JP6438362B2 - Station-side terminator and communication control method - Google Patents

Description

  The present invention relates to a station-side terminal device and a communication control method.

  In recent years, social systems in which communication and automobile / road traffic infrastructure are closely related, such as ITS (Intelligent Transport Systems) and automatic driving, have been studied. In these social systems, automobiles and the like are required to perform highly reliable and highly efficient autonomous driving and route setting. For this purpose, it is essential to establish a communication infrastructure for performing cooperative operations with other vehicles, obtaining peripheral information, and exchanging with a traffic control center or an external monitoring center of vehicle body status.

  When such an environment is assumed, it is important to develop a communication system that performs broadband communication with a high-speed terminal installed in many automobiles. Candidates for communication infrastructures suitable for these include broadband mobile communication and systems capable of relatively short range communication such as Wi-Fi. In addition, an optical communication system that performs direct optical communication with a moving terminal is also a promising candidate as a means for performing ultra-wideband communication directly with a moving body, and is not easily affected by radio wave shadows or electromagnetic interference (for example, (See Patent Document 1 or Non-Patent Document 2).

  A method of communicating with a vehicle using optical space communication will be described with reference to FIG. FIG. 1 is a diagram for explaining a communication method with a vehicle using optical space communication. As shown in FIG. 1, the moving body is provided with an optical signal receiving device (demodulation unit) and a transmitting device (modulation unit), and the infrastructure side is along the moving direction (road, trajectory, etc.) of the moving body. In addition, a leaky optical fiber that outputs optical signals to space, a light receiving unit that receives optical signals, and a signal control unit (optical signal transmitting unit and receiving unit that receives signals from the light receiving unit) connected thereto are installed. The signal control unit is connected to the station building and the like.

  When communication from the mobile unit to the signal control unit is performed, the optical signal transmission unit of the mobile unit emits light, outputs an optical signal, and the light receiving unit that connects this optical signal to the signal control unit receives and controls the signal. To the department. Also, when a signal is transmitted from the signal control unit to the moving body, the optical signal output from the signal transmitting unit is received by the leaking optical fiber, the optical signal is output to the space, and the optical signal receiving unit of the moving body receives The communication is performed by. In the above method, an optical signal is emitted into the space for communication, but the same method can be used for wireless communication using a leaky coaxial cable.

  On the other hand, in recent years, the introduction of FTTH (Fiber To The Home) has been promoted along with the spread of broadband services. The main form of FTTH is a PON (Passive Optical Network) system.

  In a point-to-multipoint optical communication system such as a PON system, one station-side terminal device (OLT: Optical Line Terminal) and at least one subscriber-side terminal device (ONU: Optical Network Unit) Is connected.

  A PON system is known as point-to-multipoint optical communication. The PON system will be described with reference to FIG. FIG. 2 is a diagram for explaining the PON system. As shown in FIG. 2, the PON system has a point-to-multipoint between an OLT and a plurality of ONUs via an optical transmission line (for example, an optical fiber transmission line) and a 1 to n (n is a natural number) optical splitter. This is a network for point communication. As a typical standard of the gigabit class PON, there is EPON (Ethernet (registered trademark) PON) standardized by IEEE 802.3. For example, 10G-class 10G-EPON is standardized in EPON, for example, in the IEEE 802.3av study group.

  DBA (Dynamic Bandwidth Allocation) is an example of a characteristic optical communication method using point-to-multipoint like PON. The DBA will be described with reference to FIG. FIG. 3 is a diagram for explaining DBA. As shown in FIG. 3, the DBA causes the ONU to report the amount of data in the queue provided in the ONU by the REPORT message, and notifies the ONU of the upstream bandwidth allocation result by the GATE message. The amount of data in the queue in the ONU is monitored based on the received report message, and the transmission order and the amount of data that can be transmitted are assigned to each ONU by an algorithm. Also, in order to prevent a collision between a message transmitted from one ONU and a message from another ONU, a guard time is provided at the timing at which the ONU transmits a message.

Hiroshi Matsubara, Shingo Nakagawa, Kazuhiro Nakamura, Kiyotaka Seki, “High-speed and large-capacity railway communication environment”, RRR 2010.6 Takashi Tsuchiya, Kiyotaka Seki, Shinichiro Haruyama, "Trends and Challenges of High-Speed and Large-Capacity Mobile Communication Technology in Railways", RTRI Report Vol.22, No.6, Jun 2008

  However, in the conventional technology, in the point-to-multipoint optical communication system, when the positional relationship between the OLT and the ONU changes with time, there is a problem that the guard time increases and the bandwidth utilization efficiency decreases. .

  For example, in an optical space communication system using a leaky optical fiber as shown in FIG. 1, there is a possibility that a plurality of moving bodies may exist in one arranged leaky optical fiber in consideration of traffic conditions on a road or a track. There is. Further, it is economically advantageous to install a single leaky optical fiber among a plurality of moving bodies.

