JP2572056B2 - Image transmission device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image transmitting apparatus for transmitting image data by full-duplex communication.

[Prior Art] Conventionally, an image communication apparatus having an image transmission function according to an error control procedure has been known. For example, as described in NTT's “Facilities” (VOL.38 No.5, page 59, 1986), half-duplex communication is performed for the pre-procedure and post-procedure, and only when image transmission is performed. Devices for performing double communication are known.

On the receiving side of such a communication device, first, the initial identification signal NS
Notifies the transmitting side that it has an error control function by F (non-standard device) and DIS (digital identification signal). On the transmission side, on the other hand, the reception command signal NSS (non-standard device setting)
Transmit CS (digital command signal). This instructs the receiving side to perform the error control procedure, and then transmits a training check signal TCF. The training check signal TCF is composed of all "0" signals, and is transmitted for 1.5 seconds at the actual transmission speed among the image signal transmission speeds of 9600 bps, 7200 bps, 4800 bps, and 2400 bps.

The transmitting side confirms that the receiving side has returned the reception preparation confirmation signal CFR in response to the training check signal TCF, and starts transmitting the image signal.

In response to this, the image signal received on the receiving side is decoded, and an error is monitored. Then, when an error is detected, an error notification signal NACK is transmitted at that time.

On the transmission side, the error notification signal NACK is
, And transmission of the image signal is interrupted when the error notification signal NACK is detected. Then, the error notification signal NA
After receiving the control signal sent from the receiving side following CK,
The image signal is retransmitted from the place designated by the control signal.

Thus, error-free high quality facsimile transmission is performed.

[Problems to be Solved by the Invention] However, such a conventional image communication system has the following disadvantages.

In a communication line, the line state may be different between the direction from the transmitting side to the receiving side and the direction from the receiving side to the transmitting side. For this reason, even if the image signal is normally transmitted from the transmission side to the reception side, the error notification signal transmitted when a reception error is detected is not correctly detected by the transmission side, and the Normal error control procedures may not be performed. As a result, a drawback (a first drawback) of causing a state in which communication is not possible was found.

In addition, communication failure may occur due to propagation delay of a communication line. That is, even if the receiving side detects an error in the image signal and transmits the error notification signal NACK, a delay time of, for example, about 1 second may be required for the error notification signal NACK to reach the transmission side. . Therefore, in such a case, it is necessary for the transmitting side to always store data for about 2 seconds in order to retransmit the image data. For example, when the transmission speed of image data is 9600 bps, a memory capacity of 2.4 Kbytes (9600 × 2 = 8 = 2400 bytes) is required. Further, when the detection time of the error notification signal NACK and the influence of the echo suppressor in international communication are taken into account, a larger memory capacity is required.

Therefore, when a facsimile apparatus having a small memory capacity is used for communication on a line having a large propagation delay, image retransmission cannot be performed, resulting in a defect (second defect) that communication failure occurs.

In order to avoid the above-mentioned second drawback, it is only necessary to incorporate a large-capacity memory. However, a drawback that the apparatus becomes larger and costs increase (third drawback).
Is seen.

Therefore, in view of the above, an object of the present invention is to perform a training check sequence by performing full-duplex communication,
The determination as to whether or not full-duplex communication is possible and the determination as to whether or not the line state (communication state by the set modem) is good are performed at the same time, thereby shortening the time required for the communication procedure. It is an object of the present invention to provide an image transmitting apparatus which can be completed.

[Means for Solving the Problems] In order to achieve the above object, an image transmitting apparatus according to the present invention, which transmits image data by full-duplex communication, transmits image data prior to transmitting image data. Means for transmitting a training check signal, and, during transmission of the training check signal, a predetermined response signal indicating that the training check signal transmitted from the receiving side via the backward channel has been successfully received. It has means for receiving, and means for determining whether to transmit image data by full-duplex communication based on whether or not the response signal has been received.

[Operation] In the present invention, during transmission of the training check signal,
Upon receiving a predetermined response signal indicating that the training check signal transmitted from the receiving side via the backward channel has been successfully received, transmission of image data by full-duplex communication is determined based on the presence or absence of the response signal. Decide whether to do it.

EXAMPLES Hereinafter, the present invention will be described in detail based on examples.

FIG. 1 is a schematic diagram of an image communication system according to the present invention. That is, in an image communication system for transmitting and receiving image data by full-duplex communication, during a training check sequence performed prior to transmission of the image data,
When a predetermined response signal cannot be received on the transmitting side, image data is transmitted by half-duplex communication.

The image communication system will be described in more detail as follows.

First, a training check signal (TCF) is transmitted from the transmitting side to the receiving side before transmitting the image signal. During this time, the receiving side checks the training check signal and transmits a predetermined response signal (for example, an error notification signal used in an error control procedure) from the receiving side to the transmitting side only when the signal is good. I do. The transmitting side monitors the reception state of the response signal while transmitting the training check signal, and determines whether the response signal can be normally received. As a result, when it is determined that the line state cannot receive the response signal, the image signal is transmitted by the half-duplex communication (that is, there is no error control procedure).

