JPH01292964A - Picture-writing transmission system - Google Patents

Abstract

PURPOSE:To always select an optimum retransmission system by measuring a transmission error rate of a transmission line by utilizing a routine bit pattern continued from a training signal, and thereafter, determining the retransmission system. CONSTITUTION:As for writing/picture data which is transmitted to a receiving side facsimile through a telephone circuit 38 from a transmitting side facsimile 31, the number of error bits in a transmission line is counted by comparing a routine bit pattern which is determined in advance and a routine bit pattern continued from a training signal being receiving data by an error bit counter 43 in a receiving side facsimile 32. As a result, a bit error rate in the transmission line and a retransmission system being suitable for its error rate are collated with a selection table 44 of the retransmission system which is stored as a table, a transmission system being suitable for the transmission line is determined from the bit error rate, and it is informed to the transmitting side facsimile 31. In this way, an optimum retransmission system can always be selected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a transmission method used in a facsimile machine that transmits documents and drawings using a telephone line.

This invention relates to a calligraphy transmission method for correcting a transmission error K due to noise or the like occurring on a transmission path by retransmitting the part of the calligraphy data where the transmission error occurred, and obtaining error-free calligraphy data.

[Conventional technology]

Figure 6 shows the International Telegraph and Telephone Advisory Committee, Research Committee No. 8 (
Error Correction Method (ECM: ErrorCo) is one of the conventional retransmission methods officially recognized in 8G Vial.
3 is a collective signal communication diagram showing the operation of RRRECTION MODE. In the figure, 1 is the receiving facsimile (
N to convey the receiving function of 几 to the sending facsimile machine (S)
8F (Non standard function: Non 5 standard Fa
) signals and DID (digital identification)
2 is a DCS (Digital Command Signal) that conveys the transmission mode (resolution, data compression method, etc.) determined by the transmitting side to the receiving side.
gnal) signal, 3 is a training test to see if the receiving side demodulator can correctly demodulate the analog signal sent through the telephone line into the original digital signal. Notes A, 4
sends the training results [7 Axis C8) K
Confirmation to Receive (Confirmation to Receive) signal when training is successful.
ive) signal, )L/-=7 FTT in case of failure
() Failure to Train
ing) signal is sent. 5 is a training note that is attempted again immediately before the calligraphy data transmission.B16 is a calligraphy data frame that carries calligraphy data.7 is PP5-EOP (end of partial page procedure: Partial Pagef13igna-En) indicating the end of transmission of one block of calligraphy data.
d of Procedure) signal, and 8 is a PP request (partial page retransmission request) signal that requests retransmission of a document frame with a transmission error.
9 is an MCF (Message Confirmation: Message Confirmation) signal indicating that all received calligraphic data has been correctly received and the next block can be received.
firmation) signal.

In addition, FIG. 7 shows the HD used for the calligraphy data frame 6.
FIG. 2 is a diagram showing a frame structure called LC (high-level data link control procedure). In the figure, 10 is a flag pattern indicating a frame break, 11 is an HD field called an address field and a control field.
LC frame header, 12 is the ladder 11 to this frame
is a frame identifier indicating that is a drawing data frame, FCD (, y7 kushimiri encoded data: Fac
sjmjleCoded Data ) pattern is set. Reference numeral 13 indicates a frame number indicating the serial number within the block of the drawing data 14, 14 indicates the encoded drawing data, and 15 indicates a 7-frame check sequence for checking errors occurring on the transmission path.

Next, the operation of the retransmission method in the conventional document and image transmission method will be explained with reference to FIGS. 6 and 7. Note that the retransmission method shown in Figure 6 uses a certain amount of calligraphy data (called a block).
is first transmitted, and the part of the calligraphy data where the transmission error occurred (
Since error correction is carried out by retransmitting only the drawing data frame at a time later, this method is called the -batch retransmission method.

First, the N5F-DIS signal 1 informs the transmitting facsimile (8) that the receiving facsimile (几) has an error correction function based on the batch retransmission method.