  In the prior art, since a guard time setting method in point-to-multipoint communication is not considered, it is difficult to efficiently communicate with a plurality of mobile objects. Note that the smaller the guard time, the more data can be transmitted within a certain time, and the bandwidth utilization efficiency is improved.

  The station-side terminator of the present invention includes a transmitter that transmits an optical signal to a plurality of subscriber-side terminators whose positions change with time, and a receiver that receives the optical signal transmitted by the subscriber-side terminator. And an optical signal transmitted from the subscriber-side terminating device as a response to the optical signal until an optical signal transmitted from the subscriber-side terminating device is received by the receiving unit. A measuring unit for measuring round-trip communication delay time, and light transmitted by one of the subscriber-side termination devices based on the round-trip communication delay time each time a predetermined condition is satisfied The time when the signal is received by the receiving unit is the time when the receiving unit receives the optical signal transmitted by another subscriber-side terminating device that transmits the optical signal after the one subscriber-side terminating device. A time interval setting unit that corrects a time interval between times when optical signals are transmitted by each subscriber-side terminating device, and the subscriber-side terminating device is configured to transmit the optical signal based on the time interval. And a transmission time designating unit for designating the time for transmitting.

  The communication control method of the present invention is a communication control method executed in a communication system having a station-side terminal device and a plurality of subscriber-side terminal devices whose positions change with time. An optical signal transmitted from the subscriber-side terminating device as a response to the optical signal transmitted by the station-side terminating device in the transmitting step; Receiving step, a measuring step for measuring the round-trip communication delay time from the execution of the transmission step to the execution of the reception step, and the round-trip communication delay time each time a predetermined condition is satisfied Based on the time when the optical signal transmitted by one of the subscriber-side terminators is received by the receiving step is the optical signal after the one subscriber-side terminator. The time interval between the time when the optical signal is transmitted by each subscriber-side terminal device is set so that the optical signal transmitted by the other subscriber-side terminal device is transmitted before the time when the signal is received by the receiving step. It includes a time interval setting step of correcting, and a transmission time specifying step of specifying a time at which the subscriber-side terminating device transmits an optical signal based on the time interval.

  According to the present invention, in a point-to-multipoint optical communication system, even when the positional relationship between the OLT and the ONU changes with time, it is possible to suppress an increase in guard time and a decrease in bandwidth utilization efficiency. The

FIG. 1 is a diagram for explaining a communication method with a vehicle using optical space communication. FIG. 2 is a diagram for explaining the PON system. FIG. 3 is a diagram for explaining DBA. FIG. 4 is a diagram for explaining a method of measuring a delay time between OLT and ONU. FIG. 5 is a diagram for explaining the guard time. FIG. 6 is a diagram for explaining the guard time. FIG. 7 is a diagram for explaining a method of measuring the delay time between the OLT and the ONU when the ONU moves. FIG. 8 is a diagram illustrating an example of a configuration of the communication system according to the first embodiment. FIG. 9 is a diagram illustrating an example of the configuration of the communication system according to the first embodiment. FIG. 10 is a diagram illustrating an example of a configuration of the communication system according to the first embodiment. FIG. 11 is a diagram illustrating an example of a configuration of a communication system and a station-side termination device according to the first embodiment. FIG. 12 is a diagram for explaining an example of processing of the communication system according to the first embodiment. FIG. 13 is a flowchart illustrating an example of processing of the communication system according to the first embodiment. FIG. 14 is a flowchart illustrating an example of processing of the communication system according to the first embodiment. FIG. 15 is a diagram for explaining an example of processing of the communication system according to the second embodiment. FIG. 16 is a flowchart illustrating an example of processing of the communication system according to the second embodiment. FIG. 17 is a flowchart illustrating an example of processing of the communication system according to the second embodiment. FIG. 18 is a diagram illustrating an example of a configuration of a communication system and a station-side termination device according to the third embodiment. FIG. 19 is a diagram for explaining an example of processing of the communication system according to the third embodiment. FIG. 20 is a diagram for explaining an example of processing of the communication system according to the third embodiment. FIG. 21 is a flowchart illustrating an example of processing of the communication system according to the third embodiment. FIG. 22 is a flowchart illustrating an example of processing of the communication system according to the third embodiment. FIG. 23 is a diagram for explaining an example of processing of the communication system according to the fourth embodiment. FIG. 24 is a flowchart illustrating an example of processing of the communication system according to the fourth embodiment. FIG. 25 is a diagram illustrating an example of a computer in which a station-side terminal device is realized by executing a program.

  Below, the station side termination device and the communication control method according to the present application will be described in detail based on the drawings. Note that the station-side terminal device and the communication control method according to the present application are not limited by this embodiment.

[First Embodiment]
In the following embodiments, the configuration and processing flow of the communication system according to the first embodiment will be described, and finally the effects of the first embodiment will be described. The communication system according to the first embodiment includes a station-side terminal device. The communication control method is executed in the communication system according to the first embodiment.

