JP2792920B2 - Facsimile communication method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a facsimile communication system, and more particularly, to a facsimile communication system that uses an ECM system of facsimile communication to reduce a data error rate due to line noise.

(Prior Art) In recent years, facsimile communication systems have become more sophisticated with the advancement of facsimile machines.

For example, in ECM (Error Corre
ction Mode) is one of them.

The ECM method is an error correction method in facsimile communication defined by CCITT recommendation T30, which transmits coded image data in HDLC (High Level Data Link Control) frame format, and an error occurred on the receiving side during transmission. When it is detected that the data transmission has ended, the receiving side returns a negative acknowledgment (PP
R) A signal is sent to the transmitting side to request retransmission of the frame. Further, in the ECM system, it is possible to change the frame size between pages of a document being communicated, and this is performed by transmitting a PPS-EOM signal from the transmission side.

(Problems to be Solved by the Invention) However, in such a conventional facsimile communication system, the ECM system is not always effective for a data error caused by line noise or loss.

That is, there are stationary noise (white noise, etc.) and impulse noise that occurs suddenly. Although the influence of stationary noise can be reduced by the advance of modem technology, the impulse noise can be reduced. It is difficult to remove an object (impulse noise). In the case of a line with many impulse noises, the number of retransmissions increases even if the ECM method is used, and the data error rate cannot be reduced effectively.
There is also a method of lowering the transmission speed of the modem and retransmitting it, but this is not an effective method. When the ECM method is used, the effect of impulse noise differs depending on the size of a data frame to be transmitted. For example, when one impulse noise occurs in a 256 byte frame, EC
In the M system, this 25-byte frame is retransmitted, and not only is the retransmission time wasted, but if the frame is large, the communication time becomes longer and the probability of impulse noise mixing increases. Therefore, if the frame size is reduced (for example, changed from 256 bytes to 64 bytes), the influence of the impulse noise is reduced. It becomes possible to reduce. However, in the conventional ECM system, when there are a plurality of documents, the frame size can be changed only for each page, and the frame size cannot be changed in one document.

In the present invention, the number of data errors caused by the impulse noise is reduced by applying the data frame changing function in the ECM system to reduce the influence of the impulse noise in one document.

(Object of the Invention) Therefore, the present invention reduces the probability that a data error occurs again due to impulse noise or the like by changing the frame size of image information in which a data error has occurred using the ECM method. An object of the present invention is to provide a facsimile communication system with improved noise immunity to stationary noise.

According to the present invention, in order to achieve the above object, the transmitting side divides image information into a plurality of frames and transmits the frame, the receiving side stores the received image in the image memory, and the received image information has an error. In a facsimile communication system in which a frame number having error image information is notified and a retransmission is requested, and the transmitting side retransmits only the image information of the notified frame number, when the transmitting side receives a retransmission request notification, It is determined whether to change the frame size of the image information based on a predetermined determination criterion such as the number of frames of the requested image information or the number of receptions of the frame number, and when it is determined that the frame size is to be changed, a predetermined facsimile control signal is output. When the transmission information is transmitted after adding transmission information indicating a change in the frame size, the receiving side transmits the frame size to a predetermined facsimile control signal. The transmission side adds the transmission information indicating the change and transmits the frame number. At the time of retransmission after the frame size change, the transmitting side associates the frame number before the frame size change with the frame number after the frame size change, and After adding to the image information and transmitting, the receiving side changes the frame size,
The retransmission request is made based on the transmitted frame number.

 Hereinafter, a specific description will be given based on examples of the present invention.

 1 to 6 show an embodiment of the present invention.

FIG. 1 is a block diagram of a facsimile apparatus 1 applied to a facsimile communication system of the present invention. The facsimile apparatus 1 includes a network control unit 2, a model 3, a communication control unit 4, a system control unit 5, an encoding / decoding unit. 6, comparison memory unit 7, operation port 8, image memory 9, scanner 10, plotter 11,
Tonal signal generation circuit 12 and tonal signal detection circuit 13
Etc. are provided.

A line is connected to the network control unit 2, and the network control unit 2 connects and disconnects the line. When transmitting, the modem 3 modulates a transmission signal into a form suitable for transmission on a line, and demodulates a modulation signal sent from the line when receiving. The communication control unit 4 controls communication between a transmission signal and a reception signal. The system control unit 5 stores a basic program as the facsimile apparatus 1 and a ROM (Read) for storing a program for facsimile communication processing of the present invention.
Only Memory), and controls each unit of the facsimile machine 1 according to a program in the ROM to control the facsimile machine 1
As well as the facsimile communication process of the present invention. The encoding / decoding unit 6 compresses and reproduces image data according to a predetermined encoding method. The comparison memory unit 7 stores a determination value based on a predetermined determination criterion such as the number of retransmission-requested frames and the number of retransmissions of the retransmitted frame number, and the system control unit 5 changes the frame size based on the determination value. It is determined whether or not to perform.

