JP2011124759A - Communication system, station-side communication device, and slave clock correction device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform time synchronization of a station-side communication device and a subscriber-side communication device by a simple method. <P>SOLUTION: The station-side communication device 1 includes: a measurement unit 11 which measures an RTT value between the own device and a subscriber-side communication device 2; a time synchronization frame generation unit 12 which generates a time synchronization frame by inserting the measured RTT value into a frame; and a time stamp insertion unit 15 which inserts the time stamp of a master clock 14 into the time synchronization frame thus generated and transmits the time stamp to the subscriber-side communication device 2. A slave clock correction device 4 includes: a time synchronization frame extraction unit 41 which extracts a time synchronization frame transmitted to the subscriber-side communication device 2; and a time stamp correction unit 42 which corrects the time stamp of a slave clock 43 based on the RTT value and the time stamp contained in the time synchronization frame thus extracted. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention includes, for example, a communication provided with a station-side communication device connected to a subscriber-side communication device, and a slave clock correction device that synchronizes the slave clock of the subscriber-side communication device with the master clock of the station-side communication device. It is about the system.

  IEEE 1588 called Precision Time Protocol was standardized in 2002 as a method for realizing highly accurate time synchronization on Ethernet (registered trademark, hereinafter omitted). If this method is used, it becomes possible to time-synchronize terminals such as sensors and actuators on the Ethernet on the order of sub-milliseconds (for example, see Non-Patent Document 1).

  In IEEE 1588 disclosed in Non-Patent Document 1, time synchronization is performed by exchanging messages between a master clock and a slave clock arranged on a network. Message exchange for synchronization is roughly divided into two phases: OC (Offset Correction) and DM (Delay Measurement).

  In OC, the master clock periodically sends a Sync message to the slave clock. In the Sync message, an estimated time stamp when the message is sent is stored. Next, the master clock sends a Follow-up message storing the exact time (TM1) at which the Sync message was sent to the slave clock.

  Next, the slave clock calculates an offset value from the reception time TS1 of the Sync message and the received TM1. If the delay is negligible, the master and slave clocks are time synchronized at this point.

  In DM, the slave clock sends a delay_request message to the master clock. At this time, the slave clock obtains an accurate message transmission time TS3. The master clock stores the message reception time TM3 in the delay_response message and sends it back to the slave clock. The slave clock calculates a delay amount between the master clock and the slave clock from these values, and uses this for correction to realize time synchronization.

  In this method, when a time stamp is inserted into a frame between a master clock and a slave clock, the delay amount after insertion is required to be a fixed delay amount. Therefore, a mounting position of a TSU (Time Stamp Unit) for inserting a time stamp into a message is inserted between a MAC (Media Access Controller) and a PHY (Physical Layer).

  When these functions are realized via the Ethernet network, a buffer or the like built in the switch causes the delay amount to fluctuate. Conventionally, such a case can be solved by incorporating a boundary clock function of IEEE 1588 that varies the delay amount in the switch. A switch such as a buffer whose delay amount can be variable has a slave function in one of the switches and a master function in the other. The slave port of this switch synchronizes the boundary clock by exchanging messages with the master clock, and the master port of the switch uses the boundary clock to realize time synchronization of the slave clocks under it.

JP 2009-005070 A

IEEE (Institute of Electrical and Electronics Engineers) 802.3ah-2004 (427, 428 pages)

  However, a GE-PON (Gigabit Ethernet-Passive Optical Network) system that performs communication by connecting the IEEE 1588 to an OLT (Optical Line Terminal: station side communication device) and an ONU (Optical Network Unit: subscriber side communication device). When this is applied, the delay varies due to the influence of the OLT and ONU frame storage buffers, so it is necessary to install a boundary clock function in each network device. Such a configuration is added to the existing GE-PON system. There is a problem that it is difficult to install.

  The present invention has been made to solve the above-described problems. Time synchronization is performed between a station side communication device and a subscriber side communication device by a simpler method than applying IEEE 1588 to a GE-PON system. An object of the present invention is to provide a communication system, a station-side communication device, and a slave clock correction device that can be realized.

