JP2008177913A - Communication equipment and clock reproduction method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide communication equipment which can reduce the influences of each of lack of packets and discontinuity of an arrival order of the packets and can be stably operated by simple processing, and a clock reproduction method therefor. <P>SOLUTION: A slave unit 10 sets time information about the slave unit 10 and order information included in received packets in the received packets by a transmitting/receiving interval comparison part 50, checks at least either of replacement or the lack of the arrival order of the packets based on the time information and the order information about this reception and time information of transmission included in the packets, calculates intervals between pieces of time information about the transmission and the reception by control according to the above check result, calculates difference between the calculated intervals of the pieces of time information about the transmission and the reception as time information intervals of the transmission/reception, a smoothing part 52 smoothes the packets for over the time information intervals of the transmission/reception corresponding to a value calculated by the control according to a checking result and corrects misalignment included in packets before and after the checked packets. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a communication device and a clock recovery method thereof. In particular, the communication apparatus according to the present invention relates to a slave apparatus that synchronizes a clock of a slave apparatus with a reference master clock distributed from a master apparatus connected to an IP (Internet Protocol) network. The clock recovery method according to the present invention also relates to a method of recovering a slave side clock with respect to a master side clock supplied via an IP network in synchronization with the master clock.

  Synchronous clock transmission in the IP network uses a method in which a transmission time stamp, which is time information at the time of transmission, and a sequence number, which is a sequential number of packets, are given to a packet transmitted from a master device to a slave device. The transmission time stamp is a continuous number sequence generated according to a certain rule based on the master clock. Specifically, the transmission time stamp is an output generated by a counter of several tens of bits that operates based on the master clock. Each time a slave device receives a packet, the slave device generates and stores a reception time stamp that is time information at the time of reception. The reception time stamp is a sequence of several tens of bits generated according to the same rule as that of the master device based on the slave clock. Further, the slave clock has the same frequency, multiplied frequency, or divided frequency as the master clock.

  The slave device calculates the transmission interval and the reception interval using the transmission time stamp, the reception time stamp, and the sequence number described above, detects the frequency difference between the master clock and the slave clock, and corrects the slave clock.

  First, the transmission time stamp interval is calculated from the transmission time stamp and the sequence number, and the reception time stamp interval is calculated from the reception time stamp and the sequence number. The difference between the transmission time stamp and the transmission time stamp is calculated from the difference between the transmission time stamp interval and the reception time stamp interval. Ideally, the transmission interval and the reception interval are the same, so if the master clock and slave clock frequencies are the same, the transmission timestamp interval and the reception timestamp interval will be equal if the frequencies are exactly the same. No difference occurs. Conversely, when a difference occurs, the frequency is inconsistent. When the difference is positive, the slave clock frequency is lower than the master clock. When the difference is negative, the slave clock frequency is higher than the master clock. When the frequency mismatch is detected, the slave device feeds back the transmission / reception time stamp difference and corrects the slave clock.

  When the slave clock is a multiple of the master clock frequency, the value obtained by multiplying the transmission time stamp interval is compared with the reception time stamp interval, and if the frequency is a divided frequency, the frequency division number is added to the reception time stamp interval. A process of comparing the value multiplied by the reciprocal with the transmission time stamp interval is required.

  However, the packet arrival delay time on the IP network has a variation called jitter on the IP network, and the transmission interval and the reception interval are not necessarily the same microscopically. Rather, the packet arrival delay times are almost inconsistent.

  Therefore, even when the master clock frequency and the slave clock frequency completely match, the transmission time stamp interval and the reception time stamp interval do not match, and it appears as a frequency mismatch. When the slave device corrects the slave clock each time, the correction is erroneously performed and the jitter becomes large. In particular, when a burst delay or a reversal of the arrival order of packets occurs, the influence becomes large.

  There are two ways to deal with this problem. The first method is a method of smoothing or averaging a difference in a certain section of a transmission / reception time stamp and correcting it using this result. The purpose of this method is that the transmission interval and the reception interval match in the long term, so that the difference calculated for each received packet is accumulated for a long period of time and smoothed to reduce the effects of jitter on the IP network. It is to reduce.

  However, there is a limit to the interval that can be accumulated, and the transmission interval and the reception interval cannot be completely matched. Therefore, the effects of jitter on the IP network cannot be completely wiped out.

  Therefore, the second method is a method of suppressing the output jitter of the slave clock by using a PLL (Phase Locked Loop) having a slow response characteristic to reduce the gain adjustment gain. As a result, even if a transmission / reception time stamp difference is detected, it is gently corrected to suppress the influence of IP network jitter.

  A specific example in this technical field will be disclosed. Patent document 1 is a proposal about clock synchronization on a packet network. In Patent Document 1, in a packet network that relays between TDM (Time Division Multiplex) lines, a process for calculating the shortest packet transmission time in a continuous time interval on the packet network and a change in the shortest packet transmission time are traced. A method of regenerating the clock synchronization at the entrance and exit of the packet network.

Patent Document 2 is a data communication method, a data communication apparatus, and a data communication system. Patent Document 2 calculates the number of received packets within a predetermined packet time based on a sequence number assigned to a packet received by a receiving device even if a packet loss occurs. And adjusting the operating frequency according to the comparison result to adjust the reference frequency for data processing in the receiving apparatus.
JP 2004-274766 A Japanese Patent Laid-Open No. 2003-37620

  However, with the above-described two methods alone, several problems arise when the packet arrival order is discontinuous, such as packet loss or packet arrival order reversal. First, since the frequency information having continuity is interrupted due to packet loss, the master clock frequency cannot be accurately reproduced. When a packet loss occurs, the slave device has no way of knowing the transmission time stamp of the lost packet and no reception stamp is generated, so the slave device calculates the transmission / reception time stamp difference between the lost packet and the preceding and subsequent packets. I couldn't. In the slave device, the master clock frequency information having continuity is interrupted by the missing packet, and as a result, the master clock frequency cannot be accurately calculated.

By correcting the slave clock using this inaccurate master clock frequency information, the master clock frequency cannot be accurately reproduced. Specifically, it is assumed that the frequency of the master clock and the slave clock are completely the same, and the jitter on the IP network is canceled in the section of the packets with sequence numbers 0 and 6. In this case, the cumulative value of the transmission / reception time stamp difference is assumed to be 0 from the assumption in the section of the packets having the sequence numbers 0 and 6. However, for example, if a packet with sequence number 2 is lost, transmission / reception time stamp difference information cannot be calculated in the section of packets with sequence numbers 1 and 3, resulting in an invalid section. Since the slave device calculates the difference in the interval excluding this interval, the transmission / reception time stamp difference value of the packet interval of sequence numbers 0 and 1, 3 and 4, 4 and 5, and 5 and 6 is -1700,
Assuming -900, 500 and 500, the cumulative value of these difference values is -1600. Thus, when a packet is lost, the slave device calculates a value different from the original frequency difference information, and corrects the slave clock with this inaccurate information.

  Secondly, a complicated processing circuit for countering arrival order is prepared. If the continuity of the packet arrival order is lost and a packet other than the desired sequence number is received, it is known at the time of receiving the packet whether the desired packet was lost on the network or the packet arrival order was reversed. I can't. For this reason, as a coping method, the first coping method is a method of invalidating a section between a desired packet and a packet adjacent to this packet and performing the same processing as when a packet is lost. This method causes the master clock frequency not to be accurately reproduced as described in the case of packet loss.

  In the second coping method, the sequence number and transmission / reception time stamp of each received packet are stored in the memory, and each time a packet is received, the memory is searched for packet information of the sequence number that follows. As a result of the search, the slave device calculates a transmission / reception time stamp difference if packet information is stored, and if not stored, the slave device defers the calculation. In addition, when the delay fluctuation on the network is large, a request to increase the number of packets to be stored according to the delay fluctuation is generated. As a result, the memory capacity increases, and at the same time, the slave device also increases the number of searches and the search time. It becomes large and the processing of the apparatus becomes complicated.

  Thirdly, when the arrival order of packets becomes discontinuous, the delay and jitter on the network are larger than usual. Therefore, the method of smoothing the transmission / reception time stamp difference as usual will regenerate stable clocks. It becomes difficult. When packet loss or arrival order inversion occurs, traffic on the network is high. Therefore, it is assumed that the network device that relays the packet is overloaded and the processing time is increased accordingly. In the assumed state, the network delay and jitter are large, the reception time stamp interval is larger than usual, and the variation is also large. As a result, if the same smoothing method is applied to the slave device, the error component due to such variations cannot be removed, and the master clock frequency cannot be calculated accurately. Since the slave clock is corrected with this inaccurate master clock frequency information, the slave device cannot accurately reproduce the master clock frequency.

  The present invention eliminates such drawbacks of the prior art, reduces the effects caused by packet loss and discontinuity in the arrival order of packets, and communication apparatus that can be stably operated with simple processing and its clock recovery. It aims to provide a method.

  In order to solve the above-described problem, the present invention provides a communication device on a slave side that receives a packet including transmission time information and transmission order information supplied from a master side via a communication network. The time information of this device and the order information included in the packet are set as the reception time information and the order information of reception in the packet received by this device, and the time information of this reception and the order information of reception and the time information of transmission included in the packet And at least one of the packet supply order and missing, based on the transmission order information, calculates the interval between transmission and reception time information by control according to the result of the check, and calculates the calculated transmission and reception And a comparison means for calculating a difference in time information interval as a time information interval for transmission and reception and outputting a value indicated by the difference obtained by the calculation. Smoothing means for calculating an average value by smoothing a packet supplied over a transmission / reception time information interval corresponding to the value by control according to the result, and gain adjustment for generating information for adjusting the gain according to the average value Means for generating a reference clock in the apparatus, and time information generating means for receiving the clock and generating the reception time information at a predetermined interval. Is characterized in that the generated reception time information is input to the comparison means.

