JP2904350B2 - Facsimile machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] In the present invention, image data is divided into a plurality of data frames and transmitted, and a data error is generated from a receiving facsimile apparatus that has received the image information. The present invention relates to a facsimile apparatus having a function of, when a data frame is designated, retransmitting the designated data frame while downshifting a data transmission rate under a predetermined condition.

[Prior Art] Generally, telephone lines are used for facsimile communication. In the case of long-distance communication such as communication with foreign countries, the state of the telephone line tends to fluctuate under the influence of noise and the like. If the facsimile communication is executed in such a line state that is liable to fluctuate, transmission errors of image information frequently occur, and it becomes impossible to reproduce an accurate image on the receiving side.

By the way, in a normal facsimile apparatus such as the G3 standard, at the time of starting communication, a line state is checked by modem training, and a data transmission speed when transmitting image information is determined according to the line state. Has become.

In recent years, the CCITT has additionally recommended a transmission control procedure called an error correction mode (hereinafter, abbreviated as ECM) in the form of a supplement (Annex A) to Recommendation T.30 in which facsimile apparatuses conforming to the G3 standard are compliant. I have.

When performing facsimile communication using this ECM, image information is transmitted in block units composed of a plurality of data frames, and if an error occurs in the transmitted image information, the data frame in error is retransmitted while retransmission is performed. When the number of times exceeds a certain number, the data transmission speed is shifted down and image information is transmitted.

In this case, it is assumed that the line state is good immediately after the start of communication, and the line state is extremely deteriorated after the start of image information transmission. In this case, the data transmission rate is initially
For example, image information is transmitted at 9600 bps.

However, after this, transmission errors frequently occur due to deterioration of the line condition, and the retransmission process is repeated a certain number of times. If transmission is not performed correctly in this retransmission, the data transmission speed is shifted down to 7200 bps, and the retransmission process is similarly repeated a certain number of times. In addition, if transmission is not performed correctly by this retransmission, the next worst case is 4800 bps.
It will be shifted down to 0 bps.

As described above, in the conventional ECM, if the line condition deteriorates after the transmission of the image information, the data transmission speed is shifted down by one step, so it takes time until the retransmission process of the image information succeeds. There was a problem that the communication time was long.

In the above-mentioned ECM, the image information after encoding and compression is divided into 256 bytes (octet; 1 byte (= 1 octet) = 8 bits) or a frame size of 64 bytes from the beginning, and the image for one frame is divided. As shown in FIG. 7 (a), the information is transmitted in a state where it is shaped into a frame FLM in the format of HDLC (High Level Data Link Control) procedure.

Here, this frame FLM is composed of a (head) flag sequence F composed of a predetermined pit pattern, an address field A composed of a predetermined bit pattern (global address), a control field C composed of a bit pattern unique to the facsimile apparatus, and an information field. I, a frame check sequence FCS for error detection, and a (tail) flag F are sequentially arranged.

The information field I includes a facsimile control field FCF in which a facsimile transmission procedure signal is arranged, and a facsimile information field FIF in which various types of information added to the facsimile transmission procedure signal are arranged.

In this case, the facsimile control field FCF contains the facsimile coded data FC of the facsimile transmission procedure signal.
D is arranged, and in the facsimile information field FIF, a frame number FNo indicating a frame order and encoded frame data FDc of one frame size FSZ are arranged.

Further, since the frame number FNo is composed of an 8-bit binary number, only a serial number from 0 to 255 can be taken. Therefore, 256 consecutive frames are set as one block, and a retransmission request is made from the receiving side in block units. Like that. If the image information for one page cannot be transmitted in one block, the remaining part is set in the next block and transmitted.

At the time of a retransmission request, the receiving side responds to the transmitting side a frame of a facsimile transmission procedure signal PPR (partial page request signal) as shown in FIG. In addition, the facsimile transmission procedure signal contains the necessary parameters,
It is exchanged in the same frame format as this partial page request signal PPR, but in the following description, for example,
Described as a PPR signal.

This PPR signal is transmitted to the facsimile control field FCF.
In addition, a bit pattern (PP
R) is located and also facsimile information field FIF
Is arranged with 256-bit error map data EMp.

The error map data EMp contains data “0” for a frame in which a transmission error has not occurred and data “1” for a frame in which a transmission error has occurred among the transmitted frame data of one block. Are arranged in frame order.

Upon receiving the PPR signal, the transmission side transmits again only the frame data of the frame in which the data “1” is set in the error map data EMp to the reception side.

By repeatedly performing this retransmission request until transmission errors of all the frames are eliminated, it is possible to record and output a received image without losing on the receiving side.

[Problems to be Solved by the Invention] As described above, in the conventional ECM, if the line state deteriorates after the start of the transmission of the image information, the communication time increases, and the ECM is appropriately set and effective. There was a problem that it was not used.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a facsimile apparatus capable of solving the above-mentioned problems and shortening the communication time while effectively using the ECM.

Means for Solving the Problems According to the present invention, image information is divided into a plurality of data frames and transmitted, and the data frame in which a data error has occurred is specified from a receiving facsimile apparatus that has received the image information. Then, in a facsimile apparatus having a function of shifting down the data transmission rate under predetermined conditions while retransmitting the designated data frame, the number of data frames of the transmitted image information and A calculating means for calculating an error frame rate based on the number of data frames specified from, and, when retransmitting the error frame, shifting a data transmission rate according to a calculation result of the calculating means and the number of retransmissions Data transmission control means for selectively controlling either down or maintaining the same data transmission speed is provided. Further, the data transmission control means, according to the error frame rate,
The data transmission speed is shifted down by one or more steps. Further, when the number of data frame retransmissions reaches a predetermined value, the data transmission control means changes the mode of determining the data transmission speed at the time of retransmitting the data frame based on the data error frame rate.

[Operation] Therefore, by determining the data transfer rate to be set based on the total number of transmitted frames and the number of frames in which a data error has occurred, an appropriate data transmission rate is set according to the line state. Retransmission is not repeated unnecessarily, and the communication time is shortened.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a facsimile apparatus according to one embodiment of the present invention.

In FIG. 1, a CPU (central processing unit) 1 is for performing control processing of the entire facsimile apparatus and facsimile transmission control procedure processing, and its control program is stored in a ROM (read only memory) 2. The work area and the transmission buffer are stored in a RAM (random access memory) 3. The transmission buffer has a storage capacity of at least 64 Kbytes (K = 1024) so that one block of a 256-byte frame can be stored.

The scanner 4 is for reading a transmission original at a predetermined resolution, and the plotter 5 is for storing and outputting a received image at a predetermined resolution. The operation display unit 6 is for operating the facsimile machine.

The encoding / decoding unit 8 encodes and compresses the transmission image signal and decodes the received image information into the original image signal. The modem 8 uses a public telephone line network or the like which is an analog line network as a transmission line. It modulates and demodulates digital data so that it can be used, and the controller 9 is for connecting the facsimile machine to the public telephone network. The network control device 9 has an automatic transmission / reception function.

Further, the central processing unit 1, the ROM 2, the RAM 3, the scanner 4, the blotter 6, the operation display unit 6, the parameter memory 7, the encoding / decoding unit 7, the modem 8, and the network control device 9 are interconnected via the system bus 10. Is exchanging data.

Next, the transmission operation of the facsimile apparatus of this embodiment having the above configuration will be described.

In this case, as shown in FIGS. 2 (a) and 2 (b),
First, the operator sets a document to be transmitted on the scanner 4 and performs a predetermined transmission operation such as inputting a destination on the operation display unit 6 (process 21). As a result, when the network control device 9 performs a calling operation (process 22) and the receiving facsimile device receives a call, a transmission control procedure is started as shown in FIG.
First, a CED signal and a DIS signal are transmitted from the receiving side (process 23).

The transmitting side transmits the DCS signal, the modem training signal, and the TCF signal in response thereto (process 24). In the DCS signal transmitted here, the highest data transmission rate of 9600 bps is specified.

The receiving side checks the constant data transmitted by the TCF signal to determine the line state, and transmits a CFR signal when the data error rate is equal to or less than a certain value.

When the transmitting side receives the CFR signal (Y in process 25), the scanner 4 is activated to read the transmitted document (process 26). The read image information is transmitted to the encoding / decoding unit 7.
Is encoded by The encoded image information is set in the FIF of the data frame in the HDLC procedure, for example, in 256-byte units. Further, this data frame has a maximum of 256 frames as one block.

Therefore, if one frame has 256 bytes, one block has a maximum of 64 Kbytes. The image information for one block is temporarily stored in the RAM 3, and the total number N of the frames is stored in the RAM 3 (process 27).

