JPS61127271A - Facsimile communication system - Google Patents

Abstract

PURPOSE:To communicate even when circuit condition to a transmission side from a reception side is deteriorated by transmitting an image signal without taking any error control procedure even when a circuit condition is judged to be impossible to receive an error informing signal, at the time of transmission of a training signal to the reception side from the transmission side. CONSTITUTION:The transmission part monitors a receiving condition of error informing signal PIS by means of PIS detecting circuit 11 and control portion 2 during a transmis sion period of training signal TCF. When the error informing signal PIS is not received normally, the transmission device sets up a communication mode which doesn't use the error control procedure after judging that a circuit condition proceeding from a receiving part to a transmitting part by the control portion 2 is abnormal. On the other hand its transmission device transmits a receiving instruction signal NSC.DCS and informs that it performs communication to a receiving part without an error control after confirming to receive a standard confirmation signal CFR from the receiving part. After then the receiving part sets up its own communication mode according as an information that the transmission part performs communication with out error control and continue to perform a receiving operation of picture signal. Accordingly the error informing signal PIS is not transmitted from the receiving part to transmitting part at all.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to improvements in facsimile communication systems.

[Technical background of the invention]

Conventionally, many facsimile communication systems having error control procedures have been used. FIG. 4 shows an example of the procedure. In the figure, when the sending side and the receiving side are connected by a call from the sending side, the receiving side first sends an initial identification signal NSF/Dis and uses the NSF signal to confirm that it has error III m II capability. inform. In response, the transmitting side transmits a reception command signal N5S-DO8 to instruct the receiving side to perform transmission in a mode using the error ill m procedure using the NSS signal, and then transmits a training signal TCP. At this time, this training signal TCP consists of all "O" signals, and has a transmittable image signal transmission speed of 9600t) pS.

7200bpS, 4800 bps, 2400
It is transmitted for 1.5 seconds at the actual transmission rate of bps. Then, on the transmitting side, this training signal T
When it is confirmed that the reception preparation confirmation signal CFR has been returned from the receiving side in response to the transmission of the CP, the transmission of the image signal is started.

On the other hand, the receiving side decodes the received image signal and monitors for errors. For example, if the number of pixels in one line is not a normal value, it is determined that this is an error and at that point it sends an error notification signal PIS. Send. The transmitting side monitors the arrival of the error notification signal PIS during the transmission of the image signal, and interrupts the transmission of the image signal when this signal PIS is detected. Then, following the error notification signal PIS, a control signal (a signal indicating in which line an error has occurred) sent from the receiving side is received, and the image signal of the line designated by this IIIwJ signal is retransmitted.

In this way, error-free, high-quality facsimile transmission can be performed.

[Problems with background technology]

However, in this conventional facsimile communication method,
It had the following drawbacks. That is, the line state of a communication line may differ depending on the direction of the line, that is, the direction from the transmitting side to the receiving side and the direction from the receiving side to the transmitting side. Therefore, if only the condition of the line from the receiving side to the transmitting side deteriorates, even if the image signal is transmitted normally from the sending side to the receiving side, if an error is detected, the error notification signal will be sent to the sending side. If the error is not detected, normal error control procedures are not performed between the transmitter and the receiver, resulting in communication failure.

[Purpose of the invention]

The present invention provides a facsimile communication system that can reliably transmit image signals without becoming unable to communicate even when the condition of the line from the receiving side to the sending side deteriorates, thereby improving reliability. The purpose is to

[Summary of the invention]

In order to achieve the above object, the present invention uses an error control procedure from the receiving side to the transmitting side during transmission of an image signal training signal from the transmitting side to the receiving side, which is performed prior to the transmission of the image signal. An error notification signal is transmitted, the sending side monitors the reception status of this error notification signal, determines whether or not the error notification signal can be received normally, and detects an error detection signal in a line state where it is not possible to receive the error notification signal. When it is determined that there is an error control procedure, the image signal is transmitted without any error control procedure.

[Embodiments of the invention]

FIG. 1 is a circuit block diagram of a facsimile transmitting/receiving device having a function of implementing a facsimile communication system according to an embodiment of the present invention. In the figure, an image signal output from an image signal generation section (not shown) is modulated by a modulation/demodulation section 2 under the control of a control section 1, and then outputted by a PIS filter 3 into an error notification signal P Is (tone signal of 4621tz).
After that, the changeover switch 4, the transmission filter 5 consisting of a low-pass filter, and the transmission equalizer 6
are transmitted to the line 7 via the respective channels. In addition, various Ii
The i control signal and the error notification signal PIS are generated from the tone sending section 8 in accordance with instructions from the control section 2, and are transmitted through the changeover switch 4, the transmission filter 5, and the transmission equalizer 6, which are switched according to the instructions from the control section 2. and is transmitted to line 7.

On the other hand, the image signal arriving via the line 7 is transmitted to the reception equalizer 9
After passing through the receiving filter 1o consisting of a band pass filter
The PIS component is removed, and then the signal is supplied to the modulation/demodulation section 1 and subjected to I[TA. The signal is then decoded by the control unit 2, and errors in the image signal are detected for each line. Also, the error notification signal PIS that arrived via line 7 is P
IS detected by the IS detection circuit 11, and the detection signal is sent to the control unit 2.
will be introduced in

Next, based on the above configuration, 7? of this embodiment? The taxi communication method will be explained. FIGS. 2 and 3 show the control procedure. When the sending side and the receiving side are connected by the sending side calling, the receiving side first sends the initial identification signal N5.
F-Dis is transmitted, and in response to this, the transmitting side transmits a reception command signal N5S-DO8, and then subsequently transmits a training signal TCP.

Now, at this time, in parallel with the operation of receiving the training signal TCP, on the receiving side, the control section 2 drives the tone sending section 8 to transmit the error notification signal PIS. On the other hand, the transmitting side monitors the reception status of the error notification signal PIS using the PIS detection circuit 11 and the control unit 2 during the transmission period of the training signal TCP, and when it is received normally, the line from the receiving side to the transmitting side is is determined to be in good condition, and the communication mode using the error control procedure is set as is. After confirming that the reception preparation confirmation signal CFR has been returned from the reception side, the transmission of the image signal is started as shown in FIG. The error control operation when an error is detected on the receiving side during transmission of this image signal is as described above with reference to FIG. 4.

On the other hand, when the error notification signal PIS from the receiving side is not normally received during the transmission period of the training signal TCP, the transmitting side device determines that the condition of the line from the receiving side to the transmitting side is defective by the control unit 2. to set a communication mode that does not use error control procedures. After confirming the reception of the reception preparation confirmation signal CFR from the receiving side, the third
As shown in the figure, the receiving command signal N5C-DO8 is transmitted to notify the receiving side that communication will be performed without error control, and then the training signal TCP is transmitted again. Then, after confirming that the reception preparation confirmation signal CFR has been returned from the receiving side in response to the training signal TCP, the transmission of the image signal is started. On the other hand, at this time, the receiving side sets its own communication mode in response to the notification from the transmitting side that communication will be performed without error control, and thereafter performs image signal reception operations according to this communication mode. Therefore, no error notification signal PIS is transmitted from the receiving side to the transmitting side.

As described above, in this embodiment, the error notification signal PIS is sent from the receiving side to the transmitting side during training for transmitting image signals from the transmitting side to the receiving side to determine the state of the line, and if the state of the line is bad. In this case, error control is not performed in the subsequent image signal transmission operation, so the condition of the line from the transmitting side to the receiving side is good, but the condition of the line from the receiving side to the transmitting side is good. Even if an error occurs on the receiving side when the receiver is defective, it is possible to eliminate the problem of communication being impossible due to the error.

In this case, the quality of the received image signal will deteriorate due to not performing error control, but generally speaking, if it is determined that the condition of the line from the transmitting side to the receiving side is good at the training stage, errors will be eliminated. The probability of this occurring is very small and poses no major problem in practice. On the other hand, being able to prevent communication failure as described above is more effective as a bridging effect.

In addition, in this embodiment, the state of the line from the receiving side to the transmitting side is determined by the error notification signal PI, which is already used for error control.
In addition, this signal PIS is transmitted during the transmission period of the training signal TCP in parallel with the image signal training, so there is no need to prepare a completely new control signal, and the image signal transmission The state of the line from the receiving side to the transmitting side can be determined without increasing the number of procedures up to the start point, and thereby the existing communication control procedure can be easily implemented without significantly changing it.

It should be noted that the present invention is not limited to the above-described embodiments, and for example, the circuit configuration of the facsimile transmitting/receiving device, the configuration of the error notification signal PIS, etc. can be modified in various ways without departing from the gist of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, during the transmission of an image signal training signal from the transmitting side to the receiving side, which is performed prior to the transmission of the image signal, an error is transmitted from the receiving side to the transmitting side. An error notification signal used in the control procedure is transmitted, and the sending side monitors the reception status of this error notification signal to determine whether or not the error notification signal can be received normally, and if the error detection signal is not received. Error l1 when it is determined that the line status is possible.
By transmitting the image signal without the lf1 procedure, even if the line condition from the receiving side to the transmitting side deteriorates, the image signal can be reliably transmitted without communication being disabled. Accordingly, it is possible to provide a facsimile communication method that can improve reliability.

[Brief explanation of drawings]

1 to 3 are for explaining a facsimile communication system according to an embodiment of the present invention. 3 and 3 are diagrams showing the control procedure of the same communication system, respectively, and FIG. 4 is a diagram showing the control procedure of the conventional facsimile communication system. N5F-Dis...Initial identification signal, NSS/DO8
, N5C-DO8...Reception command signal, TCP...Training signal, CFR...Reception semi-failure confirmation signal, PI
S...Error notification signal, 1...Modulation/demodulation unit, 2...
Control part, 3... PIS filter, 4... Changeover switch, 5... Transmission filter, 6... Transmission equalizer, 7.
. . Line, 8 . . . Tone sending section, 9 . . . Reception equalizer, 10 . . . Reception filter, 11 . . . PIS detection circuit. Applicant's agent Patent attorney Takehiko Suzue 1S1 Figure 2

Claims (1)

[Claims] In a facsimile communication system equipped with an error control procedure, the receiving side performs error detection during image signal transmission, and when an error is detected, the receiving side sends an error notification signal to the transmitting side to request retransmission of the image signal. The error notification signal is transmitted from the reception side to the transmission side during transmission of a training signal from the transmission side to the reception side, which is performed prior to transmission of the image signal, and the reception status of this error notification signal is monitored on the transmission side. to determine whether or not the line state is such that the error notification signal can be received, and when it is determined that the line state is such that the error notification signal cannot be received, the image signal is transmitted without the error control procedure. A facsimile communication method characterized by the following: