JPS63207233A - Error resending control system - Google Patents

Abstract

PURPOSE:To communicate a resending request signal to a transmission side device without fail even a long-distance line to which an echo suppressor is added by adding an attenuation function stopping signal in a transmission line besides the resending request signal when an error is detected at the received transmission signal. CONSTITUTION:When it is detected that image data PIX1 is an error, a command is issued from an error detecting terminal 24 to a resending request switch 410, a transmission/reception change-over switch 401 is thrown to a transmission side and a synthesizing signal of 350Hz and 2100Hz from a 350Hz oscillator 406 and a 2100Hz oscillator 407 or a sequential signal is sent. At this time, the suppression loss of an echo suppressor is removed, a level adjusting device 409 is prepared so that the echo suppressor can be always released without fail even when it is connected to any line of many and unspecified destinations and the area of a break-in W and a tone disabler circuit in the echo suppressor can be used together.

Description

[Detailed Description of the Invention] [Field of Industrial Application] Is this invention applicable to facsimiles, etc.? This invention relates to an error retransmission control system suitable for long-distance communication such as international lines in data transmission.

[Conventional technology]

FIG. 2 is a block diagram showing the overall configuration of a facsimile apparatus. Hereinafter, the background of the error retransmission control system of the present invention will be explained with reference to FIG.

When transmitting image information to a remote party through a telephone line, the line interface 109 to the transmitting end 189 communication line 19. Assuming that a link has been established through the receiving end 20 and the line interface 115 on the receiving side, whether manually or automatically, the transmitting operator will A desired document 100 is set on the transmitter, and after a data link is established through the communication line 19, transmission is started.

At this time, as shown in FIG. 3, the transmitting side sends an inquiry signal ENO to the receiving side, and the receiving side first confirms reception preparation by sending an acknowledgment ACK in response.
Next, the transmitting side transmits a control signal C0NT of initial conditions such as resolution and transmission speed, and receives an acknowledgment ACK from the receiving side. Now it is possible to transmit image data PIX1, PIX2, etc., and the image information of the original 100 in FIG. 2 is read through the lens 102, and the photo sensor 106
After the output is prepared for various operations by the transmission picture processor 105, it is encoded and compressed by the encoder 106 in order to save time by encoding and compressing. When one line of information is encoded as the main scan of the original 100, the sequence control 111 encodes the information to obtain the next image information.
Start the motor drive circuit 112 and drive the step motor 1.
16 is moved one step, and the drive roller 101 advances the document by 100 YI lines. The digital signal from the encoder 106 is sent via the image data processor 11 to the transmitting data processor 107 for adding an error-detectable code, for example, a cyclic redundancy check (hereinafter referred to as CRC).
The signal enters the modem 108 via the line interface 109, is converted into an analog signal, and is sent out to the communication line 19 through the transmission side input/output terminal 18 of the line interface 109.

The analog signal input to the receiving side input/output terminal 20 is converted into a form suitable for the receiving input of the modem 116 by the line interface 115, and the analog signal is digitized. Here, the input terminal of the modem 108 is indicated by 55,
The modem 108 and line interface 109 are collectively called a modem interface 15, and the line interface 115 and modem 116 are called a modem interface 21. Further, after error detection is performed on the signal digitized by the modem 116 and the CRC code added by the reception data processor 117, only the compressed and encoded image data is passed through the image data input terminal 27 to the decoder. 118, it is restored to the original image data string, and in the reception picture processor 119, it is converted into printing data by the thermal head 120 and printed on the recording paper 124. Each time the sequence control 121 is restored, the step motor 125 is activated (operation is performed for each line). 124 in one step. At this time, the time required for compression encoding changes depending on the amount of information in the document 100, and intermittent drive is the reason why the step motor 123 is used. In this way, one line The step motor 126 advances each time, and the contents of the document are sequentially recorded on the recording paper 124.Image data PIX1
to PIXn are transmitted sequentially, and the last image data P
When the transmission of IXn is finished, it sends the image data end signal END, and if the receiving side sends it normally and there is no error, it notifies the sending side of the positive response 〇K, and the sending side receives this signal. , transmits the transmission end signal FIN, and then releases the communication line 19.

