WO2013030934A1

WO2013030934A1 - Communication system, subscriber side optical communication device, station side optical communication device, control device and power-saving control method

Info

Publication number: WO2013030934A1
Application number: PCT/JP2011/069486
Authority: WO
Inventors: 文彦田野; 潤水口; 平野　幸男
Original assignee: 三菱電機株式会社
Priority date: 2011-08-29
Filing date: 2011-08-29
Publication date: 2013-03-07
Also published as: TW201310929A

Abstract

In the present invention, a communication system is provided with ONUs (ONU 1-1 to 1-n) and the ONU (1-1) that operates using a clock extracted from optical signals received from an OLT (2) by a receiver (13) and operates using a free-running clock in TRx sleep mode. The communication system is also provided with a time lag calculation unit (155) that measures the time lag between the OLT (2) clock and the free-running clock of the ONU (1-1), and with a sleep time calculation unit (254) that calculates the sleep time so as to prevent time stamp drift, on the basis of the time lag and a threshold that determines whether or not there is a time stamp drift. The ONU (1-1) uses the sleep time calculated by the sleep time calculation unit (254) as the sleep time for the TRx sleep mode.

Description

Communication system, subscriber side optical communication apparatus, station side optical communication apparatus, control apparatus, and power saving control method

The present invention relates to a communication system, a subscriber-side optical communication device, a station-side optical communication device, a control device, and a power saving control method.

In the PON (Passive Optical Network) system, standardization of a power saving control protocol for powering down an ONU (Optical Network Unit) when there is no traffic is being studied (for example, see Non-Patent Document 1 below).

In the power saving control, for example, a plurality of sleep modes such as a Tx sleep mode in which the transmission function is intermittently stopped and a TRx sleep mode in which the transmission / reception function is intermittently stopped are used. When performing power saving control, negotiation is performed between the OLT and the ONU for exchanging compatible sleep modes and parameters related to power saving control, and power saving control is performed based on parameters agreed upon by this negotiation. Is implemented.

Between the OLT and each ONU, in a normal state in which the ONU receives a signal transmitted from the OLT, the ONU performs clock synchronization based on the received signal. However, for example, while the transmission / reception function is stopped in the TRx sleep mode, the ONU uses the built-in clock source. Therefore, there is a problem that a clock deviation between the OLT and the ONU occurs when returning from the stop state, and link breakage may occur due to time stamp drift. The time stamp drift is a state in which the clock deviation between the OLT and the ONU exceeds a threshold value. In the PON system, when the time stamp drift occurs, it is determined that the ONU and the OLT cannot be synchronized, and a process of disconnecting the PON link is performed. Done.

The present invention has been made in view of the above, and obtains a communication system, a subscriber side optical communication apparatus, a station side optical communication apparatus, a control apparatus, and a power saving control method capable of avoiding time stamp drift. With the goal.

In order to solve the above-described problems and achieve the object, the present invention is capable of transitioning to a transmission / reception sleep mode in which a station-side optical communication device, a transmitter, and a receiver are intermittently stopped. A subscriber-side optical communication device that operates using a clock extracted from the optical signal received from the station-side optical communication device and operates using a free-running clock while the receiver is in a stopped state. A time error calculating unit for measuring an error between the clock of the optical communication apparatus on the station side and the free-running clock of the optical communication apparatus on the subscriber side, and determining whether a time stamp drift has occurred A sleep time calculation unit for calculating a sleep time of the transmitter and the receiver based on a threshold value and the error so as not to cause a time stamp drift, and Device uses a sleep time during which the sleep time calculating unit has calculated as the sleep time of the transceiver sleep mode, characterized in that.

The subscriber-side optical communication device, the station-side optical communication device, the control device, and the power saving control method according to the present invention have the effect that time stamp drift can be avoided.

FIG. 1 is a diagram illustrating a configuration example of a communication system according to the first embodiment. FIG. 2 is a diagram illustrating an operation example of the Tx sleep mode. FIG. 3 is a diagram illustrating an operation example of the TRx sleep mode. FIG. 4 is a diagram illustrating an example of a conventional procedure for negotiation at the time of initialization. FIG. 5 is a diagram showing an example of a transition sequence to a conventional power save mode. FIG. 6 is a diagram illustrating an example of a sleep time and an aware time in the Tx sleep mode and the TRx sleep mode according to the first embodiment. FIG. 7 is a chart diagram illustrating an example of a procedure for measuring time lag according to the first embodiment. FIG. 8 is a chart diagram illustrating an example of a negotiation procedure according to the first embodiment. FIG. 9 is a diagram illustrating an example of a data format when the sleep time and the aware time are notified. FIG. 10 is a diagram illustrating a configuration example of a communication system according to the second embodiment. FIG. 11 is a chart illustrating an example of a procedure for measuring the time lag according to the second embodiment. FIG. 12 is a diagram illustrating a configuration example of a communication system according to the third embodiment. FIG. 13 is a chart diagram illustrating an example of a procedure for measuring time lag according to the third embodiment. FIG. 14 is a diagram illustrating a configuration example of a communication system according to the fourth embodiment. FIG. 15 is a chart diagram illustrating an example of a procedure for measuring time lag according to the fourth embodiment. FIG. 16 is a flowchart illustrating an example of a mode selection procedure according to the fifth embodiment.

Embodiments of a subscriber-side optical communication device, a station-side optical communication device, a control device, and a power saving control method according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a diagram showing a configuration example of a first embodiment of a communication system according to the present invention. The communication system according to the present embodiment includes ONUs (subscriber side optical communication apparatuses) 1-1 to 1-n (n is an integer of 1 or more) and OLT (station side optical communication apparatus) 2. .

The ONU 1-1 is a WDM (Wavelength Division Multiplexing) 11 that wavelength-multiplexes upstream and downstream data, a transmitter 12 that converts an electrical signal into an optical signal, and a receiver that converts the received optical signal into an electrical signal. Device 13, transmission buffer 14, control unit (control device) 15, reception buffer 16, and PHY (physical layer processing unit) 17. The control unit 15 includes a selector 151, an MPCP control unit 152, a power save (power saving) control unit 153, a free-running clock control unit 154, and a time shift calculation unit (clock error calculation unit) 155. The PHY unit 17 includes a receiver 171 and a transmitter 172. The configuration of the ONUs 1-2 to 1-n is the same as that of the ONU 1-1.

The OLT 2 includes a WDM 21, a transmitter 22 that converts an electrical signal into an optical signal and transmits it, a receiver 23 that converts the received optical signal into an electrical signal, a transmission buffer 24, and a control unit (control device) 25. A reception buffer 26 and a PHY (physical layer processing unit) 27. The control unit 25 includes a free-running clock control unit 251, an MPCP control unit 252, a power save control unit 253, and a sleep time calculation unit 254. The PHY unit 27 includes a receiver 271 and a transmitter 272.

First, the operation during normal time (when the ONU 1-1 is not in the sleep mode (power saving mode)) will be described. The PHY 17 of the ONU 1-1 is connected to a user terminal or the like. The receiver 171 of the PHY 17 passes the data received from the user terminal or the like to the control unit 15, and the control unit 15 stores the received data in the transmission buffer 14 as uplink data. The MPCP control unit 152 performs transmission / reception processing of the MPCP message exchanged with the OLT 2. The MPCP control unit 152 reads the uplink data from the transmission buffer 14 within the time period permitted for transmission based on the bandwidth allocation notification transmitted from the OLT 2 as an MPCP message, and transmits the uplink data as an optical signal via the transmitter 12 and the WDM 11. Send to.

In OLT 2, the receiver 13 converts the electrical signal received from the ONU 1-1 via the WDM 21 and outputs it to the MPCP control unit 252. When the data (electrical signal) input from the receiver 23 is data to be transmitted to the upper network via the PHY 27 such as the core network, the MPCP control unit 152 stores the data in the reception buffer 26 and receives the data. If the data input from the device 23 is an MPCP message, processing based on the message is performed. The data stored in the reception buffer 26 is transmitted to the upper network or the like via the control unit 25 and the transmitter 272.

The free-running clock control unit 251 of the OLT 2 has an internal clock source such as an oscillator / resonator and supplies a clock from the internal clock source to the MPCP control unit 252. The MPCP control unit 252 operates based on the clock supplied from the free-running clock control unit 251. In addition, the MPCP control unit 252 allocates a band to each of the ONUs 1-1 to 1-n based on the band allocation request transmitted as the MPCP message of the ONUs 1-1 to 1-n, and uses the allocation result as a band allocation notification. Transmit to the ONUs 1-1 to 1-n via the transmitter 22.

Also, the receiver 271 of the OLT 2 passes the data received from the upper network or the like to the control unit 25, and the control unit 25 stores the data in the transmission buffer 24. The MPCP control unit 252 transmits the data stored in the transmission buffer 24 as an optical signal to the ONUs 1-1 to 1-n via the transmitter 22 and the WDM 21.

The receiver 13 of the ONU 1-1 receives the optical signal transmitted from the OLT 2 via the WDM 11 and converts it into an electrical signal. The receiver 13 also has a CDR (Clock Data Recovery) function, extracts the clock and downlink data transmitted from the OLT 2 from the signal converted into an electrical signal, and extracts the extracted downlink data to the MPCP control unit 152. And the extracted clock is output to the selector 15. In the present embodiment, a clock extracted by the receiver 13 (that is, a clock regenerated based on an optical signal from the OLT 2) is referred to as a reference clock. Here, the receiver 13 has the CDR function, but the CDR may be provided as a component independent of the receiver 13.

When the downlink data input from the receiver 13 is data addressed to a user terminal or the like connected via the PHY 17, the MPCP control unit 152 stores the data in the reception buffer 16 and receives the data from the receiver 13. If the input downlink data is an MPCP message, processing based on the message is performed. Data stored in the reception buffer 16 is transmitted to the user terminal or the like via the control unit 15 and the transmitter 172.

The free-running clock control unit 154 has an internal clock source such as an oscillator / resonator and outputs a clock (free-running clock) from the internal clock source to the selector 151. The selector 151 supplies the clock from the receiver 13 to the MPCP control unit 152 when the clock (reference clock) is input from the receiver 13, and the selector 151 when the clock (reference clock) is not input from the receiver 13. The clock (self-running clock) from the running clock control unit 154 is supplied to the MPCP control unit 152. The MPCP control unit 152 operates based on the clock supplied from the selector 151. In addition, the MPCP control unit 152 manages time, extracts a time stamp indicating the time managed by the OLT 2 stored in the MPCP message such as a bandwidth allocation notification, and sets the time managed by itself to the time stamp. Synchronize (time stamp synchronization). Also, the time managed by itself is incremented by one count based on the input clock. The receiver 13 may output an idle signal or the like to the selector 151 instead of the reference clock regenerated based on the optical signal from the OLT 2. In such a case, the receiver 13 generates a control signal for identifying whether the signal output to the selector 151 is a reference clock or an idle signal, and outputs the control signal to the selector 151. The selector 151 outputs a reference clock or a free-running clock based on this control signal.

Next, the power saving control of this embodiment will be described. Here, it is assumed that the ONU 1-1 has two power save modes as a power saving mode, a Tx sleep mode in which the transmission function is intermittently stopped and a TRx sleep mode in which the transmission / reception function is intermittently stopped. When the MPCP control unit 152 receives a message related to power saving control, the MPCP control unit 152 notifies the power save control unit 153 of information related to power saving control (such as a sleep mode type and a sleep time) based on the message. The power save control unit 153 performs power save control such as stop and start on the transmitter 12 and the receiver 13 based on these pieces of information.

FIG. 2 is a diagram illustrating an operation example in the Tx sleep mode, and FIG. 3 is a diagram illustrating an operation example in the TRx sleep mode. As shown in FIG. 2, in the Tx sleep mode, a stop period in which Tx (transmitter 12) is stopped and a start time in which Tx is in a start state are alternately repeated. As shown in FIG. 3, in the TRx sleep mode, a stop period in which TRx (transmitter 12 and receiver 13) is stopped and a start-up time in which TRx is started are alternately repeated. In the following description, the length of the stop period is called sleep time, and the length of activation time is called aware time. In the Tx sleep mode, not only the transmitter 12 but also other functional units that perform processing related to transmission from the ONU 1-1 to the OLT 2 may be stopped during the stop time period. Similarly, in the TRx sleep mode, not only the transmitter 12 and the receiver 13 but also other functional units that perform processing related to reception from the OLT 2 may be stopped during the stop time period.

