JP2579464B2 - Data communication method - Google Patents

Description

Description: TECHNICAL FIELD [0001] The present invention relates to transmitting data in units of a transmission data frame composed of one or a plurality of data frames via an analog transmission path using a modulation / demodulation device, and transmitting one transmission signal from a transmission station. The receiving station that has received the data frame transmits a response data frame including response data indicating the reception state of each data frame included in the received transmission data frame to the transmitting station, and the transmitting station that has received the response data frame Checking the response data included in the response data frame to determine a data frame in which a reception error has occurred, and resending the data frame determined to be the reception error when determining at least one data frame in which the reception error has occurred. Data communication method.

[Prior Art] In general, in a data communication apparatus, various error correction techniques are used to transmit data without errors, and one of them is so-called automatic retransmission request control.

In this automatic retransmission request control, transmission data is configured by adding error detection information (for example, a CRC (Cyclic Redundancy Check) code, etc.) and forming a predetermined data frame or data block. Based on the error detection information included in the block, it is determined whether or not an error has occurred in the received data, and if an error has occurred, negative acknowledgment information is returned to the transmitting device, and if there is no error, an acknowledgment information is returned to the transmitting device. I do. Then, when the negative acknowledgment information is returned, the transmitting device transmits the data frame or data block in which the error has occurred again. Thereby, correct data can be transmitted.

However, in the automatic retransmission request control, if the characteristics of the transmission path are deteriorated, and if negative acknowledgment information is returned and the frequency of retransmission of the data frame or data block increases, the transmission time becomes longer, which is not preferable.

Therefore, when the retransmission of a data frame or a data block becomes large, the data transmission speed is sequentially reduced (shifted down) to control the occurrence of a data error due to the influence of the characteristics of the transmission line, or the data transmission is temporarily performed by disconnecting the line. It was terminated and data transmission was performed again.

However, in such a conventional method, the downshift or the data transmission is aborted only based on the phenomenon that a data error has occurred. In some cases, such as when superimposition is performed, downshifting may be performed in a state where it is not necessary to downshift, so that there has been a problem that transmission efficiency may be deteriorated.

[Purpose] The present invention has been made to solve the above-described disadvantages of the related art, and has as its object to provide a data communication method capable of improving transmission efficiency.

[Configuration] According to the present invention, a modem transmitting and receiving a single transmission data frame from a transmission station while transmitting data in units of a transmission data frame composed of one or a plurality of data frames via an analog transmission path using a modem is provided. Transmitting a response data frame composed of response data indicating the reception state of each data frame included in the received transmission data frame to the transmitting station, and the transmitting station receiving the response data frame is included in the response data frame. In a data communication method for examining response data, determining a data frame in which a reception error has occurred, and determining one or more data frames in which a reception error has occurred, retransmitting the data frame determined to be a reception error. Is a parameter obtained from the demodulation means of the modem in the response data frame. If the transmitting station determines that the response data frame includes a reception error of one or more data frames, the transmitting station adds the line quality information including the tap coefficient data or the error power data. Examine the quality information, if the reception error and the cause is determined to be based on static factors, reduce the transmission speed of the modem and retransmit the data frame determined to be a reception error at that time, When it is determined that the cause of the reception error is based on a dynamic factor, the data frame determined to be a reception error is retransmitted while maintaining the transmission rate of the modem, and the same type of reception error is repeated. In some cases, the number of data frames included in the transmission data frame unit is reduced stepwise, and the data determined to be a reception error is reduced. It is obtained so as to retransmit the data frame.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

In general, there are four causes of data errors: amplitude and phase distortions due to transmission path characteristics, random noise, burst noise, and impulse noise. Hereinafter, the first two are referred to as static factors because they do not fluctuate significantly in the same transmission, and the other two are referred to as dynamic factors because they change in time series.

For static factors, it is effective to set the data transmission rate to a level that is not affected by such factors, and for dynamic factors, data retransmission by automatic retransmission request control is effective. is there.

In other words, if the data transmission speed is high, the operation of the modem (modulator / demodulator) is easily affected by static factors, and if a certain line quality (S / N) cannot be obtained, data errors may occur frequently. Therefore, when a data error occurs due to a static factor, the frequency of occurrence of the data error can be reduced by executing the shift-down control for reducing the data transmission speed.