Here, it is rare that the image data PIX1 to PIXn are always transmitted in the same key, and data errors often occur on the communication line 19 due to some kind of noise interference. The receiving side determines whether the received data is error based on the contents of the CRC code added by the transmitting side, but if the receiving side determines that the image data PIX4 is in error as shown in Figure 2, the receiving side A retransmission request signal RQ is sent from the terminal. For this retransmission request signal RQtS, if there is not much transmission delay, only a tone may be used, but if the delay in the transmission system cannot be identified, a tone signal followed by data that is transmitted to notify the direct number Send out a signal.

When this transmitted direct number is called an address, the transmission speed of the address data signal is often set to a low transmission speed, giving priority to reliability. For the sake of simplicity, the tone signal containing address data will be referred to as a retransmission request signal RQ. The receive data processor 117 always uses the CRC
Error detection is performed using the code, and when an error is detected, it is notified to the modem interface 21 from the retransmission request output 57, and the modem interface 21 is notified through the communication line 19.
5, is detected by the retransmission detection circuit in the modem interface 15, is transmitted from the retransmission request manual 53 to the transmission data processor 107, and a sequence is activated to resend the data stored in the memory. It looks like this.

It is used in such facsimile communications as shown in Fig. 3. 1 is a block diagram showing a conventional error retransmission control method; FIG.

In the diagram? 19.21+z is the modem interface, 107 is the transmission data processor, 1174 is the reception data processor, and the modem interfaces 19 and 21 are interconnected by a communication line 19. Further, 12 is a memory in which transmission signals are stored; 16;
14 is a switch that selects between each transmission signal once stored in this memory 12 and a transmission signal that is not stored, and 14 is a tester that adds check bits such as a CRC code to the data from this switch 13 and sends it to the modem interface 15. 16 is a retransmission detection circuit connected to the modem interface 15; and 17 is a retransmission control circuit connected to the retransmission detection circuit 16 to control the switch 13N and the memory 12. Further, 22 is an error detection circuit connected to the modem interface 21, 26 is a memory for storing data from the modem interface 21 under the control of the error detection circuit 22, and 25 is connected to the error detection circuit 22 and the This is a retransmission request circuit that sends a retransmission request signal to the modem interface 21.

Next, the operation will be explained. A transmission signal is input from a signal input terminal 11 and stored in a memory 12, and at the same time, a direct signal is normally sent to a check bit adding circuit 14 through a switch 16. Further, when the retransmission control circuit 17 operates, that is, when the retransmission detection circuit 16 detects a retransmission request signal, the image data stored in the memory 16 is outputted by the switch 13 and sent to the check bit addition circuit 14. . For example, CRC
A check bit such as a code that can detect errors on the receiving side is added, and the data is converted into digital to analog (hereinafter referred to as D/A conversion) by the modem interface 15 and output from the input/output terminal 18 on the transmitting side to the communication line 19. Ru. At this time, if a retransmission request signal RQ from the receiving side is detected by the retransmission detection circuit 16 while the modem interface 15 is transmitting data, the above-mentioned retransmission control circuit 17 controls the reswitch 16, and the memory As described above, the image data stored in the image data 12 is added with a check bit in the check bit adding circuit 14 and sent out via the modem interface 15. The signals transmitted in this way and entering the receiving side input/output terminal 20 through the communication line 19 are converted from analog to digital (hereinafter referred to as A/D conversion) through the receiving side modem interface 21.
Thereafter, the image data is input to the memory 23 and sent to the error detection port W&22. The error detection circuit 22 detects the presence or absence of an error in the data string including check bits such as an added CRC code, and if there is no error, the contents of the memory 26 are sent to the image data output terminal 27 for the next image restoration. Send them off to the stage.

On the other hand, when an error is detected by the error detection circuit 22, a command is issued from the error detection terminal 24 to the retransmission request circuit 25, and even though the ℃ signal is being received, the retransmission request signal R
Q is sent from the output terminal 57 to the communication line 19 through the modem interface 21 and the receiving side input/output terminal 20.