[Configuration of First Embodiment]
First, a method for measuring the delay time between the OLT and the ONU, that is, the RTT will be described with reference to FIG. FIG. 4 is a diagram for explaining a method of measuring a delay time between OLT and ONU. As shown in FIG. 4, the time described in the GATE frame transmitted by the OLT is T ₁ , the time when the ONU receives the GATE frame is T ₂ , the time when the ONU transmits the REPORT frame is T ₃ , and the ONU transmits Assuming that the time described in the REPORT frame is T ₄ and the time when the OLT receives the REPORT frame is T ₅ , the RTT is calculated by Equation (1).

The OLT has a function of designating the time when the ONU transmits a frame. T ₄ is a time specified by the OLT and transmitted by the ONU to the REPORT frame. T ₁ and T ₄ are absolute times or times measured by OLT, and T ₂ and T ₃ are times actually measured by the ONU. The difference between T ₄ and T ₁ is the processing time in the ONU when no RTT occurs, and is equal to the difference between T ₃ and T ₂ as shown in equation (2).

  Further, the range, that is, the distance between the OLT and the ONU can be calculated from the equation (3). In the formula (3), C is the speed of light.

Here, the guard time will be described with reference to FIGS. 5 and 6. 5 and 6 are diagrams for explaining the guard time. First, in the example of FIGS. 5 and 6, at time _{T 12} the frame transmitted from ONU # 1, has reached the OLT at the time _{T 13.} Also, from time _{T 12,} the frame transmitted from the ONU # 2 at time _{T 22} to time set as a guard time has elapsed, it has reached the OLT at the time _{T 23.}

  In the example of FIG. 5, the frame transmitted first reaches the OLT after the frame transmitted later. On the other hand, in FIG. 6 in which the guard time is set larger, the frame transmitted earlier reaches the OLT before the frame transmitted later. As described above, since the delay time varies depending on the distance to the OLT, it is necessary to set the guard time to be somewhat large in order to prevent reversal of the time when the optical signal reaches the OLT and collision.

  However, the larger the guard time, the more data that can be transmitted per unit time. For this reason, in 1st Embodiment, guard time is set as small as possible, ensuring normal communication.

A method for measuring the delay time between the OLT and the ONU when the ONU moves will be described with reference to FIG. FIG. 7 is a diagram for explaining a method of measuring the delay time between the OLT and the ONU when the ONU moves. As shown in FIG. 7, in a communication system to which a point-to-multipoint communication method such as PON is applied, an ONU may be mounted on a moving body such as an automobile or a train. In this case, since the position of the ONU with respect to the OLT changes with time, the RTT also changes with time. For example, in FIG. 7, the RTT at time t = 0 is T ₅ -T ₄ . On the other hand, the RTT at time t = y is T _{n + 10} −T _{n + 9} .

  Here, the configuration of the communication system according to the first embodiment will be described with reference to FIGS. 8, 9, and 10. 8, FIG. 9 and FIG. 10 are diagrams illustrating an example of the configuration of the communication system according to the first embodiment.

  The connection form of the communication system according to the first embodiment may be various forms depending on the position where the OLT is installed. When the communication distance between the OLT and the ONU changes as the ONU moves, the RTT also changes. . For example, as shown in FIG. 8, the OLT and the plurality of ONUs are connected by an optical fiber and optical communication means. The optical communication means outputs an OLT optical signal to space by a leaking optical fiber, an LED, or the like. The optical communication means outputs the optical signal from the ONU as a direct optical signal to the optical fiber.

  The OLT may use a PD (Photo Diode) or the like to convert an optical signal received from the ONU as an optical signal for an optical fiber. Further, the communication system may include a RoF (Radio over Fiber) that converts an optical signal from the OLT into a wireless signal as it is, performs communication, and converts a wireless signal from the ONU into an optical signal as it is. Also, as shown in FIG. 8, the optical communication means is arranged along the vicinity of the ONU movement path, and is configured to continue communication. For example, it is conceivable that the optical communication means is laid along the road along which the ONU moves.

  With the above configuration, when the ONT moves along the optical communication means while the OLT performs point-to-multipoint communication by DBA, the communication distance between the OLT and the ONU changes with time, so the RTT also changes. To do. Further, the communication system may have a PON / bus type configuration as shown in FIG. 9 or a ring type configuration as shown in FIG.

  Next, each unit of the communication system and the station-side terminal device according to the first embodiment will be described with reference to FIG. FIG. 11 is a diagram illustrating an example of a configuration of a communication system and a station-side termination device according to the first embodiment. As shown in FIG. 11, the communication system 1 includes a station-side terminal device (OLT) 10 and a plurality of subscriber-side terminal devices (ONU) 20. The OLT 10 and the subscriber-side terminal device 20 are connected by an optical transmission line. The optical transmission line includes, for example, an optical fiber and a space.

  The OLT 10 includes a transmission unit 101, a reception unit 102, a measurement unit 103, a storage unit 104, a calculation unit 105, a guard time setting unit 106, and a transmission time designation unit 107.