If the receiving side cannot receive the training check signal (TCF) properly, the receiving side does not transmit a response signal (error notification signal) to the transmitting side and performs communication according to a conventional procedure.

According to such a procedure, both the transmitting side and the receiving side can simultaneously check the signal reception status in one training check sequence, so that the first disadvantage described above can be eliminated.

In addition, by providing a timer function (time measurement function) to each of the transmission side and the reception side, and by operating the timer function during the training check sequence,
It is possible to eliminate the second and third drawbacks caused by the propagation delay of the line.

FIG. 2 is a block diagram showing one embodiment of a GIII facsimile apparatus to which the present invention is applied. In this figure, 1 is an image reading section for reading image data and converting it into an electric signal, 2 is a control signal generating section for controlling communication, and 3 is an image signal obtained by the reading section 1 and generated from the control signal generating section 2. A switching circuit for selecting one of the selected control signals; 4 a modulator for modulating the output signal of the switching circuit 3 (CCITT recommendation V21 modulator for control signals, V2 for image signals)
7 is a transmission control unit for controlling a transmission procedure, 6 is a backward signal generation unit (a backward tone of a V27ter or V29 modulator has a single tone (2900 Hz) outside the required modulation band.
7 or less, or a low-speed modulator of 75 baud or less), 7 is a switching circuit for switching between the modulation signal 4a and the backward signal 6a, 8 is a 2-wire 4-wire conversion circuit, 9 is a 2-wire transmission line, Reference numeral 10 denotes a backward signal detection unit that detects a backward signal sent from the receiving side via the transmission line 9, 11 denotes a demodulation unit that demodulates a modulation signal sent via the transmission line 9, and 12 denotes a backward signal. A control signal analysis unit that analyzes a communication control signal based on output signals of the signal detection unit 10 and the demodulation unit 11, 13 is a received image recording unit, and 14 is a control procedure shown in FIGS. ) Is stored in the ROM, and 15 is a RAM for storing various data.

Next, an operation for transmitting image data will be described with reference to a block diagram shown in FIG.

The control signal of 300 bps sent from the receiving side via the transmission line 9 is split by the two-wire / four-wire conversion circuit 8 and input to the backward signal detection unit 10 and the demodulation unit 11, respectively. In this case, since the input signal is a control signal of 300 bpa, the output of the backward signal detection unit 10 is meaningless and the demodulation unit
Only 11 outputs are valid. The output signal of the demodulation unit 11 is analyzed by the control signal analysis unit 12. The transmission control unit 5 generates a control signal corresponding to the analyzed control signal from the control signal generation unit 2 and inputs the control signal to the modulation unit 4 via the switching circuit 3. The modulation output 4a output from the modulation unit 4 is introduced into a two-wire / four-wire conversion circuit 8 via a switching circuit 7 and sent out to a transmission line 9.

FIG. 3 is a diagram showing a process when the facsimile apparatus shown in FIG. 2 performs full-duplex communication, and FIG. 4 is a diagram showing a process when the device performs half-duplex communication.

FIG. 5 is a timing chart showing control signals transmitted from the transmitting side and the receiving side, respectively, including the propagation delay time.

FIG. 6 is a flowchart showing a control procedure to be executed by the transmitting facsimile apparatus, and FIG. 7 is a flowchart showing a control procedure to be executed by the receiving facsimile apparatus.

First, referring to FIG. 3, FIG. 6, and FIG.
The process of performing image transmission by double communication will be described.

As shown in FIG. 3, the transmitting side receives the pre-procedure signal 16 sent from the receiving side, and determines whether or not the receiving side has the dual communication function (step S6-).
1). As a result, if it is determined that full-duplex communication is possible, the receiving-side pre-procedure signal 17 informs the receiving side of the full-duplex communication.
Command to perform double communication (step S6-2, step
S7-1). Following this, the sending side is a line (transmission path)
Training check signal to check the condition of
18 (TCF) is sent out by the high-speed modem (step S6-
3).

On the other hand, the receiving side monitors the reception state while receiving the training check signal 18 (step S7-2) (step S7-3). Usually a training check signal
Since the state 18 is a series of “0” states, the receiving side detects a predetermined number of “0” series (the training check signal 18).
While the data is still present on the transmission path), an ACK signal 19 is transmitted to the transmitting side by a backward channel as a signal for confirming that full-duplex communication is possible (step S7-4). In this embodiment, a signal having the same format as the error notification signal NACK is used as the ACK signal.

On the transmitting side, when the backward signal detector 10 detects the ACK signal 19 while the training check signal 18 is being transmitted (step S6-4), it determines that full-duplex communication is possible and performs a training check. The transmission of the signal 18 is stopped (step S6-5), and the image communication 20 by full-duplex communication is started (step S6-6).

Next, referring to FIG. 4, FIG. 6, and FIG.
The process of performing image transmission by double communication will be described.

