WO2013161110A1

WO2013161110A1 - Communication system, communication device and time information correction method

Info

Publication number: WO2013161110A1
Application number: PCT/JP2012/079383
Authority: WO
Inventors: 平野　幸男; 雄末廣; 健一名倉
Original assignee: 三菱電機株式会社
Priority date: 2012-04-27
Filing date: 2012-11-13
Publication date: 2013-10-31

Abstract

The objective of the present invention is to achieve a communication system, communication device, and time information correction method which, in a communication system in which a plurality of communication devices are connected, is capable of operating using more accurate time information even in a case in which a cyclic signal to be a reference from the outside is not received. The communication system as laid out in the invention is a communication system in which an Optical Line Terminal (1) and a plurality of Optical Network Units (2) are connected via an optical transport line. The Optical Line Terminal (1) is provided with control signal transmission means (15) which generates a control signal that includes a reference time and a reference clock, and which transmits the control signal to the Optical Network Units (2). The Optical Network Units (2) are provided with clock comparison means (25) which compares an operating clock of the Optical Line Terminal (1) with an operating clock generated within the device itself and retains the comparison result, and time correction means (25) which corrects the reference time on the basis of the comparison results and an internal clock generated within the device itself.

Description

COMMUNICATION SYSTEM, COMMUNICATION DEVICE, AND TIME INFORMATION CORRECTION METHOD

The present invention relates to a communication system that operates by performing time synchronization among a plurality of communication apparatuses connected by an optical transmission line, a communication apparatus applicable to the communication system, and a time information correction method.

In a communication system in which a station side communication device and a subscriber side communication device are connected by a communication line, not only a basic service in which a subscriber connects to a network and performs time synchronization to communicate data, but also a communication line is used. It is also possible to provide other additional services from the network side to the subscriber side. As an example of this additional service, there is a delivery service with an accurate time.

PON (Passive Optical Network) system is a communication system that can realize such services. The PON system is composed of a station side communication device (Optical Line Terminal, hereinafter referred to as OLT), one or a plurality of subscriber side communication devices (Optical Network Unit, hereinafter referred to as ONU), an optical fiber, and an optical coupler. Since a plurality of ONUs can be accommodated by one OLT, it is possible to provide basic services and additional services at a low price. Here, OLT and ONU are Ethernet (registered trademark) Passive Optical Network (hereinafter, EPON) devices conforming to IEEE std 802.3.

The ONU extracts the operation clock from the optical signal transmitted from the OLT and acquires relative time information from the value of the 32-bit Timestamp area inside the GATE frame by the control signal (GATE frame) transmitted by the OLT for each ONU. To do. The OLT transmits the operation clock superimposed on the optical transmission signal, receives the REPORT frame transmitted by each ONU, and determines the propagation delay corresponding to the distance of each ONU from the value of the internal Timestamp area. It is obtained and corrected for each ONU, and the relative time is set in the Timestamp area of the GATE frame and transmitted. Thereby, OLT and ONU can make a clock frequency and relative time correspond. Also, according to IEEE std 802.3, the GATE frame and REPORT frame used for matching the relative time are transmitted and received in a relatively short time of less than 1 second. Can be corrected every moment.

Recently, in a communication system such as a PON system, a sleep function for temporarily powering down an ONU optical transceiver has been studied in order to meet the demand for power saving. In the conventional communication system, when the sleep function is used, the ONU periodically stops the optical transmitter / receiver, so that the transmission optical signal from the OLT cannot be received. Since the ONU extracts the clock from the transmission optical signal from the OLT, the clock cannot be regenerated while the optical transceiver is stopped. Therefore, during this period, the own apparatus operates using a clock (self-running clock) managed by the ONU itself that is not synchronized with the OLT operation clock. In general, it is difficult to provide an ONU with an accurate self-running clock from the viewpoint of cost, etc., and an ONU that is operated with a self-running clock must have an accurate time for a terminal connected to the own device. Cannot output. For example, when the self-running clock of the ONU is deviated from the actual time by 50 ppm, when the optical transceiver is stopped for 0.8 seconds, it is shifted by 40 microseconds during the stop. For example, the time accuracy (less than a few microseconds) required in the TD-SCDMA (Time Division Synchronous Code Division Multiple Access) communication method will be exceeded.

In addition, when a failure occurs in the transmission path between the OLT and the ONU, the ONU cannot receive the transmission optical signal from the OLT, and therefore cannot regenerate the clock. Cannot output.

The present invention is for solving the above-described problems, and is a case where a subscriber-side communication device does not receive an optical signal from a station-side communication device in a communication system in which a plurality of communication devices are connected. However, it is an object to obtain a communication system, a communication apparatus, and a time information correction method that can operate using more accurate time information.

A communication system according to the present invention is a communication system in which a station-side communication device and a plurality of subscriber-side communication devices are connected via an optical transmission line, and the station-side communication device includes a control including a reference time and a reference clock. A control signal transmitting means for generating a signal and transmitting a control signal to the subscriber-side communication device; the subscriber-side communication device receives the control signal transmitted from the station-side communication device; Extraction means for extracting the time and reference clock, comparison between the reference clock acquired by the extraction means and the internal clock generated in its own device, and comparison by the clock comparison means for holding the comparison result, and comparison by the clock comparison means Time correction means for correcting the reference time based on the result and an internal clock generated in the own apparatus.

The communication system according to the present invention is a communication system in which a station-side communication device connected to a reference time generator and a plurality of subscriber-side communication devices are connected via an optical transmission line, the station-side communication device Is generated in the device itself with reference time input means for receiving the reference time including the time information and the periodic signal generated by the reference time generator, and the periodic signal extracted from the control signal received by the reference time input means. A clock comparison unit that compares the operation clock and holds the comparison result, and a time correction unit that corrects the reference time based on the comparison result by the clock comparison unit and the operation clock generated in the device. Prepare.

The communication device according to the present invention is a communication device applicable to a communication system in which a plurality of communication devices are connected via an optical transmission line, and receives time information and a periodic signal from a control signal input from the outside. Extraction means to extract, the periodic signal extracted by the extraction means, and the operation clock generated in its own device is compared, the clock comparison means for holding the comparison result, the comparison result by the clock comparison means, Time correction means for correcting the time information extracted by the extraction means based on the operation clock generated in the own apparatus.

The time information correction method according to the present invention is a time information correction method applicable to a communication system in which a station-side communication device and a subscriber-side communication device are connected via an optical transmission line. Generates a control signal including the reference time and the operation clock of its own device, and transmits the control signal to the subscriber side communication device, and the subscriber side communication device is transmitted in the control signal transmission step. A control signal receiving step for receiving a control signal, an extraction step for extracting a reference time and an operation clock of the station side communication device from the control signal received in the control signal receiving step, and a subscriber side communication device are extracted in the extraction step. A clock comparison step for comparing the operation clock of the station-side communication device and the operation clock generated in its own device and holding the comparison result; Comprising comparison results stored in compare step, based on the operation clock generated by the subscriber-side communication device, and the time information correction step of correcting the reference time extracted in the extraction step.

Further, the time information correction method according to the present invention is a time information correction method applicable to a communication system in which a station side communication device connected to a reference time generation device and a subscriber side communication device are connected via an optical transmission line. The station side communication device receives the reference time including the time information generated by the reference time generator and the periodic signal, the reference time receiving step, and the periodic signal received in the reference time receiving step A time for correcting the reference time based on the clock comparison step for comparing with the operation clock generated in step (1) and holding the comparison result, the comparison result in the clock comparison step, and the operation clock generated in the own device. A correction step, and a reference time transmission step of transmitting the reference time corrected in the time correction step to the subscriber-side communication device.

According to the present invention, in a communication system in which a plurality of communication devices are connected, even when an optical signal including time information or the like is not received from another device, the operation is performed using more accurate time information. Can do.

FIG. 1 is a block diagram showing a configuration of the communication system shown in the first embodiment. FIG. 2 is a diagram illustrating an example of a reference time used in the communication system according to the first embodiment. FIG. 3 is a sequence diagram showing an RTT calculation operation in the communication system shown in the first embodiment. FIG. 4 is a block diagram showing normal operation in the communication system shown in the first embodiment. FIG. 5 is a sequence diagram showing a time synchronization operation in the communication system shown in the first embodiment. FIG. 6 is a graph showing an nth-order curve of correction values in the communication system shown in the first embodiment. FIG. 7 is a diagram showing a frame configuration of a control signal in the communication system shown in the first embodiment. FIG. 8 is a block diagram showing a configuration of the communication system shown in the second embodiment.

Hereinafter, embodiments of a communication system, a communication device, and a time information correction method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
The communication system according to Embodiment 1 of the present invention will be described using a PON (Passive Optical Network) system as an example. FIG. 1 shows a configuration diagram of a communication system according to Embodiment 1 of the present invention. The scope of application of the present invention is not limited to the PON system, and any communication system that performs operations such as communication by performing time synchronization may be used. In FIG. 1, a station side communication device (hereinafter referred to as OLT) 1 is connected to a plurality of subscriber side communication devices (hereinafter referred to as ONUs) 2 via optical fibers and an optical distributor 6.

The OLT 1 is connected to the outside via the reference time input port 3 and the line port 4, and the ONU 2 is connected to the outside via the line port 4 and the synchronization time output port 5. The OLT 1 is connected to a reference time generator (not shown in FIG. 1) via a reference time input port 3, and is also connected to an upper network. The ONU 2 is connected to a terminal or the like not shown in FIG. The optical distributor 6 is a passive element that branches an optical fiber connecting the OLT 1 and the ONU 2 into a predetermined number (for example, 32 branches).

The OLT 1 includes a reference time input unit 11, a line time generation unit 12, a delay adjustment unit 13, a time distribution unit 14, and a line IF unit 15. The reference time input unit 11 receives a reference time signal from an external reference time generator. The line time generation unit 12 has a 32-bit free-running counter and generates time information to be transmitted to the ONU 2. The delay adjusting unit 13 calculates a delay time for each ONU 2 based on the control signal from the ONU 2. The time distribution unit 14 corrects the time information transmitted to the ONU 2 based on the time information generated by the line time generation unit 12 and the delay time calculated by the delay adjustment unit 13. The OLT line IF unit 15 includes an optical transceiver for transmitting and receiving optical signals to and from the ONU 2.

The ONU 2 includes a line IF unit 21, a line time synchronization unit 22, a free-running time generation unit 23, a temperature measurement unit 24, a time correction unit 25, a reference time extraction unit 26, a time selection unit 27, and a time output unit 28. . The line IF unit 21 is connected to the OLT 1 via the line port 4 and includes an optical transceiver that transmits and receives an optical signal to and from the OLT 1. The line time synchronization unit 22 includes a free-running counter and synchronizes with the operation clock of the OLT 1 based on the optical signal from the OLT 1. The free-running time generation unit 23 includes a free-running counter and operates in synchronization with an oscillator clock (internal clock) in the ONU 2. The temperature measurement unit 24 measures the temperature in the ONU 2 (particularly, the temperature near the oscillator). The time correction unit 25 compares a counter that operates in synchronization with the internal clock in the ONU 2 with a counter that operates in synchronization with the periodic signal generated in the OLT 1 (operation clock of the OLT 1). A hit difference is calculated, and a correction value to be described later is created based on the comparison result. The reference time extraction unit 26 extracts the reference time included in the synchronization signal (Timesync frame) transmitted from the OLT 1. The time selection unit 27 selects one of the time information input from the line time synchronization unit 22 and the time correction unit 25 and outputs it to the time output unit 28. The time output unit 28 outputs time information to a terminal connected to the ONU 2. Here, all ONUs 2 in the communication system will be described as having the same configuration, but the present invention is not limited to this, and at least a part of the ONUs only needs to have the time correction function according to the present invention.

An example of the reference time input to the OLT 1 is shown in FIG. Here, the reference time is assumed to be composed of two signals of a one-second pulse and time (minute) information. For example, ZDA message example of NMEA message used in National Marine Electronics Association (NMEA) -0183, which is used in GPS (Global Positioning System) receiver as standard. Is an ASCII code, and consists of header, UTC (Universal Coordinated Time), UTC hour, minute, second, date, correction time to local time, checksum and their delimiters. The rise of the 1-second pulse indicates the time expressed by the ZDA message. Here, the reference time shown in FIG. 2 is used. However, the present invention is not limited to this. For example, only one of time information and a periodic signal such as a 1-second pulse may be used.

Next, a method for calculating a transmission delay time (Round Trip Time, hereinafter referred to as RTT) between the OLT 1 and the ONU 2 will be described with reference to FIG. Here, it is assumed that the OLT 1 and each ONU 2 conform to IEEE std 802.3, and RTT measurement is performed during MPCP (Multipoint MAC Control Protocol) processing for registering the ONU 2 to which the OLT 1 is connected. The line time generation unit 12 of the OLT 1 has a free-running 32-bit counter that counts every 16 ns obtained based on the operation clock of the OLT 1, and when the OLT 1 registers the ONU 2 by MPCP processing, the control signal (Discovery The value (T0) of the free-running counter is inserted as Timestamp into the GATE frame) and transmitted to each ONU 2 via the line IF unit 15 (step S101). At this time, the line IF unit 15 transmits a signal synchronized with the operation clock of the OLT 1.

The ONU 2 that has received the Discovery GATE frame extracts the operation clock of the OLT 1 by the line IF unit 21 and passes the extracted operation clock to the line time synchronization unit 22. Further, when the line IF unit 21 receives the Discovery GATE frame, the line IF unit 21 transfers the Discovery GATE frame to the line time synchronization unit 22. The line time synchronization unit 22 has a 32-bit counter that counts every 16 ns obtained based on the extracted operation clock, and loads the value of Timestamp (T0 = T0a) included in the Discovery GATE frame into the 32-bit counter. (Step S102). After that, the ONU 2 inserts the value (T1a) of the self-running counter in its own device into the Timestamp in the REGISTER frame sent to request the OLT 1 to register its own device, and sends it via the line IF unit 22 (Step S103).

In the OLT 1, when the line IF unit 15 receives the REGISTER frame transmitted from the ONU 2, the line IF unit 15 transfers the REGISTER frame to the delay adjustment unit 13. The delay adjustment unit 13 extracts Timestamp from the REGISTER frame, calculates the RTT, and notifies the line time generation unit 12 of the calculated RTT. FIG. 3 shows the RTT calculation method when there are two ONUs. For both ONUs, the counter value (T2 or T3) when the OLT receives a REGISTER frame transmitted from the ONU 2 RTT can be calculated by subtracting the time stamp value (T1a or T1b) of the frame.

Further, by the same MPCP process, the line time generation unit 12 transmits a GATE frame (control signal used for band allocation) to the ONU 2 via the line IF unit 15. The line time synchronization unit 22 of the ONU 2 that has received the GATE frame extracts the value of Timestamp included in the GATE frame, and synchronizes the self-running counter of the own device based on the clock of the OLT 1. Also, a REPORT frame including the time information of the ONU 2 as Timestamp is transmitted to the OLT 1 via the line IF unit 21 as a response signal to the GATE frame. Both the GATE frame and the REPORT frame have a Timestamp, and the delay adjustment unit 13 can periodically measure the RTT of the ONU 2. Thereby, it is possible to follow the RTT fluctuation caused by the wander. With these processes, the relative time can be synchronized between the OLT 1 and the ONU 2 in the EPON system.

Next, the reference time output operation for a terminal connected to a normal ONU will be described with reference to FIG. 1 and FIG.
First, the reference time generator 9 generates a reference time and transmits it to the OLT 1. Here, the reference time is described as being generated outside the OLT 1. However, the present invention is not limited to this, and a configuration in which a reference time generating unit is provided inside the OLT 1 may be used. The reference time generated by the reference time generator 9 is input to the reference time input unit 11 via the reference time input port 3. When receiving the reference time, the reference time input unit 11 transmits the received reference time to the time distribution unit 14. When the time distribution unit 14 transmits the reference time in conformity with IEEE std 802.1AS, the time distribution unit 14 first converts the UTC into a PTP (Precision Time Protocol) format. Here, the PTP format is a format that expresses time in seconds (48 bits) and nanoseconds (32 bits), taking into account leap years and leap seconds, based on January 1, 1970, 0:00:00. The conversion from the UTC format to the PTP format can be expressed by the following conversion formula.
PTP.seconds = elapsed days (UTC.year-month-"1970.1.1") * 60 * 60 * 24 + leap seconds + (UTC.hour * 60 + UTC.minute) * 60 + UTC.second
PTP. Nanosecond = UTC.millisecond * 1,000,000

The time distribution unit 14 that has received the reference time from the reference time input unit 11 adds a reference time (hereinafter referred to as a corrected reference time) to which about 1/2 (downward propagation delay) of RTT input from the delay adjustment unit 13 is added. To the line IF unit 15. Further, the line time generation unit 12 transmits the value of the free-running counter to the time distribution unit 14. The time distribution unit 14 that has received the value of the free-running counter of the OLT 1 from the line time generation unit 12 inserts the corrected reference time and the value of the free-running counter into the control signal (Timesync frame) and transmits the control signal to the line IF unit 15. . The line IF unit 15 transmits a Timesync frame to the ONU 2 via the line port 4.

The line IF unit 21 of the ONU 2 that has received the Timesync frame outputs the Timesync frame to the reference time extraction unit 26. The reference time extraction unit 26 extracts the corrected reference time inserted in the Timesync frame and the free-running counter value of the OLT 1 and transmits it to the time output unit 28. Further, the line time synchronization unit 22 continuously transmits the value of the 32-bit counter relatively synchronized with the line time generation unit 12 of the OLT 1 to the time selection unit 27 using the GATE frame periodically transmitted from the OLT 1. To do. In normal times, the time selection unit 27 transmits this counter value to the time output unit 28. When the value of this counter matches the counter value in the Timesync frame, the time output unit 28 synchronizes with the reference time extracted from the Timesync frame. That is, since the free-running counter of the line time synchronization unit 22 is relatively synchronized with the free-running counter of the OLT 1, the counter value of the OLT 1 in which the free-running counter of the line time synchronization unit 22 is associated with the correction reference time. Can be made to be the correction reference time. Thereafter, the 1-second pulse and time information shown in FIG. 2 are generated at the timing when nanoseconds become zero, and are output from the synchronization time output port 5 to the terminal 8.

As described above, if the ONU2 free-running counter value matches the counter value in the Timesync frame, and if it synchronizes with the reference time, the ONU2 free-running counter value makes a round, and the reference There may be a time lag. In order to prevent this, it is possible to synchronize with the reference time by looking at the coincidence with the counter value to which the offset is added in advance and synchronizing with the corrected reference time shifted by this offset. That is, a fixed value is added to the free-running counter value inserted and transmitted from the OLT 1 into the Timesync frame, and the time corresponding to this offset value is added to the corrected reference time and output to a terminal connected to the ONU 2 or the like.

The synchronization procedure to the reference time transmitted from the OLT 1 of the ONU 2 described above will be described with reference to FIG. The ONU 2 receives a GATE frame from the OLT 1 periodically or irregularly. This GATE frame includes the free-running counter value of OLT1, and substitutes the free-running counter value of OLT for the free-running counter of ONU2. Thereby, ONU2 can operate a self-running counter in the state relatively synchronized with the free-running counter of OLT1. In addition, when the free-running counter value at the time of transmission of the Timesync frame transmitted from the OLT 1 matches the free-running counter value at which the OLT 1 in the ONU 2 is synchronized, the free-running counter value at the time of transmission of the Timesync frame to the ONU 2 Synchronize with the reference time corresponding to.

Next, a method for creating a correction value for correction performed when the ONU 2 stops the line IF unit 21 for the purpose of power saving or when a failure occurs in the transmission path between the OLT 1 and the ONU 2 will be described. In the first embodiment, the internal clock in the ONU 2 and the operation clock in the OLT 1 are compared, the difference (difference per unit time) is calculated, and the correction value is calculated based on this. An error (difference) per unit time between the free-running counter synchronized with the clock of the oscillator provided in the ONU 2 and the free-running counter synchronized with the clock extracted from the optical signal received from the OLT 1 is calculated. Based on the above, the ONU 2 calculates the correction value of the clock of the oscillator and corrects the reference time using this correction value, so that it can be operated using more accurate time information, and more accurate time information can be obtained. Can be output to the terminal.

The self-running time generation unit 23 of the ONU 2 loads the Timestamp value of the GATE frame into the 32-bit counter and makes it self-run. On the other hand, the operation clock of the 32-bit counter is operated not by the clock (clock extracted from the optical signal transmitted from the OLT 1) passed from the line IF unit 21, but by the oscillator clock provided in the ONU 2 itself. The counter value obtained by operating with the clock of this oscillator is continuously transmitted to the time correction unit 25. Here, the advance of 16 ns when the 32-bit counter is operated with the clock of the oscillator included in the ONU 2 itself may be slightly different from the advance of the free-running counter of the line time synchronization unit 22 synchronized with the OLT 1 clock. The temperature measurement unit 24 measures the temperature in the ONU 2, for example, the ambient temperature of the oscillator provided in the free-running time generation unit 23, and notifies the time correction unit 25 of the measured temperature.

The time correction unit 25 obtains a difference per unit time between the counter value of the input line time synchronization unit 22 and the counter value of the free-running time generation unit 23, and holds the difference value and the temperature at that time. Here, when the reception interval of the GATE frame is short and the difference is not clearly obtained, the value is not loaded every time the GATE frame is received, but for example every 1 second (62.5 million times of 16 ns) by the oscillator. The counter value of the line time synchronization unit 22 may be loaded. Based on the difference between the temperature thus obtained and the counter value, the time correction unit 25 corrects the counter value transmitted by the self-running time generation unit 23 based on the current temperature and transmits the corrected value to the time selection unit 27. For example, as shown in FIG. 6, the difference between the ONU temperature and the counter value per unit time is plotted, an n-th order approximate curve is obtained, and the correction value can be estimated from the temperature when the correction is performed. . In addition, in order to remove wander factors such as temperature changes in the optical fiber, the temperature and difference values acquired a long time ago are discarded, and an approximate curve is obtained using only the most recent value (within a fixed time). The difference may be estimated from the current temperature.

Also, this correction value may be created for each time zone. In Fig. 6, the left side is an example of calculating the n-th order curve during the day (average from 6 o'clock to 18 o'clock), and the right side is calculated using the correction value creation procedure during night (average from 18 o'clock to 6 o'clock). This is an example of calculating an nth order curve. In this example, the influence of the wander of the transmission line during the day is greater than that at night. By using different correction values for each time zone, more accurate correction can be performed.

Next, for example, when a failure occurs in the transmission path between the OLT 1 and the ONU 2 or when the ONU 2 is in a sleep state (power saving state) in which the receiver is temporarily stopped, the reference from the OLT to the ONU 2 An operation when no time is input will be described. In this case, the ONU 2 can calculate the reference time using the self-running counter synchronized with the clock of the oscillator in the own device and the calculated correction value, and even if the reference time is not input from the OLT Good time information can be transmitted to a connected terminal or the like.

When the line IF unit 21 of the ONU 2 is stopped for the purpose of power saving or when a transmission path failure such as the optical distributor 6 or the optical fiber is detected, the detected information is notified to the time selection unit 27. When receiving this notification, the time selection unit 27 selects the counter value from the time correction unit 25 and outputs it to the time output unit 28. Since this counter value is corrected for the temperature inside the ONU 2 and corrected for the wander of the transmission line, it simulates the counter value of the line time synchronization unit 22 before a stop or failure occurs. The line IF unit 21 generates a reference time based on the counter value received from the time selection unit 27 and transmits the reference time to a terminal or the like connected to the ONU 2.

Here, control signals between the OLT 1 and the ONU 2 will be described with reference to FIG. Here, a GATE frame and a REPORT frame conforming to IEEE 802.3 are used, and a Timestamp area into which the value of the free-running counter of the transmission source is inserted is provided. Further, the Timesync frame transmitted from the OLT 1 is provided with a TODx, i region for inserting time information, and a Timestamp region including a free-running counter value of the OLT 1 corresponding to this time information.

Since the communication system according to the first embodiment is configured as described above, the time output unit 28 can generate the aforementioned 1-second pulse and time information based on the corrected counter value. Even when an outage or a transmission path failure occurs, it is possible to operate time information with high accuracy and to output more accurate time information to the terminal.

Here, the time correction when the reference time is output to the terminal connected to the ONU 2 is shown, but it can be applied if the ONU 2 operates based on the clock of the oscillator in its own device. Needless to say, the content is not limited.

Embodiment 2. FIG.
In the first embodiment, a configuration in which the time correction function is provided on the ONU side is shown. In the second embodiment, a configuration in which the time correction function is provided on the OLT side is shown. FIG. 8 shows a configuration diagram of a communication system according to the second embodiment. In FIG. 8, the same or similar components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. In FIG. 8, the free-running time generation unit 16 includes a free-running counter synchronized with the clock of the oscillator in the OLT 1, and the temperature measurement unit 17 measures the temperature in the OLT 1 (particularly, near the oscillator). The time correction unit 18 compares a periodic signal (1 second pulse) input from the outside with an operation clock in the OLT, and corrects the reference time based on the comparison result. The time selection unit 19 selects one of the reference time input from the reference time input unit 11 or the reference time input from the time correction unit 18 and outputs the selected time to the time distribution unit 14.

Hereinafter, the operation will be described with reference to FIG.
In FIG. 8, the OLT 1 receives a reference time from an external reference time generator via the reference time input port 3. The input reference time is the same as the reference time described in the first embodiment. When the reference time input unit 11 receives the reference time of FIG. Since the time selection unit 19 normally notifies the time distribution unit 14 of the time from the reference time input unit 11 as usual, the following operation is the same as that of the first embodiment, and the reference time is output from the synchronization time output port 5 of the ONU 2. Time information synchronized with the time can be output.

Here, when the free-running time generation unit 16 of the OLT 1 receives the time from the reference time input unit 11, it loads a value into the free-running counter. The count of the free-running counter is synchronized with the operation clock of OLT1. Since the frequency at which the operation clock of the OLT 1 and the time of the reference time input port 3 are not necessarily coincident with each other, there is a deviation from the time counter of the free-running time generation unit 16 every time the time is input. That is, there may be a difference between the 1-second cycle calculated based on the operation clock of the OLT 1 and the 1-second cycle of the 1-second pulse included by the reference time. The temperature measurement unit 17 of the OLT 1 measures the ambient temperature of the oscillator in the OLT 1 and passes it to the time correction unit 18. The time correction unit 18 compares the one-second pulse of the reference time input unit 11 with the operation clock calculated by the free-running time generation unit 16, obtains a difference per second, and compares this difference with the difference. Keep temperature. The time correction unit 18 corrects the time transmitted by the self-running time generation unit 16 based on the current temperature and transmits the corrected time to the time selection unit 19 based on the difference between the temperature and the time thus obtained.

When the reference time input unit 11 detects that the input time information has been interrupted, the time selection unit 19 selects the time from the time correction unit 18 and outputs it. Since this time is corrected for the temperature inside the OLT 1, it simulates the time received from the reference time input port 3 before the time input failure occurs.

According to the second embodiment, since the time selection unit 19 can generate a time corresponding to the reference time based on the corrected time, it is possible to output more accurate time information from the ONU 2 even when a time input failure occurs.

In each of the above embodiments, it goes without saying that the embodiments may be combined with each other without departing from the essence of the invention.

1 station side communication device (OLT), 2 subscriber side communication device (ONU), 3 standard time input port, 4 line port, 5 synchronous time output port, 6 optical distributor, 7 upper network device, 8 terminal, 9 standard Time generator, 11 reference time input unit, 12 line time generation unit, 13 delay adjustment unit, 14 time distribution unit, 15 line IF unit, 21 line IF unit, 22 line time synchronization unit, 23 free-running time generation unit, 24 Temperature measurement unit, 25 time correction unit, 26 reference time extraction unit, 27 time selection unit, 28 time output unit.

Claims

A communication system in which a station side communication device and a plurality of subscriber side communication devices are connected via an optical transmission line,
The station side communication device is:
A control signal transmitting means for generating a control signal including a reference time and a reference clock and transmitting the control signal to the subscriber side communication device;
The subscriber side communication device is:
Extracting means for receiving a control signal transmitted from the station side communication device, and extracting a reference time and a reference clock from the received control signal;
A clock comparison unit that compares the reference clock acquired by the extraction unit with an internal clock generated in the device and holds a comparison result;
Time correction means for correcting the reference time based on a comparison result by the clock comparison means and an internal clock generated in the device itself;
A communication system comprising:
The station-side communication device includes a delay adjustment unit that calculates a delay time for each of the plurality of subscriber-side communication devices, and adjusts a reference time for the corresponding subscriber-side communication device based on the delay time,
The control signal transmission means generates a control signal including a reference time adjusted by the delay adjustment unit, and transmits the control signal to the subscriber side communication device;
The communication system according to claim 1.
The communication system according to claim 1, wherein the reference clock is an operation clock of the station side communication device.
The subscriber-side communication device includes a condition storage unit that stores an ambient condition when the comparison is performed by the clock comparison unit,
The time correction means corrects the reference time based on the ambient conditions stored by the condition storage means and the ambient conditions when the correction is performed;
The communication system according to claim 1.
The ambient condition is an oscillator that generates an operation clock of the subscriber side communication device or a temperature around the oscillator.
The communication system according to claim 4.
The ambient condition stored by the condition storage means is a time at which an error is calculated by the clock comparison means,
The time correction means corrects the reference time based on the time stored by the condition storage means and the time when correction is performed;
The communication system according to claim 4.
The subscriber-side communication device includes a first free-running counter that is synchronized with an operation clock of the station-side communication device, and a second free-running counter that is operated in synchronization with an operation clock generated in the own device. Prepared,
The clock comparison means obtains a difference value per unit time between the first free-running counter and the second free-running counter;
The communication system according to any one of claims 1 to 6, wherein:
A communication terminal is connected to the subscriber side communication device,
The subscriber side communication device comprises time information output means for outputting the reference time corrected by the time correction means to the communication terminal;
The communication system according to any one of claims 1 to 6, wherein:
A communication system in which a station side communication device connected to a reference time generator and a plurality of subscriber side communication devices are connected via an optical transmission line,
The station side communication device includes a reference time input means for receiving a reference time including a time signal and a periodic signal generated by a reference time generator,
A clock comparison means for comparing a periodic signal extracted from the control signal received by the reference time input means with an operation clock generated in the own apparatus, and holding a comparison result;
Time correction means for correcting the reference time based on a comparison result by the clock comparison means and an operation clock generated in the device itself;
A communication system comprising:
A communication device applicable to a communication system in which a plurality of communication devices are connected via an optical transmission line,
Extraction means for extracting time information and a periodic signal from a control signal input from the outside;
A clock comparison unit that compares the periodic signal extracted by the extraction unit with an operation clock generated in the device and holds the comparison result;
Time correction means for correcting the time information extracted by the extraction means based on the comparison result by the clock comparison means and the operation clock generated in the device itself;
A communication apparatus comprising:
The extraction means extracts time information and a periodic signal from a control signal transmitted by another communication device in the communication system,
The periodic signal is an operation clock of the other communication device;
The communication device according to claim 10.
The extraction means extracts a reference time including time information and a periodic signal from a control signal received from a reference time generator,
The periodic signal is a periodic pulse generated by the reference time generator;
The communication device according to claim 10.
Comprising condition storage means for storing ambient conditions when the comparison is made by the clock comparison means;
The time correction means corrects the time information based on the ambient conditions stored by the condition storage means and the ambient conditions when the correction is performed;
The communication device according to any one of claims 10 to 12, wherein:
A time information correction method applicable to a communication system in which a station side communication device and a subscriber side communication device are connected via an optical transmission line,
A control signal transmission step in which the station side communication device generates a control signal including a reference time and an operation clock of the own device, and transmits the control signal to the subscriber side communication device;
A control signal receiving step in which the subscriber side communication device receives the control signal transmitted in the control signal transmitting step;
An extraction step of extracting a reference time and an operation clock of the station side communication device from the control signal received in the control signal reception step;
The subscriber side communication device compares the operation clock of the station side communication device extracted in the extraction step with the operation clock generated in the own device, and holds a comparison result, a clock comparison step,
A time information correction step for correcting the reference time extracted in the extraction step based on the comparison result stored in the clock comparison step and the operation clock generated in the subscriber side communication device;
A time information correction method comprising:
A time information correction method applicable to a communication system in which a station side communication device and a subscriber side communication device connected to a reference time generation device are connected via an optical transmission line,
A reference time receiving step in which the station side communication device receives a reference time including a time signal and a periodic signal generated by a reference time generator;
A clock comparison step of comparing the periodic signal received in the reference time reception step with an operation clock generated in the device, and holding a comparison result;
A time correction step of correcting the reference time based on a comparison result in the clock comparison step and an operation clock generated in the own device;
A reference time transmission step of transmitting the reference time corrected in the time correction step to the subscriber side communication device;
A time information correction method comprising: