JP2005195507A - Method for time synchronization via network - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To appropriately perform time synchronization with respect to a plurality of terminals connected to a network. <P>SOLUTION: A terminal 101 acquires deviation T<SB>D</SB>of clocked time of an internal clock 116 in an own terminal 101 from an NTP server 102 by using an NTP protocol, compares the value of T<SB>D</SB>with a set value T<SB>S</SB>stored in a setting table of the terminal 101, and determines a correction amount ΔT on time of the internal clock 116 according to the result of comparison. Specifically, the correction amount ΔT is set for T<SB>D</SB>when the absolute value of T<SB>D</SB>is equal to or less than the set value T<SB>S</SB>while the correction amount ΔT is set for T<SB>S</SB>when the absolute value of T<SB>D</SB>is larger than the set value T<SB>S</SB>. This prevents clocked time of the internal clock 116 from being corrected to inappropriate value owing to fluctuation in the state of the network. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for synchronizing time in a plurality of terminals connected to a network and a terminal for executing the method.

  In recent years, with rapid development of communication infrastructure, it has been attempted to construct a system for performing ensembles (sessions) using a plurality of geographically separated computer terminals via a network. For example, it is considered that each user connects a terminal (hereinafter referred to as MIDI terminal) conforming to the MIDI (Musical Instrument Digital Interface) standard to the Internet and plays a specific part of the same music.

  In such a system, a communication packet including performance information is transmitted from one terminal to another terminal, and conversely, a performance information packet from another terminal is received by the terminal. The packet to be transmitted has a time stamp indicating the timing of processing the musical tone information (musical tone generation / stopping, timbre change, etc.) included in the packet. With reference to the stamp, the performance information received at the timing according to the time stamp is processed. By exchanging musical tone information in this way and synchronizing various performance processes such as sound generation timing, a session using a plurality of MIDI terminals is established via the network.

  At this time, it is assumed that each terminal has a clock that serves as a reference for the operation of the terminal, and that the clocks are synchronized with each other. This is because, if the clocks are not synchronized, even if an appropriate time stamp is attached to the packet, the processing time differs depending on the terminal, resulting in a problem for the session. However, in general, any clock may be distorted, and it cannot be guaranteed that the clock of each terminal is operating without erraticness. Therefore, it is a common practice to adjust the clock of each terminal via a network.

  Various techniques exist for a method of adjusting the time of a clock of a terminal connected to a network (see, for example, Patent Document 1). As a typical example, there is a method using NTP (network time protocol) and its simple version, SNTP (simple network time protocol). Specifically, a certain terminal transmits a packet with the time indicated by its own clock to the NTP server, and upon receiving this packet, the NTP server transmits a new packet to the terminal. This packet is given the time when the packet from the terminal is received and the time when the new packet is transmitted. The terminal that receives this packet calculates the time difference between its own terminal and the server from both times attached to the packet, and adjusts its own clock. In this way, synchronization is achieved by setting the clocks of all terminals to the clocks of the NTP server.

  However, in the above-described method, the time adjustment is performed via the network, so it is inevitable that the time is affected by the network state. For example, it is known that the load on the network and the state of the usable bandwidth may change with time, which means that the delay time of the packet used for time adjustment may also change. Further, in the NTP protocol, it is assumed that the delay time of the time adjustment packet is the same between the forward path and the return path (see Non-Patent Document 1). Therefore, when a time adjustment packet received by a certain terminal arrives by a large delay due to some sudden influence or the like, there is a possibility that the time of the terminal is set to be shifted. In particular, if a large delay occurs in only one of the forward and return routes during the transmission and reception of time adjustment packets, the precondition of the time adjustment principle will be lost in the first place, resulting in a significant shift in the terminal clock. It will be set to the time.

