JP2008118270A - Delay measurement system and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a delay measurement system capable of measuring a delay time at a communication speed on a network by reducing the effect of an error in time that a terminal acquires and an error in timing when the terminal captures a packet. <P>SOLUTION: Transmission-side and reception-side terminals each acquire the time of an external timer at intervals of constant time by an internal timer, relate a constant internal elapsed time as an elapsed time that the internal timer indicates to the acquired time of the external timer, take a packet sent from a sending-out device to a receiving device and having a transmission number out of the network, and relate the transmission number extracted from the packet to a reception-time internal elapsed time as an elapsed time that the internal timer indicates when the packet is extracted. An analyzing device removes a high-frequency component during error variation between the constant internal elapsed time and external time, calculates external time based upon the external time having the high-frequency component removed, and calculates a difference between external times calculated on the transmission side and reception side as a delay time. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for measuring a delay time in communication on a network.

  One of the performance indexes of a packet network is a delay time that is a time required for a packet to pass through the packet network. Such network delay time is measured by connecting two measuring terminals each having an independent clock to the packet network, recording the time Ts at which one terminal transmits the packet to the packet network, This is realized by recording the time Te at which the packet is received from the packet network at the terminal and calculating Te-Ts.

  In this measurement method, it is necessary to perform time adjustment between terminals in advance. Therefore, in a device that measures delay measurement at the communication speed on the network, using a clock external to the terminal without performing prior time synchronization between the bases installed facing the network to be measured, A method of statistically calculating a communication delay between bases is known (for example, see Patent Document 1).

On the other hand, as a method of performing time adjustment between terminals in advance, the measurement device communicates with a server that manages time on the network using NTP (Network Time Protocol) before measurement, so that the built-in measurement device can be used. A method is known in which the time of a clock is set and the time between bases measured by the measuring device is synchronized using a time-set internal clock.
In addition, the measuring device is configured at a low cost using a personal computer (hereinafter referred to as a PC) having a built-in clock, and the time of the built-in clock of the measuring device is synchronized with the method described above, With this measuring device, the time of communication at the base is measured. There is known a method for measuring delays at a large number of bases by using a large number of measuring apparatuses configured in this manner at low cost (for example, see Patent Document 2).
Japanese Patent No. 3480701 Japanese Patent Application No. 2003-5190

However, in the mechanism for determining the time when a packet is captured using an external clock or the internal clock of a PC, there are the following problems, which cause a decrease in accuracy when measuring the time. Yes. Therefore, there is a problem that the delay time calculated based on the measured time cannot be measured accurately.
(1) Non-linear fluctuation of the internal clock The internal clock of the PC is not subject to fluctuations in the time or delay caused by deviations in the oscillation frequency due to the PC's individual time advance or delay error, temperature change, etc. There is an error. In particular, it is known that fluctuation errors are not linear and cannot be easily solved by mathematical formulas (see: Japanese Patent Application Laid-Open No. 2001-053792, Japanese Patent Application No. 2003-5190).
(2) Variation in time obtained from an external clock When a PC obtains time from an external clock, depending on the interface used to connect the PC and the external clock, there are various processing overheads in that interface. The obtained time includes a random error due to overhead.
Due to the reasons (1) and (2) above, errors occur in the internal clock time of the PC and in the time when the time is obtained from the external clock.

In addition, the following problem exists in the mechanism for capturing packets from the network, which causes a decrease in accuracy for detecting an accurate time.
(3) Error in packet capture timing Generally, an OS (operating system) operates in a multitasking manner, and a specific process cannot monopolize a CPU (central processing unit). For this reason, a process (or application) that captures a packet may be interrupted by an interruption or the like by another process, and a capture timing may be delayed.

  The present invention has been made in view of such circumstances, and the object of the present invention is to reduce the influence of the error of the time acquired by the terminal and the error of the timing of capturing the packet by the terminal, thereby reducing the communication speed on the network. It is an object to provide a delay measurement system and method capable of measuring a delay time.

  The present invention has been made to solve the above-described problems, and the invention according to claim 1 is a delay measurement system for measuring and calculating a delay time of a packet passing through a network, and calculating an elapsed time from activation. A first internal clock that counts time, obtains the time of the external clock at every elapse of a predetermined time by the first internal clock, and is a first constant internal elapsed time that is an elapsed time indicated by the first internal clock And the first external time, which is the time of the acquired external clock, is stored in the first external time storage means, and the packet including the transmission number transmitted from the transmission device to the reception device is extracted from the network, First transmission information registration by associating a transmission number extracted from the packet with a first reception internal elapsed time which is an elapsed time indicated by the first internal clock when the packet is extracted A first terminal registered in the stage, and a second internal clock that counts an elapsed time from startup, obtains the time of the external clock at every elapse of a predetermined time by the second internal clock, and The second constant internal elapsed time, which is the elapsed time indicated by the internal clock, and the second external time, which is the time of the acquired external clock, are associated and stored in the second external time storage means, and the receiving device A packet to be received is extracted from the network, and a transmission number extracted from the packet is associated with a second reception internal elapsed time which is an elapsed time indicated by the second internal clock when the packet is extracted. The second terminal registered in the transmission information registration means, the first external time and the first constant internal elapsed time are read from the first external time storage means, and the first constant internal elapsed time is read. Time and first The high frequency component in the first error fluctuation (external time fluctuation value FOT) at the external time is removed, and the first constant internal elapsed time and the high frequency component that are before and after the first reception internal elapsed time are removed. A first linear function is calculated from the first external time and the first reception internal elapsed time is substituted into the first linear function to calculate the external time as the first calculated external time. First time calculation means (time correction unit and time calculation unit), the second external time, and the second constant internal elapsed time are read from the second external time storage means, and the second constant time is calculated. The high frequency component in the second error variation between the internal elapsed time and the second external time is removed, and the second constant internal elapsed time and the high frequency component before and after the second reception internal elapsed time are Removed second external time, etc. A second time calculation means for calculating a second linear function and substituting the second internal time for reception in the second linear function to calculate an external time as a second calculated external time; A delay measuring system comprising: a delay calculating unit that calculates a difference between the first calculated external time and the second calculated external time with the same transmission number as a delay time; It is.

  According to a second aspect of the present invention, the first time calculation means is configured to start measurement and end measurement in a certain period with the horizontal axis as the first constant internal elapsed time and the vertical axis as the first external time. And obtaining a third linear function passing through two points of the first internal elapsed time and the first external time, and substituting the value of the first internal elapsed time for the third linear function. 1 calculated external time, and subtracting the first calculated external time from the first external time to calculate the first error fluctuation, and the second time calculating means The second constant internal elapsed time, the vertical axis as the second external time, and the two points of the second internal elapsed time and the second external time at the measurement start and measurement end in a certain period A fourth linear function passing through is obtained, and the fourth linear function is A second calculated external time is calculated by substituting a value between, and the second error fluctuation is calculated by subtracting the second calculated external time from the second external time. The delay measurement system according to claim 1.

  According to a third aspect of the present invention, the first time calculation means removes spike-like noise from the first error fluctuation before removing a high-frequency component in the first error fluctuation, and The time calculation means of 2 removes spike-shaped noise from the second error fluctuation before removing the high frequency component in the second error fluctuation. The delay measurement system described.

  According to a fourth aspect of the present invention, the analysis device includes a plurality of first time calculation units that calculate first calculation external times corresponding to the plurality of first terminals, and a plurality of the calculation externals. A first packet time selecting means for selecting the first calculated external time having the highest frequency in which the difference between the first calculated external times calculated for the time is equal to or less than a predetermined value; A plurality of second time calculation units for calculating the second calculated external time corresponding to the two terminals, and a difference between the second calculated external times calculated for the plurality of calculated external times is predetermined. Second packet time selection means for selecting the second calculated external time with the highest frequency that is less than or equal to the first value, wherein the delay calculation means is selected by the first packet time selection means. From the calculated external time of 1, the second packet time selection means A delay measurement system according to any one of claims 1 to 3, and calculates the delay time by subtracting the second calculation external time selected.

  The invention according to claim 5 is a delay measurement method used in a delay measurement system for measuring and calculating a delay time of a packet passing through a network, and has a first internal clock for measuring an elapsed time from activation. The time of the external clock is acquired at every elapse of a predetermined time by the first internal clock, and the first predetermined internal elapsed time that is the time indicated by the first internal clock and the time of the acquired external clock are 1 is associated with the external time and stored in the first external time storage means, the packet including the transmission number transmitted from the transmission device to the reception device is extracted from the network, the transmission number extracted from the packet, and the packet Is associated with the first reception internal elapsed time, which is the time indicated by the first internal clock at the time of taking out, and is registered in the first transmission information registration means, and the elapsed time from the start is counted. A second internal clock that acquires the time of the external clock every time a predetermined time elapses from the second internal clock, and the second constant internal elapsed time that is the time indicated by the second internal clock and the The second external time which is the time of the acquired external clock is associated and stored in the second external time storage means, the packet received by the receiving device is taken out from the network, the transmission number extracted from the packet, The second internal time at the time of reception, which is the time indicated by the second internal clock when the packet was taken out, is associated with the second transmission information registration means, and the first external time and the first 1 constant internal elapsed time is read out from the first external time storage means, a high frequency component in a first error variation between the first constant internal elapsed time and the first external time is removed, and the first Receive 1 A first linear function is calculated from the first constant internal elapsed time before and after the hour internal elapsed time and the first external time from which the high-frequency component has been removed, and the first linear function is converted into the first linear function. The external time is calculated as the first calculated external time by substituting the reception internal elapsed time, and the second external time and the second constant internal elapsed time are read from the second external time storage means. The high-frequency component in the second error variation between the second constant internal elapsed time and the second external time is removed, and the second constant internal elapsed time before and after the second reception internal elapsed time. A second linear function is calculated from the time and the second external time from which the high frequency component has been removed, and the second external time is determined by substituting the second reception internal elapsed time for the second linear function. Calculated as the external time of the transmission number The delay measurement method is characterized in that a difference between the first calculated external time and the second calculated external time that coincide with each other is calculated as a delay time.

  According to the present invention, by using a statistical method using a time including an error obtained from an external clock and a time when the internal clock fluctuates, the influence of the time error acquired by the terminal is reduced. Thus, the delay time at the communication speed on the network can be measured.

  Further, according to the present invention, spike noise can be easily detected by performing spike noise removal processing and band-pass filter processing after removing trend from the measured data. There is an effect that processing can be executed.

  In addition, according to the present invention, after the spike noise removal processing is performed on the measured data, the measured data is analyzed without being affected by the sudden noise in the measurement by executing the band pass filter processing. There is an effect that can be done.

  In addition, according to the present invention, from data captured by a plurality of parallel terminals, by selecting small delay data captured by the majority method, the influence of timing errors at which the terminal captures packets is reduced. It is possible to measure the delay in the communication speed on the network.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram showing a configuration during measurement of the delay measurement system according to the embodiment of the present invention.
The sending device A and the receiving device B are connected via a tap TAPA, a network NW to be measured, and a tap TAPB. Note that the sending device A, the tap TAPA, the network NW, the tap TAPB, and the receiving device B are connected in this order, and adjacent components are connected via the network.
Here, the network NW between the tap TAPA and the tap TAPB is a network for which the delay time is measured by the delay measurement system.

Further, a repeater HUBA is connected to the tap TAPA. A terminal PCA1, a terminal PCA2, and a terminal PCA3 are further connected to the repeater HUBA. Terminal PCA1, terminal PCA2 and terminal PCA3 are each connected to an external clock TA.
Here, the tap TAPA and the repeater HUBA, and the repeater HUBA and the terminal PCA1, the terminal PCA2, and the terminal PCA3 are connected by a network, respectively.
Further, the terminal PCA1, the terminal PCA2, the terminal PCA3 and the external clock TA are connected by a network or USB (Universal Serial Bus).

