JPS59198039A - Error control system of data transmitter utilizing telephone network - Google Patents

Abstract

PURPOSE:To attain efficiently error control by using a tone signal as a backward signal requesting retransmission in response to erroneous data. CONSTITUTION:A receiver (b) detects the presence of a signal at a carrier detector 14 through a hybrid circuit 9' and a demodulator 13, and checks erroneous data in the unit of blocks at an error code detector 15. Further, a sequence number error detector 16 checks data block which is not coincident with the order of received data. When there is any data error, a control section 18 actuates a tone generator 17 for a prescribed time and transmits a tone signal via the hybrid circuit 9'. A transmitter (a) detects the tone signal by a tone detector 10 through a hybrid circuit 9 and executes the retransmission of data by a control section 11.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an error control method for eliminating data errors caused by transmission errors by retransmission correction in digital facsimile communication using a telephone network.

Conventionally, when a transmission error occurs in facsimile communication using the telephone network, the receiver processes the error in the facsimile data and cannot reproduce the received image correctly. The method of pre-replacement line replacement is used. This method compensates for data errors, but does not faithfully reproduce transmitted data.

Automatic repeat correction (ARQ) has become popular as an error control method for eliminating errors in received data, and a typical example of this is the level data link control (HDLC) procedure. When HDLC is applied to a telephone network, it is generally necessary to use a half-duplex communication method because the two-wire subscriber telephone network occupies the main part of the telephone network. Additional time is required to obtain a response from the receiver indicating the presence or absence of data errors 9, and switching time is also required to switch the signal transmission direction, resulting in an extremely inefficient method.

Therefore, a method can be considered in which a two-wire line is frequency-divided to form transmission paths for forward transmission from the transmitter and reverse transmission from the receiver, and perform error control using a full-duplex system. This method is full-duplex, so for forward data,
It is possible to return responses in the opposite direction immediately, making it very efficient. However, the telephone network has a limited frequency band, and dividing the frequency band reduces the I@power direction band, which increases the forward data error rate and reduces transmission efficiency. There is a bottleneck in letting it happen.

The present invention has been made in view of the above-mentioned conventional iir kL@, and therefore, an object of the present invention is to use a tone signal as a backward (reverse direction) signal to request retransmission for erroneous 9 data. , it is an object of the present invention to provide a new error control force formula that can efficiently perform error control in a telephone network, eliminating the above-mentioned drawbacks.

In order to achieve the above object, the error control system according to the present invention is based on the error control system based on the ARQ system in the telephone network, in which a transmitter that transmits digital data divides the transmission data into blocks, and divides the transmission data into blocks. The receiving device includes a data generator including means for adding a sequence number in accordance with the transmission order and a code for error detection, and a tone signal detector indicating a request for error retransmission, and the receiving device includes an error code detector and a sequencer. A number anomaly detector, a tone signal generator that sends a tone signal to issue a retransmission request only for received data blocks that are determined to be errors, and a tone signal generator that monitors the reception interval of data blocks and checks whether a data block is received within that interval. Further, at the beginning of a communication control procedure for error control between the transmitting and receiving devices, the transmitting device receives a response signal transmitted from the receiving device in response to a command signal transmitted from its own device. The data block is configured to include a timer that counts the time required until reception is detected, and means that determines the sequence number of the data block to start retransmission based on the count result.

That is, in the present invention, a device that transmits data using a telephone network can execute an error control force equation based on the AI (Q method), and can reproduce error-free data on the receiving device side. The device divides the transmission data into pieces with a specified data block length or less, and adds a sequence number according to the transmission order using a sequence number addition machine J/S equipped for each block.Furthermore, a code generator for error detection is used. adds an error detection code to the data and sends it to the line.

In this process, a unique synchronization code or delimiter is generally inserted at the boundary of block division to indicate the boundary, and a cyclic redundancy check (CRC) code is used as an example of an error detection code. The modem sends a modulated signal to the

The receiving device uses each detector to check the sequence number and error detection code added to each block of data obtained by demodulating the data to check its validity. As a result, if a data block determined to be an error appears, the tone signal generator transmits a tone signal to the transmitter to request retransmission of the data block in which the error was detected.

When the tone detector detects this tone, the transmitter determines that a retransmission request is rare, and retransmits the data block. In the HDhC procedure, since the response signal for requesting retransmission includes the sequence number 1d of the data block to be retransmitted, the retransmitted data block is uniquely determined.

However, if a tone signal is used as a response signal, it is difficult to transmit such detailed 1D information.

To this end, the present invention includes means for counting the time required for the command signal transmitted by the transmitter to be returned from the receiver for I, t > each signal, and a data block that starts retransmission based on the counting results.・A turnaround time consisting of the round-trip transmission and reception time including propagation delay on the transmission path and the processing time required for transmission and reception in the receiving device, and a means for determining the tone number of the tone signal. Retransmission is started from the data block with the latest sequence number among the cheater blocks that have been transmitted before the alland time.

The effect of using a tone signal as a response signal in the opposite direction is
When tone signals can be transmitted in an extremely narrow band and full-duplex communication is performed by band division on a two-wire transmission line, the reduction in the forward direction band can be kept to a minimum.
It becomes possible to transmit a response signal for a retransmission request without substantially deteriorating the data transmission characteristics in the @power direction.

Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1(aL(b)) is a block diagram showing one embodiment of the present invention.

Referring to FIG. 1(a), Φ), (a) is a transmitting device,
(b) shows a receiving device, and the transmitting device shown in (a) generates original data to be transmitted in a data generation unit 1,
The data length is counted by a block length counter 2, and the block is divided by a block division circuit 3 so that the data length of the block is equal to or less than a predetermined length. A sequence number adding circuit 4 adds a sequence number corresponding to the transmission order to the polluted data block 20, and an error detection encoder 5 adds the data block 2 containing the sequence number.
An error detection code is added to check for errors in data in 0. A data generating section 6 is configured including these components, and a data block 20 is output. This output is stored in a buffer memory 7 for error control and transmitted to the line through a modulator 8 and a node 9 in sequence number order.

In the receiving apparatus, as shown in FIG. 12(b), the carrier detector 14 detects the presence or absence of a signal through the hybrid circuit 9' and the demodulator 13, and determines whether the demodulated data is erroneous or not. The ll code detector 15 checks data errors in block units. Furthermore, the sequence number abnormality detector 16 determines that the sequence number does not match the order of the received data among the cheater blocks that have passed the erroneous 9 chains in the error code detector 15 and are determined to have no errors. The cheater block is treated as an abnormal sequence number and is subject to a retransmission request. When the control unit 18 receives notification of a data error from the error code detector 15 and the sequence number abnormality detector 16, it immediately activates the tone generator 17 for a certain period of time and transmits data to the line via the hybrid circuit 9'. Send a tone signal.

The transmitting device @ detects this tone signal with a tone detector 10 via the hybrid 9, and notifies the controller 11 of the detected tone signal.

Knowing that retransmission requests are rare, the control unit 11 instructs the buffer memory 7 to start retransmission from a data block whose sequence number goes back a certain value. In this way, the retransmission of the erroneous 9 data is executed, and the receiving device discards the error data proc and accepts only the correct data, so that the data error can be corrected at the receiving device when the retransmission is executed. become.

FIG. 2 shows an example of a data block. In this embodiment, a block of data in the Hl)LC procedure is called a frame. The data block 20 is composed of a synchronization code 21 indicating a block boundary, a control code 22 including a sequence number, data 23 included in the transmission/1D information, and an error detection code 24.

FIG. 3 shows electric scum vectors of forward and reverse signals resulting from band division. A modulated wave by a high-speed data modem is transmitted in the forward direction, and a tone signal is transmitted in the reverse direction. - As an example, looking at CCITT Recommendation ■1 Recommendation A127 compliance, the electric scum vector 31
00 to 500) (The electric waste vector is extremely small at z. If the electric waste vector 32 of the tone signal is placed in the center of this band, it is easy to separate the two signals by band division, and the frequency division It becomes economically possible to realize band rejection filters and band extraction filters for this purpose.

On the other hand, if we consider the case where a 75 baud modem signal is used for the backward channel of Recommendation V127 as a response signal in the reverse direction, the electric charge vector 33 and the forward spectrum 31 will be close to each other, and the frequency will be separated. This makes separation difficult, requiring filters for separation to have steep characteristics in adjacent bands of the spectrum, making them extremely expensive.

Packed word modems allow the receiving device to send acknowledgment (ACK) signals for correctly received and negative acknowledgment (N&K) signals for errors, with the NAK signal containing the sequence number of the data block to be retransmitted. can be set.

Since it is difficult to insert a sequence number as an IfiNAK signal in response to a tone signal, the sequence number of a retransmitted data block can be determined by the method shown in FIG.

FIG. 4 is a diagram showing the sequence of signal exchange between the transmitting device and the receiving device. The transmitter measures the turnaround time Tt from transmitting the command signal 41 to receiving the response signal 42 at the beginning of communication using the timer 12 in FIG. 1(a). The transmission data block 43 is Do, D
x, l) a...0 and a sequence number are attached and transmitted. Now, if an error is detected in data block D2,
A negative acknowledgment tone signal 44 requesting retransmission is transmitted.

When the transmitting device detects this response signal, it retransmits the data block D2, which has a sequence number that is a certain value back from the data block currently being transmitted.If the data block length is L1, and the data transmission speed in the forward direction is S, then A sequence number that goes back a certain value can be defined as a sequence number older than L/8xT, which is efficient because wasteful retransmission of data blocks can be prevented. There is a large difference in the value of T between terrestrial lines and satellite lines.

Furthermore, when a cheater block that cannot be detected by the receiving device occurs, such as data blocks D5 and Do, the sequence abnormality is detected only at the time of data block l)y reception, so if a response signal is returned at this point, the above Retransmission control using calculation formulas makes it impossible to recover from errors. Therefore, with the help of the timer 19 in FIG. 1(b), it is determined that the next data block D6 to be received will not be reached when t has elapsed from the time when the data block D4 was received.
When the response signal 45 is returned, the validity of the retransmission control based on the above calculation formula can be guaranteed.

As explained above, the present invention includes a data generator 6 having a sequence number and an error 9 detection code for each block, an error code detector 15, a sequence number abnormality detector 16, a tone signal generator 17, and a tone detector. By configuring a system with 10 and 10, it has become possible to inexpensively and efficiently realize error control in full-duplex data transmission using frequency division in a telephone network.

The present invention has been described above with respect to one preferred embodiment thereof, but
It is merely an example, and the present invention is not limited to the embodiments described herein.
It goes without saying that it includes all modifications and changes within its scope.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) show an embodiment of the present invention as a transmitting device,
Block configuration diagram showing the main parts of the receiving device, Part 2
The figure shows the configuration of a data block to be transmitted. Figure 3 shows the electric wave vector and occupied frequency band of the signal transmitted in the forward direction and the reverse direction. Figure 4 shows the transmitting/receiving device that performs error control. This is a diagram showing the sequence of sending and receiving signals between the two. 1... Data generation unit, 2... Block length counter, 3
. . . block division circuit, 4 . . . sequence number addition circuit, 5 Φ error detection encoder, 6 .
9'...Hybrid circuit, 10...Tone detector, 11--Control unit, 12...Timer, 13-Fist demodulator, 14...Carrier detector, 15-Fist...Error 9 Code detector, 16...Sequence number abnormality detector, 17.
...Tone generator, 1800. control unit, 19. -, timer, 20--, -data block, 21-- synchronization signal indicating block boundary, 22-- control code including sequence number, 23-- fist data, 24-- error detection code, 31 ~゛33...Electric waste vector, 41 ''...
Command signal, 42-fist/response signal, 43...
Transmission data block, 44...Fist tone signal, 45.@
Dispute Response Signal Patent Applicant NEC Corporation Representative Patent Attorney Yutabe Kumagai Figure 3 Figure 4

Claims (1)

[Claims] In the error control system using the ARQ system in the telephone network, a transmitting device that transmits digital data divides the transmission data into blocks, adds a sequence number according to the transmission order to each block, and adds an error detection code to each block. and a tone signal detector indicating a request for error retransmission, and the receiving device includes an error code detector;
Sequence number abnormality detector, tone signal generator that sends a tone signal to request retransmission only for received data blocks that are determined to be errors, monitors the reception interval of data blocks and receives data blocks within that interval It is equipped with a timer for checking whether or not the transmitting/receiving device
At the beginning of the error control communication control procedure, the time required for the AU transmitting device to detect that it has received a response signal transmitted from the receiving device in response to the command AT signal transmitted from the own device. 1. An error control system for a data transmission device using a telephone network, comprising: a timer for counting; and means for determining a sequence number of a data block to start retransmission based on the counting result.