  In general, the allowable time lag range in a session is about several tens of milliseconds, and it is known that the performance of the performer (terminal user participating in the session) will be hindered if a lag more than this occurs. It has been. This is a more severe condition than the time error level required in the conventional streaming distribution of video that requires real-time performance to some extent. In communication via the Internet, transmission delay fluctuations (jitters) may occur temporarily exceeding this. In such a case, even if time synchronization is performed by a conventional method such as NTP, the clock of the terminal is set so as to be greatly shifted, which may hinder smooth progress of the entire session. Also, if the clocks of the terminals participating in the session are set in the same way, if only the clocks of the terminals belonging to a certain communication environment are set up significantly shifted, there is a possibility that the session no longer holds. There is even.

As described above, even if the conventional time synchronization method is applied as it is to the time adjustment of a terminal participating in a MIDI session using the Internet or the like, the time adjustment of the clock of the terminal is performed in a manner that does not hinder the session. It is difficult to do.
JP 2003-50288 A “Simple Network Time Protocol (SNTP) Version 4 for IPv4, IPv6 and OSI”, [online], Network Working Group Request for Comments: 2030, by D. Mills, Internet <URL: http: //www.faqs .org / ftp / rfc / pdf / rfc2030.txt.pdf>

  In view of the above-described points, an object of the present invention is to synchronize the time of a plurality of terminals in a MIDI session via a network without causing trouble in the session.

  In order to solve this problem, a time synchronization method of the present invention is a method of synchronizing time between a terminal having a time measuring means and a server device having a reference clock, wherein the time counted by the time measuring means and the time An acquisition step for acquiring time difference information relating to a difference from a time measured by a reference clock using a communication network, and if the time difference represented by the time difference information is equal to or less than a predetermined value, the time measured by the time measuring means is calculated by the time difference. And a correction step of correcting the time measured by the time measuring means by the predetermined value when the time difference is larger than the predetermined value.

  In a preferred embodiment, the acquisition step and the correction step are periodically repeated. The server device may be an NTP server, and the time difference information may be acquired according to an NTP protocol. The predetermined value may be determined based on the stability of the communication network.

  Further, the terminal of the present invention includes a time measuring means, a means for acquiring time difference information regarding a difference between a time measured by the time measuring means and a time measured by a reference clock of the server device via a communication network, and the time difference information. Means for correcting the timepiece by the time difference when the time difference is less than or equal to a predetermined value, and correcting the time of the time measuring means by the predetermined value when the time difference is larger than the predetermined value.

  According to the present invention, in a MIDI session via a communication network, it is possible to synchronize the times of a plurality of terminals without causing any trouble in the session.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing the overall configuration of a MIDI session system 100 according to an embodiment of the present invention. The MIDI terminals 101A, 101B, and 101C are each connected to other MIDI terminals via the Internet 103. An NTP server 102 is connected to the Internet 103. In the figure, three MIDI terminals are shown for convenience, and the number of MIDI terminals used for the session is arbitrary. Since these terminals have the same configuration, the MIDI terminals will be collectively referred to as the MIDI terminal 101 in the following.

  FIG. 2 is a configuration diagram of the MIDI terminal 101. The MIDI terminal 101 includes an input unit 110, a transmission / reception unit 111, a musical sound generation unit 112, a control unit 113, a display unit 114, a storage unit 115, an internal clock 116, and a bus 120 for connecting each element.

  The input unit 110 includes an information input device such as a keyboard and a mouse, and an operation unit for inputting performance information such as a keyboard, and supplies various user instructions and performance information to the control unit 113. The transmission / reception unit 111 is a communication interface for performing communication via the Internet 103 by wireless or wired, such as an Ethernet (registered trademark) interface or a wireless antenna. The tone generator 112 is composed of a tone generator circuit, a DSP, a speaker, and the like, and performs various tone processing such as tone generation / stop / tone color change. The control unit 113 includes a CPU, a RAM, a ROM, and the like. The control unit 113 controls each element and performs time calculation processing described later. Further, the control unit 113 operates according to the currently selected operation mode. Here, the operation mode is any one of the modes selected by the user's explicit instruction or automatically during the operation of the MIDI terminal 101. The operation mode can be switched as appropriate. By preparing a plurality of operation modes in this way, different correction processing operations are possible.

