JP2005253033A - Network synchronization device, clock transmission method, and clock transmission packet network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a user terminal to obtain a clock synchronized with a standard clock of a master station (master clock) in a packet network, where the delay time of user packet changes, depending on the length of queue at a router or at a switch. <P>SOLUTION: In this method, transmission time t1 is loaded to an inquiry packet, and t1, reception time t2 of the inquiry packet, and transmission time t3 of a reply packet are loaded to the reply packet. On the basis of the reception time of the reply packet and t1, t2, and t3 which are obtained from the reply packet, time error between the slave clock time and the master clock time is computed. A value, corresponding to the delay time of a router where the inquiry packet passes is added to t1 and rewritten, and a value corresponding to the delay time of a router, where the reply packet passes, is added to t3 and rewritten. Using t2 and t4 and rewritten t1' and t3', the time error is computed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a network synchronization apparatus, a clock transmission method, and a clock transmission packet network that perform clock synchronization in a packet network that transmits packets via a router or a switch. Here, the clock synchronization means that the local time of the slave clock of the clock supply destination is matched with the standard time obtained with the master clock of the clock supply source, or the slave clock frequency is matched with the master clock frequency.

  FIG. 17 shows a conventional network synchronization method in a digital network (Non-Patent Document 1). The master station 80 is provided with a high-precision standard clock generator 81. Here, clocks of various frequencies synchronized with the standard clock obtained by multiplying and dividing the standard clock generated by the standard clock generator 81 are referred to as “master clock (reference clock)”.

  The transmission device 82 of the master station 80 sends a signal synchronized with the master clock to the transmission path 83. The transmission device 85 of each slave station 84 extracts a clock from a signal arriving from the master station 80 via the transmission path 83 and regenerates the master clock by the master clock oscillator 86. As a result, the master clock is distributed from the master station 80 to each slave station 84. This master clock is supplied to all the transmission devices (subscriber line end station devices) 87 of the slave station 84, and each transmission device 87 sends a signal synchronized with the multiplied and divided master clock via the transmission path 88. Send it to the user's home. The transmission device (network termination device) 89 and the user terminal 90 in the user's home extract a clock from a signal arriving from the slave station 84 via the transmission path 88 and reproduce the master clock. Thereby, network synchronization can be established from the master station 80 to the user terminal 90.

  Using the master clock obtained from the network, the user terminal 90 A / D converts analog signals such as voice and video and sends them to the network. The user terminal 90 uses this master clock when D / A converting a digital signal received from the network. In this way, all user terminals accommodated in the digital network perform A / D conversion and D / A conversion using the synchronized master clock, thereby preventing slippage in the network. It becomes possible.

  On the other hand, the above network synchronization method cannot be applied as it is in a packet network that transmits packets via a router or a switch. In general, in a router and a switch, as shown in a simplified manner in FIG. 18, since signals output via an elastic store (ES) that performs clock transfer at each port are generated by independent local clocks, It is not synchronized with the master clock. Therefore, even if a signal synchronized with the master clock is transmitted from the master station to the slave station, the synchronization relationship with the master clock is lost by the router or switch of the slave station, and the master clock cannot be transmitted to the user terminal.

  As a network synchronization method in such a packet network, there is a method of generating a clock packet in which the time of a master clock of a master station is mounted as a time stamp and delivering it to a user terminal via a router or a switch. For example, NTP (Network Time Protocol) shown in the standard RFC1305 defined by IETF (Internet Engineering Task Force) (Non-patent Document 2). The principle of NTP is shown in FIG.

  It is assumed that an NTP server 91 having a master clock and an NTP client 92 that wants to obtain a time synchronized with the master clock are connected via a network 93. The NTP client 92 transmits to the NTP server 91 a clock packet (inquiry packet) carrying the transmission time t1 based on its own slave clock. The NTP server 91 generates a clock packet (answer packet) corresponding to the reception of the inquiry packet and transmits it to the NTP client 92. This reply packet includes the inquiry packet transmission time t1, the inquiry packet reception time t2 by its own master clock, and the reply packet transmission time t3. The NTP client 92 takes out the times t1, t2, and t3 described in the reply packet and records the reply packet reception time t4 using its own slave clock.

From these times, the round-trip delay time d between the NTP server 91 and the NTP client 92 is
d = (t4−t1) − (t3−t2)
It becomes. Here, assuming that the one-way delay time is d / 2 and the error between the master clock of the NTP server 91 and the clock of the NTP client 92 is c,
t1 + c + d / 2 = t2 (or t3 + d / 2 = t4 + c)
And
c = (t2-t1 + t3-t4) / 2
It becomes.

  In the NTP, the slave clock of the NTP client 92 is corrected with the error c, so that the time synchronized with the master clock of the NTP server 91 can be obtained by the NTP client 92.

  Further, the slave clock frequency of the NTP client 92 can be synchronized with the master clock frequency of the NTP server 91 by using a time stamp value to be put on a clock packet (answer packet) transmitted from the NTP server 91 to the NTP client 92.

FIG. 20 shows a configuration example of the slave clock control circuit of the NTP client 92. In the figure, the time stamp value TS (1) mounted on the clock packet transmitted from the NTP server 91 is input to the counter 95 via the switch 94 to initialize the counter value. The counter 95 counts up with the slave clock 96. The time stamp value TS (2) mounted on the clock packet that arrives at the next timing is input to the comparator 97 via the switch 94. The comparator 97 compares the value of the counter 95 (TS ′ (1) counted up from TS (1)) with TS (2). Here, if the slave clock 96 is frequency-synchronized with the master clock of the NTP server 91,
TS '(1) ＝ TS (2)
If asynchronous, the frequency error e is
e = TS '(1) -TS (2)
It becomes. By controlling the slave clock 96 with the frequency error e, the switch clock 96 can be frequency-synchronized with the master clock.
Kasai, Sakai, Sakai, Ueda, “Intuitive SDH / SONET Transmission System”, Ohm, Chapter 6 http://www.faqs.org/rfcs/rfc1305.html

  By the way, in the packet network, packets are accumulated in a buffer by a router or a switch and are waiting to be sent out, so that a delay fluctuation occurs due to the queue. Therefore, the delay time of the packet depends on the length of the queue of the router or switch that passes through, and the delay time of the forward path and the return path may be different.

