JP2009077311A - Passing time measuring instrument, control method thereof, and network relay apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a passing time measurement technique which attains a time synchronism with an excellent precision even without using a highly precisely synchronized external clock. <P>SOLUTION: Regarding a frame determined as for time synchronism, a counter circuit 303 measures a passing time from entering a switch 401 to leaving. A memory circuit 702 stores the passing time measured by the counter circuit 303 and a transmission source address of the frame relating to start of the measurement in association with each other. When the frame leaves the switch 401, based on the transmission source address of the frame, a transmission source address determination unit 72 refers to the memory circuit 702 to acquire a corresponding passing time from the counter circuit 303. A frame processing circuit 1 to (n) corresponding to a port through which the frame is passed, records the passing time acquired in the frame and produces a check code of the frame recording the passing time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to time synchronization in a communication network.

  In recent years, communication network technology has become widespread in many fields, but various devices connected via a network often require highly accurate time synchronization. This time synchronization is realized by connecting a server serving as a time reference and a client that synchronizes the time of the server with a network, and exchanging a frame with the time (for example, non-patent document). 1).

  A typical communication procedure for performing time synchronization via a network as described above is NTP (Network Time Protocol). Here, an outline of the operation of NTP will be described along “2.2 Estimation Principle of Adjustment Time” of Non-Patent Document 1. That is, as shown in FIG. 1 of the same document, in order to synchronize the client time with the server time, the time difference between the client time (Tc) and the server time (Ts) is obtained. Synchronize.

The relationship between each time in the client and the server is shown in FIG. That is, of the packet round-trip time, the time taken for the forward path is (Formula 1) of Non-Patent Document 1, and the time taken for the return path is (Formula 2).

T1-T0 = D + C (Formula 1)

T3−T2 = D−C (Formula 2)

However (
T0: Client transmission time T1: Server reception time T2: Server transmission time T3: Client reception time D: Packet transmission time C: Time shift)

When estimating the above-mentioned time lag C by NTP, it is assumed that the packet transmission time D is the same value in the forward path and the backward path, but the fact that it is not the same actually causes a decrease in time accuracy. That is, assuming that the transmission time D is the same value in the forward path and the return path, (Expression 3) is obtained from (Expression 1) and (Expression 2).

C = (T1-T0) / 2- (T3-T2) / 2 (Formula 3)

It becomes.

And

Ts: Server time Tc: Client time

In this case, the time difference C between the client time Tc and the server time Ts is calculated from the above (Equation 3).

Ts−Tc = C

Using this value, the client synchronizes time with the server. In order for the time synchronization as described above to be highly accurate, as described in Non-Patent Document 1, the transmission required time and the transmission in the forward and backward paths in the packet round trip between the client and the server are described. The condition is that the delay times are equal.
JP 2000-332809 A JP 2006-115153 A “NTP Series Part 1 About NTP” <http://tech.n-linux.com/index.php?%A5%C6%A5%AF%A5%CB%A5%AB%A5%EB%A5%CE% A1% BC% A5% C8% 2FNTP% 2FNTP% 20% A5% B7% A5% EA% A1% BC% A5% BA% 20% A5% D1% A1% BC% A5% C8% 201% 20NTP% 20% A4% CB% A4% C4% A4% A4% A4% C6>

  However, in the time synchronization realized as described above, the main cause of the decrease in accuracy is a variation in transmission delay time that occurs during frame exchange, and this variation is a network relay installed in the network. It occurs inside the device.

  In other words, a delay occurs when a frame passes through the network relay device, and the delay time varies depending on the frame processing order inside the network relay device, so it is difficult to make the frame passage delay time constant in any case. Therefore, the round-trip transmission delay time is not the same, and thus there is a problem that highly accurate time synchronization cannot be realized.

  In particular, such a variation in transmission delay time is not a problem when accuracy in milliseconds is sufficient as time synchronization accuracy, but in a system requiring accuracy of several microseconds or hundreds of nanoseconds. If that matters.