  The transmission unit 101 transmits an optical signal to a plurality of ONUs 20 whose positions change with time. The receiving unit 102 receives an optical signal transmitted by the ONU 20. The measurement unit 103 transmits an optical signal from the transmission unit 101 and performs RTT (round-trip communication) until the reception unit 102 receives an optical signal transmitted from the ONU 20 as a response to the optical signal transmitted by the transmission unit 101. Measure the delay time (Round Trip Time).

  Then, every time a predetermined condition is satisfied, the guard time setting unit 106 determines that the time at which the optical signal transmitted by one ONU of the ONUs 20 is received by the receiving unit 102 is one ONU based on the RTT. After that, the time interval between the time when the optical signal is transmitted by each ONU, that is, the guard time, so that the optical signal transmitted by another ONU that transmits the optical signal is before the time when the receiving unit 102 receives the optical signal. Correct. Moreover, the transmission time designation | designated part 107 designates the time when ONU20 transmits an optical signal based on guard time.

  Further, the calculation unit 105 can perform a predetermined calculation based on the RTT measured by the measurement unit 103 at one or a plurality of time points, and can pass the RTT obtained as a result of the calculation to the guard time setting unit 106. The predetermined calculation may be, for example, adding a predetermined value to RTT or subtracting a predetermined value from RTT. The calculation unit 105 may calculate the average of a plurality of RTTs.

  The calculation unit 105 may calculate a change amount per time of a plurality of RTTs measured by the measurement unit 103 and add the change amount to a predetermined RTT. In that case, the guard time setting unit 106 corrects the guard time based on the RTT to which the change amount is added by the calculation unit 105.

  The storage unit 104 stores the RTT measured by the measurement unit 103. Then, the guard time setting unit 106 may refer to the RTT stored in the storage unit 104 at a predetermined time and update the guard time based on the referenced RTT. The storage unit 104 stores a guard time. Then, the transmission time specifying unit 107 may refer to the guard time stored in the storage unit 104 and specify the time at which the ONU 20 transmits a signal based on the referenced guard time.

[Process of First Embodiment]
Processing of the communication system according to the first embodiment will be described with reference to FIG. FIG. 12 is a diagram for explaining an example of processing of the communication system according to the first embodiment. First, in the past DBA cycle, the measurement unit 103 measures the RTT of an arbitrary ONU. Then, the guard time setting unit 106 updates the guard time using the RTT measured by the measuring unit 103 as a correction value and reflects it in the guard time of the current DBA cycle. By repeating this operation, the station-side terminal device 10 continuously corrects the RTT, and copes with the RTT change accompanying the change in the distance between the ONU and the OLT.

  Further, the calculation unit 105 may calculate an average RTT change amount per time based on a plurality of RTT measurement results, and add the RTT value immediately before the reflection to perform correction. Thereby, for example, the influence of measurement failure can be avoided by excluding the value at the time of measurement failure from the calculation. In addition, it may be determined that the measurement has failed if it exceeds the preset allowable range, or if the allowable range is not reached, or it is determined that the measurement has failed if extreme fluctuations have occurred compared to past measured values. May be. Further, the time from the RTT measurement to the reflection of the RTT correction value can be arbitrarily set, for example, on the condition that the transmission of the uplink signal does not affect the condition.

  In addition, when the ONU continues to move and enters a different OLT section, the OLT starts communication in the OLT section where the ONU is different by providing RTT change information, history information, etc. to the OLT that takes over in advance. It is possible to assist to start smoothly.

  The processing of the first embodiment will be described using the flowcharts shown in FIGS. 13 and 14. 13 and 14 are flowcharts illustrating an example of processing of the communication system according to the first embodiment. As shown in FIG. 13, first, the measurement unit 103 performs RTT measurement (step S101). Then, the guard time setting unit 106 updates the guard time using the RTT measured by the measuring unit 103 as a correction value and reflects it in the guard time having a predetermined cycle (step S102). Thereafter, the measurement unit 103 further measures RTT (step S101) and repeats the process.

  Further, as shown in FIG. 14, the measurement unit 103 may perform RTT measurement a plurality of times. As shown in FIG. 14, first, the measurement unit 103 performs RTT measurement n times (step S111). Then, the calculation unit 105 calculates the average of the measurement values as a correction value (Step S112). For example, the calculation unit 105 calculates the average RTT change amount per hour by calculating the average of the measurement values, and adds it to the RTT value immediately before the reflection. Then, the guard time setting unit 106 updates the guard time using the RTT calculated by the calculation unit 105 as a correction value, and reflects it in the guard time having a predetermined period (step S113). Thereafter, the measurement unit 103 further measures RTT (step S111) and repeats the process.

[Effect of the first embodiment]
In the first embodiment, the transmission unit 101 transmits an optical signal to a plurality of ONUs 20 whose positions change with time. The receiving unit 102 receives an optical signal transmitted by the ONU 20. The measuring unit 103 measures the RTT until the optical signal transmitted from the ONU 20 is received by the receiving unit 102 as a response to the optical signal transmitted by the transmitting unit 101. .