Further, since impulse noise or burst noise occurs suddenly, even when the data transmission speed is high, it is unlikely that data errors due to only such dynamic factors will occur continuously over a relatively long period. . Therefore, the same data transmission speed can be maintained by performing automatic retransmission request control for retransmitting data in which an error has occurred. However, data errors due to only dynamic factors may occur at a relatively high frequency. In such a case, it is possible to control the occurrence of data errors by reducing the amount of data transmitted at one time. it can.

In a data communication device using an analog transmission line such as a public telephone line as a transmission line, such as a facsimile device, a modem is used to transmit digital data through the analog transmission line.

Examples of this modem include a V29 modem (16-level quadrature amplitude modulation system) recommended by CCITT (International Telegraph and Telephone Consultative Committee),
A modulation speed of 2400 baud and a transmission speed of 9600 bps, and a V27ter modem (8-phase differential phase modulation system, modulation speed of 1600 baud and transmission speed of 4800 bps) are used. The V29 modem has 7200,4800bps fallback speed and V27t
Each er modem has a fallback speed of 2400bps.

As shown in FIG. 1, the demodulation section of the modem of these types basically includes a demodulator 1 for removing a carrier component of the received signal FR and extracting a baseband signal SB, and a baseband signal SB. (Automatic adaptive equalizer) 2 for correcting distortion such as the amplitude and phase of the transmission path in, and a decoder 3 for determining and outputting the corresponding received data DR from the output of the equalizer 2 It is configured.

Among them, the tap coefficient data TP indicating the degree of distortion such as the amplitude and phase of the transmission path is output from the equalizer 2, and the signal configuration of the received signal (baseband signal SB) is output from the decoder 3 (see FIG. Error power data EP corresponding to the position error in FIG. FIG. 2 shows a signal configuration diagram in the V29 modem.
Point RP indicates the position of the received signal.

Since the tap coefficient data TP indicates the degree of distortion in the amplitude and phase of the transmission path, it is possible to determine the status of the above-described static factor. Also, error power data
When the value of EP is sufficiently smaller than 1/2 of the intersymbol distance d in the signal configuration diagram, transmission is performed if the distortion of the amplitude and phase of the transmission path is small, and if the value is near 1/2 of the intersymbol distance d. It can be determined that the distortion of the amplitude / phase of the road is large.

That is, when a reception error occurs, if the value of the tap coefficient data TP is larger than a predetermined value, it can be determined that a transmission path failure due to a static factor has occurred. If the value is equal to or less than the value, it can be determined that a transmission path failure due to a dynamic factor has occurred. When a reception error occurs, the error power data EP
If the value of is about half of the intersymbol distance d, it can be determined that a transmission path failure due to a dynamic factor has occurred, and the value of the error power data EP is smaller than 1/2 of the intersymbol distance d. When it is sufficiently small, it can be determined that a transmission path failure due to a dynamic factor has occurred.

Therefore, when the receiving apparatus detects an error in the received data, the value of the tap coefficient data TP or the error power data EP obtained from the demodulation unit in the receiving apparatus is determined to determine the cause of the data error at that time. Thus, appropriate processing can be performed.

The form of data transmission in a facsimile machine is
First, data is transmitted from the transmitting device side, and the result is responded from the receiving device side, so-called half-duplex transmission, so when transmitting data by automatic retransmission request control,
The greater the amount of data transmitted at one time, the more the transmission efficiency can be improved.

Therefore, in the present invention, at the time of starting the transmission, the highest data transmission speed among the mutually usable data transmission speeds is set as the data transmission speed, and the capacity of the data transmission buffer memory provided in both devices allows. The number of data frames transmitted in one data transmission is set as large as possible.

Then, when the receiving apparatus detects a data error, tap coefficient data obtained from the demodulation unit of the modem of the receiving apparatus.
The cause of the data error is determined from the history of TP or error power data EP, and if it is determined to be a static cause, the data transmission speed is shifted down and the number of data frames set from the data frame in which the data error occurred is set. Resend.

When it is determined that the data frame is a dynamic factor, the data frame having the number of frames set at that time is transmitted from the data frame in which the data error has occurred simply by the automatic retransmission request control. When the occurrence is continuous to some extent, the number of data frames transmitted in one data transmission is reduced stepwise, and the data frames of the set number of frames are retransmitted from the data frame in which the data error has occurred. It is possible to control the occurrence of data errors due to dynamic factors.