The sending side 7 axis (S) decides to transmit the calligraphy data 14 using the -batch retransmission method and transmits it to the receiving side facsimile (fL) using the DO8 signal 2. Here, the N8F-DIS signal 1 and the DCS signal 2 are transmitted using a modulation/demodulation method (for example, a frequency sequence with a transmission capacity of 300 bits/second) that can be transmitted reliably, albeit at a low speed, in order to transmit signals without errors. (softkeying method).

On the other hand, since the document data 14 has a large amount of data, it is transmitted using a modulation/demodulation method that transmits at high speed (for example, an eight-phase phase shift keying method having a transmission capacity of 9600 bits/second). These two types of modulation/demodulation systems are always provided in a modulation/demodulator that implements the binary code signaling system defined in Recommendation T.30 of the International Telegraph and Telephone Advisory Committee.

However, modulation/demodulation systems that enable high-speed transmission are generally more susceptible to the effects of noise and are more likely to cause transmission errors.

Subsequently, the sending facsimile (8) sends out the training signal A3 using the same high-speed modulation and demodulation method used to transmit the calligraphic data. The training signal A3 is a signal for synchronizing the modulator and demodulator, for example, a long training signal specified by the International Telegraph and Telephone Advisory Committee Recommendations V, 29 and V, 27ter, followed by a long training signal for <1.5 seconds. The receiving facsimile (几) demodulates the training signal A3 into a digital signal using a demodulator, and confirms the success of the training by confirming the continuous data @0" for 1.5 seconds. It makes a judgment and responds with CFR signal 4. CFR signal 4 is transmitted using a low-speed modulation/demodulation method.

Therefore, when the sending facsimile <S> receives the CFR signal 4, it sends out the training signal B5. This training signal No. 1 Blj, ) training signal A3 to 1.
This is only the long training signal excluding the 5 second data "O". The purpose of this training signal B5 is
The purpose of this method is to adjust the demodulation timing of the demodulator again before starting the transmission of calligraphic data.

Subsequently, calligraphy data 14 is transmitted. Although facsimile calligraphy data 14 uses one page as its data unit, the page is divided into one or more blocks and transmitted on the transmission path. The example shown in Figure 6 is an example in which one page of calligraphy data fits within one block of five frames, but in the case of calligraphy data 14, which has a large amount of data, one page of data is divided into multiple blocks. Each block is further divided into multiple frames and transmitted. The calligraphy data frame 6' includes the thus divided calligraphy data 14 in its data portion, and the calligraphy data frame 6, which is composed of an address field and a control field, is provided with a header in seven frames on the ladder 11. Furthermore, an identification code FCD indicating that it is calligraphy data 14 is included in the frame identifier 12, and the frame structure has a serial frame number 13 within each block.

The 7-frame check sequence 15 is constructed of 2 bytes by performing a predetermined polynomial calculation on all data from the frame header 11 to the drawing data 14 sandwiched between the frames 10. On the receiving facsimile side, a similar polynomial operation is performed on the received data and the result of the operation is compared with the value of the received frame check sequence 15. Here, if there is no error in transmission, these two values match, and if a transmission error occurs, these two values differ. By this comparison, the receiving facsimile machine can know the transmission error that occurred in the drawing data frame 6.

In the example shown in Figure 6, 1 page of calligraphy data is divided into 1 block 5.
The second frame and the fourth frame are divided into frames and transmitted.
This shows a case where a transmission error occurs in a frame. The receiving side 7 axis') (R) uses the 7 frame check sequence 15 of each drawing data frame 6,
Second. Detect a transmission error in the fourth frame.

In the case of Fig. 6, the sending side facsimile (8) is
When the page and l block of calligraphic data 14 have been transmitted, a PP8-EOP signal 7 is sent to the receiving side facsimile K to notify the end of block transmission. At this time, the receiving facsimile (几) has already detected that there was a transmission error in the second and fourth frames of the calligraphic data frame 6, so the sending facsimile (S)
The P-fold signal 8 requests retransmission of the two erroneous drawing data frames 6.