Further, a repeater HUBB is connected to the tap TAPB. A terminal PCB1, a terminal PCB2, and a terminal PCB3 are further connected to the repeater HUBB. Terminal PCB1, terminal PCB2, and terminal PCB3 are each connected to an external clock TB.
The connection between the respective components connected to the tap TAPB is the same as the connection between the respective components connected to the tap TAPA.

In addition, about the network used as the measuring object, the structure installed in the side close | similar to the transmission apparatus A is made into the structure of a transmission side, and the structure installed in the side close | similar to the receiving apparatus B is demonstrated as a structure of the receiving side.
That is, the configuration on the transmission side is connected to the tap TAPA, and the configuration on the reception side is connected to the tap TAPB. As described above, since the configuration on the transmission side and the configuration on the reception side are the same, only the configuration on the transmission side will be described below.

Next, each configuration used at the time of measurement of the delay measurement system will be described with reference to FIG.
The sending device A is a device that sends a packet including a transmission number for each packet to the receiving device B via the network NW to be measured. The packet transmitted by the transmitting apparatus A is, for example, a packet transmitted by the RTP protocol (Real time Transport Protocol), and the transmission number is a sequence number of the packet in the RTP protocol.
The sequence number is added as header information in the transmitted packet, and the information included in the data portion of the packet is arbitrary.
The receiving device B is a device that receives the packet sent from the sending device A.

The tap TAPA takes out a packet from the network between the transmission apparatus A and the network NW, and distributes the taken-out packet to the connected hub HUBA. Here, the tap TAPA takes out the packet in layer 1 of the communication layer. The tap TAPA is, for example, a tap and is a device that extracts a packet from the network.
The hub HUBA receives the packet from the tap TAPA and distributes the received packet to the connected terminals. Here, the hub HUBA distributes packets to connected terminals in the layer 1 of the communication layer. The hub HUBA is, for example, a repeater HUB and is a device that distributes packets.

The external clock TA measures the time inside the external clock TA and returns the time measured internally by the external clock TA to the connected terminal in response to an inquiry from the connected terminal.
Here, the external clock TA and the external clock TB are synchronized in time.
For example, the external clock TA and the external clock TB each access the NTP server via the network and acquire time information from the NTP server via the network. The external clock TA and the external clock TB can acquire current time information with an accuracy of ± hundreds of microseconds by accessing an NTP server.

Alternatively, for example, the external clock TA and the external clock TB acquire the time information by receiving the transmitted time information by GPS (Global Positioning System) or CDMA (Code Division Multiple Access), respectively. Thereby, the accuracy of the time information to be acquired is ± 10 microseconds.
The external clock TA and the external clock TB are synchronized with the time of the acquired time information, so that the internal clocks of the external clock TA and the external clock TB match.
As an example, the external clock TA and the external clock TB measure the time in units of hours, minutes, seconds, milliseconds, and microseconds, and the accuracy is ± 10 microseconds.

  Terminal PCA1, terminal PCA2, and terminal PCA3 each have the same configuration. Only the terminal PCA1 will be described here. Here, a case where there are three terminals each on the transmission side and the reception side will be described, but the number of each terminal is arbitrary. However, for the processing of the packet time selection unit 306, which will be described later, it is preferable that there are three or more terminals on both the transmission side and the reception side.

The terminal PCA1 includes an internal clock unit PCTA1, a transmission information registration unit 312, an external time registration unit 313, a transmission side packet data storage unit 112, and a transmission side external clock data storage unit 113. In FIG. 1, the transmission information registration unit 312 and the external time registration unit 313 are not shown.
The internal clock unit PCTA1 measures an internal elapsed time that is an elapsed time since the terminal PCA1 is activated, and registers the current internal elapsed time being measured in response to an inquiry from the transmission information registration unit 312. Respond to unit 312. The internal clock unit PCTA1 is built in the terminal PCA1.

Specifically, the internal clock unit PCTA1 measures the internal elapsed time by counting the number of clocks output from the crystal oscillator used in the terminal PCA1. Since the time interval of the clock output from the crystal oscillator is constant, the internal clock unit starts up the terminal PCA1 by multiplying the clock time interval (that is, 1 / clock frequency) by the counted number of clocks. The internal elapsed time can be calculated.
For example, the internal clock unit calculates the elapsed time by calculating the number of elapsed clocks divided by the clock frequency from the number of elapsed clocks since activation and the clock frequency. However, since the clock frequency has deviation and fluctuation as described in “(3) Error of packet capture timing” above, this elapsed time is not necessarily accurate.

  The transmission information registration unit 312 acquires the internal elapsed time from the internal clock unit PCTA1 as the reception internal elapsed time in response to receiving the transmission information output from the sending device A via the tap TAPA and the hub HUBA. Then, the transmission number is extracted from the received transmission information, and the extracted transmission number and the acquired internal elapsed time at reception are associated with each other and registered in the transmission side packet data storage unit 112.

The external time registration unit 313 acquires the external time from the external clock TA for every fixed time measured by the internal clock unit PCTA1, and acquires the acquired external time and the fixed internal elapsed time that is the internal elapsed time. Are registered in the transmission-side external clock data storage unit 113.
Here, the transmission-side external clock data storage unit 113 records the acquired external time with the internal elapsed time every fixed time, so that the time axis is set every fixed time, as will be described later. In the case of the internal elapsed time, it is possible to easily execute frequency analysis, frequency band pass / band removal processing, and the like for the acquired external time.

  In terminal PCA1, transmission side packet data storage unit 112 and transmission side external time data storage unit 113 are detachable from terminal PCA1. For example, the transmission side packet data storage unit 112 and the transmission side external time data storage unit 113 are connected to the terminal PCA1 at the time of measurement, and when the delay time is analyzed after the measurement is completed, The connection with the PCA 1 is released, and the PCA 1 is connected to an analysis device described later.