  Then, every time a predetermined condition is satisfied, the guard time setting unit 106 determines that the time at which the optical signal transmitted by one ONU of the ONUs 20 is received by the receiving unit 102 is one ONU based on the RTT. After that, the time interval between the time when the optical signal is transmitted by each ONU, that is, the guard time, so that the optical signal transmitted by another ONU that transmits the optical signal is before the time when the receiving unit 102 receives the optical signal. Correct. Moreover, the transmission time designation | designated part 107 designates the time when ONU20 transmits an optical signal based on guard time.

  In DBA, it is necessary to set a guard time as an overhead for avoiding signal collision. Since the guard time is set based on the RTT, the guard time can be further shortened by accurately grasping the RTT.

  According to the first embodiment, the OLT 10 can accurately grasp a change in the RTT and set a minimum guard time while avoiding a collision. Therefore, even when the positional relationship between the OLT 10 and the ONU 20 changes with time, it is possible to prevent the guard time from increasing and the bandwidth utilization efficiency from decreasing.

  Further, the calculation unit 105 may calculate a change amount per time of a plurality of RTTs measured by the measurement unit 103 and add the change amount to a predetermined RTT. In that case, the guard time setting unit 106 corrects the guard time based on the RTT to which the change amount is added by the calculation unit 105. Thereby, even if it is a case where the measurement of RTT fails, RTT at the time of failure can be estimated from the amount of change, and the influence of measurement failure can be reduced.

  Furthermore, as an additional effect of performing RTT measurement multiple times, when an extreme change occurs in the measured RTT in a very short time without causing a measurement error, or when it suddenly stops changing It is estimated that an extreme speed change has occurred. In this case, it can be assumed that a failure such as a traffic accident has occurred in the ONU 20. When the OLT 10 senses such a change, an emergency alarm such as accident information can be issued to an arbitrary engine to promptly deal with a failure. Further, since the OLT 10 knows the relationship between the position and the RTT, it is possible to determine the point where the failure has occurred, and for example, it is possible to grasp the exact position of the traffic accident.

[Second Embodiment]
The RTT correction is not necessarily performed in every cycle, and may be performed at an arbitrary timing. In the second embodiment, a case will be described in which RTT correction is performed at a timing when a predetermined condition is satisfied.

[Configuration of Second Embodiment]
The basic configuration of the second embodiment is the same as that of the first embodiment. After the RTT is measured by the measurement unit 103, the guard time setting unit 106 determines that a predetermined condition is satisfied when a predetermined number of communications are performed between the OLT 10 and the ONU 20, and based on the RTT Correct the guard time.

[Process of Second Embodiment]
Processing of the communication system according to the second embodiment will be described with reference to FIG. FIG. 15 is a diagram for explaining an example of processing of the communication system according to the second embodiment. As shown in FIG. 15, the measurement unit 103 measures RTT during the RTT measurement period. The calculation unit 105 calculates the average RTT. Then, after the correction RTT reflection standby period has elapsed, the guard time setting unit 106 reflects the past information in the guard time in the reflection period based on the result calculated by the calculation unit 105.

  The corrected RTT reflection standby period is provided, for example, when the RTT change of the moving body is sufficiently small and it is not necessary to immediately perform the correction according to the immediately following RTT change. The corrected RTT reflection standby period is, for example, a standby time required to reach a stage where it can be determined that a state in which the influence on the band control or the like may occur is reached, and after the standby time has elapsed (after a plurality of polling cycles), Perform the correction.

  At that time, if the upper and lower limits of the moving speed of the ONU 20 are known in advance, the range in which the RTT changes can be grasped in advance, so the waiting time may be arbitrarily set in consideration of these changes. . Also, the RTT change amount is calculated by performing RTT measurement a plurality of times, the number of cycles until the RTT becomes an allowable upper and lower limit value is calculated from the RTT change amount, and the cycle for reflecting the RTT correction (until the reflection is performed) May be determined. Further, the correction value of the RTT that is actually reflected may be an average value calculated from a plurality of RTTs by measuring the RTT a plurality of times as in the first embodiment.

  The processing of the second embodiment will be described using the flowcharts shown in FIGS. 16 and 17. 16 and 17 are flowcharts illustrating an example of processing of the communication system according to the second embodiment. As shown in FIG. 16, first, the measurement unit 103 measures RTT (step S201). Then, the guard time setting unit 106 waits for m cycles without updating the guard time (step S202). At the same time, the calculation unit 105 calculates the RTT change amount and feeds back the calculated change amount to increase or decrease the standby period (step S203).

  Then, after the standby period has elapsed, the guard time setting unit 106 updates the guard time using the RTT measured by the measurement unit 103 as a correction value, and reflects it in the guard time of a predetermined cycle (step S204). Thereafter, the measurement unit 103 further measures RTT (step S205) and repeats the process.

  In addition, as shown in FIG. 17, the measurement unit 103 may perform RTT measurement a plurality of times. As shown in FIG. 17, first, the measurement unit 103 performs RTT measurement n times (step S211). Then, the calculation unit 105 calculates the average of the measurement values as a correction value (Step S212). For example, the calculation unit 105 calculates the average RTT change amount per hour by calculating the average of the measurement values, and adds it to the RTT value immediately before the reflection.

  Then, the guard time setting unit 106 waits for m cycles without updating the guard time (step S213). At the same time, the calculation unit 105 compares the RTT before and after the average value calculation, calculates the amount of change, and feeds back the calculated amount of change to increase or decrease the standby period (step S214). Then, the guard time setting unit 106 updates the guard time using the RTT calculated by the calculation unit 105 as a correction value, and reflects it in the guard time having a predetermined period (step S215). Thereafter, the measurement unit 103 further measures RTT (step S216) and repeats the process.

[Effects of Second Embodiment]
In the second embodiment, the guard time setting unit 106 satisfies a predetermined condition when a predetermined number of communications are performed between the OLT 10 and the ONU 20 after the RTT is measured by the measurement unit 103. The guard time is corrected based on the RTT. Thereby, the number of times of RTT correction and guard time update can be reduced, and the load due to the calculation process can be reduced.

[Third Embodiment]
In the third embodiment, a case where RTT is measured using a management frame such as OAM (Operation Administration and Maintenance) or OMCI (ONU Management and Control Interface) will be described.

[Configuration of Third Embodiment]
The basic configuration of the third embodiment is the same as the configuration of the first embodiment. As shown in FIG. 18, in the third embodiment, the communication system 1 includes a management frame transmission unit 108 in addition to the configuration of the first embodiment. FIG. 18 is a diagram illustrating an example of a configuration of a communication system and a station-side termination device according to the third embodiment.

  The management frame transmission unit 108 transmits a management optical signal, that is, a management frame, to the ONU 20. In the measurement unit 103, an optical signal is transmitted by the management frame transmission unit 108, an optical signal is received by the ONU 20, an optical signal is transmitted by the ONU 20 in response to the ONU 20 receiving the optical signal, and an optical signal is transmitted by the reception unit 102. Measures the RTT that occurs when is received.

[Process of Third Embodiment]
Processing of the communication system according to the third embodiment will be described with reference to FIGS. 19 and 20. 19 and 20 are diagrams for explaining an example of processing of the communication system according to the third embodiment. As illustrated in FIG. 19, the OLT 10 transmits a management frame to the ONU 20 and waits for a response from the ONU 20 to the OLT 10. And when ONU20 returns a response by DBA, the measurement part 103 will measure RTT based on the time obtained from this exchange.

  When acquiring the RTT change amount and reflecting it in the corrected RTT, the measurement unit 103 measures the RTT in a plurality of periods (measurement sequence 1 and measurement sequence 2) as shown in FIG. Then, the calculation unit 105 calculates the amount of change per unit time / cycle using Equation (4). Further, the calculation unit 105 calculates a corrected RTT from the RTT change amount obtained from Expression (4) according to Expression (5).

  The processing of the third embodiment will be described using the flowcharts shown in FIGS. 21 and 22. 21 and 22 are flowcharts illustrating an example of processing of the communication system according to the third embodiment. As shown in FIG. 21, first, the management frame transmission unit 108 transmits a management frame to the ONU 20 (step S301).

  Then, the measurement unit 103 performs RTT measurement (step S302). Then, the guard time setting unit 106 updates the guard time using the RTT measured by the measuring unit 103 as a correction value, and reflects it in the guard time having a predetermined period (step S303). Thereafter, the measurement unit 103 further measures RTT (step S301) and repeats the process.

  In addition, a process when the management frame is transmitted twice will be described with reference to FIG. As shown in FIG. 22, first, the management frame transmitting unit 108 transmits the first management frame to the ONU 20 (step S311). Then, the measurement unit 103 performs the first RTT measurement (step S312). Further, the management frame transmission unit 108 transmits the second management frame to the ONU 20 (step S313). Then, the measurement unit 103 performs the second RTT measurement (step S314).

  Then, the calculating unit 105 calculates the RTT change amount from the two RTTs measured by the measuring unit 103 (step S315). Furthermore, the guard time setting unit 106 updates the guard time using the correction RTT obtained from the RTT change amount as a correction value, and reflects it in the guard time having a predetermined period (step S316). Thereafter, the measurement unit 103 further performs RTT measurement (step S311) and repeats the process.

[Effect of the third embodiment]
The management frame transmission unit 108 transmits a management optical signal, that is, a management frame, to the ONU 20. In the measurement unit 103, an optical signal is transmitted by the management frame transmission unit 108, an optical signal is received by the ONU 20, an optical signal is transmitted by the ONU 20 in response to the ONU 20 receiving the optical signal, and an optical signal is transmitted by the reception unit 102. Measures the RTT that occurs when is received. Unlike the GATE-REPORT, the management frame transmitted by the management frame transmitting unit 108 can exchange arbitrary contents between the OLT-ONU at an arbitrary timing. The OLT 10 can measure the RTT at an arbitrary timing.

[Fourth Embodiment]
In the fourth embodiment, a method for measuring the RTT by comparing the time when the data transmitted by the ONU arrives at the OLT and the actual arrival time will be described.