The above PP5-EOP signal 7 and PPRP number 8 are.

In order to ensure accurate transmission, data is transmitted using a modulation/demodulation method that transmits data at low speed.

When the sending facsimile (8) receives the PP multiplied signal 8, it first sends the training signal B5 as before, and then sends the calligraphic data frame 6 for which there was a retransmission request.
In other words, only the second frame and the fourth frame are retransmitted at once using a high-speed modulation/demodulation method.

When the receiving facsimile machine receives the first block, it performs calculations for each frame according to the contents of the received frame, and compares it with frame check sequence 15 to detect the occurrence of transmission errors. I'm checking.

If there is no transmission error in the retransmitted document/picture data frame 6, the receiving facsimile sends a continuation (PPS-
Even if it receives the EOP signal 7, it does not send a retransmission request PP signal, but responds with an MCF signal 9 indicating the normal end of reception.

In other words, in the batch retransmission method shown in FIG. Save it in buffer memory.

(b) The receiving facsimile (几) retains at least the calligraphic data frame 6 onward in which a transmission error was detected in the receiving side pack memory without outputting it to recording paper, etc., until the error part is corrected by retransmission. Continue in that state.

Therefore, it is necessary to prepare memory for one block on both the transmitting side and the receiving side.

Next, FIG. 8 shows a communication signal diagram of another retransmission method. In this method, the calligraphy data 14 is divided into multiple frames and transmitted, and the receiving side facsimile receives the calligraphy data frame 6.
When a transmission error is detected, retransmission is immediately requested. In this method, the drawing data frame 6 in which a transmission error has occurred is sequentially retransmitted, so this method is tentatively called the sequential retransmission method.

In FIG. 8, 16 is N58 (non-standard function setting; Non-5) which transmits the transmission code determined by the sending facsimile (8) to the receiving facsimile, similar to the DCS signal.
1T is a retransmission request tone that requests retransmission, 18 is a retransmission request signal that conveys the number of the document data frame 6 to be retransmitted, and 19 is an EOP (end of procedure;
nd of Procedure) signal.

In the figure, other parts are the same as in the case of the batch retransmission method.

Further, FIG. 9 shows the frame structure of the retransmission request signal 18. The retransmission request signal 18 has a frame structure of HDLC()/level data link control procedure), and the flag pattern 10, HDLC 7-frame header 11, and frame check sequence 15 are the same as those in FIG. The frame identification code included in the identifier 12 indicates the retransmission request signal 18. 20 is the retransmission request 7 frame number, which is the frame number of the drawing data frame 6 in which a transmission error was detected and required retransmission.

Reference numeral 21 indicates the drawing data transmission speed, and indicates the transmission speed used when transmitting the drawing data. The document data transmission rate 21 is set to another transmission rate (for example, 7200 bits/sec) when the transmission rate does not disappear even after repeated retransmissions are attempted several times at a high transmission rate (for example, 9600 bits/sec). This is an attempt to transmit calligraphy and drawing data in seconds (seconds).

Next, the operation of the sequential retransmission system will be explained using FIGS. 8 and 9. First, the N5F-DIS signal 1 informs the transmitting facsimile (S) that the receiving facsimile (几) has an error correction function using the sequential retransmission method. The sending facsimile (S) decides to transmit the calligraphy data 14 using the sequential retransmission method, and sends an Na3 signal 1 to that effect.
In step 6, send the information to the receiving facsimile machine (R). Na3 signal 1
Similarly to DCS signal 2, signal 6 is also transmitted using a low-speed modulation/demodulation method. Next, 7 aximi on the sending side! j (S) sends out a training signal A3 using a high-speed modulation/demodulation method. The receiving facsimile (几) uses a demodulator to demodulate the training signal A3 into a digital signal, as in the case of the batch retransmission method, and determines that the training has been successful by confirming the data 10" for 1.5 seconds, and transmits the CFR. , signal 4 as a response. When the sending facsimile (8) receives the CFR signal 4, it sends out the training signal B5 and then moves on to transmitting the calligraphy data frame 6. The structure of the calligraphy data frame 6 is shown in FIG. The frame structure is exactly the same as that used in the batch retransmission method shown in .The receiving side facsimile (几)
It is the same as in the case of the batch retransmission method that the transmission error can be detected from the contents of the drawing data frame 6 and the frame check sequence 15.

In the sequential retransmission method, when the receiving facsimile detects that there is a transmission error in document data seam 6, that is, in the example of FIG. 8, it detects a transmission error in the second frame, it immediately requests a retransmission. A tone 17 is transmitted to interrupt the reception of the drawing data frames 6 after the third frame. The sending facsimile constantly monitors whether or not a retransmission request tone 1γ is sent even while transmitting the document data frame 6, and in FIG. 8, a retransmission request tone 17 is sent after transmitting the third frame. I came to realize that A. At this point, the transmission of the calligraphy data 7 frame 6 is temporarily interrupted and the transmission of the retransmission request signal 18 is awaited.

The receiving facsimile (R) transmits the retransmission request tone 17 for a sufficient period of time for the transmitting facsimile (8) to detect it, and then transmits the retransmission request signal 1 using a low-speed modulation/demodulation method.
Send 8. The transmission side 7 axis IJ(S) retransmits the calligraphy data 14 from the calligraphy data 7 frame 6 having the retransmission request frame number 20 transmitted by the retransmission request signal 18 to the item number. When starting retransmission, a retransmission request signal 18 is sent.
First, the training signal B5 is sent out at the calligraphy data transmission rate 21 transmitted, and then the calligraphy data frame 6 for which retransmission was requested is sent out. The procedure for retransmitting the drawing data frame 6 for the 47th frame is exactly the same as that for the 27th frame. When five frames have been transmitted in this manner, the sending facsimile (S) sends out an EOP signal 19 indicating the end of the procedure. The receiving facsimile (fL) immediately responds with the MCF signal 9 since it has received all of the calligraphic data 14 without errors.

Here, in the sequential retransmission method, (/→ Every time there is a transmission comb, a retransmission request signal 18
is sent.

After transmitting a certain calligraphy data frame 6, the sending end 7 pixel (8) transmits that calligraphy data frame 6 to the sender's pants for a period of time during which a retransmission request tone 17 for that calligraphy data frame 6 is expected to be returned. Just store it in memory.

(e) The receiving facsimile (R) can immediately output the correctly received calligraphic data frame 6.

The following points can be mentioned.

FIG. 10 shows a comparison table of the two retransmission methods described above, ie, the batch retransmission method and the sequential retransmission method. As you can see from this comparison table.

(1) Transmission) When the Ab rate is low, the sequential retransmission method is more convenient because it allows the receiving side to immediately obtain an output. (2) When the transmission error rate is high, the number of retransmission requests is small. Therefore, a batch retransmission method using a low-speed modulation/demodulation method for requesting retransmission and requiring fewer signal communications can shorten the transmission time.

[Problem to be solved by the invention]

Since the conventional document and image transmission system is configured as described above, in the retransmission system, when the sending facsimile (8) transmits the DCS signal 2 or the N13 signal 16, regardless of the transmission error rate on the transmission path, - Determining whether to use a batch retransmission method or a sequential retransmission method. For this reason, since the batch retransmission method is used for lines with low error rates,
Due to a transmission error 9 that occurred in a frame near the beginning of a block, much of the subsequent normally received calligraphy data 14 could not be output until the block transmission was completed;
Since the sequential retransmission method was used for a line with a high error rate, there was a problem in that retransmission requests were generated many times and the transmission time became long.