As shown in FIG. 4, when the transmitting side does not detect the ACK signal 19 from the receiving side for some reason (step S6-4), the transmitting side waits for a certain time (step S6-3 → S6). -4 → S6-7) Then, the transmission of the training check signal 18 is stopped (step S6-8).

On the other hand, the receiving side waits for reception of the image signal 20 (see FIG. 3) by full-duplex communication (step S7-4 → S7-5 → S7).
-6) Since the image signal 20 does not arrive, the time is over (step S7-8), and the reception preparation confirmation signal 21 is transmitted to the transmitting side via the 300 bps modem (step S7-9).
As a result, preparations are made for performing image communication by half-duplex communication (step S7-12).

On the transmitting side, when the reception preparation confirmation signal 21 is detected by the 300 bps model (step S6-9), it is determined that full-duplex communication is impossible, and the image communication 22 by half-duplex communication is performed.
Is started (step S6-12).

The "T1 time over" shown in step S6-7 in FIG. 6 will be described in further detail.

"T1" is a set value of a timer provided on the transmission side, and the specific length is shown in FIG. FIG. 5 shows the timing of the pre-message procedure including the propagation delay time by the line. Td shown in FIG. 5 represents a required propagation time from when the signal is transmitted to when the signal arrives at the other party. In this embodiment, control is performed so that the duration of the training check signal (TCF) matches the set value of the T1 timer.

As is clear from FIG. 5, T1 is determined as follows.

T1 = Td × 2 + (Testing time of TCF signal on the receiving side = T
r) + (Test time of ACK signal on transmission side = Tt) Further, T1 has to be determined in relation to the storage capacity of the memory provided on the transmission side. For example, when Td = 1 second, T1 = 2 seconds even if Tr = Tr = 0 seconds. Therefore, the amount of data transmitted in 2 seconds is 9600 × 2 × 1/8 = 2400 bytes when the transmission speed is 9600 bps.

Therefore, when the storage capacity of the transmission side is small, it is necessary to set the timer set value T1 small. As a result, if the required arrival time of the ACK signal sent from the receiving side exceeds the set time T1 during the training check sequence, it is determined that the propagation delay time of the line is too large (that is, the error Even if the broadcast signal NACK can be detected, it is determined that normal retransmission processing is not possible), and the image signal is transmitted (image transmission by half-duplex communication) without an error control procedure.

In this case, the quality of the received image signal is degraded by not performing the error control.However, in general, if it is determined that the state of the line from the transmitting side to the receiving side is good at the training check stage. The probability of occurrence of an error is very small, and there is no serious problem in practical use.

FIG. 8 is a block diagram showing another embodiment of the present invention. In this figure, the same elements as those shown in FIG. 2 are denoted by the same reference numerals. In the embodiment shown in FIG. 2, the backward signal generating unit 6 and the backward signal detecting unit 6 are used to perform full-duplex communication. The word signal generator 6 and the detector 7 are eliminated. Therefore,
The demodulator 11 of the transmitting modem is used as a detector for the backward signal, and the modulator 4 of the receiving modem is used as a generator of the backward signal.

The present invention is not limited to the above-described embodiments. For example, the circuit configuration of the facsimile apparatus and the configuration of the error notification signal can be variously modified without departing from the paper of the present invention. is there.

[Effect of the Invention] As described above, according to the present invention, during transmission of a training check signal, a response signal from the receiving side indicating that the training check signal has been successfully received is received via the backward channel. Therefore, the time required for the procedure is shorter than that in which the response signal is received after the transmission of the training check signal is completed. In addition, whether or not full-duplex communication is possible can also be determined.

[Brief description of the drawings]

1 is a diagram showing a schematic configuration of the present invention, FIG. 2 is a block diagram showing an embodiment of a facsimile apparatus to which the present invention is applied, FIG. 3 is a diagram showing a process of performing full-duplex communication, FIG. The figure shows the process of performing half-duplex communication, FIG. 5 shows the propagation delay state of the control signal, FIG. 6 shows the flowchart showing the control procedure on the transmitting side, and FIG. 7 shows the control procedure on the receiving side. FIG. 8 is a block diagram showing another embodiment. 2 ... control signal generator, 3 ... switching circuit, 4 ... modulator, 5 ... transmission controller, 6 ... backward signal generator, 7 ... switching circuit, 8 ... 2-wire 4-wire conversion Circuit, 9 ...
Transmission line, 10: backward signal detection unit, 11: demodulation unit, 12: control signal analysis unit.

Continued on the front page (72) Inventor Yasuhide Ueno 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Yoshihiro Sakamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeshi Ono 3- 30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-60-232744 (JP, A) JP-A-61-252754 (JP, A)

Claims (1)

(57) [Claims] 1. An image transmitting apparatus for transmitting image data by full-duplex communication, comprising: means for transmitting a training check signal prior to transmission of image data; Means for receiving a predetermined response signal indicating that the training check signal transmitted via a word channel has been successfully received; transmission of image data by full-duplex communication depending on whether or not the response signal has been received Means for determining whether or not to perform the image transmission.