  The display unit 114 includes a display device such as a liquid crystal display, and presents various types of information including the setting state of the MIDI terminal 101 to the user. The storage unit 115 is a storage device such as a RAM, an EEPROM, or a hard disk, and stores MIDI music data, and also stores a setting table 121 (to be described later) that is referred to when the time synchronization process is executed. The internal clock 116 generates a reference time that is a reference for all processing operations in the terminal 101. Specifically, processing such as adding a time stamp to a packet to be transmitted and comparing a time stamp added to a received packet is all performed based on the time counted by the internal clock 116.

  FIG. 3 shows the contents of the setting table 121 stored in the storage unit 115. As shown in the figure, the setting table 121 stores an operation mode related to the time difference correction process and a setting value representing the upper limit of the time difference correction amount in association with each other.

The time difference correction processing operation will be described below.
The time difference correction process according to the present invention includes two stages. The first is processing for determining the network delay time. The second is processing for determining the amount of time (hereinafter referred to as a correction amount) ΔT for correcting the internal clock 116 based on the determined delay time and the contents of the setting table described above.

  FIG. 4 shows a process for determining the network delay time. In this embodiment, SNTP (Simple Network Time Protocol) defined in RFC2030, which is a simplified version of NTP, is employed. Hereinafter, a method for determining a delay time based on the SNTP protocol will be described with reference to FIG.

First, the MIDI terminal 101 transmits a packet for requesting time adjustment to the NTP server 102 at time T ₁ indicated by the internal clock 116 of the terminal itself (step S101). At this time, the time stamp “T ₁ ” is attached to the packet. The time stamp is preferably described in milliseconds.

The NTP server 102 receives this packet at time T ₂ indicated by the internal clock of the NTP server 102 (hereinafter referred to as a reference clock) (step S102). Then, as a response to the packet, to the terminal 101 a new packet, and transmits at time T ₃ indicated by the reference clock of the NTP server 102 (step S103). Time stamps “T ₂ ” and “T ₃ ” are attached to this packet. When the MIDI terminal 101 receives this packet at time T ₄ indicated by the internal clock 116 (step S 104), the MIDI terminal 101 uses the following formula to determine the internal clock 116 for the network delay time T _delay and the reference clock of the NTP server 102. time difference calculating a (shift) T _D (step S105).
( _Equation 1) T _delay = (T ₄ −T ₁ ) − (T ₂ −T ₃ ) (1)
(Equation 2) T _D = {(T ₂ −T ₁ ) + (T ₃ −T ₄ )} / 2 (2)

Next, will be described with reference mainly to FIG. 5 the process for determining the correction amount ΔT of the internal clock 116 based on the time difference T _D calculated in this manner. In the method using conventional NTP, it had a value of T _D calculated unconditionally and correction amount [Delta] T (although polarity is reversed). However, in the present invention, the following correction process is further performed to determine the final correction amount ΔT. This will be described below. The amount such displacement T _D and correction amount ΔT of the time is actually exist code. This is because there are two possibilities of the clock deviation: whether the clock is advanced or delayed with respect to the reference time. However, in the following, absolute values will be indicated unless otherwise specified. That is, when there is a time lag, the amount is indicated. Needless to say, the sign of the correction amount ΔT of the time to be set should be set opposite to the direction of the time shift (the sign of the shift value).

In step S201, the deviation T _D of the internal clock 116 of the MIDI terminal 101 to the reference clock of the NTP server 102 as described above is calculated, in step S202, referring to the setting table 121 shown in FIG. 3, the current A set value T _S (positive number) corresponding to the operation mode is extracted. Then, the calculated absolute value of T _D (hereinafter simply referred to as T _D ) is compared with the extracted value of T _S. If T _D <T _S or T _D = T _S (step S203, YES), the internal clock 116 is corrected by T _{D in} step S204. If T _D > T _S (step S203, NO), the internal clock 116 is corrected by Ts (step S205). That is, even if a time lag greater than the set value T _S is calculated, the amount greater than the set value is not corrected.