  Here, as a typical example of the network relay device, an explanation of the operation of the Ethernet (registered trademark) switch and the reason why the delay time inside the Ethernet switch is not constant will be described. First, FIG. 9 shows a configuration in which the Ethernet switch 401 is connected to the client 1 (312) to the client n (314) and the server 315. In this configuration, the client 1 (312) sends out a frame 332 whose destination is the server 315 on the cable 324, and immediately after that, the client 2 (313) sends out the frame 333 whose destination is the server 315. The timing is shown in the time chart of FIG.

  That is, the frame 332 and the frame 333 arrive at the Ethernet switch 401 with a time difference Tdef shown in the time chart of FIG. Of these, the frame 332 is output on the cable 331 with a delay (point b) by a time T332 indicated by an arrow in the figure, based on the arrival time (point a). On the other hand, the frame 333 should also be output on the cable 331. While the frame 332 is already being output, the frame 332 waits until the output of the frame 332 is completed, and this waiting time is a time T333 indicated by an arrow in the figure.

  As described above, the time T332 when the frame 332 passes through the Ethernet switch 401 and the time T333 when the frame 333 passes through the Ethernet switch 401 are not the same as shown in the time chart of FIG. This indicates that it is difficult to make the frame passage delay time constant in any case.

  Here, the time T333 is a time determined by the transmission rate and the frame length of the frame 332 sent out in advance. If the transmission rate is 100 Mbps and the frame length of the frame 332 is 12320 bits, which is the maximum length of the standard, it is approximately 123 μs (microseconds).

  On the other hand, the time T332 is determined by the delay time of the internal hardware of the Ethernet switch 401, and is usually about several hundred ns (nanoseconds). Thus, the delay time for the frame to pass through the Ethernet switch 401 changes considerably on a scale of several hundred ns (nanoseconds) to 123 μs, and it is difficult to avoid this delay time change.

  As an example of the related art related to the delay time varying as described above, in the optical field network system of Patent Document 1, there is a variation in the delay time generated inside a network relay device represented by an Ethernet-compatible router or switch. Even if it occurs, high-accuracy synchronization control is required, and the following restrictions are added to realize such high-accuracy time synchronization.

1. The frame length is fixed and not more than a certain length (Patent Document 1, page 20, left 20th line).
2. Using a switching hub with a priority transmission function, the time synchronization frame is preferentially passed (from the 15th line on the left side of page 4).

  In Patent Document 1, the fluctuation of the transmission delay time is reduced by adding these restrictions 1 and 2. However, since the frame length is limited to a certain value or less, extensibility is sacrificed, Even if the frame length is set to a certain value or less, the transmission delay time fluctuates for the frame length (from the 30th line on the left side of page 4).

  Further, as an example of a technique related to the handling of time information on the network, Patent Document 2 is a technique related to a device that inserts a time stamp into a data packet (corresponding to a frame) on the network, and FIG. Shows a configuration in which this time stamp apparatus is connected to a network.

  That is, a packet is transmitted from TX, enters the time stamp device 1-1, and time stamp information is inserted into this packet (Patent Document 2, second page, third line). This time stamp information is generated based on a highly accurate external clock signal (page 5 and after line 13).

  Further, the packet leaves the time stamp device 1-1, passes through the network N, and enters the time stamp device 1-2. At this time, a time stamp is additionally added to the packet, and the packet arrives at RX. (8th page, 47th line and after). Then, the time for which the packet passes through the network N is measured from the time stamp information (timestamp # 0) and (timestamp # 1).

  Although Patent Document 2 described above is useful for grasping the arrival and departure times of packets, it is not intended to achieve high-accuracy time synchronization, and is based on the use of a high-accuracy external clock. There are many constraints such as being necessary not only for the time stamp devices 1-1 and 1-2 but also for both external clocks being synchronized with high precision.

  The present invention solves the conventional problems as described above, and its purpose is not to use an external clock synchronized with high accuracy, but also to achieve time synchronization with excellent accuracy. Is to provide.

  In order to achieve the above object, one aspect of the present invention is a transit time measuring apparatus that measures a transit time of a frame in a network relay device for time synchronization via a communication network, and the type of the frame is Determining means for determining whether or not a predetermined time synchronization is used; measuring means for measuring a transit time from entry to exit of the network relay device for the frame determined to be for time synchronization; and the measurement Storage means for associating and storing the transit time measured by the means and the transmission source address of the frame related to the start of measurement, and when the frame leaves the network relay device, the transmission source address of the frame is also stored. In addition, by referring to the storage unit, an acquisition unit that acquires the corresponding passage time from the measurement unit, and the acquired communication unit Characterized in that it has a recording means for recording the time to the frame, a generating means for generating a check code of the frame recording the transit time, the.

  As described above, according to the present invention, the delay time for each frame in a network relay device such as a switch is measured distinctly based on the coincidence of the source address, and the check code is also generated by recording it in the frame. By doing so, it is possible to accurately grasp the variation in the transmission delay time during round trips by referring to the frame, and to realize high-accuracy time synchronization in consideration thereof.

  Hereinafter, a plurality of best embodiments for carrying out the present invention will be described with reference to the drawings. Note that assumptions common to the explanation in the background art and problems are omitted as appropriate.

[1. First Embodiment] Corresponding to Claims 1 and 4 In the first embodiment, there is provided a transit time measuring device for measuring the transit time of a frame in a network relay device and a control method thereof for time synchronization via a communication network. FIG. 1 is a configuration diagram illustrating a state in which the Ethernet switch 401, the client 1 (312) to the client n (314), and the server 315 are connected to the transit time measuring apparatus 601 according to the first embodiment.

[1-1. Schematic configuration of the first embodiment]
Among these, a typical example of the client 1 (312) to the client n (314) and the server 315 is a PC (personal computer) equipped with network interface hardware such as a LAN board. Although not shown, the Ethernet switch 401 includes a plurality of physical layer ports for interfacing with the client and the server, and further has a function of sending out to a predetermined port according to the destination address of the arrived frame. .

[1-2. Configuration of transit time measuring device]
Further, as shown in FIG. 1, the transit time measuring apparatus 601 includes PHY1 (606) to PHYn (609) as physical layer ports (referred to as “PHY”) for interfacing with a client and a server. Are collectively referred to as node-side ports. The transit time measuring device 601 includes PHY2-1 (602) to PHY2-n (605) as physical layer ports for interfacing with the Ethernet switch 401, and these are collectively referred to as switch-side ports. To do.

  The counter circuit 303 monitors the signal lines 316 to 323 and measures the transit time of frames flowing through them. The frame processing circuit 1 (304) to the frame processing circuit n (307) are counter circuits 303. It is means for receiving the measured passage time and adding the passage time to each corresponding frame, and corresponds to the recording means and the generation means of the present invention.

  More specifically, the counter circuit 303 corresponds to the measurement unit of the present invention. As shown in the partial configuration diagram of FIG. 2, a control circuit 701 and a memory circuit corresponding to the storage unit of the present invention are provided. 702. Among these, the control circuit 701 includes a frame type determination unit 71 corresponding to the determination unit of the present invention, and a transmission source address determination unit 72 corresponding to the acquisition unit of the present invention.

[1-3. Outline of action)
As an outline of the operation of the transit time measuring apparatus 601 configured as described above, the frame type determination unit 71 determines whether or not the frame type is for a predetermined time synchronization, and thus determines that the frame type is for time synchronization. The counter circuit 303 measures the passing time from the entry to the exit to the exit 401 for the received frame. Further, the memory circuit 702 stores the passage time measured by the counter circuit 303 as described above and the transmission source address of the frame related to the measurement start in association with each other. Here, the passing time is a counter value that is updated and changed every time from the start to the end of the measurement, and is simply expressed as “counter” in FIG. 2.

  When the frame exits from the switch 401, the transmission source address determination unit 72 refers to the memory circuit 702 based on the transmission source address of the frame, and the corresponding transit time is read from the counter circuit 303. get. Then, the frame processing circuits 1 to n corresponding to the port through which the frame has passed record the acquired passage time in the frame, and generate a check code for the frame in which the passage time is recorded.

[1-4. Example of processing procedure)
An example of a specific processing procedure for realizing the above-described schematic action by the transit time measuring apparatus is shown in the flowchart of FIG. That is, the counter circuit 303 monitors the state of each port (steps S01 and S02), and determines the type (step S03) of the frame that has arrived at the node side port (step S04). If the frame is a time-synchronized frame by this determination (step S05), a transit time measurement counter is started (step S06), and the transmission source address of the frame is stored in association with the counter (step S07).

On the other hand, for the frame that has arrived at the switch side port (step S09), if the determined type is (step S10) a time synchronization frame (step S11), the transmission source address of that frame is stored in each memory source 702. Compare with the address (step S12), and if there is a match (step S13), the corresponding counter is stopped (step S14), and processing for adding the count value at that time to the data portion of the frame is performed (step S13). Step S15).
Both the time synchronization frame and the other frames are output from the opposite port corresponding to the incoming port (step S08).

[1-5. Illustration〕
Furthermore, an example of the above processing is shown. In this example, it is assumed that the frames 322 and 333 arrive at the passing time measuring device 601 at the timing shown in the time chart of FIG. 4 and are sent to the cable 331. The configuration of the frames 332 and 333 is shown in FIG. As shown, it is assumed that each field includes a destination address, a transmission source address, a frame type, a data portion, and an FCS (check code).

  Among these, the type of frame is distinguished depending on whether the value of “frame type” is 0 (: time synchronization frame) or 1 (: other general frame), and for the time synchronization frame, the transit time is measured and added to the frame. However, it is assumed that the general frames other than the time synchronization frame only pass through the transit time measuring device 601, and the measurement and addition processing are not performed.

(1) First, when the frame 332 from the client 1 (312) enters the transit time measuring device 601 from PHY1 (606) at the timing shown in the time chart of FIG. 4, the control circuit 701 of the counter circuit 303 of FIG. To determine the frame type.
(2) When the frame is determined to be a time synchronization frame, the counter 703 of the memory circuit 702 is started, and at the same time, the transmission source address of the frame 332 shown in the frame configuration of FIG. 5 is stored in the transmission source address storage unit 704 and associated with the counter 703.

(3) For the next incoming frame 333, the control circuit 701 in the counter circuit 303 determines whether the frame type is a time synchronization frame.
(4) When it is determined that the frame is a time synchronization frame, the counter 705 of the memory circuit 702 is started, and at the same time, the transmission source address of the frame 333 is stored in the transmission source address storage unit 706.

(5) On the other hand, the frame 332 that first passed through the transit time measuring device 601 passes through the Ethernet switch 401 of FIG. 1 and enters PHY2-n (605).
(6) At this time, as shown in the time chart of FIG. 4, since the frame 332 is being output to the PHY2-n (605), the subsequent frame 333 to be output to the same PHY2-n (605) A standby state is entered inside the Ethernet switch 401.

(7) Since the type of the frame 332 that has entered the transit time measuring device 601 from the PHY2-n (605) is determined by the control circuit 701 in the counter circuit 303 shown in FIG. 2, it is a time synchronization frame. The transmission source address of the frame 332 is compared with the transmission source addresses stored in the transmission source address storage units 706 to 708 of the memory circuit 702.
(8) In this comparison, when the transmission source address of the frame 332 matches, for example, the content of the transmission source address storage unit 704, the corresponding counter 703 is stopped and the count value is sent to the frame processing circuit n (307). This count value coincides with the delay time of T332 shown in the time chart 1 of FIG. 4, that is, the time difference between the points a and b.
(9) The count value is added to the data portion of the frame 332 by the frame processing circuit n (307).

(10) When the output of the frame 332 from the Ethernet switch 401 is completed, the output of the subsequent frame 333 that has been waiting is started.
(11) At this time, the type of the frame 333 entered from PHY2-n (605) is determined by the control circuit 701 in the counter circuit 303. In this case, since it is a time synchronization frame, the transmission source of this frame 333 The address is compared with each source address stored in the source address storage units 706 to 708 of the memory circuit 702.
(12) In this comparison, when the transmission source address of the frame 333 matches the content of the transmission source address storage unit 706, for example, the corresponding counter 705 is stopped and the count value is sent to the frame processing circuit n (307). This count value coincides with the delay time of T333 shown in the time chart of FIG. 4, that is, the time difference between the points c and d.
(13) The count value is added to the data portion of the frame 333 by the frame processing circuit n (307).

[1-6. Example of using delay time)
As described above, when the delay time in the forward path measured by the passage time measuring device 601 is Tdnt1, and the delay time in the return path is Tdnt2, the time lag between the client and the server is accurately calculated using the following equation 4. I can do it.

C = ((T1-T0) -Tdnt1) / 2-((T3-T2) -Tdnt2) / 2 (Formula 4)

However (
Tdnt1: Delay time in the forward path measured by the transit time measuring device Tdnt2: Delay time in the return trip measured by the transit time measuring device T0: Client transmission time T1: Server reception time T2: Server transmission time T3: Client Reception time C: Time lag)

The above is the operation when there is one transit time measuring device.

  In the case of the network configuration of FIG. 6 by combining a plurality of pairs of switches and passage time measuring devices as shown in FIG. 1, the count value added to the frame is Add it. For example, in the configuration of FIG. 6, a count value 1 is added to the frame from the client 807 by passage of the passage time measurement device 804, and then the count value 2 is passed by passage of the passage time measurement device 805. Addition in the order of the count value 3 by the passage of the device 806 is performed.

[1-7. Effects of the first embodiment]
As described above, the delay time for each frame in a network relay device such as a switch is measured by discriminating based on the match of the source address, and it is recorded in the frame to generate a check code, With reference to the frame, it is possible to accurately grasp the variation in the transmission delay time in the round trip and the like, and to realize high-accuracy time synchronization in consideration thereof.

  In other words, even when a difference in round trip transmission delay time of the time synchronization frame occurs in the Ethernet switch, it is possible to achieve highly accurate time synchronization. Conventionally, in order to minimize delay time variation in the Ethernet switch When it is necessary to limit the frame length to a certain value or less, if the present invention is applied, the frame length is not limited, and a large amount of information can be transmitted efficiently.

[2. Second Embodiment] ... Corresponding to Claim 2 In the first embodiment described so far, the measured delay time is sequentially added to the frame (FIG. 6), whereas in the second embodiment, In this example, delay times are added sequentially.

  That is, in the example shown in FIG. 7, the transit time measuring devices 804 to 806 according to the first embodiment are connected in multiple stages for each of a plurality of corresponding network relay devices, that is, Ethernet switches 801 to 803, and each transit time is set. The recording means of the measuring devices 804 to 806 is configured to sequentially add the measured passing time to the passing time up to the previous stage recorded in the frame and record it.

When this second embodiment is applied to an NTP frame, the measured −Tdnt1 is added to the time T0 in Expression 4, and −Tdnt2 is added to T2.

C = ((T1-T0) -Tdnt1) / 2-((T3-T2) -Tdnt2) / 2 (Formula 4)

However (
Tdnt1: Delay time in the forward path measured by the transit time measuring device Tdnt2: Delay time in the return trip measured by the transit time measuring device T0: Client transmission time T1: Server reception time T2: Server transmission time T3: Client Reception time C: Time lag)

  Thus, by sequentially adding the delay time, that is, the passage time, and re-recording, the amount of data required for recording is limited even when measuring in multiple stages, and there is no need to change the existing NTP frame configuration. High-precision time synchronization is possible without changing the software running on the server.

[3. Third Embodiment] ... Corresponding to Claim 3 As shown in FIG. 8, the third embodiment is configured by changing each configuration of the transit time measuring apparatus shown in the first embodiment or the second embodiment to a transit time measuring unit 6. As an Ethernet switch 3 with a transit time measuring function, it is integrated with an Ethernet switch LSI (302) which is a network relay device.

  In this way, by integrating the function of the present invention into a network relay device such as an Ethernet switch, it is possible to perform highly accurate time synchronization with the Ethernet switch alone without the need for complicated wiring work. The reliability of the device can also be improved.

[4. Other embodiments]
In addition, this invention is not limited to the said embodiment, The thing illustrated below and other embodiment other than that are included. For example, each of the embodiments described above is divided into functional units such as a counter circuit, a frame processing circuit, a control circuit, and a memory circuit for convenience. However, as an implementation, hardware configuration units and functions realized by hardware are used. The way of dividing the functions realized by software and the specific configuration can be freely changed.

The figure which shows the structure of 1st Embodiment of this invention. The figure which shows the structure of the counter circuit in 1st Embodiment of this invention. The flowchart which shows the process sequence in 1st Embodiment of this invention. The time chart showing the output timing of the flame | frame in 1st Embodiment of this invention. The figure which shows the structure of the flame | frame in 1st Embodiment of this invention. The conceptual diagram which shows the state in which a count value is added to a flame | frame every time it passes each switch in 1st Embodiment of this invention. The conceptual diagram which shows the state in which the count value of a flame | frame is added every time it passes each switch in 2nd Embodiment of this invention. The figure which shows the structure of 3rd Embodiment of this invention. The figure which shows the state through which a flame | frame passes a switch.

Explanation of symbols

303 ... Counter circuits 304 to 307 ... Frame processing circuit 601 ... Passing time measuring device 701 ... Control circuit 71 ... Frame type determination unit 72 ... Source address determination unit 702 ... Memory circuit

Claims (4)

A passage time measuring device that measures a passage time of a frame in a network relay device for time synchronization via a communication network,
Discriminating means for discriminating whether or not the type of frame is for a predetermined time synchronization;
For the frame determined to be for time synchronization, measuring means for measuring a transit time from entry to exit to the network relay device;
Storage means for storing the passage time measured by the measurement means and the transmission source address of the frame related to the measurement start in association with each other;
When a frame leaves the network relay device, referring to the storage unit based on the source address of the frame, an acquisition unit that acquires the corresponding transit time from the measurement unit;
Recording means for recording the acquired transit time in the frame;
Generating means for generating a check code of the frame in which the transit time is recorded;
A transit time measuring apparatus comprising: The transit time measuring device according to claim 1 is connected in multiple stages for each of a plurality of corresponding network relay devices,
The recording means of each transit time measuring device is configured to record the transit time that is measured by sequentially adding the transit time to the previous transit time recorded in the frame. Passing time measuring device.   A network relay device incorporating the transit time measuring device according to claim 1. A method for controlling a transit time measuring device for measuring a transit time of a frame in a network relay device for time synchronization via a communication network,
A determination process for determining whether the type of frame is for a predetermined time synchronization; and
For the frame determined to be for time synchronization, a measurement process for measuring a transit time from entry to exit from the network relay device;
A storage process for correlating the passage time measured in the measurement process and the transmission source address of the frame related to the measurement start in a predetermined storage unit;
When a frame leaves the network relay device, referring to the storage means based on the source address of the frame, an acquisition process for acquiring the corresponding transit time based on the measurement process;
A recording process for recording the acquired transit time in the frame;
Generation processing for generating a check code of the frame in which the transit time is recorded;
The control method of the transit time measuring device characterized by including.

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