JP2013038692A - Optical communication system, control method therefor, and customer-side device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent enlarged recognition deviation between a station-side device and a customer-side device during a certain period in a sleep mode.SOLUTION: The customer-side device (ONU) includes the sleep mode and a non-sleep mode. In the sleep mode, the customer-side device (ONU) generates a period Tb, in which communication between the customer-side device (ONU) and a station-side device (OLT) is suspended, and a period Ta, in which communication between the customer-side device (ONU) and the station-side device (OLT) is possible. In a normal mode of the customer-side device (ONU), clock is synchronized between the customer-side device (ONU) and the station-side device (OLT). If a lapse period of the sleep mode reaches a set continuation period, the customer-side device (ONU) terminates the sleep mode and shifts to the normal mode.

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.

  However, when the ONU enters the power saving mode, there is a possibility that the ONU cannot receive the clock transmitted from the OLT. For this reason, when a certain period in the sleep mode is managed by both the OLT and the ONU, there is a possibility that the period grasped by the OLT and the period measured by the ONU may deviate.

  An object of the present invention is to prevent an increase in recognition deviation between a station-side device and a home-side device during a certain period in the sleep mode.

  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. The home device has a sleep mode and a non-sleep mode. 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 second period in the sleep mode of the home side device to the home side device, and synchronizes the clock of the station side device and the clock of the home side device in the non-sleep mode of the home side device. When the elapse period of the sleep mode reaches the set duration, the home device ends the sleep mode and shifts to the non-sleep mode.

  According to this configuration, it is possible to prevent an increase in recognition deviation between the station side device and the home side device during a certain period in the sleep mode. The internal clock of the station side device and the internal clock of the home side device are independent. 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 longer the sleep mode continues, the longer the period between the second period measured by the home-side device and the second period measured by the station-side device. There is a possibility that the gap will increase. When the elapsed period of the sleep mode reaches the set duration, the home device ends the sleep mode and shifts to the non-sleep mode. As a result, it is possible to prevent the recognition shift in the second period from increasing between the home-side device and the station-side device.

  Preferably, when the period preset in the home device as the sleep mode period is greater than the set duration of the sleep mode, the home device performs the transition from the sleep mode to the non-sleep mode, After synchronizing the clock of the station side device and the clock of the home side device, it returns to the sleep mode.

  According to this configuration, it is possible to prevent the sleep mode period from becoming shorter than the initially set period. Furthermore, since the sleep mode is resumed after the clocks are synchronized between the station-side device and the home-side device in the non-sleep mode, the recognition gap in the second period is reduced in the resumed sleep mode. Therefore, it is possible to prevent the recognition shift in the second period from increasing between the home side device and the station side device.

  Preferably, the home side device measures the elapsed time of the sleep mode using the clock of the home side device, and shifts to the non-sleep mode when the elapsed time of the sleep mode reaches the set duration. Is sent to the station side device.

  According to this configuration, the home side device measures the sleep mode period based on the clock of the home side device, and when the elapse period of the sleep mode reaches the set continuous period, the home side device Therefore, the station side device can reliably detect that the home side device shifts to the non-sleep mode. Therefore, the clock can be synchronized between the station side device and the home side device in the non-sleep mode.

  Preferably, when the elapsed time of the sleep mode measured by the station side device reaches the set duration, the station side device transmits an instruction to shift to the non-sleep mode to the home side device.

  According to this configuration, when the elapsed time of the sleep mode measured by the station side device reaches the set duration, the station side device transmits an instruction to shift to the non-sleep mode to the home side device. The home apparatus can be reliably shifted to the non-sleep mode. Therefore, the clock can be synchronized between the station side device and the home side device in the non-sleep mode.