  In a conventional NTP that transmits time information using a packet, the one-way delay time is assumed to be half of the round-trip delay time. However, as shown in FIG. 21, if the forward and backward delay times w1 and w2 differ depending on the delay time in the router or switch, the error c based on this assumption becomes inaccurate, and the time of the slave clock is changed to the master clock. It becomes difficult to synchronize accurately. That is, it is difficult for the user terminal to obtain an accurate master clock from the NTP server.

  On the other hand, even in the case of frequency synchronization, since the delay time in the router or switch differs for each clock packet (w2 ≠ w3), the frequency error between the master clock and the slave clock cannot be obtained accurately.

  The present invention enables a user terminal to obtain a clock synchronized with a standard clock (master clock) of a master station in a packet network in which the delay time of user packets varies depending on the queue length of a router or switch. An object is to provide a network synchronization device, a clock transmission method, and a clock transmission packet network.

(Clock transmission method)
According to the first aspect of the present invention, the clock supply source has a high-precision master clock, the clock supply destination has a self-running slave clock, the inquiry packet is transmitted from the clock supply destination to the clock supply source, When sending a reply packet to the inquiry packet from the supply source to the clock supply destination, the inquiry packet is loaded with the transmission time t1 by the slave clock, the answer packet is received with the inquiry packet reception time t2 by the master clock, and the reply packet is transmitted. Time t3 is mounted, and the error of the slave clock time with respect to the master clock time is calculated from the reception time t4 of the response packet by the slave clock and the values of t1, t2, and t3 obtained from the response packet, and according to the error Adjust the slave clock to master clock In the clock transmission method for adjusting to the time of, the value corresponding to the delay time of the router or switch through which the inquiry packet passes is rewritten by adding to t1, and the value according to the delay time of the router or switch through which the answer packet passes is The error of the slave clock time with respect to the master clock time is calculated using t1 and t3 integrated with t2 and t4.

  The clock supply source has a master counter that counts up with a high-precision master clock, and the clock supply destination has a slave counter that counts up with a self-running slave clock. The clock packet with the master counter value as time information is sent from the clock to the clock supply destination, the time information loaded in the clock packet is initialized in the slave counter, and the slave clock is self-running, and arrives at the next timing In a clock transmission method in which the time information mounted on the clock packet is compared with the value of the slave counter, the slave clock is adjusted according to the error, and the process of adjusting the slave clock frequency to the master clock frequency is repeated for each arrival of the clock packet. The clock packet passes Rewriting by accumulating a value corresponding to the delay time of the router or switch to the time information which is mounted to the clock packet, and compares the initial set and the value of the slave counter of the slave counter in accordance with the time information.

(Clock transmission packet network)
According to a third aspect of the present invention, the clock supply source has a high-precision master clock, the clock supply destination has a self-running slave clock, the inquiry packet is transmitted from the clock supply destination to the clock supply source, When sending a reply packet to the inquiry packet from the supply source to the clock supply destination, the inquiry packet is loaded with the transmission time t1 by the slave clock, the answer packet is received with the inquiry packet reception time t2 by the master clock, and the reply packet is transmitted. Time t3 is mounted, and the error of the slave clock time with respect to the master clock time is calculated from the reception time t4 of the response packet by the slave clock and the values of t1, t2, and t3 obtained from the response packet, and according to the error Adjust the slave clock to master clock In the clock transmission packet network that matches the time of, the router or switch through which the inquiry packet and the reply packet pass is rewritten by adding a value corresponding to the delay time through which the inquiry packet passes to t1 to obtain the delay time through which the reply packet passes. A network synchronization device is provided that adds and rewrites the corresponding value to t3, and the clock supply destination calculates the error of the time of the slave clock with respect to the time of the master clock using t2 'and t4' rewritten as t2 and t4. .

  According to a fourth aspect of the present invention, the clock supply source has a master counter that counts up with a high-precision master clock, the clock supply destination has a slave counter that counts up with a self-running slave clock, and the clock supply source The clock packet loaded with the master counter value as time information is sent from the clock to the clock supply destination, the slave counter is initialized with the time information loaded in the clock packet, and the slave clock self-runs and arrives at the next timing A clock transmission packet network that compares the time information mounted on the clock packet with the value of the slave counter, adjusts the slave clock according to the error, and adjusts the slave clock frequency to the master clock frequency every time the clock packet arrives The clock packet is A network synchronization device that rewrites the time information by adding a value corresponding to the delay time through which the clock packet passes to a router or switch that has a clock, and the clock supply destination initializes the slave counter according to the time information of the clock packet. Compare with the value of the slave counter.

  Here, there are a plurality of clock supply sources operating with different master clocks, and an identifier of each clock supply source is assigned to the clock packet so that a plurality of clock packets are transferred within the same packet network. (Claim 5). Further, when the clock supply destination inputs the first clock packet among the plurality of clock packets and adjusts the slave clock frequency to the master clock frequency, the arrival of the first clock packet is interrupted for a certain period of time. The second clock packet may be input to the slave counter, and the slave counter may be initialized by the time information mounted on the second clock packet.

  Also, a terminal that needs to match the master clock frequency sends a multicast request for a clock packet to the router or switch, and uses the clock packet multicast from the router or switch based on the request to change the slave clock frequency to the master clock frequency. The router or the switch may be configured to start the multicast of the clock packet with the requested terminal as the clock supply destination (Claim 7).

  Further, for a router or switch included in a path through which a plurality of clock packets pass, a clock packet of a path that minimizes the number of routers or switches that do not include a network synchronization device may be selected. ).

(Network synchronization device)
According to a ninth aspect of the present invention, in the network synchronization device of the clock transmission packet network according to the third aspect, the local time t1 at the time of transmission mounted in the inquiry packet input to the router or the switch is set in the counter, and the inquiry is made. Counting up until a packet is output, t1 accumulating means for overwriting t1 with the counter value when the inquiry packet is output, and a standard time t3 at the time of transmission mounted in the reply packet input to the router or switch T3 integrating means for setting the counter, counting up until the answer packet is output, and overwriting t3 with the value when the answer packet is output.

  According to a tenth aspect of the present invention, in the network synchronization device for the clock transmission packet network according to the fourth aspect, the time information mounted on the clock packet input to the router or the switch is set in the counter, and the clock packet is output. Time information integration means for counting up until the clock packet is output and overwriting the time information with the value when the clock packet is output.

  In the present invention, when a master clock is distributed to a user terminal or the like using a clock packet, a delay fluctuation generated in the clock packet is measured by a router or a switch, and time information (time stamp) mounted on the clock packet is corrected. To do. Thereby, the time information when there is no delay fluctuation equivalently can be obtained. Therefore, since the user terminal can obtain time information with no error, time synchronization or frequency synchronization can be accurately obtained with the master clock.

(First Embodiment of Clock Transmission Method of the Present Invention)
FIG. 1 shows a first embodiment of the clock transmission method of the present invention. In FIG. 1, the clock client transmits an inquiry packet carrying a transmission time t1 based on its own slave clock to the clock server. When this inquiry packet arrives at the first router / switch, the delay time is added to the transmission time t1. The result is t1 ′, and the transmission time t1 in the inquiry packet is rewritten to t1 ′ for transmission. When this inquiry packet arrives at the second router / switch, the delay time is added to the transmission time t1 '. The result is t1 ", and the transmission time t1 'in the inquiry packet is rewritten to t1" and output. If there are other routers / switches that pass through, the delay times are sequentially integrated each time the routers / switches pass through, and the transmission time is rewritten.

  The transmission time t1 "described in the inquiry packet arriving at the clock server corresponds to the transmission time when the inquiry packet arrives without any delay at the intermediate router / switch, as shown by the broken line in FIG. That is, correction is made so that no error occurs even if the delay time in the router / switch in the middle fluctuates.

  The clock server generates a response packet corresponding to the reception of the inquiry packet and transmits it to the clock client. This reply packet includes the inquiry packet transmission time t1 ", the inquiry packet reception time t2 by its own master clock, and the reply packet transmission time t3. This reply packet is input to the first router / switch. Then, the delay time there is added to the transmission time t3, and the result is set to t3 ', and the transmission time t3 in the reply packet is rewritten to t3', and the reply packet is transmitted to the second router / switch. Upon arrival, the delay time there is added to the transmission time t3 '. The result is set to t3 ", and the transmission time t3' in the reply packet is rewritten to t3" for transmission. In each case, each delay time is sequentially integrated and the transmission time is rewritten every time it passes.

  The clock client receives the reply packet, takes out the times t1 ", t2, and t3" described therein, and records the reply time t4 of the reply packet by its own slave clock. The transmission time t3 "described in the reply packet corresponds to the transmission time when the reply packet arrives without any delay at the middle router / switch, as shown by the broken line in FIG. The delay time at each router / switch in the direction from the clock client to the clock server and from the clock server to the clock client is Although passing through the same router / switch, they are independent of each other, and can cope with an arbitrary delay time according to each situation.

From these times, the round-trip delay time d between the clock server and the clock client is
d = (t4−t1 ″) − (t3 ″ −t2)
It becomes. Here, assuming that the one-way delay time is d / 2, and the error between the master clock of the clock server and the slave clock of the clock client is c,
t1 "+ c + d / 2 = t2 (or t3" + d / 2 = t4 + c)
And
c = (t2-t1 "+ t3-t4") / 2
It becomes.

  By correcting the time of the slave clock of the clock client by this error c, the time synchronized with the master clock of the clock server can be obtained by the clock client. The difference from the conventional NTP is that the inquiry packet transmission time t1 and the response packet transmission time t3 are corrected so as to be equivalent to the case where there is no delay in the middle of the router / switch. As a result, the assumption that the one-way delay time is half of the round trip is correct, and the error c between the clock clock master clock and the clock client slave clock is accurate.

  By the way, even when the time of the slave clock of the clock client is set to the master clock of the clock server, an error gradually occurs due to a slight frequency difference between the two clocks. In this case, the inquiry packet and the reply packet are exchanged again, the time error c is obtained, and the slave clock of the clock client is corrected. By repeating such correction, the slave clock of the clock client can be always synchronized with the master clock of the clock server.

  Note that the adjustment of the delay time of the router / switch in this embodiment is also effective when frequency synchronization of the master clock and the slave clock is taken, and will be described below as a second embodiment.

(Second Embodiment of Clock Transmission Method of the Present Invention)
FIG. 2 shows a second embodiment of the clock transmission method of the present invention. In FIG. 2, the clock server has a counter that counts up with an oscillator that oscillates a master clock, generates a clock packet (1) with this counter value as a time stamp value TS (1), and unilaterally clocks it. Send to client. When this clock packet (1) is input to the first router / switch, the delay time there is added to the time stamp value TS (1). The result is TS ′ (1), and the time stamp TS (1) in the clock packet (1) is rewritten to TS ′ (1) and transmitted. When this clock packet (1) arrives at the second router / switch, the delay time is added to the time stamp value TS ′ (1). The result is TS "(1), and the time stamp value TS '(1) in the clock packet (1) is rewritten to TS" (1) and transmitted. When there are other routers / switches that pass through, the delay times are sequentially integrated and the time stamp value is rewritten each time it passes through.

  The time stamp TS "(1) mounted on the clock packet (1) is shown at the transmission time when the clock packet (1) arrives without any delay at the intermediate router / switch, as shown by the broken line in FIG. That is, it is corrected so that an error does not occur even if the delay time in the router / switch in the middle changes.For the clock packet (2) transmitted at the next timing, the router / switch By rewriting the time stamp value TS (2) to TS ′ (2), TS ″ (2) each time it passes, the delay time in the router / switch is absorbed.

  The clock client receives the clock packet (1), takes out the mounted time stamp value TS "(1), inputs it to a counter (corresponding to 95 in FIG. 20), and initializes it. Counts up with an oscillating oscillator (corresponding to 96 in FIG. 20). The value counted up from TS "(1) is compared with the time stamp value TS" (2) of the next arriving clock packet (2). Thus, the frequency error e between the master clock of the clock server and the slave clock of the clock client can be obtained, and by correcting the frequency of the slave clock of the clock client by this frequency error e, the frequency error e of the master clock of the clock server can be obtained. A synchronized slave clock can be obtained, ie when the counter value is ahead Lowering the frequency of the oscillator little. On the contrary, a little increase the frequency of the oscillator in the case of those of the counter value is delayed.

  In the same manner, each time a clock packet (3), (4),... Arrives, it is repeated and the value counted up from the previous time stamp value TS "(i) and the current time stamp value TS" (i + By comparing the oscillation frequency of the slave clock by comparing 1), the progress of the master clock of the clock server and the slave clock of the clock client can be matched.

  Even if a packet loss occurs in the middle of a clock packet, the slave clock of the clock client is free-running. Therefore, by comparing the time stamp value mounted on the next clock packet, the frequency error e can be reduced. Frequency synchronization can be achieved.

  Further, the transmission interval of clock packets may be constant or variable. However, by making the transmission interval of the clock packet constant, the increase in the upper digits of the time information (time stamp) mounted on the clock packet becomes constant. Therefore, it is possible to adopt a remainder time stamp (Residual Time Stamp) system in which the upper digits of the time information are omitted and only the lower digits are mounted. That is, it is possible to estimate an increase in the upper digit of the counter of the clock client, and if the numerical value comparison is performed by supplementing the estimated value, the frequency error e can be similarly calculated.

  Further, in the case of the remainder time stamp method, when one clock packet loss occurs, the arrival interval of arriving clock packets is doubled. That is, the increase in the upper digit of the counter and the increase in the time stamp of the clock packet are almost doubled. Therefore, when a clock packet loss is detected, a method of estimating an increase in the upper digits according to the loss is used.

(Third embodiment of the clock transmission method of the present invention)
FIG. 3 shows a third embodiment of the clock transmission method of the present invention. In this embodiment, both the time synchronization in the first embodiment and the frequency synchronization in the second embodiment are taken. First, the clock server master clock and the clock client slave clock are synchronized. Then, frequency synchronization is taken continuously. As a result, if time synchronization is performed by a sequence of inquiry packets and response packets similar to NTP only once at the beginning, then frequency synchronization is performed by transmitting a unidirectional clock packet from the clock server to the client server. Time synchronization can be maintained.

  In FIG. 3, the clock client transmits an inquiry packet carrying a transmission time t1 based on its own slave clock to the clock server. The router / switch to which this inquiry packet arrives sequentially accumulates each delay time each time it passes through and rewrites the transmission time t1.

  The clock server puts the inquiry packet transmission time t1 ", the inquiry packet reception time t2 by its own master clock, the response packet transmission time t3, and the time stamp value TS (1) as an answer packet to the inquiry packet. Transmit the clock packet (1) The router / switch to which this clock packet (1) arrives accumulates each delay time each time it passes and rewrites the transmission time t3 and the timestamp value TS (1). It should be noted that both t3 and TS (1) may be counter values that are counted up by an oscillator that oscillates the master clock.

The clock client receives the clock packet (1), extracts the time t1 ", t2, t3" and the time stamp value TS "(1) described therein, and receives the clock packet (1) by its own slave clock. Time t4 is recorded, and from these times, the error c between the clock server and the clock client is
c = (t2-t1 "+ t3-t4") / 2
It becomes. By correcting the slave clock of the clock client with this error c, the time synchronized with the master clock of the clock server can be obtained by the clock client.

  Next, the clock client inputs the time stamp value TS "(1) mounted in the clock packet (1) into a counter (corresponding to 95 in FIG. 20) and initializes it. This counter oscillates the slave clock. It counts up with an oscillator. By comparing the value counted up from TS "(1) with the time stamp value TS" (2) of the next arriving clock packet (2), the master clock of the clock server is compared. The frequency error e of the slave clock of the clock client can be obtained, and the slave clock synchronized with the master clock of the clock server can be obtained by correcting the frequency of the slave clock of the clock client by this frequency error e.

  In the same manner, each time a clock packet (3), (4),... Arrives, it is repeated and the value counted up from the previous time stamp value TS "(i) and the current time stamp value TS" (i + By comparing the oscillation frequency of the slave clock by comparing 1), the progress of the master clock of the clock server and the slave clock of the clock client can be matched. In this way, if the time is first adjusted between the clock server and the clock client, the slave clock of the clock client can be always synchronized with the master clock of the clock server by frequency synchronization of both clocks thereafter.

(Fourth Embodiment of Clock Transmission Method of the Present Invention)
FIG. 4 shows a fourth embodiment of the clock transmission method of the present invention. In this embodiment, both the time synchronization in the first embodiment and the frequency synchronization in the second embodiment are taken. First, the frequency synchronization of the master clock of the clock server and the slave clock of the clock client is taken. The time synchronization is taken at an appropriate timing. As a result, first, frequency synchronization is achieved by transmitting a unidirectional clock packet from the clock server to the client server, and the progress of the master clock and the slave clock are matched. Thereafter, the time synchronization between the inquiry packet and the reply packet similar to NTP can be taken to eliminate the time lag between the two.

  In FIG. 4, the clock server has a counter that counts up with an oscillator that oscillates a master clock, generates a clock packet (1) with this counter value as a time stamp value TS (1), and unilaterally clocks it. Send to client. The clock client inputs the time stamp value TS "(1) mounted in the clock packet (1) into a counter (corresponding to 95 in FIG. 20) and initializes it. This counter is counted by an oscillator that oscillates the slave clock. By comparing the value counted up from TS "(1) with the time stamp value TS" (2) of the next arriving clock packet (2), the master clock of the clock server and the clock client The frequency error e of the slave clock can be obtained, and the slave clock frequency synchronized with the master clock of the clock server can be obtained by correcting the frequency of the slave clock of the clock client with this frequency error e.

  Similarly, by adjusting the oscillation frequency of the slave clock every time the clock packet (3), (4),... Arrives, the progress of the master clock of the clock server and the slave clock of the clock client can be matched. However, the time synchronization sequence is performed at an appropriate timing.

  That is, the clock client transmits an inquiry packet carrying the transmission time t1 based on its own slave clock to the clock server. The router / switch at which this inquiry packet arrives sequentially accumulates the respective delay times each time it passes and rewrites the transmission time. The clock server puts the inquiry packet transmission time t1 ", the inquiry packet reception time t2 by its own master clock, the response packet transmission time t3, and the time stamp value TS (3) as an answer packet to the inquiry packet. Transmit the clock packet (3) The router / switch to which this clock packet (3) arrives accumulates each delay time each time it passes, and rewrites the transmission time t3 and the timestamp value TS (3). Go.

The clock client receives the clock packet (3), extracts the time t1 ", t2, t3" and the time stamp value TS "(3) described therein, and receives the clock packet (1) by its own slave clock. Time t4 is recorded, and from these times, the error c between the clock server and the clock client is
c = (t2-t1 "+ t3-t4") / 2
It becomes. By correcting the slave clock of the clock client with this error c, the time synchronized with the master clock of the clock server can be obtained by the clock client.

  In addition, the value counted up from the previous time stamp value TS "(2) is compared with the time stamp value TS" (3) of the clock packet (3), and the slave clock frequency of the clock client is corrected by the error. By doing so, a slave clock frequency-synchronized with the master clock of the clock server can be obtained.

  As described above, if the clock server and the clock client synchronize the frequency of the clock server master clock and the clock client slave clock, the clock client slave clock is synchronized with the clock server master clock. be able to. After that, by transmitting a clock packet from the clock server to the clock client and continuing frequency synchronization as in the third embodiment, both time and frequency can be adjusted to the clock server.

  The clock server and the clock client of the third embodiment and the present embodiment are configured to have the respective functions shown in the first embodiment and the second embodiment, but require a completely new configuration. Not what you want. For example, in the clock server, when an inquiry packet is received while transmitting a clock packet for frequency synchronization, a transmission time t3 is mounted as a time stamp value TS (i), and further, time information t1 " When the clock client receives a clock packet having only the time stamp value TS (i), the clock client performs frequency synchronization processing and mounts time information t1 ", t2, and t3". When the received clock packet is received, time synchronization processing is performed as a reply packet to the inquiry packet, and frequency synchronization processing may be performed using the time stamp value TS (i) corresponding to the time information t3 ".

(First Embodiment of Clock Transmission Packet Network of the Present Invention)
FIG. 5 shows a first embodiment of the clock transmission packet network of the present invention. In the present embodiment, the clock transmission method of the present invention is shown in the first embodiment (time synchronization) shown in FIG. 1, the third embodiment shown in FIG. 3, and the fourth embodiment shown in FIG. 4 (time synchronization and frequency). This is a clock transmission packet network corresponding to (synchronization).

  In FIG. 5, a master station 10 operates with a standard clock generator 11 that generates a highly accurate standard clock, a master clock obtained by multiplying or dividing the standard clock, and a clock server 12 that transmits and receives clock packets, a clock A router or switch (router / switch) 13 that routes packets and user packets, and a network synchronization device 14 that performs control according to the delay time of the router 13 with respect to a clock packet passing therethrough are provided.

  A slave station 16A connected to the master station 10 via a transmission line 15 includes a router or switch (router / switch) 17 and a network synchronization device 18 similar to the master station 10. A network termination device 20 and a clock client (user terminal) 21 are connected to a user premises connected to the slave station 16A via the transmission line 19. The network synchronization devices 14 and 18 have a configuration in which the functions are added as part of the functions of the routers / switches 13 and 17.

  Here, the transmission path of the clock packet (inquiry packet) transmitted from the clock client 21 toward the clock server 12 is indicated by a solid arrow, and the clock packet (answer packet) transmitted from the clock server 12 toward the clock client 21 is indicated. This transmission path is indicated by a dashed arrow. The sequence of time synchronization between the clock server 12 and the clock client 21 is as described above.

  As the number of terminals in the clock transmission packet network increases, the capacity of the clock server 12 of the master station 10 is limited, so that clock packets are directly exchanged with the clock clients 21 of all terminals in the network. It becomes difficult. In this case, the clock client 23, the master clock 24, and the clock server 25 are installed like the slave station 16B. Clock packets are exchanged between the clock server 12 of the master station 10 and the clock client 23 of the slave station 16B according to the above-described method, and the master clock 24 of the slave station 16B is corrected by an error with respect to the master clock of the master station 10. Similarly, clock packets are exchanged between the master clock 24 and the clock server 25 and the clock client 21 in the user's home, and the clock of the clock client 21 is corrected. Thereby, the slave clock of the clock client 21 in the user's home can be matched with the master clock of the clock server 12 of the master station 10 while reducing the load on the clock server 12 of the master station 10.

(First Embodiment of Network Synchronization Device of the Present Invention)
FIG. 6 shows a first embodiment of the network synchronization apparatus of the present invention. Here, the configuration of the clock transmission packet network shown in FIG. 5 will be described as an example, but the network synchronization device 14 in the router / switch 13 of the master station 10 and the network synchronization in the router / switch 17 of the slave stations 16A and 16B. The device 18 has the same configuration, and one port is the clock client side and the other port is the clock server side.

  In the figure, a packet input from the clock client side is input to the router / switch function unit 30 via the packet identification circuit 31, routed to the target port according to the IP address, etc., and via the packet identification circuit 32. Output to the clock server side. When the packet identification circuit 31 identifies the inquiry packet from the header value indicating the NTP protocol, the packet identification circuit 31 extracts the time stamp t 1 (t 1 ′) indicating the transmission time and loads it into the counter 33. The counter 33 counts up at a frequency f corresponding to the unit time of the NTP time stamp. When the packet identification circuit 32 identifies the inquiry packet output from the router / switch function unit 30, the transmission accumulated by the value counted up by the counter 33, that is, the time spent in the routing process of the router / switch function unit 30 is obtained. Overwrite the time t1 '(t1 ").

  In the configuration shown in FIG. 6, since a plurality of inquiry packets from a plurality of input ports are sent to one output port, the packet identification circuit 32 performs a rewriting process of the transmission time corresponding to each inquiry packet. It has become. That is, the counter 33 corresponding to each inquiry packet sends the IP address, the time stamp value t1 (t1 ') before rewriting, the counter value t1' (t1 ") to the packet identification circuit 32 in association with each other, and the packet identification circuit 32 In 32, by comparing with the IP address of the inquiry packet that passes through, t1 (t1 ') corresponding to each inquiry packet is overwritten with t1' (t1 ").

  Next, processing of reply packets from the clock server to the clock client will be described. The packet input from the clock server side is input to the router / switch function unit 30 via the packet identification circuit 34, routed to the target port according to the IP address and the like, and the packet client side via the packet identification circuit 35 Is output. When the packet identification circuit 34 identifies the reply packet from the header value indicating the NTP protocol, the packet identification circuit 34 extracts the time stamp t3 (t3 ') indicating the transmission time and loads it into the counter 36. The counter 36 is counted up at a frequency f corresponding to the unit time of the NTP time stamp. When the packet identification circuit 35 identifies the answer packet output from the router / switch function unit 30, the transmission is accumulated by the value counted up by the counter 36, that is, the time spent in the routing process of the router / switch function unit 30. Overwrite the time t3 '(t3 ").