[Configuration of Fourth Embodiment]
The basic configuration of the fourth embodiment is the same as the configuration of the first embodiment. In the fourth embodiment, the calculation unit 105 calculates the difference between the time when the optical signal transmitted by the ONU 20 is scheduled to be received by the reception unit 102 and the time when the optical signal is actually received by the reception unit 102. Is added to a predetermined RTT. The guard time setting unit 106 corrects the guard time based on the RTT to which the difference is added by the calculation unit 105.

[Process of Fourth Embodiment]
Processing of the communication system according to the fourth embodiment will be described using FIG. FIG. 23 is a diagram for explaining an example of processing of the communication system according to the fourth embodiment. As shown in FIG. 23, when the OLT 10 communicates with the ONU 20 by the DBA, the upstream data from the ONU 20 is transmitted at the time designated by the OLT 10, so the OLT 10 previously determines the arrival time of the upstream data from the ONU 20. Predictable.

  When the estimated arrival time predicted by the OLT is different from the actual arrival time, or when the difference between the estimated arrival time and the actual arrival time is greater than or equal to a predetermined value, the calculation unit 105 calculates the actual arrival time and the actual arrival time. The difference from the arrival time is regarded as the RTT change amount due to the movement of the ONU 10, and the RTT can be corrected based on the difference between the estimated arrival time and the actual arrival time.

For example, as shown in FIG. 23, when the estimated arrival time is T ₀ and the actual arrival time is T ₁ , the difference is T ₁ −T ₀ . This difference is a value obtained by communication in one cycle, and correction can be performed by adding this value to the RTT before correction. Further, the guard time setting unit 106 may determine whether or not to update the guard time based on whether or not the difference is equal to or greater than a predetermined threshold.

  The process of the fourth embodiment will be described using the flowchart shown in FIG. FIG. 24 is a flowchart illustrating an example of processing of the communication system according to the fourth embodiment. As shown in FIG. 24, the measurement unit 103 calculates the difference between the actual arrival time and the expected arrival time of the data from the ONU 20 (step S401). Then, the guard time setting unit 106 updates the guard time based on the RTT corrected based on the difference and reflects it in the guard time having a predetermined period (step S402). Thereafter, the measurement unit 103 further calculates a difference (step S401) and repeats the process.

[Effect of the fourth embodiment]
The calculation unit 105 adds the difference between the time when the optical signal transmitted by the ONU 20 is scheduled to be received by the reception unit 102 and the time when the optical signal is actually received by the reception unit 102 to a predetermined RTT. . The guard time setting unit 106 corrects the guard time based on the RTT to which the difference is added by the calculation unit 105. Thereby, a difference can be acquired from all signals transmitted using DBA, such as GATE-REPORT, a control frame, and a main signal (a frame on which data from a user is placed). In addition, since it is not necessary to secure a special frame for RTT measurement or a special data area in the frame, function development is facilitated.

[Other Embodiments]
It is also possible to implement the present invention by an embodiment that combines the unique configuration and processing of each embodiment. For example, by combining the third embodiment and the fourth embodiment, the OLT transmits a management frame to the ONU, predicts the arrival time of the response to the management frame, and calculates the RTT based on the difference from the actual arrival time. You may make it measure. Furthermore, the timing at which the measured RTT is reflected in the guard time may be determined by the method of the second embodiment.

[System configuration, etc.]
Further, each component of each illustrated apparatus is functionally conceptual, and does not necessarily need to be physically configured as illustrated. In other words, the specific form of distribution / integration of each device is not limited to that shown in the figure, and all or a part thereof may be functionally or physically distributed or arbitrarily distributed in arbitrary units according to various loads or usage conditions. Can be integrated and configured. Further, all or any part of each processing function performed in each device is realized by a CPU (Central Processing Unit) and a program analyzed and executed by the CPU, or hardware by wired logic. Can be realized as

  In addition, among the processes described in the present embodiment, all or part of the processes described as being automatically performed can be manually performed, or the processes described as being manually performed can be performed. All or a part can be automatically performed by a known method. In addition, the processing procedure, control procedure, specific name, and information including various data and parameters shown in the above-described document and drawings can be arbitrarily changed unless otherwise specified.

[program]
FIG. 25 is a diagram illustrating an example of a computer in which a station-side terminal device is realized by executing a program. The computer 1000 includes a memory 1010 and a CPU 1020, for example. The computer 1000 also includes a hard disk drive interface 1030, a disk drive interface 1040, a serial port interface 1050, a video adapter 1060, and a network interface 1070. These units are connected by a bus 1080.

  The memory 1010 includes a ROM (Read Only Memory) 1011 and a RAM (Random Access Memory) 1012. The ROM 1011 stores a boot program such as BIOS (Basic Input Output System). The hard disk drive interface 1030 is connected to the hard disk drive 1090. The disk drive interface 1040 is connected to the disk drive 1100. For example, a removable storage medium such as a magnetic disk or an optical disk is inserted into the disk drive 1100. The serial port interface 1050 is connected to a mouse 1110 and a keyboard 1120, for example. The video adapter 1060 is connected to the display 1130, for example.

