JP2000022678A - Data transmission terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform synchronization at the time of data transmission between terminal equipment. SOLUTION: LAN telephone sets 200 and 300 are prepared between a LAN 100, are respectively provided with a transmission buffer 330 and a reception buffer 331 and mutually transmit data accompanying a transmission clock different from the transmission clock for reception from the transmission buffer. Prescribed data are transmitted from the side of the telephone set 200 to the side of the LAN telephone set 300, and when the data are stored in the reception buffer 331, the change amount at each prescribed cycle of a stored data amount is detected by a monitoring part 360. At the time of the detection, the presence/ absence of clock correction is decided based on a statistical arithmetic operation processing. In the case of judging that the clock correction is required, a clock for correction is generated in a clock generation part 370 and the synchronization with the clock on a transmission side is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to real-time data transmission of video and audio using an asynchronous network represented by a local area network. To correct the technology.

[0002]

2. Description of the Related Art Asynchronous networks represented by local area networks (hereinafter referred to as LANs) have become very widespread among offices, and printers and large-capacity disks are shared. Utilization of e-mails etc. contributes to economic effects and productivity improvement in office work.

[0003] Information browsing using the Internet and WWW connecting a LAN to a wide area network has spread to homes by dial-up connection through a provider that is an Internet access provider.

[0004] By the way, services using an asynchronous network, such as information browsing using e-mail and the Internet, are of the type in which information is mainly stored in a server and distributed to terminals according to demands from users.

[0005] Recently, services using an asynchronous network include moving pictures and moving pictures from basic services such as telephones, which conventionally use networks with established bandwidths such as public telephone networks and ISDN networks. Services that require real-time properties, such as multimedia services combining voice, are gradually being realized.

[0006] The principle of the asynchronous network is described as CSMA /
Taking an example of a LAN typified by the IEEE 802.3 system based on the CD system, data transmission from a terminal is controlled by carrier sensing and collision detection on a trunk line having a transmission rate of 10 Mbps. That is, when there is no data originating from another terminal connected to the LAN, 10Mbp regardless of the data rate between the terminals.
s at the transmission speed of LA.
This means that a time component (clock component) cannot be transmitted via N.

For example, in the telephone service of the ISDN line, the transmitting terminal and the receiving terminal obtain the same octet clock and bit clock from the ISDN line of the synchronous network which is the master of the timing, so that the transmitting data and the receiving data must be transmitted. Is one-to-one.

On the other hand, assuming a telephone service for performing 64 kbps digital encoding between terminals directly connected to the LAN or between terminals via the LAN, as in the case of the ISDN line, the transmitting terminal is When the audio data encoded by the 64 kbps clock based on the oscillation source of the audio data reaches the receiving terminal via the LAN and is decoded from the encoded audio, the clock which is the change timing of the clock and data is displayed on the LAN. The component cannot be transmitted.

Therefore, a PLL employed in high-speed transmission
(Phased lock loop) cannot be used, and a 64 kbps clock based on another oscillation source of the receiving terminal must be used.

If the transmitting terminal and the receiving terminal have separate oscillation sources, the oscillation frequencies of the two oscillation sources have an error on the order of ppm and fluctuate depending on environmental conditions such as temperature. The difference is accumulated as the buffer capacity within the time period during which the terminals are linked, and if the buffer capacity is exceeded, an overrun or underrun error occurs.

[0011] This is because the audio data input to the audio codec via the buffer at the receiving terminal is deficient or indefinite data is inserted. When analog decoding is performed, audio loss or noise occurs. It becomes a surface.

On the other hand, technology for monitoring the buffer capacity and adjusting the oscillation source of the receiving terminal to the oscillation source of the transmitting terminal has also been actively developed, and an example thereof is disclosed in, for example, Japanese Patent Application Laid-Open No. 9-252292. I have. This technology monitors the capacity of a buffer to absorb the difference between the frequency of the transmitting terminal oscillation source and the frequency of the receiving terminal oscillation source, and directly uses the increase or decrease to extract data from the output terminal of the receiving buffer. It is intended to control the oscillation frequency of the receiving-side terminal oscillation source, which is the source of the generation, at any time.

However, this technique focuses only on the difference between the transmission clock of the transmitting terminal and the receiving clock of the receiving terminal. In other words, an ideal communication environment in which the receiving buffer input terminal of the receiving terminal is written by the transmitting clock of the transmitting terminal without passing through the network, and the output terminal of the same receiving buffer is read by the receiving clock of the receiving terminal. Is assumed.

As a practical problem, the transmission clock of the transmitting terminal and the input of the receiving buffer of one receiving terminal, which should be the same in an ideal communication environment, between the transmitting terminal and the receiving terminal connected to the asynchronous network. The clock written to the end has fluctuation mainly due to the following two points.

The first factor is a problem peculiar to an asynchronous network such as a LAN. If there is a sudden increase in network traffic when transmitting from a transmitting terminal, data transmission occurs due to collision of transmission data or congestion. Stagnates and waits for data in the transmission buffer.

The second factor can be said for both the transmitting terminal and the receiving terminal. However, the CP between the codec in the terminal connected to the LAN and the LAN interface is not used.
U-system firmware is running data,
Of these, the function of switching a complex task structure managed by the operating system, which is a basic function, may not operate immediately.

For example, from the transmission buffer, the LAN control LS
Even if there is a transmission transfer request to the I internal transmission buffer, processing may not be immediately switched to the requested transmission transfer task, and data that cannot be transferred from the transmission buffer waits in the transmission buffer as it is.

Similarly, at the receiving terminal, a LAN control LSI
In some cases, the reception transfer task from the internal reception buffer to the reception buffer is not activated, and a wait may occur in the LAN control LSI internal reception buffer.

The data input timing at the receiving buffer input terminal of the receiving terminal is delayed by these two factors. If the factors are resolved, the data input timing is shortened at short intervals so that the data which has been stored in the standby mode is compensated. The signal arrives at the input end of the receiving buffer, and the timing fluctuates greatly.

In the invention disclosed in Japanese Patent Application Laid-Open No. 9-252292, the difference between the oscillation source frequencies in the order of ppm between the two terminals is synchronized by reflecting the transition amount of the reception buffer address to the immediate oscillator. When the fluctuation occurs, the control of the oscillator cannot be performed because it cannot follow the change of the reception buffer address which greatly increases or decreases, so that the center frequency of the oscillator is shifted, and the target encoding obtained by dividing the frequency is obtained. As a result, the clock cannot be obtained correctly.

This means that, in general, it is not possible to satisfy the AC characteristics required by the coded clock and the synchronous clock (8 kHz) required by the audio codec, and thus correct audio cannot be reproduced. is there.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides means for absorbing the difference between the oscillation source frequencies built in the transmitting terminal and the receiving terminal and establishing synchronization by using a receiving buffer amount of the receiving terminal. The present invention is intended to provide an apparatus which obtains a correction clock corresponding to the increase / decrease data, and synchronizes the transmission clock with the transmission clock by using the correction clock.

[0023]

The present invention comprises the following means in order to solve the above-mentioned problems. That is,

A transmission buffer for storing transmission data and a reception buffer for storing reception data are provided between networks, and a transmission clock different from a reception-side transmission clock is transmitted from the transmission buffer. A data transmission terminal device for mutually transmitting predetermined data, wherein when predetermined data is transmitted from a transmission destination terminal device and stored in the reception buffer, a predetermined period of the stored data amount is obtained. The amount of change is detected, a correction clock corresponding to the amount of change is obtained using a statistical method, and the reception-side transmission clock is corrected with the correction clock to synchronize with the transmission-side clock. A data transmission terminal device characterized in that it is designed.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described with reference to preferred embodiments. FIG. 1 is a block diagram of a LAN telephone provided between networks according to the embodiment.

LAN which is a local area network
A LAN private branch exchange 101 for controlling and managing a voice call between terminals connected to the LAN is connected to the LAN 100.
N telephone 300 is connected. Also, a router 102 for connecting to a wide area network is connected.

The block configuration inside the LAN telephone 300 includes a LAN control unit 320 connected to the LAN 100 and a dedicated LAN control unit buffer 321.
In the telephone 300, the CPU 310 controls the whole as a main processor, and the LAN control unit 320, the transmission buffer 330, and the reception buffer 331 are connected to the CPU bus 311.

Although not shown, the CPU 310 includes a ROM and a RAM.
Operating system (OS) for executing LAN telephone firmware, transfer control program 3
51 and a statistical calculation program 350 for performing a statistical calculation described later are stored. Regarding the transfer control program 351 and the statistical calculation program 350,
It is displayed outside the CPU 310 for easy understanding.

