KR910000705B1 - Error send again method - Google Patents

Abstract

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Description

Error retransmission method

1 is a schematic configuration diagram of a facsimile apparatus adapted to the present invention.

2A and 2B show a data structure of one frame and a data structure of one block.

3 is a transmission time relationship diagram.

4 is a flowchart for explaining the operation of the transmitter.

5 is a flowchart for explaining the operation of the receiver.

* Explanation of symbols for main parts of the drawings

1: transmitter 2: receiver

3: communication line 4: reading part

5: coding processor 6, 14: control unit

7,16: Image information 8: Error memory

9, 13 modem 10, 12 circuit control unit

11: tone signal detector 15: tone signal generator

17: frame number memory 18: decoding processing unit

19: register

The present invention relates to an error retransmission method capable of preventing a transmission error when transmitting image information by a facsimile apparatus or the like.

In a conventional facsimile apparatus, image information is converted into a digital signal and transmitted through a telephone line. By the way, when the transmission is performed via a telephone line, there is a drawback that a transmission error is likely to occur due to mixing of various noises. Therefore, the error retransmission method of conventionally framing data on the transmitting side, error detection for each frame on the receiving side, returning a retransmission request signal when an error is detected, and retransmitting an error frame Has been used.

In this error retransmission method, a tone signal of a specific frequency is used for the retransmission request signal, and the transmitting side that detects the transfer of the tone signal determines that an error occurs in the frame preceding the frame currently being transmitted. It is known to retransmit the preceding frame after the frame currently being transmitted.

In this case, since it is a precondition that the tone signal is detected until the transmission of the frame following the frame in which the error is detected, the allowable transmission delay is determined in accordance with the transmission time of one frame.

Therefore, in consideration of the use of a line with a large transmission delay, for example, a satellite line, it is necessary to increase the transmission time by increasing the number of data in one frame. However, when the number of data per frame increases, the error rate increases and the transmission efficiency decreases.

As a method of solving this problem, for example, Japanese Patent Laid-Open No. 55-4104 discloses a method of equal display. In this system, a signal indicating the frame number which was an error is conveyed as a retransmission request signal in order to exclude the effect of the transmission delay.

That is, since it is possible to determine which frame has an error at the time when the retransmission request signal is detected, it is not affected by the transmission delay. The sender needs a large memory to accumulate a large amount of transmitted data, and also needs to send a frame number and require a modem for the sender and the receiver to receive it. have.

SUMMARY OF THE INVENTION The present invention provides an error retransmission method that uses a tone signal carrying method having a simple configuration, can cope with a line having a large transmission delay, and can reduce the occurrence of an error again during retransmission. do.

The present invention blocks and transmits a predetermined number of frames, performs error detection for each transmitted frame, stores the frame number where an error is detected, and retransmission request in response to the retransmission request performed for each block. Retransmit and validly receive only the data of the last error detected frame among the retransmitted blocks.

In the present invention, as described above, since a predetermined number of frames are blocked and transmitted, and retransmission requests are made for each block, the allowable transmission delay can be increased without increasing the number of data per frame. In addition, since only the frames that had an error last time are valid and received among the retransmitted blocks, the error at the time of retransmission can be reduced again.

Hereinafter, an embodiment of the present invention will be described taking a facsimile apparatus as an example.

1 shows a schematic configuration of a facsimile apparatus, and is configured to connect the transmitter 1 and the receiver 2 to a communication line 3 such as a telephone line.

The transmitting unit 1 includes a reading unit 4, an encoding processing unit 5, a control unit 6, an image information memory 7, an error memory 8, a modem 9, a line control unit 10, and a tone signal detecting unit ( 11) and so on. The control part 6 is comprised by the microprocessor, and is made to process according to a predetermined program. The reading unit 4 reads the content of the original by an image sensor such as a charge coupled device (CCD), converts it into a digital signal, and sends it to the encoding processing unit 5. The coding processing unit 5 encodes the digital signal in a predetermined format, compresses the data, and stores the data in the image information memory 7 in sequence under the control of the control unit 6. The control unit 6 reads the encoded data stored in the image information memory 7 every predetermined length, for example, every 256 bytes, and displays a framing pattern, frame number, and CRC (Cyclic redundancy) for synchronization as shown in FIG. 2A. The error detection data by the check code) is added to form one frame.