In the following description, the transmission side packet data storage unit 112, the transmission side packet data storage unit 122, the transmission side packet data storage unit 132, the reception side packet data storage unit 212, the reception side packet data storage unit 222, and the reception side packet data storage will be described. The unit 232 will be collectively described as a packet data storage unit.
Further, hereinafter, the transmission side external time data storage unit 113, the transmission side external time data storage unit 123, the transmission side external time data storage unit 133, the reception side external time data storage unit 213, the reception side external time data storage unit 223, and The reception-side external time data storage unit 233 will be described as an external time data storage unit.

Next, each configuration at the time of analyzing the delay time of the delay measurement system will be described with reference to FIGS. In the figure, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
As shown in FIG. 2, the analysis apparatus PC7, which is an analysis terminal, is connected to the transmission side packet data storage unit 112 and the transmission side external time data storage unit 113 that are disconnected from the terminal PCA1 of FIG. Is done. Similarly, the analysis apparatus PC7 is connected to the other packet data storage unit in FIG. 1 and the external time data storage unit.
In the following, the analysis apparatus PC7 will be described as an analysis terminal PC7.

The transmission-side external clock correction data storage unit 114 and the transmission-side packet time data storage unit 115 connected to the analysis terminal PC7 are storage units used to calculate the delay time for the terminal PCA1 in the analysis terminal PC7. It is.
A storage unit corresponding to the transmission-side external clock correction data storage unit 114 and the transmission-side packet time data storage unit 115 is connected to the analysis terminal PC7 for each terminal on the transmission side and reception side.

  In addition, the transmission side packet time selection data storage unit 106 on the transmission side and the reception side packet time selection data storage unit 206 on the reception side are connected to the analysis terminal PC7. A delay result report storage unit 301 is connected to the analysis terminal PC7.

Referring to FIG. 2, the analysis terminal PC7 calculates a delay time based on the connected packet data storage unit and the external time data storage unit, and outputs the calculated delay time as a delay result report storage unit. 301 is registered. The configuration of the analysis terminal PC7 and each storage unit will be described with reference to FIG.
In FIG. 2, each storage unit is illustrated as being outside the analysis terminal PC7. However, each storage unit may be inside the analysis terminal PC7, and the analysis terminal PC7, each storage unit, Are connected, and each storage unit can be accessed from the analysis terminal PC7.

Next, the configuration of the analysis terminal PC7 and each storage unit will be described with reference to FIG.
The analysis terminal PC7 has a time correction unit, a time calculation unit, an external clock correction data storage unit, and a packet time data storage unit for each terminal used for measurement.
For example, the configuration corresponding to the terminal PCA1 includes a transmission side external clock data storage unit 113, a transmission side packet data storage unit 112, a time correction unit 314, a transmission side external clock correction data storage unit 114, a time calculation unit 315, and a transmission side. This is a packet data storage unit 115.
The analysis terminal PC7 has the same configuration for other terminals.

Further, when there is a packet time data storage unit on the transmission side, the analysis terminal PC 7 selects a piece of information by statistical processing from information registered in the packet time data storage unit on the transmission side. have.
The output of the packet time selection unit 306 on the transmission side is output to the transmission side packet time selection data storage unit 106 and registered.
The configuration of the analysis terminal PC7 described above is the same on the transmission side and the reception side.

  The analysis terminal PC7 has a delay calculation unit 507 connected to the transmission side packet time selection data storage unit 106 and the reception side packet time selection data storage unit 206. The output of the delay calculation unit 507 is a delay result report. Connected to the storage unit 301. In the analysis terminal PC7, one delay calculation unit 507 and one delay result report storage unit 301 are provided.

  Next, a time correction unit 314, a time calculation unit 315, a transmission side external clock data correction storage unit 113, a transmission side packet time data storage unit 112, a transmission side external time correction data storage unit 114, a transmission side packet corresponding to the terminal PCA1 A configuration of the time data storage unit 115 will be described. The configuration corresponding to the terminal PCA2, the terminal PCA3, the terminal PCB1, the terminal PCB2, and the terminal PCB3 has the same configuration as the configuration corresponding to the terminal PCA1.

The time correction unit 314 reads the external time and the fixed internal elapsed time from the transmission-side external clock data correction storage unit 113, sets the horizontal axis as the read fixed internal elapsed time, and sets the vertical axis as the read external time from the external time. The corrected external time is calculated by removing a predetermined high-frequency component, and the read fixed internal elapsed time and the corrected external time are associated with each other and registered in the transmission-side external time correction data storage unit 114.
Details of processing executed by the time correction unit 314 will be described later.

The time calculation unit 315 reads the extracted transmission number and the received internal elapsed time from the transmission-side packet time data storage unit 112, and the associated constant internal elapsed time and the corrected external time from the time correction unit 314 to the transmission side. By substituting the read internal elapsed time at the time of reception into a linear function (linear function) that is input via the external time correction data storage unit 114 and calculated from the input fixed internal elapsed time and the corrected external time A calculated external time that is a calculated external time is calculated, and the transmission number and the calculated calculated external time are associated with each other and registered in the transmission side packet time data storage unit 115.
Details of the processing executed by the time calculation unit 315 will be described later.

The packet time selection unit 306 receives the transmission number and the calculated external time from the time calculation unit (315, 325, 335) via the transmission side packet time data storage unit (115, 125, 135) for each of a plurality of terminals. The calculated external time for each of the plurality of terminals having the same input transmission number is extracted, the difference of the calculated external time for each of the extracted terminals is calculated, and the calculated mutual difference is determined in advance. The calculated external time having the highest frequency that is less than or equal to the value and the transmission number are associated with each other and registered in the transmission side packet time selection data storage unit 106.
Details of processing executed by the packet time selection unit 306 will be described later.

  The delay calculation unit 507 receives, on the transmission side, the associated transmission number and the calculated external time from the packet time selection unit 306 via the transmission side packet time selection data storage unit 106 and is associated on the reception side. The transmission number and the calculated external time are input from the transmission side packet time selection data storage unit (not shown) via the reception side packet time selection data storage unit 206, and the transmission side calculated external time and reception with the same transmission number are received. The difference from the calculated external time on the side is calculated as a delay time, and the calculated delay time is registered in the delay result report storage unit 301.

  When there is only one terminal on each of the transmission side and the reception side, the delay calculation unit 507 transmits the associated transmission number and the calculated external time from the time calculation unit 315 to the transmission side packet time data on the transmission side. Input via the storage unit 115, and on the receiving side, the associated transmission number and calculated external time are input from the time calculation unit (not shown) via the reception side packet time data storage unit 1 (not shown). Then, the difference between the calculated external time on the transmitting side and the calculated external time on the receiving side with the same transmission number may be calculated as the delay time.

Next, processing executed by the time correction unit 314 will be described with reference to FIGS.
First, the associated internal elapsed time IT and external time OT are read from the transmission-side external clock data correction storage unit 113 (step S401).
Next, the horizontal axis is the internal elapsed time IT, the vertical axis is the external time OT (see the waveform P1 in FIG. 5A), the measurement starts (S1 in FIG. 5A), and the measurement ends (FIG. 5A ) Is calculated as a temporary function (straight line P2 in FIG. 5A) passing through two points with S2) (step S402).

Next, a calculated external time COT that is a value obtained by substituting each value of the internal elapsed time IT into the calculated linear function is calculated (step S403).
Next, the external time fluctuation value FOT (FIG. 5A) is subtracted from the external time OT by subtracting the calculated external time COT calculated by substituting the internal elapsed time IT associated with the external time OT into the obtained linear function. Here, only three points of FOT 1, 2, and 3 are illustrated) (that is, error fluctuation) is calculated (step S404).

The external time fluctuation value FOT calculated in this way is as shown in FIG. 5B, for example, where the horizontal axis is the internal elapsed time IT and the vertical axis is the external time fluctuation value FOT.
As shown in FIG. 5B, in the calculated external time fluctuation value FOT, data having an accidentally large error may occur, and the value is far from the average value in the vicinity. There are places that become spikes when viewed on the graph. Such spike noise is hereinafter referred to as spike noise.

Next, returning to the description of FIG. 4, spike noise is removed from the external time fluctuation value FOT, and a spike noise elimination external time fluctuation value SFOT is calculated (step S405).
Specifically, a median or average value filter is applied to the external time fluctuation value FOT. As a result, it is possible to remove data whose value is far from the average value in the vicinity in the external time fluctuation value FOT. The median value or average value filter is a predetermined filter.
Note that the removal of spike noise here does not delete the data detected as spike noise from the external time fluctuation value FOT, but replaces the data detected as spike noise with the median or average filter value. That is.

In order to eliminate spike noise, spike noise is first detected from the external time fluctuation value FOT, and a predetermined median or average value filter is applied only to the detected spike noise of the external time fluctuation value FOT. May be.
Here, the spike noise from the external time fluctuation value FOT may be detected as spike noise when the external time fluctuation value FOT is equal to or greater than a predetermined value.
Alternatively, in the detection of spike noise from the external time fluctuation value FOT, the value of the external time fluctuation value FOT is larger than the predetermined average value of the external time fluctuation value FOT in the vicinity. In such a case, it may be detected as spike noise.

As an example, the data before removing spike noise is the waveform shown in FIG. 6A, and the data after removing spike noise is the waveform shown in FIG. 6B.
As a specific process used here, as a filter process, first, a filter that calculates a median value of five data before and after the data is used. Next, data whose difference between the data and the calculated median is less than 15 μsec is extracted as spike noise and removed.
Comparing before and after noise removal, it can be seen that the waveform is more stable after removal than before removal. Before removal, sudden noise-like data is ± 80 μsec.On the other hand, after removal noise-like data is within ± 20 μsec. Even when using an average filter, the same result can be obtained. I can do it.

Returning to the description of FIG. 4, the spike noise elimination external time fluctuation value SFOT is corrected, and the corrected external time fluctuation value MSFOT is calculated (step S406).
The correction processing here refers to processing such as applying a low-pass filter to the spike noise removal external time fluctuation value SFOT, performing linear approximation processing, or performing polygonal line approximation processing.

FIG. 7 shows a corrected external time fluctuation value MSFOT when processing using a low-pass filter is executed as correction processing.
FIGS. 7A and 7B show information about the low-pass filter, and show the impulse response and the amplitude characteristic, respectively.
This low-pass filter has a cutoff frequency of 0.01 Hz and removes 0.02 Hz or more. The specifications of the low-pass filter are as follows. It is a weighted average of FIR type. The normalized cutoff frequency is 0.001 Hz, that is, the cutoff frequency is 0.01 Hz, and the sampling period is 0.1 second (10 Hz). The number of taps is 1001. Further, a Hamming window function is used for correcting the amplitude characteristic.

FIG. 7C is a graph in which the horizontal axis is the internal elapsed time IT and the vertical axis is the corrected external time fluctuation value MSFOT. For reference, FIG. 7C also shows a graph in which the horizontal axis is the internal elapsed time IT and the vertical axis is the external time OT that is the original data.
From this, it can be seen that the corrected external time fluctuation value MSFOT has a smooth outline as compared with the external time OT which is the original data. Further, it can be seen that there is no noise component in the corrected external time fluctuation value MSFOT, and the corrected external time fluctuation value MSFOT penetrates around the center of the external time OT.

Next, the calculated external time COT is added to the corrected external time fluctuation value MSFOT to calculate the corrected external time MOT (step S407).
Next, the corrected external time MOT and the internal elapsed time IT associated with the corrected external time MOT are associated and registered in the transmission-side external clock correction data storage unit (step S408).

As shown in FIG. 5 (a), the time correction unit 314 uses the internal elapsed time IT as the horizontal axis and the external time OT as the vertical axis, as shown in FIG. Then, after the intercept is made zero, spike noise removal processing and low-pass filter processing are executed.
As described above, the time correction unit 314 performs the low-pass filter processing by executing the low-pass filter processing after setting the slope to zero and then setting the intercept to zero (so-called trend removal processing). The result of the filtering process is appropriate.
In addition, since the time correction unit 314 executes the low-pass filter process after removing the spike noise, the result of the low-pass filter process becomes appropriate.

The data trend removal processing is the following processing. Since the Fourier transform decomposes data / functions into a set of sine / cosine functions, it is assumed to be stationary. Therefore, when the trend is included in the original data, it is necessary to remove it.
In the embodiment, the data is the external time OT, and linear trend removal by linear regression is executed as a trend removal method. In the embodiment, the Fourier transform is not directly performed on the external time OT which is data, but in the low-pass filter processing, the data is set as a set of sine / cosine functions and a certain band is removed. is doing. Therefore, the accuracy in the low-pass filter process is improved by removing the trend from the external time OT.

Next, processing executed by the time calculation unit 315 will be described with reference to FIG.
First, the time calculation unit 315 reads the extracted transmission number and reception internal elapsed time from the transmission-side packet time data storage unit 112, and the associated constant internal elapsed time and corrected external time from the time correction unit 314. Input via the transmission-side external time correction data storage unit 114.
Next, the time calculation unit 315 searches for the fixed internal elapsed time before and after the input internal elapsed time at the reception from the input constant internal elapsed time. Next, using the fixed internal elapsed time before and after the search as a search key, the corrected external time is searched from the input fixed internal elapsed time and the corrected external time.

In FIG. 8, the internal elapsed time at the time of reception will be described as Ca, the constant internal elapsed time before and after CREF1 and CREF2, and the corrected external time before and after will be described as tREF1 and tREF2.
As shown in FIG. 8B, when the internal elapsed time is plotted on the horizontal axis, the constant internal elapsed time CREF1, the reception internal elapsed time Ca, and the constant internal elapsed time CREF2 elapse in this order.
Based on the detected result, the time calculation unit 315 calculates the corrected external time ta corresponding to the reception internal elapsed time Ca that is the packet arrival as shown in FIG.
A process in which the time calculation unit 315 calculates the corrected external time ta will be described below.

First, a linear function is calculated with the values at two points on the horizontal axis and the vertical axis as a constant internal elapsed time CREF1 and a corrected external time tREF1, and a constant internal elapsed time CREF2 and a corrected external time tREF2.
Next, a value obtained by assigning the reception internal elapsed time Ca to the calculated linear function is calculated as the corrected external time ta.

  The time calculation unit 315 performs the external time calculated by substituting the read internal elapsed time for reception into the linear function calculated from the input constant internal elapsed time and the corrected external time as described above. The calculated external time is calculated, and the transmission number and the calculated calculated external time are associated with each other and registered in the transmission side packet time data storage unit 115.

Next, processing executed by the packet time selection unit 306 will be described.
First, for the sake of explanation, the determination logic when there are three terminal PCs having the minimum configuration will be specifically described. Even when the number of terminal PCs is n (where n is a natural number greater than 3), the logic is the same.

Measurement is performed by three terminal PCs.
Handles the data obtained from the three terminals PC1, PC2 and PC3 Transmitter side packet time data 1, 2, 3
Receiver side packet time data 1, 2, 3
<Description of logic when there are three terminal PCs>
Difference calculation: Calculate the difference in packet transit time between PC1,2,3
dif [1,2] = | PC1-PC2 |, dif [1,3] = | PC1-PC3 |
dif [2,1] = | PC2-PC1 |, dif [2,3] = | PC2-PC3 |
dif [3,1] = | PC3-PC1 |, dif [3,2] = | PC3-PC2 |
Difference comparison: If one of the difference calculation results is within a certain range, the two units are similar.
The number that falls within a certain range with dif [x, y] is the corresponding frequency (pct [x]). Here, pct is an abbreviation for pair-count.
Difference determination: Judge the value of the corresponding frequency (pct [x]) and select the data with the maximum value of the corresponding frequency Select the data of the terminal (PC) with the maximum value

  As exception processing in the difference determination, if there is no superiority or inferiority in the value of the corresponding frequency, a PC with a lower number is selected. Also, if the values of the corresponding frequencies are all zero, it is not adopted because it is inaccurate data.

  In the passage time difference dif calculation, for simplification of explanation, dif [x, y] and dif [y, x] are separately calculated, but these two are the same value. Therefore, it is possible to calculate dif [x, y] and dif [y, x] by one calculation of dif [x, y] or dif [y, x].

Next, an actual example selected by the packet time selection unit 306 is shown.
Time acquisition device: 3 terminals, allowable time: 10μsec
Here, the allowable time is a predetermined value determined in advance.
It is assumed that the acquired time information (that is, calculated external time) is as follows.
Equipment 1 9: 00.000000
Device 2 9: 00.000020
Device 3 9: 00.000005

<Comparison result> Applicable frequency
dif [1,2] = | PC1-PC2 | = 20, dif [1,3] = | PC1-PC3 | = 5 1
dif [2,1] = | PC2-PC1 | = 20, dif [2,3] = | PC2-PC3 | = 15 0
dif [3,1] = | PC3-PC1 | = 5, dif [3,2] = | PC3-PC2 | = 15 1
Therefore, the packet time selection unit 306 selects “9: 00.000000”, which is the time (that is, the calculated external time) of the device 1 having the highest frequency of matching. In this case, apparatus 1 and apparatus 3 have the highest corresponding frequency, and the value of the corresponding frequency is the same, but the time of apparatus 1 is selected because a lower number PC was selected by exception processing. .