The one block corresponds to the 960 designated as the image information PIX.
The data is continuously transmitted at a time at a data transmission rate of 0 bps (process 28).

Assuming that the transmitted original is one page and the image information is 64 Kbytes or less, the PPS / EOP signal is transmitted after all the image information is transmitted at once (process 29).

The receiving side receives the transmitted image information, checks for a data error, and if there is no error, transmits an MCF signal.

When the transmitting side receives the MCF signal here (Y in process 30), it transmits a DCN signal to restore the line (process 3).
1).

Next, a case where the line condition is initially good and deteriorates during the transmission of the image information PIX will be described. In this case, as shown in FIG. 4, the first image information is transmitted in the same manner as described above.
It runs at a data transmission rate of 00 bps, followed by PPS / EOP
A signal is transmitted.

Here, if a data error occurs in the transmitted image information due to the deterioration of the line condition, the receiving side detects the data error and determines which frame of the image information of one block having a maximum of 256 frames has an error. Remember. Then, after receiving the PPS / BOP signal, a PPR signal is transmitted, and this signal notifies the transmitting side of the frame position where the data error has occurred.

When the transmitting side receives the PPR signal here (N in FIG. 2, process 30), it checks the number of past retransmissions (process 3).
2). Since this is the first retransmission (N in process 32), P
The image information corresponding to the frame position indicated by the PR signal is
Read from M3. Then, retransmission is performed with a predetermined data frame (process 33). In the PPR signal, a plurality of frames can be designated, and the image information of each designated frame is sequentially transmitted. When the image information ends, a PPS / EOP signal is transmitted (to process 29).

Thereafter, the above processing is repeated, and if the data is not correctly received on the receiving side, the position of the frame in which the data error has occurred is notified again by the PPR signal. In this case, the corresponding data frame is similarly retransmitted.

When the number of times of retransmission of the image information becomes three (Y in process 32), the number n of frames notified as a data error by the PPR signal is determined (process 34). Next, the set data transmission rate is determined. Now, since it is 9600 bps (from processing N to processing 36 and processing 36 Y),
The ratio of the number n of frames with data errors to the total number N of frames transmitted first, that is, the error rate
n / N is calculated and compared with a predetermined constant value a (process 37).

The error rate n / N becomes larger as the line condition becomes worse. The constant value a is set to the value of the error rate n / N when the line state is extremely windowed and the data transmission speed is to be set to 2400 bps.

Therefore, when the error rate n / N is equal to or more than the fixed value a (Y in step 37), the transmitting side thereafter sets the data transmission rate to 2400.
Control the modem 8 etc. to make the bps (processing 3
8). Next, as shown in FIG. 4, a CTC signal is transmitted to the receiving side to notify that the data transmission speed should be shifted down to 2400 bps (process 39).

The receiving side receives the CTC signal and
Set the internal state to the data transmission rate of ps and send the CTR signal.

After confirming the CTR signal (processing 40), the transmitting side
Retransmit the image information of the frame specified by the signal (Process 4
1) Subsequently, a predetermined PPS / EOP signal is transmitted (process 29).

In this case, since the data transmission speed is the lowest, it is possible to transmit correctly even if the line condition is quite poor. Therefore, the receiving side receives the image information without any data error and returns the MCF signal (Y in process 30).

Here, the transmitting side transmits the DCN signal and disconnects the line (process 31).

As a result, the line condition is initially good and the image information PI
Even in the case of extreme deterioration during X transmission, as shown in FIG. 4, the image information can be correctly transmitted by performing only one downshift of the data transmission speed.

On the other hand, when the value of the error rate n / N is less than the constant value a in the processing 37 (N in the processing 37), the value of the error rate n / N and the preset constant value b are then determined. A comparison is made (operation 42). Here, if the value of the error rate n / N is equal to or greater than the fixed value b (Y in process 42), the data transmission speed is 4800 bps.
On the other hand, when the value of the error rate n / N is less than the constant value b (Y in step 42), the error rate is set to 7200 bps (step 44).

The value of the constant value b is a value for setting the data transmission speed according to the line state, similarly to the above a.

Thereafter, the image information is retransmitted at the set data transmission rate in the same manner as described above.