The reception buffer 331 is connected to the CPU bus 311.
Of the other receiving buffer 33
1 is connected to the decoding unit 342 of the audio codec 340.
Is connected. The decoding unit 342 to which the reception data is transferred from the reception buffer 331 is a handset 4
An analog signal is output to the receiving unit of 00.

On the other hand, the analog audio input from the transmitter of the handset 400 is digitally encoded by the encoding unit 341 of the audio codec 340 and supplied to the transmission buffer 330. Receive buffer capacity monitoring unit 3 for monitoring the address of the receive buffer 331
60 and the voltage converter 37 of the encoded clock generator 370
1 is connected to the CPU bus 311, and both are controlled by the statistical calculation program 350.

The coded clock generator 370 is provided with a voltage controlled oscillator 372 called a VCO whose oscillation frequency is changed by the voltage converter 371, and includes a transmission buffer 330, a reception buffer 331, and an audio codec 3.
A common clock for transmission and reception is supplied to 40.

Next, the operation of the LAN telephone constructed as described above will be described. L of asynchronous network
The LAN private branch exchange 101 connected to the AN 100 centrally controls outgoing / incoming calls related to voice calls using the TCP / IP protocol.

A voice packet including a coded voice obtained by digitally converting an analog voice by a voice codec built in a LAN telephone is transmitted between terminals using the UDP / IP protocol.

When the voice packet is received by the LAN telephone 300 on the UDP / IP protocol frame,
The AN control unit 320 decomposes the frame structure and accumulates received voice data of several tens of bytes in one voice packet in the LAN control unit buffer 321, and at the same time, the CPU 310
To notify the reception voice data arrival by interruption.

The CPU 310 executes the CP
The received voice data stored in the LAN control unit buffer 321 under the control of the LAN control unit 320 is read out via the U bus 311 and transferred to the input terminal of the reception buffer 331.

The received voice data transferred to and stored in the reception buffer 331 is encoded by the coded clock generator 370.
Are sequentially extracted in accordance with the reception buffer transfer clock which is equivalent to the encoding clock generated by the
The data is supplied to the decoding unit 342 and subjected to digital-analog conversion. Then, the analog signal output from the audio codec 340 is reproduced by the handset 400.

The speed of the encoded clock differs depending on the audio codec standard. For example, G. If the audio codec is 728, the frequency is 16 kHz; 64 kHz for 711
z.

The above is the general buffer configuration.
It corresponds to the data delay on N, etc.
Since the encoding clocks of the AN telephone 200 and the LAN telephone 300 are different, overflow and underflow of the reception buffer will occur eventually.

Next, a description will be given of the operation of a configuration using the synchronization means and the statistical calculation program 350, which are the main components of this embodiment, in this buffer configuration. Note that the control of the statistical calculation program 350 in this example is actually
Reading / writing the reception buffer capacity monitoring unit 360 and the oscillator control unit 371 from the U310 via the CPU bus 311.

LAN telephone 200 and LAN telephone 300
Immediately after the voice call is established and the call is started,
The reception buffer 331 is empty. In this state, the statistical calculation program 350 stops the reception buffer transfer clock for guiding data from the reception buffer output terminal to the audio codec, starts monitoring the address transition of the reception buffer through the reception buffer capacity monitoring unit 360, and
In the process of writing data during reception to the reception buffer by 310, the process waits until data is accumulated up to the reference point address located at the middle point with respect to the full address of the reception buffer.

In this state, the voltage-controlled oscillator 372 does not receive an instruction to increase or decelerate the clock to the coded clock generator 370 from the statistical calculation program 350, and is in a free-run state at the center frequency according to the oscillator specification.

When data is accumulated up to the reference point address of the receiving buffer, the statistical calculation program 350 releases the stopped receiving buffer transfer clock, and starts data transfer from the receiving buffer output terminal to the audio codec decoding unit 342. I do. Note that the receive buffer transfer clock at the time of release is the same as the receive encoding clock.

It is assumed that the transmission coded clock of the LAN telephone 200 on the transmitting side is different from the transmission coded clock of the LAN telephone 30 on the receiving side.
In the ideal state where the received coded clock of 0 is completely the same and there is no delay due to other factors, when one data is written to the input terminal of the receive buffer 331, one data is stored in the receive buffer 331. Since the data is transferred from the output terminal 331 to the decoding unit 342, the reception buffer 331 is always
Address does not move from the reference point address.

However, actually, the transmission coded clock of the LAN telephone 200 which is the transmission side and the LAN clock which is the reception side
Since the reception encoded clock of the telephone 300 is shifted on the order of ppm, the address of the reception buffer 331 is
In addition to increasing / decreasing in almost constant time in increasing or decreasing direction, L
Due to the data delay of the AN and the like, a large change exceeding the above-described increase / decrease width appears at the address of the reception buffer 331.

The statistical calculation program 350 statistically measures the measured address position data for each variable statistical period depending on the setting, and repeats the clock correction. In the statistical cycle, the statistical calculation program 350 measures the address position at every address monitoring unit time obtained by dividing the set statistical cycle into n equal parts through the reception buffer capacity monitoring unit 360.

This measurement is repeated, and the statistical operation program 350 calculates, from the obtained address position data, address change amount data n which is a change amount from the immediately preceding address position.
Each sample is obtained, the frequency distribution is developed on the memory, and the standard deviation is calculated by the average value and the following equation (1). And
The determination of data rejection is made based on the standard deviation.

[0047]

(Equation 1)

For example, FIG. 2 is a diagram for explaining the statistical calculation process. Samples 0 to n are address change amounts per unit time, and one cycle is used to determine a standard deviation according to the above equation (1). Based on the standard deviation, a determination as to whether data is rejected is made. ing. FIG.
The distribution diagrams shown in (m), (a) and (c) have a high frequency of peaks based on a statistical method, exhibit sharp peaks around the peaks, and have a normal distribution. It is determined that there is no problem with the data transmission quality on the network, or that the frequency is low even if data delay or the like has occurred, and that the clock correction can be performed on a negligible level.

On the other hand, the distribution chart shown in (b) has a low frequency of peak values, does not show a normal distribution based on a statistical method, and the measured values vary due to an increase in traffic on the LAN, and the clock correction is not performed. Data is rejected as not possible.

As a result of the above determination, when it is determined that the clock can be corrected, from the frequency distribution of the address change amount, which is the change for each address monitoring unit time obtained in the statistical cycle,
An address change amount having a frequency peak is obtained, and a correction value corresponding to this value is written to the oscillator control unit 371 of the encoded clock generation unit 370.

The oscillator control unit 371 converts the correction value set by the statistical calculation program 350 into a voltage, and controls the voltage of the voltage control oscillator 372. At the same time, the oscillator control section 371 holds the value, and locks the oscillation frequency of the voltage controlled oscillator 372 to be constant until the setting is changed next time. For example, when the clock correction is stopped due to the data rejection determination, the voltage controlled oscillator 372 continues to oscillate with the last corrected setting.

Although the statistical calculation program 350 does not perform the upper limit and lower limit management of the reception buffer,
This is carried out by a transfer control program 351 that performs normal transfer processing between the LAN control buffer 321 and the transmission buffer 330 and the reception buffer 331 in the LAN control LSI 320, and manages the upper and lower limits of the transmission and reception buffers.

As described above, by repeating the clock correction while paying attention only to the address change amount while performing the statistical data rejection determination, the coded clocks of the LAN telephone 200 and the LAN telephone 300 are synchronized.

[0054]

Thus, according to the present invention, it is possible to provide a terminal device which eliminates the problems described in the prior art by simply adding relatively inexpensive hardware.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a LAN network according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a statistical calculation process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 LAN private branch exchange 102 router 200, 300 LAN telephone 310 CPU 320 LAN control part 321 LAN control buffer 330 transmission buffer 331 reception buffer 340 audio codec 370 encoding clock generation part 400 handset

Claims (1)

[Claims] A transmission buffer for storing transmission data and a reception buffer for storing reception data, wherein the transmission buffer is different from a transmission clock for a reception side from the transmission buffer. A data transmission terminal device for mutually transmitting predetermined data together with a clock, wherein when predetermined data is transmitted from a transmission destination terminal device and stored in the reception buffer, a predetermined amount of the stored data is determined. A change amount for each cycle is detected, a correction clock corresponding to the change amount is obtained using a statistical method, and the reception-side transmission clock is corrected with the correction clock to synchronize with the transmission-side clock. A data transmission terminal device characterized in that the data transmission terminal device is adapted to be used.