  Preferably, the set duration is defined by an allowable range of an error between the clock of the station side device and the internal clock of the home side device and the length of the second period, and the station side device and the home side device Smaller than the maximum measurement deviation between

  According to this configuration, the home device can be shifted to the non-sleep mode before the recognition of the second period is completely shifted between the station device and the home device. The maximum value of the measurement deviation is a value when the second period measured by the station side apparatus and the second period measured by the home side apparatus do not overlap on the time axis. That is, the maximum value of the magnitude of the deviation is equal to the length of the second period. Before the second period is completely deviated between the station side device and the home side device, the sleep mode is terminated, so that the station side device and the home side device can It is possible to prevent communication from becoming impossible at all.

  An optical communication system control method according to 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. The first period during which the communication between the home side device and the station side device is stopped in the sleep mode, and the communication between the home side device and the station side device is performed in the sleep mode. In the non-sleep mode of the home side device that generates the second period that is enabled, the step of synchronizing the clock of the station side device and the clock of the home side device; and the second period in the sleep mode of the home side device And a step of ending the sleep mode of the home side device and shifting to the non-sleep mode when the elapsed period of the sleep mode of the home side device reaches the set duration

  According to this configuration, it is possible to prevent an increase in recognition deviation between the station side device and the home side device during a certain period in the sleep mode.

  A home-side device according to another aspect of the present invention is a home-side device connected to a station-side device via a passive optical network, and communicates between the station-side device and the home-side device in a non-sleep mode. And the communication between the station side device and the home side device is stopped in the first period in the sleep mode, and the communication between the station side device and the home side device is enabled in the second period in the sleep mode. The communication unit, the mode setting unit for switching the mode of the home side device between the sleep mode and the non-sleep mode, and the clock of the home side device are synchronized with the clock of the station side device in the non-sleep mode of the home side device A measuring unit. When the elapsed period of the sleep mode reaches the set duration, the mode setting unit ends the sleep mode and shifts the mode of the home device to the non-sleep mode.

  According to this configuration, it is possible to prevent an increase in recognition deviation between the station side device and the home side device during a certain period in the sleep mode.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent that the shift | offset | difference of recognition between a station side apparatus and a home side apparatus about a certain period in sleep mode expands.

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 wake-up period and sleep period which OLT manages, and the wake-up period and sleep period which ONU measures. FIG. 6 is a sequence diagram for explaining processing for returning the mode of the ONU 102 from the sleep mode to the normal mode according to the first embodiment. 3 is a flowchart for explaining processing according to the first embodiment. FIG. 11 is a sequence diagram for explaining processing for returning the mode of the ONU 102 from the sleep mode to the normal mode according to the second embodiment. 10 is a flowchart for explaining processing according to the second 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.

  In the embodiment of the present invention, the ONU 102 measures the elapsed time of the sleep mode using the clock of the ONU 102. When the elapsed period of the sleep mode reaches the set continuation period, the ONU 102 ends the sleep mode and shifts to the normal mode. In the normal mode, the clock is synchronized between the OLT 101 and the ONU 102. Therefore, when the sleep mode is started next in the ONU 102, there is no difference between the period managed by the OLT 101 and the period managed by the ONU 102. Therefore, according to the embodiment of the present invention, it is possible to prevent the recognition shift between the station-side apparatus and the home-side apparatus for a certain period during the sleep mode from increasing.

  Further, in the embodiment of the present invention, when the period preset in the ONU 102 as the period of the sleep mode is longer than the duration period of the sleep mode, the ONU 102 shifts from the sleep mode to the normal mode, and the clock of the OLT 101 After synchronizing with the clock of the ONU 102, it returns to the sleep mode. Thereby, it is possible to prevent the period in which the ONU 102 is in the sleep mode from becoming shorter than the preset period. Therefore, the effect of saving the power of the ONU 102 is enhanced.

Hereinafter, embodiments will be described in detail with reference to the drawings.
[Embodiment 1]
In the first embodiment, the trigger for terminating the sleep mode is transmission of an abort request from the ONU.

  FIG. 8 is a sequence diagram for explaining processing for returning the mode of the ONU 102 from the sleep mode to the normal mode according to the first embodiment. Referring to FIG. 8, ONU 102 executes a process for ending the sleep mode when the elapsed period from the start of the sleep mode reaches a set duration. Specifically, the ONU 102 sends an abort request for returning from the sleep mode to the normal mode to the OLT 101 during the period Ta. Further, the ONU 102 returns from the sleep mode to the normal mode. When the OLT 101 receives the abort request from the ONU 102, the OLT 101 ends the management of the periods Ta and Tb.

  Next, the OLT 101 transmits the MPCP frame to the ONU 102. The MPCP frame includes an MPCP time stamp generated based on the internal clock of the OLT 101. The ONU 102 receives the MPCP frame and corrects the deviation of the internal clock of the ONU 102 with respect to the clock of the OLT 101 using the MPCP time frame. As a result, the internal clock of the ONU 102 is synchronized with the clock of the OLT 101.

  When the duration of the sleep mode set in the ONU 102 is shorter than the sleep mode period set by the OLT 101, the ONU 102 ends the sleep mode in the middle of the sleep mode period set by the OLT 101. In this case, the OLT 101 transmits a sleep instruction to the ONU 102 in order to resume the sleep mode of the ONU 102 and designates the periods Ta and Tb. The ONU 102 transmits a control frame indicating consent to the sleep instruction to the OLT 101 and shifts to the sleep mode.

  By sending an abort request from the ONU 102 to the OLT 101, the OLT 101 can reliably detect that the ONU 102 returns to the normal mode. As described above, the internal clock of the ONU 102 can be synchronized with the clock of the OLT 101 during the normal mode. Therefore, the clock can be synchronized between the station side device and the home side device in the normal mode. By synchronizing the clocks between the station side device and the home side device, it is possible to synchronize the period Ta managed by the OLT 101 and the period Ta measured by the ONU 102 in the resumed sleep mode.

  In the sleep mode, the ONU 102 is in a communicable state during the period Ta. Therefore, when the period Ta managed by the OLT 101 and the period Ta measured by the ONU 102 do not overlap at all on the time axis, communication between the OLT 101 and the ONU 102 cannot be realized during the sleep mode. That is, when the magnitude of the difference between the period measured by the OLT 101 and the period measured by the ONU 102 becomes equal to the length of the period Ta, the above-described state occurs.

  For these reasons, the duration of the sleep mode for returning the ONU 102 mode from the sleep mode to the normal mode is such that the period Ta managed by the OLT 101 and the period Ta measured by the ONU 102 do not overlap at all on the time axis. It is set so that the phenomenon does not occur. More specifically, the maximum value of the duration time of the sleep mode is determined from the length of the period Ta and the allowable range of the clock frequency between the OLT 101 and the ONU 102.

  In one form, the maximum value of the duration of the sleep mode is determined by dividing the length of the period Ta by the allowable range of the clock frequency. For example, when Ta = 10 ms and the allowable range of the clock frequency = 200 ppm (± 100 ppm), the maximum value of the duration time of the sleep mode is 10 ms / 200 ppm = 5 seconds. On the other hand, the length of the normal mode period temporarily returned during the sleep mode is not particularly limited.

  The duration of the sleep mode may be stored in advance in the ONU 102 or specified from the OLT 101. The timing at which the OLT 101 designates the duration time of the sleep mode is not particularly limited. For example, the OLT 101 may specify the duration of the sleep mode before the sleep mode is started. Alternatively, the OLT 101 can specify the duration of the sleep mode after the sleep mode of the ONU 102 is started.

  FIG. 9 is a flowchart for explaining processing according to the first embodiment. Referring to FIG. 9, in step S11, ONU 102 determines whether or not the sleep mode has been continued for a predetermined period. Specifically, the ONU 102 measures the period of the sleep mode (periods Ta and Tb) according to the internal clock of the ONU 102. It is determined whether or not the measured period, that is, the elapsed period of the sleep mode has reached the set duration. For example, as the predetermined period, the maximum value of the sleep mode duration described above is applied.