In this way, the cause of the data error is identified,
By taking a corresponding action, efficient half-duplex transmission can be performed.

FIG. 3 shows a data communication system according to an embodiment of the present invention. In this embodiment, data transmission is performed by the half-duplex transmission described above.

In the figure, in a transmission device TX, transmission data formed from a data processing unit 11 is temporarily stored in a buffer memory 13 in a communication control device 12, and is sequentially read out according to a transmission control procedure executed by a transmission control unit 14, A predetermined number of frames in a state of being framed in a predetermined format (described later),
The signal is modulated via the modem 15 and transmitted to the transmission line 16.

In the receiving device RX, the data transmitted via the transmission line 16 is demodulated by the modem 21 of the communication control unit 20, and the received data output from the modem 21 is stored in the buffer memory 22 and the received data analyzing unit 23 Detects a data error.

The reception control unit 24 that controls the entire communication control unit 20 receives the error power data EP from the modem 21 and notifies the reception data analysis unit 23 of a data error detection result. 24 responds to the transmission device TX with the reception result in a predetermined format (described later), and stores only the reception data of the frame without data error in the buffer memory 22.
And outputs it to the data processing unit 25.

Now, in this embodiment, various transmission control procedure data and transmission data are exchanged in a framed state in the HDLC (high level data ring control) procedure, and the basic configuration is shown in FIG. .

As shown in the figure, one data frame includes a flag F indicating the beginning of the frame, an address field A indicating the destination of the frame, a control field C indicating the contents of a command or response in the HDLC procedure, and an information field including data to be transmitted. I, a cyclic redundancy check code CRC for detecting a transmission error, and a flag F representing the rear end of the frame. However, the cyclic redundancy check code CRC is formed by applying data from the address field A to the information field I to a predetermined generating polynomial.

Therefore, the reception data analysis unit 23 in the communication control unit 20 of the reception device RX detects that an error has occurred in the reception data based on the cyclic redundancy check code CRC.

Further, as shown in FIG. 5 (a), the transmission device TX
The data formed by continuously forming the data frames FL1 to FLn are transmitted as one data, and the information field I of the first frame is the number of frames to be transmitted as shown in FIG. Number data to represent
The IFN and the transmission data of the first frame are included, and the information field I of the second to n-th frames includes the transmission data of each frame as shown in FIG. The number of bits of the data divided into each frame is set to, for example, about 2048 bits (= 256 octets (bytes)).

The response signal RFL for the receiving device RX to respond to the transmitting device TX about the reception status of the transmission data has a format as shown in FIG. 5D. Note that this response signal
The RFL is transmitted from the receiving device RX to the transmitting device TX while being included in the information frame I of HDLC.

That is, a response field identification code TN1 for indicating that an acknowledgment or a negative acknowledgment field follows, and an n-bit response indicating an acknowledgment or a negative acknowledgment for the received data of the first to nth frames in bit order The field FR includes an error power data identification code TN2 for indicating that error power data follows, and error power data DEP.

And each bit AN ₁ ～ANn response field FR, the value is to 1 if an error in the received data of the corresponding frame has occurred, thereby, data in any data frame FL1~FLn the transmitting device TX It can be determined whether an error has occurred.

Considering that data transmission is performed from the transmitting device TX to the receiving device RX with the above configuration, first,
With the transmission path between TX and RX established,
Functions and buffer memory provided by the terminal from RX 22
Is transmitted to the transmitting device TX, thereby setting the data transmission rate used first by the transmitting device TX, and the size of the buffer memory 13 of its own terminal and the buffer memory 22 of the receiving device RX. Set the optimal number of frames from.

Here, assuming that the number of frames is set to 5, data TFL1 for the first five frames of the transmission data is transmitted for the first time (see FIG. 6). At this time, 5 is set as the frame number data IFN in the first data frame.

When the first data transmission is completed, the receiving device RX
Thereafter, a response signal RFL1 in which the occurrence state of the reception error for each frame and error power data at that time are set is returned to the transmission device TX.

Here, the following table shows a part of an example of the history of data transmission in the transmitting device TX and the receiving device RX, and based on this, an execution example of the automatic retransmission request control according to an embodiment of the present invention will be described.

In this table, the transmission data number is a number sequentially assigned from the first frame data when the transmission data is divided into frame data of a predetermined length, and the frame number is a plurality of frames transmitted at one time. Are given only to the transmission, and x in the column indicates an unused portion. In this communication control example,
It is assumed that the cause of the data error is a dynamic factor.

First, all five frames of data are received without error in the first time, and all bits of the response field FR of the response signal RFL being responded from the receiving device RX to the transmitting device TX are set to 0. Indicates that five frames of data are transmitted from the frame having the transmission data number 6.

In the second data transmission, a data error occurs in the frame having the frame number 2 (that is, the frame having the transmission data number 7), and the response field FR of the response signal RFL is generated.
Since the bit AN ₂ 2 bit of the is to 1, the transmitter TX compares the error power data DEP of the response signal RFL 1/2 of the distance between signals d, in this case, the error power data Since the DEP was not in the vicinity of 1/2 of the inter-signal distance d, it was determined that this data error was due to a dynamic factor, and in the next third data transmission, five frames from the frame whose transmission data number was 7 were transmitted. Are transmitted.

In the third data transmission, all five frame data are received without error, and the previous bit of the response field is set to 0. Therefore, in the fourth data transmission, five frames from the frame whose transmission data number is 12 Data is being transmitted.

In the fourth data transmission, errors occurred in the second, third, and fifth data frames. Therefore, in the fifth data transmission, five data frames were transmitted from the frame having the transmission data number of 13 and the fifth data transmission was performed. In the data transmission, an error has occurred in the third and fifth data frames. Therefore, in the sixth data transmission, five data frames are transmitted from the frame whose transmission data number is 15, and in the sixth data transmission, two data frames are transmitted. An error has occurred in the data frame of the frame.

When a data error due to a dynamic factor occurs three consecutive times in this way, the transmitting device TX reduces the number of frames transmitted in one data transmission by one step. In this case, the number of frames to be reduced is set to 1, so that in the seventh and subsequent data transmissions, the number of data frames transmitted in one data transmission is set to four. As a matter of course, 4 is set in the frame number data IFN included in the first frame. The frequency of occurrence of data errors as a condition for reducing the number of frames as described above is not limited to three consecutive data errors, and the number can be set to a value as appropriate.

Thus, in the seventh data transmission, four data frames are transmitted from the frame whose transmission data number is 16. In the seventh data transmission, all data frames were received without data errors, so in the eighth data transmission, four data frames were transmitted from the frame with the transmission data number 20 and the eighth data transmission In the transmission, all data frames were received without any data error. Therefore, in the ninth data transmission, four data frames were transmitted from the frame having the transmission data number 24, and in the ninth data transmission, all the data frames were transmitted. A data frame has been transmitted.

As described above, when the number of data frames transmitted at one time is smaller than the initially set maximum number, all the data frames have been received in a state of no data error for a predetermined number of times (in this case, three times). Is transmitted, the transmitting device TX increases the number of data frames transmitted at one time by one step. When recovering the number of data frames transmitted at one time, the number of data transmissions that do not cause a data error is not limited to three.

Therefore, in this case, in the tenth and subsequent data transmissions, the number of data frames transmitted in one data transmission returns to 5. As a matter of course, the frame number data IFN included in the first frame also returns to 5.

Thus, in the tenth data transmission, five data frames are transmitted from the frame whose transmission data number is 28.

The above control procedure is performed by the transmitting device TX to the receiving device RX.
It is sequentially executed repeatedly until the transmission data to
Thereby, data transmission in one communication is performed.

In addition, the receiving device RX responds that one or more data frames have an error, and a response signal at that time.
The error power data DEP included in the RFL is equal to the distance d between the signals.
If it is near 1/2, the transmitting device TX determines that the cause of the data error is a static factor, and executes the well-known downshift control to change the data transmission speed of the modems 15 and 21. At the same time, data transmission is continued from the frame in which the data error has occurred. At this time, the number of data frames transmitted at one time is set to the initially set maximum number.

In this way, when an error occurs in the received data, the cause of the error is determined, and a measure corresponding to the cause is performed. Therefore, the data communication of the automatic retransmission request control in the half-duplex transmission is very efficient. You can do it.