Next, determination logic in which the number of terminal PCs processed by the packet time selection unit 306 is expanded to n will be described.
Since the measurement is performed with n units, the conditions are as follows.
That is, transmitting side packet time data 1,2,3, ..., n handling data obtained from terminal PC1, terminal PC2, terminal PC3, ..., terminal PCn
Receiver side packet time data 1,2,3, ..., n

<Description of logic when there are n terminal PCs>
Difference calculation: Calculate the difference in packet transit time between PC1,2,3
dif [1,2] = | PC1-PC2 |, dif [1,3] = | PC1-PC3 |…, dif [1, m] = | PC1-PCm |, dif [1, n] = | PC1- PCn |
dif [2,1] = | PC2-PC1 |, dif [2,3] = | PC2-PC3 |…, dif [2, m] = | PC2-PCm |, dif [2, n] = | PC2- PCn |
dif [3,1] = | PC3-PC1 |, dif [3,2] = | PC3-PC2 |…, dif [2, m] = | PC3-PCm |, dif [2, n] = | PC3- PCn |
:
dif [m, 1] = | PCm-PC1 |, dif [m, 2] = | PCm-PC2 |, dif [m, 3] = | PCm-PC3 |…, dif [m, n] = | PCm- PCn |
Difference comparison: Compares whether any of the difference calculation results are within a certain range.
The number that falls within a certain range with dif [x, y] is the corresponding frequency (pct [x]).
Difference determination: The value of the corresponding frequency (pct [x]) is determined, and data is selected.
Select the PC data with the maximum value.
If there is no superiority or inferiority as exception processing, select a PC with a lower number.
As exception processing, if all zeros, the data is inaccurate and is not adopted.

Next, the logic of the process in the packet time selection unit 306 will be described using an example in which there are five terminal PCs.
Time acquisition device: 5 units, allowable time: 10μsec
Here, the allowable time is a predetermined value determined in advance.
Acquired time information (that is, calculated external time)
Equipment 1 9: 00.000000
Device 2 9: 00.000020
Device 3 9: 00.000005
Equipment 4 9: 00.000010
Device 5 9: 00.000009
<Comparison result> Applicable frequency
dif [1,2] = 20 dif [1,3] = 5 dif [1,4] = 10 dif [1,5] = 9 3
dif [2,1] = 20 dif [2,3] = 15 dif [2,4] = 10 dif [2,5] = 11 1
dif [3,1] = 5 dif [3,2] = 15 dif [3,4] = 5 dif [3,5] = 4 3
dif [4,1] = 10 dif [4,2] = 10 dif [4,3] = 5 dif [4,5] = 1 4
Therefore, the packet time selection unit 306 selects “9: 00.000010”, which is the time (that is, the calculated external time) of the device 4 having the highest corresponding frequency.

  The packet time selection unit 306 registers the calculated external time selected as described above and the transmission number in the transmission side packet time selection data storage unit 106 in association with each other.

The statistical processing method used in the present invention is “selection of data by majority vote”, “selection of data by majority vote” from a plurality of data is a method in which the mode value is expanded, and the problems of the following other methods Each has an advantage.
(Method 1) The average value or the median value is different when the number is small, and there is a problem that when there is a large outlier, the error is increased due to the influence of the value.
(Method 2) With the mode value, there is no problem when a plurality of data are close to each other, but when all are discrete values, there is a problem that it is necessary to discard the data.
In contrast to Method 1 and Method 2, the statistical processing method according to the present invention, “selection of data by majority vote” is a case where the number is small, and if there is a large outlier, the error is large due to the effect of that value. There is an effect of not becoming. In addition, even when a plurality of pieces of data are all discrete values, there is an effect that data can be selected by majority without having to discard the data.

  The packet time selection unit 306 selects the calculated external time from one terminal by “selection of data by majority vote” described above, but is not limited to this, and the average value described above Alternatively, one calculated external time may be calculated from a plurality of calculated external times by the median value, or one calculated external time may be selected from the plurality of calculated external times by the mode value.

  Note that storage units such as the transmission-side external clock data correction storage unit 113, the transmission-side packet time data storage unit 112, the transmission-side external time correction data storage unit 114, and the transmission-side packet time data storage unit 115 are hard disk devices and magneto-optical devices. A non-volatile memory such as a disk device or flash memory, a storage medium such as a CR-ROM that can only be read, a volatile memory such as a RAM (Random Access Memory), or a combination thereof To do.

  Note that the transmission information registration unit 312 and the external time registration unit 313 in FIG. 1 and the processing units of the time correction unit 314, the time calculation unit 315, the packet time selection unit 306, and the delay calculation unit 507 in FIG. Or may be realized by a memory and a microprocessor.

  The processing unit may be realized by dedicated hardware. The processing unit includes a memory and a CPU (central processing unit), and a program for realizing the functions of the processing unit is provided. The function may be realized by loading it into a memory and executing it.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes design and the like within a scope not departing from the gist of the present invention.

  The present invention is suitable for use in a packet network delay measurement system.

It is a block diagram which shows the structure at the time of the measurement of the delay measuring system by one Embodiment of this invention. It is a block diagram which shows the structure of the memory | storage part at the time of the analysis of the delay measurement system by one Embodiment of this invention. It is a block diagram which shows the structure at the time of the analysis of the delay measurement system by one Embodiment of this invention. It is a flowchart figure explaining the process in a time correction part. It is the 1st explanatory view explaining processing in a time amendment part. It is the 2nd explanatory view explaining processing in a time amendment part. It is the 3rd explanatory view explaining processing in a time amendment part. It is explanatory drawing explaining the process in a time calculation part.

Explanation of symbols

A Sending device B Receiving device TAPA Tap TAPB Tap HUBA Repeater HUBB Repeater TA External clock TB External clock PCA1 Terminal PCA2 Terminal PCA3 Terminal PCB1 Terminal PCB2 Terminal PCB3 Terminal 112, 122, 132 Transmission side packet data storage 113, 123, 133 Transmission side External clock data storage unit PC7 Analysis terminal 314 Time correction unit 315 Time calculation unit 306 Packet time selection unit 507 Delay calculation unit 114, 123, 134 Transmission side external time correction data storage unit 115, 125, 135 Transmission side packet time data storage unit 106 transmission side packet time selection data storage unit 206 reception side packet time selection data storage unit 301 delay result report storage unit

Claims (5)

It is a delay measurement system that measures and calculates the delay time of packets passing through the network,
A first internal clock that counts the elapsed time since startup, obtains the time of the external clock at every elapse of a predetermined time by the first internal clock, and is the elapsed time indicated by the first internal clock A packet including a transmission number sent from the sending device to the receiving device, associating the fixed internal elapsed time of 1 with the first external time, which is the time of the acquired external clock, in the first external time storage means First transmission by associating the transmission number extracted from the network and the first internal elapsed time during reception, which is the elapsed time indicated by the first internal clock when the packet was extracted A first terminal registered in the information registration means;
A second internal clock that counts the elapsed time from startup, obtains the time of the external clock at every elapse of a fixed time by the second internal clock, and is the elapsed time indicated by the second internal clock 2 is stored in the second external time storage means in association with the second external time that is the time of the acquired external clock, the packet received by the receiving device is extracted from the network, The transmission number extracted from the packet is associated with the second reception internal elapsed time, which is the elapsed time indicated by the second internal clock when the packet is extracted, and registered in the second transmission information registration means. Two terminals,
The first external time and the first constant internal elapsed time are read from the first external time storage means, and a first error variation between the first constant internal elapsed time and the first external time The first linear function is calculated from the first constant internal elapsed time before and after the first reception internal elapsed time and the first external time from which the high frequency component is removed. A first time calculating means for calculating an external time as a first calculated external time by substituting the first reception internal elapsed time for the first linear function, the second external time, and the A second constant internal elapsed time is read out from the second external time storage means, a high frequency component in a second error variation between the second constant internal elapsed time and the second external time is removed, and Second received internal elapsed time A second linear function is calculated from the second constant internal elapsed time before and after and the second external time from which the high frequency component is removed, and the second internal internal elapsed time at reception is calculated as the second linear function. Substituting for the second time calculation means for calculating the external time as the second calculated external time, and the difference between the first calculated external time and the second calculated external time with the same transmission number An analysis device having a delay calculation means for calculating the delay time;
A delay measurement system comprising: The first time calculation means includes:
With the horizontal axis as the first constant internal elapsed time and the vertical axis as the first external time, the first internal elapsed time and the first external time at the measurement start and measurement end in a fixed period A third linear function passing through two points is obtained, a value of the first internal elapsed time is substituted into the third linear function, a first calculated external time is calculated, and the first external time is calculated from the first external time. Calculating the first error variation by subtracting the calculated external time of 1;
The second time calculating means is
With the horizontal axis as the second constant internal elapsed time and the vertical axis as the second external time, the second internal elapsed time and the second external time at the measurement start and measurement end in a fixed period A fourth linear function passing through two points is obtained, a value of the second internal elapsed time is substituted into the fourth linear function, a second calculated external time is calculated, and the second external time is calculated from the second external time. Calculating the second error variation by subtracting the calculated external time of 2;
The delay measurement system according to claim 1. The first time calculation means includes:
Before removing the high frequency component in the first error fluctuation, spike noise is removed from the first error fluctuation;
The second time calculating means is
Removing spike-like noise from the second error fluctuation before removing a high-frequency component in the second error fluctuation;
The delay measurement system according to claim 1 or 2, wherein The analysis device is
A plurality of first time calculation units for calculating a first calculated external time corresponding to the plurality of first terminals;
First packet time selection means for selecting the first calculated external time having the highest frequency in which the difference between the calculated first calculated external times is equal to or less than a predetermined value; ,
A plurality of second time calculation units for calculating a second calculated external time corresponding to the plurality of second terminals;
Second packet time selecting means for selecting the second calculated external time having the highest frequency in which the difference between the second calculated external times calculated by the plurality of calculated external times is equal to or less than a predetermined value; ,
Have
The delay calculating means subtracts the second calculated external time selected by the second packet time selecting means from the first calculated external time selected by the first packet time selecting means. The delay measurement system according to claim 1, wherein the delay measurement system is calculated. A delay measurement method used in a delay measurement system that measures and calculates a delay time of a packet passing through a network,
A first internal clock that counts the elapsed time from the start, obtains the time of the external clock at every elapse of a fixed time by the first internal clock, and is the first time indicated by the first internal clock A packet including the transmission number sent from the sending device to the receiving device, in association with the first external time that is the time of the acquired external clock in association with the first external time stored in the first external time storage means First transmission information registration by associating a transmission number extracted from the network and extracted from the packet with a first reception internal elapsed time which is a time indicated by the first internal clock when the packet is extracted Register with the means,
A second internal clock that counts the elapsed time since startup, obtains the time of the external clock at every elapse of a predetermined time by the second internal clock, and is a time indicated by the second internal clock. A predetermined internal elapsed time and a second external time which is the time of the acquired external clock are stored in the second external time storage means, and a packet received by the receiving device is extracted from the network, The transmission number extracted from the second transmission information registration means in association with the second reception internal elapsed time, which is the time indicated by the second internal clock when the packet is extracted,
The first external time and the first constant internal elapsed time are read from the first external time storage means, and a first error variation between the first constant internal elapsed time and the first external time The first linear function is calculated from the first constant internal elapsed time before and after the first reception internal elapsed time and the first external time from which the high frequency component is removed. The external time is calculated as the first calculated external time by substituting the first reception internal elapsed time for the first linear function, and the second external time and the second constant internal elapsed time are calculated. Are read from the second external time storage means, the high frequency component in the second error variation between the second constant internal elapsed time and the second external time is removed, and the second internal time elapsed during reception The second one before and after time A second linear function is calculated from the internal elapsed time and the second external time from which the high frequency component has been removed, and the external time is determined by substituting the second internal internal elapsed time for reception into the second linear function. Calculating as a second calculated external time, and calculating a difference between the first calculated external time and the second calculated external time with the same transmission number as a delay time;
A delay measuring method.

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