Figure 5 is a time chart showing the state of transmission and reception when this retransmission request is made. In Figure 3? Although it has been explained that the error occurred in the image data PIX4, here, due to the overlapping of the figures, the image data PIX1 is shown as having an error. The transmitted data is transmitted due to a transmission delay T1 due to the communication line 19 as shown in FIG. 5(a).
After some time, it is received as shown in FIG. 5(c). On the receiving side,
Picture flag FP, which is an identification code indicating that it is an image
After detecting, the error detection circuit 22 shown in FIG. 4 is activated to detect an error in the image data PIX1. Here, a training signal is required at the beginning of the signal to synchronize with the modulation correlation of transmission and reception of the modem and to perform phase equalization, and this is indicated by TR8. When the image data PIX1 is determined to be an error, the retransmission request signal RQ'Y shown in FIG. If the transmission delay is large, address data is added after training according to the modem's transmission speed and transmitted to the sending side as described above.This retransmission request signal RQ&!, @Figure 5 (
As shown in bl, the retransmission request signal RQ is detected after time T2, which is the sum of the communication line 190 time delay and the time delay required for retransmission control. On the sending side, at this point, the image data PIX
After completely transmitting this image data PIX2, it waits for 13 hours until the retransmission request signal RQ expires, and then sends a [training signal] from the transmitting side to the receiving side in order to establish a data link between the modems again. TR8'a' is emitted. Following this, the image data PIX1 check bit CRC, which was erroneously received before the picture flag FP, is sequentially sent out.

When this retransmitted image data PIX1 is correctly received, image data PIX2, PIX! 1,... are transmitted.

FIG. 6 (at shows the configuration of the tone signal retransmission request circuit 25, in which an oscillator 50 outputs a signal of, for example, 350 Hz, and the retransmission request switch 51 is controlled by the error output 24 of the error detection circuit 22. , when there is a retransmission request command, the retransmission request output 57 also outputs the retransmission request signal R.
Send Q. On the other hand, FIG. 6(b) shows the configuration of the retransmission detection circuit 16 on the transmitting side, in which the retransmission request manual 53 is connected to the detector 5.
2, and this detector 52 generates a frequency of 350 Hz.
When the tone is detected, the retransmission control circuit 17, which controls the transmission data activated by the retransmission detection output 54, comes into operation.

If there is address data after the 350 Hz tone, data decoding begins, and an address in memory is determined from the decoded address data and transmitted.

The explanation so far has been based on the assumption that a signal always reaches the other party regardless of whether it is transmitted or received, but in real communication lines2, it is often the case that either transmission or reception is transmitted. If this is not done reliably, transmission may be interrupted or interrupted.

Assuming such a case, in an error retransmission control system that recovers from transmission errors that occur on the receiving side while transmission continues, it is necessary to ensure a means for reliably transmitting the error to the transmitting side. The most difficult problem is that the transmitter sends a large signal of about -8 dBm as a transmission signal, but the transmission level is lower than the retransmission request signal RQY generated from the receiving side.
It is to be detected at a signal level of 40 to -50 dBm. If there is a retransmission request signal RQ in the frequency band of the transmitted signal, it cannot be distinguished from the transmitted signal at all, and the retransmission request signal RQ must necessarily be set outside the frequency band of the transmitted signal. Needless to say, this situation is shown in Figure 7 using a telephone line as an example, where the vertical axis is the gain and the horizontal axis is the frequency.The band of the telephone line is usually 0.3 KHz.
to 3.4 KHz and is outside the occupied band of the modem modulation signal used as the retransmission request signal RQ. The occupied band of this modulation signal is determined by the modulation speed, and is 450 tl at 2400 baud, 9600 pits per second (hereinafter referred to as BPS), and 7200 BPS.
z ~ 2950Hz, 4800BPS at 1600 baud is 950Hz ~ 2650Hz, 2400B at 1200 baud
PS is known to occupy 115011z to 2450 HzY. The tone part of the retransmission request signal RQ is 300 to 4501'lz or 295
Frequencies between 0 and 3400 Hz are used. Figure 2
For example, 1 is a single tone of 350 Hz, 2 is a single tone of 3200 Hz, and in the case of 6.4, 300 to 450 Hz is used as a puncture word channel, and it is usually used in the band 75)1z8[.