In the above example, the initial data transmission rate is 9600
As described in the case of setting to bps, when the transmitting side transmits a DCS signal, a modem training signal, and a TCF signal (processing 24), the receiving side transmits an FTT signal when detecting a data error of a certain value or more. I do.

Upon receiving the FTT signal (N in process 25), the transmitting side shifts down the data transmission speed by one step (process 45), and again
Transmit DCS signal, modem training signal and TCF signal. After this, when the FTT signal is received again,
Similarly, the data transmission speed is shifted down.

Then, the transmission of the image information is executed at the data transmission speed when the CFR signal is received.

As described above, when image information is transmitted at a data transmission rate other than 9600 bps and the number of retransmissions is three or more (Y in process 32), after the number of error frames n is determined (process 3
4) If the data transmission speed at that time is, for example, 2400 bps (Y in process 35), the process cannot be shifted down any further, so the process 31 is entered next and transmission is stopped.

At 4800 bps (the processing 36 from the processing 35 N, the processing 46 from the processing 36 N, and the processing 46 Y), it is set to 2400 bps (to the processing 38).

At 7200 bps (the processing 36 from the processing 35 N, the processing 46 from the processing 36 N, and the processing 46 N), the error rate n / N
Is compared with the constant value c (process 47). Here, when the value of the error rate n / N is equal to or greater than the fixed value c (Y in processing 47), the error rate is set to 2400 bps (to processing 38), and the error rate n / N is set.
Is less than the fixed value c (N of processing 47), 4800bp
Set to s (process 43).

Thus, each data transmission rate initially set is:
In response to the deterioration of the line condition at that time, the transmission is shifted down and retransmission processing is executed.

As described above, according to the present embodiment, if the transmitting side retransmits the image information of a predetermined frame a certain number of times and fails to correctly transmit the image information to the receiving side, the transmitting side returns the total of one block transmitted first. The number of frames N and the number n of frames for which retransmission is specified by the PPR signal from the receiving side are determined, and the error rate is determined.
In accordance with n / N, the data transmission speed to be set next by downshifting is determined.

Thus, in the next retransmission, image information can be transmitted at an appropriate data transmission rate according to the line state. Therefore, if the line condition deteriorates during image information transmission, the retransmission that causes a data error will not be repeated indiscriminately as in the related art, and the communication time will be shortened.

By the way, in the above-described embodiment, the error rate is lent as a ratio n / N of the number n of retransmitted frames to the total number N of frames in one block. Next, another method of calculating the error rate will be described.

Now, assume that a transmission procedure as shown in FIG. 5 is executed. That is, the transmitting side transmits the image information of the first block of the frame number a, receives a retransmission request for the frame number b from the receiving side, retransmits the request, and the transmission is successful. . Next, the image information of the second block of the number of frames c is transmitted, and the number of frames d therein is retransmitted, and the transmission is successful. Next, the image information of the third block of the number of frames e is transmitted, and thereafter, the retransmission of the number of frames f results in an error in the number of frames g, and the retransmission is performed. Further, the number of frames h out of the number of frames g results in an error. At this point, the transmitting side transmits a CTC signal to execute the downshift of the data transmission speed.

The following equations (I), (II), (III), and (IV) show various methods for calculating the error rate.

(Number of retransmission frames) / (number of transmission frames) = (b + d +
f + g + h) / (a + b + c + d + e + f + g) (number of retransmission frames per page) / (number of transmission frames per page) = (b + d) / (a + c) (number of error blocks) / (number of transmission blocks) = (3/3)
(III) (Number of error pages) / (Number of transmitted pages) = (2/2) (I
V) Equation (I) determines the error rate as a ratio of the number of retransmitted frames to the number of transmitted frames. In the above example,
The number of frames (b + d + f + g + h) is changed to the number of frames (a +
b + c + d + e + f + g). Formula (II)
Is calculated as the ratio of the number of retransmission frames to the number of transmission frames per page. In the above example, the number of frames is calculated by dividing the number of frames (b + d) by the number of frames (a + c).

Equation (III) is obtained as a ratio of the number of blocks having an error to the number of transmitted blocks. In the above example, the error rate is (3/3). Expression (IV) is obtained as a ratio of the number of pages having an error to the number of transmitted pages. In the above example, the EF rate is (2/2).

