JP3833164B2 - Clock signal adjustment device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a clock signal adjustment device for synchronizing clock signals used in a plurality of terminal devices connected to a network.
[0002]
[Prior art]
When communicating between terminal devices connected via a network, for example, an Internet (IP) protocol may be used. In a network using the IP protocol, packet communication is performed. Accordingly, when streaming real-time data such as voice, each voice packet transmitted from the transmission-side terminal device is temporarily buffered by the reception-side terminal device and then output as voice. Therefore, the clock signals used in the transmission side and reception side terminal devices do not need to be completely synchronized. However, when viewed over a long period of time, the reception side terminal device must have the same frequency on the transmission side and reception side. The buffer overflowed or underflowed, causing interruptions in the sound and extending the delay time.
[0003]
In order to solve this problem, for example, in the case of a one-to-one stream, reference information for frequency adjustment is included in the voice packet transmitted by the transmission side terminal device, and the reception side terminal device clocks based on this reference information. The present applicant has proposed an adjustment (Japanese Patent Application No. 2001-182931).
[0004]
[Problems to be solved by the invention]
However, the above technique can be applied only to one-to-one streams, and cannot be applied to many-to-many streams and bidirectional streams.
[0005]
An object of the present invention is to provide a clock signal adjusting device that can easily match the frequency of the clock signal of each terminal device even in a many-to-many or bidirectional network.
[0006]
[Means for Solving the Problems]
The clock signal adjustment device according to one aspect of the present invention is premised on a plurality of terminal devices each connected to a network. These terminal devices include a clock signal source. A transmission unit that transmits a clock signal adjustment signal to another terminal device via a network is provided in a predetermined one of the plurality of terminal devices. Various protocols can be used as communication protocols via this network. For example, an IP protocol can be used. Adjustment means is provided in another terminal device. This adjustment means makes the frequency of the clock signal of the other terminal device coincide with the predetermined clock signal of the terminal device by the clock signal adjustment signal received via the network.
[0007]
In the clock signal adjustment device configured as described above, the frequency of the clock signal of another terminal device can be matched with the frequency of the clock signal of one terminal device determined in advance. Therefore, in a many-to-many network or the like, the frequency of the clock signal of each terminal device can be matched.
[0008]
The adjustment signal is a signal representing transmission interval information transmitted at intervals . This signal is generated based on the clock signal of the terminal device that transmits the adjustment signal. The other terminal device has means for acquiring the reception interval information every time the adjustment signal is received. The reception interval information is generated based on the clock signal of the terminal device that has received the adjustment signal. The adjusting unit corrects the frequency of the clock signal based on the transmission interval information and the reception interval information. For example, the frequency can be corrected based on the ratio of the deviation between the transmission interval and the reception interval with respect to the reception interval.
[0009]
When a signal representing transmission interval information is transmitted from another transmission device of one terminal device to another terminal device, the transmission interval information is generated based on a clock signal of the terminal device that generates the transmission interval information. The reception interval information is generated based on the clock signal of the terminal device that generates the reception interval information. Therefore, if there is no frequency shift in the clock signals of these terminal devices, the transmission interval and the reception interval coincide. However, if there is a difference in the frequency of the clock signal between the terminal devices, the transmission interval and the reception interval are different. The greater the difference between the transmission interval and the reception interval, the greater the difference in clock signal frequency. Therefore, by adjusting the frequency according to this difference, the frequencies of all the clock signals can be matched.
[0010]
The interval at which the adjustment signal is transmitted can be set gradually longer. In this case, it is desirable to use packet communication for communication on the network. When the transmission interval of the adjustment signal is short, when packet communication is used, the adjustment error increases due to the influence of packet fluctuations. If the transmission interval is lengthened, it takes time until the frequencies of the clock signals match. Therefore, the transmission interval is initially shortened and roughly adjusted, and thereafter the transmission interval is gradually increased to reduce the error.
[0011]
In addition to the configuration in which the adjustment signal transmission interval is set to be gradually longer from the start of adjustment as described above, the adjustment signal that has been generated up to now when one of the other terminal devices is activated is reset. The transmission unit may be configured to newly start transmission of the adjustment signal. In this case, the adjusting means adjusts the frequency of the clock signal within the allowable frequency range. This allowable frequency range is gradually set narrower, for example, every time frequency adjustment is performed.