  In order to solve the above-mentioned problem, the present invention receives a packet including transmission time information and transmission order information supplied from the master side via the communication network on the slave side, and regenerates the synchronous clock. In this clock recovery method, this method sets the time information on the slave side and the order information included in the packet as the received time information and the received order information in the received packet, and the received time information and the received order information Based on the transmission time information and the transmission order information included in the packet, at least one of the packet supply order and missing is checked, and the interval between the transmission and reception time information is calculated by the control according to the check result. Then, the difference between the calculated transmission and reception time information intervals is calculated as the transmission and reception time information interval, and the value indicated by the calculation is output. A second step of smoothing a packet supplied over a transmission / reception time information interval corresponding to the value by a control according to the result of examination, and calculating an average value, and according to the average value A third step of generating information for gain adjustment, a fourth step of generating a reference clock on the slave side, and a fifth step of generating reception time information at predetermined intervals in response to the supply of this clock. And a sixth step of stamping the reception time information generated in the supplied packet.

  According to the communication device and the clock recovery method thereof of the present invention, a packet including transmission time information and transmission order information is generated based on the master clock of the master device, and distributed to the slave device via the IP network. The time information of the slave device and the order information included in the packet are set as the reception time information and the reception order information in the received packet, and the reception time information and the reception order information and the transmission time information and the transmission order included in the packet are set. Based on the order information, check at least one of the packet supply order and missing, calculate the interval between transmission and reception time information by the control according to the result, and calculate the transmission and reception time information The difference between the two is calculated as the transmission / reception time information interval, and the value indicated by the calculation is output. The frequency difference obtained from the packets before and after the packet where packet loss or change of the arrival order of packets occurred by smoothing the packets supplied over the transmission / reception time information interval corresponding to the value by control Based on the information, it is compensated as the frequency difference information of the preceding and succeeding packets, corrected, the gain adjusting means generates information for adjusting the gain according to the average value, the clock generating means generates the reference clock in the slave device, By generating the reception time information at predetermined intervals by the time information generation means, the continuity of the frequency information can be maintained, and the influence on the slave clock reproduction by the abnormal packet can be easily reduced.

  Next, an embodiment of a communication apparatus according to the present invention will be described in detail with reference to the accompanying drawings. Referring to FIG. 1, the embodiment of the communication device according to the present invention sets the time information of the slave device and the order information included in the packet in the packet received by the transmission / reception interval comparison unit 50 as the reception time information and the reception order information. Based on the reception time information and reception order information and the transmission time information and transmission order information included in the packet, at least one of the supply order of the packets (replacement of arrival order) and missing is examined, The interval between the transmission and reception time information is calculated by the control according to the checked result, the difference between the calculated transmission and reception time information is calculated as the transmission and reception time information interval, and the difference obtained by the calculation is indicated. The value is output, and the packets supplied over the transmission / reception time information interval corresponding to the value are smoothed by the control according to the result checked by the smoothing unit 52, and the average value is calculated. Based on the frequency difference information obtained from the packet before and after the packet in which the arrival order is changed or lost, it is compensated as the frequency difference information of the preceding and succeeding packets, corrected, and the gain adjustment unit 54 responds to the average value The slave clock unit 56 generates the reference clock for the slave device, and the time stamp generator 58 generates the reception time information in the same manner as the transmission time information generated by the master device. As a result, the continuity of the frequency information can be maintained, and the influence of the abnormal packet on the slave clock reproduction can be easily reduced.

  In this embodiment, the communication device of the present invention is applied to the slave device 10 of the communication system. The illustration and description of parts not directly related to the present invention are omitted. In the following description, the signal is indicated by the reference number of the connecting line in which it appears.

  The communication system 12 of the present embodiment includes a master device 14 and a plurality of slave devices 10, 16, 18 and 20 as shown in FIG. In the communication system 12, the master device 14 and each of the plurality of slave devices 10, 16, 18 and 20 are connected to an IP (Internet Protocol) network 32 by signal lines 22 to 30.

  As shown in FIG. 3, the master device 14 includes a master clock unit 34, a time stamp generation unit 36, a sequence number generation unit 37, a data generation unit 38, and a packet generation unit 40. The master device 14 has a function of transmitting a packet to each of the slave devices 10, 16, 18, and 20 via the IP network 32. The packet has a header storing a header, a time stamp, a sequence number, and data from the top of the packet. The header includes, in a predetermined area, the addresses of the transmission source / destination of the master device 14 and the slave devices 10, 16, 18 and 20, respectively. The time stamp, sequence number, and data payload will be described later.

  The master clock unit 34 has a function of generating time information serving as a reference for the master device 14 and the plurality of slave devices 10, 16, 18 and 20, and includes a reference oscillator. The master clock unit 34 transmits the generated time information, that is, the clock 42 to the time stamp generation unit 36.

  The time stamp generator 36 has a function of incrementing the counter value at a predetermined time interval based on the supplied clock 42, and includes a counter that counts the increment. Since this counter value is used as the time stamp 44, it is possible to refer to this counter value from the packet generation unit 40, and the packet generation unit 40 transmits a packet at a predetermined counter value interval.