  Next, a specific example of time correction processing will be described with reference to FIGS. 6 and 7. In the following, it is assumed that the operation mode of the MIDI terminal 101 is set to “M3”.

FIG. 6 shows the value of T _{D and} the value of T _S when the time correction processing described with reference to FIGS. 4 and 5 described above is executed periodically (every time t ₀ ) during the session. It is shown. The horizontal axis represents time (t ₀ units), and the vertical axis the values of T _D in the figure, in the figure represents the correction amount ΔT of the internal clock 116.

In the upper diagram of FIG. 6, the time difference T _D changes with an error of about 20 ms until the time “6t ₀ ”. This means that there is a steady fluctuation (jitter) of delay time of about 20 ms in the network. However, it can be seen that the value of T _D suddenly increases at time “6t ₀ ”. Since the value after time “7t ₀ ” is almost the same as the value before time 5t ₀ , the value of T _D obtained at time “6t ₀ ” was suddenly affected by the network load. It is presumed that it does not represent a true time lag. As can be seen from the lower diagram of FIG. 6, even in such a case, the correction amount ΔT always takes a value in the range of ± 30 ms.

That is, rather than correcting the internal clock 116 immediately follow the value of this T _D, corrects within a predetermined value. Accordingly, even if the value of the delay time T _D which deviated from the normal value is calculated, there is no possibility that inappropriate modifications of the internal clock 116 is performed. As a result, time synchronization is not greatly disturbed, and a stable session is realized.

FIG. 7 shows another example of the time correction operation. As in FIG. 6, the values of T _D and T _S when the time adjustment processing is executed periodically are shown. The horizontal axis represents time (t ₀ units), and the vertical axis the values of T _D in the figure, in the figure represents the correction amount ΔT of the internal clock 116.

In the above diagram of FIG. 7, the time until the "5t _0" is the value of T _D to a certain extent have remained, takes a large value in the vicinity of the time "7t _0", time "8t _0" and later gradually It turns out that it has decreased. In this example, unlike the case shown in FIG. 6, the value of T _D since the time "8t _0" since not returned to its previous value in real and not due to a temporary change in the state of the network It is estimated that a time lag actually occurs for some reason near the time “7t ₀ ”. That is considered to indicate that according to the value of T _D at time "7t _0" should be modified internal clock.

As can be seen from the lower diagram of FIG. 7, even in such a case, the upper limit of the correction amount ΔT for one correction is 30 ms, which is a set value. In fact, if you look at by comparing the upper and lower figures of FIG. 7, the value of the calculated T _D each for performing one of the modifications that can be read are reduced extent by about 30 ms. Then, when it becomes from the time "7t _0" to "10t _0" enough time has elapsed time "17t _0", that is, after about ten times of the fixes were made, the value of T _D is as before 0 This is around ± 20 ms, which indicates that the synchronization of the internal clock 116 has been restored.

  That is, when a correction greater than the amount that can be corrected by one correction process is necessary, the correction process is repeated to realize the time correction of the desired correction amount ΔT. In this way, even if a large change in network delay time actually occurs and the internal clock has to be significantly corrected, the internal clock 116 is reliably synchronized by repeatedly performing the correction process. It becomes possible to make it.

As described above, in the case of detecting the displacement T _D big time, whether it is the be of transient due to temporary factors network should not correct the internal clock to the value Even when the timekeeping time of the clock is actually deviated and should be corrected to the value as it is, it can be appropriately handled.

Note that the number of operation modes to be set and the set value T _S in each mode can be arbitrarily set. For example, the user of the MIDI terminal 101 may write in the setting table 121. Alternatively, the MIDI terminal 101 may automatically set. Specifically, the terminal 101 may measure the network state and automatically determine the set value Ts based on the network state. For example, the state of the network can be periodically measured and rewritten so that the set value Ts is decreased when the network is stable and the set value Ts is increased when the network is unstable. Moreover, it is good also as acquiring the information regarding a network state from an external server. Thereby, the user does not need to be aware of the state of the network and can concentrate on the performance.

