JPH03165193A - Error re-transmission system for transmission or color still picture - Google Patents

Abstract

PURPOSE:To ensure the quality of data, to attain accurate correspondence of error and to attain smooth retransmission by detecting an error in the unit of block and using only a frame number in the block so as to apply error retransmission. CONSTITUTION:A video signal subjected to A/D conversion passes through a signal line 11 and is stored in a frame memory 12 and then the video signal passes through a signal line 13 and is inputted to a coding section 14, data compression is applied and the result is stored in a transmission buffer 16 of a fixed capacity through a signal line 15 and the result is used as a unit block. Then the compressed data inputted to a transmission control section 18 through a signal line 17 is divided into (n) and sent in HDLC(high level data link control procedure) respectively. Each frame consists of the data added with a frame number before the data. After the reception of one block at a receiver side, error check is applied in the unit of frame and when an error is detected, the frame number is informed to a sender side to apply retransmission request and the sender side resends only the error frame when the retransmission request is received from the receiver side. Thus, the retransmission time at error production is reduced and the picture data quality is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an error retransmission method when transmitting a color still image via a telephone line.

(Prior Art) Conventionally, there is an image transmission system as a system for exchanging still images such as photographs and drawings with a distant place using a telephone line. Connect your computer through a telephone line,
Examples include transmitting color still images stored in memory within one computer to another computer over its connected telephone line.

In the color still image transmission method used in the above-mentioned image transmission system, etc., one screen worth of image data is retransmitted when an error occurs. For this reason, there was a problem in that it required a long time to correct the error.

As a method to solve this problem, JP-A-1-138
As described in Publication No. 885, the transmitting side divides one screen worth of color still image data into multiple blocks with block numbers and error check codes and transmits them for all blocks over a telephone line, and then the receiving side A method in which an error check is performed for each block, a block number is sent for the block in which an error has occurred, a retransmission request is made, and only the blocks for which this retransmission request has been received are retransmitted on the transmitting side. Problem) However, in the above-mentioned conventional system, there is a problem that the retransmission speed cannot be sufficiently increased because error retransmission processing is performed after screen transmission/reception. Further, in the conventional method described above, only a CRC error is treated as an error, so there is a problem that sufficient image quality cannot be ensured.

SUMMARY OF THE INVENTION An object of the present invention is to provide an error retransmission method for color still image transmission that solves these conventional problems, reduces retransmission time when an error occurs, and improves image data quality.

(Means for Solving the Problems) In the error retransmission method for transmitting color still images of the present invention, in the error retransmission method for transmitting color still images, the transmitting side divides compressed image data for one screen into blocks. Then, the divided block is further divided into n frames, a frame number is added to each of the n frames, and transmitted using the HDLC procedure. After receiving one block, the receiving side performs an error check on a frame-by-frame basis. If an error is detected, the sender is notified of the frame number added to the error frame and requests retransmission, and if the sender receives a retransmission request from the receiver, it resends only the error frame. There are certain characteristics.

Furthermore, in the error retransmission method for transmitting color still images, if a predetermined number of retransmission requests are made for the same frame, the transmitting side retransmits the error frame at a lower transmission speed. be.

(Operation) In the present invention, the transmitting side divides compressed image data for one screen into blocks, further divides the divided blocks into n frames, and assigns a frame number to each of the n frames. 1 (transmitted by DLC procedure,
After receiving one block, the receiving side performs an error check on a frame-by-frame basis, and if an error is detected, it notifies the transmitting side of the frame number added to the error frame and requests retransmission. When a retransmission request is received, only the error frame is retransmitted. Furthermore, when retransmission requests for the same frame reach a predetermined number of times, the transmitting side retransmits the error frame at a lower transmission rate.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram of the configuration of the transmitting side of an image transmission system showing one embodiment of the present invention.

In Figure 1, 11.13.15.17 are signal lines, 1
2 is a frame memory, 14 is an encoding section, 16 is a transmission buffer, and 18 is a transmission control section.

The A/D converted video signal passes through a signal line 11 and is stored in a frame memory 12. Thereafter, the video signal passes through a signal line 13, is inputted to an encoding unit 14, where it is data compressed, passes through a signal line 15, and is stored in a fixed capacity transmission buffer 16, which becomes a unit block. Next, the compressed data inputted to the transmission control unit 18 through the signal line 17 is divided into n pieces and each piece is transmitted by HDLC: (high level data link control procedure). Each frame is constructed by adding a frame number in front of the data.

FIGS. 2 and 3 are processing flowcharts on the transmitting and receiving sides for explaining an error retransmission system showing an embodiment of the present invention. The operation of this embodiment will be described below according to the flows shown in FIGS. 2 and 3.

The transmitting side first transmits one block of compressed image data stored in the transmission buffer 16 using n HDLC frames (steps 21 and 22). As mentioned above, a frame number is added to each frame. After sending all frames, a response from the receiving side is awaited (steps 23 and 24). This response indicates the presence or absence of an error for each frame, and the error may be a CRC error, carrier disconnection, or the like. Details of the error notification method will be explained later in the reception process. If there are no errors in all frames in the block, check whether one screen has ended or not (step 29), if the next block exists, start transmitting the next block (step 30), and perform the processes from step 21 onwards. Do the same as above.

If there is an error in even one frame in the block (Step 25), add 1 to the number of errors, and if it is less than the specified number of times (Step 26), retransmit all error frames at the same speed.Step 28). Wait for a response from the side (step 23.24). If the number of errors has reached a predetermined number (step 26), the transmission speed of the modem is lowered (step 27), and the retransmission process is performed again.

The receiving side first receives one frame (steps 31 and 3).
2) Check for errors (step 33). As described above, this error is a CRC error, a carrier disconnection, or the like. If there is an error, the frame number of the error frame is stored (step 34). Next 1
Step 35: Check whether block reception is complete or not.
), if all the frames in the block have not been received, the process moves to step 31.32, where the next frame is received. After all frames have been received, the error frame number stored in step 34 is sent as a response (step 36). This method is shown in FIG. In Figure 4, the memory for the number of frames in the block is secured, the bit of the frame number where the error occurred (n bits in this case) is set to "1", the other bits are set to "0", and the error command is issued. and HDL
Transmitted using C frames.

After the processing in step 36, it is checked whether the response is an error response or a normal response (step 37), and if it is a normal response, it is determined whether one screen has ended (step 40). If it is not finished yet, reception of the next block is started and the process moves to steps 31 and 32. If an error response is sent, count the number of error occurrences (step 38), the specified number of times (K times).
If an error occurs, reduce the transmission speed (step 3).
9), the process moves to steps 31 and 32 for retransmission and reception.

The count and number of errors should be the same as on the sending side.

As described above, in this embodiment, one screen of compressed image data is divided into blocks, and after the blocks are transmitted and received, error retransmission is performed, so that retransmission speed can be increased. Furthermore, in this embodiment, carrier disconnection errors are detected in addition to CRC errors as errors, so that the quality of transmitted images can be improved.

Furthermore, in this embodiment, if an error occurs several times in a row, the transmission speed is lowered and retransmitted, which is advantageous in cases where the line quality is poor.

(Effects of the Invention) As explained above in detail, according to the present invention, errors are detected in block units and error retransmission is performed only using the frame number within the block, so the capacity of the sending and receiving buffer memory is also reduced. There is no need to hold one screen, and resending can be done smoothly.

Furthermore, since the transmission speed can be reduced depending on the line quality, data quality can be ensured, and since HDLC is used, errors can be handled accurately.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the transmitting side of an image transmission system showing an embodiment of the present invention, Fig. 2 is a processing flow diagram of the transmitting side in the embodiment of the present invention, and Fig. 3 is a receiving side diagram of the image transmission system in the embodiment of the present invention. FIG. 4 is a diagram showing an example of the configuration of an HDLC frame for error occurrence notification. 11, 13.15.17: Signal line, 12: Frame memory, 14: Encoding unit, 16: Transmission buffer,
18: Transmission control unit.

Claims (2)

[Claims] (1) In the error retransmission method for transmitting color still images, the sending side divides the compressed image data for one screen into blocks, further divides the divided blocks into n frames, and transmits the n frames. HDL by adding a frame number to each frame of
After receiving one block, the receiving side performs an error check on a frame-by-frame basis, and if an error is detected, it notifies the transmitting side of the frame number added to the error frame and requests retransmission. An error retransmission method characterized in that the transmitting side retransmits only the error frame when receiving a retransmission request from the receiving side. (2) When retransmission requests for the same frame reach a predetermined number of times, the transmitting side retransmits the error frame at a lower transmission rate.
Error retransmission method described.