As shown in FIG. 6, one block is determined in units of four frames.

The image information memory 7 makes it possible to accumulate at least two blocks of encoded data. The modem 9 modulates the data framed by the control unit 6 into a signal that can be transmitted to the communication line 3, and transmits it to the communication line 3 through the line control unit 10. The tone signal detection unit 11 is for detecting a tone signal of a predetermined frequency conveyed when error detection is performed in the reception unit 2, and the detection signal is sent to the control unit 6. The control part 6 sets the NG bit of the error memory 8 in response to this detection signal, and stores that there was an error transmission. The receiving section 2 includes a line control section 12, a modem section 13, a control section 14, a tone signal generating section 15, an image information memory 16, a frame number memory 17, a decoding processing section 18, And a recording unit 19 or the like.

Here, the modem 13 demodulates the signal modulated by the modem 9 of the transmitter 1 in its original form and sends it to the controller 14. The control unit 14 has a microprocessor similarly to the control unit 6 described above, and performs various processes in accordance with a processing program. When the control unit 14 receives the demodulated data from the modem 13, the control unit 14 performs calculation or the like every frame and compares it with the error rja output data and stores the data in the image information memory 16 in sequence. The frame number memory 17 stores the number of a frame in which an error is detected, and makes it possible to store at least four numbers. The decoding processing unit 18 expands the coded data taken out from the chemical information memory 16 in the same form as the output of the reading unit 4 and sends it to the recording unit 19.

The recording unit 19 prints on the recording paper based on the data from the decoding processing unit 18. The tone signal generator 15 outputs a tone signal of a predetermined frequency according to the instruction of the controller 14, and this signal is sent to the transmitter 1 via the line controller 12 and the communication line 3, and the tone It is detected by the signal detector 1.

The operation of the present invention by the above configuration will be described with reference to FIGS. 2 to 5.

When the message transmission (phase C) in the facsimile communication starts, the original reading unit 4 converts the digital signal to display black information by itself, and then is encoded by the encoding processing unit 5, It is accumulated in the image information memory 7 one by one.

The control unit 6 extracts the coded data of a predetermined length from the image information memory 7, adds error detection data by framing pattern, frame number, CRC operation, etc. to form one frame, and the modem and line control unit (in order of frame number). 10) perform transmission. It is assumed that the data of the frames 1-4 (block) are transferred in steps S1, S2, and S3.

The receiving unit 2 receives in the order of frames 1-4 after the delay time of the communication line 3 elapses. Here, for example, an error occurs during the transmission of frame 2, and frames 1, 3, and 4 are normally transmitted.

When the reception unit 2 receives the frame 1, the process proceeds to step S5, step S6, and step S8. However, when the frame 2 is received, an error is detected in step S6 when the frame 2 is received. The frame number " 2 " is stored in the frame number memory 17. The frame number " 2 "

Subsequently, when frames 3 and 4 are received, and a predetermined operation is performed on the frame number at step S8 to determine the end of one block, the process proceeds to step S9 and the contents of the frame number memory 17 are checked. In step S12, it is detected that there is an error frame in one block. In the above-described steps, the data of the frames 1-4 are stored in the image information memory 16, respectively.

Proceeding to step S12, the control unit 14 gives an instruction to the tone signal generating unit 15, and the transmitting unit 1 has already started transmitting the frame 5 (block 2) as shown in FIG. Doing. For example, it is assumed that a tone signal is received during transmission of frame 6. FIG.

When the tone signal detection unit 11 detects the tone signal, the tone signal detection unit 11 sends the detection signal to the control unit 5. The control part 6 sets the NG bit of the error memory 8 based on this detection signal, and stores that the tone signal was conveyed. When the transfer of frame 6 ends and the process proceeds from step S1 to step S2, it is determined whether or not the tone signal is conveyed depending on whether the NG bit of the error memory 8 is set. Since the tone signal has been conveyed, it is determined that there is an error in the frame in any of the preceding blocks, and the flow proceeds to step S4.

In step S4, the retransmission setting of the preceding block 1 is performed, and the NG bit is reset in the error memory 5. Then, the transmission of the block 2 is emphasized, and the retransmission of the block 1 is performed.

On the other hand, the receiver 2 reads only the frame number from among the frames continuously sent after carrying the tone signal, and determines whether or not the number is the same as the number stored in the frame number memory 17. It performs in step S13 and step S14. That is, it is detected that a signal arrives at the frame in which the error occurred in the preceding block.

As described above, the transmitter 1 transmits frames 5 and 6 after the block 1 is sent out until the transfer of the tone signal is detected, but at the previous step in steps S13 and S14, i. It is not determined as frame 2, and the data of these frames 5 and 6 are not accepted.

Subsequently, block 1 is retransmitted again, but proceeds from step S14 to step S16 only at the time of retransmission with frame 2. Then, the data of the retransmitted frame 2 is sequentially stored in the same place as the previous time of the image information memory 16, and the flow advances from step S16 to step S17. If there is no error in the retransmitted frame 2, the flow advances from step S17 to step S18.

The number " 2 " stored in the frame number memory 17 is erased and the flow returns to step S13. After the frame is checked, the retransmitted frame 3 returns to step S9 when the end of the retransmission block is determined based on the calculation result of the frame number in step S15.

If the error frame number "2" is deleted and the process proceeds from step S9 to step S10, the data of the block 1 stored in the image information memory 16 is sequentially sent to the decoding processing unit 18 to decode the decoding block. The data thus obtained is printed on the recording paper by the recording unit 19.

On the other hand, when there is an error in the retransmitted frame 2, since the erasure of the frame number "2" is not performed, when step S9 returns, it is determined that there is an error frame again, and the tone signal is conveyed again. Is carried out.

After the tone signal is conveyed, the same processing as described above is performed in the transmitting section 1 and the receiving section 2. When the retransmitted block 1 is received without a space, the transmitter 1 repeats step S1, step S2, and step S8 to perform block 2 transmission in frame number order.

If there is an error in each frame, the receiver 2 repeats step S5, step S6, and step S8 to receive the block 2, and from step S8 to step S9, through step S10. Proceed to and perform the block 2 argument.

Thereafter, the above-described steps are repeated to transmit and receive the remaining blocks, and when the end of the previous block is detected in steps S8 and S11 of the transmission and reception 1 and the reception unit 2, the processing proceeds to the next process. In addition, in the above-described embodiment, the case where only one transmission is used and the other is reception is described. However, the present invention is not limited thereto, and the present invention can also be applied to the case where both can be transmitted and received.

As described above, the present invention blocks and transmits a predetermined frame, performs error detection on the transmitted block for each frame, stores the frame number in which an error is detected, requests retransmission for each block, and responds to the retransmission request. Since the block is retransmitted and only the data of the frame in which the previous error is detected in the retransmitted block is valid and received, the allowable transmission delay becomes the transmission time required for one block, and the transmission delay is performed without much data per frame. This large line can be used, and since the data of the frame correctly received in the previous block is not received from the retransmitted block, the occurrence of an error due to retransmission can be reduced again.

Claims (1)

A predetermined number of frames are blocked and transmitted, an error is detected for each transmitted frame, a number of frames where an error is detected is stored, retransmission requests are executed for each block, and resends the preceding block in response to the retransmission request. And only the data of the frame in which the previous error was detected in the retransmitted block is valid and received.

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