JP6025700B2 - Time synchronization system, slave device, and time synchronization method - Google Patents

Description

  The present invention relates to a time synchronization system, a slave device, and a time synchronization method.

  A typical application example of time synchronization in a network is time synchronization between base station apparatuses of a mobile phone network. In order to enable seamless communication during handover when a terminal moves between areas, it is necessary to maintain frequency synchronization and time synchronization between base station apparatuses. The base station apparatus generally uses a GPS time received from a GPS (Global Positioning System) satellite as a reference time for synchronization. Depending on the installation location of the base station device, the base station device may not be able to receive radio waves from GPS satellites. Even in such a case, time synchronization is required.

  As a typical means of time synchronization performed via a network, there is a method using an NTP (Network Time Protocol) and an NTP server. In NTP, GPS satellites and atomic clocks are the highest time sources, and servers connected in a hierarchical structure enable time synchronization in milliseconds while mutually correcting transmission path delays. However, time synchronization by NTP has a problem that the synchronization accuracy depends on the physical distance of the network to the NTP server and the network delay. In addition, in time synchronization between base station apparatuses of a cellular phone network, time synchronization accuracy in units of microseconds is required, so that time synchronization by NTP lacks performance.

  IEEE (The Institute of Electrical and Electronics Engineers) defines IEEE 1588 as a standardization technique for performing time synchronization in a packet network. IEEE 1588 defines a protocol between a MASTER device serving as a time transmission source and a SLAVE device synchronized with time information received as a packet from the MASTER device.

  IEEE 1588 defines a packet exchange procedure for transmitting and receiving time information called a PTP (Precision Time Protocol) packet, its format, a method for correcting a time error due to a transmission line delay between the MASTER device and the SLAVE device, and the like. This enables time synchronization between devices with sub-microsecond order accuracy. Further, as a process in the SLAVE apparatus after acquiring the time from the MASTER apparatus, a statistical process that averages fluctuations in the acquisition time is performed to improve the stability of the synchronization time.

  IEEE 1588 defines a sequence for calculating, as a correction value, a delay amount generated on a transmission path between a MASTER device and a SLAVE device. In addition, when the PTP packet passes through a relay device that exists between the MASTER device and the SLAVE device, fluctuations in the transmission path delay occur, a TC (transparent clock that corrects the residence time of the PTP packet in the device) ) Function is defined. If all the relay devices connected between the MASTER device and the SLAVE device are equipped with the TC function, the in-device dwell time generated by passing through the relay device among the fluctuations in the transmission line delay is calculated. The factor can be corrected.

  Moreover, there exists Unexamined-Japanese-Patent No. 2009-77207 (patent document 1) as background art of this technical field. In this publication, “filtering for RTT is performed to remove packets that are greatly deviated from the average value of delay time, and client time is controlled using only data in the vicinity of the average value of delay time. Alternatively, filtering for RTT is performed. The client time is controlled using only data that falls within the error range estimated from the previous RTT, or if the RTT or one-side delay time changes suddenly, it is considered that the path switching has occurred and the hold is performed. “Transition to over operation, and an offset value is given so as to cancel the change at that time” (see summary).

JP 2009-77207 A

  If there is a relay device that does not have the TC function installed between the MASTER device and the SLAVE device, fluctuation occurs in the transmission path delay between the MASTER device and the SLAVE device, and the fluctuation is not corrected in the relay device. . Therefore, when the SLAVE device performs time synchronization, the fluctuation becomes an error, and the time synchronization accuracy deteriorates. In such a case, the SLAVE device performs a process of integrating the times acquired from the packets and averaging the errors in order to absorb fluctuations. Therefore, there is a problem that it takes time for the SLAVE device to synchronize with the MASTER device.

  However, in a transmission line in which the TC function is implemented in all the relay apparatuses or the traffic fluctuation is small, fluctuations in the transmission line delay do not occur or are negligibly small. Therefore, in such a case, the SLAVE device does not necessarily perform the above-described averaging process, and only the demerit that it takes time until time synchronization is performed by performing the above-described averaging process.

  In the technique described in Patent Document 1, the SLAVE device removes packets that deviate significantly from the average delay time (that is, packets with large fluctuations in transmission line delay). Therefore, it takes time for the SLAVE device to perform time synchronization by performing the process of calculating the average value. In addition, the SLAVE device cannot perform time synchronization until it receives a packet with a small fluctuation in transmission line delay.

  One aspect of the present invention is a master device that transmits a time synchronization packet, and a slave that receives the time synchronization packet from the master device via a network and performs time synchronization with the master device using the received time synchronization packet. A first time synchronization received from the master device, the slave device holding history information indicating a history of transmission line delay times used in time synchronization by a time synchronization packet from the master device. First time information of the master device at the time of transmission of the first time synchronization packet is extracted from the packet, the second time synchronization packet is transmitted to the master device, and the third time is received from the master device. Extracting second measurement time information of the master device at the time of receiving the second time synchronization packet from the synchronization packet The measurement time of the slave device when the first time synchronization packet is received, the measurement time of the slave device when the second time synchronization packet is transmitted, the first measurement time information, and the second measurement time information, Based on the first time, the first transmission line delay time is calculated, time synchronization is performed using the fourth time synchronization packet received after the first time synchronization packet and the third time synchronization packet, and the fourth time synchronization packet is used. When maintaining the first time synchronization process in the time synchronization, the time synchronization is performed based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first transmission line delay time, and the fourth When switching from the first time synchronization process to the second time synchronization process in the time synchronization by the time synchronization packet, refer to the history information, Calculating a first statistical value of sending passage delay time, it performs time synchronization based on the first statistics and the measurement time information of the extracted master device from said fourth time synchronization packet, a time synchronization system.

  According to one embodiment of the present invention, the time required for time synchronization can be shortened and transition to a highly accurate time synchronization state can be made according to the network environment.

It is explanatory drawing which shows the system outline example of a time synchronous system. It is a block diagram which shows the structural example of a SLAVE apparatus. It is a sequence diagram which shows an example of the time delay correction | amendment between a MASTER apparatus and a SLAVE apparatus. FIG. 11 is a sequence diagram showing an example of time synchronization processing when the transmission line delay time is constant (the transmission line delay is not fluctuated). FIG. 11 is a sequence diagram showing an example of time synchronization processing when the transmission line delay time fluctuates (the transmission line delay fluctuates). It is a sequence diagram which shows an example of the time synchronization method in case it does not fluctuate in a transmission line delay. It is a sequence diagram which shows an example of the time synchronization method in case there is fluctuation in a transmission line delay. It is explanatory drawing which shows an example of the internal process at the time synchronization of a SLAVE apparatus when there exists fluctuation in a transmission line delay. It is a flowchart which shows the operation example until time delivery by a SLAVE apparatus.

  Embodiments of the present invention will be described below with reference to the drawings. It should be noted that this embodiment is merely an example for realizing the present invention, and does not limit the technical scope of the present invention. In each figure, the same reference numerals are given to common configurations.

  FIG. 1 shows an outline example of a time synchronization system. The time synchronization system includes a MASTER device 1-1, a relay device 1-10, a SLAVE device 1-2, a base station device 1-3, and a GPS antenna 1-8. The time synchronization system is connected to the main signal NW network 1-7, and is a master device 1-1 that is the highest-order device of the time synchronization system, and a slave device 1 that operates in synchronization with the time of the master device 1-1. Are connected in a hierarchical manner via the relay device 1-10. In this example, a base station device 1-3 that operates as a terminal device of the time synchronization system is connected.

  The MASTER device 1-1 and the relay device 1-10, and the relay device 1-10 and the SLAVE device 1-2 are connected by a communication line capable of bidirectional communication. The SLAVE device 1-2 distributes the time to the base station device 1-3. The MASTER device 1-1 is connected to the GPS antenna 1-8, extracts time information from the GPS signal 1-9 received from the GPS satellite 1-4, and synchronizes its internal clock with the extracted time information.

  Further, the MASTER device 1-1 generates, from the extracted time information, for example, a PTP packet 1-5 that is an example of a time synchronization packet and conforms to IEEE 1588. The MASTER device 1-1 transmits the PTP packet 1-5, the main signal packet 1-6, and the like to the SLAVE device 1-2, which is a subordinate device, via the relay device 1-10.

  In addition, the structure which does not include the relay apparatus 1-10 may be sufficient as the time synchronization system of a present Example. In this case, the MASTER device 1-1 directly transmits the generated PTP packet 1-5, the main signal packet 1-6, and the like to the SLAVE device 1-2.

  The SLAVE device 1-2 extracts the time information of the MASTER device 1-1 from the PTP packet 1-5 received from the MASTER device 1-1, and synchronizes the internal clock with the extracted time information. Further, the SLAVE device 1-2 transmits time information and a main signal packet to the base station device 1-3. The base station apparatus 1-3 extracts the time from the received time information. In this way, the time synchronization system of this embodiment can distribute the time to a terminal device that does not have a GPS antenna.

  The SLAVE device 1-2 and the base station device 1-3 may be the same casing. The time synchronization means that the SLAVE device 1-2 synchronizes the time of an internal clock 8-8 described later with the time held by the clock of the MASTER device 1-1.

  Here, for simplification of the following description, the difference between time and time will be described. The time is identification information indicating a certain point in time, such as 12:00:00. Furthermore, if the order and the difference can be defined between a plurality of times, and if the differences at the two times are equal, the intervals at the two times are assumed to be equal. That is, time is an interval measure. On the other hand, time is an amount indicating the width of time. That is, time is defined as the difference between two time points, and is expressed as the accumulation of unit time. For example, the time represented as the difference between the time 12:00:00 and the time 13:00:00 is 1 hour 00 minutes 00 seconds.

  FIG. 2 is a block diagram illustrating a configuration example of the SLAVE device 1-2. The SLAVE device 1-2 includes a CPU 8-12 as a processor, a memory 8-13, a secondary storage device 8-14, a packet transmission / reception unit A8-1 and a packet transmission / reception unit B8-10 as input / output interfaces, including. The memory 8-13 includes a packet identification unit 8-2, a time information extraction unit 8-3, a time information comparison unit 8-4, a calculation unit 8-5, a control unit 8-6, and an internal clock correction unit 8-. 7, an internal clock 8-8, and an internal clock information extraction unit 8-9 are stored.

  Each unit stored in the memory 8-13 is a program. Each program is executed by the CPU 8-12 to perform a predetermined process using a storage device and a communication port (communication device). Therefore, in the present embodiment and other embodiments, the description with each part as the subject may be the description with the CPU 8-12 as the subject. Alternatively, the processing executed by each unit is processing performed by a computer and a computer system on which the program operates. The CPU 8-12 operates as a functional unit (means) that realizes a predetermined function by operating according to a program.

  The packet transmission / reception unit A8-1 transmits / receives the PTP packet to / from the MASTER device 1-1 and transmits the received PTP packet to the packet identification unit 8-2. The packet identifying unit 8-2 identifies the type of the PTP packet received from the packet transmitting / receiving unit A8-1. If the PTP packet is a sync message described later, a value is further stored in a CF (correction field) area. It is determined whether or not it has been done.

  The packet identification unit 8-2 transmits the identified packet type and identification result to the control unit 8-6. The packet identification unit 8-2 transmits the received PTP packet to the time information extraction unit 8-3. The time information extraction unit 8-3 extracts time information and a value stored in the CF area from the received PTP packet. The time information extraction unit 8-3 transmits the time information to the time information comparison unit 8-4, the calculation unit 8-5, and the internal clock correction unit 8-7, and the value stored in the CF area is calculated by the calculation unit 8- Send to 5.

