and to identify the ONU 4 that is highly likely to be the abnormal ONU.

  Each of the above-described embodiments is a preferred embodiment of the present invention, and the present invention is not limited to this, and various modifications can be made based on the technical idea of the present invention.

In addition, by recording the processing procedure for realizing the OLT as each embodiment described above on a recording medium as a program, the above-described functions according to each embodiment of the present invention can be performed by a program supplied from the recording medium. It can be realized by causing a CPU of a computer constituting the system to perform processing.
In this case, the present invention can be applied even when an information group including a program is supplied to the output device from the above recording medium or from an external recording medium via a network.
That is, the program code itself read from the recording medium realizes the novel function of the present invention, and the recording medium storing the program code and the signal read from the recording medium constitute the present invention. It will be.
As this recording medium, for example, a hard disk, an optical disk, a magneto-optical disk, a floppy disk, a magnetic tape, a nonvolatile memory card, a ROM, or the like may be used.

  According to the program according to the present invention, each function in each of the above-described embodiments can be realized by the OLT controlled by the program.

[Appendix]
A part or all of the above embodiment can be described as the following supplementary notes, but is not limited to the following.

[Appendix 1]
A station side optical network terminator used by being connected to a plurality of subscriber side terminators via a transmission line branched by a branch device,
Scheduling means for allocating exclusive transmission timing to each subscriber-side terminal device;
Control signal transmitting means for transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling means to each of the subscriber-side terminal devices;
Monitoring means for monitoring an optical signal received via the transmission line,
The scheduling means performs scheduling so as to include a non-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals,
The station-side optical network termination device, wherein the monitoring means monitors the reception state in the no-communication state.

[Appendix 2]
The station side optical network termination device according to appendix 1, wherein the scheduling means periodically sets the no-communication state during normal operation.

[Appendix 3]
The station according to claim 1, wherein the scheduling means performs scheduling so as to include the no-communication state for each period in which exclusive transmission timing is allocated to all the subscriber-side terminal devices to which transmission timing is assigned. Side optical network termination device.

[Appendix 4]
The station-side optical network according to claim 1, wherein the scheduling unit performs scheduling so as to include the no-communication state immediately after the transmission timing every time an exclusive transmission timing is assigned to each subscriber-side terminal device. Termination equipment.

[Appendix 5]
5. The apparatus according to claim 1, further comprising an abnormality determination unit that determines that an abnormality has occurred when the monitoring unit detects an optical reception level that is equal to or higher than a predetermined value in the no-communication state. Station-side optical network terminator.

[Appendix 6]
A plurality of subscriber-side terminators are connected to the station-side optical network terminator according to any one of appendices 1 to 5 via a transmission line branched by the branch device. An optical communication system.

[Appendix 7]
An abnormality detection method by a station-side optical network termination device used by being connected to a plurality of subscriber-side termination devices via a transmission line branched by a branching device,
A scheduling step of assigning exclusive transmission timing to each subscriber-side terminal device;
A control signal transmission step of transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling step to each of the subscriber-side terminal devices;
A monitoring step of monitoring an optical signal received via the transmission path,
In the scheduling step, scheduling is performed so as to include a no-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals,
In the monitoring step, the abnormality detection method characterized by monitoring including the reception state in the non-communication state.

[Appendix 8]
The abnormality detection method according to appendix 8, wherein in the scheduling step, the no-communication state is periodically set during normal operation.

[Appendix 9]
9. The abnormality according to claim 8, wherein the scheduling step performs scheduling so as to include the no-communication state for each period in which exclusive transmission timing is allocated to all the subscriber-side terminal devices to which transmission timing is assigned. Detection method.

[Appendix 10]
9. The abnormality detection method according to claim 8, wherein, in the scheduling step, scheduling is performed so that the no-communication state is included immediately after the transmission timing every time an exclusive transmission timing is assigned to each subscriber-side terminal device.

[Appendix 11]
11. The method according to any one of appendices 8 to 10, further comprising an abnormality determination step of determining that an abnormality has occurred when an optical reception level equal to or higher than a predetermined value is detected in the no-communication state by the monitoring step. Anomaly detection method.

[Appendix 12]
A program for a station side optical network terminator used by being connected to a plurality of subscriber side terminators via a transmission line branched by a branch device,
A scheduling procedure for allocating exclusive transmission timing to each subscriber-side terminal device;
A control signal transmission procedure for transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling procedure to each subscriber-side terminal device;
A monitoring procedure for monitoring an optical signal received via the transmission line, and causing the computer of the station side optical network termination device to execute,
In the scheduling procedure, scheduling is performed so as to include a no-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals.
In the monitoring procedure, monitoring is performed including the reception state in the non-communication state.

[Appendix 13]
The program according to appendix 12, wherein in the scheduling procedure, the no-communication state is periodically set during normal operation.

[Appendix 14]
13. The program according to claim 12, wherein in the scheduling procedure, scheduling is performed so as to include the no-communication state for each period in which exclusive transmission timing is allocated to all the subscriber-side terminal devices to which transmission timing is assigned. .

[Appendix 15]
13. The program according to appendix 12, wherein in the scheduling procedure, every time an exclusive transmission timing is assigned to each subscriber-side terminal device, scheduling is performed so that the no-communication state is included immediately after the transmission timing.

[Appendix 16]
An additional feature of causing the computer of the station side optical network termination device to execute an abnormality determination procedure for determining that an abnormality has occurred when an optical reception level of a predetermined value or more is detected in the no-communication state by the monitoring procedure. The program according to any one of 12 to 15.

1 OLT
DESCRIPTION OF SYMBOLS 11 Optical multiplexer / demultiplexer 12 Optical receiver 13 Optical reception level measurement part 14 Abnormal ONU detection part 15 Transmission timing control part 16 Optical transmission part 2 Optical coupler 3 Optical fiber 4 ONU

Claims (8)

A station side optical network terminator used by being connected to a plurality of subscriber side terminators via a transmission line branched by a branch device,
Scheduling means for allocating exclusive transmission timing to each subscriber-side terminal device;
Control signal transmitting means for transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling means to each of the subscriber-side terminal devices;
Monitoring means for monitoring an optical signal received via the transmission line,
The scheduling means performs scheduling so as to include a non-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals,
The station-side optical network termination device, wherein the monitoring means monitors the reception state in the no-communication state.   2. The station side optical network termination device according to claim 1, wherein the scheduling means periodically sets the no-communication state during normal operation.   2. The scheduling according to claim 1, wherein the scheduling unit performs scheduling so as to include the no-communication state for each period in which exclusive transmission timing is allocated to all the subscriber-side terminal devices to which transmission timing is assigned. Station side optical network terminator.   2. The station side light according to claim 1, wherein the scheduling unit performs scheduling so as to include the no-communication state immediately after the transmission timing every time an exclusive transmission timing is assigned to each subscriber-side terminal device. Network termination equipment.   5. The apparatus according to claim 1, further comprising an abnormality determination unit that determines that an abnormality has occurred when an optical reception level that is equal to or higher than a predetermined value is detected by the monitoring unit in the no-communication state. The station side optical network terminator described.   A plurality of the subscriber-side terminators are connected to the station-side optical network terminator according to any one of claims 1 to 5 via a transmission path branched by the branch device. An optical communication system. An abnormality detection method by a station-side optical network termination device used by being connected to a plurality of subscriber-side termination devices via a transmission line branched by a branching device,
A scheduling step of assigning exclusive transmission timing to each subscriber-side terminal device;
A control signal transmission step of transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling step to each of the subscriber-side terminal devices;
A monitoring step of monitoring an optical signal received via the transmission path,
In the scheduling step, scheduling is performed so as to include a no-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals,
In the monitoring step, the abnormality detection method characterized by monitoring including the reception state in the non-communication state. A program for a station side optical network terminator used by being connected to a plurality of subscriber side terminators via a transmission line branched by a branch device,
A scheduling procedure for allocating exclusive transmission timing to each subscriber-side terminal device;
A control signal transmission procedure for transmitting a control signal for performing data transmission along the transmission timing assigned by the scheduling procedure to each subscriber-side terminal device;
A monitoring procedure for monitoring an optical signal received via the transmission line, and causing the computer of the station side optical network termination device to execute,
In the scheduling procedure, scheduling is performed so as to include a no-communication state in which all of the connected terminal devices on the subscriber side stop sending optical signals.
In the monitoring procedure, monitoring is performed including the reception state in the non-communication state.

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