  The configuration shown in FIG. 6 is a configuration in which the response packet from one input port is routed to any one output port, while the value of the counter 36 is sent to the packet identification circuit 35 of all output ports. It has become. That is, the counter 36 corresponding to the reply packet associates the IP address with the time stamp value t3 (t3 ') and the counter value t3' (t3 ") before rewriting, and sends them to the packet identification circuit 35. In this case, t3 (t3 ') corresponding to the answer packet is overwritten with t3' (t3 ") by collating with the IP address of the answer packet passing through.

  When many inquiry packets and answer packets are concentrated and a plurality of inquiry packets and answer packets stay in the router / switch function unit 30, counters 33 and 36 provided for each port are provided. A plurality of them may be arranged so that each counter responds to each inquiry packet or answer packet that is sequentially input. On the contrary, when there are few inquiry packets and only one inquiry packet stays in the router / switch function unit 30, the counter 33 provided for each of a plurality of ports on the clock client side is consolidated into one. It is also possible.

(Second Embodiment of Clock Transmission Packet Network of the Present Invention)
FIG. 7 shows a second embodiment of the clock transmission packet network of the present invention. This embodiment is a clock transmission packet network corresponding to the second embodiment (frequency synchronization) shown in FIG. 2 of the clock transmission method of the present invention. In the clock transmission packet network of the first embodiment shown in FIG. 5, the frequency synchronization of the master clock and the slave clock is unilaterally repeated from the clock server 12 to the clock client 21 with a clock packet loaded with time information of the master clock. This can be realized by transmitting. That is, in the clock transmission packet network of FIG. 5, it is possible to perform time synchronization and frequency synchronization of the master clock and the slave clock at the same time. However, when only frequency synchronization is performed, the configuration of this embodiment is adopted.

  In the figure, a master station 10 operates with a standard clock generator 11 that generates a high-accuracy standard clock, a clock server 41 that operates with a master clock obtained by multiplying or dividing the standard clock, and generates a clock packet. And a router or switch (router / switch) 13 that routes user packets, and a network synchronization device 42 that performs control according to the delay time of the router 13 with respect to clock packets that pass.

  The slave station 43A connected to the master station 10 via the transmission path 15 includes the same router / switch 17 and network synchronization device 44 as the master station 10. A network termination device 20 and a clock client (user terminal) 45 are connected to the user's home connected to the slave station 43A via the transmission line 19. The network synchronization devices 42 and 44 have a configuration in which the functions are added as part of the functions of the routers / switches 13 and 17. Here, the transmission path of the clock packet transmitted from the clock server 41 toward the clock client 45 is indicated by a broken line.

  The slave station 43B includes a clock client 45 that receives a clock packet from the clock server 12 of the master station 10 and performs frequency synchronization with the master clock according to the above-described method, and a clock server 46 that generates the clock packet. Similarly, clock packets are transmitted and received between the clock server 46 and the clock client 45 in the user's home, and the frequency synchronization of the slave clock of the clock client 45 is achieved.

(Second Embodiment of Network Synchronization Device of the Present Invention)
FIG. 8 shows a second embodiment of the network synchronization apparatus of the present invention. Here, the configuration of the clock transmission packet network shown in FIG. 7 will be described as an example. However, the network synchronization device 42 in the router / switch 13 of the master station 10 and the network synchronization in the router / switch 17 of the slave stations 16A and 16B. The device 44 has the same configuration, with one port being the clock client side and the other port being the clock server side.

  In the figure, a packet input from the clock server side is input to a router / switch function unit 30 via a packet identification circuit 34, routed to a target port according to an IP address or the like, and is transmitted via a packet identification circuit 35. Output to the clock client side. When the packet identification circuit 34 identifies the clock packet from the header value indicating the packet type or application, the packet identification circuit 34 extracts the time stamp value TS (i) (TS ′ (i)) indicating the transmission time, and loads it into the counter 36. The counter 36 is counted up at a frequency f corresponding to unit time. When the packet identification circuit 35 identifies the clock packet output from the router / switch function unit 30, the time accumulated by the value counted up by the counter 36, that is, the time spent in the routing process of the router / switch function unit 30. Overwrite the stamp value TS '(i) (TS "(i)).

  In the configuration shown in FIG. 8 (1), since the clock packet from one input port is routed to a plurality of output ports, the packet identification circuit 35 rewrites the transmission time corresponding to each clock packet. It is configured. That is, the counter 36 corresponding to the clock packet includes a destination, a source address, a time stamp value TS (i) (TS ′ (i)) before rewriting, and a counter value TS ′ (i) (TS ″ (i)). Are associated with each other and output to the packet identification circuit 35, and the packet identification circuit 35 collates with the destination, source address, etc. of the input clock packet, thereby TS (i) (TS ′ (i)) corresponding to the clock packet. Is overwritten with TS '(i) (TS "(i)).

  Further, when many clock packets are concentrated and stay in the router / switch function unit 30, as shown in FIG. 8 (2), a counter 36 is arranged for each output port and sequentially inputted. Each counter may correspond to each clock packet.

  By performing the processing as shown in FIG. 2 in such network synchronization devices 42 and 44, the clock client 45 can synchronize the frequency of the master clock and the slave clock.

(Third embodiment of the clock transmission packet network of the present invention)
FIG. 9 shows a third embodiment of the clock transmission packet network of the present invention. The feature of this embodiment is that the clock packet duplication function is arranged as a clock packet duplication unit 47 outside the routers / switches 13 and 17 in the clock transmission packet network of the second embodiment shown in FIG. . Thereby, a clock packet can be multicast to a plurality of user terminals.

(Fourth embodiment of the clock transmission packet network of the present invention)
FIG. 10 shows a fourth embodiment of the clock transmission packet network of the present invention. The feature of this embodiment is that a plurality of master stations (standard clock generators) exist in the clock transmission packet network of the second embodiment shown in FIG. The clock servers 41 of the master station 10A and the master station 10B generate clock packets loaded with time stamp values based on different master clocks. These two clock packets are given an identifier (for example, a clock supply source ID) so that the respective generation sources can be known. As a result, the clock client (user terminal) 45 can select a plurality of clock packets and synchronize the frequency with the corresponding master clock. The same applies when there are a plurality of slave stations 43B.

  Further, as shown in FIG. 11, when the first clock packet among the plurality of clock packets is input and the slave clock frequency is synchronized with the master clock frequency, clock packet loss occurs, The arrival of clock packets may be interrupted for a certain period of time. In this case, the second clock packet can be inputted and synchronized with the second mask clock frequency by the time stamp value mounted on the second clock packet.

(Fifth embodiment of the clock transmission packet network of the present invention)
FIG. 12 shows a fifth embodiment of the clock transmission packet network of the present invention. The embodiment described above is an example in which clock packets loaded with the time stamp value of the master clock are distributed from the master station 10 to the user terminal. The feature of this embodiment is that when the standard clock generator 11 is on the user terminal side, the clock packet is transmitted from the user terminal side to another user terminal via the master station 10 or the slave station 43A. .

  In this case, there are a method in which the user packet transmitted between the clock packet and the user terminal is in a different format, and a method in which the time stamp value of the master clock is mounted in the user packet. An example of a clock packet using an ether frame is shown in FIG. By setting the destination MAC address as a specific multicast address, it is possible to multicast the clock packet by a router / switch in the middle, and to distinguish the clock packet from other user packets. A bold line indicates a payload area, and a CS-ID (clock supply source ID) is used to identify a plurality of master clocks as in the embodiment shown in FIG. The SN (sequence number) is used for detecting the loss of the clock packet and confirming the identity of the clock packet. TS (time stamp) is time information of the master clock, and in the case of the remainder time stamp method, only the lower digits of the time information are mounted. PAD is a byte added to satisfy the standard of the minimum length (64 bytes) of the ether frame. FCS is an error detection code for performing error detection of an Ethernet frame.

  An example of a clock packet using a VLAN (Virtual LAN) tag is shown in FIG. FIG. 13 (3) shows an example of a user packet when the user terminal has a master clock and the time information of the master clock is mounted on the user packet. The payload area in the bold line is the same as in the case of the ether frame, but the C-SN of the user packet is a sequence number given when carrying a valid time stamp, and the S-SN is all frames carrying user data. Is the sequence number attached to Whether or not a valid time stamp is mounted can be identified by the value of the Type field, the value of CS-ID, and the value of C-SN. The clock packet can define the clock packet format by using the application port number or the like in the IP packet in addition to the Ethernet frame for identifying the clock packet and similarly defining the sequence number and the time stamp.

(Sixth embodiment of the clock transmission packet network of the present invention)
14 and 15 show a sixth embodiment of the clock transmission packet network of the present invention. The embodiment described above is an example in which a clock packet is broadcast to each user terminal. The feature of this embodiment is that the clock packet is multicasted based on a request from the user terminal side, instead of fixedly assigning the transmission destination of the clock packet.

  FIG. 14 shows a state in which a request packet is transmitted from the user terminal to newly register a port to be multicast, and FIG. 15 shows a clock packet route after multicast registration. The user terminal 48 that needs to match the master clock frequency sends a multicast request to the routers or switches 17 and 13 using a general multicast protocol such as IP or Ethernet (registered trademark). In response to the request, the routers or switches 17 and 13 start distributing clock packets to the newly requested user terminal 48. For example, an Ether packet in which GARP (Generic Attribute Registration Protocol) that distributes packets only to necessary terminals is defined is assumed. Thus, since the master station 10 and the slave station 43A multicast the clock packet to the newly registered port, the clock packet is distributed to the user terminal 48 that transmitted the request packet.

(Seventh embodiment of the clock transmission packet network of the present invention)
FIG. 16 shows a seventh embodiment of the clock transmission packet network of the present invention. In the present embodiment, there are a slave station 43A having the network synchronization device 44 of the present invention and a slave station 43D not having the network synchronization device 44, and the clock client 45 receives a clock packet from a transfer path via each of the slave stations 43A and 43D. Shall arrive each. The clock packet arriving at the clock client 45 via the slave station 43A having the network synchronizer 44 can be accurately controlled because the time information integrates the delay time of the router / switch. On the other hand, the clock packet that arrives at the clock client 45 via the slave station 43D that does not have the network synchronization device 44 becomes an error in the delay time of the router / switch as in the conventional case, and accurate synchronization control cannot be performed. Therefore, an accurate master clock can be obtained by adopting a clock packet from a route that does not pass through the slave station 43D that does not have the network synchronization device 44 as much as possible.

  In the network synchronizers 42 and 44 of the present invention, the number of passages a is written in the clock packet that passes. On the other hand, in the clock packet passing through the routers / switches 13 and 17, for example, the number of times b of IP packet passing by TTL (Time To Live) is described. The difference between the number of passages b and the number of passages a is the number of passages of a router / switch that does not have a network synchronization device. In the example of FIG. 16, the difference in the number of passages of the clock packet that has passed through the slave station 43A is 0, the difference in the number of passages of the clock packet that has passed through the slave station 43D is 1, and the value is minimized in the clock packet selector 51. The clock packet that has passed the path is selected and sent to the clock client 45.

The figure which shows 1st Embodiment of the clock transmission method of this invention. The figure which shows 2nd Embodiment of the clock transmission method of this invention. The figure which shows 3rd Embodiment of the clock transmission method of this invention. The figure which shows 4th Embodiment of the clock transmission method of this invention. The figure which shows 1st Embodiment of the clock transmission packet network of this invention. The figure which shows 1st Embodiment of the network synchronization apparatus of this invention. The figure which shows 2nd Embodiment of the clock transmission packet network of this invention. The figure which shows 2nd Embodiment of the network synchronization apparatus of this invention. The figure which shows 3rd Embodiment of the clock transmission packet network of this invention. The figure which shows 4th Embodiment of the clock transmission packet network of this invention. The figure which shows the operation example of 4th Embodiment of the clock transmission packet network of this invention. The figure which shows 5th Embodiment of the clock transmission packet network of this invention. The figure which shows the flame | frame structure of a clock packet. The figure which shows 6th Embodiment (1) of the clock transmission packet network of this invention. The figure which shows 6th Embodiment (2) of the clock transmission packet network of this invention. The figure which shows 7th Embodiment of the clock transmission packet network of this invention. The figure explaining the conventional network synchronization method in a digital network. The figure explaining the sending clock of the router in a packet network. The figure explaining the principle of NTP. The figure which shows the structural example of the slave clock control circuit of a clock client. The figure explaining the error of NTP.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Master station 11 Standard clock generator 12 Clock server 13, 17 Router / switch 14, 18 Network synchronization device 15, 19 Transmission path 16 Slave station 20 Network termination device 21, 23 Clock client 24 Master clock 30 Router / switch function part 31 , 32, 34, 35 Packet identification circuit 33, 36 Counter 31 User packet queue 32 Clock packet queue 41, 46 Clock server 42, 44 Network synchronization device 43 Slave station 45 Clock client 47 Clock packet replication unit 48 User terminal