This invention was made to solve the above-mentioned problems, and the transmission error rate on the transmission path at any given time is determined by using a fixed bit pattern following a training signal (for example, 1.5 seconds of continuous @O''). The aim is to obtain a document and image transmission method that can make the most of the advantages of each method, by measuring the retransmission method using data (e.g. data) and selecting the optimal retransmission method according to the error rate. .

[Means to solve the problem]

The calligraphy and drawing transmission system of the present invention includes a calligraphy data generation unit that generates encoded calligraphy data on the sending and receiving facsimile connected via a telephone line, and retransmits the calligraphy data that has been transmitted twice. A fixed bit pattern following the training signal is generated from a bit pattern generator on a surface plate according to a control command from the communication control unit, and the drawing data is subsequently modulated. to the telephone line via the device.

In addition, on the receiving side facsimile, the received signal is demodulated by the receiving side modulator and demodulator, which has the same function as the sending side modulator, and the received data is compared with a predetermined standard bit pattern using an error pit counter to count the number of error bits. In addition to temporarily storing the counted and received calligraphy data in a backup memory, the system selects the transmission method most suitable for the transmission path from a table that stores bit errors on the transmission path and a selection table of retransmission methods suitable for the bit errors. Extended CF that expands the selection result
This notification is sent to the sending facsimile using a multiplication signal or a tone signal.

[For production]

In this invention, the calligraphy data transmitted from the sending facsimile to the receiving facsimile via the telephone line is transmitted by comparing the received data with a predetermined surface bit pattern by an error bit counter in the receiving facsimile. #14) Count the number of bits on the transmission path, and as a result, calculate the bit error rate by comparing it with a retransmission method selection table that stores the bit error rate on the transmission path and the retransmission method suitable for that error rate. A transmission method suitable for the transmission path is selected from among them, and the selection result is notified to the transmitting facsimile by an extended CF multiplication signal or a tone signal.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a facsimile according to the present invention. In the figure, 31 is the sending facsimile (C8), 32 is the receiving facsimile (几), and 33 is the receiving facsimile (C8).
Reference numeral denotes a calligraphy data generation unit that generates coded calligraphy and drawing data; 34 refers to a transmitting side buffer memory that stores the nine calligraphy data 14 once transmitted in preparation for retransmission; and 35 indicates at least two types of modulation and demodulation methods, high speed and low speed. 36 is a transmitting side communication control unit, and 37 is a regular bit pattern generator that generates a regular bit pattern following the training signal. 38 is a telephone line which is a transmission path.

Further, 39 is a receiving modem having the same function as the transmitting modem 35, and 40 is a receiving facsimile (R).
32 is a communication control unit, 41 is a receiving side buffer memory used when it is necessary to store the received calligraphy data 14 at one point as in the case of batch retransmission/reception, and 42 is a buffer memory for storing the received calligraphy data 14. It is an output section for outputting document and image data, and generally includes a decoder for decoding encoded data. 43 is an error bit counter that counts the number of error bits by comparing received data with a predetermined surface bit pattern; 44 is a table that stores the bit error rate in the transmission path and the retransmission method suitable for it; This is a selection table of retransmission methods.

FIG. 2 shows a signal communication diagram according to the present invention. The same parts as in FIG. 6 are indicated by the same reference numerals.9 In FIG. 2, 22 is an extended N8S signal or an extended DC signal.
28 is a training signal X, and 23 is an extended OF damage signal.

Furthermore, the frame structure of one extended NSS signal 22 is shown in FIG. The frame has an HDLC7 frame configuration, a flag pattern 10, a frame header 11 with address and control fields, a frame check sequence 15 of -11 in the HDLC frame configuration, and a pattern indicating N88 is stored in the frame identifier 12. It's worth it. 24 are normal NSS signal parameters,
This also includes instruction data for the modulation/demodulation method and data transmission speed used in document and image transmission. 25 is a retransmission method selection request added in the present invention, and the sending facsimile (8) 31 indicates selectable retransmission methods in this request to the receiving facsimile (R) 32, and Request 5 to select the optimal retransmission method according to the bit error rate of the transmission path.