However, when the two-wire system is used to realize bidirectional communication, which can be easily realized when the transmission and reception are separated like in a 4-wire system, the modulation band shown in 4 is used during transmission.
The transmitting side must detect the retransmission request signal RQ from the receiving side. Furthermore, in long-distance lines such as international lines, echo suppressors 200 and 201 shown in Figure 8 are inserted in order to eliminate the difficulty of hearing the speaker due to echoes. , the echo suppressors 200 and 201 are operated to block the signal from the receiving side, and the signal on the transmitting side is extremely attenuated due to line loss and suppressor loss, reaching a practically undetectable level. Since the purpose of this is to produce an inaudible echo, it is natural that the echo will be at a level that cannot be detected. Figure 8 shows the configuration of the communication line 19 in such a long-distance line. A communication line including an echo suppressor is shown in the figure.A signal inputted to the transmitting side input/output terminal 18 is separated by a 2-wire to 4-wire converter 28 at a terminal station and guided to a suppression loss circuit 29. At this time, the value of the suppression loss is determined by the control circuit 30, and shows different values depending on the conditions of the transmission level and reception level.
As shown in Figure 9 (al), depending on the magnitude of the reception level and transmission level, if there is no signal X, only the transmission signal Y, or in the interrupt W region called break-in, the signal passes through without loss.Reception If the level is large, it will be in the suppression Z region, and a minimum loss of 50 dB will occur, and if the level is changed, a loss of 50 dB or more will occur.The transmitted signal passes through the transmission path 62 and is interrogated by the receiving side receive loss circuit 64.The value of this torque receive loss is determined by the control circuit. 35, it is converted into two wires by the two-wire to four-wire converter 67 in a state without loss, and is output from the receiving side input/output terminal 20.
) Insertion of 6 dB (maximum 7 dBY) as receiving bus loss in the region Y only for the transmitting signal at 8) serves to lower the level in the case of mutual communication. Figure 9 (b) shows the characteristics of this receiving bus loss, and is the content of the recommendations of the CCITT, which is the standard.

Returning to FIG. 8, the retransmission request signal RQ+ is connected to the receiving side input/output terminal 20, to the 2-wire to 4-wire converter 67, to the subrepression/loss circuit 36. Transmission path 33. Receive loss circuit 31.2 line-4
It passes through the line converter 28 and enters the transmitting side input/output terminal 18 (
Ru. However, on the receiving side, if a signal of a certain level is continuously transmitted from the transmitting side, the suppression loss circuit 66 is controlled to 50 dB or more. At this time, even if the retransmission request signal RQ is issued from the receiver input/output terminal 20, it is necessary to generate the retransmission request signal RQY to overcome the reception level.

Further, details of the echo suppressor are shown in FIG. 10, and the function of the echo suppressor 200 in the block diagram in FIG. 8 will be explained. 2-wire to 4-wire converter 28 in FIG.
The transmit signal from the transmit signal input is 60 dB from the transmit signal input 204.
The 60 dB suppressor circuit 219 transmits the signal from the transmitting signal output 205 to the transmitting communication line through the suppressor circuit 219. It works only when the signal level is high, and a 60 dB attenuator is inserted.If the reception level at this time is 31 dBm or higher, this corresponds to a low transmission level, and when the other party is talking,
This prevents echoes from the other party from getting around. -10,000, the received signal from the other party is received from the received signal input 206 to 6
The received signal output 202 is routed through seven attenuators with dB pads 210 to a 2-wire to 4-wire converter 28 . At this time, the attenuation by the 6 dB pad 210 is to reduce the received signal χ in the break-in W region during mutual communication, as described above.

In the break-in W region, that is, when the receiving level is smaller than the transmitting level, the transmitting/damaging signal input 2 in FIG.
The transmission output from 04 is 6 dB.The reference level is matched with the receiving side at pad 215.0OH2~3500
The signal passes through the H2 bandpass filter 216, is continuously detected by the detector 217, and is input to the break-in level comparator 218.

-10,000, Received signal input 20S, 6 dB pad 21
The received signal passing through 0 is amplified by a receiving amplifier 206, and the gain of this receiving amplifier 206 is adjusted in advance to a -16 dBm standard between a transmission level reference signal and a reception level reference signal. Same after this < 500 Hz
~3500Hz band pass filter 207Y passes,
The level is detected by the detector 208, passed through the peak detector 220, and sent to the break-in level comparator 218, where it is compared with the signal from the detector 217, and as mentioned above, the transmission level is -31 dB lower than the reception level.
m or more, 60 d in the echo suppressor
B The suppressor 219 is released and the signal is sent to the other party from the transmit signal output 205 without attenuation. On the other hand, the output of the break-in comparator 218 is sent to the break-in timing circuit 214, which outputs the output from the suppression level comparator 209 and the suppression timing 21.
It will be disabled until there are no more 2 transmit signals. This state is called transmission mode.

@9 Suppression Z area in Figure No. (a) C: When the reception level is larger than the transmission level, the transmission signal and reception signal are compared by the break-in level comparator 218, and the output of the peak detector 220 is If it is large,
Output t! Corresponding to a transmission level of -31 dBm or less, the suppression level comparator 209 operates, and the output of the suppression timing 212 causes the 60 dB suppressor circuit 219 to operate,
Suppresses echoes that reach the transmitter side. This state corresponds to the receiving mode. Moreover, in said transmission mode! The signal is being sent to the other party, and the other party's echo suppressor 2
01's 60 dB suppressor works to suppress the echo, and in receive mode, the 6.0 dB suppressor 219 attenuates the received signal from the other party. In this case, the echo suppressor 200 has a tone-disabler 308, which has a tone-disabler function that allows the other party to intentionally interrupt the transmission while it continues. Reception of 500 Hz ~ 3500
Hz bandpass filter 207 and transmitting 500tlz
The output of the ~3500Hz bandpass filter 216 is guided to the mixer 213, the normal bypass 604 is prohibited, and the 2
100Hz band redirect filter 300 and 210
It is input to both of the 0Hz bandpass filters 302.

This 2100 fiz range is $2100Hz±15H
CCI T T hs is specified as -12±6 dBm. If there is no 2100 Hz transmitting or receiving path, then there is no 2 band reject filter 300 output kZ, only the 2100 Hz band pass filter output, peak detector 301 output tB, and peak detector 606 output. Bm0, and the relationship is A>H, and the level comparator 305, which is designed to produce an output only when A<B, does not generate anything. 2100■2 is sent from either or both of the transmission and reception paths (then, the output B of the peak detector 301, 303,
A becomes A<B, and 250 m5ec±150 m5e
A disable circuit 607 is operated through a delay circuit 606 of c, and the 60 dB suppressor 219Y% eliminates the transmission attenuation.

At this time, the bypass 604 plays the role of canceling the disabler 607 when the transmission signal is lost, and always
>BK is the way to go.

The above state is expressed by the echo suppressors 200 and 201 in FIG.
Considering this, during transmission from the transmitting side, the suppression loss circuit 29 does not attenuate, and the receive loss circuit 64 of the echo suppressor 201 also does not attenuate, and in this case, if 210082 transmissions are received from the receiving side while transmission continues, the register floss 64
In the state of break-in W, the 6 dB pad switch 211 in FIG. 10 is turned on, and the 6 dB pad 210Y is attenuated, but the suppression loss times wi! ! 66 is in a state with no attenuation, and the receive loss circuit 61 is in a state with 6 dB of attenuation.

Compared to the case where 2100 Hz transmission is not performed, the signal level increases by the amount reduced by the suppression loss circuit 660, and reaches a level that can be transmitted to the transmission 1i111.

[Problem that the invention seeks to solve]

Since the conventional error retransmission control system is configured as described above, no matter what level the echo suppressor 200, 201 is attached to the international communication line, the break-in W is always effective to eliminate suppression loss. In order to secure the area, should the level of the retransmission request signal RQ be set at the upper limit of the permissible transmission level? (However, even with this upper limit level KN, it is difficult to make the suppression loss circuit 66Y lossless. communication line 19, there is always suppression loss χ″′0
If the retransmission request signal RQ is not transmitted, interruptions, omissions, errors, etc. of the transmitted data may occur. There was a problem in that the reliability of data communication deteriorated significantly.

This invention was made to solve the above-mentioned problems, and eliminates the suppression loss of the echo suppressor during the period during which the retransmission request signal RQ′ft is generated, thereby ensuring that the retransmission request signal RQχ is transmitted to the transmitting side. The purpose of this study is to obtain an error retransmission control method that can

[Means to solve the problem χ]

In the error retransmission control method according to the present invention, a receiving device has a plurality of tone signals, and when an error tone is detected in a received transmission signal, it sends those tone signals to the transmitting device, and at least one of the tone signals is transmitted to the receiving device. In addition, to the χ retransmission request signal,
At least one other is assigned to the attenuation function stop signal in the transmission line.

[Effect]

When the error receiving device in this invention detects an error in the received transmission signal, it sends a tone signal to the transmitting device, and activates the echo-disabler circuit using the attenuation function stop signal in the transmission line included in the tone signal. By eliminating the suppression loss of the echo suppressor, the retransmission request signal in the tone signal is reliably transmitted to the transmitting device.

〔Example〕

Hereinafter, FIG. 7 will be described as an embodiment of the present invention. Part 1
In the figure, 401 is a transmission/reception changeover switch, 402 is a reception amplifier connected to the reception side of this transmission/reception changeover switch 401, 406 is a modem reception section connected to this reception amplifier 402, and 404 is this modem reception section. 406 is a modem transmitting section forming the modem 116; 405 is an address latch connected to this modem transmitting section 404;
6 is a 350 Hz oscillator, 407 is a 2100 Hz oscillator, 408 is these 60512 oscillators 406, 2100
A mixer to which the FJz oscillator 407 and the modem transmitter 404 are connected, 409iz a level adjuster connected to this mixer 408, and 401 the address latch 40.
5 and the transmission/reception changeover switch 401.

Furthermore, 420 is a modem transmitter, 421 is a 350 Hz
A reject filter 422 is a transmission level adjuster 42 connected to this 350Hz reject filter 421.
6 is the 6dB connected to this sending level adjustment Jl [422
pad, 424 is a phase correction circuit, 425I is 6 d above
This is a canceller in which the signals at both ends of the B pad 4230 are given -1 directly and the other signal is given via the phase correction circuit 424, and is arranged within these Q emodem interfaces 15.

Further, 426 is an automatic gain control circuit (hereinafter referred to as AGCI1g circuit) connected to the canceller 425;
7 is a 350 Tlz resonator connected to this AGC 426, 429 is a 350 T1z amplifier connected to this 350 Hz resonator 428, and these are arranged within the detector 52.

Next, the operation will be explained.The signal that enters the receiver 1 from the 11 output terminal 20 is amplified by the receiver amplifier 402 to a level suitable for the modem receiver 406, and then
After conversion, the image data is sent to human power 56 and decoded. In the decoded data, the address included in the picture flag FP in FIG. 5 is always decoded and sent to the address launch 405.
If there is no error in the received data, the addresses are updated to new addresses one after another. Here, when it is detected that the image data PIX1 is erroneous as shown in FIG.
5 memorizes the address of the received data at this time, turns the transmit/receive switch 401 to the transmit side, mixes the data in the mixer 408, passes through the level adjuster 409, and outputs the 350 Hz oscillator 406 and the 2100 Hz oscillator 4.
A composite signal of 350 Hz and 2100 Hz from 07 or a sequential signal is transmitted. - After sending out the tone for the last period, the address data in the address latch 405 is input to the sound modem transmitter 404 and continues to be sent. At this time, the transmission level of one facsimile machine is set to eliminate the suppression loss of the above-mentioned echo suppressor, and to ensure that the echo suppressor is always canceled regardless of the line connected to an unspecified number of destinations. and a level adjuster 40 that can independently adjust the response transmission level at the time of reception.
9 is prepared so that the break-in W region of 8 and the tone day sweeper circuit 308 can always be used together with the echo suppressor. Now, if the retransmission request signal RQ sent in this way is on the sending side, for example, -8 dB
Considering the attenuation of the line, monitoring the retransmission request signal RQa' from the receiving side while transmitting the transmission signal of m is -40
The retransmission request signal RQ, which has a level of about dBm, must be monitored, making it difficult to monitor the retransmission request signal RQ. Q is on the transmitting side, and the image data PIX1 is sent from the modem input terminal 55 to the modem transmitter 420.
For example, in the case of 9600 BPS, 450 Hz to 295
A 350 Hz retransmission request signal R included in the modulated signal in such a manner that it does not affect the modulated signal over 0 Hz.
Ingredients corresponding to Q will be rejected. It is rejected when 350 Hz is used to detect the retransmission request signal RQ.
In the wire system S, since signals are applied to the same terminal for transmission and reception, this is to prevent the own signal from being confused with the retransmission request signal RQ. Therefore, this 350Hz redirect filter has an attenuation level of about 50 dB and a
A narrowband reject filter is required that does not affect Hz. The modulated signal from which 350 Hz has been removed in this way is adjusted to a predetermined level by a sending level adjuster 422, and after being attenuated by a 6 dB pad 426, for example, -8 dB.
It is continuously transmitted from the transmitting side input/output terminal 18 at a transmission level of Bm. This transmitting side input/output terminal 18 is connected to the fd in Fig. 5.
A composite or sequential signal of 2100 Hz and 350 Hz is sent as the retransmission request signal RQ shown in 1. The signal at the transmitting side input/output terminal 18 has a -8 dBm 45
0Hz~295011z transmit signal and -40dBm 21
A retransmission request signal RQ by a combination of 00 Hz and 350 Hz or a sequential I-100 signal is mixed. This mixed signal is directly input to the canceller 425, and is also input to the canceller 425 from the input side of the 6 dB pad 423 via the phase correction circuit 424. At this time, if there is no retransmission request signal RQ, one side of the 6 dB pad on both sides of the transmitted signal! It is adjusted so that the output of the gear/cellar 425 is -50 dBm by performing phase correction corresponding to the line impedance. Here, retransmission request signal RQ
When a composite or sequential signal of 2100 Hz and 350 Hz is input, the canceler 425 outputs an output of the potential difference between the two ends of the 6 dB pad 423, the gain is made constant by the AGC 426, and the 350 Hz bandpass filter 427.350 Hz resonator 428 Accuracy < 3
50) Detect the presence or absence of lz 3501]z amplifier 429
Output the signal to retransmission detection output 54 through.

Here, the phase correction circuit 424 is a 6 dB pad 423 that reduces the change in line impedance seen from the transmitting side input/output terminal 18, and is capable of exhibiting a canceller effect even against a wide range of impedance changes. This is essential for more reliable retransmission signal extraction. In addition, as another function of the echo suppressor, 250 m5ec±1
By taking a pause time χ in the range of 50 m5ec,
There is also a function to remove 60 dB suppression. Although this function is not effective during continuous transmission, it is useful when establishing a transmission link to eliminate the influence of the echo suppressor.

In addition, although the case of facsimile communication was explained in the above embodiment, it may be applied to other data communication, and the same effects as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the present invention, the receiving device has a plurality of tone signals to be transmitted when an error Z is detected in the received transmission signal, and at least one of the tone signals is included in the retransmission request signal. Since the other one is assigned to the attenuation function stop signal in the transmission line, the echo dabra circuit is activated by the attenuation function stop signal in the transmission line included in the tone signal to remove the suppression loss of the echo suppressor. However, even over long-distance lines such as international communication lines equipped with echo suppressors, the retransmission request signal in the tone signal is reliably transmitted to the transmitting device, and the transmitted data is free from interruptions, omissions, and errors. etc., which has the effect of greatly improving the reliability of data communications.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an error retransmission control method according to an embodiment of the present invention, FIG. 2 is a block diagram showing the overall configuration of a facsimile machine to explain the backglanton, and FIG. 3 shows its operation. FIG. 4 is a block diagram showing the conventional error retransmission control system, FIG. 5 is a sequence diagram showing the transmission and reception of signals, FIG. 6 is a block diagram showing the retransmission request circuit and retransmission detection circuit, and FIG. Fig. 7 is an explanatory diagram showing the range of the retransmission request signal, Fig. 8 is a block diagram showing the relationship between the echo suppressor and the communication line, and Fig. 9 shows each area of the echo suppressor according to the relationship between the transmission level and the reception level. FIG. 10 is a block diagram showing details of the echo suppressor. 406! X350tlz oscillator, 407km2100H
z generator, 409 is level adjuster, 421 is 350Hz
Reject filter, 423 is attenuator (6dB padded)
, 424 is a phase correction circuit, and 425 is a canceller. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.掠筭Figure 5 (a) Sendsugi Qi 9 Figure 6 KH: i! Khi' Umbrella 400 buried stones Figure 9

Claims (4)

[Claims] (1) In an error retransmission control method in which a retransmission request signal is sent from the receiving device to the transmitting device when an error occurs in the transmission signal transmitted from the transmitting device to the receiving device, the receiving device , having a plurality of tone signals, and using at least one of the tone signals as the retransmission request signal,
Further, an error retransmission control method characterized in that at least one other signal is assigned to an attenuation function stop signal in a transmission line. (2) The receiving device sets the signal level of the tone signal when receiving the transmission signal independently of the signal level when transmitting the transmission signal. Error retransmission control method described. (3) The transmitting device removes the frequency component assigned to the retransmission request signal from the transmission signal to the receiving device, cancels frequency components other than the retransmission request signal, and transmits the tone signal. The error retransmission control system according to claim 1, wherein the retransmission request signal is extracted from the error retransmission control system. (4) The transmitting device passes the received tone signal through an attenuator, and separates a signal obtained from the input side of the attenuator and a signal obtained from the output side of the attenuator via a phase correction circuit. 2. The error retransmission control method according to claim 1, wherein the retransmission request signal is detected by inputting it to a canceller to cancel the modulated signal regardless of the line impedance of a connected communication line.