  If it is determined that the sleep mode has been continued for a predetermined period (YES in step S11), the process proceeds to step S12. On the other hand, when it is determined that the elapsed period of the sleep mode has not reached the predetermined period (NO in step S11), the process proceeds to step S13. In step S13, the ONU 102 determines to continue the sleep mode. The process returns from step S13 to step S11. That is, the processes in steps S11 and S13 are repeated until the elapsed period of the sleep mode reaches a predetermined period.

  In step S <b> 12, the ONU 102 transmits an abort request to the OLT 101. Subsequently, in step S14, the ONU 102 shifts from the sleep mode to the normal mode.

  The OLT 101 ends the management of the sleep mode periods Ta and Tb in response to the termination request. Next, the OLT 101 generates an MPCP frame and transmits the MPCP frame to the ONU 102 (step S15). The MPCP frame includes an MPCP time stamp generated based on the OLT 101 clock.

  In step S <b> 16, the ONU 102 receives the MPCP frame from the OLT 101. The ONU 102 corrects the internal clock of the ONU 102 based on the MPCP time stamp.

  In step S <b> 17, the OLT 101 determines whether or not the sleep mode has ended midway. When the elapse period of the sleep mode of the ONU 102 is shorter than the sleep mode period grasped by the OLT 101, the OLT 101 determines that the sleep mode has been terminated halfway. In this case (YES in step S17), the process proceeds to step S18.

  On the other hand, when the sleep mode period grasped by the OLT 101 is equal to the sleep mode elapsed period of the ONU 102 (NO in step S17), the process ends. In this case, the timing at which the ONU 102 shifts to the sleep mode is not particularly limited, and the ONU 102 shifts from the normal mode to the sleep mode at an appropriate timing.

  In step S18, the OLT 101 transmits a sleep instruction to the ONU 102. In step S <b> 19, the ONU 102 accepts the sleep instruction from the OLT 101. In step S20, the ONU 102 shifts to the sleep mode. As a result, the sleep mode of the ONU 102 is resumed.

  The timing for shifting to the sleep mode is notified from the OLT 101 to the ONU 102. However, the timing for shifting to the sleep mode may be notified from the ONU 102 to the OLT 101.

  During the normal mode, processing for synchronizing the clock of the OLT 101 and the internal clock of the ONU 102 is executed. After that, since the sleep mode is started, the ONU 102 starts the sleep mode at a timing grasped by the OLT 101. Thereby, in the sleep mode after the normal mode, it is possible to reduce the difference in recognition of the period between the OLT 101 and the ONU 102. Preferably, the periods Ta and Tb can be synchronized between the OLT 101 and the ONU 102. Therefore, according to the first embodiment, it is possible to prevent the recognition shift between the station side device and the home side device from expanding for a certain period in the sleep mode.

[Embodiment 2]
In the second embodiment, the trigger for terminating the sleep mode is transmission of an abort request from the OLT. In this respect, the second embodiment is different from the first embodiment.

  FIG. 10 is a sequence diagram for explaining processing for returning the mode of the ONU 102 from the sleep mode to the normal mode according to the second embodiment. Referring to FIGS. 8 and 10, in the second embodiment, when the sleep mode of ONU 102 is continued for a predetermined period, OLT 101 issues an abort request for requesting ONU 102 to return from the sleep mode to the normal mode. Send to. The ONU 102 returns from the sleep mode to the normal mode in response to an abort request from the OLT 101. Note that the ONU 102 may transmit a consent to the abort request. Since the subsequent processing is the same as the processing according to the first embodiment, the processing of the OLT 101 and the ONU 102 after the normal mode is not repeated.

  FIG. 11 is a flowchart for explaining processing according to the second embodiment. With reference to FIGS. 9 and 11, in the second embodiment, the process of step S12A is executed instead of the process of step S12. In this respect, the second embodiment is different from the first embodiment. In step S <b> 12 </ b> A, when the elapsed time of the sleep mode of the ONU 102 measured on the OLT 101 side reaches a predetermined period, the OLT 101 transmits an abort request to the ONU 102. Since the processing of the other steps shown in FIG. 11 is the same as the processing of the corresponding steps of FIG. 9, the following description will not be repeated.