Also in OLT 2, power save control of OLT 2 is performed by the power save control unit 253, but since this is the same as the conventional one, description thereof is omitted.

Here, conventional power saving control will be described. FIG. 4 is a diagram illustrating an example of a conventional procedure for negotiation at the time of initialization. First, at initialization such as when the ONU is started up, a discovery sequence for exchanging information necessary for communication is performed between the OLT and the ONU, and then negotiation is performed. FIG. 4 shows an example of the conventional procedure of this negotiation. First, a request for transmitter initialization time and transmitter / receiver initialization time is transmitted from the OLT to the ONU (step S101). Upon receiving this request, the ONU transmits its own transmitter initialization time and transmitter / receiver initialization time (step S102). The transmitter initialization time and the transmitter / receiver initialization time are times until the transmitter (or the transmitter and the receiver) are actually operable when the transmitter (or the transmitter and the receiver) is turned on. .

Next, the OLT sets the sleep time and the aware time in the power save mode and notifies the ONU (step S103). The ONU transmits a response to the notified sleep time and aware time (step S104). Through the above procedure, the sleep time and the aware time are agreed between the OLT and the ONU. In conventional power saving control, a common value is set for the sleep time and the aware time regardless of the type of power save mode (Tx sleep mode, TRx sleep mode, etc.).

FIG. 5 is a diagram showing an example of a transition sequence to a conventional power save mode (Tx sleep mode or TRx sleep mode). When power mode transition permission is transmitted from the OLT (step S201), the ONU notifies the OLT of the power save transition and transitions to the power save mode (step S202). When transitioning to the Tx sleep mode, the Tx stop state and activation state are alternately performed, and when transitioning to the TRx sleep mode, the TRx halt state and activation state are alternately performed.

The OLT periodically transmits a bandwidth allocation notification to the ONU, for example (step S203), and transmits a bandwidth request when the bandwidth allocation notification is received (step S204). In this case, it is assumed that the bandwidth allocation notification is periodically transmitted even after the ONU transitions to the power save mode.

During normal operation, the ONU performs time stamp synchronization with the OLT based on the OLT time stamp stored in the MPCP message received from the OLT, and further operates using the clock extracted from the signal received from the OLT. Thus, clock synchronization can be performed, and synchronization with the time managed by the OLT is realized. However, in the conventional power saving control described with reference to FIGS. 4 and 5 described above, the clock cannot be extracted if the receiver 13 stops in the TRx sleep mode. Therefore, during this time, the ONU uses a free-running clock, and due to the frequency deviation between the OLT and the internal clock of the ONU, the deviation from the time managed by the OLT increases as the sleep time increases. For this reason, a transition from the stop state of the TRx sleep mode to the start state or the normal state is received to receive a bandwidth permission notification, and the time stamp stored in the bandwidth permission notification and the time managed by the ONU (counter based on the free-running clock) If the difference between the time and the time obtained by incrementing is larger than the threshold value, a time stamp drift occurs and the link between the OLT and the ONU is disconnected.

In this embodiment, the sleep time of the TRx sleep mode is adjusted in order to prevent the occurrence of time stamp drift in the above-described conventional power saving control. The following description will be given assuming that the sleep times of the Tx sleep mode and the TRx sleep mode are set independently, but the sleep times of the Tx sleep mode and the TRx sleep mode may be common. The aware time may be set independently in the Tx sleep mode and the TRx sleep mode or may be common. When the OLT 2 does not consider whether or not the ONU 1-1 is in the power save mode when transmitting the bandwidth allocation notification (for example, periodically transmits the bandwidth allocation notification regardless of whether the power save mode is stopped or activated) If), the aware time may be determined in any way. Further, the aware time may be lengthened as the sleep time is shortened.

FIG. 6 is a diagram illustrating an example of the sleep time and the aware time in the Tx sleep mode and the TRx sleep mode according to the present embodiment. The upper part shows the sleep time and the aware time in the Tx sleep mode, and the lower part shows the sleep time and the aware time of the present embodiment in the TRx sleep mode. In the example of FIG. 6, the sleep time in the TRx sleep mode is shorter than that in the Tx sleep mode, and the amount of time in the TRx sleep mode is increased as much as the sleep time in the TRx sleep mode is shortened. The setting method of the awareness time is not limited to this.

Next, a method for setting the sleep time in the TRx sleep mode of the present embodiment will be described. In this embodiment, a time lag (clock error) with respect to the time of OLT 2 when operating with a free-running clock for a certain time is calculated, and the time stamp drift is calculated based on the calculated time lag as the sleep time in TRx sleep mode. Set the length so that it does not occur. Specifically, for example, the sleep time is set as follows. When the clock frequency of OLT2 is f [Hz] and the relative error of the clock frequency of ONU1-1 with respect to the clock frequency of OLT2 is e, the clock frequency of ONU1-1 is (1 + e) f [Hz]. Here, assuming that the sleep time in the TRx sleep mode is t _s [s], the time shift t _d [s] of the ONU 1-1 with respect to the OLT 2 when the sleep time expires and the power is turned on is It can be shown by (1). It is assumed that the ONU 1-1 time is synchronized with the OLT 2 time at the start of the sleep time.
t _d = {e / (1 + e)} t _s (1)

Assuming that the threshold of time lag at which time stamp drift occurs is t _th [s], time stamp drift occurs when t _d > t _th . Therefore, since the time stamp drift does not occur if the following expression (2) is satisfied, the sleep time t _s [s] is determined so as to satisfy the following expression (2).
t _d ≦ t _th (2)

As the relative error e, a fixed value based on a specification value or a measurement result measured in advance may be used. However, since the relative error e may change depending on the environment or the like, it is more accurately obtained by actual measurement. Therefore, in the present embodiment, the time lag is measured as follows, and the relative error e is obtained based on this measured value. After obtaining the relative error e, the above equation (1) is substituted into the equation (2), and t _s [s] is determined so as to satisfy the following equation (3). For example, since the longer the sleep time, the higher the power saving effect, t _s [s] can be determined as the maximum value in a range that satisfies the following (3).
{E / (1 + e)} t _s ≦ t _th (3)

説明 Explain how to measure the time difference FIG. 7 is a chart showing an example of a procedure for measuring the time lag according to the present embodiment. As shown in FIG. 7, first, information necessary for power saving (including sleep time and aware time for each power saving mode) is negotiated between OLT 2 and ONU 1-1 (step S1). This negotiation will be described later. The TRx sleep mode sleep time set at the time of negotiation is not measured at this time, so a sufficiently short value is set as an initial value in order to prevent time stamp drift. For example, even if the assumed maximum relative error is assumed, a short value is set so that time stamp drift does not occur.