In addition, the setting of t ₀ in FIG. 6 and FIG. 7, in other words, the setting of the frequency for performing the correction process and the setting of the timing can be performed by an arbitrary method. For example, you may set based on the stability of a network. Further, it is preferable to perform the music regularly (for example, every second) during the performance of the music (during the session), but it may be performed every predetermined measure. Further, it is preferable to set the time at least once at the start of the music.

  Needless to say, the time synchronization method of the present invention is not limited to a session system using a MIDI terminal, but can be applied to, for example, a video / audio data transmission / reception system such as streaming delivery that requires real-time performance.

<Modification>
FIG. 8 shows a MIDI session system 200 according to a modification of the present invention. In this modification, the sequencers 201A to 201C and sound sources 202A to 202C are used instead of the MIDI terminals 101A to 101C. FIG. 9 shows the configuration of the sequencer 201. As shown in the figure, the sequencer 201 does not include the musical sound generator 112 and does not have a function of generating musical sounds. Instead, an interface unit 117 corresponding to the MIDI standard for communicating with the sound source 202 is provided. The sound source 202 is a sound source compliant with the MIDI standard and the like, and communicates with the sequencer 201 via an interface (not shown). When the sequencer 201 acquires performance information from the sound source 202 via the interface unit 117, the sequencer 201 processes information such as volume and tone on the acquired performance information based on predetermined setting conditions, and performs the processed performance. Information is output to the sound source 202. When the sound source 202 receives the processed performance information, the sound source 202 generates a musical tone based on the processed performance information. In FIG. 9, only one sound source is shown for one sequencer for convenience, but it goes without saying that a plurality of sound sources may be used.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this, and can be modified as appropriate.

1 is an overall configuration diagram of a MIDI session system according to an embodiment of the present invention. It is a block diagram of the MIDI terminal which concerns on the same embodiment. It is a figure which shows the content of the setting table which concerns on the MIDI terminal. In the same embodiment, it is a sequence chart showing the process which determines the delay time difference and the time gap according to the NTP protocol. It is a flowchart for the time correction process which concerns on embodiment of this invention. It is an example which shows a time-dependent change of the time difference which concerns on the same embodiment. It is an example which shows a time-dependent change of the time difference which concerns on the same embodiment. It is a whole block diagram of the MIDI session system which concerns on the modification of this invention. It is a figure which shows the structure of the sequencer 201 which concerns on the modification.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 ... MIDI session system, 101 ... MIDI terminal, 102 ... NTP server, 103 ... Internet, 110 ... Input part, 111 ... Transmission / reception part, 112 ... Musical sound generation part, 113 ... Control unit, 114 ... Display unit, 115 ... Storage unit, 116 ... Internal clock ..., 117 ... Interface unit, 120 ... Bus, 121 ... Setting table .

Claims (6)

A method of synchronizing time between a terminal having a time measuring means and a server device having a reference clock,
An acquisition step of acquiring, using a communication network, time difference information relating to a difference between a time measured by the time measuring means and a time measured by the reference clock;
If the time difference represented by the time difference information is less than or equal to a predetermined value, correct the time measured by the time measuring means by the time difference, and if the time difference is greater than the predetermined value, the time measured by the time measuring means by the predetermined value. A time synchronization method comprising: a correction step for correcting The time synchronization method according to claim 1, wherein the obtaining step and the correcting step are periodically repeated. The synchronization method according to claim 1, wherein the server device is an NTP server, and the time difference information is acquired according to an NTP protocol. The time synchronization method according to claim 1, wherein the predetermined value is determined based on stability of the communication network. Timekeeping means,
Means for acquiring, via a communication network, time difference information relating to the difference between the time measured by the time measuring means and the time measured by the reference clock of the server device;
Means for correcting the clock by the time difference if the time difference represented by the time difference information is less than or equal to a predetermined value, and correcting the time of the time measuring means by the predetermined value if the time difference is greater than the predetermined value; A terminal having The terminal according to claim 5, wherein the terminal is a MIDI terminal.

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