The operation port 8 has ten keys, operation keys, and a display unit. When operated by an operator, a message for confirming the operation is displayed, and information is exchanged between the operator and the facsimile machine 1. The image memory 9 has a storage capacity capable of storing image information of a large number of pages (for example, about 60 pages).
It is divided into 6 bytes x 256 frames). Image memory 9
Accumulates image information in the block. As the scanner 10, for example, an image reading device using a CCD (Charge Coupled Device) is used, and the scanner 10 reads and outputs image information of an original line by line. As the plotter 11, for example, a thermal recording device using a thermal element is used, and the plotter 11 performs recording directly on thermal recording paper or indirectly via an ink sheet on ordinary recording paper.
The tonal signal generation circuit 12 outputs transmission information indicating a frame size change as a predetermined tonal signal under the control of the communication control unit 4, and the tonal signal detection circuit 13 indicates a frame size change received via the network control unit 2. A predetermined tonal signal is detected.

 Next, the operation will be described.

The present invention is characterized in that at the time of facsimile communication, the frame size of a frame in which a data error has occurred in one page is changed using the ECM method.

First, an error detection method for image information in the ECM method will be described.

FIG. 2 shows a control sequence when an error occurs in the image information frame on the receiving side, and an error occurs in each of the "1", "3", and "254" frames in 256 frames for one page. If an error has occurred, the transmitting side transmits a PPS signal (partial page end signal) and an EOP signal, and then the receiving side transmits a PPR signal (partial page request signal) to output frame numbers “1”, “3” where an error has occurred. "," 254 "is notified to the transmission side. Upon receiving the PPR signal, the transmitting side retransmits only the frame in which the error has occurred, and transmits the PPS signal and the EOP signal again. At this time, if no error has occurred on the receiving side,
The receiving side sends an MCF signal (message confirmation signal), and the sending side sends a DCN signal (line disconnection signal) to end the communication.

Image information for one page is HDLC (High Level Data Link Contr
ol) Each frame is transmitted after being decomposed into 256 frames in a frame configuration, and a frame number and error detection information (for example, a CRC signal) are added to each frame. This error detection information is based on the FCS bit (Frame Check Sequenc
When the CRC signal of the FCS bit is "0", it is determined that there is no error, and when it is "1", it is determined by the receiving side that there is an error. In the PPR frame, the FIF bit (facsimile information field) is composed of 256 bits, and each bit corresponds to the frame number of the image information. The frame number in which an error has occurred is set to "1" and transmitted to notify the transmitting side of the frame number to be retransmitted.
The above is the outline of the ECM method.

Next, communication processing when a data error occurs, which is a point of the present invention, will be described with reference to the control sequence shown in FIG. 3 and the flowcharts shown in FIGS.
In the facsimile communication system of this embodiment, it is assumed that the facsimile apparatus 1 shown in FIG. 1 is installed on both the transmitting side and the receiving side.

The control signal indicated by a solid line in FIG. 3 is transmitted at a transmission speed V21 (200 bps) according to the CCITT recommendation, and the training check signal TCF and the image information frame indicated by a broken line are transmitted by a high-speed modem (for example, 9600 bps). In FIG. 3, a transmitting facsimile apparatus (hereinafter referred to as a transmitting side) transmits a CNG signal (ringing tone), and a receiving facsimile apparatus (hereinafter referred to as a receiving side) returns a CED signal (called station identification signal). . Next, when the receiving side sends out the NSF signal (non-standard function identification signal) and the DIS signal (digital identification signal), the transmitting side sends the NSS signal (non-standard function setting signal) and the TCF signal.
A signal is transmitted, and upon completion of the training check, the receiving side returns a CFR signal (reception preparation confirmation signal). When the reception preparation is completed, the transmitting side transmits the image information in the HDLC frame configuration, and one page (256 bytes per frame is 256 bytes)
When the transmission is completed, a PPS signal and an EOP signal (procedure end signal) are transmitted. At this time, the receiving side checks the CRC signal of each frame of the image information, and determines that there is an error when the CRC signal is “1”. Here, the first frame and 100
Assuming that an error has occurred in frame No.
An R signal is used to notify the transmitting side of these frame numbers for retransmission requests.

Here, processing after the occurrence of an error frame on the transmitting side and the receiving side will be described with reference to the flowcharts shown in FIGS. 4 (a) and 4 (b).

Upon receiving the PPR signal (step P ₁ ), the transmitting side refers to the criterion value (the number of error frames, the number of retransmission requests for frame numbers, etc.) stored in the comparison memory unit 7 for determining a change in the frame size ( Step P ₂ ) It is determined whether or not to change the frame size (Step P ₃ ). If the number of error frames or the number of retransmission requests for a predetermined frame number is large and exceeds the determination reference value, the frame size is changed, and a predetermined tonal signal (for example, 2100 Hz) is sent out by the tonal signal generation circuit 12 and the frame size is changed. Is notified to the receiving side.

After transmitting the PPR signal (step P ₁₁ ), the receiving side checks whether or not the tonal signal has been transmitted by the tonal signal detection circuit 13 (step P ₁₂ ), and upon receiving the tonal signal, reduces the frame size. the recognized (step P _13), the tonal signal for confirmation is sent by the tonal signal generating circuit 12 (step P
₁₄ ). The reason why the notification of the confirmation of the change in the frame size is transmitted / received by the tonal signal is that simplification of the communication procedure and reduction of the communication time are taken into consideration. Therefore, it may be added to other facsimile control signals by bit information.

When the transmitting side receives the tonal signal (step P ₆ ),
If the frame size is reduced from, for example, 256 bytes to 64 bytes, the frame is divided into four frames of 64 bytes each, and the frame numbers are, for example, the first from 0 to 63 out of 256 bytes, the second from 64 to 127 out of 256 bytes, It is assumed that the 65th to 191st are assigned as 3rd, the 192nd to 255th are assigned as 4th, and so on. If the frame in which the error has occurred is No. 1 based on this new frame number assignment, it becomes (1-1, 1-2, 1-3, 1-4), and 100
In the case of the number, it is (100-1, 100-2, 100-3, 100-4). These new frame numbers are added to the FIF (facsimile information field) bits of the HDLC structure as shown in FIG. 5, and the structure of the FIF bits is newly added 8 bits as shown in FIG. To be transmitted.

The transmitting side transmits the image information reduced to 64 bytes in the HDLC configuration shown in FIGS. 5 and 6 (step P ₈ ), and the receiving side transmits the normal EC.
Receives this image information in the M system, determines whether there is an error with the newly set frame number, and responds (step
P ₁₅ ). Next, the transmitting side checks whether or not an MCF signal (message confirmation signal) has been transmitted from the receiving side to the transmitted image information (step P ₉ ). If no MCF signal has been received, the frame requested to be retransmitted is sent. It sends the image information of the number (step P _7, P ₈₎ to end the transmission process by running the retransmission until it receives an MCF signal.

Returning again to FIG. 3, after the transmitting side receives the tonal signal,
As described above, the frame size is reduced, and the error frame is retransmitted.
If an error occurs in the first frame, the receiving side will use PPR
These new frame numbers are signaled. The transmitting side retransmits according to the PPR signal, and upon receiving the MCF signal, transmits a DCN signal (disconnection command signal) to complete the transmission.

By reducing the frame size of the image information in one page as in the facsimile communication method, even when impulse noise is generated on the line, the probability that impulse noise is mixed in each frame is reduced. As a result, the rate of occurrence of data errors can be reduced. Therefore, it is possible to improve the noise resistance to non-stationary noise such as impulse noise.

(Effect) According to the present invention, the frame size of image information in which a data error has occurred is changed using the ECM method.
It is possible to reduce the probability of a data error re-occurring due to impulse noise or the like, and to improve noise resistance against non-stationary noise in facsimile communication.

[Brief description of the drawings]

1 to 6 are diagrams showing an embodiment of a facsimile communication system according to the present invention. FIG. 1 is a block diagram of a facsimile apparatus applied to the facsimile communication system, and FIG. 2 is a facsimile communication system. FIG. 3 is a control sequence diagram when the frame size is changed, FIGS. 4A and 4B are flowcharts showing a program for changing the frame size, FIG. The figure shows the HDLC frame structure of the image information, and FIG. 6 shows the FIF bit structure of FIG. DESCRIPTION OF SYMBOLS 1 ... Facsimile apparatus, 2 ... Network control part, 3 ... Modem, 4 ... Communication control part, 5 ... System control part, 6 ... Encoding / decoding part, 7 ... Comparison memory part, 8 ... ... Opport, 9 ... Image memory, 10 ... Scanner, 11 ... Plotter, 12 ... Tonal signal generation circuit, 13 ... Tonal signal detection circuit.

Claims (1)

(57) [Claims] 1. A transmitting side divides image information into a plurality of frames and transmits the frame. A receiving side stores a received image in an image memory, and when there is an error in the received image information, notifies a frame number having the erroneous image information. In a facsimile communication system in which the retransmission request is made and the transmitting side retransmits only the image information of the notified frame number, when the transmitting side receives the retransmission request notification, the number of frames or the frame number of the retransmitted image information It is determined whether or not to change the frame size of the image information based on a predetermined determination criterion such as the number of times of reception, and when it is determined that the frame size is to be changed, transmission information indicating a change in the frame size is added to a predetermined facsimile control signal. When the transmission information is transmitted, the receiving side transmits a predetermined facsimile control signal by adding transmission information indicating a change in frame size to a predetermined facsimile control signal, On the retransmission after the frame size change, the transmitting side associates the frame number before the frame size change with the frame number after the frame size change, adds these frame numbers to the image information, and transmits the image information. A facsimile communication method, wherein after the frame size is changed, the retransmission request is made based on the transmitted frame number.