The frame structure of the extended CF multiplied signal 3 is shown in FIG. The extended CF multiplied signal 3 is also configured as an HDLC frame, and the frame identifier 12 includes a pattern indicating the CF multiplied signal. Reference numeral 26 indicates a retransmission method instruction, which is a field for informing the sending facsimile IJ(S) 31 of the retransmission method selected by the receiving facsimile (box) 32.

Further, FIG. 5 shows a configuration diagram of the training signal X28 used in the transmission system of the present invention. training signal x2
The first half of 8 (pressure in the figure) is based on the International Telegraph and Telephone Advisory Committee Recommendation v
, 29 or V, 27 ter.

Also, the second half (right side in the figure) is the bit pattern of the surface plate,
For example, it is continuous "O" data for 1.5 seconds as specified in International Telegraph and Telephone Advisory Committee Recommendation T.30. This regular bit pattern may be any other bit pattern, or may have an HDLCO frame configuration.

If 1.5 seconds of continuous @O'' data is used, the training signal X28 becomes training No. 1 A 3 ,!: the same.

Next, the operation of the calligraphy and picture transmission system of the present invention will be explained using FIGS. 1 to 5. First, the receiving facsimile (
The receiving facsimile (几) 32 uses the DI8 and N8F signal 1 to send two retransmissions, that is, -
Indicates that it has both batch retransmission and sequential retransmission functions. Sending side facsimile (8) 31 also has these 2
If it is possible to operate in two methods, the sending side communication control unit 36 uses the retransmission method selection request 25 field of the extended NSS signal 22 to inform the receiving side facsimile that both the batch retransmission method and the sequential retransmission method are possible. (几) Notify 32.

In addition, the modulation/demodulation method and transmission speed used for document transmission are determined and specified in the NSS signal parameters 24 of the extended N88 signal 22 as before.

Subsequently, training/fllX 28 t-transmission is performed from the transmitting modem 35 at that transmission rate. As for the training signal X2B, first, the long training signal 29 is generated from the transmitting modem 35 under the control of the transmitting side communication control section 36, and then the constant temperature bit pattern 30 is generated from the surface plate bit pattern generator 37, respectively. The receiving facsimile 32 waits for the training signal X28 at the print data transmission rate notified by the extended NSS signal 22.

If the long training signal 29' of the training signal X28 cannot be successfully received by the receiving modem 39, the receiving side communication control section 40 responds with the FTt signal as in the conventional case. When the training using the long training signal 29 is successful and demodulation of the digital signal starts in the receiving modem 39, the error bit counter 32 detects that the fixed bit pattern 30 sent following the long training signal 29 is determined in advance. The number of bits that do not match is counted. When the reception of the surface plate bit pattern 30 is finished, the receiving side communication control unit 40
selects a retransmission method suitable for the transmission path from the number of error bits counted by the error bit counter 43 and the retransmission method selection table 44. That is, the receiving side communication control unit 40 determines whether the batch retransmission method or the sequential retransmission method is suitable for the current transmission path, and transmits the determination result to the extended CF' signal 2.
The sending facsimile (S) 31 is notified in the retransmission method instruction field 26 of No. 3, and the facsimile (S) 31 enters a waiting state for receiving document and image data using the determined retransmission method. By receiving the extended CFRF signal 23, the transmitting facsimile (8) 31 can successfully train the receiving modem 39 at the transmission rate specified by the Na3 signal parameters 24 of the extended NSS signal 22, and the receiving facsimile (8) ) 32 is preparing for reception using the retransmission method notified by the retransmission method instruction 26 of the extended OF damage signal 3. Then, the sending facsimile (8) 31 starts transmitting the calligraphic data using the retransmission method specified by the training signal B5.

The subsequent signal communication procedure is the same as in the conventional device.