The OLT 2 transmits a bandwidth allocation notification frame A including a time stamp (step S2). Specifically, the MPCP control unit 252 of the OLT 2 generates a bandwidth allocation notification frame A and transmits it to the OLT 1-1 via the transmitter 22 and the WDM 21.

When the ONU 1-1 receives the frame A, the ONU 1-1 synchronizes the time managed by the time stamp stored in the frame A (time stamp synchronization) (step S3). Specifically, in the ONU 1-1, the frame A is input to the MPCP control unit 152 via the WDM 11 and the receiver 13, and the MPCP control unit 152 synchronizes the time managed by itself with the time stamp stored in the frame A. . At this time, since the receiver 13 is activated, the reference clock is supplied to the MPCP control unit 152, and the OLT 2 and the ONU 1-1 are synchronized.

When it is time to transition to the TRx sleep mode, the power save control unit 153 turns off the power of the receiver 13 and enters a sleep (stop) state (step S4). The self-running clock is supplied to the MPCP control unit 152 from the time when the power of the receiver 13 is turned off, and the MPCP control unit 152 starts from the TRx sleep mode after t1 [s] from the time when the power of the receiver 13 is turned off. Return to normal state (step S5). Note that t1 [s] is the initial value of the sleep time in the TRx sleep mode set by negotiation in the first step S5.

Next, the ONU 1-1 receives the bandwidth allocation notification frame B transmitted from the OLT 2 (step S6). Then, the ONU 1-1 calculates a time lag between the time stamp stored in the frame B and the time managed by the own device (that is, the free-running clock) (step S7). Specifically, the ONU 1-1 that has received the frame B is input to the MPCP control unit 152 via the WDM 11 and the receiver 13, and the MPCP control unit 152 manages the time stamp stored in the frame B and the own device. Is transferred to the time lag calculation unit 155. The time lag calculation unit 155 calculates the difference between the time stamp stored in the frame B and the time managed by the own device (time stamp of the ONU 1-1).

The ONU 1-1 transmits the calculated time lag to the OLT 2 using the frame C (step S8). Specifically, the data is transferred to the MPCP control unit 152, and the MPCP control unit 152 stores the time lag in the MPCP message and transmits it to the OLT 2.

Steps S2 to S8 are repeated M (M is an integer equal to or greater than 1) times. OLT2 receives the frame C, holds the time shift that has been stored in the frame C, determine the relative error on the basis of the M time shift between t1 [s] and, t _s which satisfies the above (3) [S] is obtained (step S9). Specifically, the frame C is input to the MPCP control unit 252 via the WDM 21 and the receiver 23, and the MPCP control unit 252 passes M time lags and t1 [s] to the sleep time calculation unit 254. The sleep time calculation unit 254 obtains an actual measurement value of the time shift by statistical processing or the like based on the M time shifts. A method for obtaining the measured value of the time lag will be described later. Then, by substituting t1 [s] to t _s [s] in equation (1), by substituting the measured value of the time displacement to t _d, determine the relative error e by solving for e. Then, using the obtained e and the threshold value t _th , t _s [s] satisfying the above expression (3) is obtained.

Thereafter, the ONU 1-1 and the OLT 2 negotiate and set the sleep time of the TRx sleep mode to t _s [s] obtained in step S9 (step S10). When the TRx sleep mode sleep time and the TRx sleep mode aware time are changed from the initial values (for example, when the awareness time is increased as shown in FIG. 6), the awareness time is also negotiated in step S10. Reset it. Thereafter, when the ONU 1-1 transitions to the TRx sleep mode, it operates using the sleep time and the aware time set in step S10.

Here, t1 [s] is described as a constant value in the process of M iterations, but t1 [s], that is, the sleep time may be gradually increased in the process of repetition. The longer t1 [s], the better the measurement accuracy of the time lag. However, if t1 [s] is set short, time stamp drift may occur. Therefore, if the counter of the number of repetitions is i, when i = 1 (initial calculation), t1 [s] is set to a short value, and after step S8, the OLT 2 detects one time lag as the above time lag measurement. Using the value, t _s [s] satisfying the above equation (3) is obtained. In the process of i = 2, the obtained t _s [s] is used as t1 [s]. In this case, since it is necessary to notify the obtained t _s [s] (that is, t1 [s]) from the OLT 2 to the OLT 1-1, for example, in step S2 of i = 2, t1 [s] is stored in the bandwidth allocation notification. And notify. You may notify t1 [s] separately from a bandwidth allocation notification. In this case, for example, because they seek relative error in each iteration, determined measured values of the relative error by statistical processing such as the M relative error in step S9, t _s [s satisfying the above formula (3) ] May be obtained.

Next, a method for determining the actual measurement value of the time lag using the M time errors (time lag or relative error) in step S9 will be described. As a method of determining the actual measurement value, (1) a method of selecting the maximum value from the measured M time errors, and (2) a method of taking a weighted average of the measured M time errors are considered. It is not limited to.

(2) The method of taking the weighted average of the measured M time errors is specifically calculated as follows, for example. It is assumed that when M measurements are taken, the error increases or decreases with each measurement. For example, when t1 [s] is extended for each repetition as described above, the Mth measurement result is more reliable than the first measurement result. Therefore, a highly reliable measured value can be obtained by increasing the weight when taking the average from the first time to the Mth time.

For example, measured values x ₁ , x ₂ ,..., X _{M of M} time errors from the first to M times in M measurements.
Is obtained. In this case, the actual measurement value y determined by the weighted average is obtained by the following equation (4).
y = x ₁ w ₁ + x ₂ w ₂ +... + x _M w _M (4)
However,
w ₁ + w ₂ + ... + w _M = 1
w ₁ <w ₂ <... <w _M

Also, the number of repetitions (number of measurements) M is a parameter and can be changed according to the situation. If M is small, the accuracy of error measurement is high, but the measurement time is reduced. If M is large, the accuracy of error measurement is small and the measurement time is long. The reason why the accuracy decreases when M is small is that the number of digits for recording time is finite.

Further, the threshold value t _th for determining the occurrence of the time stamp drift can also be changed depending on the application.

As described above, the measurement of the time lag described with reference to FIG. 7 (steps S2 to S10) may be performed as one operation in the TRx sleep mode of the ONU 1-1, and is not an operation in the TRx sleep mode. You may define and implement as another mode (measurement mode etc.).

In this embodiment, the time lag calculation unit 155 is provided separately from the MPCP control unit 152, but the MPCP control unit 152 may have the function of the time lag calculation unit 155. Similarly, the MPCP control unit 252 may have the function of the sleep time calculation unit 254.

Next, an example of the negotiation procedure of this embodiment will be described. FIG. 8 is a chart showing an example of the negotiation procedure of the present embodiment. Steps S101 and S102 in FIG. 8 are the same as the conventional procedure described in FIG. After step S102, the OLT 2 of the present embodiment sets the sleep time and the aware time in the power save mode for each mode and notifies the ONU (step S103a). At this time, the sleep time and the aware time in the Tx sleep mode may be set in any manner. The sleep time in the TRx sleep mode is set to a short value so that time drift does not occur as described above. The ONU 1-1 transmits a response to the notified sleep time and aware time (step S104a).

By the above procedure, the sleep time and the aware time for each mode are agreed between the OLT 2 and the ONU 1-1.

FIG. 9 is a diagram showing an example of a data format when notifying the sleep time and the aware time from the OLT 2 to the ONU 1-1 at the time of negotiation. FIG. 9 shows an example of a data format based on IEEE P1904.1 ^™ . The data format when the sleep time and the aware time are notified by negotiation is not limited to this, and for example, ITU-T G. The sleep time and the aware time for each mode may be notified in a data format based on 988.

As described above, in this embodiment, the ONU 1-1 sets the predetermined time TRx to the stop state, and after the stop state ends, the time stamp received from the OLT 2 is updated based on the free-running clock. Find the difference from the time you manage. Then, a relative error between the OLT 2 and the ONU 1-1 is obtained based on the obtained difference (time lag), and a sleep time within a range in which the time stamp drift does not occur is obtained based on the relative error and the time stamp drift threshold. Thus, the sleep time is set as the TRx sleep mode. For this reason, time stamp drift can be avoided.

Embodiment 2. FIG.
FIG. 10 is a diagram illustrating a configuration example of the communication system according to the second embodiment of the present invention. The communication system according to the present embodiment includes ONUs 1a-1 to 1a-n and an OLT 2a. The ONU 1a-1 of the present embodiment is the same as the ONU 1-1 of the first embodiment, except that it includes a time lag calculation unit 155a instead of the time lag calculation unit 155 of the ONU 1-1 of the embodiment. The OLT 2a of the present embodiment is the same as the OLT 2 of the first embodiment except that the sleep time calculation unit 254 is deleted from the OLT 2 of the embodiment. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

In the first embodiment, as described with reference to FIG. 7, the OLT 2 obtains the sleep time in the TRx sleep mode in which the time stamp drift does not occur based on the actually measured value of the time lag, and then obtains the sleep time obtained by the negotiation as the OLT 2 and the ONU 1 Agreed with -1. In the present embodiment, the ONU 1-1 obtains the sleep time in the TRx sleep mode in which the time stamp drift does not occur based on the actually measured value of the time lag.

FIG. 11 is a chart showing an example of a procedure for measuring time lag according to the present embodiment. Steps S1 to S7 in FIG. 11 are the same as those in the first embodiment. Then, after step S2 to step S7 are repeated M times, the time lag calculating unit 155a of the ONU 1-1 is based on the measured values of M time lags as in the sleep time calculating unit 254 of the OLT 2 of the first embodiment. Then, the measured value of the time lag is obtained by statistical processing or the like (step S11), and the sleep time is obtained using the measured value of the time lag so that the time stamp drift does not occur as in the sleep time calculation unit 254 of the OLT 2 of the embodiment. (Step S12). That is, in this embodiment, the time lag calculation unit 155a also has a function as a sleep time calculation unit. As in the first embodiment, t1 [s] may be increased for each repetition.

In the present embodiment, the ONU 1-1 retains the sleep time determined to prevent the occurrence of the time stamp drift as the sleep time of the TRx sleep mode by the above processing, and the TRx sleep mode is used by using the sleep time. Perform the operation. The OLT 2 operates on the assumption that the sleep time has not been changed (the sleep time agreed by the negotiation in step S1 remains). Therefore, when the OLT 2 transmits the bandwidth allocation notification, it is considered whether the ONU 1-1 is in the stopped state or the activated state (the transmission timing is controlled so that the bandwidth allocation notification is transmitted during the activated state). ), It is desirable to lengthen the awareness time by increasing the sleep time so that the bandwidth allocation notification can be received during the activation state known by the OLT 2 as in the example of FIG. 6 of the first embodiment. . When the OLT 2 transmits a bandwidth allocation notification, if the ONU 1-1 is not in the stopped state or the activated state, the aware time may be set in any way. The operations of the present embodiment other than those described above are the same as those of the first embodiment.

As described above, in this embodiment, the ONU 1-1 obtains the relative error between the clocks of the OLT 2 and the ONU 1-1 based on the measurement value of the time difference obtained in the same manner as in the first embodiment. Based on the stamp drift threshold value, the sleep time within a range where the time stamp drift does not occur is obtained and set as the sleep time of the TRx sleep mode. For this reason, time stamp drift can be avoided as in the first embodiment. Further, in the first embodiment, it is necessary to execute a transmission operation that is not in the conventional procedure of transmitting the frame C. However, in this embodiment, there is no need for this transmission operation, and the OLT 2 side performs the same operation as the conventional one. It's okay.

Embodiment 3 FIG.
FIG. 12 is a diagram illustrating a configuration example of the communication system according to the third embodiment of the present invention. The communication system according to the present embodiment includes ONUs 1b-1 to 1b-n and an OLT 2a. The ONU 1b-1 according to the present embodiment includes a time shift calculation unit b instead of the time shift calculation unit 155a, and connects the free-running clock control unit 154 and the time shift calculation unit 155b to extract the reference clock extracted by the receiver 13. Is the same as the ONU 1a-1 in the second embodiment, except that it can be input to the MPCP control unit 152. Components having the same functions as those in the second embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

In

Embodiments

1 and 2, the time lag was measured by setting TRx to the stop state during t1 [s]. In the present embodiment, the time lag is measured in the normal state without stopping TRx. Since it is a normal state, the reception of the optical signal from the OLT 2 is continued, and the time lag can be measured while the clock synchronization with the OLT 2 is maintained. Therefore, even if t1 [s], which is the time difference measurement time, is increased, time stamp drift does not occur.

FIG. 13 is a chart showing an example of the procedure for measuring the time lag according to the present embodiment. Steps S1 to S3 in FIG. 13 are the same as those in the first embodiment. After step S3, the ONU 1-1 keeps the normal state, the MPCP control unit 152 measures t1 [s] using the reference clock, and operates the free-running clock during that time (step S13). The time lag calculation unit 155b obtains a measurement time based on the free-running clock from the start time to the end time of t1 [s] (for example, by incrementing the counter). Then, the difference between the time measured by the free-running clock and t1 [s] is obtained as a time lag (step S14). Then, steps S2, S3, S13, and S14 are repeated M times, and thereafter, steps S11 and S12 are performed in the same manner as in the second embodiment to obtain the sleep time. Then, the obtained sleep time is held as the sleep time of the TRx sleep mode, and the operation of the TRx sleep mode is performed using the sleep time. The operations of the present embodiment other than those described above are the same as those of the second embodiment.

In this example, the ONU 1-1 obtains the sleep time in the TRx sleep mode and holds only the ONU 1-1, and the OLT 2 does not grasp the obtained sleep time. However, the ONU 1-1 obtains the sleep time after step S12. The sleep time may be notified to the OLT 2 and the negotiation may be performed again using the sleep time for which the OLT 2 has been notified.

As described above, in this embodiment, the time difference between the OLT 2 clock and the free-running clock is measured in the normal state. For this reason, the same effects as those of the first embodiment can be obtained, and the synchronization with the reference clock is maintained, so that time stamp drift does not occur. Therefore, t1 [s] can be set long, and the measurement accuracy of the time lag can be improved.

Embodiment 4.
FIG. 14 is a diagram illustrating a configuration example of the communication system according to the fourth embodiment of the present invention. The communication system according to the present embodiment includes ONUs 1c-1 to 1c-n and an OLT 2b. The ONU 1c-1 of the present embodiment connects the free-running clock control unit 154 and the MPCP control unit 155 so that the reference clock of the receiver 13 can be input to the MPCP control unit 152, and the time lag calculation unit 155 is deleted. Except for this, it is the same as the ONU 1-1 of the first embodiment. The OLT 2b of the present embodiment is the same as the OLT 2 of the first embodiment except that the sleep time calculation unit 254a is provided instead of the sleep time calculation unit 254 of the first embodiment. Components having the same functions as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and redundant description is omitted.

FIG. 15 is a chart showing an example of a procedure for measuring time lag according to the present embodiment. Step S1 in FIG. 15 is the same as that in the first embodiment. In the present embodiment, the OLT 2 transmits the bandwidth allocation notification frame A as in the first embodiment, but at this time, the transmission time is recorded (step S2a). Specifically, the MPCP control unit 252 notifies the transmission time to the sleep time calculation 254a, and the sleep time calculation 254a records the transmission time. Step S3 is the same as that in the first embodiment. After step S3, the ONU 1-1 measures t1 [s] with the free-running clock in the normal state (step S13a). Then, when t1 [s] ends with the free-running clock, frame D, which is a response frame of frame A, is transmitted (step S15). The frame D may be any frame as long as the OLT 2 can recognize that it is a response frame of the frame A that notifies the end of t1 [s]. For example, the identifier indicating the frame that notifies the end of t1 [s] defined in advance is stored in the frame type of frame D and transmitted. Further, the value of t1 [s] may be stored in the frame D and transmitted.

When the OLT 2 receives the frame D, the sleep time calculation unit 254a performs a relative error based on the recorded transmission time, reception time of the frame D, RTT (Round Trip Time), and t1 [s]. Is obtained (step S16). That is, the sleep time calculation unit 254a of the present embodiment also has a function as a time lag calculation unit. Specifically, the sleep time calculation unit 254a calculates a relative error based on, for example, the following formula (5). In the PON system, since RTT is generally measured, the measurement result may be used as the RTT value.
Relative error = (frame D reception time−frame A transmission time−RTT−t1 [s]) / t1 [s] (5)

Then, after repeating steps S2a, S3, S13a, S15, and S16 M times, the sleep time calculation unit 254a obtains an actual value of the relative error by statistical processing or the like based on the M relative errors, and based on the actual value. Thus, the sleep time is calculated so that time stamp drift does not occur (step S17). The method for calculating the sleep time is the same as in the first embodiment. Thereafter, negotiation is performed again using the calculated sleep time as the sleep time of the TRx sleep mode (step S10). The operations of the present embodiment other than those described above are the same as those of the first or third embodiment. Here, the relative error is obtained in step S16, and the process for obtaining the relative error is repeated M times. However, in step S16, the time lag (the reception time of frame D−the transmission time of frame A−RTT−t1 [ s]) may be obtained, an actual value of the time deviation may be obtained by statistical processing or the like based on the M time deviations, and a relative error may be obtained based on the actual measurement value.

In this example, the OLT 2 calculates the relative error based on the frame transmission / reception time. However, the ONU 1-1 manages its own device at the time of starting and ending t1 [s] with the free-running clock. A time lag between the free-running clock and the reference clock may be obtained based on the time to be updated (time updated by the reference clock), and the sleep time may be obtained based on the time lag.

As described above, in the present embodiment, the ONU 1-1 measures t1 [s] with the free-running clock from the time when the frame A is received from the OLT 2 in the normal state, and the frame D is detected after the elapse of t1 [s]. Send. The OLT 2 obtains a relative error based on the recorded transmission time, the reception time of the frame D, the RTT, and t1 [s], and the TRx sleep so that the time stamp drift does not occur based on the obtained relative error. The sleep time of the mode was set. For this reason, the same effect as in the first embodiment can be obtained, and the synchronization with the reference clock is maintained, so that time stamp drift does not occur. Therefore, t1 [s] can be set long, and the measurement accuracy of the time lag can be improved.

Embodiment 5.
FIG. 16 is a flowchart showing an example of the mode selection procedure of the communication system according to the fifth embodiment of the present invention. The configuration of the communication system of the present embodiment is described as being the same as that of the first embodiment, but is not limited to this and may be the configurations of the second to fourth embodiments. In the present embodiment, the sleep times of the TRx sleep mode and the Tx sleep mode can be set independently.

As described in the first to fourth embodiments, when the sleep time of TRx sleep is set so that time stamp drift does not occur, the sleep time is shortened, so that the power consumption may increase compared to the conventional case. Depending on the performance of the optical device, it may not respond to the sleep time (the sleep time in the TRx sleep mode is shorter than the minimum value of the sleep time depending on the performance of the optical device). In this case, the Tx sleep mode is applied instead of the TRx sleep mode. In addition, since the Tx sleep mode reduces the amount of power consumption compared to the TRx sleep mode at the same sleep time, there is no sleep time for the sleep mode in the negotiation so that the power consumption can be reduced as much as possible in the Tx sleep mode. Maximum value that does not cause link breakage due to signal (link breakage due to no transmission from ONU1-1 for a certain period of time, for example, OLT2 disconnects link with ONU1-1 if there is no transmission from ONU1-1 for a certain period of 1 second) Set to.

For example, the mode selection shown in FIG. 16 is performed by the MPCP control unit 252 of the OLT 2, but is not limited thereto, and may be performed by the ONU 1-1 (power save control unit 153, etc.). When the OLT 2 obtains the sleep time of the TRx sleep as in the first embodiment, the OLT 2 may select the mode, and the time stamp drift does not occur as in the second embodiment. When the OLT 2 is not notified of the sleep time of the TRx sleep obtained in the above, the ONU 1-1 may perform mode selection. Here, as an example, it is assumed that the MPCP control unit 252 of the OLT 2 performs mode selection.

As shown in FIG. 16, first, the MPCP control unit 252 determines that the sleep time obtained from the error for the ONU 1-1 (the sleep time obtained so that the time stamp drift described in the first to fourth embodiments does not occur) is optical. It is determined whether or not the sleep time obtained from the performance of the device is not less than the minimum value (step S21). When the sleep time obtained from the error is smaller than the minimum value of the sleep time obtained from the performance of the optical device (No in step S21), the Tx sleep mode is applied to the ONU 1-1 (step S22).

If the sleep time obtained from the error is equal to or greater than the minimum value of the sleep time obtained from the performance of the optical device (step S21, Yes), it is determined whether the power consumption of the TRx sleep mode is smaller than the power consumption of the Tx sleep mode. (Step S23). When the power consumption in the TRx sleep mode is smaller than the power consumption in the Tx sleep mode (step S23, Yes), the TRx sleep mode is applied to the ONU 1-1 (step S24). When the power consumption in the TRx sleep mode is equal to or higher than the power consumption in the Tx sleep mode (No in step S23), the Tx sleep mode is applied to the ONU 1-1 (step S25). The operations of the present embodiment other than those described above are the same as those of the first to fourth embodiments.

As described above, in this embodiment, the comparison result between the sleep time obtained from the error and the minimum value of the sleep time obtained from the performance of the optical device, and the comparison result between the power consumption in the TRx sleep mode and the Tx sleep mode, Based on, the mode selection of the power save mode was made. For this reason, the same effects as those of the first embodiment can be obtained, and a mode that satisfies the restrictions on the performance of the optical device and has a higher power consumption effect can be selected.

As described above, the communication system, the subscriber side optical communication apparatus, the station side optical communication apparatus, the control apparatus, and the power saving control method according to the present invention are useful for the PON system, and in particular, the PON system that performs the power saving control. Suitable for

1-1 to 1-n, 1a-1 to 1a-n, 1b-1 to 1b-n, 1c-1 to 1c-n ONU
2,2a, 2b OLT
11, 21 WDM
12, 22

Transmitter

13, 23

Receiver

14, 24

Transmission buffer

15, 25

Control unit

16, 26

Reception buffer

17, 27 PHY
151 Selector 152,252 MPCP control unit 153,253 Power save control unit 154,251 Self-running clock control unit 155,155a, 155b Time shift calculation unit 254,254a Sleep time calculation unit 171,271 Receiver 172,272 Transmitter

Claims

Transition to the station side optical communication device and transmission / reception sleep mode in which the transmitter and the receiver are intermittently stopped is possible, and a clock extracted from the optical signal received from the station side optical communication device by the receiver is used. A subscriber-side optical communication device that operates using a self-running clock while the receiver is in a stopped state, and a communication system comprising:
A time error calculator for measuring an error between the clock of the station-side optical communication device and the self-running clock of the subscriber-side optical communication device;
A sleep time calculation unit for calculating a sleep time of the transmitter and the receiver so as not to generate a time stamp drift, based on a threshold for determining whether or not a time stamp drift occurs and the error;
With
The said subscriber side optical communication apparatus uses the sleep time which the said sleep time calculation part calculated as the sleep time of the said transmission / reception sleep mode, The communication system characterized by the above-mentioned.
The subscriber side optical communication device includes the time error calculation unit,
The station-side optical communication device includes the sleep time calculation unit,
2. The communication system according to claim 1, wherein the station-side optical communication device notifies the subscriber-side optical communication device by negotiation of the sleep time calculated by the sleep time calculation unit.
The communication system according to claim 1, wherein the subscriber-side optical communication device includes the time error calculation unit and the sleep time calculation unit.
The station-side optical communication device includes the time error calculation unit and the sleep time calculation unit,
The station side optical communication device holds the transmission time when the frame is transmitted to the subscriber optical communication device,
The subscriber optical communication device is:
In a normal state in which the transmitter and the receiver operate, a predetermined time is measured with a free-running clock starting from the time when the frame is received from the station-side optical communication device, and the frame is measured at the end of the measurement of the predetermined time. A response frame to the station side optical communication device,
The communication system according to claim 1, wherein the time error calculation unit obtains the error based on the transmission time, the reception time of the response frame, the predetermined time, and a round trip delay time.
The subscriber optical communication device is:
By updating the transmitter and the receiver for a predetermined time, the time managed by the own device is updated with the self-running clock of the own device for the predetermined time,
The time error calculation unit includes: a time of the local apparatus after the predetermined time has elapsed; and a time stamp in the local optical communication apparatus stored in a frame received from the local optical communication apparatus after the predetermined time has elapsed. The communication system according to claim 1, wherein the error is obtained based on the error.
The subscriber optical communication device is:
In a normal state in which the transmitter and the receiver operate, a predetermined time is measured by the extracted clock, and a result obtained by measuring from the start to the end time of the predetermined time with a free-running clock and the predetermined time The communication system according to claim 1, wherein the error is obtained based on the error.
The subscriber optical communication device is:
Based on a result obtained by measuring a predetermined time with a free-running clock in a normal state in which the transmitter and the receiver operate and measuring with a reference clock from the start to the end of the measurement of the predetermined time. 4. The communication system according to claim 1, 2, or 3, wherein the error is obtained.
The process for obtaining the error is repeated a predetermined number of times,
The sleep time calculation unit obtains a relative error between the self-running clock and the reference clock in the subscriber optical communication device based on the error for a predetermined number of times, and calculates the sleep time based on the relative error and the threshold value. 8. The communication system according to claim 4, wherein the communication system is calculated.
The communication system according to claim 8, wherein the relative error is obtained based on a maximum value of the error for the predetermined number of times.
The communication system according to claim 8, wherein the relative error is obtained based on a weighted average of the errors for the predetermined number of times.
The communication system according to any one of claims 4 to 10, wherein, in the repetition of the predetermined number of times, the predetermined time is increased for each repetition.
The subscriber optical communication device is:
It is possible to transition to a transmission sleep mode in which the transmitter is intermittently stopped,
The station side optical communication device or the subscriber optical communication device is:
When the sleep time calculated by the sleep time calculation unit is shorter than the minimum time that can be set in the receiver and the transmitter, the transmission sleep mode is selected as a power save mode to be applied to the subscriber optical communication device The communication system according to any one of claims 1 to 11, wherein:
The station side optical communication device or the subscriber optical communication device is:
When the sleep time calculated by the sleep time calculation unit is equal to or longer than a minimum time that can be set in the receiver and the transmitter, the transmission sleep mode is used as a power save mode to be applied to the subscriber optical communication device. The communication system according to claim 12, wherein a mode with low power consumption is selected from the transmission / reception sleep mode.
14. The sleep time in the transmission sleep mode is set to a value within a range in which no link breakage occurs because a signal from the optical communication apparatus on the subscriber side is not received for a certain period of time. The communication system described.
A clock extracted from an optical signal received from the station-side optical communication apparatus by the receiver, which is connected to the station-side optical communication apparatus, can be changed to a transmission / reception sleep mode in which the transmitter and the receiver are intermittently stopped. A subscriber-side optical communication device that operates using a free-running clock while the receiver is in a stopped state,
A time error calculator that measures an error between the clock of the station-side optical communication device and the free-running clock;
With
Based on a threshold for determining whether or not time stamp drift has occurred and the error, the transmitter and the receiver sleep time calculated so as not to generate time stamp drift are used as sleep times in the transmission / reception sleep mode, A subscriber-side optical communication apparatus.
The station side optical communication device connected to the subscriber side optical communication device,
The subscriber-side optical communication device is capable of transition to a transmission / reception sleep mode in which a transmitter and a receiver are intermittently stopped, and a clock extracted from an optical signal received from the station-side optical communication device by the receiver And operate using a free-running clock while the receiver is in a stopped state,
An error between the clock of the station side optical communication apparatus measured by the subscriber side optical communication apparatus and the self-running clock of the subscriber side optical communication apparatus and a threshold value for determining whether or not time stamp drift has occurred Based on a sleep time calculation unit for calculating a sleep time of the transmitter and the receiver so as not to generate a time stamp drift,
A station-side optical communication apparatus comprising:
A clock extracted from an optical signal received from the station-side optical communication apparatus by the receiver, which is connected to the station-side optical communication apparatus, can be changed to a transmission / reception sleep mode in which the transmitter and the receiver are intermittently stopped. A control device in a subscriber-side optical communication device that operates using a free-running clock while the receiver is in a stopped state,
A time error calculator for measuring an error between the clock of the station side optical communication device and the self-running clock of the subscriber side optical communication device;
With
Based on a threshold for determining whether or not time stamp drift has occurred and the error, the transmitter and the receiver sleep time calculated so as not to generate time stamp drift are used as sleep times in the transmission / reception sleep mode, A control device characterized by that.
A control device in the station side optical communication device connected to the subscriber side optical communication device,
The subscriber-side optical communication device is capable of transition to a transmission / reception sleep mode in which a transmitter and a receiver are intermittently stopped, and a clock extracted from an optical signal received from the station-side optical communication device by the receiver And operate using a free-running clock while the receiver is in a stopped state,
An error between the clock of the station side optical communication apparatus measured by the subscriber side optical communication apparatus and the self-running clock of the subscriber side optical communication apparatus and a threshold value for determining whether or not time stamp drift has occurred Based on a sleep time calculation unit for calculating a sleep time of the transmitter and the receiver so that a time stamp drift does not occur,
A control device comprising:
Transition to the station side optical communication device and transmission / reception sleep mode in which the transmitter and the receiver are intermittently stopped is possible, and a clock extracted from the optical signal received from the station side optical communication device by the receiver is used. A power-saving control method in a communication system comprising: a subscriber-side optical communication device that operates using a self-running clock while the receiver is in a stopped state,
A time error calculation step of measuring an error between the clock of the station side optical communication device and the self-running clock of the subscriber side optical communication device;
A sleep time calculating step for calculating a sleep time of the transmitter and the receiver so as not to generate a time stamp drift, based on a threshold for determining whether a time stamp drift occurs and the error; and
The subscriber-side optical communication device uses the sleep time calculated by the sleep time calculation unit as the sleep time in the transmission / reception sleep mode, and
A power saving control method comprising: