JP5712855B2 - Optical communication system, control method of optical communication system, and home side apparatus - Google Patents

Description

  The present invention relates to an optical communication system, an optical communication system control method, and a home-side apparatus.

  One form of realizing FTTH (Fiber To The Home) that provides a network access service to each home by optical fiber is PON (Passive Optical Network). Today, EPON, which is a PON to which Ethernet (registered trademark) technology is applied, is widely used for FTTH services.

  The feature of PON is that a home-side device (ONU (Optical Network Unit)) installed in a home or the like and a station-side device (OLT (Optical Line Terminal)) installed in a telephone office or the like connect between them. By sharing a part of the optical fiber and performing communication, an optical access service can be provided at a low cost. Specifically, in the PON, one OLT and a plurality of ONUs are connected by an optical fiber via an optical splitter. The optical splitter passively branches or multiplexes a signal from an input signal without particularly requiring an external power supply.

  On the other hand, in recent years, attention has been paid to power saving of network devices. For this reason, the power saving of the communication apparatus used for PON is also requested | required. According to one proposed method, when the ONU is not in communication with the OLT, a part of the ONU function is shifted from the normal mode to the power saving mode. In this specification, “power saving mode” is also referred to as “sleep mode”.

  For example, Japanese Unexamined Patent Application Publication No. 2010-1114830 (Patent Document 1) discloses a technique for reducing the power consumption of an ONU. Specifically, the transmission unit of the OLT includes a downlink buffer unit and a power saving mode control unit. The downlink buffer unit accumulates user frames that are sequentially transmitted to each ONU. When the user frame to be transmitted to a certain ONU is not accumulated in the downlink buffer unit, the power saving mode control unit transmits a power saving mode setting frame describing the power saving mode time to the ONU. The power saving mode time is shorter than one round time, that is, the time from when the OLT transmits the uplink bandwidth allocation control frame to the ONU until the uplink bandwidth allocation control frame is transmitted to the ONU again. On the other hand, when the receiving unit of the ONU receives the power saving mode setting frame, the receiving unit sets the receiving unit to the power saving mode for the power saving mode time described in the power saving mode setting frame. .

JP 2010-1114830 A

  Generally, in the PON, time is synchronized between the OLT and the ONU using a mechanism called “Network Synchronization”. Specifically, the ONU regenerates a clock from a data signal sent from the OLT and operates with a clock synchronized with the OLT.

  When the ONU shifts to the sleep mode, some functions of the ONU are stopped. For this reason, there is a possibility that the time cannot be synchronized between the OLT and the ONU. Therefore, when an arbitrary period in the sleep mode is measured by both the OLT and the ONU, there is a possibility that the period is not recognized between the OLT and the ONU.

  An object of the present invention is to reduce a difference in recognition of a period between a station side device and a home side device during a sleep mode of the home side device.

  An optical communication system according to an aspect of the present invention includes a station-side device and a home-side device connected to the station-side device via a passive optical network. In the sleep mode, the home side device stops the communication between the home side device and the station side device, and the second period during which communication between the home side device and the station side device is possible. And generate. The station side device designates the first and second periods to the home side device, and measures the first and second periods using the clock of the station side device. The home side device corrects the first or second period designated by the station side device by using the clock error of the internal clock of the home side device with respect to the clock of the station side device, and the corrected first or second period. The period of 2 is measured using the internal clock of the home device.

  According to this configuration, during the sleep mode of the home side device, it is possible to reduce the difference in recognition of the period between the station side device and the home side device. In the sleep mode of the home side device, the home side device measures the first or second period based on the internal clock of the home side device. On the other hand, the station-side device measures the first and second periods based on the clock of the station-side device. The internal clock of the station side device and the internal clock of the home side device are independent. Therefore, due to the clock error of the internal clock of the home side device with respect to the clock of the station side device, the first and second periods measured by the station side device deviate from the first and second periods measured by the home side device. there is a possibility. By correcting the first or second period measured by the home side device using the clock error, both the first period and the second period are synchronized between the station side device and the home side device. Can do.

  In this specification, the term “first period or second period” is not limited to include only one of “first period” and “second period”. ”And“ second period ”may be included.

  Preferably, the home device corrects the first or second period using a clock error in the non-sleep mode.

  According to this configuration, since the first period or the second period is corrected when the sleep mode is not set, when the home side device subsequently shifts to the sleep mode, the station side device and the home side device Both the first period and the second period can be synchronized between. The “non-sleep mode” can include any mode other than the sleep mode. That is, the “non-sleep mode” is not limited to a specific mode.

  Preferably, the home device corrects the first or second period using a clock error before measuring the first period or the second period.

  According to this configuration, the first or second period is corrected in advance before the home device measures the first or second period. Accordingly, it is possible to reduce the difference in recognition of the period between the station side device and the home side device during the sleep mode of the home side device.

  Preferably, the home-side apparatus corrects the first period using the clock error during the measurement of the first period, or corrects the second period using the clock error during the measurement of the second period. To do.

  According to this configuration, the first period is corrected while the home device measures the first period, or the second period is corrected while the second period is measured. In the sleep mode of the side device, the discrepancy in the period recognition can be reduced between the station side device and the home side device. It should be noted that only one of the “first period” and the “second period” is not corrected, and both the “first period” and the “second period” are corrected. May be.

  Preferably, the station side device transmits an MPCP frame including a time stamp of the station side device to the home side device. The time stamp is generated based on the clock of the station side device. The home-side device calculates a clock error using the MPCP frame sent from the station-side device, and corrects the first or second period using the calculated clock error.

  According to this configuration, for example, when the home device receives an MPCP frame during measurement of the second period, the home device can calculate a clock error based on the time stamp in the MPCP frame. The clock error is not limited to be calculated every time an MPCP frame is received. For example, the clock error may be calculated every two or more predetermined reception times of the MPCP frame. Alternatively, the clock error may be calculated based on the MPCP frame received by the home device when a certain time or more has elapsed since the calculation of the clock error based on the previous MPCP frame. Thereby, during the sleep mode of the home side device, the discrepancy in the recognition of the period can be reduced between the station side device and the home side device.

  Preferably, the station side device transmits an MPCP frame including a time stamp of the station side device to the home side device. The time stamp is generated based on the clock of the station side device. The home side device calculates the clock error using the MPCP frame sent from the station side device, accumulates the calculated clock error, and uses the accumulated clock error to calculate the first or second period. to correct.

  According to this configuration, for example, when the home device receives an MPCP frame during measurement of the second period, the home device calculates the clock error based on the time stamp in the MPCP frame and accumulates the clock error. To do. For example, when the cumulative value of the clock error exceeds a predetermined value, or when the cumulative number exceeds the predetermined number, the first period or the second period is corrected. The clock error is not limited to be calculated every time an MPCP frame is received. For example, the clock error may be calculated every two or more predetermined reception times of the MPCP frame. Thereby, during the sleep mode of the home side device, the discrepancy in the recognition of the period can be reduced between the station side device and the home side device.

  An optical communication system according to another aspect of the present invention includes a station-side device and a home-side device connected to the station-side device via a passive optical network. In the sleep mode, the home side device stops the communication between the home side device and the station side device, and the second period during which communication between the home side device and the station side device is possible. And generate. The station-side device designates the first and second periods to the home-side device, and measures the first and second periods using the clock of the station-side device. The home side apparatus converts the first or second period designated by the station side apparatus into the MPCP time stamp amount, and measures the first or second period using the MPCP time stamp.