  The sequence number generation unit 37 has a counter that increments by one every time a packet is generated, and transmits this counter value as a sequence number 45 to the packet generation unit 40.

  The data generation unit 38 has a function of generating data to be transmitted from the master device 14 to each of the slave devices 10, 16, 18 and 20. The data generation unit 38 sends the generated data 46 to the packet generation unit 40.

  The packet generator 40 stores the supplied time stamp 44, sequence number 45 and data 46 in each predetermined area following the header from the beginning of the packet, generates a packet 48, and transmits the generated packet 48 It has the function to do.

  Each of the slave devices 10, 16, 18 and 20 includes the same components. Therefore, in order to avoid complications due to repeated description, the slave device represents the slave device 10 and describes each component with reference to the slave device 10.

  As shown in FIG. 1, the slave device 10 includes a transmission / reception interval comparison unit 50, a smoothing unit 52, a gain adjustment unit 54, a slave clock unit 56, and a time stamp generation unit 58. The transmission / reception interval comparison unit 50 extracts the information included in the packet 48 supplied from the master device 14, and determines the transmission information interval calculated based on the extracted information and the slave device 10 according to the supplied packet 48. It has a function of comparing the calculated reception information interval to obtain a transmission / reception interval. This comparison is also a frequency comparison between the reference oscillator of the master device and the slave clock of the slave device. The transmission / reception interval comparison unit 50 includes an information extraction unit 60, a marking unit 62, a history extraction unit 64, a sequence number confirmation unit 66, an interval calculation unit 68, and an interval comparison unit 70.

  The information extraction unit 60 has a function of decomposing the packet 48 transmitted from the master device 14, extracting the time stamp and sequence number included in the packet 48 as transmission extraction information 72, and outputting the extracted information. The information extraction unit 60 transmits the transmission extraction information 72 as the current transmission time stamp and the current sequence number to the history extraction unit 64, the sequence number confirmation unit 66, and the interval calculation unit 68, respectively.

  The stamping unit 62 has a function of stamping the time stamp 74 received from the time stamp generating unit 58 as the current reception time stamp every time the packet 48 is received from the master device 14. The stamping unit 62 also has a function of extracting a sequence number included in the packet 48 received from the master device 14. The stamping unit 62 transmits the stamped time stamp and the extracted sequence number to the history extracting unit 64 and the interval calculating unit 68 as reception extraction information 76. The reception extraction information 76 is a current reception time stamp and a current sequence number for the transmission extraction information 72.

  The history extraction unit 64 includes time stamp history extraction units 78 and 80. The history extracting unit 64 has a function of storing the current time stamp and the current sequence number in association with each other, and outputting the stored time stamp and the sequence number as transmission history information 82 and reception history information 84 based on the previous confirmation result. Time stamp history extraction units 78 and 80 output transmission history information 82 and reception history information 84 to sequence number confirmation unit 66 and interval calculation unit 68, respectively. The transmission history information 82 is usually a transmission time stamp and a sequence number stored last time. When the previous transmission / reception interval calculation processing is skipped due to the change of the arrival order of packets, the time stamp history extraction unit 78 outputs the transmission time stamp and sequence number stored before the packet for which processing has been skipped. The reception history information 84 is also usually a reception time stamp and a sequence number stored last time. When the previous transmission / reception interval calculation processing is skipped due to the change of the arrival order of packets, the time stamp history extraction unit 80 outputs the reception time stamp and sequence number stored before the packet for which processing has been skipped.

  The sequence number confirmation unit 66 compares the current sequence number included in the transmission extraction information 72 with the previous sequence number included in the transmission history information 82 based on the new and old of these numbers, and checks the sequence number order and the missing sequence number. It has a function of generating a control signal according to the check result. The sequence number confirmation unit 66 transmits the current transmission to the transmission interval calculation unit 86 and the reception interval calculation unit 88 of the interval calculation unit 68 when the current sequence number is larger than the previous sequence number and the current sequence number and the previous sequence number are serial numbers. A control signal 90 for instructing calculation of an interval between the time stamp and the previous transmission time stamp is generated and output. The sequence number confirmation unit 66 also sets the current transmission time to the transmission interval calculation unit 86 and the reception interval calculation unit 88 when the current sequence number is larger than the previous sequence number and there is a missing number between the current sequence number and the previous sequence number. A control signal 90 is transmitted to instruct the calculation of the interval between the stamp, the missing time stamp, and the stored transmission time stamp. At this time, the control signal 90 is also supplied to the smoothing unit 52.

  Further, when the current sequence number is smaller than the previous sequence number and the arrival sequence is reversed between the current sequence number and the previous sequence number, the sequence number confirmation unit 66 sends a transmission interval calculation unit 86 and a reception interval calculation unit 88 to each other. A control signal 90 for instructing to skip processing is output. At the same time, the sequence number confirmation unit 66 transmits the transmission history information 82 and the reception history information 84 to be transmitted next to the time stamp history extraction units 78 and 80, the transmission time stamp and the sequence number stored before the skipped packet, In addition, a control signal 90 instructing transmission of the reception time stamp and the sequence number is output. The sequence number confirmation unit 66 also outputs a control signal 90 to the smoothing unit 52.