[0012]
When one of a plurality of terminal devices is activated, another terminal device may already be activated. In this state, in order to make the frequency of the clock signal of one terminal device coincide with the frequency of the clock signal of one predetermined terminal device, an adjustment signal is transmitted from one predetermined terminal device. When newly started, since the interval between the adjustment signals is initially narrow, there is a possibility that the clock signal of the terminal device that has already been started and the frequency of the clock signal already matches may be greatly shifted. However, since the permissible frequency range of each adjustment means is limited and the range is gradually narrowed, the permissible frequency range in the terminal device whose frequency has already been adjusted is narrow, and the frequency of the clock signal is large. There is no deviation.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
The clock signal adjustment apparatus according to one embodiment of the present invention is installed in a plurality of terminal apparatuses, for example, transmission / reception apparatuses 4 connected to a network 2 as shown in FIG. As the network 2, a LAN or a WAN can be used.
[0019]
The transmission / reception device 4 can transmit and receive audible frequency signals, for example, audio signals in a many-to-many manner via the network 2. Each of the audible frequency signal sources, for example, a microphone 6 and sound emission means, for example, a speaker 8, I have. Stream communication technology is used for communication using these audio signals.
[0020]
As illustrated in FIG. 1, the transmission / reception device 4 includes a transmission device 10 and a reception device 12. In the transmission device 10, an audio signal collected by the microphone 6 is amplified by an amplifier 14 and digitized by an A / D converter 16 based on a clock signal described later. This digitized audio signal is input to the input buffer 18. The output signal of the input buffer 18 is encoded into compressed audio encoded information by the encoding circuit 20 and stored in the transmission buffer 22. The transmission unit 24 assembles the data in the transmission buffer 22 into packets and transmits the packets to the network 2 at regular time intervals. These packets are transmitted based on the RTP protocol.
[0021]
Accordingly, each packet includes an RTP header, and the RTP header includes transmission time information, for example, a transmission time stamp. Furthermore, the sequence number is also included in the RTP header. The transmission time stamp represents a time when the time stamp counter 23 is generated based on a clock signal generated by a clock signal source, for example, the voltage controlled oscillator 25, and samples the head data of the packet. The sequence number indicates the order of packets.
[0022]
The receiving device 12 includes a receiving unit 24 that receives packets from the network 2. The receiving unit 24 decomposes the packet into compressed audio coding information and stores the packet in the reception buffer 26. The compressed audio coding information in the reception buffer 26 is decoded and expanded by the decoding unit 28 and converted into a digital audio signal. This digital audio signal is stored in the output buffer 30 and converted into an analog audio signal by the D / A converter 32. A clock signal is also used for this conversion. The analog audio signal is amplified by the amplifying unit 34 and amplified from the speaker 8.
[0023]
The clock signal used by the A / D converter 16 and the D / A converter 32 is generated by the voltage controlled oscillator 25. This clock signal is corrected by the correction unit 36. The correction unit 36 is supplied with a reception time stamp that is generated each time the time stamp counter 25 receives a packet.
[0024]
In each of the transmission / reception devices 4, the frequency of the clock signal needs to be matched before, for example, transmission of an audio signal from a certain transmission / reception device. In this case, the master transmitter / receiver (for example, an arbitrary transmitter / receiver) 4 among the transmitters / receivers 4 sends a packet as a clock signal adjustment signal at a time interval as shown in FIG. Then, the data is transmitted to another transmission / reception device 4 by broadcast or multicast. This packet includes an elapsed time Ts from the time when the clock signal adjustment signal was previously transmitted, and an identifier of the transmission source (master transmission / reception device), for example, an IP address. This elapsed time is calculated based on the clock signal of the master transmission / reception device. However, when this clock signal adjustment signal is initially transmitted, the elapsed time is zero.
[0025]
Each time a transmission / reception apparatus (slave transmission / reception apparatus) other than the master transmission / reception apparatus receives a clock signal adjustment signal, the time stamp counter 23 is based on the clock signal of the slave transmission / reception apparatus in which the time stamp counter 23 is provided. Generate a reception timestamp. This reception time stamp is supplied to the correction unit 36 and stored in the correction unit 36. Then, the difference between this reception time stamp and the reception time stamp when the clock signal adjustment signal was received last time is calculated, and the reception interval Tr shown in FIG. 3B is calculated. However, when the clock signal adjustment signal is received for the first time, it is only stored in the correction unit 36 and the reception interval Tr is not calculated.
[0026]
The correction unit 36 uses the transmission interval Ts and the reception interval Tr to match the frequency of the clock signal of the slave transmission / reception device with the frequency of the clock signal of the master transmission / reception device. Originally, the transmission interval Ts and the reception interval Tr coincide. However, when affected by fluctuations in the network 2 or the like, an error occurs between the two. Therefore, a * (Tr−Ts) / Tr is calculated (where a is a predetermined coefficient), this adjustment value is calculated, and the frequency of the voltage controlled oscillator 25 of the slave transceiver is adjusted based on this adjustment value. To do.
[0027]
As shown in FIG. 3A, the transmission interval Ts is set to be gradually longer although it is short initially. If the transmission interval Ts is short, the influence of fluctuations in the network 2 is large, so that even if adjustment is performed, the frequency error of the clock signal of the master transmission / reception device and the slave transmission / reception device is large. When the transmission interval Ts is long, the error in the frequency of the clock signal between the master transmission / reception device and the slave transmission / reception device becomes small, but the time required for adjustment becomes long. Therefore, the transmission interval is changed as described above, and the clock signal is initially roughly adjusted to gradually reduce the error.
[0028]
When a transmission / reception device that has been functioning as a master transmission / reception device stops due to a failure or the like, another transmission / reception device becomes a master transmission / reception device. Also in this case, the frequency of the clock signal is adjusted between the new master and slave transmission / reception devices as described above.
[0029]
In addition, when a slave transmitter / receiver that is activated in addition to the slave transmitter / receiver that is already activated exists, the frequency between the master transmitter / receiver and the slave transmitter / receiver is increased. Need to match. At this time, as described above, since the transmission interval is initially set to be short and gradually set to be long, the clock signal adjustment signal is also supplied to the already-activated slave transmission / reception device, so that the frequencies match. There is a possibility that the clock of the already-activated slave transmission / reception device is deviated from the clock signal of the master transmission / reception device.
[0030]
Therefore, in the slave transmission / reception apparatus, an allowable frequency range is set that indicates how much the frequency is allowed to change from the current frequency to the high frequency and how much the frequency is allowed to be changed to the low frequency side. When an instruction to change the frequency within the allowable frequency range is given, the frequency is adjusted as such. However, when the change of the frequency exceeding the allowable frequency range is instructed, only the upper limit value or the lower limit value of the allowable frequency range is set to change the frequency. Moreover, this allowable frequency range is gradually narrowed as shown in FIG. 4 each time the frequency is changed.
[0031]
Therefore, the allowable frequency range is narrow in the already-activated slave transmission / reception device whose frequency matches the clock signal of the master transmission / reception device. In this state, when a newly activated slave transmission / reception device is generated, the master transmission / reception device transmits a clock adjustment signal at a short transmission interval, and an instruction is determined to greatly adjust the frequency of the clock signal. However, since this value is larger than the allowable frequency range in the already-initiated slave transmission / reception apparatus, the frequency exceeding the upper limit value or the lower limit value of this allowable frequency range is not changed, and the clock signal of the already-initiated slave transmission / reception apparatus is not changed. The frequency does not fluctuate greatly.
[0032]
The newly activated slave transmission / reception device sends a recognition signal to the master transmission / reception device at the time of activation, and requests the master transmission / reception device to transmit a clock adjustment signal from the beginning (from a short transmission interval). .
[0033]
FIG. 5 is a flowchart showing a process performed by the slave reception device every time each slave transmission / reception device receives a clock signal adjustment signal.
[0034]
First, when the clock signal adjustment signal is received, it is determined whether the master transmission / reception device has been changed or whether the slave transmission / reception device is being activated (step S2). If the answer to this determination is yes, the allowable frequency range is set to an initial value (a value with the largest frequency fluctuation range) (step S4), and this process is terminated.
[0035]
If the answer to the determination in step S2 is no, an adjustment value is determined as described above (step S6). Next, it is determined whether this adjustment value is a value within the allowable frequency range (step S8). If the answer is yes, the allowable frequency range is updated so as to narrow (step S10), the frequency of the voltage controlled oscillator 25 is adjusted based on the adjustment value (step S12), and this process is terminated. If the answer to the determination in step S8 is no, the adjustment value is replaced with an allowable value (step S14). That is, if the adjustment value is positive, the upper limit value of the allowable frequency range at that time is changed, or if the adjustment value is negative, the lower limit value is changed. And step S12 is performed and this process is complete | finished. Note that the allowable frequency range gradually decreases toward a predetermined value (a value that changes the frequency only slightly), and is thereafter fixed to the predetermined value.
[0036]
As in the first embodiment, when the network 2 is a LAN or WAN, it is possible to match the frequencies of the clock signals of the transmission / reception devices 4 by multicast or broadcast. However, it is often difficult to use multicast or broadcast in order to match the frequency of the clock signal between the transmitting and receiving apparatuses connected to different LANs or WANs in a wide area network such as the Internet.