Claims (10)

The clock supply source has a high-precision master clock, the clock supply destination has a self-running slave clock,
When an inquiry packet is transmitted from the clock supply destination to the clock supply source and a response packet for the inquiry packet is transmitted from the clock supply source to the clock supply destination, a transmission time t1 by the slave clock is transmitted to the inquiry packet. The answer packet includes the t1 and the inquiry packet reception time t2 and the answer packet transmission time t3 according to the master clock, and is obtained from the answer packet reception time t4 and the answer packet according to the slave clock. In the clock transmission method, an error of the slave clock time with respect to the master clock time is calculated from the values of t1, t2, and t3, and the slave clock is adjusted according to the error to adjust the slave clock time to the master clock time.
A value corresponding to the delay time of the router or switch through which the inquiry packet passes is added to the t1 and rewritten, and a value according to the delay time of the router or switch through which the answer packet passes is added to the t3 and rewritten, A clock transmission method characterized in that an error in the time of the slave clock with respect to the time of the master clock is calculated using t1 'and t3' rewritten with t2 and t4. The clock supply source has a master counter that counts up with a high-precision master clock, the clock supply destination has a slave counter that counts up with a self-running slave clock,
A clock packet in which the value of the master counter is mounted as time information is transmitted from the clock supply source to the clock supply destination, the time information mounted in the clock packet is initialized in the slave counter, and the slave clock is automatically used. The time information mounted on the clock packet that arrives at the next timing is compared with the value of the slave counter, and the slave clock is adjusted according to the error to adjust the slave clock frequency to the master clock frequency. In a clock transmission method that repeats every arrival of the clock packet,
The value corresponding to the delay time of the router or switch through which the clock packet passes is added to the time information mounted on the clock packet and rewritten, and the slave counter initial setting and the slave counter value are set according to the time information. And a clock transmission method characterized in that a comparison is made. The clock supply source has a high-precision master clock, the clock supply destination has a self-running slave clock,
When an inquiry packet is transmitted from the clock supply destination to the clock supply source and a response packet for the inquiry packet is transmitted from the clock supply source to the clock supply destination, a transmission time t1 by the slave clock is transmitted to the inquiry packet. The answer packet includes the t1 and the inquiry packet reception time t2 and the answer packet transmission time t3 according to the master clock, and is obtained from the answer packet reception time t4 and the answer packet according to the slave clock. A clock transmission packet network that calculates an error of the slave clock time with respect to the master clock time from the values of t1, t2, and t3, and adjusts the slave clock according to the error to match the master clock time. In Stomach,
The router or switch through which the inquiry packet and the reply packet pass is rewritten by adding a value corresponding to the delay time through which the inquiry packet passes to t1, and the value according to the delay time through which the reply packet passes through a network synchronizer that integrates and rewrites at t3;
The clock transmission packet network, wherein the clock supply destination calculates an error of the time of the slave clock with respect to the time of the master clock by using t1 'and t3' rewritten as the t2 and t4. The clock supply source has a master counter that counts up with a high-precision master clock, the clock supply destination has a slave counter that counts up with a self-running slave clock,
A clock packet having the master counter value mounted as time information is transmitted from the clock supply source to the clock supply destination, the slave counter is initialized with the time information mounted in the clock packet, and the slave clock is automatically set. The time information mounted in the clock packet that arrives at the next timing is compared with the value of the slave counter, and the slave clock is adjusted according to the error to adjust the slave clock frequency to the master clock frequency. In a clock transmission packet network that repeats every arrival of the clock packet,
A router or switch through which the clock packet packet passes, and a network synchronization device that integrates and rewrites the time information with a value corresponding to a delay time through which the clock packet passes,
The clock transmission packet network, wherein the clock supply destination performs initial setting of the slave counter and comparison with a value of the slave counter in accordance with time information of the clock packet. The clock transmission packet network according to claim 4,
There are a plurality of clock supply sources operating with different master clocks, each clock supply source identifier is given to the clock packet, and a plurality of clock packets are transferred within the same packet network. A clock transmission packet network. The clock transmission packet network according to claim 5,
When the clock supply destination inputs the first clock packet of the plurality of clock packets and matches the slave clock frequency to the master clock frequency, the arrival of the first clock packet is a fixed time. A clock transmission packet network characterized by inputting a second clock packet in the event of interruption, and initializing the slave counter according to time information mounted on the second clock packet. The clock transmission packet network according to claim 4 or 5,
The terminal that needs to match the master clock frequency sends a multicast request for the clock packet to the router or switch, and sets the slave clock frequency using the clock packet multicast from the router or switch based on the request. Means for performing processing to match the master clock frequency,
The clock transmission packet network, wherein the router or the switch is configured to start multicasting the clock packet with the requested terminal as the clock supply destination. The clock transmission packet network according to claim 5,
A clock transmission packet network characterized in that, for a router or a switch included in a path through which each of the plurality of clock packets passes, a clock packet of a path that minimizes the number of routers or switches not including the network synchronization device is selected. . The network synchronization device for a clock transmission packet network according to claim 3,
The local time t1 at the time of transmission mounted in the inquiry packet input to the router or switch is set in a counter, the count is incremented until the inquiry packet is output, and the value of the counter when the inquiry packet is output T1 accumulating means for overwriting t1
A standard time t3 at the time of transmission mounted in the answer packet input to the router or switch is set in a counter, counted up until the answer packet is output, and a value when the answer packet is output is A network synchronization apparatus comprising t3 accumulating means for overwriting t3. The network synchronization device for a clock transmission packet network according to claim 4,
The time information mounted on the clock packet input to the router or switch is set in a counter, counted up until the clock packet is output, and the value when the clock packet is output is overwritten on the time information. A network synchronization apparatus comprising time information integrating means for performing

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