  A communication system according to the present invention includes a station-side communication device connected to a subscriber-side communication device, and a slave clock correction device that synchronizes the slave clock of the subscriber-side communication device with the master clock of the station-side communication device. The station side communication device measures the RTT (Round Trip Time) value between itself and the subscriber side communication device, and inserts the RTT value measured by the measurement unit into the frame to generate the time synchronization frame. A time synchronization frame generation unit to be generated; and a time stamp insertion unit that inserts a time stamp of the master clock into the time synchronization frame generated by the time synchronization frame generation unit and transmits the time stamp to the subscriber side communication device. The slave clock correction device extracts the time synchronization frame extracted from the time stamp insertion unit to the time synchronization frame transmitted to the subscriber side communication device. If, on the basis of the RTT values and the time stamp contained in the time synchronization frame extracted by the frame extraction unit for time synchronization, in which a time stamp correction unit for correcting the time stamp of the slave clock.

  According to the present invention, since it is configured as described above, instead of mounting a boundary clock on each network device, an arbitrary counter and the RTT value of each subscriber-side communication device defined by IEEE 802.3ah are used. Thus, a function equivalent to the case where IEEE 1588 is applied can be realized by a simple method.

It is a figure which shows the structure of the communication system which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of OLT which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the slave clock correction apparatus which concerns on Embodiment 1 of this invention. It is a flowchart which shows the time synchronous process by OLT which concerns on Embodiment 1 of this invention. It is a flowchart which shows the time synchronous process by the slave clock correction apparatus which concerns on Embodiment 1 of this invention. It is a figure which shows the structure of the communication system which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of OLT which concerns on Embodiment 2 of this invention. It is a figure which shows the structure of the slave clock correction apparatus which concerns on Embodiment 2 of this invention. It is a flowchart which shows the time synchronous process by OLT which concerns on Embodiment 2 of this invention. It is a flowchart which shows the time synchronous process by the slave clock correction apparatus which concerns on Embodiment 2 of this invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Embodiment 1 FIG.
1 is a diagram showing a configuration of a communication system according to Embodiment 1 of the present invention.
As shown in FIG. 1, the communication system includes an OLT (station side communication device) 1 connected to a carrier side parent terminal device and an ONU (subscriber side communication device) connected to each subscriber side child terminal device. 2, an optical fiber that connects the OLT 1 and the plurality of ONUs 2, and a slave clock correction device 4 that synchronizes the slave clock of the ONU 2 with the master clock of the OLT 1.

FIG. 2 is a diagram showing a configuration of the OLT 1 according to the first embodiment of the present invention.
As shown in FIG. 2, the OLT 1 includes an MPCP (Multi-Point Control Protocol) processing unit (measurement unit) 11, a time synchronization frame generation unit 12, a buffer 13, an OLT counter 14, and a time stamp insertion unit 15. The

  The MPCP processing unit 11 recognizes a plurality of ONUs 2 connected to the communication system, and measures RTT (Round Trip Time: round trip delay time from OLT 1 to ONU 2) value necessary for communication between each ONU 2 and OLT 1 Is to do. The RTT information indicating the RTT value measured by the MPCP processing unit 11 is transmitted to the time synchronization frame generation unit 12.

  The time synchronization frame generation unit 12 generates a predetermined time synchronization frame corresponding to each ONU 2 based on the RTT information transmitted from the MPCP processing unit 11. The time synchronization frame generation unit 12 generates a time synchronization frame by storing the RTT information for each ONU 2 acquired from the MPCP processing unit 11 in the frame. The time synchronization frame generated by the time synchronization frame generation unit 12 is transmitted to the buffer 13.

  The buffer 13 temporarily stores a frame including a time synchronization frame and a user frame transmitted from the time synchronization frame generation unit 12. The time synchronization frame stored in the buffer 13 is extracted by the time stamp insertion unit 15.

  The OLT counter 14 serves as a master clock for the OLT 1. A time stamp, which is time information indicated by the OLT counter 14, is transmitted to the time stamp insertion unit 15.

  The time stamp insertion unit 15 inserts the time stamp transmitted from the OLT counter 14 into the time synchronization frame extracted from the buffer 13. The time synchronization frame in which the time stamp is inserted by the time stamp insertion unit 15 is transmitted and stored in the buffer of the ONU 2. The time stamp insertion unit 15 is arranged closer to the ONU 2 than the buffer 13 and is configured to have a fixed delay until the time synchronization frame transmitted from the time stamp insertion unit 15 reaches the ONU 2 buffer. .

FIG. 3 is a diagram showing the configuration of the slave clock correction apparatus 4 according to the first embodiment of the present invention.
As shown in FIG. 3, the slave clock correction device 4 includes a time synchronization frame extraction unit 41, a time stamp correction unit 42, and an ONU counter 43.

  The time synchronization frame extraction unit 41 extracts a time synchronization frame from the frames stored in the buffer of the ONU 2. The time synchronization frame extracted by the time synchronization frame extraction unit 41 is transmitted to the time stamp correction unit 42, and frames including other user frames are transmitted to the child terminal device.

  The time stamp correction unit 42 calculates a time stamp obtained by correcting the time stamp of the ONU counter 43 based on the RTT information and the time stamp included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41. It is. The time stamp corrected by the time stamp correction unit 42 is transmitted to the ONU counter 43.

  The ONU counter 43 serves as a slave clock for the ONU 2 corresponding to the OLT 1. The ONU counter 43 changes its own time stamp to the time stamp transmitted from the time stamp correction unit 42 and performs time synchronization with the OLT counter 14 which is the master clock of the OLT 1. The time stamp by the ONU counter 43 is output to the corresponding ONU 2.

Next, time synchronization processing of the communication system configured as described above will be described. FIG. 4 is a flowchart showing time synchronization processing by the OLT 1 according to the first embodiment of the present invention.
FIG. 5 is a flowchart showing time synchronization processing by the slave clock correction apparatus 4 according to Embodiment 1 of the present invention.
In the time synchronization processing by the OLT 1, as shown in FIG. 4, first, the MPCP processing unit 11 measures the RTT value (step ST41). That is, the MPCP processing unit 11 recognizes a plurality of ONUs 2 connected to the communication system, and measures an RTT value that is a round trip delay time between each ONU 2 and the OLT 1. The RTT information indicating the RTT value for each ONU 2 measured by the MPCP processing unit 11 is transmitted to the time synchronization frame generation unit 12.

  Next, the time synchronization frame generator 12 generates a time synchronization frame (step ST42). In other words, the time synchronization frame generation unit 12 generates the time synchronization frame corresponding to each ONU 2 by storing the RTT information for each ONU 2 transmitted from the MPCP processing unit 11 in the frame. The time synchronization frame generated by the time synchronization frame generator 12 is stored and held in the buffer 13.

  Next, the time stamp insertion unit 15 inserts a time stamp (step ST43). That is, the time stamp insertion unit 15 inserts the time stamp transmitted from the OLT counter 14 into the time synchronization frame extracted from the buffer 13. The time synchronization frame in which the time stamp is inserted by the time stamp insertion unit 15 is transmitted to the buffer of the corresponding ONU 2.

  Next, in the time synchronization processing by the slave clock correction device 4, as shown in FIG. 5, the time synchronization frame extraction unit 41 first extracts a time synchronization frame (step ST51). That is, the time synchronization frame extraction unit 41 extracts a time synchronization frame from the frames stored in the ONU 2 buffer. The time synchronization frame extracted by the time synchronization frame extraction unit 41 is transmitted to the time stamp correction unit 42.

  Next, the time stamp correction unit 42 corrects the time stamp (step ST52). That is, the time stamp correction unit 42 corrects the time stamp of the ONU counter 43 based on the RTT information and the time stamp included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41.

Here, when the RTT value is RTT, the time stamp is TS, and the delay amount from the ONU 2 to the slave clock correction device 4 is α, the corrected time stamp TS_eff is calculated by TS_eff = TS + (RTT / 2) + α. Is done.
The time stamp corrected by the time stamp correction unit 42 is transmitted to the ONU counter 43, and the ONU counter 43 changes its own time stamp to the corrected time stamp.
As a result, time synchronization between the ONU counter 43 that is the slave clock of the ONU 2 and the OLT counter 14 that is the master clock of the OLT 1 can be performed.

  Note that the above time synchronization processing starts communication in order to prevent the user data from being buffered in the downstream buffer of the ONU 2 by the communication system and the α value that is the delay amount from the ONU 2 to the slave clock correction device 4 from fluctuating. Do before. Although the time synchronization frame is periodically transmitted from the OLT 1 even after the start of communication, the slave clock correction device 4 provides a constant threshold value for the fluctuation of the α value and detects fluctuations greater than the threshold value. Do not perform time synchronization processing.

  As described above, according to the first embodiment, the OLT counter 14 and the ONU counter 43 are provided in place of the boundary clock, and the master clock and the slave clock are obtained by using the RTT value for each ONU 2 in the OLT 1. Therefore, the time synchronization between the OLT 1 and the ONU 2 can be performed with a simple configuration.

Embodiment 2. FIG.
FIG. 6 is a diagram showing the configuration of a communication system according to Embodiment 2 of the present invention.
As shown in FIG. 6, in the communication system, the first and second OLTs 1a and 1b are connected to the parent terminal device, and the first and second ONUs 2a and 2b are connected to each child terminal device via the slave clock correction device 4, so It is structured in structure.

FIG. 7 is a diagram showing the configuration of the OLT 1 (first OLT 1a) according to Embodiment 2 of the present invention.
The OLT 1 according to the second embodiment shown in FIG. 7 adds a correction frame extraction unit 16 and a second time stamp correction unit (master time stamp correction unit) 17 to the configuration of the OLT 1 according to the first embodiment shown in FIG. It is a thing. Other configurations are the same, and the same reference numerals are given and the description thereof is omitted. The second OLT 1b is configured similarly to the first OLT 1a.

  The correction frame extraction unit 16 extracts a correction frame including a master clock correction value for correcting the master clock from the frames transmitted from the corresponding first ONU 2a. The correction frame extracted by the correction frame extraction unit 16 is transmitted to the second time stamp correction unit 17.

  The second time stamp correction unit 17 corrects the time stamp of the OLT counter 14 based on the master clock correction value included in the correction frame transmitted from the correction frame extraction unit 16. The time stamp corrected by the second time stamp correction unit 17 is transmitted to the OLT counter 14. The second time stamp correction unit 17 is set to OFF when the own device is on the master side.

Further, the OLT counter 14 changes its own time stamp to the time stamp transmitted from the second time stamp correction unit 17. When the second time stamp correction unit 17 is OFF, the OLT counter 14 does not change the time stamp.
Further, the time stamp insertion unit 15 inserts the time stamp transmitted from the OLT counter 14 into the time synchronization frame extracted from the buffer 13, and further determines whether the own device is the first OLT 1a or the second OLT 1b. OLT information to be displayed and priority information indicating whether or not the own device is the master side are added.

FIG. 8 is a diagram showing the configuration of the slave clock correction apparatus 4 according to the second embodiment of the present invention.
The slave clock correction device 4 according to the second embodiment shown in FIG. 8 deletes the time stamp correction unit 42 and the ONU counter 43 from the configuration of the slave clock correction device 4 in the first embodiment shown in FIG. Time stamp correction unit (first slave time stamp correction unit) 44, fourth time stamp correction unit (second slave time stamp correction unit) 45, first ONU counter 46, second ONU counter 47, priority extraction unit (selection) Section) 48, a slave clock selector (selection section) 49, an offset calculation section 50, and an offset notification section 51 are added. Other configurations are the same, and the same reference numerals are given and the description thereof is omitted.

  Here, the time synchronization frame extracting unit 41 extracts the time synchronization frame from the frames stored in the buffers of the first and second ONUs 2a and 2b, and uses the time synchronization frame as the third and fourth time stamps. It transmits to the correction | amendment parts 44 and 45 and the priority extraction part 48. FIG.

  When the third time stamp correction unit 44 determines from the OLT information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41 that the time synchronization frame is transmitted from the first OLT 1a. In this case, the time stamp of the first ONU counter 46 is corrected based on the RTT information and the time stamp included in the time synchronization frame. The time stamp corrected by the third time stamp correction unit 44 is transmitted to the first ONU counter 46.

  When the fourth time stamp correction unit 45 determines from the OLT information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41 that the time synchronization frame is transmitted from the second OLT 1b. In this case, the time stamp of the second ONU counter 47 is corrected based on the RTT information and the time stamp included in the time synchronization frame. The time stamp corrected by the fourth time stamp correction unit 45 is transmitted to the second ONU counter 47.

  The first ONU counter 46 serves as a slave clock for the first ONU 2a corresponding to the first OLT 1a. The first ONU counter 46 changes its own time stamp to the time stamp transmitted from the third time stamp correction unit 44 and performs time synchronization with the OLT counter 14 which is the master clock of the first OLT 1a. The time stamp by the first ONU counter 46 is transmitted to the slave clock selector 49 and the offset calculation unit 50.

  The second ONU counter 47 serves as a slave clock for the second ONU 2b corresponding to the second OLT 1b. The second ONU counter 47 changes its own time stamp to the time stamp transmitted from the fourth time stamp correction unit 45 and performs time synchronization with the OLT counter 14 which is the master clock of the second OLT 1b. The time stamp by the second ONU counter 47 is transmitted to the slave clock selector 49 and the offset calculation unit 50.

  The priority extraction unit 48 extracts the priority information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41, and the master side of the first ONU counter 46 and the second ONU counter 47 The ONU counter corresponding to the OLT is selected. Selection information indicating the first ONU counter 46 or the second ONU counter 47 selected by the priority extraction unit 48 is transmitted to the slave clock selector 49.

  The slave clock selector 49 selects the first ONU 2a corresponding to the time stamp of the ONU counter selected from the first ONU counter 46 or the second ONU counter 47 based on the selection information transmitted from the priority extraction unit 48. , 2b.

The offset calculation unit 50 calculates an offset value (master clock correction value) between the time stamp transmitted from the first ONU counter 46 and the time stamp transmitted from the second ONU counter 47. Master clock correction information indicating the master clock correction value calculated by the offset calculation unit 50 is transmitted to the offset notification unit 51.
The offset notification unit 51 stores the master clock correction information transmitted from the offset calculation unit 50 in a correction frame, and transmits it to the first and second OLTs 1a and 1b via the corresponding first and second ONUs 2a and 2b.

Next, time synchronization processing of the communication system configured as described above will be described. FIG. 9 is a flowchart showing time synchronization processing by the OLT 1 (first OLT 1a) according to the second embodiment of the present invention. FIG. 10 is a flowchart showing time synchronization processing by the slave clock correction apparatus 4 according to Embodiment 2 of the present invention.
In the time synchronization processing by the communication system according to the second embodiment shown in FIGS. 9 and 10, the description of the same processing as the time synchronization processing by the communication system according to the first embodiment shown in FIGS.

  In the time synchronization processing by the first OLT 1a, as shown in FIG. 9, first, the MPCP processing unit 11 measures the RTT value (step ST91). Next, the time synchronization frame generator 12 generates a time synchronization frame (step ST92).

  Next, the correction frame extraction unit 16 extracts a correction frame (step ST93). That is, the correction frame extraction unit 16 extracts a correction frame from the frame received from the corresponding first ONU 2a. The correction frame extracted by the correction frame extraction unit 16 is transmitted to the second time stamp correction unit 17.

Next, the second time stamp correction unit 17 determines whether the own device is the OLT on the master side (step ST94).
In step ST94, if the second time stamp correction unit 17 determines that the own time unit is not the OLT on the master side, the second time stamp correction unit 17 then corrects the time stamp (step ST95). That is, the second time stamp correction unit 17 corrects the time stamp of the OLT counter 14 based on the master clock correction value included in the correction frame transmitted from the correction frame extraction unit 16. The time stamp corrected by the second time stamp correction unit 17 is transmitted to the OLT counter 14, and the OLT counter 14 changes its own time stamp to the corrected time stamp.

  On the other hand, when the second time stamp correction unit 17 determines in step ST94 that the self-timer is the OLT on the master side, the process of step ST95 is skipped. Thereafter, the sequence proceeds to step ST96.

  Next, the time stamp insertion unit 15 inserts a time stamp (step ST96). The time synchronization frame in which the time stamp is inserted by the time stamp insertion unit 15 is transmitted and stored in the buffer of the corresponding first ONU 2a.

  In addition, although the time synchronization process by 1st OLT1a was demonstrated above, it is the same also about the time synchronization process by 2nd OLT1b, The description is abbreviate | omitted.

  Next, in the time synchronization processing by the slave clock correction device 4, as shown in FIG. 10, first, the time synchronization frame extraction unit 41 extracts a time synchronization frame (step ST101). That is, the time synchronization frame extraction unit 41 extracts a time synchronization frame from the frames stored in the buffers of the first and second ONUs 2a and 2b. The time synchronization frame extracted by the time synchronization frame extraction unit 41 is transmitted to the third and fourth time stamp correction units 44 and 45 and the priority extraction unit 48.

  Next, the third time stamp correction unit 44 or the fourth time stamp correction unit 45 corrects the time stamp (step ST102). That is, when the third time stamp correction unit 44 determines from the OLT information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41 that the time synchronization frame is from the first OLT 1a. The time stamp of the first ONU counter 46 is corrected based on the RTT information and the time stamp included in the time synchronization frame. The time stamp corrected by the third time stamp correction unit 44 is transmitted to the first ONU counter 46, and the first ONU counter 46 changes its own time stamp to the corrected time stamp.

  Similarly, the fourth time stamp correction unit 45 determines that the time synchronization frame is from the second OLT 1b from the OLT information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41. In this case, the time stamp of the second ONU counter 47 is corrected based on the RTT information and the time stamp included in the time synchronization frame. The time stamp corrected by the fourth time stamp correction unit 45 is transmitted to the second ONU counter 47, and the second ONU counter 47 changes its own time stamp to the corrected time stamp.

  Next, the priority extraction unit 48 selects a time stamp (step ST103). That is, the priority extraction unit 48 extracts priority information included in the time synchronization frame transmitted from the time synchronization frame extraction unit 41, and selects the master information from the first ONU counter 46 and the second ONU counter 47. The ONU counter corresponding to the OLT on the side is selected. The selection information indicating the first ONU counter 46 or the second ONU counter 47 selected by the priority extraction unit 48 is transmitted to the slave clock selector 49, and the slave clock selector 49 displays the time stamp of the selected ONU counter. Output to the corresponding first and second ONUs 2a and 2b.

  On the other hand, the offset calculation unit 50 calculates a master clock correction value (step ST104). That is, the offset calculation unit 50 calculates an offset value (master clock correction value) between the time stamp transmitted from the first ONU counter 46 and the time stamp transmitted from the second ONU counter 47. Master clock correction information indicating the master clock correction value calculated by the offset calculation unit 50 is transmitted to the offset notification unit 51.

  Next, the offset notification unit 51 notifies the master clock correction value (step ST105). That is, the offset notification unit 51 stores the master clock correction information transmitted from the offset calculation unit 50 in the correction frame, and transmits it to the first and second OLTs 1a and 1b via the corresponding first and second ONUs 2a and 2b.

  As a result, time synchronization between the first and second ONU counters 46 and 47 that are the slave clocks of the first and second ONUs 2a and 2b and the OLT counter 14 that is the master clock of the first and second OLTs 1a and 1b can be performed.

  Further, since the master clock correction value is periodically collected from the slave clock correction device 4 to maintain synchronization and is collected from the plurality of slave clock correction devices 4, even when a transmission line abnormality occurs in one system The other system can maintain synchronization.

  When the slave clock correction device 4 cannot extract the time synchronization frame from the OLT 1 that is the master clock for a certain period of time, the slave clock selector 49 switches the clock by the slave clock selector 49 and stops sending the correction frame.

  As described above, according to the second embodiment of the present invention, the slave clocks of the first and second ONUs 2a and 2b corresponding to the time synchronization frames of the first and second OLTs 1a and 1b can be used in the communication system having the duplex structure. Since the time synchronization is performed and the offset values of the time stamps of the slave clocks of the first and second ONUs 2a and 2b are calculated to correct the master clocks of the first and second OLTs 1a and 1b, the first configuration is simplified. , 2OLT 1a, 1b and the first and second ONUs 2a, 2b can be synchronized in time.

  1 OLT (station side communication device), 1a, 1b 1st, 2nd OLT, 2 ONU (subscriber side communication device), 2a, 2b 1st, 2nd ONU, 4 slave clock correction device, 11 MPCP processing unit (measurement unit), 12 time synchronization frame generation unit, 13 buffer, 14 OLT counter, 15 time stamp insertion unit, 16 correction frame extraction unit, 17 second time stamp correction unit (master time stamp correction unit), 41 time synchronization frame extraction unit 42 Time stamp correction unit, 43 ONU counter, 44, 45 Third and fourth time stamp correction unit (first and second slave time stamp correction unit), 46, 47 First and second ONU counter, 48 Priority extraction unit (Selection unit), 49 slave clock selector (selection unit), 50 offset calculation unit, 51 offset Notification unit.

Claims (8)

In a communication system comprising a station-side communication device connected to a subscriber-side communication device, and a slave clock correction device that time-synchronizes the slave clock of the subscriber-side communication device with the master clock of the station-side communication device,
The station side communication device is:
A measuring unit for measuring an RTT (Round Trip Time) value between the own device and the subscriber side communication device;
A time synchronization frame generation unit for generating a time synchronization frame by inserting an RTT value measured by the measurement unit into a frame;
A time stamp insertion unit that inserts a time stamp of the master clock into the time synchronization frame generated by the time synchronization frame generation unit and transmits the time stamp to the subscriber side communication device;
The slave clock correction device includes:
A time synchronization frame extraction unit for extracting a time synchronization frame transmitted from the time stamp insertion unit to the subscriber side communication device;
And a time stamp correction unit for correcting a time stamp of the slave clock based on an RTT value and a time stamp included in the time synchronization frame extracted by the time synchronization frame extraction unit. system. When the RTT value is RTT, the time stamp is TS, and the delay amount from the subscriber side communication device to the own device is α, the time stamp correction unit is TS + (RTT / 2) + α 2. The communication system according to claim 1, wherein the value calculated by the step is used as a time stamp of the slave clock. The master side corresponding to the slave clocks of the master side and slave side station side communication devices connected to the subscriber side communication device and the subscriber side communication devices connected to the master side and slave side station side communication devices And in a communication system comprising a slave clock correction device that synchronizes time with the master clock of the slave side station side communication device,
The station side communication device is:
A measuring unit for measuring an RTT value between the own device and the subscriber side communication device;
A time synchronization frame generation unit for generating a time synchronization frame by inserting an RTT value measured by the measurement unit into a frame;
Insert the time stamp of the master clock and the priority information indicating whether the own device is the master side into the time synchronization frame generated by the time synchronization frame generation unit, and transmit it to the subscriber side communication device A time stamp insertion part;
A correction frame extraction unit that extracts a correction frame including an offset value for correcting the time stamp of the master clock from the frame received from the subscriber side communication device;
A master time stamp correction unit that corrects the time stamp of the master clock based on the offset value included in the correction frame extracted by the correction frame extraction unit when the own device is not the master side;
The slave clock correction device includes:
A time synchronization frame extraction unit for extracting a time synchronization frame transmitted from the time stamp insertion unit to the subscriber side communication device;
Based on the RTT value and the time stamp included in the time synchronization frame extracted by the time synchronization frame extraction unit, the slave of the subscriber side communication device connected to the master side and slave side station side communication devices First and second slave time stamp correction units for correcting clock time stamps;
Based on the priority information included in the time synchronization frame extracted by the time synchronization frame extraction unit, a slave clock time stamp corresponding to the master side communication device is output to the subscriber terminal device. A selection section;
An offset calculation unit for calculating an offset value of the time stamp corrected by the first and second slave time stamp correction units;
A communication system, comprising: an offset notification unit that inserts an offset value calculated by the offset calculation unit into a correction frame and notifies the station side communication device via the subscriber side communication device. In the station side communication device connected to the subscriber side communication device,
A measuring unit for measuring an RTT value between the own device and the subscriber side communication device;
A time synchronization frame generation unit for generating a time synchronization frame by inserting an RTT value measured by the measurement unit into a frame;
A time stamp insertion unit that inserts a time stamp of its own master clock into the time synchronization frame generated by the time synchronization frame generation unit and transmits the time stamp to the subscriber side communication device; Station side communication device. In the station side communication device connected to the subscriber side communication device,
A measuring unit for measuring an RTT value between the own device and the subscriber side communication device;
A time synchronization frame generation unit for generating a time synchronization frame by inserting an RTT value measured by the measurement unit into a frame;
Inserting in the time synchronization frame generated by the time synchronization frame generation unit the time stamp of the master clock of the own device and the priority information indicating whether the own device is the master side, to the subscriber side communication device A time stamp insertion part to be transmitted;
From the frame received from the subscriber side communication device, the subscriber side communication corresponding to the master clock of the slave clock of the subscriber side communication device corresponding to the master clock of the own device and the master clock of the other station side communication device A correction frame extraction unit that extracts a correction frame including an offset value with the time stamp of the slave clock of the device;
A master time stamp correction unit that corrects the time stamp of the master clock based on an offset value included in the correction frame extracted by the correction frame extraction unit when the own device is not the master side; A station side communication device characterized. In a slave clock correction device that connects with a subscriber-side communication device and synchronizes the slave clock of the subscriber-side communication device with the master clock of the station-side communication device,
Time synchronization frame transmitted from the station side device to the subscriber side communication device, including an RTT value between the station side communication device and the subscriber side communication device and a master clock time stamp of the station side communication device A time synchronization frame extracting unit for extracting
A slave comprising: a time stamp correction unit for correcting a time stamp of the slave clock based on an RTT value and a time stamp included in the time synchronization frame extracted by the time synchronization frame extraction unit; Clock correction device. When the RTT value is RTT, the time stamp is TS, and the delay amount from the subscriber side communication device to the own device is α, the time stamp correction unit is TS + (RTT / 2) + α The slave clock correction apparatus according to claim 6, wherein the value calculated by the step is used as a time stamp of the slave clock. In the slave clock correction device for synchronizing the slave clock of the subscriber side communication device connected to the master side and slave side station side communication devices with the master clock of the corresponding master side and slave side station side communication devices,
The RTT value between the station side communication device and the subscriber side communication device, the master clock time stamp of the station side communication device, and the station side communication device transmitted from the station side device to the subscriber side communication device A time synchronization frame extracting unit for extracting a time synchronization frame including priority information indicating whether the master is on the master side;
Based on the RTT value and the time stamp included in the time synchronization frame extracted by the time synchronization frame extraction unit, the slave of the subscriber side communication device connected to the master side and slave side station side communication devices First and second slave time stamp correction units for correcting clock time stamps;
Based on the priority information included in the time synchronization frame extracted by the time synchronization frame extraction unit, a time stamp of a slave clock corresponding to the master side communication device is output to the subscriber terminal device. A selection section;
An offset calculation unit for calculating an offset value of the time stamp corrected by the first and second slave time stamp correction units;
A slave clock correction apparatus comprising: an offset notification unit that inserts an offset value calculated by the offset calculation unit into a correction frame and notifies the station side communication device via the subscriber side communication device .

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