  According to this configuration, it is possible to increase the possibility that the MPCP time stamp is synchronized between the station side device and the home side device in the second period. Accordingly, it is possible to prevent the first and second periods from being cumulatively shifted between the station side device and the home side device.

  An optical communication system control method according to still another aspect of the present invention is an optical communication system control method including a station-side device and a home-side device connected to the station-side device via a passive optical network. Then, using the clock of the station side device, the first period during which the home side device stops communication with the station side device in the sleep mode of the home side device, and between the home side device and the station side device in the sleep mode. A second period in which communication is possible, a step of calculating a clock error of the internal clock of the home device relative to the clock of the station device, and a step of setting using the clock error The step of correcting the set first or second period, and measuring the first or second period set in the setting step using the clock of the station side device, and correcting the first and second periods And a step of measuring with the second period the internal clock of the optical network unit.

  According to this configuration, during the sleep mode of the home side device, it is possible to reduce the difference in recognition of the period between the station side device and the home side device.

  A home-side device according to still another aspect of the present invention is a home-side device connected to a station-side device via a passive optical network, and the station-side device and the home-side device during a first period in the sleep mode. A communication unit that stops communication between the station side device and the home side device during the second period in the sleep mode, and measurement for measuring the first and second periods A part. The measuring unit corrects the first or second period specified by the station side device using the clock of the station side device using the clock error of the internal clock of the home side device with respect to the clock of the station side device, and the correction The measured first or second period is measured using the internal clock of the home device.

  According to this configuration, during the sleep mode of the home side device, it is possible to reduce the difference in recognition of the period between the station side device and the home side device.

  ADVANTAGE OF THE INVENTION According to this invention, the shift | offset | difference of period recognition can be made small between a station side apparatus and a home side apparatus in the sleep mode of a home side apparatus.

1 is a block diagram showing a schematic configuration of an EPON system 100 according to an embodiment of the present invention. It is a block diagram which shows schematic structure of OLT which concerns on embodiment of this invention. It is a block diagram which shows schematic structure of ONU which concerns on embodiment of this invention. It is the figure which showed the structure of the control frame. It is a sequence diagram for demonstrating the process of OLT and the process of ONU for shifting ONU to sleep mode. It is a sequence diagram for demonstrating the process of OLT for waking up ONU in a sleep state, and the process of ONU. It is a figure for demonstrating the problem which may arise when a shift | offset | difference arises between the rising period and sleep period which OLT manages, and the rising period and sleep period which ONU measures. 6 is a diagram for explaining clock error calculation processing according to the first embodiment; FIG. It is a figure explaining the process for ONU which concerns on Embodiment 1 correct | amends the period of a sleep mode. 3 is a flowchart for explaining processing according to the first embodiment. It is a figure explaining the process for ONU which concerns on Embodiment 2 correct | amends the period of a sleep mode. 10 is a flowchart for describing processing according to Embodiment 2 for correcting a period during which the ONU is in a sleep mode. FIG. 10 is a diagram for describing processing for correcting the period of the sleep mode by the ONU according to the third embodiment. 10 is a flowchart for describing processing according to Embodiment 3 for correcting a period during which the ONU is in a sleep mode. FIG. 10 is a diagram for explaining one implementation example of a method for specifying a period according to a fourth embodiment. FIG. 25 is a diagram for explaining another implementation example of the method for specifying a period according to the fourth embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and description thereof will not be repeated.

  FIG. 1 is a block diagram showing a schematic configuration of an EPON system 100 according to an embodiment of the present invention. Referring to FIG. 1, EPON system 100 includes OLT 101, ONUs 102-1, 102-2,..., 102 -n, PON line 104, and splitter 105. In the following, when the ONUs 102-1 to 102-n are generally described, or when one of the ONUs 102-1 to 102-n is representatively described, the ONUs 102-1 to 102-n are referred to as “ ONU102 ".

  The OLT 101 is installed in a telephone station, for example. Each of the ONUs 102-1 to 102-n is installed, for example, in the home of a network access service subscriber.

  A user terminal 111 is connected to each of the ONUs 102-1 to 102-n. The number of user terminals 111 connected to each ONU 102 is not particularly limited. For example, a plurality of user terminals may be connected to one ONU. The user terminal 111 is, for example, a personal computer, but is not limited to this.

  The PON line 104 is an optical fiber. The optical signal transmitted from the OLT 101 passes through the PON line 104 and is branched to the ONUs 102-1 to 102-n by the splitter 105. On the other hand, the optical signals transmitted from the ONUs 102-1 to 102-n are converged by the splitter 105 and sent to the OLT 101 through the PON line 104. The splitter 105 passively branches or multiplexes the signal from the input signal without particularly requiring external power supply.

  The OLT 101 receives data via the host network 109 and outputs the data to the PON line 104. According to the physical configuration of the PON, all of the ONUs 102-1 to 102-n can receive the data transmitted from the OLT 101. Therefore, the OLT 101 inserts an identifier LLID (Logical Link ID) indicating the number of the ONU that should receive the transmission frame in the preamble portion of the transmission frame. Each ONU collates the LLID included in the frame received from the OLT with its own LLID notified in advance from the OLT. If the LLID included in the frame matches its own LLID, the ONU receives the frame; otherwise, the ONU discards the frame.

  On the other hand, the optical signals transmitted from the respective ONUs merge at the splitter 105. For this reason, it is necessary to control so that the signals (upstream signals) from the ONUs do not collide after being joined by the splitter 105.

  Based on the control frame (report) transmitted from the ONUs 102-1 to 102-n, the OLT 101 calculates the transmission start time and permitted transmission amount of the data stored in the buffers in the ONUs 102-1 to 102-n. . Next, the OLT 101 transmits the control frame (grant) in which the instruction signal is inserted to the ONUs 102-1 to 102-n via the PON line 104 and the splitter 105.

  For example, the ONU 102-1 receives an uplink information frame from the user terminal 111 via the home network 110. The ONU 102-1 temporarily stores the uplink information frame in the buffer. The ONU 102-1 notifies the OLT 101 of the length of data in its own buffer by a report at the time designated by the grant. The ONU 102-1 receives the grant with the instruction signal inserted from the OLT 101, and based on the instruction signal, transmits the data in its own buffer together with the report to the OLT 101.

  Each of the ONU 102-1 to ONU 102-n has a sleep function. The sleep function is a function for setting a part of modules constituting the ONU to a power saving state when there is no traffic between the ONU and the OLT. By the sleep function, the ONU state (mode) shifts from the normal mode to the sleep mode. After a set sleep mode period (referred to as a sleep period) has elapsed, the state of the ONU returns from the sleep mode to the normal mode. In the embodiment of the present invention, the ONU 102 is set to the sleep mode in response to a sleep instruction from the OLT.

  FIG. 2 is a block diagram showing a schematic configuration of the OLT according to the embodiment of the present invention. Referring to FIG. 2, OLT 101 includes a reception unit 11, a buffer memory 12, and a transmission unit 14. The receiving unit 11, the buffer memory 12, and the transmitting unit 14 are used for downlink communication (communication from the OLT 101 to the ONU 102).

  The receiving unit 11 transfers the downlink data frame received from the upper network 109 to the buffer memory 12. The buffer memory 12 stores the downlink data frame sent from the receiving unit 11. The transmission unit 14 transmits the data frame to the PON line 104.

  The OLT 101 further includes a reception unit 15, a frame reproduction unit 17, a buffer memory 18, and a transmission unit 19. The receiving unit 15, the frame reproducing unit 17, the buffer memory 18, and the transmitting unit 19 are used for uplink communication (communication from the ONU 102 to the OLT 101).

  The receiving unit 15 receives the data frame or control frame transmitted from the ONU 102 via the PON line 104. The frame playback unit 17 reads the header portion of the frame, and thereby determines whether the frame received by the OLT 101 is a data frame or a control frame such as a report frame. The data frame is transferred from the frame reproducing unit 17 to the buffer memory 18. On the other hand, the control frame is transferred from the frame reproduction unit 17 to the communication control unit 20.

  A control frame based on the control protocol is transmitted between the OLT and the ONU. Examples of such control protocols include MPCP (Multi-Point Control Protocol) protocol and OAM (Operations, Administration and Maintenance) protocol. The control protocol is not limited to these.

  The buffer memory 18 accumulates the data frame transferred from the frame reproducing unit 17. The transmission unit 19 transmits the data frame stored in the buffer memory 18 to the upper network 109.

  The OLT 101 further includes a communication control unit 20, a clock pulse generation unit 22, and a clock count unit 24.

  The communication control unit 20 controls a logical link (MPCP link) between the OLT 101 and the ONU 102. Specifically, the communication control unit 20 generates an MPCP frame (gate) for teaching the timing of transmitting an uplink signal to the ONUs 102-1 to 102-n. The MPCP frame generated by the communication control unit 20 is sent to the transmission unit 14. The transmission unit 14 outputs the MPCP frame to the PON line 104.

  The receiving unit 15 receives from each of the ONUs 102-1 to 102-n an MPCP frame (report) for reporting the amount of uplink data stored in each ONU. The report received by the reception unit 15 is sent to the communication control unit 20 by the frame reproduction unit 17.

  The clock pulse generator 22 is constituted by a known oscillation circuit including a crystal resonator, for example, and generates a clock pulse. The clock pulse is used for controlling the operation of the communication control unit 20. The clock count unit 24 counts clock pulses and sends a clock count value to the communication control unit 20. The communication control unit 20 creates a time stamp included in the MPCP frame based on the clock count value. Hereinafter, the time stamp included in the MPCP frame is referred to as “MPCP time stamp”. Note that the OLT 101 is not limited to the one having the clock pulse generation unit, and a clock may be supplied from the outside of the OLT 101 to the OLT 101, and the supplied clock may be used as the clock of the OLT 101. In the following, the “OLT clock” means a clock used by the OLT 101, and may include both a clock generated inside the OLT 101 and a clock supplied to the OLT 101 from the outside of the OLT 101.

  The OLT 101 further includes a power saving setting unit 30. The power saving setting unit 30 sets each of the ONUs 102-1 to 102-n to the sleep mode. The power saving setting unit 30 includes a traffic monitoring unit 31, a power saving determination unit 32, and a sleep instruction generation unit 33.

  The traffic monitoring unit 31 monitors the presence of data communication between the OLT 101 and the ONU 102 by monitoring the traffic between the OLT 101 and the ONU 102. The traffic monitoring unit 31 sends the monitoring result to the power saving determination unit 32. For example, the presence / absence of data communication between the OLT 101 and the ONU 102 can be determined from the destination address and source address of the data frame.

  The power saving determination unit 32 determines whether each ONU should be set to the sleep mode based on the monitoring result of the traffic monitoring unit 31. Specifically, the power saving determination unit 32 includes determination units 32-1 to 32-n corresponding to the ONUs 102-1 to 102-n, respectively. The determination unit 32-1 receives a monitoring result regarding the presence / absence of data communication between the OLT 101 and the ONU 102-1 from the traffic monitoring unit 31. The determination unit 32-1 determines that the state of the ONU 102-1 should be set to the sleep mode when data communication is not performed between the OLT 101 and the ONU 102-1. Since each operation of determination units 32-2 to 32-n is similar to the above-described operation of determination unit 32-1, detailed description thereof will not be repeated.

  The determination method of the power saving determination unit 32 is not limited to the above method. For example, the power saving determination unit 32 stores in advance the data communication results of each of the ONUs 102-1 to 102-n (for example, the data communication results for one day), and based on the results, each ONU 102- It may be determined whether or not the state 1 is set to the sleep mode.

  The determination results of the determination units 32-1 to 32-n are sent to the sleep instruction generation unit 33. The sleep instruction generation unit 33 generates a sleep instruction for setting the corresponding ONU state to the sleep mode based on the determination results of the determination units 32-1 to 32-n. The sleep instruction generation unit 33 transmits the sleep instruction to the transmission unit 14. The transmission unit 14 outputs a sleep instruction to the PON line 104. The ONU that has received the sleep instruction sets its own mode to the sleep mode.

  Further, when a certain ONU 102 needs to return to the normal mode while the ONU 102 is in the sleep mode, the communication control unit 20 instructs the sleep instruction generation unit 33 to generate a wake-up instruction. The sleep instruction generation unit 33 generates a wake-up instruction according to an instruction from the communication control unit 20. This wake-up instruction is an instruction for canceling the sleep mode. The communication control unit 20 may generate a wake-up instruction.

  FIG. 3 is a block diagram showing a schematic configuration of the ONU according to the embodiment of the present invention. Referring to FIG. 3, ONU 102 includes a reception unit 41, a buffer memory 42, and a transmission unit 44. The receiving unit 41, the buffer memory 42, and the transmitting unit 44 are used for uplink communication.

  The receiving unit 41 transfers the uplink data frame received from the home network 110 to the buffer memory 42. The buffer memory 42 accumulates the upstream data frame sent from the receiving unit 41. The transmission unit 44 transmits the data frame to the PON line 104.

  The ONU 102 further includes a receiving unit 45, a frame reproducing unit 47, a buffer memory 48, and a transmitting unit 49. The receiving unit 45, the frame reproducing unit 47, the buffer memory 48, and the transmitting unit 49 are used for downlink communication.

  The receiving unit 45 receives the data frame or control frame transmitted from the OLT 101 via the PON line 104. The receiving unit 45 reads the header portion of the frame. If the LLID included in the frame matches the LLID of the ONU 102, the receiving unit 45 receives the frame, and if not, the receiving unit 45 discards the frame.

  The frame reproducing unit 47 reads the header portion of the frame, and thereby determines whether the frame received by the ONU 102 is a data frame or a control frame. The data frame is transferred from the frame reproducing unit 47 to the buffer memory 48. On the other hand, the control frame is transferred from the frame reproduction unit 47 to the communication control unit 50.

  The buffer memory 48 accumulates the data frame transferred from the frame reproduction unit 47. The transmission unit 49 transmits the data frame stored in the buffer memory 48 to the home network 110.

  The ONU 102 further includes a communication control unit 50, a clock pulse generation unit 52, and a clock count unit 54.

  The communication control unit 50 receives an MPCP frame (for example, an MPCP gate frame) sent from the OLT 101, and outputs an MPCP frame (for example, a report frame) for responding to the frame. Similar to the data frame, the MPCP frame created by the communication control unit 50 is sent to the transmission unit 44. The transmission unit 44 outputs the MPCP frame to the PON line 104.

  The clock pulse generator 52 is configured by a known oscillation circuit including a crystal resonator, for example, and generates a clock pulse. The clock pulse is used for controlling the operation of the communication control unit 50, for example. The clock count unit 54 counts clock pulses and sends a clock count value to the communication control unit 50. The communication control unit 50 creates a time stamp included in the MPCP frame based on the clock count value.

  In order to realize control according to the MPCP protocol between the OLT 101 and the ONU 102, it is required that the MPCP time stamp generated by the ONU 102 be synchronized with the MPCP time stamp generated by the OLT 101. Therefore, the communication control unit 50 extracts a time stamp included in the MPCP frame sent from the OLT 101. The communication control unit 50 corrects the count value of the clock count unit 54 using the extracted time stamp. Furthermore, the communication control unit 50 measures sleep mode periods Ta and Tb, which will be described later.

  The ONU 102 further includes a power saving setting unit 60. The power saving setting unit 60 sets the ONU 102 to the sleep mode according to the sleep instruction from the OLT 101. The power saving setting unit 60 includes a sleep mode setting unit 62 and a sleep instruction receiving unit 63.

  The sleep instruction from the OLT 101 is received by the receiving unit 45. The sleep instruction is sent to the power saving setting unit 60 by the frame reproduction unit 47. The sleep instruction receiving unit 63 receives the sleep instruction and transmits the sleep instruction to the sleep mode setting unit 62. The sleep mode setting unit 62 sets the ONU 102 to the sleep mode by receiving a sleep instruction from the sleep instruction receiving unit 63.

  The length of the sleep period is set by a sleep instruction. In the sleep mode, the sleep mode setting unit 62 basically stops the transmission unit 44 and the reception unit 45. However, in the present embodiment, the transmission unit 44 and the reception unit 45 are temporarily restored in the sleep mode, and the ONU 102 becomes communicable with the OLT 101.

  When the sleep instruction receiving unit 63 receives the wake-up instruction from the OLT 101 via the receiving unit 45 and the frame reproducing unit 47, the sleep mode setting unit 62 cancels the sleep mode of the ONU 102 and sets the ONU 102 to the normal mode. Return to.

  The functional blocks shown in FIGS. 2 and 3 can be realized by hardware such as a CPU and a memory or software executed by the CPU. Therefore, the method for realizing each functional block is not particularly limited. A plurality of functional blocks may be integrated into one block. For example, in each of the OLT 101 and the ONU 102, a clock count unit may be incorporated in the communication control unit.

  FIG. 4 is a diagram showing the structure of the control frame. Referring to FIG. 4, the control frame includes a destination address, a source address, a length / type, an opcode, a time stamp, data, padding, and FCS.

  In the opcode field, a code for identifying the type of control frame is inserted. In MPCP, both messages using messages such as Discovery Gate, Register Request, Register (Register), Gate (also called normal gate; Gate), Register ACK (Register Ack), and Report (Report) are used. Communication is established. These messages are identified by the opcode, and the contents of the data field are different for each message.

  In the case of a sleep instruction, for example, a code indicating the sleep mode is inserted in the length / type field. Further, the data field includes, for example, information related to the sleep mode period. For example, a clock count value (or time stamp) indicating the start and end of the sleep mode is included in the data field.

  In the case of the wake-up instruction, for example, a code indicating the wake-up instruction is inserted into the length / type field.

  When the ONU 102 accepts the sleep instruction or the wake-up instruction, the ONU 102 transmits a control frame indicating the consent to the OLT 101. In the length / type field of this control frame, a code indicating consent to the sleep instruction or a code indicating consent to the wake-up instruction is inserted.

  In order to time-division multiplex the upstream signal of each ONU, the time stamp needs to be synchronized between the OLT and each ONU. In this embodiment, a method of maintaining synchronization between the OLT and the ONU using a time stamp included in the MPCP frame is employed. That is, the OLT includes its current clock count value as a time stamp in the MPCP frame, and then transmits the frame to the ONU. The ONU corrects the time stamp of the MPCP frame generated by itself based on the time stamp.

  FIG. 5 is a sequence diagram for explaining OLT processing and ONU processing for shifting the ONU to the sleep mode. Referring to FIG. 5, before ONU 102 shifts to the sleep mode, the state of ONU 102 is the normal mode. Based on the traffic status of the ONU 102, the OLT 101 determines to shift the ONU 102 to the sleep mode. For example, when there is no traffic between the OLT 101 and the ONU 102, the ONU 102 is shifted to the sleep mode.

  At time t1, the OLT 101 transmits a sleep instruction to the ONU 102, and the ONU 102 receives the sleep instruction. When the ONU 102 accepts the sleep instruction, the ONU 102 transmits a control frame indicating the acceptance to the OLT 101. The control frame indicating acceptance is generated by, for example, the communication control unit 50 shown in FIG.

  Next, the ONU 102 shifts to the sleep mode. In the sleep mode, a wakeup period Ta and a sleep period Tb occur. The wake-up period Ta is a period during which the ONU 102 becomes communicable with the OLT 101. For example, the wakeup period Ta is used as a period for checking whether the ONU 102 needs to return from the sleep mode to the normal operation mode. The sleep period Tb is a period during which the communication modules (the transmission unit 44 and the reception unit 45) of the ONU 102 are set in the power saving state. During the sleep period Tb, communication between the ONU 102 and the OLT 101 is stopped. In this specification, the state of the ONU 102 in the wakeup period Ta is referred to as “wakeup state”, and the state of the ONU 102 in the sleep period Tb is referred to as “sleep state”.

  In this embodiment, the periods Ta and Tb are alternately repeated while the ONU 102 is in the sleep mode. However, the periods Ta and Tb may not be arranged densely on the time axis. That is, an additional period may be inserted between the period Tb and the period Ta or between the period Ta and the period Tb. The state or processing of the ONU 102 in this additional period is not particularly limited.

  In this embodiment, the OLT 101 sets the periods Ta and Tb, and specifies the set periods Ta and Tb to the ONU 102. For example, the OLT 101 sets the lengths of the periods Ta and Tb, the clock count values indicating the start and end of the periods Ta and Tb, and notifies the ONU 102 of them. In such a form, the ONU 102 generates the wakeup period Ta and the sleep period Tb according to the clock count value specified by the OLT 101.

  When the periods Ta and Tb are densely arranged, the end of the period Ta coincides with the start of the period Tb, and the start of the period Ta coincides with the end of the period Tb. Therefore, only the information indicating the start and end of the period Ta or only the information indicating the start and end of the period Tb may be included in the sleep instruction. Such information is included in the data frame of the control frame corresponding to the sleep instruction, for example (see FIG. 4).

  The information indicating the start and end of the period Ta may be a clock count value or a time stamp value indicating the start and end of the period Ta. Alternatively, a clock count value indicating the start of the period Ta and an increment value of the clock count corresponding to the length of the period Ta may be used. The same applies to information indicating the start and end of the period Tb.

  In this embodiment, the sleep instruction control frame is not transmitted between the OLT 101 and the ONU 102 until the OLT 101 instructs to wake up the ONU 102 or until the ONU 102 wakes up spontaneously. On the other hand, the OLT 101 repeatedly transmits the MPCP frame to the ONU 102 regardless of the mode (normal mode or sleep mode) of the ONU 102. Therefore, when the ONU 102 receives the MPCP frame during the period Ta, the ONU 102 can correct the time stamp generated based on the internal clock of the ONU 102 in accordance with the time stamp included in the MPCP frame.

  When an event for waking up the ONU 102 in the sleep state occurs, the OLT 101 wakes up the ONU 102. Such an event occurs, for example, when data to be transmitted from the OLT 101 to the ONU 102 arrives at the OLT 101.

  FIG. 6 is a sequence diagram for explaining OLT processing and ONU processing for waking up an ONU that is in a sleep state. Referring to FIG. 6, at a certain time t2 during period Tb, an event for waking up ONU 102 occurs. When the event occurs, the ONU 102 is in a sleep state. Accordingly, the OLT 101 waits until the OLT 101 starts the period Ta. The OLT 101 grasps the start of the period Ta by measuring time according to the clock of the OLT 101.

  As described above, the OLT 101 designates the periods Ta and Tb for the ONU 102. Ideally, the clock of the OLT 101 and the internal clock of the ONU 102 are always synchronized. Therefore, the periods Ta and Tb measured by the ONU 102 are synchronized with the periods Ta and Tb measured (managed) by the OLT 101, respectively.

  At a certain time t3 in the period Ta, the OLT 101 transmits a control frame (wake-up instruction) for instructing the ONU 102 to wake up. When the ONU 102 receives this control frame, the ONU 102 shifts from the sleep mode to the normal state (normal mode). After the ONU 102 returns to the normal mode, data can be transmitted and received between the OLT 101 and the ONU 102.

  As described above, the power saving method according to the present embodiment requires that the periods Ta and Tb managed and measured by the OLT 101 and the periods Ta and Tb measured by the ONU 102 be synchronized with each other. However, in the sleep mode, the communication function of the ONU 102 only returns intermittently. For this reason, the ONU 102 measures the periods Ta and Tb using the internal clock of the ONU 102.

  On the other hand, generally, in Ethernet (registered trademark), a clock error within ± 100 ppm is allowed. Therefore, when the ONU 102 and the OLT 101 operate asynchronously, there is a possibility that the periods Ta and Tb managed (measured) by the OLT 101 and the periods Ta and Tb measured by the ONU 102 may be shifted from each other. For example, assuming that the length of the sleep mode is 10 seconds, an error of ± 1 (msec), that is, a maximum error of 2 msec may occur.

  FIG. 7 is a diagram for explaining problems that may occur when a deviation occurs between the wake-up period and sleep period managed by the OLT and the wake-up period and sleep period measured by the ONU. Referring to FIG. 7, at time t4 in period Tb, an event for waking up ONU 102 occurs. The OLT 101 waits for an ONU 102 wake-up instruction until the period Ta starts.

  The OLT 101 manages the periods Ta and Tb according to the clock of the OLT 101. On the other hand, the ONU 102 measures the periods Ta and Tb according to the internal clock of the ONU 102. In the period Ta that the OLT 101 grasps, the OLT 101 sends a wake-up instruction to the ONU 102. However, for the ONU 102, the wake-up instruction is sent during the sleep period Tb. Therefore, the ONU 102 cannot receive the wake-up instruction sent from the OLT 101. Since the ONU 102 does not receive the wake-up instruction, the control frame indicating consent is not transmitted from the ONU 102 to the OLT 101.

  Since the control frame indicating acceptance cannot be received, the OLT 101 resends the wake-up instruction to the ONU 102 during the next period Ta (time t5). However, the periods Ta and Tb measured by the ONU 102 are shifted from the management (measurement) periods Ta and Tb by the OLT 102. For this reason, for the ONU 102, the time t5 is the time during the sleep period Tb. Therefore, the ONU 102 cannot receive the wake-up instruction sent again from the OLT 101. Therefore, for example, the sleep mode is continued until a period first designated by the sleep instruction elapses. In this case, there is a concern that the resumption of communication between the ONU 102 and the OLT 101 may be delayed.

  According to the embodiment of the present invention, the ONU 102 corrects the period Ta or the period Tb set by the OLT 101 using the error of the internal clock of the ONU 102 with respect to the clock of the OLT 101. Only one of the period Ta and the period Tb may be corrected, or both may be corrected. Then, the ONU 102 measures the corrected period Ta or the corrected period Tb using the internal clock of the ONU 102. As a result, the difference in recognition between the OLT 101 and the ONU 102 can be reduced for the periods Ta and Tb during the sleep mode of the ONU 102. More preferably, the periods Ta and Tb managed by the OLT 101 and the periods Ta and Tb measured by the ONU 102 can be synchronized with each other.

Hereinafter, embodiments will be described in detail with reference to the drawings.
[Embodiment 1]
FIG. 8 is a diagram for explaining clock error calculation processing according to the first embodiment. Referring to FIG. 8, in the first embodiment, the error of the internal clock of ONU 102 with respect to the clock of OLT 101 is calculated from the progress of the MPCP time stamp generated by OLT 101 and the progress of the internal clock of ONU 102. .

  In the first embodiment, time measurement is started with an arbitrary time point as a reference. Specifically, the MPCP timestamp increment value and the ONU 102 internal clock increment value until an arbitrary period elapses from the reference time point are obtained. The length of the period for time measurement need not be a specific length. The length of this period is measured as t for the MPCP time stamp, and as T for the internal clock of the ONU 102. The MPCP time stamp is synchronized with the OLT 101 clock.

  The ratio between the OLT clock frequency and the ONU clock frequency is defined as (ONU clock frequency) / (OLT clock frequency). This ratio is expressed as T / t. The ONU 102 calculates the ratio (T / t) using the increment value of the MPCP time stamp and the increment value of the internal clock of the ONU 102.

  The ONU 102 corrects the period Ta or the period Tb specified by the OLT 101 using a clock error, that is, a ratio (T / t). The OLT 101 may calculate the ratio (T / t). Further, only one of the period Ta and the period Tb may be corrected, or both may be corrected. In the following description, it is assumed that both the periods Ta and Tb are corrected.

  FIG. 9 is a diagram for explaining processing for the ONU according to Embodiment 1 to correct the sleep mode period. Referring to FIG. 9, the periods measured by the MPCP time stamp are Ta and Tb. When the ONU 102 measures the periods Ta and Tb designated from the OLT 101 using the internal clock, the periods Ta1 and Tb1 are measured. In the example shown in FIG. 9, Ta1 <Ta and Tb1 <Tb. However, when Ta1> Ta and Tb1> Tb, correction according to the following description is performed.

  The ONU 102 corrects the period Ta1 using the clock error. As a result, the period Ta1 measured by the ONU 102 is corrected to (Ta1 + T1). T1 = Ta × (T / t). T / t is (ONU clock frequency) / (OLT clock frequency). By such correction, the length of the period (Ta1 + T1) becomes equal to the length of the period Ta.

  Similarly, the ONU 102 corrects the period Tb1 using the clock error. As a result, the length of the period Tb1 is corrected to (Tb1 + T2). T2 = Tb × T / t. By correcting the period Tb1, the length of the period (Tb1 + T1) becomes equal to the length of the period Tb.

  The ONU 102 measures the corrected period (Ta1 + T1). The length of the period (Ta1 + T1) is equal to the period Ta. Therefore, the period Ta measured by the OLT 101 and the period measured by the ONU 102 (corrected Ta, that is, Ta1 + T1) are synchronized. That is, the recognition of the period Ta matches between the OLT 101 and the ONU 102.

  Next, the ONU 102 measures the corrected period (Tb1 + T2). By the correction of the period Ta1, the timing when the ONU 102 ends the measurement of the period (Ta1 + T1) and the timing when the OLT 101 ends the measurement of the period Ta are synchronized.

  The timing to end the measurement of the period Ta is equivalent to the timing to start the measurement of the period Tb. Therefore, the timing for starting the measurement of the period Tb is synchronized between the OLT 101 and the ONU 102.

  The length of the period (Tb1 + T2) is equal to the period Tb. Therefore, the timing for ending the measurement of the period Tb is synchronized between the OLT 101 and the ONU 102. The timing to end the measurement of the period Tb is equivalent to the timing to start the measurement of the period Ta. Therefore, the timing for starting the measurement of the period Ta is synchronized between the OLT 101 and the ONU 102. When the periods Ta and Tb are alternately repeated in the sleep mode, the start and end of each period can be synchronized with each other between the OLT 101 and the ONU 102 by the above correction.

  A specific example of the process shown in FIG. The specific examples are for understanding the present invention and are not intended to limit the present invention.

  For example, Ta = 10 milliseconds and Tb = 100 milliseconds. Furthermore, it is assumed that T / t is measured as 1.001, that is, 100 ppm. The ONU 102 corrects the period Ta specified by the OLT to 10 × 1.001 = 10.01 milliseconds. Similarly, the ONU 102 corrects the period Tb = 100 × 1.001 = 100.1 milliseconds specified by the OLT. The ONU 102 measures 10.1 milliseconds and 100.1 milliseconds according to the internal clock of the ONU 102.

  The process for obtaining the clock error between the MPCP time stamp and the internal clock of the ONU 102 can be executed at an arbitrary timing. However, during the sleep period, the MPCP timestamp value created by the ONU 102 may not match the MPCP timestamp value created by the OLT 101. For this reason, it is preferable that the time measurement for evaluating the clock error and the calculation of the clock error are performed in a period other than the sleep period of the ONU 102, that is, in the non-sleep mode period. The non-sleep mode period is, for example, a “normal mode” period. As described above, in the normal mode, the ONU 102 receives the MPCP frame from the OLT 101 and synchronizes the MPCP timestamp value of the ONU 102 with the MPCP timestamp value of the OLT 101. Therefore, the clock error can be accurately calculated in the normal mode. However, when another non-sleep mode exists in addition to the normal mode, the clock error may be calculated during the period of the mode.

  FIG. 10 is a flowchart for explaining processing according to the first embodiment. Referring to FIG. 10, in step S11, the ONU 102 measures an error of the internal clock of the ONU 102 with respect to the MPCP time stamp. As described above, the ONU 102 measures the clock error (T / t) based on the increment value of the MPCP time clock corresponding to a certain period and the increment value of the internal clock of the ONU 102 corresponding to the period.

  In step S12, the ONU 102 corrects the period Ta designated by the OLT 101 based on the clock error. In step S13, the ONU 102 corrects the period Tb designated by the OLT 101 based on the clock error.

  In this embodiment, the processing of steps S12 and S13 is executed before the ONU 102 measures the periods Ta and Tb. For example, the processes in steps S12 and S13 are executed in the normal mode. The order of processing in steps S12 and S13 is not limited. The process of step S13 may be executed before the process of step S12.

  In step S14, the ONU 102 measures the period of the sleep mode (periods Ta and Tb). Step S14 includes steps S14A and S14B. In step S14A, the ONU 102 measures the corrected period Ta ((Ta1 + T1) shown in FIG. 9). In step S14B, the ONU 102 measures the corrected period Tb ((Tb1 + T2) shown in FIG. 9).

  In this embodiment, the processes of steps S14A and S14B are repeatedly executed alternately. If the ONU 102 receives a wake-up instruction from the OLT 101 during the period Ta, the process of step S14 ends. Alternatively, when the sleep period instructed by the sleep instruction from the OLT 101 ends, the process of step S14 ends.

  As described above, in the first embodiment, the ONU 102 corrects the periods Ta and Tb set by the OLT 101 using the clock error before starting measurement of the periods Ta and Tb. The periods Ta and Tb are set based on the MPCP time stamp, that is, the OLT 101 clock. In the sleep mode, the ONU 102 measures the periods Ta and Tb based on the internal clock of the ONU 102.

  Due to a clock error between the OLT 101 and the ONU 102, the period set by the OLT 101 (the period measured by the OLT 101) may be different from the period measured by the ONU 102.

  In the first embodiment, the ONU 102 corrects the period in advance before measuring the period set by the OLT 101 based on the clock error. In one form, in the normal mode that is the non-sleep mode, either one or both of the periods Ta and Tb are corrected. When the ONU 102 has a non-sleep mode other than the normal mode, one or both of the periods Ta and Tb may be corrected in that mode. Thereby, the periods Ta and Tb can be synchronized between the OLT 101 and the ONU 102 in the sleep mode.

  Furthermore, the period Ta may be corrected before the period Ta is measured, and may be corrected, for example, during the period Tb. Similarly, the correction of the period Tb may be performed before the measurement of the period Tb. For example, during the measurement of the period Ta, or, for example, another period is inserted between the period Ta and the period Tb, When it is repeated, the correction of the period Ta may be corrected in the period before that, and it is corrected to the period immediately before the period Ta or the period immediately after the previous period Ta (period immediately before the period Tb). May be. Similarly, the period Tb may be corrected to a period immediately before the period Tb or a period immediately after the previous period Tb (period immediately before the period Ta).

[Embodiment 2]
In the second embodiment, the ONU corrects these periods using a clock error during measurement of the wakeup period and the sleep period.

  FIG. 11 is a diagram for explaining processing for the ONU according to Embodiment 2 to correct the period of the sleep mode. Referring to FIG. 11, each time the ONU 102 receives an MPCP frame from the OLT 101, the ONU 102 corrects the MPCP time stamp generated by the ONU 102.

  The OLT 101 transmits an MPCP frame including the time stamp value X to the ONU 102. When the ONU 102 receives the MPCP frame, the value of the MPCP timestamp generated by the ONU 102 is Y.

  The ONU 102 measures the period Ta according to the internal clock and generates an MPCP time stamp. In the sleep mode, it is possible that the internal clock of the ONU 102 is not synchronized with the clock of the OLT 101. Therefore, the MPCP timestamp value X of the OLT 101 and the MPCP timestamp value Y of the ONU 102 can be different from each other. As shown in FIG. 11, the difference between the MPCP time stamp of the ONU 102 and the time stamp of the OLT 101 is (XY). The MPCP time stamp difference (XY) represents the clock error between the OLT 101 and the ONU 102.

  The ONU 102 corrects the MPCP timestamp value to the OLT MPCP timestamp value. Therefore, the MPCP timestamp value of the ONU is corrected from Y to X. Further, the ONU 102 corrects the period Ta using the period corresponding to the time stamp (XY). For example, as shown in FIG. 11, if (XY) is positive, the end of the period Ta measured by the ONU 102 becomes longer by (XY). When (XY) is negative, the end of the period Ta measured by the ONU 102 is shortened by (XY). In this way, by correcting the period measured by the ONU 102, the end of the period Ta can be synchronized between the OLT 101 and the ONU 102.

  Similar to the first embodiment, in the second embodiment, the end of the period Ta and the start of the period Tb are substantially the same. Therefore, the start of the period Tb can be synchronized between the OLT 101 and the ONU 102. That is, the start of the period Tb is corrected using the clock error (= XY). Further, the ONU 102 corrects the end timing of the period Tb using this clock error (= XY). That is, the ONU 102 corrects the period Tb using the clock error during the measurement of the period Tb.

  By correcting the period Tb, the end of the period Tb can be synchronized between the OLT 101 and the ONU 102. Furthermore, when the periods Ta and Tb occur alternately in the sleep mode, the start and end of each period can be synchronized between the OLT 101 and the ONU 102 by the above correction.

  FIG. 12 is a flowchart for describing processing according to the second embodiment for correcting the period during which the ONU is in the sleep mode. Referring to FIG. 12, in step S21, OLT 101 transmits an MPCP frame to ONU 102. In step S22, the ONU 102 receives the MPCP frame from the OLT 101. In step S <b> 23, the ONU 102 corrects the MPCP time stamp of the ONU 102 using the time stamp included in the MPCP frame sent from the OLT 101. In step S24, the ONU 102 corrects the periods Ta and Tb using the MPCP time stamp correction value (the above (XY)).

  As described above, according to the second embodiment, each time the ONU 102 receives an MPCP frame generated by the OLT 101, the ONU 102 calculates a difference between the MPCP time stamp generated by the OLT 101 and the MPCP time stamp generated by the ONU 102. The ONU 102 corrects the periods Ta and Tb designated from the OLT 101 by using the difference between the MPCP time stamps as a clock error. This makes it possible to match the period recognition between the OLT 101 and the ONU 102.

  Note that the present invention is not limited to the case where the clock error is calculated every time the ONU 102 receives an MPCP frame. For example, the ONU 102 may calculate the clock error every two or more predetermined reception times of the MPCP frame by the ONU 102. For example, one clock error may be calculated for two receptions of MPCP frames. In this way, the clock error calculation frequency can be made smaller than the ONU 102 MPCP frame reception frequency.

  Alternatively, the clock error may be calculated based on the MPCP frame received by the ONU 102 when a certain time or more has elapsed since the calculation of the clock error based on the previous MPCP frame. Also in these cases, the ONU 102 can realize the correction of the sleep mode period according to the second embodiment based on the calculated clock error.

  Similarly to the first embodiment, the ONU 102 is not limited to correcting both the periods Ta and Tb, and may correct only one of the periods Ta and Tb. That is, in this embodiment, the ONU 102 corrects the period Ta during the measurement of the period Ta, or corrects the period Tb during the measurement of the period Tb. Such a correction can also correct the sleep mode period.

[Embodiment 3]
In the third embodiment, similar to the processing according to the second embodiment, the ONU corrects the sleep mode period using the difference (clock error) in the MPCP time stamp. In the third embodiment, the ONU accumulates clock errors, and corrects the period set by the OLT based on the accumulated value.

  FIG. 13 is a diagram for explaining processing for the ONU according to Embodiment 3 to correct the sleep mode period. Referring to FIG. 13, each time the ONU 102 receives an MPCP frame from the OLT 101, the ONU 102 corrects the MPCP time stamp. Since such correction is substantially the same as the correction according to the second embodiment, detailed description will not be repeated.

  The OLT 101 transmits an MPCP frame including the time stamp value X1 to the ONU 102 during the period Ta. The MPCP timestamp value generated by the ONU 102 at the same time is Y1. The ONU 102 receives the MPCP frame from the OLT 101 and calculates the MPCP time stamp difference (X1−Y1). Similar to the second embodiment, the MPCP time stamp difference corresponds to the clock error of the internal clock of the ONU 102 with respect to the clock of the OLT 101.

  In the next generation period Ta, the OLT 101 generates an MPCP frame including the time stamp value X 2 and transmits the MPCP frame to the ONU 102. The MPCP timestamp value generated by the ONU 102 at the same time is Y2. The ONU 102 calculates the MPCP time stamp difference (X2−Y2) and calculates the accumulated value of the time stamp difference (= (X1−Y1) + (X2−Y2)).

  Similarly, the ONU 102 calculates the difference between the MPCP time stamps every time it receives an MPCP frame from the OLT 101, and accumulates the difference. The cumulative value Z of the MPCP time stamp differences is expressed according to the following equation.

Z = (X1-Y1) + (X2-Y2) + ... + (Xn-Yn)
For example, when the cumulative value Z exceeds a predetermined value, the ONU 102 corrects the periods Ta and Tb. By this correction, the periods Ta and Tb can be synchronized between the OLT 101 and the ONU 102.

  FIG. 14 is a flowchart for describing processing according to the third embodiment for correcting the period in which the ONU is in the sleep mode. Referring to FIG. 14, in step S31, OLT 101 transmits an MPCP frame to ONU 102. In step S <b> 32, the ONU 102 receives an MPCP frame from the OLT 101. In step S33, the ONU 102 corrects the MPCP time stamp of the ONU 102 using the time stamp included in the MPCP frame sent from the OLT 101.

  In step S34, the ONU 102 accumulates the difference of the MPCP time stamp. In step S <b> 35, the ONU 102 determines whether or not the cumulative value Z of the MPCP time stamp difference is larger than a predetermined value. The predetermined value can be appropriately set in terms of the operation of the PON system. In one form, the predetermined value is 50% of the length of the period Ta.

  If cumulative value Z is equal to or smaller than the predetermined value (NO in step S35), the process returns to step S31. Therefore, the processes of steps S31 to S34 are repeated until the accumulated value Z exceeds a predetermined value. On the other hand, when cumulative value Z exceeds a predetermined value (YES in step S35), ONU 102 corrects periods Ta and Tb using cumulative value Z.

  As described above, according to the third embodiment, the ONU 102 calculates the difference between the MPCP time stamp generated by the OLT 101 and the MPCP time stamp generated by the ONU 102. The ONU 102 accumulates the difference. When the accumulated value Z exceeds the predetermined value, the ONU 102 corrects the periods Ta and Tb. This makes it possible to synchronize the periods Ta and Tb between the OLT 101 and the ONU 102, so that the period recognition can be matched between the OLT 101 and the ONU 102.

  In the above embodiment, as a condition for correcting the periods Ta and Tb, the condition that the cumulative value Z exceeds a predetermined value is shown. However, the conditions for correcting the periods Ta and Tb are not limited to this. For example, when the number of clock errors accumulated reaches a predetermined number (not particularly limited as long as it is 2 or more), the periods Ta and Tb may be corrected using the accumulated value Z.

  Further, as in the second embodiment, the clock error is not limited to be calculated every time the ONU 102 receives an MPCP frame. Therefore, for example, the ONU 102 may calculate the clock error every two or more predetermined reception times of the MPCP frame by the ONU 102. In this way, the clock error calculation frequency can be made smaller than the ONU 102 MPCP frame reception frequency.

  Alternatively, the clock error may be calculated based on the MPCP frame received by the ONU 102 when a certain time or more has elapsed since the calculation of the clock error based on the previous MPCP frame. Also in these cases, the ONU 102 can obtain the accumulated value Z by accumulating the calculated clock errors. Therefore, the correction of the sleep mode period according to the third embodiment can be realized.

  Similarly to the second embodiment, the ONU 102 is not limited to correcting both the periods Ta and Tb, and may correct only one of the periods Ta and Tb.

[Embodiment 4]
The fourth embodiment relates to a method in which the OLT specifies the lengths of the periods Ta and Tb. The method for specifying a period according to the fourth embodiment can be applied to any of the first to third embodiments.

  FIG. 15 is a diagram for explaining one implementation example of the method for specifying a period according to the fourth embodiment. Referring to FIG. 15, OLT 101 designates MPCP time stamps corresponding to the start and end of periods Ta and Tb to ONU 102. The MPCP timestamp value Xk indicates the start of the period Ta, and the MPCP timestamp value Xl indicates the end of the period Ta and the start of the period Tb. Further, the MPCP time stamp value Xm indicates the end of the period Tb.

  The OLT 101 designates the MPCP timestamp value Xk to the ONU 102 in order to designate the start of the period Ta. The OLT 101 designates the MPCP time stamp value Xl to the ONU 102 in order to designate the end of the period Ta and the start of the period Tb. Further, the OLT 101 designates the MPCP timestamp value Xm to the ONU 102 in order to designate the end of the period Tb. The ONU 102 converts the period Ta designated by the OLT 101 into a time stamp amount (X1-Xk). Similarly, the ONU 102 converts the period Tb specified by the OLT 101 into a time stamp amount (Xm-Xl).

  The ONU 102 shifts to the sleep mode according to the procedure shown in FIG. In the sleep mode, the ONU 102 measures the period Ta or the period Tb using the MPCP time stamp generated based on the internal clock of the ONU 102. As described above, since the ONU 102 can receive the MPCP frame from the OLT 101 during the period Ta, the MPCP time stamp can be synchronized between the ONU 102 and the OLT 101. Therefore, it is possible to prevent the periods Ta and Tb from being cumulatively shifted between the OLT 101 and the ONU 102.

  FIG. 16 is a diagram for explaining another implementation example of the method for specifying a period according to the fourth embodiment. Referring to FIG. 16, based on the MPCP time stamp of OLT 101, OLT 101 designates the lengths of periods Ta and Tb to ONU 102. Specifically, the period Ta is the difference between the MPCP timestamp values Xl and Xk (= Xk−Xl), and the period Tb is the difference between the MPCP timestamp values Xm and Xl (= Xl−Xm). The OLT 101 designates (Xk−X1) and (X1−Xm) for the ONU 102. Thereby, ONU102 can grasp | ascertain the length of period Ta, Tb.

  In this case as well, the ONU 102 can convert the periods Ta and Tb designated from the OLT 101 into time stamp amounts. For example, the converted time stamp amount is equal to the time stamp amount specified from the OLT 101. The ONU 102 shifts to the sleep mode according to the procedure shown in FIG. 5, and measures the period Ta or the period Tb using the MPCP time stamp.

  As described above, according to the fourth embodiment, the ONU 102 converts the first or second period designated by the OLT 101 into the MPCP time stamp amount, and uses the MPCP time stamp to set the period Ta or the period Tb. measure. Thereby, it is possible to prevent the periods Ta and Tb from being cumulatively shifted between the OLT 101 and the ONU 102.

  In the first embodiment, the ONU 102 corrects the set period based on the clock error before measuring the period set by the OLT 101. On the other hand, in the second and third embodiments, the ONU 102 corrects the period based on the clock error while measuring the period set by the OLT 101. That is, the timing at which the ONU 102 corrects the period set by the OLT 101 is different between the first embodiment and the second and third embodiments. Therefore, Embodiment 1 and Embodiment 2 can be combined. Alternatively, Embodiment 1 and Embodiment 3 can be combined. In these cases, the period set by the OLT 101 is corrected before and during the measurement. Therefore, it is possible to further reduce the difference in recognition of the period between the OLT 101 and the ONU 102.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and is intended to include meanings equivalent to the scope of claims for patent and all modifications within the scope.

  11, 15, 41, 45 Receiver, 12, 18, 42, 48 Buffer memory, 14, 19, 44, 49 Transmitter, 17, 47 Frame playback unit, 20, 50 Communication control unit, 22, 52 Clock pulse generation Unit, 24, 54 clock count unit, 30, 60 power saving setting unit, 31 traffic monitoring unit, 32 power saving determining unit, 32-1 to 32-n determining unit, 33 sleep instruction generating unit, 62 sleep mode setting unit, 63 Sleep instruction receiving unit, 100 EPON system, 104 PON line, 105 splitter, 109 host network, 110 home network, 111 user terminal.

Claims (7)

A station side device,
A home-side device connected to the station-side device via a passive optical network,
In the sleep mode, the home side device is capable of communication between the home side device and the station side device during a first period in which communication between the home side device and the station side device is stopped. And generating a second period of
The station-side device designates the first and second periods as the home-side device, measures the first and second periods using a clock of the station-side device,
The station side device transmits an MPCP frame including a time stamp of the station side device to the home side device,
The time stamp is generated based on the clock of the station side device,
The home side device uses the MPCP frame sent from the station side device to calculate a clock error of the internal clock of the home side device relative to the clock of the station side device, and accumulates the calculated clock error. Then, using the accumulated clock error, the first or second period designated by the station side apparatus is corrected, and the corrected first or second period is used as the internal clock of the home side apparatus. An optical communication system that uses and measures.   The optical communication system according to claim 1, wherein the home device corrects the first or second period using the clock error in a non-sleep mode.   2. The optical communication system according to claim 1, wherein the home-side apparatus corrects the first or second period using the clock error before measuring the first or second period. The home device corrects the first period using the clock error during the measurement of the first period, or corrects the second period using the clock error during the measurement of the second period. The optical communication system according to claim 1, wherein the period is corrected. The home side apparatus converts the first or second period designated by the station side apparatus into an MPCP time stamp amount, and measures the first or second period using the MPCP time stamp. The optical communication system according to any one of claims 1 to 4 . A control method of an optical communication system comprising a station side device and a home side device connected to the station side device via a passive optical network,
Using the clock of the station side device, a first period in which the home side device stops communication with the station side device in the sleep mode of the home side device, and the home side device and the station in the sleep mode Setting a second period during which communication with the side device is possible;
Using the MPCP frame including the time stamp of the station side device generated based on the clock of the station side device, a clock error of the internal clock of the home side device with respect to the clock of the station side device is calculated and calculated. Accumulating the clock error,
Using the accumulated clock error, correcting the first or second period set in the setting step;
The first or second period set in the setting step is measured using the clock of the station side device, and the corrected first or second period is measured using the internal clock of the home side device. A control method for an optical communication system. A home-side device connected to the station-side device via a passive optical network,
Communication between the station side device and the home side device is stopped during the first period in the sleep mode, and communication between the station side device and the home side device is stopped during the second period in the sleep mode. A communication part to enable,
A measurement unit for measuring the first and second periods,
The communication unit receives an MPCP frame including a time stamp of the station side device generated based on the clock of the station side device from the station side device,
The measurement unit calculates a clock error of the internal clock of the home side device with respect to the clock of the station side device using the MPCP frame sent from the station side device, accumulates the calculated clock error, The first or second period specified by the station side apparatus using the clock of the station side apparatus is corrected using an accumulated clock error, and the corrected first or second period is Home-side device that measures using the internal clock of the home-side device.

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