In the above-described embodiment, the receiving device RX includes error power data in the response signal responding to the transmitting device TX, and the transmitting device TX determines the cause of the data error. The cause of the error may be determined, and the determination result may be transmitted to the transmitting device TX. At that time, the number of data frames to be transmitted at one time can be set in the receiving device, and the number can be responded to the transmitting device or the transmission device can be instructed to execute the downshift control. In this case, when responding to the cause of the data error, the result of one data transmission can be included in the response signal.

In the above-described embodiment, the cause of the data error is determined based on the error power data. Alternatively, the cause of the data error may be determined based on the tap coefficient data TP described above. In addition, the cause of the data error can be determined based on other information obtained from the modem of the receiving device, such as a frequency offset.

Still further, in the embodiment described above, the transmission 1
Frame number data indicating the number of data frames transmitted at one time is arranged at the head of the data of the frame, but this frame number data can be excluded. In this case, the end of one data transmission can be detected by monitoring the interruption of the carrier by the receiving device.

Further, the present invention can be applied to a data communication device other than a facsimile device.

[Effects] As described above, according to the present invention, data is transmitted in units of a transmission data frame including one or a plurality of data frames via an analog transmission path using a modem, and one transmission is performed from a transmission station. The receiving station that has received the data frame transmits a response data frame including response data indicating the reception state of each data frame included in the received transmission data frame to the transmitting station, and the transmitting station that has received the response data frame Checking the response data included in the response data frame to determine a data frame in which a reception error has occurred, and resending the data frame determined to be the reception error when determining at least one data frame in which the reception error has occurred. In the data communication method, the receiving station includes, in the response data frame, the modem. While adding the channel quality information including the tap coefficient data or the error power data obtained from the demodulation means of the transmitter, the transmitting station has determined that the response data frame includes one or more data frame reception errors. In this case, the line quality information is examined, and if it is determined that the cause of the reception error is based on a static factor, the transmission speed of the modem is reduced and the data determined to be a reception error at that time. Retransmitting the frame, and when determining that the cause of the reception error is based on a dynamic factor, retransmitting the data frame determined to be a reception error while maintaining the transmission rate of the modem, and When the reception error is repeated, the number of data frames included in the transmission data frame unit should not be reduced stepwise. Since a data frame determined to be a reception error is retransmitted, when a transmission line failure occurs, appropriate measures are taken according to the type of the transmission line failure, and as a result, even when a transmission line failure occurs, An effect is obtained that transmission efficiency is good and appropriate data communication becomes possible.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a demodulation unit of a modem, FIG. 2 is a signal configuration diagram showing an example of a signal space used by the modem, and FIG. 3 illustrates a data communication system according to an embodiment of the present invention. FIG. 4 is a signal arrangement diagram showing an example of a frame configuration of transmission data, FIGS. 5 (a) to 5 (d) are signal arrangement diagrams showing examples of various transmission data, and FIG. 5 is a time chart illustrating an example of a transmission state. TX: transmitting device, RX: receiving device, 12, 20, communication control device, 13, 22, buffer memory, 14: transmission control unit, 1
5, 21 modem, 16 transmission line, 23 reception data analysis unit, 24 reception control unit.

Claims (1)

(57) [Claims] 1. A receiving station that transmits data in units of a transmission data frame composed of one or a plurality of data frames via an analog transmission path by using a modem and receives one transmission data frame from a transmission station. A response data frame consisting of response data indicating the reception state of each data frame included in the received transmission data frame is transmitted to the transmitting station, and the transmitting station receiving the response data frame transmits the response data frame included in the response data frame. In the data communication method for retransmitting the data frame determined to have an error when determining a data frame in which the reception error has occurred and determining one or more data frames in which the reception error has occurred, the receiving station includes: In the response data frame, the tap coefficient data obtained from the demodulation means of the modem is described. If the transmitting station determines that the response data frame contains a reception error of one or more data frames, the transmitting station adds the line quality information to the response data frame. Investigation and, if it is determined that the cause of the reception error is based on static factors, reduce the transmission speed of the modem and retransmit the data frame determined to be a reception error at that time, When it is determined that is based on a dynamic factor, while retransmitting the data frame determined to be a reception error while maintaining the transmission rate of the modem, when the same type of reception error is repeated,
A data communication method characterized by retransmitting a data frame determined as a reception error while gradually reducing the number of data frames included in the transmission gator frame unit.