[0037]
In this case, as in the second embodiment shown in FIG. 6, the clock signal adjustment signals are transferred to different LANs or WANs using unicast to match the clock signal frequencies of the respective networks. . That is, one transmission / reception device (may be the master transmission / reception device 4M or the slave transmission / reception device 4S) existing in one network 40 is set as a transmission / reception device for transfer. In this transmission / reception apparatus, information necessary for transmission such as an identifier of the master transmission / reception apparatus 4M existing in another network 42 to which the clock signal adjustment signal is transferred, for example, an IP address, is set. This transmission / reception apparatus transfers the clock signal adjustment signal to the transfer destination master transmission / reception apparatus 4M by unicast at intervals.
[0038]
The master transmission / reception device of another network 42 adjusts the frequency of the clock signal based on the clock signal adjustment signal from the transfer source in the same manner as the slave transmission / reception device of the first embodiment. Thereafter, the frequency of the clock signal of the slave transmission / reception device is matched with the frequency of the clock signal of the master transmission / reception device 4M for the slave transmission / reception device 4S of the network 42 in the same manner as in the first embodiment. Similarly, by transmitting a clock signal adjustment signal from any one of the transmission / reception devices of the network 42 to the master transmission / reception device 4M of the further network 44, each of the clock signals in the networks 40, 42, 44 is similarly transmitted. The frequencies can be matched.
[0039]
In the above-described embodiment, the transmission / reception device 4 that transmits and receives audio signals is used as the terminal device. This considers the transmission and reception of audio signals in both directions. However, when only transmitting and receiving in one direction, the terminal device is provided with only the transmission device 10 and the reception device 12 is provided. Can also be used. Also, as terminal devices, not only communication by audio signals but also communication by video signals, and conversely, each terminal device is provided with controlled devices and control information for controlling these controlled devices is provided. You can also use what you send and receive. In the above embodiment, the master transmission / reception device transmits information indicating the transmission interval as the clock signal adjustment signal. Instead, the master transmission / reception device transmits a transmission time stamp, and the slave transmission / reception device transmits the transmission time stamp. The transmission interval may be obtained by obtaining the difference.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to easily match the frequencies of clock signals of a plurality of other terminal devices with the frequency of the clock signal of one terminal device.
[Brief description of the drawings]
FIG. 1 is a block diagram of a transmission / reception apparatus provided with a clock signal adjustment apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a network using the transmission / reception apparatus of FIG.
3 is a diagram illustrating a transmission interval and a reception interval of a clock signal adjustment signal in the transmission / reception apparatus of FIG. 1. FIG.
4 is a diagram illustrating an adjustment state of a frequency of a clock signal in the transmission / reception apparatus of FIG. 1;
5 is a flowchart of frequency signal adjustment processing in the transmission / reception apparatus of FIG. 1;
FIG. 6 is a block diagram showing a plurality of networks using a clock signal adjustment device according to a second exemplary embodiment of the present invention.
[Explanation of symbols]
2 Network 4 Transmission / reception device 10 Transmission device 12 Reception device 24 Transmission unit (transmission means)
36 Correction unit (adjustment means)

Claims (3)

Transmission that is connected to a network and is provided in a predetermined one of a plurality of terminal devices each including a clock signal source, and transmits a clock signal adjustment signal to the other terminal devices via the network Means,
Adjusting means provided in the other terminal device and adapted to match the frequency of the clock signal of the other terminal device with the predetermined clock signal of the terminal device by the clock signal adjustment signal received via the network And
Equipped ,
The adjustment signal is transmitted at intervals, and is a signal representing transmission interval information generated based on a clock signal of a terminal device that transmits the adjustment signal,
Each time the other terminal device receives the adjustment signal, means for obtaining the reception interval information based on the clock signal of the other terminal device,
Have
The said adjustment means is a clock signal adjustment apparatus which correct | amends the frequency of the said clock signal based on the difference of the said transmission interval information and the said reception interval information .   2. The clock signal adjustment device according to claim 1, wherein an interval at which the adjustment signal is transmitted is set gradually longer from the start of adjustment.   3. The clock signal adjustment device according to claim 2, wherein when one of the other terminal devices is activated, the transmission unit transmits the adjustment signal, and the adjustment unit is configured to transmit the clock signal within an allowable frequency range. A clock signal adjusting device that adjusts the frequency of a signal, and wherein the allowable frequency range is gradually narrowed.

Images