JPH02193437A - Videotex system - Google Patents

Abstract

PURPOSE:To realize an automatic resending function and obtain an image having no quality deterioration without altering a center-side device at all by sending a request-to-respond signal automatically from a terminal according to a detection signal when an error is detected from a code for error detection in an image signal packet. CONSTITUTION:A modem 11 is switched by a changeover switch between a transmission line 21 and a telephone set side. Start image information is received after a changeover button is pressed. When a packet error is detected by error inspection, corresponding packet information is discarded, a request to resend the entire image is made automatically, and the image of a part consisting of a correct packet is displayed. Error inspection is performed as to a packet which is resent and when no error is found in the packet, the part of the image consisting of the packet is appended.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field to which the invention pertains) The present invention relates to a videotex system that allows a receiving terminal device to request retransmission from an image information transmitting section and improves the quality of both sides of reception.

(Prior Art) The Videotex system is a center-to-end information service in which image information is transmitted from an information center in response to a request signal from a receiving terminal device. If the quality of the image information received and displayed by the receiving terminal device is not good, a retransmission request is made so that a screen that satisfies the user can be obtained.

For example, in the Captain method, which is the standard method for Videotex in Japan, the transmission format of the downlink signal from the center regarding image information is as shown in Figure 4. flag F, 2 indicates the start of the packet, 3 indicates the packet containing image information data, and 4 indicates the CRC (Cyclic Red
5 is the flag F that represents both the end and start of the packet, 6 is the flag that represents the end of the packet, and 7 is the clear screen command (CS) that clears the screen on the display and returns it to the default state.
).

In this transmission format, as mentioned above, the clear screen command (CS) for clearing the screen display and returning it to the default state is placed at the beginning of the first packet of the image information signal. A 2-byte cyclic redundancy check code (CRC code) specified by CITT is added to the end of each packet up to the end to detect signal errors during transmission. When a data error occurs on the transmission path and the error is detected by the CRC code, it is stipulated that an error message marked "x" be displayed at the left end of the header section on the CRT display.

Even if an error is detected, Videotex does not use the information to improve the quality. Even if a data error occurs, the transmission characteristics of the 0-line are that the received screen is simply displayed in a degraded manner. If the received image quality is not good and the received image quality has deteriorated, the user can press the resend request button to transmit the image information again from the center after seeing the l x n display indicating that the image information is double-sided or captain. A method is adopted in which the message is repeated until it is received.

Figure 5 shows the reception operation flow using the captain method described above. When the captain center and the terminal are connected, the captain user presses the switch button to switch the captain terminal from the telephone (1). Receive start screen information from the center and perform error checking (2)
), the screen corresponding to the information is displayed regardless of whether there is an error or not (3). At this time, if there is an error, an "x" is also displayed. Next, enter the search phase, press the button to request the transmission of the required screen information (4), receive the information (5), perform an error check on the received information (6),
Double-sided display is performed regardless of whether there is an error (7). At this time, if there is an error, a re ×11 mark is added and displayed on the screen. Regarding retransmission request (8), the subscriber sees the ×” mark and resends the message. If there is no retransmission request, the subscriber proceeds to the first search flow (9), which is performed manually, and the same procedure is repeated thereafter.

Therefore, when trying to obtain a screen with good quality, the user has to judge the quality each time, or, like the captain mentioned above,
It was necessary to press the resend request button without overlooking the marked error message, which took time.

In general, error correction (FEC) and automatic repeat transmission (ARQ) methods are used to improve the reliability of data signals.
Such techniques are used. In these technologies, a processing circuit for adding codes for error correction or detection in the transmitter,
and a code processing circuit for error correction or detection in the receiving section, and error correction or retransmission processing is performed between them. Therefore.

Applying these technologies to large-scale Videotex systems, especially the current Captain system, requires major equipment modifications not only to the receiving terminal equipment, but also to the center-side transmitter, or the installation of new processing circuits, which are not already available. It is not easy to implement this method using the current method.

(Purpose of the Invention) The present invention does not require any modification or installation of new equipment on the image information center side, and can be performed by simply adding a circuit or performing software processing on the receiving terminal device. This is intended to improve the quality of received images by automatically retransmitting image information signals.

(Structure of the Invention) (Characteristics of the Invention and Differences from the Prior Art) In order to achieve the above object, the present invention provides an error detection code (for example, C in the case of a captain) in a receiving terminal device.
RC code), the data error signal (error detection ON signal) of the received signal is extracted, a retransmission request signal is generated based on it, and the signal is automatically sent to the information center as a signal from the terminal device. A retransmission request signal is automatically sent based on error detection using an error detection code, and when a retransmission request is automatically sent, the received information for one screen in which the error was detected is discarded and not displayed. A means for not displaying a screen with degraded quality until screen information is received, and a clear screen command that automatically sends a retransmission request signal based on error detection by an error detection code 1 If a manual screen request is made, a clear screen command is provided. However, if a retransmission request signal is automatically sent, it will ignore the clear screen command in the subsequent image information signal, and at the same time display the screen based on the information packet that was received correctly, The receiving terminal device has a means for displaying only the screen of packets that have been correctly received by retransmission without displaying the screen of the packets that have been received, and it is possible to shorten the time required until all the image information is correctly received. Main characteristics.

The conventional technology significantly shortens the time required for image information to be transmitted from the center until a good screen is received, and the receiving terminal can be easily accessed without major modification of the transmitter at the center or installation of a new processing circuit. The difference is that the received image quality of the device is improved.

(Example) Fig. 1 shows a configuration diagram of an embodiment of a receiving terminal device implemented in the method of the present invention, in which 11 is a modem, and a transmission line 21 can be switched to the telephone side by a changeover switch (not shown). . 12 is an interface of the modem 11, 13 is a keypad, and a signal emitted from the keypad is received by a remote control light receiving section 14. 15 is a memory with a built-in program; 16 is a CPU that controls the entire receiving terminal; 17
18 is a display control circuit for the television receiver (TV) 22, and 18 is an external output interface, which is connected to, for example, a hard copy device, a melody data generator, etc. 23. 19 is a D/A converter that converts the digital output of the display control circuit 17 into an analog output; 20 is a horizontal/vertical timing generation circuit for the receiver 21; each of the blocks 12, 14.
15, 17 and 18 are connected to the CPU 16 via a data bus 24.

Next, the operation sequence of the method of the present invention using the above receiving terminal device will be explained with reference to the operation flowcharts of FIGS. 2 and 3.

Figure 2 shows that when a signal is detected and displayed on the receiver 22 using an error detection code, a retransmission request signal is sent to the transmission line 22 based on the detected signal.
Automatically sent to the center via 1.

This is a case where all image information for one screen in which an error has been detected is discarded.

First, after connecting to the Captain communication network, the subscriber presses a switch button from the telephone side to the Captain terminal (1). After receiving the start screen information, an error check is performed (2). If there is no error, the screen is displayed (3). If there is an error, discard the screen information. 4) Request automatic retransmission of the screen (5),
The subscriber requests inspection after receiving a correct screen, which automatically repeats the retransmission mode until an error-free screen is received (
6) Receive primary double-sided information.

Next, an error check is performed and if there is no error (7), a screen display is performed (8). If there is an error, the extra screen information is discarded as described above (9), an automatic retransmission request is made (10), the retransmission request is repeated until a screen without errors is received, and the screen information without errors is displayed on the receiver screen. (11). Next, if there is another search request, request information is transmitted (12), and the next screen information is received.

When the search is completed, go to the end flow.

In FIG. 3, packets in which errors are detected are discarded.

This is a case where the clear screen command of the retransmitted image information signal is ignored and, at the same time, the screen is displayed based on the correctly received information packet.

First, after pressing the switch button (1), the receiver receives the start screen information (2), and if a packet error is found through error checking (3), the packet information is discarded and a retransmission request for the entire screen is automatically made. In addition to (4), display the part made up of the correct packet on the screen (5), check for errors in the packet sent by retransmission, and if there is no error in the packet, the part made up of that packet is displayed. Add part of the screen. At this time, the clearance command will be ignored.

Next, the search begins (6). After receiving the first double-sided information in the same way as above (7), the screen automatically displays only the correct packet part (8). The error in that part is eliminated by retransmission. In this case, the clearance command is ignored and the screen is added.

Next, if there is another search request, the search request is made manually and the same process as described above is repeated. When the search is completed, the process enters the end flow.

As described above, in the method of the present invention, when the Videotex information center receives a duplex request signal from a user, it transmits the image information of the requested screen number to the receiving terminal device. In the Captain described above, when the screen request signal is received, the Videotex communication processing device! Image information stored in the information processing device (CAPF) of the information center is retrieved according to instructions from the VCP, stored in the vCP, and then transmitted to the subscriber terminal (receiving terminal device). If the user thinks that there is no problem with the received image displayed on the subscriber terminal, he/she requests a new screen according to the captain's guidance on the M4 floor structure until he/she obtains the desired information. However, if the quality of the received screen deteriorates due to a data error during transmission, the user can press the resend button and continue requesting retransmission until the correct screen is received.

vC when a retransmission request signal is sent from the subscriber terminal.
The same image information stored in P is sent out again.

(Effects of the Invention) As explained above, according to the method of the present invention, when an error is detected by the error detection code in both signal packets, a retransmission request signal is automatically transmitted from the terminal based on the detection signal. Therefore, the automatic retransmission function can be realized by making slight circuit modifications to the receiving terminal device without making any changes to the center side device, and a screen without quality deterioration can be obtained.

In addition, even if there is an error in the received image information and an error is detected by the error detection code in the receiving terminal device, the terminal interprets the control signal or screen information signal of the received data to the extent possible and transfers the image information to the CRT. It is displayed on the display. Therefore, if data is received incorrectly, a very difficult to read screen will be displayed. However, in the method of the present invention, incorrect image information data is discarded and not displayed, and is displayed only when correct image information is received, so that the screen that is difficult to see does not come into contact with the user's eyes, and the correct image information is displayed. This allows the user to see only the user's information, providing a comfortable environment for the user.

Furthermore, the data for one image has a length of several hundred to several kilobytes, and since this is packetized, the double-sided information for one image is made up of a very large number of packets. If the transmission path characteristics are not too bad and the frequency of data errors is low, even with the above method, the probability of receiving both sides correctly is high.However, if the transmission path characteristics are poor, long image information data may be completely erroneous. The probability that the message will be received without any error is small, and with the method described above, it will take a long time until the target screen is displayed. However, since the probability that the same packet will be erroneous in successive retransmission requests from the beginning of a double-sided request is extremely low, we decided to keep the correctly received data packets alive and discard only the incorrectly received data packets. The time required for the screen to be completely received can be shortened, and the usage environment can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of a receiving terminal device implemented in the method of the present invention, FIGS. 2 and 3 are flowcharts explaining the operation sequence of the method of the present invention, and FIG. 4 is a diagram of a conventional captain method. FIG. 5 is a diagram showing a transmission format, and is a diagram showing a reception operation flow of a conventional captain. 11...Modem, 12...Modem interface,
13...Keypad, 14...Remote control light reception m, 15...Memory, 16...CPU, 17...
Display control circuit, 18...external output interface, 1
9... Digital-to-analog converter, 20... Horizontal/vertical timing generation circuit, 21... Transmission line, 22...
- TV receiver, 23...hard copy device, melody data generator, 24...data bus. Patent applicant: Nippon Telegraph and Telephone Corporation

Claims (1)

[Claims] Image information signals are transmitted in multiple packets, and the first packet contains a clear screen command for clearing the screen being displayed, and the tail of each packet contains a code for detecting signal errors during transmission. In the videotex system, the image information signal is transmitted from the image information transmitter to the image information transmitter in the Videotex system, which allows the receiver terminal to request the image information transmitter to retransmit the screen currently being displayed on the receiver terminal. When a signal is detected by a certain error detection code, means for automatically sending a retransmission request signal based on the signal, means for discarding all image information for one screen where an error is detected, A videotex system characterized in that the receiving terminal device includes means for discarding the detected packet and ignoring the clear screen command of the retransmitted image information signal.