In addition, when determining an error block or an error page in the formulas (III) and (IVd), when the number of error frames exceeds a certain rate with respect to the total number of frames of the block or page, the block or the error page is determined. It is conceivable that the page is determined to be an error. Further, each time a preset number of frames is transmitted, the number of frames in which an error has occurred may be identified and calculated based on the ratio. Further, each time a predetermined area of the transmission document is transmitted, the ratio can be calculated from the ratio of the total number of transmitted frames to the number of frames in which an error has occurred.

On the other hand, it is assumed that communication is started at 9600 bps and the error rate is calculated as described above. When shifting down the data transmission rate based on the calculated error rate, for example, as shown in FIG. 6, 7200 bps when the error rate is 25% or less, and 4800b when the error rate is more than 25% and 75% or less.
When the value exceeds ps and 75%, the data transmission speed is determined by setting a threshold value, such as 2400 bps.

In this case, the threshold value may be determined by determining the line state from the error rate at 9600 bps, and determining the data transmission speed at which a data error can be avoided by experiments or the like.

In the embodiment described with reference to FIGS. 1 to 4, in the case of a data error, the retransmission processing is performed three times at the data transmission rate, but it is obvious that the number of times can be set arbitrarily. Also, in the case of the flowchart shown in the figure, if the initial data transmission speed is, for example, 9600 bps and the line condition gradually deteriorates, the data transmission speed shifts down three times from 7200 bps to 2400 bps. For example, the transmission process may be interrupted when the downshift is performed for the second time.

One frame of image information is 256 bytes, but C
Needless to say, 64 bytes can be used as recommended by CITT.

[Effects of the Invention] As described above, according to the present invention, image information is divided into a plurality of data frames and transmitted, and a data error is received from the receiving facsimile apparatus receiving the image information. When the data frame is designated, the designated data frame is retransmitted, while the facsimile apparatus having the function of shifting down the data transmission speed under a predetermined condition has the number of transmitted image information data frames. Calculating means for calculating an error frame rate based on the number of data frames specified by the receiving side; and, when retransmitting the error frame, the calculation result of the calculating means, and the number of data retransmissions. Data transmission control means for selectively controlling the transmission speed to either downshifting or maintaining the same data transmission speed. Thus, the data retransmission mode and the data transmission rate according to the line state are set, and as a result, the retransmission is not repeated unnecessarily, and the communication time is shortened.

[Brief description of the drawings]

FIG. 1 is a block diagram of a facsimile apparatus according to an embodiment of the present invention, FIGS. 2 (a) and 2 (b) are flowcharts showing transmission processing of the facsimile apparatus, and FIG. 3 is transmission in normal transmission processing. FIG. 4 is a time chart showing a transmission control procedure when retransmission is performed, and FIG. 5 is a time chart showing an example of a transmission control procedure for explaining another method of calculating an error rate. FIG. 6 is an explanatory view showing an example of a method of setting a transmission speed for shifting down, and FIG. 7 (a) shows a frame format when transmitting framed image information in an error correction mode according to the prior art. FIG. 6B is an explanatory diagram showing an example of a signal indicating a retransmission request. 1 ... CPU, 2 ... ROM, 3 ... RAM, 4 ... Scanner,
5: Plotter, 6: Operation display unit, 7: Encoding / decoding unit, 8: Modem, 9: Network controller, 10: System bus, 11: Parameter memory.

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 1/32-1/34 H04L 1/00 H04L 1/08-1/24

Claims (3)

(57) [Claims] An image information is divided into a plurality of data frames and transmitted, and when the data frame in which a data error has occurred is specified from a receiving facsimile apparatus which has received the image information, the specified data is transmitted. In a facsimile apparatus having a function of shifting down the data transmission rate under a predetermined condition while retransmitting the frame, the number of data frames of the transmitted image information and the number of data frames specified by the receiving side are determined. Calculating means for calculating the error frame rate based on the number and the number of retransmissions, when retransmitting the error frame, the data transmission speed is shifted down or the same data transmission speed is maintained according to the calculation result of the calculating means and the number of retransmissions. A facsimile apparatus comprising a data transmission control means for selectively controlling any one of them. 2. The facsimile apparatus according to claim 1, wherein said data transmission control means shifts down a data transmission speed by one step or a plurality of steps according to said error frame rate. 3. The data transmission control means, when the number of data frame retransmissions reaches a predetermined value, changes a data transmission rate determination mode based on the data error frame rate when retransmitting data frames. Claim 1
Or a facsimile apparatus according to claim 2.