  The interval calculation unit 68 includes a transmission interval calculation unit 86 and a reception interval calculation unit 88. The interval calculation unit 68 calculates the interval between the current transmission time stamp and the previous transmission time stamp in the adjacent sequence numbers and the interval between the current reception time stamp and the previous reception time stamp in response to reception of the control signal 90. It has a function. In addition, the interval calculation unit 68 generates an interval by interpolation from the current transmission time stamp and the previous transmission time stamp in accordance with reception of the control signal 90 generated when the loss is detected, and the current reception time stamp and the previous reception time stamp. Has a function of calculating the interval by interpolation. Needless to say, the transmission interval calculation unit 86 has the above-described transmission interval calculation function, and the reception interval calculation unit 88 has the above-described reception interval calculation function. The transmission interval calculation unit 86 and the reception interval calculation unit 88 also have an arithmetic function for dividing, for example, between one sequence number or a predetermined sequence number n. The division value may be newly set as the intervals 92 and 94 under the above-described conditions.

  The transmission interval calculation unit 86 outputs the calculated interval 92 between the current transmission time stamp and the previous transmission time stamp to the interval comparison unit 70. The reception interval calculation unit 88 also outputs the calculated interval 94 between the current reception timestamp and the previous reception timestamp to the interval comparison unit 70.

  The interval comparison unit 70 has a function of calculating a difference between the interval 92 and the interval 94 as a transmission / reception time stamp interval. Since the transmission / reception time stamp interval is time information generated according to the master clock and the slave clock, the frequency information of these clocks is reflected. Therefore, the interval comparison unit 70 can also be said to be a frequency comparison between the master clock and the slave clock. The interval comparison unit 70 outputs the calculated transmission / reception time stamp interval 96 to the smoothing unit 52.

  The smoothing unit 52 has a function of, for example, smoothing transmission / reception time stamp interval data based on the supplied transmission / reception time stamp interval 96 and calculating an average value of transmission / reception intervals. The smoothing unit 52 outputs the calculated transmission / reception interval average value 98 to the gain adjusting unit 54.

  However, when the smoothing unit 52 receives a control signal 90 corresponding to a lack or order reversal in the transmission / reception time stamp interval 96 used in smoothing, there is a smoothing section in which the packet arrival order is discontinuous. The output of the calculated transmission / reception interval average value 98 to the gain adjustment unit 54 may be suspended, and the output may be carried over to the next smoothing section. Similarly, when the transmission / reception time stamp interval 96 used for smoothing exceeds a predetermined threshold, the smoothing unit 52 suspends the output of the calculated transmission / reception interval average value 98 to the gain adjustment unit 54 and smoothes the output next time. It is preferable to carry over to the section.

  The gain adjustment unit 54 has a function of generating the gain adjustment information 100 based on the supplied transmission / reception interval average value 98. When the transmission time stamp interval is smaller than the reception time stamp interval, the gain adjustment unit 54 determines that the slave clock frequency is higher than the master clock, and lowers the frequency of the time information 102 generated by the slave clock unit 56. The gain adjustment information 100 to be generated is generated. Further, when the transmission time stamp interval is larger than the reception time stamp interval, the gain adjustment unit 54 determines that the frequency of the slave clock is lower than the master clock, and the frequency of the time information 102 generated by the slave clock unit 54 Is generated. The gain adjustment unit 54 outputs the generated gain adjustment information 100 to the slave clock unit 56.

  The slave clock unit 56 has a function of generating time information serving as a reference for the slave device 10 based on the gain adjustment information 100 supplied. The slave clock unit 56 outputs the slave clock 102 that is the generated time information to the time stamp generation unit 58.

  The time stamp generator 58 has a function of incrementing the counter value at a predetermined time interval based on the supplied slave clock 102, and includes a counter that counts the increment. Since this counter value is used as a reception time stamp, it is output to the stamping unit 62 as a time stamp 74.

  By configuring in this way, the difference between the transmission / reception time stamps is calculated by the transmission / reception interval comparison unit 50 in the slave device 10, the calculated difference is treated as a total value, and the value obtained by dividing the total value is the difference between the sequence numbers. As a result, it is possible to maintain the continuity of the frequency information, accumulate the transmission / reception time stamp difference in the smoothing unit 52 for a long period, smooth the error, absorb the error of the difference calculated by prediction, and reduce the influence. .

  Next, the operation in the slave device 10 to which the communication device of the present invention is applied will be briefly described. In the slave device 10, the effects of packet loss and packet arrival order discontinuity are that the process of maintaining the continuity of frequency information and the packet arrival order reversal even when the packet arrival order becomes discontinuous. This is reduced by not processing each received packet when it occurs.

  As shown in FIG. 4, the slave device 10 defines the interval 110 between the sequence numbers 0 and 1 to be represented by (0, 1). The interval 112 is expressed as (1,3), the interval 114 as (3,4), the interval 116 as (4,6), and the interval 118 as (6,7). The interval 112 is equal to the sum of the differences of (1,2) and (2,3). The interval 116 is also equal to the sum of the differences of (4,5) and (5,6), but the packet arrival order of sequence numbers 5 and 6 is reversed, and the interval 122 is a negative value. Processing becomes complicated. Therefore, when the arrival order of packets becomes discontinuous as indicated by (4,5) indicated by interval 120 and (5,6) indicated by interval 122, that is, for example, the sequence of the received packet in the packet of sequence number 5 If a packet whose number should arrive before the expected value is received, it is not processed. For example, when a packet whose sequence number is 3 or 6 is received after the expected value, the difference between the transmission and reception time stamps is calculated. It is good to calculate and correct.

  In addition, when the packet with the sequence number 2 is lost, the transmission / reception timestamp difference between the sequence numbers 1 and 2 and the sequence numbers 2 and 3 cannot be calculated. However, the difference between the transmission time stamps of sequence numbers 1 and 3 can be calculated. As described above, this is the total value of the differences between sequence numbers 1 and 2 and sequence numbers 2 and 3. The slave device 10 compensates the value obtained by dividing the total value as the difference between the sequence numbers 1 and 2 and the sequence numbers 2 and 3. As a result, the slave device 10 can maintain the continuity of the frequency information. If this compensation is viewed microscopically, there is a possibility of increasing the error in frequency information, but the slave device 10 accumulates and smoothes the transmission / reception time stamp difference for a long period of time. The slave device 10 does not correct the slave clock based on the frequency information every time. Therefore, the error of the difference calculated by prediction hardly affects the slave device 10.

  Further, when the packet arrival order of the second problem is reversed as in sequence numbers 5 and 6, the slave device 10 determines that the difference between the transmission / reception time stamps of sequence numbers 4 and 6 is the sequence numbers 4 and 5 and the sequence number The sum of the differences between the numbers 5 and 6 is used. The slave device 10 treats the value obtained by dividing the difference between the sequence numbers 4 and 6 as the difference between the sequence numbers 4 and 5 and the difference between the sequence numbers 5 and 6 and searches backward and forward packets. As a result, the slave device 10 can avoid a troublesome process of calculating a difference. Similarly to packet loss, this processing also tends to increase the frequency information error when viewed microscopically. However, the smoothing process or the like hardly causes an influence. Therefore, the effect is the same as when processing is performed for each packet.

  Next, a method for reproducing a stable clock even when the arrival order of packets is discontinuous will be described. The communication between the master device 14 and the slave device 10 in FIG. 5 is smoothing in which the average smoothing section 124 is between the sequence numbers 100 and 200 and the packet arrival order is discontinuous between the sequence numbers 200 and 300. Between the section 126 and the sequence numbers 300 and 400, the smoothed section 128 after the network stabilization is shown. The slave device 10 holds the correction to the slave clock when the smoothing interval where the packet arrival order is discontinuous or the transmission / reception time stamp difference exceeds a predetermined value, and the difference information of the transmission / reception time stamp is Carry over to the smoothing section. Therefore, the slave device 10 reduces the influence by avoiding correction to the slave clock due to a delay generated in a burst manner and increasing the smoothing interval by using the frequency information of the plurality of intervals 130 as between the sequence numbers 200 and 400. be able to. Moreover, the continuity of the frequency information can be maintained by carrying forward the transmission / reception time stamp difference information of the section in which the packet arrival order is not reached.

  The basic operation of the solution to the above two problems will be described. When receiving the packet, the slave device 10 compares it with the sequence number of the difference calculation target packet. If the sequence number of the received packet is newer, the slave device 10 calculates a transmission / reception time stamp difference from the difference calculation target packet. The difference calculation target packet is the packet with the latest sequence number, and is basically the packet received last time. When the difference between the sequence numbers of the received packet and the difference calculation target packet is n, the difference calculation result is divided into n and compensated as the transmission / reception time stamp difference of the packet of each sequence number. Thereafter, the transmission / reception time stamp and sequence number of the received packet are overwritten on the information of the difference calculation target packet. If the sequence number of the received packet is older, the calculation of the transmission / reception time stamp, the overwrite of the information of the difference calculation target packet, etc. are not processed.

  Next, it will be specifically described with reference to FIG. When the sequence number 1 packet in FIG. 6 is received, the sequence number of the difference calculation target packet is 0. Therefore, the transmission / reception time stamp difference is calculated as usual, and the packet of sequence number 1 is included in the difference calculation target packet information. Overwrite information.

  Following this, when a packet with sequence number 3 is received due to packet loss, the sequence number of the difference calculation target packet is 1, and there are two gaps in the sequence number. Therefore, the slave device 10 calculates a transmission / reception time stamp from the difference calculation target packet. In this case, the transmission time stamp interval is 2000, and the reception time stamp interval is 1600. The transmission / reception time stamp interval is 400 because ((reception time stamp interval) − (transmission time stamp interval)) / n. The slave device 10 compensates the transmission / reception time stamp interval, that is, the value 200 divided by n = 2 according to the two gaps as the transmission / reception time stamp difference between the sequence numbers 1 and 2 and the sequence numbers 2 and 3. Thereafter, the information of the sequence number 3 is overwritten on the information of the difference calculation target packet.