  The hard disk drive 1090 stores, for example, an OS 1091, an application program 1092, a program module 1093, and program data 1094. In other words, a program that defines each process of the station-side terminal device is implemented as a program module 1093 in which a code executable by a computer is described. The program module 1093 is stored in the hard disk drive 1090, for example. For example, a program module 1093 for executing processing similar to the functional configuration in the station-side terminal device is stored in the hard disk drive 1090. The hard disk drive 1090 may be replaced by an SSD (Solid State Drive).

  The setting data used in the processing of the above-described embodiment is stored as program data 1094 in, for example, the memory 1010 or the hard disk drive 1090. Then, the CPU 1020 reads the program module 1093 and the program data 1094 stored in the memory 1010 and the hard disk drive 1090 to the RAM 1012 and executes them as necessary.

  The program module 1093 and the program data 1094 are not limited to being stored in the hard disk drive 1090, but may be stored in, for example, a removable storage medium and read out by the CPU 1020 via the disk drive 1100 or the like. Alternatively, the program module 1093 and the program data 1094 may be stored in another computer connected via a network (LAN (Local Area Network), WAN (Wide Area Network), etc.). The program module 1093 and the program data 1094 may be read by the CPU 1020 from another computer via the network interface 1070.

1 communication system 10 station side terminal equipment (OLT)
20 Subscriber-side terminal unit (ONU)
DESCRIPTION OF SYMBOLS 101 Transmission part 102 Reception part 103 Measurement part 104 Storage part 105 Calculation part 106 Guard time setting part 107 Transmission time designation part 108 Management frame transmission part

Claims (5)

A transmitter for transmitting optical signals to a plurality of subscriber-side terminal devices, each of which changes with time;
A receiver for receiving an optical signal transmitted by the subscriber-side terminal device;
A round-trip communication delay from when an optical signal is transmitted from the transmitter to the subscriber-side terminating device until an optical signal transmitted from the subscriber-side terminated device is received by the receiver as a response to the optical signal A measuring unit for measuring time;
After the round-trip communication delay time is measured by the measurement unit, the subscriber is determined based on the round-trip communication delay time each time a predetermined number of communications are performed between the own device and the subscriber-side terminal device. The other subscriber side that transmits the optical signal after the one subscriber-side termination device is the time at which the optical signal transmitted by one subscriber-side termination device of the side termination devices is received by the receiving unit A time interval setting unit that corrects a time interval between times at which optical signals are transmitted by each subscriber-side terminal device, so that an optical signal transmitted by the terminal device is before the time at which the receiving unit receives the optical signal; ,
A transmission time designating unit for designating a time at which the subscriber-side terminal device transmits an optical signal based on the time interval;
A station-side terminator characterized by comprising: Calculating a change amount per time of a plurality of round-trip communication delay times measured by the measurement unit, further comprising a calculation unit for adding the change amount to a predetermined round-trip communication delay time;
2. The station-side termination device according to claim 1, wherein the time interval setting unit corrects the time interval based on a round-trip communication delay time to which the change amount is added by the calculation unit. The calculating unit calculates a difference between a time when the optical signal transmitted by the subscriber-side terminal device is scheduled to be received by the receiving unit and a time when the optical signal is actually received by the receiving unit. Add to round trip communication delay time,
The station-side termination device according to claim 2, wherein the time interval setting unit corrects the time interval based on a round-trip communication delay time to which the difference is added by the calculation unit. A management signal transmitter for transmitting a management optical signal to the subscriber-side terminal device;
The measuring unit receives an optical signal transmitted from the subscriber-side termination device as a response to the optical signal after the management signal transmission unit transmits the optical signal to the subscriber-side termination device. 4. The station-side termination device according to claim 1, wherein a round-trip communication delay time until it is determined is measured. 5. A communication control method executed in a communication system having a station-side terminal device and a plurality of subscriber-side terminal devices whose positions change with time,
The station-side termination device transmits an optical signal to the subscriber-side termination device; and
A receiving step in which the station side terminating device receives an optical signal transmitted from the subscriber side terminating device as a response to the optical signal transmitted in the transmitting step;
A measurement step of measuring a round-trip communication delay time from the execution of the transmission step to the execution of the reception step;
After the round-trip communication delay time is measured by the measurement step, each time a predetermined number of communications are performed between the station-side terminal device and the subscriber-side terminal device, based on the round-trip communication delay time, The time at which the optical signal transmitted by one subscriber-side termination device among the subscriber-side termination devices is received by the reception step is another time for transmitting the optical signal after the one subscriber-side termination device. A time interval for correcting the time interval between the times when the optical signals are transmitted by the subscriber-side terminators so that the optical signals transmitted by the subscriber-side terminators are before the time when they are received by the receiving step. A setting process;
A transmission time designating step of designating a time at which the subscriber-side terminating device transmits an optical signal based on the time interval;
The communication control method characterized by including.

Images