  The calculation unit 8-5 calculates a transmission path delay time between the MASTER device 1-1 and the SLAVE device 1-2 based on the received time information. The transmission path delay time is the time required from when the MASTER device 1-1 transmits a PTP packet until the SLAVE device 1-2 receives the PTP packet.

  Further, in the average mode to be described later, for example, the calculating unit 8-5 calculates the statistical value of the transmission line delay time by integrating the values of the transmission line delay time, and uses the calculated statistical value as the time information comparison unit 8. -4 and the internal clock correction unit 8-7. In addition, the calculation unit 8-5 calculates a value indicating fluctuation of the transmission path delay fluctuation, and transmits the calculated value to the time information comparison unit 8-4.

  In the following description, unless otherwise specified, the transmission line delay represents a transmission line delay between the MASTER device 1-1 and the SLAVE device 1-2. Note that the fluctuation in the transmission path delay refers to a difference between the packet transmission interval time on the packet transmission side and the packet arrival interval time on the packet reception side. The fluctuation of the transmission path delay occurs, for example, when the PTP packet passes through the relay apparatus 1-10 and the packet stays in the apparatus or due to the influence of the traffic on the transmission path. Hereinafter, the fluctuation of the transmission line delay may be simply referred to as fluctuation.

  The time information comparison unit 8-4 compares the time newly determined by the internal clock correction unit 8-7 with the time received from the internal clock 8-8 and calculates a difference. The time information comparison unit 8-4 determines that the time synchronization is completed if the calculated difference is equal to or less than the set threshold value, and transmits the determination result to the control unit 8-6. Further, the time information comparison unit 8-4 determines whether or not the fluctuation of the transmission path delay received from the calculation unit 8-5 is equal to or less than the set threshold value, and transmits the determination result to the control unit 8-6. .

  The control unit 8-6 selects a time synchronization method based on the determination result received from the packet identification unit 8-2, the determination result received from the time information comparison unit 8-4, and the like, and the internal clock correction unit 8-7 Instructs time synchronization using the time synchronization method selected in the above. If the determination result received from the time information comparison unit 8-4 is time synchronization completion, the control unit 8-6 notifies the time synchronization completion to the internal clock information extraction unit 8-9.

  The internal clock correction unit 8-7 uses the time synchronization method selected by the control unit 8-6 to transmit the time information received from the time information extraction unit 8-3 and the transmission path delay received from the calculation unit 8-5. The current time is determined from the statistical value of time or transmission line delay time. The internal clock correction unit 8-7 transmits the determined time information to the internal clock 8-8. Further, the internal clock correction unit 8-7 receives the time information received from the time information extraction unit 8-3, the transmission path delay time received from the calculation unit 8-5, the determined time information, and the like as will be described later. Write to 15.

  The internal clock 8-8 synchronizes its own time with the received time information, and transmits its own time information to the time information comparison unit 8-4. The internal clock information extraction unit 8-9 extracts the time from the internal clock 8-8. When receiving the time synchronization completion notification from the control unit 8-6, the internal clock information extracting unit 8-9 extracts the time from the internal clock 8-8, and generates a packet including the extracted time information. The internal clock information extracting unit 8-9 transmits the generated packet to the packet transmitting / receiving unit B8-10. The packet transmitting / receiving unit B8-10 transmits the packet received from the internal clock information extracting unit 8-9 to the base station device 1-3.

  The secondary storage device 8-14 holds a synchronization history table 8-15. The synchronization history table 8-15 includes history information of the transmission line delay time calculated by the calculation unit 8-5. For example, the synchronization history table 8-15 includes the time of the MASTER device 1-1 extracted by the time information extraction unit 8-3 from the PTP packet, the transmission path delay time, and the internal clock correction unit 8-7 of the MASTER device 1-1. A history of correspondence between the time of 1 and the time calculated from the transmission line delay time is stored.

  FIG. 3 shows a sequence of PTP messages defined in IEEE 1588 as an example of a sequence of messages transmitted and received between the MASTER device 1-1 and the SLAVE device 1-2 in order to synchronize the time of the SLAVE device 1-2. Indicates. 3A to 7A, the relay device 1-10 is omitted.

  First, a PTP packet defined by IEEE 1588 will be described. Sync Message 2-7, Delay_Req Message 2-8, and Delay_Resp Message 2-9 are PTP packets defined in IEEE 1588.

  In the Sync Message 2-7, time information of the MASTER device 1-1 at the time when the MASTER device 1-1 transmits the Sync_Message 2-7 is embedded. The Delay_Req Message 2-8 and the Delay_Resp Message 2-9 are transmitted and received in order to correct the transmission line delay between the MASTER device 1-1 and the SLAVE device 1-2.

  In IEEE 1588, in order to maintain time synchronization accuracy, a method of repeatedly transmitting / receiving Sync Message 2-7, Delay_Req Message 2-8, and Delay_Resp Message 2-9 between the MASTER device 1-1 and the SLAVE device 1-2 is adopted. ing.

  Next, a time synchronization sequence will be described. When information is transmitted and received between two devices connected by a transmission path, a transmission path delay corresponding to the transmission distance occurs. For this reason, when a device transmits a message having time information at a certain point, the device receiving the message needs to correct the received time information in consideration of a delay due to the transmission path. IEEE 1588 takes this into consideration, and adopts a method of correcting the time by detecting the time lag between the two devices and the transmission path delay time.

  The MASTER device 1-1 periodically transmits / receives a PTP message by the IEEE 1588 protocol according to the PTP message transmission interval 2-1. At this time, the PTP message transmission interval 2-1 is determined by the SLAVE device 1-2. The SLAVE device 1-2 transmits information on the PTP message transmission interval 2-1 to the MASTER device 1-1 using the PTP message. The MASTER device 1-1 transmits a PTP message according to the PTP message transmission interval 2-1 obtained from the received PTP message.