Further, although the frame structure of the extended NSS signal 22 has been described in the above embodiment, it may be an extended DCS signal including a retransmission method selection request 25. In addition, we have given two examples of forwarding methods, the batch retransmission method and the sequential retransmission method, but even with the same batch retransmission method,
The present invention produces similar effects in the case of a method with a large frame size and a method with a small frame size.

〔Effect of the invention〕

As described above, according to the present invention, the training signal
In order to determine the retransmission method after measuring the transmission error rate of the transmission path using the fixed-temperature bit pattern in the WA
This has the effect that the optimum retransmission method can always be selected even in a communication network where the error rate varies greatly depending on the transmission path and route arrangement method where the b rate changes.

[Brief explanation of the drawing]

FIG. 1 is a facsimile configuration diagram realizing a transmission method according to an embodiment of the present invention, FIG. 2 is a signal communication diagram according to the transmission method of this invention, and FIG. 3 includes a retransmission method selection request used in this invention. 7-lem configuration diagram of extended N88 signal, 4th
The figure also shows a frame configuration diagram of an extended CFRF signal including a retransmission method instruction used in this invention, FIG. 5 shows a configuration diagram of a training signal X used in this invention, and FIG. 6 shows signal communication using the conventional batch retransmission method 7 is a configuration diagram of a document data frame used in the batch retransmission method and the sequential retransmission method, and FIG. 8 is a signal communication diagram in the conventional sequential retransmission method.
FIG. 9 is a frame configuration diagram of a retransmission request signal used in the conventional sequential retransmission method, and FIG. 1O is a comparison diagram comparing the batch retransmission method and the sequential retransmission method. In the figure, 22 is an extended N8S signal, 23 is an extended CFR
Signal 25 is a retransmission method selection request, 28 is a training signal
35 is a transmitting side modem, 39 is a receiving side modem, 37 is a regular bit pattern generator, 36 is a transmitting side communication control unit,
4° is the receiving side communication control unit, 42 is the calligraphy data output unit, 4
3 is an error bit counter, and 44 is a retransmission method selection table. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Patent applicant: Mitsubishi Electric Corporation 22-ki) 1; 5! ENSS number 23: Main broadbow seven-hi CFR Ig number 28: Train buoy name number

Claims (1)

[Claims] The sending facsimile machine and the receiving facsimile machine are connected by a telephone line, and on the sending side, encoded digital calligraphy data is generated in a calligraphy data generation section, and the said calligraphy data is temporarily stored in a buffer memory on the sending side in preparation for retransmission. Then, communication of calligraphic data and transmission control signals using a predetermined binary code signal system is performed by a modem, and control for the communication is performed according to commands from the transmission side communication control unit. A fixed bit pattern is generated from a fixed bit pattern generator following the training signal, and on the receiving side, demodulation is performed by a modulator/demodulator similar to that on the transmitting side, and communication control is performed by a receiving side communication control unit, The calligraphy data received by the modulator/demodulator is temporarily stored in a reception buffer memory, and the received encoded calligraphy data is decoded and output from the calligraphy data output section, and the training data transmitted from the sending facsimile is decoded. The demodulated digital signal and a predetermined standard bit pattern are compared with an error bit counter, and the same calligraphy data is retransmitted and corrected in order to correct any transmission errors that occurred on the transmission path during the transmission of the calligraphy data. It adopts a retransmission method, and has a reproduction method selection table in which the bit error rate in the transmission path and the retransmission method for document and image data suitable for the bit error rate are stored in advance, and which method is used for the receiving facsimile. A retransmission method selection request requesting selection of a retransmission method to be used is transmitted to the transmitting side facsimile using an extended extended NSS signal or an extended extended DCS signal, and the error bit counter converts the training signal into a training signal. Measure the bit error rate of the transmission path from the following fixed bit pattern, select the transmission method most suitable for the transmission path from the measured bit error rate and the retransmission method selection table, and use the result as an extended CFR signal,
Alternatively, there is a calligraphic transmission method in which a tone signal is used to notify the sending facsimile machine and select the most suitable retransmission method for the transmission path.