  According to the second embodiment, the OLT 101 transmits an abort request (instruction) for shifting to the normal mode to the ONU 102. As a result, the ONU 102 can be reliably shifted to the normal mode. Therefore, as in the first embodiment, the clock can be synchronized between the OLT 101 and the ONU 102 in the normal mode.

  As in the first embodiment, processing for synchronizing the clock of the OLT 101 and the internal clock of the ONU 102 is executed during the normal mode. After that, since the sleep mode is started, the ONU 102 starts the sleep mode at a timing grasped by the OLT 101. Therefore, according to the second embodiment, as in the first embodiment, it is possible to prevent an increase in recognition gap between the station side device and the home side device during a certain period in the sleep mode. it can.

  In the above-described embodiment, the case where the non-sleep mode includes only the normal mode has been described. However, the non-sleep mode may include other modes in addition to the normal mode. If the clock can be synchronized between the OLT 101 and the ONU 102 at any timing during the non-sleep mode, the types of the non-sleep mode and the operations of the OLT 101 and the ONU 102 in the non-sleep mode are particularly limited. is not.

  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,
The home side device has a sleep mode and a non-sleep mode, and in the sleep mode, a first period during which communication between the home side device and the station side device is stopped, and the home side device Generating a second period during which communication with the station side device is possible,
The station-side device designates the second period in the sleep mode of the home-side device to the home-side device, and sets the clock of the station-side device and the clock of the home-side device of the home-side device. Synchronize in non-sleep mode,
The optical communication system, in which the home device ends the sleep mode and shifts to the non-sleep mode when the elapsed period of the sleep mode reaches a set duration.   When the period preset in the home device as the sleep mode period is greater than the set duration of the sleep mode, the home device transitions from the sleep mode to the non-sleep mode. The optical communication system according to claim 1, wherein the communication system returns to the sleep mode after synchronizing the clock of the station side device and the clock of the home side device.   The home side device measures the elapsed period of the sleep mode using the clock of the home side device, and when the elapsed period of the sleep mode reaches the set duration, the non-sleep mode The optical communication system according to claim 1, wherein a notification for shifting to a mode is transmitted to the station side device.   When the elapsed time of the sleep mode measured by the station-side device reaches the set duration, the station-side device gives an instruction to shift to the non-sleep mode to the home-side device. The optical communication system according to claim 1, wherein the transmission is performed.   The set continuation period is determined based on an allowable range of an error between the clock of the station side device and the internal clock of the home side device and the length of the second period. The optical communication system according to any one of claims 1 to 4, wherein the optical communication system is smaller than a maximum value of measurement deviation between the device and the home-side device. 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,
A first period in which communication between the home side device and the station side device is stopped in the sleep mode, and the home side device and the station side device have a sleep mode and a non-sleep mode. Synchronizing the clock of the station-side device and the clock of the home-side device in the non-sleep mode of the home-side device that generates a second period during which communication is possible;
Setting the second period in the sleep mode of the home device;
A step of ending the sleep mode of the home-side device and shifting to the non-sleep mode when the elapsed time of the sleep mode of the home-side device reaches a set duration. A control method of a communication system. A home-side device connected to the station-side device via a passive optical network,
In the non-sleep mode, communication is performed between the station-side device and the home-side device, communication between the station-side device and the home-side device is stopped in a first period in the sleep mode, and the sleep mode A communication unit that enables communication between the station-side device and the home-side device in a second period of time;
A mode setting unit that switches the mode of the home side device between the sleep mode and the non-sleep mode;
In the non-sleep mode of the home side device, comprising a measuring unit for synchronizing the clock of the home side device with the clock of the station side device,
The mode setting unit, when the elapsed period of the sleep mode reaches a set duration, ends the sleep mode and shifts the mode of the home side device to the non-sleep mode, apparatus.

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