  The MASTER device 1-1 records the time Ta held by the MASTER device 1-1, and at the same time transmits a Sync Message 2-7 including the time Ta to the SLAVE device 1-2. When the packet transmitting / receiving unit A8-1 receives the Sync Message 2-7, the internal clock information extracting unit 8-9 extracts and records the time Tb of the internal clock 8-8 at the time of receiving the Sync Message 2-7.

  Through the above-described processing, the SLAVE device 1-2 obtains information on the time Ta when the MASTER device 1-1 sends out the Sync Message 2-7 and the time Tb when it receives the Sync Message 2-7.

  Subsequently, the SLAVE device 1-2 generates a Delay_ReqMessage 2-8. The packet transmission / reception unit A8-1 sends a packet Delay_ReqMessage to the MASTER device 1-1. The internal clock information extraction unit 8-9 extracts and records the time Tc of the internal clock 8-8 at the time when the Delay_ReqMessage 2-8 is sent.

  The MASTER device 1-1 receives the Delay_ReqMessage 2-8 and records the time Td held by the MASTER device at the time of receiving the Delay_ReqMessage 2-8. The MASTER device 1-1 generates a Delay_RespMessage 2-9 including the time Td and sends it to the SLAVE device 1-2. Through the processing described above, the SLAVE device 1-2 obtains information on the time Tc at which the Delay_ReqMessage 2-8 is transmitted and the time Td at which the MASTER device 1-1 receives the Delay_ReqMessage 2-8.

  The calculation unit 8-5 transmits the transmission path delay time in the direction in which information is transmitted from the MASTER device 1-1 to the SLAVE device 1-2 from the four pieces of time information Ta to Td, and the SLAVE device 1-2 to the MASTER device 1. -1 can be calculated with the transmission line delay time in the direction in which information is transmitted to -1.

  Here, in the delay calculation in the IEEE 1588 protocol, it is assumed that transmission path delays in both directions of the MASTER apparatus 1-1 to the SLAVE apparatus 1-2 and the SLAVE apparatus 1-2 to the MASTER apparatus 1-1 are symmetric. A transmission line delay time is calculated. That is, the calculation unit 8-5 calculates the transmission line delay time d by the following formula.

  d = {(Tb−Ta) + (Td−Tc)} / 2

  As described above, the SLAVE device 1-2 uses the transmission path delay time and the Sync Message transmitted from the MASTER device 1-1 to subordinate the time of the SLAVE device 1-2 to the time of the MASTER device 1-1. Can be operated. It should be noted that the MASTER device 1-1, the SLAVE device 1-2, and the base station device connected in multiple stages by executing a similar sequence between the SLAVE device 1-2 and the base station device 1-3. 1-3 time synchronization can be realized.

  Hereinafter, the time synchronization accuracy in IEEE 1588 when the value of the transmission line delay time is constant (no fluctuation in the transmission line delay) and when the value is fluctuating (the fluctuation in the transmission line delay) will be described.

  FIG. 4 shows an example of time synchronization processing in the SLAVE device 1-2 when there is no fluctuation in the transmission line delay. The transmission path delay time calculation sequence 3-2 is the same as the sequence described in FIG. In FIG. 4, since there is no fluctuation in the transmission line delay, all the values of the transmission line delay time d are equal to the values calculated by the transmission line delay time calculation sequence 3-2.

  The fact that the transmission line delay time is constant (the transmission line delay does not fluctuate) means that the time from when the MASTER device 1-1 transmits the PTP packet until the SLAVE device 1-2 receives the PTP packet. Is constant. Accordingly, the SLAVE device 1-2 can extract the time embedded in the Sync Message 2-7 and add the transmission line delay time to the time, thereby accurately acquiring the current time. The time can be precisely synchronized with 1.

  FIG. 5 shows an example of time synchronization processing in the SLAVE device 1-2 when there is fluctuation in the transmission line delay. For example, when the PTP packet transmitted from the MASTER device 1-1 passes through the relay device 1-10 such as a hub and the traffic on the transmission path (network) fluctuates, the value of the transmission path delay time is not constant and varies. (That is, there is fluctuation in the transmission line delay). That is, since the transmission line delay time Δd fluctuates, the value calculated by the SLAVE device 1-2 in the transmission line delay time calculation sequence 4-2 similar to FIG. 3 is different from the value of the transmission line delay time Δd. An error occurs.

  At this time, if the SLAVE device 1-2 calculates the current time using the time embedded in the Sync Message 2-7 and the value calculated in the transmission path delay time calculation sequence 4-2, the above error may occur. An error occurs and the time synchronization accuracy deteriorates.

  IEEE 1588 defines a TC function as one means for correcting a time error due to the fluctuation of the transmission line delay described above. The TC function is a function of adding, to the PTP packet as a correction value, the time (retention time in the apparatus) required for the relay apparatus 1-10 that transfers the PTP packet to receive and transmit the PTP packet. .

  The relay apparatus 1-10 writes the correction value calculated by the TC function in the CF area in the PTP packet. If the relay apparatus 1-10 is equipped with this TC function, it is possible to correct fluctuations in transmission path delay caused by passing through the relay apparatus 1-10, and to suppress deterioration in time synchronization accuracy. However, when the relay apparatus 1-10 does not implement the TC function, another method must be used to correct the fluctuation of the transmission path delay.

  FIG. 6 shows an example of a time synchronization method when there is no fluctuation in the transmission line delay. The SLAVE device 1-2 acquires the transmission path delay time d by the sequence described in FIG. Subsequently, the packet transmission / reception unit A8-1 receives the Sync Message 2-7 in which the time of the MASTER device 1-1 is embedded, and the time information extraction unit 8-3 extracts the time information of the MASTER device 1-1. . Here, when there is no fluctuation in the transmission line delay, the transmission line delay time of this Sync Message is equal to the previously calculated transmission line delay time d.

  That is, the clock time of the MASTER device 1-1 when the SLAVE device 1-2 receives the Sync Message is equal to the time obtained by adding the transmission line delay time d to the time embedded in the Sync Message. Therefore, the internal clock correction unit 8-7 can calculate the current time by adding the transmission line delay time d calculated by the calculation unit 8-5 to the time information extracted by the time information extraction unit 8-3. . The internal clock correction unit 8-7 transmits the calculated current time to the internal clock 8-8.

  In other words, the SLAVE device 1-2 can immediately know the time of the MASTER device 1-1 from the time information of the MASTER device 1-1 embedded in the Sync Message and the transmission path delay time d, and has high accuracy. Time synchronization. Hereinafter, this time synchronization method is referred to as a high-speed mode.

  In addition, when the relay apparatus 1-10 corrects the fluctuation of the transmission line delay by the TC function, the calculation unit 8-5 reflects the correction value on the transmission line delay time calculated using the above-described method. The SLAVE device 1-2 can calculate the transmission line delay time d with high accuracy even if there is a fluctuation in the transmission line delay by this processing. Therefore, even when the relay apparatus 1-10 corrects the transmission path delay fluctuation by the TC function, the SLAVE apparatus 1-2 can perform high-speed and high-accuracy time synchronization using the high-speed mode.

  When the SLAVE device 1-2 performs time synchronization in the high speed mode, the time synchronization is completed after the SLAVE device 1-2 is activated in order to perform time synchronization without correcting errors due to fluctuations in the SLAVE device 1-2. However, there is an advantage that the time until the time is distributed to the base station device 1-3 is short. However, when the fluctuation of the transmission line delay time is large and the fluctuation of the transmission line delay is not corrected by the TC function, the time synchronization accuracy in the SLAVE device 1-2 deteriorates.

  FIG. 7A shows an example of a time synchronization method when there is fluctuation in the transmission line delay. When there is fluctuation in the transmission line delay and the fluctuation in the transmission line delay is not corrected by the TC function of the relay apparatus 1-10, the transmission line delay time Δd calculated by the SLAVE apparatus 1-2 is equal to the actual transmission line delay time. Different. Therefore, as described above, the difference between Δd and the actual transmission line delay time becomes a time error. Since the time acquired by the SLAVE device 1-2 varies, the time needs to be smoothed by another means. Hereinafter, the smoothing means will be described.

  FIG. 7B shows an example of internal processing of time synchronization in the SLAVE device 1-2 when there is fluctuation in the transmission line delay. The calculation unit 8-5 extracts, from the synchronization history table 8-15, the time acquired from the Sync Message received from the MASTER device 1-1 and the time calculated by the sequence in FIG. 3 using the Sync Message. The calculator 8-5 integrates the extracted two time errors (that is, the transmission path delay time calculated by the sequence in FIG. 3) to calculate a statistical value. The internal clock correction unit 8-7 corrects the time of the internal clock 8-8 using the statistical value.

  FIG. 7B shows an example in which the calculation unit 8-5 applies the least square method to the history of time information stored in the synchronization history table 8-15 as the process of calculating the statistical value. Specifically, the calculation unit 8-5 uses the sequence in FIG. 3 to calculate the model function of the time of the MASTER device 1-1 obtained from the Sync Message from the Sync Message 1-2 by the SLAVE device 1-2. As a result, the model function is generated. The internal clock correction unit 8-7 calculates the current time by substituting the time information of the MASTER device 1-1 extracted by the time information extraction unit 8-3 into the model function, and uses the calculated current time as the internal clock. Send to 8-8. Although FIG. 7B shows an example in which the model function is a linear function, the order of the model function is not limited. Further, the calculation unit 8-5 may generate the model function using a method other than the least square method.

  While the calculating unit 8-5 calculates the statistical value, the SLAVE device 1-2 cannot perform time synchronization. In addition, the SLAVE device 1-2 needs to acquire many samples of the time of the MASTER device 1-1 included in the PTP packet in order to obtain a stable offset value. In addition, the SLAVE device 1-2 needs to continue to accumulate time errors in order to improve the accuracy of time synchronization even after obtaining statistical values once. Hereinafter, this synchronization method is referred to as an average mode.

  When the SLAVE device 1-2 performs time synchronization in the average mode, even if there is fluctuation in the transmission line delay and the relay apparatus 1-10 does not correct the transmission line delay time using the TC function, There is an advantage that accurate time synchronization is possible. However, since the SLAVE device 1-2 needs to calculate the statistical value when the average mode is used, there is a demerit that it takes time from device activation to time synchronization compared to the high-speed mode.

  The SLAVE device 1-2 needs to consider the presence or absence of fluctuations in the transmission line delay in order to realize high-speed and highly accurate time synchronization. However, since the fluctuation of the transmission line delay varies depending on the environment of the transmission line (network) between the MASTER apparatus 1-1 and the SLAVE apparatus 1-2, the SLAVE apparatus 1-2 has a highly accurate and efficient time. In order to realize the synchronization, it is necessary to select a time synchronization method according to the environment of the transmission path.

  FIG. 8 is a flowchart showing an operation example until the SLAVE device 1-2 is activated and time distribution is performed to the base station device 1-3. As described above, the fluctuation of the transmission path delay is fluctuation (retention time in the apparatus) generated by passing through the relay apparatus 1-10 installed between the MASTER apparatus 1-1 and the SLAVE apparatus 1-2. And fluctuations caused by traffic on the transmission path.

  If these fluctuations do not occur or if the relay apparatus 1-10 has a function for correcting fluctuations, it is possible to perform highly accurate time synchronization in a short time in the high-speed mode. If these fluctuations occur and the function of correcting the fluctuations is not implemented in the relay apparatus 1-10, using the average mode can suppress errors due to fluctuations and perform highly accurate time synchronization. .

  The SLAVE device 1-2 according to the present embodiment, for example, determines whether the relay device 1-10 has a function of correcting fluctuation, compares the fluctuation of the transmission line delay with the threshold value, and obtains the acquisition time and the internal clock. The presence or absence of a correction function in the network and the presence or absence of fluctuation are determined by processing such as comparing the time difference of 8-8 with a threshold value. The SLAVE device 1-2 switches the time synchronization method from the high-speed mode to the average mode when it is determined that there is no correction function in the network and fluctuation has occurred.

  The SLAVE device 1-2 determines whether or not the residence time in the device is corrected based on whether or not the TC function is installed in the relay device 1-10. That is, if the SLAVE device 1-2 determines that the relay device 1-10 does not include the TC function, the SLAVE device 1-2 determines that the relay device 1-10 does not include the correction function.

  When the SLAVE device 1-2 determines that the TC function is not implemented in the relay device 1-10, the SLAVE device 1-2 determines the presence or absence of fluctuation due to network traffic by comparing the fluctuation of the transmission path delay time with a predetermined threshold value. To do. That is, if the SLAVE device 1-2 determines that the fluctuation exceeds the threshold, the SLAVE device 1-2 determines that fluctuation has occurred. Further, even when the SLAVE device 1-2 does not obtain a determination result that the fluctuation has occurred in the above-described processing, if the time error does not converge to the required accuracy within the predetermined time limit, the fluctuation occurs. It is determined that

  Hereinafter, specific steps in FIG. 8 will be described. First, the SLAVE device 1-2 is activated (S7-1). The processing from when the SLAVE device 1-2 is activated until the time synchronization is started is as follows. The SLAVE device 1-2 and the MASTER device 1-1 transmit and receive an ARP packet and recognize each other's MAC address. Subsequently, the SLAVE device 1-2 makes a PTP packet transmission request to the MASTER device 1-1. At this time, the SLAVE device 1-2 and the MASTER device 1-1 also transmit / receive information necessary for transmission / reception of the PTP packet (for example, which device becomes the MASTER, information on the time source in the MASTER device). To do. The SLAVE device 1-2 starts time synchronization after the above processing.

  Subsequently, the control unit 8-6 instructs the internal clock correction unit 8-7 to perform time synchronization in the high speed mode, and the internal clock correction unit 8-7 starts time synchronization using the high speed mode (S7-2). ). Note that the SLAVE device 1-2 may periodically receive a Sync Message from the MASTER device, and perform time synchronization on the received Sync Message in parallel with the steps described below. The SLAVE device 1-2 calculates a transmission line delay time d once or a plurality of times in the high-speed mode based on the PTP packet received from the MASTER device 1-1, and starts the steps described later.

  The packet identification unit 8-2 determines whether a value is stored in the CF area of the PTP packet received from the MASTER device 1-1, and transmits the determination result to the control unit 8-6 (S7-3). ). Note that the packet identification unit 8-2 can determine whether or not the TC function is implemented in the relay device 1-10 based on the determination.

  When the TC function is implemented in the relay apparatus 1-10, the correction value calculated by the relay apparatus 1-10 using the TC function is written in the CF area in the PTP packet. Therefore, if a value is stored in the CF area, the TC function is implemented in the relay device 1-10, and the control unit 8-6 corrects the fluctuation of the transmission line delay by the relay device 1-10. Judge. At this time, the control unit 8-6 does not issue an instruction for mode switching to the internal clock correction unit 8-7, and the SLAVE device 1-2 continues time synchronization in the high-speed mode (S7-3: Yes). ).

  Here, in the network between the MASTER device 1-1 and the SLAVE device 1-2, the time synchronization system includes the relay device 1-10 that implements the TC function, and the relay device 1 that does not implement the TC function. -10 is included. In this case, the relay apparatus 1-10 equipped with the TC function writes the correction value in the CF area of the PTP packet received from the MASTER apparatus 1-1. Accordingly, in step S7-3, the packet identification unit 8-2 determines that the TC function is implemented in the relay device 1-10.

  However, when the time synchronization system has the above-described configuration, the relay apparatus 1-10 that does not have the TC function causes fluctuations in the transmission line delay, and the fluctuations are not corrected. Therefore, the SLAVE apparatus 1 -2 needs to consider the fluctuation in time synchronization. Therefore, the SLAVE device 1-2 performs the following steps.

  The calculator 8-5 calculates the transmission line delay time d (S7-4). The time information comparison unit 8-4 compares an error between the time in the internal clock 8-8 and the time calculated from the Sync Message with a predetermined threshold (S7-5). The time information comparison unit 8-4 compares the difference between the transmission line delay time d calculated in step S7-4 and the transmission line delay time calculated at the time of the latest time with a predetermined threshold value. May be. The time information comparison unit 8-4 transmits the determination result to the control unit 8-6.

  If the value of the fluctuation of the transmission line delay is large, the error between the internal clock 8-8 of the SLAVE device 1-2 and the time calculated from the Sync Message becomes large. Therefore, when the time information comparison unit 8-4 determines that the error is within the threshold, the control unit 8-6 determines that there is no fluctuation in the transmission line delay. At this time, the control unit 8-6 does not issue a mode switching instruction to the internal clock correction unit 8-7, and the SLAVE device 1-2 continues time synchronization in the high-speed mode. The control unit 8-6 notifies the internal clock information extraction unit 8-9 of the completion of time synchronization (S7-5: Yes).

  The internal clock information extracting unit 8-9 extracts the time from the internal clock 8-8, generates a packet including the extracted time information, and transmits the packet to the packet transmitting / receiving unit B8-10. The packet transmitting / receiving unit B8-10 distributes the packet received from the internal clock information extracting unit 8-9 to the base station device 1-3 (S7-6).

  When the time information comparison unit 8-4 determines that the error exceeds the threshold (S7-5: No), the control unit 8-6 determines whether a predetermined time limit is exceeded (S7- 8). In order to consider whether the time limit is due to the error between the internal clock 8-8 of the SLAVE device 1-2 and the time calculated from the Sync Message due to fluctuation or an error immediately after the start of time synchronization, for example, This is a preset value.

  The time limit is measured, for example, from the start of step S7-2 or from the start of step S7-3. Further, the control unit 8-6 may determine whether the number of times that the SLAVE device 1-2 has received the Sync Message exceeds the predetermined threshold, for example, instead of the time limit.

  When it determines with the control part 8-6 having exceeded the time limit (S7-8: Yes), it determines with the fluctuation | variation having generate | occur | produced. Accordingly, at this time, the control unit 8-6 instructs the calculation unit 8-5 to calculate the statistical value of the transmission line delay time used in the average mode, and the internal clock correction unit 8-7 Instructs the synchronization method to transition to the average mode. The internal clock correction unit 8-7 starts time synchronization in the average mode (S7-10).

  When it is determined that the time limit has not been exceeded (S7-8: No), the control unit 8-6 is configured to perform time synchronization again based on the Sync Message periodically received from the MASTER device 1-1. The clock correction unit 8-7 is instructed (S7-9). At this time, the time information comparison unit 8-4 compares the newly calculated error with a predetermined threshold value.

  In step S7-3, when the packet identification unit 8-2 determines that the TC function is not implemented in the relay apparatus 1-10 (S7-3: No), the calculation unit 8-5 The fluctuation of the transmission line delay time d is calculated from the history information stored in -15. Note that the variation may be a statistical value or the like representing the variation of the transmission path delay time. The calculation unit 8-5 uses the history information stored in the synchronization history table 8-15, for example, the deviation value or dispersion of the transmission path delay time d, the maximum value of the transmission path delay time d, and the transmission path delay time d. The difference of the minimum value of is calculated. The control unit 8-6 compares the fluctuation of the transmission line delay time d with a predetermined threshold (S7-7).

  When the control unit 8-6 determines that the variation in the transmission line delay time d is equal to or less than the threshold value (S7-7: Yes), the control unit 8-6 does not issue an instruction to switch the mode to the internal clock correction unit 8-7. The SLAVE device 1-2 continues time synchronization in the high-speed mode. The SLAVE device 1-2 transitions to the processing in step S7-5 described above.

  Moreover, if it determines with the fluctuation | variation of the transmission line delay time d exceeding a threshold value (S7-7: No), the control part 8-6 will determine with a fluctuation | variation. At this time, the control unit 8-6 instructs the calculation unit 8-5 to calculate the statistical value of the transmission path delay time used in the average mode. The control unit 8-6 instructs the internal clock correction unit 8-7 to shift the time synchronization method to the average mode (S7-10).

  The time information comparison unit 8-4 compares an error between the time in the internal clock 8-8 of the SLAVE device 1-2 and the time calculated from the Sync Message using the average mode with a predetermined threshold ( S7-11). The time information comparison unit 8-4 transmits the comparison result to the control unit 8-6. When the time information comparison unit 8-4 determines that the error is within the threshold (S7-11: Yes), the control unit 8-6 notifies the internal clock information extraction unit 8-9 of completion of time synchronization. Then, the SLAVE device 1-2 starts time distribution to the subordinate base station device 1-3 (S7-6).

  When the time information comparison unit 8-4 determines that the error exceeds the threshold (No in S7-11), the control unit 8-6 instructs the internal clock correction unit 8-7 to perform time synchronization again. (S7-12). That is, the SLAVE device 1-2 performs the following processing. The SLAVE device 1-2 uses the high-speed mode again based on the Sync Message periodically received from the MASTER device 1-1, and performs a predetermined number of time synchronizations, and the calculation unit 8-5 calculates the transmission path delay time. Calculate the statistics again. The internal clock correction unit 8-7 calculates the time based on the statistical value calculated again using the average mode. Subsequently, the time information comparison unit 8-4 compares again the error between the newly calculated time and the time in the internal clock 8-8 of the SLAVE device 1-2 with a predetermined threshold value (S7-10). .

  After starting the time distribution to the base station device 1-3, the SLAVE device 1-2 determines the PTP packet communication state with the MASTER device 1-1 (S7-13). When the SLAVE device 1-2 determines that the transmission of the PTP packet from the MASTER device 1-1 continues (S7-13: No), the SLAVE device 1-2 continues time distribution to the base station device 1-3, The PTP packet communication state with the MASTER device 1-1 is determined again.

  When the SLAVE device 1-2 determines that the transmission of the PTP packet from the MASTER device 1-1 is cut off (S7-13: Yes), the SLAVE device 1-2 distributes the time to the base station device 1-3. Is stopped (S7-14). The SLAVE device 1-2 determines the PTP packet communication recovery status with the MASTER device 1-1 (S7-15).

  If the SLAVE device 1-2 determines that the transmission of the PTP packet from the MASTER device 1-1 has been resumed (S7-15: Yes), the SLAVE device 1-2 returns to step S7-2 and executes the above-described flow again. If the SLAVE device 1-2 determines that the transmission of the PTP packet from the MASTER device 1-1 has not been resumed (S7-15: No), the SLAVE device 1-2 determines again the PTP packet communication recovery status with the MASTER device 1-1. To do. Note that some of Step S7-3, Step S7-5, Step S7-7, and Step S7-8 may be omitted.

  As shown in FIG. 8, the SLAVE device 1-2 selects an appropriate time synchronization method according to the network environment. That is, the SLAVE device 1-2 performs time synchronization in the high speed mode when it is determined that no fluctuation has occurred, and performs time synchronization in the average mode when it is determined that fluctuation has occurred. The SLAVE device 1-2 can realize time synchronization with high accuracy and time efficiency by selecting the synchronization method in this way.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments are described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Each of the above-described configurations, functions, processing units, processing means, and the like may be realized by hardware by designing a part or all of them with, for example, an integrated circuit. Each of the above-described configurations, functions, and the like may be realized by software by interpreting and executing a program that realizes each function by the processor. Information such as programs, tables, and files for realizing each function can be stored in a memory, a hard disk, a recording device such as an SSD (Solid State Drive), or a recording medium such as an IC card, an SD card, or a DVD.

Claims (10)

A master device that transmits a time synchronization packet;
A slave device that receives the time synchronization packet from the master device via a network, and performs time synchronization with the master device by the received time synchronization packet;
The slave device is
Holding history information indicating a history of transmission line delay time used in time synchronization by the time synchronization packet from the master device,
From the first time synchronization packet received from the master device, extract the first measurement time information of the master device at the time of the first time synchronization packet transmission,
A second time synchronization packet is transmitted to the master device;
From the third time synchronization packet received from the master device, second measurement time information of the master device at the time of receiving the second time synchronization packet,
The measurement time of the slave device when the first time synchronization packet is received, the measurement time of the slave device when the second time synchronization packet is transmitted, the first measurement time information, and the second measurement time information, Based on the first transmission path delay time,
Performing time synchronization by the fourth time synchronization packet received after the first time synchronization packet and the third time synchronization packet;
In the time synchronization by the fourth time synchronization packet, when maintaining the first time synchronization process, the time is determined based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first transmission line delay time. Synchronize,
In the time synchronization by the fourth time synchronization packet, when switching from the first time synchronization process to the second time synchronization process, the first statistical value of the transmission line delay time is calculated with reference to the history information. A time synchronization system that performs time synchronization based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first statistical value. The time synchronization system according to claim 1,
The condition for switching from the first time synchronization process to the second time synchronization process is that there is no transmission path delay time correction function in the network and that the time synchronization packet is transmitted from the master device to the slave device. A time synchronization system including at least one of fluctuations in the transmission line delay time in which is greater than a predetermined value. The time synchronization system according to claim 2,
The time synchronization system, wherein the fluctuation of the transmission line delay time is represented by a second statistical value of the transmission line delay time in the history information. The time synchronization system according to claim 3,
The slave device does not have a function for correcting the transmission line delay time in the network, and when the fluctuation of the transmission line delay time represented by the second statistical value is larger than a predetermined value, the slave device starts from the first time synchronization process. A time synchronization system that switches to the second time synchronization process. The time synchronization system according to claim 2,
The fluctuation of the transmission line delay time includes the time obtained by adding the first transmission line delay time to the measurement time information of the fourth time synchronization packet, and the measurement time in the slave device when the fourth time synchronization packet is received. A time synchronization system, represented by the error between. The time synchronization system according to claim 5,
The slave device does not have a function of correcting the transmission line delay time in the network, and when the fluctuation of the transmission line delay time represented by the error is larger than a predetermined value, A time synchronization system that switches to time synchronization processing. The time synchronization system according to claim 5,
In the slave device, the network does not include the correction function of the transmission line delay time, and the fluctuation of the transmission line delay time represented by the error is larger than a predetermined value, and the measurement is performed after starting synchronization with the master device. A time synchronization system that switches from the first time synchronization process to the second time synchronization process when a time limit for starting is exceeded. The time synchronization system according to claim 2,
The slave device determines a presence or absence of the correction function based on whether or not a correction value of a transmission line delay time is included in a time synchronization packet received from the master device. A slave device that receives a time synchronization packet including measurement time information of the master device from a master device connected via a network, and performs time synchronization with the master device based on the measurement time information,
Holding history information indicating a history of transmission line delay time used in time synchronization by the time synchronization packet from the master device,
From the first time synchronization packet received from the master device, extract the first measurement time information of the master device at the time of the first time synchronization packet transmission,
A second time synchronization packet is transmitted to the master device;
From the third time synchronization packet received from the master device, second measurement time information of the master device at the time of receiving the second time synchronization packet,
The measurement time of the slave device when the first time synchronization packet is received, the measurement time of the slave device when the second time synchronization packet is transmitted, the first measurement time information, and the second measurement time information, Based on the first transmission path delay time,
Performing time synchronization by the fourth time synchronization packet received after the first time synchronization packet and the third time synchronization packet;
In the time synchronization by the fourth time synchronization packet, when maintaining the first time synchronization process, the time is determined based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first transmission line delay time. Synchronize,
In the time synchronization by the fourth time synchronization packet, when switching from the first time synchronization process to the second time synchronization process, the first statistical value of the transmission line delay time is calculated with reference to the history information. A slave device that performs time synchronization based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first statistical value. A time synchronization method in a slave device that receives a time synchronization packet including measurement time information of the master device from a master device connected via a network and performs time synchronization with the master device based on the measurement time information. ,
The slave device holds history information indicating a history of transmission line delay time used in time synchronization by a time synchronization packet from the master device,
The method
From the first time synchronization packet received from the master device, extract the first measurement time information of the master device at the time of the first time synchronization packet transmission,
A second time synchronization packet is transmitted to the master device;
From the third time synchronization packet received from the master device, second measurement time information of the master device at the time of receiving the second time synchronization packet,
The measurement time of the slave device when the first time synchronization packet is received, the measurement time of the slave device when the second time synchronization packet is transmitted, the first measurement time information, and the second measurement time information, Based on the first transmission path delay time,
Performing time synchronization by the fourth time synchronization packet received after the first time synchronization packet and the third time synchronization packet;
In the time synchronization by the fourth time synchronization packet, when maintaining the first time synchronization process, the time is determined based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first transmission line delay time. Synchronize,
In the time synchronization by the fourth time synchronization packet, when switching from the first time synchronization process to the second time synchronization process, the first statistical value of the transmission line delay time is calculated with reference to the history information. A method including performing time synchronization based on the measurement time information of the master device extracted from the fourth time synchronization packet and the first statistical value.

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