  Although not shown, for example, packets with sequence numbers 2 and 3 may continue to be lost. In this case, the sequence number of the difference calculation target packet is 1 when the packet of sequence number 4 is received. Therefore, there are three gaps in the sequence number interval. Therefore, the slave device 10 divides the result of calculating the transmission / reception time stamp from the difference calculation target packet into three by n = 3. The slave device 10 compensates the divided values as transmission / reception time stamp differences of sequence numbers 1 and 2, sequence numbers 2 and 3, and sequence numbers 3 and 4, respectively. Thereafter, the slave device 10 may overwrite the information of the sequence number 4 on the information of the difference calculation target packet.

  As shown in FIG. 6, the case where the arrival order of sequence numbers 5 and 6 is switched will be described. When the packet with the sequence number 6 is received, the sequence number of the difference calculation target packet is 4. Therefore, there are two openings in the sequence number. In this case, the slave device 10 calculates the difference between the transmission / reception time stamps from the difference calculation target packet (2000-1000 = 1000). The slave device 10 compensates the value 500 obtained by dividing the calculation result into two as the transmission / reception time stamp differences (intervals) of the sequence numbers 4 and 5 and the sequence numbers 5 and 6, respectively. Thereafter, the slave device 10 overwrites the information of the sequence number 6 on the information of the difference calculation target packet. Even if the packet with the sequence number 5 is received thereafter, the slave device 10 does not perform any processing upon receiving this packet because the sequence number of the difference calculation target packet is 6 and the sequence number of the received packet is older. do not do.

  The solution will now be described with reference to FIG. In the smoothing sections 132, 134, and 136 for calculating the transmission / reception time stamp difference, when packet loss or arrival order inversion occurs, the smoothing section 134 or the transmission / reception time stamp difference is greater than a predetermined value, the smoothing section 134 The slave clock is not corrected using the transmission / reception time stamp difference at, and the difference is carried forward to the next smoothing section 136.

  If packet loss or arrival order inversion does not occur in the next smoothing section 136, the slave device 10 adds the carry-over value of the transmission / reception timestamp difference at the interval (200,300) and the transmission / reception timestamp difference at the interval (300,400). Is calculated (3400 + (-3200) = 200). If this total value is within a predetermined value range, the slave device 10 corrects the slave clock using the total value of this interval and the previous differential carry-over value. Even in the next smoothing interval, if packet loss, arrival order inversion occurs, or the transmission / reception time stamp difference is large, the slave device 10 carries over the difference repetition processing until the network is stabilized.

  In addition, although the present Example described the synchronous clock transmission system in the IP network using a time stamp and a sequence number, since the transmission time stamp interval becomes constant by making the transmission interval of the master device constant, Synchronous clock transmission can be realized only with the sequence number information.

  By operating in this way, even if a packet is lost, it is possible to maintain the continuity of frequency information by predicting and compensating for the frequency difference between the lost packet and the previous and next packets from the previous and next packets, The influence on the slave clock due to packet loss can be reduced.

  In addition, this makes it possible to reduce the circuit by reducing the memory for transferring the arrival sequence of packets and the like, and to eliminate complicated processing.

  Furthermore, the influence of delay on the network can be reduced by avoiding correction of slave clock due to a section in which the packet arrival order becomes discontinuous, a section with a large network delay, and carry over of transmission / reception time stamp difference information in this section. it can.

It is a block diagram which shows the schematic structure of the slave apparatus in the communication system to which the communication apparatus which concerns on this invention is applied. It is a figure which shows the schematic structure in the communication system of FIG. FIG. 2 is a block diagram illustrating a schematic configuration of a master device included in the communication system of FIG. 1. 3 is a timing chart for explaining a communication method for a case where the arrival order of packets in the communication system of FIG. 1 is discontinuous. 3 is a timing chart for explaining a communication method for a case where the arrival order of packets in the communication system of FIG. 1 is discontinuous. It is a timing chart explaining the communication method with respect to the case where the packet in the communication system of FIG. 1 is missing. 3 is a timing chart for explaining a communication method for a case where the arrival order of packets in the communication system of FIG. 1 is discontinuous.

Explanation of symbols

10 Slave device
50 Transmit / Receive interval comparator
52 Smoothing part
54 Gain adjuster
56 Slave clock section
58 Time stamp generator
60 Information extractor
62 Stamped part
64 History extractor
66 Sequence number confirmation part
68 Interval calculator
70 Interval comparison unit

Claims (10)

In the communication device on the slave side that receives the packet including the transmission time information and the transmission order information supplied from the master side via the communication network, the device includes:
The time information of the device and the order information included in the packet are set as the reception time information and the reception order information in the packet received by the device, and the reception time information and the reception order information and the transmission included in the packet are set. Based on the time information and the transmission order information, at least one of the supply order and lack of the packets is checked, and an interval between the transmission and reception time information is calculated by control according to the check result. A comparison unit that calculates a difference between the calculated transmission and reception time information as a transmission / reception time information interval, and outputs a value indicated by the calculation;
Smoothing means for smoothing packets supplied over the transmission / reception time information interval corresponding to the value by control according to the examination result, and calculating an average value;
Gain adjusting means for generating information for gain adjustment according to the average value;
Clock generating means for generating a reference clock in the apparatus;
Time information generating means for receiving the clock and generating the reception time information at predetermined intervals;
The time information generation means inputs the generated reception time information to the comparison means. 2. The apparatus according to claim 1, wherein the comparison unit extracts extraction time information and transmission order information from the packet;
The reception time information is set in the supplied packet, the transmission order information included in the packet supplied as the reception order information is extracted, and the reception time information and the reception order information are output. Engraving means,
Based on the reception time information and the reception order information and the transmission time information and the transmission order information, at least one of the supply order and lack of the packets is checked, and a control signal corresponding to the result of the check Confirmation control means for generating
Storage means for storing the transmission time information and the transmission order information and the reception time information and the reception order information over a predetermined period, and having a history for these information;
First interval calculation means for calculating a transmission time interval between the latest transmission time information and the previous transmission time information and a reception time interval between the latest reception time information and the previous reception time information;
A communication apparatus comprising: a second interval calculation unit that calculates a difference between the transmission time interval and the reception time interval.   3. The apparatus according to claim 2, wherein the first interval calculation means calculates the transmission time interval and the reception time interval, and the transmission time calculated by a control signal generated in response to occurrence of the packet loss. Dividing the interval and the reception time interval by a value indicated by a difference in order information of previous and subsequent packets with respect to the lost packet, and setting the obtained division value as the transmission time interval and the reception time interval. A communication device.   3. The apparatus according to claim 2, wherein the confirmation control unit compares the sequence information included in the supplied packet with the sequence information stored in the storage unit, and generates the control signal according to the comparison result. A communication device characterized by:   3. The apparatus according to claim 2, wherein the confirmation control means is based on difference information that is a difference between the transmission time interval and the reception time interval in a smoothing section including a packet in which an abnormality has occurred in response to the occurrence of an abnormality in the packet. A communication apparatus that generates a control signal that avoids correction and carries over the difference information to a next smoothing interval. In a clock recovery method for receiving a packet including transmission time information and transmission order information supplied from a master side via a communication network on a slave side and recovering a synchronous clock, the method includes:
The slave time information and the order information included in the packet are set as the reception time information and the reception order information in the received packet, the reception time information and the reception order information, the transmission time information included in the packet, and Based on the transmission order information, at least one of the supply order and lack of the packets is examined, and the interval between the transmission and reception time information is calculated by control according to the examined result, and the calculated A first step of calculating a difference between transmission and reception time information as a transmission / reception time information interval, and outputting a value indicated by the difference obtained by the calculation;
A second step of calculating an average value by smoothing the packets supplied over the transmission / reception time information interval corresponding to the value by control according to the examination result;
A third step of generating information for gain adjustment according to the average value;
A fourth step of generating a reference clock on the slave side;
A fifth step of receiving the clock and generating the reception time information at predetermined intervals;
And a sixth step of imprinting the reception time information generated in the supplied packet. The method according to claim 6, wherein the first step is a seventh step of extracting transmission time information and transmission order information from the packet;
The transmission order information extracted from the packet is set as reception order information, and the transmission time information, the transmission order information, the reception time information set in the supplied packet, and the reception order information. On the basis of at least an eighth step of examining at least one of the packet supply order and missing, and generating a control signal according to the examined result;
A ninth step of storing the transmission time information and the transmission order information and the reception time information and the reception order information over a predetermined period;
A tenth step of calculating a transmission time interval between the latest transmission time information and the previous transmission time information and a reception time interval between the latest reception time information and the previous reception time information;
A clock recovery method comprising: an eleventh step of calculating a difference between the transmission time interval and the reception time interval.   The method according to claim 7, wherein the tenth step calculates the transmission time interval and the reception time interval, and calculates the transmission time interval calculated by a control signal generated in response to occurrence of the packet loss. The reception time interval is divided by a value indicated by a difference in order information of previous and subsequent packets with respect to the lost packet, and the obtained division value is set as the transmission time interval and the reception time interval. Clock recovery method.   8. The method according to claim 7, wherein the eighth step compares the order information included in the supplied packet with the order information stored in the storage means, and generates the control signal according to the comparison result. And a clock recovery method.   The method according to claim 7, wherein the eighth step is based on difference information that is a difference between the transmission time interval and the reception time interval in a smoothing section including a packet in which an abnormality has occurred in response to the occurrence of an abnormality in the packet. A clock recovery method characterized by generating a control signal that avoids correction and carries over the difference information to the next smoothing interval.

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